KR920004949B1 - Making process for the electic steel plate - Google Patents

Abstract

A fabrication method for electric steel plate, which composition is 0.02-0.08 C, 2.5-4.0 Si, 0.05-0.20 Mn, 0.02-0.04 S and the remainder of Fe, in wt.%, is characterized by, after hot-rolling slab: (1) pre-annealing it at 750-1000 deg.C for 1-30 min; (2) cooling it down to 500-550 deg.C at a speed of 30-120 deg.C/sec; (3) homogenization treating it at 500-550 deg.C for 30 sec-20 min; (4) forming it by cold rolling for two times till its final thickness is 0.200-0.285 mm including intermidate annealing. It prevents from 1st normal recrystallization grain growth by addition of MnS and it can be applied to magnetic core materials for transformer and generator.

Description

Manufacturing method of oriented electrical steel sheet with excellent magnetic properties

1 is a graph showing the change in the texture of the primary cold rolled plate and the iron loss of the hot annealing plate according to the cooling rate during pre-annealing.

2 is a graph showing the change in texture of the primary cold rolled sheet according to the cracking time after cooling during pre-annealing.

3 is a (110) pole figure showing the change in texture of the decarbonized annealing plate according to the pre-annealing method.

The present invention relates to a method for producing a grain-oriented electrical steel sheet using MnS as the primary recrystallization normal growth inhibitor and subjected to two cold rollings. More specifically, the magnetic properties are controlled by appropriately controlling preliminary annealing conditions prior to cold rolling. The manufacturing method of the grain-oriented electrostatic steel plate to improve.

A grain-oriented electrical steel sheet is used as an iron core material for electrical equipment such as transformers and generators, and has a high magnetic flux density in the rolling direction and low magnetic loss.

A grain-oriented electrical steel sheet is used as an iron core material for electrical equipment such as transformers and generators, and has a high magnetic flux density in the rolling direction and low magnetic loss.

In order to manufacture oriented electrical steel sheets with excellent magnetic properties, secondary recrystallization of the (110) [001] orientation with good orientation in the rolling direction during high temperature annealing during the manufacturing process must be performed. The addition of an inhibitor to prevent normal recrystallization grains other than the [001] orientation from growing normally, and the primary recrystallization grains of the (110) [001] orientation, which are the nuclei of the secondary recrystallization, facilitate the primary recrystallization grains of the other orientation. It is necessary to form a primary recrystallization aggregate that can be encroached and grow into secondary recrystallization.

For example, in a grain-oriented electrical steel sheet using MnS, the primary recrystallized texture is formed by (60) secondary cold rolling at about 60%, and the main component is (111) [112] (110) [001], and the subcomponent is (110) [001. ], The high magnetic flux density oriented electrical steel sheet using MnS + AlN, which has a higher suppression force, has a primary reinforcing structure of primary recrystallized texture by cold rolling of about 85% or more. 111) [112], (112) [011], and the magnetic properties are excellent when the subcomponents are formed as (110) [001], (100) [011].

Recently, as the necessity of energy saving increases rapidly, the desire to reduce electric power loss also increases, and directional electrical steel sheets with less iron loss are required.

Iron loss is roughly classified into hysteresis loss and eddy current loss. Vortex loss which occupies about 70% or more of iron loss in oriented electrical steel is proportional to the square of plate thickness. Will be lowered.

However, when the plate thickness is rolled thinly, the growth driving force of the primary recrystallization increases, and the secondary primary because the preferred primary recrystallized texture is not formed due to the increase of the rolling stability direction (100) in the cold rolled structure. In addition to unstable recrystallization, even if secondary recrystallization occurs, the lower limit of the plate thickness, which can be stably manufactured by the conventional method, is 0.30 mm because the orientation of the (110) [001] orientation is deteriorated and the magnetic properties deteriorate. .

Conventional techniques for producing grain-oriented electrical steel sheet with a thickness of less than 0.30 mm have been proposed in US Pat. No. 3,333,993 to compensate for the increase in primary recrystallization growth driving force. By adding an emulsion (or S) to the MgO slurry (S Slurry) is applied to the plate surface to prevent the loss of S from the matrix structure during high temperature annealing or to spread the S into the matrix structure.

However, this method is disadvantageous in that the hydration rate of the MgO slurry is increased as a result of having to agitate the annealing separator for a long time so that the emulsion (or S) can be uniformly dispersed, thereby forming a glassy film after high temperature annealing.

In addition, recently, in the high magnetic flux density oriented electrical steel sheet using MnS + AlN as an inhibitor, a method of manufacturing a thin oriented electrical steel sheet by increasing the inhibitory power by further adding Cu and Sn upon melting is known, but this method is known. According to the present invention, Cu, Sn and other elements are expensive, and thus production costs are increased. In particular, Sn inhibits decarburization as a surface active element, which increases the decarbonization time.

Compared with the conventional technology, the thin plate thickness is less than 0.30 mm only by controlling the primary recrystallized texture without supplementing the inhibitory force of the present invention to produce a grain-oriented electrical steel sheet having excellent magnetic properties.

Therefore, the present invention hot rolled the steel slab in a conventional manner, and then, by appropriately controlling the pre-annealed conditions, thereby forming an aggregate structure in which the strength of the (100) orientation is reduced in the primary cold rolled plate. From the primary recrystallization annealing plate, the strength of the (111) [112] direction and the (110) direction is constant, but the thickness of the plate is formed by forming the primary recrystallization texture with reduced strength of the (100) [011] direction. When manufacturing a thin 0.200-0.285mm secondary recrystallization occurs stably, and relates to a method for producing a grain-oriented electrical steel sheet with improved magnetic properties.

Hereinafter, the present invention will be described in detail.

In the present invention, a steel slab composed of C: 0.02-0.08%, Si: 2.5-4.0%, Mn: 0.05-0.20%, S: 0.01-0.04%, and the remaining Fe is heated by a conventional method. In the method of manufacturing a grain-oriented electrical steel sheet by cold rolling, decarburization, high temperature annealing including intermediate annealing after rolling and preannealing, the preannealing is heated at 750-1000 ° C. for 1-30 minutes and then 30 ° C. Cooling down to 500-550 ℃ at a cooling rate of -120 ℃ / sec and cracking at this temperature range for 30 seconds-20 minutes, after which the final sheet thickness is 0. The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties of performing two cold rollings including intermediate annealing so as to be 200-0.285 mm.

It is not yet clear why the primary cold-rolled plate structure changes according to the pre-annealing method, but one possibility is that the thermal stress in the matrix structure when cooling above the critical cooling rate from high temperature to low temperature is unknown. The residual thermal stress is different according to the orientation of the tissue, and it is thought that the primary cold rolled texture is changed as a result of the action of selectively removing residual thermal stress by cracking at a constant temperature. .

The pre-annealed initial temperature should be at least 750 ° C. in order to obtain the minimum necessary thermal stress. However, if the initial annealing temperature exceeds 1000 ° C., not only the crystal grains of the hot rolled sheet surface layer grow coarsely but also the re-crystallized particles in the center are recrystallized. Since recrystallization occurs unstable, 750-1000 ° C. is preferred, and the more preferred pre-anneal initial temperature is 775-930 ° C.

The holding time at the initial temperature should be at least 1 minute in order to make the temperature of the steel sheet uniform, but if it exceeds 30 minutes, the secondary recrystallization will be unstable due to the change in the structure of the hot rolled steel sheet, and therefore 1 minute-30 Minutes are preferred. If the cooling rate from 750-1000 ℃ to 500-550 ℃ is less than 30 ℃ / sec, thermal stress is not generated weakly. If it exceeds 120 ℃ / sec, the plate shape after cooling becomes very uneven and cold rolled. In addition to deterioration of the properties, the cold-rolled structure becomes uneven and secondary recrystallization occurs unstable, so 30 ° C / sec-120 ° C / sec is preferable.

If the cracking temperature after cooling is less than 500 ℃ is insufficient removal of the thermal stress, if it exceeds 550 ℃ it is difficult to selectively remove the thermal stress (500) 550 degreeC is preferable. In addition, if the cracking time at 500-550 ℃ is less than 30 seconds, the thermal stress is insufficient to remove, if it exceeds 20 minutes, the thermal stress is almost removed to reduce the (100) structure in the cold rolled plate Since it is difficult to obtain, it is preferable to carry out for 30 seconds to 20 minutes, and more preferable cracking treatment time is about 1 minute to 10 minutes.

The secondary cold reduction rate is 50-65%, which is the rolling reduction rate of a conventional oriented electrical steel sheet, and when the secondary cold rolling is performed at a reduction rate outside this range, the orientation of the secondary recrystallization deteriorates.

The thickness of the final plate is limited to 0.200-0.285mm, because the improvement of the magnetic properties is insufficient when it exceeds 0.285mm, the secondary recrystallization occurs unstable when thinner than 0.200mm.

When the content of the carbon of the steel slab is less than 0.02% by weight of the non-uniformity of the tissue as well as the amount of α-γ phase transformation during hot rolling, less than 0.08% by weight of the decarbonization time in the industrial aspect is much Since it is not brittle, 0.02-0.08% by weight is preferred, and the most preferred amount of carbon is 0.04-0.06% by weight.

Mn and S are elements necessary to form MnS compound, which is a primary recrystallization inhibitor, and when the amount of Mn and S is out of the range of 0.05-0.20 wt% and 0.01-0.04 wt%, respectively, the desired secondary recrystallization is unstable. It is undesirable because it happens.

Hereinafter, the present invention will be described in more detail with reference to Examples.

By weight, steel rolls composed of C: 0.041%, Si: 3.17%, Mn: 0.062%, S: 0.025%, and the remaining Fe to 2.0 mm were heated annually at 900 ° C. for 2 minutes. After cooling to 530 ℃ at a cooling rate of 10 ℃ / seconds -120 ℃ / second as shown in Figure 1 and pre-annealed to change the crack time at this temperature to 0 seconds-20 minutes as shown in Figure 2 In this case, in order to change the cooling rate, cooling in the air (10 ° C / sec), cooling by compressed air (30 ° C / sec), oil cooling by polymer quenching agent (Polymer Quenchant), 15 ° C The method of water cooling with water (120 ° C./sec) was used.

The preannealed plate was first cold rolled from 2.0mm to 0.575mm thick and then annealed in dry hydrogen atmosphere for 3 minutes at 930 ℃, followed by secondary cold rolling to 0.23mm thickness for 3 minutes at 820 ℃. Decarburization and primary recrystallization annealing in a humid hydrogen and nitrogen mixed atmosphere.

The decarburized annealing plate was coated with MgO slurry, an annealing separator, and then heated to 15 ° C./sec from 800 ° C. to 950 ° C. at high temperature in an dry hydrogen atmosphere, followed by secondary recrystallization heat treatment, and then purified at 1200 ° C. for 10 hours. Treatment Heat Treatment was performed.

During pre-annealing during the manufacturing process, the cooling rate was changed from 900 ° C. to 530 ° C. at 10 ° C./sec-120° C./sec. The change in the surface strength (P _hk1 ) and the iron loss in the high temperature annealing plate were measured and shown in FIG. 1. Fig. 2 shows the change of the surface strength of the primary cold rolled plate with the crack time when it is changed to the second-20 minutes.

In addition, the cooling rate from 900 ℃ to 530 ℃ 10 ℃ / second during the preliminary annealing in the manufacturing process and the comparative material subjected to the crack treatment at 530 ℃ for 10 seconds and the cooling rate from 900 ℃ to 530 ℃ 50 ℃ / The (110) pole figure showing the primary recrystallized texture in the decarburized annealing plate of the invention material which was subjected to cracking treatment at 530 ° C. for 3 minutes was shown in FIG. 3, and FIG. 3a is the (110) pole figure of the comparative material. (B) is the (110) pole viscosity of this invention material.

As shown in FIG. 1, the comparative material having a cooling rate of 10 ° C / sec or less for the present invention having a cooling rate from 900 ° C to 530 ° C of 30 ° C / sec-120 ° C / sec upon preliminary annealing (10 ° C / sec or less) It can be seen that the (100) surface strength of the primary cold rolled sheet is reduced and the magnetic properties (iron loss) are improved, as shown in FIG. 2, and the cracking time at 530 ° C is 30 seconds-20 minutes. In the case of the present invention it can be seen that the (100) surface strength is reduced compared to the comparative material (not implemented, 10 seconds or less).

Here, the (100) face strength is a numerical value representing the strength of the (100) [011] orientation, so that the strength of the (100) [011] orientation in the primary cold rolled sheet aggregate is reduced compared to that of the comparative material in the present invention. It can be seen that the difference between the primary cold rolled sheet aggregates is also shown in the primary recrystallized aggregates.

As shown in FIG. 3, in the case of the present invention, it is possible to obtain a tissue having a reduced orientation of (100) [011], which is a harmful orientation to secondary recrystallization, compared to the comparative material, and from this, (1 0 0) [011] The primary recrystallized texture with reduced orientation can be formed, and even in thin oriented electrical steel sheets less than 0.30 mm thick, it is possible to stably generate secondary recrystallization of the (110) [001] orientation having excellent orientation.

Example 2

By weight%, C: 0.043%, Si: 3.22%, Mn: 0.068%, S: 0.022%, and the initial temperature as shown in Table 1 using a 2.0mm thick hot rolled sheet composed of the remaining Fe as a starting material After heating for 10 seconds -40 minutes at 700 ° C-1050 ° C and immediately cooling to 450 ° C-600 ° C at a cooling rate of 10 ° C / second-150 ° C / second, and then pre-annealing to crack 10 seconds-30 minutes at ionicity. It was.

After pickling the treated material, the first cold rolled to a thickness of 0.75mm, 0.72mm, 0.575mm, 0.5mm, 0.45mm, and after annealing in dry hydrogen atmosphere for 3 minutes at 930 ° C for 0.3 at a reduction ratio of about 60%, respectively. Secondary cold rolling was performed in mm, 0.285 mm, 0.23 mm, 0.20 mm, and 0.18 mm thicknesses.

After the treated material was decarburized and primary recrystallized annealed in a mixed atmosphere of hydrogen and nitrogen at 820 ° C. for 3 minutes, MgO slurry, an annealing separator, was applied, followed by secondary annealing incidence and magnetic properties after high temperature annealing in a dry hydrogen atmosphere. It measured and the result is shown in following Table 1.

TABLE 1a

TABLE 1b

As shown in Table 1, the invention material (1-24) to perform a pre-annealed in a pre-annealed condition in accordance with the present invention is magnetic properties, that is, magnetic flux density compared to the comparative material (aw) to a pre-annealed condition deviating from the present invention And it can be seen that iron loss is excellent.

As described above, the present invention hot rolls the steel slab in a conventional manner, and then controls the pre-annealing conditions appropriately and cold rolls twice so that the plate thickness is 0.200-0.285mm, thereby improving the magnetic properties of the grain-oriented electrical steel sheet. There is an effect that can be improved.

Claims (1)

The steel slab composed of C: 0.02-0.08%, Si: 2.5-4.0%, Mn: 0.05-0.20%, S: 0.01-0.04%, and the remaining Fe, by weight, hot rolled and preannealed in a conventional manner. In the method of producing a grain-oriented electrical steel sheet by cold rolling, decarburization, high temperature annealing, including the intermediate annealing, after the pre-annealing is heated for 1-30 minutes at 750-1000 ℃ 30 ℃ / sec-120 Cooled to 500-550 ° C at a cooling rate of ° C / sec and cracked at this temperature range for 30 seconds to 20 minutes, followed by two times of intermediate annealing so that the final sheet thickness is 0.200-0.285mm after preannealing. A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties for cold rolling.

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