Cast steel shot and grit abrasives - produced from boron contg. steel to avoid intermediate hardening heat treatment

摘要

Cast steel shot, having a tempered martensite structure of hardness 40-50 HRC, is produced by (a) directing a stream of refined molten steel through a fluid stream under pressure and into a fluid quenching bath, and (b) tempering the cast shot. Alternatively, grit having a martensite structure of full hardness may be produced by crushing the cast shot instead of step (b). Also claimed is as-cast steel shot having a martensite structure of full hardness (and its prodn. by step (a)) made of steel of compsn. (by wt.) 0.6-1.20%C, 0.50-2.26% Mn, 0.3-1.80% Si, 0.0-0.1% S, 0.0001-0.01% B, balance Fe and impurities. Addition of boron improves hardenability of the steel, and at levels of 62 HRC, improves hardness by about two points HRC so that an intermediate hardening heat treatment can be eliminated even when the shot is to be ground to form grit. These properties are obtained with grains coarsening as a result of boron addition.