Patent ID: 6361620
Filing Date: 2002-03-26
Classification: C21D

Abstract:
Process for the inhibition control in the production of grain-oriented electrical sheets where a silicon steel is cast in slabs, then brought to high temperature and hot-rolled; and the thus obtained hot-rolled strip is annealed and quenched, cold-rolled and the thus obtained cold-rolled strip is subjected to primary recrystallization annealing, nitrided and then subjected to secondary recrystallization annealing, said process being characterized by the combination in cooperative relationship of the following steps:(i) continuously casting a silicon steel having a content of copper, carbon and aluminum respectively in the following ranges 800-1800 ppm, 50-500 ppm, 250-350 ppm; (ii) heating the continuously cast slabs at a temperature comprised between 1150 and 1320Â° and hot-rolling them; (iii) bringing the thus obtained strip to 1100-1150Â° C., cooling it to 850-950Â° C., keeping it at this temperature for 30-100 s and then quenching it from 550-850Â° C. in order to obtain a strip in which the effective inhibition (Iz) for controlling grain growth, calculated according to the empirical formula: Iz=1.91 Fv/r where Fv is the volume fraction of the useful precipitates and r is the mean radius of said precipitates, ranges between 400 and 1300 cmâˆ’1; and(iv) carrying out said primary recrystallization annealing continuously between 800 and 950Â° C., in a wet nitrogen-hydrogen atmosphere for a period of time of between 20 and 150 seconds to produce a primary recrystallized strip; and then continuously nitriding said recrystallized strip at a temperature between 850 and 1050Â° C. [for a time between 5 and 120 seconds], in a wet nitriding atmosphere comprising ammonia at a level of from 1 to 35 standard liters per kg. of strip and from 0.5 to 100 g/m3 of water vapor.