UNIT 5

Ferrous Material

5.1 Introduction to Ferrous Material

Metal and alloys: -

Metals are polycrystalline bodies consisting of a great number of fine crystals. Pure metals possess lose friends and do not have the required properties. So, alloys are produced by melting or sintering two or more metals or metal and nonmetals together. Metals and alloys are further classified into two:

a)     Ferrous metals

b)    Non-ferrous metals

Ferrous metals: Ferrous metals are those which have the iron as their mean constituent such as pig iron, cast iron, wrought iron and steels.

Nonferrous metals: Nonferrous metals are those which have a metal other than iron as their main constituent such as copper, aluminum, brass, bronze, silver etc.

Engineering materials: -

These are of two types

a)     Metallic materials

b)    Nonmetallic materials

5.2 Carbon Steel

Carbon steel is a steel with carbon content from about 0.05to 2.1 % by weight.

Classification of carbon Steel

Typically, classification of carbon Steel in 4 part according to carbon content:

Low carbon Steel-

Typically contains 0.05% to 0.30 % carbon content. Sometimes is known as mild steel also which has tensile strength of 555 N/ and hardness of 140 BHN.

Medium carbon Steel: -

Typically has a carbon range of 0.30 % to 0.60 % and a manganese content ranging from 0.06% to 1.65 %. This product is stronger than low carbon Steel.

High carbon Steel: -

Commonly known as carbon tool Steel. it typically has a carbon range of between 0.60 % and 1.50% very strong used for springs tools and high strength wires.

Ultra-high carbon Steel: -

Approximately 1.50 – 2.0% carbon content Steel that can be tempered to great hardness. Used for special purposes like (non-industrial purpose) knife, axles or punches.

Types of carbon Steel: -

a)     4140 Steel

b)    4145 Steel

300M Steel

Properties of carbon Steel

The carbon content, microstructure and properties compare as

Industrial application: - The industrial application of carbon steel:

5.3 Alloy Steel

Alloy Steel that is alloyed with a variety of elements in total amount between 1.0 % and 50% by weight to improve its Mechanical properties. Alloy steel characterized in in two parts as per alloy percentage.

1)     High alloy Steel

2)     Low alloy Steel

High alloy Steel: High alloy Steel are defined by a high percentage of alloying elements. Its most common high alloy steel is stainless steel which contains at least 12% chromium. Stainless steel is generally split into three basic types which are martensite, territic and austenitic.

Low alloy Steel: - Low alloy steels have a much lower percentage of alloying elements usually 1to 5%, these steels have very different strains and uses.

Effects of alloying elements-; Steel is a combination of iron and carbon. Steel is alloyed with various element to improve physical properties.

1)     Carbon: - The most common important constituent of Steel is it raises tensile strength, hardness and resistance to wear and abrasion. It lowers ductility, toughness and machinability.

2)     Chromium (Cr): -; Increase tensile strength, hardness, toughness resistance to wear and abrasion, resistance to corrosion and scaling at elevated temperature.

3)     Columbium (CB): - Used as stabilizing element in stainless steel each has a high affinity for carbon and forms carbides which are uniformly dispersed throughout the Steel.

4)     Copper (Cu): - It significant amount is detrimental to hot working Steel. Copper negatively affects forge welding. Copper can be detrimental to surface quality.

5)     Manganese (MN): - A deoxidizer and degasifier and reacts with Sulphur to improve forge ability. It increases tensile strength, hardness, hardenability and resistance to wear.

6)     Molybdenum (MO): -; increases strength, hardness, hardenability and toughness as well as creep resistance and strength at elevated temperature.

7)     Nickel (Ni): - Increases strength hardness without ductility and toughness. It also increases resistance to corrosion.

8)     Phosphorus (P): - increase strength and hardness and improve machinability however it adds mark brittleness or cold shortness to Steel.

9)     Silicon (Si): - deoxidizer and degasifier increases tensile and yield strength, hardness, forge ability E and magnetic permeability.

10) Sulphur (S): - improve machinability in free cutting steels but without sufficient manganese. It produces brittleness at red heat.

11) Titanium (Ti): - improve strength and corrosion resistance limits austenite grain size.

12) Tungsten (W): increase hardness. Particularly at elevated temperature due to stable carbides, refines grain size.

13) Vanadium (V): - increase strength, hardness, creep resistance, and impact resistance due to formation of heart vanadium carbides.

Stainless steel: - Stainless Steel contains chromium together with nickel as alloy and rest is iron. It has been defined as that Steel which when correctly he treated and finished. Resist oxidation and corrosive attack from most corrosive media. Stainless steel surface is responsible for corrosion resistance. Minimum chromium content of 12 percentage required for the film’s formation. 12 percentage sufficient to resist the most severe atmospheric corrosive conditions. Additional of nickel improves ductility and imparts strength. Addition of molybdenum improves its resistance to sulfuric, sulfuric acid and organic acids. Addition of manganese increase hot workability of the Steel.

Classification of stainless steel: -

On basis of their Alpha structure, stainless steel is classified as follows:

1)     Martensite stainless steel: - Di Steel contain 12 – 16% chromium and 0.1 to 1.2% carbon. This structure contains hard martensite phase after hardening.

2)     Ferritic stainless steel: - Ferritic stainless steels are known hard enable and contain 16 – 30% chromium and 0.08 – 0.2 V carbon structure of these consist of ferrite face which cannot be hardened by heat treatment.

3)     Austenitic stainless steel: - Additional of substantial quantities of nickel to high chromium alloy gives rise to austenitic Steel. It has good resistance to many acids (even hotter called nitric acid). Slight amount of W or Mo are added in such Steel to increase its strength at elevated temperature.

Tool Steel: -

Tool steel is a variety of carbon steel and alloy Steel that are particularly well suitable to be made into tools. Their sustainability comes from their distinctive hardness, resistance to abrasion and D formation and their ability to hold a cutting edge at elevated temperature. Tool steels are suited for use in the shipping of other materials with a carbon content between 0.5% – 1.5%, tool Steel are manufactured under carefully controlled condition to produce the required quantity.

The presence of carbide in their Matrix plays the dominant role in the quantities of tool Steel. The four major alloying elements that from carbides in tool Steel are tungsten, chromium, vanadium and molybdenum. The rate of dissolution of the different carbides into the austenite form of iron determines the high temperature performance of Steel. Proper heat treatment of steel is important for adequate performance. The manganese content is after kept low to minimize the possibility of cracking during water quenching.

There are six groups of tool steels water hardening, cold work, shock resistance, high speed, hot work and special purpose. The choice of group to select depend on working temperature, required surface hardness, strength and toughness requirements. These tools are used for cutting, pressing, extruding and coining of metal.

Sensitization of stainless steel: -

Sensitization of Steel refers to the precipitation of carbides of grain boundaries in a stainless steel or alloy, causing the alloy to be susceptible to intragranular corrosion.

Certain alloys, when exposed to temperature characterized as a sensitizing temperature become partially susceptible to intergranular corrosion. Intergranular corrosion is caused by the recreation of impurities at the grain boundaries for depletion of one of the alloying elements in the grain boundaries in the case of austenitic stainless steel. When they are sensitized by heating to about 900 degree – 1500°F, depletion of chromium in grain boundary occurs. This result in susceptibility to intergranular corrosion.

5.4 Designation of carbon steel and alloy Steel

Carbon steel and alloy Steel are designed a four-digit number, where by the first digit indicates the main alloying element, the second digit indicates top grid element and the last two digits indicate the amount of carbon, in hundreds of percent by weight. For example, a 1060 steel is plain carbon steel containing 0.60 weight percent C.

The 'H' suffix can be added to any designation to denote hardenability.

Major classification of Steel

Carbon and alloy Steel grades

5.5 Cast iron

Cast iron is basically an alloy of iron and carbon and is obtained by re melting. Pig iron with coke, limestone and steel scrap in furnace known as cupola. The carbon content in cast iron varies from 1.7% – 6.67%.

Classification of cast iron

The cast iron is classified into seven major kinds as follows:

1)     Grey cast iron

2)     White cast iron

3)     Mottled cast iron

4)     Malleable cast iron

5)     Nodular cast and ductile cast iron

6)     Machanite cast iron

Types and their composition:

1)     Grey cast iron: - Grey cast iron is grey in colour which is due to the carbon being principally in the form of graphite. It contains

C = 2.5 to 3.6%

Si = 1.1 to 2.8%

Mn = 0.4 to 1.0%

P = less than 0.15%

S = less than 0.1 %

Fe = remaining

2)     White cast iron: - The white color is due to the fact that the carbon is thin iron in in combined form as iron carbide which is commonly specified as cementite. It is the hardest constituent of iron

C = 3.2 - 3.6%

Si = 0.4 – 1.1%

Mg = 0.1 – 0.4%

P = less than 0.3 %

S = less than 0.2 %

Fe = remaining

Ductile cast iron:

When small quantities of magnesium or cerium is added to cast iron then graphite content is converted into nodular or idle form and it is well dispersed throughout the material.

Carbon = 3.2 % 4.2 %

Silicon = 1.0 – 4.0 %

Magnesium= 0.1 – 0.8%

Nickel = 0.0 – 3.5%

Manganese = 0.5 – 0.1%

Iron = remaining

Malleable cast iron: - malleable cast iron that easily workable. It typically created using heat treatment processes on white cast iron. the white cast iron is heated for 1 to 2 days after which it is cooled, when finished. Malleable cast iron can be bent and manipulated to achieve unique shape and sizes.

C = 2.5%

Si = 1.0 %

Mn = 0.55%

Iron = remaining

Industrial application:

Industrial application explains according to classification: -

Grey cast iron application- The grey cast iron casting is mainly used for machine tool bodies, automotive cylinder blocks, pipes and pipes fittings and agricultural implement.

White cast iron- For reducing malleable iron casting. For manufacturing those components or parts which require a band and abrasion resistance surface such as rim of car and railways brake blocks.

Malleable cast iron- Malleable cast iron is generally used to form automobile paints, agricultural implementation, door keys, spanner, mrutings of all sorts, seat wheels, cranks, levers, waned components of sewing machines and textiles machine parts.

Hair we have specified some material (microstructure and properties)

Mild steel

Physical properties: - Some mild steel's physical properties are as follows

b.    Low carbon Steel

Physical properties: - Some low carbon steel properties are as follows

3.High carbon Steel

Physical properties: - High carbon steel physical properties are as follows

Questions: -

a)     Grey cast iron

b)    White cast iron

c)     Ductile cast iron

d)    Malleable cast iron

5.     What are alloy steels?

6.     What are plain carbon steels? discuss in brief the classification of plain carbon steels and also state few application of different plain carbon Steel?

7.     Explain the effect of alloying element?

8.     What did you understand about designation of Steel?

9.     Discuss in brief the effect of impurities in cast iron.

10. Write short note on