Phase stabilization by ultra grain refinement inmetastable austenite

When steels have a high martensitic transformation temperature above room temperature, the transformation behavior is not affected by the difference in the austenite (y) grain size, because they have a large chemical driving force for the martensitic transformation. However, in the case of metastable γ phase, the stability of γ depends on they grain size because the chemical driving force is not so large that the nucleation of martensite is affected by the size of room. In this paper, the behavior of martensitic transformation was investigated in a metastable austenitic steel (13Cr-11Ni steel) with different grain size from 0.8μm to 80μm and the mechanism of γ phase stabilization was discussed in connection with the morphological change of martensite. As a result, it was found that ultra grain refinement to the revel of submicron causes a change in the transformation mechanism from "multi variant" to "single variant" and that the difficulty of single variant transformation leads to the phase stabilization of γ.