Back stress evolution and iso-volume fraction lines in a Cr–Ni–Mo–Al–Ti maraging steel in the process of martensitic transformation

The quantitative identification of the back stress evolution is carried out for a Cr–Ni–Mo–Al–Ti maraging steel in the process of martensitic transformation under thermomechanical loading conditions. The evolution depends on the direction of the applied stress: tensile, compressive or shear. The iso-volume fraction lines (the iso-ξ lines) are determined between the transformation-start and -finish lines on the applied stress–temperature plane. The iso-ξ lines are composed of a tensile-branch and a compressive-branch, each of which is parallel to the martensite-start line. The interaction point of the tensile- and compressive-branches of the iso-ξ line shifts to the direction of the back stress evolution. The almost hold stress-independent martensite-finish line, identified in a previous paper (Mater. Sci. Eng. A308 (2001) 25) is proved to be attributed to the back stress evolution.