WO2012041054A1

WO2012041054A1 - Production method of grain-oriented silicon steel with high magnetic flux density

Info

Publication number: WO2012041054A1
Application number: PCT/CN2011/072768
Authority: WO
Inventors: 徐琪; 沈侃毅; 李国保; 靳伟忠; 金冰忠; 宿德军; 张仁彪; 刘海
Original assignee: 宝山钢铁股份有限公司
Priority date: 2010-09-30
Filing date: 2011-04-14
Publication date: 2012-04-05
Also published as: US20130233450A1; MX2013003367A; CN102443736B; EP2623621A4; RU2013114861A; JP5864587B2; EP2623621A1; CN102443736A; KR101451824B1; KR20130049823A; RU2552562C2; MX350000B; EP2623621B1; JP2013545885A

Abstract

A production method of grain-oriented silicon steel with high magnetic flux density includes the following steps: 1) smelting and casting, wherein the components of molten steel are: C 0.035-0.065wt%, Si 2.9-4.0wt%, Mn 0.05-0.20wt%, S 0.005-0.012wt%, Als 0.015-0.035wt%, N 0.004-0.009wt%, Sn 0.005-0.090wt%, Nb 0.200-0.800wt%, and balance Fe; 2) hot rolling; 3) normalization; 4) cold rolling; 5) decarburization annealing; 6) coating MgO; 7) high-temperature annealing, wherein the temperature is raised to 700-900 ℃ firstly, and then to 1200 ℃ at a velocity V_{2nd heating} of 9-17 ℃ / hr, and holding for 20 hours; 8) applying insulation coating.

Description

Method for producing high magnetic flux density oriented silicon steel product

The present invention relates to a method of producing oriented silicon steel, and more particularly to a method of producing a high magnetic flux density oriented silicon steel product. Background technique

The production method of the traditional high magnetic flux density oriented silicon steel is as follows: steelmaking by converter (or electric furnace), secondary refining and alloying, continuous casting into slab, the basic chemical composition is: s so / C 0.06~0.10%, Mn 0.03 to 0.1%, S 0.012 to 0.050%, Als 0.02 to 0.05%, N 0.003 to 0.012%, and some component systems further contain one or more of elements such as Cu, Mo, Sb, B, and Bi, and the rest. It is an element of iron and inevitable impurities. The slab is heated to a temperature above 1350 °C in a special high-temperature heating furnace, and is kept for more than 45 minutes, so that the favorable inclusions MnS or A1N are fully dissolved, and then rolled, and the finishing temperature reaches 950 ° C or higher. Quickly spray water to below 500 ° C, then take up. In order to precipitate a small, dispersed second phase particle, ie, an inhibitor, in the silicon steel matrix during the subsequent normalization process; after the hot-rolled plate is normalized, pickling is performed to remove the surface iron oxide scale; cold rolling is performed to roll the sample to the finished product thickness. Decarburization annealing and coating of an annealing separator with MgO as the main component, the [C] in the steel sheet is removed to the extent that it does not affect the magnetic properties of the finished product (generally should be less than 30 ppm); during the high temperature annealing, the steel sheet occurs twice. Recrystallization, formation and purification of magnesium silicate underlayer (removing elements such as S and N in steel which are harmful to magnetic properties), etc., obtaining high magnetic induction oriented silicon steel with high degree of orientation and low iron loss; Insulating coatings and stretch annealing provide oriented silicon steel products in commercial applications.

The disadvantages of the above production methods are: In order to fully dissolve the inhibitor, the heating temperature is up to 1400 ° C, which is the limit level of the conventional furnace. In addition, since the heating temperature is high, the burning is large, the heating furnace needs frequent repair, and the utilization rate is low. At the same time, high energy consumption and large edge cracking of the hot rolled coil make the cold rolling process difficult to produce, the finished product rate is low, the magnetic properties of the finished product are not ideal, and the cost is high.

In view of the above problems, researchers at home and abroad have carried out a large number of studies to reduce the heating temperature of oriented silicon steel. The main improvement trend is divided into two according to the heating temperature range. One is that the slab heating temperature is between 1250 and 1320 °. C, using A1N and Cu inhibitors; the other is the slab heating temperature of 1100 ~ 1250 ° C, mainly using decarburization after nitriding formation inhibitors to obtain inhibition ability. At this stage, the low temperature slab heating technology has developed rapidly. For example, US Patent No. 5,049,205 and Japanese Patent Laid-Open No. 5-112827 use slab heating below 1200 °C for final cold rolling.

80% of the large cold rolling reduction rate, and after continuous denitrification treatment with ammonia gas after decarburization annealing, secondary recrystallized grains with higher orientation are obtained. However, this method can obtain the inhibition ability by using the method of nitriding formation inhibitor after decarburization of the substrate, and it is difficult to overcome the problems of serious oxidation of the surface of the steel strip, difficulty in nitriding and unevenness in the actual control, thereby causing the obtained inhibitor. Difficulties are formed in the steel sheet, and the distribution is uneven, thereby affecting the suppression ability and the uniformity of the secondary recrystallization, resulting in uneven magnetic properties of the final product.

Chinese patent CN 200510110899 describes a new process for slab heating below 1200 ° C, and decarburization annealing of the cold rolled sheet that has been rolled to the finished thickness, but requires strict control of the dew point during the nitriding process. At the same time, new problems of difficulty in decarbonization will be introduced.

Recently, Korean patent KR 2002074312 proposes a method of decarburization and nitriding with slab heating after slab heating below 1200 °C. Although this can solve the problem of post-decarburization difficulty or post-nitriding difficulty, it is still unavoidable. Uneven nitriding causes problems such as uneven magnetic properties and high cost of the product.

Nb element is added to steelmaking. As proposed in Japanese Patent No. JP6025747 and JP6073454, 0.02 to 0.20% of Nb is added to the steelmaking component for the purpose of recrystallizing the hot rolled sheet by forming precipitates such as tantalum carbide and tantalum nitride. The microstructure is refined to improve the grain distribution and aggregate structure of the decarburization annealed sheet, and acts as an auxiliary inhibitor in the high temperature annealing process to suppress the growth of normal grains, thereby improving the magnetic properties of the oriented silicon steel. However, the problem with this patent is that in order to obtain precipitates such as tantalum nitride before hot rolling, high temperature slab heating technology must be employed, which inevitably leads to problems such as large burning loss, high energy consumption, low yield, and high cost.

Nitride added to the MgO release agent, as proposed in Japanese Patent No. 51106622 and U.S. Patent No. 417,1994, the addition of nitrates of Al, Fe, Mg and Zn to the MgO release agent, which are decomposed during high temperature annealing and infiltrated into the plate. nitrogen. However, since the products of decomposition of these nitrides are nitrogen oxides, oxygen, and the like, there is a danger of explosion in actual production.

It is proposed in Japanese Patent No. JP52039520 and U.S. Patent No. 4,010,050 to add a sulfamic acid as a nitriding raw material for pyrolysis. However, as an organic substance, the decomposition temperature of sulfamic acid is low (about 205 ° C), and [N] which is decomposed in actual production is difficult to penetrate into the steel sheet at a low temperature.

Japanese patents JP61096080 and JP62004881 respectively propose to add Mn and Si Nitride to meet nitriding during high temperature annealing. However, this method has a problem in that since the above-mentioned nitride has high thermal stability, its decomposition efficiency is low, and it is necessary to lengthen the annealing time or increase the amount of nitride to satisfy the nitriding requirement.

The control of the temperature rise rate of the high-temperature annealing, as proposed in Japanese Patent No. JP54040227 and JP200119751, can be achieved by lowering the temperature increase rate in the high-temperature annealing process to obtain the high-flux density oriented silicon steel. However, simply lowering the rate of temperature rise will result in a significant drop in production efficiency. Summary of invention

The object of the present invention is to provide a method for producing a high magnetic flux density oriented silicon steel product, which solves the problem of nitriding difficulty in producing high magnetic induction oriented silicon steel by low temperature slab heating technology, and at the same time adopts low temperature heating technology to effectively ensure a series of equipment such as a steelmaking furnace. It is safe, stable and has a long service life. Since the steel sheet is nitrided during the high-temperature annealing process, it can ensure the secondary recrystallization is perfect, and finally obtain a high magnetic flux density oriented silicon steel product with excellent magnetic properties.

The technical solution of the present invention is

By adding a suitable Nb content to the steelmaking, the steel sheet is more susceptible to nitrogen absorption during the high temperature annealing process because the nitrogen content determines whether the magnetic properties of the final finished sheet are up to standard. By adding a nitrogen-containing compound to the MgO release agent, it is applied to the surface of the steel sheet, and is thermally decomposed during the high-temperature annealing process, thereby achieving a uniform purpose of nitriding into the steel sheet. In the high-temperature annealing process, according to the Nb content in the steel, the nitrogen content before the second temperature rise, and the secondary temperature rise temperature, different heating rates are adjusted to ensure the secondary recrystallization is perfect, and finally a high magnetic flux density excellent in magnetic properties is obtained. Oriented silicon steel products.

Specifically, a method for producing a high magnetic flux density oriented silicon steel product of the present invention includes the following steps:

1) Smelting and casting

The weight percentage of the oriented silicon steel composition is: C 0.035-0.065%, Si 2.9-4.0%, Mn 0.05-0.20%, S 0.005-0.012%, Als 0.015-0.035%, N 0.004-0.009%,

Sn 0.005-0.090%, Nb 0.200-0.800%, the rest is Fe and unavoidable inclusions; steel is produced by converter or electric furnace, and molten steel is obtained by secondary refining and continuous casting to obtain slab;

2) Hot rolling

The slab is heated in the heating furnace to 1090~1200 °C, rolling below 1180 °C, finishing at 860 °C or more, laminar cooling after rolling, and coiling below 650 °C; Normalization process: normalizing temperature is 1050~1180. C, time l~20sec, normalization temperature 850-950 V, time 30~200sec; then cooling, cooling rate 10~60 °C/sec;

4) Cold rolling

After normalization, the steel plate is rolled to the thickness of the finished plate, and the cold rolling reduction rate is ≥75% _;

5) Decarburization annealing

Heating rate 15~35 °C/sec, decarburization temperature 800 860 °C, holding temperature 90~160sec; Since nitriding is carried out during high temperature annealing, as long as the decarburization requirement is reached during decarburization annealing, the detachment is simplified Carbon process.

6) MgO coating

The surface of the steel plate is coated with MgO as the main component, 0.1~10% NH ₄ C1 and 0.5~30% P ₃ N ₅ , and the balance is MgO, in weight percentage;

7) High temperature annealing

The temperature is raised once, firstly heated to 700 °C ~ 900 °C, and then heated to 1200 °C twice at the temperature increase rate V, and then kept for 20 hours for purification annealing; wherein, V _ΜΆ = 9 °C / hr~17. C/hr;

8) Insulation coating

An insulating coating is applied on the surface of the high temperature annealed sheet, and a high magnetic flux density oriented silicon steel excellent in magnetic properties is obtained by hot drawing flat annealing. The present invention adds an appropriate amount of Nb to the steelmaking composition. The purpose is to have two points: On the one hand, when Nb is contained in the oriented silicon steel, it is easier to complete the nitriding at high temperature annealing. This is because the electron filling of the sub-dilayer sub-layer of the Nb atom is less saturated with respect to Fe and Mn, so that nitride formation is easier and the nitride is more stable. On the other hand, this part of the nitrogen atoms which are infiltrated during high-temperature annealing can form the main inhibitor A1N necessary for high magnetic flux density oriented silicon steel with Als, and can simultaneously obtain precipitates in the form of Nb ₂ N and NbN. This part of Nb nitride can act as an auxiliary suppression (J, which enhances the effect of suppressing the growth of normal grains, and finally improves the magnetic properties of the oriented silicon steel finished board.

In the present invention, an appropriate amount of NH ₄ C1 and P ₃ N _{5 is} added to the MgO coating liquid. The purpose is to use nitriding in the high temperature annealing process to complete nitriding into the plate, thereby replacing the nitriding by ammonia decomposition during the decarburization annealing process, and the greatest benefit is to ensure more uniform nitriding in the plate. In addition, the two inorganic nitrides, NH ₄ C1 and P ₃ N ₅ , are selected as the nitriding raw material for pyrolysis. Because the decomposition temperature of NH ₄ C1 is 330~340 °C, and the decomposition temperature of P ₃ N ₅ is about 760 °C. Different nitride decomposition temperature regions ensure that the active nitrogen atoms are uniformly released over a long period of time during high-temperature annealing, thereby completing nitriding into the steel sheet and maintaining the nitrogen content [N] at 200-250 ppm. Within the standard range.

The present invention requires control of the secondary heating rate during high temperature annealing. The purpose is to ensure excellent magnetic properties of the final product by setting an appropriate secondary heating rate. This is because the temperature range of secondary recrystallization of oriented silicon steel is covered during the secondary heating of high temperature annealing. Therefore, a suitable heating rate can make the Gaussian grain orientation which grows in the secondary recrystallization process better, the off angle is < 3 °, and the magnetic properties are better.

In the high-temperature annealing process of the present invention, the relatively slow temperature rise ensures the secondary recrystallization is perfect, and the finished product has good magnetic properties. This is because secondary recrystallization occurs during the secondary temperature rise of the high temperature annealing, and this is also the process in which the A1N inhibitor is coarsened and decomposed, and the inhibition force disappears. If it is within this temperature range, if the heating rate is too fast, the secondary recrystallization will not be completed, but the inhibitor will be decomposed and failed, the secondary recrystallization of the finished product is imperfect, and the magnetic deterioration is serious. Detailed description of the invention

The present invention will be further described below in conjunction with the embodiments.

Example 1

The chemical compositions described in Table 1 were smelted and cast. The slabs of different compositions were placed in a heating furnace at 1155 ° C for 1.5 hours and then hot rolled to a hot rolled sheet having a thickness of 2.3 mm. The rolling and finishing temperatures were 1062 ° C and 937 ° C, respectively. A two-stage normalization is applied to the hot rolled sheet: (1120 °C xl 5sec) + (870 °C xl 50sec), followed by cooling at -15 °C/sec. After pickling, it is cold rolled to a thickness of 0.30 mm. Then, decarburization annealing was carried out at a heating rate of 25 ° C/sec, a decarburization temperature of 820 ° C, and an average temperature of 140 s. A separator containing MgO as a main component and containing 4.5% NH ₄ C1 and 15% P ₃ N ₅ was applied. When annealing at a high temperature, the temperature is first raised to 800 ° C to obtain a nitrogen content b before the second temperature rise; the temperature is further raised to 1200 ° C, and then the temperature is maintained for 20 hours for purification annealing. After unwinding, it is coated with an insulating coating and stretched and flattened. Among them, the nitrogen content b before the second temperature rise and the magnetic properties of the finished product are shown in Table 1.

Chemical composition

Real second rise

C Si Mn S Als N Sn Nb B ₈ pre-warming nitrogen

% % % % % % % % TW/kg Example content b (ppm)

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 21 1 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 ratio

More

0.046 3.0 0.08 0.006 0.028 0.008 0.072 0.18 173 1.87 1.1 1 case

1

Than

More

0.053 3.5 0.15 0.01 1 0.019 0.006 0.014 0.84 292 1.86 1.12 Example

2

It can be seen from Table 1 that the selection of the chemical components in the examples conforms to the standard range of [smelting and casting] in the production process, and the selection of the Nb component in the comparative example does not meet the standard range of 0.200-0.800%, so The nitrogen content [N] before the temperature rise is not within the standard range of 200~250ppm, which ultimately leads to poor performance of the iron loss (P _17/5 ) and magnetic induction (B ₈ ) of the oriented silicon steel. Example 2

The composition and weight percentage of the oriented silicon steel slab are C: 0.050%, Si: 3.25%, Mn: 0.15%, S: 0.009%, Als: 0.032%, N: 0.005%, Sn: 0.02%, Nb: 0.5% The rest are Fe and inevitable impurities. The slab was placed in a heating furnace at 1155 ° C for 1.5 hours and then hot rolled to a hot rolled sheet having a thickness of 2.3 mm. The rolling and finishing temperatures were 1080 ° C and 910 ° C, respectively. Two-stage normalization is applied to the hot rolled sheet: (1110 °C x l0sec) + (910 °C x l20sec), followed by cooling at -35 °C / sec. After pickling, it is cold rolled to a thickness of 0.30 mm. Then, decarburization annealing was carried out at a heating rate of 25 ° C / sec, a decarburization temperature of 840 ° C, and an average temperature of 130 s. The coating is mainly composed of MgO, and different contents of NH ₄ C1 and P ₃ N _{5 are added} . When annealing at a high temperature, the temperature is first raised to 800 ° C to obtain a nitrogen content b before the second temperature rise; the temperature is further raised to 1200 ° C, and then the temperature is kept for 20 hours for purification annealing. After unwinding, it is coated with an insulating coating and stretched and flattened. Among them, the nitrogen content b before the second temperature rise and the magnetic properties of the finished product are shown in Table 2.

Table 2 Effect of NH ₄ C1 and P ₃ N ₅ content on nitrogen content and magnetic properties before secondary heating Nitrogen content before secondary heating B8 P17/50 Example Li ₄ C1 (%) P ₃ N ₅ (%)

b (ppm) (T) ( 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 Comparative Example 1 6.4 0.4 178 1.87 1.10

2 2.4 30.2 268 1.88 1.06

3 10.5 30.5 283 1.83 1.16 As can be seen from Table 2, the choice of NH ₄ C1, P ₃ N ₅ in the examples is in accordance with the standard range of [MgO coating] in the production process of the invention, 0.1~10%, 0.5-30%, and Comparative Example NH ₄ C1, P ₃ N ₅ The selection does not meet the requirements, which will cause the nitrogen content before the second temperature rise [N] is not within the 200~250ppm standard, which will eventually lead to the iron loss of the oriented silicon steel finished board (P ₁₇ / ₅ o) and magnetic (B ₈ ) performance is poor. Example 3

The composition and weight percentage of the oriented silicon steel slab are C: 0.050%, Si: 3.25%, Mn: 0.15%, S: 0.009%, Als: 0.032%, N: 0.005%, Sn: 0.02%, Nb content (a ) : 0.2-0.8%, the rest is Fe and unavoidable impurities. The slab was placed in a heating furnace at 1115 ° C for 2.5 hours and then hot rolled to a hot rolled sheet having a thickness of 2.3 mm, and the rolling and finishing temperatures were 1050 and 865 ° C, respectively. The two-stage normalization was applied to the hot rolled sheet: (1120 ° C x 15 sec) + (900 ° C x l20 sec), followed by cooling at -25 ° C / sec. After pickling, it is cold rolled to a thickness of 0.30 mm. Then, decarburization annealing was carried out at a heating rate of 25 ° C / sec, a decarburization temperature of 850 ° C, and an average temperature of 115 s. The coating was mainly composed of MgO, and 7.5% NH ₄ C1 and 12.5% P ₃ N _{5 were added} . During the high-temperature annealing process, the temperature is first raised to 700 ° C to 900 ° C, as the initial temperature (c) of the second temperature rise, and the nitrogen content before the second temperature rise (b) is obtained. Then heat up to 1200 with a certain secondary heating rate (V) . C, and then heat-treating for 20 hours for purification annealing. After unwinding, it is coated with an insulating coating and stretched and flattened.

Table 3 Effect of different normalization and nitriding processes on magnetic properties of finished products

As can be seen from Table 3:

In the examples and the comparative examples, the Nb content (a), the pre-heating pre-nitrogen content (b), and the secondary heating initiation temperature (c) are the same; the actual secondary heating rate in the embodiment is 9 °C/hr 17 °C/hr, and the difference between the theoretical value and the actual value is positive, the magnetic properties of the finished product are better; However, the comparative example is reversed, so the magnetic properties of the finished board are poor. The high magnetic induction oriented silicon steel produced by the low temperature slab heating technology has the advantages of long life of the heating furnace, low energy consumption and low cost. However, for a long time, there are problems such as uneven decarburization and nitriding in the post-process and difficulty in effective adjustment and control in the production process, which affects the local or overall inhibition ability in the substrate, resulting in imperfect secondary recrystallization, product magnetic properties. Can be unstable.

In summary, the present invention is a novel high magnetic flux density oriented silicon steel production method based on a low temperature slab heating process, which effectively solves the above problems. It is characterized in that by adding a suitable Nb content in the steel making, the steel sheet is more likely to absorb nitrogen during the high-temperature annealing process; by adding a nitrogen-containing compound to the MgO separating agent, it is thermally decomposed during the high-temperature annealing process to reach the steel sheet. The purpose of uniform nitriding. In the high-temperature annealing process, the temperature rise rate is controlled according to the Nb content, the nitrogen content, and the secondary temperature rise temperature in the steel, thereby ensuring the secondary recrystallization is completed, and finally obtaining a high magnetic flux density oriented silicon steel product excellent in magnetic properties.

Claims

The method for producing a high magnetic flux density oriented silicon steel product includes the following steps:

1) Smelting and casting

The weight percentage of the oriented silicon steel composition is: C 0.035-0.065%, Si 2.9-4.0%, Mn 0.05-0.20%, S 0.005-0.012%, Als 0.015-0.035%, N 0.004-0.009%, Sn 0.005-0.090%, Nb 0.200-0.800%, the rest is Fe and inevitable inclusions; steel is produced by converter or electric furnace, and molten steel is obtained by secondary refining and continuous casting to obtain slab;

2) Hot rolling

The slab is heated in a heating furnace to 1090~1200 °C, rolled below 1180 °C, rolled up at 860 °C, laminar cooling after rolling, and coiled below 650 °C;

3) Normalization

Normalization process: normalizing temperature 1050~1180. C, time l~20sec, normalization temperature 850-950 V, time 30~200sec; then cooling, cooling rate 10~60 °C/sec;

4) Cold rolling

5) Decarburization annealing

Heating rate 15~35 °C/sec, decarburization temperature 800 860 °C, holding temperature 90~160sec;

6) MgO coating

7) High temperature annealing

8) Insulation coating

An insulating coating is applied on the surface of the high temperature annealed sheet, and subjected to hot drawing and flat annealing to obtain a magnetic high-strength magnetic flux-oriented silicon steel.