Effect of quench rate and refrigeration on the mechanical properties of HP9-4-20 steel

Abstract

Difficulties in obtaining adequate mechanical properties in the HP9-4-20 portion of the B83 structural midcase have raised some questions concerning the effect of quench rate and post-quench refrigeration on the strength and toughness of the material. As a result, a program was initiated to determine if either of these parameters contributed to the observed degradation in properties or whether some other step in the processing history of the material was responsible. Initially, the nominal cooling rate of a full size mid-case was calculated numerically using a finite difference thermal conduction code. A series of HP9-4-20 steel samples was then processed with quench rates which bracketed this calculated cooling rate. It was found that neither quench rate nor refrigeration had a significant effect on the mechanical properties at cooling rates that might reasonably be encountered in production hardware. Consequently, it was concluded that the inadequate mechanical properties exhibited by early B83 mid-case components were related to an improper tempering heat treatment, and not an inadequate quench.