Effect of heat input on HAZ toughness in HSLA steels

AbstractCommercial 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, Widmanstatten 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...