End and Centre Defects Analysis of 40Cr Grinding Bar

After annealing, straightening and smooth turning, the finished product 40Cr grinding bar inspection revealed that some polished end face had serious depression and centre hole defects. Formation reason of the defects was analyzed with the methods such as macroscopic analysis, metallographic test, SEM observation, EDS analysis etc. The result show that the end and centre defects of 40Cr grinding bar were formed during the straightening process after the annealing treatment because of the internal tensile stress in the bar. At the same time, the inclusions were thin and length, opposite and concentrated along axial center of the sample, which may be the cause for formation the centre hole defects.