KR20180072105A - Method for manufacturing grain oriented electrical steel sheet - Google Patents

Abstract

The present invention provides a method of manufacturing an oriented electrical steel sheet which improves magnetism of an initial cast. According to an embodiment of the present invention, the method of manufacturing an oriented electrical steel sheet comprises: a step of heating a slab comprising 2.8-3.6 wt% of Si, 0.02-0.04 wt% of Al, 0.2 wt% or lower (excluding 0) of Mn, 0.003-0.0075 wt% of N, 0.04-0.07 wt% of C, 0.006 wt% or lower (excluding 0) of S, 0.02-0.075 wt% of P, and the remainder consisting of Fe and inevitable impurities; a step of hot-rolling the slab to manufacture a hot-rolled sheet; a step of cold-rolling the hot-rolled sheet to manufacture a cold-rolled sheet; a step of firstly annealing the cold-rolled sheet for recrystallization; and a step of secondly annealing the cold-rolled sheet of which first recrystallization annealing is completed for recrystallization. The cold-rolled sheet consists of the initial cast from an end to 4.5-10 m in a rolling direction and the remainder of an ordinary cast. An annealing temperature of the initial case is higher than an annealing temperature of the ordinary cast by 5-20°C in the first recrystallization annealing step.

Description

[0001] METHOD FOR MANUFACTURING GRAIN ORIENTED ELECTRICAL STEEL SHEET [0002]

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 in which the magnetic properties of the steel sheet are improved.

Electric steel sheets have excellent electromagnetic characteristics, and their demand is increasing in accordance with the recent demand for clean energy for energy saving and environmental pollution prevention. Such electric steel sheets can be classified into a directional electric steel sheet and a non-oriented electric steel sheet, and the double-directional electric steel sheet has excellent magnetic properties in the rolling direction and is a steel sheet used for an iron core such as a transformer.

In order to secure low iron loss, which is one of the physical properties showing excellent magnetic properties, the primary recrystallization occurring in the decarburization annealing process, which is one of the primary recrystallization annealing processes performed after completion of the cooling rolling, It is important to control the secondary recrystallization occurring in the recrystallization annealing process (high temperature annealing process).

In particular, the magnetic properties of the oriented electrical steel sheet depend on how well the {110} <001> texture is formed in the secondary recrystallization.

In order to form such excellent secondary recrystallization, the size of the primary recrystallized grains forming the secondary recrystallization in the decarburization annealing process, which is one of the primary recrystallization annealing processes, must be appropriately controlled. If the size of the primary recrystallization granules is large, secondary recrystallization does not occur well, scrap due to fine granulation occurs, and when the size of the primary recrystallization granules becomes too small, the secondary recrystallization annealing process causes the secondary recrystallization to occur at a low temperature Secondary recrystallization, which is not good in direction, occurs due to the occurrence of iron loss. Therefore, it is possible to ensure low iron loss, that is, excellent magnetic quality, by forming primary recrystallization of a proper size.

As a result, the size of the first primary recrystallization should be adjusted to ensure excellent magnetic quality. Factors that can control the size of primary recrystallization are material quality and annealing conditions. In the past, the same annealing conditions were applied without distinction between the general cast steel and the scrap steel. In this case, the iron loss of the main steel piece becomes poorer than that of the general cast steel, and the steel product is scrapped and the productivity is lowered.

In one embodiment of the present invention, a method of manufacturing a directional electrical steel sheet is provided. More specifically, it is intended to provide a method for producing a grain-oriented electrical steel sheet in which the magnetic properties of the steel sheet are improved.

A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes: 2.8 to 3.6% of Si, 0.020 to 0.040% of Al, 0.20% or less of Mn (excluding 0%), 0.0075%, C: 0.04 to 0.07%, S: 0.0060% or less (excluding 0%) and P: 0.02% to 0.075%, the balance being Fe and other unavoidable impurities; Hot rolling the slab to produce a hot rolled sheet; Cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; A first recrystallization annealing of the cold rolled sheet; And secondary recrystallization annealing the cold rolled sheet after the primary recrystallization annealing has been completed.

The cold-rolled sheet consists of an ultra-slab from 4.5 to 10 m in length in the rolling direction and the remaining general slabs. In the primary recrystallization annealing step, the annealing temperature of the slab is annealed at a temperature of 5 to 20 ° C higher than the annealing temperature of the slab.

In the primary recrystallization annealing step, the annealing temperature of the brittle material is 865 to 870 캜, and the annealing temperature of the general bell-jar can be 850 to 860 캜.

After the step of cold-rolling and producing the cold-rolled sheet, the cold-rolled sheet superalloy may contain 10 to 20 ppm less Al than the general cast steel of the cold-rolled sheet.

After the step of cold-rolling to produce a cold-rolled sheet, the cold-rolled steel sheet may contain 270 to 280 ppm of Al, and the cold rolled sheet may contain 285 to 300 ppm of Al.

After the step of cold-rolling to produce a cold-rolled sheet, the cold-rolled sheet may contain 3 to 10 ppm more N than a general cast steel of the cold-rolled sheet.

After the step of cold-rolling to produce a cold-rolled sheet, the cold-rolled steel sheet may contain 55 to 65 ppm of N, and the cold rolled sheet may contain 40 to 50 ppm of N.

After the primary recrystallization annealing step, the average recrystallized grain size of the grain of the grain in the grain of the cold-rolled sheet and the grain size of the average grain size of the grain in the grain of the grain may be equal to or less than 1 탆.

After the primary recrystallization annealing step, the average recrystallized grain size of the beads can be 20.5 to 21.5 占 퐉, and the average recrystallized grain size of the general cast steel can be 21 to 22 占 퐉.

After the step of producing the hot-rolled sheet, the step of annealing the hot-rolled sheet may be further included.

Decarburization and soaking can be achieved in the primary recrystallization annealing step.

The grain-oriented electrical steel sheet according to one embodiment of the present invention is improved in iron loss of the main shaft, and does not scrap an ultra-slab.

1 is a schematic view of a cold rolled sheet according to an embodiment of the present invention.
Fig. 2 is a scanning electron microscope (SEM) photograph showing the recrystallization of the primary crystals after the primary recrystallization annealing in the comparative example.
Fig. 3 is a scanning electron microscope (SEM) photograph showing the recrystallization of the sintered body after the primary recrystallization annealing in the comparative example.
Fig. 4 is a photograph showing the surface state of the steel sheet according to the temperature at an interval of 20 占 폚 from 1040 占 폚 to 1140 占 폚 in the secondary recrystallization annealing for the superalloy in the comparative example.
5 is a photograph showing a surface state of a steel sheet according to a temperature at an interval of 20 DEG C from 1040 DEG C to 1140 DEG C in a secondary recrystallization annealing for a general cast steel in a comparative example.

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.

In the conventional method for producing a grain-oriented electrical steel sheet, the iron loss characteristics of the cast steel were inferior to the iron loss characteristics of the cast steel, and there was a problem in productivity such as scrapping of the cast steel. In one embodiment of the present invention, the cause of the iron loss in the case of a steel core is compared with that of a general steel cast, and the problem is solved.

The role of Al in electrical steel is very important. This is because the precipitate is formed by reacting with nitrogen introduced in the step of annealing of nitrogen (N) or the primary recrystallization annealed step contained in the steel component, thereby suppressing the grain growth and determining the grain size of the primary recrystallization.

In the steel, Al reacts with the input N to form AlN precipitates, which interfere with grain growth. The crystal grain size of the primary recrystallization is determined according to the starting point of AlN precipitate formation and the grain size of the precipitate.

That is, the larger the size of the AlN precipitates, the larger the grain size of the primary recrystallization. When the content of Al forming the AlN precipitates is high, a large amount of coarse AlN precipitates. That is, as the content of Al increases, the grain size of the primary recrystallization increases.

On the other hand, in the production of cast steel in steelmaking, continuous casting is carried out for the purpose of increasing productivity and reducing cost. In the case of secondary casting, the contact time with the atmosphere is long and reoxidation occurs. In addition, nitrogen gas existing in the atmosphere partially penetrates and N is higher than that of general cast steel.

If the primary recrystallization annealing is performed under the same annealing condition, the difference in recrystallized grain sizes after the primary recrystallization annealing is inevitable even though the contents of Al and N are different from each other. As a result, the core loss of the main chain is lower than the core loss of the main core, and scrap processing of the superframe is inevitable.

In one embodiment of the present invention, attention is paid to such a problem, and by improving the iron loss of the primary cast steel by changing the primary recrystallization annealing conditions of the primary cast steel and the general cast steel, it is not necessary to scrap the cast steel and the productivity is improved.

1 is a schematic view of a cold rolled sheet according to an embodiment of the present invention. the x direction is the width direction of the steel sheet, the y direction is the rolling direction of the steel sheet, and the z direction is the thickness direction of the steel sheet. In one embodiment of the present invention, the superalloy means a portion from 4.5 to 10 m in the rolling direction from the end of the cold-rolled sheet. General casting refers to the remainder of the casting except for the first casting.

A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes: 2.8 to 3.6% of Si, 0.020 to 0.040% of Al, 0.20% or less of Mn (excluding 0%), 0.0075%, C: 0.04 to 0.07%, S: 0.0060% or less (excluding 0%) and P: 0.02% to 0.075%, the balance being Fe and other unavoidable impurities; Hot rolling the slab to produce a hot rolled sheet; Cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; A first recrystallization annealing of the cold rolled sheet; And secondary recrystallization annealing the cold rolled sheet after the primary recrystallization annealing has been completed.

Hereinafter, each step will be described in detail.

First, in terms of% by weight, Si: 2.8 to 3.6%, Al: 0.020 to 0.040%, Mn: 0.20% or less (excluding 0%), N: 0.0030 to 0.0075%, C: 0.04 to 0.07% % Or less (excluding 0%) and P: 0.02% to 0.075%, and the balance heats the slab containing Fe and other unavoidable impurities.

Hereinafter, each component of the slab will be described.

Si: 2.8 to 3.6 wt%

Silicon (Si) is a basic composition of an electrical steel sheet, which increases the resistivity of the steel sheet and serves to lower core loss, that is, iron loss, of the transformer. If the Si content is too small, the resistivity decreases and the iron loss characteristic deteriorates. Secondary recrystallization may become unstable due to the existence of a phase transformation section at high temperature annealing. When Si is excessively contained, the brittleness of the steel becomes large, cold rolling becomes extremely difficult, the content of C for containing an austenite fraction of 40% or more is greatly increased, and secondary recrystallization becomes unstable. Therefore, Si may contain 2.8 to 3.6% by weight.

Al: 0.020 to 0.040 wt%

Aluminum (Al) is finally made of nitride of (Al, Si) N, (Al, Si, Mn) N type as a component acting as an inhibitor, and if its content is too small, If too much, the nitride of the Al system precipitates and grows too much, and the effect as an inhibitor becomes insufficient. Therefore, the content of Al is set to 0.020 to 0.040% by weight.

Mn: not more than 0.20% by weight

Manganese (Mn) has the effect of reducing the iron loss by increasing the resistivity as Si, and reacting with the 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 added too much, since the austenite phase transformation is promoted during hot rolling, the size of the primary recrystallized grains is reduced to make the secondary recrystallization unstable. Therefore, Mn should be 0.20 wt% or less.

N: 0.0030 to 0.0075 wt%

If N is contained in excess in the steelmaking step, unnecessary precipitates are formed in the hot rolling step, so that the heat treatment time can not be shortened in the preliminary annealing step sought in the present invention, and the size of the first recrystallization step becomes small, The temperature is lowered, and the crystal grains that are not {110} <001> orientations cause secondary recrystallization, which deteriorates the magnetism. Also, since it takes a long time to remove N from the second crack section of the final annealing process, it is difficult to produce a highly directional electric steel sheet having high productivity. If N is too small, the amount of AlN precipitated in the hot rolling becomes small, so that the crystal grains become larger than the proper size during the primary recrystallization annealing, and the secondary recrystallization starting temperature rises, so that excellent magnetic properties can not be obtained. Therefore, N is limited to 0.0030 to 0.0075% by weight.

C: 0.04 to 0.07 wt%

Carbon (C) is an austenite stabilizing element, and it causes a phase transformation at a temperature of 900 ° C or higher, thereby finely dividing the coarse columnar structure occurring in the performance process, and suppressing the slab center segregation of S. However, if the content is too large, coarse carbides are precipitated and it becomes difficult to remove carbon during decarburization. Therefore, C is set at 0.04 to 0.07% by weight.

S: 0.0060% by weight or less

Sulfur (S) has the effect of enlarging the initial grain size before cold rolling, and thus plays a role of increasing the number of grains having a {110} < 001 > orientation nucleated in the strain band in the primary recrystallization process. However, if it is included too much, since it is reusable when hot-rolled slab is heated, the size of the primary recrystallized grains is reduced to lower the secondary recrystallization starting temperature to deteriorate the magnetic properties. In addition, since it takes a long time to remove S in the solid state in the secondary crack region of the final annealing process, the productivity of the oriented electrical steel sheet is lowered. Therefore, S is set to 0.0060 wt% or less.

P: 0.02% to 0.075%

Phosphorus (P) accelerates the growth of the primary recrystallized grains in the low-temperature directional electrical steel sheet, thereby raising the secondary recrystallization temperature and increasing the degree of integration of the {110} <001> orientation in the final product. On the other hand, P not only reduces the iron loss of the final product by increasing the number of grains having a {110} < 001 > orientation in the primary re-crystal plate, The {110} < 001 > density of the product is improved and the magnetic flux density is also increased. P also segregates in the grain boundaries to a high temperature of about 1000 캜 during secondary recrystallization annealing to retard the decomposition of the precipitates and to reinforce the restraining force. 0.02% by weight or more is necessary for this action of P to be exhibited properly. However, if P is included too much, the size of the primary recrystallized grains is rather reduced, which not only makes the secondary recrystallization unstable but also increases the brittleness and hinders the cold rolling property. Therefore, P is set to 0.02 to 0.075% by weight

The slab thus formed is heated. The heating temperature of the slab is not limited. However, if the slab is heated to a temperature of 1300 ° C or less, it is possible to prevent the columnar structure of the slab from being grown to a great extent, thereby preventing cracking of the slab in the hot rolling process. Thus, the heating temperature of the slab may be between 1050 ° C and 1300 ° C.

Next, the slab is hot-rolled to produce a hot-rolled sheet. The hot rolling temperature is not limited, and in one embodiment hot rolling may be terminated at 950 ° C or lower. Thereafter, it is water-cooled and can be wound at 600 ° C or less. And can be manufactured by hot rolling to a hot rolled sheet having a thickness of 1.5 to 4.0 mm.

Next, the hot-rolled sheet can be subjected to hot-rolled sheet annealing if necessary. In the case of annealing the hot-rolled sheet, the hot-rolled sheet may be annealed at a temperature of 1000 to 1100 ° C to make the hot-rolled sheet uniform, and then cooled to 890 to 930 ° C after cooling.

Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet. Cold rolling is carried out by using a cold rolling method using a reverse rolling mill or a tandem rolling mill by a plurality of cold rolling methods including one cold rolling, a plurality of cold rolling, or an intermediate annealing to produce a cold rolled sheet having a thickness of 0.1 mm to 0.5 mm can do.

Further, warm rolling in which the temperature of the steel sheet is maintained at 100 캜 or higher during cold rolling can be performed.

In addition, the final rolling reduction through cold rolling can be from 50 to 95%.

Next, the cold-rolled cold-rolled sheet is subjected to primary recrystallization annealing. Primary recrystallization occurs in which the core of the goss grain is generated in the primary recrystallization annealing step.

As described above, the cold rolled cold rolled steel sheet can be divided into a super cast steel and a general cast steel. In this case, the time of contact with the atmosphere is long, so that the content of Al is lower than that of general cast, and the content of N is higher than that of general cast. The superstructure contains 10 to 20 ppm less Al than the general slab of the cold-rolled plate and contains 3 to 10 ppm more N. Specifically, the superalloy contains 270 to 280 ppm of Al, and the general cast includes 285 to 300 ppm of Al. Also, the superalloy includes 55 to 65 ppm of N, and the general cast of the cold-rolled sheet contains N to 40 to 50 ppm.

In one embodiment of the present invention, it has been found that the content of Al and N in the cast steel and the cast steel is different from each other, which causes poor iron loss of the cast steel, By changing the annealing conditions in the recrystallization annealing, it was intended to improve the iron loss characteristics of the bead core.

In one embodiment of the present invention, the annealing temperature of the bead core is annealed by 5 to 20 占 폚 higher than the annealing temperature of the annealed bead, thereby improving the iron loss of the bead core. When the difference between the annealing temperature of the bead core and the annealing temperature of the general cast steel is too small, the grain size of the primary recrystallization formed in the cast steel becomes significantly smaller than the grain size of the primary recrystallization formed in the general cast steel. As a result, It becomes poor. On the other hand, when the difference between the annealing temperature of the beeswax and the annealing temperature of the general beeswax is too large, the recrystallized grains grow to a great extent in the superabrasive and the crystal growth driving force falls, so that stable secondary recrystallization is not formed.

Concretely, the annealing temperature of the beeswax is 865 to 870 ° C, and the annealing temperature of the ordinary bees can be 850 to 860 ° C.

By differently controlling the annealing conditions in the superalloy and the general cast steel, the difference in the average grain size of the recrystallized carbides formed in the cast steel and the general cast steel after the first recrystallization annealing can be minimized. Specifically, the average recrystallized grain size of the steel sheet may be the same as the average recrystallized grain size of the general cast steel, or the difference may be 1 탆 or less. By uniformly forming the grain size of the recrystallization in this manner, recrystallization of the Goss orientation in the secondary recrystallization annealing step, which will be described later, can be stably formed not only in general cast steel but also in cast steel. Specifically, after the primary recrystallization annealing step, the average recrystallized grain size in the superalloy can be 20.5 to 21.5 mu m, and the average recrystallized grain size in the general cast can be 21 to 22 mu m.

Decarburization and nitriding of the steel sheet can be performed during the primary recrystallization annealing process. For decarburization and nitriding, primary recrystallization annealing can be performed in a mixed gas atmosphere of steam, hydrogen, and ammonia.

Next, the cold-rolled sheet having undergone the primary recrystallization annealing is subjected to secondary recrystallization annealing. At this time, after the annealing separator is applied to the cold-rolled sheet having undergone the primary recrystallization annealing, secondary recrystallization annealing can be performed. At this time, the annealing separator is not particularly limited, and an annealing separator containing MgO as a main component may be used.

The step of secondary recrystallization annealing includes a temperature rising step and a cracking step. The step of raising the temperature is a step of raising the temperature of the cold-rolled sheet after the first recrystallization annealing to the temperature of the cracking step, causing secondary recrystallization in the {110} < 001 > Goss orientation.

The secondary recrystallization annealing can be carried out at a temperature raising rate of 5 to 30 占 폚 / hr and a final reached temperature of 1100 to 1300 占 폚. If the heating rate is less than 5 ° C / hr, the productivity is lowered due to the increase of the annealing time, and the primary recrystallized grains become large before reaching the secondary recrystallization temperature, so that the driving force of the secondary recrystallization can be weakened. If the temperature raising rate exceeds 30 ° C / hr, a temperature deviation occurs between the inside and the outside of the coil, so that the secondary recrystallization does not occur uniformly and the magnetism is deteriorated.

If the temperature of the cracking step is less than 1100 ° C, the small crystal grains can not be completely removed from the secondary recrystallized grains, so that the iron loss characteristic is bad. When the temperature of the cracking step is more than 1300 ° C, the coil is deformed and the productivity is deteriorated.

Thereafter, an insulating film may be formed on the surface of the grain-oriented electrical steel sheet or a magnetic domain refining treatment may be carried out, if necessary. In one embodiment of the present invention, the alloy component of the grain-oriented electrical steel sheet refers to a base steel sheet excluding a coating layer such as an insulating coating.

Hereinafter, the present invention will be described in more detail with reference to examples. However, these embodiments are only for illustrating the present invention, and the present invention is not limited thereto.

Comparative Example

A slab composed of 3.15% of Si, 0.052% of C, 0.09% of Mn, 0.029% of Al, 0.005% of S, 0.0049% of N and impurities inevitably incorporated with the remainder Fe was heated at 1150 ° C Followed by hot rolling to a thickness of 2.3 m. The hot-rolled sheet was annealed at 1085 ° C, then cracked at 910 ° C during the cooling process, and then pickled. The pickling plates were cold rolled to a final thickness of 0.23 mm. The contents of Al and N in the cold rolled cold rolled steel sheet were measured from the end to 8 m. The Al content and the N content of the beeswax were 277ppm and 60ppm, respectively.

The cold-rolled sheet was subjected to primary recrystallization annealing by keeping it at 855 DEG C for 180 seconds without separating the superalloy and the normal cast steel. The atmosphere was adjusted to an atmosphere containing water vapor (H ₂ O), H _2, and ammonia gas. Scanning electron micrographs of the primary castings and general castings after the first recrystallization annealing are shown in Figs. 2 and 3, respectively. As shown in FIG. 2 and FIG. 3, it can be confirmed that the recrystallized grain size of the stainless steel is significantly smaller than that of the general cast steel. Specifically, it can be confirmed that the average grain size of the recrystallized grains of the stainless steel slab is 20 μm, and the average grain size of the recrystallized grains of the general cast slab is 22 μm.

Thereafter, MgO coating was performed and secondary recrystallization annealing was performed to finally obtain a grain-oriented electrical steel sheet. During the secondary recrystallization annealing, the superalloys and the general cast steel are heated from 1040 캜 to 1140 캜 at an interval of 20 캜, and the surface states of the steel sheet according to the temperatures are shown in Figs. 4 and 5. 1040, 1060, 1100, 1120, and 1140 degrees from the left.

As shown in FIG. 4, it can be seen that the start of secondary recrystallization starts at 1160 ° C. in the superalloy, and the secondary recrystallization continues for a long time. On the other hand, as shown in FIG. 5, it can be confirmed that the start of the secondary recrystallization starts at 1180 ° C. in the general cast steel, and the secondary recrystallization occurs in a comparatively short time.

Finally, the insulating solution was applied and the iron loss was measured. Iron loss was measured by single sheet method and iron loss was measured until magnetization at 50 Hz and 1.7 Tesla. Iron loss convenience normal state (W _17/50) it was that the superior one, Chaozhou convenience iron loss (W _17/50), and is the 0.826W / kg to 0.004W / kg differences, poor Chaozhou convenience as iron loss 0.822W / kg Respectively.

Example

A slab composed of 3.15% of Si, 0.052% of C, 0.09% of Mn, 0.029% of Al, 0.005% of S, 0.0049% of N and impurities inevitably incorporated with the remainder Fe was heated at 1150 ° C Followed by hot rolling to a thickness of 2.3 m. The hot-rolled sheet was annealed at 1085 ° C, then cracked at 910 ° C during the cooling process, and then pickled. The pickling plates were cold rolled to a final thickness of 0.23 mm.

The cold-rolled steel sheets were subjected to primary recrystallization annealing at 865 ° C for 8 m from the end, and at 855 ° C for 180 sec. The atmosphere was adjusted to an atmosphere containing water vapor (H ₂ O), H _2, and ammonia gas. It can be confirmed that the average grain size of the recrystallized grains of the stainless steel is 21.5 탆 and the average grain size of the recrystallized grains of the general cast steel is 22 탆 and a difference of 0.5 탆 is generated

Thereafter, MgO coating was performed and secondary recrystallization annealing was performed to finally obtain a grain-oriented electrical steel sheet.

Finally, the insulating solution was applied and the iron loss was measured. Iron loss was measured by single sheet method and iron loss was measured until magnetization at 50 Hz and 1.7 Tesla. Second cast iron loss and general convenience weeks (W _17/50) was measured as 0.822W / kg, it was found to have both excellent early cast steel and plain cast iron loss.

It will be understood by those of ordinary skill 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 practiced. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (10)

(Excluding 0%), N: 0.0030 to 0.0075%, C: 0.04 to 0.07%, and S: 0.0060% or less in terms of% by weight, Si: 2.8 to 3.6%, Al: 0.020 to 0.040% (Excluding 0%) and P: 0.02% to 0.075%, the remainder comprising Fe and other unavoidable impurities;
Hot rolling the slab to produce a hot rolled sheet;
Cold-rolling the hot-rolled sheet to produce a cold-rolled sheet;
Subjecting the cold-rolled sheet to primary recrystallization annealing; And
And secondary recrystallization annealing the cold rolled sheet after the primary recrystallization annealing has been completed,
The cold-rolled sheet consists of an ultra-slab in the rolling direction, 4.5 to 10 m from the end, and the remaining general slab,
Wherein said step of annealing said primary recrystallization anneal said primary annealing temperature to a temperature higher by 5 to 20 占 폚 than the annealing temperature of general annealing furnace. The method according to claim 1,
Wherein the annealing temperature in the primary recrystallization annealing step is 865 to 870 캜 and the annealing temperature in the general annealing step is 850 to 860 캜 in the primary recrystallization annealing step. The method according to claim 1,
Wherein the cold rolled steel sheet comprises 10 to 20 ppm less Al than the general steel sheet of the cold rolled steel sheet after the step of cold rolling the cold rolled steel sheet. The method according to claim 1,
Wherein the cold rolled steel sheet comprises 270 to 280 ppm of Al, and the general cast steel of the cold rolled steel sheet contains 285 to 300 ppm of Al. The method according to claim 1,
Wherein the cold rolled steel sheet has a N content of 3 to 10 ppm higher than that of the cold rolled steel sheet in the cold rolled steel sheet. The method according to claim 1,
Wherein the cold rolled steel sheet comprises 55 to 65 ppm of N, and the general cast steel of the cold rolled steel sheet contains 40 to 50 ppm of N after the step of cold-rolling the cold rolled steel sheet. The method according to claim 1,
Wherein the average recrystallized grain size of the steel sheet is equal to or smaller than the average recrystallized grain size of the steel sheet after the primary recrystallization annealing step. The method according to claim 1,
After the primary recrystallization annealing step, the average recrystallized grain size in the cast steel is 20.5 to 21.5 占 퐉 and the average recrystallized grain size in the general cast steel is 21 to 22 占 퐉. The method according to claim 1,
Further comprising the step of annealing the hot-rolled steel sheet after the step of producing the hot-rolled steel sheet. The method according to claim 1,
Wherein decarburization and sedimentation are performed in the primary recrystallization annealing step.

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