Investigation of the effect of grain size on the strain-induced martensitic transformation in a high-Mn stainless steel using nanoindentation

The formation of strain-induced martensite (SIM) during nanoindentation experiments was investigated in a Ti-bearing high-Mn stainless steel with three different grain sizes, e.g. coarse-grained, ultrafine-grained and nano-grained structures. In the nanoindentation load–displacement curves, there was clear distinction in the number of pop-ins from five in the coarse-grained structure to one in the nano-grained structure representing the difference in the susceptibility to formation of SIM. It was found that grain refining down to the nano scale leads to a significant restriction in the formation of SIM. This can be attributed to the increased stability of austenite as a result of increase in the stacking fault energy by reducing grain size.