Alloy Steels

To obtain special properties, some elements such as nickel, chromium, manganese, etc., are added to the carbon steel. Steels thus formed are called alloy steels.

The addition of alloying elements is effected to attain one or more of the following properties:

1. To improve the fine-grain size content of steel.
2. To improve case-hardening properties.
3. To improve the elastic properties of steel.
4. To improve corrosion and fatigue resistance.
5. To improve hardness and toughness.
6. To improve machinability.
7. To improve tensile strength.

Alloying materials have the following properties:

1. Nickel: It increases toughness and improves responses to heat treatment. When added in large quantities, it provides special electrical and magnetic properties.
2. Chromium: Helps to provide stainless properties in steel. It is used in making tool steels and electrical plates.
3. Manganese: Improves heat treatment properties and is used in high-speed tool steels.
4. Tungsten: It retains the hardness property of steel and toughness at a high temperature. It is used exhaustively in the manufacture of tools, dies, valves, magnets, etc.
5. Silicon: It provides high electrical resistance and magnetic permeability in electrical machinery.
6. Copper: It improves corrosive resistance even when added in minute quantities.

Some of the alloy steels are discussed below:

1. Silicon Steel

Silicon steel has high electrical properties and has very low magnetic hysteresis when present in about 3.5%.

Silicon steel is used in the manufacture of different materials in combination with other metals with a lesser percentage. The various materials made include springs, internal combustion engines, laminations of electrical machines, etc.

2. Nickel Steel

The percentage of nickel added varies from 2 to 40. Elastic limit and toughness are increased with about 4% of nickel. The tensile strength is highly increased with 20% nickel. To make the steel non-corrosive and non-magnetic, the nickel percentage should be about 27%. If the nickel content is 3.5% and about 0.3% of carbon, the nickel steel formed is highly ductile and such a material is used for long span bridges.

3. Manganese Steel

The steel attains very high tensile strength with toughness and non-magnetic properties when the presence of manganese is around 12.5%. Manganese steel is weldable and forgeable. Heat-treated cast manganese steel in bar form is extremely ductile that it can bent when cold without fracturing. Manganese steel has a high percentage of elongation. It is used in the jaws of crushers, rails, helmets, shields, etc.

4. Tungsten Steel

The hardening and magnetic properties are improved with the addition of tungsten to steel. The addition of a high percentage of tungsten makes the steel retain its hardness even at a high temperature. It is used for making permanent magnet and high-speed cutting tools.

5. Stainless Steel

Stainless steel is of chromium-based steel. They form two groups, viz., plain chromium and high-chromium low-nickel steel and chromium nickel steel. The first type is used for dies, valves and cutlery and can be heat-treated. These steels can be heat-treated chromium nickel steels, which are non-magnetic and can not be hardened. They have high resistance to corrosion. Further, they may be cold or hot worked, pressed, welded, barbed or soldered.