Study On Nitriding Process Of Grain-oriented Silicon Steel In Low-temperature Procedure

Grain-oriented silicon steel is the indispensable soft magnetic alloy in electricity, electronics and military industry, and is mainly used for various types of transformer and rectifier core. Grain-oriented silicon steel has complex process, and its quality has indicated the producing level on special steel of a country. Compared with Japan, the manufacturing technology of grain-oriented silicon steel has been falling behind in China. The reheating temperature of hot bands is about1350℃in conventional process of grain-oriented silicon steel, existing heavy energy consumption and pollution. The manufacturing technology of grain-oriented silicon steel at low reheating temperature can drop the reheating temperature below1200℃and significantly reduce cost of production, which must be nitrided by using ammonia decomposition.In present study, three necessary keys including process parameters, nitriding homogeneity and the element effect of Sn have been investigated, and obtain the results as follows:1. Based on the relation between decomposed ratio of ammonia and temperature, experimental temperature from750℃to790℃has been obtained, at which ammonia can completely decompose and nitrogen atoms can successfully infiltrate into steel sheets.2. The relation between nitriding quantity and three influence factors including nitriding temperature, nitriding time and proportion of ammonia was investigated, and proportion of ammonia is the most important factor and the effect of nitriding time is in the next place. Furthermore the experience formula is obtained.3. The nitriding uniformity has important effect on the magnetic properties, and the air pressure of ammonia and the nitriding position are the two key factors on the nitriding uniformity.4. The element of Sn segregates at the grain boundary in grain-oriented silicon steel sheets, and plays the role of assistant inhibitor. The proper Sn can reduce grain size after secondary recrystallization and is favorable to develop strong Goss texture. In addition, it is found that there exist a liner relation of quantity between ammonia and Sn.