Alloy Steel Welded pipe and Tube
Alloy steels are made by combining carbon steel with one or more alloying elements such as manganese, silicon, nickel, titanium, copper, chromium and aluminium. These metals are added to produce specific properties that are not found in regular carbon steel. The elements are added in different combinations making the material take on different aspects such as increased hardness, increased strength, increased corrosion resistance, improved ductility and weldability can also change. Alloy steels are generally more responsive to heat and mechanical treatments than carbon steel.
Properties of Alloy Steel
- Stabilizing ferrite – Aluminium, silicon, vanadium and molybdenum have effects on lowering carbon solubility.
- Graphitizing – Silicon, nickel and cobalt can decrease the stability in steel promoting breakdown and formation of free graphite.
- Increase corrosion resistance – Aluminium, silicon and chromium form protective oxide layers on the surface, thereby protecting the metal from further deterioration in harsh environments.
- Stabilizing austenite – Elements like nickel, cobalt, manganese and copper increases the temperature between which austenite exists.
- Decrease of eutectoid concentration – Tungsten, silicon, chromium, nickel and molybdenum all can help to lower the eutectoid concentration of carbon.
Uses of Alloy Steel
- Aluminium (0.95-1.30%) – Can limit the growth of austenite grains.
- Copper (0.1-0.4%) – It can produce hardening properties.
- Nickel (2-20%) – It increases the toughness and hardness, while also improving resistance to corrosion and oxidization.
- Boron (0.001-0.003%) – A hardening agents that improves deformability and machinability.
- Lead – Lead is added to carbon steel via mechanical dispersion during pouring, to improve machinability.
- Manganese (0.25-0.13%) – It increases the strength high temperature by eliminating the formation of iron sulphides.