JPH06299245A - Production of grain-oriented silicon steel sheet having uniform high magnetic flux density in longitudinal direction of coil - Google Patents

Abstract

PURPOSE:To produce a grain-oriented silicon steel sheet having a uniform and stable high magnetic flux density in the longitudinal direction of a coil by holding coarse hot rolled stock having a specified compsn. constituted of C, Si, Mn, S, Se, Al, N and Fe to a prescribed temp. and continuously executing finish rolling and cold rolling. CONSTITUTION:A cast slab contg., by weight, <=0.095% C, <=7.0%. Si, 0.03 to 0.16% Mn, 0.005 to 0.032% S and/or Se, 0.008 to O.052% acid soluble Al and 0.003 to 0.010% N, and the balance Fe with inevitable impurities is heated and is subjected to rough rolling, and this roughly hot rolled stock is coiled as hot-rolled. The roughly hot rolled stock is held to a temp. at which AlN is not substantially precipitated or above and is successively swept out at >=1.90 deg.C, and the heel of the preceding stock is joined with the tip of the succeeding stock. Next, the coarse hot rolled stock is continuously subjected to finish hot rolling to regulate its sheet thickness into <=1.7mm. At this time, the finish inlet temp. is preferably regulated to a desired temp. + or -20 deg.C over the whole length of the coil. After that, the hot rolled stock is subjected to rolling for one time or two times including process annealing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a unidirectional electrical steel sheet having a high magnetic flux density, which is used as a soft magnetic material for an iron core of an electric device, in the longitudinal direction of the coil with uniform characteristics.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet has a Miller index (11
0) It is composed of crystal grains having an orientation that can be expressed as <001>, and the <100> direction, which is the easy axis of magnetization, is arranged parallel to the rolling direction. Therefore, the unidirectional electrical steel sheet has excellent magnetization characteristics in the rolling direction. Such a specific orientation is a so-called secondary crystal in which primary crystal grains having a (100) <001> orientation are selectively grown by high-temperature annealing a steel sheet having a final thickness by hot rolling, annealing and cold rolling. Obtained by recrystallization. The unidirectional electrical steel sheet is mainly used as a soft magnetic material for transformers or generator iron cores, and has magnetism characteristics (relationship between magnetic field strength and magnetic flux density) and iron loss characteristics (magnetic flux density). And the iron loss) must be good.

The quality of the magnetization characteristics is determined by the magnitude of the magnetic flux density (generally indicated by the value of B _8. Tesla) induced in the iron core with respect to a constant magnetic field applied. Iron loss (displayed as the value of W _17/50. Watt / kg) is the power loss consumed as heat energy in the iron core when a predetermined AC magnetic field is applied to the iron core, and its value is small. Is desired. For the quality of iron loss, the thickness, resistivity, impurities,
The residual strain has an influence, but the magnetization characteristic (B ₈ ) also has a great influence. From the above, improving the magnetization characteristics enables downsizing of the electric device and energy saving by reducing iron loss.

As a method for producing a high magnetic flux density unidirectional electrical steel sheet, a method by Satoru Taguchi et al. Is disclosed in Japanese Examined Patent Publication No. 40-15644. In order to obtain a stable product by this method, the hot rolling conditions disclosed in JP-A-48-51852, which is an invention of Sakakura Akira, are important. That is, in order to stably perform the secondary recrystallization, it is necessary to shorten the residence time of the material in the AlN precipitation region during hot rolling based on the idea that AlN is not precipitated in an excessively large size.
It is necessary to cool rapidly from the 1N precipitation temperature or higher. If this condition is not satisfied, secondary recrystallization defects (called fine grains) will occur.

A specific method for carrying out the hot rolling condition of such an idea by a generally used continuous hot rolling machine is as follows. After heating a 150-300 mm thick slab produced by continuous casting or slabbing, 30
It is hot-rolled to an intermediate thickness of -60 mm and then hot-rolled to a final plate thickness by a continuous finishing hot rolling machine. Recently, continuous casting is performed directly to a thickness of 30 to 60 mm without performing rough hot rolling, and then heated to a high temperature, or by utilizing the sensible heat of the slab without heating, the final finishing hot rolling machine is used. It may be hot rolled to thickness.

The temperature history of the steel sheet during hot rolling for achieving an appropriate AlN precipitation state in accordance with such an actual hot rolling method is as follows. At the intermediate thickness stage (usually 30 to 60 mm) before entering the continuous finishing hot rolling machine, cooling efficiency is poor when trying to cool to below the precipitation temperature of AlN, and the temperature of the surface portion and the center portion is large due to the thick plate thickness. Since the difference becomes large, the existing state of AlN differs in the plate thickness direction and is not appropriate. Further, when cooling is performed in the intermediate thickness stage, the deformation resistance of the steel material increases due to the decrease in the steel plate temperature, and the processing power required for the continuous finishing hot rolling machine increases, which is not economical.

On the other hand, a method of maintaining the temperature higher than the precipitation region of AlN up to the intermediate thickness stage and quenching when entering the continuous finishing hot rolling machine when the plate thickness becomes thin is It is desirable because it makes AlN uniform in the thickness direction and reduces the power required for the continuous finishing hot rolling machine. Based on the above idea, in order to control the AlN of the hot rolled sheet to an appropriate state, it is adopted to set the temperature before entering the continuous finishing hot rolling machine to a predetermined temperature or higher.

By the way, recently, there is a tendency to increase the unit weight of the coil in order to improve the production efficiency and improve the yield.
The rolling time for finishing hot rolling per coil becomes longer,
Since the crude hot-rolled material before the final hot-rolling will stay, the temperature of the coil tail portion will drop, and secondary recrystallization failure may occur. Alternatively, although secondary recrystallization occurs, since the AlN precipitation state in the coil longitudinal direction is different, there arises a problem that the magnetic flux density of the obtained product is not uniform in the coil longitudinal direction. It is conceivable to raise the temperature of the entire coil in order to prevent the deterioration of the magnetic characteristics due to the temperature decrease of the coil tail portion.

In this case, there is a problem that the heating energy is increased, or equipment measures for increasing the slab heating more than the present are required. In addition, when the temperature of the entire coil is increased, a secondary recrystallization defect portion (called a line mixture) elongated in the rolling direction may occur in the head portion having a high continuous hot rolling temperature. This wire mixing occurs remarkably when a continuous cast slab is used, but it also occurs in other low C and high Si steel materials.

This line mixing is likely to occur when the hot rolling temperature is high and recrystallization is difficult during hot rolling, as shown in Japanese Patent Laid-Open No. 54-120214. The temperature at which recrystallization is most likely is around 1100 ° C., which is almost the same as the precipitation temperature range of AlN, and it is very difficult to satisfy both recrystallization and precipitation control at the same time. In particular, if the unit weight of the coil is increased to increase the production efficiency, the temperature difference between the head and the tail becomes large, and the problem becomes more serious.

Due to this difference, when the secondary recrystallized state is different, the magnetic characteristics vary. Generally, according to JIS, the grain size of grain-oriented electrical steel sheets is determined by the iron loss value in the magnetic characteristics, so if the iron loss varies within one coil, the magnetic characteristics over the entire length were evaluated. After that, it is necessary to divide the coil into products according to the grade. By this work, the product becomes a small coil and the inventory increases, and problems such as the addition of the work amount occur. To solve this problem, Japanese Patent Publication No. 62-1458
As disclosed in JP-A-57-165102, a method of changing the cooling rate at the time of annealing a hot-rolled sheet between the head and the tail is adopted. There is a method of heating or keeping the temperature.

[0012]

DISCLOSURE OF THE INVENTION The present invention eliminates fluctuations between recrystallization in the coil longitudinal direction during hot rolling and precipitation of AlN, and allows secondary recrystallization to be performed uniformly, so that it is uniform and stable in the coil longitudinal direction. The present invention provides a method for producing the high magnetic flux density unidirectional electrical steel sheet.

[0013]

[Means for Solving the Problems] The gist of the invention is as follows. C: 0.095% or less by weight ratio,
Si: 7.0% or less, Mn: 0.03 to 0.16%, S
And Se alone or in combination: 0.005-0.03
2%, oxidizable Al: 0.008 to 0.052%, N:
A casting slab containing 0.003 to 0.010%, balance: Fe and unavoidable impurities is heated and rough hot rolled, and the rough hot rolled material is wound in a hot state, and the rough hot rolled material is substantially AlN. After the temperature is kept above the temperature at which it does not precipitate, the material is sequentially discharged, the leading end of the trailing material is joined to the trailing end of the preceding material, and the rough hot-rolled material is continuously hot-rolled to form a hot-rolled sheet. A method for producing a grain-oriented electrical steel sheet having a uniform high magnetic flux density in the longitudinal direction of a coil, characterized by performing two rolling cycles with rolling or intermediate annealing.

The present invention will be described in detail below. The present inventors first investigated the relationship between the continuous finish hot rolling inlet temperature and the magnetic flux density that most corresponds to the secondary recrystallization state in the magnetic properties. About 0.056% C, 3.20% S as a component
i, 0.070% Mn, 0.023% S, 0.029%
A 15 ton continuous cast slab containing acid-soluble Al and 0.0078% N was 40 mm thick by 3-pass rough hot rolling, 2.3 mm hot rolling by continuous finishing, and was annealed at 1120 ° C for 2 min, followed by rapid cooling. Then, it is rolled to 0.30 mm, decarburized and annealed at 830 ° C., and an annealing and separating agent containing MgO as a main component is applied.
FIG. 1 shows the relationship between the magnetic flux density (B ₈ ) and the continuous finish hot rolling inlet temperature of the product that was annealed at 200 ° C. for 20 hours at high temperature.

As can be seen from this figure, B ₈ is extremely lowered when the temperature is too low or too high. If this is low, the AlN inconvenience disclosed in JP-A-48-51852 is caused,
That is, the secondary recrystallization defect due to excessive precipitation of AlN is caused, and the low case is caused by the linear secondary recrystallization defect disclosed in JP-A-54-120214. It was also found that the higher the temperature, the better the B ₈ within that limit temperature.
In particular, the temperature continuously decreases from the front end to the rear end of the hot-rolled coil, and there is an average temperature difference of about 90 ° C between the head and the tail, so that the inside of one coil (corresponding to the product) Will change the magnetic properties.

The present inventors have confirmed that this change in B ₈ also corresponds to the iron loss (W _17/50 ) and corresponds to W _17/50 of about 0.025 w / kg at _0.1T . From such knowledge,
The present inventors have succeeded in manufacturing a coil having a constant magnetic characteristic by eliminating a change in magnetic characteristic in the coil by a new method. The embodiment will be described.

First, the reasons for limiting the steel components will be described. In the present invention, the molten steel may be produced by any method such as a converter or an electric furnace, but its content must be within the following range. If C is too much, the decarburization annealing time becomes long and it is not economical, so the content is made 0.095% or less. When the amount of C is too small, the magnetic properties tend to deteriorate, but it is not limited because it is not related to the method of obtaining the uniform properties which is the object of the present invention.

When Si is increased, the iron loss is improved, which is desirable. On the other hand, when the nonferrous component is increased, the magnetic flux density is deteriorated. Therefore, the amount of Si depends on whether the product requires the iron loss or the magnetic flux density. Just decide. However, 7.0
If it exceeds 0.1%, cracking is likely to occur in the cold rolling process in the middle, and neither iron loss nor magnetic flux density is improved as characteristics, so 7.0% or less is the limiting condition.

In the present invention, MnS or MnSe and its composite and AlN are used as precipitates necessary for secondary recrystallization. Therefore, in order to secure the necessary minimum MnS or MnSe, Mn is 0.03% or more, S or Se.
Is 0.005% or more, acid-soluble Al is 0.008% or more, and N is 0.003% or more. On the other hand, if the amount of these precipitation constituents is too large, solution treatment becomes insufficient during slab heating, and secondary recrystallization failure occurs. As its limit, M
n is 0.16%, S or Se is 0.032%, and oxide-soluble Al is 0.052%.

If N exceeds 0.010%, blisters on the surface of the steel sheet called blister occur. The balance is Fe
And unavoidable impurities. The molten steel containing the above components is cast, then heated, roughly hot rolled, and wound in a high temperature state.
The greatest feature of the present invention lies in this step. That is, after the finish hot rolling, the crude hot rolled material is once wound around a coil in a state where the plate thickness is large and the temperature is high, and the temperature is made uniform throughout. It is to finish hot rolling after homogenizing.

Next, the rough material wound in this coil state is finish hot-rolled while being unwound one by one. The second characteristic of the present invention is that the first rough hot-rolled material has a trailing end. The purpose is to join the tips of the crude hot rolled materials. In this way, by making the crude hot-rolled material continuous, it is possible to perform the finish hot-rolling at a constant speed, and the temperature of the crude hot-rolled material is constant, and the temperature is uniform over the entire length of the coil. Then, the state of AlN as an inhibitor becomes constant.

In particular, when the thickness of the hot-rolled sheet becomes thin, the temperature generally decreases toward the rear end in one coil as the finish hot-rolling progresses, and the AlN state becomes non-uniform. By controlling the AlN of the secondary recrystallization hot rolled sheet to a constant state by the method, a constant secondary recrystallization state can be maintained even if the product coil has a higher unit weight than ever before, and the magnetic characteristics are stable. To do. The hot-rolled sheet which has been finished hot-rolled is cut into a predetermined length and wound into a coil.

In particular, when the product sheet thickness is to be reduced in order to improve the iron loss, the hot-rolled sheet thickness becomes thin because the optimum cold rolling rate for secondary recrystallization is determined. The present invention is extremely effective. With a product sheet thickness of 0.23 mm, a hot-rolled sheet thickness of about 1.7 mm, which gives a cold rolling rate of about 87%, is suitable, but with this sheet thickness or less, the finish inlet temperature drops significantly, and the application effect of the present invention is It's a lot.

When the finish inlet temperature is set in the range of 20 ° C. above and below the entire coil, B ₈ is 0.
Since 02T, W _17/50 is within 0.04w / kg and falls within the JIS standard 1 grade, even if the coil is large, certain magnetic characteristics according to the hot rolling temperature can be obtained and the iron loss Since there is no grade difference, the product can be stably shipped as a large single-weight coil, for example, 13 tons or more, without splitting the coil.

By the way, under the condition that the rough hot-rolled material is hot-wound, it is essential that AlN is not precipitated at this stage. However, for precipitation of AlN, C, Si, Al,
Since N influences, a temperature not lower than 1090 ° C. is desirable in the range of the component of the present invention. Then, as for time, if it is above this temperature, it is a substantial rolling time range 10
There is no problem if it is less than min.

The hot-rolled sheet obtained under the above conditions is processed into a product by the usual method of combining rolling or annealing once or twice for producing a grain-oriented electrical steel sheet. In the present invention,
Since AlN is used as an inhibitor, it is most effective to apply it to the method of Japanese Patent Publication No. 40-15644, which is based on a high final cold rolling rate. Therefore, an embodiment of this method will be described as an example.

The hot rolled sheet is annealed at 900 to 1150 ° C. for about 2 minutes and then rapidly cooled. This hot-rolled sheet annealing increases the magnetic flux density of the secondary recrystallized sheet. Next, the final plate thickness is made at a rolling rate of 80% or more. If the thickness of the final product is reduced, the required thickness of the hot-rolled sheet is also reduced, which causes a problem that the rolling load in hot rolling increases and the shape of the sheet thickness becomes defective.

Therefore, depending on the performance of the hot rolling equipment, there is also adopted a method in which a thick hot rolled sheet is put up, cold rolling of about 35% is carried out on the hot rolled sheet, and then the above-mentioned annealing and final cold rolling are carried out. These cold-rolled sheets are decarburized and annealed at about 850 ° C. within about 5 minutes, and then MgO, which prevents seizure between the sheets,
A separating material such as Al ₂ O ₃ is applied to form a coil. Then, high temperature annealing for the purpose of purification and secondary recrystallization is performed at a temperature of about 1200 ° C. for 5 hours or more. Thereafter, it is usually surface-coated into a product.

[0029]

【Example】

(Example 1) 0.058% C, 2.85% Si, 0.0
7% Mn, 0.024% S, 0.027% acid soluble A
1, 250 ton thickness, 13 ton cast slab containing 0.007% N was heated to 1400 ° C, then rough hot rolled to 35mm thickness, rolled up at 1190 ° C, and sequentially dispensed, finishing inlet temperature was 1170 ° C 1. Start hot rolling at a constant speed, 2.
Finished to a thickness of 3 mm. On the other hand, the leading end of the trailing material was joined to the trailing end of this leading material in the running state at the front position of the finishing hot rolling, and the succeeding material was continuously hot rolled for finishing after the preceding material.

The finishing inlet temperature of this succeeding material is 116 at the head.
The temperature was 0 ° C., and the temperature continuously decreased thereafter, but it was 1152 ° C. even in the bottom part having the lowest temperature. After the final hot rolling, the joint was cut before winding, to obtain a 13 ton coil. The hot rolled sheet of the following material was annealed at 1120 ° C. for 2 minutes, cold rolled to a thickness of 0.30 mm, decarburized and annealed at 850 ° C. for 150 seconds, and MgO was applied as an annealing separator.
The product was annealed at 00 ° C. for 20 hours at high temperature and an insulating coating was applied. In addition, in a continuous line for performing this insulation coating, iron loss was continuously measured in a running state.

[0031] In the magnetic properties are Epstein measurement at this time, the head _{... B 8 = 1.93T, W 17/50} = 1.02w / kg buttocks _{... B 8 = 1.93T, W 17/50} = 1.03w / kg, and the iron loss between both ends showed a constant value. Thus, the 13 ton coil showed extremely uniform magnetic characteristics over the entire length.

Example 2 As a comparative example, the same cast slab as in Example 1 was heated to 1400 ° C., and then rough hot rolled to a thickness of 35 mm and finish hot rolled to a hot rolled sheet having a thickness of 1.6 mm. At this time, the finish inlet temperature was 1150 ° C. at the head, the temperature continuously decreased as the rolling proceeded, and was 1064 ° C. at the tail. Next, as an example of the present invention, the above slab is roughly hot rolled to a thickness of 35 mm, wound at 1178 ° C., and sequentially dispensed, finishing hot rolling is started at a constant speed at a finishing inlet temperature of 1153 ° C., and a thickness of 1.6 mm is obtained. Finished

On the other hand, the leading end of the trailing material is joined to the trailing end of the preceding material in the running state at the front surface of the finishing hot rolling, and the trailing material is continuously hot rolled to finish the running material. .6 mm
Made thick The finish inlet temperature of this succeeding material is 1151 at the head.
C., and the temperature dropped continuously thereafter, but it was 1139 ° C. even in the bottom part having the lowest temperature. After the final hot rolling, the joint was cut before winding, to obtain a 13 ton coil.

This succeeding material and the comparative hot rolled material were heated at 1100 ° C. for 2 hours.
After annealing for min, cold-roll to 0.18 mm thickness and
Decarburization annealing was performed for 0 sec, MgO was applied as an annealing separating material, high temperature annealing was performed at 1200 ° C. for 20 hours, and an insulating coating was applied to obtain a product. In the annealing line for this insulating coating, the iron loss was continuously measured while running.

The magnetic characteristics at this time are measured by Epstein,
The comparative material has a head: B ₈ = 1.91T, W _17/50 = 0.80w / kg, buttocks B ₈ = 1.72T, W _17/50 = extremely large due to secondary recrystallization failure. , The iron loss between both ends was continuously changing. Therefore, there was no choice but to cut from the head according to the iron loss level to form a small coil. On the other hand, the material of the present invention has a head portion ... B ₈ = 1.91 T, W _17/50 = 0.80 w / kg, and a bottom portion ... B ₈ = 1.91 T, W _17/50 = 0.82 w / kg. The iron loss between both ends was almost constant, and a 13 ton coil was evaluated as one product.

(Example 3) 0.060% C, 3.15%
Si, 0.07% Mn, 0.025% S, 0.030%
Acid-soluble Al, 250 mm thickness containing 0.008% N,
After heating a 13 ton cast slab to 1400 ° C, rough hot rolling to a thickness of 35 mm, winding at 1140 ° C, homogenizing the temperature of the rough bar using an auxiliary heating device, and then sequentially paying it out,
When the finishing inlet temperature was 1173 ° C., hot rolling for finishing was started at a constant rate to finish to a thickness of 2.3 mm. On the other hand, the leading end of the trailing material was joined to the trailing end of the preceding material in the running state at the front surface of the finish hot rolling, and the trailing material was continuously hot rolled after the leading material.

The finish inlet temperature of the trailing material is 116 at the head.
The temperature was 8 ° C., and the temperature dropped continuously thereafter, but it was 1160 ° C. even in the bottom part having the lowest temperature. After the finish hot rolling, it was cut at the joint portion before winding, to obtain a 13 ton coil. The hot rolled sheet of the succeeding material is cold rolled to a thickness of 1.6 mm,
Anneal for 2 min at 00 ℃, cold-roll to 0.18 mm thickness, and
Decarburization annealing was performed at 30 ° C. for 120 seconds, MgO was applied as an annealing separating material, high temperature annealing was performed at 1200 ° C. for 20 hours, and an insulating coating was applied to obtain a product. In addition, in a continuous line for performing this insulation coating, iron loss was continuously measured in a running state.

[0038] In the magnetic properties are Epstein measurement at this time, the head _{... B 8 = 1.93T, W 17/50} = 0.77w / kg buttocks _{... B 8 = 1.92T, W 17/50} = 0. It was 79 w / kg, and the iron loss between both ends showed a constant value. This coil was evaluated as a single product with 13 tons.

[0039]

According to the present invention, since uniform magnetism is obtained in the longitudinal direction of the coil, quality control and inventory control are easy, and a large unit weight product can be secured.

[Brief description of drawings]

FIG. 1 is a chart showing the influence of a finish hot rolling inlet temperature on a magnetic flux density.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shigeru Nishibayashi 20-1 Shintomi, Futtsu-shi Nippon Steel Co., Ltd. Technology Development Division (72) Inventor Kiyoshi Ueno 20-1 Shintomi, Futtsu-shi Nippon Steel Co., Ltd. Technology Development Division

Claims (4)

[Claims] 1. A weight ratio of C: 0.095% or less, Si: 7.0% or less, Mn: 0.03 to 0.16%, S and Se alone or in combination: 0.005 to 0. .0
32%, Oxide-soluble Al: 0.008 to 0.052%, N: 0.003 to 0.010%, balance: Fe, and a cast slab containing inevitable impurities are heated and rough hot rolled, and the rough hot rolled. The material is wound in the hot state, and the hot rolled material is maintained at a temperature above which AlN does not substantially precipitate,
After that, it is sequentially paid out, and after joining the leading end of the following material to the trailing end of the preceding material, the rough hot-rolled material is continuously finish hot-rolled to form a hot-rolled sheet, and ordinary single rolling or intermediate annealing is performed. A method for producing a grain-oriented electrical steel sheet having a uniform high magnetic flux density in the longitudinal direction of a coil, which comprises rolling twice. 2. The method according to claim 1, wherein the finish hot rolling is performed over the entire length of the coil so that the finish inlet temperature is within a range of 20 ° C. above and below the desired temperature. 3. The method according to claim 1 or 2, wherein the plate thickness after the finish hot rolling is 1.7 mm or less. 4. The crude hot-rolled material is wound as it is, 109
The method according to any one of claims 1, 2 and 3, wherein the material is discharged at a temperature of 0 ° C or higher, and the leading end of the trailing material is joined to the trailing end of the preceding material.