Understanding room temperature deformation behavior through indentation studies on modified 9Cr–1Mo steel weldments

Deformation behavior of boron free (P91) and boron added (P91B) modified 9Cr–1Mo steel weldments was studied at room temperature using an indentation technique. A sub-structure consisting of sub-grains was observed in the inter-critical heat affected zone (ICHAZ), whereas lath martensitic structure was observed in the coarse grain heat affected zone (CGHAZ) of the P91 weldment. Consequently, weldment showed significant variation in hardness as well as strain rate sensitivity in different regions of the HAZs. On the other hand, P91B steel weldment showed small variation in hardness and strain rate sensitivity, which was commensurate with uniform microstructure consisting of lath martensite. These differences in microstructures as well as hardness values also reflected in large variation in creep depth in P91 compared to the small variation in P91B weldment.