Popular alloying additions to steel include: aluminum (Al), chromium (Cr), cobalt (Co), niobium/columbium (Nb, Cb), copper (over 0.6%), manganese (over 1.6%), molybdenum (Mo), nickel (Ni), silicon (over 0.6%), titanium (Ti), tungsten (W), vanadium (V) and zirconium (Zr).
As a general rule, to obtain greater strength add carbon (C), manganese (Mn) or nickel (Ni); to obtain better corrosion resistance add chromium (Cr) or copper (Cu); for better machinability add lead (Pb), sulfur (S) or selenium (Se); for better properties at high temperature add tungsten (W) or molybdenum (Mo). Let’s explore some of these elements in more detail (Table 1).
Since carbon is such an important element, we should list the general effects of adding carbon to steel, namely:
- Raising the ultimate strength
- Enhancing the abrasive (wear) resistance
- Improving the uniformity of hardness
- Increasing the depth of hardening
- Intensifying the fineness of fracture
- Lowering the hardening and quenching temperature
- Reducing the shock resistance
- Increasing the resistance to machinability
- Lessening the heat conductivity
- Lowering the ductility and toughness
- Diminishing the electrical or magnetic conductivity
- Chromium, which is a carbide-former, increases both the hardness and wear resistance of the case and strengthens the core
- Nickel to increase strength and toughness in the core
- Vanadium to improve the strength and ductility, especially elasticity and shock resistance
- Molybdenum to raise the ultimate strength, hardness and toughness and to promote the retention of high hardness at elevated service temperature
More to follow...