Research On Diffusion Laws Of Silicon In Ferrosilicon Alloy

Silicon steel is a kind of soft magnetic material commonly used in power, electronic and military industry.6.5wt% silicon steel is even called "arts and crafts of steel". But once the silicon content of the steel reaches 6.5wt%, its toughness and ductility will be very low and can’t be produced by normal rolling methods. Nowadays, only CVD technology makes its industrialization production come true. This paper is based on CVD technology. In study of the production method, general rules of siliconizing rate and necessary diffusion time was studied. The analysis of the diffusion of ferrosilicon alloy and its influence factors, finds a solution to eliminate Kirkendall holes’generation, lays the foundation for industrialization production of this material.In this dissertation, siliconizing and diffusion treatment under high temperature is studied. The result indicated that siliconizing rate is affected by four factors, It increases with the raise of temperature, the concentration or the flow and the flow of reactant gas, strip’s thickness. But to a certain extent, it will reach its saturation and doesn’t increase; The maximum value of the siliconizing rate is inversely proportional to the thickness of the steel strip. Besides, there is a linear relationship between the necessary processing time of diffusion treatment and the square of the thickness of the steel strip,In order to better understand the diffusion law of ferrosilicon alloy, its influence factors and diffusion mechanism is studied. And some ferrosilicon alloy diffusion couples are prepared for high temperature diffusion treatment. By using EDS detection technology, the silicon content distribution which changes with time in ferrosilicon alloy is measured. The mutual diffusion coefficient under the temperature range from 1000 to 1200℃ and silicon content range from 4 to 14wt% is gained. Besides, the diffusion activation energy and the frequency factor is gained.In this dissertation, it’s also analyzed that the generation of Kirkendall holes is due to the large difference between the diffusion rates of the iron and silicon elements. It leads to the void aggregation and the generation of holes. Generally, the holes generates where the silicon content is 12wt%, and it won’t move with the treatment of diffusion. By comparing with different siliconizing temperature and reaction gas concentration, the silicon steel section observed by SEM indicates that lowering the siliconizing temperature isn’t the solution to eliminating holes. And the control of reaction gas’s concentration can significantly decreases the number of holes and holes’sizes. The diffusion treatment can restrain these smaller holes.The siliconizing flux and diffusion flux are calculated when the holes generate and don’t generate, and a judging formula which can eliminate the holes is gained. I.e., if "Jreac≤3Jdiff" is satisfied, holes won’t generate or can be restrained by diffusion treatment.