JP2023089089A - Grain-oriented electromagnetic steel sheet and method for producing the same - Google Patents

Abstract

To provide a grain-oriented electromagnetic steel sheet having improved magnetism by comprising plural cold rolling and decarbonization annealing steps, and a method for producing the same.SOLUTION: A method for producing a grain-oriented electromagnetic steel sheet has the steps of: heating a slab; hot-rolling the slab to produce a hot-rolled steel sheet; subjecting the hot-rolled steel sheet to hot-rolled sheet annealing; subjecting the hot-rolled steel sheet subjected to the hot-rolled sheet annealing to primary cold rolling; subjecting the steel sheet subjected to the primary cold rolling to decarburization annealing; subjecting the steel sheet completed with the decarburization annealing to secondary cold rolling; subjecting the steel sheet completed with the secondary cold rolling to continuous annealing; and subjecting the steel sheet subjected to the continuous annealing to batch annealing.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a grain-oriented electrical steel sheet and a manufacturing method thereof, and more particularly, to a grain-oriented electrical steel sheet having improved magnetic properties by including a plurality of cold rolling and decarburization annealing processes and a manufacturing method thereof.

A grain-oriented electrical steel sheet is a soft magnetic material having excellent magnetic properties in the rolling direction, composed of crystal grains having a crystal orientation of {110}<001>, also known as Goss orientation.
After heating the slab, the grain-oriented electrical steel sheet is rolled to a final thickness through hot rolling, hot-rolled sheet annealing, and cold rolling, and then subjected to high-temperature annealing for primary recrystallization annealing and secondary recrystallization formation. manufactured through
Generally, the secondary recrystallization annealing process for grain-oriented electrical steel sheets requires a long-time refining annealing at a low temperature rise rate and a high temperature, so it can be said to be a process that consumes a lot of energy. In order to manufacture a grain-oriented electrical steel sheet having excellent magnetic properties by forming secondary recrystallization through such extreme processes, the following difficulties arise in the process.

First, heat treatment in the coil state causes a temperature difference between the outer winding portion and the inner winding portion of the coil, and the same heat treatment pattern cannot be applied to each portion. of magnetic deviation occurs. Second, the surface is coated with MgO after decarburization annealing, and various surface defects are generated in the process of forming a base coating during high temperature annealing, which reduces yield. Thirdly, the decarburized sheet after decarburization annealing is wound into a coil, then annealed at a high temperature, then flattened and annealed again for insulation coating, so the production process is divided into three steps, which reduces the yield. A problem arises.
In order to overcome such limitations in the process, techniques have been proposed that utilize normal crystal growth without utilizing the secondary recrystallization phenomenon by controlling the decarburization annealing and cold reduction rate. However, in continuous annealing, there is a limit to the grain growth of the final grain due to the short heat treatment time of the water content, and the crystal grain cannot grow to have an optimum grain size, and there is a limit to the iron loss improvement.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a grain-oriented electrical steel sheet and a method of manufacturing the same, which include a plurality of cold rolling and decarburizing annealing steps to improve magnetic properties.

A method for manufacturing a grain-oriented electrical steel sheet according to the present invention includes heating a slab, hot rolling the slab to manufacture a hot-rolled steel sheet, hot-rolling the hot-rolled steel sheet, and performing hot-rolled sheet annealing. Primary cold rolling of the hot-rolled steel sheet, decarburization annealing of the primary cold rolled steel sheet, secondary cold rolling of the decarburized and annealed steel sheet, and completion of the secondary cold rolling. continuously annealing the steel sheet and batch annealing the continuously annealed steel sheet.

The slab contains Si: 1.0% to 4.0%, C: 0.1% to 0.4%, and the balance consists of Fe and unavoidable impurities,
It is preferred to further include Mn: 0.1% by weight or less and S: 0.005% by weight or less.

The step of annealing the hot-rolled sheet of the slab includes a decarburization process,
The step of annealing the hot-rolled sheet includes annealing at a temperature of 850 ° C to 1000 ° C and a dew point temperature of 50 ° C to 70 ° C,
The decarburization annealing of the first cold rolled steel sheet is characterized by annealing at a temperature of 850-1000°C and a dew point temperature of 50-70°C.

The step of decarburizing and annealing the primary cold-rolled steel sheet includes annealing in an austenite single phase region or a region in which a composite phase of ferrite and austenite exists,
After decarburization annealing of the primary cold-rolled steel sheet, the average diameter of grains is 150-250 μm,
The step of decarburizing and annealing the first cold-rolled steel plate and the step of secondarily cold-rolling the steel plate that has been decarburized and annealed are repeated two or more times.

The continuous annealing step includes annealing at a temperature of 850° C. to 1000° C. and a dew point temperature of 50° C. to 70° C. for 1 to 5 minutes,
The batch annealing step includes annealing at a temperature of 1000° C. to 1200° C. and a dew point temperature of −20° C. or less for 1 to 8 hours,
After the step of batch annealing, the volume fraction of grains forming an angle of 15° or less from {110}<001> is 40% or more;
The area fraction of crystal grains having a diameter of 1000 μm to 5000 μm in all crystal grains is 20 to 70%.

The grain-oriented electrical steel sheet according to the present invention is characterized in that the area fraction of crystal grains having a diameter of 1000 μm to 5000 μm in all crystal grains is 20 to 70%.

The electrical steel sheet contains, in weight percent, Si: 1.0% to 4.0%, C: 0.005% or less (excluding 0%), the balance being Fe and inevitable impurities,
Mn: 0.1% by weight or less and S: 0.005% by weight or less,
The volume fraction of crystal grains forming an angle of 15° or less from {110} <001> is 40% or more,
The ratio (D2/D1) of the diameter (D1) of the circumscribed circle to the diameter (D2) of the inscribed circle is 95 area % or more of the total Goss crystal grains. and

The grain-oriented electrical steel sheet according to the present invention has excellent magnetic properties by stably forming Goss crystal grains having a large diameter while utilizing normal crystal growth.
Moreover, since AlN and MnS are not used as grain growth inhibitors, there is no need to heat the slab at a high temperature of 1300° C. or higher.
In addition, it becomes unnecessary to remove N and S, which are precipitates, and the purification annealing time can be relatively shortened, so productivity can be improved.
In addition, it is possible to provide a grain-oriented electrical steel sheet having magnetic properties with cracks in the width direction.

4 is a photograph of the surface of a grain-oriented electrical steel sheet manufactured from Inventive Material 2, observed with a scanning electron microscope. 4 is a photograph of the surface of a grain-oriented electrical steel sheet manufactured as Comparative Material 2, observed with a scanning electron microscope.

Terms such as first, second and third are used to describe various parts, components, regions, layers and/or sections, but are not limited thereto. These terms are only used to distinguish one portion, component, region, layer or section from another portion, component, region, layer or section. Thus, a first portion, component, region, layer or section discussed below could be referred to as a second portion, component, region, layer or section without departing from the scope of the present invention.
The terminology used herein is for the purpose of referring to particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms also include the plural forms unless the language clearly dictates the contrary. As used herein, the meaning of "comprising" embodies certain properties, regions, integers, steps, acts, elements and/or components and may include other properties, regions, integers, steps, acts, elements and/or It does not exclude the presence or addition of ingredients.
When a portion is referred to as being “on” another portion, it may be “directly on” the other portion, or there may also be other portions interposed therebetween. In contrast, when a portion is referred to as being "directly on" another portion, there is no intervening portion.
Although not defined differently, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. have. Terms defined in commonly used dictionaries are additionally construed to have a meaning consistent with the relevant technical literature and the presently disclosed subject matter, and are not to be construed in an ideal or highly formal sense unless defined.
Also, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.
Further containing an additional element in an embodiment of the present invention means that iron (Fe), which is the balance, is included in place of the added amount of the additional element.

Hereinafter, embodiments of the present invention will be described in detail so that those having ordinary knowledge in the technical field to which the present invention belongs can easily carry them out. This invention may, however, be embodied in many different forms and is not limited to the embodiments set forth herein.
A method for manufacturing a grain-oriented electrical steel sheet according to the present invention includes heating a slab, hot rolling the slab to manufacture a hot-rolled steel sheet, hot-rolling the hot-rolled steel sheet, and performing hot-rolled sheet annealing. Primary cold rolling of the hot-rolled steel sheet, decarburization annealing of the primary cold rolled steel sheet, secondary cold rolling of the decarburized and annealed steel sheet, and completion of the secondary cold rolling. continuously annealing the annealed steel sheet; and batch annealing the continuously annealed steel sheet.

Each step will be specifically described below.
First, heat the slab.
The slab contains Si: 1.0% to 4.0%, C: 0.1% to 0.4%, and the balance consists of Fe and unavoidable impurities in weight percent.
The reasons for limiting the composition are as follows.
Silicon (Si) lowers the magnetic anisotropy of the electrical steel sheet, increases the resistivity, and improves iron loss. If the Si content is less than 1.0% by weight, the iron loss becomes inferior, and if it exceeds 4.0% by weight, the brittleness increases. Therefore, the content of Si in the grain-oriented electrical steel sheet after the slab and final annealing stage can be 1.0-4.0 wt%. More specifically, the Si content is 1.5 to 3.5% by weight.

Carbon (C) in the slab needs a process in which the Goss crystal grains in the surface layer diffuse to the center during the intermediate decarburization annealing and the final decarburization annealing. The content of C is 0.1-0.4% by weight. More specifically, the content of C in the slab is 0.15-0.3% by weight. In addition, the carbon content in the final grain-oriented electrical steel sheet after the final annealing step in which decarburization is completed is 0.0050 wt% or less, more specifically, 0.002 wt% or less.
The slab further contains Mn: 0.1 wt% or less and S: 0.005 wt% or less.

Mn and S form MnS precipitates to hinder the growth of Goss grains that diffuse to the center during the decarburization process. Therefore, Mn and S are preferably not added. However, considering the amount that is unavoidably mixed in during the steelmaking process, Mn and S in the grain-oriented electrical steel sheet after the slab and final annealing stage are Mn: 0.1% by weight or less, S: 0.005% by weight. Each is controlled below.
The balance consists of Fe and unavoidable impurities. The unavoidable impurities are impurities mixed in during the steelmaking stage and the manufacturing process of the grain-oriented electrical steel sheet, and are widely known in the relevant field, so a detailed description thereof will be omitted. Specifically, ingredients such as Al, N, Ti, Mg, and Ca react with oxygen in steel to form oxides, and must be strongly suppressed. It can be managed at 0.005% by weight or less. The addition of elements other than the alloy components described above in one embodiment of the present invention is not excluded, but may be variously included within a range that does not impair the technical idea of the present invention. When the additional element is further included, the remaining Fe is included instead.

More specifically, the slab contains Si: 1.0% to 4.0%, C: 0.1% to 0.4%, and the balance consists of Fe and unavoidable impurities.
The slab heating temperature is 1100° C. to 1350° C., which is higher than the normal heating temperature. If the slab is heated at a high temperature, the hot-rolled structure becomes coarse, which adversely affects the magnetism. However, in the method for producing a grain-oriented electrical steel sheet according to the present invention, since the carbon content of the slab is relatively high, the hot-rolled structure does not coarsen even if the slab is reheated at a high temperature. Reheating is even more advantageous during hot rolling.

Next, the slab is hot rolled to produce a hot rolled steel sheet.
In the hot rolling, a hot-rolled sheet having a thickness of 1.5 to 4.0 mm is produced by hot rolling so that a proper rolling reduction can be applied in the final cold rolling stage to produce a final product thickness.
The hot-rolling temperature and cooling temperature are not particularly limited, but as an example of excellent magnetism, the hot-rolling end temperature is set to 950° C. or less, and the coil is wound at 600° C. or less after rapid cooling with water.
Next, the hot-rolled steel sheet is subjected to hot-rolled sheet annealing. At this time, hot-rolled sheet annealing includes a decarburization process. Specifically, the hot-rolled sheet is annealed at a temperature of 850°C to 1000°C and a dew point temperature of 50°C to 70°C.
After the annealing described above, additional annealing is performed at a temperature of 1000 to 1200° C. and a dew point temperature of 0° C. or less. After the hot-rolled sheet is annealed, it is pickled.

Next, primary cold rolling is performed to produce a cold-rolled steel sheet.
It is considered effective to carry out cold rolling once at a high reduction rate close to 90% in the normal manufacturing process of grain-oriented electrical steel sheets. This is to create an environment favorable for grain growth of only the Goss grains in the primary recrystallized grains. However, the method for producing a grain-oriented electrical steel sheet according to the present invention does not utilize the abnormal grain growth of Goss orientation grains, but internally diffuses Goss grains in the surface layer generated by decarburization annealing and cold rolling. Therefore, it is advantageous to form a large number of Goss orientation crystal grains in the surface layer.
Therefore, when cold rolling is performed at a rolling reduction of 50% to 70%, a large number of Goss textures are formed in the surface layer. More specifically, it is 55% to 65%.
Next, the cold-rolled steel sheet is decarburized and annealed. At this time, the decarburization annealing step is performed in an austenite single phase region or a region where a composite phase of ferrite and austenite exists. Specifically, it is annealed at a temperature of 850°C to 1000°C and a dew point temperature of 50°C to 70°C. Also, the atmosphere is a mixed gas atmosphere of hydrogen and nitrogen. Also, the amount of decarburization during decarburization annealing is 0.0300% by weight to 0.0600% by weight. After the annealing described above, additional annealing is performed at a temperature of 1000 to 1200° C. and a dew point temperature of 0° C. or less.
During the decarburization annealing process, the crystal grains on the surface of the electrical steel sheet grow coarsely, but the crystal grains inside the electrical steel sheet remain as a fine structure. After such decarburization annealing, the average grain diameter is between 150 μm and 250 μm. At this time, the grains are surface ferrite grains. The diameter of a crystal grain means the diameter of a hypothetical circle having the same area as the crystal grain.

Next, the steel sheet that has been decarburized and annealed is subjected to secondary cold rolling. Since the secondary cold rolling is the same as the primary cold rolling, a detailed description is omitted.
The decarburization annealing of the cold-rolled steel sheet and the secondary cold rolling of the decarburized steel sheet may be repeated twice or more. By repeating the treatment two or more times, a large number of Goss textures are formed on the surface layer.
Next, the steel sheet after secondary cold rolling is continuously annealed.
The continuous annealing step anneals at a temperature of 850°C to 1000°C and a dew point temperature of 50°C to 70°C. A cold-rolled sheet before continuous annealing is in a state where decarburization annealing is performed and the carbon content remains 40% to 60% with respect to the carbon weight of the slab. Therefore, in the stage of continuous annealing, the crystal grains formed in the surface layer part diffuse inside while carbon escapes. At the stage of continuous annealing, decarburization can be carried out so that the carbon content in the steel sheet is 0.005% by weight or less.

In the continuous annealing step, annealing is performed for 1 to 5 minutes. The purpose of the continuous annealing step is to grow grains to a certain size or more after decarburizing the carbon in the steel. The reason is that the fraction of Goss grains continuously increases through the process of decarburization and subsequent grain growth. This is because the Goss grains grow while encroaching on the surrounding Non-Goss grains. However, considering the productivity of continuous annealing, the annealing time is limited to within several minutes, so it can be said that crystal growth is restricted. The present invention claims that additional batch annealing is effective in reducing iron loss by inducing crystal growth. At this time, the Goss fraction does not increase, but the iron loss decreases due to the effect of the increase in grain size.
After the continuous annealing step, an annealing separator is applied. Since the annealing separator is widely known in the technical field, a detailed description thereof will be omitted. For example, an annealing separator based on MgO can be used.

Next, the continuously annealed steel sheet is batch annealed. Batch annealing means that the steel sheet is coiled and annealed.
During the batch annealing stage, a texture with diffuse Goss orientation develops during the continuous annealing stage. In the method for producing a grain-oriented electrical steel sheet according to the present invention, the Goss texture has a grain diameter of 5 mm or less, unlike the case where the grains grow due to conventional abnormal grain growth. Specifically, the grain fraction with a diameter of 1000um to 5000um is increased. Therefore, there are a large number of Goss grains, which are smaller in grain size than conventional grain-oriented electrical steel sheets manufactured by abnormal grain growth, but the size of the grains minimizes core loss. It is sized appropriately so that it can be More specifically, the area fraction of crystal grains having a diameter of 1000 μm to 5000 μm in all crystal grains is 20 to 70%. At this time, the area fraction of crystal grains is measured on a plane parallel to the rolled surface (ND surface) of the steel sheet. More specifically, the area fraction of crystal grains having a diameter of 1000 μm to 5000 μm in all crystal grains is 20 to 60%. More specifically, the area fraction of crystal grains having a diameter of 1000 μm to 5000 μm in all crystal grains is 20 to 50%.
The batch annealing step can be annealing at a temperature of 1000° C. to 1200° C. and a dew point temperature of −20° C. or lower.
Batch annealing is performed for 1 to 8 hours. More specifically, it is annealed for 2 to 5 hours.
In addition, in the method for producing a grain-oriented electrical steel sheet according to the present invention, the magnetism is improved due to the high Goss fraction. Specifically, the volume fraction of crystal grains forming an angle of 15° or less from {110}<001> is 40% or more, more specifically 40% to 75%, and even more specifically 45 to 60%. .

In the grain-oriented electrical steel sheet according to the present invention, the area fraction of crystal grains having a diameter of 1000 μm to 5000 μm in all crystal grains is 20 to 70%.
Since the area distribution of crystal grains has been described in detail in relation to the method of manufacturing the grain-oriented electrical steel sheet, redundant description will be omitted.
The electrical steel sheet contains, by weight percent, Si: 1.0% to 4.0%, C: 0.005% or less (excluding 0%), and the balance consisting of Fe and unavoidable impurities.
The electrical steel sheet further contains Mn: 0.1% by weight or less and S: 0.005% by weight or less.
Except for C, the contents of the component restrictions are the same as those of the slab, so redundant description is omitted.
The volume fraction of crystal grains forming an angle of 15° or less from {110}<001> is 40% or more.
Goss grains having a ratio (D2/D1) of the diameter (D1) of the circumscribed circle to the diameter (D2) of the inscribed circle of 0.5 or more account for 95 area % or more of all Goss grains. The manufacturing process unique to the present invention forms grains of the aforementioned morphology.

Since the grain-oriented electrical steel sheet according to the present invention has a high Goss fraction, its magnetism is improved. Specifically, the iron loss (W _17/50 ) is 1.3 W/kg or less, more specifically the iron loss (W _17/50 ) is 1 to 1.3 W/kg, and more specifically 1. 1 to 1.25 W/kg. Iron loss W _17/50 is the magnitude of iron loss (W/kg) induced at 1.7 Tesla and 50 Hz conditions.
Specific examples of the present invention are described below. However, the following examples are only specific examples of the present invention, and the present invention is not limited to the following examples.

Example 1
A slab containing Si: 2.32%, C: 0.195%, and the balance being Fe and unavoidable impurities, in weight percent, was heated at a temperature of 1250°C, hot rolled, and then annealed at a temperature of 950. °C and a dew point temperature of 60°C. Thereafter, the steel sheet was cooled, pickled, and cold-rolled at a rolling reduction of 65% to produce a cold-rolled sheet with a thickness of 0.8 mm.
The cold-rolled sheet is decarburized and annealed again at a temperature of 950° C. in a wet mixed gas atmosphere of hydrogen and nitrogen (dew point temperature 60° C.) for 80 seconds, and then cold-rolled again at a reduction rate of 65% to obtain a thickness. A 0.28 mm cold-rolled sheet was produced.
After that, during the final annealing, decarburization annealing was performed for 2 minutes in a wet mixed gas atmosphere of hydrogen and nitrogen (dew point temperature 60°C) at a temperature of 950°C. or a mixed gas atmosphere of hydrogen and nitrogen at 1200° C. in a coil state for the time shown in Table 1 below.
Table 1 is a table showing the Goss fraction of crystal grains, the area fraction of crystal grains having a size of 1 mm or more and 5 mm or less, and iron loss of grain-oriented electrical steel sheets after high-temperature annealing according to Examples. As the Goss fraction, the volume fraction of crystal grains forming an angle of 15° or less from {110}<001> was measured. After the surface of the finally obtained steel sheet was washed, iron loss was measured under conditions of 1.7 Tesla and 50 Hz using a single sheet magnetic measurement method.

表１に示すように、バッチ焼鈍を適切な時間の間に行った発明材１～発明材４は、直径が１～５ｍｍである結晶粒の面積分率が高いことを確認できる。ゴス分率が比較材に比べて比較的低くても鉄損がむしろ優れていることを確認できる。
図１および図２では、発明材２および比較材２で製造した方向性電磁鋼板の表面を走査電子顕微鏡で観察した写真を示す。
図１および図２で確認できるように、発明材２で製造した方向性電磁鋼板の結晶粒が比較的大きく形成されたことを確認できる。

As shown in Table 1, it can be confirmed that the invention materials 1 to 4, which were batch-annealed for an appropriate time, had a high area fraction of crystal grains with a diameter of 1 to 5 mm. It can be confirmed that even though the Goss fraction is relatively low compared to the comparative material, the iron loss is rather excellent.
1 and 2 show photographs of the surfaces of the grain-oriented electrical steel sheets produced from Inventive Material 2 and Comparative Material 2 observed with a scanning electron microscope.
As can be seen from FIGS. 1 and 2, it can be seen that the crystal grains of the grain-oriented electrical steel sheet manufactured from Inventive Material 2 are relatively large.

The present invention is not limited to the above embodiments and/or examples, but can be manufactured in various forms different from each other. It should be understood that other specific forms are possible without changing the basic concept or essential features. Accordingly, the embodiments and/or examples described above are to be considered in all respects as illustrative and not restrictive.

Claims (9)

heating a slab containing, in weight percent, Si: 1.0% to 4.0%, C: 0.1% to 0.4%, the balance being Fe and unavoidable impurities;
hot-rolling the slab to produce a hot-rolled steel sheet;
hot-rolled steel plate annealing the hot-rolled steel plate;
primary cold rolling of the annealed hot-rolled steel sheet;
decarburizing and annealing the first cold-rolled steel sheet;
secondary cold rolling the steel sheet that has been decarburized and annealed;
continuously annealing the secondary cold-rolled steel sheet; and batch annealing the continuously annealed steel sheet,
The step of hot rolling is performed after heating the slab at a temperature of 1100° C. to 1350° C.,
The step of manufacturing the hot-rolled steel sheet includes setting the hot-rolling end temperature to 950° C. or less and winding at 600° C. or less,
The hot-rolled steel sheet has a thickness of 1.5 to 4.0 mm,
The rolling reduction in the primary cold rolling step and the secondary cold rolling step is 50% to 70%, respectively,
In the batch annealing step, annealing is performed at a temperature of 1000° C. to 1200° C. and a dew point temperature of −20° C. or lower for 1 to 8 hours. The method of claim 1, wherein the annealing of the hot-rolled sheet comprises a decarburization process. 3. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the step of annealing the hot-rolled sheet is performed at a temperature of 850.degree. C. to 1000.degree. C. and a dew point temperature of 50.degree. The step of decarburizing and annealing the primary cold-rolled steel sheet is performed at a temperature of 850°C to 1000°C and a dew point temperature of 50°C to 70°C. A method for producing a grain-oriented electrical steel sheet according to item 1. The step of decarburizing and annealing the primary cold-rolled steel sheet is performed in a single austenite phase region or a region in which a composite phase of ferrite and austenite exists. A method for producing a grain-oriented electrical steel sheet according to item 1. The direction according to any one of claims 1 to 5, characterized in that after the step of decarburizing and annealing the primary cold rolled steel sheet, the grains have an average diameter of 150 to 250 µm. A method for producing a flexible electrical steel sheet. The steps of decarburizing and annealing the primary cold-rolled steel plate and secondary cold-rolling the steel plate that has undergone the decarburization annealing are repeated twice or more. 7. The method for producing a grain-oriented electrical steel sheet according to any one of 6. The grain-oriented electrical steel sheet according to any one of claims 1 to 7, wherein the step of continuous annealing is performed at a temperature of 850°C to 1000°C and a dew point temperature of 50°C to 70°C. Production method. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 8, wherein the continuous annealing step is annealing for 1 to 5 minutes.

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