光纤激光焊接950 MPa级车用TWIP钢接头组织和性能

Microstructure and mechanical properties of fiber laser welding of 950 MPa grade twinning-induced plasticity steel for automotive industry

对950 MPa级车用孪生诱发塑性钢(TWIP950)板材进行光纤激光对接焊,分析接头微观组织和微区成分,进行显微硬度测试和室温拉伸试验,研究其不同应变速率下的拉伸性能及断裂行为.结果表明,焊缝区奥氏体组织粗化和锰元素烧损导致其出现硬度低于母材的软化现象,而热影响区发生硬化现象.随应变速率增加,母材与焊接接头的抗拉强度由负应变速率敏感性改变为正应变速率敏感性;母材与焊接接头的塑性随应变速率增加呈先下降再升高又下降的变化趋势.不同应变速率拉伸后接头均断裂在焊缝区,随应变速率增加,接头韧性断裂特征未见明显变化.

Laser welding of 950 MPa twinning induced plasticity steel( TWIP950) for automotive industry was performed using a fiber laser in a butt-joint configuration. The microstructure and chemical compositions of the welded joint( WJ)of TWIP950 steel were characterized. The microhardness of the WJ was tested. The tensile properties and fracture behavior of the investigated materials at various strain rates were examined using tensile testing machine at room temperature. The results showed that the microstructure of fusion zone( FZ) was mainly austenitic dendrite. The softening phenomenon took place in FZ due to the evaporation loss of manganese and grain coarsening in FZ. The microhardness of the outer heat-affected zone( HAZ)was higher than that of the base metal( BM). The TWIP950 BM and WJ showed strain rate sensitivity and it changed from negative to positive with increasing strain rate. The ductility of the TWIP950 BM and WJ decreased first,then increased and decreased again with increasing strain rate. The tensile specimens of the TWIP950 WJ failed in the FZs at all strain rates,and the typical ductile fracture characteristics of the tensile fracture surface did not change with increasing strain rate.