Microstructure and fatigue properties of resistance spot welding joints of 1.4003 stainless steel and Q345NQR2 weathering steel
王羽 1王红伟 1梁涛 1闫国瑞 1宋睿2
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作者信息
1. 中车唐山机车车辆有限公司,河北 唐山 063000
2. 大连交通大学材料科学与工程学院,辽宁 大连 116028
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摘要
通过金相组织分析、硬度试验、脉动拉伸疲劳试验及疲劳断口形貌分析,研究了 1.5 mm 1.4003+3 mm Q345NQR2电阻点焊接头的组织和疲劳性能.结果表明:Q345NQR2钢母材组织为白色铁素体+层片状珠光体,1.4003铁素体不锈钢母材组织为多边形或无规则型铁素体,Q345NQR2侧HAZ分为正火细晶区和过热粗晶区,正火细晶区珠光体较细小,过热粗晶区珠光体较粗大,1.4003铁素体不锈钢侧HAZ为单一块状的多边形铁素体,晶粒度4～5级,熔核区显微组织为少量珠光体、贝氏体、板条马氏体与极少量残余奥氏体混合组织.熔核区硬度值在425HV～505HV之间,明显高于母材及熔合线处硬度.疲劳断口位于熔核区,其接头指定寿命为1×107次循环下的中值疲劳强度,2.875 kN.
Abstract
Through metallographic structure analysis,hardness test,pulsating tensile fatigue test and fatigue fracture morphology analysis,the microstructure and fatigue properties of resistance spot welding joints of 1.5 mm 1.4003 stainless steel+3 mm Q345 weathering steel were studied.The results showed that the structure of Q345NQR2 steel base metal was white ferrite+lamellar pearlite,the structure of 1.4003 ferritic stainless steel base metal was polygonal or irregular ferrite,the thermal influence of Q345NQR2 was divided into normalized fine grain area and superheated coarse grain area,the pearlite in the normalized fine grain area was finer,the pearlite in the superheated coarse grain area was coarse,the 1.4003 ferritic stainless steel side heat affected zone was a single block polygonal ferrite,the grain size was 4～5 grade,and the microstructure of the molten core area was a small amount of pearlite,bainite,slatted martensite mixed tissue with a very small amount of residual austenite.The hardness value of the molten core zone was between 425HV～505HV,which was significantly higher than the hardness at the base metal and the fusion line.The fatigue fracture is located in the molten core zone and has a median fatigue limit of 2.875 kN at a specified life of 1×107 cycles.
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