To decrease the car body weight and improve crash safety, tailor-welded blanks have been used for car body materials. In the past, little research had been conducted on the formability of the weld metal (WM). This study focuses on the bendability of the WM evaluated by the bending test. The main results are as follows. (1)The bendability of the laser-welded specimens was better than that of the plasma-welded specimens. (2) The bendability of the weld line (WL) was related to the homogeneity of the WM structure, and increased with increasing homogeneity. (3) The surface roughness of the WL has no effect on the bendability of the WL. (4) The deformation of the bent surface of the WL changed with the WL width, and the bendability increased as the WL narrowed because the bent surface showed increasing uniaxial stretching deformation.

In this study, we develop a method for identifying the ductile fracture limit in a stress triaxial range corresponding to surface cracks, such as upsetting in cold forging. A series of fracture tests including 4 types of notched round bar tensile tests and 3 types of 3-point bending tests are carried out experimentally and numerically. All investigation is conducted using carbon steel S45C. The loading path of stress triaxiality at the fracture point of the specimens is identified by finite element analysis (FEA), and the parameters of the exponential ductile fracture model are determined. Critical compression ratios of upsetting tests are predicted using the ductile fracture model taking into account the positive stress triaxiality. Furthermore, the fracture surface of each specimen is observed by scanning electron microscopy (SEM), and the diameter distribution of the dimples is investigated.