Unit-5

Alloying of Steel

Question 1: Explain Various Kinds of Steel with their Properties.

A1:

2.     Heat Resisting Steel-

Steels which are satisfactory up to about

operating temperature are: C= 0.15%, Si = 0.5-20%, Mn = 0.5% maximum, Ni = none, Cr = 1 to 6%, Mo = 0.5%.

Uses: These are used in the valves of internal combustion engines in rolled or in forged condition. For higher temperature up to

, steels containing up to 22% nickel and 26% chromium are used.

3.     Silicon Steel-

4.     Stainless Steel-

Out of this group the former has C= 0.8%. Cr = 12 to 20% and latter has C = 0.1 to 0.2%, Cr = 12 to 20% and Ni = 2%.

These steels can be heat – treated.

Uses: For dies, valves and cutlery.

b.     Chromium- Nickel Steel:

These steels are non-magnetic and cannot be hardened.

They have varieties due to varying contents of chromium and nickel respectively e.g., small quantity of copper, tungsten and molybdenum is also added to these steels.

They have high resistance to corrosion and may be cold or hot worked, pressed welded, brazed or soldered.

These steels are poor conductors of heat and electricity.

Uses: It is used in making utensils.

Question 2: Write a note on various types of stainless steel with their properties.

A2: Stainless steel is divided into three different classes on the basis of the phase constituent of the microstructure. These are;

2.     Properties of Ferrite stainless steel:

3.     Properties of Austenitic stainless steel:

Question 3: What is Maraging Steel?

A3: Maraging steels are carbon free iron-nickel alloys with additions of cobalt, molybdenum, titanium and aluminium. Maraging steels are characterized with superior strength combined with excellent toughness properties and weldability. The term ‘maraging’ refers to the strengthening mechanisms and was coined from a combination of martensite and age-hardening; ‘mar’ refers to martensite and ‘aging’ refers to the age hardening heat treatment. Maraging steel is forged by a martensitic transformation followed by subsequent age-hardening.

These steels are a special class of low-carbon ultra-high-strength steels that derive their strength not from carbon, but from precipitation of intermetallic compounds. The principal alloying element is 15 to 25 wt.% nickel (Ni). Secondary alloying elements, which include cobalt (Co), molybdenum (Mo), aluminium (Al), and titanium (Ti), are added to produce inter metallic precipitates.

Question 4: What is Cast iron? Define Gray Cast iron and white cast iron with their properties.

A4: Cast iron is very useful engineering material. It contains more carbon percentage (approx., 2%<C<4.5%).

When pig iron is melted with coke and limestone in cupola furnace, it produces cast iron.

Coke acts as fuel and limestone acts as flux.

Fluxes are used to separate the impurities from the pig iron.

Properties:

Composition-

Properties:

Tensile strength varies between 1500 and 4000 kg/

.

2.     White Cast Iron:

White cast iron is a type of carbon-iron alloy that contains carbon content greater than 2% in the form of cementite. The name white cast is derived from its white surface, which is caused by carbide impurities that allows cracks throughout the metal.

Properties-

Question 5: Differentiate between malleable and Speroidal cast iron with their properties.

A5:

Composition:

Properties-

2.     Spheroidal Cast Iron:

Spheroidal Graphite Cast Iron 600/3, also known as Ductile Cast Iron.

Composition:

Properties:

Question 6: Define copper with its physical properties.

A6: Copper-

Physical properties:

Question 7: Elaborate some of the alloys of copper.

A7: Major Alloys of Copper are:

Brass is an alloy of copper and zinc. In brasses Cu and Zn proportions vary and gives rise of various types of brasses and improve its properties.

Good property brasses can be achieved by adding a small amount of alloying elements. As addition of lead alloy by 1 to 1.5% improves its strength and machining property but reduces its thermal and electrical conductivity.

 Th e importance of brass is its corrosion resistant property towards exposure of environment. Thus, brass is used for electroplating of metals. They have good fabrication property.

Classification:

Various types of Brasses:

Its composition is 85%Cu + 15%Zn.

Its composition is 70%Cu + 30%Zn.

Its composition is 63%Cu + 37%Zn

Its composition is 60%Cu + 40%Zn

2.     Bronze (Cu-Tin Alloy):

To Bronzes are the alloys of copper and tin. The composition of bronzes generally 75 to 95%copper and 5 to 25% tin.

Bronzes are hard and resistant to surface wear. Corrosion resistant properties of bronzes are comparatively better than brasses.

Classification:

3.     Phosphor Bronze-

Properties:

Composition:

87-90% Cu, 9-10% Sn and 1-3% P.

4.     Silicon Bronze-

Properties:

Composition:

96% Cu+ 3% Si + 1% Mg or Zn.

5.     Beryllium Bronze:

Composition:

97.7% Cu and 2.3% beryllium.

6. Cupro-Nickel alloy:

It refers to a mixture consisting of copper and other elements like nickel and various strengthening components like manganese and iron among other.

Addition of Nickel on to Copper and other elements merely strengthens this material, makes it ductile and shiny.All these are characteristics of a high-quality metallic material.

Copper-nickel alloy pipe can withstand extremely high temperatures. In fact, this is one of its utmost outstanding elements which makes it popular in several applications. This material is known for enduring temperatures that even exceed 760 degrees Celsius.

Question 8: What is Aluminium? Explain with its physical properties.

A8.

Question 9: Define Alloys of Aluminium with their properties.

A9. Cu-Al Alloy (Y-alloys):

2.     Mg-Alloy:

3.     Nickel-based Superalloys:

PROPERTIES:

Question 10: Mention the Nickel and Titanium based superalloys with their properties and uses.

A10: There are three types of Ni-base superalloys:

• Nickel base,

• Nickle-lron base

• Cobalt base.

The alloys contain high Cr with Ti, Al to from precipitates and additions of Mo, Co, Nb, Zr, B,Fe.

Titanium Alloy:

Titanium alloys are alloys that contains traces of aluminum, molybdenum, vanadium, niobium, tantalum, zirconium, manganese, iron, chromium, cobalt, nickel, and copper.

Such alloys have very high tensile strength and toughness (even at extreme temperatures). They are light in weight, have extraordinary corrosion resistance and the ability to withstand extreme temperatures.

Titanium alloys possess high specific properties, have a good fatigue strength/tensile strength ratio with a distinct fatigue limit, and some retain considerable strength at temperatures up to 400–500°C.

Uses:

Titanium has outstanding corrosion resistance to seawater, and thus is used in propeller shafts, rigging and other parts of boats that are exposed to seawater. Titanium and its alloys are used in airplanes, missiles, and rockets where strength, low weight, and resistance to high temperatures are important.