Microstructure and Toughness in HAZ of HQ130 Steel

The effec of different peak temperature (Tm) and cooling time (t_8/5) on microstructure, hardness, impact toughness and fracture morphology in the heat-affected zone (HAZ) of HQ130 steel was studied by using matallography, SEM and the weld thermo-simulation test.Experimental results indicated that the impact toughness in the simulated HAZ was higher when Tm=1350℃ and t_8/5 from 5s to 2s.But when t_8/5=40s, impact toughness decreased obvioulsy.Impact toughness was decreased when Tm change from 1350℃ to 800℃, under the conditions of a single thermal cycle.There was a brittle zone in the vicinity of Tm=800℃,where the inpact toughness was considerably lower.There was softened zone in the vicinity of Tm=700℃, where the hardness was decreased but the toughness was higher.In practical welding application of multi-layer and multi-pass welding, the welding heat input should be strictly limited (q/v≤ 20kJ/cm), to reduce the softness and brittleness in the HAZ of HQ130 steel.