低合金钢制方管闪光对焊裂纹的原因分析  

Cause analysis of crack in flash butt welding of low alloy steel square pipe

作　　者：孙乾 徐瑞亮 尹海元 李承 朱高峰 刘珊珊 SUN Qian;XU Ruiliang;YIN Haiyuan;LI Cheng;ZHU Gaofeng;LIU Shanshan(Technology Center,Laiwu Branch,Shandong Iron&Steel Co.,Ltd.,Jinan 271104,China;Shandong Lubi Building Materials Co.,Ltd.,Jinan 271104,China;Marketing Corporation,Shandong Iron&Steel Co.,Ltd.,Jinan 271104,China)

机构地区：[1]山东钢铁股份有限公司莱芜分公司技术中心,山东济南271104 [2]山东鲁碧建材有限公司,山东济南271104 [3]山东钢铁股份有限公司营销总公司,山东济南271104

出　　处：《物理测试》2024年第1期37-43,共7页Physics Examination and Testing

摘　　要：针对7.5 mm厚Q355B钢带焊接制方管时横向焊接裂纹问题,经成分分析、力学性能检验、金相组织等检验,结果表明,母材钢带组织为铁素体+珠光体+极少量贝氏体,符合标准要求;方管起裂位置在焊缝热影响区,裂纹末端金属晶粒扭曲,属于应力裂纹撕裂后延展形貌,组织为塑韧性极差的魏氏组织,且焊缝处存在严重割裂基体连续性的大尺寸簇状夹杂物;综合分析,认为焊接功率较大、冷却速度过快,导致焊缝生成粗大的魏氏组织,严重降低焊缝塑韧性,结合焊缝熔池Si、Mn氧化物等夹杂排出不净,割裂焊接处组织连续性,在后续矫正工序拉应力作用下,形成裂纹延展,是造成焊后横向裂纹的主要原因。通过优化闪光对焊工艺,合理控制焊缝奥氏体晶粒尺寸,可有效避免该类问题。Aiming at the transverse welding crack problem of Q355B steel strip(thickness of 7.5 mm)during the preparation of square pipe by welding,the composition analysis,mechanical property inspection and metallographic structure inspection were conducted.The results showed that the structure of base metal steel strip was composed of ferrite+pearlite+very small amount of bainite,which could meet the standard requirements.The crack initiation position of the square tube was in the heat-affected zone of the weld.The metal grains were distorted at the end of crack,which belonged to the extension morphology after stress crack tearing.The microstructure was the Widmannstatten structure with extremely poor plastic toughness,and there were large-size cluster inclusions at the weld which severely cut the continuity of the matrix.After comprehensive analysis,it was believed that the high welding power and too fast cooling speed led to the formation of coarse Widmannstatten structure at the weld,which seriously reduced the ductility and toughness.Combined with the impurity discharge of inclusions such as Si and Mn oxides in the weld pool,the continuity of the weld was destroyed.Under the action of tensile stress in the subsequent correction process,the crack extension was formed,which was the main reason to cause transverse cracks after welding.Such kind of problems could be avoided by optimizing the flash butt welding process and reasonably controlling the austenite grain size in the weld.

关 键 词：Q355B钢带 珠光体 焊接 裂纹 魏氏组织 

分 类 号：TG457.11[金属学及工艺—焊接]