JP2002348613A - Manufacturing method of grain-oriented electrical steel sheet with excellent punchability that does not require decarburization annealing - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a method for producing a grain-oriented electrical steel sheet having good magnetic properties and punching properties without requiring decarburization annealing. SOLUTION: By mass, C ≦ 0.005%, Si: 2.5-4.5%, acid-soluble Al: 0.020-0.040%, N: 0.0030-0.010%, 0.003% ≦
(S + 0.405Se) ≦ 0.014%, Mn: A slab containing 0.05 to 0.14% is heated to a temperature range of less than 1280 ° C., hot-rolled, and subjected to hot-rolled sheet annealing or not, and to 85% or more. The final cold rolling of the rolling reduction, primary recrystallization annealing without decarburization, Mg
When applying an annealing separator mainly containing O and performing finish annealing, the hot finish rolling start temperature is set to more than 975 ° C., and the rolling reduction R2 of the finishing final stand, and the rolling reduction R1 immediately before, the following: Either is satisfied, and the total oxide mass of the steel sheet after the secondary recrystallization is less than 2.0 g / m ² . When 0.3 ≦ R1,
When 0.1 <R2 (condition 1) and 0.3 ≦ R2, 0.1 <R1 (condition 2).

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 grain-oriented electrical steel sheet which is used as an iron core of a transformer or the like, and is particularly excellent in punching property.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet is mainly used as an iron core material for transformers and other electric equipment, and has magnetic properties,
It is required to have excellent magnetic properties such as iron loss properties.
A grain-oriented electrical steel sheet is manufactured by generating secondary recrystallization in the final finish annealing step, and developing a so-called Goss structure having a {110} plane on the steel sheet surface and a <001> axis in the rolling direction. . In order to obtain a grain-oriented electrical steel sheet having good magnetic properties, the axis of easy magnetization is <001.
> It is necessary to align the shaft highly in the rolling direction.

[0003] Taguchi et al. Discloses a technique for producing a grain-oriented electrical steel sheet having a high magnetic flux density, as disclosed in Japanese Patent Publication No. 40-15644, or by Imanaka et al. There is a technique disclosed in Japanese Unexamined Patent Publication (Kokai) No. H11-26095. In the former, AlN and MnS function as main inhibitors, and in the latter, MnS, MnSe, and Sb function as main inhibitors. In each of these techniques, MnS is used as an inhibitor. However, in order to completely dissolve the amount of MnS required to function as an inhibitor during secondary recrystallization, the slab is heated to a high temperature of about 1400 ° C. in hot rolling. Must be heated. The heating temperature of the slab is 200 ° C. or more higher than the heating temperature of the ordinary steel slab, which leads to an increase in equipment and energy costs. There is a problem that linear secondary recrystallization failure due to coarsening of crystal grains during heating is likely to occur.

[0004] With respect to the above-mentioned technology, Japanese Patent Laid-Open Publication No.
No. 6522, Mn is set to 0.08 to 0.45.
%, S is set to 0.007% or less, and a method of manufacturing a grain-oriented silicon steel sheet that enables low-temperature slab heating by not using MnS as an inhibitor has been proposed. By the way, in the manufacture of the conventional industrialized grain-oriented electrical steel sheet, it is essential to contain more than 0.04% by mass of carbon in the manufacturing process even when any of the above inhibitors is used. Normal grain-oriented electrical steel containing about 3 to 4% of Si together with C undergoes γ-α transformation in the process of receiving the heat history from casting to hot rolling. Is considered to be effective in stably generating secondary recrystallization of a product plate.

On the other hand, in products, C must be reduced to 0.0050% or less in order to ensure non-magnetic aging, and thus decarburization annealing is essential. The decarburizing annealing is usually performed at about 800 to 900 ° C. in a wet hydrogen-containing atmosphere. The annealing time required for decarburization is determined by the amount of carbon in the steel and the degree of oxidation of the atmosphere (P _H2O / P _H2 ), and is further proportional to the square of the thickness of the steel sheet. Further, since the grain-oriented electrical steel sheet contains about 3% of Si, in a decarburizing annealing atmosphere, decarburization becomes more difficult due to oxidation of the surface layer.

[0006] In particular, the grain-oriented electrical steel sheet used for large-sized rotating equipment is used as a higher-grade grade of high-grade non-oriented electrical steel sheet. That the properties are good,
There is a demand for a thick plate that can be easily laminated. However, in the production of a grain-oriented electrical steel sheet having a product thickness of more than 0.35 mm, it is necessary to perform decarburizing annealing twice or more with pickling or an extremely long decarburizing annealing, which is very costly. Was not realistic.

In particular, in the production of a grain-oriented electrical steel sheet using low-temperature slab heating for forming an inhibitor in an acquired manner, in order to control the primary recrystallized grain size within a certain range, it is necessary to change the annealing temperature according to the components. It must be controlled in conjunction with decarburization and formation of the surface oxide layer, and actual operation requires great care and monitoring. Further, when decarburization annealing is performed, silicon oxide (silica) is inevitably generated on the steel sheet surface. In this case, if MgO is used as an annealing separator during the secondary recrystallization annealing, a glass film containing forsterite as a main component is formed on the steel sheet after the secondary recrystallization annealing by a reaction between silica and MgO. Although this glass film is effective as an insulating film, it is very hard and has poor punching properties in a punching step in the production of an iron core. Therefore, a unidirectional electrical steel sheet without a glass film has been required.

As a method for solving this, 1) The thickness of the oxide layer after decarburizing annealing is set to 3 μm or less, and M is used as an annealing separator.
a method mainly using fine-grained Al ₂ O ₃ instead of gO (JP-A-53-22113, JP-A-56-6983, and JP-A-59-96278); 2) Mainly MgO A method in which chloride, nitrate, or the like such as Li, K, Na, Ba, or Ca is added to an annealing separator to destroy once formed forsterite during secondary recrystallization annealing (Japanese Patent Laid-Open No. 5-3).
No. 11353), 3) A method of forcibly removing the glass film by pickling the unidirectional electrical steel sheet after the secondary recrystallization manufactured by a usual method ("Punching quality of a conventional unidirectional electrical steel sheet"). And 4) a method of removing silica once formed by pickling after decarburizing annealing.

However, in these methods, the application of Al ₂ O ₃ is difficult in 1), the additives are expensive in 2), and the equipment is damaged by vaporization during secondary recrystallization annealing, so that the content is low. In 3) and 4), it is necessary to add a pickling step, and there is a disadvantage that the cost is high. In addition, a number of techniques have already been disclosed as to a method for producing a grain-oriented electrical steel sheet without performing decarburization annealing. JP-A-55-73818 discloses that C is 0.0
Disclosed is a method of performing ordinary box annealing or open coil annealing after omitting decarburizing annealing after setting the final sheet thickness by a double cold rolling method of 2% and a first cold rolling reduction of 50% or more. are doing. However, in this method, since the primary recrystallization and the secondary recrystallization are annealed in the form of a coil, the influence of the temperature deviation due to the coil position is large, and it is difficult to implement industrially.

Japanese Unexamined Patent Publication (Kokai) No. 57-114614 discloses that an Al-containing unidirectional silicon steel sheet slab is subjected to rough rolling at a low temperature of 1250 ° C. or less, and a cumulative rolling reduction of 8 at 900 ° C. or more.
0% or more and at least one pass 35% or more and 900
A method is disclosed in which strain accumulation rolling at a cumulative reduction rate of 40% or more is performed at a temperature of not more than 40 ° C. to omit low-temperature slab heating and decarburizing annealing. However, in such hot rolling, 9
Under a high pressure in a low temperature range of 00 ° C. or less, the texture state is considered to be different, and the magnetic flux density B8 of the product is 1.90.
Below and low.

[0011] Further, in JP-A-6-346147 and JP-A-7-26328, Cu: 0.05-2.
A method of adding 00% or Sb: 0.010 to 0.100% as an inhibitor component is disclosed, but a satisfactory result has not been obtained.

[0012]

SUMMARY OF THE INVENTION The present invention is based on the premise that low-temperature slab heating is performed, so that the C content in molten steel is reduced to the extent that decarburization annealing is not required, and a raw material for forming a glass film containing forsterite as a main component. An object of the present invention is to provide a method capable of stably producing a grain-oriented electrical steel sheet having excellent magnetic properties and punching properties by not forming silica, which is a decarburization anneal, by omitting decarburization annealing.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and the gist thereof is as follows. (1) In mass%, C ≦ 0.005%, Si: 2.5 to 4.5%, acid-soluble Al: 0.020 to
0.040%, N: 0.0030 to 0.010%, 0.1%
003% ≦ (S + 0.405Se) ≦ 0.014%, M
n: a slab containing 0.05 to 0.14%, the balance being Fe and unavoidable impurities, heated to a temperature range of less than 1280 ° C., hot-rolled, and subjected to hot rolled sheet annealing or not, Manufacture of unidirectional electrical steel sheet which is subjected to primary recrystallization annealing without decarburization, applied with an annealing separator, and then subjected to finish annealing after final cold rolling to a final thickness of 85% or more and applying a reduction ratio of 85% or more. In the method, the starting temperature of the finish rolling in the hot rolling is set at more than 975 ° C., and the rolling reduction R2 of the finishing final stand of the finish rolling and the rolling reduction R1 immediately before the final stand are defined as the following conditions 1,
A method for producing a grain-oriented electrical steel sheet having excellent punchability and not requiring decarburization annealing, characterized by satisfying any one of the conditions 2.

When 0.3 ≦ R1, 0.1 <R2 (Condition 1) When 0.3 ≦ R2, 0.1 <R1 (Condition 2) However, R1 = (t _f2 −t _f1 ) / t _f2 R2 = (t _f1 −t _f ) / t _f1 t _f : Finished thickness (mm) t _f1 : Finished thickness of the final tund entrance (mm) t _f2 : Immediately before the finished final stand Entrance thickness (m
m) (2) The reduction ratio R2 of the final stand in the finish rolling of the hot rolling and the reduction ratio R1 just before the final stand.
(1) The method for producing a grain-oriented electrical steel sheet excellent in punching properties which does not require decarburizing annealing as described in (1). (3) Nitriding the strip using ammonia gas in a strip state running between the primary recrystallization annealing and the secondary recrystallization annealing, (1) or (2).
A method for producing a grain-oriented electrical steel sheet having excellent punching properties that does not require the decarburization annealing described. (4) The total oxide mass of the steel sheet after the secondary recrystallization annealing is 1.
0 g / m ² or less (1) to (3)
The method for producing a grain-oriented electrical steel sheet having excellent punching properties that does not require decarburization annealing according to any one of the above items. (5) The atmosphere at the time of primary recrystallization annealing is set such that P _H2O / P _H2 is less than 0.01, the annealing temperature is 800 to 920 ° C., and the soaking time is 30 seconds to 200 seconds.
(4) A method for producing a grain-oriented electrical steel sheet having excellent punchability and not requiring decarburization annealing as described in any of (4). (6) Li, K, Na, Ba, Ca, Mg, Zn, Fe, Z per 100 parts by mass of MgO as an annealing separator
One or two or more selected from chlorides, nitrates, sulfides, and sulfates of r, Sr, Sn, and Al are 0.1 to 2
(1) A unidirectional electrical steel sheet excellent in punching properties which does not require decarburizing annealing as described in any one of (1) to (5), wherein an annealing separator added with 0.0 parts by mass is applied. Manufacturing method. (7) The decarburizing annealing described in any one of (1) to (6), wherein the hydrated moisture of the annealing separator mainly composed of MgO is less than 2.0%. A method for producing unidirectional electrical steel sheets with excellent punching properties. (8) The method according to any one of (1) to (7), wherein the degree of atmospheric oxidation (P _{H2 O} / P _H2 ) up to 800 ° C. during the heating and heating in the secondary recrystallization annealing is less than 0.02. The method for producing a grain-oriented electrical steel sheet having excellent punching properties that does not require decarburizing annealing described in the paragraph. (9) The composition of the atmosphere gas at the time of heating and heating in the secondary recrystallization annealing is a mixture of N ₂ , H ₂ , and an inert gas, and N ₂ is 50 V
(1) to (8), wherein the method for producing a grain-oriented electrical steel sheet having excellent punchability and not requiring decarburization annealing is described in any one of (1) to (8).

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The present inventors have paid attention to the reduction ratio after the last two passes of the latter stage of the finish hot rolling, which has not been noticed in the past, and utilizing this phenomenon, the reduction of 85% or more on the premise of low-temperature slab heating. Research has been conducted to establish a method for stably producing a grain-oriented electrical steel sheet with excellent magnetic properties without decarburizing annealing, which is manufactured by a manufacturing process by final high-pressure cold rolling that applies a reduction rate. The invention has been completed.

The grain-oriented electrical steel sheet to which the present invention is directed is:
Molten steel obtained by a conventionally used steelmaking method is continuously cast into a slab directly, or molten steel is poured into a mold and solidified to form a steel ingot, which is slab-rolled into a slab, Next, after hot rolling to obtain a hot rolled sheet, annealing is performed if necessary, and then a single cold rolling step in which a reduction rate of more than 85% is applied or a final step of applying a reduction rate of more than 85%. It is manufactured by a process of performing a primary recrystallization annealing, nitriding, application of an annealing separator, and a final finish annealing after making a final thickness by two or more cold rollings including an intermediate annealing including a cold rolling step.

The present inventors have focused on the rolling reduction of the material after the final two passes of finish rolling (hereinafter simply referred to as finish rolling) in hot rolling, and conducted extensive research from various viewpoints. It has been found that the strain accumulation phenomenon of the material after the last two passes of rolling and the magnetic properties of the product are closely related. The relationship between the reduction ratio distribution and the magnetic properties of the final hot-rolling finishing stand and the immediately preceding stand will be described in detail based on experiments.

C = 0.003 mass%, Si = 3.15-
A slab containing 3.35% by mass, Al = 0.025 to 0.027% by mass, and N = 0.0078 to 0.0083% by mass is slab-heated at 1150 ° C and hot rolled. The temperature was set to 1000 to 1050 ° C., and the reduction ratio (R2) of the final pass of the finish rolling and the reduction ratio (R1) of the previous pass were variously changed to obtain hot-rolled steel strips of various plate thicknesses.

The hot-rolled steel sheets were then heated at 1120 ° C. for 3 hours.
After performing hot-rolled sheet annealing for about 10 minutes and pickling,
By warm rolling at 50 ° C., the final cold rolling reduction was fixed at 90%, and the final rolled product thickness was 0.22 to 0.50 mm. Then, N ₂ : H ₂ = 45: 55 by volume ratio, dew point +2
Primary recrystallization annealing was performed at 820 to 860 ° C. for 90 seconds in a non-decarburizing atmosphere at 0 ° C. to make the primary recrystallization particle size 21 to 24 μm. Thereafter, using an atmosphere containing ammonia in a running strip state, the total N in the steel is 200 to 220 pp.
A nitriding treatment was performed so as to obtain m. Next, an annealing separator mainly composed of MgO is applied, and a secondary recrystallization annealing is performed at a temperature rising rate of 15 ° C./hour in an atmosphere of N ₂ : H ₂ = 25: 75 at a volume ratio up to 1200 ° C., Purification treatment was performed at 1200 ° C. for 30 hours in an atmosphere of H ₂ : 100%. Thereafter, an insulating tension film containing aluminum phosphate and chromic acid as main components was applied and baked.

The resulting magnetic properties (magnetic flux density B8
(T)) is shown in FIG. As is clear from FIG. 1, when the rolling reduction of at least one of the final two passes of the finish rolling is 0.3 or more and the other is also 0.1 or more, B8 exceeds 1.84T, and one direction. Can meet the specifications of conductive electrical steel sheets. In addition, the rolling reduction of the last two passes is both 30%
In the above case, a product having a high magnetic flux density of B8 ≧ 1.90T is obtained.

Further, with the same material and manufacturing method, the hot-rolled finish rolling ratio is set to R1 = R2 = 0.32 and R1 = R2 = 0.5.
FIG. 2 shows the magnetic characteristics (magnetic flux density B8 (T)) when the cold rolling reduction was changed in various types. As apparent from FIG. 2, when the final cold rolling reduction is 85% or more, B8
A product having a high magnetic flux density of ≧ 1.90T has been obtained.

Although the scientific reasons for the present invention are not always clear, the present inventors speculate as follows. According to Arai et al. (“Materials Science Foru
m ”Vols. 204-206 (1996) pp. 617-622), with a cold rolling reduction of 9
At 5%, the deviation from the Goss azimuth increases and the magnetic flux density decreases. In this case, S = 3.3%, C =
0.05%, and a γ phase exists during hot rolling.

On the other hand, according to Iwanaga et al. (“Journal of Mat
erials Engineering and Performance ”Volume3 (2) Apr
il 1994 p223), a good magnetic flux density is obtained even at a cold rolling reduction of 95%. It is stated that in this case, the texture at the stage corresponding to the hot rolled sheet is different from the usual, so that the magnetic properties are improved at a high cold rolling reduction. In the present invention, since the C content is small, there is no γ phase in all the steps, and it is an α single phase. Therefore, it corresponds to the case of Iwanaga et al., And it is considered that good magnetic properties can be obtained at a high cold rolling reduction. At this time, the orientation corresponding to Goss of # 9 becomes strong in the primary recrystallization texture. In the α-single-phase material, strain is accumulated at a relatively high pressure rate at the stand at the end of hot rolling, and recrystallization occurs at each part in the subsequent hot rolled sheet annealing, and the grain size before cold rolling is relatively small. Since it becomes smaller, it is estimated that various orientations are present, and an appropriate texture is obtained at a high rolling reduction in the subsequent cold rolling.

The reasons for limiting the present invention will be described below. First, the component composition of the present invention is as follows. In addition, all the component compositions defined in the present invention are mass%.
It is. C: 0.0050% or less; C is 0.0050 in the final product
%, Magnetic aging occurs when used in so-called electrical equipment such as a transformer, and the characteristics of the equipment deteriorate. Therefore, decarburization annealing is conventionally required in the middle of the production of a grain-oriented electrical steel sheet. . However, in the present invention, in order not to perform decarburization annealing, the content is set to 0.0050% or less. This is one of the major features of the present invention.

Si: 2.5-4.5%; Si increases the specific resistance of the steel sheet and contributes to a reduction in iron loss. Si content is
If it is less than 2.5%, the effect of reducing iron loss is not sufficient, and in the finish annealing at a high temperature performed for purification and secondary recrystallization, randomization of crystal orientation due to α-γ transformation occurs and sufficient magnetic properties are obtained. I can't get it. On the other hand, if it exceeds 4.5%, the cold rollability is impaired, and the production becomes difficult. Therefore, the content of Si is set to 2.5 to 4.5%. In addition, it is preferably in the range of 3.0 to 3.7%.

Mn: 0.05 to 0.14%; unavoidably present in molten steel, but is not essential as an inhibitor element because it is nitrided. However, Mn is an element effective for preventing cracking during hot rolling due to hot embrittlement, and its effect cannot be obtained at less than 0.05%. on the other hand,
When added in excess of 0.14%, MnS, M
The solid solution of nSe becomes non-uniform, causing a change in magnetic characteristics, and the quality is not stable. Therefore, the Mn content is 0.1.
05 to 0.14%. In addition, preferably 0.08 to
The range is 0.11%.

Al: 0.020-0.040%; Al
Is an element that forms AlN and acts as an inhibitor. If the Al content is less than 0.020%, the suppression power is not sufficiently ensured, while if it exceeds 0.040%, the effect is impaired, so the content is set to 0.020 to 0.040%. The preferred range is 0.024 to 0.030%.
It is.

N: 0.003-0.010%; N is A
It is an element that forms 1N and acts as an inhibitor. In the present invention, AlN precipitates almost completely at the time of hot-rolling heating, so that it is limited by the balance with Al. When the N content is less than 0.003%, the suppressing force is not sufficiently secured, and the magnetic properties are inferior due to poor secondary recrystallization. A preferred range is 0.006 to 0.008%.

Se and S: 0.003% ≦ S + 0.40
5Se ≦ 0.014%; In the production of a grain-oriented electrical steel sheet that is completely solid-dissolved by high-temperature hot-rolling heating, S and Se are effective elements that form MnS and MnSe and act as inhibitors. However, in the present invention, since the slab heating is performed at a relatively low temperature of 1280 ° C. or less, the content of both elements is preferably small.

In the present invention, since the low-temperature slab heating is performed, the precipitate distribution at the time of casting remains as it is. Therefore, when the content is large, the non-uniformity of the precipitate occurs due to the non-uniform temperature at the time of hot rolling heating. Magnetic fluctuation (so-called skid mark) occurs after the next recrystallization. Therefore, the upper limit is S + 0.405Se ≦
0.014%. If the amount is too small, the secondary recrystallization becomes unstable, so the lower limit is made 0.003% or more.

In the present invention, in addition to the above-mentioned elements as inhibitor components, Sn, Sb, P, C
Since r and Cu also act advantageously, they can be contained together with the above components. The preferable addition range of these components is 0.02 to 0.3%, respectively. Furthermore, Ni
Is 0.03-0.3%, Mo and Cd are 0.005-0.3%.
It is effective at 3%.

Next, the manufacturing process of the present invention will be described.
The molten steel composed of the above components is directly converted into a slab by continuous casting, or the molten steel is poured into a mold and solidified to form a steel ingot, which is subjected to slab rolling to form a slab. , And then hot-rolled. Alternatively, a method of performing so-called thin slab casting with a casting thickness of 30 to 75 mm, which has begun to be widely used in recent years, and omitting rough rolling and performing finish rolling may be used.

The maximum rolling reduction R2 of the final stand of the finish rolling in the hot rolling and the rolling reduction R1 immediately before the final stand satisfy one of the following conditions. It is a feature of. When 0.3 ≦ R1, 0.1 <R2 (Condition 1) When 0.3 ≦ R2, 0.1 <R1 (Condition 2) However, R1 = (t _f2 −t _f1 ) / T _f2 R2 = (t _f1 −t _f ) / t _f1 t _f : Finished thickness (mm) t _f1 : Finished finish tund entrance thickness (mm) t _f2 : Finished finish stand _immediately before entrance ( m
m) By satisfying the above conditions of temperature and rolling reduction, it is possible to manufacture a grain-oriented electrical steel sheet having good magnetic properties without having C during casting and hot rolling. Further, when both R1 and R2 are 0.3 or more, better magnetic characteristics can be obtained. Although the upper limit of the rolling reduction is not particularly defined from the viewpoint of magnetic properties, the rolling reduction per pass is limited to about 0.6 at ordinary hot rolling equipment capacity.

Further, the starting temperature of the finish rolling needs to be higher than 975 ° C. At 975 ° C. or lower, there is no effect of improving the texture by strong pressure. Although the upper limit is not particularly specified, the slab heating temperature of the present invention is lower than 1280 ° C., and thus is usually 1150 ° C. or lower. By hot rolling 1.
The steel sheet having a thickness of 5 to 20 mm is subjected to hot-rolled sheet annealing or omitted depending on desired magnetic properties, and then subjected to cold rolling. At this time, the rolling reduction of the final cold rolling needs to be 85% or more. If it is less than this, secondary recrystallization does not sufficiently proceed, and the magnetic properties deteriorate. Although the upper limit is not particularly specified, in order to reduce the rolling reduction to 96% or more with a normal cold rolling mill,
The thickness of the hot-rolled plate must be very large, which is not practical.

The steel sheet having a thickness of 0.15 to 0.50 mm by cold rolling is subsequently subjected to primary recrystallization annealing. The annealing temperature at this time is preferably set to 800 to 920 ° C., and it is preferable to appropriately adjust the annealing temperature so that the primary recrystallized grain size is in an appropriate range. Next, the total oxide mass after the secondary recrystallization will be described. With the same material and manufacturing method as in the previous experiment, with a final plate thickness of 0.4 mm, CaCl ₂ was added to the annealing separator in various amounts and subjected to secondary recrystallization annealing to reduce the total oxide mass on the steel sheet surface to 0%. .1 to
FIG. 3 shows the relationship between the number of times of punching and the height of burrs on the steel sheet after punching when a punching test was performed using a product with 3.5 g / m ² . From FIG. 3, the burrs height is 50
It can be seen that the number of punches exceeding μm sharply decreases as the total oxide mass on the steel sheet surface increases, and that it exceeds 30,000 times, which is the criterion for the evaluation of punchability, when it exceeds 1.0 g / m ² .

[0036] SiO ₂ on the surface of the steel sheet to not decarburization annealing in the present invention is difficult to be formed, thereby producing a grain-oriented electrical steel sheet having no glass coating film consisting mainly of forsterite. However, since the grain-oriented electrical steel sheet contains a large amount of Si as a component, a minimum amount of SiO ₂ is formed by primary recrystallization annealing in actual industrial production, and a glass film can be formed. Therefore, in order not to form the glass film more stably,
i) atmosphere during primary recrystallization annealing, ii) hydration water of MgO,
It is preferable to use at least one of means such as iii) an additive to MgO, and iv) atmosphere adjustment in the secondary recrystallization finish annealing. Thus, the total oxide mass of the steel sheet after the secondary recrystallization is controlled to be 1.0 g / m ² or less. Hereinafter, the respective means i) to iv) will be described in detail.

I) In order to minimize the formation of SiO _{2 in} the primary recrystallization annealing so that the glass film is not uniformly formed over the entire area of the steel sheet after the secondary recrystallization annealing, the P in the annealing atmosphere is required.
The _{H2 O} / P _H2 desirable to less than 0.01. ii) The hydration moisture of the annealing separator is preferably less than 2.0%. If it is 2.0% or more, a glass film is formed after the secondary recrystallization annealing. iii) Li, K, Na, Ba, Ca, M
When one or more selected from chlorides, nitrates, sulfides, and sulfates of g, Zn, Fe, Zr, Sr, Sn, and Al are added, they are once formed in the secondary recrystallization annealing. Can destroy glass film. In the present invention, the amount of SiO ₂ generated by decarburization annealing is very small,
The amount of addition may be smaller than that of the prior art, and MgO: 100
The total amount of the additives is 0.1 to 20.0 parts by mass with respect to parts by mass. If the amount is less than 0.1 part by mass, there is no effect. If it exceeds 20 parts by mass, it vaporizes during secondary recrystallization annealing and damages the equipment.
When the added amount is in the range of 0.1 to 20.0 parts by mass, sufficient punching properties can be secured. Desirable addition amount is 0.1 to
5.0 parts by mass. iv) By making the degree of atmospheric oxidation (P _H2O / P _H2 ) up to 800 ° C. during the heating and heating of the secondary recrystallization annealing less than 0.02, the glass film is formed over the entire area of the steel sheet after the secondary recrystallization annealing. It is possible not to form them uniformly. As a method of adjusting the degree of oxidation in the atmosphere, a method of changing the mixing ratio of H ₂ % is preferable.

The steel sheet after the primary recrystallization annealing is subjected to a nitriding treatment for strengthening the inhibitor. As nitriding increase,
If it is less than 0.0050%, it hardly contributes to the strengthening of the inhibitor, and if it exceeds 0.0150%, the glass coating is destroyed, so that it is limited. In the nitriding treatment, it is preferable to use ammonia gas in a running strip state. Also, after the primary recrystallization annealing and before the secondary recrystallization finishing annealing, Mg
An annealing separator mainly composed of O is applied and wound into a coil. A chloride or the like may be added to the annealing separator for the purpose of improving magnetic properties.

The coil is subsequently subjected to a secondary recrystallization finish annealing. In the secondary recrystallization finishing annealing, the temperature is raised at a rate of 5 to 30 ° C./hour. At this time, the composition of the atmosphere gas was N ₂ ,
Although H ₂ and inert gas are mixed, in the present invention, since there is almost no oxide layer on the surface of the steel sheet, the inhibitor Al
In order to suppress the early decomposition of N and obtain good magnetic properties, it is preferable to set N ₂ in the atmosphere gas to 50 vol% or more.

Thereafter, after the temperature was raised to 1100 ° C. or more, H
₂ : Purification for 10 hours or more in 100% atmosphere. After the secondary recrystallization, the steel sheet is washed and removed of the annealing separator, and then coated with an insulating film and baked to obtain a product. In order to further improve the magnetic characteristics, a known magnetic domain segmentation process may be performed.

[0041]

Embodiments will be described below. (Preparation of hot-rolled steel strip) In mass%, C: 0.003%, S
i: 3.20%, Mn: 0.10%, S: 0.0078
%, Acid-soluble Al: 0.027%, N: 0.0075%
And the balance 25 consisting of Fe and unavoidable impurities
After heating a 2mm thick slab at a temperature of 1150 ° C,
First, rough rolling is performed, followed by finishing hot rolling, at an inlet temperature of 1025 to 1050 ° C., and hot rolling steel strips of 3.8 mm and 2.4 mm are prepared on the six finishing stands under the following sheet thickness conditions. did. The winding temperature was 530-600 ° C.

Condition 1: 93 → 65 → 50 → 30 → 1
6.0 → 6.7 → 3.8 (mm) Condition 2: 80 → 55 → 30 → 15 → 5.5 → 4.
7 → 3.8 (mm) Condition 3: 93 → 65 → 50 → 20 → 7.0 → 4.
2 → 2.4 (mm) Condition 4: 80 → 55 → 30 → 15 → 3.4 → 2.
9 → 2.4 (mm) (Example 1) This hot-rolled sheet was subjected to hot-rolled sheet annealing and acid pickling in which it was kept at 1100 ° C. for 30 seconds, kept at 900 ° C. for 30 seconds and rapidly cooled, then passed. Cold rolling was performed at a temperature between 175 and 225 ° C. to obtain sheet thicknesses of 0.335 mm and 0.40 mm. Thereafter, primary recrystallization annealing at 835 ° C. for 90 seconds was performed by N2: 25%, H2: 75%, Dp = 0 ° C. (P _H2O
/ P _H2 : 0.0081). Thereafter, it was nitrided with ammonia gas in a running strip state to a nitrogen content of 195 to 225 ppm. Next, an annealing separator containing MgO as a main component was applied, and
The secondary recrystallization annealing was performed at a heating rate of 15 ° C./hour in an atmosphere of N ₂ = 25% and H ₂ = 75% up to ° C. Then H ₂ = 1
A purification treatment at 1200 ° C. for 30 hours at 00% was performed, and a good adhesion insulating film containing phosphate as a main component was applied by a flattening treatment, and the magnetic properties were measured. The results are shown in Tables 1 and 2.

[0043]

[Table 1]

[0044]

[Table 2]

As can be seen from Tables 1 and 2, when both the reduction ratios R1 and R2 of the hot rolling finish rolling of the present invention were 30% or more, good magnetic properties were obtained at any plate thickness. On the other hand, when the rolling reduction was less than 30% in each of the comparative examples, the magnetic properties were inferior. Further, from Table 2, when the rolling reduction of the cold rolling was less than 85%, the result was that the magnetic properties were slightly inferior.

[0046]

As described above, in the present invention,
By defining the hot rolling finish inlet temperature, the reduction rate of the last two passes of hot rolling, and the cold rolling rate, it is possible to stabilize good magnetic properties by a manufacturing method based on low-temperature slab heating without decarburization. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the rolling reduction in the last two passes of hot rolling and magnetic properties (magnetic flux density B8 (T)).

FIG. 2 shows the rolling reduction and the magnetic properties (magnetic flux density B8) of cold rolling.
(T)) is a graph showing the relationship.

FIG. 3 is a graph showing the relationship between the number of punches and the height of burrs for each total oxide mass on the steel sheet surface.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C23C 8/26 C23C 8/26 (72) Inventor Noriyoshi Fujii 1 Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka -1 Inside Nippon Steel Corporation Yawata Works (72) Inventor Yoshifumi Ohata 1-1 Inside Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Inside Nippon Steel Corporation Yawata Works (72) Inventor Haru Tanaka F-term (Reference) 4K028 AA02 AB01 AC04 4K033 AA02 CA09 CA10 FA01 FA03 FA05 HA01 HA02 JA01 LA01 MA02 MA03 RA04 SA03 TA02

Claims (9)

[Claims] 1. The method according to claim 1, wherein C ≦ 0.005% by mass%, Si:
2.5-4.5%, acid-soluble Al: 0.020-0.0
40%, N: 0.0030 to 0.010%, 0.003
% ≦ (S + 0.405Se) ≦ 0.014%, Mn:
A slab containing 0.05 to 0.14%, the balance being Fe and unavoidable impurities, is heated to a temperature range of less than 1280 ° C., hot-rolled, and subjected to hot rolled sheet annealing or not, and is subjected to 85% After making the final sheet thickness by final cold rolling applying the above reduction rate, in the method for producing a unidirectional electrical steel sheet which performs primary recrystallization annealing without decarburization, applies an annealing separator, and performs finish annealing. The start temperature of the finish rolling in hot rolling is set to more than 975 ° C., and the rolling reduction R2 of the finishing final stand of finish rolling and the rolling reduction R1 immediately before the final stand are defined as conditions 1 and 2 defined below. A method for producing a grain-oriented electrical steel sheet having excellent punchability and not requiring decarburization annealing, characterized by satisfying any of the above. When 0.3 ≦ R1, 0.1 <R2 (Condition 1) When 0.3 ≦ R2, 0.1 <R1 (Condition 2) However, R1 = (t _f2 −t _f1 ) / T _f2 R2 = (t _f1 −t _f ) / t _f1 t _f : Finished thickness (mm) t _f1 : Finished finish tund entrance thickness (mm) t _f2 : Finished finish stand _immediately before entrance ( m
m) 2. The rolling reduction R2 of the finishing stand in the finish rolling of the hot rolling and the rolling reduction R1 just before the final stand are all 0.3 or more. A method for manufacturing a grain-oriented electrical steel sheet with excellent punching properties that does not require decarburization annealing. 3. The decarburizing annealing according to claim 1 or 2, wherein the strip is nitrided by using ammonia gas in a strip state running after the primary recrystallization annealing until the secondary recrystallization annealing. A method for manufacturing a grain-oriented electrical steel sheet with excellent punchability that is not required. 4. The steel sheet according to claim 1, wherein the total oxide mass of the steel sheet after the secondary recrystallization annealing is 1.0 g / m ² or less.
3. A method for producing a grain-oriented electrical steel sheet having excellent punchability and not requiring decarburization annealing according to any one of Items 3 to 3. 5. The atmosphere during primary recrystallization annealing is P _H2O / P
_The decarburizing annealing according to any one of claims 1 to 4, wherein _H2 is less than 0.01 and the annealing temperature is 800 to 920 ° C and the soaking time is 30 seconds to 200 seconds. A method for producing a grain-oriented electrical steel sheet with excellent punchability. 6. As an annealing separating agent, Li, K, Na, Ba, Ca, Mg, Zn, 100 parts by mass of MgO are used.
One, two or more selected from chlorides, nitrates, sulfides, and sulfates of Fe, Zr, Sr, Sn, and Al.
6. A grain-oriented electrical steel sheet having excellent punchability and not requiring decarburizing annealing according to claim 1, wherein an annealing separator added with 1 to 20.0 parts by mass is applied. Manufacturing method. 7. The hydrated water of the annealing separator mainly composed of MgO is less than 2.0%.
The method for producing a grain-oriented electrical steel sheet having excellent punching properties that does not require decarburization annealing according to any one of the above items. 8. 800 ° C. at the time of heating for secondary recrystallization annealing
8. The method according to claim 1, wherein the atmosphere oxidation degree (P _{H2 O} / P _H2 ) is less than 0.02. Manufacturing method of grain-oriented electrical steel sheet. 9. The method according to claim 1, wherein the composition of the atmosphere gas at the time of heating and heating in the secondary recrystallization annealing is a mixture of N ₂ , H ₂ and an inert gas, and N ₂ is 50 vol% or more. 1-8
The method for producing a grain-oriented electrical steel sheet having excellent punching properties that does not require decarburization annealing according to any one of the above items.