Gas tungsten arc welding is widely employed to fabricate large sized motor casings made of 18Ni 250 maraging steel. However, small transverse cracks have been found to appear at the interface of the dark etched heat affected zone (HAZ) of such weldments after about a year of welding, prior to aging treatment. In order to understand the delayed cracking phenomena vis-à-vis the influence of multiple weld passes, thermal cycles were obtained at different locations of the heat affected zone. The results suggest the formation of two more HAZs designated as HAZ III and HAZ IV in addition to those two currently reported in the literature. The two regions namely, HAZ III and HAZ IV, respectively correspond to peak aging and under aging conditions of the alloy. In order to examine the effect of these thermal cycles on the environmentally assisted cracking of the weldment, thermal simulations corresponding to various HAZs were applied on to specimens with Gleeble. They were examined for their susceptibility to EAC in neutral and acidified 0.1 M NaCl solutions. The study reveals that it is only the HAZ IV, lying at the interface of the dark etched HAZ, corresponding to under aging condition, is responsible for the weld failure.

气体钨极电弧焊被广泛用于制造由18Ni 250马氏体时效钢制成的大型电动机外壳。但是，发现在焊接大约一年后，在时效处理之前，此类焊件的深色蚀刻热影响区（HAZ）的界面处会出现小的横向裂纹。为了了解相对于多次焊道的影响而出现的延迟开裂现象，在热影响区的不同位置获得了热循环。结果表明，除了文献中当前报道的这两个HAZ以外，还形成了另外两个HAZ III和HAZ IV。HAZ III和HAZ IV这两个区域分别对应于合金的峰值时效和时效条件。为了检查这些热循环对焊件的环境辅助开裂的影响，将与各种热影响区相对应的热模拟应用于带有Gleeble的样品。在中性和酸化的0.1 M NaCl溶液中检查了它们对EAC的敏感性。研究表明，与老化条件相对应的，仅仅是暗腐蚀HAZ界面处的HAZ IV导致了焊接失效。