JP3061491B2 - Method for producing unidirectional electrical steel sheet with excellent magnetic properties - Google Patents

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 thick unidirectional electrical steel sheet having almost no glass coating (forsterite coating), and has excellent cutting properties and punching properties and good magnetic properties. The present invention relates to an inexpensive method for manufacturing an electromagnetic steel sheet.

[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 is required to have excellent magnetic properties such as excitation properties and iron loss properties. Numerical values representing the excitation characteristics include a magnetic field strength of 800 A
/ Flux density B ₈ in m are usually used. As a numerical value representing the iron loss characteristic, the iron loss W _17/50 per kg when magnetized at a frequency of 50 Hz to 1.7 Tesla (T) is used. The magnetic flux density is the largest controlling factor of the iron loss characteristics. Generally, the higher the magnetic flux density, the better the iron loss characteristics. In general, when the magnetic flux density is increased, the secondary recrystallized grains become large, and the iron loss characteristics may become poor.
In contrast, by controlling the magnetic domain, the iron loss characteristics can be improved regardless of the particle size of the secondary recrystallized grains.

[0003] This grain-oriented electrical steel sheet is produced by causing secondary recrystallization in the final finish annealing step to develop a so-called Goss structure having {110} on the steel sheet surface and a <001> axis in the rolling direction. Have been. In order to obtain good magnetic properties, the <001> axis, which is the axis of easy magnetization, needs to be highly aligned in the rolling direction.

[0004] As a typical production technique of such a high magnetic flux density unidirectional magnetic steel sheet, Satoru Taguchi et al.
No. 0-15644 and Japanese Patent Publication No. 51 by Takuichi Imanaka
There is a method described in JP-A-13469. In the former, MnS and AlN are used, and in the latter, MnS, MnSe, Sb are used.
Are used as the main inhibitors.

[0005] Therefore, in the current technology, it is essential to appropriately control the size, morphology and dispersion state of the precipitates functioning as these inhibitors. With regard to MnS, in the current process, MnS is used during slab heating before hot rolling.
Is once dissolved completely and then precipitated during hot rolling. A temperature of about 1400 ° C. is required to completely dissolve the required amount of MnS for secondary recrystallization. This is more than 200 ° C. higher than the slab heating temperature of ordinary steel, and this high-temperature slab heating treatment has the following disadvantages. That is, 1) a high-temperature slab heating furnace dedicated to directional magnetic steel is required. 2) The unit energy consumption of the heating furnace is high. 3) The amount of the molten scale increases, and the adverse effect on the operation is large as seen in so-called scraping.

In order to avoid such a problem, the slab heating temperature may be reduced to the same level as that of ordinary steel.
Means to use less or not to use at all, which necessarily leads to instability of secondary recrystallization. For this reason, in order to realize low-temperature slab heating, it is necessary to strengthen the inhibitor with a precipitate other than MnS in some form, and to sufficiently suppress normal grain growth during finish annealing.
Such inhibitors include nitrides, as well as sulfides.
Oxides and grain boundary precipitation elements are conceivable. Known techniques include, for example, the following.

[0007] In Japanese Patent Publication No. 54-24684, As,
A method has been disclosed in which a slab heating temperature is set in a range of 1050 to 1350 ° C. by including grain boundary segregation elements such as Bi, Sn, and Sb in steel. JP-A-52-24116 discloses that Al, Zr, Ti, B, Nb, Ta, V, C
A method has been disclosed in which a slab heating temperature is adjusted to a range of 1100 to 1260 ° C. by containing a nitride-forming element such as r or Mo. In Japanese Patent Application Laid-Open No. 57-158322, low-temperature slab heating is performed by lowering the Mn content and the Mn / S ratio to 2.5 or less, and the addition of Cu stabilizes the secondary recrystallization. A technique for doing so has been disclosed.

On the other hand, there has been disclosed a technique in which the metal structure is improved in combination with the reinforcement of the inhibitor. That is, in JP-A-57-89433, elements such as S, Se, Sb, Bi, Pb, Sn and B are added in addition to Mn, and the columnar crystal ratio of the slab and the secondary cold rolling reduction are combined. Thereby, low-temperature slab heating at 1100 to 1250 ° C. is realized. Further, JP-A-59-190
Japanese Patent No. 324 discloses a technique for stabilizing the secondary recrystallization by forming an inhibitor mainly composed of Al, B and nitrogen in addition to S or Se, and subjecting the inhibitor to pulse annealing at the time of primary recrystallization annealing after cold rolling. It was published. As described above, great efforts have been made so far to realize low-temperature slab heating in the production of grain-oriented electrical steel sheets.

In Japanese Patent Application Laid-Open No. 59-56522, Mn is 0.08 to 0.45% and S is 0.00
A technique has been disclosed that enables low-temperature slab heating by reducing the content to 7% or less. By this method, the problem of occurrence of defective linear secondary recrystallization of a product due to coarsening of slab crystal grains during heating of a high-temperature slab was solved. On the other hand, a workability with important is coating properties with magnetic properties when used in consumer oriented electrical steel sheet. Normally, the grain-oriented electrical steel sheet is surface-treated by a glass coating and an insulating coating formed at the time of final finish annealing.

The glass film is a film mainly composed of forsterite (Mg ₂ SiO ₄ ), which is a reaction product of MgO as an annealing separator and SiO _{2 as} an oxide film formed during decarburization. The glass coating is hard and highly wearable, and has a remarkable effect on the durability of tools at the time of slit cutting, punching, and the like when processing an electromagnetic steel sheet. For example, when performing a punching process on a grain-oriented electrical steel sheet having a glass coating, a die is worn, and the return of the punched sheet is increased by punching about several thousand times, so that a problem occurs during use. . For this reason, it is necessary to re-grind the mold, replace it with a new one, and the like.

[0011] This results in a reduction in the work efficiency of the iron core processing at the customer and an increase in cost. Similarly, the adverse effect of the glass coating is also a problem on the slitting property and the cutting property. A method for producing a grain-oriented electrical steel sheet having almost no glass coating is disclosed in, for example, JP-A-53-22.
There is one disclosed in JP-A-113. In the decarburizing annealing, the thickness of the oxide film is set to 3 μm or less, and fine alumina containing 5 to 40% of hydrous silicate mineral powder is used as an annealing separator. This is applied to a steel plate and finish annealing is performed. According to this, an oxide film is made thin, and a glass coating which is easy to peel off is formed by blending a hydrated mineral, thereby obtaining a film having a metallic luster.

Japanese Patent Application Laid-Open No. 56-65883 discloses a method for suppressing the formation of a glass film by using an annealing separating agent. An annealing method in which 20 parts by weight of an impurity removing additive and 10 parts by weight of an inhibitor are mixed with aluminum hydroxide. There is a method in which a separating agent is applied to a steel sheet to form a thin glass film of 0.5 μm or less. JP-A-59-96278 discloses Al ₂ O having a low reactivity with SiO _{2 of} an oxide layer formed by decarburizing annealing.
₃ and M reduced in activity by firing at a high temperature of 1300 ° C or higher
There is an annealing separator composed of gO. According to this, formation of forsterite is suppressed.

Each of these prior arts is a grain-oriented electrical steel sheet called a normal orient core, and has a magnetic flux density of 1.8.
It is based on a low-grade grain-oriented electrical steel sheet as low as 8 Tesla or less, and may have an effect similar to that of the present invention in that it has almost no glass coating. The technology for developing high-grade grain-oriented electrical steel sheets with low iron loss has not yet been obtained.

[0014]

In recent years, there has been a growing need to use a grain-oriented electrical steel sheet having almost no glass coating in place of an existing high-grade non-oriented electrical steel sheet for applications such as iron core materials for turbine generators. Was. With respect to the above-mentioned applications, unidirectional magnetic properties are more important than those of other non-oriented electrical steel sheets, and thus the need to use grain-oriented electrical steel sheets has increased. In addition, a material that has almost no glass with good workability, such as punching, cutting, and slitting, is required. On the other hand, the main process of manufacturing the grain-oriented electrical steel sheet after hot rolling is hot-rolled sheet annealing-cold rolling-decarburizing annealing-finish annealing, which is the main process after hot-rolling the non-oriented electrical steel sheet. It is more complicated than cold rolling and annealing. for that reason,
From the viewpoint of manufacturing cost, the grain-oriented electrical steel sheet is considerably higher than the non-oriented electrical steel sheet.

Further, in a normal pickling line or a tandem cold rolling line, there is a limit to the thickness of a sheet that can be passed, and there is a possibility that breakage may occur when a cold rolled material having a large thickness is passed.
Therefore, when a thick material having a thickness of 0.5 mm or the like is to be manufactured by cold rolling once, it is necessary to reduce the cold rolling rate because the thickness of the cold rolled material has an upper limit. Further, in the production of grain-oriented electrical steel sheets, hot-rolled sheet annealing is usually performed for the purpose of making the structure after hot rolling non-uniform and performing a precipitation treatment. For example, in a production method using AlN as a main inhibitor, Japanese Patent Publication No.
As disclosed in Japanese Patent Publication No. 820, a method of controlling an inhibitor by performing AlN precipitation treatment in hot-rolled sheet annealing is adopted. In recent years, the production process of such grain-oriented electrical steel sheets that consume a large amount of energy has been reviewed, and there has been an increasing demand for simplification of the process and energy. In order to respond to such a demand, in a manufacturing method using AlN as a main inhibitor, a method in which the precipitation treatment of AlN in hot-rolled sheet annealing is replaced by high-temperature winding after hot rolling (Japanese Patent Publication No. 59-1984)
No. 45730). Certainly, even if the hot-rolled sheet annealing is omitted by this method, the magnetic properties can be secured to some extent. However, in a normal method of winding in a coil shape of 5 to 20 tons, the inside of the coil during the cooling process is reduced. In this case, a difference in the thermal history is generated, and the precipitation of AlN is inevitably inconsistent, and the final magnetic properties vary depending on the location in the coil, resulting in a decrease in yield.

Therefore, the present inventors have focused on the recrystallization phenomenon after the final pass of the finish hot rolling, which has hardly been noticed in the past,
Utilizing this phenomenon, a method of omitting hot-rolled sheet annealing in a production method by once cold rolling under a high pressure of 80% or more (Japanese Patent Laid-Open No.
-263923, JP-A-2-263924). These techniques are characterized in that the hot-rolled sheet has a fine recrystallized structure by applying high pressure under the final three passes of finishing hot rolling and holding at a high temperature after the end of hot rolling.
It has become possible to achieve both slab heating at a temperature lower than 280 ° C. and omission of hot-rolled sheet annealing.

Regarding hot rolling of a grain-oriented electrical steel sheet, poor secondary recrystallization due to coarse growth of slab crystal grains during high-temperature slab heating (for example, 1300 ° C. or higher) (the generation of linear fine grains continuous in the rolling direction) 960) during hot rolling to prevent
A method has been proposed in which recrystallization high-pressure rolling is performed at a temperature of １１1190 ° C. and a rolling reduction of 30% or more per pass to cut coarse crystal grains (Japanese Patent Publication No. 60-37172). Although this method certainly reduces the generation of linear fine grains, it is premised on a manufacturing process in which hot-rolled sheet annealing is performed.

Further, in the production method using MnS, MnSe, and Sb as inhibitors, the method comprises the steps of:
Hot rolling at a reduction rate of 10% or more at a temperature of 3% and then cooling at a cooling rate of 3 ° C./sec or more
There has been proposed a method of precipitating S and MnSe uniformly and finely to improve magnetic properties (JP-A-51-20716). In addition, hot rolling is performed at a low temperature to suppress the progress of recrystallization,
There has been proposed a method of improving magnetic properties by preventing the {110} <001> -oriented grains formed by shear deformation from being reduced by subsequent recrystallization (Japanese Patent Publication No. 59-1984).
No. 32526, JP-B-59-35415).

Even in these methods, production by a single cold rolling method without annealing of a hot-rolled sheet has not even been studied. In addition, in hot rolling of silicon steel slabs containing ultra-low carbon, hot-rolling under low temperature and large pressure to accumulate strain in the hot-rolled sheet, and subsequent recrystallization in hot-rolled sheet annealing, coarse grains unique to ultra-low carbon material Has been proposed (Japanese Patent Publication No. 59-34212).
No.). However, even in this method, production by a single cold rolling method without annealing of a hot-rolled sheet has not even been studied. Accordingly, a technique in which the present inventors have achieved both the low-temperature slab heating and the omission of hot-rolled sheet annealing as described above (Japanese Patent Laid-Open No. 2-263923).
It is understood that the significance of the present invention is large, but the present invention provides a method for producing a unidirectional magnetic steel sheet having a larger thickness and less glass coating.

[0020]

According to the present invention, C:
0.021 to 0.075%, Si: 2.5 to 4.5%,
Acid-soluble Al: 0.010-0.060%, N: 0.00
10 to 0.0130%, S + 0.405Se: 0.01
A slab comprising 4% or less, Mn: 0.05 to 0.8%, the balance being Fe and unavoidable impurities is heated at a temperature of less than 1280 ° C, then hot-rolled, and continuously reduced without performing hot-rolled sheet annealing. Cold-rolled at a rate of 60 to 79%, then decarburized, coated with an annealing separator, finish-annealed, and coated with an insulating coating agent. The hot rolling end temperature is from 800 to 1100 ° C.
The cumulative rolling reduction of the final three passes of hot rolling is set to 40% or more, the temperature of the steel sheet between the passes of cold rolling is set to 250 ° C. or less, and the primary recrystallization from the completion of decarburizing annealing to the start of final finishing annealing. The average grain size of the grains is 18 to 30 μm, and after the hot rolling, the steel sheet is subjected to nitriding treatment until the start of the secondary recrystallization of the final finish annealing,
As an annealing separator, Li,
K, Na, Ba, Ca, Mg, Zn, Fe, Zr, S
Excellent in magnetic properties characterized by applying an annealing separator containing 2 to 30 parts by weight of one or more selected from chlorides, nitrates, sulfides and sulfates of r, Sn, Al. An object of the present invention is to provide a method for producing a unidirectional magnetic steel sheet having a large thickness and a small glass coating.

[0021]

The grain-oriented electrical steel sheet to which the present invention is directed is:
Molten steel obtained by a conventional steelmaking method is cast by a continuous casting method or an ingot-making method, and if necessary, a slab is sandwiched by a lump-forming step, and subsequently hot-rolled into a hot-rolled sheet, and then hot-rolled. It is manufactured by successively performing cold rolling at a rolling reduction of 60 to 79%, decarburizing annealing, and final finishing annealing without performing strip annealing. The present inventors have limited the thickness of the cold-rolled material,
It was necessary to reduce the rolling reduction, and measures to improve the magnetic properties with a rolling reduction of less than 80% were extensively studied.
As a result, it was found that not unnecessarily increasing the sheet temperature between the cold rolling passes is effective for obtaining good magnetic properties at a low cold rolling reduction of less than 80%.

Hereinafter, a detailed description will be given based on experimental results. FIG. 1 is a graph showing the effect of the temperature of a steel sheet between passes during cold rolling on the magnetic flux density of a product. Here, C: 0.
030% by weight, Si: 2.81% by weight, acid-soluble Al:
0.034% by weight, N: 0.0060% by weight, S: 0.
007% by weight, Mn: 0.14% by weight, and the balance F
e and a 40 mm thick slab consisting of unavoidable impurities
The sheet was heated to 50 ° C. to form a hot-rolled sheet having a thickness of 2.0 mm in six passes.
At this time, the pass schedule is 40 → 26 → 15 → 8 → 5
→ 3 → 2 (mm), and the hot rolling end temperature was 938 ° C. In this case, the cumulative rolling reduction in the last three passes was 75%. Air-cooled for 4 seconds after hot rolling, then water-cooled to 550 ° C, 550 ° C
Was subjected to a winding simulation in which the furnace was cooled for one hour and then cooled. Thereafter, the hot-rolled sheet is pickled, and then the reduction rate is reduced to 75%.
% To obtain a cold rolled sheet having a thickness of 0.50 mm. At this time, when the plate thickness is 1.5 mm and 1.0 mm, 50 ° C. × 5 minutes (soaking)
100 ° C x 5 minutes (soaking), 150 ° C x 5 minutes (soaking), 200 ° C x 5 minutes (soaking), 250 ° C x 5 minutes (soaking), 300 ° C x 5 minutes (soaking), 350 ℃ × 5
Eight kinds of cold-rolled sheets which were subjected to eight kinds of aging treatments (minute (soaking), no aging treatment) were prepared.

Then, the temperature was maintained at 830 ° C. for 400 seconds,
Decarburization annealing was performed at a temperature of 20 ° C. × 20 seconds. After a while, 75
During the heat treatment at 30 ° C. for 30 seconds, NH ₃
The gas was mixed in, causing the steel sheet to absorb nitrogen. At this time, the N content of the steel sheet was 0.0198 to 0.0240% by weight. When the average grain size of the primary recrystallized grains in the entire thickness of the steel sheet was measured using an optical microscope and an image analyzer, 22 to
It was 23 μm. Next, Mg is added to the plate after the nitriding treatment.
An annealing separator in which 5 parts by weight of CaCl ₂ was added to 100 parts by weight of O was applied, and final finish annealing was performed. The steel sheet after the final finish annealing did not form any coating and showed a uniform metallic luster. As is clear from FIG.
Good magnetic flux density is obtained below 50 ° C.

Although the reason why the relationship as shown in FIG. 1 is established is not always clear, the present inventors speculate as follows. Conventionally, the cold-rolling rate is known as a controlling factor of the cold-rolled recrystallization texture, and in particular, {110} <001>,
The amount of {111} <112> orientation grains is important. The {110} <001> orientation grains in the recrystallized texture
It reaches a maximum when the rolling reduction is 60 to 70%, and decreases as the rolling reduction increases in the rolling reduction range exceeding 70%.

On the other hand, {111} <1 in the recrystallized texture
The grain orientation of <12> tends to increase as the rolling reduction increases in the rolling reduction range up to about 90%. On the other hand, inter-pass aging in cold rolling tends to promote the formation of the deformation zone during cold rolling, and tends to increase the {110} <001> orientation grains nucleated from the deformation zone in the recrystallized texture. This interpass aging, on the other hand, tends to reduce the amount of {111} <112> oriented grains in the recrystallized texture.

Therefore, from the viewpoint of the abundance of the {110} <001> -oriented grains and the {111} <112> -oriented grains in the recrystallized texture, the aging between passes reduced the cold rolling rate. Will have the same effect as For this reason,
In order to make the recrystallized texture obtained at a high cold rolling reduction of 80% or more as close as possible to a low cold rolling reduction of less than 80% as possible, it is necessary to minimize the influence of aging between passes as in the present invention. It is considered effective.

The method for producing a grain-oriented electrical steel sheet according to the present invention using such components and steps is characterized by a surface treatment method in the process of applying an annealing separator, finishing annealing and applying an insulating coating agent. The final cold rolled material is decarburized and annealed in a continuous line. By this decarburizing annealing, removal of C in the steel and primary recrystallization are performed, and at the same time, an oxide film mainly composed of SiO ₂ is formed on the surface of the steel sheet. Decarburization annealing is 800-8
At 75 ° C., the atmosphere is controlled by controlling the dew point in N ₂ + H ₂ .

For example, a nitriding treatment is performed in the same line or in another line after the second half or after the decarburizing annealing. However, this nitriding treatment may be performed between the end of hot rolling and the start of secondary recrystallization of final finish annealing. The nitriding amount at this time is 1 ppm or more, and preferably 15 % as the N amount after the nitriding treatment.
Treated as 0-300 ppm. Thereafter, an annealing separating agent is applied, dried, wound up, and finish annealed. At this time, as an annealing separator, Li,
K, Na, Ba, Ca, Mg, Zn, Fe, Zr, S
One obtained by adding 2 to 30 parts by weight of one or more of chlorides, carbonates, nitrates, sulfides, and sulfates of n, Sr, and Al is used.

As in the present invention, MnS is used as an inhibitor.
In the step of using an (Al, Si) N-based inhibitor without using Al, the secondary recrystallization initiation temperature is 1100 ° C.
Before and after, it is higher than that of the conventional high magnetic flux density directional magnetic steel sheet using AlN, MnS or the like as an inhibitor. For this reason, it is necessary to keep the inhibitor strength at a certain level while suppressing the formation of a glass film and performing a decomposition reaction up to the secondary recrystallization start temperature region. This is because, in the step in which the formation of the glass film is started once by the annealing separator, and then the decomposition reaction proceeds, the decomposition of the inhibitor proceeds rapidly from the time when the decomposition of the glass film starts.

The finish annealing is preferably carried out at a temperature rise during which the formation and decomposition of the glass coating proceeds, preferably with N _{2 being} 30% or more. Thereby, the stabilization of (Al, Si) N is maintained, and good secondary recrystallized grains are obtained. The high magnetic flux density material having almost no annealed glass coating is subjected to application of an insulating coating agent and heat flattening at 800 to 900 ° C. in a continuous line for forming correction and strain relief annealing.

Next, the reasons for limiting the constituent elements of the present invention will be described. First, the reasons for limiting the components of the slab and the slab heating temperature will be described in detail. C is 0.021% by weight
(Hereinafter simply abbreviated as%), the secondary recrystallization becomes unstable, and even when secondary recrystallization occurs, B ₈ > 1.80.
Since (T) is difficult to obtain, the content is set to 0.021% or more. on the other hand,
If the amount of C is too large, the decarburization annealing time becomes long and it is not economical.

If the content of Si exceeds 4.5%, cracking at the time of cold rolling becomes remarkable, so the content is set to 4.5% or less. If it is less than 2.5%, the specific resistance of the material is too low, and a low iron loss required for a transformer core material cannot be obtained. Desirably, it is at least 3.2%. Al is AlN or (Al, Si) nitride necessary for stabilizing secondary recrystallization.
To secure s, 0.010% or more of acid-soluble Al is required. If the acid-soluble Al content exceeds 0.060%, the AlN of the hot-rolled sheet becomes inappropriate and secondary recrystallization becomes unstable.

N is 0.00 in a normal steel making operation.
It is difficult to reduce the content to less than 10%, and it is not economically preferable.
When the content exceeds 30%, “steel surface swelling” called blister occurs, so the content is set to 0.0130% or less. Mn
Even if S and MnSe are present in the steel, it is possible to improve the magnetic properties by properly selecting the conditions of the manufacturing process. However, when S or Se is high, a secondary recrystallization defective portion called linear fine grain tends to occur. To prevent the occurrence of the secondary recrystallization defective portion, (S + 0.40
5Se) ≦ 0.014% is desirable. If S or Se exceeds the above-mentioned value, the probability of occurrence of a secondary recrystallization defective portion increases, no matter how the manufacturing conditions are changed, which is not preferable. In addition, the time required for purification in the final finish annealing is too long, which is not preferable.
Or, it is meaningless to increase Se unnecessarily.

The lower limit of Mn is 0.05%. 0.0
If it is less than 5%, the shape (flatness) of the hot rolled sheet obtained by hot rolling, particularly, the side edge of the strip becomes corrugated, which causes a problem of lowering the product yield. On the other hand, if the Mn content exceeds 0.8%, the magnetic flux density of the product is lowered, which is not preferable. Therefore, the upper limit of the Mn content is set to 0.8%. In addition, Sn, S, which is known as an inhibitor constituent element,
A small amount of b, Cr, Cu, Ni, B, Ti or the like may be contained.

The heating temperature of the slab is limited to less than 1280 ° C. for the purpose of reducing the cost as compared with ordinary steel. Preferably it is 1200 ° C or lower. The subsequent hot-rolling process is usually performed after heating a slab having a thickness of 100 to 400 mm.
Each of them consists of rough hot rolling and finish hot rolling performed in a plurality of passes. The method of rough hot rolling is not particularly limited, and is performed by a usual method. The feature of the present invention lies in finish hot rolling subsequent to rough hot rolling. Finish hot rolling is usually performed by high-speed continuous rolling of 4 to 10 passes. Normally, in the rolling distribution of the finish hot rolling, the rolling reduction is higher in the former stage and the rolling reduction is lower in the latter stage so that the shape is good. Rolling speed is usually 100-3000m
/ min, and the time between passes is 0.01 to 100 seconds.

In the present invention, only the hot rolling end temperature and the cumulative rolling reduction in the last three passes of the hot rolling are limited, and other conditions are not particularly limited. It is also preferable to carry out high pressure reduction before the step described above, because recrystallization occurs to some extent and the structure is improved. Even in the final three passes, strong pressure reduction in the final pass is effective in promoting recrystallization after hot rolling.

Next, the reasons for limiting the hot rolling conditions will be described. The hot rolling end temperature was set to 800 to 1100 ° C. 11
If the temperature is higher than 00 ° C., the reduction in strain due to dynamic recovery during rolling is large, and recrystallization after the end of hot rolling hardly occurs. On the other hand, 800
If the temperature is lower than 0 ° C., the temperature is too low, so that subsequent recrystallization hardly occurs after the end of hot rolling, and the magnetic flux density of the product is undesirably reduced.

On the other hand, the cumulative rolling reduction in the final three passes of the hot rolling was set to 40% or more. Below this value, the effect of recrystallization after hot rolling is insufficient, which is not preferable. The upper limit of the cumulative rolling reduction in the final three passes is not particularly limited, but it is industrially difficult to apply a cumulative rolling reduction of 99.9% or more. After final pass of hot rolling, usually 0.1-10
After air cooling for about 0 seconds, it is water cooled, wound up at a temperature of 300 to 700 ° C., and gradually cooled. The cooling process is not particularly limited, but air cooling for 1 second or more after hot rolling is preferable in order to advance recrystallization. This hot-rolled sheet is continuously cold-rolled at a rolling reduction of 60 to 79% without annealing the hot-rolled sheet to form a cold-rolled sheet of 0.4 to 1.0 mm.

The reason why the thickness of the cold-rolled sheet is specified to be 0.4 to 1.0 mm is for the purpose of the present invention to obtain a thick unidirectional magnetic steel sheet. On the other hand, if it exceeds 1.0 mm, decarburizing annealing takes too much time, which is not preferable. The reason why the rolling reduction is defined as 60 to 79% is that if the material is too thick as a cold rolled material, it is necessary to lower the cold rolling ratio inevitably because the material is easily broken at the time of passing the pickling line or the cold rolling line. Because there is. The upper limit comes from the limitation of the thickness of the cold-rolled material, while the lower limit is specified because the magnetic flux density must be kept high. The temperature of the steel sheet between the cold rolling passes was 250 ° C. or less. If the temperature exceeds this, as shown in FIG. 1, the influence of aging between passes occurs, so that in the case of a low cold rolling reduction as in the present invention, the magnetic flux density is rather lowered, which is not preferable.

The method of cold rolling is not particularly limited. Either the tandem type or the reverse type may be used.
It is sufficient to keep the temperature between passes below 250 ° C.
Although the number of passes is not particularly limited, it is meaningless to take the number of passes more than 100 times unnecessarily.
The steel sheet after such cold rolling is subjected to decarburizing annealing, application of an annealing separating agent, and final finish annealing by a usual method to be a final product. Here, the reason why the average grain size of the primary recrystallized grains from the completion of the decarburizing annealing to the start of the final finishing annealing is set to 18 to 30 μm is that B ₈ (T) ≧ 1.88 in the range of this value. This is because a magnetic flux density can be obtained.

As the annealing separating agent, Li, K, Na, Ba, Ca, Mg, Zn, F
One or more selected from chlorides, carbonates, nitrates, sulfides, and sulfates of e, Zr, Sr, Sn, and Al are used, to which 2 to 30 parts by weight are added. If the amount is less than 2 parts by weight, it is difficult to obtain a product having almost no glass coating on the entire surface of the coil. On the other hand, if it exceeds 30 parts by weight, the component elements of the additive diffuse and penetrate into the steel to affect the inhibitor, cause grain boundary etching, and affect the subsequent purification, which is not preferable. With these additives, the MgO and the oxide film have a low melting point in the first stage at the time of finishing annealing and the temperature is raised, and a moderately thin forsterite film is formed.

Next, the growth and additional oxidation of forsterite are prevented, and at the later stage of the temperature rise, the coating layer is decomposed by the etching reaction of Fe in the coating, and a surface having almost no glass coating is obtained. The glass coating amount at this time was 0.5 g / m ^2.
It is as follows. When the content is 0.5 g / m ² or less, it is far more advantageous in terms of processability than in the case of having a normal glass coating. The conditions of the final annealing are particularly important in the step of appropriately forming and decomposing the glass coating as described above in the final annealing process as in the present invention.

Normally, in the final finish annealing of the grain-oriented electrical steel sheet, N ₂ , H ₂ , or a mixed gas thereof is used as the atmosphere gas. It is important to stabilize the inhibitors. For this reason, it is preferable to use N ₂ , H _2, and other inert gases in which the temperature N _{2 is} 30% or more during the temperature rise. On the other hand, in the case of N ₂ 100%, depending on the physical property value of MgO, the space between the steel sheets becomes extremely oxidizable, and the steel sheet surface is oxidized, so that unevenness is likely to occur. Preferably a N ₂ 30 to 90%. The area where the N ₂ gas increases to 30% or more may be the whole area at the time of temperature rise, but the most preferable condition is from 700 ° C. to the point of reaching the soaking temperature.

In the present invention, the soaking temperature in the final annealing is advantageously set to 1180 to 1250 ° C. In the present invention, when the soaking temperature of the final finishing annealing is reached, the decomposition of the glass coating is completed. Depending on the temperature at this time, further thermal etching occurs, and the steel sheet is further mirror-finished. This further increases the iron loss improving effect.

If the soaking temperature is lower than 1180 ° C., this effect is weak and disadvantageous to purification. On the other hand, if the temperature exceeds 1250 ° C., there is a problem in that the mirror effect is limited, the coil shape may be deteriorated, and the edge portion may be seized. In the present invention, the processing conditions of the insulating coating agent are preferably as follows. For a grain-oriented electrical steel sheet having a normal glass coating, the amount of adhesion is 3 when applying and baking a tension-imparting insulating coating agent.
It is processed at about 5 g / m ² . This is due to the effect of thick internal oxidation of the glass film,
This is because there is a limit in improving iron loss due to the problem of increase in the coating weight, and magnetism is deteriorated due to a decrease in the space factor. In the product having no glass coating according to the present invention, the tension imparting type insulating coating agent is treated at 2.5 to 15 g / m ² .

The insulating coating agent component is not particularly limited. For example, 100 parts by weight (in terms of solid content) of a colloidal solution of SiO ₂ , SnO ₂ , Al ₂ O _3, etc., Al, Mg, C
130 to 200 parts by weight of a first phosphate such as a, chromic acid,
Alternatively, the amount of the chromate is 12 to 40 parts by weight as CrO ₃ . Atmospheric conditions during heat flattening are not particularly limited, but P H ₂ O / P H ₂
≦ 0.1 and H ₂ ≧ 5% are desirable. This is limited when heat flattening a steel sheet having no glass coating at a high temperature as in the present invention because oxidation is apt to occur in a furnace, so that the magnetism and the adhesion of the coating on the surface are kept good.

The mechanism by which the present invention can provide an ultra-low iron loss material having almost no glass coating is considered as follows. In the present invention, an appropriate amount of a glass coating is formed before the temperature rise of the finish annealing by the reaction between the novel annealing separator and the decarbonated film. As a result, an appropriate sealing effect is generated on the surface of the steel sheet, thereby stabilizing (Al, Si) N and preventing additional oxidation of the steel sheet.

Next, the glass coating layer is decomposed by chemical etching with an additive component at the later stage of the finish annealing when the temperature is raised, and SiO ₂ in the oxide is reacted with MgO on the surface. Thereafter, a thermal etching effect is provided in the high-temperature soaking stage of the finish annealing. At this stage, the irregularities on the surface of the steel sheet steel caused by the surface roughening during cold rolling and the unevenness of the oxide film during decarburization annealing are smoothed to a mirror-like surface.
This is because the disappearance of the glass coating at a high temperature facilitates the movement of atoms on the surface and lowers the surface tension, resulting in smoothing.

In order to stabilize the decomposition of the inhibitor (Al, Si) N during the glass film decomposition process until the completion of the secondary recrystallization at the time of raising the temperature, the N ₂ ratio in the atmosphere is preferably 30% by weight of N ₂ . With the above atmosphere, the temperature is kept extremely stable, and good secondary recrystallization can be obtained. The requirement that the steel sheet be subjected to nitriding treatment before the start of the secondary recrystallization of the final finish annealing after hot rolling is defined as the inhibitor required for the secondary recrystallization in the process assuming low-temperature slab heating as in the present invention. This is because the strength tends to be insufficient.

The nitriding method is not particularly limited, but may be a method of nitriding by mixing NH ₃ gas into the annealing atmosphere after decarburizing annealing, a method using plasma, a method in which a nitride is added to an annealing separating agent, and the final finishing is performed. Any method may be used, such as a method in which nitrogen generated by the decomposition of nitrides during the temperature rise of annealing is absorbed in the steel sheet, or a method in which the steel sheet is nitrided by increasing the N ₂ partial pressure in the atmosphere of the final finish annealing. The amount of nitriding is not particularly limited, but 1 ppm or more is required.

[0051]

EXAMPLES Example 1 C: 0.036% by weight, Si: 3.10% by weight, Mn:
0.14% by weight, S: 0.006% by weight, acid soluble A
1: a slab containing 0.030% by weight and N: 0.0060% by weight, the balance being Fe and inevitable impurities and having a thickness of 40 mm was heated at a temperature of 1150 ° C., and then hot-rolled at 1050 ° C .; 40 → 23 → 14 → 9 → 6 → 3.5 → 2
A hot rolled sheet was prepared by hot rolling with a pass schedule of (mm).
At this time, the hot rolling end temperature was 926 ° C., and in this case, the cumulative rolling reduction in the last three passes was 78%. Winding simulation was performed in which air cooling was performed for 4 seconds after hot rolling, water cooling to 550 ° C., holding at 550 ° C. for 1 hour, and furnace cooling.

Thereafter, the hot-rolled sheet was pickled and then cold-rolled at a reduction of 75% to obtain a cold-rolled sheet having a thickness of 0.50 mm. At this time, when the thickness is 1.2 mm, no aging treatment, 100 ° C x
Three types of cold-rolled sheets were prepared which were subjected to three types of aging treatment for 5 minutes (soaking) and 300 ° C. × 5 minutes (soaking). Then 8
Decarburization annealing was performed at 30 ° C. for 300 seconds and at 850 ° C. for 20 seconds. Thereafter, during the heat treatment at 770 ° C. for 30 seconds, NH ₃ gas was mixed into the atmosphere gas to cause the steel sheet to absorb nitrogen.

At this time, the N content of the steel sheet is 0.0218 to 0.2.
It was 0244% by weight. The average grain size of the primary recrystallized grains of the steel sheet at a total thickness was measured using an optical microscope and an image analyzer, and was found to be 22 to 24 μm. Next, Ca was added to the steel sheet after the nitriding treatment with respect to 100 parts by weight of MgO.
An annealing separator containing 10 parts by weight of Cl ₂ was applied, and N ₂ was added.
75%, in H ₂ 25% of the atmospheric gas at 15 ° C. / time 12
The temperature was raised to 00 ° C., and final finishing annealing was performed at 1200 ° C. in an atmosphere of 100% H ₂ for 20 hours. Table 1 shows the experimental conditions and the magnetic properties and surface conditions of the product.

[0054]

[Table 1]

Example 2 C: 0.040% by weight, Si: 3.09% by weight, Mn:
0.14% by weight, S: 0.007% by weight, acid soluble A
1. A slab having a thickness of 40 mm, containing 0.028% by weight of N and 0.0030% by weight of N, the balance being Fe and unavoidable impurities, was heated at a temperature of 1150 ° C., and then hot rolled in 6 passes. It was a hot-rolled sheet of 3 mm. At this time, the rolling reduction is 40 → 2
4 → 16 → 11 → 6.6 → 3.9 → 2.3 (mm) At this time, the hot rolling end temperature is 947 ° C. In this case,
The cumulative rolling reduction in the last three passes was 79%. Winding simulation was performed in which the steel sheet was air-cooled for 2 seconds after hot rolling, water-cooled to 550 ° C., held at 550 ° C. for 1 hour, and cooled in a furnace.

Thereafter, the hot-rolled sheet was pickled and then cold-rolled in the same direction at a rolling reduction of 78% to obtain a cold-rolled sheet having a thickness of 0.50 mm. At this time, two types of cold-rolled sheets having a thickness of 1.5 mm and 1.0 mm and having been subjected to two types of aging treatment of 350 ° C. × 5 minutes (soaking) without aging were prepared. Then 830
C. for 300 seconds, and decarburization annealing at 870.degree. C. for 20 seconds. Thereafter, during a heat treatment at 750 ° C. for 30 seconds, NH ₃ gas was mixed into the atmosphere gas to cause the steel sheet to absorb nitrogen.

At this time, the N content of the steel sheet was 0.0231 to 0.0
245% by weight. The average grain size of the primary recrystallized grains of the steel sheet at a total thickness was measured using an optical microscope and an image analyzer and found to be 25 to 26 μm. Next, an annealing separator was applied to the steel sheet after the nitriding treatment under the same conditions as in Example 1, and final finish annealing was performed. Table 2 shows the experimental conditions and the magnetic properties and surface conditions of the product.

[0058]

[Table 2]

Example 3 C: 0.031% by weight, Si: 3.01% by weight, Mn:
0.14% by weight, S: 0.006% by weight, acid soluble A
l: A 30 mm thick slab containing 0.029% by weight and N: 0.0040% by weight, the balance being Fe and unavoidable impurities, was heated at a temperature of 1150 ° C, and then hot-rolled at 1050 ° C. The allocation is 30 → 20 → 13 → 8 → 5 → 3.
0 → 2.0 (mm). At this time, the hot rolling end temperature was 86
2 ° C., in which case the cumulative rolling reduction for the last three passes is 75
%Met. After air cooling for 1 second after hot rolling, water cooling to 400 ° C,
A winding simulation in which the furnace was cooled at a temperature of 400 ° C. for one hour and then cooled was performed.

Thereafter, the hot-rolled sheet was pickled and then cold-rolled at a reduction of 70% to obtain a cold-rolled sheet having a thickness of 0.60 mm. At this time, when the thickness is 1.5 mm, 1.2 mm, 0.8 mm, 50
Two types of cold-rolled sheets subjected to two types of aging treatments of (C) 5 minutes (soaking) and 300 ° C x 5 minutes (soaking) were prepared. Next, decarburizing annealing was performed at 840 ° C. for 400 seconds. Thereafter, during a heat treatment at 750 ° C. for 30 seconds, NH ₃ gas was mixed into the atmosphere gas to cause the steel sheet to absorb nitrogen.

At this time, the N content of the steel sheet is 0.0218 to 0.02.
It was 0240% by weight. The average grain size of the primary recrystallized grains of the steel sheet was measured using an optical microscope and an image analyzer, and was found to be 21 to 22 μm. Next, an annealing separator containing MgO as a main component was applied to the steel sheet after the nitriding treatment, and final finish annealing was performed by a known method.
Table 3 shows the experimental conditions and the magnetic properties and surface conditions of the product.

[0062]

[Table 3]

[0063] N ₂ 25% cold-rolled sheet of 0.50mm thickness as described in Example 4 Example 2 +
850 ° C × 400 in an atmosphere of 75% H ₂ and a dew point of 50 ° C
After decarburizing annealing for 2 seconds, 750 ° C, N ₂ 25% + H ₂ 75% +
In a dry atmosphere of NH ₃ , a nitriding treatment was performed so that the steel sheet [N] amount was 230 ppm to obtain a test material. At this time, the average primary recrystallization particle size was 21 to 23 μm.

An annealing separator having the composition shown in Table 4 was applied to the steel sheet, and the steel sheet was heated in an annealing atmosphere of 50% N _{2 and} 50% H _2.
The temperature was raised to 1180 ° C at 0 ° C / hour,
By a final finish annealing carried out in a time H ₂ 100% in the annealing atmosphere. Next, 50 ml of 20% colloidal silica + 50 ml of 20% colloidal SnO ₂ + CrO ₃ as an insulating coating agent
6 g of the coating agent after drying was 7.5 g /
m ² , and then subjected to strain relief annealing and baking treatment at 880 ° C. × 60 seconds. Table 5 shows the results of the surface conditions and magnetic properties of the steel sheet in this experiment.

[0065]

[Table 4]

[0066]

[Table 5]

Example 5 The steps up to nitriding were performed under the same conditions as in Example 4.
The amount of nitrogen after nitriding and the average particle size of primary recrystallization are the same as in Example 4. An annealing separator having a composition as shown in Table 6 was applied to this steel sheet, and was subjected to finish annealing under the conditions shown in Example 1. This steel sheet is coated with 20% colloidal silica 100ml + 50% aluminum phosphate 55ml + CrO2 as an insulating coating agent.
A coating agent consisting of ₃ 5 g in weight after drying 0-1
Baking at 850 ° C. for 30 seconds and strain relief annealing were performed in the range of 0 g / m ² . Table 7 shows the results of the surface condition and magnetic properties of the steel sheet in this step.

[0068]

[Table 6]

[0069]

[Table 7]

[0070]

In the present invention, the hot rolling end temperature, the cumulative rolling reduction in the last three passes of hot rolling, the temperature of the steel sheet between the passes of cold rolling,
After the decarburization annealing is completed, the average primary grain size of the recrystallized grains is controlled between the start of final finishing annealing, the steel sheet is nitrided, and chlorides, nitrates, sulfides, and sulfates are added to the annealing separator. And
Since the hot rolled sheet annealing can be omitted to obtain a unidirectional electrical steel sheet having a low cold rolling reduction rate and good magnetic properties and having no thick glass coating with a large thickness, the industrial effect is extremely large. .

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the temperature of a steel sheet between passes during cold rolling on the magnetic flux density of a product.

Continuing from the front page (72) Inventor Hiroaki Masui 1-1, Tobata-cho, Tobata-ku, Kitakyushu Nippon Steel Corporation Inside Yawata Works (72) Inventor, Kisumi Ishibashi 1-1-1, Tobata-cho, Tobata-ku, Kitakyushu New Nippon Steel Corporation Yawata Works (56) References JP-A-2-263923 (JP, A) JP-A-2-263924 (JP, A) JP-A-4-324 (JP, A) JP 57-134519 (JP, A) JP-A-57-47829 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 22/00-22/86 C21D 8/12 C22C 38 / 00 303 C22C 38/06

Claims (1)

(57) [Claims] 1. A weight ratio of C: 0.021 to 0.075%, Si: 2.5 to 4.5%, acid-soluble Al: 0.010 to 0.060%, N: 0.0010% 0.0130%, S + 0.405Se: 0.014% or less, Mn: 0.05 to 0.8%, 1280 slabs composed of Fe and unavoidable impurities.
After heating at a temperature of less than 100 ° C., it is hot-rolled, continuously cold-rolled at a reduction rate of 60 to 79% without performing hot-rolled sheet annealing, then decarburized annealing, coated with an annealing separating agent, and subjected to finish annealing. And
In a method for producing a thick unidirectional magnetic steel sheet having a thickness of 0.4 to 1.0 mm to which an insulating coating agent is applied, the hot rolling end temperature is set to 800
~ 1100 ° C and the cumulative rolling reduction of the last three passes of hot rolling is 4
0% or more, the temperature of the steel sheet between the cold rolling passes is set to 250 ° C. or less, and the average grain size of the primary recrystallized grains from the completion of decarburizing annealing to the start of final finishing annealing is set to 18 to 30 μm. The steel sheet is subjected to a nitriding treatment until the start of the secondary recrystallization of the post-final finish annealing, and Li, K, Na, Ba, Ca, Mg, Zn, Fe,
Magnetic properties characterized by applying an annealing separator containing 2 to 30 parts by weight of one or more selected from chlorides, nitrates, sulfides and sulfates of Zr, Sr, Sn, Al. Method for producing unidirectional magnetic steel sheet with excellent thickness and less glass coating.