"BRIGHT BAND" DEFECT ON FRACTURE SURFACE IN Cr-Ni STRUCTURAL STEELS

The investigations were conducted by TEM, SEM and IMP techniques on the problem of "bright band" defect found occasionally on the longitudinal macroscopic fracture surface in commercial Cr-Ni structural steels, e. g. 30CrMnSiNi, 40CrNiMo, 4SCrNi, etc. The influence of "bright band" on their mechanical properties has also been evaluated. Results showed that the "bright band" defect is the hydrogen damage which is caused by hydrogen interdendritic segregation during solidification of steel ingots. This defect may lower obviously the impact toughness, reduction of area as well as elongation of the steels. The mechanism of its formation and the prevention have been discussed.