分别采用焊前预热和不预热的两种焊接工艺对X70管线钢进行焊接, 采用光学显微镜、拉伸试验机和冲击试验机研究了焊接接头的显微组织、拉伸性能和冲击性能。结果表明: 焊前预热接头的组织多为细小的针状铁素体、多边形铁素体等, 而不预热接头的组织中晶粒明显长大, 出现粗大粒状贝氏体和少量马氏体;焊前预热的焊接接头其抗拉强度和冲击韧性较不预热的好些, 但不预热焊接工艺焊接的接头仍能满足性能要求;考虑工程到建设成本方面, 不预热的焊接工艺可用于X70钢焊接。

X70 pipeline steel was welded using two welding processes with preheating and without preheating before welding, respectively. The microstructure, tensile property and impact property of welded joints were studied by optical microscopy, tensile testing and impact testing. The results show that the microstructure of the joint with preheating before welding consisted of small acicular ferrites and polygonal ferrites. The grains of the joint without preheating grew up significantly, coarse granular bainites and a small amount of martensites could be found in its microstructure. The joint with preheating had the better tensile strength and impact toughness, compared to that without preheating. But the properties of the joint without preheating still met requirements. Considering the engineering economic costs, the process without preheating can be used in the welding of X70 steel.