KR20230092578A - Flattening annealing method of grain-oriented electrical steel sheet - Google Patents

Abstract

A flattening annealing method of a grain-oriented electrical steel sheet according to an embodiment of the present invention, wherein flattening annealing is performed after high-temperature annealing, comprises the steps of: cooling in a slow cooling section including a first slow cooling temperature (T_s1) and a second slow cooling temperature (T_s2); and cooling in a rapid cooling section including a first rapid cooling temperature (T_r1) and a second rapid cooling temperature (T_r2) after the slow cooling section, wherein a temperature difference in the rapid cooling section and a temperature difference in the slow cooling section may satisfy formula 1. <formula 1> 100 <= ((T_r1 - T_r2) - (T_s1 - T_s2)) <= 400 Therefore, provided is a grain-oriented electrical steel sheet having excellent magnetism.

Description

Flattening annealing method of grain-oriented electrical steel sheet {FLATTENING ANNEALING METHOD OF GRAIN-ORIENTED ELECTRICAL STEEL SHEET}

The present invention relates to electrical steel sheets, and more particularly, to a flattening annealing method for grain-oriented electrical steel sheets.

Grain-oriented electrical steel sheet uses an abnormal grain growth phenomenon called secondary recrystallization to form a Goss texture throughout the steel sheet, so it has excellent magnetic properties in the rolling direction and electrons that require excellent unidirectional magnetic properties like a transformer. It is a soft magnetic material used as the iron core of equipment. The magnetic properties may be expressed as magnetic flux density and iron loss.

As the magnetic flux density increases, a grain-oriented electrical steel sheet in which crystal grain orientations are accurately arranged in the {110} <001> orientation can be obtained, and hysteresis loss is reduced, so that miniaturization and high efficiency of electrical equipment can be obtained at the same time. The iron loss is the power loss consumed as thermal energy when an arbitrary alternating magnetic field is applied to the steel sheet, and varies greatly depending on factors such as the magnetic flux density and sheet thickness of the steel sheet, the amount of impurities in the steel sheet, the specific resistance, and the size of secondary recrystallized grains do. The higher the magnetic flux density and the specific resistance, the thinner the sheet thickness, and the smaller the amount of impurities in the steel sheet, the lower the iron loss, thereby increasing the efficiency of the electric device.

Unlike normal grain growth, the secondary recrystallization of the grain-oriented electrical steel sheet occurs when the movement of normally growing grain boundaries is suppressed by precipitates, inclusions, or elements that are dissolved or segregated at grain boundaries. In addition, in order to grow crystal grains with a high degree of integration for the Goss orientation, component control in steelmaking, slab reheating in hot rolling, control of hot rolling process parameters, hot rolled sheet annealing heat treatment, primary recrystallization annealing, secondary recrystallization Complex processes such as annealing are required, and these processes must be managed very precisely and strictly.

In this way, substances such as precipitates or inclusions that inhibit grain growth are called grain growth inhibitors or inhibitors, and in the grain-oriented electrical steel sheet manufacturing technology by secondary recrystallization of the Goss orientation, strong grain growth inhibitors are used. Thus, research on a technology for securing excellent magnetic properties by forming secondary recrystallization having a high degree of integration for the Goss orientation is being actively conducted.

The grain-oriented electrical steel sheet is subjected to long-term high-temperature annealing in a coil state for the secondary recrystallization, and in the process, shape defects due to residual stress and coil weight occur. In order to remove this, flattening annealing is performed after high temperature annealing, and the flattening annealing requires a cooling technology to control not only the residual stress generated in the high temperature annealing, but also the new stress generated during cooling of the flattening annealing. Therefore, in order to manufacture a grain-oriented electrical steel sheet having excellent magnetism, it is necessary to control the temperature pattern in the cooling section of the flattening annealing.

A technical problem to be solved by the present invention is to provide a method for manufacturing a grain-oriented electrical steel sheet that controls not only to remove residual stress generated during high-temperature annealing of a grain-oriented electrical steel sheet, but also to prevent generation of new stress generated during flattening annealing.

According to an embodiment of the present invention, the flattening annealing method for grain-oriented electrical steel sheet is a method for flattening grain-oriented electrical steel sheet in which flattening annealing is performed after high-temperature annealing, wherein the flattening annealing is performed at a first slow cooling temperature (T _s1 ) and a second Step of cooling in a slow cooling section including 2 slow cooling temperature (T _s2 ), and after the slow cooling section, first quenching temperature (T _r1 ) and second quenching temperature (T _r2 ) Cooling in a quenching section including Including, the temperature difference in the rapid cooling section and the temperature difference in the slow cooling section may satisfy Equation 1 below.

<Equation 1>

100 ≤ ((T _r1 -T _r2 ) - (T _s1 -T _s2 )) ≤ 400

In one embodiment, the temperature difference (T _s1 -T _s2 ) in the slow cooling section may be 10 °C or more. In one embodiment, the temperature difference (T _s1 -T _s2 ) in the slow cooling section may be 10 to 50 °C or more.

In one embodiment, the first slow cooling temperature (T _s1 ) It may be 750 to 900 ℃. In one embodiment, the second slow cooling temperature (T _s2 ) It may be 700 to 850 ℃.

In one embodiment, the temperature difference (T _r1 -T _r2 ) in the quenching section may be 130 to 430 °C. In one embodiment, the first quenching temperature (T _r1 ) may be 700 to 850 ℃.

In one embodiment, the second quench temperature (T _r2 ) It may be 270 to 700 ℃. In one embodiment, the core loss of the grain-oriented electrical steel sheet may be 0.76 W/kg or less.

In one embodiment, after the step of cooling in the quenching section, the step of irradiating a laser beam to the surface of the grain-oriented electrical steel sheet may be further included. In one embodiment, the flattening annealing method of the grain-oriented electrical steel sheet may be performed under a gas atmosphere of at least one of hydrogen, nitrogen, an inert gas, and a combination thereof. In one embodiment, the hydrogen ratio may be 5 vol% or less.

According to an embodiment of the present invention, the method for manufacturing a grain oriented electrical steel sheet controls the slow cooling section and the rapid cooling section during flattening annealing so as to eliminate residual stress generated during high temperature annealing and prevent new stress generated during flattening annealing from occurring. It is possible to provide a grain oriented electrical steel sheet having excellent magnetism by controlling the temperature.

Figures 1a and 1b is a flow chart for a flattening annealing method of a grain-oriented electrical steel sheet according to an embodiment of the present invention.

Terms such as first, second and third are used to describe, but are not limited to, various parts, components, regions, layers and/or sections. These terms are only used to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first part, component, region, layer or section described below may be referred to as a second part, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is only for referring to specific embodiments and is not intended to limit the present invention. As used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite. The meaning of "comprising" as used herein specifies particular characteristics, regions, integers, steps, operations, elements and/or components, and the presence or absence of other characteristics, regions, integers, steps, operations, elements and/or components. Additions are not excluded.

When a part is referred to as being “on” or “on” another part, it may be directly on or on the other part or may be followed by another part therebetween. In contrast, when a part is said to be “directly on” another part, there is no intervening part between them.

Although not defined differently, all terms including technical terms and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted as having meanings consistent with related technical literature and currently disclosed content, and are not interpreted in ideal or very formal meanings unless defined.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

Figures 1a and 1b is a flow chart for a flattening annealing method of a grain-oriented electrical steel sheet according to an embodiment of the present invention.

Referring to Figure 1a, according to an embodiment of the present invention, the flattening annealing method of the grain-oriented electrical steel sheet is a first slow cooling temperature (T _s1 ) And the second slow cooling temperature (T _s2 ) Cooling in a slow cooling section including ( S100) and, after the slow cooling section, cooling to a quenching section including a first quenching temperature (T _r1 ) and a second quenching temperature (T _r2 ) (S200) may be included. The flattening annealing of the grain-oriented electrical steel sheet may be performed after high-temperature annealing for secondary recrystallization of the grain-oriented electrical steel sheet.

In the flattening annealing method of the grain-oriented electrical steel sheet, performing the flattening annealing after the high-temperature annealing and the high-temperature annealing is performed to remove residual stress generated in the high-temperature annealing. The flattening annealing method of the grain-oriented electrical steel sheet may be for controlling the temperature pattern of the cooling section.

The first slow cooling temperature (T _s1 ) and the second slow cooling temperature (T _s2 ) Cooling in a slow cooling section including a step (S100) is a step of slowly cooling the grain-oriented electrical steel sheet on which high temperature annealing is completed. The step of cooling in the slow cooling section (S100) may be a step for removing residual stress formed in the grain-oriented electrical steel sheet and correcting the shape after the high-temperature annealing is completed.

The first slow cooling temperature (T _s1 ) may mean a temperature immediately after the high temperature annealing is completed. The second slow cooling temperature (T _s2 ) The grain-oriented electrical steel sheet is gradually cooled from the temperature immediately after the high-temperature annealing is completed, and the temperature of the first quench section (T _r1 ) immediately before the start or the first quench section described later can mean

In one embodiment, the first slow cooling temperature (T _s1 ) It may be a temperature range of 750 to 900 ℃. Outside the upper limit of the temperature range, there is a high possibility of residual stress during cooling and it is difficult to suppress additional oxidation. there is.

In one embodiment, the second slow cooling temperature (T _s2 ) It may be in the temperature range of 700 to 850 ℃. If the temperature exceeds the upper limit of the temperature range, the temperature at which quenching starts is high and the temperature difference increases during quenching, so there is a high possibility of residual stress due to thermal stress. If it is out of the lower limit of the temperature range, in order to control the temperature difference in the slow cooling section, the temperature of the flattening annealing cracking section is too low, and the strength of the steel sheet is high, so it is difficult to correct the shape.

In one embodiment, the temperature difference (T _s1 -T _s2 ) in the slow cooling section may be 10 °C or more. Specifically, the temperature difference in the slow cooling section may be in the range of 10 to 80 °C. More specifically, the temperature difference in the slow cooling section may be in the range of 10 to 50 °C.

The temperature difference (T _s1 -T _s2 ) of the slow cooling section means the difference between the first slow cooling temperature and the second slow cooling temperature. When the temperature difference in the slow cooling section is outside the upper limit of the range, there is a problem in that the length of the annealing furnace is excessively increased in order to apply the same cooling rate, and when the temperature difference is out of the lower limit of the temperature range, the temperature at which rapid cooling starts is There is a problem with a high possibility that residual stress may occur due to an increase in stress.

After the slow cooling section, the first quenching temperature (T _r1 ) and the second quenching temperature (T _r2 ) cooling to a quenching section including (S200) rapidly cooling the grain-oriented electrical steel sheet that has passed through the slow cooling section will be. The step of cooling with the quenching section (S200) is formed in the grain-oriented electrical steel sheet in the flattening annealing process as well as serving to remove the residual stress formed in the high-temperature annealing process by forming a pattern of flattening annealing together with the slow cooling section It can play a role in removing residual stress. When the residual stress is formed in the flattening annealing process, there is a problem in that magnetism is deteriorated even if the magnetic domain refinement treatment is performed.

The first rapid cooling temperature (T _r1 ) may mean a temperature immediately after the second slow cooling temperature (T _s2 ). Accordingly, the first quenching temperature (T _r1 ) may be equal to or lower than the second slow cooling temperature. The second quenching temperature (T _r2 ) may be a temperature at which the grain-oriented electrical steel sheet is rapidly cooled from the first quenching temperature (T _r1 ) to a room temperature range.

In one embodiment, the first quench temperature may be in the temperature range of 700 to 850 °C. When the temperature exceeds the upper limit of the temperature range, there is a problem in that the temperature at which quenching starts is high and the temperature difference during quenching increases, so that residual stress due to thermal stress is highly likely to occur. If it is out of the lower limit of the temperature range, in order to control the temperature difference in the slow cooling section, the temperature of the flattening annealing cracking section is too low, and the strength of the steel sheet is high, so it is difficult to correct the shape.

In one embodiment, the second quench temperature may be in the temperature range of 270 to 700 °C. If it is out of the upper limit of the temperature range, there is a high possibility of residual stress due to thermal stress due to an increase in the temperature difference between the quenching section and the quenching section to a temperature close to room temperature after the quenching section, and the lower limit value of the temperature range If it deviates, there is a problem that the temperature difference between the quench section increases and there is a high possibility of residual stress due to thermal stress. After the second rapid cooling temperature, for example, rapid cooling may be performed to a temperature close to room temperature.

In one embodiment, the temperature difference (T _r1 -T _r2 ) in the quenching section may be in the range of 130 to 430 °C. The temperature difference (T _r1 -T _r2 ) in the quench section means a difference between the first quench temperature and the second quench temperature.

When the temperature difference in the quenching section exceeds the upper limit of the temperature range, there is a problem in that residual stress is excessively formed due to an increase in thermal stress generated during cooling, and when the temperature difference exceeds the lower limit of the temperature range, the quenching section Thereafter, there is a high possibility of residual stress due to thermal stress due to an increase in the temperature difference in the section rapidly cooled to a temperature close to room temperature.

In one embodiment, the temperature difference between the temperature difference in the quenching section and the temperature difference in the slow cooling section may satisfy Equation 1 below.

<Equation 1>

100 ≤ ((T _r1 -T _r2 ) - (T _s1 -T _s2 )) ≤ 400

Equation 1 means the difference between the temperature difference in the rapid cooling section and the temperature difference in the slow cooling section. The difference between the temperature difference between the rapid cooling section and the temperature difference between the slow cooling section may be 100 to 400.

When the difference value exceeds the upper limit of the difference value, there is a problem in that magnetic domain iron loss is deteriorated due to excessive thermal stress in the quenching section. When the difference value is out of the lower limit of the difference value, there is a problem in that the equipment length of the cooling section becomes too long and cooling does not proceed sufficiently. Accordingly, when the difference value satisfies the above range, a grain oriented electrical steel sheet having excellent magnetism can be manufactured.

In one embodiment, the core loss of the grain-oriented electrical steel sheet may be in the range of 0.76 W/kg or less. In one embodiment, the core loss may be in the range of 0.76, specifically, 0.73 W/kg or less. When the iron loss of the grain-oriented electrical steel sheet satisfies the above range, the efficiency of the electrical device may be increased. If the core loss of the grain-oriented electrical steel sheet is greater than the above range, there is a problem in that the efficiency of the electrical device is lowered.

Referring to Figure 1b, according to another embodiment of the present invention, the flattening annealing method is a first slow cooling temperature (T _s1 ), a second slow cooling temperature (T _s2 ) Cooling to a slow cooling section including (S100) and the After the slow cooling section, the first quenching temperature (T _r1 ) and the second quenching temperature (T _r2 ) step of cooling in a quenching section including (S200), and after the step of cooling in the quenching section, the surface of the grain-oriented electrical steel sheet It may include irradiating a laser beam on (S300). Detailed descriptions of the slow cooling step (S100) and the rapid cooling step (S200) are the same as those of FIG. 1 described above to the extent that they do not contradict each other.

The laser beam may be irradiated to the surface of the grain-oriented electrical steel sheet for temporary magnetic domain refinement of the grain-oriented electrical steel sheet. In one embodiment, the laser beam may be, for example, a CO ₂ laser beam. The laser beam may be irradiated in a width direction of the grain-oriented electrical steel sheet.

In one embodiment, the flattening annealing method may include a soaking step before the slow cooling step. The soaking step may be in the same range as the aforementioned first slow cooling temperature (T _s1 ). In one embodiment, the flattening annealing method may be performed in a gas atmosphere. The gas atmosphere may be a gas atmosphere of at least one of hydrogen, nitrogen, an inert gas, and a combination thereof. Specifically, the gas atmosphere may use dry hydrogen and nitrogen, for example.

In one embodiment, the ratio of the hydrogen in the gas atmosphere may be 5 vol% or less. By satisfying the hydrogen ratio of 5 vol% or less, there is an advantage of preventing further oxidation.

Hereinafter, specific embodiments of the present invention will be described. However, the following examples are only specific examples of the present invention, but the present invention is not limited to the following examples.

Examples and Comparative Examples

After high-temperature annealing of the grain-oriented electrical steel sheet, the grain-oriented electrical steel sheet having a thickness of 0.23 mm from which unreacted MgO was removed was coated with insulation, and flattening annealing was performed at 850 °C. The temperature difference between the slow cooling section and the rapid cooling section immediately after the flattening annealing cracking section was controlled as shown in Table 1 1 below.

The furnace time, which is the time from charging to extraction in the slow cooling section, was 4 seconds, and the furnace time in the rapid cooling section was 6 seconds. After the flattening annealing was completed, a continuous mode CO ₂ laser (TEM ₀₀ ) beam was irradiated to the surface of the grain-oriented electrical steel sheet for temporal domain refinement.

The laser beam has an oval shape with a width and a length of 0.1 mm and 10 mm, respectively ^. was irradiated with a laser. Table 1 shows the magnetic properties of the grain-oriented electrical steel sheet according to each flattening annealing cooling condition.

In Table 1 below, the iron loss was measured using a single sheet measurement method, and the iron loss W17/50 is a loss (W/kg) when a magnetic flux density of 1.7 Tesla is induced at a frequency of 50 Hz.

division Slow cooling section temperature difference (T _s1 -T _s2 )
[℃] Temperature difference between quenching section (T _r1 -T _r2 )
[℃] (T _r1 -T _r2 ) -
(T _s1 -T _s2 )
[℃] iron loss
[W/kg] Comparative Example 1 10 540 530 0.79 Comparative Example 2 10 440 430 0.77 Invention example 1 10 340 330 0.73 Invention Example 2 10 140 130 0.73 Comparative Example 3 40 510 470 0.77 Invention Example 3 40 410 370 0.73 Invention Example 4 40 310 270 0.72 Invention example 5 40 210 170 0.72

Looking at Table 1, when the cooling rate is controlled so that the difference between the temperature difference between the rapid cooling section and the slow cooling section (T _r1 -T _r2 ) - (T _s1 -T _s2 ) is 100 or more and 400 or less, the iron loss It may be 0.76 W/kg or less. In Comparative Examples 1 to 3 in which the difference value is out of the above range, it can be confirmed that the iron loss value is increased and the magnetic properties are deteriorated.

The present invention is not limited to the above embodiments and / or embodiments, but can be manufactured in various different forms, and those skilled in the art to which the present invention belongs may change the technical spirit or essential features of the present invention. It will be appreciated that it may be embodied in other specific forms without Therefore, it should be understood that implementations and/or examples described above are illustrative in all respects and not restrictive.

Claims (12)

In the flattening annealing method of grain-oriented electrical steel sheet, which performs flattening annealing after high-temperature annealing,
The flattening annealing is a first slow cooling temperature (T _s1 ) And the second slow cooling temperature (T _s2 ) Cooling to a slow cooling section including; and
After the slow cooling section, a first quenching temperature (T _r1 ) And a step of cooling to a quenching section including a second quenching temperature (T _r2 ),
Flattening annealing method of a grain-oriented electrical steel sheet in which the temperature difference in the quenching section and the temperature difference in the slow cooling section satisfy Equation 1 below.
<Equation 1>
100 ≤ ((T _r1 -T _r2 ) - (T _s1 -T _s2 )) ≤ 400
According to claim 1,
The temperature difference in the slow cooling section (T _s1 -T _s2 ) is a flattening annealing method of grain-oriented electrical steel sheet of 10 ℃ or more.
According to claim 1,
The temperature difference (T _s1 -T _s2 ) in the slow cooling section is a flattening annealing method of grain-oriented electrical steel sheet of 10 to 50 ℃ or more.
According to claim 1,
The first slow cooling temperature (T _s1 ) Flattening annealing method of grain-oriented electrical steel sheet of 750 to 900 ℃.
According to claim 1,
The second slow cooling temperature (T _s2 ) Flattening annealing method of grain-oriented electrical steel sheet of 700 to 850 ℃.
According to claim 1,
The temperature difference (T _r1 -T _r2 ) in the quenching section is 130 to 430 ℃ flattening annealing method of grain-oriented electrical steel sheet.
According to claim 1,
The first quench temperature (T _r1 ) Flattening annealing method of grain-oriented electrical steel sheet of 700 to 850 ℃.
According to claim 1,
The second quenching temperature (T _r2 ) is 270 to 700 ℃ flattening annealing method of grain-oriented electrical steel sheet.
According to claim 1,
Flattening annealing method of the grain-oriented electrical steel sheet having an iron loss of 0.76 W / kg or less of the grain-oriented electrical steel sheet.
According to claim 1
After the step of cooling to the quenching section, the flattening annealing method of the grain-oriented electrical steel sheet further comprising the step of irradiating a laser beam to the surface of the grain-oriented electrical steel sheet.
According to claim 1,
The flattening annealing method of the grain-oriented electrical steel sheet is a flattening annealing method of the grain-oriented electrical steel sheet carried out under a gas atmosphere of at least one of hydrogen, nitrogen, an inert gas, and a combination thereof.
According to claim 11,
Flattening annealing method of a grain-oriented electrical steel sheet in which the hydrogen ratio is 5 vol% or less.

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