装配条件对X80钢外根焊接头成分与性能的影响

X80钢管道铜衬垫外根焊全自动焊接过程中，装配条件的改变对铜衬垫熔化导致的Cu元素向焊缝扩散及接头的力学性能具有一定影响。系统地分析了不同对口间隙与错边量对X80钢管道铜衬垫外根焊全自动电弧焊接接头的Cu元素含量和力学性能的影响。通过能谱分析和化学成分分析对焊缝中的Cu元素含量进行表征，利用拉伸试验、常温冲击试验及背弯和侧弯试验测量不同装配条件下接头的力学性能。结果表明，对口间隙大于1.0 mm或错边量大于3.0 mm的装配条件下焊缝成形质量差；在保证获得良好焊缝成形的条件下，对口间隙和错边量的增大会导致根焊层底部Cu含量的增加，但不同条件下焊缝的Cu元素含量均低于0.5%(质量分数)，铜衬垫的使用对焊缝Cu元素含量影响不大。接头的力学性能测试结果显示，不同装配条件下得到的接头抗拉强度和冲击韧性差异较小，且拉伸试样均断裂在母材位置，热影响区的冲击韧性优于焊缝，而对口间隙和错边量的增加会降低接头的弯曲性能。创新点： 研究了不同装配条件对X80钢管道铜衬垫外根焊接头的Cu元素含量和力学性能的影响，发现对口间隙和错边量的增大会导致根焊层底部Cu元素含量的少量增加及接头弯曲性能的下降，而对接头的抗拉强度及冲击韧性无显著影响。

Effect of assembly conditions on composition and mechanical properties of X80 steel outer root welded joints

Abstract: During fully automatic welding process of X80 steel pipe copper liner outer root welding, change of assembly conditions has an effect on diffusion of Cu element into welded joints due to melting of copper liner and mechanical properties of welded joints. Effect of different counter gaps and misalignment on Cu element content and mechanical properties of X80 steel pipe copper liner outer root welded joints by fully automatic arc welding were systematically analyzed. Cu element content of the weld was characterized by energy spectrum analysis and chemical composition analysis, and mechanical properties of welded joints were measured under different assembly conditions by tensile tests, room temperature impact tests, and back and side bending tests. The results showed that welded joints were poorly formed under the assembly conditions with a butt gap more than 1.0 mm or a misalignment more than 3.0 mm. Under the condition of ensuring good formation of weld, the increase in butt gap and misalignment would lead to an increase in Cu content at the bottom of the root weld layer, while Cu element content of the weld under different conditions was less than 0.5%, and the use of copper liner had little effect on Cu element content of the weld. The mechanical properties of welded joints showed that differences in tensile strength and impact toughness of welded joints obtained under different assembly conditions were small, and tensile specimens were fractured at the base metal, and impact toughness of heat-affected zone was better than that of the weld, while the increase in the amount of butt gap and misalignment would reduce bending properties of welded joints.Highlights: Effects of different assembly conditions on Cu content and mechanical properties of the outer root welded joints of copper liner of X80 steel pipe were studied. It was found that increase of butt clearance and misalignment would lead to a small increase in Cu content at the bottom of root welding layer and a decrease in bending properties of welded joints, while it had no significant effect on tensile strength and impact toughness of welded joints.