Influence of Work-Hardening and Lower Temperatures on the Yield Stress of Austenitic Stainless Steel X2CrNi18-10 under Combined Tension-Torsion Loading

This study investigates the impact of work-hardening and lower temperatures on the mechanical properties of austenitic stainless steel X2CrNi18-10 under multiaxial stress. For this purpose, the yield behavior of hollow tubular specimens under combined torsion-tension loading is examined using a servo-hydraulic testing system MTS809.10S. Yield points are determined for different tension-to-torsion ratios using 1) solution-annealed specimens tested at room temperature, 2) pre-strained specimens with 3.6% alpha'-martensite tested at room temperature, and 3) solution-annealed specimens tested at -20 degrees C. Experimental results show that the yield stresses of the solution-annealed material at room temperature and at -20 degrees C can be reasonably approximated using the von Mises and the isotropic Hosford yield hypothesis. Contrary, the yield stresses of the work-hardened material cannot be fitted with isotropic yield hypotheses because the required torsional stress component to induce plastic deformation is much higher than suggested in those criteria. This effect is mainly attributed to the strain hardening behavior of the X2CrNi18-10, showing a comparatively high rate of work-hardening especially at low strains. A suitable approach for fitting the yield points of the work-hardened material is found with the anisotropic yield hypothesis according to Hosford.