Control of temper embrittlement in Ni-Cr-Mo-V steel by combining intercritical and low temperature austenitizing heat treatments

Abstract

It is demonstrated in three heats of a Ni-Cr-Mo-V steel that dramatic reductions in both initial transition temperatures and susceptibility to temper embrittlement may be achieved by intercritical heat treatments. However, it appears that the temperature control necessary to ensure sufficient strength in large forgings of this class of steel will preclude the use of the treatment as a substitute for a complete austenitize. An approach to exploit the intercritical treatment as a conditioning procedure is described following the discovery that much of the reduced embrittlement susceptibility is remembered after a low temperature austenitize. Thus, by combining an intercritical and low temperature austenitize, the available temperature range for the intercritical treatment is widened because the minimum strength requirement is eliminated. Also, the full austenitize allows conventional tempering treatments to be used. The results are supported by fractography, metallography and Auger analysis.