PRODUCTION OF GRAIN-ORIENTED SILICON STEEL SHEET HAVING CONTROLLED SECONDARY RECRYSTALLIZED GRAIN BOUNDARY

摘要

PURPOSE:To control secondary recrystallized grain boundaries and to produce a grain- oriented silicon steel sheet with low iron loss by subjecting a slab of silicon steel with a specific composition to hot rolling, cold rolling, and decarburizing annealing, applying proper local strain to the resulting steel sheet, and then carrying out specific heat treatment. CONSTITUTION:A slab of a silicon steel having a composition consisting of, by weight, 0.025-0.075% C, 2.5-4.5% Si, =0.012% S, 0.010-0.060% acid soluble AL, =0.010% N, 0.05-0.45% Mn, and the balance Fe with inevitable impurities is heated to =1200 deg.C and hot-rolled and is then cold-rolled once or cold-rolled twice or more while process- annealed between the cold rolling stages so as to be formed to the final sheet thickness. Subsequently, the resulting steel sheet is subjected to decarburizing annealing and then to high-temp. finish annealing after the application of a separation agent at annealing. At this time, after the decarburizing annealing, local strain is applied to the steel sheet to the extent causing no recrystallization and heat treatment consisting of local heating at 500-850 deg.C for a short time in a gaseous mixture of H2 and N2 containing NH3 is applied to the steel sheet. By this method, the size of secondary recrystallized grains formed in the course of finish annealing can be controlled, and the iron loss in the resulting grain-oriented silicon steel sheet can be reduced.