2014 年 55 巻 642 号 p. 615-619
The stress-strain behavior of and martensite volume fraction vs. plastic strain curve for type 304 stainless steel at room temperature were investigated by uniaxial tension and compression experiments. The equivalent stress-equivalent plastic strain curve was not affected by hydrostatic pressure up to 0.2 of equivalent plastic strain, and the equivalent stress under compressive loading becomes larger than that under tensile loading at large strains. Similarly, such a hydrostatic pressure dependence was observed in the martensite volume fraction vs. equivalent plastic strain curve. For better understanding of microstructural aspects, TEM (Transmission Electron Microscope) and EBSD (Electron Backscattering Diffraction) observations were performed on the deformed specimens. From the TEM images, it was found that more shear bands and those intersections, which were the dominant nucleation sites of α'-martensitic transformation, were induced under compression than those under tension. From the EBSD images, it was found that orientations stable against deformation-induced martensitic transformation (γ and γ directions) are the preferred orientations under tensile loading. In addition, material parameters in the strain-induced martensitic transformation model proposed by Olson and Cohen imply that shear bands and their intersections are more likely to be formed under compression as corroborated by the results of TEM observation.