Alloy Steels means the alloy of steel with some other metal or metals. This “Other metal” has a remarkable effect on the properties of steel. For example, ordinary steel tends to rust in humid air but addition of some chromium and nickel to steel gives an alloy steel which does not rust at all. Some of important alloy steels are as following:

1. Stainless Steel: Stainless Steel is an alloy steel containing up to 18 per cent of chromium and nickel. Stainless Steel is resistant to corrosion. It is used for making utensils and surgical instruments etc.
2. Manganese Steel: Steel containing 7 to 20 per cent of manganese is very hard, tough and resistant to wear and tear. Manganese steel is used for making steel helmets, rock-crushing machinery and burglarproof safes.
3. Tungsten Steel: Steel having 15 to 20 per cent of tungsten, 5 per cent of chromium and a little of vanadium is called tungsten steel. It retains hardness even at high temperatures. Tungsten steel is used for making drilling tools and cutting tools for high speed lathes.
4. Silicon Steel: Silicon steel containing about 15 per cent of silicon is extremely hard and resistant to acids. It is used for making pumps and pipes for carrying acids. Silicon steel containing up to 35 per cent silicon is used for making transformers and electromagnets.
5. Cobalt steel: Steel containing up to 35 per cent possesses exceptionally good magnetic properties. So, cobalt steel is used for making permanent magnets.
6. Nickel Steel: Nickel steel containing about 3.5 per cent nickel is hard and elastic and resists corrosion. It is used for making bicycle parts, automobile parts and aero planes parts (like wire cable, gears, drive, shafts and propeller shafts). It is the percentage of nickel is 36 per cent, and then this nickel steel is used for making scientific instruments. The nickel steel containing 46 per cent nickel is used for making lamp bulbs and radio valves.
7. Chromium Steel: It contains about 2 to 4 per cent of chromium. It has high tensile strength. Chromium steel is used for making ball bearings, cutting tools such as files, and cutlery.