In structural materials, it is investigated to make crystal grain size less than 1μm in order to improve strength and toughness. Authors reported that fine ferrites were obtained by laser irradiation in steel. However, it is not made clear that an effect of laser irradiation on the materials which do not have a transformation. In this study, we performed laser irradiation for austenite stainless steel SUS304 as the materials which did not have a transformation and investigated an effect of laser irradiation on grain refinement. Solution treatments were performed for SUS304 and their initial grain size became 23 and 68μm. Then they were given four kinds of strain ε and irradiated laser under some laser traveling speeds v and some defocus distances fd. As the result, they became recrystallization grain and their size were obtained about 10 and 15 μm, for initial grain size respectively, under the best condition (laser power=1.5kW, fd=60mm, v=350 mm/min, ε= 40%). Then a recrystallization grain size was caused by each factor of laser traveling speed (heating temperature, heating time), strain and defocus distance. Furthermore, as an electro-gas arc weld of SUS304, the grain size was 40μm in heat affected zone, was irradiated after shot peening, it was clarified that fine grain was obtained from 10 to 15μm at the heat affected zone.
