取向硅钢脱碳退火后渗氮过程的数值模拟研究

Numerical Simulation of Nitriding Process of Oriented Silicon Steel after Decarburization and Annealing

根据脱碳退火后硅钢带试样表面氧化层特征和元素辉光光谱的分析结果对氧化层进行了简化,并研究渗氮热力学和氮在钢带内部的扩散机理,优化了气固表面综合传质系数,建立了低温取向硅钢渗氮的数学模型。通过不同渗氮条件下的模拟结果与实验结果对比发现,平均拟合优度达到0.85,表明所建模型可靠性较高。渗氮初期(0~20 s)氮含量增加非常缓慢,随着渗氮时间的延长氮含量增速加快然后趋于稳定,在渗氮20~50 s的条件下,氮含量近似呈直线增加。提高氨气浓度和渗氮温度能使氮含量显著增加,可通过调整渗氮工艺参数使钢带在渗氮后保持适当的渗氮量,实验和模拟结果均表明,在渗氮温度750~800℃、NH3体积浓度2%左右、渗氮30~40 s的条件下可获得较为理想的氮含量(150~300)ppm。

According to the characteristics of oxidation layer on the surface of decarburized annealed sample and the analysis results of glow spectrum of elements, the oxide layer was simplified. The thermodynamics of nitriding and the diffusion mechanism of nitrogen in steel strip were studied. The comprehensive mass transfer coefficient of gas-solid surface was optimized and the mathematical model of nitriding of low-temperature oriented silicon steel was established. By comparing the simulation results with the experimental results under different nitriding conditions, it is found that the average goodness of fit is 0.85, which indicates that the reliability of the model is high. At the beginning of nitriding(0-20 s), the nitrogen content increases very slowly, and with the increase of nitriding time, the increase rate of nitrogen content increases then tends to be stable. Under the condition of nitriding for 20-50 s, the nitrogen content increases approximately in a straight line. Increasing ammonia concentration and nitriding temperature can significantly increase nitrogen content. The proper nitriding rate can be maintained after nitriding by adjusting the nitriding process parameters. The experimental and simulation results show that, under the conditions of nitriding temperature of 750 ℃, NH3 volume concentration about 2% and nitriding for 30-40 s, an ideal nitrogen content of(150-300 ppm.) can be obtained.