Unit - 2

Classification and application of plain carbon steels

2.1 Classification and application of plain carbon steels

Carbon steel is an iron-carbon alloy, which contains up to 2.1 wt.% carbon. For carbon steels, there is no minimum specified content of other alloying elements; however, they often contain manganese. The maximum manganese, silicon and copper content should be less than 1.65 wt. %, 0.6 wt. % and 0.6 wt. %, respectively.

Classification of carbon steel and their properties

Carbon steel can be classified into three categories according to its carbon content: low-carbon steel (or mild-carbon steel), medium-carbon steel and high-carbon steel their carbon content, microstructure and properties compare as follows:

 Low-carbon steel

Low-carbon steel is the most widely used form of carbon steel. These steels usually have a carbon content of less than 0.25 wt.%. They cannot be hardened by heat treatment (to form martensitic) so this is usually achieved by cold work.

Carbon steels are usually relatively soft and have low strength. They do, however, have high ductility, making them excellent for machining, welding and low cost. High-strength, low-alloy steels (HSLA) are also often classified as low-carbon steels, however, also contains other elements such as copper, nickel, vanadium and molybdenum. Combined, these comprise up to 10 wt.% of the steel content. High-strength, low-alloy steels, as the name suggests, have higher strengths, which is achieved by heat treatment. They also retain ductility, making them easily formable and machinable. HSLA are more resistant to corrosion than plain low-carbon steels.

Medium-carbon steel

Medium-carbon steel has a carbon content of 0.25 – 0.60 wt. % and a manganese content of 0.60 – 1.65 wt. %. The mechanical properties of this steel are improved via heat treatment involving autenitising followed by quenching and tempering, giving them a martensitic microstructure. Heat treatment can only be performed on very thin sections, however, additional alloying elements, such as chromium, molybdenum and nickel, can be added to improve the steels ability to be heat treated and, thus, hardened. Hardened medium-carbon steels have greater strength than low-carbon steels, however, this comes at the expense of ductility and toughness.

High-carbon steel

High-carbon steel has a carbon content of 0.60– 1.25 wt.% and a manganese content of 0.30 – 0.90 wt.%. It has the highest hardness and toughness of the carbon steels and the lowest ductility. High-carbon steels are very wear-resistant as a result of the fact that they are almost always hardened and tempered.

Tool steels and die steels are types of high-carbon steels, which contain additional alloying elements including chromium, vanadium, molybdenum and tungsten. The addition of these elements results in the very hard wear-resistant steel, which is a result of the formation of carbide compounds such as tungsten carbide (WC).

Production and processing

Carbon steel can be produced from recycled steel, virgin steel or a combination of both. Virgin steel is made by combining iron ore, coke (produced by heating coal in the absence of air) and lime in a blast furnace at around 1650 °C. The molten iron extracted from the iron ore is enriched with carbon from the burning coke. The remaining impurities combine with the lime to form slag, which floats on top of the molten metal where it can be extracted.

The resulting molten steel contains roughly 4 wt.% carbon. This carbon content is then reduced to the desired amount in a process called decarburization. This is achieved by passing oxygen through the melt, which oxidizes the carbon in the steel, producing carbon monoxide and carbon dioxide.

Applications of carbon steel:

Low-carbon steel

Low carbon steels are often used in automobile body components, structural shapes (I-beams, channel and angle iron), pipes, construction and bridge components, and food cans.

Medium-carbon steel

As a result of their high strength, resistance to wear and toughness, medium-carbon steels are often used for railway tracks, train wheels, crankshafts, and gears and machinery parts requiring this combination of properties.

High-carbon steel

Due to their high wear-resistance and hardness, high-carbon steels are used in cutting tools, springs high strength wire and dies.

Key takeaways:

Low-carbon steel is the most widely used form of carbon steel. These steels usually have a carbon content of less than 0.25 wt.%. They cannot be hardened by heat treatment (to form martensitic) so this is usually achieved by cold work.

2.2 Examples of alloy steel such as Hadfield Manganese Steel

• Hadfield manganese metal is largely excessive-carbon excessive-manganese metal in which carbon content material is round 1.1–1.4% with 11–14% manganese.
• The alloy is mainly made for excessive-put on resistance utility and its excessive paintings hardening cappotential makes it relevant for diverse programs such as armors. Microstructurally Hadfield manganese metal should be completely austenitic without the presence of any carbide withinside the microstructure.
• Manganese metal has no same in it cappotential to paintings-harden. Although it's miles typically mentioned that a most hardness of approximately 550 BHN is obtainable, common most hardness on worn castings is withinside the 400–450 BHN range. It is usually believed that manganese metal has negative abrasion resistance except it's been paintings-hardened.
• This isn't always a legitimate generalization. Controlled abrasion assessments and area assessments on prehardened castings have proven no development in put on resistance (Avery, 1974). If the manganese metal is utilized in programs for which it became designed, in which gouging and excessive-pressure abrasion predominate, the metal will swiftly paintings-harden.
• The excessive paintings-hardening potential permits manganese metal to soak up big quantity of electricity via the strain-hardening mechanism.
• At the opposite extreme, excellent sand strolling over manganese metal will put on a deep groove withinside the casting.
• It is not unusualplace exercise to pre-harden railway music paintings via way of means of mechanical or explosive techniques (ASM, 1980).
• The reason of this isn't always to enhance put on resistance however alternatively to offset one in every of manganese metal’s disadvantages, particularly its low-preliminary yield electricity.
• During trackwork provider, metallic glide happens beneathneath effect situations inflicting a extrade in dimensions. This necessitates the elimination of the extra flowed metallic via way of means of grinding and, in a few cases, weld rebuilding of low spots which may also have advanced in significantly pounded areas.
• The plastic deformation which happens in provider does increase the yield electricity to greater glide-resistant ranges however it's miles greater fee powerful to paintings-harden castings artificially earlier than setting them into provider, thereby lowering renovation costs.

 2.3 Ball Bearing Steels

• Most ball bearings are made from a sort of metallic called excessive carbon chromium metallic, frequently known as chrome metallic. This is used for motives of price and durability.
• Bearings also are crafted from different substances including chrome steel, ceramics and plastic. Chrome metallic will corrode if uncovered to moisture so, in which corrosion resistance is needed, bearings crafted from 440 grade chrome steel are frequently used.
• This is a completely hard, magnetic metallic with properly corrosion resistance however now no longer appropriate to be used with salt water and plenty of chemicals. 316 grade chrome steel is used for extra corrosive programs however it's far a whole lot softer so can simplest be used in which hundreds and speeds are low.
• Ceramics (zirconia and silicon nitride) are properly for terribly corrosive or high temperature use whilst diverse kinds of plastic are appropriate for properly to superb corrosion resistance even though simplest appropriate for low load and coffee speed. 316 chrome steel bearings, ceramic bearings and plastic bearings are non-magnetic.
• The cloth for rolling bearing ball bearing balls varies broadly and is continually commonly targeted at the ring substances. This guarantees that the interaction of cage, internal ring, and outer ring withinside the machine is harmonised.
• This is specially essential whilst the software entails heating or cooling the bearings. It is essential that ball bearing strolling homes are continually good. The maximum not unusualplace ball substances are indexed beneath with relation to the hoop cloth. For those ball bearings, hardened metallic balls are regularly used.
• The most customarily used cloth is a stainless steel with approximately 1crbon and 1.5% chrome. The homes of metallic balls of martensitic stainless steel lead them to specially properly perfect to ball bearing production, considering that they make solid additives which can be resistant and convincingly long lasting in non-stop operation. Balls product of curler bearing metallic are strong and long lasting. Susceptibility to corrosion has a tendency to be low, in order that cylindrical rollers and needle rollers are product of this cloth.
• But lubrication is indispensable. For ball bearings product of plastic, unhardened stainless balls are normally used. They are noticeably corrosion-resistant and also are very immune to saltwater and alkalis. Hardened balls want now no longer be used for plastic ball bearings.
• The most permissible load is already restricted via way of means of the boundaries of the cloth withinside the plastic rings. Stainless metallic balls fee much less than glass balls.

2.4 Tool Steels – Classification

Tool steels are a own circle of relatives carbon and alloy steels having wonderful traits consisting of hardness, put on resistance, toughness, and resistance to softening at accelerated temperatures. Tool steels include carbide-forming factors consisting of chromium, vanadium, molybdenum and tungsten in exclusive combinations. They additionally incorporate cobalt or nickel which improves their high-temperature performance. They are commonly heat-dealt with to enhance the hardness and used for stamping, forming, shearing and slicing metals and forming of plastics. They are categorized in keeping with their composition and houses into diverse categories.

Classifications

Tools steels fall into three basic categories:

• Cold work tool steels
• Hot work tool steels
• High-speed tool steels

Cold-work steels are further subdivided into:

• Air-hardening
• Medium-alloy cold-work steels
• High-carbon, high-chromium cold-work steels
• Oil-hardening cold-work steels

Hot work steels are subdivided into:

• Chromium
• Tungsten
• Molybdenum hot work steels

High-speed tool steels are divided into:

• Molybdenum
• Tungsten
• Intermediate high-speed steels

Other types of tool steels include:

• Water-hardening tool steels
• Shock-resistant tool steels
• Low-carbon tool steels
• Low-alloy special purpose tool steels.

Key takeaways:

Tool steels are a own circle of relatives carbon and alloy steels having wonderful traits consisting of hardness, put on resistance, toughness, and resistance to softening at accelerated temperatures.

2.5 Composition, application and commercial heat treatment practice for HSS

Composition

• Tool metallic is any of diverse carbon steels and alloy steels which are specially well-applicable to be made into equipment and tooling, which include slicing equipment, dies, hand equipment, knives, and others. Their suitability comes from their one-of-a-kind hardness, resistance to abrasion and deformation, and their cappotential to keep a slicing facet at expanded temperatures.
• As a result, device steels are applicable to be used withinside the shaping of different materials, as as an instance in slicing, machining, stamping, or forging. With a carbon content material among 0.5% and 1.5%, device steels are synthetic below cautiously managed situations to supply the desired quality. The presence of carbides of their matrix performs the dominant position withinside the traits of device metallic.
• The 4 main alloying factors that shape carbides in device metallic are: tungsten, chromium, vanadium and molybdenum.
• The fee of dissolution of the special carbides into the austenite shape of the iron determines the high-temperature overall performance of metallic (slower is better, making for a warmness-resistant metallic). Proper warmness remedy of those steels is crucial for good enough overall performance. The manganese content material is frequently stored low to limit the opportunity of cracking at some stage in water quenching. There are six organizations of device steels: water-hardening, cold-work, surprise-resistant, high-speed, hot-work, and unique purpose.
• The desire of institution to pick out relies upon on cost, running temperature, required floor hardness, strength, surprise resistance, and sturdiness requirements. The greater extreme the carrier condition (better temperature, abrasiveness, corrosiveness, loading), the better the alloy content material and consequent quantity of carbides required for the device metallic. Tool steels are used for slicing, pressing, extruding, and coining of metals and different materials.
• Their use in tooling is essential; injection molds as an instance require device steels for his or her resistance to abrasion- an crucial criterion for mould sturdiness which allows masses of heaps of moldings operations over its lifetime. The AISI-SAE grades of device metallic is the maximum not unusualplace scale used to become aware of diverse grades of device metallic. Individual alloys inside a grade are given a number; as an instance: A2, O1, etc.

Application:

• Tool steels are excessive-quality, carbon and alloy steels which might be normally used to make cutters, reamers, bits and many others used for machining metals, plastics, and wood.
• They are typically melted in furnaces and processed to provide them houses required for shaping different metals into beneficial components. They are ingot-forged wrought merchandise able to withstanding excessive temperatures and heavy loads.
• Tool steels commonly incorporate carbide formers like chromium, vanadium, molybdenum and tungsten in distinct combos and cobalt or nickel for reinforcing overall performance at excessive temperatures.
• Tool metallic is a form of carbon alloy metallic this is well-matched for device manufacturing, along with hand equipment or system dies. Its hardness, resistance to abrasion and cappotential to maintain form at elevated temperatures are the important thing houses of this material.
• Tool metallic is normally utilized in a warmth dealt with circumstance which affords elevated hardness. Several grades have extra resistance to corrosion because of brought chemical houses along with vanadium. Also, with sure grades the manganese content material is constrained with the intention to limit the capacity of cracking at the same time as water quenching. Other grades provide diverse techniques apart from water to quench the material, along with oil.

Commercial heat treatment practice for HSS

• The water hardening sorts of device metal are blanketed with the aid of using AS1239 ‘W’ grades and those are shallow hardening. These steels comprise round 1crbon and can have small additions of vanadium for grain refining and toughness.
• Depth of hardening is round 3 millimetres whilst quenched from the ordinary hardening temperature of 780°C and could boom to round six millimetres with the aid of using growing the quenching temperature to 870°C. Toughness will lower with the better quench temperature.
• Other than that the heating medium for those steels need to be impartial in recognize to decarburisation. The maximum important a part of the warmth remedy cycle is the quenching device which may also use bloodless water or 10% brine answers to reap most hardness.
• Vigorous agitation is important to make sure even and high-quality quenching as too s3ow a price of cooling may also result in gentle spots. The favored process is to quench right into a fluidised mattress furnace or salt tubtub held simply above the Ms point.
• This lets in the cooling price to overlook the important regions of the ‘S’ curve wherein carbide precipitation occurs.
• The device is permitted to equalise at temperature withinside the quenching tubtub after which is eliminated and nevertheless air cooled to handwarm (about 50 - 60°C) for tempering.

2.6 Secondary hardening

• A in addition growth in hardening that is viable to attain all through the tempering cycle, because of the sub-microscopic precipitation of exceptional alloy carbide particles. In a few alloys, in which a section transformation does now no longer take place, secondary hardening can be the handiest technique with the aid of using which the alloy may be hardened.
• The more potent the secondary hardening (which means greater extreme carbide precipitation), the better the tempering resistance of hot-paintings device steels. Such precipitation depth relies upon on the quantity of alloy factors in stable solution, that is associated with the alloy composition and warmth treating exercise received with the aid of using molybdenum, vanadium, or tungsten alloying.
• The graph suggests a schematic of hardness after tempering and the impact of secondary hardening in high-alloy steels. Observe that high-temperature hardness is handiest viable thru precipitation hardening because of alloy carbides (secondary hardening).
• At low temperatures, hardness is much less than martensite because of the presence of retained austenite, that is removed after high-temperature tempering.

2.7 Stainless Steels – Classification

Stainless steels are in general grouped into

• Martensitic stainless steels
• Ferritic stainless steels
• Austenitic stainless steels
• Duplex (ferritic-austenitic) stainless steels
• Precipitation-hardening stainless steels

Alloying metallic elements added during the making of the steel increase corrosion resistance, hardness, or strength. The metals used most commonly as alloying elements in stainless steel include chromium, nickel, and molybdenum.

Stainless steels are available in the form of

• Plate
• Sheet
• Strip
• Foil
• Bar
• Wire
• Pipes
• Tubes

Stainless steels are a iron-based alloy containing at between 10.5% to 30% Cr. Stainless steel achieve its stainless characteristic through the formation of an invisible and adherent chromium-rich oxide surface film.

Other alloying elements added to improve the characteristics of the stainless steel include nickel, molybdenum, copper, titanium, aluminum, silicon, niobium, nitrogen, sulphur, and selenium.

Carbon is normally in amounts from 0.03% to more than 1.0% in some martensitic grades.

Selection of stainless steels are in general based on

• Corrosion resistance
• Fabrication characteristics
• Availability
• Mechanical properties for specific temperature ranges
• Product cost

Since stainless steel resists corrosion, maintains its strength at high temperatures, and is easily maintained, it is widely used in items such as automotive and food processing products, as well as medical and health equipment. The most common US grades of stainless steel are:

TYPE 304

The most commonly specified austenitic (chromium-nickel stainless class) stainless steel, accounting for more than half of the stainless steel produced in the world. This grade withstands ordinary corrosion in architecture, is durable in typical food processing environments, and resists most chemicals. Type 304 is available in virtually all product forms and finishes.

TYPE 316

Austenitic (chromium-nickel stainless class) stainless steel containing 2%-3% molybdenum (whereas 304 has none). The inclusion of molybdenum gives 316 greater resistance to various forms of deterioration.

TYPE 409

Ferritic (plain chromium stainless category) stainless steel suitable for high temperatures. This grade has the lowest chromium content of all stainless steels and thus is the least expensive.

TYPE 410

The most widely used martensitic (plain chromium stainless class with exceptional strength) stainless steel, featuring the high level of strength conferred by the martensitics. It is a low-cost, heat-treatable grade suitable for non-severe corrosion applications.

TYPE 430

The most widely used ferritic (plain chromium stainless category) stainless steel, offering general-purpose corrosion resistance, often in decorative applications.

2.8 Composition

• Stainless metallic's resistance to rusting effects from the presence of chromium withinside the alloy, which paperwork a passive movie that protects the underlying fabric from corrosion attack, and may self-heal withinside the presence of oxygen.:
• Corrosion resistance may be extended in addition through the subsequent means: boom chromium content material to greater than 11d nickel to as a minimum 8d molybdenum (which additionally improves resistance to pitting corrosion)
• The addition of nitrogen additionally improves resistance to pitting corrosion and will increase mechanical power. Thus, there are various grades of stainless-steel with various chromium and molybdenum contents to in shape the surroundings the alloy have to endure.
• Resistance to corrosion and staining, low maintenance, and acquainted luster make stainless-steel an excellent fabric for plenty programs in which each the power of metallic and corrosion resistance are required. Moreover, stainless-steel may be rolled into sheets, plates, bars, wire, and tubing.
• These may be utilized in cookware, cutlery, surgical instruments, fundamental appliances, vehicles, production fabric in huge buildings, business equipment (e.g., in paper mills, chemical plants, water treatment), and garage tanks and tankers for chemical compounds and meals products.
• The organic cleanability of stainless-steel is advanced to each aluminum and copper, having a organic cleanability similar to glass Its cleanability, power, and corrosion resistance have triggered the usage of stainless-steel in pharmaceutical and meals processing plants.

Key takeaways:

• Corrosion resistance may be extended in addition through the subsequent means: boom chromium content material to greater than 11d nickel to as a minimum 8d molybdenum (which additionally improves resistance to pitting corrosion)

 2.9 Application and general heat treatment practice for Stainless Steels

Application

• Automotive and transportation Stainless metallic turned into brought in car withinside the Thirties via way of means of Ford to fabricate their idea cars. Since then, it's far used to provide a lot of car components inclusive of exhaust systems, grills, and trims.
• With advancing technology, stainless-steel is being favoured via way of means of producers to make structural components. It is likewise closely featured in different fields of transportation like freighting to make delivery containers, avenue tankers and refuse vehicles.
• It’s resistance to corrosion makes it perfect to move chemicals, beverages and meals products. The low renovation of stainless-steel additionally makes it an clean and cost-powerful steel to easy and sustain. Medical technology Stainless metallic is desired in easy and sterile environments because it is easy to easy and does now no longer effortlessly corrode. Stainless is used withinside the manufacturing of a extensive variety of clinical gadget, such as surgical and dental instruments.
• It is likewise utilized in constructing operation tables, kidney dishes, MRI scanners, cannulas, and steam sterilizers. Most surgical implants, inclusive of alternative joints and synthetic hips are crafted from stainless-steel, in addition to a few becoming a member of gadget like stainless-steel pins and plates to restore damaged bones. Building trade Due to its electricity, resistance, and flexibility, stainless-steel software has emerge as a crucial detail of the constructing trade.
• It is generally featured withinside the indoors on countertops, backsplashes, and handrails, and is likewise used externally in cladding for excessive effect buildings. It is a not unusualplace function in current structure because of its weldability, clean renovation and appealing finish, that's used withinside the Eurostar Terminal in London and the Helix Bridge in Singapore.
• With the motion in the direction of sustainable constructing, stainless-steel, that's a noticeably recyclable steel, is turning into an increasing number of optimum to apply in construction.
• With a elegant or grain finish, it has aesthetically captivating homes and may useful resource in enhancing herbal lights withinside the constructing. Aircraft construction
• The aviation enterprise additionally has a choice for stainless-steel. It is utilized in diverse programs such as the frames of aeroplanes due to its electricity and capacity to resist excessive temperatures. It also can be carried out in jet engines as it could assist save you towards its rusting.
• Why now no longer additionally study plane grade aluminum. Stainless metallic is likewise an vital a part of the touchdown gear. Its electricity and stress can deal with the burden of the touchdown plane.
• Food and the catering enterprise In the meals and catering enterprise, stainless-steel is used to fabricate kitchen accessories, cookware, and cutlery. Utensils inclusive of knives are made the usage of much less ductile grades of stainless-steel.
• The extra ductile grades are used to make grills, cookers, saucepans, and sinks. Stainless metallic also can be used to complete freezers, dishwashers, refrigerators, and countertops. In meals manufacturing, stainless-steel is right as it doesn’t have an effect on the flavor of the meals.
• It is likewise corrosion resistant, and for this reason capable of maintain acidic beverages such as orange juice. The ease of cleansing stainless-steel makes it hard to harbour bacteria, including to its usefulness in meals storage.

General heat treatment practice for Stainless Steels

• Stress relieving beneath 400°C is the maximum not unusualplace practice, however the end result is most effective mild strain relief. Stress relieving at temperatures of as much as 425 to 925°C will considerably lessen residual stresses which in any other case reason dimensional instability or strain corrosion cracking.
• One hour of strain relieving at 870°C relieves approximately 85% of residual stresses. However, this temperature variety can precipitate carbides at grain boundary, ensuing in sensitization that influences corrosion resistance in lots of media. Stabilized stainless steels or low-carbon kind steels are favored to keep away from those effects.
• Full answer remedy of stainless steels, through heating to approximately 1080°C observed through fast cooling, removes all residual stresses. However, it isn't realistic for maximum massive or complicated fabrications. While appearing cold-running of austenitic stainless steels to enhance electricity, compressive yield electricity and proportional restriction will generally tend to growth with low temperature strain relieving.
• Stress relieving is achieved at temperatures of as much as 345 to 425°C, if intergranular resistance isn't important.
• Higher temperatures will degrade the cloth electricity and, hence, they're now no longer favored for strain relieving cold-labored merchandise. Stainless metallic weld merchandise are heated to temperatures beneath fashionable annealing temperatures, to limit excessive residual stresses, whilst annealing observed through welding isn't possible.
• Stress relieving is regularly done on massive or problematic weld sections, or on distinctive weldments composed of low alloy metallic welded to stainless-steel. Stress relieving of Ferritic or martensitic stainless steels will mood weld and warmth affected zones, similarly to healing of corrosion resistance in a few types.
• Annealing temperatures are exceedingly low for those stainless-steel grades.

Key takeaways:

• Stress relieving is achieved at temperatures of as much as 345 to 425°C, if intergranular resistance isn't important.

2.10 Classification and applications of steels

Classification of steel:

Carbon steel can be classified into three categories according to its carbon content: low-carbon steel (or mild-carbon steel), medium-carbon steel and high-carbon steel their carbon content, microstructure and properties compare as follows:

 Low-carbon steel

• Low-carbon steel is the most widely used form of carbon steel. These steels usually have a carbon content of less than 0.25 wt.%. They cannot be hardened by heat treatment (to form martensitic) so this is usually achieved by cold work.
• Carbon steels are usually relatively soft and have low strength. They do, however, have high ductility, making them excellent for machining, welding and low cost.
• High-strength, low-alloy steels (HSLA) are also often classified as low-carbon steels, however, also contains other elements such as copper, nickel, vanadium and molybdenum.
• Combined, these comprise up to 10 wt.% of the steel content. High-strength, low-alloy steels, as the name suggests, have higher strengths, which is achieved by heat treatment. They also retain ductility, making them easily formable and machinable. HSLA are more resistant to corrosion than plain low-carbon steels.

Medium-carbon steel

• Medium-carbon steel has a carbon content of 0.25 – 0.60 wt. % and a manganese content of 0.60 – 1.65 wt. %.
• The mechanical properties of this steel are improved via heat treatment involving autenitising followed by quenching and tempering, giving them a martensitic microstructure.
• Heat treatment can only be performed on very thin sections, however, additional alloying elements, such as chromium, molybdenum and nickel, can be added to improve the steels ability to be heat treated and, thus, hardened. Hardened medium-carbon steels have greater strength than low-carbon steels, however, this comes at the expense of ductility and toughness.

High-carbon steel

• High-carbon steel has a carbon content of 0.60– 1.25 wt.% and a manganese content of 0.30 – 0.90 wt.%. It has the highest hardness and toughness of the carbon steels and the lowest ductility. High-carbon steels are very wear-resistant as a result of the fact that they are almost always hardened and tempered.
• Tool steels and die steels are types of high-carbon steels, which contain additional alloying elements including chromium, vanadium, molybdenum and tungsten. The addition of these elements results in the very hard wear-resistant steel, which is a result of the formation of carbide compounds such as tungsten carbide (WC).

Applications

Low-carbon steel

• Low carbon steels are often used in automobile body components, structural shapes (I-beams, channel and angle iron), pipes, construction and bridge components, and food cans.

Medium-carbon steel

• As a result of their high strength, resistance to wear and toughness, medium-carbon steels are often used for railway tracks, train wheels, crankshafts, and gears and machinery parts requiring this combination of properties.

High-carbon steel

• Due to their high wear-resistance and hardness, high-carbon steels are used in cutting tools, springs high strength wire and dies.

2.11 Effect of alloying elements

• An alloying detail can adjust the mechanical and chemical houses of metal. Alloys are frequently used to regulate one-of-a-kind attributes of the metal to make it extra viable. A aggregate of carbon and iron, metal profits blessings consisting of corrosion resistance and introduced power whilst alloyed with different factors.
• Many factors may be alloyed with metal; take a look at out this manual to the outcomes of those not unusualplace alloying factors. Chromium Chromium is one of the maximum not unusualplace factors used to create a metal alloy, and it’s consequently one of the maximum not unusualplace metals in a home. When extra than eleven percentage of a metal alloy is made of chromium, it’s known as stainless metal. Stainless metal may be very proof against corrosion, and it’s additionally resistant to oxidation.
• It’s more potent and tougher than fundamental metal and capable of be dealt with at fairly excessive temperatures with out issue. Vanadium Vanadium is any other detail that’s generally used to create metal alloys.
• Vanadium provides elevated power and hardness to the metal, which then turns into extra wear-resistant and higher capable of manage surprise impacts. This is because of the truth that vanadium continues the grain boom at bay—smaller grain sizes bring about higher effect resistance.
• This alloy is maximum generally used for excessive-pace steel-reducing tools. Manganese Manganese is used to alloy metal for metals that want to be forged. Manganese offers the metal better power, higher hardness, and extra resistance to wear.
• This is proper even at extraordinarily excessive temperatures. As a result, the steel alloy is capable of be fashioned and fashioned into a whole lot of gadgets with extra ease than with different steel alloys or with metal alone. Nickel The addition of nickel to metal is any other not unusualplace creation. The addition of sufficient nickel turns the metal into what's known as austenitic stainless metal, that is more difficult and tougher however no much less ductile.
• It has a excessive corrosion resistance even at intense temperatures. Nickel metal alloys are particular in that they are able to uphold their power even in extraordinarily bloodless temperatures.
• The temperature variety in nickel metal alloy is one of the maximum diverse. For all of your steel alloy needs, search for a depended on steel alloy supplier. Here at Wieland Diversified, we goal to deliver precisely what you want.

Key takeaways:

• An alloying detail can adjust the mechanical and chemical houses of metal. Alloys are frequently used to regulate one-of-a-kind attributes of the metal to make it extra viable. A aggregate of carbon and iron, metal profits blessings consisting of corrosion resistance and introduced power whilst alloyed with different factors.

References:

1. Introduction to Physical Metallurgy 29st revised edition, 2009 Sidney H.Avner McGraw-Hill,1964.

2. Engineering Physical Metallurgy and Heat Treatment 21st revised edition, 1988 Yu Lakhtin Mir publishers, Moscow, Russia.

3. Introduction to Engineering Metallurgy 21st revised edition, 2007 Dr. B K Agrawal Tata Mc-GraHill.

4. Metallurgy for Engineers 4th Revised edition 1987 E C Rollason E. Arnold.

Unit - 2

Classification and application of plain carbon steels

2.1 Classification and application of plain carbon steels

Carbon steel is an iron-carbon alloy, which contains up to 2.1 wt.% carbon. For carbon steels, there is no minimum specified content of other alloying elements; however, they often contain manganese. The maximum manganese, silicon and copper content should be less than 1.65 wt. %, 0.6 wt. % and 0.6 wt. %, respectively.

Classification of carbon steel and their properties

Carbon steel can be classified into three categories according to its carbon content: low-carbon steel (or mild-carbon steel), medium-carbon steel and high-carbon steel their carbon content, microstructure and properties compare as follows:

 Low-carbon steel

Low-carbon steel is the most widely used form of carbon steel. These steels usually have a carbon content of less than 0.25 wt.%. They cannot be hardened by heat treatment (to form martensitic) so this is usually achieved by cold work.

Carbon steels are usually relatively soft and have low strength. They do, however, have high ductility, making them excellent for machining, welding and low cost. High-strength, low-alloy steels (HSLA) are also often classified as low-carbon steels, however, also contains other elements such as copper, nickel, vanadium and molybdenum. Combined, these comprise up to 10 wt.% of the steel content. High-strength, low-alloy steels, as the name suggests, have higher strengths, which is achieved by heat treatment. They also retain ductility, making them easily formable and machinable. HSLA are more resistant to corrosion than plain low-carbon steels.

Medium-carbon steel

Medium-carbon steel has a carbon content of 0.25 – 0.60 wt. % and a manganese content of 0.60 – 1.65 wt. %. The mechanical properties of this steel are improved via heat treatment involving autenitising followed by quenching and tempering, giving them a martensitic microstructure. Heat treatment can only be performed on very thin sections, however, additional alloying elements, such as chromium, molybdenum and nickel, can be added to improve the steels ability to be heat treated and, thus, hardened. Hardened medium-carbon steels have greater strength than low-carbon steels, however, this comes at the expense of ductility and toughness.

High-carbon steel

High-carbon steel has a carbon content of 0.60– 1.25 wt.% and a manganese content of 0.30 – 0.90 wt.%. It has the highest hardness and toughness of the carbon steels and the lowest ductility. High-carbon steels are very wear-resistant as a result of the fact that they are almost always hardened and tempered.

Tool steels and die steels are types of high-carbon steels, which contain additional alloying elements including chromium, vanadium, molybdenum and tungsten. The addition of these elements results in the very hard wear-resistant steel, which is a result of the formation of carbide compounds such as tungsten carbide (WC).

Production and processing

Carbon steel can be produced from recycled steel, virgin steel or a combination of both. Virgin steel is made by combining iron ore, coke (produced by heating coal in the absence of air) and lime in a blast furnace at around 1650 °C. The molten iron extracted from the iron ore is enriched with carbon from the burning coke. The remaining impurities combine with the lime to form slag, which floats on top of the molten metal where it can be extracted.

The resulting molten steel contains roughly 4 wt.% carbon. This carbon content is then reduced to the desired amount in a process called decarburization. This is achieved by passing oxygen through the melt, which oxidizes the carbon in the steel, producing carbon monoxide and carbon dioxide.

Applications of carbon steel:

Low-carbon steel

Low carbon steels are often used in automobile body components, structural shapes (I-beams, channel and angle iron), pipes, construction and bridge components, and food cans.

Medium-carbon steel

As a result of their high strength, resistance to wear and toughness, medium-carbon steels are often used for railway tracks, train wheels, crankshafts, and gears and machinery parts requiring this combination of properties.

High-carbon steel

Due to their high wear-resistance and hardness, high-carbon steels are used in cutting tools, springs high strength wire and dies.

Key takeaways:

Low-carbon steel is the most widely used form of carbon steel. These steels usually have a carbon content of less than 0.25 wt.%. They cannot be hardened by heat treatment (to form martensitic) so this is usually achieved by cold work.

2.2 Examples of alloy steel such as Hadfield Manganese Steel

• Hadfield manganese metal is largely excessive-carbon excessive-manganese metal in which carbon content material is round 1.1–1.4% with 11–14% manganese.
• The alloy is mainly made for excessive-put on resistance utility and its excessive paintings hardening cappotential makes it relevant for diverse programs such as armors. Microstructurally Hadfield manganese metal should be completely austenitic without the presence of any carbide withinside the microstructure.
• Manganese metal has no same in it cappotential to paintings-harden. Although it's miles typically mentioned that a most hardness of approximately 550 BHN is obtainable, common most hardness on worn castings is withinside the 400–450 BHN range. It is usually believed that manganese metal has negative abrasion resistance except it's been paintings-hardened.
• This isn't always a legitimate generalization. Controlled abrasion assessments and area assessments on prehardened castings have proven no development in put on resistance (Avery, 1974). If the manganese metal is utilized in programs for which it became designed, in which gouging and excessive-pressure abrasion predominate, the metal will swiftly paintings-harden.
• The excessive paintings-hardening potential permits manganese metal to soak up big quantity of electricity via the strain-hardening mechanism.
• At the opposite extreme, excellent sand strolling over manganese metal will put on a deep groove withinside the casting.
• It is not unusualplace exercise to pre-harden railway music paintings via way of means of mechanical or explosive techniques (ASM, 1980).
• The reason of this isn't always to enhance put on resistance however alternatively to offset one in every of manganese metal’s disadvantages, particularly its low-preliminary yield electricity.
• During trackwork provider, metallic glide happens beneathneath effect situations inflicting a extrade in dimensions. This necessitates the elimination of the extra flowed metallic via way of means of grinding and, in a few cases, weld rebuilding of low spots which may also have advanced in significantly pounded areas.
• The plastic deformation which happens in provider does increase the yield electricity to greater glide-resistant ranges however it's miles greater fee powerful to paintings-harden castings artificially earlier than setting them into provider, thereby lowering renovation costs.

 2.3 Ball Bearing Steels

• Most ball bearings are made from a sort of metallic called excessive carbon chromium metallic, frequently known as chrome metallic. This is used for motives of price and durability.
• Bearings also are crafted from different substances including chrome steel, ceramics and plastic. Chrome metallic will corrode if uncovered to moisture so, in which corrosion resistance is needed, bearings crafted from 440 grade chrome steel are frequently used.
• This is a completely hard, magnetic metallic with properly corrosion resistance however now no longer appropriate to be used with salt water and plenty of chemicals. 316 grade chrome steel is used for extra corrosive programs however it's far a whole lot softer so can simplest be used in which hundreds and speeds are low.
• Ceramics (zirconia and silicon nitride) are properly for terribly corrosive or high temperature use whilst diverse kinds of plastic are appropriate for properly to superb corrosion resistance even though simplest appropriate for low load and coffee speed. 316 chrome steel bearings, ceramic bearings and plastic bearings are non-magnetic.
• The cloth for rolling bearing ball bearing balls varies broadly and is continually commonly targeted at the ring substances. This guarantees that the interaction of cage, internal ring, and outer ring withinside the machine is harmonised.
• This is specially essential whilst the software entails heating or cooling the bearings. It is essential that ball bearing strolling homes are continually good. The maximum not unusualplace ball substances are indexed beneath with relation to the hoop cloth. For those ball bearings, hardened metallic balls are regularly used.
• The most customarily used cloth is a stainless steel with approximately 1crbon and 1.5% chrome. The homes of metallic balls of martensitic stainless steel lead them to specially properly perfect to ball bearing production, considering that they make solid additives which can be resistant and convincingly long lasting in non-stop operation. Balls product of curler bearing metallic are strong and long lasting. Susceptibility to corrosion has a tendency to be low, in order that cylindrical rollers and needle rollers are product of this cloth.
• But lubrication is indispensable. For ball bearings product of plastic, unhardened stainless balls are normally used. They are noticeably corrosion-resistant and also are very immune to saltwater and alkalis. Hardened balls want now no longer be used for plastic ball bearings.
• The most permissible load is already restricted via way of means of the boundaries of the cloth withinside the plastic rings. Stainless metallic balls fee much less than glass balls.

2.4 Tool Steels – Classification

Tool steels are a own circle of relatives carbon and alloy steels having wonderful traits consisting of hardness, put on resistance, toughness, and resistance to softening at accelerated temperatures. Tool steels include carbide-forming factors consisting of chromium, vanadium, molybdenum and tungsten in exclusive combinations. They additionally incorporate cobalt or nickel which improves their high-temperature performance. They are commonly heat-dealt with to enhance the hardness and used for stamping, forming, shearing and slicing metals and forming of plastics. They are categorized in keeping with their composition and houses into diverse categories.

Classifications

Tools steels fall into three basic categories:

• Cold work tool steels
• Hot work tool steels
• High-speed tool steels

Cold-work steels are further subdivided into:

• Air-hardening
• Medium-alloy cold-work steels
• High-carbon, high-chromium cold-work steels
• Oil-hardening cold-work steels

Hot work steels are subdivided into:

• Chromium
• Tungsten
• Molybdenum hot work steels

High-speed tool steels are divided into:

• Molybdenum
• Tungsten
• Intermediate high-speed steels

Other types of tool steels include:

• Water-hardening tool steels
• Shock-resistant tool steels
• Low-carbon tool steels
• Low-alloy special purpose tool steels.

Key takeaways:

Tool steels are a own circle of relatives carbon and alloy steels having wonderful traits consisting of hardness, put on resistance, toughness, and resistance to softening at accelerated temperatures.

2.5 Composition, application and commercial heat treatment practice for HSS

Composition

• Tool metallic is any of diverse carbon steels and alloy steels which are specially well-applicable to be made into equipment and tooling, which include slicing equipment, dies, hand equipment, knives, and others. Their suitability comes from their one-of-a-kind hardness, resistance to abrasion and deformation, and their cappotential to keep a slicing facet at expanded temperatures.
• As a result, device steels are applicable to be used withinside the shaping of different materials, as as an instance in slicing, machining, stamping, or forging. With a carbon content material among 0.5% and 1.5%, device steels are synthetic below cautiously managed situations to supply the desired quality. The presence of carbides of their matrix performs the dominant position withinside the traits of device metallic.
• The 4 main alloying factors that shape carbides in device metallic are: tungsten, chromium, vanadium and molybdenum.
• The fee of dissolution of the special carbides into the austenite shape of the iron determines the high-temperature overall performance of metallic (slower is better, making for a warmness-resistant metallic). Proper warmness remedy of those steels is crucial for good enough overall performance. The manganese content material is frequently stored low to limit the opportunity of cracking at some stage in water quenching. There are six organizations of device steels: water-hardening, cold-work, surprise-resistant, high-speed, hot-work, and unique purpose.
• The desire of institution to pick out relies upon on cost, running temperature, required floor hardness, strength, surprise resistance, and sturdiness requirements. The greater extreme the carrier condition (better temperature, abrasiveness, corrosiveness, loading), the better the alloy content material and consequent quantity of carbides required for the device metallic. Tool steels are used for slicing, pressing, extruding, and coining of metals and different materials.
• Their use in tooling is essential; injection molds as an instance require device steels for his or her resistance to abrasion- an crucial criterion for mould sturdiness which allows masses of heaps of moldings operations over its lifetime. The AISI-SAE grades of device metallic is the maximum not unusualplace scale used to become aware of diverse grades of device metallic. Individual alloys inside a grade are given a number; as an instance: A2, O1, etc.

Application:

• Tool steels are excessive-quality, carbon and alloy steels which might be normally used to make cutters, reamers, bits and many others used for machining metals, plastics, and wood.
• They are typically melted in furnaces and processed to provide them houses required for shaping different metals into beneficial components. They are ingot-forged wrought merchandise able to withstanding excessive temperatures and heavy loads.
• Tool steels commonly incorporate carbide formers like chromium, vanadium, molybdenum and tungsten in distinct combos and cobalt or nickel for reinforcing overall performance at excessive temperatures.
• Tool metallic is a form of carbon alloy metallic this is well-matched for device manufacturing, along with hand equipment or system dies. Its hardness, resistance to abrasion and cappotential to maintain form at elevated temperatures are the important thing houses of this material.
• Tool metallic is normally utilized in a warmth dealt with circumstance which affords elevated hardness. Several grades have extra resistance to corrosion because of brought chemical houses along with vanadium. Also, with sure grades the manganese content material is constrained with the intention to limit the capacity of cracking at the same time as water quenching. Other grades provide diverse techniques apart from water to quench the material, along with oil.

Commercial heat treatment practice for HSS

• The water hardening sorts of device metal are blanketed with the aid of using AS1239 ‘W’ grades and those are shallow hardening. These steels comprise round 1crbon and can have small additions of vanadium for grain refining and toughness.
• Depth of hardening is round 3 millimetres whilst quenched from the ordinary hardening temperature of 780°C and could boom to round six millimetres with the aid of using growing the quenching temperature to 870°C. Toughness will lower with the better quench temperature.
• Other than that the heating medium for those steels need to be impartial in recognize to decarburisation. The maximum important a part of the warmth remedy cycle is the quenching device which may also use bloodless water or 10% brine answers to reap most hardness.
• Vigorous agitation is important to make sure even and high-quality quenching as too s3ow a price of cooling may also result in gentle spots. The favored process is to quench right into a fluidised mattress furnace or salt tubtub held simply above the Ms point.
• This lets in the cooling price to overlook the important regions of the ‘S’ curve wherein carbide precipitation occurs.
• The device is permitted to equalise at temperature withinside the quenching tubtub after which is eliminated and nevertheless air cooled to handwarm (about 50 - 60°C) for tempering.

2.6 Secondary hardening

• A in addition growth in hardening that is viable to attain all through the tempering cycle, because of the sub-microscopic precipitation of exceptional alloy carbide particles. In a few alloys, in which a section transformation does now no longer take place, secondary hardening can be the handiest technique with the aid of using which the alloy may be hardened.
• The more potent the secondary hardening (which means greater extreme carbide precipitation), the better the tempering resistance of hot-paintings device steels. Such precipitation depth relies upon on the quantity of alloy factors in stable solution, that is associated with the alloy composition and warmth treating exercise received with the aid of using molybdenum, vanadium, or tungsten alloying.
• The graph suggests a schematic of hardness after tempering and the impact of secondary hardening in high-alloy steels. Observe that high-temperature hardness is handiest viable thru precipitation hardening because of alloy carbides (secondary hardening).
• At low temperatures, hardness is much less than martensite because of the presence of retained austenite, that is removed after high-temperature tempering.

2.7 Stainless Steels – Classification

Stainless steels are in general grouped into

• Martensitic stainless steels
• Ferritic stainless steels
• Austenitic stainless steels
• Duplex (ferritic-austenitic) stainless steels
• Precipitation-hardening stainless steels

Alloying metallic elements added during the making of the steel increase corrosion resistance, hardness, or strength. The metals used most commonly as alloying elements in stainless steel include chromium, nickel, and molybdenum.

Stainless steels are available in the form of

• Plate
• Sheet
• Strip
• Foil
• Bar
• Wire
• Pipes
• Tubes

Stainless steels are a iron-based alloy containing at between 10.5% to 30% Cr. Stainless steel achieve its stainless characteristic through the formation of an invisible and adherent chromium-rich oxide surface film.

Other alloying elements added to improve the characteristics of the stainless steel include nickel, molybdenum, copper, titanium, aluminum, silicon, niobium, nitrogen, sulphur, and selenium.

Carbon is normally in amounts from 0.03% to more than 1.0% in some martensitic grades.

Selection of stainless steels are in general based on

• Corrosion resistance
• Fabrication characteristics
• Availability
• Mechanical properties for specific temperature ranges
• Product cost

Since stainless steel resists corrosion, maintains its strength at high temperatures, and is easily maintained, it is widely used in items such as automotive and food processing products, as well as medical and health equipment. The most common US grades of stainless steel are:

TYPE 304

The most commonly specified austenitic (chromium-nickel stainless class) stainless steel, accounting for more than half of the stainless steel produced in the world. This grade withstands ordinary corrosion in architecture, is durable in typical food processing environments, and resists most chemicals. Type 304 is available in virtually all product forms and finishes.

TYPE 316

Austenitic (chromium-nickel stainless class) stainless steel containing 2%-3% molybdenum (whereas 304 has none). The inclusion of molybdenum gives 316 greater resistance to various forms of deterioration.

TYPE 409

Ferritic (plain chromium stainless category) stainless steel suitable for high temperatures. This grade has the lowest chromium content of all stainless steels and thus is the least expensive.

TYPE 410

The most widely used martensitic (plain chromium stainless class with exceptional strength) stainless steel, featuring the high level of strength conferred by the martensitics. It is a low-cost, heat-treatable grade suitable for non-severe corrosion applications.

TYPE 430

The most widely used ferritic (plain chromium stainless category) stainless steel, offering general-purpose corrosion resistance, often in decorative applications.

2.8 Composition

• Stainless metallic's resistance to rusting effects from the presence of chromium withinside the alloy, which paperwork a passive movie that protects the underlying fabric from corrosion attack, and may self-heal withinside the presence of oxygen.:
• Corrosion resistance may be extended in addition through the subsequent means: boom chromium content material to greater than 11d nickel to as a minimum 8d molybdenum (which additionally improves resistance to pitting corrosion)
• The addition of nitrogen additionally improves resistance to pitting corrosion and will increase mechanical power. Thus, there are various grades of stainless-steel with various chromium and molybdenum contents to in shape the surroundings the alloy have to endure.
• Resistance to corrosion and staining, low maintenance, and acquainted luster make stainless-steel an excellent fabric for plenty programs in which each the power of metallic and corrosion resistance are required. Moreover, stainless-steel may be rolled into sheets, plates, bars, wire, and tubing.
• These may be utilized in cookware, cutlery, surgical instruments, fundamental appliances, vehicles, production fabric in huge buildings, business equipment (e.g., in paper mills, chemical plants, water treatment), and garage tanks and tankers for chemical compounds and meals products.
• The organic cleanability of stainless-steel is advanced to each aluminum and copper, having a organic cleanability similar to glass Its cleanability, power, and corrosion resistance have triggered the usage of stainless-steel in pharmaceutical and meals processing plants.

Key takeaways:

• Corrosion resistance may be extended in addition through the subsequent means: boom chromium content material to greater than 11d nickel to as a minimum 8d molybdenum (which additionally improves resistance to pitting corrosion)

 2.9 Application and general heat treatment practice for Stainless Steels

Application

• Automotive and transportation Stainless metallic turned into brought in car withinside the Thirties via way of means of Ford to fabricate their idea cars. Since then, it's far used to provide a lot of car components inclusive of exhaust systems, grills, and trims.
• With advancing technology, stainless-steel is being favoured via way of means of producers to make structural components. It is likewise closely featured in different fields of transportation like freighting to make delivery containers, avenue tankers and refuse vehicles.
• It’s resistance to corrosion makes it perfect to move chemicals, beverages and meals products. The low renovation of stainless-steel additionally makes it an clean and cost-powerful steel to easy and sustain. Medical technology Stainless metallic is desired in easy and sterile environments because it is easy to easy and does now no longer effortlessly corrode. Stainless is used withinside the manufacturing of a extensive variety of clinical gadget, such as surgical and dental instruments.
• It is likewise utilized in constructing operation tables, kidney dishes, MRI scanners, cannulas, and steam sterilizers. Most surgical implants, inclusive of alternative joints and synthetic hips are crafted from stainless-steel, in addition to a few becoming a member of gadget like stainless-steel pins and plates to restore damaged bones. Building trade Due to its electricity, resistance, and flexibility, stainless-steel software has emerge as a crucial detail of the constructing trade.
• It is generally featured withinside the indoors on countertops, backsplashes, and handrails, and is likewise used externally in cladding for excessive effect buildings. It is a not unusualplace function in current structure because of its weldability, clean renovation and appealing finish, that's used withinside the Eurostar Terminal in London and the Helix Bridge in Singapore.
• With the motion in the direction of sustainable constructing, stainless-steel, that's a noticeably recyclable steel, is turning into an increasing number of optimum to apply in construction.
• With a elegant or grain finish, it has aesthetically captivating homes and may useful resource in enhancing herbal lights withinside the constructing. Aircraft construction
• The aviation enterprise additionally has a choice for stainless-steel. It is utilized in diverse programs such as the frames of aeroplanes due to its electricity and capacity to resist excessive temperatures. It also can be carried out in jet engines as it could assist save you towards its rusting.
• Why now no longer additionally study plane grade aluminum. Stainless metallic is likewise an vital a part of the touchdown gear. Its electricity and stress can deal with the burden of the touchdown plane.
• Food and the catering enterprise In the meals and catering enterprise, stainless-steel is used to fabricate kitchen accessories, cookware, and cutlery. Utensils inclusive of knives are made the usage of much less ductile grades of stainless-steel.
• The extra ductile grades are used to make grills, cookers, saucepans, and sinks. Stainless metallic also can be used to complete freezers, dishwashers, refrigerators, and countertops. In meals manufacturing, stainless-steel is right as it doesn’t have an effect on the flavor of the meals.
• It is likewise corrosion resistant, and for this reason capable of maintain acidic beverages such as orange juice. The ease of cleansing stainless-steel makes it hard to harbour bacteria, including to its usefulness in meals storage.

General heat treatment practice for Stainless Steels

• Stress relieving beneath 400°C is the maximum not unusualplace practice, however the end result is most effective mild strain relief. Stress relieving at temperatures of as much as 425 to 925°C will considerably lessen residual stresses which in any other case reason dimensional instability or strain corrosion cracking.
• One hour of strain relieving at 870°C relieves approximately 85% of residual stresses. However, this temperature variety can precipitate carbides at grain boundary, ensuing in sensitization that influences corrosion resistance in lots of media. Stabilized stainless steels or low-carbon kind steels are favored to keep away from those effects.
• Full answer remedy of stainless steels, through heating to approximately 1080°C observed through fast cooling, removes all residual stresses. However, it isn't realistic for maximum massive or complicated fabrications. While appearing cold-running of austenitic stainless steels to enhance electricity, compressive yield electricity and proportional restriction will generally tend to growth with low temperature strain relieving.
• Stress relieving is achieved at temperatures of as much as 345 to 425°C, if intergranular resistance isn't important.
• Higher temperatures will degrade the cloth electricity and, hence, they're now no longer favored for strain relieving cold-labored merchandise. Stainless metallic weld merchandise are heated to temperatures beneath fashionable annealing temperatures, to limit excessive residual stresses, whilst annealing observed through welding isn't possible.
• Stress relieving is regularly done on massive or problematic weld sections, or on distinctive weldments composed of low alloy metallic welded to stainless-steel. Stress relieving of Ferritic or martensitic stainless steels will mood weld and warmth affected zones, similarly to healing of corrosion resistance in a few types.
• Annealing temperatures are exceedingly low for those stainless-steel grades.

Key takeaways:

• Stress relieving is achieved at temperatures of as much as 345 to 425°C, if intergranular resistance isn't important.

2.10 Classification and applications of steels

Classification of steel:

Carbon steel can be classified into three categories according to its carbon content: low-carbon steel (or mild-carbon steel), medium-carbon steel and high-carbon steel their carbon content, microstructure and properties compare as follows:

 Low-carbon steel

• Low-carbon steel is the most widely used form of carbon steel. These steels usually have a carbon content of less than 0.25 wt.%. They cannot be hardened by heat treatment (to form martensitic) so this is usually achieved by cold work.
• Carbon steels are usually relatively soft and have low strength. They do, however, have high ductility, making them excellent for machining, welding and low cost.
• High-strength, low-alloy steels (HSLA) are also often classified as low-carbon steels, however, also contains other elements such as copper, nickel, vanadium and molybdenum.
• Combined, these comprise up to 10 wt.% of the steel content. High-strength, low-alloy steels, as the name suggests, have higher strengths, which is achieved by heat treatment. They also retain ductility, making them easily formable and machinable. HSLA are more resistant to corrosion than plain low-carbon steels.

Medium-carbon steel

• Medium-carbon steel has a carbon content of 0.25 – 0.60 wt. % and a manganese content of 0.60 – 1.65 wt. %.
• The mechanical properties of this steel are improved via heat treatment involving autenitising followed by quenching and tempering, giving them a martensitic microstructure.
• Heat treatment can only be performed on very thin sections, however, additional alloying elements, such as chromium, molybdenum and nickel, can be added to improve the steels ability to be heat treated and, thus, hardened. Hardened medium-carbon steels have greater strength than low-carbon steels, however, this comes at the expense of ductility and toughness.

High-carbon steel

• High-carbon steel has a carbon content of 0.60– 1.25 wt.% and a manganese content of 0.30 – 0.90 wt.%. It has the highest hardness and toughness of the carbon steels and the lowest ductility. High-carbon steels are very wear-resistant as a result of the fact that they are almost always hardened and tempered.
• Tool steels and die steels are types of high-carbon steels, which contain additional alloying elements including chromium, vanadium, molybdenum and tungsten. The addition of these elements results in the very hard wear-resistant steel, which is a result of the formation of carbide compounds such as tungsten carbide (WC).

Applications

Low-carbon steel

• Low carbon steels are often used in automobile body components, structural shapes (I-beams, channel and angle iron), pipes, construction and bridge components, and food cans.

Medium-carbon steel

• As a result of their high strength, resistance to wear and toughness, medium-carbon steels are often used for railway tracks, train wheels, crankshafts, and gears and machinery parts requiring this combination of properties.

High-carbon steel

• Due to their high wear-resistance and hardness, high-carbon steels are used in cutting tools, springs high strength wire and dies.

2.11 Effect of alloying elements

• An alloying detail can adjust the mechanical and chemical houses of metal. Alloys are frequently used to regulate one-of-a-kind attributes of the metal to make it extra viable. A aggregate of carbon and iron, metal profits blessings consisting of corrosion resistance and introduced power whilst alloyed with different factors.
• Many factors may be alloyed with metal; take a look at out this manual to the outcomes of those not unusualplace alloying factors. Chromium Chromium is one of the maximum not unusualplace factors used to create a metal alloy, and it’s consequently one of the maximum not unusualplace metals in a home. When extra than eleven percentage of a metal alloy is made of chromium, it’s known as stainless metal. Stainless metal may be very proof against corrosion, and it’s additionally resistant to oxidation.
• It’s more potent and tougher than fundamental metal and capable of be dealt with at fairly excessive temperatures with out issue. Vanadium Vanadium is any other detail that’s generally used to create metal alloys.
• Vanadium provides elevated power and hardness to the metal, which then turns into extra wear-resistant and higher capable of manage surprise impacts. This is because of the truth that vanadium continues the grain boom at bay—smaller grain sizes bring about higher effect resistance.
• This alloy is maximum generally used for excessive-pace steel-reducing tools. Manganese Manganese is used to alloy metal for metals that want to be forged. Manganese offers the metal better power, higher hardness, and extra resistance to wear.
• This is proper even at extraordinarily excessive temperatures. As a result, the steel alloy is capable of be fashioned and fashioned into a whole lot of gadgets with extra ease than with different steel alloys or with metal alone. Nickel The addition of nickel to metal is any other not unusualplace creation. The addition of sufficient nickel turns the metal into what's known as austenitic stainless metal, that is more difficult and tougher however no much less ductile.
• It has a excessive corrosion resistance even at intense temperatures. Nickel metal alloys are particular in that they are able to uphold their power even in extraordinarily bloodless temperatures.
• The temperature variety in nickel metal alloy is one of the maximum diverse. For all of your steel alloy needs, search for a depended on steel alloy supplier. Here at Wieland Diversified, we goal to deliver precisely what you want.

Key takeaways:

• An alloying detail can adjust the mechanical and chemical houses of metal. Alloys are frequently used to regulate one-of-a-kind attributes of the metal to make it extra viable. A aggregate of carbon and iron, metal profits blessings consisting of corrosion resistance and introduced power whilst alloyed with different factors.

References:

1. Introduction to Physical Metallurgy 29st revised edition, 2009 Sidney H.Avner McGraw-Hill,1964.

2. Engineering Physical Metallurgy and Heat Treatment 21st revised edition, 1988 Yu Lakhtin Mir publishers, Moscow, Russia.

3. Introduction to Engineering Metallurgy 21st revised edition, 2007 Dr. B K Agrawal Tata Mc-GraHill.

4. Metallurgy for Engineers 4th Revised edition 1987 E C Rollason E. Arnold.

Unit - 2

Classification and application of plain carbon steels

2.1 Classification and application of plain carbon steels

Carbon steel is an iron-carbon alloy, which contains up to 2.1 wt.% carbon. For carbon steels, there is no minimum specified content of other alloying elements; however, they often contain manganese. The maximum manganese, silicon and copper content should be less than 1.65 wt. %, 0.6 wt. % and 0.6 wt. %, respectively.

Classification of carbon steel and their properties

Carbon steel can be classified into three categories according to its carbon content: low-carbon steel (or mild-carbon steel), medium-carbon steel and high-carbon steel their carbon content, microstructure and properties compare as follows:

 Low-carbon steel

Low-carbon steel is the most widely used form of carbon steel. These steels usually have a carbon content of less than 0.25 wt.%. They cannot be hardened by heat treatment (to form martensitic) so this is usually achieved by cold work.

Carbon steels are usually relatively soft and have low strength. They do, however, have high ductility, making them excellent for machining, welding and low cost. High-strength, low-alloy steels (HSLA) are also often classified as low-carbon steels, however, also contains other elements such as copper, nickel, vanadium and molybdenum. Combined, these comprise up to 10 wt.% of the steel content. High-strength, low-alloy steels, as the name suggests, have higher strengths, which is achieved by heat treatment. They also retain ductility, making them easily formable and machinable. HSLA are more resistant to corrosion than plain low-carbon steels.

Medium-carbon steel

Medium-carbon steel has a carbon content of 0.25 – 0.60 wt. % and a manganese content of 0.60 – 1.65 wt. %. The mechanical properties of this steel are improved via heat treatment involving autenitising followed by quenching and tempering, giving them a martensitic microstructure. Heat treatment can only be performed on very thin sections, however, additional alloying elements, such as chromium, molybdenum and nickel, can be added to improve the steels ability to be heat treated and, thus, hardened. Hardened medium-carbon steels have greater strength than low-carbon steels, however, this comes at the expense of ductility and toughness.

High-carbon steel

High-carbon steel has a carbon content of 0.60– 1.25 wt.% and a manganese content of 0.30 – 0.90 wt.%. It has the highest hardness and toughness of the carbon steels and the lowest ductility. High-carbon steels are very wear-resistant as a result of the fact that they are almost always hardened and tempered.

Tool steels and die steels are types of high-carbon steels, which contain additional alloying elements including chromium, vanadium, molybdenum and tungsten. The addition of these elements results in the very hard wear-resistant steel, which is a result of the formation of carbide compounds such as tungsten carbide (WC).

Production and processing

Carbon steel can be produced from recycled steel, virgin steel or a combination of both. Virgin steel is made by combining iron ore, coke (produced by heating coal in the absence of air) and lime in a blast furnace at around 1650 °C. The molten iron extracted from the iron ore is enriched with carbon from the burning coke. The remaining impurities combine with the lime to form slag, which floats on top of the molten metal where it can be extracted.

The resulting molten steel contains roughly 4 wt.% carbon. This carbon content is then reduced to the desired amount in a process called decarburization. This is achieved by passing oxygen through the melt, which oxidizes the carbon in the steel, producing carbon monoxide and carbon dioxide.

Applications of carbon steel:

Low-carbon steel

Low carbon steels are often used in automobile body components, structural shapes (I-beams, channel and angle iron), pipes, construction and bridge components, and food cans.

Medium-carbon steel

As a result of their high strength, resistance to wear and toughness, medium-carbon steels are often used for railway tracks, train wheels, crankshafts, and gears and machinery parts requiring this combination of properties.

High-carbon steel

Due to their high wear-resistance and hardness, high-carbon steels are used in cutting tools, springs high strength wire and dies.

Key takeaways:

Low-carbon steel is the most widely used form of carbon steel. These steels usually have a carbon content of less than 0.25 wt.%. They cannot be hardened by heat treatment (to form martensitic) so this is usually achieved by cold work.

2.2 Examples of alloy steel such as Hadfield Manganese Steel

• Hadfield manganese metal is largely excessive-carbon excessive-manganese metal in which carbon content material is round 1.1–1.4% with 11–14% manganese.
• The alloy is mainly made for excessive-put on resistance utility and its excessive paintings hardening cappotential makes it relevant for diverse programs such as armors. Microstructurally Hadfield manganese metal should be completely austenitic without the presence of any carbide withinside the microstructure.
• Manganese metal has no same in it cappotential to paintings-harden. Although it's miles typically mentioned that a most hardness of approximately 550 BHN is obtainable, common most hardness on worn castings is withinside the 400–450 BHN range. It is usually believed that manganese metal has negative abrasion resistance except it's been paintings-hardened.
• This isn't always a legitimate generalization. Controlled abrasion assessments and area assessments on prehardened castings have proven no development in put on resistance (Avery, 1974). If the manganese metal is utilized in programs for which it became designed, in which gouging and excessive-pressure abrasion predominate, the metal will swiftly paintings-harden.
• The excessive paintings-hardening potential permits manganese metal to soak up big quantity of electricity via the strain-hardening mechanism.
• At the opposite extreme, excellent sand strolling over manganese metal will put on a deep groove withinside the casting.
• It is not unusualplace exercise to pre-harden railway music paintings via way of means of mechanical or explosive techniques (ASM, 1980).
• The reason of this isn't always to enhance put on resistance however alternatively to offset one in every of manganese metal’s disadvantages, particularly its low-preliminary yield electricity.
• During trackwork provider, metallic glide happens beneathneath effect situations inflicting a extrade in dimensions. This necessitates the elimination of the extra flowed metallic via way of means of grinding and, in a few cases, weld rebuilding of low spots which may also have advanced in significantly pounded areas.
• The plastic deformation which happens in provider does increase the yield electricity to greater glide-resistant ranges however it's miles greater fee powerful to paintings-harden castings artificially earlier than setting them into provider, thereby lowering renovation costs.

 2.3 Ball Bearing Steels

• Most ball bearings are made from a sort of metallic called excessive carbon chromium metallic, frequently known as chrome metallic. This is used for motives of price and durability.
• Bearings also are crafted from different substances including chrome steel, ceramics and plastic. Chrome metallic will corrode if uncovered to moisture so, in which corrosion resistance is needed, bearings crafted from 440 grade chrome steel are frequently used.
• This is a completely hard, magnetic metallic with properly corrosion resistance however now no longer appropriate to be used with salt water and plenty of chemicals. 316 grade chrome steel is used for extra corrosive programs however it's far a whole lot softer so can simplest be used in which hundreds and speeds are low.
• Ceramics (zirconia and silicon nitride) are properly for terribly corrosive or high temperature use whilst diverse kinds of plastic are appropriate for properly to superb corrosion resistance even though simplest appropriate for low load and coffee speed. 316 chrome steel bearings, ceramic bearings and plastic bearings are non-magnetic.
• The cloth for rolling bearing ball bearing balls varies broadly and is continually commonly targeted at the ring substances. This guarantees that the interaction of cage, internal ring, and outer ring withinside the machine is harmonised.
• This is specially essential whilst the software entails heating or cooling the bearings. It is essential that ball bearing strolling homes are continually good. The maximum not unusualplace ball substances are indexed beneath with relation to the hoop cloth. For those ball bearings, hardened metallic balls are regularly used.
• The most customarily used cloth is a stainless steel with approximately 1crbon and 1.5% chrome. The homes of metallic balls of martensitic stainless steel lead them to specially properly perfect to ball bearing production, considering that they make solid additives which can be resistant and convincingly long lasting in non-stop operation. Balls product of curler bearing metallic are strong and long lasting. Susceptibility to corrosion has a tendency to be low, in order that cylindrical rollers and needle rollers are product of this cloth.
• But lubrication is indispensable. For ball bearings product of plastic, unhardened stainless balls are normally used. They are noticeably corrosion-resistant and also are very immune to saltwater and alkalis. Hardened balls want now no longer be used for plastic ball bearings.
• The most permissible load is already restricted via way of means of the boundaries of the cloth withinside the plastic rings. Stainless metallic balls fee much less than glass balls.

2.4 Tool Steels – Classification

Tool steels are a own circle of relatives carbon and alloy steels having wonderful traits consisting of hardness, put on resistance, toughness, and resistance to softening at accelerated temperatures. Tool steels include carbide-forming factors consisting of chromium, vanadium, molybdenum and tungsten in exclusive combinations. They additionally incorporate cobalt or nickel which improves their high-temperature performance. They are commonly heat-dealt with to enhance the hardness and used for stamping, forming, shearing and slicing metals and forming of plastics. They are categorized in keeping with their composition and houses into diverse categories.

Classifications

Tools steels fall into three basic categories:

• Cold work tool steels
• Hot work tool steels
• High-speed tool steels

Cold-work steels are further subdivided into:

• Air-hardening
• Medium-alloy cold-work steels
• High-carbon, high-chromium cold-work steels
• Oil-hardening cold-work steels

Hot work steels are subdivided into:

• Chromium
• Tungsten
• Molybdenum hot work steels

High-speed tool steels are divided into:

• Molybdenum
• Tungsten
• Intermediate high-speed steels

Other types of tool steels include:

• Water-hardening tool steels
• Shock-resistant tool steels
• Low-carbon tool steels
• Low-alloy special purpose tool steels.

Key takeaways:

Tool steels are a own circle of relatives carbon and alloy steels having wonderful traits consisting of hardness, put on resistance, toughness, and resistance to softening at accelerated temperatures.

2.5 Composition, application and commercial heat treatment practice for HSS

Composition

• Tool metallic is any of diverse carbon steels and alloy steels which are specially well-applicable to be made into equipment and tooling, which include slicing equipment, dies, hand equipment, knives, and others. Their suitability comes from their one-of-a-kind hardness, resistance to abrasion and deformation, and their cappotential to keep a slicing facet at expanded temperatures.
• As a result, device steels are applicable to be used withinside the shaping of different materials, as as an instance in slicing, machining, stamping, or forging. With a carbon content material among 0.5% and 1.5%, device steels are synthetic below cautiously managed situations to supply the desired quality. The presence of carbides of their matrix performs the dominant position withinside the traits of device metallic.
• The 4 main alloying factors that shape carbides in device metallic are: tungsten, chromium, vanadium and molybdenum.
• The fee of dissolution of the special carbides into the austenite shape of the iron determines the high-temperature overall performance of metallic (slower is better, making for a warmness-resistant metallic). Proper warmness remedy of those steels is crucial for good enough overall performance. The manganese content material is frequently stored low to limit the opportunity of cracking at some stage in water quenching. There are six organizations of device steels: water-hardening, cold-work, surprise-resistant, high-speed, hot-work, and unique purpose.
• The desire of institution to pick out relies upon on cost, running temperature, required floor hardness, strength, surprise resistance, and sturdiness requirements. The greater extreme the carrier condition (better temperature, abrasiveness, corrosiveness, loading), the better the alloy content material and consequent quantity of carbides required for the device metallic. Tool steels are used for slicing, pressing, extruding, and coining of metals and different materials.
• Their use in tooling is essential; injection molds as an instance require device steels for his or her resistance to abrasion- an crucial criterion for mould sturdiness which allows masses of heaps of moldings operations over its lifetime. The AISI-SAE grades of device metallic is the maximum not unusualplace scale used to become aware of diverse grades of device metallic. Individual alloys inside a grade are given a number; as an instance: A2, O1, etc.

Application:

• Tool steels are excessive-quality, carbon and alloy steels which might be normally used to make cutters, reamers, bits and many others used for machining metals, plastics, and wood.
• They are typically melted in furnaces and processed to provide them houses required for shaping different metals into beneficial components. They are ingot-forged wrought merchandise able to withstanding excessive temperatures and heavy loads.
• Tool steels commonly incorporate carbide formers like chromium, vanadium, molybdenum and tungsten in distinct combos and cobalt or nickel for reinforcing overall performance at excessive temperatures.
• Tool metallic is a form of carbon alloy metallic this is well-matched for device manufacturing, along with hand equipment or system dies. Its hardness, resistance to abrasion and cappotential to maintain form at elevated temperatures are the important thing houses of this material.
• Tool metallic is normally utilized in a warmth dealt with circumstance which affords elevated hardness. Several grades have extra resistance to corrosion because of brought chemical houses along with vanadium. Also, with sure grades the manganese content material is constrained with the intention to limit the capacity of cracking at the same time as water quenching. Other grades provide diverse techniques apart from water to quench the material, along with oil.

Commercial heat treatment practice for HSS

• The water hardening sorts of device metal are blanketed with the aid of using AS1239 ‘W’ grades and those are shallow hardening. These steels comprise round 1crbon and can have small additions of vanadium for grain refining and toughness.
• Depth of hardening is round 3 millimetres whilst quenched from the ordinary hardening temperature of 780°C and could boom to round six millimetres with the aid of using growing the quenching temperature to 870°C. Toughness will lower with the better quench temperature.
• Other than that the heating medium for those steels need to be impartial in recognize to decarburisation. The maximum important a part of the warmth remedy cycle is the quenching device which may also use bloodless water or 10% brine answers to reap most hardness.
• Vigorous agitation is important to make sure even and high-quality quenching as too s3ow a price of cooling may also result in gentle spots. The favored process is to quench right into a fluidised mattress furnace or salt tubtub held simply above the Ms point.
• This lets in the cooling price to overlook the important regions of the ‘S’ curve wherein carbide precipitation occurs.
• The device is permitted to equalise at temperature withinside the quenching tubtub after which is eliminated and nevertheless air cooled to handwarm (about 50 - 60°C) for tempering.

2.6 Secondary hardening

• A in addition growth in hardening that is viable to attain all through the tempering cycle, because of the sub-microscopic precipitation of exceptional alloy carbide particles. In a few alloys, in which a section transformation does now no longer take place, secondary hardening can be the handiest technique with the aid of using which the alloy may be hardened.
• The more potent the secondary hardening (which means greater extreme carbide precipitation), the better the tempering resistance of hot-paintings device steels. Such precipitation depth relies upon on the quantity of alloy factors in stable solution, that is associated with the alloy composition and warmth treating exercise received with the aid of using molybdenum, vanadium, or tungsten alloying.
• The graph suggests a schematic of hardness after tempering and the impact of secondary hardening in high-alloy steels. Observe that high-temperature hardness is handiest viable thru precipitation hardening because of alloy carbides (secondary hardening).
• At low temperatures, hardness is much less than martensite because of the presence of retained austenite, that is removed after high-temperature tempering.

2.7 Stainless Steels – Classification

Stainless steels are in general grouped into

• Martensitic stainless steels
• Ferritic stainless steels
• Austenitic stainless steels
• Duplex (ferritic-austenitic) stainless steels
• Precipitation-hardening stainless steels

Alloying metallic elements added during the making of the steel increase corrosion resistance, hardness, or strength. The metals used most commonly as alloying elements in stainless steel include chromium, nickel, and molybdenum.

Stainless steels are available in the form of

• Plate
• Sheet
• Strip
• Foil
• Bar
• Wire
• Pipes
• Tubes

Stainless steels are a iron-based alloy containing at between 10.5% to 30% Cr. Stainless steel achieve its stainless characteristic through the formation of an invisible and adherent chromium-rich oxide surface film.

Other alloying elements added to improve the characteristics of the stainless steel include nickel, molybdenum, copper, titanium, aluminum, silicon, niobium, nitrogen, sulphur, and selenium.

Carbon is normally in amounts from 0.03% to more than 1.0% in some martensitic grades.

Selection of stainless steels are in general based on

• Corrosion resistance
• Fabrication characteristics
• Availability
• Mechanical properties for specific temperature ranges
• Product cost

Since stainless steel resists corrosion, maintains its strength at high temperatures, and is easily maintained, it is widely used in items such as automotive and food processing products, as well as medical and health equipment. The most common US grades of stainless steel are:

TYPE 304

The most commonly specified austenitic (chromium-nickel stainless class) stainless steel, accounting for more than half of the stainless steel produced in the world. This grade withstands ordinary corrosion in architecture, is durable in typical food processing environments, and resists most chemicals. Type 304 is available in virtually all product forms and finishes.

TYPE 316

Austenitic (chromium-nickel stainless class) stainless steel containing 2%-3% molybdenum (whereas 304 has none). The inclusion of molybdenum gives 316 greater resistance to various forms of deterioration.

TYPE 409

Ferritic (plain chromium stainless category) stainless steel suitable for high temperatures. This grade has the lowest chromium content of all stainless steels and thus is the least expensive.

TYPE 410

The most widely used martensitic (plain chromium stainless class with exceptional strength) stainless steel, featuring the high level of strength conferred by the martensitics. It is a low-cost, heat-treatable grade suitable for non-severe corrosion applications.

TYPE 430

The most widely used ferritic (plain chromium stainless category) stainless steel, offering general-purpose corrosion resistance, often in decorative applications.

2.8 Composition

• Stainless metallic's resistance to rusting effects from the presence of chromium withinside the alloy, which paperwork a passive movie that protects the underlying fabric from corrosion attack, and may self-heal withinside the presence of oxygen.:
• Corrosion resistance may be extended in addition through the subsequent means: boom chromium content material to greater than 11d nickel to as a minimum 8d molybdenum (which additionally improves resistance to pitting corrosion)
• The addition of nitrogen additionally improves resistance to pitting corrosion and will increase mechanical power. Thus, there are various grades of stainless-steel with various chromium and molybdenum contents to in shape the surroundings the alloy have to endure.
• Resistance to corrosion and staining, low maintenance, and acquainted luster make stainless-steel an excellent fabric for plenty programs in which each the power of metallic and corrosion resistance are required. Moreover, stainless-steel may be rolled into sheets, plates, bars, wire, and tubing.
• These may be utilized in cookware, cutlery, surgical instruments, fundamental appliances, vehicles, production fabric in huge buildings, business equipment (e.g., in paper mills, chemical plants, water treatment), and garage tanks and tankers for chemical compounds and meals products.
• The organic cleanability of stainless-steel is advanced to each aluminum and copper, having a organic cleanability similar to glass Its cleanability, power, and corrosion resistance have triggered the usage of stainless-steel in pharmaceutical and meals processing plants.

Key takeaways:

• Corrosion resistance may be extended in addition through the subsequent means: boom chromium content material to greater than 11d nickel to as a minimum 8d molybdenum (which additionally improves resistance to pitting corrosion)

 2.9 Application and general heat treatment practice for Stainless Steels

Application

• Automotive and transportation Stainless metallic turned into brought in car withinside the Thirties via way of means of Ford to fabricate their idea cars. Since then, it's far used to provide a lot of car components inclusive of exhaust systems, grills, and trims.
• With advancing technology, stainless-steel is being favoured via way of means of producers to make structural components. It is likewise closely featured in different fields of transportation like freighting to make delivery containers, avenue tankers and refuse vehicles.
• It’s resistance to corrosion makes it perfect to move chemicals, beverages and meals products. The low renovation of stainless-steel additionally makes it an clean and cost-powerful steel to easy and sustain. Medical technology Stainless metallic is desired in easy and sterile environments because it is easy to easy and does now no longer effortlessly corrode. Stainless is used withinside the manufacturing of a extensive variety of clinical gadget, such as surgical and dental instruments.
• It is likewise utilized in constructing operation tables, kidney dishes, MRI scanners, cannulas, and steam sterilizers. Most surgical implants, inclusive of alternative joints and synthetic hips are crafted from stainless-steel, in addition to a few becoming a member of gadget like stainless-steel pins and plates to restore damaged bones. Building trade Due to its electricity, resistance, and flexibility, stainless-steel software has emerge as a crucial detail of the constructing trade.
• It is generally featured withinside the indoors on countertops, backsplashes, and handrails, and is likewise used externally in cladding for excessive effect buildings. It is a not unusualplace function in current structure because of its weldability, clean renovation and appealing finish, that's used withinside the Eurostar Terminal in London and the Helix Bridge in Singapore.
• With the motion in the direction of sustainable constructing, stainless-steel, that's a noticeably recyclable steel, is turning into an increasing number of optimum to apply in construction.
• With a elegant or grain finish, it has aesthetically captivating homes and may useful resource in enhancing herbal lights withinside the constructing. Aircraft construction
• The aviation enterprise additionally has a choice for stainless-steel. It is utilized in diverse programs such as the frames of aeroplanes due to its electricity and capacity to resist excessive temperatures. It also can be carried out in jet engines as it could assist save you towards its rusting.
• Why now no longer additionally study plane grade aluminum. Stainless metallic is likewise an vital a part of the touchdown gear. Its electricity and stress can deal with the burden of the touchdown plane.
• Food and the catering enterprise In the meals and catering enterprise, stainless-steel is used to fabricate kitchen accessories, cookware, and cutlery. Utensils inclusive of knives are made the usage of much less ductile grades of stainless-steel.
• The extra ductile grades are used to make grills, cookers, saucepans, and sinks. Stainless metallic also can be used to complete freezers, dishwashers, refrigerators, and countertops. In meals manufacturing, stainless-steel is right as it doesn’t have an effect on the flavor of the meals.
• It is likewise corrosion resistant, and for this reason capable of maintain acidic beverages such as orange juice. The ease of cleansing stainless-steel makes it hard to harbour bacteria, including to its usefulness in meals storage.

General heat treatment practice for Stainless Steels

• Stress relieving beneath 400°C is the maximum not unusualplace practice, however the end result is most effective mild strain relief. Stress relieving at temperatures of as much as 425 to 925°C will considerably lessen residual stresses which in any other case reason dimensional instability or strain corrosion cracking.
• One hour of strain relieving at 870°C relieves approximately 85% of residual stresses. However, this temperature variety can precipitate carbides at grain boundary, ensuing in sensitization that influences corrosion resistance in lots of media. Stabilized stainless steels or low-carbon kind steels are favored to keep away from those effects.
• Full answer remedy of stainless steels, through heating to approximately 1080°C observed through fast cooling, removes all residual stresses. However, it isn't realistic for maximum massive or complicated fabrications. While appearing cold-running of austenitic stainless steels to enhance electricity, compressive yield electricity and proportional restriction will generally tend to growth with low temperature strain relieving.
• Stress relieving is achieved at temperatures of as much as 345 to 425°C, if intergranular resistance isn't important.
• Higher temperatures will degrade the cloth electricity and, hence, they're now no longer favored for strain relieving cold-labored merchandise. Stainless metallic weld merchandise are heated to temperatures beneath fashionable annealing temperatures, to limit excessive residual stresses, whilst annealing observed through welding isn't possible.
• Stress relieving is regularly done on massive or problematic weld sections, or on distinctive weldments composed of low alloy metallic welded to stainless-steel. Stress relieving of Ferritic or martensitic stainless steels will mood weld and warmth affected zones, similarly to healing of corrosion resistance in a few types.
• Annealing temperatures are exceedingly low for those stainless-steel grades.

Key takeaways:

• Stress relieving is achieved at temperatures of as much as 345 to 425°C, if intergranular resistance isn't important.

2.10 Classification and applications of steels

Classification of steel:

Carbon steel can be classified into three categories according to its carbon content: low-carbon steel (or mild-carbon steel), medium-carbon steel and high-carbon steel their carbon content, microstructure and properties compare as follows:

 Low-carbon steel

• Low-carbon steel is the most widely used form of carbon steel. These steels usually have a carbon content of less than 0.25 wt.%. They cannot be hardened by heat treatment (to form martensitic) so this is usually achieved by cold work.
• Carbon steels are usually relatively soft and have low strength. They do, however, have high ductility, making them excellent for machining, welding and low cost.
• High-strength, low-alloy steels (HSLA) are also often classified as low-carbon steels, however, also contains other elements such as copper, nickel, vanadium and molybdenum.
• Combined, these comprise up to 10 wt.% of the steel content. High-strength, low-alloy steels, as the name suggests, have higher strengths, which is achieved by heat treatment. They also retain ductility, making them easily formable and machinable. HSLA are more resistant to corrosion than plain low-carbon steels.

Medium-carbon steel

• Medium-carbon steel has a carbon content of 0.25 – 0.60 wt. % and a manganese content of 0.60 – 1.65 wt. %.
• The mechanical properties of this steel are improved via heat treatment involving autenitising followed by quenching and tempering, giving them a martensitic microstructure.
• Heat treatment can only be performed on very thin sections, however, additional alloying elements, such as chromium, molybdenum and nickel, can be added to improve the steels ability to be heat treated and, thus, hardened. Hardened medium-carbon steels have greater strength than low-carbon steels, however, this comes at the expense of ductility and toughness.

High-carbon steel

• High-carbon steel has a carbon content of 0.60– 1.25 wt.% and a manganese content of 0.30 – 0.90 wt.%. It has the highest hardness and toughness of the carbon steels and the lowest ductility. High-carbon steels are very wear-resistant as a result of the fact that they are almost always hardened and tempered.
• Tool steels and die steels are types of high-carbon steels, which contain additional alloying elements including chromium, vanadium, molybdenum and tungsten. The addition of these elements results in the very hard wear-resistant steel, which is a result of the formation of carbide compounds such as tungsten carbide (WC).

Applications

Low-carbon steel

• Low carbon steels are often used in automobile body components, structural shapes (I-beams, channel and angle iron), pipes, construction and bridge components, and food cans.

Medium-carbon steel

• As a result of their high strength, resistance to wear and toughness, medium-carbon steels are often used for railway tracks, train wheels, crankshafts, and gears and machinery parts requiring this combination of properties.

High-carbon steel

• Due to their high wear-resistance and hardness, high-carbon steels are used in cutting tools, springs high strength wire and dies.

2.11 Effect of alloying elements

• An alloying detail can adjust the mechanical and chemical houses of metal. Alloys are frequently used to regulate one-of-a-kind attributes of the metal to make it extra viable. A aggregate of carbon and iron, metal profits blessings consisting of corrosion resistance and introduced power whilst alloyed with different factors.
• Many factors may be alloyed with metal; take a look at out this manual to the outcomes of those not unusualplace alloying factors. Chromium Chromium is one of the maximum not unusualplace factors used to create a metal alloy, and it’s consequently one of the maximum not unusualplace metals in a home. When extra than eleven percentage of a metal alloy is made of chromium, it’s known as stainless metal. Stainless metal may be very proof against corrosion, and it’s additionally resistant to oxidation.
• It’s more potent and tougher than fundamental metal and capable of be dealt with at fairly excessive temperatures with out issue. Vanadium Vanadium is any other detail that’s generally used to create metal alloys.
• Vanadium provides elevated power and hardness to the metal, which then turns into extra wear-resistant and higher capable of manage surprise impacts. This is because of the truth that vanadium continues the grain boom at bay—smaller grain sizes bring about higher effect resistance.
• This alloy is maximum generally used for excessive-pace steel-reducing tools. Manganese Manganese is used to alloy metal for metals that want to be forged. Manganese offers the metal better power, higher hardness, and extra resistance to wear.
• This is proper even at extraordinarily excessive temperatures. As a result, the steel alloy is capable of be fashioned and fashioned into a whole lot of gadgets with extra ease than with different steel alloys or with metal alone. Nickel The addition of nickel to metal is any other not unusualplace creation. The addition of sufficient nickel turns the metal into what's known as austenitic stainless metal, that is more difficult and tougher however no much less ductile.
• It has a excessive corrosion resistance even at intense temperatures. Nickel metal alloys are particular in that they are able to uphold their power even in extraordinarily bloodless temperatures.
• The temperature variety in nickel metal alloy is one of the maximum diverse. For all of your steel alloy needs, search for a depended on steel alloy supplier. Here at Wieland Diversified, we goal to deliver precisely what you want.

Key takeaways:

• An alloying detail can adjust the mechanical and chemical houses of metal. Alloys are frequently used to regulate one-of-a-kind attributes of the metal to make it extra viable. A aggregate of carbon and iron, metal profits blessings consisting of corrosion resistance and introduced power whilst alloyed with different factors.

References:

1. Introduction to Physical Metallurgy 29st revised edition, 2009 Sidney H.Avner McGraw-Hill,1964.

2. Engineering Physical Metallurgy and Heat Treatment 21st revised edition, 1988 Yu Lakhtin Mir publishers, Moscow, Russia.

3. Introduction to Engineering Metallurgy 21st revised edition, 2007 Dr. B K Agrawal Tata Mc-GraHill.

4. Metallurgy for Engineers 4th Revised edition 1987 E C Rollason E. Arnold.