In engineering fields, metals have great importance because of every smallest part, and big machines are normally made up of metal. i.e., from the manufacturing of a needle to a big ship, metal is used. Metal is a kind of mineral substance, which is obtained from the mines after cleaning the raw materials. This raw material is known as ore.
Elements that are electropositive in nature are called metals. They have a tendency to lose electrons and form positive ions. eg., Copper, iron, aluminum, sodium, etc. Metals can be molded into a required shape because the properties of metals are based on the purposes for which they are to be employed. e.g., High hardness and strength are used to make cutting tools and soft metals which can be further used for specific purposes. In this chapter, we will study some classifications of metals and their properties.
Classification of Metals
Metals are divided into two groups on the basis of iron particles in them which are as follows.
Ferrous Metals
Metals which contain iron as a major content are called ferrous metals. These metals are attracted by magnets and their melting point is high. Ferrous metals of different properties are used for various purposes.
Some ferrous metals are as follows.
- Pig iron
- Cast iron
- Wrought iron
- Steel
1. Pig Iron
Pig iron is obtained by the chemical reduction of iron ore. This process of reduction of the iron ore to pig iron is known as smelting.
The main raw materials required for producing pig iron are as below.
(i) Iron ore
Iron ores used are magnetite, haematite, limonite, and carbonate. These ores contain iron in different proportions and are naturally available.
(ii) Coke
Coke is the fuel used to give the necessary heat to carry on the reducing action. The carbon from the coke in the form of carbon monoxide combines with the iron ore to reduce it to iron.
(iii)Flux
This is the mineral substance charged into a blast furnace to lower the melting point of the ore and it combines with the non-metallic portion of the ore to form a molten slag.
Limestone is the flux which is mostly used in the blast furnace.
2. Cast Iron
Cast iron is an alloy of iron, carbon, and silicon. The carbon content ranges from 4 to 4.5% and the remaining miscellaneous impurities such as silicon, phosphorous, sulfur, and manganese. It can be produced by melting pig iron in a cupola crucible. Cast iron is very brittle and weak in tension. Therefore, it cannot be used for making bolts and machine parts.
Machine bases, tables, and slideways are made up of cast iron because it is dimensionally stable after a period of aging. Due to its graphite content, cast iron provides an excellent bearing and sliding surface.
The following are the types of cast iron.
(i) Grey Cast Iron
It contains 2.5 to 3.7% carbon and 1 to 2.5% silicon. Grey cast iron is widely used for casting because of its ability to reduce vibration and minimize tool chatter.
Grey cast iron, when not alloyed, is quite brittle and has relatively low tensile strength. Due to this reason, it is not used for making components subjected to high stress or impact loads.
Grey cast iron is often alloyed with nickel, chromium, vanadium, or copper to make it tough. Grey cast iron is weldable but the base metal needs preheating.
The melting point is lower than that of steel and as grey cast iron possesses good fluidity, intricate casting can be made.
(ii) White Cast Iron
White cast iron contains 1.75 to 2.3% carbon, 8.5 to 1.2% silicon, 0.12% to 0.35% sulfur, and 0.05 to 0.20% phosphorous. This is very hard and difficult to machine and for this reason, it is used in components that should be abrasion-resistant. White cast iron is produced by lowering the silicon content and by rapid cooling. When cooled in this manner, it is called chilled cast iron. White cast iron cannot be welded.
(iii) Malleable Cast Iron
Malleable cast iron has increased ductility, tensile strength, and toughness when compared with grey cast iron. Malleable cast iron is produced from white cast iron by a prolonged heat treatment process lasting for about 30 h.
(iv) Nodular Cast Iron
This is very similar to malleable cast iron. But this is produced without any heat treatment. Nodular cast iron is also known as nodular iron, ductile iron, and spheroidal graphite iron. This has good machinability, castability, resistance to wear, low melting point, and hardness.
Malleable and nodular castings are used for machine parts where there is a higher tensile stress and moderate impact loading. These castings are less expensive and are an alternative to steel casting.
Uses of Cast Iron
Some uses of cast iron are as follows.
(i) It is mainly used for manufacturing bases of machines.
(ii) It is used in the main hole cover, flushing cistern, and sanitary manufacturing.
(ii) It is widely used in casting.
(iv) It is used in tables, gates, lamp-posts, etc.
3. Wrought Iron
Wrought iron is the purest form of iron. The analysis of wrought iron shows as much as 99.9% of iron. When heated, wrought iron does not melt, but only becomes pasty and in this form, it can be forged to any shape.
Composition of Wrought Iron
| Carbon | 0.02 to 0.03% |
| Silicon | 0.1 to 0.2% |
| Manganese | 0.02 to 0.1% |
| Sulfur | 0.02 to 0.04% |
| Phosphorous | 0.05 to 0.2% |
Steel (Plain Carbon Steel)
Steel is fundamentally an alloy of iron and carbon, with the carbon content varying up to 1.5%. The carbon is present in a combined state. Steels are of different types as follows.
(i) Dead mild steel
(ii) Mild steel
(iii) Medium carbon steel
(iv) High-carbon steel
Plain carbon steels are classified according to their carbon content.
Classification of Content of Plain Carbon Steels
| Name of the Plain Carbon Steel | Percentage of Carbon | Properties and Uses |
| Dead mild steel | 01 to 0.125% | High tensile. Used for making wire rods. thin sheets and solid drawn tubes |
| Mild steel | 0.15 to 0.3% | Relatively soft and ductile Used for general workshop purposes, boilerplates, bridgework, structural sections, and drop forgings |
| Medium carbon | 0.3 to 0.5% | Used for making axles, drop forgings, high-tensile tubes, wires, and agricultural tools. |
| Medium carbon | 0.5 to 0.7% | Harder, tougher, and less pliable. Used for making springs, locomotive tires, large forging dies, wire ropes, hammers, and snaps for riveters. |
| High carbon steel | 0.7 10 0.9% | Harder, less ductile, and slightly less tough Used for making springs, small forging dies, shear blades, and wood chisels. |
| High carbon steel | 0.9 to 1.1% | Used for making cold chisels, press die punches, woodworking tools, axes, etc. |
| High carbon steel | 1.1% to 1.4% | Used for making hand files, drills, gauges, metal cutting tools, and razors. |
Steel Plants in India
| SL No | Name of the Steel Plant | State |
| 01 | Tata Iron and Steel | Bihar |
| 02 | Indian Iron and Steel | West Bengal |
| 03 | Visweshvaraiah Iron & Steel | Karnataka |
| 04 | Bhilai Steel Plant | Chhattisgarh |
| 05 | Durgapur Steel Plant | West Bengal |
| 06 | Alloy Steel Plant (Durgapur) | West Bengal |
| 07 | Bokaro Steel Plant | Bihar |
| 08 | Rourkela Steel Plant | Rourkela, Orissa |
| 09 | Salem Steel Plant (stainless steel production) | Tamilnadu |
| 10 | Vishakhapatnam Steel Plant | Andhra Pradesh |
Non-Ferrous Metals
Materials can be categorized into metals and alloys, ceramic materials, organic polymers, composites, and semiconductors. The elements of tools, machines, and equipment should be made of such material which has properties suitable for the conditions of operation.
In the universe, such metals (both ferrous and non-ferrous) and nonmetals are leather, rubber asbestos, plastic, ceramics, organic polymers, composites, and semiconductors.
1. Aluminum
It is a white metal produced by electrical processes from the oxide (alumina), which is prepared from a clay mineral called bauxite. Bauxite is hydrated aluminum oxide. The chief impurities are oxide, silica, clay, and titanium oxide.
Characteristics of Aluminium
(i) It is a very good conductor of electricity and heat and its melting point is 660°C.
(ii) It is light metal and its specific gravity is 2.7.
(iii) Its ultimate tensile strength is 483 MPa.
(iv) It is ductile and malleable. So, it is broadly used for overhead cables.
(v) It has no major effect on the environment.
(vi) It is mainly used in aircraft and automobile parts.
2. Copper
It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable. A freshly exposed surface has a reddish-orange color. It is used as a conductor of heat and electricity, a building material, and a constituent of various metal alloys.
Characteristics of Copper
(i) Its electrical conductivity is 59.6 x 10⁶ S/m.
(ii) Its ultimate tensile strength is 220 MPa.
(iii) Copper does not react with water but slowly reacts with atmospheric oxygen.
(iv) It forms the basis of brasses and bronzes.
(v) Its melting point is 1083°C.
3. Brass
Brass is an alloy of copper and zinc. The fundamental binary alloy comprises 60% copper and 40% zinc. It is a very useful metal due to its qualities.
Characteristics of Brass
(i) It has greater strength than copper and aluminum.
(ii) It has a bad effect on the environment.
(iii) It is very hard as compared to copper and aluminum.
(iv) It is ductile and malleable.
(v) It has an ultimate tensile strength of 550 MPa.
4. Bronze
Bronze is a common alloy of copper and tin. The wide range of composition of these alloys comprises 75 to 95% copper and 5 to 25% tin.
characteristics of Bronze
(i) It has more strength than aluminum and copper.
(ii) Its machinability is more.
(iii) It has no effect on the environment.
(iv) It has more melting points than aluminum but less than copper.
5. Gun Metal
Gun metal is a non-ferrous alloy and contains 88% ly copper, 10% tin, and 2% zinc. It also contains a little bit of lead and nickel. It is a strong alloy and used for manufacturing of bush, tope, bearing, ship fitting, etc.
Characteristics of Gun Metal
(i) It is too hard and strong.
(ii) It is wear-resistant and used to make a bush.
(iii) It contains good machinability.
(iv) It is brittle metal.
Properties of metals
The properties of metals can be discussed in the following categories.
1. Physical Properties of Metals
The natural properties of the metals are called the physical properties. These properties are known by touching or seeing the metal.
These properties of metals are as follows.
(i) Colour
Different metals have different colors and from the colors, we can easily recognize the metal. e.g., T copper is of a distinctive red color, gold has gold color silver has white color, etc.
Metals differ based on their weight. A metal such as aluminum is lighter metal (specific gravity 2.8) than many others and a metal, such as lead, is a heavy metal (specific gravity 9).
(iii) Structure
Generally, metals can also be differentiated by their internal microstructure. Metals such as wrought iron and aluminum will have a fibrous structure and metals such as cast iron and bronze will have a granular structure.
(iv) Conductivity
Thermal conductivity and electrical conductivity are the measure of the ability of a material to conduct heat and electricity, respectively.
The conductivity will vary from metal to metal. In metals, copper and aluminum are good conductors of heat and electricity.
(v) Magnetic Property
A metal is said to possess magnetic properties if it is attracted by a magnet. Almost all ferrous metals, except some types of stainless steel, can be attracted by a magnet and all non-ferrous metals and their alloys will not be attracted by a magnet.
(vi) Fusibility
It is the property possessed by a metal by virtue of which it melts when heat is applied. Many materials are subjected to the transformation in shape from solid to liquid at different temperatures. Tin has a low melting temperature (232°C) and tungsten molts at a high temperature (3370°C).
2. Mechanical Properties of Metals
The properties of the metal by virtue of which the metal can withstand the action of external force are called mechanical properties.
The mechanical properties of a metal are as follows.
(i) Ductility
A metal is said to be ductile when it may be drawn out in tension without rupture. Wire drawing depends upon ductility for its successful operation.
A ductile metal must be both strong and plastic copper and aluminum are good examples of ductile metals.
(ii) Malleability
Malleability is permanently extending in all directions without rupture by hammering, rolling, etc. to change the size and shape of metals. The lead is a malleable metal.
(iii) Hardness
Hardness is a measure of a metal’s ability to withstand scratching, wear, abrasion, and penetration.
(iv) Brittleness
Brittleness is the property of a metal that permits no permanent deformation before breaking. Cast iron is an example of a brittle metal and it will break rather than bend under shock or impact.
(v) Toughness
Toughness is the property of a metal to withstand shock or impact by which it can be turned or twisted without breaking.
Toughness is the property opposite of brittleness. The wrought iron is an example of a tough metal.
(vi) Tenacity
The tenacity of a metal is its ability to resist the effect of tensile forces without rupture. Mild steel, wrought iron, and copper are examples of tenacious metals.
(vii) Elasticity
The elasticity of a metal is its power of returning to its original shape when the applied force is released. A properly heat-treated spring is a good example of elasticity.
3. Chemical Properties of Metals
Metals are very reactive. Metals tend to lose electrons easily and form positively charged ions, therefore metals are called electropositive elements. Sodium metal forms sodium ions Na⁺, Mg⁺ forms positively charged magnesium ions Mg2+, and aluminum forms aluminum ions A1³+. The electropositive nature allows metals to form compounds with other elements easily. Metals when burned in the presence of oxygen, combine with oxygen to form metallic oxides which are basic in nature. Metals differ in their reactivity with acids. Most metals react with acids and most metals corrode when they are exposed to the atmosphere.
e.g., the iron gets rusty after some time if it is not painted. Titanium is highly resistant to corrosion.