Effect of back stress evolution due to martensitic transformation on iso-volume fraction lines in a Cr–Ni–Mo–Al–Ti maraging steel

The effect of the back stress evolution on the iso-martensite volume fraction lines (the iso-ξ lines) is experimentally investigated in a Cr–Ni–Mo–Al–Ti maraging steel in the process of martensitic transformation by identifying the iso-ξ lines inside the transformation zone bounded by the martensite-start and -finish lines. Each iso-ξ line is composed of a tensile-branch and a compressive-branch, which are parallel to the tensile- and compressive-branches of the martensite-start line, respectively. When the back stress evolves due to martensitic transformation, the iso-ξ line translates as a whole into the direction of the back stress evolution with its slope unchanged. The ordinate of the intersection point of both branches stands for the value of the back stress. The back stress evolution identified in the present tests well supplements the evolution response determined in a quite different way in the unloading tests described in [Mater. Sci. Eng. A (2002) in press].