JPH0657855B2 - Method for producing low iron loss unidirectional silicon steel sheet having excellent surface properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) Low iron loss unidirectional silicon steel sheet, surface property improvement when it is also particularly thin, and further improvement of magnetic flux density by control of secondary recrystallization texture. The technical content described in this specification in relation to is to propose the results of development research on enabling the production of the silicon steel sheet in a stable process.

( _Prior Art) Unidirectional silicon steel sheet can be used as an iron core material for transformers and electric equipment, has a high magnetic flux density (represented by a B ₁₀ value), and has an iron loss (represented by a W _17/50 value). Low) is required.

To achieve this goal, a great number of improvements have been made so far, and today, with magnetic flux density B ₁₀ value of 1.89T or more, iron loss W
A unidirectional silicon steel sheet having a low iron loss of _17/50 value of 1.05 W / kg or less has come to be manufactured.

However, the production of unidirectional silicon steel sheets with lower iron loss became an urgent issue after the energy crisis, and today, mainly in Europe and the United States, a system for giving bonuses to ultra-low iron loss silicon steel sheets (Loss evalution system) Is becoming popular.

As a method for producing a unidirectional silicon steel sheet with a significantly reduced iron loss value, the following method has recently been proposed.

That is, Japanese Patent Publication No. 57-2252, Japanese Patent Publication No. 57-53419, Japanese Patent Publication No. 58-5968, Japanese Patent Publication No. 58-26405, Japanese Patent Publication No. 58-26406,
As described in JP-B-58-26407 and JP-B-58-36051, Al is used as an inhibitor for suppressing the growth of crystal grains having an unsuitable orientation in final annealing.
Utilizing N precipitation phase, and introducing artificial grain boundaries on the surface of the steel sheet by irradiating the surface of the unidirectional silicon steel sheet of the product with a laser beam at an interval of a few mm approximately at right angles to the rolling direction,
This is a method of reducing iron loss by using this artificial grain boundary.

However, in the proposed method of introducing artificial grain boundaries, the high dislocation density region is locally formed, so that the product subjected to such treatment has a problem that it can be stably used only at a low temperature of about 350 ° C or lower.

In the method for producing a unidirectional silicon steel sheet using an AlN precipitation phase as cited above, in the case of ordinary steel, slab heating before hot rolling is performed in order to dissociate and dissolve MnS that coexists with AlN as an inhibitor. However, if slab heating is performed at such a high temperature, hot cracking is likely to occur during slab heating or hot rolling, and surface defects easily occur in the product. If the content of Si that inhibits the above exceeds 3.0%, the surface properties of the product will be significantly deteriorated.

In this regard, as previously disclosed by the inventors in Japanese Patent Laid-Open No. 59-85820, when an AlN precipitation phase is used, a high Si content S
Focusing on the fact that i3.1-4.5% silicon steel material is essentially suitable for obtaining products with high magnetic flux density and low iron loss, and solve the drawback of surface quality deterioration As a means, high Si can be obtained by concentrating Mo in the surface layer of the material before hot rolling.
The surface property can be made good even with the content. However, the surface quality of the product has been greatly improved by this new method compared to before, but recently, to obtain low iron loss, especially 0.23 to 0.17 mm
With regard to thin products, the effect of improving the surface properties is small and it remains a big problem.

Apart from this, the use of the AlN precipitate phase is originally based on the strong cold rolling single method, so when trying to manufacture a thin product, the secondary recrystallized grains became extremely unstable and strongly accumulated in the Goss orientation. There is also a problem that it is difficult to develop secondary recrystallized grains.

Most recently, in Japanese Patent Laid-Open No. 59-126722, in order to stably manufacture a thin product using an AlN precipitation phase under a high Si content, the conventional single strong cold rolling method was drastically used. Changed 2
It has been disclosed that a single cold rolling is applied to a hot rolled material having a composition in which a small amount of Cu and Sn are added in addition to AlN.

This method is effective in stably reducing the iron loss of thinned products, but it usually requires high temperature heating of the slab under the condition that the amount of Si is increased. If it is difficult to obtain, problems such as the fact that the cost of the product will be significantly increased due to the addition of small amounts of Sn and Cu to stabilize the secondary recrystallized grains will still be solved. There are many left.

(Problems to be Solved by the Invention) By the way, as a method for reducing the core loss of the unidirectional silicon steel sheet, the Si content in the silicon steel is increased and the product sheet thickness is reduced.

It is basically considered to improve the purity of the steel sheet and to develop fine secondary recrystallized grains without reducing the Goss orientation integration degree of the product secondary recrystallized grains.

First of all, increase the Si content from the usual 3.0%,
Regarding normal product thickness 0.35, thinner than 0.30mm 0.23, 0.
Attempts have been made to make it 20 mm, but in both cases, the secondary recrystallized structure becomes non-uniform, and there arises a problem that the Goss orientation integration degree decreases.

If the Si content is increased more than usual in accordance with the addition, hot embrittlement becomes remarkable, hot cracking occurs during slab heating or hot rolling, and the surface properties of the product have already been significantly deteriorated. Stated.

On the other hand, regarding the improvement of the purity of steel sheets or the improvement of the directionality thereof, it has reached the point where it is considered to be extreme at present. For example, the Goss orientation of the secondary recrystallized grains of the current product has already accumulated within an average of 3 ° to 4 ° in the rolling direction, and it is the metallurgy to further reduce the grain size in such a highly accumulated state. It is said to be extremely difficult.

In view of the above-mentioned recent trends in the prior art, the present invention has an industrially stable thin unidirectional silicon steel sheet with extremely excellent surface properties, extremely low iron loss, and high magnetic flux density. It is an object of the present invention to provide a method which can be manufactured particularly advantageously.

(Means for Solving Problems) The above purpose is fulfilled as follows.

Si3.1-4.5wt%, Mo0.003-0.1wt%, acid-soluble Al0.005-0.06wt%, and one or two of S and Se in total amount
A slab containing 0.005 to 0.1 wt% of steel is hot-rolled to form a hot-rolled sheet, which is then subjected to primary cold rolling with a reduction rate of 10 to 60%, and then 500 to 900 for both the temperature raising process and the temperature lowering process. After intermediate annealing that heats or cools between 5 ° C and 5 ° C / s in particular, secondary cold rolling with a reduction rate of 75 to 90% is applied to finish to a final sheet thickness of 0.1 to 0.25 mm, and this thin cold rolled sheet When decarburizing / primary recrystallization annealing is performed in wet hydrogen, a treatment that causes the formation of heterogeneous minute region compartments on the surface of the steel sheet through the subsequent high temperature finish annealing is performed in advance, and finally,
A method for producing a low iron loss thin unidirectional silicon steel sheet having excellent surface properties, characterized by performing high temperature finish annealing (first invention).

Si3.1-4.5wt%, Mo0.003-0.1wt%, acid-soluble Al0.005-0.06wt%, and one or two of S and Se in total amount
A slab containing 0.005 to 0.1 wt% is hot-rolled into a hot-rolled sheet, which is then subjected to primary cold rolling with a reduction rate of 10 to 60%, and then 500 to 900 for both the temperature raising process and the temperature lowering process. After intermediate annealing that heats or cools between 5 ℃ and 5 ℃ per second, the reduction rate
A thin cold-rolled sheet that has been subjected to 75-90% secondary cold rolling to a final sheet thickness of 0.1-0.25 mm is decarburized in wet hydrogen, subjected to primary recrystallization annealing, and then subjected to high temperature finish annealing, and further A method for producing a low iron loss thin unidirectional silicon steel sheet having excellent surface properties, characterized by forming heterogeneous minute region sections on the surface of the steel sheet (second invention).

The inventors of the present invention, when producing a thin unidirectional silicon steel sheet by utilizing an AlN precipitate phase under a high silicon content of 3.1 to 4.5 wt%, add a small amount of Mo to the surface of the material. A product with excellent properties can be obtained, and by adopting two cold rolling methods including intermediate annealing of rapid heating and quenching, it is possible to manufacture a unidirectional silicon steel sheet having low iron loss in an extremely stable process. After discovering this, they have completed the above inventions.

First, an experimental case that led to the completion of the present invention will be specifically described.

C 0.047wt%, Si 3.43wt%, Mo 0.022wt%, acid soluble Al 0.
Steel ingot containing 028 wt% and S 0.025 wt% (test steel I) and C 0.055 wt%, Si 3.45 wt%, acid-soluble Al 0.026
A steel ingot (comparative steel I) containing wt%, S 0.025 wt%, Sn 0.12 wt% and Cu 0.08 wt% was heated at 1420 ° C. for 4 hours to dissociate and solidify the inhibitor, and then hot rolling. Then 2.2m
A hot rolled sheet with a thickness of m

After that, after performing the primary cold rolling at a rolling reduction of 70% or less, 107
Intermediate annealing was performed at 0 ° C for 3 minutes. During this intermediate annealing, a temperature rise from 500 ° C. to 900 ° C. was subjected to a rapid heat treatment of 10 ° C./s, and after the intermediate annealing, a rapid cooling treatment was performed from 900 ° C. to 500 ° C. at a rate of 15 ° C./s.

After that, 0.20 mm after secondary cold rolling with 70% to 91% reduction.
After the cold-rolled sheet having the final thick sheet thickness, decarburization and primary recrystallization annealing were performed in wet hydrogen at 840 ° C.

After that, an annealing separating agent containing MgO as a main component is applied on the surface of the steel sheet, and the temperature is raised at 7 ° C / hr between 850 ° C and 1100 ° C for secondary recrystallization, and then at 1200 ° C for 12 hours. Purification annealing was performed in dry hydrogen for an hour.

FIG. 1 shows the magnetic properties and surface defect occurrence rate of the product at that time (block occurrence rate of surface scratches present on the surface of the steel sheet is expressed in%).

As is clear from the plot indicated by the ● mark in FIG. 1, the product of the sample steel I containing Mo in the material is magnetic when the reduction ratio of the primary cold rolling is 10 to 60% (especially 20 to 40%). It is noted that the characteristics are good and that the surface defect occurrence rate of the product is 1.5% or less (0.5% or less in the reduction ratio of the primary cold rolling of 20 to 50%).

On the other hand, the magnetic properties of the product made from Comparative Steel I with the conventional composition are shown in the plot with ○ in the figure, and the B ₁₀ value, W
_{Both of the 17/50} values are slightly worse than those of the sample _steel I, and the surface defect occurrence rate of the product is extremely high at 6 to 18%.

Next, C 0.053%, Si 3.44%, Mo 0.025%, acid-soluble Al 0.03
A steel ingot (test steel II) containing 0% and S 0.021% was heated at 1440 ° C. for 3 hours to dissociate the inhibitor and form a solid solution, and then hot rolling was performed to obtain a hot rolled sheet having a thickness of 2.2 mm.

After that, primary cold rolling with a reduction rate of about 40% was performed, and then intermediate annealing was performed at 1050 ° C. for 3 minutes. 500 during this intermediate annealing
Temperature rising rate from ℃ to 900 ℃, 900 ℃ to 50 after intermediate annealing
The experiment was conducted at a cooling rate of 0 ° C. in the range of 1 ° C. to 100 ° C. per second.

After the intermediate annealing, the steel sheet is subjected to secondary cold rolling with a rolling reduction of about 83% to obtain a final cold-rolled sheet with a thickness of 0.23 mm, after which decarburization and primary recrystallization annealing are performed in wet hydrogen at 850 ° C. , MgO on the steel plate surface
850 ℃ to 1100 after applying an annealing separator containing
After re-crystallizing by heating up to 10 ℃ at 10 ℃ / hr, 1200 ℃
Purification annealing was performed in dry hydrogen for 10 hours. The magnetic characteristics of the product at that time are shown in FIG.

As can be seen from Fig. 2, during the intermediate annealing, the temperature was from 500 ℃ to 900 ℃.
When the heating rate up to 5 ° C. and the cooling rate from 900 ° C. to 500 ° C. after the intermediate annealing are 5 ° C./s or more, and 10 ° C./s or more, a product having remarkably excellent magnetic properties can be obtained.

The reason why the characteristics are improved by the rapid heating / quenching treatment during the intermediate annealing has been already disclosed by the inventors in JP-A-59-35625 (supra).
It is considered that this is because it is advantageous to preferentially develop the texture of {110} <001> orientation, as disclosed in. In addition, as mentioned above, in the method for producing a thin unidirectional silicon steel sheet using the AlN precipitation phase of the cold rolling double rolling method in Japanese Patent Laid-Open No. 59-126722, the conventional strong cold rolling single rolling method is used. In contrast to the fact that the fine precipitation treatment of AlN by the quenching treatment after the homogenizing annealing in FIG. 3 is only applied to the cooling process after the intermediate annealing after the primary cold rolling, in the present invention, only the quenching after the intermediate annealing is required. First, it was newly clarified that excellent magnetic properties can be obtained only when Mo is contained in combination with rapid heating in the temperature rising process of intermediate annealing.

Further, the following experiment was conducted in consideration of the above conditions.

C 0.049%, Si 3.42%, Mo 0.025%, acid soluble Al 0.025%,
Steel ingot containing S 0.025% (test steel III), C 0.049
%, Si 3.46%, acid-soluble Al 0.025%, S 0.025%, Sn 0.05
%, Cu ingot containing 0.1% (test steel IV), C 0.048%,
All steel ingots (test steel V) containing Si 3.43%, acid-soluble Al 0.026%, and S 0.024% were heated at 1420 ° C for 4 hours to dissociate and solidify the inhibitor, and then hot rolled. A 2.0 mm thick hot rolled sheet was used.

After that, after performing the primary cold rolling at a reduction rate of about 50%, 1050
Intermediate annealing was performed at 0 ° C for 3 minutes. During this intermediate annealing
The temperature rise from 500 ℃ to 900 ℃ is rapid heat treatment at a heating rate of 11 ℃ / s, and the cooling rate is 15 ℃ from 900 ℃ to 500 ℃ after the intermediate annealing.
/ S was quenched.

After that, secondary cold rolling was performed at a reduction rate of approximately 80% to obtain a final cold-rolled sheet having a thickness of 0.20 mm, but warm rolling was performed at approximately 300 ° C. during the cold rolling.

After that, degreasing the steel plate surface and decarburizing in wet hydrogen at 840 ° C.
When performing primary recrystallization annealing, especially in this case, after performing this annealing, dilute aqueous solution of MgSO ₄ (0.01 mol at 80 ° C)
/ l) is sprayed 0.7m at 7mm intervals in the direction perpendicular to the rolling direction.
8 m / hr from 840 ℃ to 1050 ℃ after coating and drying in m width and applying annealing separation material mainly composed of MgO on the steel plate surface
The temperature was raised in order to carry out secondary recrystallization, and further purification annealing was carried out in dry hydrogen at 1200 ° C. for 10 hours. For comparison, decarburization-1
After the secondary recrystallization annealing, an annealing separator having MgO as a main component was applied to the surface of the steel sheet, and then secondary recrystallization and purification annealing were also performed on the ordinary process material at the same time.

Table 1 shows the magnetic properties and surface defect occurrence rate of the product at that time (block occurrence rate of surface scratches existing on the steel plate surface is expressed in%).

As is clear from Table 1, the test steel with Mo added to the material II
The magnetic properties of the product by I are as follows: B ₁₀ value is 1.94T, W _17/50 value is
Good at 0.77 to 0.85 W / kg, and the product surface defect rate is 0.6%
~ 0.9%. On the other hand, the magnetic properties of the test steels IV and V of the conventional composition have B ₁₀ value of 1.93T and W _17/50 value of 0.83 to 0.92.
W / kg, worse than the Mo-added material, and the surface defect rate of the product is extremely high at 8.7 to 11.2%.

Next, the dilute aqueous solution of MgSO ₄ was sprayed onto the surface of the decarburized primary recrystallization annealed sheet at a width of 7 mm at intervals of 7 mm at a right angle to the rolling direction, and the magnetic properties were the same as those of the sample steel III containing Mo. The iron loss at W _17/50 is _0.77 W / kg, which is extremely good. Also, in the magnetic properties of the test steels IV and V having the conventional composition, the iron loss in the process of applying the dilute aqueous solution of MgSO ₄ is about 0.06 to 0.09 W / kg as compared with the normal process (comparative material). is there.

In order to produce a low iron loss thin unidirectional silicon steel sheet with excellent magnetic properties and surface properties of the product from these experimental examples, a small amount of Al, Mo and Sb are added in combination in the high silicon material, Cold rolled 2
It has been shown to be accomplished by the combination of employing a batch method and compartmentalizing with a dilute aqueous solution or suspension coating containing the specified element on the final cold-rolled sheet surface.

As already disclosed in Japanese Patent Laid-Open No. Sho 60-89521, some of these structures are formed on the surface of the steel sheet after decarburization and primary recrystallization annealing,
As a method for producing a unidirectional silicon steel sheet with low iron loss by alternately partitioning a decarburization promotion region or a decarburization delay region almost at right angles to the rolling direction to develop heterogeneous secondary recrystallized grains, the present inventors , Which is a cold rolling process including intermediate annealing of rapid heating / quenching before the final cold rolled sheet surface application.
By using the rolling method, particularly stable growth of secondary recrystallized grains can be achieved.

Next, C 0.053%, Si 3.39%, Mo 0.026%, acid-soluble Al 0.02
A steel ingot containing 3% and S 0.023% is heated at 1380 ° C for 6 hours to dissociate and solidify the inhibitor, and then hot rolled to 2.0 m.
A hot rolled sheet with a thickness of m

After that, it was cold-rolled twice (50% primary cold reduction and 80% secondary cold reduction) with intermediate annealing at 970 ° C for 3 minutes.
The final cold rolled sheet had a thickness of 0.20 mm. 50 during this intermediate annealing
The temperature rise from 0 ℃ to 900 ℃ is rapid heat treatment at a heating rate of 12 ℃ / s, and the cooling rate from 900 ℃ to 500 ℃ is 13 ℃ /
s.

After that, decarburization and primary recrystallization annealing were performed in wet hydrogen at 835 ° C, and then an annealing separator containing MgO as a main component was applied, and then 850
The temperature was raised from 10.degree. C. to 10.degree. C./hr to carry out secondary recrystallization, and then purified annealing was carried out at 1200.degree. C. for 8 hours in dry hydrogen.

After that, a pulse laser was used to irradiate in a line shape (line width 0.3 mm width) in a direction perpendicular to the rolling direction at 8 mm intervals, and then pickling treatment was performed to remove a part of the base metal at the laser irradiation position and then a solution of SbCl ₃ After immersing in (80 ℃, 0.01mol / l), form an insulating film mainly composed of phosphate and colloidal silica.
Recovery / recrystallization annealing was performed at 0 ° C. for 3 hours also as strain relief annealing. The magnetic property of the product at that time is B ₁₀ value 1.94T, W
_{At a 17/50} value of 0.78 W / kg, the surface defect occurrence rate (the rate of block generation of surface scratches existing on the steel sheet surface is expressed in%) was 1.3%, which was very good.

As already disclosed in Japanese Patent Laid-Open No. 60-255926, some of these structures are non-homogeneous by removing a part of finish-annealing or a unidirectional silicon steel sheet coated with an insulating film after finish-annealing. By partitioning the regions, it is possible to stably manufacture a unidirectional silicon steel sheet having excellent iron loss.

As described above, the present invention is that Mo is added to the material,
Adopting the cold rolling twice method, limiting the rate of temperature rise / fall in intermediate annealing, and forming dissimilar microregions on the steel sheet during decarburization / primary recrystallization annealing or after finish annealing This makes it possible to manufacture a unidirectional silicon steel sheet having good iron loss and surface properties in a stable process, which is different from the above-mentioned prior art in the basic idea, and those The effect obtained by adopting the process is far superior to the conventional one.

(Function) In each invention, Si is an element effective in increasing the electrical resistance of the silicon steel sheet and reducing the overcurrent loss as described above. Especially, in order to reduce the iron loss of thin products, it is necessary to set it to 3.1 wt% or more. There is. However, if the Si content exceeds 4.5 wt%, brittle cracking tends to occur during cold rolling, so the Si content should be 3.1
The range was up to 4.5 wt%. The Si content of conventional unidirectional silicon steel sheet using AlN as an inhibitor is 2.
It is about 8 to 3.0 wt%, and when Si is increased, the first
The surface properties of the products are remarkably deteriorated as in the case of the test steels I and II shown in the figure.
By adding 3 to 0.1 wt% of Mo, it became possible to prevent the generation of surface defects.

If the amount of Mo added to this material is less than 0.003 wt%, the magnetic properties are not improved and the ability to prevent the generation of surface defects is weak, and if decarburization exceeds 0.1%, decarburization in steel is delayed from 0.003 to 0.1 wt%.
It should be limited to the range of%.

Al combines with N contained in steel to form AlN fine precipitates and acts as a strong inhibitor. In particular, in the production of thin unidirectional silicon steel sheet, acid-soluble Al in the range of 0.005 to 0.06 wt% is necessary to develop the secondary recrystallized grains strongly integrated in the Goss orientation.

AlN as an inhibitor when acid-soluble Al is less than 0.005 wt%
The amount of fine precipitates is insufficient, and the {110} <001> orientation is 2
The development of secondary recrystallized grains becomes insufficient. On the other hand, when it exceeds 0.06 wt%, the development of secondary recrystallized grains in the {110} <001> orientation becomes remarkably poor.

S and Se form a dispersed precipitation phase of MnS or MnSe together with AlN to enhance the inhibitor effect. If the total amount of S or Se is less than 0.005 wt%, the inhibitor effect by MnS or MnSe is weak, while if the total amount exceeds 0.1 wt%, the hot and cold workability deteriorates significantly.
It is necessary that the total amount of one or two of these is within the range of 0.005 to 0.1 wt%. Even within such a total amount range, when S is less than 0.005 wt% or Se is 0.003 wt%
If the amount is less than 0.005% by weight, the inhibitor effect is insufficient. If the amount exceeds 0.05% by weight, hot and cold workability deteriorates.
Is preferably in the range of 0.003 to 0.05 wt%.

As the material compatible with the method of each invention, as described above, 3.
It must contain 1 to 4.5% of Si and a small amount of Mo, Al, S and Se, but it does not prevent the presence of other known elements added to ordinary silicon steel. .

For example, it is preferable that Mn is contained in an amount of about 0.02 to 2 wt%.

Further, C is necessary for causing γ transformation in a part of the steel sheet during annealing of the hot rolled sheet in relation to the fine precipitation of AlN. In the present invention, the Si content is 3.1 to 4.5 wt% and the C content is contained. Amount is 0.030
About 0.080 wt% is suitable.

Further, it may contain 0.2 wt% or less in total of any one or more of Sn, Cu, and B as a known primary recrystallization grain growth inhibitor that may be added to ordinary silicon steel. . In addition, it is permissible to contain a small amount of general unavoidable elements such as Cr, Ti, V, Zr, Nb, Ta, Co, Ni, P and As.

Next, a series of manufacturing steps of the present invention will be described.

First, as a means for smelting the raw material used in the method of the present invention, an LD converter, an open hearth furnace or other known steel-making methods can be used, and it goes without saying that vacuum treatment and vacuum melting may be used in combination. Is.

Further, as a means for producing a slab, in addition to the usual ingot-bulk rolling method, continuous casting can also be preferably used.

The silicon steel slab obtained as described above is heated by a known method and then subjected to hot rolling. The thickness of the hot-rolled sheet obtained by this hot rolling varies depending on the reduction rate in the subsequent cold-rolling step, but is usually preferably about 1.5 to 3.0 mm.

In this invention, it is necessary to add a small amount of Mo to the raw material in order to obtain a silicon steel sheet having a good surface quality. However, as disclosed by the inventors in JP-A-59-85820. It is of course possible to use a means for concentrating Mo on the surface layer of the steel sheet by applying a Mo compound to the surface by the end of hot rolling.

The hot-rolled sheet that has been hot-rolled is then subjected to primary cold-rolling, but before the primary cold-rolling, C in the hot-rolled sheet may be added depending on the case.
In order to disperse the particles in a uniform manner, uniform annealing is performed in the temperature range of 900 to 1200 ° C., followed by quenching.

The reduction ratio in the primary cold rolling is slightly different depending on the product sheet thickness, but in order to obtain a thin product having good characteristics according to the present invention, as is clear from FIG. 1, it is 10 to 60% (desirably 20%).
Limited to ~ 50%).

The next intermediate annealing is performed at a temperature of 900 to 1100 ° C for about 30 seconds to 30 minutes, but in order to stably obtain good magnetic properties, the temperature should be raised from 500 ° C to 900 ° C and after the intermediate annealing. It is desirable to lower the temperature from 900 ° C. to 500 ° C. to 5 ° C./s or more, and 10 ° C./s or more. For this rapid heating and quenching treatment, a known method such as an ordinary continuous furnace or batch furnace may be used.

The next secondary cold rolling is as shown in Fig. 1 and Fig. 3.
Applies with a reduction rate of 70 to 90% and finishes the final cold rolled sheet thickness of 0.1 to 0.25 mm.

The purpose of each invention is to manufacture thin high magnetic flux density magnetic steel sheets, and the thickness of the hot rolled sheet is about 1.5 to 3.0 mm.
By finishing the thin final cold-rolled sheet with a thickness of 0.1 to 0.25 mm at the respective reduction ratios of the cold rolling and the secondary cold rolling shown in FIGS.

At this time, as disclosed in JP-B-54-13866, aging treatment at 50 to 600 ° C. may be performed between a plurality of passes.

Decarburization annealing which also serves as primary recrystallization is applied to a cold plate having a thin plate thickness of 0.1 to 0.25 mm in this manner in a temperature range of about 750 to 870 ° C. This decarburization annealing is usually performed in a wet hydrogen gas atmosphere with a dew point of approximately 30 to 65 ° C or hydrogen
It may be performed for several minutes in a nitrogen mixed gas atmosphere.

Then, the decarburized and annealed steel sheet is coated with an annealing separator containing MgO as a main component and subjected to finish annealing to develop secondary recrystallized grains in the {110} <001> orientation. The specific conditions of this finish annealing may be the same as those conventionally known, but usually 1150
It is desirable to raise the temperature to 1250 ° C. at a temperature rising rate of 3 to 50 ° C./hr to develop secondary recrystallized grains, and then perform a purification annealing for 5 to 20 hours in dry hydrogen.

Then, after finishing the final cold rolling, the steel sheet finished to the product sheet thickness is subjected to decarburization / primary recrystallization annealing treatment after surface degreasing. As already mentioned in the first invention, decarburization / A unidirectional silicon steel sheet with low iron loss can be manufactured by forming compartments of different minute regions on the surface of the steel sheet after primary recrystallization annealing.

This method of forming a section of a heterogeneous minute area on the surface of a steel sheet is an area in which a minute strain is introduced or a different tension acts on the surface of the steel sheet due to laser, electric discharge machining, scribing or ball-point pen-shaped spheres (Japanese Patent Publication No. No. 23647, Shokoku 58-296
No. 8, Japanese Patent Application Laid-Open No. 60-89545, Japanese Patent Application No. 59-261740 and Japanese Patent Application Laid-Open No. 57-18810) Temperature unevenness is created on the surface of the steel sheet by heat treatment at a local position on the surface of the steel sheet (Japanese Patent Application Laid-Open No. Sho 59-100221, JP-A-60-114519
Nos. 60-103120 and 60-103132).

After such treatment, an annealing separator containing MgO as a main component is applied on the surface of the steel sheet, and finish annealing is applied to {110}.
Develop secondary recrystallized grains that are strongly integrated in the <001> orientation. The specific conditions of this finish annealing may be the same as those of the conventionally known annealing method, but usually 1150 to 1250 ° C. to 3 to 50 ° C.
After raising the temperature at a heating rate of / hr to develop secondary recrystallized grains, it is desirable to carry out a purification annealing for 5 to 20 hr in dry hydrogen.

An insulating coating is provided on the forsterite coating on the surface of the steel sheet after finish annealing to ensure reliable insulation. However, as already mentioned in the second aspect of the present invention, on the surface of the steel sheet subjected to finish annealing. A unidirectional silicon steel sheet with low iron loss can be manufactured by forming different minute sections.

In this case, Japanese Patent Publication No. 57-22525, Japanese Patent Publication No. 57-53419, Japanese Patent Publication No.
58-5968, Japanese Patent Publication No. 58-26405, Japanese Patent Publication No. 58-26406, Japanese Patent Publication No. 58-26407 and Japanese Patent Publication No. 58-36051, the artificial grain boundary introduction method by the laser irradiation method is only low temperature. Since it has a drawback that it cannot be used stably, it is necessary to adopt a method of partitioning and forming a heterogeneous region on the surface of a steel sheet by a method in which the magnetic properties do not deteriorate even if high-temperature strain relief annealing is performed.

As for the method of partitioning inhomogeneous regions where magnetic properties do not deteriorate even when subjected to high-temperature annealing, d) partitioning regions of different thickness of the forsterite coating on the surface of the steel sheet (see JP-A-60-92479), b forsterite Differently forming tension coatings on the coating (Japanese Patent Laid-Open No. 60-103182) c. As described above, after locally removing the forsterite coating using a laser or the like, the local area is recovered and re-formed. It is possible to use, for example, crystallization to partition non-uniform secondary recrystallized grains (see JP-A-59-100222).

Furthermore, in order to guarantee reliable insulation after such treatment, it is possible to apply and bake an insulating coating mainly composed of phosphate and colloidal silica in the use of a large capacity transformer of up to 1 million KVA. This is of course necessary, and a conventionally known method may be used as it is for forming the insulating coating baking layer.

After forming such an insulating coating, strain relief annealing is performed at a temperature of 600 ° C. or higher, and the above-described manufacturing method of the present invention does not cause deterioration of magnetic characteristics even when subjected to such high temperature annealing. It is a feature.

Example 1 A continuously cast slab containing C 0.054%, Si 3.36%, Mo 0.024%, acid-soluble Al 0.025%, Se 0.020%.
After heating at 1420 ° C. for 4 hours, hot rolling was performed to obtain a hot rolled sheet having a thickness of 2.2 mm. Then, after performing 40% primary cold rolling, 1100
Intermediate annealing was performed at 2 ° C for 2 minutes. During this intermediate annealing
A rapid heat treatment was performed at 12 ° C / s from 500 ° C to 900 ° C, and an intermediate annealing was performed, followed by a rapid cooling process at 18 ° C / s from 900 ° C to 500 ° C. Then, about 83% secondary cold rolling was performed to obtain a final cold rolled sheet having a thickness of 0.23 mm, and then decarburization / primary recrystallization annealing was performed in wet hydrogen at 840 ° C.

After that, a pulse laser was used to irradiate linearly (line width 0.3 mm width) in a direction perpendicular to the rolling direction at intervals of 8 mm, and then a SnCl ₃ (0.01 mol / l, 90 ° C.) solution was applied to this laser irradiation position.

After that, an annealing separator containing MgO as a main component was applied on the surface of the steel sheet, the temperature was raised from 850 ° C to 1100 ° C at 10 ° C / hr for secondary recrystallization, and then purified at 1200 ° C for 15 hours in dry hydrogen. Annealed.

After that, an insulating coating mainly composed of phosphate and colloidal silica was baked, and then strain relief annealing was performed at 800 ° C. for 2 hours. The magnetic properties and surface properties of the product at that time were as follows.

The magnetic properties were B ₁₀ 1.94T, W _17/50 0.79W / kg, and the surface properties were 0.8% in terms of the block occurrence rate of surface defects, which was very good.

Example 2 A continuous casting slab containing C 0.056%, Si 3.41%, Mo 0.025%, acid-soluble Al 0.030%, Se 0.020%, Sn 0.1%, Cu 0.1% was heated at 1430 ° C. for 4 hours and then hot-worked. Rolled to a thickness of 2.2 mm. Then about 40% of 1
After the subsequent cold rolling, intermediate annealing was performed at 1050 ° C. for 5 minutes. During this intermediate annealing, the temperature from 500 ° C to 900 ° C should be 15 ° C
/ S rapid heat treatment and intermediate annealing after 900 ℃ to 500 15
After the rapid heat treatment at .degree. C./s and the intermediate annealing, a rapid cooling process at 20.degree. C./s was performed from 900.degree. Next, a secondary cold rolling of about 85% was performed to obtain a cold rolled sheet having a thickness of 0.20 mm. During this cold rolling, warm rolling was performed at 250 ° C. After that, decarburization and primary recrystallization annealing are performed in wet hydrogen at 850 ° C, and then an annealing separator mainly composed of MgO is applied, and then 850 ° C to 1100 ° C to 8 ° C.
After gradually heating at a heating rate of 1 hour / hour, purification annealing was performed at 1200 ° C. for 10 hours in a hydrogen atmosphere.

After that, on the surface of the steel plate, 0.5mm width, 8m in the direction perpendicular to the rolling direction
After introducing scribing at m intervals, baking treatment is performed on the insulating coating mainly composed of phosphate and colloidal silica, and the temperature is increased to 5 ° C at 800 ° C.
Strain relief for time and recovery / recrystallization annealing were performed.

The magnetic properties and surface properties of the obtained product were as follows.

Magnetic properties B ₁₀ 1.94T, W _{17/50 0.76W} / kg, and the block occurrence rate of surface defects of surface texture was 1.1%, which was extremely good.

Example 3 A continuously cast slab containing C 0.053%, Si 3.38%, Mo 0.026%, acid-soluble Al 0.030%, and S 0.028% is heated at 1400 ° C. for 5 hours and hot-rolled to a thickness of 2.0 mm.

After that, it was cold-rolled twice (first cold rolling rate: 60%, second cold rolling rate: 75%) with intermediate annealing at 980 ° C for 3 minutes.
The final cold rolled sheet had a thickness of 23 mm. In this intermediate annealing, 500 ℃ to 900 ℃ 13 ℃ / s, 900 ℃ to 500 ℃ 15 ℃
/ S was rapidly heated and cooled. After that, it was subjected to primary recrystallization annealing that also functions as decarburization in wet hydrogen at 840 ° C, and then a marking was introduced on the surface of the steel sheet at a width of 0.5 mm in the direction perpendicular to the rolling direction and at intervals of 8 mm, and then SbCl ₃ was placed at that position. (0.01 mol / l, 80 ° C. solution) was applied. After that, an annealing separating agent containing MgO as a main component was applied, followed by secondary recrystallization by raising the temperature from 850 ° C to 1050 ° C at 8 ° C / hr and then performing a purification annealing in dry hydrogen at 1200 ° C for 10 hours. After that, an insulating film was formed. The magnetic properties and surface properties of the product at that time were as follows.

Magnetic property B ₁₀ : 1.94T, W _17/50 : 0.77W / kg The block occurrence rate of surface defects of surface texture was 1.3%, which was extremely good.

(Effect of the Invention) As is clear from the above description, according to the method of the present invention, B ₁₀
Is 1.92T or more, and iron loss is 0.85W / kg (0.23mm thickness) or less, and it is possible to industrially stably manufacture thin unidirectional silicon steel sheet with excellent product surface properties. It has a remarkable effect.

Further, according to the present invention, the material is made to contain Mo and Al to form the final cold-rolled sheet by the cold-rolling twice method, and then, during decarburization / primary recrystallization annealing or on the surface of the steel sheet after finish annealing. By forming the heterogeneous minute region section, a non-uniform and fine-grained Goss-oriented secondary recrystallization structure is developed, and a product having excellent iron loss characteristics and surface properties can be manufactured in a stable process.

[Brief description of drawings]

Fig. 1 shows the relationship between the magnetic properties of the product and the reduction ratio of the primary cold rolling and the secondary cold rolling, and the condition of the surface texture. Fig. 2 shows the heating rate and cooling rate during intermediate annealing. It is a figure which shows the relationship between the magnetic characteristic of a product and a product.

Claims (2)

[Claims] 1. Si 3.1 to 4.5 wt%, Mo 0.003 to 0.1 wt%, acid soluble Al 0.005 to 0.06 wt%, and one or two of S and Se in total amount.
After slab containing 0.005 ~ 0.1wt%, is hot-rolled into hot-rolled sheet, primary cold-rolling with a reduction rate of 10 ~ 60% is performed, then 500 ~ 900
Heating rate in the temperature raising process up to ℃ 5 ℃ per second
Above, after the intermediate annealing at the cooling rate of 5 ℃ per second or more in the cooling process in the temperature range from 900 ℃ to 500 ℃, the secondary cold rolling with the reduction rate of 75 to 90% is applied and the thickness of 0.1 to 0.25 mm is obtained. Finished to the final thickness and decarburized this thin cold rolled sheet in wet hydrogen. 1
During the subsequent recrystallization annealing, the surface property is characterized in that it is subjected in advance to a treatment to obtain the formation of foreign microregions on the surface of the steel sheet through the subsequent high-temperature finishing annealing, and finally to the high-temperature finishing annealing. Of excellent low iron loss thin unidirectional silicon steel sheet. 2. Si 3.1 to 4.5 wt%, Mo 0.003 to 0.1 wt%, acid-soluble Al 0.005 to 0.06 wt%, and one or two of S and Se in total amount.
After hot rolling a slab containing 0.005 to 0.1wt%, it is subjected to primary cold rolling with a rolling reduction of 10 to 60%, and then from 500 ℃ to 900
Heating rate in the temperature raising process up to ℃ 5 ℃ per second
Above, after the intermediate annealing at the cooling rate of 5 ℃ per second or more in the cooling process in the temperature range from 900 ℃ to 500 ℃, the secondary cold rolling with the reduction rate of 75 to 90% is applied and the thickness of 0.1 to 0.25 mm is obtained. The thin cold-rolled sheet finished to the final sheet thickness is characterized by decarburizing / primary recrystallization annealing in wet hydrogen, then high-temperature finish annealing, and forming a heterogeneous minute region section on the surface of the steel sheet. A method of manufacturing a low iron loss thin unidirectional silicon steel sheet having excellent surface properties.