某18CrNi8钢制针阀体在进行可靠性试验时，运行10 h即发生端面销孔开裂。通过宏观检验、化学成分分析、扫描电镜分析、金相检验以及硬度测试等方法对销孔开裂的原因进行了分析。结果表明：该针阀体销孔开裂模式为脆性断裂。由于热处理工艺不当，销孔表面碳势过高形成了网状碳化物，不仅破坏了基体的连续性，还使得销孔部位成为高淬硬区，晶界被弱化，在内应力和外加轴向应力作用下，裂纹萌生并不断扩展最终导致该销孔开裂。最后提出了相应的预防措施。

Cracking occurred in the pinhole at the end face of a needle valve body made of 18CrNi8 steel during reliability test for about 10 h. The cracking causes of pinhole were analyzed by macroscopic examination, chemical composition analysis, scanning electron microscopy analysis, metallographic examination and hardness test. The results show that the cracking mode of needle valve body pinhole was brittle fracture. The surface carbon potential of pinhole was so high that reticulated carbide formed due to improper heat treatment process, which destroyed the continuity of matrix, the pinhole part became high hardening zone and the grain boundary was weakened. Under the action of internal stress and external axial stress, crack initiated and propagated and eventually led to the pinhole cracking. Finally, the preventions were put forward.