Recrystallization And Grain Growth Behaviors Of316L Stainless Steel Fiber

Abstract:316L stainless steel fibers have excellent properties in electronic conductivity, yield strength, corrosion resistance and abrasion resistance, which are considered as the most promising structural and functional integrated materials. As one of the fabrication process for316L stainless steel fiber, bundle drawing method can reduce the drawing time so as to improve the production efficiency. At present, much works have already been done on the grain growth behavior of cold-worked centimeter or millimeter materials. However, researches on the basic theory of the mirostructure of the cold-worked fiber materials were still limited. Little information can be obtained about the recrystallization and grain growth behaviors of316L stainless steel fibers up to now. Thus, control of grain size and morphology was difficult, which seriously restricted their service performance and applications.In this paper, the recrystallization and grain growth behaviors of316L stainless steel fibers with different diameters were investigated using isothermal annealing tests. The average grain sizes of each annealed specimens were measured using an image analyzer, and the grain growth equations of the fibers with different diameters were constructed based on the classic theory of normal growth. The activation energies for grain growth of the two stainless steel fibers were also determined. Meanwhile, efforts have been paid on analyzing the effect of annealing factors on the textures of316L stainless steel fibers.The microstructure of the as-received316L stainless steel fiber was fiber-like. The precipitated particles appeared on the fiber surfaces, which were considered to be M23C6carbide precipitates. The phases of the as-received fibers are essentially γ-austenite crystalline phase. Compared to bulk austenitic stainless steel, the grain size of316L stainless steel fiber increased with the annealing time and temperature. The grain size of316L stainless steel fiber with a large diameter was larger than that with a small diameter, when treated under the same annealing condition.Specimens were isothermal held for various heating time periods from5min to30min in the temperature range from800℃to950℃, and a variation of grain size with holding time period was investigated by quantitative metallography. The value of grain growth exponent n was calculated and the kinetics rates were plotted by using the Arrhenius equation. The activation energies of the grain growth for316L stainless steel fibers with different diameters were determined to be: Q12μm=407KJ/mol, Q20μm=150KJ/molThe crystallographic textures that formed during drawing and annealing processes were determined by means of conventional X-ray texture analysis. There showed a fiber texture approximated by a<111> and a<100> component in the drawed and annealed316L stainless steel fibers, which were similar to the texture components of metal with FCC structure. After annealing, the textures with the orientations of<111> and <100> in the fibers change to some extent, but still have considerable intensities, which play a major role in the increase of the activation energy.