焊后热处理对拘束焊焊缝金属冲击韧性与断裂韧性的影响

针对DH36钢厚板拘束焊焊接接头进行了620 ℃ × 2 h的焊后热处理,测试了热处理前后焊缝金属的冲击韧性和断裂韧性,对比分析冲击韧性与断裂韧性的差异,同时研究了焊后热处理的影响及其韧化机制. 结果表明,焊态下焊缝金属的冲击韧性良好,而断裂韧性较差;焊后热处理后,冲击韧性没有明显变化,但断裂韧性显著上升,平均CTOD值由0.123 mm显著升高至0.707 mm. 一方面,焊后热处理引起位错密度降低,位错缠结显著减少,细小碳化物析出并球化,有利于韧性的改善;另一方面,焊后热处理可消除大厚板拘束焊产生的应变时效局部脆化现象,提高断裂韧性. 由于冲击韧性与断裂韧性测试结果存在较大差异,采用单一温度的冲击韧性评估拘束焊焊缝金属的韧性与结构安全性可能存在风险.

Effects of PWHT on the impact toughness and fracture toughness of the weld metal under restraint welding

The post-weld heat treatment (PWHT) was conducted on the thick-plate DH36 weld metal under restraint welding, and the impact toughness and fracture toughness of the weld metal before and after PWHT were tested. The differences between the effects of PWHT on the impact toughness and fracture toughness were compared and analyzed, and its toughening mechanisms were investigated. The results show that the weld metal has well impact toughness on as-welded (AW) condition, but its fracture toughness is poor. After PWHT, there is no obvious change in the impact toughness of weld metal, but the fracture toughness increases significantly, with the average CTOD value rising from 0.123 mm to 0.707 mm. PWHT causes the improvement of toughness through the decrease of dislocation density, the significant reduction of dislocation tangles, and the precipitation and spheroidization of fine carbides. It can meanwhile eliminate the local embrittlement inside of the weld metal caused by the strain aging effects, thus improving the toughness. In addition, the results of the tested impact toughness of weld metal are quite different from those of the fracture toughness. Therefore, there may be risks in using single-temperature impact toughness as the only criterion to evaluate the toughness and the safety of the thick-plate weld metal under restraint welding.