A New Etching Method of Deformation-induced Martensite in Type 304 Stainless Steel Hot Rolled Plate

Abstract

A two-step etching method was devised so as to visualize the deformation-induced martensitic phase, α', in an austenitic stainless steel SUS304. The method, a combination of an electrolytic and a chemical etching, selectively etched α' phase. The visualization of martensitic phase utilizes the etch-pit row formed by the present etching method. In a 3 mm-thick plate subjected to a three-point plane-strain bending using a punch of 6 mm in radius, the amount of surface-strain was almost constant in an angle range of ±35° from the bending center, but decreased in higher angles where the amount of the surface-strain remained higher than that on the outer surface. The amount of α' was higher on the inner surface than that on the outer surface even at the same level of strain. The amount of spring-back was 10° in 180° bending, presumably due to the different distributions of α' phase.