Effect of heat treatment of the properties of high carbon alloyed steels

Abstract

1. Steels containing 0.5% C are much stronger and more ductile than steels with 0.8–1.25% C. However, the surface decarburization of the case hardened layer to 0.5% C may lead to a decrease in the strength because it induces tensile stresses in the surface region of the case hardened layer. 2. When the quenching temperatures of Kh2N4, Kh2N4V, and other steels containing 0.8–1.25% C are increased, then, the hardness, the resistance to bending, and the wear resistance decrease because of the increase in the amount of residual austenite. Steels with smaller amounts of alloyed elements and also steels with 0.5% C are not very sensitive to increases in the quenching temperature. The mechanical characteristics of these steels decrease only as the result of overheating. 3. High temperature tempering preceding quenching of steels of the Kh2N4 type improves the mechanical properties. This results confirms the usefulness of this operation for case hardened 20Kh2N4A steel. High temperature tempering is undesitable for case hardened 12KhN3A steel and also for other less alloyed steels. 4. Double high temperature tempering preceding quenching increases the resistance to bending and the impact strength of case hardened samples of 18Kh2N4VA steel. 5. Treatment at very low temperature increases the hardness and the wear resistance but decreases the impact strength and in most cases decreases the resistance to bending of steels with 0.8–1.25% C. 6. The increase in the hardness of case hardened machine parts as a result of treatment at low temperature results from the increase in the compression stresses in the case hardened layer during the transformation of the residual austensite into martensite. However, treatment at very low temperature increases the brittleness of the case hardened layer.