| 摘要 |
PROBLEM TO BE SOLVED: To stably produce a grain-oriented silicon steel sheet high in magnetic flux density, at the time of rolling a silicon steel sheet having a specified compsn., by executing annealing for the steel sheet before final cold rolling by two stage soaking and next adopting specified cooling conditions. SOLUTION: A silicon steel slab contg., by weight, 0.025 to 0.080% C, 2.5 to 4.5% Si, <=0.015% S, 0.015 to 0.040% acid soluble Al, <0.010% N and 0.050 to 0.45% Mn is heated at <=1280 deg.C and is rolled. Next, it is subjected to rolling including process annealing so as to regulate the final rolling ratio to >=80% and is then subjected to decarburizing annealing and finish annealing to obtain a grain-oriented silicon steel sheet. At this time, the annealing before the final cold rolling is executed by two stage soaking, the high temp. side is soaked at 1000 to 1175 deg.C within 180sec, thereafter, the low temp. side is retained at 800 to 950 deg.C for 30 to 300sec and, next, cooling is executed to 400 to 550 deg.C at a rate of >=20 deg.C/sec. It is held in the above temp. range for 10 to 60sec and is subjected to cooling faster than natural cooling. Then, till the start of secondary recrystallization, nitriding treatment is executed. |
