CHAPTER 9 Engineering Alloys 1

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

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

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

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

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.

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

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

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.

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

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

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

Types of cast irons 13

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

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.

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

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

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

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