Abstract: The vertical-cracking on spring buffer of a train produced were found after quenching.Quenching cracking reason of the spring was analysis by using chemical compositions analysis,hardness test,facture analysis,inclusion and microstructure observation.The results show that the main reasons of the cracking were the thick,big and large amount of zonal segregation and large nonmetallic inclusions which were distributed in rolling direction of the materials during the quench hardening.The inlusion and the zonal segregation made the homogeneity of microstructure and properties get worse,the large nonmetallic inclusions became the crack region.The crack was formed and propagated as a function of structure strain.