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从整车试验中发生内漏的304不锈钢换热器失效问题入手,采用宏观检查、金相检验、能谱分析和有限元仿真模拟方法,从组织形貌、合金元素扩散、应力集中等角度分析了不锈钢换热器钎焊接头的失效原因,讨论了不等间隙接头的形成原因及对接头应力集中情况的影响。结果表明:换热器失效原因为产品凸台处钎焊接头发生疲劳断裂,裂纹在钎缝圆角处萌生,并在剪应力作用下扩展至钎缝下侧界面,随后沿强度相对较低的钎焊界面进一步扩展。钎焊过程中接头成形较好,无明显焊接缺陷。但由于焊前装配误差造成凸台位置接头钎焊间隙不等,工况下局部位置的应力集中使得接头服役寿命有所降低。
Beginning with the failure of 304 stainless steel heat exchanger with internal leakage during the vehicle test, macroscopic examination, metallographic examination, energy spectrum analysis and finite element simulation are used to analyze the failure of 304 stainless steel heat exchanger. The reasons for the failure of stainless steel heat exchanger brazed joints were discussed, and the formation of unequal gap joints and the influence of stress concentration on the joints were discussed. The results show that the failure of the heat exchanger is due to the fatigue fracture of the brazed joint at the bosses of the product. The crack initiation occurs at the fillet of the brazing seam and extends to the interface below the brazing seam under the effect of shear stress. Brazing interface to further expand. During the brazing process, the joint is well formed with no obvious welding defects. However, due to pre-welding assembly errors caused by the boss position joints brazing gap ranging from the local conditions under stress concentration makes the service life of joints reduced.