The flow behaviour of Modified 9Cr-1Mo (Grade 91) steel base and weld has been evaluated at room temperature (RT), 350°C, 450°C, and 550°C. Tensile test specimens were extracted from the Grade 91 base material and from weldments produced using the automated Gas Tungsten Arc Welding (GTAW) process, followed by a post-weld heat treatment (PWHT) at 760°C for 3 hours. The experimental true stress – plastic strain curves obtained from these specimens were fitted to several constitutive models, including the Holloman, Ludwik, Ludwigson, Swift, Voce and Ramberg-Osgood equations. The Voce model most accurately represents the flow behaviour across the different temperatures for both the base and weld metal. Furthermore, the tensile properties predicted using the Voce equation viz. yield strength, ultimate tensile strength and uniform plastic strain have been found to be in good agreement with the experimental results. SEM images show a higher void size dependence on temperature in weld metals.
Singh et al. (2025) studied this question.