Significant enhancement of tensile properties through combination of severe plastic deformation and reverse transformation in an ultrafine/nano grain lath martensitic steel

In this paper, microstructural evolution together mechanical properties variation in a Fe-24Ni (wt%) lath martensitic steel processed by accumulative roll bonding (ARB) and reverse transformation was investigated. The microstructural analysis indicated that after 6-cycle of the ARB process ultrafine/nano structure having mean grain size below 200 nm is obtained. Furthermore, the typical lath martensitic structure transformed to complicated microstructure consisting of ultrafine equiaxed ferrite (alpha-Fe) as well as ultrafine grains of austenite (gamma-Fe). The results also showed that by increasing the number of ARB cycle martensite starting (M-s) temperature decreased. As well, tensile test results showed that both the yield strength and uniform tensile elongation improved considerably by 6-cycle of the ARB process. Increasing uniform elongation can be attributed to stabilization of austenite during the ARB process.