A substantial improvement of tensile properties through microstructure engineering in a high Ni-0.2C TRIP steel under severe plastic deformation

Abstract

In the present paper, microstructural evolution and mechanical properties changes of an ultrafine-grains (UFGs) Fe-24Ni-0.2C steel processed via accumulative roll bonding (ARB) is investigated. Characterization of microstructure with Electron Backscatter Diffraction (EBSD) technique revealed that a substantial grain refinement happened after 6-cycle ARB process. As well, elongated UFGs austenite with mean grain size smaller than 200 nm was obtained in such a condition. Furthermore, phase analysis map acquired from EBSD technique revealed that the microstructure of the starting sheet contained martensite (>30%) which transformed to austenite after 6 cycles of ARB process. Such a phenomenon indicated that, through grain refinement, austenite stabilization is attainable with the ARB process. It was also found that yield/tensile strengths, as well as toughness of the ARB processed specimens are enhanced, particularly when the ARB cycle is increased. Finally, it was established that deformation-induced martensite transformation provides extra strain hardening capability ensuing a substantial enhancement of uniform elongation and toughness in the UFGs metastable austenitic steel. This UFGs steel showed considerable uniform elongation and ultrahigh strength at 6-cylce ARB process.