Alloying of Steels

Steels are alloyed with other elements to improve the properties as compared to the plain carbon steel. For example, grain size of steel can be controlled by the addition of alloying elements, such as aluminium, boron, vanadium, titanium.

1. Carbon

A small amount of carbon (C) in the range of 0.80% gives hardness and tensile strength to the steel and makes it responsive to heat treatment.

2. Manganese

Manganese (Mn) acts as a deoxidizer and improves strength and heat treat response. It’s usually 1%–2% in steel.

3. Aluminium

Aluminium (Al) is a strong deoxidizer and helps in grain size control.

4. Boron

Boron (B) is added in trace amounts (0.0005–0.003%) to improve hardenability and grain refinement.

5. Phosphorus

Phosphorus (P) increases strength but reduces ductility at low temperature. Excess phosphorus can cause cold shortness.

6. Silicon

Silicon (Si) is another common deoxidizer. In special steels (1.5%–2.5%), it improves hardenability and electrical properties.

7. Sulphur

Sulphur (S) up to 0.33% is added for machinability in free-cutting steels. Excess S leads to hot shortness.

8. Chromium

Chromium (Cr) improves hardness and corrosion resistance. Stainless steels contain 12%–25% Cr.

9. Titanium

Titanium (Ti) forms stable carbides and is used in 18-8 stainless steels for carbide precipitation control.

10. Columbium (Niobium)

Similar to titanium, used in welding electrodes and stainless steels to prevent intergranular corrosion.

11. Molybdenum

Molybdenum (Mo) enhances hardness, toughness, and creep strength at high temperatures.

12. Tungsten

Tungsten (W) refines grain size and improves cutting edge. 17–20% W is used in high-speed steels.

13. Vanadium

Vanadium (V) refines grain size and enhances shock resistance in tool steels.

14. Nickel

Nickel (Ni) improves strength and toughness, especially at low temperatures. Used in gas turbine blades.

15. Copper

Copper (Cu) improves corrosion resistance and tensile strength, with little loss in ductility.

16. Hydrogen

Excess hydrogen causes embrittlement and porosity in steels.

Summary Table