Quantification of the hardness response in the heat-affected zone of low alloy steels subjected to temper bead welding

Abstract

The tempering response in the heat-affected zone (HAZ) of low alloy steels during temper bead welding is heavily dependent on the experienced thermal history. Past work has developed quantification approaches for isothermal tempering conditions and single non-isothermal tempering cycles, whereas the temper bead welding processes impart multiple non-isothermal cycles throughout the HAZ. This work outlines a novel methodology for tempering response quantification that allows for prediction of the HAZ hardness in multipass welding. The quantification approach utilizes a modification of the Grange-Baughman tempering parameter that converts non-isothermal cycles into an equivalent isothermal cycle and correlate this with the resulting hardness. This relationship can be utilized to evaluate hardness distributions throughout the HAZ of low alloy steel temper bead weldments based on the experienced thermal histories. It was shown that, in contrast with conventional heat treatment, the temper bead welding in Grade 22 steel results in nucleation of high density, finely dispersed Fe-Cr rich carbides. The proposed methodology was applied for evaluation of the HAZ hardness in a particular heat of Grade 22 steel, resulting from multiple tempering reheats, and was experimentally validated using a three-layer weld overlay. It was found that the peak temperature of weld tempering cycles was the most significant factor in controlling HAZ hardness.