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.