某工程机械销轴在服役过程中发生断裂。通过宏观观察、化学成分分析及金相检验等方法，对该工程机械销轴断裂的原因进行了分析。结果表明：销轴在焊接过程中形成淬硬的马氏体组织，产生较大的内应力，加上焊材和热影响区界面熔合带内杂质富集，形成微裂纹源，在外力作用下微裂纹扩展，并最终导致销轴发生了脆性断裂。

A construction machinery pin shaft cracked during service. The causes of cracking on construction machinery pin shaft were analyzed by means of macroscopic observation, chemical composition analysis and metallographic examination. The results show that the hardened martensite structure was formed during the pin shaft welding process, which producted a large internal stress. In addition, with the enrichment of impurities in the fusion zone at the interface between the welding material and the heat affected zone, a source of microcracks was formed. The microcracks expanded under the external force and eventually led to the brittle fracture of pin shaft.