Analysis on Quenching Cracking in Sustain Top

The reasons of quenching cracking in the big sustain top used in the universal grinder were analyzed through macroscopic inspection, metallographic examination, hardness testing and fracture analysis. The results showed that the cracking had the characteristics of longitudinal cracking and cross-sectional cracking in the large non-hardened parts. The critical reason was that there were loose, nonmetallic inclusions, serious netted carbide in the central of big sustain top, which weakened the strength of fragile split. The maximal shearing and axial tensile stress exceed the strength of fragile split when sustain top was quenched, which resulted in the longitudinal cracking and cross-sectional cracking.