Kinematic and thermal characteristic of discontinuous plastic flow in metastable austenitic stainless steels

Abstract

The strain induced martensitic phase stabilizes the propagation of macroscopic shear band during displacement-controlled uniaxial tensile test of metastable austenitic stainless steels (316 L, 304) at liquid helium temperature (4.2 K). It leads to huge Lüders-type deformation, high hardening and large ductility of the specimen. In Lüders range, shear band develops across the specimen in discontinuous and sequential way, which is reflected by stress oscillation on stress-strain curve and comb-like profile of temperature recorded during tests (so called discontinuous plastic flow - DPF). Based on the time responses of temperature and elongation transducers, a full picture of the localized deformation behaviour of specimen at 4.2 K was obtained, including its both spatial and temporal features. Moreover, the experimental results clarified that DPF has mechanical origin and it is accompanied by thermal effects. The model of temperature distribution during DPF was proposed. The model involves temperature effects driven by the elastocaloric phenomenon (experimentally identified at 4.2 K) and the plastic power dissipation. Based on the model, kinematic and thermal limits of DPF in the austenitic stainless steels were determined. • The study clarified that discontinuous plastic flow (DPF) has mechanical origin. • The strain induced martensitic phase stabilizes the propagation of shear band in austenitic stainless steel at 4.2 K. • The elastocaloric effect is confirmed during the uniaxial tensile test of austenitic stainless steel at 4.2 K. • The kinematic and thermal limits of DPF in 316 L were determined. • The crack jumps in CT specimen and the rapture of the specimen take place in accordance to the DPF.