Fe-C-Si合金固态脱碳过程氧化层演变规律

Evolution of oxide layer during solid decarburization of Fe-C-Si alloy

结合钢铁行业综合低碳减排研究现状,提出了电炉+固态脱碳制备硅钢的工艺构想。由于在固态脱碳过程中钢表面会形成氧化层,试验以1 mm Fe-Si-C(Si 1.5%~3.5%;C 0.18%~0.48%(质量分数))合金为研究对象,在H_(2)O-H_(2)气氛下开展固态脱碳研究,以此来揭示脱碳过程中表面氧化的规律。利用FactSage热力学软件绘制H_(2)O-H_(2)气氛下Fe-C-Si氧化热力学平衡相图,明确了各温度、气氛条件下Fe、Si选择性氧化的热力学规律。在1423 K温度下开展固态脱碳试验,结果表明,脱碳效果良好,脱碳后碳质量分数可达到0.02%以下;气氛pH_(2)O/pH_(2)小于0.31时(pH_(2)O、pH_(2)分别为水蒸气和氢气的分压),固态脱碳后Fe-C-Si合金表面氧化物主要为SiO2,气氛pH_(2)O/pH_(2)达到0.34时,脱碳后Fe-C-Si合金表面氧化物主要由SiO2和Fe2SiO42种氧化物组成,随着气氛氧化性的增强,表面氧化物由SiO2转变为Fe2SiO4,这与热力学分析结果一致。试验利用扫描电子显微镜对脱碳后氧化层形貌、厚度进行观察分析,结果表明,在1423 K下,pH_(2)O/pH_(2)=0.31时3.5%Si合金薄带氧化层内氧化物为细小球状SiO2,pH_(2)O/pH_(2)=0.56时氧化层内SiO2尺寸增大,且在氧化层与基体之间形成了一条明显的深色条状带;1.5%Si硅钢固态脱碳后所形成的氧化层内高度弥散分布着粒度细小的球状SiO2,在氧化层与基体之间并没有形成可作为分界线的条状SiO2带。研究氧化层生长动力学发现,1423 K下Fe-1.5%Si-C硅钢氧化层生长速率最大,1363 K下Fe-3.5%Si-C硅钢氧化层生长速率最小,这主要是因为脱碳过程形成了一种“蜂窝状”的氧化层结构,并不断向基体内部生长。

Combined with the research status of comprehensive low-carbon emission reduction in iron and steel industry,the process concept of electric furnace+solid state decarburization is put forward,which oxidation will be formed on the surface.Taking 1 mm Fe-Si-C(Si 1.5%-3.5%,C 0.18%-0.48%(mass percent))alloy as the research object,the solid state decarburization experiment was carried out in H_(2)O-H_(2)atmosphere to reveal the law of surface oxidation in the decarburization process.The thermodynamic equilibrium phase diagram of Fe-C-Si oxidation under H_(2)O-H_(2)atmosphere was drawn by using FactSage thermodynamic software,and the thermodynamic laws of Fe and Si selective oxidation under various temperature and atmosphere conditions were clarified.The solid-state decarburization experiment was carried out at a temperature of 1423 K.The results show that the decarburization effect is good,and the carbon content after decarburization can reach below 0.02%SiO2,when the atmosphere pH_(2)O/pH_(2)reaches 0.34,the surface oxide of the Fe-C-Si alloy after decarburization is mainly composed of SiO2 and Fe2SiO4,which is consistent with the thermodynamic analysis results.The morphology and thickness of the oxide layer after decarburization were analyzed by scanning electron microscope and energy dispersive spectrometer.The results showed that at 1423 K,when pH_(2)O/pH_(2)=0.31,the oxide in the oxide layer of 3.5%Si alloy strip was fine spherical SiO2,when pH_(2)O/pH_(2)=0.56,the size of SiO2 in the oxide layer increases,and an obvious dark strip is formed between the oxide layer and the substrate.The inner height of the oxide layer formed after solid decarburization of 1.5%Si silicon steel Spherical SiO2 with fine particle size is dispersed,and there is no strip-like SiO2 band that can be used as a boundary between the oxide layer and the substrate.Studying the growth kinetics of the oxide layer,it is found that the growth rate of the oxide layer of 1.5%Si silicon steel is the largest at 1423 K,and the growth rate of the oxide layer of 3.5%Si silicon steel is the smallest at 1363 K.This is mainly because the decarburization process forms a"honeycomb"oxide layer structure,and continue to grow into the substrate.