Microstructural and Substructural Variations during Symmetric and Microstructural and Substructural Variations during Symmetric and Asymmetric Cyclic Loading of AISI 304LN Stainless Steel

Abstract

The primary aim of this investigation is to examine the influence of symmetric and asymmetric cyclic loading on (i) accumulation of plastic strain that occur during cyclic deformation of AISI 304 LN stainless steel and (ii) the attendant in-situ microstructural and substructural variations. Stress-controlled cyclic tests have been carried out at 300 K for positive and zero mean stress levels with varying stress amplitudes in order to attain both symmetric and asymmetric loading conditions. Cyclically deformed samples were studied using XRD and TEM to assess the possible structural alterations. The results highlight that the nature of strain accumulation is dependent on the combinations of mean stress and stress amplitude. Strain accumulation is more in asymmetric loading compared to that in symmetric loading. TEM and XRD results indicate that considerable amount of austenite transforms to martensite during asymmetric cyclic loading and the amount of martensite varies with the nature of the imposed stresses. It is observed that dislocation cells and tangles preferably form due to asymmetric loading. The nature of the substructure in asymmetrically loaded specimens is significantly different than that observed in specimens subjected to symmetric loading.