Behavior of Cu precipitates during thermo-mechanical cycling in the weld CGHAZ of Cu-containing HSLA steel

Abstract

The behavior of Cu precipitates in the weld coarse-grained heat-affected zone (CGHAZ) of 1.5 wt% Cucontaining high strength low-alloy (HSLA) steel subjected to a thermal/thermo-mechanical welding cycle and post-weld heat-treatment (PWHT) was evaluated. The welding cycles of CGHAZ and PWHT were simulated by the Gleeble system. The hardness was measured at each PWHT condition, and observation and analysis of the Cu particles were performed using HRTEM. The hardness decreased initially with an increasing PWHT time at 550 °C. However, the peak hardness resulting from precipitation of Cu particles occurred after about 60 min at 550 °C. In the thermo-mechanical cycle, the peak hardness appeared at an earlier PWHT time. These results correspond with the HRTEM observations in which Cu particles were observed at an earlier PWHT time and larger Cu particles were observed at the same given PWHT time after the thermo-mechanical cycle. Thus, this paper confirms that the kinetics of Cu precipitation can be accelerated by an intrinsic mechanical cycle during the welding cycle.