The effect of ferrite phases on the micromechanical response and crack initiation in the intercritical heat-affected zone of a welded 9Cr martensitic steel

This paper presents a crystal plasticity model to predict the tensile response and crack initiation in a mixed ferrite-martensite material with a low volume fraction of pro-eutectoid ferrite, representative of a welding-induced intercritical heat-affected zone. It is shown that small volume fractions of ferrite can have a significant effect on material strength and ductility depending on the ferrite grain orientation. For relatively soft ferrite grains, microcracks can grow across interferrite ligaments with damage accumulating in the ferrite, leading to a reduction in strength and strain hardening, but with little influence on ductility; in contrast, relatively hard ferrite grains act to accelerate microcrack initiation, leading to reduced ductility, with negligible influence on strain hardening up to the maximum load.This publication has emanated from research conducted with the financial support of Science Foundation Ireland under grant no. 14/IA/2604 and the College of Engineering and Informatics at NUI Galway. The authors are grateful to the Irish Center for High‐End Computing (ICHEC) for supporting the computational work (uleng040b). The authors are grateful for the helpful discussions with the Mechanics team (NUI Galway and UL). The assistance of Mr Edward Meade of the Bernal Institute at UL is also gratefully acknowledged.peer-reviewe