Effect of loading modes on mechanical property and strain induced martensite transformation of austenitic stainless steels

Abstract

Driven by a good combination of strength and ductility, austenitic stainless steels have attracted much interest in the past decade. These metastable alloys fall into the category of transformation induced plasticity (TRIP) steels in which high strength and excellent ductility can be achieved due to their strain-induced martensitic transformation at ambient temperature. However, there are few reports on the detail of promoting this phase transformation and enhancing the TRIP effect during deformation only by changing the loading mode. In present work, the effect of loading modes on mechanical property and microstructure of austenitic stainless steels was investigated under various temperatures. The tensile tests results reveal that cyclic tensile loading and unloading (CTLU) mode can strongly influence the deformation behavior of AISI 304 steel. There is no difference at high temperature tension by different loading modes. Compared with the conventional monotonic tensile loading (MTL) mode, the elongation has been slightly reduced by CTLU mode at cryogenic temperature. However, CTLU mode can improve both strength and ductility of AISI 304 steel at room temperature. An in situ X-ray diffraction has been carried out to identify and evaluate strain-induced martensitic transformation by different loading modes at room temperature. Experimental results showed that the fraction of strain-induced martensite increases when unloading happens. It indicated that CTLU mode can enhance strain hardening in AISI 304 stainless steel, which prolongs the time to neck formation to a significant extent. Consequently the TRIP effect is enhanced. © right.