Martensitic transformation in SUS 316LN austenitic stainless steel at RT

The results of high-accuracy magnetic measurements on SUS 316LN austenitic stainless steel compressively deformed at room-temperature (RT) are reported here. Even after the mild-deformation of ～25% true-strain (εt), the ferromagnetic phase ( α´-martensite) could be clearly observed which increased sharply on further deformation. The amount of α´was very small (0.18 vol.% at εt≈60%) when compared to the reported data for other grades of austenitic steels such as 304, 304L, 316 and 316L. The strain-induced α´-martensite is further studied by the magnetic hysteresis loops. The coercivity (HC) and remanence (Mr) were analyzed by subtracting the paramagnetic contribution of the bulk austenite structure. While HC was found to decrease with α´, Mr remained same (～67 emu/g) when normalized to the volume fraction of α´. The decreasing HC with increasing α´and/ or εt is presumed to be due to the domain wall pinning at the grain boundaries when the cluster size exceeds the domain wall width.