钎焊间隙对钎焊接头残余应力的影响

Effect of brazing gap on residual stress of brazed joints

在等静压石墨/BNi-2/304不锈钢套管式真空钎焊试验的基础上,使用有限元分析软件对钎焊接头在不同钎焊间隙下残余应力的大小和分布进行模拟,结合试验对模拟结果进行分析说明,判断接头薄弱区。结果表明,对于等静压石墨管和不锈钢管钎焊接头,304不锈钢侧和BNi-2钎料层中的残余应力对接头强度的影响不大;随着钎焊间隙增加,径向残余应力减小,接头强度提升,但钎焊间隙过大时会使接头拉断,影响母材连接;通过模拟分析发现,当钎焊间隙为50μm左右时,母材连接不充分;当钎焊间隙为150μm左右时,获得良好接头;当钎焊间隙为250μm左右时,受304侧与石墨侧的径向残余应力共同作用下,接头产生环形裂纹;当钎焊间隙为350μm左右时,沿轴线方向距接头顶部约900μm、沿径向方向距钎料约600~1000μm处的等静压石墨为接头薄弱区,并产生环状裂纹衍生至接头端面。

On the basis of vacuum brazing test of isostatic pressed graphite/BNi-2/304 stainless steel,residual stress and distribution of brazed joints under different brazing gaps were simulated by finite element analysis software,and simulation results were analyzed and explained in combination with the test to identify weak area of brazed joints.The results showed that residual stress in 304 stainless steel side and BNi-2 brazing filler metal layer had little effect on strength of brazed joints for isostatic pressed graphite pipe and stainless steel pipe brazed joints.With the increase of brazing gap,radial residual stress decreased and strength of brazed joints increased.However,when brazing gap was too large,brazed joints were broke by tensile force and affected connection of base metal.The simulation analysis showed that connection of base metal was not sufficient when brazing gap was about 50μm.When brazing gap was about 150μm,good brazed joints were obtained.When brazing gap was about 250μm,brazed joints produced annular cracks under combined action of radial residual stress on the 304 side and the graphite side.When brazing gap was about 350μm,weak area of brazed joints was isostatic pressed graphite about 900μm away from the top of brazed joints along the axis and 600~1000μm away from brazing filler metal along the radial direction,and annular cracks were derived to the end face of brazed joints.