Abstract
It is known that the ductility of steel lowers, when the prestrain is given to steel product. In the other, it has been clarified that the generation of the ductile crack of virgin steel can be evaluated by ductility limit curve presented by the relationship between stress triaxiality and equivalent plastic strain. In this paper, by using As-Rolled steel and TMCP steel for the sample material, the effect of the prestrain on the ductile fracture behavior was investigated. In the As-Rolled steel, the lowering of the ductility limit curve by the prestrain was confirmed. And, local cleavage crack was observed only in the fracture surface of test piece in which ductility limit curve lowers. From these results, it was clarified that the main factor of the ductility limit curve lowering was the generation of local cleavage crack. Then, we developed the technique which could uniformly evaluate the generation of the ductile crack by ductility limit curve of the virgin material by considering local cleavage crack.
