Abstract
The surface roughening (Ra), martensitic phase transformation (MPT), and grain misorientation (GMO) behavior of stainless steel 304 and 316 in various grain sizes (Dg) were studied experimentally, including five cycles of sequential uniaxial tensile stress testing and Scanning Electron Microscope-Electron Back Scattered Diffraction (SEM-EBSD) investigation. The MPT and GMO characteristics were sequentially investigated using tensile testing and SEM-EBSD analysis. The correlation between MPT, GMO, martensitic volume fraction (Mf), and Ra behavior were investigated. The experimental results showed that increasing the total strain from 5.0% to 25.0% increased the MPT, GMO, and Mf, which were transformed from the metastable austenitic phase in stainless steel (SUS) 304. The increasing total strain increased Ra for all kinds of Dg. Furthermore, SUS 304 and SUS 316 were used to compare the roughening mechanism. The MPT was very high and spread uniformly in fine grain of SUS 304 thin foil, but the MPT was low and not uniform in coarse grain of SUS 304 thin foil. There was no MPT in SUS 316 thin foil, both in coarse and fine grain. The GMO in fine grains, both in SUS 304 and SUS 316 thin foils, spread uniformly. The GMO in coarse grains, both in SUS 304 and SUS 316 thin foils, did not spread uniformly. Surface roughness increased higher in coarse grain than fine grain for both of SUS 304 and SUS 316 thin foil. SUS 304 increased higher than SUS 316 thin foil. The effect of inhomogeneous deformation due to the MPT is a more important factor than GMO in coarse grain.
Highlights
Micro metal forming, for austenitic stainless steel (ASS), is a promising approach in the biomedical, electronic, chemical, electrical power, food, and nuclear industries [1], ASS has excellent corrosion resistance and processability [1,2]
The correlations between surface roughness behavior with strain level without annealing have been revealed in previous study, showing that surface roughness increases proportional in coarse grain and does not increase proportional in fine grain during uniaxial tensile test [29]
The inverse pole figure (IPF) map derived by EBSD reflects the locally discovered orientation
Summary
Micro metal forming, for austenitic stainless steel (ASS), is a promising approach in the biomedical, electronic, chemical, electrical power, food, and nuclear industries [1], ASS has excellent corrosion resistance and processability [1,2]. The high demand for microparts has received significant attention in recent decades [2,3]. Microforming technology has a number of challenges, such as the limitation of material applications and the high cost of mass production [1,2,3]. When ASS is subjected to plastic deformation, martensitic-induced transformation occurs in the ASS [1]. The transformed martensitic volume fraction increases with the increase in plastic deformation [1,2,3]. Martensitic transformation reduces the toughness but increases the strength of ASS [4,5]. When subjected to plastic deformation, austenitic stainless steel, as a metastable phase, undergoes a transformation from Face Centered Cubic (FCC) austenite to Body
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