点焊后TRIP600钢板的疲劳性能

Fatigue performance of TRIP600 steel plate after spot welding

对最佳点焊工艺下强度为600 MPa的TRIP钢接头进行疲劳试验,获得了钢板点焊后接头的S-N曲线,结合硬度分布和疲劳断口形貌结果,分析了点焊后TRIP600钢板的疲劳寿命大幅降低的原因。结果表明,点焊后TRIP600钢板的疲劳极限为75 MPa,仅为母材的15.6%。焊后钢板疲劳裂纹源均产生在熔核周边未焊合的高温热影响区,高温淬火马氏体区与超级贝氏体最高温度回火最低硬度区的交界部位。该区强度最低,极易发生塑性变形,并引起应力集中。此处的淬火马氏体组织粗大,脆性较大,延塑性很低,且存在较大的残余拉应力,以及轴向拉应力和幅向应力的复合应力,使裂纹极易萌生并扩展。

Fatigue test of TRIP 600 steel plate joints under the best spot welding process was carried out and the S-N curve of steel plate joint after welding was obtained.According to the hardness distribution and fatigue fracture morphology results,the cause of severe reduction of the fatigue life of TRIP600 steel plate after welding was analyzed.The results show that fatigue limit of the steel plate after spot welding is only 75 MPa,which is 15.6％ of the base metal.Fatigue crack source of steel plate after welding is located in the high temperature heat affected zone,which arounds the molten core,transition area between the martensite zone by high temperature quenching and the lowest hardness zone of super bainite zone by high temperature tempering.The strength of this region is the lowest,which is easily to occur plastic deformation and lead to stress concentration.The microstructure of this zone is coarse and brittle quenching martensite which has lower plasticity and contains a larger residual tensile stress and the complex stress consisting of the axial tensile stress and circumferential stress,which makes the crack initializes and propagates extremely easily.