Method for manufacturing grain-oriented electrical steel sheet
In a grain-oriented electrical steel sheet which is manufactured from a thin slab without using an inhibitor forming component, excellent magnetic properties are stably achieved. In a method for manufacturing a grain-oriented electrical steel sheet, a slab heating and annealing are performed under specific conditions.
1. A method for manufacturing a grain-oriented electrical steel sheet, comprising:
subjecting molten steel to continuous casting to form a slab with a thickness of 25 mm or more and 100 mm or less, the molten steel having a chemical composition containing, in mass %,
C: 0.002% or more and 0.100% or less,
Si: 2.00% or more and 8.00% or less,
Mn: 0.005% or more and 1.000% or less,
sol.Al: less than 0.0100%,
N: less than 0.0060%,
S: less than 0.0100%, and
Se: less than 0.0100%, with the balance being Fe and inevitable impurities;
heating the slab in a tunnel furnace;
hot rolling the heated slab to obtain a hot-rolled steel sheet;
optionally hot band annealing the hot-rolled steel sheet;
subjecting the hot-rolled steel sheet to cold rolling to obtain a cold-rolled steel sheet with a final sheet thickness;
subjecting the cold-rolled steel sheet to primary recrystallization annealing; and
subjecting the cold-rolled steel sheet after the primary recrystallization annealing to secondary recrystallization annealing,
wherein in the heating of the slab, the slab is heated while being conveyed along a casting direction at a rate of 10 m/min or more, a heating temperature is 1000° C. or more and 1300° C. or less and a heating time is 60 seconds or more and 600 seconds or less, and
a time from completion of the slab heating to start of the hot rolling is 100 seconds or less,
wherein (i) when the hot band annealing is performed,
a time to reach 900° C. from 400° C. in a heating process of the hot band annealing is 100 seconds or less, and
a soaking temperature in the hot band annealing is 950° C. or more, and
wherein (ii) when the hot band annealing is not performed,
the cold rolling has two or more rolling operations with intermediate annealing performed therebetween,
a time to reach 900° C. from 400° C. in a heating process of the first intermediate annealing is 100 seconds or less, and
a soaking temperature in the first intermediate annealing is 950° C. or more.
2. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the chemical composition contains, in mass %,
S: less than 0.0030%, and
Se: less than 0.0030%.
3. The method for manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein the chemical composition further contains, in mass %, one or more selected from the group consisting of
Cr: 0.01% or more and 0.50% or less,
Cu: 0.01% or more and 0.50% or less,
P: 0.005% or more and 0.50% or less,
Ni: 0.001% or more and 0.50% or less,
Sb: 0.005% or more and 0.50% or less,
Sn: 0.005% or more and 0.50% or less,
Bi: 0.005% or more and 0.50% or less,
Mo: 0.005% or more and 0.100% or less,
B: 0.0002% or more and 0.0025% or less,
Nb: 0.0010% or more and 0.0100% or less, and
V: 0.0010% or more and 0.0100% or less.
4. The method for manufacturing a grain-oriented electrical steel sheet according to claim 3 , wherein the heating of the slab is at least partially performed by induction heating.
5. The method for manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein the heating of the slab is at least partially performed by induction heating.
6. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the chemical composition further contains, in mass %, one or more selected from the group consisting of
Cr: 0.01% or more and 0.50% or less,
Cu: 0.01% or more and 0.50% or less,
P: 0.005% or more and 0.50% or less,
Ni: 0.001% or more and 0.50% or less,
Sb: 0.005% or more and 0.50% or less,
Sn: 0.005% or more and 0.50% or less,
Bi: 0.005% or more and 0.50% or less,
Mo: 0.005% or more and 0.100% or less,
B: 0.0002% or more and 0.0025% or less,
Nb: 0.0010% or more and 0.0100% or less, and
V: 0.0010% or more and 0.0100% or less.
7. The method for manufacturing a grain-oriented electrical steel sheet according to claim 6 , wherein the heating of the slab is at least partially performed by induction heating.
8. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the heating of the slab is at least partially performed by induction heating.