Microfractographic features in fracture surfaces for tensile, fatigue, impact, three point bending specimens of cold forging die steels with Rockwell C scale hardness number of 52 to 68 are presented. The emphasis is placed upon the stretched zone formation ahead of the fatigue crack and the relation between the stretched zone width and fracture toughness. Fatigue crack initiation behavior of plane and notched specimens are also characterized in low cycle up to giga-cycle ranges. A couple of microfractographic analyzed results for failed actual cold forging dies are exemplified. It can be concluded that qualitative and quantitative analysis by use of microfractograpy are possible for cold forging die failures.
