Definition of Metal and Alloy
• The basic chemical elements are divided into metals and non-metal• however there is no sharp
dividing line between the two.
Metals• A metal may be defined as a chemical element that
possesses ‘Metallic properties’ • Metallic properties’ are defined as:
–good thermal and electrical conductivity- Capability of being permanently shaped or
deformed at room temperature–in electrolysis, carries a positive charge that
is liberated at the cathode.(-)
Non - Metals
• Chemical elements lacking these properties are classed Non – Metals most non-metallic elements do not possess ‘metallic properties’, and in electrolysis the non-metals carry negative charges that are liberated at the anode. Of all the natural chemical elements, about 70 are metals and, of these 39 are used commercially.
Alloy
• An alloy is a Metallic , but it is not a single chemical element. • An alloy is formed by the union or
mixture of two or more metals; in some cases, it may consist of one or more metals and nonmetal.
Ferrous material
• Ferrous material refers to those materials whose main constituent is iron
• One very special property of ferrous materials is that, their properties can be altered by heat treatment processes or by addition of small quantities of alloying elements
Ferrous material
• Iron is the name given to the metal, whose chemical symbol is Fe and refers to pure
• Pure iron is relatively soft and less strong. Its melting point is about 1540°C
• Steel, on the other hand, is an alloy of iron and carbon; the percentage of carbon theoretically varies from 0 to 2%. However in actual practice, carbon rarely exceeds 1.25–1.3%.
CLASSIFICATION OF STEELS• Steel can be classified into:Plain carbon steel: Plain carbon steel is that steel in
which the only alloying element present is carbonAlloy steel: elements like chromium, nickel, tungsten, molybdenum, and vanadium are also present and they make an appreciable difference in the properties of steel.
Plain carbon steel• Since the properties of plain carbon steels are so
dependent upon their carbon percentage:(i) Low carbon or dead mild steel having carbon below 0.15%,(ii) Mild steel having carbon between 0.15–0.3%,(iii) Medium carbon steel having carbon between 0.3–0.7%, and(iv) High carbon steels having carbon content above 0.7% (the higher practical limit of C% is 1.3%). • As the carbon percentage increases, the strength and
hardness of plain carbon steel increases while ductility decreases
Microstructure, mechanical properties, and uses of plain carbon steels
WROUGHT IRON
• It is the purest form of iron; although it may contain traces of carbon.
• It is very costly and its use has been almosttotally replaced by cheaper steel.
CAST IRON• Cast irons contain more than 2% carbon. • Carbon content of most cast irons is between 3 to 4 per
cent.Melting point of cast iron is much lower than that of steel. Most of the castings produced in a cast iron foundry are of grey cast iron. These are cheap and widely used.
• There are many varieties of cast iron:- (i) Grey cast iron,- (ii) White cast iron,- (iii) Malleable cast iron,- (iv) Nodular cast iron, and- (v) Alloy cast iron.
ALLOY STEELS
• The main object of alloying in steels are:- (i) Alloy steels can be hardened by heat treatment processes to greater depth and with lessdistortion and less chance of cracking. -(ii) Alloying develops corrosion resisting property as in stainless steels.-(iii) Alloying develops the property of red hardness as in cutting tool.-(iv) Alloying develops the strength and toughness of steels as in high strength low alloy (HSLA) steels.-(v) Some alloy steel show a marked resistance to grain growth and oxidation at high temperatures
ALLOY STEELS• Stainless steels. These steels are called stainless because they
do not corrode.-(i) Ferritic stainless steel. These steels contain a maximum of 0.15% carbon, 6–12% chromium,0.5% nickel besides iron and usual amounts of manganese and silicon. These steels are stainless and relatively cheap-(ii) Martensitic stainless steel. These stainless steels have 12–18% chromium but contain higher carbon percentage (0.15–1.2%).• -(iii) Austenitic stainless steels. These are the most important
and costliest among all stainless steels. In these steels, besides chromium, nickel is also added
The most common amongst stainless steel is 18/8 steel. Its composition is 18% chromium, 8% nickel, 0.08–0.2% carbon, manganese 1.25% maximum and silicon 0.75% maximum.
ALLOY STEELSTool steels:High speed steel (HSS) is the name given to a most common tool steel. Its name implies that it can cut steel at high cutting speeds. At high cutting speed, the temperature rise is higher but high speed steel tools can retain their hardness up to 600–625°C. A typical composition of H.S.S. is tungsten 18%, chromium 4%, vanadium 1%, carbon 0.75–1%, rest iron.
Non-ferrous metals and alloys
• Non-ferrous metals and alloys do not contain any significant quantity of iron. The most common nonferrous metals used in engineering applications are copper, aluminium, tin, lead and zinc. Nickel
PROPERTIES AND USES OF NON-FERROUS METALS
• Copper : is a corrosion resistant metal of an attractive reddish brown color. It is an extremely good conductor of heat and electricity.
• Aluminum : is also very corrosion resistant (because an adherent oxide layer protects it from further oxidation).
PROPERTIES AND USES OF NON-FERROUS METALS
• Tin: It has an attractive silvery white colour. It has very good resistance to acid corrosion
• Lead: Lead is a heavy metal with dull grey appearance. It has good corrosion resistance and has got good malleability
• Zinc: Zinc possesses a bluish grey metallic appearance. It has high corrosion resistance. In fact, steel sheets are often covered by a thin coating of zinc.
ALLOYS OF COPPER• BrassBrass is an alloy of copper and zinc. Commercially, two types of brasses are most important:1. Alpha brass. It contains up to 36% zinc and remainder is copper.2. Alpha-Beta brass. It contains from 36% to 46% Zn, remainder is copper.• α-brasses can be sub-divided into two groups:(i) red-brasses containing up to 20% Zn, and(ii) yellow brasses containing over 20% Zn.
ALLOYS OF COPPER
• Bronzes: Bronze is an alloy of copper and tin although commercial bronzes may contain other elements besides tin. In fact, alloys of copper with aluminium, silicon and beryllium, which may contain no tin are also known as bronzes.
ALLOYS OF COPPER
• CUPRO-NICKELS• Cupro-nickels are alloys of copper and nickel• Cupro-nickels are silvery white in colour and
have extremely good corrosion-resistance They also possess good strength, hardness and ductility
