Heat treatment of some temperature-resistant carburizing steels

Abstract

The heat treatment of some Mo-Cr-V secondary hardening carburizing steels was investigated. The compositions selected for study were chosen because 1) they can be readily softened by annealing, and 2) they do not require excessively high temperatures for carburizing. Both of these characteristics are desired for ease of manufacturing.After carburizing these steels at 955° C and oil quenching, the as-quenched core hardness is retained with little change for tempering temperatures up to 600° C, but the case hardness decreases slowly with increasing tempering temperature, reaching values of 52–54 Rc after tempering at 550° C. The case depths, case carbon content, retained austenite content and residual stress resulting from carburizing the experimental alloys were compared with the same properties measured on SA E 8620 steel. It was found that the surface oxides which form on V-bearing steels during heat treatment in endothermic gas-base carburizing atmospheres interfere with carburizing. For this reason, steels with 0.15 wt. pct. V or less are preferred for carburizing.Because of their enhanced resistance to softening at elevated temperatures compared to conventional carburizing steels, carburized secondary hardening steels should provide improved resistance to surface damage under conditions of marginal lubrication.