Influence of mechanically induced hardening on the generation of welding residual stresses

• Applicant: Dr.-Ing. Thomas Nitschke-Pagel
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2015 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 273371116

When steels are welded, the large temperature difference between weld and base metal causes stresses which can lead to cyclic plastic deformation, especially in the heat-affected zone. This process directly affects the development of welding residual stresses, as these are often limited by the yield strength. Therefore, suboptimal modelling of the mechanical hardening can lead to discrepancies between numerically and experimentally determined welding residual stresses. In the first research project concerning this topic, the mechanical hardening behavior of welded high-alloy steels was studied, which are not subject to any phase transformations. In a continuation project, the analyses shall be extended to steels with phase transformations, which additionally affect the hardening state. Since high-strength phases are present, structural hardening effects superpose those of the mechanical hardening. Moreover, transformation plasticity occurs which accounts for additional mechanical hardening. Finally, it is unclear if and how a mechanical hardening state is transferred from one phase to another during a transformation.Therefore, the aim of the continuation project is to fill the knowledge gap which is responsible for the significant discrepancies between computationally and experimentally obtained residual stresses in welded steels with phase transformations. To this end, the material behavior of two structural steels with different yield strengths is characterized comprehensively. Based on these results, simulations will be performed using different material models, whose results have to be compared to experimentally obtained residual stresses and hardening effects. Eventually, the optimal way of modeling mechanical hardening in steels with phase transformations for computing realistic results by welding simulation will be identified.

• DFG Programme: Research Grants