KR20190077891A - Method for manufacturing non-oriented electrical steel sheet - Google Patents

Abstract

According to an embodiment of the present invention, a method for manufacturing a non-oriented electrical steel sheet comprises the following steps of: manufacturing a slab from molten steel; manufacturing a hot rolled plate by continuously hot rolling the slab; and manufacturing a cold rolled plate by cold rolling the hot rolled plate. The step of manufacturing the hot rolled plate includes a rough rolling step and a finish rolling step. Moreover, tension measured in front of a first rolling mill in case of finish rolling can be 0.2 to 1.5 kgf/mm^2.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a non-

To a method for producing a non-oriented electrical steel sheet. More particularly, the present invention relates to a method of manufacturing a non-oriented electrical steel sheet excellent in shape and magnetism at the same time by using a facility in which a continuous casting process and a hot rolling process are directly connected.

The non-oriented electrical steel sheet is generally made of a steel sheet having a small thickness, and is laminated and used. The motors produced by laminating the non-oriented electrical steel sheets are used in the field of household appliances or equipment, or as auxiliary motors for automobiles, precisely controlling the plate thickness is essential for this. Also, in order to increase the energy efficiency, it has been required to develop a technique for reducing the loss occurring in the motor, and a technique for improving the magnetic flux density for miniaturization of the motor has been developed.

In the nonoriented electric steel sheet, the magnetic properties can be evaluated by iron loss and magnetic flux density. Both properties are greatly affected by the precipitates and inclusions formed in the high temperature process after the solidification of the steel. In the double iron loss, there is a disturbance of the magnetic migration due to the fine precipitates, and the loss due to the iron loss is represented by an increase in the iron loss. The magnetic flux density of the precipitates or inclusions formed in the high temperature process interferes with the movement of the crystal grains and thus affects the formation of aggregate structure, so that the magnetic flux density of the steel sheet after the final annealing changes. Therefore, effective use of inclusions and precipitates in steel is one of the most important techniques for securing the magnetic properties of the non-oriented electrical steel sheet.

Each individual process step during manufacture affects the magnetic properties of the final product. For this reason, for example, the microstructure state in the steel changes due to the path sequence and the load applied to the hot-rolled coil in each rolling pass, the state of the rolling roll, the frictional force, the reduction rate, and the growth of the precipitate is also affected. In addition, these effects not only occur in the unit process, but also affect the characteristics of the final product.

Of these, the roughness after the cold rolling and the shape of the plate are greatly influenced by the load applied to the hot-rolled coil, the state of the rolling roll, the frictional force, the reduction rate and so on. The roughness and the shape of the plate are important factors in determining the magnetic properties of the laminated core when the plates are laminated. Therefore, there is a need for a technique for controlling this.

A non-oriented electrical steel sheet and a manufacturing method thereof. More specifically, the present invention provides a method of manufacturing a non-oriented electrical steel sheet excellent in both shape and magnetism by using a facility in which a continuous casting process and a hot rolling process are directly connected.

A method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes the steps of: preparing a slab from a molten steel; Continuously hot rolling the slab to produce a hot rolled sheet; And cold rolling the hot rolled sheet to produce a cold rolled sheet. The step of producing the hot rolled sheet includes rough rolling and finish rolling, and the finish rolling can perform the first rolling under a tension of 0.2 to 1.5 kgf / mm < ² >.

In the step of producing the slab, the thickness of the slab may be 50 mm to 100 mm.

In the slab production step, the slab contains 0.005% or less of N, 0.05% or less of C, 6.5% or less of Si, 3.5% or less of Al and 0.02 to 3.0% And inevitable impurities.

0.005% to 5.0% of Cr, 0.003% to 0.1% of P, 0.1% or less of Sn, 0.0005 to 0.005% of Ca, 0.05% or less of As and 0.003% or less of Be of the slab , 0.003% or less of Se, 0.003% or less of S, and 0.005% or less of Mg.

The slab may further include at least one member selected from Cu, Sb, Zr, V, Ti, Co, Pb, Nb and B,

After the step of producing the slab, the step of heating the slab may further include the step of heating the slab.

In the step of producing hot rolled plates, hot rolling can be started within 5 minutes after 90% or more of the slabs have solidified.

After the rough rolling step, heating the roughly rolled bar may be further included.

In the step of producing the hot-rolled sheet, at least 90% by volume of the slab is solidified, and the step of finish rolling after 1 to 15 minutes can be completed.

The reduction rate in the finishing rolling step may be 5 to 20% higher than the reduction rate in the rough rolling step.

The reduction ratio in the finishing rolling step may be 85 to 95%.

The finish rolling step may include a pass performed through a mill having a coefficient of friction of 0.3 or less.

After 90% by volume or more of the slab has solidified, the temperature of the surface of the plate may be 1100 ° C or more for 5 minutes or less.

After 90 vol% or more of the slab has solidified, the temperature of the plate surface may be 800 ° C or higher for 30 minutes or less.

In the finishing rolling step, lubricating oil of 0.01 to 50 L / min can be sprayed to a surface area of 1 m ² of the steel sheet.

After the step of manufacturing the hot-rolled sheet, the difference in thickness between the thickest portion and the thinnest portion of the hot-rolled sheet may be 40 占 퐉 or less except for 30 mm at the widthwise edge of the hot-rolled sheet.

In the analysis of the texture of the hot-rolled sheet, the intensity of the texture of the {100} plane with the rolled surface of 15 ° or less is {111} And may be 0.5 to 50 times the strength of the texture that is 15 DEG or less.

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

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

The reduction rate in the step of producing the cold-rolled sheet may be 50 to 92%.

After the step of producing the cold-rolled sheet, the thickness difference between the thickest portion and the thinnest portion of the cold-rolled sheet may be 3 탆 or less, except for 30 mm at the widthwise edge of the cold-rolled sheet.

After the step of producing the cold-rolled sheet, the surface roughness Ra of the upper and lower surfaces of the cold-rolled sheet may be 0.05 to 0.5 占 퐉, respectively.

After the step of producing the cold-rolled sheet, the sum of the surface roughness Ra of the upper and lower surfaces of the cold-rolled sheet may be 0.5 탆 or less.

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

The steel sheet obtained in the step of final annealing the cold rolled sheet can satisfy the following formulas (1) and (2).

B ₂₅ ≥0.79 × (2.156-0.0413 × [Si] -0.0604 × [Al]) in the formula (1)

Equation _{(2) W 15/50 /(t+0.01×t} 1 .5 + 0.001 × t 2) ≤ 10

(In this case, B ₂₅ represents a magnetic flux density value (T) measured at 2500A / m, [Si] and [Al] denotes the Si content (% by weight) in the slab, W _15/50 is in the standing wave 1.5T 50Hz (W / kg) measured at the time when the steel sheet is magnetized so as to have the magnetic flux density of the steel sheet, and t represents the thickness (mm) of the cold-rolled sheet.

After the step of producing the cold-rolled sheet, the intensity of the aggregate structure having an angle formed by the {100} plane with the rolled surface of 15 ° or less is {111} Deg.] Or less.

The non-oriented electrical steel sheet according to an embodiment of the present invention can be manufactured by the above-described manufacturing method.

According to an embodiment of the present invention, a non-oriented electrical steel sheet excellent in shape and magnetism can be manufactured by applying a process in which a continuous casting process and a hot rolling process are directly connected.

Specifically, a non-oriented electrical steel sheet having a small crown and surface roughness, a low iron loss and a high magnetic flux density can be produced.

1 is a graph schematically showing the temperature of a plate surface with time in a manufacturing method according to an embodiment of the present invention.
2 is a graph schematically showing the temperature of a plate surface over time in a manufacturing method according to another embodiment of the present invention.
3 is a graph schematically showing the temperature of a plate surface over time in a manufacturing method according to another embodiment of the present invention.
4 is a schematic diagram of a lay-out of an apparatus for implementing a manufacturing method according to an embodiment of the present invention.

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.

A method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes the steps of: preparing a slab from a molten steel; Continuously hot rolling the slab to produce a hot rolled sheet; And cold rolling the hot rolled sheet to produce a cold rolled sheet.

Hereinafter, each step will be described in detail.

First, a slab is prepared from molten steel. As a method for producing a slab, a slab may be produced by continuously casting molten steel, or may be manufactured using strip casting.

The thickness of the slab may be between 50 mm and 100 mm. When the thickness of the slab exceeds 100 mm, not only high-speed casting is difficult but also the rolling load during rough rolling can be increased. If it is less than 50 mm, the temperature of the cast steel may drop rapidly and it may be difficult to form a uniform structure.

The slab contains, by weight%, N: not more than 0.005%, C: not more than 0.05%, Si: not more than 6.5%, Al: not more than 3.5% and Mn: not more than 0.02 to 3.0% have.

Hereinafter, the alloy composition of the slab will be described.

N: 0.005 wt% or less

Nitrogen (N) is an element that forms a nitride in steel and adversely affects iron, especially iron. Therefore, N may be contained in the slab in an amount of 0.005 wt% or less. More specifically, N may be contained in the slab in an amount of 0.0005 to 0.005% by weight.

C: not more than 0.05% by weight

Carbon (C) is an element that forms a carbide in the steel and adversely affects the iron, especially iron. It also plays a role in forming aggregate structure favorable to magnetism during cold rolling or hot rolling. C may be contained in the slab in an amount of 0.05% by weight or less. And may include a decarburization process in the process of manufacturing an electrical steel sheet. In this case, carbon may be contained in an amount of 0.005% by weight or less in the electrical steel sheet. More specifically, C may be contained in the slab in an amount of 0.001 to 0.01% by weight. In an embodiment of the present invention, when the lower limit of the alloy components is not limited, it can be interpreted as excluding 0% by weight.

Si: not more than 6.5% by weight

Silicon (Si) is an element capable of lowering iron loss by significantly increasing resistivity in steel. Further, when added as a ferrite stabilizing element, the ferrite phase is retained even when the annealing temperature is increased. As a result, it is an element which enables high-temperature annealing to grow crystal grains for reduction of iron loss. When Si is added too much, rolling at room temperature may be impossible due to the regular arrangement of steel. Therefore, Si can be contained in the slab at not more than 6.5% by weight. More specifically, Si may be contained in the slab in an amount of 0.3 to 6.0% by weight.

Al: 3.5 wt% or less

Aluminum (Al) is an element capable of significantly increasing the resistivity in the steel and lowering the iron loss. Further, when the ferrite stabilizing element is added as the ferrite stabilizing element, the ferrite phase is maintained even when the annealing temperature is increased to enable high temperature annealing It is an element. When too much aluminum is added, the coagulating bath surface is irregularly reacted with the performance flux or the like during continuous casting, thereby making it impossible to perform stable casting. Therefore, Al can be contained in the slab in an amount of 3.5% by weight or less. More specifically, Al may be contained in the slab in an amount of 0.0005 to 3.0% by weight.

Mn: 0.02 to 3.0 wt%

Manganese (Mn) is an element that increases the resistivity in the steel to lower the iron loss. It also forms a coarse MnS precipitate by binding with S in the steel and stabilizes the influence of fine precipitates that interfere with the magnetic migration. When the addition amount is too small, the above-mentioned role may not be sufficiently exhibited. When Mn is added in an excessive amount as an austenite stabilizing element, an austenite phase is formed in the annealing temperature range, and iron loss can be increased. Therefore, Mn may be contained in the slab in an amount of 0.02 to 3.0% by weight. More specifically, Mn may be contained in the slab in an amount of 0.05 to 2.5% by weight.

0.005% to 5.0% of Cr, 0.003% to 0.1% of P, 0.1% or less of Sn, 0.0005 to 0.005% of Ca, 0.05% or less of As and 0.003% or less of Be of the slab , 0.003% or less of Se, 0.003% or less of S, and 0.005% or less of Mg.

Ni: 0.005% to 5.0%

Nickel (Ni) is an element that increases the resistivity in the steel to lower the iron loss, and is an element that can improve the magnetic flux density when added as a magnetic material. When Ni is included too little, the above-mentioned role may not be sufficiently exhibited. Also, when Ni is added in an excessive amount as an austenite stabilizing element, an austenite phase is formed in an annealing temperature range, and iron loss can be increased. Therefore, Ni may be contained in the slab in an amount of 0.005 to 5.0% by weight. More specifically, Ni may be included in the slab in an amount of 0.01 to 2.5% by weight.

Cr: 0.005 to 5.0 wt%

Chromium (Cr) is an element that can lower the iron loss by raising the resistivity in the steel. It is an element that helps to improve the strength of the steel and to obtain high strength properties. In addition, a dense oxide film is formed on the surface to reduce the necessity of the secondary insulation coating, and it is an element which can greatly improve the corrosion resistance. When Cr is included too little, the above-mentioned role may not be sufficiently exhibited. When Cr is added in excess, the oxides in the steel increase, which hinders the magnetic migration, thereby increasing the iron loss and reducing the saturation magnetic flux density. Therefore, Cr may be contained in the slab in an amount of 0.005 to 5.0% by weight. More specifically, Cr may be contained in the slab in an amount of 0.01 to 2.5% by weight.

P: 0.003% to 0.1%

Phosphorus (P) is an element capable of increasing iron specific resistance and lowering iron loss, and is an element capable of improving magnetic flux density when added as a magnetic material. When P is included too little, the above-mentioned role may not be fully exercised. When P is added in an excess amount, segregation occurs in the in-core crystal grain boundaries, and the bonding force between grain boundaries can be significantly weakened. Therefore, P may be contained in the slab in an amount of 0.003% to 0.1% by weight. More specifically, P may be contained in the slab in an amount of 0.005 to 0.05% by weight.

0.1% by weight or less of Sn,

Tin (Sn) is a segregation source and is an element that improves magnetism while improving aggregate structure during annealing and does not form precipitates. When Sn is added in an excessive amount, the fracture of the rolled sheet may be caused to occur at the time of normal temperature rolling in the ferrite, and slip may occur on the surface during rolling. Therefore, Sn can be contained in the slab at 0.1 wt% or less. More specifically, Sn may be contained in an amount of 0.001 to 0.1% by weight.

Ca: 0.0005 to 0.005 wt%

Calcium (Ca) is an element that bonds with S in the steel to form sulfides. When Ca is added in an excessive amount, an oxide in the steel is formed, which may adversely affect iron loss. Therefore, Ca may be contained in the slab in an amount of 0.0005 to 0.005% by weight. More specifically, Ca may be contained in an amount of 0.0005 to 0.0.003% by weight.

As: not more than 0.05% by weight

Arsenic (As) is an element that forms aggregate structure favorable to magnetism when added to steel, but increases iron loss when added excessively. Therefore, As can be contained in the slab in an amount of 0.05 wt% or less. More specifically, As may be contained in an amount of 0.0005 to 0.03% by weight.

Be: 0.003 wt% or less

Beryllium (Be) is an element that forms complex precipitates. When excess amount is added, it is possible to form a precipitate that is dissolved in the steel and interferes with the magnetic domain movement. Therefore, Be can be contained in the slab in an amount of 0.003% by weight or less. More specifically, Be may be contained in the slab in an amount of 0.0001 to 0.003% by weight.

Se: 0.003% by weight or less

Selenium (Se) is an element that forms complex precipitates. When excess amount is added, it is possible to form a precipitate that is dissolved in the steel and interferes with the magnetic domain movement. Therefore, Se can be contained in the slab in an amount of 0.003% by weight or less. More specifically, Se may be contained in the slab in an amount of 0.0001 to 0.003% by weight.

S: not more than 0.003% by weight

Sulfur (S) is an element that forms a complex precipitate. When excess amount is added, it is possible to form a precipitate that is dissolved in the steel and interferes with the magnetic domain movement. Therefore, S can be contained in the slab at 0.003 wt% or less. More specifically, S may be contained in the slab in an amount of 0.0005 to 0.003% by weight.

Mg: 0.005 wt% or less

Magnesium (Mg) is an element that bonds with S in the steel to form a sulfide, and also forms an oxide by binding with oxygen. A precipitate which interferes with the migration of the magnetic domain can be formed. Therefore, Mg can be contained in the slab in an amount of 0.005 wt% or less. More specifically, Mg may be contained in the slab in an amount of 0.0001 to 0.003% by weight.

At least one selected from Cu, Sb, Zr, V, Ti, Co, Pb, Nb and B: 1.0%

The above-described elements may be added individually or in a total amount of 1.0% by weight or less. Cu can improve the strength and corrosion resistance of steel and increase the resistivity to reduce iron loss, but it can deteriorate iron loss when precipitates that interfere with magnetic migration by binding with S in steel. The other elements do not have a great effect on the magnetic properties when added in small amounts or are elements that exhibit more improved effects, or they are liquefied at high temperatures when they are added in excess to deteriorate the continuous casting or precipitate to deteriorate the magnetic properties It is preferable to control them individually or in a total amount of 1.0 wt% or less.

In the case of containing only one kind of the above-mentioned elements, each may be contained in an amount of 1.0 wt% or less, and in the case of containing two or more kinds of the above-mentioned elements, the amount thereof may be 1.0 wt% or less.

After the step of manufacturing the slab, the slab may further include a first cooling step for cooling the slab. Specifically, the first cooling step may be performed at a temperature of 1200 ° C to 950 ° C for 20 seconds to 100 seconds. If the cooling step is performed too long, a large amount of nitride, sulfides, oxides, and the like may be formed. If the cooling step is performed too hastily, breakage of the slab edge due to abrupt temperature decrease may occur.

After the step of producing the slab, the step of heating the slab may further include the step of heating the slab. The slab heating temperature may be above 1100 ° C. By further including a step of heating the slab, rough rolling can be smoothly performed in a rough rolling step to be described later.

The step of producing the slab means that at least 90% by volume of the slab is solidified. More specifically, 90% by volume or more of the total volume of the slab is solid. When more than 90% by volume of the slab is coagulated and rolled, a developed aggregate structure is formed at the time of rolling so that an electric steel sheet excellent in magnetism can be produced, while the hot rolling operation can be stably performed.

Next, the slab is continuously hot-rolled to produce a hot-rolled sheet. In this case, the meaning of continuous means that the casting apparatus for slab manufacturing and the hot rolling mill for hot rolling are directly connected (in-line). That is, the concept is distinguished from continuous slab cutting and hot rolling in a batch manner, and the slab is rolled immediately without cutting.

After at least 90% by volume of the slab has solidified, hot rolling may begin within 5 minutes. By starting the hot rolling in such a short time, deterioration of the magnetic property due to excessive inclusions formed at the time of solidification can be prevented, and formation of aggregate structure favorable to magnetism during hot rolling can be smoothly performed.

The step of producing the hot rolled sheet includes rough rolling and finish rolling.

First, the rough rolling step is a step of roughly rolling a slab to produce a bar having a thickness of 25 mm or less. More specifically, the thickness of the roughly rolled bar may be 10 to 25 mm. If the thickness of the bar is 10 mm too thin, the amount to be cut by the roughing mill is increased, which may result in an unstable state due to an increase in load on the roughing mill. When the thickness of the bar is too thick, the rolling load on the finishing mill may increase, which may reduce the ducting property.

And a second cooling step of cooling the hot rolled steel sheet after the rough rolling step. Specifically, the second cooling step may be performed for 5 to 20 seconds of cooling from 1000 ° C to 750 ° C. The inclusions and precipitates formed in accordance with the change of the temperature during the process of manufacturing the hot rolled sheet are greatly changed. At this time, it is very advantageous to reduce the number of micro precipitates and total precipitates by performing the second cooling step.

After the rough rolling step, heating the roughly rolled bar may be further included. The heating temperature of the bar may be 1000 ° C or higher. By further including a step of heating the bar, the finish rolling in the finish rolling step to be described later can be smoothly performed.

Next, the finishing rolling step is specifically a step of finishing the bars to produce a hot rolled sheet having a thickness of 0.8 to 3.0 mm.

In one embodiment of the present invention, the finish rolling may have a tension of 0.2 to 1.5 kgf / mm < ² > measured before the first rolling mill. Depending on the magnitude of the tension at the time of rolling, the state of stress at the time of plastic deformation of the steel changes and the shape of the deformed structure and its texture change. In addition, since the microstructure at the time of rolling the steel is changed, control of the tension to an appropriate range can suppress the formation of a deformed structure unfavorable to magnetism, and ultimately an electric steel sheet which is advantageous in magnetic properties and in surface shape and quality. Specifically, the first pass of the finishing rolling can be performed under a tension of 0.2 to 1.5 kgf / mm ² . Specifically, the tension measured in the front of the first rolling mill is shown by a in Fig. When the finishing rolling is performed with only one rolling mill, it means that the rolling mill is the rolling mill in which the steel sheet first passes during a plurality of rolling, when the rolling is performed with a plurality of rolling mills. The tensile force at this time is a force applied to the front and rear of the plate. In the case of representing the force per unit area normally expressed, the sectional area varies depending on the width and thickness of the plate, and therefore it is not suitable for use in steel processes varying in various thicknesses. , The force which is applied to the full width of the plate regardless of the width of the plate used for the control of the equipment is expressed by the tension. At this time, the minimum steel sheet width is 900 mm, the maximum width is 1200 mm, and the steel sheet width is 1200 mm to 1500 mm, which is 20% added to the tensile strength value of the present invention. More specifically, the first pass of the finish rolling can be performed under a tension of 0.25 to 1.4 kgf / mm < ² >.

90% by volume or more of the slab is solidified, and the finishing step after 1 to 15 minutes can be finished. By completing the slab rough rolling and finishing rolling in such a short period of time, deterioration of magnetism due to excessive inclusions can be prevented, and formation of aggregate structure favorable to magnetism during hot rolling can be smoothly performed.

The reduction rate in the finishing rolling step may be 5 to 20% higher than the reduction rate in the rough rolling step. By setting the reduction rate in the finishing rolling step to be high in this way, it is possible to more smoothly form an aggregate structure favorable to magnetism. More specifically, the reduction ratio in the finishing rolling step may be 85 to 95%. By controlling the reduction in the above-mentioned range, it is possible to prevent deterioration of magnetic property due to excessive inclusions formed at the time of solidification. Further, an aggregate structure favorable to magnetism can be smoothly formed. At this time, the reduction rate is calculated as (1- [thickness after rolling]) / [thickness before rolling].

The finish rolling step may include a pass performed through a mill having a coefficient of friction of 0.3 or less. When the finishing rolling step is performed in a single pass, the single pass can be performed through a mill with a friction coefficient of 0.3 or less, and when the finishing rolling step is performed in multiple passes, Is not more than 0.3. Specifically, the coefficient of friction of the rolling mill means the coefficient of friction of the rolling mill contacting the rolling mill with the steel sheet. When the coefficient of friction is too high, a deformed structure is formed by pressing of the surface. These deformed structures adversely affect surface morphology and magnetism.

After the finish rolling step, it may further include winding the hot rolled sheet.

After 90% by volume or more of the slab has solidified, the temperature of the surface of the plate may be 1100 ° C or more for 5 minutes or less. When the above-mentioned time is prolonged, the magnetism becomes extremely unfavorable and a nick or the like may be generated on the surface.

Further, after 90 vol% or more of the slab has solidified, the temperature of the surface of the plate may be 800 ° C or more for 30 minutes or less. Carbides and complex precipitates are formed at a temperature of 800 DEG C or higher. By shortening this time, the formation of carbides and complex precipitates can be suppressed and an electric steel sheet excellent in magnetic properties can be produced.

1 to 3 schematically show the temperature of the plate surface with time in the manufacturing method according to an embodiment of the present invention. 1 to 3 show the time (t1) at which the plate surface temperature is 1100 DEG C and the time (t2) at 800 DEG C or more.

In the finishing rolling step, lubricating oil of 0.01 to 50 L / min can be sprayed to a surface area of 1 m ² of the steel sheet. As such an appropriate amount of lubricant is injected, a large amount of magnetically favorable texture can be generated. In addition, it is possible to produce an electric steel sheet excellent in roughness and plate shape.

The amount of lubricating oil sprayed onto the surface of the steel sheet may vary depending on the use point of the lubricating oil during finishing rolling. Since the plate thickness is thick at the front end of the finish rolling when the finish rolling including a plurality of passes proceeds, the lubricating oil may be used at 1 to 50 L / min per 1 m ² of the surface area of the steel plate. Since the thickness of the steel sheet at the rear end of the finish rolling is thin, the lubricating oil may be used at 0.01 to 1 L / min per 1 m ² of the surface area of the steel sheet. If the path is even, divide by 2 to separate the front and back ends. If the path is an odd number, divide it by 2, then round it up, shear it down, and down it to the next. For example, in the case of 5-pass, the front end is 3 pass in the early stage and the 4-pass pass is in the rear end. The amount of lubricating oil injected means the sum of the lubricating oil sprayed on both the upper and lower surfaces of the steel plate.

The lubricating oil exhibits the same effect regardless of the timing of the finishing rolling, and it is necessary to inject lubricating oil in the passing plate of the finishing mill in which the steel sheet is continuous, for at least one second or more. More preferably, it is effective to inject lubricating oil in the entire region of the finish rolling.

Lubricant refers to a mixture of water and oil from which ordinary impurities have been removed. Usually, 200 parts of water and 0.1 to 10 parts of oil are mixed with the skin.

The hot-rolled sheet thus produced is excellent in shape. Specifically, the hot-rolled sheet has a very small crown. In one embodiment of the present invention, the crown means a thickness difference between the thickest portion and the thinnest portion except for 30 mm at the widthwise edge. Specifically, the thickness difference between the thickest portion and the thinnest portion of the hot-rolled sheet may be 40 占 퐉 or less except for 30 mm at the widthwise edge of the hot-rolled sheet.

In addition, the manufactured hot-rolled sheet had an aggregate structure in which the angle formed by the {100} plane with the rolled surface was 15 ° or less, and the intensity of {111} Lt; RTI ID = 0.0 > 50 < / RTI > As a result, a number of texture structures favorable to magnetism are finally formed, and an electric steel sheet excellent in magnetism can be manufactured.

After the finish rolling step, a third cooling step may be further included. Specifically, the third cooling step may be performed for 2 to 20 seconds of cooling from 800 [deg.] C to 650 [deg.] C. The inclusions and precipitates formed in accordance with the change in temperature during the process of annealing the hot-rolled steel sheet largely fluctuate. By performing the third cooling step at this time, it is very advantageous to reduce the number of micro precipitates and total precipitates.

After the step of producing the hot-rolled sheet, the step of pickling the hot-rolled sheet may be further included. By pickling the hot rolled plate, the oxide layer formed on the hot rolled plate surface can be removed.

After the step of producing the hot-rolled sheet, the step of annealing the hot-rolled sheet may be further included. The annealing temperature of the hot-rolled sheet can be controlled to 850 DEG C or higher to increase the crystal orientation favorable to magnetism.

Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet. Specifically, the hot rolled sheet is cold rolled to produce a cold rolled sheet having a thickness of 0.095 to 1.0 mm. The reduction rate in the step of producing the cold-rolled sheet may be 50 to 92%. The cold-rolled sheet may be subjected to rolling once or twice or more with intermediate annealing.

As described above, the crown of the hot-rolled sheet becomes very small, and thereby the crown of the cold-rolled sheet becomes very small. Specifically, the thickness difference between the thickest portion and the thinnest portion of the cold-rolled sheet may be 3 占 퐉 or less except for 30 mm at the widthwise edge of the cold-rolled sheet.

The surface roughness of the cold-rolled sheet is also excellent. Specifically, the surface roughness Ra of the upper and lower surfaces of the cold-rolled sheet may be 0.05 to 0.5 占 퐉. The sum of the upper and lower surface roughness Ra of the cold-rolled sheet may be 0.5 탆 or less. The crown and surface roughness are important factors for determining the magnetic properties in the laminated core when the steel sheet is laminated.

After the step of producing the cold-rolled sheet, the step of finally annealing the cold-rolled sheet may be further included. The final annealing temperature may be 600 to 850 占 폚. The annealing time may be 6 hours or less. The step of final annealing the cold rolled sheet may include a decarburization process. Decarburization can be carried out by adjusting the atmosphere gas to a dew point of 10 ° C to 30 ° C. At least 50% by volume of the atmosphere gas may contain nitrogen.

If the dew point is too low, decarburization may not occur smoothly. When the dew point is too high, an oxide layer is formed on the surface of the steel, decarburization does not occur easily, and the magnetism may be disadvantageous. When the annealing temperature is too low, decarburization does not occur smoothly, and when the annealing temperature is too high, the shape may become poor.

The steel sheet obtained in the final annealing step of the cold-rolled sheet has excellent iron loss and magnetic flux density. Specifically, the following formulas (1) and (2) can be satisfied.

B ₂₅ ≥0.79 × (2.156-0.0413 × [Si] -0.0604 × [Al]) in the formula (1)

Equation _{(2) W 15/50 /(t+0.01×t} 1 .5 + 0.001 × t 2) ≤ 10

In this case, B ₂₅ represents the magnetic flux density value (T) measured at 2500 A / m, [Si] and [Al] represent the Si content (wt%) in the slab, and W _{15 /} (W / kg) measured when the steel sheet is magnetized to have magnetic flux density, and t represents the thickness (mm) of the cold-rolled sheet.

Equation (1) indicates that the magnetic flux density produced by one embodiment of the present invention is superior to the magnetic flux density calculated by the content of Si and Al, and is independent of the content of Si and Al. This shows that the manufacturing method according to the example is excellent.

Equation (2) indicates that the iron loss produced by one embodiment of the present invention is excellent when the elements of the steel sheet thickness are excluded, indicating that the manufacturing method according to one embodiment of the present invention is superior.

In the analysis of the texture of the cold-rolled sheet, the intensity of the aggregate structure having an angle formed by the {100} plane with the rolled surface of not more than 15 ° is not less than the angle formed by the {111} It can be 1.5 times higher than the strength of the texture of less than 15 degrees. As a result, a number of texture structures favorable to magnetism are finally formed, and an electric steel sheet excellent in magnetism can be manufactured.

4 shows a lay-out of an apparatus for implementing the manufacturing method according to an embodiment of the present invention.

4, the molten steel is injected into the tundish 20 from the castor 10, and the slab a produced as it passes through the plunger 30 is rolled in a bar shape through the roughing mill 40. The rolled bar is rolled into a hot-rolled steel sheet by a finishing mill 50. The produced hot-rolled steel sheet is then produced as a non-oriented electrical steel sheet through the cold rolling process and the cold-rolled steel sheet annealing process.

The non-oriented electrical steel sheet according to an embodiment of the present invention can be manufactured by the above-described manufacturing method.

Hereinafter, preferred embodiments and comparative examples of the present invention will be described. However, the following examples are only a preferred embodiment of the present invention, and the present invention is not limited to the following examples.

Example 1

0.003% of N, 0.003% of N, 0.01% of Ni, 0.01% of Cr, 0.01% of Sn, 0.01% of S, 0.001% : Experiments were conducted using molten steel containing Fe outer minor component and residual Fe of 0.01%, Ca: 0.001%, As: 0.003%, Mg: 0.0005%, Se: 0.0003%, Be: 0.0003% Respectively. After the slab was manufactured, the cooling time from 1200 캜 to 950 캜 was 30 seconds, the cooling time from 1000 캜 to 750 캜 was 10 seconds, and the cooling time from 800 캜 to 650 캜 after finishing rolling was 10 seconds. Conditions other than the above are detailed in Table 1 below.

The tension refers to the tension at the time of rolling, and represents the magnitude of the tension at the first forming section (a) of the bar. The friction coefficient means the lowest friction coefficient among the friction coefficients measured in each rolling mill during finishing rolling through a multi-stage rolling mill. The {100} hot rolled plate and {111} hot rolled plate were measured by XRD or EBSD in cross section between the rolling direction and the thickness direction at an area of 1 cm ² or more, ) Means the random contrast strength of the {100} plane and the {111} plane parallel to the plate surface of the hot-rolled plate. The hot rolled plate crown means the thickness difference between the thickest portion and the thinnest portion of the plate excluding the 30 mm from the edge of the hot rolled plate.

The {100} annealed sheet, {111} annealed sheet and cold-rolled sheet crown items were measured in the same manner as the above-described hot-rolled sheet, but subjected to cold-rolled and annealed sheets.

The upper surface roughness refers to the average roughness measured on the upper surface of the cold-rolled and annealed plate, and the lower roughness refers to the average roughness measured on the lower surface.

Psalm name tension
(kgf / mm ² ) Coefficient of friction Slab
thickness
(mm) Rough rolling thickness (mm) Finishing Thickness (mm) Time (minutes) to the end of hot rolling after solidification Time (min) above 1100 ℃ after solidification 800 ° C after solidification
~ 1100 ℃
Time (minutes) Amount of lubricating oil
(L / min) A-1 0.1 0.23 55 25 3 5 4 5 2 A-2 0.3 0.06 93 25 2.5 4 3 4 5 A-3 0.51 0.12 93 25 2.5 6 5 5.5 20 A-4 1.21 0.4 93 18 One 4 3 5 30 A-5 0.45 0.21 93 18 2 4 3 3.5 20 A-6 1.36 0.28 93 18 2 7 6 5 40 A-7 1.82 0.28 93 18 2 4 3 5 30 A-8 2.63 0.35 93 18 2 4 3 5 30 A-9 0.76 0.2 95 18 1.5 4 3 5 30 A-10 0.76 0.2 95 18 1.5 4 3 50 30 A-11 0.76 0.2 95 18 1.5 4 3 5 0 A-12 0.76 0.2 95 18 1.5 4 3 5 100

Psalm name {100} hot rolled plate {111} hot rolled sheet Hot rolled plate crown (㎛) Cold rolled sheet thickness
(mm) Cold rolled sheet crown
(탆) Surface illumination
(탆) Illuminance
(탆) {100} annealed plate {111} annealed plate A-1 0.5 3.1 44 0.25 6.3 0.54 0.51 1.3 3.4 A-2 1.3 2 18 0.25 1.4 0.23 0.26 5.1 2.3 A-3 3.2 1.8 22 0.35 0.4 0.13 0.16 6.1 2.6 A-4 0.5 1.8 54 0.25 8.2 0.26 0.28 2.1 5.4 A-5 12.3 0.8 26 0.2 1.2 0.09 0.12 5.6 1.3 A-6 3.7 2.6 23 0.25 2.5 0.11 0.12 5.3 2.3 A-7 0.2 4.3 45 0.25 5.7 0.73 0.65 2.3 4.5 A-8 0.5 1.2 47 0.25 7.3 0.62 0.71 1.4 4.8 A-9 9.3 0.7 24 0.25 0.6 0.06 0.13 5.4 1.4 A-10 0.1 3.2 53 0.25 1.1 0.31 0.14 1.6 2.3 A-11 One 3.4 75 0.25 4.3 0.06 0.13 1.3 3.1 A-12 1.4 4.1 45 0.25 3.6 0.21 0.23 1.2 4.3

Psalm name B25 (T) Iron loss (W15 / 50, W / kg) Equation (1) Right value Equation (2) Left term value Remarks A-1 1.59 3.23 1.591 12.85 Comparative material A-2 1.65 1.82 1.591 7.24 Invention material A-3 1.68 1.93 1.591 5.48 Invention material A-4 1.53 2.91 1.591 11.58 Invention material A-5 1.66 1.72 1.591 8.56 Invention material A-6 1.69 1.73 1.591 6.88 Invention material A-7 1.55 2.53 1.591 10.07 Comparative material A-8 1.56 3.03 1.591 12.06 Comparative material A-9 1.68 1.76 1.591 7 Invention material A-10 1.58 2.87 1.591 11.42 Invention material A-11 1.55 2.78 1.591 11.06 Invention material A-12 1.57 2.73 1.591 10.86 Invention material

As shown in Tables 1 to 3, when the finishing rolling was carried out under an appropriate tension, and the friction coefficient of the finishing mill and the injection amount of the lubricating oil were appropriately controlled, it was confirmed that the manufactured steel sheet had excellent crown, surface roughness and magnetic properties .

Although the finish rolling was carried out under proper tensile force, when the friction coefficient of the finishing mill or the injection amount of the lubricating oil was not properly controlled for more than 800 ° C after solidification, the surface roughness of the produced steel sheet was excellent, but the crown and magnetic properties were comparatively It can be confirmed that it is inferior.

If the finish rolling is not carried out under an appropriate tension, the crown, surface roughness and magnetism of the produced electric steel sheet are all inferior.

Example 2

0.02% of P, 0.001% of Sn, 0.001% of S, 0.001% of S, 0.02% of Ni, 0.002% of Ca, 0.001% of Ca, 0.005% of As, 0.005% of As, %, Se: 0.0002%, Be: 0.0001%, and less than 1% total Fe. The raw material was prepared from a slab having a thickness of 90 mm. Rolled to a bar having a thickness of 18 mm, and the first forming pass of the finish rolling was carried out under a tension of 1.01 kgf / mm ² . The deformation modulus of the rolling roll at the entire pass was 0.15 while rolling to successive final passes. Rolled into a hot rolled sheet having a thickness of 1.5 mm in the final rolling line. The time to completion of hot rolling after solidification of the slab was controlled to 6 minutes, the time of 1100 ° C or more after solidification was controlled to 4 minutes, and the time of 800 ° C or more after solidification to 5.5 minutes. Thereafter, pickling was carried out, followed by cold rolling and then annealing to produce a non-oriented electrical steel sheet.

Specimen (% by weight) N C Si Al Mn B-1 0.002 0.002 3.4 0.3 0.5 B-2 0.002 0.002 0.5 0.001 0.5 B-3 0.002 0.002 1.5 0.2 0.5 B-4 0.002 0.002 2.5 0.001 0.5 B-5 0.002 0.002 3.5 0.1 0.5 B-6 0.002 0.002 3.4 0.3 0.5

Psalter {100} hot rolled plate {111} hot rolled sheet Hot rolled plate crown Cold rolled sheet crown (㎛) Surface illumination
(탆) Illuminance
(탆) {100} annealed plate {111} annealed plate B-1 2.5 1.5 14 2.5 0.21 0.12 4.11 1.7 B-2 2.8 1.2 21 1.6 0.31 0.13 3.73 2.1 B-3 2.4 1.2 19 1.9 0.23 0.2 3.98 1.2 B-4 2 1.4 17 2 0.21 0.14 3.35 1.9 B-5 3.8 1.1 29 2.7 0.28 0.22 4.06 1.7 B-6 3.2 1.3 34 1.9 0.12 0.1 5.27 1.8

Psalter B25 (T) Cold rolled sheet thickness
(mm) Iron loss
(W15 / 50, W / kg) Equation (1) Right value Equation (2) Left term value Remarks B-1 1.67 0.2 1.65 1.58 8.21 Invention material B-2 1.7 0.25 1.72 1.69 6.84 Invention material B-3 1.69 0.35 1.82 1.64 5.17 Invention material B-4 1.68 0.35 1.85 1.62 5.25 Invention material B-5 1.68 0.5 2.21 1.58 4.39 Invention material B-6 1.67 0.5 2.15 1.58 4.27 Invention material

As can be seen from Tables 4 to 6, even if the composition of the alloy is changed variously, it can be confirmed that the manufactured electric steel sheet has excellent crown, surface roughness and 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. As will be understood by those skilled in the art. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

100: non-oriented electrical steel sheet manufacturing apparatus 10: castor
20: Tundish 30: Player
40: rough rolling mill 50: finishing mill
a: tension measuring position t1: time at 1100 ° C or higher
t2: time at 800 DEG C or higher

Claims (27)

Producing a slab from molten steel;
Continuously hot rolling the slab to produce a hot rolled sheet; And
And cold rolling the hot rolled sheet to produce a cold rolled sheet,
Wherein the step of producing the hot rolled sheet comprises rough rolling and finishing rolling, wherein the finishing rolling has a tension of 0.2 to 1.5 kgf / mm ² measured in front of the first rolling mill. The method according to claim 1,
In the step of producing the slab, the thickness of the slab is 50 mm to 100 mm. The method according to claim 1,
Wherein the slab contains 0.005% or less of N, 0.05% or less of C, 6.5% or less of Si, 3.5% or less of Al, and 0.02 to 3.0% of Mn in weight% A method for producing a non-oriented electrical steel sheet comprising Fe and unavoidable impurities. The method of claim 3,
Wherein the slab comprises 0.005 to 5.0% of Ni, 0.005 to 5.0% of Cr, 0.003 to 0.1% of P, 0.1 to 0.1% of Sn, 0.0005 to 0.005% of Ca, 0.003% or less of S, 0.003% or less of S, and 0.005% or less of Mg, based on the total weight of the non-oriented electrical steel sheet. 5. The method of claim 4,
Wherein the slab further comprises at least one component selected from Cu, Sb, Zr, V, Ti, Co, Pb, Nb and B in an amount of 1.0 wt% or less. The method according to claim 1,
Further comprising the step of heating the slab after the step of manufacturing the slab. The method according to claim 1,
Wherein in the step of producing the hot-rolled sheet, hot rolling is started within 5 minutes after at least 90% by volume of the slab has solidified. The method according to claim 1,
Further comprising the step of: after the rough rolling, heating the roughly rolled bar. The method according to claim 1,
Wherein in the step of producing the hot-rolled steel sheet, at least 90% by volume of the slab is solidified, and after 1 to 15 minutes, the finish rolling step is completed. The method according to claim 1,
Wherein the reduction ratio in the finish rolling step is 5 to 20% higher than the reduction rate in the rough rolling step. The method according to claim 1,
Wherein the reduction ratio in the finishing rolling step is 85 to 95%. The method according to claim 1,
Wherein said finishing rolling step comprises a pass performed through a mill having a coefficient of friction of 0.3 or less. The method according to claim 1,
Wherein a time at which the surface temperature of the plate surface is 1100 ° C or higher after coagulation of 90% by volume or more of the slab is 5 minutes or less. The method according to claim 1,
Wherein the time at which the temperature of the surface of the plate is 800 DEG C or higher after the coagulation of 90 vol% or more of the slab is 30 minutes or less. The method according to claim 1,
Wherein the lubricating oil is sprayed at a rate of 0.01 to 50 L / min with respect to a surface area of 1 m ² of the steel sheet in the finishing rolling step. The method according to claim 1,
Wherein the thickness difference between the thickest portion and the thinnest portion of the hot-rolled sheet is 40 占 퐉 or less, except for 30 mm at the widthwise edge of the hot-rolled sheet. The method according to claim 1,
In the analysis of the texture of the hot-rolled sheet, the intensity of the aggregate structure having an angle formed by the {100} plane with the rolled surface of not more than 15 ° is not less than an angle formed by the {111} Is 0.5 to 50 times the strength of the aggregate structure having a grain size of 15 占 or less. The method according to claim 1,
Further comprising the step of pickling the hot rolled steel sheet after the step of producing the hot rolled steel sheet. The method according to claim 1,
Further comprising a 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 the reduction rate in the step of producing the cold-rolled sheet is 50 to 92%. The method according to claim 1,
Wherein the thickness difference between the thickest portion and the thinnest portion of the cold-rolled sheet is 3 占 퐉 or less, except for 30 mm at the widthwise edge of the cold-rolled sheet. The method according to claim 1,
Wherein the surface roughness (Ra) of the upper and lower surfaces of the cold-rolled sheet is 0.05 to 0.5 탆, respectively, after the step of producing the cold-rolled sheet. The method according to claim 1,
Wherein the sum of the surface roughness (Ra) of the upper and lower surfaces of the cold-rolled sheet after the step of producing the cold-rolled sheet is 0.5 占 퐉 or less. The method according to claim 1,
Further comprising the step of final annealing the cold-rolled sheet after the step of producing the cold-rolled sheet. 25. The method of claim 24,
Wherein the steel sheet obtained in the step of final annealing the cold-rolled sheet satisfies the following formulas (1) and (2).
B ₂₅ ≥0.79 × (2.156-0.0413 × [Si] -0.0604 × [Al]) in the formula (1)
Equation _{(2) W 15/50 /(t+0.01×t} 1 .5 + 0.001 × t 2) ≤ 10
(In this case, B ₂₅ represents a magnetic flux density value (T) measured at 2500A / m, [Si] and [Al] denotes the Si content (% by weight) in the slab, W _15/50 is in the standing wave 1.5T 50Hz (W / kg) measured at the time when the steel sheet is magnetized so as to have the magnetic flux density of the steel sheet, and t represents the thickness (mm) of the cold-rolled sheet. The method according to claim 1,
In the analysis of the texture of the cold-rolled sheet, an intensity of an aggregate structure having an angle formed by the {100} plane with the rolled surface is 15 ° or less, the angle formed by the {111} Is 1.5 times or more higher than the strength of the aggregate structure of 15 DEG or less. 27. The method according to any one of claims 1 to 26,
The non-oriented electrical steel sheet produced by the above production method.

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