Abstract: The quenching cracking causes of integrated forged hammer core for 3000kJ hydraulic piling hammer were analyzed by means of macro analysis, micro fracture analysis, energy spectrum analysis, dye flaw detection, chemical composition analysis, macroscopical examination and metallographic analysis. The results show that there are a lot of non-metallic inclusions and serious segregation in the matrix which leads to axle journal fracture; the chemical composition segregation of large ingot(300t and above) is a root cause of quenching failure of large-section solid forgings.