Method for producing non-oriented electrical steel sheet
A non-oriented electrical steel sheet is produced by subjecting a steel slab containing, in mass %, C: not more than 0.0050%, Si: 1.0 to 6.5%, Mn: 0.05 to 2.0%, S: not more than 0.0050%, Al: not more than 0.01%, N: not more than 0.0050%, Ti: not more than 0.0030%, Nb: not more than 0.0030% and O: not more than 0.0050% to a hot rolling, a cold rolling and a finish annealing, the finish annealing conducted under conditions that a soaking temperature T (° C.) satisfies the following equation (1): ( 8 0 0 0 + 400 × Si ( mass % ) ) { ( - log ( Al ( mass % ) × N ( mass % ) ) + 1.7 + 0.2 × Si ( mass % ) } - 2 7 3 . 1 5 ≤ T ≤ 1200 , ( 1 ) and an atmosphere in the finish annealing is a mixed gas composed of one or more selected from nitrogen, hydrogen and noble gas with a nitrogen content of not more than 50 vol % and a dew point of not higher than −20° C., whereby a non-oriented electrical steel sheet achieving a high magnetic flux density and a low iron loss is produced.
1 . A method for producing a non-oriented electrical steel sheet comprising:
hot rolling a steel slab having a chemical composition comprising C: not more than 0.0050 mass %, Si: 1.0 to 6.5 mass %, Mn: 0.05 to 2.0 mass %, S: not more than 0.0050 mass %, Al: not more than 0.01 mass %, N: 0.0031 to 0.0050 mass %, Ti: not more than 0.0030 mass %, Nb: not more than 0.0030 mass %, 0: not more than 0.0050 mass % and the remainder being Fe and inevitable impurities,
subjecting the hot-rolled sheet to a single cold rolling or two or more cold rollings having an intermediate annealing interposed therebetween to have a final sheet thickness, and to a finish annealing,
wherein a soaking temperature T (° C.) in the finish annealing satisfies the following equation (1):
(
8
0
0
0
+
400
×
Si
(
mass
%
)
)
{
(
-
log
(
Al
(
mass
%
)
×
N
(
mass
%
)
)
+
1.7
+
0.2
×
Si
(
mass
%
)
}
-
2
7
3
.
1
5
≤
T
≤
1200
,
(
1
)
an atmosphere in the finish annealing is a mixed gas containing one or more selected from N 2 , H 2 and a noble gas and having a N 2 content of not more than 50 vol % and a dew point of the atmosphere of not higher than −45° C., and
wherein an amount of N in the steel sheet after the finish annealing is lower than the amount of N in the steel slab by at least 0.0006 mass %.
2 . The method for producing a non-oriented electrical steel sheet according to claim 1 , wherein the steel slab contains P: 0.03 to 0.20 mass %, in addition to the above chemical composition.
3 . The method for producing a non-oriented electrical steel sheet according to claim 1 , wherein the steel slab contains one or two selected from Sn: 0.005 to 0.20 mass % and Sb: 0.005 to 0.20 mass %, in addition to the above chemical composition.
4 . The method for producing a non-oriented electrical steel sheet according to claim 1 , wherein the steel slab contains one or more selected from Ca, Mg and REM by 0.0005 to 0.020 mass % in total, in addition to the above chemical composition.
5 . The method for producing a non-oriented electrical steel sheet according to claim 1 , wherein the steel slab contains one or more selected from Cu, Ni and Cr by 0.01 to 1.0 mass %, in addition to the above chemical composition.
6 . The method for producing a non-oriented electrical steel sheet according to claim 2 , wherein the steel slab contains one or two selected from Sn:
0.005 to 0.20 mass % and Sb: 0.005 to 0.20 mass %, in addition to the above chemical composition.
7 . The method for producing a non-oriented electrical steel sheet according to claim 2 , wherein the steel slab contains one or more selected from Ca, Mg and REM by 0.0005 to 0.020 mass % in total, in addition to the above chemical composition.
8 . The method for producing a non-oriented electrical steel sheet according to claim 3 , wherein the steel slab contains one or more selected from Ca, Mg and REM by 0.0005 to 0.020 mass % in total, in addition to the above chemical composition.
9 . The method for producing a non-oriented electrical steel sheet according to claim 6 , wherein the steel slab contains one or more selected from Ca, Mg and REM by 0.0005 to 0.020 mass % in total, in addition to the above chemical composition.
10 . The method for producing a non-oriented electrical steel sheet according to claim 2 , wherein the steel slab contains one or more selected from Cu, Ni and Cr by 0.01 to 1.0 mass %, in addition to the above chemical composition.
11 . The method for producing a non-oriented electrical steel sheet according to claim 3 , wherein the steel slab contains one or more selected from Cu, Ni and Cr by 0.01 to 1.0 mass %, in addition to the above chemical composition.
12 . The method for producing a non-oriented electrical steel sheet according to claim 4 , wherein the steel slab contains one or more selected from Cu, Ni and Cr by 0.01 to 1.0 mass %, in addition to the above chemical composition.
13 . The method for producing a non-oriented electrical steel sheet according to claim 6 , wherein the steel slab contains one or more selected from Cu, Ni and Cr by 0.01 to 1.0 mass %, in addition to the above chemical composition.
14 . The method for producing a non-oriented electrical steel sheet according to claim 7 , wherein the steel slab contains one or more selected from Cu, Ni and Cr by 0.01 to 1.0 mass %, in addition to the above chemical composition.
15 . The method for producing a non-oriented electrical steel sheet according to claim 8 , wherein the steel slab contains one or more selected from Cu, Ni and Cr by 0.01 to 1.0 mass %, in addition to the above chemical composition.
16 . The method for producing a non-oriented electrical steel sheet according to claim 9 , wherein the steel slab contains one or more selected from Cu, Ni and Cr by 0.01 to 1.0 mass %, in addition to the above chemical composition.
17 . The method for producing a non-oriented electrical steel sheet according to claim 1 , wherein after the finish annealing, the steel sheet contains N in an amount that is in a range of from 0.0022 mass % or less.
18 . The method for producing a non-oriented electrical steel sheet according to claim 1 , wherein after the finish annealing, the steel sheet contains N in an amount that is in a range of from 0.0012 mass % to 0.0021 mass %.
19 . The method for producing a non-oriented electrical steel sheet according to claim 1 , wherein the amount of N in the steel sheet after the finish annealing is lower than the amount of N in the steel slab by an amount that is in a range of from 0.0006 mass % to 0.0017 mass %.
20 . The method for producing a non-oriented electrical steel sheet according to claim 1 , wherein the amount of N in the steel slab is from 0.0032 to 0.0050 mass %.
21 . The method for producing a non-oriented electrical steel sheet according to claim 1 , wherein the soaking temperature T (° C.) in the finish annealing satisfies the following equation (2):
(
8
1
0
0
+
4
0
0
×
S
i
(
mass
%
)
)
{
(
-
log
(
Al
(
mass
%
)
×
N
(
mass
%
)
)
+
1
.
7
+
0
.
1
5
×
S
i
(
mass
%
)
}
-
2
7
3
.
1
5
≤
T
≤
1200.
(
2
)