Failure analysis of cold forged 37Cr4 alloy M10x28 bolts

This paper covers experimental and numerical studies on the crack evolution on cold forged 37Cr4 high strength steel M10x28 bolts. Numerical simulations of forging operations were prepared on SIMUFACT FORMING finite element software. Failure evolution in simulations was predicted by using Cockroft-Latham damage model. Possible surface defects on work-pieces were also considered in the study. Artificial surface defects were generated on work-pieces by using electric discharge machine to determine the effects of defects on crack formation and propagation. As followings, numerical predictions on crack evolution were verified by conducting forging experiments. It was determined that deviation of the punch during forging led formation of shear cracks on the bolt head. Artificial surface defect was found to trigger crack evolution and affect the shape and propagation of the crack. Shear cracks propagated though the head of the bolt with 52° inclination angle while cracks triggered by surface defect propagated perpendicularly though longitudinal axis of the bolt.