Alloy Steel

Plain C steels contain C in the range of 0.04 to I .2. Additionally they contain Mn as 0.3 to 1.04%, Si as up to 0.3%, S as 0.04% Max P as 0.05% Max. Other Carbon no element has important effect on mechanical properties except that Mn might provide some harden-ability. S and P are undesirable elements. Some advantages in terms of enhanced mechanical properties and corrosion resistance are obtained by adding one or several alloying elements as like Si, Mn, Ni, Cr, Mo, W, V, u, B, Al. The various advantages of alloy steel as:

• Higher hardness, robustness and strength, hardness on surface and above bigger cross-section.
• Better harden-ability and retention of hardness at higher temperatures as good for creep and cutting tools.
• High resistance against oxidation and corrosion.

The properties of steel affected by the alloying elements are described below:

(a) By strengthening ferrite while forming a solid solution. Hence the strengthening effects of various alloying elements are in this order: Cr, V, W, Mo, Nickel, Mn and Silicon.

(b) By forming carbides which are stronger and harder. Carbides of Cr and V are hardest and after tempering, strongest against wear particularly. High alloy tool steel use this effect.

(c) Ni and Mn lower the austenite formation temperature when other alloying elements raise such temperature. Most elements shift eutectoid composition to lower Carbon % age.

(d) More elements shift the isothermal transformation curve or TTT to lower temperature, hence lowering the critical cooling rate. Mn, Ni, Cr and Mo are prominently effective in this respect. Effects of individual alloying elements on properties of steel as: