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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。
The fatigue test of the TRIP steel joint under the optimal spot welding process with the strength of 600 MPa was carried out. The SN curve of the joint after the spot welding of the steel plate was obtained. The fatigue life of the TRIP600 steel after spot welding was analyzed according to the hardness distribution and the results of the fatigue fracture appearance Reasons for drastic reduction. The results show that the fatigue limit of TRIP600 after spot welding is 75 MPa, only 15.6% of the base metal. The sources of fatigue cracks in the welded steel plate all produced the high temperature heat affected zone (HAZ) around the nugget, the boundary between the high temperature quenched martensite and the lowest tempering temperature of the superbainite. This area has the lowest strength, is prone to plastic deformation and causes stress concentration. Here quenched martensite coarse, brittle, low ductility, and there is a large residual tensile stress, as well as the axial tensile stress and the stress composite stress, the crack easily sprout and expansion.