酸轧2 GPa热成形钢焊缝断带原因分析及对策

针对某企业生产2 GPa热成形钢酸轧后焊缝断带的问题,利用金相显微镜和扫描电镜对断带试样进行了分析,并通过对焊接及酸轧工艺过程的调查,确定了焊缝断带的原因:带钢焊缝二次回火不充分,存在回火马氏体脆性组织;由于带钢强度高,圆盘剪易崩刃,切边质量较差,在轧制过程中形成边裂缺陷,当边裂缺陷处于焊缝时,诱导存在回火马氏体脆性组织的焊缝解理开裂,在张力的作用下撕扯开裂并贯穿整个焊缝而造成。为此,对焊缝二次回火工艺参数进行了优化,提高了加热功率和降低了带钢速度,以保证焊缝充分回火得到回火索氏体组织,避免了回火脆性组织;同时,通过优化圆盘剪工艺参数及加强剪切带钢边部质量检验,避免了酸轧后的边裂缺陷,杜绝了轧制时2 GPa高强带钢由于边裂缺陷诱发焊缝撕裂而造成的断带事故。

Causes analysis and countermeasures of welding seam breakage during picklingand cold rolling of 2 GPa hot forming steel strip

Aiming at the problem of welding seam breakage during pickling and cold rolling of 2 GPa hot forming steel strips in an enterprise, the broken strip samples were analyzed by metallographic microscope and scanning electron microscope, and the welding and rolling process were inspected. The reasons were found out. The secondary tempering of the welding seam was insufficient, and the tempered martensitic brittle structure was obtained. Meanwhile, due to the high strength of the strip, the disc shear was easy to chip, and the quality of the trimming was relatively low, and edge crack defects were formed during the rolling process. When the edge crack defects were in the welding seam, cleavage cracking were induced by tempered martensitic brittle structure, and the crack was torn and penetrated through the entire welding seam to cause the strip breakage. Therefore, the process parameters of the secondary tempering of the welding seam were optimized, the heating power was increased and the strip speed was reduced to ensure that the welding seam was fully tempered to obtain a tempered sorbite structure, and the tempered brittle structure was avoided. The process parameters of the disc shear was optimized and the edge quality of the sheared strip was inspected to avoid the edge crack defect after pickling and cold rolling, and welding seam breakage accident of the 2 GPa high-strength strip during rolling was avoided.