JPH1046252A - Production of superlow core loss grain oriented magnetic steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably produce a superlow core loss grain oriented silicon steel sheet by heating a silicon steel slab contg. specified amounts of Si, C, Mn, S, acid soluble Al, N, Sn and Fe to a specified temp., executing hot rolling, subjecting it to final cold rolling at a specified draft, specifying the roughness of the surface, coating it with Al2 O3 , regulating the magnetic domains and executing insulating coating. SOLUTION: A silicon steel slab contg., by weight 2.5 to 4.5% Si, 0.025 to 0.085% C, 0.05 to 0.45% Mn, <=0.015% S, 0.01 to 0.04% acid soluble Al, <=0.01% N, 0.02 to 0.15% Sn, and the balance substantial Fe is subjected to hot rolling at <=1280 deg.C. It is subjected to cold rolling for >= two times including process annealing, the final draft is regulated to >=80%, and the surface roughness in the direction perpendicular to the rolling direction in the cold rolled sheet is regulated to <=0.2μm by the average roughness. It is subjected to decarburizing annealing, nitriding treatment and finish annealing. At the time of the decarburzing annealing, the ratio of partial pressure of water vapor/hydrogen in the atmospheric gas is preferably regulated to 0.058 to 0.15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an ultra-low iron loss unidirectional electrical steel sheet having a mirror surface obtained by performing magnetic domain control on a high magnetic flux density unidirectional electrical steel sheet having extremely high smoothness on the surface of the steel sheet. Things.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for reducing iron loss from the viewpoint of energy saving. In response to this, amorphous metal has recently appeared, and has been adopted by some transformer manufacturers, and has obtained excellent iron loss characteristics. To counter this, intensive studies have been made on grain-oriented electrical steel sheets, and some proposals have been made. In addition to metallurgical methods such as increasing the magnetic flux density, reducing the size of secondary recrystallized grains, reducing the thickness, and increasing the surface tension of the surface coating, the methods used to reduce iron loss are physical methods. A magnetic domain control technique by laser irradiation, plasma irradiation, or the like has been proposed. However, since this method cannot be used for a wound iron core transformer requiring strain relief annealing, it can be used for both stacked and wound transformers. As a magnetic domain control method, a method of forming a groove with a toothed roll on the surface of a product, for example, as disclosed in
No. 117218, a method of forming a groove in a cold rolled sheet by etching, for example, Japanese Patent Publication No. 3-69968 or a method of forming a groove in a cold rolled sheet by a laser, for example, Japanese Patent Application Laid-Open No. 61-75506. Disclosed.

As another iron loss reducing method, there is a method of making the surface of a steel sheet smooth (mirror surface) by electrolytic polishing or chemical polishing (Japanese Patent Publication Nos. 52-24499 and 56-4150). . In this method, it is known that the higher the degree of smoothness, the more effective the iron loss reduction, and if this method is combined with the magnetic domain control technique, a very excellent ultra-low iron loss material can be obtained (Japanese Patent Application Laid-Open No. 54-43115). Gazette). However, since this method lacks industriality, a method of using Al ₂ O ₃ as an annealing separator or a method of adding a chlorine compound or the like in MgO has recently been proposed as a method for obtaining this mirror surface. For example, Japanese Patent Application Laid-Open No. Hei 7-118750 discloses a method for obtaining a mirror surface by eliminating the reaction product with an annealing separator Al ₂ O ₃ by lowering the atmosphere dew point during decarburizing annealing as much as possible to suppress the formation of an oxide layer. Has been proposed.

Japanese Patent Application Laid-Open No. 8-3648 describes the composition of an annealing separator Al ₂ O ₃ . Also, JP-A-4-21451 and JP-A-4-21452 disclose a method of obtaining an ultra-low iron loss material by controlling the magnetic domain of a steel sheet having a mirror surface to withstand strain relief annealing and applying a tension coating. is suggesting.

[0005] Japanese Patent Application No. 08-017371 discloses that a groove is formed at a thickness stage during cold rolling and then finished to a product thickness.
A manufacturing method for processing by the above method is proposed.

[0006]

SUMMARY OF THE INVENTION The present invention proposes a method for producing an ultra-low iron loss unidirectional electrical steel sheet which is stabilized by making the surface roughness after finish annealing extremely low.

[0007]

SUMMARY OF THE INVENTION According to the present invention, the roll roughness of a cold rolling mill is controlled to be lower than usual so as to reduce the surface roughness of a steel sheet after cold rolling and to obtain an extremely excellent mirror surface after finish annealing. It is a feature. That is, by weight ratio, Si: 2.5
-4.5%, C: 0.025-0.085%, Mn:
0.050 to 0.45%, S ≦ 0.015%, acid-soluble Al: 0.01 to 0.040%, N: ≦ 0.010%,
After heating the electromagnetic steel slab consisting of 0.02 to 0.15% of Sn and the balance Fe and unavoidable impurities at a temperature of 1280 ° C. or lower, hot-rolled and hot-rolled sheet annealing is performed, and once or intermediate annealing is performed. Cold rolling is performed to reduce the final rolling ratio to 80% or more and the surface roughness in the direction perpendicular to the rolling direction of the cold-rolled sheet to an average roughness of 0.20 μm or less by two or more rollings, and then decarburizing annealing , Nitriding treatment, applying Al ₂ O ₃ as an annealing separator,
This is a method for producing an ultra-low iron loss unidirectional magnetic steel sheet having a mirror surface, wherein a magnetic domain is controlled after finish annealing and a tension coating is applied.

Further, in the above method, the steam / hydrogen partial pressure ratio PH ₂ O / PH ₂ of the degassing annealing atmosphere gas is set to 0.0
How the range of from 58 to 0.150, or a mixed gas of H ₂ and N ₂ in the atmospheric gas finish annealing Atsushi Nobori process, the ratio of N ₂ soaked at 1100 ° C. or more temperature of at least 50% This is a method of annealing in an H ₂ atmosphere in this soaking temperature range.

Further, in the above method, the magnetic domain control method is such that the width is 10 to 500 μm in a range of 90 ° to 45 ° with respect to the rolling direction on the surface of the steel sheet in the thickness step during the final cold rolling.
Depth is plate thickness t × 1/8 to 1/30, interval is 1 in the rolling direction
This is a method in which a groove of about 20 mm is formed in a dot shape or a line shape to withstand strain relief annealing. In addition, as a method of controlling the magnetic domain, a known method such as laser irradiation may be employed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on experiments. Experiment 1. C: 0.055%, Si: 3.25 by weight ratio
%, Mn: 0.10%, P: 0.025%, S: 0.0
07%, acid-soluble Al: 0.028%, Sn: 0.05
%, Cr: 0.12%, and N: 0.0080%, a 2.3 mm thick hot rolled sheet was annealed at 1120 ° C. + 900 ° C., quenched, pickled, and cold rolled to obtain a sheet thickness of 0.1 mm. Finished to 23mm.

In this cold rolling, rolling is performed while changing the roughness of the cold rolling roll, and the average roughness of the surface of the cold rolled sheet (in the direction perpendicular to the rolling direction).
0.30 μm 0.25 μm 0.20 μm
Four levels of ≦ 0.15 μm were produced. The cold rolled sheet was washed with oil, and decarburized annealing was performed at 830 ° C. for 90 seconds, H ₂ : 75% +
N ₂ 25%, dew point 40 ° C. (PH ₂ O / PH ₂ = 0.1
The test was performed in the atmosphere of 0).

Next, nitriding treatment is performed at 750 ° C. for 30 seconds.
The test was performed in a mixed gas of N ₂ , H ₂ and ammonia, the nitrogen content of the steel sheet was adjusted to 200 ppm, Al ₂ O ₃ was used as an annealing separator, and the atmosphere gas N ₂ : 90 in the final annealing temperature raising process was used.
%, H _2: done with 10% mixed gas 1200 ° C. x2
The 0-hour purification annealing was performed in a H ₂ atmosphere gas. Thereafter, the film was washed with water and subjected to a tension coating mainly composed of chromic anhydride and aluminum phosphate.

Thereafter, the magnetic domain was controlled by irradiating the laser beam with a laser beam at an interval of 5 mm in a direction perpendicular to the rolling direction. FIG. 1 shows the magnetic characteristics thus obtained. From this figure, it can be seen that the lower the roughness of the cold rolled sheet, the lower the iron loss. This product is used as a core material for a stacking transformer that does not require strain relief annealing. Experiment 2. Surface average roughness of cold rolled sheet used in experiment 1 ≤
The relationship between the decarburizing annealing atmosphere dew point and iron loss was examined using 0.15 μm.

Decarburizing annealing conditions are 830 ° C. for 30 seconds, atmosphere gas H ₂ : 75% + N ₂ : 25%, dew point of the atmosphere gas is 1) 25 ° C., 2) 30 ° C., 3) 35 ° C., 4) 40 ° C. ,
5) 45 ° C and 6) 50 ° C. The following steps were performed in the same manner as in Experiment 1. The results are shown in FIG. From now on PH
Ultra low iron loss is obtained in the range of ₂ O / PH ₂ : 0.058 to 0.150. When PH ₂ O / PH ₂ exceeds 0.150, the number of oxidized layers of the decarburized annealed sheet increases, and this oxide layer reacts with the annealing separator Al ₂ O ₃ , resulting in inferior mirror finish of the steel sheet after finish annealing. Come. The amount of the oxide layer of the decarburized annealed sheet is smaller as the roughness of the cold-rolled sheet is smaller when compared at the same dew point.

The lower the dew point, the smaller the amount of oxidation and the easier it is to obtain a mirror surface. However, if the dew point is lower than 0.058, decarburization becomes worse and the development of secondary recrystallized grains is hindered. Experiment 3. The hot rolled sheet used in Experiment 1 was 1120 ° C + 900 ° C
After quenching, rapid cooling, pickling and cold rolling were performed. In this cold rolling, rolling was performed with the roll roughness changed as in Experiment 1.

During the cold rolling, a hole of 15 μm was formed by a laser beam at a thickness step of 0.32 mm. The perforations were formed as a series of points having a diameter of about 100 μmφ and an interval of 100 μm. After perforation, the product was rolled to a product thickness of 0.27 mm. After that, oil washing and decarburization annealing were performed at 830 ° C. for 120 seconds,
_{2: 75% + N 2:} 25%, was conducted in an atmospheric gas having a dew point of 40 ° C.. Subsequently, nitriding treatment, Al ₂ O ₃ application, finish annealing, and coating treatment were performed in the same manner as in Experiment 1. FIG. 3 shows the magnetic properties of the product thus obtained.

This result also indicates that the lower the roughness of the cold rolled sheet, the lower the iron loss. In addition, since this product does not lose its effect even when subjected to strain relief annealing, it can be stacked and used as a core material for a double-sided transformer. Next, the reasons for limiting the component composition of the starting material in the present invention will be described. S
i is preferably large in order to obtain a low iron loss, but if the Si content exceeds 4.5% and becomes too large, cracks and breaks frequently occur during cold rolling of the material, and stable cold rolling is performed. Make work impossible.

If the content of C exceeds 0.085% and becomes too large, the decarburization annealing time becomes long and the productivity is impaired. If the content of Mn is too small, secondary recrystallization becomes unstable, while if it is too large, it becomes difficult to obtain a product having a high magnetic flux density. The appropriate content is 0.050 to 0.45
%. S forms MnS as is well known, and suppresses the growth of primary recrystallized grains. In the present invention, the inhibitor required to develop secondary recrystallized grains is characterized in that it is built after decarburization annealing, and that fine precipitates are dispersed before cold rolling adjusts the primary recrystallized grain size. It is not preferable in the present invention to obtain a high magnetic flux density steel sheet. Therefore, S
Is set to 0.015% or less. The preferable range of S is 0.003 to 0.010%. S is 0.003%
If the amount is smaller, the grain growth becomes more sensitive to the annealing temperature, and it becomes difficult to adjust the grain size.

Although Al combines with nitrogen to form AlN, in the present invention, it is essential to form (Al, Si) N by nitriding the steel in a later step, ie, completion of the primary recrystallization. Therefore, a certain amount of free Al is required. Therefore, as acid-soluble Al, 0.1.
010 to 0.040%. N needs to be 0.010% or less. If it exceeds 0.010%, blistering of the steel sheet surface called blister occurs, and it is difficult to adjust the primary recrystallization structure. Although not particularly limited to the lower limit, 0.00
About 2% is good.

Sn improves the texture after decarburizing annealing and prevents coarsening of secondary recrystallized grains. The appropriate amount of Sn is 0.02-
The content is 0.15%. If the content is less than 0.15%, the effect is weak. On the other hand, if the content is more than 0.15%, nitriding becomes difficult and secondary recrystallized grains hardly develop. Preferably, 0.03 to 0.10% is good. The inclusion of trace amounts of Cu, P, and Ti in steel does not impair the gist of the present invention.

Next, the manufacturing process of the present invention will be described. The electromagnetic steel slab is obtained by smelting steel in a melting furnace such as a converter or an electric furnace, vacuum degassing as necessary, and then by continuous casting or by ingot-casting and slab rolling. Slab heating is performed prior to hot rolling. By performing the slab heating at a low temperature of 1280 ° C. or less, the consumption of the heating energy is reduced, and the AlN in the steel is not completely dissolved to form an incomplete solid solution state.

The slab is hot-rolled to produce a hot-rolled sheet having a predetermined thickness. Next, the hot-rolled sheet is annealed at 900 ° C. to 1150 ° C. for a short time, pickled, and cold-rolled. The cold rolling reduction is required to be 80% or more in order to obtain a high magnetic flux density. In this cold rolling, it is necessary to lower the roll roughness so that the average roughness of the cold rolled sheet in the direction perpendicular to the rolling direction is 0.20 μm or less. In this case, it is not particular about rolling by combining rolls having different roughnesses. The reason why the average roughness in the direction perpendicular to the rolling direction is specified is that in normal rolling, the roughness in the direction perpendicular to the rolling direction is larger than that in the rolling direction.

Following this treatment, decarburizing annealing and nitriding treatment
I do. The decarburization annealing is performed by a known method.
Oxide layer (Fayalite)
(Fe _TwoSiO_Four) And SiO_TwoAmount) can be generated
It is desirable to reduce as much as possible. PH defined in the present invention
_TwoO / PH_TwoIs 0.058 to 0.150.

If it is smaller than 0.058, the decarburization becomes poor,
Inhibits the development of secondary recrystallized grains. On the other hand, if it exceeds 0.150, the generation amount of the oxide layer sharply increases, the mirror finish after finish annealing decreases, and an ultra-low iron loss cannot be obtained. The nitriding treatment is performed, for example, as disclosed in JP-A-2-77525.
It is performed by running the strip in a mixed gas of hydrogen, nitrogen and ammonia.

It is necessary to use an annealing separator which does not form a forsterite film after the finish annealing. Therefore, Al ₂ O ₃ or a material containing Al ₂ O ₃ as a main component is used. In the finish annealing, the atmosphere gas during the temperature raising process is a mixed gas of N ₂ and H ₂ , and the ratio of N ₂ is 50% or more, preferably 75% or more. If the ratio of N ₂ is lower than this, the development of secondary recrystallized grains becomes unstable.

Thereafter, a tension film is formed. As the tension film, for example, a coating liquid mainly comprising colloidal silica and aluminum phosphate according to JP-A-48-39338, a coating liquid mainly comprising colloidal silica and magnesium phosphate according to JP-A-50-79442, Alternatively, a method of baking an alumina sol and a coating solution containing boric acid as main components according to Japanese Patent Application No. 4-222879 may be employed.

In addition, any other film having good adhesion and capable of applying tension to a steel sheet can be used. Next, magnetic domain control is performed. As a magnetic domain control method, a known laser irradiation, a groove forming method using a toothed roll, an etching method, or the like may be employed. In addition, a description will be given of processing conditions for perforating at the thickness stage during cold rolling, which is a magnetic domain control method that resists strain relief annealing, which is a feature of the present invention.

The width of the perforations (grooves) is 10 to 500 μm. If it exceeds 500 μm, the magnetic flux density deteriorates greatly,
No iron loss reduction effect is observed. On the other hand, it is very difficult to make it smaller than 10 μm. The direction of the grooves is 90 ° to 45 ° with respect to the rolling direction. When the angle is smaller than 45 °, the effect of subdividing the magnetic domain is weakened, and the iron loss reduction is small. Groove spacing is 1
２０20 mm. Less than 1 mm is industrially difficult, while 2
If it exceeds 0 mm, the reduction in iron loss becomes small. In the case of point-shaped perforations, the interval between perforations is not particularly limited, but since the magnetic domain has the widest width of about 2 mm, it is not preferable to exceed this. Groove depth is 1/30 to 1/8 of plate thickness at the time of groove formation
Good range. If it is shallower than 1/30, iron loss reduction is weak and 1
If it is deeper than / 8, the magnetic flux density is degraded, and the iron loss characteristics are also deteriorated.

Although it is effective to use a laser beam or a plasma flame for forming the grooves, high-pressure water may be used. After that, it is rolled to the product thickness. This rolling eliminates formation defects and burrs generated during groove formation, improves the structure of the heat affected zone, and further promotes the development of the Goss structure in addition to the magnetic domain control effect as compared to the case where irradiation is performed at the product thickness. Has the effect of doing Although the reason for this is not clear, it is presumed that strain is introduced into the structure of the heat-affected zone by rolling, and the amount of strain is suitable for the development of the Goss structure. Examples will be described below.

[0030]

EXAMPLE C: 0.057% by weight, Si: 3.5
%, Mn: 0.10%, P: 0.025%, S: 0.0
10%, acid-soluble Al: 0.027%, Sn: 0.05
%, N: 0.0078%, a hot-rolled sheet having a thickness of 2.3 mm was annealed at 1120 ° C. + 900 ° C., quenched, pickled, cold rolled, and finished to a thickness of 0.23 mm.

At the time of this cold rolling, rolling is performed while changing the roughness of the cold rolling roll, and the surface roughness in the direction perpendicular to the rolling direction of the cold rolled sheet is adjusted.
0.25 μm ≦ 0.10 μm. The cold rolled sheet was washed with oil, and decarburized annealing was performed at 840 ° C. for 90 seconds, H ₂ : 75% +
The test was performed in an atmosphere of N ₂ : 25% and a dew point of 45 ° C. Next, nitriding was performed at 750 ° C. × 30 in a mixed gas of N ₂ , H ₂ and ammonia to adjust the nitrogen content of the steel sheet to 220 ppm.

Thereafter, Al ₂ O ₃ was used as an annealing separator, and the atmosphere gas in the final annealing temperature raising process was changed to N ₂ gas.
Purification annealing at 1200 ° C. for 20 hours was performed in an H ₂ atmosphere gas. Then, after washing with water, the rolling direction and 7
A groove having a width of 50 μm and a pitch of 5 mm and a depth of 12 μm was formed in the direction of 5 °.

After annealing at 850 ° C. for 2 hours, a coating solution containing chromic anhydride and aluminum phosphate as main components was applied, and annealing was performed at 850 ° C. for 30 seconds. The magnetic properties obtained are shown below. Surface roughness of cold rolled sheet Iron loss (W17 / 50) (W / kg) 0.25 μm 0.074 ≦ 0.10 μm 0.069

[0034]

As described above, the present invention controls the surface roughness in the direction perpendicular to the cold-rolled sheet rolling direction in cold rolling,
In addition, by appropriately controlling the decarburizing annealing conditions and the finish annealing conditions, it is possible to easily manufacture an ultra-low iron loss unidirectional electrical steel sheet having a mirror surface. Further, by performing the magnetic domain control processing on the steel sheet, the iron loss can be further improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the average roughness of a cold rolled sheet and iron loss in Experiment 1.

FIG. 2 is a diagram showing a relationship between decarburization annealing atmosphere gas dew point and iron loss in Experiment 2.

FIG. 3 is a diagram showing the relationship between the average roughness of a cold rolled sheet and iron loss in Experiment 3.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyasu Fujii 1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Nippon Steel Corporation Yawata Works (72) Inventor Shuichi Yamazaki 20-Shintomi, Futtsu-shi, Chiba 1 Nippon Steel Corporation Technology Development Division (72) Inventor Katsuro Kuroki 59 Nippon Steel Plant Design Co., Ltd.

Claims (4)

[Claims] Claims: 1. A weight ratio of Si: 2.5 to 4.5%,
C: 0.025-0.085%, Mn: 0.050-
0.45%, S ≦ 0.015%, acid-soluble Al: 0.0
1 to 0.040%, N: ≦ 0.010%, Sn: 0.0
An electromagnetic steel slab consisting of 2 to 0.15%, the balance being Fe and unavoidable impurities, is heated at a temperature of 1280 ° C. or lower, then hot-rolled, hot-rolled and annealed, and inserted once or by intermediate annealing. Cold rolling is performed so that the final rolling reduction is 80% or more and the surface roughness in the direction perpendicular to the cold rolling direction is 0.20 μm or less in average, and then decarburizing annealing and nitriding. A method for producing an ultra-low iron loss unidirectional magnetic steel sheet having a mirror surface, comprising applying a treatment, annealing Al ₂ O ₃ as a separating agent, performing final annealing, controlling magnetic domains, and applying an insulating coating. 2. The ultra-low iron loss unidirectional with a mirror surface according to claim 1, wherein the steam / hydrogen partial pressure ratio PH ₂ O / PH ₂ of the atmosphere gas of the decarburizing annealing is in the range of 0.058 to 0.150. Manufacturing method of conductive electrical steel sheet. Wherein using the finish annealing Atsushi Nobori process gas mixture atmosphere gas of H ₂ and N _2, and the ratio of N ₂ to soak at a temperature above 1100 ° C. to 50% or more, at the soaking temperature range method for producing a ultra-low core loss grain-oriented electrical steel sheet having a mirror surface according to claim 1 or 2, wherein the annealing in an H ₂ atmosphere. 4. The steel sheet surface has a width of 90 ° to 45 ° with respect to a rolling direction at a thickness of 90 ° to 45 ° in a thickness step during the final cold rolling.
2. The mirror surface according to claim 1, wherein the perforations are formed in a dotted or linear manner with a thickness of t.times.1 / 8 to 1/30 and a spacing of 1 to 20 mm in the rolling direction. Manufacturing method of ultra-low iron loss unidirectional electrical steel sheet.