Effect of heat input on HAZ toughness in HSLA steels

Abstract

Commercial HSLA steel plates having different process routes, compositions, and microstructures have been welded at heat inputs from 1·5 to 9 kJ mm⁻¹. Charpy V-notch tests were used to characterize the toughness of the resulting HAZ in the as-welded and post-weld heat-treated conditions. In general, increasing the heat input lowered the low-temperature impact toughness through the formation of high-temperature transformation products such as proeutectoid ferrite, Widmanstätten ferrite, and upper bainite. However, a controlled-rolled low-carbon HSLA steel containing nickel and molybdenum exhibited good impact toughness in all welding conditions, this being attributable to a HAZ consisting mostly of acicular ferrite. Low-carbon controlled-rolled steels had better impact characteristics than quenched-and-tempered steels. Stress relief after welding generally had no significant effect on the low-temperature toughness. Hardness values in the HAZ indicated that the steels were unlikely to be susceptible to hydrogen-induced cold cracking.