Abstract

To form a required shape of the advanced high strength steels especially DP steel sheets, shearing process being one of major processes is commonly used. In general, although the good cut-edge with small fracture could be achieved by setting small shearing clearance, the tearing being a major defect commonly occurred on the cut-edge. Therefore, in the present research, a tearing mechanism on the DP steel sheet, grade SPFC980Y (JIS) during shearing process is investigated and clearly clarified based on the microstructure evolution, fracture mechanism, and stress distribution analysis. The microstructure evolutions on both tensile test specimen and sheared workpiece were performed to clarify the fracture mechanism. The angle between shear band and elongated grain flow direction is examined based on tensile test and it is used to predict an angle of initial fracture and its propagation on the shearing process as well. By associated with stress distribution analysis generated in shearing zone during shearing phase, the results revealed that the fracture propagated out of shearing zone and the fracture could be easily delayed. This resulted in that the tearing could be generated in the case of SPFC980Y. Vice versa, the fracture propagation is all in shearing zone, the fracture could not be delayed and the fracture completely generated on the cut-edge in the case of SPCC. In the present resents, the tearing mechanism on the DP steels in shearing process is clearly characterized.

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