Published Paper Details:

Material strengthening that occurs during cold forming is an important means for increasing the stability of car body components. For this reason, different types of steel have been developed with increased strengthening potential in recent decades. A general problem occurs, if cold-formed components are joined by welding, since the welding locally resets the elaborately adjusted material condition. The present study investigates the interrelation of the strain hardening and the applied TIG (Tungsten-Inert-Gas) welding process, with a particular focus on a TRIP and a TWIP steel with high Mn contents. The investigations comprise hardness and microindentation tests as well as X-ray diffraction experiments of specimen that are pre-deformed to specific strains and subsequently TIG-welded with various linear energies. Instrumented microindentation tests are performed to determine force - indentation depth curves. The characteristic values derived from those curves are compared with results of a systematic peak profile analyses of measured X-ray interference lines. The results show that the measurement methods used enable detailed statements about the strengthening condition after cold forming and the local changes in the weld seam environment. Finally, the integral widths of X-ray diffraction lines can be correlated very well with distributions of local microhardness and can further be used to interpret the relationships between strain- and transformation-induced strengthening, deformation-induced retained austenite transformation and thermally induced softening. The results highlight the changes of the material states induced by welding and therefore emphasize the need to optimize welding practices and therefore improve the performance of high-strength steels in industrial applications.