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本文通过使用宏观观察、金相分析、断口分析和电子背散射衍射（EBSD)等分析手段对高频焊管焊后弯管开裂的原因进行了分析。结果表明焊缝区域晶粒内部多边形化的亚晶是导致汽车排气管焊缝区域韧性下降、硬度升高的原因，最后在弯管成型时，焊缝处受到拉应力导致开裂。从焊缝处的发现的晶粒内存在的大量多边形化的亚晶的现象推断出出现问题的工艺段，通过改进，消除了弯管成型开裂的情况。

The reason of the Weld Joint Cracking on high frequency welding pipe was investigated by using macroscopic observation、metallographic technology、fracture analysis and EBSD technology.The resuits show that the the subgrains of polygonization are the reason that cause the ductility decreasing and the hardness rising,the weld joint cracked because of the tensile stress when the pipe was bended.We found the place where the processing set-up was wrong by analysing the phenomenon and solved the cracking problem through the improvement.