U.S. patent application number 13/823424 was filed with the patent office on 2013-09-12 for method for manufacturing oriented silicon steel product with high magnetic-flux density.
The applicant listed for this patent is Bingzhong Jin, Weizhong Jin, Guobao Li, Hai Liu, Kanyi Shen, Dejun Su, Qi Xu, Renbiao Zhang. Invention is credited to Bingzhong Jin, Weizhong Jin, Guobao Li, Hai Liu, Kanyi Shen, Dejun Su, Qi Xu, Renbiao Zhang.
Application Number | 20130233450 13/823424 |
Document ID | / |
Family ID | 45891877 |
Filed Date | 2013-09-12 |
United States Patent
Application |
20130233450 |
Kind Code |
A1 |
Xu; Qi ; et al. |
September 12, 2013 |
METHOD FOR MANUFACTURING ORIENTED SILICON STEEL PRODUCT WITH HIGH
MAGNETIC-FLUX DENSITY
Abstract
A method for manufacturing an oriented silicon steel product
with high magnetic-flux density comprises the following procedures:
1) smelting and casting, wherein the oriented silicon steel is
composed of, by weight, 0.035.about.0.065% of C, 2.9.about.4.0% of
Si, 0.05.about.0.20% of Mn, 0.005.about.0.01% of S,
0.015.about.0.035% of Al, 0.004.about.0.009% of N,
0.005.about.0.090% of Sn, 0.200.about.0.800% of Nb, the rest being
Fe; and after being smelted, molten steel is secondarily refined
and continuous casted into steel slabs; 2) hot rolling; 3)
normalizing; 4) cold rolling; 5) decarburization annealing; 6) MgO
coating; 7) high temperature annealing: said sheets are firstly
heated to 700.about.900.degree. C. and then secondarily heated to
1200.degree. C. at temperature rise rate of 9.about.17.degree.
C./hr and maintained at 1200.degree. C. for 20 hr; 8) coating an
insulation layer. According to the present invention, steel sheets
can be fully nitrided during high temperature annealing, which can
ensure a secondary re-crystallization to take place perfectly,
thereby, the oriented silicon steel sheets with high magnetic-flux
density can be achieved. The present invention solves the problem
of nitriding that is encountered in production of
high-magnetic-induction oriented silicon steel by the technique to
heat steel slabs to a lower temperature.
Inventors: |
Xu; Qi; (Shanghai, CN)
; Shen; Kanyi; (Shanghai, CN) ; Li; Guobao;
(Shanghai, CN) ; Jin; Weizhong; (Shanghai, CN)
; Jin; Bingzhong; (Shanghai, CN) ; Su; Dejun;
(Shanghai, CN) ; Zhang; Renbiao; (Shanghai,
CN) ; Liu; Hai; (Shanghai, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Xu; Qi
Shen; Kanyi
Li; Guobao
Jin; Weizhong
Jin; Bingzhong
Su; Dejun
Zhang; Renbiao
Liu; Hai |
Shanghai
Shanghai
Shanghai
Shanghai
Shanghai
Shanghai
Shanghai
Shanghai |
|
CN
CN
CN
CN
CN
CN
CN
CN |
|
|
Family ID: |
45891877 |
Appl. No.: |
13/823424 |
Filed: |
April 14, 2011 |
PCT Filed: |
April 14, 2011 |
PCT NO: |
PCT/CN11/72768 |
371 Date: |
March 14, 2013 |
Current U.S.
Class: |
148/522 |
Current CPC
Class: |
C22C 38/001 20130101;
C22C 38/02 20130101; C22C 38/06 20130101; C21D 8/1233 20130101;
C22C 38/12 20130101; C21D 8/0284 20130101; C22C 38/008 20130101;
C21D 8/1255 20130101; C21D 8/1261 20130101; C21D 8/0263 20130101;
C21D 8/1283 20130101; C22C 38/04 20130101; C21D 8/1272 20130101;
H01F 1/16 20130101; C21D 8/12 20130101; C21D 8/1222 20130101 |
Class at
Publication: |
148/522 |
International
Class: |
C21D 8/02 20060101
C21D008/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2010 |
CN |
201010298954.7 |
Claims
1. A method for manufacturing an oriented silicon steel product
with high magnetic-flux density comprising the following steps:
casting oriented silicon steel into steel slabs after the silicon
steel is smelted and secondarily refined, wherein the oriented
silicon steel is composed of, by weight, 0.035.about.0.065% of C,
2.9.about.4.0% of Si, 0.05.about.0.20% of Mn, 0.005.about.0.01% of
S, 0.015.about.0.035% of Al, 0.004.about.0.009% of N,
0.005.about.0.090% of Sn, 0.200.about.0.800% of Nb, the rest being
Fe and unavoidable inclusions; heating said steel slabs in a
heating furnace to 1090.about.1200.degree. C.; hot rolling said
steel slabs into steel plates at a beginning temperature of
1180.degree. C. and finishing hot rolling said steel slabs at a
finishing temperature of 860.degree. C.; cooling said steel plates
using laminar flow of water to below 650.degree. C.; coiling said
steel plates into coiled-shape plates; normalizing said
coiled-shape plates at a normalization temperature of
1050.about.1180.degree. C. for 1.about.20 sec and at a
normalization temperature of 850.about.950.degree. C. for
30.about.200 sec, and then immediately thereafter cooling down the
plates at a cooling rate of 10.about.60.degree. C./sec; wherein
after being normalized, cold rolling said steel plates into steel
sheets with a thickness of a finished sheet at a rolling
compression ratio not less than 75%; decarburizing said steel
sheets to a temperature of 800.about.860.degree. C. at a
temperature rise rate of 15.about.35.degree. C./sec and maintained
at the temperature for 90.about.160 sec; coating said steel sheets
with a coating including, by weight, 0.1.about.10% of NH.sub.4Cl
and 0.5.about.30% of P.sub.3N.sub.5, and MgO as the rest component
where the MgO is a main component; heating said steel sheets to a
temperature of 700.about.900.degree. C., and then heating said
steel sheets to 1200.degree. C. at a secondary temperature rise
rate of 9.about.17.degree. C./hr and maintained at 1200.degree. C.
for 20 hr; and coating surfaces of the steel sheets with an
insulation layer.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for manufacturing
oriented silicon steel sheet, and particularly, to a method for
manufacturing oriented silicon steel sheet with a high
magnetic-flux density.
BACKGROUND OF THE INVENTION
[0002] The conventional process for manufacturing oriented silicon
steel with high magnetic-flux density is as follows. After being
smelted in a convertor or electric furnace, molten steel is
secondarily refined and alloyed, and then continuous-casted into
steel slabs. Its basic chemical compositions are: Si
2.5.about.4.5%, C 0.06.about.0.10%, Mn 0.03.about.0.1, S
0.012.about.0.050, Al 0.02.about.0.05%, N 0.003.about.0.012. Some
composition systems further contain one or more of the elements Cu,
Mo, Sb, B, Bi, etc. The rest is Fe and unavoidable impure
inclusions. A steel slab is heated to a temperature over 1350 in a
special furnace and maintained at the temperature for more than 45
min so as to make the advantageous inclusions MnS or AlN fully
solid-dissolved, then rolled into steel plates with a finishing
temperature up to over 950.degree. C.; and then a plate is cooled
rapidly to below 500.degree. C. by jetting water, thereafter,
coiled to be coil-shaped. Subsequently, during normalization, fine
and dispersed second phase particles, namely depressant, separate
out of silicon steel body. After being normalized, the hot rolled
steel plates are pickled and removed of oxidized scale, and then
cold-rolled into sheets of the thickness of finished steel sheet
product. A cold rolled sheet is decarburization annealed and coated
with an anneal insulator (main composition is MgO). The carbon in
the sheet is decarburized to the extent as not to influence the
magnetic property of the finished steel sheet product (generally it
shall be below 30 ppm); during being high temperature annealed, the
steel sheet generates physical and chemical changes such as
secondary re-crystallization, formation of bottom layer of
magnesium silicate and purification (elements S, N, etc., harmful
to magnetic property, are eliminated from the steel sheet), and is
made to be a highly-oriented, low-iron-loss and
high-magnetic-induction silicon steel sheet; finally, after being
coated with insulation layer and tension-annealed, the silicon
steel sheet is made to be commercially available oriented silicon
steel sheet product.
[0003] The shortcomings of the above manufacturing process is that
the heating temperature must be up to 1400.degree. C. in order to
have the depressant fully solid-dissolved. This is the upmost level
of a conventional heating furnace. In addition, because of the high
heating temperature, burning loss is big and the heating furnace
needs to be frequently mended, thus resulting in a low utilization.
Also, energy consumption is high. Moreover, the hot rolled
coil-shaped plate often has larger edge cracks, which may cause
difficulty in the subsequent cold rolling procedure, and result in
a low yield rate, unsatisfactory magnetic property B.sub.8 of the
finished product, and higher manufacture cost.
[0004] In view of the problem above, both domestic and foreign
researchers have carried out a lot of research with the aim to
reduce the heating temperature of oriented silicon steel. The
research can be categorized into two types. One is to heat a steel
slab to a temperature within the range of 1250.about.1320.degree.
C. and to use AlN and Cu as a depressant. The other is to heat a
slab to a temperature within the range of 1100.about.1250.degree.
C. and to acquire depression capability by employing a depressant
which is formed by nitriding after decarburization.
[0005] Nowadays, there has been a rapid development in the
technique for heating a steel slab at a lower temperature. For
example, in US patent U.S. Pat. No. 5,049,205 and Japanese patent
publication JPA 1993-112827, a steel slab is heated to a
temperature not higher than 1200.degree. C. and rolled into plates.
In the finishing cold rolling procedure, a plate is rolled into
sheets with a great rolling compression ratio of 80%, and the
rolled steel sheet is continuous nitriding treated by use of
ammonia after they are decarburization annealed in order to obtain
highly oriented secondarily re-crystallized grains. In this
technique, however, because the depressing effect is obtained by a
depressant which is generated by nitriding of the rolled steel
sheet after it is decarburized, it is very difficult, in actual
control, to avoid the problems such that the steel sheet will have
severely oxidized surfaces and it is hard to be nitrided evenly.
Therefore, it will lead to the difficulty for obtained-type
depressant to generate and evenly distribute in the steel sheet,
and thus it will affect depressing effect and evenness of
secondarily re-crystallized grains, and finally result in uneven
magnetic property of the finished silicon steel sheet product.
[0006] Chinese Patent CN 200510110899 describes a new process,
where steel slabs are heated at a temperature not higher than
1200.degree. C., and the cold rolled steel sheets, which have been
rolled to the thickness of the finished product, are nitrided prior
to decarburized annealing. In this process, however, it is
necessary to strictly control the dew point during nitriding, and
there will occur a new problem that decarburization becomes more
difficult.
[0007] Recently, Korean Patent KR 2002074312 disclosed that steel
slabs are heated to a temperature not higher than 1200.degree. C.,
and rolled sheets are decarburized and nitrided simultaneously.
Although the difficulties in post-rolling decarburization and
post-rolling nitriding can be solved, however, uneven nitriding is
still unavoidable and thus will give rise to uneven magnetic
property of the finished silicon steel sheet product, and
manufacture cost may be higher.
[0008] Adding element Nb is also proposed. For example, in Japanese
patents JP 6025747 and JP 6073454, Nb of 0.02.about.0.20% is added
in the compositions of smelted steel. It is aimed at generating
niobium carbide and niobium nitride and thereby to fine the
re-crystallized texture, improving grain distribution and
collective texture of the decarburization annealed steel sheets,
taking the niobium carbide and niobium nitride as an auxiliary
depressant to depress the growing up of the normal grains during
high temperature annealing, and thus improving the magnetic
property of silicon steel sheets. However, a problem with the
patents is that the steel slabs must be heated to a very high
temperature in order to parse out niobium nitride before hot
rolling, and this will certainly lead to a greater burning loss,
higher energy consumption, a lower ratio of the finished product,
and a higher manufacture cost.
[0009] According to Japanese patent JP51106622 and US patent U.S.
Pat. No. 4,171,994, nitrates of Al, Fe, Mg and Zn are added into a
separant MgO. It aims at making them decomposed during high
temperature anneal and thus releasing nitrogen oxide so as to
nitride steel sheets. However, the nitrogen oxide and oxygen out of
the decomposed nitrates may lead to an explosion risk in practical
production.
[0010] According to Japanese patent JP52039520 and American patent
U.S. Pat. No. 4,010,050, sulfanilic acid is added in separant MgO.
It is aimed at making sulfanilic acid decompose in high temperature
and thus release nitrides for nitriding. However, being a organic
substance, sulfanilic acid will decompose at a lower temperature
(about 205.degree. C.), the nitrogen released at so low temperature
is hard to make steel sheet nitrided.
[0011] According to Japanese patents JP 61096080 and JP62004811,
nitriding of steel sheets during high temperature anneal is
realized by adding nitrides of Mn and Si. However, a problem with
this method lies in that these nitrides have a high
thermostability. Therefore, they can not be decomposed effectively
and quickly. In order to meet nitriding requirement, it is
necessary to prolong the period of high temperature annealling or
to increase the quantity of those nitrides.
[0012] With regard to temperature rise rate during high temperature
annealing, Japanese patents JP 54040227 and JP200119751 put forward
that oriented silicon steels with high magnetic-flux density can be
obtained by reducing temperature rise rate in the course of high
temperature annealing. However, simply reducing temperature rise
rate may result in a greatly reduced production rate.
SUMMARY OF THE INVENTION
[0013] The object of the present invention is to provide a method
for manufacturing an oriented silicon steel product with high
magnetic-flux density, which solves the difficulty in nitriding for
manufacturing oriented silicon steel sheet with high magnetic-flux
density where steel slabs are heated at a lower temperature. The
present invention efficiently ensures safe and stable operation and
a long life of smelting furnaces by a technique of heating at a
lower temperature. In the manufacture process, oriented silicon
steel sheets can be fully nitrided during high temperature
annealing, which can ensure secondary re-crystallization to take
place perfectly, and thereby, the oriented silicon steel sheets
with high magnetic-flux density and premium magnetic property can
be achieved.
[0014] The invention adopts the following technical solution.
[0015] During smelting, a certain amount of Nb is added in the
compositions of oriented silicon steel so as to make oriented
silicon steel sheet be easy to be nitrided because the nitrogen
content in steel is crucial in deciding whether the magnetic
property of the finished oriented silicon steel sheet product meet
specifications. Some nitrates are added in MgO separant and the MgO
separant added with nitrates is applied on the surfaces of the
steel sheets before the sheets are high temperature annealed.
During high temperature annealing, the nitrates decompose and
release nitrogen which can make the steel sheets fully nitrided.
The temperature rise rate during high temperature annealing is
regulated according to the Nb content, N content prior to secondary
heating and the beginning temperature of secondary heating, thus
ensuring secondary re-crystallization to take place perfectly, and
thereby, the oriented silicon steel sheets with high magnetic-flux
density and premium magnetic property can be achieved.
[0016] Specifically, a method for manufacturing an oriented silicon
steel product with high magnetic-flux density is provided according
to the present invention. The method includes the following
procedures:
[0017] 1) Smelting and Casting
[0018] The oriented silicon steel is composed of, by weight,
0.035.about.0.065% of C, 2.9.about.4.0% of Si, 0.05.about.0.20% of
Mn, 0.005.about.0.01% of S, 0.015.about.0.035% of Al,
0.004.about.0.009% of N, 0.005.about.0.090% of Sn,
0.200.about.0.800% of Nb, the rest is Fe and unavoidable
inclusions. After being smelted, molten steel is secondarily
refined and then casted into steel slabs.
[0019] 2) Hot Rolling
[0020] Said steel slabs are heated in a heating furnace to
1090.about.1200.degree. C., and then, are hot rolled into steel
plates at a beginning temperature of 1180.degree. C. and are
finished with the hot rolling step at a finishing temperature of
860.degree. C., said steel plates are cooled by laminar flow of
water to below 650.degree. C. and then coiled into coiled-shape
plates.
[0021] 3) Normalization
[0022] A coiled-shape plate is normalized at the normalization
temperature of 1050.about.1180.degree. C. for 1.about.20 sec and
then at the normalization temperature of 850.about.950.degree. C.
for 30.about.200 sec, and thereafter, is cooled down at a cooling
rate of 10.about.60.degree. C./sec;
[0023] 4) Cold Rolling
[0024] After being normalized, the steel plate is cold rolled into
steel sheets with the thickness of the finished oriented silicon
steel sheet product at a rolling compression ratio not less than
75%;
[0025] 5) Decarburization Annealing
[0026] A steel sheet is heated to the temperature of
800.about.860.degree. C. at a temperature rise rate of
15.about.35.degree. C./sec and maintained at the temperature for
90.about.160 sec for being decarburized, herein only
decarburization must be carried out because nitriding will take
place during high temperature annealing;
[0027] 6) MgO Coating
[0028] After being decarburized, said steel sheets are covered with
a coating which is composed of, by weight, 0.1.about.10% of
NH.sub.4Cl and 0.5.about.30% of P.sub.3N.sub.5, and MgO as rest
wherein MgO is a main component.
[0029] 7) High Temperature Annealing
[0030] After being coated with the isolator, the steel sheet is
firstly heated to a temperature of 700.about.900.degree. C., and
then secondarily heated to 1200.degree. C. at temperature rise rate
V.sub.secondary temperature rise of 9.about.17.degree. C./hr and
maintained at 1200.degree. C. for 20 hr for being purification
annealed and nitrided;
[0031] 8) Coating an Insulation Layer
[0032] After being high temperature annealed, the surfaces of the
steel sheet is coated with an insulation layer, and then is tension
and leveling annealed, and finally becomes the oriented silicon
steel sheet with high magnetic-flux density and premium magnetic
property.
[0033] According to the present invention, a certain amount of Nb
is added into the silicon steel. There two reasons of doing this.
The first reason is that the oriented silicon steel with Nb in its
compositions is much easier to be nitrided, this is because the d
sublayer of sub-outer spheres of the atom of Nb is unsaturated with
electrons and so Nb is much easier to change into nitrides than Fe
and Mn, and nitride of Nb is very stable. The second reason is that
the N atoms, which penetrate into steel sheets during high
temperature annealing, can bond with Al to generate main depressant
AlN which is necessary to obtain oriented silicon steel sheet with
high magnetic-flux density, and also can be combined into Nb.sub.2N
and NbN. These nitrides of Nb can be an auxiliary depressant and
can intensify depressing effect on growth of normal crystal grains.
In general, this solution is very advantageous to improve the
magnetic property of oriented silicon steel sheet.
[0034] According to the present invention, a certain amount of
NH.sub.4Cl and P.sub.3N.sub.5 is added into a liquid MgO coating.
The intention of doing this is to use decomposition of the two
nitrides during high temperature annealing to realize nitriding of
silicon steel sheets, and thereby to replace the nitriding which
will take place by virtue of decomposition of ammonia during
decarburization anneal, the greatest benefit of this solution is to
ensure the steel sheets to be nitrided evenly. The reason of
selecting NH.sub.4Cl and P.sub.3N.sub.5 as nitriding material which
will decompose at high temperature is that NH.sub.4Cl will
decompose at 330.about.340.degree. C. and P.sub.3N.sub.5 will
decompose at 760.degree. C. or so. The decomposition of the two
different nitrides at different temperatures ensures to evenly
release active atoms of nitrogen in a relatively long time in the
procedure of high temperature annealing, this is advantageous to
nitriding of the steel sheets and to maintaining N content therein
to be within standard limits of 200.about.250 ppm.
[0035] According to the present invention, the temperature rise
rate for the secondary heating during high temperature annealing is
controlled to ensure the finished oriented silicon steel sheet
product to attain premium magnetic property by setting a proper
secondary temperature rise rate. This is because the course of
secondary temperature rise for high temperature annealing covers
the whole temperature range of secondary re-crystallization.
Therefore, a proper temperature rise rate can ensure the Gauss
grains which grow during the secondary re-crystallization to have a
much better orientation (deviation angle <3.degree.) and
magnetic property.
[0036] According to the present invention, the relatively low
temperature rise rate during high temperature annealing can refine
the secondary re-crystallization and ensure the finished steel
sheet product to have a better magnetic property. This is because
gradual coarsening and decomposition of AlN as well as the
secondary re-crystallization can take place simultaneously during
secondarily heating for high temperature annealing, and so the
depressing effect disappears simultaneously. If the temperature
rises too quickly within this temperature range, it will result in
such a case that the depressant has decomposed and lost its effect
before the secondary re-crystallization has not yet finished. As is
known, imperfect secondary re-crystallization will bring about poor
magnetic property of the finished oriented silicon steel sheet
product.
DETAILED DESCRIPTION OF THE INVENTION
[0037] The invention is now described in detail in conjunction with
following embodiments.
First Embodiment
[0038] Material steel of oriented silicon steel sheet with the
chemical compositions shown in Table 1 is smelted and casted into
slabs. The slabs with different chemical compositions are heated to
the temperature of 1155.degree. C. in a heating furnace and
maintained at the temperature for 1.5 hours, and then hot rolled
into plates of 2.3 mm thickness at a beginning temperature of
1062.degree. C. and finishing temperature of 937.degree. C. The hot
rolled plates are normalized in two phases: at 1120.degree. C. for
15 sec and at 870.degree. C. for 150 sec ((1120.degree. C..times.15
sec)+(870.degree. C..times.150 sec)), and then cooled down at the
rate of -15.degree. C./sec. After being pickled, the hot rolled
plates are cold rolled to coil-shaped steel sheets with the
thickness 0.30 mm of the finished steel sheet product, and then in
sequence, the cold rolled coil-shaped sheets are heated at
temperature rise rate of 25.degree. C./sec to decarburization
temperature of 820.degree. C. and maintained at the temperature for
140 sec for being decarburization annealed; applied and covered
with a thick layer of a separant which contains MgO as the main
component and NH.sub.4Cl of 4.5% and P.sub.3N.sub.5 of 15%; heated
to 800.degree. C. for being high temperature annealed and getting
nitrogen content b before being secondarily heated; secondarily
heated to temperature of 1200.degree. C. and maintained at the
temperature for 20 hours for being purification annealed. After
being uncoiled to steel sheets of some length, the sheets are
applied with an insulation coating layer and then are tension and
leveling annealed. The nitrogen content b prior to secondary
heating and the magnetic property of the finished steel sheet
product are both shown in Table 1.
TABLE-US-00001 TABLE 1 effect of chemical compositions on nitrogen
content before secondary heating and magnetic property N content
before secondary heating Instance C % SI % Mn % S % AL % N % Sn %
Nb % (ppm) B.sub.8 T P17/50 W/kg 1 0.035 3.2 0.20 0.010 0.015 0.009
0.090 0.20 202 1.92 0.97 2 0.041 2.9 0.10 0.005 0.025 0.006 0.070
0.36 211 1.92 0.99 3 0.052 4.0 0.05 0.008 0.035 0.004 0.005 0.64
234 1.93 0.97 4 0.065 3.5 0.15 0.012 0.022 0.007 0.035 0.80 244
1.92 0.98 Comparison 0.046 3.0 0.08 0.006 0.028 0.008 0.072 0.18
173 1.87 1.11 Examples 1 Comparison 0.053 3.5 0.15 0.011 0.019
0.006 0.014 0.84 292 1.86 1.12 Examples 2
[0039] As can be seen from Table 1, the selection of various
chemical compositions according to the embodiment is in consistence
to the standard specification (of smelting and casting) in the
production procedures of the present invention. However, the
selection of component Nb in the comparison examples is not within
the standard limits of 0.200.about.0.800, therefore, the amount of
N measured before secondary heating is not within the standard
limits of 200.about.250 ppm, and finally causes the finished
oriented silicon steel sheet product to have a larger iron loss
(P.sub.17/50) and a poor magnetic property (B.sub.8).
Second Embodiment
[0040] The oriented silicon steel slabs is composed of (by weight
percent) the following elements: C 0.05%, Si 3.25%, Mn 0.15%, S
0.009%, Al 0.032%, N 0.005%, Sn 0.02%, Nb 0.5%, the rest is Fe and
unavoidable impurities. The slabs are heated to the temperature of
1155.degree. C. in a heating furnace and maintained at the
temperature for 1.5 hours, and then hot rolled into plates of 2.3
mm thickness at a beginning temperature of 1080.degree. C. and
finishing temperature of 910.degree. C. The hot rolled plates are
normalized in two phases: at 1110.degree. C. for 10 sec and at
910.degree. C. for 120 sec ((1110.degree. C..times.15
sec)+(910.degree. C..times.120 sec)), and then cooled down at the
rate of -35.degree. C./sec. After being pickled, the hot rolled
plates are cold rolled into coil-shaped sheets with the thickness
0.30 mm of the finished steel sheet product, and then in sequence,
the cold rolled coil-shaped sheets are heated to the
decarburization temperature of 840.degree. C. at temperature rise
rate of 25.degree. C./sec and maintained at the temperature for 130
sec for being decarburization annealed; applied and covered with a
thick layer of a separant which contains MgO as the main component
and NH.sub.4Cl and P.sub.3N.sub.5 of certain small contents; heated
to 800.degree. C. for being high temperature annealed and getting
nitrogen content b before being secondary heated; secondarily
heated to temperature of 1200.degree. C. and maintained at the
temperature for 20 hours for being purification annealed. After
being uncoiled to steel sheets of some length, the sheets are
coated with an insulation layer and then are tension and leveling
annealed. The nitrogen content b prior to secondary heating and the
magnetic property of the finished steel sheet product are both
shown in Table 2.
TABLE-US-00002 TABLE 2 effect of the contents of NH.sub.4Cl and
P.sub.3N.sub.5 on nitrogen content before secondary heating and
magnetic property N content before secondary heating Instance
NH.sub.4Cl % P3N5 % (ppm) B.sub.8 T P17/50 W/kg 1 0.1 3.9 198 1.92
0.99 2 1.2 11.3 210 1.91 1.00 3 3.6 20.8 231 1.92 0.98 3 6.4 0.5
206 1.92 0.97 4 8.3 6.6 221 1.92 1.00 5 10 12.8 222 1.93 0.96 6 2.4
19.5 234 1.92 0.98 7 5.5 26.4 252 1.91 0.99 8 1.9 30 243 1.93 0.96
Comparison 6.4 0.4 178 1.87 1.10 Examples 1 Comparison 2.4 30.2 268
1.88 1.06 Examples 2 10.5 30.5 283 1.83 1.16
[0041] As can be seen from Table 2, the selection of NH.sub.4Cl and
P.sub.3N.sub.5 according to the embodiment is in consistence to the
standard ranges of 0.1.about.10% and 0.5.about.30% (of MgO coating)
in the production procedures of the present invention. Contrarily,
in the selection of NH.sub.4Cl and P.sub.3N.sub.5 in the comparison
examples, whatever one is not within the standard limits causes the
content of N measured before secondary heating to be not within the
standard limits of 200.about.250 ppm, and finally causes the
finished oriented silicon steel sheet product to have a larger iron
loss (P.sub.17/50) and a poor magnetic property (B.sub.8).
Third Embodiment
[0042] The oriented silicon steel slabs is composed of the
following components: C 0.05%, Si 3.25%, Mn 0.15%, S 0.009%, Al
0.032%, N 0.005%, Sn 0.02%, Nb (a)0.2.about.0.8%, the rest is Fe
and unavoidable inclusions. The slabs are heated to the temperature
of 1155.degree. C. in a heating furnace and maintained at the
temperature for 2.5 hours, and then are hot rolled into plates of
2.3 mm thickness at a beginning temperature of 1050.degree. C. and
finishing temperature of 865.degree. C. The hot rolled plates are
normalized in two phases: at 1120.degree. C. for 15 sec and at
900.degree. C. for 120 sec ((1120.degree. C..times.15
sec)+(900.degree. C..times.120 sec)), and then cooled down at the
rate of -25.degree. C./sec. After being pickled, the hot rolled
plates are cold rolled to coil-shaped sheets with the thickness
0.30 mm of the finished steel sheet product, and then in sequence,
the cold rolled coil-shaped sheets are heated to the
decarburization temperature of 850.degree. C. at temperature rise
rate of 25.degree. C./sec and maintained at the temperature for 115
sec for being decarburization annealed; applied and covered with a
thick layer of a separant which contains MgO as the main component
and NH.sub.4Cl of 7.5% and P.sub.3N.sub.5 of 12.5%; heated to
700.about.900.degree. C. as beginning temperature (c) of the
secondary heating in high temperature annealing and for getting
nitrogen content (b) before being secondary heated; heated to the
temperature of 1200.degree. C. at a certain temperature rise rate
(V) and maintained at the temperature for 20 hours for being
purification annealed. After being uncoiled to steel sheets of some
length, the sheets are applied with an insulation coating layer and
are tension and leveling annealed. The data of the third embodiment
are shown in Table 3.
TABLE-US-00003 TABLE 3 effect of different processes of both
normalization and nitriding on the magnetic property of the
finished silicon steel sheet product beginning N content
temperature theoretically actual before of calculated secondary
secondary secondary secondary heating difference magnetic nb
heating heating heating rate rate (.degree. C./hr) property (%)
(ppm) (.degree. C.) (.degree. C./hr) (.degree. C./hr) V.sub.upper
limit - P.sub.17/50 Instance a b c V.sub.upper limit V.sub.actual
V.sub.actual B.sub.8 T w/kg 1 0.20 186 700 17.9 16 1.9 1.90 1.00 2
0.20 184 800 14.3 14 0.3 1.90 0.98 3 0.20 189 900 10.5 9 1.5 1.91
1.01 4 0.40 204 720 18.2 17 1.2 1.92 0.96 5 0.40 207 810 14.8 14
0.8 1.91 0.99 6 0.40 211 880 12.2 12 0.2 1.93 0.93 7 0.60 231 750
18.0 17 1 1.93 0.95 8 0.60 229 850 14.3 14 0.3 1.92 0.99 9 0.80 248
780 17.9 15 2.9 1.91 1.00 10 0.80 252 860 14.8 12 2.8 1.92 0.96
Comparison 0.20 186 700 17.9 19 -1.1 1.85 1.07 Examples 1 0.20 184
800 14.3 15 -0.7 1.86 1.09 2 0.20 189 900 10.5 12 -1.5 1.85 1.08 3
0.40 204 720 18.2 20 -1.8 1.85 1.12 4 0.40 207 810 14.8 16 -1.2
1.86 1.09 5 0.40 211 880 12.2 14 -1.8 1.84 1.15 6 0.60 231 750 18.0
19 -1 1.85 1.12 7 0.60 229 850 14.3 15 -0.7 1.87 1.14 8 0.80 248
780 17.9 19 -1.1 1.86 1.10 9 0.80 252 860 14.8 17 -2.2 1.84 1.12 10
0.20 184 800 14.3 15 -0.7 1.86 1.09
[0043] As can be seen in Table 3, in the case where Nb contents
(a), N contents before secondary heating (b) and the beginning
temperatures of secondary heating (c) all are the same, and also in
the case where the actual secondary temperature rise rates in the
embodiments are 9.about.17.degree. C./hr and the differences
between the theoretically calculated values and the actual values
are positive, the magnetic properties of the finished silicon steel
sheet products in both the embodiments and the comparison examples
are better. If the conditions are reversed, the cases of the
comparative objects are adverse, and therefore, the electromagnetic
properties of the comparative objects are poor.
[0044] To manufacture the oriented silicon steel sheet by heating
steel slabs at a lower temperature has the advantages such as long
life of heating furnace, lower energy consumption and lower
manufacture cost. However, there exist the problems of uneven
decarburization and uneven nitriding in the subsequent procedures
and difficulties in efficient regulation and control in the course
of production for a long time. Such cases have had influence on the
depressing effect in some parts of a steel sheet or the whole
sheet, and thus results in imperfect secondary re-crystallization
and inconsistent magnetic property of the finished product.
[0045] In conclusion, the present invention provides a new method
for manufacturing an oriented silicon steel sheet with high
magnetic-flux density based on the procedure of heating steel slabs
at a lower temperature. According to the method of the present
invention, the above-mentioned problems are all effectively solved.
The method is characterized in that the steel sheets can be easily
nitrided during high temperature annealing by adding a certain
amount of Nb in molten steel; the steel sheets can be evenly
nitrided during high temperature annealing by adding some nitrides
into the separant MgO and letting them decomposing during high
temperature annealing; in the course of high temperature annealing,
the temperature rise rate can be controlled according to Nb
content, N content and the beginning temperature of secondary
heating so as to ensure completion of a good secondary
re-crystallization course. All these solutions ensure the
achievement of oriented silicon steel sheet with high magnetic-flux
density and premium magnetic property.
* * * * *