Cyclic Softening and Over-Softening of a 1 Percent Cr-Mo-V Steel at Elevated Temperature

Detailed results are presented of shear stress range variation during cycling of 1 per cent Cr-Mo-V test specimens within controlled total shear strain limits at 565°C. The cyclic softening induced during continuous and two-step cycling are compared. A saw-toothed pattern for the strain was maintained for each cycle giving a constant straining rate. Normal cyclic softening was found throughout the tests but another phenomenon of over-softening occurred during the two-step tests when high strain cycles took place first. A permanent history effect had been produced within the steel. This over-softening did not depend on the straining rate of the cycling or the magnitude of the initial cycle ratio. The generally accepted method of determining cyclic stress-strain curves using continuous cycling is shown to be invalid when over-softening is present.