1. CHAPTER 9
Engineering Alloys 1

2. Production of Iron and Steel
Production of pig iron Fe2O3 + 3CO 2Fe + 3CO2
Ore
Coke
Pig iron
(Liquid)
Blast Furnace
Pig iron is the intermediate product of smelting iron ore with a high-carbon fuel such as coke, usually with limestone as a flux.
Pig iron has a very high carbon content, typically 3.5–4.5%, which makes it very brittle and not useful directly as a material except for limited applications. 2

3. Steel Making
Pig iron and 30% steel scrap is fed into refractory furnace to which oxygen line is inserted.
Oxygen reacts with liquid bath to form iron oxide.
FeO + C Fe + CO
Slag forming fluxes
are added.
Carbon content and
other impurities are
lowered.
Molten steel is
continuously cast and
formed into shapes. 3

4. Heat Treatment Tempering 1. Softening 2. Hardening
Heat Treatment is the controlled heating and cooling of metals to alter their physical and mechanical properties without changing the product shape. Some of the objectives of heat treatment are:
1. Softening
2. Hardening
3. Material modification
Tempering
Tempering is the process of re-heating the steel at a relatively low temperature leading to precipitation and spheroidization.
Spheroidization is a process in which the excess-phase crystals are transformed into a globular (spheroidal) form.
 Tempering is done to develop the required combination of hardness, strength and toughness of fully hardened steels 4 4

5. Alloying element
Alloying element: a metal that is added in a small quantity to another metal tom improve the properties of alloys is called alloying element.
Below is a list of alloying elements and their contribution to the alloys in improving the properties:
Nickel – strength and toughness
Chromium – hardness and strength
Tungsten – hardness at elevated temperature
Vanadium – tensile strength
Manganese – high strength hot rolled heat treated condition
Silicon – high elastic limit
Cobalt – hardness
Molybdenum – extra tensile strength

6. Ferrous alloys: Have iron as their principal alloying metals
Types of Metal Alloys
Ferrous alloys: Have iron as their principal alloying metals
Wrought Iron
Steel Alloy
Cast Iron
Nonferrous alloys: Have a principal alloying metal other than iron.

7. Wrought Iron Very pure form of iron (Fe - 99.5%)
Produced by re-melting pig Iron and small amount of silicon, phosphorus and sulfur.
Malleable (capable of being shaped or formed, as by hammering or pressure), tough and ductile.
Can easily be forged and welded.
Not suitable for sudden shock.
Applications: crane hooks, chains, railway couplings

8. Steel Alloy (types) 1. Plain Carbon steel 2. Low alloy steels
Steels are iron-carbon alloys that may contain appreciable concentrations of other alloying elements. Carbon content can be less than 1.7%. Carbon is present in the form of iron carbide to impart hardness and strength.
Commercial steels are classified into one of three groups: 1. Plain carbon steel, 2. Low alloy steel, 3. High alloy steel
Mild (low carbon) steel (less than 0.3%C)
B. Medium-carbon steels (0.30 to 0.45% C)
C. High carbon steel (0.45 to 0.75 % C)
D. Very high carbon steel (up to 1.50 % C)
1. Plain Carbon steel
2. Low alloy steels
Austenitic
Ferritic
Martensitic
3. High alloy steels

9. Limitations of plain carbon steels
Cannot be strengthened beyond 690 MPa without losing ductility and impact strength.
Not deep-hardenable.
Low corrosion resistance.
Rapid quenching (sudden cooling from very high temperature) leads to crack and distortion.
Poor impact resistance at low temperature.

10. Type of Steel alloys 2. Low-alloy steels
Typical alloying elements include nickel, chromium, molybdenum, manganese, and silicon which add strength at room temperature. These alloys in the right combination, improve corrosion resistance.
Usage: automotive industry

11. 3. High-alloy steels (stainless steel)
Stainless steel is the most important commercial high-alloy steel. Stainless steels contain at least 12 % chromium, less that 1% carbon and many have high nickel contents.
The three basic types of stainless are:
A. Austenitic B. Ferritic C. Martensitic
Uses:
Chemical equipment, pressure vessels etc.
Machine parts, pumps, bearings, and valve parts

12. Cast Iron Cast iron contains 2-4% Carbon and 1-3% Si
Silicon is used to control the carbide (Fe3C) formation
Easily melted, very fluid, low shrinkage, easily machinable
Low impact resistance and ductility
Types of Cast Iron:
Gray cast iron
White cast iron
Malleable cast iron
Ductile cast iron 12

13. Types of cast irons 13

14. Applications of Cast Irons
Gray cast iron: used for manufacture of automobile engine parts
White Cast Iron : furniture
Malleable Cast Iron
Ductile Cast Iron: Pipes and fittings

15. Advantages and disadvantages of ferrous metals & alloys
Steel and other ferrous alloys are consumed in exceedingly large quantities because they have such a wide range of mechanical properties, may be fabricated with relative ease and are economical to produce.
Disadvantages
Relatively high density
Comparatively low electrical conductivity
Inherent susceptibility to corrosion in some common environments.

16. Non-ferrous metals and alloys
Magnesium
Titanium
Aluminium
Nickel
Copper
Zinc
Refractory metals (Mo, W)
Noble metals

17. Magnesium Alloys Titanium Alloys VERY POOR corrosion resistance
source: Mg is extracted electrolytically from concentrated magnesium chloride in seawater.
VERY POOR corrosion resistance
Main alloying additions : Al, Mn, Zn
Aerospace and materials-handling applications
Titanium Alloys
Excellent corrosion resistance
Main alloying additions : Al, V, Sn
aircraft structure parts, prosthetics
used widely in the chemical industries

18. Nickel Alloys Aluminum Alloys
Low density 2700 kg/ m3 (One-third the density of Steel)
Good corrosion resistance, electrical conductivity, ease of fabrication
Main alloying additions: Cu, Mg, Mn, Si, Zn, Sn, Li
Applications of Al alloys
– Aircraft construction
– Electric conductors
– Building construction
Nickel Alloys
Good strength and electrical conductivity
High corrosion and oxidation resistance
Main alloying additions : Cu, Al, Fe,Ti, Cr, Co
Applications:
Power generation equipment
Electrical and electronic parts
Food processing equipment

19. Copper Alloys Properties: High electrical and thermal conductivity
Good corrosion resistance
Applications:
Costume jewelry, cartridge casings, automotive radiators, electronic packaging