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 (α-Fe) as well as ultrafine grains of austenite (γ-Fe). The results also showed that by increasing the number of ARB cycle martensite starting (Ms) 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.