对3%无取向硅钢进行异步轧制以实现表面纳米化, 分别在真空和渗硅条件下进行不同参数的热处理, 研究显微组织,物相和成分的演变. 结果表明: 经过速比为1.31, 轧制道次为20, 总压下量为91%的异步轧制后, 板材表面形成了尺寸为10~20 nm, 取向呈随机分布的纳米晶; 在真空下升温, 表面纳米晶的再结晶温度明显提高; 在渗硅剂(Si粉+1% (质量分数)卤化物)中升温, 表面纳米晶的再结晶温度因外部Si原子沿着缺陷的快速扩散而进一步提高, 使得纳米晶界面能够在更高的温度下(750 ℃)发挥扩散通道作用, 促进Si原子的扩散, 并在显著地降低保温时间和(作为催化剂的)卤化物含量的同时获得致密的渗Si层.
Heat stability of nanostructure can be related to alloy element, in order to investigate the effect of external element diffusion, asymmetrical rolling was adopted to roll 3% non-oriented silicon steel to realize the surface nanocrystallization, heat-treatment with different parameters was carried out for the rolled sheet in vacuum and Si+1% (mass fraction) halide powder respectively, and different techniques were used to examine the microstructural evolution, phase transformation and Si distribution along the depth. Experimental results show that nanocrystallines about 10~20 nm in size with random orientations form in the top-surface layer after the asymmetrical rolling with the mismatch speed ratio 1.31 and rolling passes 20 for 91% reduction. In the heating process in vacuum, the recrystallization temperature of the nanocrystallines in the top surface layer of the rolled sheet was found to increase obviously comparing with that obtained after keeping at this temperature for a long duration. In the heating process in Si+1% halide powder, a further enhancement of the recrystallization temperature was observed for the nanocrystallines in the top surface layer of the rolled sheet due to the fastly diffusion of Si atoms along the defaults, then the larger volume fraction of grain boundaries can act as fast diffusion channel at higher temperature (750 ℃), that can accelerate the diffusion of Si atoms, therefore dense compound layer can be obtained within shorter duration and with lower fraction of halide (acts as activator).
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