S355系列钢冲击韧性不合格原因分析

Cause analysis of impact toughness unqualified for S355 series steel

针对S355系列钢伸长率低、低温冲击功不合格的问题,对韧性不合格的S355J2钢取样,进行拉伸试验、低温冲击试验,并对其金相组织及冲击断口形貌进行观察。结果表明:组织中存在中间偏析及魏氏体铁素体组织是造成韧性不合格的主要原因。通过对热轧控轧控冷工艺进行调整,增加道次压下率、降低精轧出口温度及冷却速率等措施,使产品韧性得到较大的提高,伸长率提升5%以上,冲击功提升5倍,达到130J以上,很好地解决了S355系列钢韧性不稳定的问题。

Aiming at the problem of low elongation and unqualified low-temperature impact energy for S355 series steel,S355 J2 steel with unqualified impact toughness was sampled for the tensile and the low temperature impact testes and the microstructure and the fracture morphology examinations.The results showed that the centerline segregation and the widmanstatten ferrite organization in the microstructure was the main cause that led to the impact toughness unqualified.Through adjusting TMCP process,increasing the pass reduction and reducing the finish rolling temperature and cooling rate,the toughness of products was greatly improved with the elongation increased by more than 5%and the impact energy by 5 times（up to more than 130 J）,which well solved the ductile instability problem of S355 series of steels.