Effect of Grain Misorientation and Martensitic Transformation on Surface Roughening Behavior in Thin Austenitic Stainless Steel Foils

Abstract

Stainless steel thin foils have unlimited applications in the field of microforming industries, making them attractive for use in industrial society. The problem hindering their use is the different mechanical properties that exist between thick and ultra-thin metals with the same plastic deformation characteristics. In this study, we compared the martensitic phase transformation (MPT) effect in SUS 304 and SUS 316, which was clarified in samples of the same grain size (Dg). The correlation between the MPT, grain misorientation (GM), and surface roughening behavior of SUS 304 and 316 thin metal foils was investigated using a uniaxial tensile test, which was repeated five times, with constant strain increments of 1.5%. Phase transformations such as MPT and GM were investigated using scanning electron microscopy/electron backscattered diffraction (SEM-EBSD). The results show that surface roughening increased proportionally in both the SUS 304 and SUS 316 thin foils with a coarse grain size (Dg of 9.0 µm). Surface roughening increased to a greater extent in the coarse-grained SUS 304 and 316 thin metal foils compared with the fine-grained (Dg 1.5 µm) samples. The SEM-EBSD results show that the grain strength of the coarse-grained SUS 316 thin metal foil was less inhomogeneous than that of the coarse-grained SUS 304 thin metal foil. The surface roughness ratio of the coarse-grained SUS 304 was higher than that of the coarse-grained SUS 316. The inhomogeneous grain strength of the fine-grained SUS 304 was similar to that of the fine-grained SUS 316. The surface roughness ratio of the fine-grained SUS 304 was similar to that of the fine-grained SUS 316. The MPT demonstrated a huge effect on the surface roughening behavior of the SUS 304 and SUS 316 samples with different Dg.

Keywords

• grain size (dg)
• grain misorientation (gm)
• martensitic phase transformation (mpt)