Hardenability of Carbon and Low-Alloy Steels
Carbon steels have wider usage than any other metal because of their versatility and low cost. Required hardenability is the most important factor influencing a choice between carbon- and alloy steel. By increasing hardenability, alloying elements extend the potential for enhanced properties to the large sections required for many applications. Alloy steels are ordinarily quench hardened and tempered to the level of strength desired for the application. Distortion during heat treatment may occur with almost any hardenable carbon or alloy steel, although distortion is usually more severe for carbon grades than for alloy grades of equivalent carbon content. The relatively low hardenability of carbon steels is a primary reason for choosing them in preference to alloy steels for parts that are to be locally heat treated by flame or induction hardening. Fabrication processes are performed on hardenable carbon and alloy steels in the unhardened condition, that is, prior to heat treating.