Method of manufacturing grain-oriented electrical steel sheet
The method includes slab-heating a steel slab to a temperature of higher than a γ-phase precipitation temperature and 1380° C. or lower, subjecting the steel slab to rough rolling including at least two passes of rolling at a predetermined temperature with an introduced sheet thickness true strain ε t of 0.50 or more and to finish rolling with a rolling finish temperature of 900° C. or higher to obtain a hot-rolled sheet, cooling the hot-rolled sheet for 1 second or longer at a cooling rate of 70° C./s or higher within 2 seconds after finish rolling, coiling the sheet at a coiling temperature of 600° C. or lower, performing hot-rolled sheet annealing for soaking at a predetermined soaking temperature, and then performing cold rolling, primary recrystallization annealing, and secondary recrystallization annealing.
1 . A method of manufacturing a grain-oriented electrical steel sheet, comprising:
preparing a steel slab having a chemical composition containing
C: 0.005 mass % to 0.085 mass %,
Si: 2.00 mass % to 4.50 mass %,
Mn: 0.03 mass % to 1.00 mass %,
sol.Al: 0.008 mass % or more and less than 0.030 mass %, and
N: 0.004 mass % to 0.009 mass % or less, and
further containing either or both of S: 0.0005 mass % to 0.02 mass % and Se: 0.0005 mass % to 0.02 mass %, with the balance being Fe and inevitable impurities,
subjecting the steel slab to slab heating to a temperature of higher than a γ-phase precipitation temperature and 1380° C. or lower, the γ-phase precipitation temperature being determined by equilibrium calculation,
next, subjecting the steel slab to rough rolling including at least two passes of rolling at a temperature of (temperature at which γ-phase fraction reaches its maximum −20° C.) or higher with an introduced sheet thickness true strain ε t of 0.50 or more for each pass to obtain a rough-rolled sheet, the temperature at which γ-phase fraction reaches its maximum being determined by equilibrium calculation,
next, subjecting the rough-rolled sheet to finish rolling where a rolling finish temperature is 900° C. or higher to obtain a hot-rolled sheet, the hot-rolled sheet having a recrystallization ratio Y of 10% or higher and 60% or less,
next, cooling the hot-rolled sheet for 1 second or longer at a cooling rate of 70° C./s or higher within 2 seconds after an end of the finish rolling,
coiling the hot-rolled sheet obtained after cooling at a coiling temperature of 600° C. or lower,
next, subjecting the hot-rolled sheet obtained after coiling to hot-rolled sheet annealing for soaking at a soaking temperature of 1000° C. or higher and (1150-2.5Y)° C. or lower for 60 seconds or longer to obtain a hot-rolled and annealed sheet, where Y (%) is a recrystallization ratio of a sheet thickness central layer of the hot-rolled sheet obtained after coiling,
next, subjecting the hot-rolled and annealed sheet to cold rolling at a rolling ratio of 88% or more and 91% or less to obtain a cold-rolled sheet with a final sheet thickness,
next, subjecting the cold-rolled sheet to primary recrystallization annealing to obtain a primary recrystallization annealed sheet, and
next, subjecting the primary recrystallization annealed sheet to secondary recrystallization annealing to obtain a grain-oriented electrical steel sheet, wherein
the sheet thickness true strain Et is calculated by the following equation (1)
ε t =−ln(sheet thickness after rolling/sheet thickness before rolling) (1).
2 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the chemical composition further contains at least one selected from the group consisting of
Sb: 0.005 mass % to 0.500 mass %, and
Sn: 0.005 mass % to 0.500 mass %.
3 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the chemical composition further contains at least one selected from the group consisting of
Ni: 0.01 mass % to 1.50 mass %,
Cr: 0.005 mass % to 0.50 mass %,
Cu: 0.03 mass % to 0.50 mass %,
P: 0.005 mass % to 0.500 mass %,
As: 0.0005 mass % to 0.050 mass %,
Bi: 0.005 mass % to 0.500 mass %,
Mo: 0.005 mass % to 0.100 mass %,
B: 0.0002 mass % to 0.0025 mass %,
Te: 0.0005 mass % to 0.0100 mass %,
Zr: 0.001 mass % to 0.010 mass %,
Nb: 0.001 mass % to 0.010 mass %,
V: 0.001 mass % to 0.010 mass %, and
Ta: 0.001 mass % to 0.010 mass %.
4 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the rough rolling includes at least one pass of rolling at a temperature of (the temperature at which γ-phase fraction reaches its maximum−20° C.) or higher and (the temperature at which γ-phase fraction reaches its maximum+50° C.) or lower.
5 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the rough rolling has four or more passes in total.
6 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the hot-rolled sheet obtained after the soaking is subjected to cooling where a first average cooling rate v 1 from the soaking temperature to 800° C. is lower than 40° C./s and a second average cooling rate v 2 from 800° C. to 650° C. is equal to or higher than v 1 .
7 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the recrystallization ratio Y is 18% or higher and 60% or less.
8 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the recrystallization ratio Y is 20% or higher and 60% or less, and skin pass rolling with an elongation rate of 0.05% or more is performed after an end of the finish rolling and before hot-rolled sheet annealing.
9 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein a magnetic flux density B 8 in a rolling direction of the grain-oriented electrical steel sheet is 1.940 T or higher.
10 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein the chemical composition further contains at least one selected from the group consisting of
Ni: 0.01 mass % to 1.50 mass %,
Cr: 0.005 mass % to 0.50 mass %,
Cu: 0.03 mass % to 0.50 mass %,
P: 0.005 mass % to 0.500 mass %,
As: 0.0005 mass % to 0.050 mass %,
Bi: 0.005 mass % to 0.500 mass %,
Mo: 0.005 mass % to 0.100 mass %,
B: 0.0002 mass % to 0.0025 mass %,
Te: 0.0005 mass % to 0.0100 mass %,
Zr: 0.001 mass % to 0.010 mass %,
Nb: 0.001 mass % to 0.010 mass %,
V: 0.001 mass % to 0.010 mass %, and
Ta: 0.001 mass % to 0.010 mass %.
11 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein the rough rolling includes at least one pass of rolling at a temperature of (the temperature at which γ-phase fraction reaches its maximum−20° C.) or higher and (the temperature at which γ-phase fraction reaches its maximum+50° C.) or lower.
12 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein the rough rolling has four or more passes in total.
13 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein the hot-rolled sheet obtained after the soaking is subjected to cooling where a first average cooling rate v 1 from the soaking temperature to 800° C. is lower than 40° C./s and a second average cooling rate v 2 from 800° C. to 650° C. is equal to or higher than v 1 .
14 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein the recrystallization ratio Y is 18% or higher and 60% or less.
15 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein the recrystallization ratio Y is 20% or higher and 60% or less, and skin pass rolling with an elongation rate of 0.05% or more is performed after an end of the finish rolling and before hot-rolled sheet annealing.
16 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein a magnetic flux density B 8 in a rolling direction of the grain-oriented electrical steel sheet is 1.940 T or higher.
17 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 3 , wherein the rough rolling includes at least one pass of rolling at a temperature of (the temperature at which γ-phase fraction reaches its maximum−20° C.) or higher and (the temperature at which γ-phase fraction reaches its maximum+50° C.) or lower.
18 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 3 , wherein the rough rolling has four or more passes in total.
19 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 3 , wherein the hot-rolled sheet obtained after the soaking is subjected to cooling where a first average cooling rate v 1 from the soaking temperature to 800° C. is lower than 40° C./s and a second average cooling rate v 2 from 800° C. to 650° C. is equal to or higher than v 1 .
20 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 3 , wherein the recrystallization ratio Y is 18% or higher and 60% or less.