Analysis of the Formation of Surface Crack on Crankshaft After Die Forging

The causes are investigated for the formation of surface crack on a crankshaft based on numerical simulation, light microscopy and SEM analysis in this study. It is concluded that inclusion is not the reason for the crack initiation. Coarse microstructure and shrinkage cavities were found in the centre of billet, and then were observed to flow to the crack by 3D simulation analysis of forging process. In order to identify the simulation result, the size and distribution of prior austenitic grain and shrinkage porosities at the crack on the crankshaft were analyzed. Results show that the size of prior austenitic grain and shrinkage porosities and the volume fraction of shrinkage porosity are larger at the crack compared with that at other part of the crankshaft. The work shows that the coarse microstructure and shrinkage cavities flowing from the centre of the billet is the cause of the surface crack during the induction hardening process.