Patent ID: 6325866
Filing Date: 2001-12-04
Classification: C21D

Abstract:
In a process for the production of grain oriented silicon steel in which a steel is produced in the molten state and is continuously cast to form slabs which are sent to a hot rolling station after intermediate heating at high temperature, and thereafter are hot-rolled to obtain a strip of the desired thickness, the strip being coiled and subsequently uncoiled and cold rolled to the desired final thickness, subjecting the cold rolled strip thus produced to final treatments including primary-recrystallization annealing and secondary-recrystallization annealing the improvement which consists essentially of:(a) continuously casting slabs having the following composition; 2.5% to 3.5% by weight of Si; from 50 to 500 ppm of C; from 250 to 450 ppm of Al.sub.sol ; less than 120 ppm of N; from 500 to 3000 ppm of Cu; and from 500 to 1500 ppm of Sn, the remainder consisting of iron and other impurities;(b) bringing said continuously cast slabs to a temperature of between 1200.degree. C. and 1320.degree. C.;(c) hot rolling the slabs of step (b) to a thickness of between 1.8 and 2.5 mm, ensuring a time of exposure to air of the strip coming from the finishing stand of at least 4 seconds at a temperature of between 1000.degree. C. and 900.degree. C., and coiling the strip at a temperature of between 550.degree. C. and 700.degree. C.;(d) single-stage cold-rolling the strip of step (c) down to the final thickness; and(e) continuous decarburization annealing by annealing between 850 and 950.degree. 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 subsequently nitriding annealing at temperature between 900 and 1050.degree. C., 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/m.sup.3 of water vapor.