Heat-affected zone softening in high-strength low-alloy steels

Abstract

The effect of the chemistry of the steel and the welding process on the softening of the heat affected zone has been investigated. It has been observed that a steel with a high carbon-equivalent exhibited maximum softening. A steel with a low carbon-equivalent with high Ms and Bs temperatures coupled with minimum critical cooling time for nil martensite and full martensite exhibited the least softening in low-heat-input welding (SMAW), whilst a steel with longer critical cooling time for full martensite exhibited more resistance to softening in high-heat-input welding (GMAW). In general, the extent and degree of softening have been observed to be maximum in GTAW and GMAW, which are high-heat-input process. Post-weld heat-treatment in the austenite region eliminated the softened zone. External cooling methods, such as copper backing and argon purging, have been found to be useful in reducing the tendency for softening.