Alloying elements are added to plain carbon steel to change the properties of iron and steel. Addition of alloying elements helps in increase of the strength, hardness, roughness & heat
resistance of steel. Common alloying elements are manganese, nickel, chromium, molybdenum, tungsten, vanadium, boron, niobium and aluminium. The limitation of carbon steel is removed
by the use of alloy steel. The presence of alloying elements improves hardness, resistance to corrosion and resistance to oxidation. The alloying steel has increased resistance to
abrasion . High temperature tools and their improved performance are due to the use of alloy steel. Alloy steels require elaborate processing, handling and finishing works.
Alloy steels are also expensive in comparison to plain carbon steel.
Tungsten
Tungsten is used as alloying element of steel to provide capability of heat resistant and resistant to corrosion.
Since, the carbide of tungsten is very hard, it is used in small quantity in tool steel. A hot work tool has tungsten in small amounts as alloying elements.
Manganese
Manganese is added to plain carbon steel for removal of oxygen and carbon. It increases tensile strength, hardness and toughness of plain carbon steel.
The plain carbon steel becomes more ductile due to the addition of manganese.All structural steel have manganese content to meet the toughness of the construction work.
Manganese steel is used for making of gears, axles, rifle barrels, spline shafts.
Nickel
Nickel is extensively used along with manganese. Low nickel contents provide strength and toughness to plain carbon steel. Increase in the nickel content produces austenite steel which
is soft, ductile, tough and non-magnetic. The popularity of nickel is because of the graphitizing effect on cementite. A little over 1% of manganese with 3% of nickel is added to produce
high quality alloy steel. Addition of chromium and molybdenum also helps in improvement of quality steel.
Chromium
Chromium provides additional strength to carbon steel. The hardness increases due to carbide stabilizing character of chromium. Nickel is added to chromium to produce wear resistant.
Nickel chromium steel is used for high temperature applications like crown wheel, shaft, bearings and gears.
Molybdenum
Addition of molybdenum to nickel chromium steel increases hardness of alloy nickel steel. Molybdenum also increases wear resistance character of alloy steel.
So, nickel chromium molybdenum steel has wide applications in transmission gears, spline shaft, pressure vessels, automobile axles and locomotive bearings.
Vanadium
Addition of vanadium produces fine grain steel. Vanadium carbide increases the abrasion and wears resistance of carborised steel. Leap springs, coil springs, heavy duty axles, gears,
valves, pinions, torsion bars and automobile parts are made out of vanadium steel. Use of chromium vanadium steel is in high speed tools and heat resisting tools.
Conveyer chains, furnace shell, rotors, burner nozzles and exhaust valves are made of chromium vanadium steel.
Other elements like cobalt, boron and titanium have special applications in alloy steel making. Cobalt is used in nickel chrome steel for production of heat resisting tools.
Titanium is used in stainless steel and special alloy steel used in chemical industries. Boron is used in alloys that have wide ranging applications in nuclear reactor and other
nuclear establishments. Addition of silicon is made to produce shock resistant tools like chisels and punches. Niobium is added to produce hot dipped metallic sheets.
Aluminium is added to produce high strength low alloy steel used in body works of automobile.