Abstract
A comparative study of the mechanisms of plastic deformation under static tensile and dynamic zero-to-peak axial loadings (R = 0) has been carried out for an annealed austenitic stainless steel Type 321S12. For the tensile test the high value of the strain-hardening exponent and the high nominal tensile strength/yield strength ratio are associated with the strengthening effects involved in an austenite-martensite transformation. To induce this transformation a minimum value of strain displacement is necessary and such strains are first attained at the surface layers and only occur in the core grains for the regime of plastic instability beyond the level of the nominal tensile strength. The S/N curve reveals three distinct regimes of fatigue and the fatigue limit is ∼ 55% higher than the macro-yield strength of the alloy. Explanations given of the fatigue-crack process in the various regimes of the S/N curve are based on a comparison of the tensile and fatigue loading conditions.
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