Microstructure And Performance Of Surface Nanocrystallization 316L Stainless Steel

Nanostructured surface layer was synthesized on 316L stainless steel by means of high-speed rotation wire-brushing deformation. The refined microstructure features were systematically characterized by optical microscopy, X-ray diffraction analysis, scanning electron microscopy and transmission electron microscopy observations. Furthermore, the microhardness was examined by microhardness tester. After HRWD treatment, obvious grain refinement was observed and a nanocrystalline surface layer was formed on 316L stainless steel. It was found that a gradient microstructure with grain size from nanoscale to microscale was obtained along the depth of its surface layer. The mean grain size in the top surface layer was approximately 12nm. The thickness of the nanocrystalline surface layer varies from a few to about 20μm depending upon the treatment duration and compressive stress. The microhardness of nanostructured surface layer was enhanced significantly, and along the depth from the top surface, In the top surface nanostructured layer, the microhardness reached 450HV, which was about three times that of the coarse-grained matrix.Rolled the samples after surface nanocrystallization to reduce the roughness caused by HRWD. Tested the surface roughness, microstructure and mechanical properties, the roughness of the sample reduced to Ra≈1.1μm, Rz≈7μm, compared with original Ra≈3.5μm, Rz≈15μm; Grain size further decreased, reduced from 12nm to 9nm; material hardness of the matrix increases rapidly, reaching twice as the original sample, while the plasticity decreased significantly.Annealled the rolling samples at different temperatures, in order to study the stability of nanocrystals. The results show that:with the increasing of temperature, the grain size increased. Below 773K the increasing is not obvious, while the annealing temperature reached 973K, the grain size increased significantly, from 9nm to 400nm.