A study on resistance welding in steel sheets for tailor welded blank: Evaluation of flash weldability and formability (2nd Report)

In a recent report [K.B. Min, K.S. Kim, S.S. Kang, A study on resistance welding in steel sheets by tailor welded blank (1st Report) — Evaluation of upset weldability and formability, J. Mater. Process. Technol., in press] discussion of the upset weldability and formability of a tailor welded blank (TWB) was discussed, the results being the followings. (1) From the result of the tensile test, the tensile strength of the location of welding is almost the same as that of the original material as long as there are no special problems at the location of welding. Rupture occurs in the material of little transformation resistance, not at the place of welding; (2) The most influencing causes of fine crystal at the place of welding are the pressure and the temperature and, especially in upset welding, the good mechanical characteristics can be obtained because the crystal of the welding part was made fine by the increase of pressure during cooling; (3) As shown by the results of the Erichson cup test, the formation ability of the welded sample was a little lower than that of the original material. Based on these results, this study presents discussion of the flash weldability and formability of TWB. In the current work, the press formability analysis of the welded parts was studied using a TWB. The press formability was tested by means of the flash weldability and the formability of two kinds of materials (SPCC and S35C). The results indicate that SPCC and S35C steel sheets show good weldability and formability after using the optimum welding conditions. The independent operation variables were characterized by the strength of the welded parts and the reproducibility of welding. The evaluation of the flash weldability and formability of SPCC and S35C by means of tensile, hardness, microstructure and V-bending tests is performed. The weldability and quality of the welded parts of the flashed SPCC steel sheet are superior to those of the S35C steel sheet, since a higher carbon content in the sheet led to a higher hardness.