不锈钢城轨车辆电阻焊疲劳性能研究

Study on Fatigue Property of Electric Resistance Welding on Stainless Steel Urban Rail Vehicles

不锈钢城轨车辆多采用SUS301L冷轧不锈钢薄板,结构以电阻焊连接为主,车辆运行过程中电阻焊接头会受到复杂载荷作用而失效,疲劳断裂是其主要的失效形式。研究电阻焊接头受力情况,对于改善和优化焊接结构设计、电阻点焊工艺及使用寿命评估具有重要意义。文章针对不同强度等级、不同厚度组合的电阻点焊接头进行疲劳试验,分析疲劳性能与SUS301L不锈钢强度和厚度的关系,结果表明:SUS301不锈钢板厚≤4 mm时,板厚的增加有助于疲劳强度的提高;奥氏体不锈钢板SUS301强度等级分别为DLT、ST、MT、HT,在材料板厚一致的条件下,电阻点焊疲劳极限随着材料抗拉强度增加呈现先上升再降低的趋势,与强度等级无直接的正比关系。对不锈钢电阻焊疲劳断裂微观分析,发现试样受力发生偏转,热影响区形成应力集中,电阻点焊试样疲劳裂纹在热影响区萌生并向母材区扩展,疲劳断口呈脆性断裂特征。

Stainless steel urban rail vehicles are mostly made of SUS301L cold-rolled stainless steel sheet and mainly in structure connected by electric resistance welding(ERW).During the operation of vehicles,ERW joints may fail under the action of complex loads and the fatigue rupture is the main form of failure.The study on the stress situation of ERW joints is of great significance for improving and optimizing the design of welded structures and the resistance spot welding process and evaluating the service life of ERW joints.This article describes the fatigue tests on resistance spot welding joints with different strength grades and different thick combinations and analyzes the relation between the fatigue property and the strength and thickness of SUS301L stainless steel sheet.Results of study show when the thickness of SUS301 stainless steel sheet is≤4 mm,the increase of sheet thickness helps to increase the fatigue strength;considering the SUS301 austenitic stainless steel sheet has the strength grades of DLT,ST,MT and HT,when the sheet thickness is the same,the fatigue limit of the resistance spot welding shows a trend of increasing at firstly and then decreasing with the increase of the tensile strength of material,without any direct proportional relation with the strength grade.The microanalysis performed on the ERW fatigue rupture of stainless steel shows that the sample has a deflection under stress,which the heat-affected zone forms the stress concentration,that the fatigue cracks of the resistance spot welding sample initiate in the heat-affected zone and expand to the base metal zone and the fatigue fracture presents the characteristic of brittle rupture.