Patent ID: 6406557
Filing Date: 2002-06-18
Classification: C21D

Abstract:
In a process for the treatment of grain oriented silicon steel wherein said silicon steel is subjected to the steps of continuous casting, hot-rolling and cold-rolling to form a cold-rolled steel which is then subjected to a continuous annealing to effect a primary recrystallization annealing and optionally carrying out decarburization before coating said cold-rolled steel with an annealing separator and annealing to effect a secondary recrystallization, the improvement comprising:(i) first, hot-rolling the silicon steel under conditions which cause the inhibition level (Iz) necessary to control grain growth, calculated according to the formula: â€ƒIz=1.91 Fv/r where Fv is the volumetric fraction of the useful precipitates and r is the mean radius of said useful precipitates, to be comprised between 400 and 1300 cmâˆ’1; (ii) second, cold rolling the product of step (i); (iii) third, performing said primary recrystallization annealing continuously between 800 and 950Â° C., in a wet nitroqen-hydrogen atmosphere to produce a primary recrystallized strip; and then continuously nitriding the primary 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 and (iv) box annealing the product of step (iii) under standard conditions.