桁架梁用热轧盘条焊接失效断裂原因分析

Cause analysis of welding failure and fracture of hot rolled wire rod for truss beam

桁架梁用热轧盘条SAE1021Cr在完成首尾焊接后,拉拔过程中焊点经常断裂。追溯盘条母材冶炼、轧制过程,确认工艺稳定,对母材化学成分、气体含量、显微组织、非金属夹杂物等进行分析,均满足产品技术条件要求。对比发现:与焊接良好样品相比,焊接断裂样品焊点区域显微组织存在大量网状铁素体、少量的粒状贝氏体及魏氏组织。分析认为:网状铁素体降低了钢的强韧性,导致焊接部位失效,拉拔时断裂,而这种不良组织是焊接工艺不合理引起的。

The welding spot of SAE1021Cr hot rolled wire rod for truss beam often breaks during drawing process after the end to end welding.Trace smelting and rolling process of wire rod base metal,confirm the process stability,analyze chemical composition,gas content,microstructure and non-metallic inclusions of base metal,all meet the requirements of product technical conditions.It is found that there are a large amount of network ferrite,a small amount of granular bainite and widmanstatten in microstructure of weld joint area of welded fracture sample compared with well welded sample.The analysis shows that network ferrite reduces strength and toughness of the steel,result in failure of welding part and fracture during drawing,which is caused by improper welding process.