Review and Summary

REVIEW AND SUMMARY

✓ This unit surveys the most commonly used ferrous and non- ferrous metals and their principal alloys for engineering applications.

✓ Ferrous alloys (steels and cast irons) are those in which iron is novig the prime constituent.

✓ Steels can be classified as follows:

1. Plain carbon steels

(i) Low-carbon steels - Those contain less than 0.25% carbon. 

(ii) Medium-carbon steels - Those containing between 0.25 and 0.60% carbon.

(iii) High-carbon steels - Those containing more than 0.60% carbon.

2. Alloy steels

(i) Low alloy steels - Those contain upto 3 to 4% of alloying elements.

(ii) High alloy steels - Those contain more than 5% of alloying elements.

✓ The alloying elements are added to enhance properties such as ole increased strength, toughness, hardenability, corrosion and wear resistance, etc.

✓ Some of the commonly used alloying elements include Mn, Si, Cr, Ni, W, Mo, V, Ti, Co, Cu and Pb.

✓ In this unit, we have discussed designation, composition, properties and typical applications of the following four important alloy steels.

1. Stainless steels,

2. Tool steels,

3. HSLA steels, and

4. Maraging steels.

✓ Stainless steels are alloys of iron, chromium, and other elements that resist corrosion from many environments.

✓ Three classes of stainless steels, on the basis of its micro- structure, are:

1. Austenitic stainless steels,

2. Ferritic stainless steels, and

3. Martensitic stainless steels.

✓ Tool steels are high-carbon alloys used to make tools and dies for cutting, forming, or otherwise shaping a material into a component or part for a specific application.

✓ HSLA (High-Strength Low-Alloy steels), also known as micro- alloyed steels, are low-carbon steels containing small amounts of alloying elements. Its primary purpose is weight reduction through increased strength.

✓ Maraging steels are low-carbon, highly alloyed steels. They are used in applications where very high tensile strength is desired.

✓ Cast irons can be defined as the ferrous alloys with greater than 2% carbon.

✓ In this unit, we have presented the designation, composition, properties, and typical applications of the following five major types of cast irons.

1. Grey cast iron,

2. White cast iron,

3. Malleable cast iron,

4. Spheroidal graphite (or nodular or ductile) cast iron, and 

5. Alloy cast iron.

✓ The microstructure of grey cast iron contains graphite flakes, which tend to be brittle. But in spheroidal graphite cast iron these graphite flakes present as spheroidal nodules, which increases toughness. The white cast iron contains the cementite structure in the pearlitic matrix. The malleable irons may be produced by heat treating certain white cast irons, which contains graphite nodules (temper carbon).

✓ Alloy cast irons have been developed to have improved or special properties, such as high corrosion resistance.

✓ All the metallic elements other than iron are referred to as non-ferrous materials.

✓ The important non-ferrous materials used in engineering practice are aluminium, copper, lead, magnesium, nickel, tin, titanium, and zinc.

✓ Copper is a highly ductile metal with high electrical conduc- tivity and the pure metal is used in many electrical and electronics applications.

✓ The important copper alloys are:

1. Brasses Cu-Zn alloys),

2. Bronzes (Cu-Sn alloys),

3. Gun metals (Cu-Sn-Zn alloys), and

4. Cupronickels (Cu-Ni alloys).

✓ Aluminium is a soft, ductile metal of low density and with a high resistance to corrosion.

✓ Types of aluminium alloys:

1. Heat-treatable aluminium alloys:

Al-Cu, Al-Cu-Ni, Al-Mg-Si, etc. alloys.

2. Non-heat-treatable aluminium alloys: 

Al-Mn, Al-Mg, Al-Si, alloys.

✓ At the end of this unit, the designation, composition, properties, and typical applications of alloys of copper and aluminium were discussed.

✓ Precipitation hardening, also known as age hardening, is the most important method of strengthening i.e., hardening the most of non-ferrous alloys by solid state reaction.

✓ Bearing materials are those materials used for making bearings.

✓ A bearing material should be hard, wear resistant; and should have a low coefficient of friction.

✓ The widely used bearing materials are:

1. White metals,

2. Copper-base alloys,

3. Aluminium-base alloys, 

4. Plastic materials, and

5. Ceramics.

KEY TERMS YOU SHOULD REMEMBER

Ferrous Metals

Steels

Plain carbon steels 

Low carbon steels

Medium carbon

steels

High carbon steels

Alloy steels

Low alloy steels

High alloy steels

AISI-SAE designation

system

Mild steels

AISI steels

HSLA steels

Alloying elements

Tool steels

Stainless steels

Austenitic stainless 

steels

Ferritic stainless 

steels 

Martensitic

stainless steels 

Maraging steels

Cast iron

Grey cast iron 

White cast iron

Malleable cast iron

Ferritic

Pearlitic

Spheroidal graphite

cast iron

Alloy cast iron 

Nodular cast iron

Ductile cast iron

Non-ferrous Metals

Copper

Copper alloys

Brasses

Gliding metal

Cartridge brass

Standard brass

Muntz metal

Naval brass 

Admiralty brass

High tensile brass

Free cutting brass

Leaded gun metal

Monel metal

Bronzes

Bell bronze

Cupronickels

Phosphor bronze

Cupronickel

Silicon bronze

Coinage bronze

Leaded bronze

Aluminium bronze

Gun metals

'K' monel

Aluminium

Aluminium alloys

Al-Cu alloys

Precipitation (or age) 

hardening

Natural ageing

Artificial ageing 

Overageing

Bearing materials

White metals

Admiralty gun metal

Duralumin

Y-alloy