Crack analysis of M2 thread rolling roll

The reason for crack of the W6Mo5Cr4V2 （M2） thread rolling roll were investigated by optical microscope （OM），hardness test，chemical composition analysis，metallographic test，micro-analysis and carbides analysis. It was found that the microstructures of the both samples were composed of tempered martensite and carbides. There were serious network carbides，angular carbides and other eutectic structure in some places. And the carbides were exceeding.Therefore，it can be concluded that there was overheating phenomenon during the heat treatment process resulted in the increase of brittle and thermal stress of the material. The surface of ?40 mmthread rolling roll cracked under thermal stress. The 23 mm thread rolling roll brittle fractured by impact force.