JPH07188753A - Production of grain-oriented silicon steel sheet extremely reduced in iron loss - Google Patents

Abstract

PURPOSE:To obtain a grain-oriented silicon steel sheet extremely reduced in iron loss by filling grooves with oxides so that the grooves filled with oxides project from the surface of the steel sheet after final finish annealing, performing annealing, and then flattening the projecting part by means of reduction by roll. CONSTITUTION:As the linear grooves to be formed in the surface of a cold rolled silicon steel sheet, any of grooves in the form of straight line, wavy line, dashed line, and dotted line will do. Although a method for forming the grooves is not particularly specified, a method where etching resist is printed and electrolytic etching is done is excellent. It is desirable that the direction of the linear grooves has an angle of 0-30 deg. with respect to the direction perpendicular to rolling direction, and also it is preferable to regulate the width of spacing between grooves, the width of a groove, and the depth of a groove to 2-30mm, 30-100mum, and 5-50mum, respectively. As the oxides to be filled into the grooves, pulverized oxides causing solid phase reaction with MgO suffice, and filling is done, e.g. by application so that the amount of projection after final finish annealing is regulated to 4-40mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented silicon steel sheet having a low iron loss, and more particularly to a method for forming a groove on the surface of the steel sheet to subdivide magnetic domains to reduce the iron loss.

[0002]

2. Description of the Related Art Grained silicon steel sheet is mainly used as an iron core of transformers and other electric equipments, and it has excellent magnetizing characteristics, especially iron loss (50Hz at a maximum magnetic flux density of 1.7T).
W _17/50 or 1.5 which is the iron loss when alternating magnetization is carried out at the frequency of
It is required that the maximum magnetic flux density of T, represented by W _15/60 , which is the iron loss when alternating magnetization is performed at a frequency of 60 Hz) is low.

For this purpose, firstly, the secondary recrystallized grains in the steel sheet must be highly aligned in the (110) [001] orientation (usually called the Goss orientation), and secondly. It is necessary to reduce impurities and precipitates existing in the final product steel as much as possible. The iron loss value of _{grain-oriented} silicon steel sheet manufactured under such consideration has been improved year by year through many improvement efforts to date, and recently, a product with a sheet thickness of _{0.23 mm} has a thickness of W _17/50.
A value of 0.83 W / kg and a value of W _15/60 of 0.35 W / lb with low iron loss are obtained.

By the way, in recent years, a technique has been developed in which nonuniformity is introduced into the surface of a steel sheet by physical means to subdivide the width of magnetic domains and further reduce iron loss. For example, Japanese Patent Publication No.
In the gazette, the surface of the final product plate is irradiated with a laser beam at intervals of several mm almost at right angles to the rolling direction, and a high dislocation density region is introduced into the surface layer of the steel plate to reduce the width of magnetic domains and reduce iron loss. The technology to do is proposed. Further, JP-A-62-1
Japanese Patent No. 96617 proposes a technique in which a plasma jet is locally introduced into the surface layer of a steel sheet to reduce the magnetic domain width and reduce iron loss.

However, these techniques release the strain introduced by the heat treatment such as the stress relief annealing after the punching, shearing and winding of the steel sheet and the baking treatment of the coating, so that the iron loss reducing effect is obtained. With the drawback of being diminished. On the other hand, in JP-A 1-211903, JP-A 2-294427 and JP-A 3-138318, a roll with protrusions is pressed against the surface of the steel sheet after the final finish annealing to form a dent or a dent. There has been proposed a heat-resistant magnetic domain subdivision technique in which fine crystal grains are formed immediately below a dent by utilizing strain energy due to processing, and the effect of the dent and the fine grain does not diminish the effect even by strain relief annealing.

However, in these techniques, the protrusions on the roll surface are greatly worn or damaged, and it is difficult to stably maintain the effect, and it is difficult to control the pressing amount of the protrusions. It is difficult to control the amount of added strain, that is, the expression of fine crystal grains is not stable. Further, Japanese Patent Laid-Open No. 1-252728 discloses a low iron material in which a surface coating of a steel sheet after final finish annealing is linearly removed by ultrasonic vibration and then electrolytically etched to form grooves to subdivide magnetic domains. A technique for manufacturing a loss-oriented silicon steel sheet is disclosed.

This technique has a large effect of reducing iron loss and is stable, but since the surface coating is made of ceramic, it is difficult to remove the coating and the efficiency is low even if the ultrasonic processing technique is used. Since it requires a coating application step, it has not been industrially put to practical use.
On the other hand, in Japanese Examined Patent Publication No. 3-99968, a linear notch (groove) is introduced on the surface of the steel sheet before decarburization / primary recrystallization annealing to perform decarburization / primary recrystallization annealing and final finishing annealing. A technique for promoting purification is disclosed in Japanese Patent Laid-Open No. 4-88121 after final cold rolling.
A magnetic domain refining technique has been proposed in which an etching resist is linearly applied by printing, a linear groove is formed by etching, the resist is then removed, and decarburization annealing and final finishing annealing are performed.

These techniques are excellent in stability against heat treatment such as strain relief annealing because they form grooves before final finishing annealing, but they are unstable in terms of iron loss reduction effect, and particularly, plasma jet and There is a problem that the iron loss reduction effect in a high magnetic field is inferior to the method of introducing a minute strain such as laser irradiation.

[0009]

DISCLOSURE OF THE INVENTION The present invention provides a magnetic domain refinement technique as described above, in which after final cold rolling, grooves are formed and decarburization annealing is performed, an annealing separator is applied, and final finishing annealing is performed. To solve the problem that the iron loss reduction effect in the high magnetic flux density region such as 1.7T is inferior to that of the magnetic domain subdivision technology of the micro strain addition method, this problem is solved, and a grain-oriented silicon steel sheet having an extremely low iron loss is solved. It is intended to provide a manufacturing method.

[0010]

DISCLOSURE OF THE INVENTION The present invention is directed to a magnetic domain refining grain oriented silicon steel sheet in which a groove is formed on the surface of the steel sheet after final cold rolling, and decarburization annealing, annealing separation agent coating and final finishing annealing are performed. In the manufacturing method of, so that the groove filling portion protrudes from the surface of the steel sheet after the final finishing annealing, after forming the groove, the groove portion is filled with an oxide before the application of the annealing separator, and the protruding portion under the roll pressure after the final finishing annealing. Is a method for producing a grain-oriented silicon steel sheet having an extremely low iron loss, and the desirable amount of protrusion of the protrusion after final annealing is 4 to 40 μm.

[0011]

In order to achieve the above object, the present inventors have used the method disclosed in Japanese Unexamined Patent Publication No. 4-88121 and have a width of 65 μm.
Form a groove with a depth of 15 μm in the direction perpendicular to the rolling direction and with a repeat interval of 4 mm in the rolling direction. After decarburization annealing, apply an annealing separator, stack and perform final finishing annealing to improve the magnetic properties. It was measured (magnetic property a).

On the other hand, using a cold-rolled plate having the same grooves formed therein, Al ₂ O ₃ powder was filled in the grooves, decarburized and annealed, and then an annealing separator was applied and laminated for final finishing annealing. Then, the magnetic property was measured (magnetic property b). FIG. 1 is a schematic cross-sectional view after final finishing annealing corresponding to the groove portion filled with Al ₂ O ₃ powder at this time.
It shows in (a). In the groove filled with Al ₂ O ₃ as shown in FIG. 1 (a), after the final finish annealing, about 5 from the surface of the steel sheet
It was protruding by μm.

After that, the projections were smoothed while lightly reducing the pressure using pinch rolls. The magnetic characteristic at this time was measured again (magnetic characteristic c). After that, a schematic sectional view of the groove filled with Al ₂ O ₃ is shown in FIG. 1 (b), and the magnetic characteristics of a, b, and c are shown in Table 1. Next, as a comparative example, using the same cold-rolled plate in which no groove was formed, decarburization annealing was performed, an annealing separating agent was applied, and the layers were laminated and subjected to final finish annealing to measure magnetic characteristics (magnetic characteristic d). Further, this sample was irradiated with a plasma jet in a direction perpendicular to rolling at a pitch of 4 mm as a repeating interval in the rolling direction, and the magnetic characteristics were measured (magnetic characteristic e).

Table 1 also shows these magnetic properties.

[0015]

[Table 1]

As shown in Table 1, the iron loss value of the sample (c) subjected to the smoothing treatment in the experimental material is extremely low, and particularly W
_{Even at 17/50} , the iron loss was 0.755 W / kg, which is equivalent to the plasma jet irradiation treatment of the comparative material (e), and W _15/60
Is also excellent in. On the other hand, the _iron loss value of the sample (b) not subjected to the smoothing treatment is W _17/50 and W _15/60 ,
There is no difference from the core loss value of the sample (a) having the effect of subdividing the magnetic domains only in the groove.

The reason why the iron loss is improved when the smoothing treatment is performed is that the oxide protrusions formed in the groove filling portion shown in the schematic cross-sectional view of FIG. It is considered that as a result of being press-fitted in the inside, a minute strain was formed just below the groove portion, which brought about a new magnetic domain refining effect. By the way, FIG. 1 is a schematic cross-sectional view after the smoothing process.
The presence of a large number of dislocation groups was recognized in the lower part of the groove of (b).

As described above, it is possible to concentrate the strain just below the groove by the method of forming the protrusions in the groove and then performing the smoothing treatment, and the magnetic domain subdivision effect for forming the groove in the base metal on the surface of the steel sheet and the groove portion. It is considered that the magnetic domain refining effect by concentrating the minute strains underneath acts additively, and an extremely excellent magnetic domain refining effect is obtained. On the other hand, in the sample which is simply filled with the groove portion and has the protruding portion, there is no difference in the groove shape of the base metal portion, so that the magnetic characteristic does not differ.

In order to bring about the concentration of micro strains in the lower part of the base metal groove by the smoothing treatment, it is necessary to form a sufficient amount of protrusions on the groove surface. The results of investigating the mechanism by which these protrusions are formed will be described below. That is, the Al ₂ O ₃ filled in the groove reacts with MgO, which is the main component of the annealing separator applied to the surface of the steel sheet, as shown in the following formula, and spinel Al ₂ O ₃ + 2MgO → Mg ₂ Al ₂ O As a result of forming ₅ , the volume expands to form a protrusion despite the progress of the sintering reaction. Therefore, MgO
As long as it is an oxide that undergoes solid-phase reaction with, any oxide may be filled, and it is desirable that the powder be as fine as possible in order to enhance the reaction activity.

Further, it is understood that the oxide may be filled at any time between the groove formation and the application of the annealing separator. Next, as a result of repeating the above-described experiment for the optimum amount of protrusion for giving the effect of such a minute strain, it was found that the amount of protrusion is preferably 4 μm or more. However, when the thickness exceeds 40 μm, the amount of strain introduced after smoothing is too large, resulting in an increase in hysteresis loss, and conversely, a deterioration in iron loss.

The present invention has been completed through earnest research based on the novel findings obtained from such experiments. Next, a method for manufacturing the grain-oriented silicon steel sheet according to the present invention will be described in detail. The material of the present invention is a known steelmaking method such as a converter,
A hot-rolled coil obtained by hot-rolling after making steel by an electric furnace or the like and further forming a slab (steel piece) by an ingot-segmentation method or a continuous casting method is used.

It is necessary that this hot rolled sheet has a composition containing 2.0 to 4.5% of Si. That is, Si is 2.0%
If it is less than 4.5%, the deterioration of iron loss is large, and if it exceeds 4.5%,
This is because the cold workability deteriorates. As for the other components, any component can be applied as long as it is a material component of the grain-oriented silicon steel sheet. Next, the final target thickness is obtained by cold rolling, but the cold rolling is performed once or twice by sandwiching the intermediate annealing. At this time, if necessary, hot rolled sheet annealing, warm rolling instead of cold rolling, or aging treatment between rolling passes can be performed.

Grooves are formed on the surface of the steel sheet for the cold-rolled sheet having the final sheet thickness. As a method of forming a groove, a method of pressing a linear protruding tooth disclosed in JP-A-2-294427 and a laser beam disclosed in JP-B-3-69968, electric discharge machining, and mechanical marking However, in order to control the groove shape correctly, the technique of printing the etching resist disclosed in Japanese Patent Laid-Open No. 4-88121 and forming the groove by electrolytic etching is the most excellent.

At this time, the region where the groove is provided on the surface of the cold rolled plate needs to be linear, and the linear shape may be a straight line, a wavy line, a broken line, or a dotted line. Further, it is desirable that the direction of the linear groove be an angle of 0 to 30 ° with respect to the direction perpendicular to the rolling, and if it exceeds 30 °, the magnetic domain refining effect is hardly obtained. Here, in particular, by slightly inclining the direction of the groove from the direction perpendicular to the rolling direction, as shown in FIG. 2, during the smoothing process of the protruding portion after the final finish annealing, the load of the reduction roll is reduced and the meandering of the steel plate is performed. Is effective in suppressing

Further, it is necessary to repeatedly provide the grooves in the rolling direction, and the proper value of the interval is 2 to 30 mm. The interval is 2
When it is less than 30 mm, hysteresis loss is increased, and iron loss is deteriorated. On the other hand, when it exceeds 30 mm, a sufficient iron loss reducing effect cannot be obtained. The cross-sectional shape of the groove is one of the main techniques of the present invention, and it is desirable that the width of the groove is 30 to 1000 μm and the depth of the groove is 5 to 50 μm. When the width of the groove is less than 30 μm, the effect of reducing iron loss is poor, and when it exceeds 1000 μm, the hysteresis loss increases and the iron loss deteriorates. Further, when the depth of the groove is less than 5 μm, the iron loss reducing action is poor, and when it exceeds 50 μm, the hysteresis loss is increased and the iron loss is deteriorated.

Oxide powder is filled in the groove portion of the cold-rolled plate having the groove thus controlled on the surface of the steel plate. Any oxide may be used as long as it is a fine powder that solid-phase reacts with MgO, for example, Al ₂ O ₃ , CaO,
SiO ₂ , CoO ₂ , CuO ₂ , TiO ₂ , NiO ₂ , MnO ₂ , SrO 2, BaO 3 and the like are suitable. The filling of the oxide with the groove may be simply applied or attached, or may be filled with a binder or plating. Further, the time for filling the groove is suitable from immediately after the groove is formed to immediately before the application of the annealing separator.

The steel sheet having such a substance deposited in the groove is subjected to decarburization annealing in an oxidizing atmosphere, and this is also sufficient under ordinary decarburization annealing conditions. At this time, a subscale is formed on the surface of the steel sheet, and the subscale and the annealing separator applied to the surface of the steel sheet undergo a solid phase reaction during final finishing annealing to form a forsterite coating. At this time, the oxide filled in the groove and the MgO in the annealing separator undergo a solid-phase reaction to form a MgO-based composite oxide, forming a protrusion from the surface of the steel sheet.
At this time, it is preferable to control the amount of oxide filling the groove so that the amount of protrusion of the protrusion is 4 to 40 μm.

That is, when the protrusion amount is less than 4 μm, the amount of minute strain just below the groove portion introduced by the smoothing process in the next step is insufficient, and good iron loss cannot be obtained. If it exceeds, the amount of strain introduced by the smoothing becomes excessive, which causes an increase in hysteresis loss, and conversely causes deterioration of iron loss. The steel sheet after the final finish annealing is smoothed after removing the unreacted separating agent. The smoothing process is a process of press-fitting a portion protruding from the steel plate surface into the steel plate, but a method of passing between a pair of corresponding rolls, supporting the flat side of the steel plate on a flat plate, or Wrap it around a drum,
This is achieved by applying roll reduction to the surface on the protruding side and press-fitting the protruding portion. At this time, even if some distortion is applied to areas other than the lower part of the steel sheet groove, and the magnetic characteristics deteriorate, such mild and sparse distortion is removed during the baking of the insulating coating in the next step, and the magnetic characteristics are restored. So no problem.

The smoothing treatment is carried out between the step of removing the unreacted separating agent and the step of applying the insulating coating, but it is of course possible to carry out these continuously. After the smoothing treatment, an insulating coating is further applied to obtain a product. At this time, a tension coating is generally used. Applying the coating is also effective for repairing the oxide sintered body in the groove portion which has been destroyed by press fitting in the smoothing process.

[0030]

【Example】

Example 1 C: 0.075%, Si: 3.25%, Mn: 0.072%, P: 0.01
%, S: 0.003%, Se: 0.019%, Sb: 0.028%, N:
After soaking the steel slab containing 0.0074% at 1420 ℃ for 10 minutes,
A hot rolled coil of 1.8 mm was obtained by hot rolling.

The hot rolled coil was annealed at 1150 ° C. for 30 seconds,
It was rapidly cooled using a mist, pickled, cold-rolled to a thickness of 0.9 mm, heat-treated at 300 ° C for 2 minutes, and then rolled again at a temperature of 150 ° C to a thickness of 0.22 mm. After cold rolling, a groove with a width of 150 μm and a depth of 15 μm was formed at an angle of 10 ° from the direction perpendicular to the rolling by a method of applying resist ink and electrolytic etching at a repeating interval of 4 mm in the direction perpendicular to the rolling, and the coil was formed.
It was divided into 10.

Next, SiO is applied to each divided coil.₂Filling amount of fine powder
After changing and embedding, H₂20%, dew point 25 ℃, N₂ 
Decarburized and annealed at 850 ° C for 2 minutes in a balanced atmosphere
It was Then each coil is TiO₂Of MgO containing 5% of
After applying the annealing separator and winding it into a coil,
It was subjected to upper annealing. The condition of final finish annealing is N₂ In 840 ℃
After holding for 20 hours at 25% N₂ And 75% H ₂ In the atmosphere
The temperature is raised to 1200 ° C at a heating rate of 6.5 ° C / hr, and H₂ In 120
After holding at 0 ° C for 10 hours, the temperature was lowered.

After removing the unreacted separating agent, the steel sheet after the final finish annealing was subjected to a smoothing treatment by measuring the amount of protrusion of each coil in the SiO ₂ filling portion into the groove and applying a reduction with two pairs of rolls. went. After that, a tension coating mainly composed of colloidal silica and magnesium phosphate was applied and baked at 800 ° C to obtain a product. The relationship between the magnetic properties of each product and the amount of protrusion after final finish annealing is shown in FIG.

Example 2 C: 0.045%, Si: 3.35%, Mn: 0.065%, P: 0.005
%, S: 0.004%, Se: 0.019%, Sb: 0.030%, three steel slabs were heated at 1400 ° C for 30 minutes and hot-rolled to form a 2.0 mm hot rolled coil. 1000 ℃ for each hot rolled coil
After hot-rolled sheet annealing for 30 seconds, it was pickled and cold-rolled to an intermediate thickness of 0.53 mm. Then, after an intermediate annealing for 1 minute at 950 ℃, 0.19mm by the second cold rolling.
And the final plate thickness.

One of the cold-rolled coils was formed by a projecting roll with a width of 2 ° in the direction of an angle of 5 ° from the direction perpendicular to the rolling.
Grooves with a depth of 00 μm and a depth of 10 μm were formed at a repeating interval of 4 mm in the direction perpendicular to the rolling direction, and after filling the grooves with Al ₂ O ₃ powder, 50%
830 in an atmosphere consisting of H ₂ , dew point 55 ° C, and N ₂ balance
Decarburization annealing was performed at 2 ° C. for 2 minutes to obtain an example. In the other one, after forming the same groove as that of the above-mentioned embodiment, the same decarburization annealing as that of the embodiment is performed as it is, and the conventional example 1 is obtained.

After the final cold rolling, the other one was subjected to the same decarburization annealing as in the above-mentioned embodiment to obtain Conventional Example 2. For these three coils, MgO containing 2% of TiO ₂ and 2% of SrSO ₄ was applied as an annealing separator, wound into a coil and subjected to final finishing annealing. The conditions for the final finish annealing are as follows: N ₂ at 850 ° C. and hold for 50 hours, then 25 ° N ₂ and 75% H ₂ at a temperature rising rate of 20 ° C./hr.
After the temperature was raised to 1200 ° C., the temperature was kept at 1200 ° C. for 10 hours in H ₂ and then lowered.

After the final finish annealing, the unreacted separating agent was removed. In the steel sheets of the examples, the amount of protrusion at the Al ₂ O ₃ filled portion into the groove was measured and was 15 μm, but the surface opposite to the protruding portion was wound around a drum and the protruding portion was smoothed by rolling down the roll. Processed. After that, three types of coils were coated with a tension coating mainly composed of colloidal silica and aluminum phosphate, and baked at 800 ° C to obtain products. However, in Conventional Example 2, after the tension coating was baked, the plasma jet was irradiated in the direction perpendicular to the rolling and at a repeating interval of 5 mm in the rolling direction.

Table 2 shows the magnetic characteristics of these three types of product coils.
Shown in.

[0039]

[Table 2]

As shown in Table 2, in the examples of the present invention, the iron loss value W at 1.5 T was higher than that in the conventional method.
_It also excels at the iron loss value W _{17/50 at} 1.7T at _15/60 .

[0041]

As described in detail above, since the grooves were filled with oxide as in the present invention and the protrusions after the final finish annealing were press-fitted and smoothed, iron loss at 1.5 T and 1.7
It is possible to effectively achieve the iron loss reducing effect in the range of the iron loss at T and a wide magnetic flux density, and it is possible to manufacture the grain-oriented silicon steel sheet having an extremely low iron loss.

[Brief description of drawings]

FIG. 1A is a schematic sectional view of a protrusion before smoothing in the present invention, and FIG. 1B is a schematic sectional view at the same position after smoothing treatment.

FIG. 2 is an explanatory diagram showing an example of the most preferable smoothing process.

FIG. 3 is a diagram showing the relationship between the amount of protrusion of the protrusions on the surface of the steel sheet after the final finish annealing and the magnetic characteristics.

Claims (2)

[Claims] 1. A method for producing a grain-division-oriented grain-oriented silicon steel sheet in which a groove is formed on the surface of a steel sheet after final cold rolling, decarburization annealing, application of an annealing separating agent and final finishing annealing are carried out. After the groove is formed, the groove is filled with an oxide before the application of the annealing separator so that the groove-filled portion protrudes from the surface of the steel sheet, and the protrusion is smoothed under roll pressure after the final finish annealing. Method for producing grain-oriented silicon steel sheet with extremely low iron loss. 2. The amount of protrusion of the protrusion after the final finish annealing is 4 to
The method for producing a grain-oriented silicon steel sheet having an extremely low iron loss according to claim 1, wherein the grain size is 40 μm.