Regularities of Oxidation and Decarburization of Special Alloy Steels in the BCC→FCC Phase Transformation Temperature Range

Abstract

Regularities of oxidation and decarburization of special alloy steels 12KhN, 30G1R, 35KhGSA, 40Kh, and 62S2KhA in the temperature range 800–950°C of their phase transformation from ferrite to austenite are investigated. It is established that for all steels there is a general regularity in steady growth of lost metal layer thickness as a result of oxidation with an increase in heating duration and temperature. For special alloy steels, the depth of the decarburized zone decreases (possibly, with a subsequent increase) with an increase in isothermal aging temperature and transition from zones for ferrite existence into austenite. Superposition of these two processes leads to an increase in decarburized zone depth on holding steel in the temperature range of the presence of ferrite. Therefore, in order to prevent the occurrence of decarburized zones that have an unfavorable effect on cold upsetting capacity for round bars, it is expedient to accelerate special alloy steel billet heating to a temperature near 900–950°C.