KR20190078099A - Manufacturing method of oriented electrical steel sheet - Google Patents

Abstract

The present invention provides a method for manufacturing an oriented electric steel sheet. The method for manufacturing an oriented electric steel sheet includes: a step of heating a slab for N applied to the slab to be equal to or less than 15 ppm and for S to be equal to or less than 20 ppm, wherein the slab includes 2.0-6.0 wt% of Si, 0.02-0.4 wt% of Sol.Al, 0.2 wt% or less (excluding 0 wt%) of Mn, 0.04-0.07 wt% of C, 0.002-0.0055 wt% of N, 0.002-0.0055 wt% of S, 0.01-0.15 wt% of Sb, and residues including Fe and inevitable impurities; a step of manufacturing a hot rolled sheet by hot rolling the slab; a step of annealing the hot rolled sheet; a step of manufacturing a cold rolled sheet by cold rolling the hot rolled sheet annealed; a step of firstly recrystallizing and annealing the cold rolled sheet; and a step of secondly recrystallizing and annealing the cold rolled sheet firstly recrystallized and annealed. In the step of annealing the hot rolled sheet, the hot rolled sheet is heated to a heating temperature (T_h) satisfying the following equation 1. The hot rolled sheet maintains a crack temperature (T_s) lower than the heating temperature (T_h). [equation1] 1100-20×[Al]/[N] < T_h< 1220-20×[Al]/[N] (unit: °C)(In equation 1, [Al] and [N] individually mean the content (wt%) of Sol.Al and N, and T_h means the heating temperature in the step of annealing the hot rolled sheet.)

Description

TECHNICAL FIELD [0001] The present invention relates to a method for manufacturing a directional electric steel sheet,

To a method for producing a directional electrical steel sheet. More specifically, the present invention relates to a method for producing a grain-oriented electrical steel sheet excellent in magnetic properties.

The grain-oriented electrical steel sheet is composed of crystal grains having a goss texture having a crystal orientation of {110} plane and a crystal orientation of the rolling direction parallel to the <001> axis, It is a magnetic material. Obtaining such {110} < 001 > texture can be achieved by a combination of various manufacturing processes, and it is very strictly possible to obtain the steel composition, the slab heating, the hot rolling, the annealing of the hot rolled steel sheet, the primary recrystallization annealing, It is important to be controlled.

Such a grain-oriented electrical steel sheet is intended to suppress the growth of the primary recrystallized grains and to exhibit excellent magnetic properties by a secondary recrystallized structure obtained by selectively growing crystal grains in a {110} < 001 > , The growth inhibitor of primary recrystallization is important. It is the core of the directional electric steel sheet manufacturing technology that, among the crystal grains whose growth is suppressed in the secondary recrystallization annealing step, the crystal grains having the aggregate structure of {110} < 001 > orientation can be preferentially grown.

One embodiment of the present invention provides a method of manufacturing a grain-oriented electrical steel sheet having excellent magnetic properties by controlling the heating temperature and the cracking temperature of the N and S and the hot-rolled steel sheet,

A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes: 2.0 to 6.0% of Si, 0.02 to 0.4% of Sol.Al, 0.2% or less of Mn (excluding 0%), 0.04 Wherein the slab contains 0 to 0.07% of N, 0.002 to 0.0055% of S, 0.002 to 0.0055% of S, 0.01 to 0.15% of Sb and the balance of Fe and unavoidable impurities, To 20 ppm or less; Hot rolling the slab to produce a hot rolled sheet; Annealing the hot-rolled sheet by hot-rolling; Cold-rolling the hot-rolled sheet annealed to produce a cold-rolled sheet; Subjecting the cold-rolled sheet to primary recrystallization annealing; And a second recrystallization annealing step in which the hot-rolled sheet is annealed at a heating temperature (T _h ) satisfying the following formula (1) (T _s ) lower than the temperature (T _h ).

[Formula 1]

1100-20 x [Al] / [N] < T _h < 1220-20 x [Al] / [N]

(In the formula 1, [Al] and [N] mean the content (% by weight) of Sol.Al and N, respectively, and T _h means the heating temperature in the step of annealing the hot-

The slab may further include at least one of 0.02 to 0.15% of Sn and 0.02 to 0.35% of Cr.

In the heating step, the slab may be heated to a temperature of 1000 to 1120 占 폚.

In the heating step, the slab may contain 17 to 30% of the austenite and the remainder ferrite in an area fraction.

In the step of hot-rolling the hot-rolled sheet, the layer-to-sheet spacing at t / 4 to 3t / 4 may be 40 탆 or less based on the thickness t of the hot-rolled sheet.

In the step of annealing the hot-rolled sheet, the amount of N dissolved in the hot-rolled sheet after heating at the heating temperature (T _h ) may be 10 ppm or less and S may be 7 ppm or less.

In the step of annealing the hot-rolled sheet, the following formula (2) can be satisfied.

[Formula 2]

50? T _h -T _s (Unit: ℃)

(Where T _h means the heating temperature in the step of annealing the hot-rolled sheet and T _s means the cracking temperature in the step of annealing the hot-rolled sheet).

In the step of annealing the hot-rolled sheet, after cracking at the cracking temperature (T _s ), N dissolved in the hot-rolled steel sheet may be 5 ppm or less and S may be 5 ppm or less.

In the primary recrystallization annealing step, simultaneous decarburization annealing is performed to satisfy the following expression (3).

[Formula 3]

F ₄₀ < 2.37 x G _s -36

(In the formula (3), the F _{40 system} refers to the area fraction (%) of the grains having a grain size of 40 탆 or more in the cold-rolled steel sheet after the simultaneous decarburization annealing, and G _s denotes the average grain size it means.)

In the method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention, when the slab is heated, the effects of excellent magnetic properties can be expected by controlling the heating temperature and the cracking temperature of the solidified N and S and the hot-

1 is a graph showing a correlation between an average grain size (grain size) and an area fraction (%) of a grain having a grain size of 40 m or more in a cold-rolled sheet.

The terms first, second and third, etc. are used to describe various portions, components, regions, layers and / or sections, but are not limited thereto. These terms are only used to distinguish any moiety, element, region, layer or section from another moiety, moiety, region, layer or section. Thus, a first portion, component, region, layer or section described below may 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 describing particular embodiments only and is not intended to limit the invention. The singular forms as used herein include plural forms as long as the phrases do not expressly express the opposite meaning thereto. Means that a particular feature, region, integer, step, operation, element and / or component is specified and that the presence or absence of other features, regions, integers, steps, operations, elements, and / It does not exclude addition.

When referring to a portion as being "on" or "on" another portion, it may be directly on or over another portion, or may involve another portion therebetween. In contrast, when referring to a part being "directly above" another part, no other part is interposed therebetween.

Unless otherwise defined, 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. Commonly used predefined terms are further interpreted as having a meaning consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or very formal meanings unless defined otherwise.

Unless otherwise stated,% means% by weight, and 1 ppm is 0.0001% by weight.

In an embodiment of the present invention, the term further includes an additional element, which means that an additional amount of the additional element is substituted for the remaining iron (Fe).

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Directional electric steel sheet manufacturing method

The grain-oriented electrical steel sheet according to an embodiment of the present invention may contain, by weight%, 2.0 to 6.0% of Si, 0.02 to 0.4% of Sol.Al, 0.2% or less of Mn (excluding 0%), 0.04 to 0.07 % Of N, 0.002 to 0.0055% of N, 0.002 to 0.0055% of S, 0.01 to 0.15% of Sb and the balance of Fe and unavoidable impurities, wherein the N content in the slab is 15 ppm or less and S is 20 ppm or less A step of hot rolling the slab to produce a hot rolled sheet, a step of annealing the hot rolled sheet to anneal the hot rolled sheet, a step of cold rolling the hot rolled sheet to obtain a cold rolled sheet, And annealing the first and second recrystallization annealed quartz plates to perform second recrystallization annealing. In the step of annealing the hot rolled sheet, the hot rolled sheet is heated to a heating temperature (T _h ) satisfying the following formula (1) T _h ) at a lower crack temperature (T _s ).

[Formula 1]

1100-20 x [Al] / [N] < T _h < 1220-20 x [Al] / [N]

(In the formula 1, [Al] and [N] mean the content (% by weight) of Sol.Al and N, respectively, and T _h means the heating temperature in the step of annealing the hot-

The slab may further include at least one of 0.02 to 0.15% of Sn and 0.02 to 0.35% of Cr.

First, the reasons for limiting the slab component will be described below.

Si: 2.0 to 6.0%

Silicon (Si) is a basic composition of an electric steel sheet, and it plays a role of lowering the core loss (iron loss) by increasing the resistivity of the material. If the Si content is less than 2.0%, the resistivity decreases and the iron loss property deteriorates. If the Si content exceeds 6.0%, the brittleness of the steel becomes large, and the cold rolling becomes extremely difficult and the formation of the secondary recrystallization may become unstable.

Sol.Al: 0.02 to 0.4%

When the content of Sol.Al added to the slab as a component acting as an inhibitor is made to be 0.02% or less, the aluminum (Al) is finally made of nitride of AlN, (Al, Si) N, (Al, Si, Mn) , Sufficient effect as an inhibitor can not be expected. If it exceeds 0.4%, the nitride of the Al system precipitates and grows too much, and the effect as an inhibitor may become insufficient.

Mn: not more than 0.2%

Manganese (Mn) has an effect of reducing the iron loss by increasing the resistivity as Si, and reacting with nitrogen introduced by the nitriding treatment together with Si to form precipitates of N (Al, Si, Mn) It is an important element for suppressing the growth of sizing and causing secondary recrystallization. However, when the Mn content exceeds 0.2%, since the austenite phase transformation is promoted during hot rolling, the size of the primary recrystallized grains can be reduced to make the secondary recrystallization unstable.

C: 0.04 to 0.07%

When carbon (C) is added in an amount less than 0.04%, there is little effect of forming a uniform microstructure by making the hot-rolled structure finer in hot rolling. When it exceeds 0.07%, coarse carbides are precipitated, , The removal of C may become difficult.

N: 0.002 to 0.0055%

When nitrogen (N) is added to the slab in an amount less than 0.002%, the effect of making the initial grain size before cold rolling is insignificant, so that the number of grains having {110} < 001 & The effect of improving the magnetic properties of the final product is not sufficient. If it exceeds 0.0055%, the size of the primary recrystallized grains becomes smaller to lower the secondary recrystallization starting temperature. This is because the crystal grains that are not in the {110} < 001 > orientation cause secondary recrystallization, It takes a long time to remove N from the second crack section of the annealing process, so it may be difficult to produce a highly directional electric steel sheet having high productivity.

S: 0.002 to 0.0055%

When sulfur (S) is added in an amount less than 0.002%, the effect of coarsening of the initial grain size before cold rolling is small, so that the number of grains having a {110} < 001 & The effect may not be sufficient. If it exceeds 0.0055%, it will be reused at the time of heating the slab, resulting in fine precipitation. Therefore, the size of the primary recrystallization granules is reduced to lower the secondary recrystallization starting temperature to deteriorate the magnetic properties. In the secondary recrystallization annealing step, It may take a lot of time to remove the S of the state.

Sb: 0.01 to 0.15%

Antimony (Sb) is segregated in grain boundaries to inhibit excessive growth of the primary recrystallized grains, but if it is less than 0.01%, it may be difficult to exhibit its function properly. If it exceeds 0.15%, the size of the primary recrystallized grains becomes excessively small and the secondary recrystallization starting temperature is lowered, so that the magnetic properties are deteriorated or the secondary recrystallization may not be formed because the suppressing ability against grain growth becomes too large.

Sn: 0.02 to 0.15%

Tin (Sn) is known as a crystal growth inhibitor since it is an element that interferes with the movement of grain boundaries as a grain boundary segregation element. By increasing the grain fraction of the Goss orientation in the primary recrystallized texture, the size of the secondary recrystallized microstructure decreases as the number of Goss bearing nuclei grown in the secondary recrystallized texture increases. As the grain size becomes smaller, . If it is less than 0.02%, the effect of decreasing the iron loss is insignificant. If it exceeds 0.15%, the crystal grain growth inhibiting ability is excessively increased and the crystal grain size of the primary recrystallized microstructure should be decreased in order to increase the grain growth driving force relatively. Must be carried out at a low temperature. As a result, it is impossible to control with an appropriate oxide layer, so that a good surface can not be obtained.

Cr: 0.02 to 0.35%

Chromium (Cr) acts to grow primary recrystallized grains with ferrite-expanded elements and increases the grain in the {110} < 001 > orientation in the primary recrystallized phase. If it is less than 0.02%, the effect may be insignificant. If it exceeds 0.35%, a dense oxide layer may be formed on the surface portion of the steel sheet in the simultaneous decarburization nitriding process to prevent the sediment.

The process conditions are described below.

First, the slab is heated so as to be incompletely fused. The heating temperature is set so that the amount of N dissolved in the slab is 15 ppm or less. Generally, the incompletely sintering temperature is below 1250 ° C. The factor that has an absolute effect on the size of the primary recrystallized grains is the amount of N reused in the slab when the slab is heated, rather than the amount of N in the steelmaking step.

The slab is heated so that the amount of N dissolved therein is 15 ppm or less and S is 20 ppm or less. When the solubility of N and S exceeds 15 ppm and exceeds 20 ppm, respectively, the average size of the primary recrystallized grains becomes smaller, so that the secondary recrystallization temperature becomes lower and the directionality deteriorates.

Specifically, the slab heating temperature may be 1000 to 1120 占 폚. If the slab heating temperature is lower than 1000 ° C, hot rolling itself is difficult. If the slab heating temperature is higher than 1120 ° C, fine precipitates are generated in the hot rolling step to reduce the size of the primary recrystallized grains, so that a stable secondary recrystallization can not be expected .

Generally, the smaller the amount of N or S dissolved in the slab, the more the average size of the primary recrystallized grains is excessively grown and the secondary recrystallization does not occur, resulting in a very poor magnetic property. Even if the average crystal grain size is reduced by lowering the primary recrystallization temperature, the problem of deteriorated surface characteristics can not be avoided. However, in the case of the present invention, since Sn and Sb are contained in the slab, grain growth is suppressed, so that there is no problem even if the amount of N and S is small.

In the heating step, the slab may contain 17 to 30% of the austenite and the remainder ferrite in an area fraction.

Since 0.04 to 0.07% by weight of C is contained in the slab, austenite is formed when the slab is heated, and this area fraction plays a large role in increasing the amount of precipitates in a large amount and forms a layered structure after hot rolling and hot- do. A layered structure interface is formed in black. The layered gap at t / 4 to 3t / 4 may be 40 占 퐉 or less based on the direction of thickness t of the hot-rolled sheet. If it exceeds 40 탆, the aggregate structure favorable to the growth of the Goss orientation during the primary recrystallization may be reduced.

Next, the heated slab is hot-rolled by a conventional method to produce a hot-rolled sheet, which is hot-rolled to a final thickness of 2.0 to 3.5 mm.

Next, the hot-rolled sheet annealing is performed in the direction of maximizing the amount of dissolved N and S dissolved as much as the slab heating, and maximizing the precipitation of fine precipitates through solidification during hot rolling and hot rolling at the time of slab heating.

The hot rolled sheet is heated at a heating temperature T _h satisfying the following formula 1 and maintained at a lower cracking temperature T _s than the heating temperature T _h .

[Formula 1]

1100-20 x [Al] / [N] < T _h < 1220-20 x [Al] / [N]

(In the formula 1, [Al] and [N] mean the content (% by weight) of Sol.Al and N, respectively, and T _h means the heating temperature in the step of annealing the hot-

As shown in the formula 1, the heating temperature (T _h ) is determined according to the ratio of [Al] / [N], so that the produced precipitate can be reused after hot rolling and the precipitate unevenness before the primary recrystallization is removed .

The hot-rolled sheet heating temperature (T _h ) is the temperature at which the subsequent primary recrystallization size is peaked. Specifically, the heating temperature (T _h ) may be 1000 to 1080 ° C, and the heating temperature (T _h ) may be set such that the content of N dissolved therein is 10 ppm or less and the content of S dissolved therein is 7 ppm or less _h ) can be set so that the precipitate can be reused.

The heating of the hot-rolled sheet is carried out at a high temperature, and the crack is grown at a cracking temperature (T _s ) lower than the heating temperature (T _h ) to grow the precipitate.

As described above, cracks are treated at a crack temperature (T _s ) lower than the heating temperature (T _h ), so that further precipitation can be prevented from being reused and the precipitate can be grown. The lower limit of the crack temperature (T _s ) may be 800 ° C or higher.

Specifically, it can be cracked at the crack temperature (T _s ) satisfying the following formula (2).

[Formula 2]

50? T _h -T _s (Unit: ℃)

(Where T _h means the heating temperature in the step of annealing the hot-rolled sheet and T _s means the cracking temperature in the step of annealing the hot-rolled sheet).

If the difference between the heating temperature (T _h ) and the cracking temperature (T _s ) is less than 50 캜, the precipitates may be continuously reused, which may impede sufficient growth of the precipitates.

Thus, after cracking at the cracking temperature (T _s ), precipitates can be grown by ensuring that N dissolved in the hot-rolled sheet is 5 ppm or less and S is 5 ppm or less.

Specifically, the soaking time in the soaking temperature (T _s) can be from 300 to 300 seconds. If it is less than 30 seconds, the growth time of the precipitate is shortened, and if it exceeds 300 seconds, the cost of the heat treatment facility is increased, and as a result, the productivity may be deteriorated.

Thereafter, cooling with water at 100 ° C or lower can be started at a temperature of 650 to 800 ° C. Thus, during cold rolling, shear band formation can be promoted to improve the primary recrystallization texture.

Next, the hot-rolled sheet annealed in the hot-rolled sheet can be cold-rolled to obtain a cold-rolled sheet having a thickness of 0.15 to 0.35 mm.

The cold-rolled cold-rolled sheet can be subjected to decarburization and nitridation annealing simultaneously in a mixed gas atmosphere of ammonia + hydrogen + nitrogen.

Concretely, at the time of primary recrystallization annealing, simultaneous decarburization annealing is performed to satisfy the following expression (3).

[Formula 3]

F ₄₀ < 2.37 x G _s -36

(In the formula (3), the F _{40 system} refers to the area fraction (%) of the grains having a grain size of 40 탆 or more in the cold-rolled steel sheet after the simultaneous decarburization annealing, and G _s denotes the average grain size it means.)

If the formula (3) is not satisfied, the grain fraction of the grain size of 40 m or more is further increased. When the coarse grain fraction of 40 탆 or more in grain size increases, the bad orientation deviating much from the Goss orientation having excellent magnetic properties grows as a secondary recrystallization due to the size advantage when the secondary recrystallization annealing is performed, and the secondary recrystallization orientation is deteriorated.

As shown in the graph of Fig. 1, the grain fraction of 40 mu m or more in grain size may vary depending on the heating temperature of the slab.

In general, nitriding is used as an inhibitor to form nitride in the steel by adding nitrogen, so that it is possible in any process after cold rolling. In other words, nitrogen can be introduced into the steel by nitriding using ammonia gas during decarburization annealing or another annealing step after decarburization annealing.

However, at the same time, decarburization and nitriding are economical and simple processes. The dew point of the mixed gas of hydrogen and nitrogen varies depending on the annealing temperature and composition ratio of the mixed gas, and is set so as to maximize the decarburization capability.

The simultaneous decarburization annealing and nitriding annealing can be performed at 800 to 950 占 폚. When the annealing temperature is less than 800 ° C, decarburization takes a long time, and the size of the primary recrystallized grains is small, so that secondary recrystallization can not be expected stably when secondary recrystallization annealing is performed. When the annealing temperature exceeds 950 DEG C, it is difficult to control the rate of the nitridation reaction, and the primary recrystallized grains are excessively grown or uneven, and it may be difficult to develop a stable secondary recrystallized structure when the secondary recrystallization annealing is performed.

The annealing time for simultaneous decarburization and nitriding is determined by the annealing temperature and the concentration of the ammonia gas introduced, and the annealing time can be 30 seconds or more. Accordingly, the size of the primary recrystallized grains can be controlled to 18 to 30 mu m.

Hereinafter, specific examples of the present invention will be described. However, the following examples are only a concrete example of the present invention, and the present invention is not limited to the following examples.

Example

[Example 1]

0.030%, P: 0.029%, N: 0.0042%, S: 0.0050%, Sn: 0.05%, Sb: 0.025% The slabs of the directional electric steel sheet containing 0.04% of Cr and the remainder Fe and inevitably contained were heated for 210 minutes under conditions as shown in Table 1 or Table 2 below. Table 1 shows the solid solution Al and solid solution N according to the slab heating temperature, and Table 2 shows the solid solution Mn and solid solubility S according to the slab heating temperature.

Thereafter, the hot rolled sheet was hot rolled to prepare a hot rolled sheet having a thickness of 2.3 mm. The hot rolled sheet was heated under different conditions as shown in Table 3 or Table 4 below. Thereafter, solid solution Al and solid solution N according to the hot-rolled sheet heating temperature are shown in Table 3, and Mn and solid solubility S according to the hot-rolled sheet heating temperature are shown in Table 4.

Slab
Heating temperature
(° C) Sol.Al
(weight%) N
(weight%) Employment Al
(weight%) Employment N
(weight%) Al (% by weight) precipitated as AlN N (% by weight) precipitated in AlN division 1200 0.0280 0.0042 0.0257 0.0030 0.0023 0.0012 Comparative Example 1150 0.0280 0.0042 0.0235 0.0019 0.0045 0.0023 Comparative Example 1120 0.0280 0.0042 0.0226 0.0014 0.0054 0.0028 Honor 1100 0.0280 0.0042 0.0221 0.0011 0.0059 0.0031 Honor 1080 0.0280 0.0042 0.0216 0.0009 0.0064 0.0033 Honor 1050 0.0280 0.0042 0.0211 0.0006 0.0069 0.0036 Honor

Slab
Heating temperature
(° C) Mn
(weight%) S
(weight%) Employment Mn
(weight%) Employment S
(weight%) Mn (% by weight) precipitated in MnS S (% by weight) precipitated in MnS division 1200 0.1000 0.0050 0.1000 0.0050 0.0000 0.0000 Comparative Example 1150 0.1000 0.0050 0.0957 0.0025 0.0043 0.0025 Comparative Example 1120 0.1000 0.0050 0.0940 0.0015 0.0060 0.0035 Honor 1100 0.1000 0.0050 0.0933 0.0011 0.0067 0.0039 Honor 1080 0.1100 0.0050 0.1026 0.0007 0.0074 0.0043 Honor 1050 0.1000 0.0050 0.0921 0.0004 0.0079 0.0046 Honor

As shown in Tables 1 and 2, in the case where the temperature of the slab is 1050 to 1120 DEG C when 0.028% of Sol. Al and 0.0042% of N are contained, the N content in the slab is 15 ppm or less and S is 20 ppm or less And can confirm the satisfaction. In the comparative examples, the heating temperature of the slab was more than 1120 DEG C, the N dissolved in the slab was not more than 15 ppm, and the S was not more than 20 ppm.

Hot-rolled plate
Heating temperature
(° C) Sol.Al
(weight%) N
(weight%) Employment Al
(weight%) Employment N
(weight%) Al (% by weight) precipitated as AlN N (% by weight) precipitated in AlN division 1150 0.0280 0.0042 0.0235 0.0019 0.0045 0.0023 Comparative Example 1100 0.0280 0.0042 0.0221 0.0011 0.0059 0.0031 Comparative Example 1080 0.0280 0.0042 0.0216 0.0009 0.0064 0.0033 Honor 1050 0.0280 0.0042 0.0211 0.0006 0.0069 0.0036 Honor 1030 0.0280 0.0042 0.0208 0.0005 0.0072 0.0037 Honor 950 0.0280 0.0042 0.0202 0.0002 0.0078 0.0040 Comparative Example

Hot-rolled plate
Heating temperature
(° C) Mn
(weight%) S
(weight%) Employment Mn
(weight%) Employment S
(weight%) Mn (% by weight) precipitated in MnS S (% by weight) precipitated in MnS division 1150 0.1000 0.0050 0.0957 0.0025 0.0043 0.0025 Comparative Example 1100 0.1100 0.0050 0.1031 0.0010 0.0069 0.0040 Comparative Example 1080 0.1000 0.0050 0.0927 0.0007 0.0073 0.0043 Honor 1050 0.1000 0.0050 0.0921 0.0004 0.0079 0.0046 Honor 1030 0.0900 0.0050 0.0820 0.0003 0.0080 0.0047 Honor 950 0.1000 0.0050 0.0915 0.0001 0.0085 0.0049 Comparative Example

As shown in Tables 3 and 4, the hot-rolled sheet heating temperature (T _h ) according to the formula 1 when the content of Sol.Al was 0.028%, the content of N was 0.0042% and the content of [Al] / [N] was 6.67 was 967 to 1087 ° C . In the case of the hot-rolled sheet heating temperature (T _h ) of 1030 to 1080 ° C, 1100-20 × [Al] / [N] <T _h <1220-20 × [Al] / [N] . In the case of the comparative examples, the equation (1) was not satisfied. It is possible to confirm the content of dissolved N and S depending on the hot-rolled sheet heating temperature (T _h ).

[Example 2]

0.030%, P: 0.029%, N: 0.0042%, S: 0.0050%, Sn: 0.05%, Sb: 0.025% 0.04% of Cr, and the remainder of Fe and inevitably contained slabs of the directional electric steel sheet were heated under different conditions as shown in Table 5 below. Thereafter, the hot rolled steel sheet was hot rolled to obtain a hot rolled steel sheet having a thickness of 2.3 mm.

Next, the hot-rolled sheet was heated while changing the conditions as shown in the following Table 5, and then maintained at a cracking temperature of 900 캜 for 70 seconds, cooled to 755 캜, and quenched in water.

After pickling, it was cold-rolled to a thickness of 0.30 mm. The cold-rolled steel sheet was subjected to simultaneous decarburization and nitriding treatment by maintaining at 855 ° C. a mixed atmosphere of 75% hydrogen and 25% nitrogen at a dew point temperature of 65 ° C. and 1% Respectively. After the simultaneous decarburization and nitriding, the nitrogen content in the steel sheet was 182 ppm.

The steel sheet was coated with MgO as an annealing separator and subjected to secondary recrystallization annealing in a coiled manner. During the secondary recrystallization annealing, the primary cracking temperature was 700 ° C, the secondary cracking temperature was 1200 ° C, and the temperature increase rate was 15 ° C per hour. On the other hand, the cracking time at 1200 占 폚 was 20 hours. The atmosphere for the secondary recrystallization annealing was a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, it was kept in a 100% hydrogen atmosphere and then cooled. The magnetic properties measured for each condition are shown in Table 5.

Slab
Heating temperature
(° C) Employment N
(ppm) Employment S
(ppm) Hot-rolled plate
Heating temperature
(° C) Equation 1 Satisfaction Hot-rolled plate
Crack temperature
(° C) Magnetic flux density
(B ₈ ) Iron loss
(W _17/50 ) division 1200 30 50 1050 X 900 1.825 1.73 Comparison 1 1150 19 25 1050 X 900 1.908 1.00 Comparative material 2 1120 14 15 1050 O 900 1.921 0.97 Inventory 1 1100 11 11 1050 O 900 1.929 0.95 Inventory 2 1080 9 7 1050 O 900 1.925 0.94 Inventory 3 1050 6 4 1050 O 900 1.931 0.94 Invention 4 1100 11 11 1150 X 900 1.898 1.05 Comparative material 3 1100 11 11 1100 X 900 1.902 1.03 Comparison 4 1100 11 11 1000 O 900 1.925 0.96 Invention Article 5 1100 11 11 950 X 900 1.89 1.01 Comparative material 5

In Table 5, solid N (ppm) means the amount of N dissolved in the slab after slab heating, and magnetic flux density (B ₈ ) indicates the magnitude of induced magnetic flux density (Tesla )to be. The iron loss (W _17/50) is the average loss (W / kg) in the rolling direction to the rolling direction when the vertical magnetic flux density of the organic 1.7Tesla is at 50Hz frequency.

The heating temperature (T _h ) of the hot-rolled sheet according to the formula 1 was 967 to 1087 캜 when Sol. Al was 0.028%, N was 0.0042%, and [Al] / [N] was 6.67.

In Inventive Samples 1 to 5, it was found that after heating the slab, the N content in the slab was 15 ppm or less and the solubilized S was 20 ppm or less. The hot-rolled sheet heating temperature (T _h ) (T _h) than exhibited a magnetic flux density and core loss characteristic is excellent because it satisfies all of the conditions of maintaining at a low soaking temperature (T _s).

On the other hand, in the case of comparative materials 1 and 2, the magnetic flux density and the iron loss were not superior to those of the inventive material since the N content in the slab was less than 15 ppm and the dissolved S was less than 20 ppm after the slab heating, 5, since the hot-rolled sheet heating temperature (T _h ) did not satisfy the formula (1), the magnetic flux density and iron loss were not superior to those of the inventive material.

[Example 3]

0.15% of Mn, 0.10% of Mn, 0.032% of P, 0.0050% of S, 0.065% of Sn, 0.025% of Sb and 0.04% of Cr, N was added under different conditions as shown in Table 6 below. The remainder of the Fe and inevitably oriented slabs of the electric steel sheet were heated at 1100 ° C and then hot rolled to produce a 2.3 mm thick hot rolled sheet.

The hot-rolled sheet was maintained at the cracking temperature for 90 seconds while cooling the hot-rolled sheet at a different heating temperature (T _h ) and hot-rolled sheet cracking temperature (T _s ), cooled to 755 ° C, Respectively.

After pickling, it was cold-rolled to a thickness of 0.30 mm. The cold-rolled plate was maintained at a temperature of 800 to 900 ° C. in a furnace at a dew point temperature of 65 ° C. and a mixed atmosphere of 75% of hydrogen and 25% of nitrogen and 1% of dry ammonia gas at the same time. Nitrided. After simultaneous decarburization, the nitrogen content in the steel sheet was 182 ppm.

The steel sheet was coated with MgO as an annealing separator and subjected to secondary recrystallization annealing in a coiled manner. During the secondary recrystallization annealing, the primary cracking temperature was 700 ° C, the secondary cracking temperature was 1200 ° C, and the temperature increase rate was 15 ° C per hour. On the other hand, the cracking time at 1200 占 폚 was 15 hours. The atmosphere for the secondary recrystallization annealing was a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, it was kept in a 100% hydrogen atmosphere and then cooled. The magnetic properties measured for each condition are shown in Table 6.

Sol.Al (wt.%) N (% by weight) Employment N
(ppm) [Al] / [N] Equation 1
Lower limit
(° C) Equation 1
maximum
(° C) Th
(° C) Ts
(° C) Magnetic flux density
(B8) Iron loss
(W _17/50 ) division 0.021 0.005 0.0016 4.2 1016 1136 1050 905 1.82 1.65 Comparative material 5 0.028 0.005 0.0011 5.6 988 1108 1050 905 1.925 0.96 Invention 7 0.031 0.005 0.001 6.2 976 1096 1125 905 1.905 One Comparative material 6 0.045 0.005 0.0004 9 920 1040 1050 905 1.85 1.51 Comparison 7 0.028 0.001 0.0009 28 540 660 1050 905 1.86 1.25 COMPARISON 8 0.028 0.005 0.0012 5.6 988 1108 1125 905 1.9 1.03 Comparative material 9 0.028 0.015 0.0038 1.87 1063 1183 1050 905 1.87 1.32 Comparative material 10 0.029 0.005 0.0011 5.8 984 1104 1050 1050 1.87 1.1 Comparative material 11

In Table 6, solid N (ppm) refers to the amount of N dissolved in the slab after heating the slab, and the lower limit corresponds to the value of [Al] / [N] at 1100-20 * [Al] / [ And the upper limit of Equation 1 is the value calculated when [Al] / [N] is substituted for 1220-20 * [Al] / [N].

T _h means the heating temperature in the step of annealing the hot-rolled sheet, and T _s means the cracking temperature in the step of annealing the hot-rolled sheet. The magnetic flux density (B ₈ ) is the magnitude (Tesla) of the induced magnetic flux density when a magnetic field of 800 A / m is added. The iron loss (W _17/50) is the average loss (W / kg) in the rolling direction to the rolling direction when the vertical magnetic flux density of the organic 1.7Tesla is at 50Hz frequency.

For the invention material 7, since the slab heating, was the dissolved N in the slab satisfy the below 15ppm, the hot-rolled plate heating temperature (T _h) that was satisfied the equation 1, since, low crack than the heating temperature (T _h) Temperature ( T _s ), the magnetic flux density and the iron loss were excellent.

In the case of the comparative material 5, since the N dissolved in the slab did not satisfy 15 ppm or less after the slab heating, the magnetic flux density and iron loss were not superior to those of the invention material.

In Comparative Examples 6 to 9, since the hot-rolled sheet heating temperature (T _h ) did not satisfy the formula (1), the magnetic flux density and iron loss were not superior to those of the inventive material.

In the case of Comparative Example 10, since the content of N added to the slab and the heating of the slab did not satisfy 15 ppm or less of N dissolved in the slab, the magnetic flux density and iron loss were not superior to those of the invention.

In Comparative Example 11, since the cracking temperature did not satisfy the condition lower than the heating temperature after the hot-rolled sheet was heated, the magnetic flux density and iron loss were not superior to those of the invention material.

[Example 4]

The steel sheet contains 3.2% Si, 0.055% N, 0.0042% Mn, 0.12% Mn, 0.026% Sol, 0.029% P, 0.0050% S, 0.05% Sn, 0.025% Sb, The slabs of Fe and inevitably contained oriented electrical steel sheets containing 0.04% of Cr and 0.04% of Cr were heated at 1090 ° C, 1110 ° C, 1150 ° C, 1175 ° C and 1200 ° C for 210 minutes, respectively, mm thick hot rolled sheet was produced.

The hot-rolled sheet was heated at 1040 占 폚, held at a cracking temperature of 890 占 폚 for 70 seconds, cooled to 755 占 폚, and quenched in water.

After pickling, it was cold-rolled to a thickness of 0.30 mm. The cold-rolled plate was maintained at a temperature of 820 to 880 DEG C in a furnace at a dew point temperature of 65 DEG C for 75 seconds and a nitrogen atmosphere of 25% and 1% of dry ammonia gas for 180 seconds, Nitrided. After simultaneous decarburization, the nitrogen content in the steel sheet was 182 ppm.

The steel sheet was coated with MgO as an annealing separator and subjected to secondary recrystallization annealing in a coiled manner. During the secondary recrystallization annealing, the primary cracking temperature was 700 ° C, the secondary cracking temperature was 1200 ° C, and the temperature increase rate was 15 ° C per hour. On the other hand, the cracking time at 1200 占 폚 was 20 hours. The atmosphere for the secondary recrystallization annealing was a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, it was kept in a 100% hydrogen atmosphere and then cooled. The average crystal grain size measured for each condition and the area fraction of the crystal grains having a grain size of 40 占 퐉 or more in the cold-rolled sheet after the simultaneous decarburization annealing are shown in Fig.

As can be seen from FIG. 1, as the slab heating temperature increases, the grain size distribution becomes larger. Therefore, when the average grain size is the same, the area fraction of grains having a grain size of 40 탆 or more increases further. When the size fraction is increased, the bad orientation deviating much from the Goss orientation having a good magnetic property also grows into secondary recrystallization due to the size advantage when secondary recrystallization annealing is performed, resulting in poor secondary orientation of the recrystallization and deterioration of product magnetism.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims and their equivalents. It will be understood that the invention may be embodied in other specific forms without departing from the spirit or scope of the invention. It is therefore to be understood that the embodiments and / or the examples described above are illustrative in all aspects and not restrictive.

Claims (9)

(Excluding 0%), C: 0.04 to 0.07%, N: 0.002 to 0.0055%, and S: 0.002%, in terms of% by weight, Si: 2.0 to 6.0%, Sol.Al: 0.02 to 0.4% To 0.0055%, Sb: 0.01 to 0.15%, the balance Fe and unavoidable impurities, wherein the slab is heated so that the amount of N dissolved in the slab is 15 ppm or less and S is 20 ppm or less;
Hot rolling the slab to produce a hot rolled sheet;
Annealing the hot-rolled sheet by hot-rolling;
Cold-rolling the hot-rolled sheet annealed to produce a cold-rolled sheet;
Subjecting the cold-rolled sheet to primary recrystallization annealing; And
And secondary recrystallization annealing the cold-rolled sheet subjected to the primary recrystallization annealing,
Wherein the hot-rolled steel sheet is annealed at a heating temperature (T _h ) satisfying the following formula (1) and maintained at a crack temperature (T _s ) lower than the heating temperature (T _h ) .
[Formula 1]
1100-20 x [Al] / [N] < T _h < 1220-20 x [Al] / [N]
(In the formula 1, [Al] and [N] mean the content (% by weight) of Sol.Al and N, respectively, and T _h means the heating temperature in the step of annealing the hot- The method according to claim 1,
The slabs
0.02 to 0.15% of Sn, and 0.02 to 0.35% of Cr. The method according to claim 1,
In the heating step,
And heating the slab to a temperature of 1000 to 1120 占 폚. The method according to claim 1,
In the heating step,
Wherein the slab comprises 17 to 30% of austenite and the remainder ferrite in an area fraction. The method according to claim 1,
In the step of hot-rolling the hot-rolled sheet,
Wherein the layered spacing at t / 4 to 3t / 4 is 40 占 퐉 or less based on the thickness (t) direction of the hot rolled sheet. The method according to claim 1,
In the step of annealing the hot-rolled sheet,
Wherein N is not more than 10 ppm and S is not more than 7 ppm after the heating at the heating temperature (T _h ). The method according to claim 1,
In the step of annealing the hot-rolled sheet,
(2). &Lt; / RTI &gt;
[Formula 2]
50? T _h -T _s (Unit: ℃)
(Where T _h means the heating temperature in the step of annealing the hot-rolled sheet and T _s means the cracking temperature in the step of annealing the hot-rolled sheet). The method according to claim 1,
In the step of annealing the hot-rolled sheet,
Wherein N is 5 ppm or less and S is 5 ppm or less after the cracking at the cracking temperature (T _s ). The method according to claim 1,
In the primary recrystallization annealing step,
And simultaneously satisfying the following formula (3): &quot; (3) &quot;
[Formula 3]
F ₄₀ &lt; 2.37 x G _s -36
(In the formula (3), the F _{40 system} refers to the area fraction (%) of the grains having a grain size of 40 탆 or more in the cold-rolled steel sheet after the simultaneous decarburization annealing, and G _s denotes the average grain size it means.)

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