35 MN液压机主缸正常作业时，缸体下部发生大量漏油现象。拆卸后通过宏观分析、磁粉检测、低倍检验、力学性能检验以及金相检验等方法对缸体周向裂纹产生原因进行分析。结果表明：裂纹源于缸体外圆R角处，由外壁向内壁扩展，缸体过渡圆弧处表面加工刀痕和力学性能远低于技术要求导致周向裂纹的产生并造成漏油现象发生。

During the normal operation of 35 MN hydraulic press, a large amount of oil leakage occurred at the lower part of the main cylinder. After disassembly, the causes of circumferential cracks in the cylinder block were analyzed by means of macroscopic examination, magnetic particle testing, macroscopic examination, mechanical property inspection and metallographic inspection. The results showed that the crack originated from the R angle of the outer circle of the cylinder and then extended from the outer wall to the inner wall. The surface machining knife mark and mechanical properties at the excessive arc of the cylinder were much lower than the technical requirements, which caused circumferential cracks and oil leakage.