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

当钢焊接时，焊缝与母材之间的巨大温差会产生应力，从而导致循环塑性变形，特别是在热影响区。这一过程直接影响焊接残余应力的发展，因为这些应力通常受到屈服强度的限制。因此，机械硬化的次优建模可能导致数值和实验确定的焊接残余应力之间的差异。在本课题的第一个研究项目中，研究了不发生任何相变的焊接高合金钢的力学硬化行为。在后续项目中，分析应扩展到具有相变的钢，相变也会影响硬化状态。由于存在高强度相，组织硬化效应叠加在机械硬化效应之上。此外，还会发生转变塑性，从而导致额外的机械硬化。最后，在转变过程中，机械硬化状态是否以及如何从一个相转移到另一个相还不清楚。因此，继续项目的目的是填补知识空白，这是负责的计算和实验之间的显著差异的残余应力焊接钢的相变。为此，对两种不同屈服强度的结构钢的材料性能进行了综合表征。基于这些结果，将使用不同的材料模型进行模拟，其结果必须与实验获得的残余应力和硬化效应进行比较。最后，确定相变钢力学硬化建模的最佳方法，以便通过焊接仿真计算真实结果。

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.