低应力破坏是焊接结构常见的断裂形式之一,为确定其影响因素,采用插销法焊接试验和扫描电镜断口观察,研究了低合金钢焊接热影响区的静载断裂特性。试验结果表明,为防止焊接热影响区产生低应力断裂,采用预热措施是十分有效的;预热80℃以上时,断裂强度与母材强度相接近。断口观察表明,不预热时绝大部分为结晶状断口,微观上呈现氢致沿晶断裂和氢致准解理断裂;预热时绝大部分是纤维状断口,微观上呈韧窝状。 Low-stress failure is one of the common forms of fracture in welded structures. To determine its influencing factors, the static load-breaking characteristics of HAZ of low-alloyed steel were studied by using the pin welding method and scanning electron microscope (SEM) fracture observations. The test results show that the preheating method is very effective to prevent low stress fracture in HAZ. When the preheating is above 80 ℃, the breaking strength is close to that of the base metal. Fracture observations show that most of the fractures are not fractured when preheated, and there are microscopic fractures of hydrogen induced quasi-cleavage and cleavage caused by hydrogen. Most of the fractures are fibrous fractures when preheated, and are microscopically dimpled.