Alloy Steels

Alloy Steels

Alloy steels are alloys of iron with the addition of one or more of the following elements:

carbon, manganese, silicon, nickel, chromium, molybdenum, and vanadium. The alloy steels cover a wide range of steels, including low-alloy steels, stainless steels, heat-resistant steels,

and tool steels.

 Some alloy steels, such as austenitic stainless steels, do not contain intentional

additions of carbon. Silicon, when required, is added as a deoxidizer to the molten steel. Nickel

provides strength and assists in hardening the steel by quenching and tempering heat treatment.

This latter effect is called hardenability, which has been described earlier. Chromium is found in

stainless steels for corrosion resistance. Chromium and molybdenum also assist in hardenability

of the low-alloy steels. Vanadium strengthens the steel by forming precipitates of vanadium

carbonitride. Vanadium is also a potent hardenability element.

Low-Alloy Steels

There is an SAE/AISI four-digit classification system for the low-alloy steels. 

As in the carbon

steels, the first two digits are for the alloy class and the last two (or three) digits are for the

carbon content. Because of the various combinations of elements, the system is more extensive

than that used for the carbon steels.

Higher Alloy Steels

There is a distinction between the low-alloy steels described above and the higher alloy steels

(usually containing over 8% alloying elements). 

The higher alloy steels include stainless steels,

tool steels, heat-resistant steels, wear-resistant steels, and ultrahigh-strength steels.