退火处理对表面纳米化316L不锈钢组织及耐腐蚀性能的影响

Effect of annealing treatment on microstructure and corrosion resistance of surface nanocrystallization 316L stainless steel

通过快速多重旋转碾压技术(FMRR)在奥氏体316L不锈钢表面制备纳米结构层,并对其进行不同温度的退火处理。采用X-射线衍射仪(XRD),透射电镜(TEM),扫描电镜(SEM)及电化学工作站对退火样品的微观结构及耐蚀性能进行了研究。结果表明:经FMRR处理60 min后,在不锈钢表面因塑性变形生成了α′马氏体相,其衍射峰的半高宽明显宽化,这是由于经过塑性变形后316L不锈钢晶粒细化和微观应变增加导致的;不锈钢表面也形成了约12 nm厚的等轴纳米晶,且晶粒呈随机取向。对样品退火处理后,α′马氏体的衍射峰强度随退火温度的增加而增强,这表明316L不锈钢的马氏体含量增加。退火后样品的晶粒尺寸有所增加,但仍为纳米级,而微观应变随退火温度增加而减少。与原始样品相比,纳米化的316L不锈钢耐蚀性明显降低,退火处理后耐蚀性进一步降低,300℃退火样品的耐蚀性最差,这是由于晶界数量、马氏体含量和残余应力共同作用所致。

The nano-structure layer was prepared on the surface of 316L austenitic stainless steel by fast mutiple rotaion rolling(FMRR) technique and the annealing treatment at different temperatures was performed. Microstructure and corrosion resistance of the annealed samples were studied by means of X-ray diffractometer(XRD), transmission electron microscopy(TEM), scanning electron microscopy(SEM) and electrochemical workstation. The results show that after FMRR treatment for 60 min, the α′-martensite phase is generated by plastic deformation on the surface layer of the stainless steel, and the half-height width of the diffraction peak is obviously wider, which is caused by the grain refinement and the increase of the micro-strain of the 316L stainless steel after the plastic deformation. The stainless steel surface also forms an equiaxed nanocrystalline of about 12 nm thickness, and the grains are randomly oriented. After annealing treatment, the diffraction peak intensity of the α′-martensite of the 316L stainless steel is enhanced with the increase of the annealing temperature, which indicates that the martensite content of the 316L stainless steel increases. The grain size of the sample after annealing increases slightly, but is still nanoscale, and the micro-strain decreases with the increase of the annealing temperature. Compared with the original sample, the corrosion resistance of the nanocrystallization 316L stainless steel is obviously reduced, the corrosion resistance after the annealing treatment is further reduced, and the corrosion resistance of the annealed sample at 300 ℃ is the worst, which is caused by the common action of the grain boundary quantity, the martensite content and the residual stress.