| Summary: | 博士 === 逢甲大學 === 纖維與複合材料學系 === 106 === In recent years, 316L stainless steel wire is frequently applied in intelligent and communicative textile structures of wearable devices and smart clothing. Due to 316L stainless steel is the medical grade and biocompatible material in series of austenitic stainless steel, and its non-toxic, conductivity, rustproof, chemical resistance, and heat resistance. In order to light the wearable devices and improve comfortableness and soft hand feel of 316L stainless steel fabrics. The diameter of 316L stainless steel wire is reduced to the size in micrometer by multi-pass drawing process and form 316L stainless steel fiber. However, a few of studies discussed about the effect to the microstructure and properties of 316L stainless steel fiber by multi-pass drawing process. Therefore, three parts in this study are discussed: (1) Crystalline phase and mechanical property of austenite stainless steel fibers after multipath cold drawing and heat treatment processes; (2) Magnetic anisotropy of ultrafine 316L stainless steel fibers; (3) Characterization of microtexture of 316L stainless steel fiber after multi-pass drawing by electron backscatter diffraction.
The first part: The crystalline phase and mechanical property of 316L stainless steel fibers after two bundle drawing paths and heat treatment at 800 °C were discussed. The identification and quantification of 316L stainless steel fibers were analyzed by an X-ray diffractometer. Results show that 316L stainless steel fiber has γ-austenite and α'-martensite phases. The strain-induced martensitic transformation took place after a drawing process at room temperature. The α'-martensite phase of the fiber was increased with an increase of specific strength and a decrease of elongation of the fiber after a drawing process; whereas the α'-martensite phase of the fiber was decreased with a decrease of specific strength and an increase of elongation of the fiber after heat treatment at 800 °C. It can be seen that the process of heat treatment benefits the plastic deformation of austenite stainless steel fiber.
The second part: The grain sizes of γ-austenite and α′-martensite were reduced to nanoscale sizes after the drawing process. XRD analysis and FIB-SEM observations showed that the newly formed α′-martensitic grains were closely arrayed in the drawing direction. The magnetic property was measured using a SQUID-VSM sample magnetometer. The magnetic anisotropy of the fibers was observed by applying a magnetic field parallel and perpendicular to the fiber axis. The results showed that the microstructure anisotropy including the shape anisotropy, magnetocrystalline anisotropy, and the orientation of the crystalline phases strongly contributed to the magnetic anisotropy.
The third part: The microstructure and microtexture of 316L stainless steel fibers after multi-pass cold drawing with intermediate heat treatment were investigated in this study. The crystalline phases of SSFs were identified and quantified using X-ray diffraction analysis. Grain orientation and boundary characterization in the mantle and core regions of drawing direction (DD) were analyzed through electron backscatter diffraction (EBSD). The coincident site lattice approach provides beneficial information for defining twin boundary and analyzing the orientation relationship between neighboring grains on the Σ3 segment. Three crystalline phases, γ, α, and σ, could be seen in XRD profiles. The formation mechanism of deformation twins was found, and two types of twin boundaries were observed in the drawn fibers by EBSD. The twin boundary generated between a {112}〈111〉 grain and a 〈100〉//DD grain is believed to nucleate at a high-angle grain boundary and then bulge into the {112}〈111〉grain.
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