Integrated Computational Materials, Process and Product Engineering – IC-MPPE 2022

Low carbon lath martensitic steels such as PH15-5 are often used in high-performance applications e.g. structural components of aircrafts. Since the development and improvement of closed die forging routes for such parts is often time-consuming and expensive, especially for microstructurally complex materials such as PH15-5, a spatially resolved prediction of their mechanical properties as a function of microstructure is essential. Current frameworks are able to model the evolution of the austenite grain size throughout thermomechanical processing. However, prediction of the martensitic substructure size, which is a decisive factor for the mechanical properties during application, requires further research. Thus, a more detailed investigation of the correlation between austenitic grain size and martensitic block size is necessary. The martensite block size depends on multiple factors such as the prior austenite strength and grain size, as well as the temperature at which the transformation occurs. With each martensitic transformation sequence, stresses are introduced into the microstructure. It is assumed that they strengthen the remaining austenite and retard subsequent transformation sequences to lower temperatures, which affects the martensitic block size. The main aim of the present research is the improvement of martensitic block size predictions as a function of the austenite grain size. This will enable reliable modelling of mechanical properties based on fundamental parameters e.g. stress affected strength of austenite. In order to investigate the influence of the local but also mean stresses induced by the martensitic transformation on the remaining austenite in-situ synchrotron x-ray diffraction and in-situ high resolution electron backscatter diffraction measurements were conducted, respectively.