U.S. patent application number 13/514342 was filed with the patent office on 2012-10-25 for non-oriented electrical steel sheet having superior magnetic properties and a production method therefor.
This patent application is currently assigned to POSCO. Invention is credited to Won-Seog Bong, Jae-Hoon Kim, Jae-Kwan Kim, Yong-Soo Kim.
Application Number | 20120267015 13/514342 |
Document ID | / |
Family ID | 44226997 |
Filed Date | 2012-10-25 |
United States Patent
Application |
20120267015 |
Kind Code |
A1 |
Kim; Jae-Hoon ; et
al. |
October 25, 2012 |
Non-Oriented Electrical Steel Sheet Having Superior Magnetic
Properties and a Production Method Therefor
Abstract
Provided are: a non-oriented electrical steel sheet having
outstanding magnetic properties and comprising, as percentages by
weight, from 1.0 to 3.0% of Al, from 0.5 to 2.5% of Si, from 0.5 to
2.0% of Mn, from 0.001 to 0.004% of N, from 0.0005 to 0.004% of S
and a balance of Fe and other unavoidably incorporated impurities,
wherein the Al, Mn, N and S are included so as to satisfy the
compositional formulae {[Al]+[Mn]}.ltoreq.3.5,
0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
300.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,400; and a production
method therefor. By optimising the Al, Si, Mn, N and S added
components in this way, the distribution density of coarse
inclusions is increased, thereby making it possible to improve
crystal-grain growth properties and domain wall mobility and so
produce the highest grade of non-oriented electrical steel sheet
having superior magnetic properties, low hardness, and superior
customer workability and productivity.
Inventors: |
Kim; Jae-Hoon; (Pohang-si,
KR) ; Kim; Jae-Kwan; (Pohang-si, KR) ; Kim;
Yong-Soo; (Pohang-si, KR) ; Bong; Won-Seog;
(Pohang-si, KR) |
Assignee: |
POSCO
Pohang-si, Gyeongsangbuk-do
KR
|
Family ID: |
44226997 |
Appl. No.: |
13/514342 |
Filed: |
December 28, 2010 |
PCT Filed: |
December 28, 2010 |
PCT NO: |
PCT/KR2010/009380 |
371 Date: |
June 7, 2012 |
Current U.S.
Class: |
148/645 ;
148/320; 75/507 |
Current CPC
Class: |
C22C 38/14 20130101;
C22C 38/008 20130101; C22C 38/04 20130101; C22C 38/60 20130101;
C21D 2211/004 20130101; H01F 1/16 20130101; C22C 38/004 20130101;
C22C 38/001 20130101; C21D 8/12 20130101; C22C 38/02 20130101; C22C
38/06 20130101; C22C 38/002 20130101 |
Class at
Publication: |
148/645 ;
148/320; 75/507 |
International
Class: |
C21D 8/02 20060101
C21D008/02; C22C 38/06 20060101 C22C038/06; C22C 38/04 20060101
C22C038/04; C22C 38/02 20060101 C22C038/02; C22B 9/00 20060101
C22B009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2009 |
KR |
10-2009-0131990 |
Dec 28, 2009 |
KR |
10-2009-0131992 |
Dec 24, 2010 |
KR |
10-2010-0135003 |
Dec 24, 2010 |
KR |
10-2010-0135004 |
Dec 27, 2010 |
KR |
10-2010-0135943 |
Claims
1. A non-oriented electrical steel sheet having superior magnetic
properties, comprising 0.7.about.3.0% of Al, 0.2.about.3.5% of Si,
0.2.about.2.0% of Mn, 0.001.about.0.004% of N, 0.0005.about.0.004%
of S, and a balance of Fe and other inevitable impurities by wt %,
and satisfying at least one of Conditions (1), (2) and (3) below:
Condition (1): 0.7.ltoreq.[Al].ltoreq.2.7,
0.2.ltoreq.[Si].ltoreq.1.0, 0.2.ltoreq.[Mn].ltoreq.1.7,
{[Al]+[Mn]}.ltoreq.2.0, 0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
230.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,000; Condition (2):
1.0.ltoreq.[Al].ltoreq.3.0, 0.5.ltoreq.[Mn].ltoreq.2.0,
{[Al]+[Mn]}.ltoreq.3.5, 0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
300.ltoreq.{([Al]+[Mn])/([N]+[S])}1,400; and Condition (3):
1.0.ltoreq.[Al].ltoreq.3.0, 2.3.ltoreq.[Si].ltoreq.3.5,
0.5.ltoreq.[Mn].ltoreq.2.0, {[Al]+[Mn]}.ltoreq.3.5,
0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
300.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,400, wherein [Al],
[Si], [Mn], [N] and [S] indicate amounts (wt %) of Al, Si, Mn, N
and S, respectively.
2. The non-oriented electrical steel sheet of claim 1, which
satisfies Condition (1) and wherein the amounts of Al, Si and Mn
satisfy Relation (1) below. Relation (1):
1.0.ltoreq.{[Al]+[Si]+[Mn]/2}.ltoreq.2.0
3. The non-oriented electrical steel sheet of claim 1, wherein the
amounts of Al and Mn satisfy Relation (2) below. Relation (2):
1.ltoreq.[Al]/[Mn].ltoreq.8
4. The non-oriented electrical steel sheet of claim 2, wherein a
cross-sectional Vickers hardness (Hv1) is 140 or less.
5. The non-oriented electrical steel sheet of claim 1, which
satisfies Condition (2) and wherein the amounts of Al, Si and Mn
satisfy Relation (3) below. Relation (3):
1.7.ltoreq.{[Al]+[Si]+[Mn]/2}.ltoreq.5.5
6. The non-oriented electrical steel sheet of claim 1, which
satisfies Condition (2) and wherein the amounts of Al and Si
satisfy Relation (4) below. Relation (4):
0.6.ltoreq.[Al]/[Si].ltoreq.4.0
7. The non-oriented electrical steel sheet of claim 5, wherein a
cross-sectional Vickers hardness (Hv1) is 190 or less.
8. The non-oriented electrical steel sheet of claim 1, which
satisfies Condition (3) and wherein the amounts of Al, Si and Mn
satisfy Relation (5) below. Relation (5):
3.0.ltoreq.{[Al]+[Si]+[Mn]/2}.ltoreq.56.5
9. The non-oriented electrical steel sheet of claim 8, wherein a
cross-sectional Vickers hardness (Hv1) is 225 or less.
10. The non-oriented electrical steel sheet of claim 1, wherein an
inclusion comprising a nitride and a sulfide alone or a combination
thereof is formed in the steel sheet, and a distribution density of
the inclusion having an average size of 300 nm or more is equal to
or greater than 0.02 number/mm.sup.2.
11. The non-oriented electrical steel sheet of claim 1, further
comprising 0.2% or less of P.
12. The non-oriented electrical steel sheet of claim 11, wherein an
inclusion comprising a nitride and a sulfide alone or a combination
thereof is formed in the steel sheet, and a distribution density of
the inclusion having an average size of 300 nm or more is equal to
or greater than 0.02 number/mm.sup.2.
13. The non-oriented electrical steel sheet of claim 1, further
comprising at least one of 0.005.about.0.2% of Sn and
0.005.about.0.1% of Sb.
14. The non-oriented electrical steel sheet of claim 13, wherein an
inclusion comprising a nitride and a sulfide alone or a combination
thereof is formed in the steel sheet, and a distribution density of
the inclusion having an average size of 300 nm or more is equal to
or greater than 0.02 number/mm.sup.2.
15. A non-oriented electrical steel sheet having superior magnetic
properties, comprising 0.7.about.3.0% of Al, 0.2.about.3.5% of Si,
0.2.about.2.0% of Mn, 0.001.about.0.004% of N, 0.0005.about.0.004%
of S, and a balance of Fe and other inevitable impurities by wt %,
wherein an inclusion comprising a nitride and a sulfide alone or a
combination thereof is formed in the steel sheet, and a
distribution density of the inclusion having an average size of 300
nm or more is equal to or greater than 0.02 number/mm.sup.2.
16. The non-oriented electrical steel sheet of claim 15, further
comprising 0.2% or less of P.
17. The non-oriented electrical steel sheet of claim 15, further
comprising at least one of 0.005.about.0.2% of Sn and
0.005.about.0.1% of Sb.
18. A method of producing a non-oriented electrical steel sheet
having superior magnetic properties, comprising subjecting a slab
comprising 0.7.about.3.0% of Al, 0.2.about.3.5% of Si,
0.2.about.2.0% of Mn, 0.001.about.0.004% of N, 0.0005.about.0.004%
of S, and a balance of Fe and other inevitable impurities by wt %
and satisfying at least one of Conditions (1), (2) and (3) below to
heating, hot rolling, cold rolling, and final annealing at
750.about.1100.degree. C.: Condition (1):
0.7.ltoreq.[Al].ltoreq.2.7, 0.2.ltoreq.[Si].ltoreq.1.0,
0.2.ltoreq.[Mn].ltoreq.1.7, {[Al]+[Mn]}.ltoreq.2.0,
0.002.ltoreq.{[N]+[S]}.ltoreq..ltoreq.0.006,
230.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,000; Condition (2):
1.0.ltoreq.[Al].ltoreq.3.0, 0.5.ltoreq.[Si].ltoreq.2.5,
0.5.ltoreq.[Mn].ltoreq.2.0, {[Al]+[Mn]}.ltoreq.3.5,
0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
300.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,400; and Condition (3):
1.0.ltoreq.[Al].ltoreq.3.0, 2.3.ltoreq.[Si].ltoreq.3.5,
0.5.ltoreq.[Mn].ltoreq.2.0, {[Al]+[Mn]}.ltoreq.3.5,
0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
300.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,400, wherein [Al],
[Si], [Mn], [N] and [S] indicate amounts (wt %) of Al, Si, Mn, N
and S, respectively.
19. The method of claim 18, wherein the slab satisfies Condition
(1) and the amounts of Al, Si and Mn satisfy Relation (1) below.
Relation (1): 1.0.ltoreq.{[Al]+[Si]+[Mn]/2}.ltoreq.2.0
20. The method of claim 18, wherein the amounts of Al and Mn
satisfy Relation (2) below. Relation (2):
1.ltoreq.[Al]/[Mn].ltoreq.8
21. The method of claim 18, wherein the slab satisfies Condition
(2) and the amounts of Al, Si and Mn satisfy Relation (3) below.
Relation (3): 1.7.ltoreq.{[Al]+[Si]+[Mn]/2}.ltoreq.5.5
22. The method of claim 18, wherein the slab satisfies Condition
(2) and the amounts of Al and Si satisfy Relation (4) below.
Relation (4): 0.6.ltoreq.[Al]/[Si].ltoreq.4.0
23. The method of claim 18, wherein the slab satisfies Condition
(3) and the amounts of Al, Si and Mn satisfy Relation (5) below.
Relation (5): 3.0.ltoreq.{[Al]+[Si]+[Mn]/2}.ltoreq.6.5
24. The method of claim 18, wherein an inclusion comprising a
nitride and a sulfide alone or a combination thereof is formed in
the steel sheet subjected to final annealing, and a distribution
density of the inclusion having an average size of 300 nm or more
is equal to or greater than 0.02 number/mm.sup.2.
25. The method of claim 18, wherein the slab is prepared by adding
0.3.about.0.5% of Al to perform deoxidation, adding remaining alloy
elements, and maintaining a temperature at
1,500.about.1,600.degree. C.
26. The method of claim 18, wherein annealing of a hot rolled sheet
is performed between the hot rolling and the cold rolling.
27. The method of claim 18, wherein the slab further comprises 0.2%
or less of P.
28. The method of claim 27, wherein an inclusion comprising a
nitride and a sulfide alone or a combination thereof is formed in
the steel sheet, and a distribution density of the inclusion having
an average size of 300 nm or more is equal to or greater than 0.02
number/mm.sup.2.
29. The method of claim 18, wherein the slab further comprises at
least one of 0.005.about.0.2% of Sn and 0.005.about.0.1% of Sb.
30. The method of claim 29, wherein an inclusion comprising a
nitride and a sulfide alone or a combination thereof is formed in
the steel sheet, and a distribution density of the inclusion having
an average size of 300 nm or more is equal to or greater than 0.02
number/mm.sup.2.
31. A non-oriented electrical steel sheet slab, comprising
0.7.about.3.0% of Al, 0.2.about.3.5% of Si, 0.2.about.2.0% of Mn,
0.001.about.0.004% of N, 0.0005.about.0.004% of S, and a balance of
Fe and other inevitable impurities by wt %, and satisfying at least
one of Conditions (1), (2) and (3) below: Condition (1):
0.7.ltoreq.[Al].ltoreq.2.7, 0.2.ltoreq.[Si].ltoreq.1.0,
0.2.ltoreq.[Mn].ltoreq.1.7, {[Al]+[Mn]}.ltoreq.2.0,
0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
230.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,000; Condition (2):
1.0.ltoreq.[Al].ltoreq.3.0, 0.5.ltoreq.[Si].ltoreq.2.5,
0.5.ltoreq.[Mn].ltoreq.2.0, {[Al]+[Mn]}.ltoreq.3.5,
0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
300.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,400; and Condition (3):
1.0.ltoreq.[Al].ltoreq.3.0, 2.3.ltoreq.[Si].ltoreq.3.5,
0.5.ltoreq.[Mn].ltoreq.2.0, {[Al]+[Mn]}.ltoreq.3.5,
0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
300.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,400, wherein [Al],
[Si], [Mn], [N] and [S] indicate amounts (wt %) of Al, Si, Mn, N
and S, respectively.
32. The non-oriented electrical steel sheet slab of claim 31, which
satisfies Condition (1) and wherein the amounts of Al, Si and Mn
satisfy Relation (1) below. Relation (1):
1.0.ltoreq.{[Al]+[Si]+[Mn]/2}.ltoreq.2.0
33. The non-oriented electrical steel sheet slab of claim 31,
wherein the amounts of Al and Mn satisfy Relation (2) below.
Relation (2): 1.ltoreq.[Al]/[Mn].ltoreq.8
34. The non-oriented electrical steel sheet slab of claim 31, which
satisfies Condition (2) and wherein the amounts of Al, Si and Mn
satisfy Relation (3) below. Relation (3):
1.7.ltoreq.{[Al]+[Si]+[Mn]/2}.ltoreq.5.5
35. The non-oriented electrical steel sheet slab of claim 31, which
satisfies Condition (2) and wherein the amounts of Al and Si
satisfy Relation (4) below. Relation (4):
0.6.ltoreq.[Al]/[Si].ltoreq.4.0
36. The non-oriented electrical steel sheet slab of claim 31, which
satisfies Condition (3) and wherein the amounts of Al, Si and Mn
satisfy Relation (5) below. Relation (5):
3.0.ltoreq.{[Al]+[Si]+[Mn]/2}.ltoreq.6.5
37. The non-oriented electrical steel sheet slab of claim 31,
further comprising 0.2% or less of P.
38. The non-oriented electrical steel sheet slab of claim 31,
further comprising at least one of 0.005.about.0.2% of Sn and
0.005.about.0.1% of Sb.
39. A method of producing a non-oriented electrical steel sheet
slab, comprising adding 0.3.about.0.5% of Al to molten steel to
perform deoxidation, adding a remainder of Al and Si and Mn, and
maintaining a temperature of the molten steel at
1,500.about.1,600.degree. C., thus obtaining the slab comprising
0.7.about.3.0% of Al, 0.2.about.3.5% of Si, 0.2.about.2.0% of Mn,
0.001.about.0.004% of N, 0.0005.about.0.004% of S, and a balance of
Fe and other inevitable impurities by wt %, and satisfying at least
one of Conditions (1), (2) and (3) below: Condition (1):
0.7.ltoreq.[Al].ltoreq.2.7, 0.2.ltoreq.[Si].ltoreq.1.0,
0.2.ltoreq.[Mn].ltoreq.1.7, {[Al]+[Mn]}.ltoreq.2.0,
0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
230.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,000; Condition (2):
1.0.ltoreq.[Al].ltoreq.3.0, 0.5.ltoreq.[Si].ltoreq.2.5,
0.5.ltoreq.[Mn].ltoreq.2.0, {[Al]+[Mn]}.ltoreq.3.5,
0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
300.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,400; and Condition (3):
1.0.ltoreq.[Al].ltoreq.3.0, 2.3[Si].ltoreq.3.5,
0.5.ltoreq.[Mn].ltoreq.2.0, {[Al]+[Mn]}.ltoreq.3.5,
0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
300.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,400, wherein [Al],
[Si], [Mn], [N] and [S] indicate amounts (wt %) of Al, Si, Mn, N
and S, respectively.
40. The method of claim 39, wherein the slab further comprises 0.2%
or less of P.
41. The method of claim 39, wherein the slab further comprises at
least one of 0.005.about.0.2% of Sn and 0.005.about.0.1% of Sb.
Description
TECHNICAL FIELD
[0001] The present invention relates to the production of a
non-oriented electrical steel sheet, and particularly to a
non-oriented electrical steel sheet of the highest quality, wherein
the components of steel are optimally designed to increase the
distribution density of coarse inclusions in steel and to improve
growth of grains and mobility of domain walls, so that magnetic
properties are enhanced, and low hardness is ensured, thus
improving productivity and punchability, and to a method of
producing the same.
BACKGROUND ART
[0002] The present invention pertains to the production of a
non-oriented electrical steel sheet useful as a material for iron
cores of rotation devices. This non-oriented electrical steel sheet
is essential in terms of converting electrical energy into
mechanical energy, and thus the magnetic properties thereof are
regarded as very important. The magnetic properties mainly include
core loss and magnetic flux density. Because the core loss is
energy that disappears in the form of heat in the course of
converting energy, it is good for it to be as low as possible. The
magnetic flux density is a power source of a rotator. The higher
the magnetic flux density, the more favorable the energy
efficiency.
[0003] Typically, a non-oriented electrical steel sheet is composed
mainly of Si in order to reduce core loss. When the amount of Si
increases, the magnetic flux density decreases. If the amount of Si
is excessively increased, processability is decreased making it
difficult to perform cold rolling. Furthermore, the lifetime of a
mold may decrease upon punching by the customer. Hence, attempts
are made to decrease the amount of Si and increase the amount of Al
so as to improve magnetic properties and mechanical properties.
However, the magnetic properties of non-oriented electrical steel
sheet of the highest quality are not obtained, and such sheets have
not yet been actually produced because of difficulties in mass
producing them.
[0004] Meanwhile, to obtain a non-oriented electrical steel sheet
with good magnetic properties, impurities including C, S, N, Ti and
so on such as fine inclusions present in steel are controlled to be
minimal and thus the growth of grains needs to be increased.
However, the control of impurities to the minimum is not easy in a
typical production process of electrical steel sheets, and the cost
of a steel making process may undesirably increase.
[0005] The impurities which were not removed in the steel making
process are present in the form of nitrides or sulfides in a slab
upon continuous casting. As the slab is re-heated to 1,100.degree.
C. or higher for hot rolling, inclusions such as nitrides or
sulfides may be re-dissolved and then finely precipitated again
upon termination of hot rolling.
[0006] The inclusions that are precipitated in typical non-oriented
electrical steel sheets include MnS and AlN, which are observed to
have a small average size of about 50 nm, and such fine inclusions
may hinder the growth of grains upon annealing thus increasing
hysteresis loss and obstructing the movement of domain walls upon
magnetization, undesirably lowering permeability.
[0007] Therefore, in the process of producing the non-oriented
electrical steel sheet, impurities are appropriately controlled
from the steel making process so that such fine inclusions are not
present, and the residual inclusions should be prevented from being
more finely precipitated via re-dissolution upon hot rolling.
DISCLOSURE
Technical Problem
[0008] Accordingly, the present invention has been made keeping in
mind the above problems occurring in the related art, and an object
of the present invention is to provide a non-oriented electrical
steel sheet of the highest quality, wherein the proportions of Al,
Si and Mn which are alloy elements of steel and N and S which are
impurity elements of steel are optimally controlled so that the
distribution density of coarse inclusions in steel is increased and
the formation of fine inclusions is decreased, thus enhancing the
growth of grains and the mobility of domain walls to thereby
manifest excellent magnetic properties, and also superior
productivity and punchability because of low hardness.
Technical Solution
[0009] In order to accomplish the above object, an aspect of the
present invention provides a non-oriented electrical steel sheet
having superior magnetic properties, comprising 0.7.about.3.0% of
Al, 0.2.about.3.5% of Si, 0.2.about.2.0% of Mn, 0.001.about.0.004%
of N, 0.0005.about.0.004% of S, and a balance of Fe and other
inevitable impurities by wt %, and satisfying at least one of
Conditions (1), (2) and (3) below: Condition (1):
0.7.ltoreq.[Al].ltoreq.2.7, 0.2.ltoreq.[Si].ltoreq.1.0,
0.2.ltoreq.[Mn].ltoreq.1.7, {[Al]+[Mn]}.ltoreq.12.0,
0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
230.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,000; Condition (2):
1.0.ltoreq.[Al].ltoreq.3.0, 0.5.ltoreq.[Mn].ltoreq.2.0,
{[Al]+[Mn]}.ltoreq.3.5, 0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
300.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,400; and Condition (3):
1.0.ltoreq.[Al].ltoreq.3.0, 0.5.ltoreq.[Mn].ltoreq.2.0,
{[Al]+[Mn]}.ltoreq.3.5, 0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
300.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,400, wherein [Al],
[Si], [Mn], [N] and [S] indicate amounts (wt %) of Al, Si, Mn, N
and S, respectively.
[0010] In the non-oriented electrical steel sheet which satisfies
Condition (1), the amounts of Al, Si and Mn may satisfy Relations
(1) and (2) below, and a cross-sectional Vickers hardness (Hv1) may
be 140 or less.
[0011] Relation (1): 1.0.ltoreq.{[Al]+[Si]+[Mn]/2}.ltoreq.2.0
[0012] Relation (2): 1.ltoreq.[Al]/[Mn].ltoreq.8
[0013] In the non-oriented electrical steel sheet which satisfies
Condition (2), the amounts of Al, Si and Mn may satisfy Relation
(2) and the following Relations (3) and (4), and a cross-sectional
Vickers hardness (Hv1) may be 190 or less.
[0014] Relation (3): 1.7.ltoreq.{[Al]+[Si]+[Mn]/2}.ltoreq.5.5
[0015] Relation (4): 0.6.ltoreq.[Al]/[Si].ltoreq.4.0
[0016] In the non-oriented electrical steel sheet which satisfies
Condition (3), the amounts of Al, Si and Mn satisfy Relations (2)
and the following Relation (5), and a cross-sectional Vickers
hardness (Hv1) may be 225 or less.
[0017] Relation (5): 3.0.ltoreq.{[Al]+[Si]+[Mn]/2}.ltoreq.6.5
[0018] The non-oriented electrical steel sheet which satisfies at
least one of Conditions (1) to (3) may have inclusions comprising
nitrides and sulfides alone or combinations thereof formed in the
steel sheet, and the distribution density of the inclusions having
an average size of 300 nm or more may be equal to or greater than
0.02 number/mm.sup.2.
[0019] The non-oriented electrical steel sheet may further comprise
0.2% or less of P.
[0020] The non-oriented electrical steel sheet may further comprise
at least one of 0.005.about.0.2% of Sn and 0.005.about.0.1% of
Sb.
[0021] Another aspect of the present invention provides a method of
producing the non-oriented electrical steel sheet having superior
magnetic properties, comprising subjecting a slab comprising
0.7.about.3.0% of Al, 0.2.about.3.5% of Si, 0.2.about.2.0% of Mn,
0.001.about.0.004% of N, 0.0005.about.0.004% of S, and a balance of
Fe and other inevitable impurities by wt % and satisfying at least
one of Conditions (1), (2) and (3) to heating, hot rolling, cold
rolling, and final annealing at 750.about.1100.degree. C.
[0022] In the method according to the present invention, inclusions
comprising nitrides and sulfides alone or combinations thereof may
be formed in the steel sheet subjected to final annealing, and the
distribution density of the inclusions having an average size of
300 nm or more may be equal to or greater than 0.02
number/mm.sup.2.
[0023] The slab may be prepared by adding 0.3.about.0.5% of Al to
perform deoxidation, adding remaining alloy elements, and
maintaining a temperature at 1,500.about.1,600.degree. C.
[0024] A further aspect of the present invention provides a
non-oriented electrical steel sheet slab, comprising 0.7.about.3.0%
of Al, 0.2.about.3.5% of Si, 0.2.about.2.0% of Mn,
0.001.about.0.004% of N, 0.0005.about.0.004% of S, and a balance of
Fe and other inevitable impurities by wt %, and satisfying at least
one of Conditions (1), (2) and (3).
[0025] The non-oriented electrical steel sheet slab, which
satisfies at least one of Conditions (1), (2) and (3), may further
comprise 0.2% or less of P.
[0026] The non-oriented electrical steel sheet slab may further
comprise at least one of 0.005.about.0.2% of Sn and
0.005.about.0.1% of Sb.
[0027] Still a further aspect of the present invention provides a
method of producing the non-oriented electrical steel sheet slab,
comprising adding 0.3.about.0.5% of Al to molten steel to perform
deoxidation, adding a remainder of Al and Si and Mn, and
maintaining the temperature of the molten steel at
1,500.about.1,600.degree. C., thus obtaining the slab comprising
0.7.about.3.0% of Al, 0.2.about.3.5% of Si, 0.2.about.2.0% of Mn,
0.001.about.0.004% of N, 0.0005.about.0.004% of S, and a balance of
Fe and other inevitable impurities by wt %, and satisfying at least
one of Conditions (1), (2) and (3).
Advantageous Effects
[0028] According to the present invention, the proportions of alloy
elements such as Al, Si and Mn and of impurity elements such as N
and S can be appropriately controlled so as to increase the
distribution density of coarse inclusions, thus enhancing the
growth of grains and the mobility of domain walls. Thereby, a
non-oriented electrical steel sheet of the highest quality having
excellent magnetic properties and very low hardness can be stably
produced. Also customer workability and productivity are superior,
and the unit cost of production of products can be decreased, thus
reducing the cost.
DESCRIPTION OF DRAWINGS
[0029] FIG. 1 is a view showing composite inclusions which are
present in a non-oriented electrical steel sheet according to the
present invention;
[0030] FIG. 2 is a graph showing whether the distribution density
of coarse composite inclusions having an average size of 300 nm or
more is equal to or greater than 0.02 number/mm.sup.2 in the
non-oriented electrical steel sheet containing 0.5.about.2.5% of Si
wherein [N]+[S] is represented on a horizontal axis and [Al]+[Mn]
is represented on a vertical axis;
[0031] FIG. 3 is a graph showing whether the distribution density
of coarse composite inclusions having an average size of 300 nm or
more is equal to or greater than 0.02 number/mm.sup.2 in the
non-oriented electrical steel sheet containing 0.2.about.1.0% of Si
wherein [N]+[S] is represented on a horizontal axis and [Al]+[Mn]
is represented on a vertical axis; and
[0032] FIG. 4 is a graph showing whether the distribution density
of coarse composite inclusions having an average size of 300 nm or
more is equal to or greater than 0.02 number/mm.sup.2 in the
non-oriented electrical steel sheet containing 2.3.about.3.5% of Si
wherein [N]+[S] is represented on a horizontal axis and [Al]+[Mn]
is represented on a vertical axis.
MODE FOR INVENTION
[0033] To solve the technical problems as mentioned above, the
present inventors have examined the effects of alloy elements and
impurity elements in steel and of the relation between respective
elements on forming the inclusions and also the effects thereof on
magnetic properties and processability, resulted in the finding
that among alloy elements of steel, the amounts of Al, Si and Mn
and the amounts of impurity elements such as N and S may be
appropriately adjusted and Al/Si and Al/Mn, Al+Si+Mn/2, Al+Mn, N+S
and (Al+Mn)/(N+S) may be optimally controlled so that the hardness
of a steel sheet is decreased and the distribution density of
coarse composite inclusions having an average size of 300 nm or
more in the steel sheet is increased, thereby drastically enhancing
magnetic properties and improving productivity and punchability,
which culminates in the present invention.
[0034] The present invention is directed to a non-oriented
electrical steel sheet of the highest quality, comprising
0.7.about.3.0% of Al, 0.2.about.3.5% of Si, 0.2.about.2.0% of Mn,
0.001.about.0.004% of N, 0.0005.about.0.004% of S, and a balance of
Fe and other inevitable impurities by wt %, wherein Al, Si, Mn, N
and S are contained so as to satisfy at least one of the following
Conditions (1), (2) and (3), and thus the distribution density of
300 nm or more sized coarse inclusions having combinations of
nitrides and sulfides is increased to be equal to or greater than
0.02 number/mm.sup.2, resulting in high magnetic properties and low
hardness.
[0035] {circle around (1)} Condition (1):
0.7.ltoreq.[Al].ltoreq.2.7, 0.2.ltoreq.[Si].ltoreq.1.0,
0.2.ltoreq.[Mn].ltoreq.1.7, {[Al]+[Mn]}.ltoreq.2.0,
0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
230.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,000
[0036] {circle around (2)} Condition (2):
1.0.ltoreq.[Al].ltoreq.3.0, 0.5.ltoreq.[Si].ltoreq.2.5,
0.5.ltoreq.[Mn].ltoreq.2.0, {[Al]+[Mn]}.ltoreq.3.5,
0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
300.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,400
[0037] {circle around (3)} Condition (3):
1.0.ltoreq.[Al].ltoreq.3.0, 2.3.ltoreq.[Si].ltoreq.3.5,
0.5.ltoreq.[Mn].ltoreq.2.0, {[Al]+[Mn]}.ltoreq.3.5,
0.002.ltoreq.{[N]+[S]}.ltoreq.0.006,
300.ltoreq.{([Al]+[Mn])/([N]+[S])}.ltoreq.1,400
[0038] As such, [Al], [Si], [Mn], [N] and [S] indicate the amounts
(wt %) of Al, Si, Mn, N and S, respectively.
[0039] In addition, the present invention is directed to the
production of the non-oriented electrical steel sheet which is
superior in both magnetic properties and processability, by adding
0.3.about.0.5% of Al to molten steel to perform deoxidation in a
steel making process, adding remaining alloy elements, and then
maintaining the temperature of the molten steel at
1,500.about.1,600.degree. C. thus manufacturing a slab having the
composition that satisfies at least one of Conditions (1), (2) and
(3), followed by heating the slab to 1,100.about.1,250.degree. C.
and then performing hot rolling wherein finish hot rolling is
conducted at 800.degree. C. or higher, carrying out cold rolling,
and then finally annealing the cold rolled sheet at
750.about.1,100.degree. C.
[0040] The alloy elements of steel, namely, Al, Si and Mn are
described below. These alloy elements are added to reduce the core
loss of an electrical steel sheet. As the amounts thereof increase,
the magnetic flux density may decrease and the processability of a
material may deteriorate. Hence, the amounts of such alloy
components are appropriately designed to improve not only the core
loss but also the magnetic flux density, and also hardness needs to
be maintained to an appropriate level or less.
[0041] Furthermore, Al and Mn combine with N and S which are
impurity elements to form inclusions such as nitrides or sulfides.
Such inclusions greatly affect magnetic properties and thus the
formation of inclusions that minimize the deterioration of magnetic
properties should be increased.
[0042] The present inventors were the first to discover that coarse
composite inclusions comprising combinations of nitrides or
sulfides may be formed when the amounts of Al, Mn, Si, N and S are
adapted for specific conditions, and have found the fact that the
distribution density of such composite inclusions to a
predetermined level or more is ensured, and thereby magnetic
properties may be drastically improved despite the addition of
minimum amounts of alloy elements that deteriorate processability,
and thus devised the present invention.
[0043] The reason why the ranges of component elements of the
present invention and the amount ratios of the component elements
are limited is described below.
[0044] [Al: 0.7.about.3.0 Wt %]
[0045] Al functions to increase resistivity of a material to reduce
core loss and to form a nitride, and is added in an amount of
0.7.about.3.0% so as to form a coarse nitride. If the amount of Al
is less than 0.7%, inclusions may not be sufficiently grown. In
contrast, if the amount thereof exceeds 3.0%, processability may
deteriorate and all processes including steel making, continuous
casting and so on may be problematic, making it impossible to
produce a steel sheet in the typical manner.
[0046] [Si: 0.2.about.3.5 Wt %]
[0047] Si functions to increase resistivity of a material to reduce
core loss. If the amount of Si is less than 0.2%, it is difficult
to expect reduction effects of core loss. In contrast, if the
amount thereof exceeds 3.5%, the hardness of a material may
increase, undesirably deteriorating productivity and
punchability.
[0048] [Mn: 0.2.about.2.0 Wt %]
[0049] Mn functions to increase resistivity of a material to reduce
core loss and to form a sulfide, and is added in an amount of 0.2%
or more. If the amount thereof exceeds 2.0%, the formation of [111]
texture that is unfavorable for magnetic properties may be
facilitated. Hence, the amount of Mn is preferably limited to
0.5.about.2.0%.
[0050] [Sn: 0.2 Wt % or Less]
[0051] Sn is preferentially segregated on the surface and the grain
boundaries and may reduce accumulated strain energy upon hot
rolling and cold rolling, so that the strength in {100} orientation
that is favorable for magnetic properties may increase whereas the
strength in {111} orientation that is unfavorable for magnetic
properties may decrease, thus achieving improvements in texture.
Hence, Sn is added in the range of 0.2% or less. Furthermore, Sn is
preferentially formed on the surface during welding to thus
suppress surface oxidation and enhance the weld properties thereby
increasing productivity of continuous lines. Also, the formation of
Al-based oxides and nitrides on the surface or the layer under the
surface may be suppressed during heat treatment, thus enhancing
magnetic properties. Upon punching by a customer, the increase in
hardness of the layer under the surface due to nitrides may be
inhibited to improve punchability.
[0052] Hence, Sn is preferably added in the range of 0.005% or
more. In contrast, if the amount of Sn exceeds 0.2%, improvements
in magnetic properties based on such an additional use thereof are
insignificant, and fine inclusions and deposits may be formed in
steel, rather than preferential segregation on the surface and the
grain boundaries, negatively affecting the magnetic properties.
Also, cold rollability and punchability may decrease and the
Erichsen number that represents the weld properties is 5 mm or
less, making it impossible to perform welding of the same species.
Thus, a low-graded material having the sum of Si and Al of less
than 2 should be undesirably used as a connection material for
continuous line working. Hence, the amount of Sn is preferably
limited to 0.005.about.0.2%.
[0053] [Sb: 0.1 Wt % or Less]
[0054] Sb is preferentially segregated on the surface and the grain
boundaries and may reduce accumulated strain energy upon hot
rolling and cold rolling, so that the strength in {100} orientation
that is favorable for magnetic properties may increase and the
strength in {111} orientation that is unfavorable for magnetic
properties may decrease, thus attaining improvements in texture.
Hence, Sb is added in the range of 0.1% or less. Furthermore, Sb is
preferentially formed on the surface during welding to thus
suppress surface oxidation and enhance weld properties thereby
increasing productivity of continuous lines. Also, the formation of
Al-based oxides and nitrides on the surface or the layer under the
surface may be suppressed during heat treatment, thus improving
magnetic properties. Upon punching by the customer, the increase in
hardness of the layer under the surface due to nitrides may be
inhibited to improve punchability.
[0055] Hence, Sb is preferably added in the range of 0.005% or
more. In contrast, if the amount of Sb exceeds 0.1%, improvements
in magnetic properties based on such an additional use thereof are
insignificant, and fine inclusions and deposits may be formed in
steel, rather than preferential segregation on the surface and the
grain boundaries, undesirably aggravating the magnetic properties.
Also, cold rollability and punchability may decrease and the
Erichsen number that represents the weld properties is 5 mm or
less, making it impossible to perform welding of the same species.
Thus, a low-graded material having the sum of Si and Al of less
than 2 should be undesirably used as a connection material for
continuous line working. Hence, the amount of Sb is preferably
limited to 0.005.about.0.1%.
[0056] [P: 0.2 Wt % or Less]
[0057] When P is added in the range of 0.2% or less, texture that
is favorable for magnetic properties may be formed, and in-plane
anisotropy and processability are improved. If the amount thereof
exceeds 0.2%, cold rollability may decrease and processability may
deteriorate. Hence, the amount of P is limited to 0.2% or less.
[0058] [N: 0.001.about.0.004 Wt %]
[0059] N is an impurity element, and may form a fine nitride during
the production process to suppress the growth of grains undesirably
deteriorating core loss. Although the formation of nitrides is
suppressed, an additional high cost and long process time are
required, and thus monetary benefits are negatively affected.
Therefore, it is preferred that an element having high affinity for
the impurity element N is positively utilized to coarsely grow
inclusions so as to reduce an influence on the growth of grains. To
coarsely grow the inclusions in this way, the amount of N is
essentially controlled in the range of 0.001.about.0.004%. If the
amount of N exceeds 0.004%, the inclusions may not be coarsely
formed undesirably increasing core loss. More preferably, the
amount of N is limited to 0.003% or less.
[0060] [S: 0.0005.about.0.004 Wt %]
[0061] S is an impurity element, and may form a fine sulfide during
the production process to thus suppress the growth of grains and
deteriorate core loss. Although the formation of sulfides is
suppressed, an additional high cost and long process time are
required, and thus monetary benefits are negatively affected. Thus,
it is preferred that an element having high affinity for the
impurity element S is positively utilized to coarsely grow
inclusions so as to reduce the influence on the growth of grains.
To coarsely grow the inclusions in this way, the amount of S is
essentially controlled in the range of 0.0005.about.0.004%. If the
amount of S exceeds 0.004%, the inclusions may not be coarsely
formed undesirably increasing core loss. More preferably, the
amount of S is limited to 0.003% or less.
[0062] In addition to the above impurity elements, inevitable
impurities such as C, Ti may be incorporated. C may cause magnetic
aging, and the amount thereof is thus limited in the range of
0.004% or less, and more preferably 0.003% or less. Ti may promote
the growth of [111] texture that is unfavorable for a non-oriented
electrical steel sheet, and the amount thereof is thus limited in
the range of 0.004% or less, and preferably 0.002% or less.
[0063] In the non-oriented electrical steel sheet that satisfies
Condition (1), the sum ([Al]+[Mn]) of Al and Mn by wt % is limited
to 2.0% or less. If the sum of Al and Mn exceeds 2.0% in steel
comprising 0.7.about.2.7% of Al, 0.2.about.1.0% of Si and
0.2.about.1.7% of Mn, the fraction of [111] texture that is
unfavorable for magnetic properties may increase, undesirably
deteriorating the magnetic properties. In the case of the
non-oriented electrical steel sheet that satisfies Condition (1),
if the sum of Al and Mn is less than 0.9%, nitrides, sulfides or
composite inclusions of these two are not coarsely formed, thus
deteriorating the magnetic properties. However, in the non-oriented
electrical steel sheet that satisfies Condition (1), Al is
contained in an amount of 0.7% or more and Mn is contained in an
amount of 0.2% or more, so that the sum of Al and Mn is 0.9% or
more, thereby preventing the deterioration of the magnetic
properties.
[0064] In the non-oriented electrical steel sheet that satisfies
Condition (2) or (3), the sum ([Al]+[Mn]) of Al and Mn by wt % is
limited to 3.5% or less. If the sum of Al and Mn exceeds 3.5% in
steel comprising 1.0.about.3.0% of Al, 0.5.about.3.5% of Si and
0.5.about.2.0% of Mn, the fraction of [111] texture that is
unfavorable for magnetic properties may increase undesirably
deteriorating the magnetic properties. In the non-oriented
electrical steel sheet that satisfies Condition (2) or (3), if the
sum of Al and Mn is less than 1.5%, nitrides, sulfides or composite
inclusions of these two are not coarsely formed, thus deteriorating
the magnetic properties. However, in the non-oriented electrical
steel sheet that satisfies Condition (2) or (3), Al is contained in
an amount of 1.0% or more and Mn is contained in an amount of 0.5%
or more, so that the sum of Al and Mn is 1.5% or more, thereby
preventing the deterioration of the magnetic properties.
[0065] In the present invention, the sum ([N]+[S]) of N and S is
limited to 0.002.about.0.006%. This is because inclusions are
coarsely formed in the above range. If the sum of N and S exceeds
0.006%, the fraction of fine inclusions may be increased,
undesirably deteriorating the magnetic properties.
[0066] Also in the present invention, the ratio of the sum
([Al]+[Mn]) of Al and Mn by wt % to the sum ([N]+[S]) of N and S by
wt % is regarded as important.
[0067] The present inventors have appreciated that, in order for
the distribution density of 300 nm or more sized coarse composite
inclusions of nitrides and sulfides to increase and become equal to
or greater than 0.02 number/mm.sup.2, ([Al]+[Mn])/([N]+[S]) should
be appropriately adjusted, and the proper range of
([Al]+[Mn])/([N]+[S]) may vary depending on the amounts of Si, Al
and Mn.
[0068] Under Condition (1) wherein the amounts of Al, Si and Mn are
slightly low, when the ratio of ([Al]+[Mn])/([N]+[S]) is slightly
low to the extent of 230.about.1000, the formation of composite
inclusions may be effectively increased. The inclusions may be
coarsely formed within the above range and thus the distribution
density of coarse composite inclusions may be increased thus
improving core loss. However, if the ratio thereof falls outside
the above range, the inclusions may not be coarsely formed and the
formation of coarse composite inclusions is low and texture that is
unfavorable for magnetic properties is formed.
[0069] In the case where the amounts of Al, Si and Mn are given as
in Condition (2) or (3), when the ratio of ([Al]+[Mn])/([N]+[S]) is
300.about.1400, the formation of composite inclusions may be
effectively increased. Specifically, when the ratio of
([Al]+[Mn])/([N]+[S]) falls in the range of 300.about.1400 under
Condition (2) or (3), inclusions may be coarsely formed thus
increasing the distribution density of coarse composite inclusions.
In contrast, when the ratio thereof falls outside the above range,
the inclusions are not coarsely formed and the formation of coarse
composite inclusions is low and texture that is unfavorable for
magnetic properties is formed.
[0070] FIG. 1 shows composite inclusions which are present in the
non-oriented electrical steel sheet according to the present
invention. When the amounts of Al, Mn, N and S are controlled in
the optimal ranges, inclusions are grown several times or more
compared to when using typical materials, thus increasing the
formation of coarse composite inclusions having an average size of
300 nm or more. Accordingly, the formation of fine inclusions
having an average size of about 50 nm may decrease, thereby
improving magnetic properties. The present inventors have
appreciated that, when the distribution density of coarse composite
inclusions as shown in FIG. 1 is equal to or greater than 0.02
number/mm.sup.2, the magnetic properties of the non-oriented
electrical steel sheet may be remarkably improved.
[0071] The accurate mechanism for forming such coarse composite
inclusions has not yet been revealed, but is assumed to take place
in the steel making process. Specifically upon initial addition of
Al in the steel making process, Al-based oxides and nitrides may be
formed due to deoxidation, and in the composition that additionally
includes the alloy elements such as Al and Mn and satisfies the
amounts of Al, Mn, Si, N and S as designed in the present invention
upon bubbling, Al-based oxides and nitrides are grown and Mn-based
sulfides may also be precipitated thereon.
[0072] FIG. 2 is a graph showing whether the distribution density
of coarse composite inclusions having an average size of 300 nm or
more is equal to or greater than 0.02 number/mm.sup.2 in the
non-oriented electrical steel sheet containing 0.5.about.2.5% of Si
wherein [N]+[S] is represented on a horizontal axis and [Al]+[Mn]
is represented on a vertical axis.
[0073] As shown in FIG. 2, in the range (within the thick line) of
the present invention that satisfies Condition (2), namely, wherein
the sum ([Al]+[Mn]) of Al and Mn by wt % is 3.5% or less and the
sum ([N]+[S]) of N and S by wt % is 0.002.about.0.006 and the ratio
of the sum of Al and Mn to the sum of N and S ([Al]+[Mn])/([N]+[S])
falls in the range of 300.about.1,400, inclusions are coarsely
formed and the distribution density of coarse composite inclusions
having an average size of 300 nm or more is greater than 0.02
number/mm.sup.2, thus exhibiting superior magnetic properties.
However, in the range falling outside the present invention
(outside the thick line), coarse inclusions are not formed and the
distribution density of coarse composite inclusions having an
average size of 300 nm or more is less than 0.02 number/mm.sup.2,
thus deteriorating texture and magnetic properties.
[0074] FIG. 3 is a graph showing whether the distribution density
of coarse composite inclusions having an average size of 300 nm or
more is equal to or greater than 0.02 number/mm.sup.2 in the
non-oriented electrical steel sheet containing 0.2.about.1.0% of Si
wherein [N]+[S] is represented on a horizontal axis and [Al]+[Mn]
is represented on a vertical axis.
[0075] As shown in FIG. 3, in the range (within the thick line) of
the present invention that satisfies Condition (1), namely, wherein
the sum ([Al]+[Mn]) of Al and Mn by wt % is 2.0% or less and the
sum ([N]+[S]) of N and S by wt % is 0.002.about.0.006 and the ratio
of the sum of Al and Mn to the sum of N and S ([Al]+[Mn])/([N]+[S])
falls in the range of 230.about.1,000, inclusions are coarsely
formed and the distribution density of coarse composite inclusions
having an average size of 300 nm or more is greater than 0.02
number/mm.sup.2, thus exhibiting superior magnetic properties.
However, in the range falling outside the present invention
(outside the thick line), coarse inclusions are not formed and the
distribution density of coarse composite inclusions having an
average size of 300 nm or more is less than 0.02 number/mm.sup.2,
thus deteriorating texture and magnetic properties.
[0076] FIG. 4 is a graph showing whether the distribution density
of coarse composite inclusions having an average size of 300 nm or
more is equal to or greater than 0.02 number/mm.sup.2 in the
non-oriented electrical steel sheet containing 2.3.about.3.5% of Si
wherein [N]+[S] is represented on a horizontal axis and [Al]+[Mn]
is represented on a vertical axis.
[0077] As shown in FIG. 4, in the range (within the thick line) of
the present invention that satisfies Condition (3), namely, wherein
the sum ([Al]+[Mn]) of Al and Mn by wt % is 3.5% or less and the
sum ([N]+[S]) of N and S by wt % is 0.002.about.0.006 and the ratio
of the sum of Al and Mn to the sum of N and S ([Al]+[Mn])/([N]+[S])
falls in the range of 300.about.1,400, inclusions are coarsely
formed and the distribution density of coarse composite inclusions
having an average size of 300 nm or more is greater than 0.02
number/mm.sup.2, thus exhibiting superior magnetic properties.
However, in the range falling outside the present invention
(outside the thick line), coarse inclusions are not formed and the
distribution density of coarse composite inclusions having an
average size of 300 nm or more is less than 0.02 number/mm.sup.2,
thus deteriorating texture and magnetic properties.
[0078] Although the coarse inclusions are mainly observed to be
combinations of nitrides and sulfides having an average size of 300
nm or more, the examples thereof may include combinations of a
plurality of nitrides or combinations of a plurality of sulfides
having an average size of 300 nm or more, and those having nitrides
or sulfides alone having a size of 300 nm or more. Herein, the
average size of the inclusions is determined by measuring the
longest length and the shortest length of the inclusions when
viewed in the cross-section of the steel sheet and averaging the
measured values.
[0079] Also in the non-oriented electrical steel sheet that
satisfies Condition (2), the amount ratio of Al to Si ([Al]/[Si])
is limited to 0.6.about.4.0. In the case where the amount ratio of
Al to Si is 0.6.about.4.0, the grains may effectively grow and the
hardness of a material may decrease thus improving productivity and
punchability. If the ratio of [Al]/[Si] is less than 0.6,
inclusions do not greatly grow undesirably decreasing the growth of
grains and deteriorating magnetic properties. Furthermore, the
amount of Si may increase, undesirably enhancing hardness. If the
ratio of [Al]/[Si] exceeds 4.0, texture of a material may become
poor undesirably deteriorating the magnetic flux density.
[0080] In the present invention, the ratio of Al to Mn ([Al]/[Mn])
is preferably limited to 1.about.8. When the ratio of Al to Mn is
1.about.8, the inclusions may effectively grow thus exhibiting
superior core loss properties. In contrast, if the ratio thereof
falls outside the above range, the growth of inclusions may
decrease and the fraction of texture that is favorable for magnetic
properties may decrease.
[0081] The limited ratio of alloy components related to resistivity
is described below. Recently, as the demand for environmentally
friendly automobiles drastically increases, there is a high need
for non-oriented electrical steel sheets usable for highly
rotatable motors. The motors used in the environmentally friendly
automobiles should greatly increase their number of rotations. When
the number of rotations of the motor is increased, the fraction of
eddy current loss in the inner core loss may be drastically
increased. To reduce such eddy current loss, resistivity should
increase.
[0082] The relation between the amounts of alloy elements of the
non-oriented electrical steel sheet and the intrinsic resistance is
represented below.
[0083] .rho.=13.25+11.3([Al]+[Si]+[Mn]/2) (.rho.: resistivity,
.OMEGA.m)
[0084] In the present invention that satisfies Condition (3),
[Al]+[Si]+[Mn]/2 is limited to 3.0 or more so as to ensure
resistivity of 47 or more.
[0085] Despite the recent development of cold rolling techniques,
the case where the resistivity exceeds 87 may increase the amounts
of alloy elements and may deteriorate processability. Because the
production of steel sheets is impossible via typical cold rolling,
the resistivity should be set to 87 or less.
[0086] In the present invention that satisfies Condition (3),
[Al]+[Si]+[Mn]/2 is controlled in the range of 3.0.about.6.5% so
that the resistivity is 47.about.87 (.OMEGA.m) and Vickers hardness
(Hv1) is 225 or less.
[0087] In the present invention that satisfies Condition (2),
[Al]+[Si]+[Mn]/2 is limited to 1.7 or more so as to ensure the
resistivity of 32 or more. Furthermore, in the present invention
that satisfies Condition (2), [Al]+[Si]+[Mn]/2 is controlled to
5.5% or less so that resistivity (intrinsic resistance) is
maintained to 75 or less and Vickers hardness (Hv1) is 190 or
less.
[0088] Also the demand for high magnetic flux density products is
drastically increasing these days to achieve high efficiency of
motors. Accordingly, there is an urgent requirement for
non-oriented electrical steel sheets having lowered resistivity and
improved magnetic flux density. In the case where magnetic flux
density properties are regarded as important, resistivity
(intrinsic resistance) is decreased to 36 or less to increase the
magnetic flux density. Moreover to correspond to high-speed
rotations, the resistivity should be controlled to at least 25.
[0089] Thus in the present invention that satisfies Condition (1),
[Al]+[Si]+[Mn]/2 is controlled to 1.0.about.2.0% so that the
resistivity is 25.about.36 (.OMEGA.m) and Vickers hardness (Hv1) is
very low to the extent of 140 or less.
[0090] Below is a description of a method of producing the
non-oriented electrical steel sheet according to the present
invention. The method of producing the non-oriented electrical
steel sheet preferably includes adding 0.3.about.0.5% of Al,
corresponding to a portion of the total amount of added Al, in the
steel making process, so that deoxidation of steel sufficiently
occurs, and adding the remaining alloy elements. Subsequently, the
temperature of molten steel is maintained at
1,500.about.1,600.degree. C. so that inclusions in steel are
sufficiently grown, after which the resultant steel is solidified
in a continuous casting process thus manufacturing a slab.
[0091] Subsequently, the slab is placed in a furnace so that it is
re-heated to 1,100.about.1,250.degree. C. If the slab is heated to
a temperature exceeding 1,250.degree. C., deposits that negatively
affect the magnetic properties may be re-dissolved, hot rolled and
then finely deposited, and thus the slab is heated to 1,250.degree.
C. or less.
[0092] Subsequently, the heated slab is hot rolled. Upon hot
rolling, finish hot rolling is preferably carried out at
800.degree. C. or more. The hot rolled sheet is annealed at
850.about.1,100.degree. C. If the annealing temperature of the hot
rolled sheet is lower than 850.degree. C., texture does not grow or
finally grows, and thus the extent of increasing the magnetic flux
density is low. In contrast, if the annealing temperature of the
hot rolled sheet is higher than 1,100.degree. C., magnetic
properties may deteriorate instead, and rolling workability may
decrease due to plate transformation. Hence, the temperature range
thereof is limited to 850.about.1,100.degree. C. More preferably
the annealing temperature of the hot rolled sheet is
950.about.1,100.degree. C. The annealing of the hot rolled sheet
may be carried out to increase the grain orientation favorable for
magnetic properties, as necessary, but may be omitted.
[0093] Subsequently, the hot rolled sheet which was annealed or not
is pickled, and cold rolled to a reduction of 70.about.95% to
obtain a predetermined sheet thickness.
[0094] The amounts of added Si, Mn and Al alloy elements that
affect cold rollability are appropriately controlled thus attaining
superior cold rollability and high reduction. Thus, one cold
rolling makes it possible to form a thin sheet having a thickness
of about 0.15 mm. Upon cold rolling, two cold rolling operations
including intermediate annealing may be conducted, as necessary, or
two annealing operations may be applied.
[0095] Subsequently, the cold rolled sheet is subjected to final
annealing. If the final annealing temperature is lower than
750.degree. C., recrystallization does not sufficiently occur. In
contrast, if the final annealing temperature exceeds 1,100.degree.
C., the surface oxide layer is deeply formed, undesirably
deteriorating magnetic properties. Hence, final annealing is
preferably conducted at 750.about.1,100.degree. C.
[0096] The finally annealed steel sheet is subjected to insulation
coating treatment using typical methods and is then discharged to
customers. Upon insulation coating, the application of a typical
coating material is possible, and either Cr-type or Cr-free type
may be used without limitation.
[0097] Below, the present invention is described by the following
examples. Unless otherwise stated, the amounts of components are
represented by wt % in the following examples.
Example 1
[0098] Vacuum melting was performed in a laboratory, thus preparing
steel ingots having the components shown in Table 1 below. As such,
the amount of each of impurity elements C, S, N, Ti was controlled
to 0.002%, and 0.3.about.0.5% of Al was added to molten steel to
facilitate the formation of inclusions, after which the remainder
of Al, and Si and Mn were added thus making steel ingots. Each of
the ingots was heated to 1,150.degree. C., and finish hot rolled at
850.degree. C. thus manufacturing a hot rolled sheet having a
thickness of 2.0 mm. The hot rolled sheet was annealed at
1,050.degree. C. for 4 min and then pickled. Subsequently, cold
rolling was conducted so that the thickness of the sheet was 0.35
mm, followed by carrying out final annealing at 1,050.degree. C.
for 38 sec.
[0099] The size and distribution density of inclusions of
respective sheets, the core loss, the magnetic flux density and
hardness were measured. The results are shown in Table 2 below. A
sample for use in observing the inclusions was manufactured using a
replica method that is typical in the steel industry, and a
transmission electron microscope was used therefor. As such, the
acceleration voltage of 200 kV was applied.
TABLE-US-00001 TABLE 1 Steel Al Si Mn C S N Ti A1 3.0 0.5 1.0 0.002
0.002 0.002 0.002 A2 2.5 0.5 1.0 0.002 0.002 0.002 0.002 A3 1.0 0.5
1.0 0.002 0.002 0.002 0.002 A4 3.0 1.0 1.0 0.002 0.002 0.002 0.002
A5 2.0 1.0 1.0 0.002 0.002 0.002 0.002 A6 1.0 1.0 1.0 0.002 0.002
0.002 0.002 A7 0.5 1.0 1.0 0.002 0.002 0.002 0.002 A8 3.5 1.5 1.0
0.002 0.002 0.002 0.002 A9 2.5 1.5 1.0 0.002 0.002 0.002 0.002 A10
1.5 1.5 1.0 0.002 0.002 0.002 0.002 A11 3.0 2.0 1.0 0.002 0.002
0.002 0.002 A12 1.5 2.0 1.0 0.002 0.002 0.002 0.002 A13 3.0 2.5 1.0
0.002 0.002 0.002 0.002 A14 2.5 2.5 1.0 0.002 0.002 0.002 0.002 A15
1.0 2.5 1.0 0.002 0.002 0.002 0.002
TABLE-US-00002 TABLE 2 Distri. Size Density Core Magnetic (Al + of
of Loss Flux Al/ Al/ Al + Mn)/ Al + Si + Inclusions Inclusions
(W15/ Density Steel Si Mn Mn N + S (N + S) Mn/2 (nm) (1/mm.sup.2)
50) (B50) Hard. Note A1 6.0 3.0 4.0 0.0040 1000 4.0 250 0 2.2 1.62
165 Comp. A2 5.0 2.5 3.5 0.0040 875 3.5 200 0 2.3 1.62 160 Comp. A3
2.0 1.0 2.0 0.0040 500 2.0 300 0.02 2.5 1.72 140 Invent. A4 3.0 3.0
4.0 0.0040 1000 4.5 250 0 2.4 1.62 157 Comp. A5 2.0 2.0 3.0 0.0040
750 3.5 500 0.07 2.0 1.67 155 Invent. A6 1.0 1.0 2.0 0.0040 500 2.5
450 0.05 2.1 1.68 150 Invent. A7 0.5 0.5 1.5 0.0040 375 2.0 50 0
2.5 1.66 145 Comp. A8 2.3 3.5 4.5 0.0040 1125 5.5 75 0 2.5 1.64 190
Comp. A9 1.7 2.5 3.5 0.0040 875 4.5 400 0.05 2.0 1.67 185 Invent.
A10 1.0 1.5 2.5 0.0040 625 3.5 600 0.08 2.0 1.68 170 Invent. A11
1.5 3.0 4.0 0.0040 1000 5.5 250 0 2.3 1.62 195 Comp. A12 0.8 1.5
2.5 0.0040 625 4.0 400 0.04 2.0 1.68 183 Invent. A13 1.2 3.0 4.0
0.0040 1000 6.0 75 0 2.0 1.61 210 Comp. A14 1.0 2.5 3.5 0.0040 875
5.5 400 0.03 1.9 1.65 190 Invent A15 0.4 1.0 2.0 0.0040 500 4.0 60
0 2.4 1.67 195 Comp.
[0100] As is apparent from Table 2, steels A3, A5, A6, A9, A10, A12
and A14 were inventive examples that satisfy Condition (2), wherein
coarse composite inclusions having a size of 300 nm or more were
observed, and the distribution density thereof was greater than
0.02(1/mm.sup.2) thus exhibiting superior magnetic properties. The
Vickers hardness (Hv1) was as low as 190 or less thus obtaining
superior productivity and customer punchability.
[0101] Whereas in steel A1, the ratio of Al/Si and Al+Mn did not
satisfy Condition (2), and thus inclusions having a size of 300 nm
or more were not observed, and core loss and magnetic flux density
were deteriorated. Also, in steels A2 and A15, the ratio of Al/Si
did not satisfy Condition (2), and thus inclusions having a size of
300 nm or more were not observed, and core loss and magnetic flux
density were deteriorated. Also in steels A4, A8, A11 and A13,
Al+Mn did not satisfy Condition (2), and thus inclusions having a
size of 300 nm or more were not observed, and core loss and
magnetic flux density were deteriorated. Also in steel A7, the
ratio of Al/Si and the ratio of Al/Mn did not satisfy Condition
(2), and thus inclusions having a size of 300 nm or more were not
observed, and core loss and magnetic flux density were
deteriorated.
Example 2
[0102] Vacuum melting was performed in a laboratory, thus preparing
steel ingots having the components shown in Table 3 below. As such,
the components of steel were controlled while variously adjusting
the amounts of impurity elements N and S, and 0.3.about.0.5% of Al
was added to molten steel to facilitate the formation of
inclusions, after which the remainder of Al, and Si and Mn were
added thus making steel ingots. Each of the ingots was heated to
1,1500, and finish hot rolled at 850.degree. C. thus manufacturing
a hot rolled sheet having a thickness of 2.0 mm. The hot rolled
sheet was annealed at 1,050.degree. C. for 4 min and then pickled.
Subsequently, cold rolling was conducted so that the thickness of
the sheet was 0.35 mm, followed by carrying out final annealing at
1,050.degree. C. for 38 sec.
[0103] The size and distribution density of inclusions of
respective sheets, the core loss, the magnetic flux density and
hardness were measured. The results are shown in Table 4 below. A
sample for observing the inclusions was manufactured using a
replica method that is typical in the steel industry, and a
transmission electron microscope was used therefor. As such, the
acceleration voltage of 200 kV was applied.
TABLE-US-00003 TABLE 3 Steel Al Si Mn C S N Ti B1 1.0 0.5 0.5 0.002
0.001 0.001 0.002 B2 1.0 0.5 0.5 0.002 0.003 0.003 0.002 B3 1.0 0.5
0.5 0.002 0.0005 0.001 0.002 B4 1.0 0.5 1.0 0.002 0.002 0.003 0.002
B5 1.2 0.5 1.2 0.002 0.0015 0.002 0.002 B6 1.2 0.5 1.0 0.002 0.0005
0.0005 0.002 B7 1.2 0.5 1.0 0.002 0.003 0.003 0.002 B8 2.0 0.5 2.0
0.002 0.001 0.003 0.002 B9 2.0 0.5 1.5 0.002 0.001 0.0015 0.002 B10
2.0 0.5 1.5 0.002 0.001 0.003 0.002 B11 2.0 0.5 1.0 0.002 0.003
0.004 0.002 B12 2.0 1.0 1.5 0.002 0.0005 0.0015 0.002 B13 2.0 1.0
1.5 0.002 0.002 0.004 0.002 B14 1.5 1.0 1.5 0.002 0.002 0.0025
0.002 B15 2.5 1.0 1.0 0.002 0.0005 0.0005 0.002
TABLE-US-00004 TABLE 4 Size Distri. Core Magnetic (Al + of Density
of Loss Flux Al/ Al/ Al + Mn)/ Al + Si + Inclusions Inclusions
(W15/ Density Steel Si Mn Mn N + S (N + S) Mn/2 (nm) (1/mm.sup.2)
50) (B50) Hard. Note B1 2.0 2.0 1.5 0.0020 750 1.8 350 0.03 2.6
1.74 135 Invent. B2 2.0 2.0 1.5 0.0060 250 1.8 75 0 3.2 1.72 135
Comp. B3 2.0 2.0 1.5 0.0015 1000 1.8 120 0 2.9 1.71 135 Comp. B4
2.0 1.0 2 0.0050 400 2.0 400 0.04 2.6 1.70 140 Invent. B5 2.4 1.0
2.4 0.0035 686 2.3 450 0.03 2.2 1.69 150 Invent. B6 2.4 1.2 2.2
0.0010 2200 2.2 50 0 2.4 1.67 150 Comp. B7 2.4 1.2 2.2 0.0060 367
2.2 350 0.02 2.3 1.70 165 Invent. B8 4.0 1.0 4.0 0.0040 1000 3.5
250 0 2.3 1.62 185 Comp. B9 4.0 1.3 3.5 0.0025 1400 3.3 450 0.05 2
1.67 170 Invent. B10 4.0 1.3 3.5 0.0040 875 3.3 550 0.08 2 1.68 170
Invent. B11 4.0 2.0 3 0.0070 429 3.0 250 0 2.2 1.65 170 Comp. B12
2.0 1.3 3.5 0.0020 1750 3.8 80 0 2.3 1.65 165 Comp. B13 2.0 1.3 3.5
0.0060 583 3.8 500 0.07 2 1.68 175 Invent. B14 1.5 1.0 3 0.0045 667
3.3 600 0.07 2 1.68 170 Invent. B15 2.5 2.5 3.5 0.0010 3500 4.0 50
0 2.2 1.65 165 Comp.
[0104] As is apparent from Table 4, steels B1, B4, B5, B7, B9, B10,
B13 and B14 were inventive examples that satisfy Condition (2),
wherein coarse composite inclusions having a size of 300 nm or more
were observed, and the distribution density thereof was greater
than 0.02(1/mm.sup.2) thus manifesting excellent magnetic
properties. The hardness was low thus obtaining superior
productivity and customer punchability.
[0105] However in steels B3, B6, B11 and B15, N+S fell outside
Condition (2), and thus inclusions having a size of 300 nm or more
were not observed, and core loss and magnetic flux density were
deteriorated. Also in steel B8, Al+Mn fell outside Condition (2),
and in steels B2 and B12, the ratio of (Al+Mn)/(N+S) fell outside
Condition (2), and thus inclusions having a size of 300 nm or more
were not observed, and core loss and magnetic flux density were
deteriorated.
Example 3
[0106] Vacuum melting was performed in a laboratory, thus preparing
steel ingots having the components shown in Table 5 below. As such,
0.3.about.0.5% of Al was added to molten steel to facilitate the
formation of inclusions, after which the remainder of Al, and Si,
Mn and P were added thus making steel ingots. Each of the ingots
was heated to 1,150.degree. C., and finish hot rolled at
850.degree. C. thus manufacturing a hot rolled sheet having a
thickness of 2.0 mm. The hot rolled sheet was annealed at
1,050.degree. C. for 4 min and then pickled. Subsequently, cold
rolling was conducted so as to form sheets having different
thicknesses in the range of 0.15.about.0.35 mm, followed by
carrying out final annealing at 1,050.degree. C. for 38 sec. The
core loss and magnetic flux density of respective sheets having
different thicknesses were measured. The results are shown in Table
6 below. A sample for observing the inclusions was manufactured
using a replica method that is typical in the steel industry, and a
transmission electron microscope was used therefor. As such, the
acceleration voltage of 200 kV was applied.
TABLE-US-00005 TABLE 5 Steel Al Si Mn P C S N Ti C1 1 3 0.2 0.03
0.002 0.002 0.002 0.002 C2 2.2 1 0.8 0.05 0.002 0.002 0.002 0.002
C3 2 1.5 1.5 0.05 0.002 0.002 0.002 0.002 C4 1.8 1.3 1.2 0.05 0.002
0.002 0.002 0.002 C5 1.3 1.8 0.6 0.08 0.002 0.002 0.002 0.002 C6
2.2 1.5 0.6 0.1 0.002 0.002 0.002 0.002 C7 1.8 1.2 1.2 0.1 0.002
0.002 0.002 0.002
TABLE-US-00006 TABLE 6 (Al + Al/ Al/ Al + Mn)/ Al + Si + Magnetic
Thickness (mm) Steel Si Mn Mn N + S (N + S) Mn/2 Properties 0.35
0.3 0.25 0.2 0.15 Note C1 0.3 5.0 1.2 0.004 300 4.1 B50 1.65 1.64
1.63 1.62 1.61 Comp. W10/400 20.2 17.8 15.7 13.4 12.3 C2 2.2 2.8
3.0 0.004 750 3.6 B50 1.67 1.66 1.65 1.64 1.63 Invent. W10/400 18.2
15.6 13.4 11.2 9.7 C3 1.3 1.3 3.5 0.004 875 4.25 B50 1.68 1.68 1.65
1.64 1.64 Invent. W10/400 18.0 15 13.6 11.5 10.1 C4 1.4 1.5 3.0
0.004 750 3.7 B50 1.68 1.65 1.66 1.65 1.63 Invent. W10/400 17.8
15.3 13.3 11.1 9.4 C5 0.7 2.2 1.9 0.004 475 3.4 B50 1.67 1.66 1.65
1.64 1.63 Invent. W10/400 18.1 15.5 13.4 11.2 9.6 C6 1.5 3.7 2.8
0.004 700 4 B50 1.67 1.66 1.65 1.64 1.64 Invent. W10/400 18.2 15.6
13.5 11.4 9.8 C7 1.5 1.5 3.0 0.004 750 3.6 B50 1.68 1.68 1.67 1.66
1.65 Invent. W10/400 19.3 16.5 14.1 11.7 10
[0107] As is apparent from Table 6, steels C2.about.C7 were
inventive examples that satisfy Condition (2), wherein the magnetic
flux density was high and the core loss was low. This is considered
to be because the composition according to the present invention
had coarsely grown inclusions and the distribution density of
coarse composite inclusions was greater than 0.02(1/mm.sup.2), and
also the texture was stable. The radio-frequency core loss
(W10/400) is surely correlated with the thickness of steel sheet.
Specifically, as the thickness of the steel sheet decreases, the
properties thereof may be improved. Compared to the steel sheet
having a thickness of 0.35 mm, the core loss of the steel sheet
having a thickness of 0.15 mm was improved by about 50%. In steel
Cl, Al+Mn and Al/Si did not satisfy Condition (2), and thus core
loss (W10/400) and magnetic flux density (B50) were
deteriorated.
Example 4
[0108] Vacuum melting was performed in a laboratory, thus preparing
steel ingots having the components shown in Table 7 below. As such,
0.3.about.0.5% of Al was added to molten steel to facilitate the
formation of inclusions, after which the remainder of Al, and Si,
Mn and P were added thus making steel ingots. Each of the ingots
was heated to 1,150.degree. C., and finish hot rolled at
850.degree. C. thus manufacturing a hot rolled sheet having a
thickness of 2.0 mm. The hot rolled sheet was annealed at
1,050.degree. C. for 4 min and then pickled. Subsequently, cold
rolling was conducted so that the thickness of the sheet was 0.35
mm, followed by carrying out final annealing at 1,050.degree. C.
for 38 sec.
[0109] The size and distribution density of inclusions of
respective sheets, the core loss, the magnetic flux density, the
Erichsen number and hardness were measured. The results are shown
in Table 8 below. A sample for observing the inclusions was
manufactured using a replica method that is typical in the steel
industry, and a transmission electron microscope was used therefor.
As such, the acceleration voltage of 200 kV was applied.
[0110] While the welding part of the hot rolled sheet was pushed-up
using a steel ball having a diameter of 20 mm at room temperature,
the height until the sheet broken was determined, which is referred
to as the Erichsen number. The case where the Erichsen number is
typically 5 mm or more makes it possible to produce continuous
lines via welding of the same species.
TABLE-US-00007 TABLE 7 Steel Al Si Mn P Sn Sb C S N Ti D1 1.0 2.5
0.5 0.01 -- -- 0.002 0.002 0.002 0.002 D2 2.5 0.8 0.8 0.11 0.03 --
0.002 0.002 0.002 0.002 D3 2.0 1.3 0.8 0.08 -- 0.005 0.002 0.002
0.002 0.002 D4 2.0 1.3 0.8 0.08 -- 0.03 0.002 0.002 0.002 0.002 D5
2.0 1.3 0.8 0.08 -- 0.07 0.002 0.002 0.002 0.002 D6 2.0 1.3 0.8
0.08 -- 0.1 0.002 0.002 0.002 0.002 D7 2.0 1.3 0.8 0.08 -- 0.15
0.002 0.002 0.002 0.002 D8 1.7 1.6 0.8 0.08 0.005 -- 0.002 0.002
0.002 0.002 D9 1.7 1.6 0.8 0.08 0.03 -- 0.002 0.002 0.002 0.002 D10
1.7 1.6 0.8 0.08 0.07 -- 0.002 0.002 0.002 0.002 D11 1.7 1.6 0.8
0.08 0.15 -- 0.002 0.002 0.002 0.002 D12 1.7 1.6 0.8 0.08 0.18 --
0.002 0.002 0.002 0.002 D13 1.7 1.6 0.8 0.08 0.25 -- 0.002 0.002
0.002 0.002 D14 1.3 2.0 0.8 0.08 0.03 -- 0.002 0.002 0.002 0.002
D15 2.2 1.6 0.6 0.05 -- 0.03 0.002 0.002 0.002 0.002 D16 2.2 1.6
0.6 0.05 0.23 -- 0.002 0.002 0.002 0.002 D17 1.5 1.0 1.2 0.19 0.05
-- 0.002 0.002 0.002 0.002 D18 1.5 1.0 1.2 0.19 -- 0.2 0.002 0.002
0.002 0.002
TABLE-US-00008 TABLE 8 Distri. Size Density Core Magnetic (Al + of
of Loss Flux Al/ Al/ Al + Mn)/ Al + Si + Inclusion Inclusion (W15/
Density Erichsen Steel Si Mn Mn N + S (N + S) Mn/2 (nm)
(1/mm.sup.2) 50) (B50) (mm) Hard. Note D1 0.4 2 1.5 0.004 375 3.75
50 0 2.2 1.66 3 204 Comp. D2 3.1 3.1 3.3 0.004 825 3.7 600 0.06 2.1
1.67 7 163 Invent. D3 1.5 2.5 2.8 0.004 700 3.7 500 0.04 1.9 1.68 7
171 Invent. D4 1.5 2.5 2.8 0.004 700 3.7 540 0.04 1.9 1.68 9 168
Invent. D5 1.5 2.5 2.8 0.004 700 3.7 600 0.07 1.9 1.68 11 175
Invent. D6 1.5 2.5 2.8 0.004 700 3.7 650 0.09 1.9 1.68 8 172
Invent. D7 1.5 2.5 2.8 0.004 700 3.7 450 0.03 2.1 1.66 4 180 Comp.
D8 1.1 2.1 2.5 0.004 625 3.7 650 0.06 2.1 1.68 8 174 Invent. D9 1.1
2.1 2.5 0.004 625 3.7 500 0.05 2.0 1.68 10 175 Invent. D10 1.1 2.1
2.5 0.004 625 3.7 600 0.08 1.9 1.68 11 177 Invent. D11 1.1 2.1 2.5
0.004 625 3.7 700 0.05 2.0 1.68 9 174 Invent. D12 1.1 2.1 2.5 0.004
625 3.7 650 0.04 2.0 1.68 7 179 Invent. D13 1.1 2.1 2.5 0.004 625
3.7 300 0.02 2.2 1.68 3 180 Comp. D14 0.7 1.6 2.1 0.004 525 3.7 400
0.03 2.0 1.68 8 183 Invent. D15 1.4 3.7 2.8 0.004 700 4.1 800 0.12
2.1 1.66 9 178 Invent. D16 1.4 3.7 2.8 0.004 700 4.1 350 0.03 2.2
1.67 4 185 Comp. D17 1.5 1.3 2.7 0.004 675 3.1 550 0.07 2.1 1.69 12
165 Invent. D18 1.5 1.3 2.7 0.004 675 3.1 300 0.02 2.2 1.68 4 170
Comp.
[0111] As is apparent from Table 8, steels D2.about.6, D8.about.12,
D14, D15 and D17 were inventive examples which satisfy Condition
(2) and in which 0.005.about.0.2% of Sn or 0.005.about.0.1% of Sb
is added, and thus, the distribution density of coarse inclusions
having a size of 300 nm or more was greater than 0.02(1/mm.sup.2),
and upon final annealing, the oxide layer and the nitride layer of
the surface were reduced thus improving core loss and magnetic flux
density. Also, the Erichsen number was high and the Vickers
hardness (Hv1) was low, thus exhibiting superior weldability,
productivity and customer punchability.
[0112] Whereas in steel D1, the ratio of Al/Si fell outside
Condition (2), and thus inclusions having a size of 300 nm or more
were not observed, and core loss and magnetic flux density were
deteriorated. Also because Sn and Sb were not added, the Erichsen
number was low and weldability was decreased and hardness was high
undesirably deteriorating processability. In steels D7 and D18, the
amount of Sb exceeded 0.1%, and in steels D13 and D16, the amount
of Sn exceeded 0.2%, and thus the Erichsen number was low and
hardness was high, resulting in decreased weldability, poor
productivity and customer punchability and inferior magnetic
properties.
Example 5
[0113] Vacuum melting was performed in a laboratory, thus preparing
steel ingots having the components shown in Table 9 below. As such,
0.3.about.0.5% of Al was added to molten steel to facilitate the
formation of inclusions, after which the remainder of Al, and Si
and Mn were added thus making steel ingots. Each of the ingots was
heated to 1,150.degree. C., and finish hot rolled at 850.degree. C.
thus manufacturing a hot rolled sheet having a thickness of 2.3 mm.
The hot rolled sheet was annealed at 1,050.degree. C. for 4 min and
then pickled. Subsequently, cold rolling was conducted so that the
thickness of the sheet was 0.50 mm, followed by carrying out final
annealing at 900.degree. C. for 30 sec.
[0114] The size and distribution density of inclusions of
respective sheets, the core loss, the magnetic flux density and
hardness were measured. The results are shown in Table 10 below. A
sample for observing the inclusions was manufactured using a
replica method that is typical in the steel industry, and a
transmission electron microscope was used therefor. As such, the
acceleration voltage of 200 kV was applied.
TABLE-US-00009 TABLE 9 Steel Al Si Mn C S N Ti E1 1.5 0.2 0.2 0.002
0.002 0.002 0.002 E2 1.5 0.2 0.5 0.002 0.002 0.002 0.002 E3 0.7 0.2
0.5 0.002 0.002 0.002 0.002 E4 2.7 0.5 0.3 0.002 0.002 0.002 0.002
E5 1.7 0.5 0.3 0.002 0.002 0.002 0.002 E6 0.7 0.5 0.3 0.002 0.002
0.002 0.002 E7 0.5 0.5 0.5 0.002 0.002 0.002 0.002 E8 0.5 0.5 0.5
0.002 0.002 0.002 0.002 E9 2.2 0.5 0.2 0.002 0.002 0.002 0.002 E10
1.2 0.5 0.2 0.002 0.002 0.002 0.002 E11 1.0 0.1 0.2 0.002 0.002
0.002 0.002 E12 1.2 0.2 0.2 0.002 0.002 0.002 0.002 E13 1.0 0.2 0.2
0.002 0.002 0.002 0.002 E14 2.2 0.7 0.2 0.002 0.002 0.002 0.002 E15
0.7 0.7 0.2 0.002 0.002 0.002 0.002 E16 1.3 0.2 0.7 0.002 0.002
0.002 0.002 E17 1.5 0.2 1.0 0.002 0.002 0.002 0.002 E18 1.2 0.2 1.0
0.002 0.002 0.002 0.002 E19 0.9 0.5 1.0 0.002 0.002 0.002 0.002 E20
0.9 0.7 0.8 0.002 0.002 0.002 0.002 E21 1.0 0.5 0.8 0.002 0.002
0.002 0.002
TABLE-US-00010 TABLE 10 Distri. Size Density Core Magnetic (Al + of
of Loss Flux Al/ Al/ Al + Mn)/ Al + Si + Inclusions Inclusions
(W15/ Density Steel Si Mn Mn N + S (N + S) Mn/2 (nm) (1/mm.sup.2)
50) (B50) Hard. Note E1 7.5 7.5 1.7 0.0040 425 1.8 450 0.40 3.2
1.73 140 Invent. E2 7.5 3.0 2.0 0.0040 500 2.0 500 0.35 3.0 1.73
140 Invent. E3 3.5 1.4 1.2 0.0040 300 1.2 300 0.30 4.0 1.74 110
Invent. E4 5.4 9.0 3.0 0.0040 750 3.4 250 0.01 3.0 1.68 157 Comp.
E5 3.4 5.7 2.0 0.0040 500 2.4 250 0.01 2.9 1.69 145 Comp. E6 1.4
2.3 1.0 0.0040 250 1.4 450 0.05 3.5 1.74 115 Invent. E7 1.0 1.0 1.0
0.0040 250 1.3 50 0.01 4.5 1.74 110 Comp. E8 1.0 1.0 1.0 0.0040 250
1.3 75 0.01 4.5 1.74 110 Comp. E9 4.4 11.0 2.4 0.0040 600 2.8 400
0.01 2.8 1.68 150 Comp. E10 2.4 6.0 1.4 0.0040 350 1.8 600 0.15 3.2
1.73 130 Invent. E11 10 5.0 1.2 0.0040 300 1.2 250 0.01 4.5 1.74
105 Comp. E12 6.0 6.0 1.4 0.0040 350 1.5 400 0.20 3.5 1.74 105
Invent. E13 5.0 5.0 1.2 0.0040 300 1.3 300 0.18 3.6 1.74 110
Invent. E14 3.1 11.0 2.4 0.0040 600 3.0 400 0.01 2.8 1.69 160 Comp.
E15 1.0 3.5 0.9 0.0040 225 1.5 150 0.01 3.9 1.74 130 Comp. E16 6.5
1.9 2.0 0.0040 500 1.9 350 0.25 2.9 1.72 130 Invent. E17 7.5 1.5
2.5 0.0040 625 2.2 250 0.01 2.8 1.69 140 Comp. E18 6.0 1.2 2.2
0.0040 550 1.9 250 0.01 2.9 1.70 130 Comp. E19 1.8 0.9 1.9 0.0040
475 1.9 200 0.01 3.2 1.70 135 Comp. E20 1.3 1.1 1.7 0.0040 425 2.0
350 0.05 3.5 1.73 140 Invent. E21 2.0 1.3 1.8 0.0040 450 1.9 400
0.05 3.3 1.73 140 Invent.
[0115] As is apparent from Table 10, steels E1-E3, E6, E10, E12,
E13, E16, E20 and E21 were inventive examples that satisfy
Condition (1), wherein the coarse inclusions having a size of 300
nm or more were observed, and the distribution density thereof was
greater than 0.02(1/mm.sup.2) thus exhibiting superior magnetic
properties, and the Vickers hardness (Hv1) was 140 or less,
resulting in good productivity and customer punchability.
[0116] Whereas in steels E4, E9 and 314, the ratio of Al/Mn and the
amount of Al+Mn fell outside Condition (1) and thus inclusions
having a size of 300 nm or more were not observed, and core loss
and magnetic flux density were deteriorated. In steels E17 and E18,
the amount of Al+Mn did not satisfy Condition (1), and thus
inclusions having a size of 300 nm or more were not observed, and
core loss and magnetic flux density were deteriorated. In steel
E19, the ratio of Al/Mn did not satisfy Condition (1), and thus
inclusions having a size of 300 nm or more were not observed, and
core loss and magnetic flux density were deteriorated. In steels
E4, E5, E9 and E14, Al+Si+Mn/2 did not satisfy Condition (1), and
thus hardness was high thereby obtaining poor productivity and
punchability.
Example 6
[0117] Vacuum melting was performed in a laboratory, thus preparing
steel ingots having the components shown in Table 11 below. As
such, 0.3.about.0.5% of Al was added to molten steel to facilitate
the formation of inclusions, after which the remainder of Al, and
Si and Mn were added thus making steel ingots. Each of the ingots
was heated to 1,150.degree. C., and finish hot rolled at
850.degree. C. thus manufacturing a hot rolled sheet having a
thickness of 2.3 mm. The hot rolled sheet was annealed at
1,050.degree. C. for 4 min and then pickled. Subsequently, cold
rolling was conducted so that the thickness of the sheet was 0.50
mm, followed by carrying out final annealing at 900.degree. C. for
30 sec.
[0118] The size and distribution density of inclusions of
respective sheets, the core loss, the magnetic flux density and
hardness were measured. The results are shown in Table 12 below. A
sample for observing the inclusions was manufactured using a
replica method that is typical in the steel industry, and a
transmission electron microscope was used therefor. As such, the
acceleration voltage of 200 kV was applied.
TABLE-US-00011 TABLE 11 Steel Al Si Mn C S N Ti F1 1.0 0.5 0.3
0.0030 0.0010 0.0010 0.0020 F2 0.7 0.3 0.2 0.0030 0.0030 0.0030
0.0020 F3 0.7 0.3 0.5 0.0030 0.0020 0.0030 0.0020 F4 0.7 0.5 0.3
0.0030 0.0010 0.0025 0.0020 F5 1.0 0.3 0.7 0.0030 0.0005 0.0005
0.0020 F6 1.0 0.3 0.7 0.0030 0.0040 0.0020 0.0020 F7 1.2 0.5 1.0
0.0030 0.0020 0.0020 0.0020 F8 1.2 0.2 0.3 0.0030 0.0015 0.0010
0.0020 F9 0.9 0.5 0.8 0.0030 0.0020 0.0020 0.0020 F10 0.9 0.5 0.8
0.0030 0.0040 0.0030 0.0020 F11 0.9 0.5 0.5 0.0030 0.0030 0.0030
0.0020 F12 0.9 0.5 0.5 0.0030 0.0020 0.0025 0.0020 F13 0.9 0.5 0.5
0.0030 0.0005 0.0005 0.0020
TABLE-US-00012 TABLE 12 Size Distri. Core Magnetic (Al + of Density
of Loss Flux Al/ Al/ Al + Mn)/ Al + Si + Inclusions Inclusions
(W15/ Density Steel Si Mn Mn N + S (N + S) Mn/2 (nm) (1/mm.sup.2)
50) (B50) Hard. Note F1 2.0 3.3 1.3 0.0020 650 1.7 350 0.150 3.2
1.73 135 Invent. F2 2.3 3.5 0.9 0.0060 150 1.1 200 0.010 4.2 1.71
130 Comp. F3 2.3 1.4 1.2 0.0050 240 1.3 300 0.200 3.5 1.74 130
Invent. F4 1.4 2.3 1 0.0035 286 1.4 450 0.050 3.4 1.73 130 Invent.
F5 3.3 1.4 1.7 0.0010 1700 1.7 50 0.010 3.5 1.69 140 Comp. F6 3.3
1.4 1.7 0.0060 283 1.7 350 0.200 3.2 1.74 140 Invent. F7 2.4 1.2
2.2 0.0040 550 2.2 250 0.010 2.9 1.68 140 Comp. F8 6.0 4.0 1.5
0.0025 600 1.6 450 0.070 3.3 1.74 140 Invent. F9 1.8 1.1 1.7 0.0040
425 1.8 550 0.080 3.1 1.73 135 Invent. F10 1.8 1.1 1.7 0.0070 243
1.8 250 0.010 3.5 1.69 135 Comp. F11 1.8 1.8 1.4 0.0060 233 1.7 500
0.150 3.2 1.73 135 Invent. F12 1.8 1.8 1.4 0.0045 311 1.7 600 0.180
3.2 1.74 135 Invent. F13 1.8 1.8 1.4 0.0010 1400 1.7 50 0.018 3.7
1.72 135 Comp.
[0119] As is apparent from Table 12, steels F1, F3, F4, F6, F8, F9,
F11 and F12 were inventive examples that satisfy Condition (1),
wherein the coarse inclusions having a size of 300 nm or more were
observed, and the distribution density thereof was greater than
0.02(1/mm.sup.2) thus exhibiting superior magnetic properties, and
hardness was low, resulting in good productivity and customer
punchability.
[0120] Whereas in steels F5, F10 and F13, the amount of N+S fell
outside Condition (1) and thus inclusions having a size of 300 nm
or more were not observed, and core loss and magnetic flux density
were deteriorated. In steel F7, the amount of Al+Mn did not satisfy
Condition (1), and thus inclusions having a size of 300 nm or more
were not observed, and core loss and magnetic flux density were
deteriorated.
Example 7
[0121] Vacuum melting was performed in a laboratory, thus preparing
steel ingots having the components shown in Table 13 below. As
such, 0.3.about.0.5% of Al was added to molten steel to facilitate
the formation of inclusions, after which the remainder of Al, and
Si and Mn were added thus making steel ingots. Each of the ingots
was heated to 1,150.degree. C., and finish hot rolled at
850.degree. C. thus manufacturing a hot rolled sheet having a
thickness of 2.0 mm. The hot rolled sheet was annealed at
1,050.degree. C. for 4 min and then pickled. Subsequently, cold
rolling was conducted so that the thickness of the sheet was 0.35
mm, followed by carrying out final annealing at 1,050.degree. C.
for 38 sec.
[0122] The size and distribution density of inclusions of
respective sheets, the core loss, the magnetic flux density and
hardness were measured. The results are shown in Table 14 below. A
sample for observing the inclusions was manufactured using a
replica method that is typical in the steel industry, and a
transmission electron microscope was used therefor. As such, the
acceleration voltage of 200 kV was applied.
TABLE-US-00013 TABLE 13 Steel Al Si Mn C S N Ti G1 3.0 2.3 1.0
0.002 0.002 0.002 0.002 G2 2.5 1.7 1.0 0.002 0.002 0.002 0.002 G3
1.0 2.3 1.0 0.002 0.002 0.002 0.002 G4 1.5 2.3 0.8 0.002 0.002
0.002 0.002 G5 2.0 2.7 0.8 0.002 0.002 0.002 0.002 G6 1.0 2.7 0.8
0.002 0.002 0.002 0.002 G7 0.5 2.7 0.8 0.002 0.002 0.002 0.002 G8
3.5 3.0 0.8 0.002 0.002 0.002 0.002 G9 2.5 3.0 0.8 0.002 0.002
0.002 0.002 G10 1.5 3.0 1.0 0.002 0.002 0.002 0.002 G11 3.0 3.2 1.0
0.002 0.002 0.002 0.002 G12 1.5 3.2 1.0 0.002 0.002 0.002 0.002 G13
3.0 2.5 1.0 0.002 0.002 0.002 0.002 G14 2.5 2.5 1.0 0.002 0.002
0.002 0.002 G15 1.0 2.5 1.0 0.002 0.002 0.002 0.002
TABLE-US-00014 TABLE 14 Size Distri. Core Magnetic (Al + of Density
of Loss Flux Al/ Al/ Al + Mn)/ Al + Si + Inclusions Inclusions
(W15/ Density Steel Si Mn Mn N + S (N + S) Mn/2 (nm) (1/mm.sup.2)
50) (B50) Hard. Note G1 1.3 3.0 4.0 0.0040 1000 5.8 250 0.01 2.0
1.62 225 Comp. G2 1.5 2.5 3.5 0.0040 875 4.7 200 0.01 2.3 1.63 195
Comp. G3 0.4 1.0 2 0.0040 500 3.8 300 0.10 2.2 1.67 200 Invent. G4
0.7 1.9 2.3 0.0040 575 4.2 400 0.20 2.2 1.66 205 Invent. G5 0.7 2.5
2.8 0.0040 700 5.1 500 0.15 2.0 1.67 200 Invent. G6 0.4 1.3 1.8
0.0040 450 4.1 450 0.09 2.1 1.66 195 Invent. G7 0.2 0.6 1.3 0.0040
325 3.6 50 0.01 2.5 1.66 190 Comp. G8 1.2 4.4 4.3 0.0040 1075 6.9
75 0.01 2.0 1.62 230 Comp. G9 0.8 3.1 3.3 0.0040 825 5.9 400 0.25
2.1 1.66 220 Invent. G10 0.5 1.5 2.5 0.0040 625 5.0 600 0.10 2.1
1.67 225 Invent. G11 0.9 3.0 4.0 0.0040 1000 6.7 250 0.005 2.3 1.62
230 Comp. G12 0.5 1.5 2.5 0.0040 625 5.2 400 0.15 2.0 1.66 220
Invent. G13 1.2 3.0 4.0 0.0040 1000 6.0 75 0.01 2.0 1.62 220 Comp.
G14 1.0 2.5 3.5 0.0040 875 5.5 400 0.10 2.1 1.64 225 Invent. G15
0.4 1.0 2.0 0.0040 500 4.0 350 0.15 2.1 1.67 210 Invent.
[0123] As is apparent from Table 14, steels G3-G6, G9, G10, G12,
G14 and G15 were inventive examples that satisfy Condition (3),
wherein the coarse inclusions having a size of 300 nm or more were
observed, and the distribution density thereof was greater than
0.02(1/mm.sup.2) thus exhibiting superior magnetic properties, and
the Vickers hardness was as low as 225 or less.
[0124] Whereas in steels G1, G8, G11 and G13, the amount of Al+Mn
fell outside Condition (3) and thus inclusions having a size of 300
nm or more were not observed, and core loss and magnetic flux
density were deteriorated. In steel G2, the ratio of Al/Si did not
satisfy Condition (3), and thus inclusions having a size of 300 nm
or more were not observed, and core loss and magnetic flux density
were deteriorated. In steel G7, Al/Si, Al/Mn, and Al+Mn did not
satisfy Condition (3), and thus inclusions having a size of 300 nm
or more were not observed, and core loss and magnetic flux density
were deteriorated. In steels G8 and G11, Al+Si+Mn/2 did not satisfy
Condition (3), and thus hardness was high, thereby deteriorating
productivity and punchability.
Example 8
[0125] Vacuum melting was performed in a laboratory, thus preparing
steel ingots having the components shown in Table 15 below. As
such, 0.3.about.0.5% of Al was added to molten steel to facilitate
the formation of inclusions, after which the remainder of Al, and
Si and Mn were added thus making steel ingots. Each of the ingots
was heated to 1,150.degree. C., and finish hot rolled at
850.degree. C. thus manufacturing a hot rolled sheet having a
thickness of 2.0 mm. The hot rolled sheet was annealed at
1,050.degree. C. for 4 min and then pickled. Subsequently, cold
rolling was conducted so that the thickness of the sheet was 0.35
mm, followed by carrying out final annealing at 1,050.degree. C.
for 38 sec.
[0126] The size and distribution density of inclusions of
respective sheets, the core loss, the magnetic flux density and
hardness were measured. The results are shown in Table 16 below. A
sample for observing the inclusions was manufactured using a
replica method that is typical in the steel industry, and a
transmission electron microscope was used therefor. As such, the
acceleration voltage of 200 kV was applied.
TABLE-US-00015 TABLE 15 Steel Al Si Mn C S N Ti H1 1.0 2.3 0.5
0.0030 0.0010 0.0010 0.0020 H2 1.0 2.3 0.5 0.0030 0.0030 0.0030
0.0020 H3 1.0 2.5 1.0 0.0030 0.0020 0.0030 0.0020 H4 1.2 2.5 1.2
0.0030 0.0015 0.0020 0.0020 H5 1.2 2.7 1.0 0.0030 0.0005 0.0005
0.0020 H6 1.2 2.7 1.0 0.0030 0.0020 0.0040 0.0020 H7 2.0 2.7 2.0
0.0030 0.0020 0.0020 0.0020 H8 2.0 3.2 1.5 0.0030 0.0010 0.0015
0.0020 H9 2.0 3.2 1.5 0.0030 0.0020 0.0020 0.0020 H10 2.0 3.2 1.0
0.0030 0.0030 0.0040 0.0020 H11 2.0 3.2 1.5 0.0030 0.0030 0.0030
0.0020 H12 1.5 3.5 1.5 0.0030 0.0020 0.0025 0.0020 H13 2.5 3.5 1.0
0.0030 0.0005 0.0005 0.0020
TABLE-US-00016 TABLE 16 Size Distri. Core Magnetic (Al + of Density
of Loss Flux Al/ Al/ Al + Mn)/ Al + Si + Inclusions Inclusions
(W15/ Density Steel Si Mn Mn N + S (N + S) Mn/2 (nm) (1/mm.sup.2)
50) (B50) Hard. Note H1 0.4 2.0 1.5 0.0020 750 3.6 350 0.15 2.2
1.67 190 Invent. H2 0.4 2.0 1.5 0.0060 250 3.6 75 0.01 2.3 1.65 190
Comp. H3 0.4 1.0 2 0.0050 400 4.0 400 0.20 2.1 1.67 190 Invent. H4
0.5 1.0 2.4 0.0035 686 4.3 450 0.08 2.1 1.67 195 Invent. H5 0.4 1.2
2.2 0.0010 2200 4.4 50 0.01 2.3 1.65 200 Comp. H6 0.4 1.2 2.2
0.0060 367 4.4 350 0.20 2.2 1.67 200 Invent. H7 0.7 1.0 4.0 0.0040
1000 5.7 250 0.01 2.1 1.63 220 Comp. H8 0.6 1.3 3.5 0.0025 1400 6.0
450 0.12 2.0 1.65 225 Invent. H9 0.6 1.3 3.5 0.0040 875 6.0 550
0.09 2.0 1.65 225 Invent. H10 0.6 2.0 3.0 0.0070 429 5.7 250 0.01
2.2 1.63 220 Comp. H11 0.6 1.3 3.5 0.0060 583 6.0 500 0.15 2.0 1.65
225 Invent. H12 0.4 1.0 3 0.0045 667 5.8 600 0.20 2.1 1.65 225
Invent. H13 0.7 2.5 3.5 0.0010 3500 6.5 50 0.01 2.1 1.62 225
Comp.
[0127] As is apparent from Table 16, steels H1, H3, H4, H6, H8, H9,
H11 and H12 were inventive examples that satisfy Condition (3),
wherein the coarse inclusions having a size of 300 nm or more were
observed, and the distribution density thereof was greater than
0.02(1/mm.sup.2) thus exhibiting superior magnetic properties.
[0128] Whereas in steels H5, H10 and H13, N+S did not satisfy
Condition (3) and thus inclusions having a size of 300 nm or more
were not observed, and core loss and magnetic flux density were
deteriorated. In steel H7, Al+Mn did not satisfy Condition (3), and
thus inclusions having a size of 300 nm or more were not observed,
and core loss and magnetic flux density were deteriorated. In
steels H2, H5 and H13, (Al+Mn)/(N+S) did not satisfy Condition (3),
and thus inclusions having a size of 300 nm or more were not
observed, and core loss and magnetic flux density were
deteriorated.
* * * * *