CMT增材X80钢组织和性能与韧性调控措施

针对油气管道在线修复需求，采用自主设计的低碳微合金焊丝，进行X80管线钢管的冷金属过渡(CMT)增材修复工艺优化研究。在管道服役后的X80管线钢管基板上制备增材体，观察显微组织形貌，并进行显微硬度、冲击试验和拉伸试验测试。试验结果表明，CMT增材体微观组织为板条贝氏体和少量准多边形铁素体。随着向基板过渡，板条铁素体逐渐转变为粒状贝氏体。CMT增材修复后X80管线钢基板热影响区没有发生软化。CMT增材体显微硬度是基板的119%；CMT增材体不同方向室温冲击吸收能量平均值约为基板的74%；CMT增材体不同方向断后伸长率平均值约为基板的66%，抗拉强度从大到小依次为扫描方向、搭接方向、垂直方向，其数值为基板抗拉强度的103%～114%。建议通过控制CMT增材体横截面上焊道边界(鱼鳞纹线)分布特征，减少金属经历的高温热循环次数，进而在一定程度上改善增材修复增材体韧性。 创新点： (1)系统研究了冷金属过渡(CMT)增材制造X80管线钢的组织和性能。 (2)提出了通过控制增材体横截面上焊道分布特征来改善增材修复增材体韧性。

Microstructure and mechanical properties of CMT additive X80 steel and control measures of toughness

Aiming to online repair needs of oil and gas pipeline, optimization of CMT additive repair process was carried out by self-designed low-carbon micro alloy welding wire. Additive manufacturing metal was prepared on X80 steel substrate after service, whose microstructure, microhardness, impact absorbed energy and tensile strength were tested. The results showed that lath bainite and a small amount of quasi-polygonal ferrite appeared in additive manufacturing metal. From additive manufacturing metal to substrate, lath ferrite transformed to granular bainite. There appeared no softening in heat affected zone of X80 steel substrate after CMT additive repair. Microhardness of additive manufacturing metal was 119% that of substrate. Average impact absorbed energy of additive manufacturing metal in different directions at room temperature was about 74% that of substrate. Average elongation of additive manufacturing metal in different directions was about 66% that of substrate. Tensile strengths of additive manufacturing metal from large to small were in the order of scanning direction, lap direction and vertical direction in turn, and tensile strength ranged from 103% to 114% that of substrate. It was suggested that controlling boundary distribution characteristics of passes (fish-scale lines) on the cross section of additive manufacturing metal could reduce its number of high temperature thermal cycles, thus to improve toughness of additive manufacturing metal to a certain extent. Highlights: (1) Microstructure and mechanical properties of cold metal transition (CMT) additive manufactured X80 pipeline steel were systematically studied. (2) It was proposed to improve toughness of additive repair additive manufacturing metal by controlling distribution characteristics of passes on the cross section of additive manufacturing metal.