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

The effect of the chemistry of the steel and the welding process on the sof tening of the heat affected zone has been investigated. It has been observe d that a steel with a high carbon-equivalent exhibited maximum softening. A steel with a low carbon-equivalent with high M-s and B-s temperatures coup led with minimum critical cooling time for nil martensite and full martensi te exhibited the least softening in low-heat-input welding (GMAW), whilst a steel with longer critical cooling time for full martensite exhibited more resistance to softening ill high-heat-input welding (GMAW). In general, th e extent and degree of softening have been observed to be maximum in GTAW a nd GMAW, which are high-heat-input process. Post-weld heat-treatment in the austenite region eliminated the softened zone. External cooling methods, s uch as copper backing and argon purging, have been found to be useful in re ducing the tendency for softening. (C) 1999 Elsevier Science S.A. All right s reserved.