Analysis of Failure of a Chassis Long Member Manufactured from E-46 Grade Hot-Rolled Steel Coil

摘要

In the present study, failure investigation was performed to find the root cause of the defects that occurred during bending operation for fabrication of a long chassis member. The component was manufactured from E-46 grade hot-rolled coil with ferrite-pearlite microstructure. Several longitudinal cracks were formed on one side of the outer bends of the long member. Detailed microstructural examination revealed occurrence of long unidirectional unbranched cracks with deposits and intermittent stringers of nonmetallic entrapments in the rolling direction. EDS analyses showed majority of these deposits and entrapments were FeO-rich manganese silicate associated with silicomanganese and ferromanganese alloy added to the molten steel for chemistry adjustment. Bending operation of the coil perpendicular to the rolling direction of steel sheet and orientation of the entrapments as well to cold form the chassis long member resulted in high degree of stress concentration around the entrapments. Finally, localized tearing of the outer surface layer of the bend at multiple locations occurred.