KR20150075250A - Non-oriented electrical steel sheets and method for manufacturing the same - Google Patents

Abstract

Disclosed is a non-oriented electrical steel sheet. A method for manufacturing the non-oriented electrical steel sheet comprises the steps of: providing a slab including 1.5-4.0 wt% of Si, less than or equal to 0.005 wt% of C (not include 0 wt%), 0.1-3.0 wt% of Al, 0.01-0.6 wt% of Mn, 0.001-0.005 wt% of S, and residual Fe and other inevitably mixed impurities; heating the slab again, hot rolling the same, and manufacturing a hot rolled steel sheet; cold rolling the hot rolled steel sheet, and manufacturing a cold rolled steel sheet; and finally annealing the cold rolled steel sheet including the temperature rising step and the cracking step, wherein temperature rising time from 650°C to the crack temperature is the same or longer than crack time of the cracking step in the temperature rising step.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a non-oriented electrical steel sheet, and more particularly, to a non-oriented electrical steel sheet having excellent magnetic properties by controlling composition and texture, annealing conditions, and the like.

The nonoriented electric steel sheet is used as an iron core material in rotating devices such as motors, generators, and stationary devices such as small transformers, and plays an important role in determining the energy efficiency of electric devices.

The nonoriented electrical steel sheet is mainly used as an iron core material for rotating equipment, and magnetic properties are very important as an important part for converting electrical energy into mechanical energy. Iron loss and magnetic flux density are mainly mentioned as magnetic properties.

Since iron loss is energy that disappears into heat during the energy conversion process, the lower the better, and the higher the magnetic flux density is the power source of the rotating body, the better the energy efficiency.

In the electrical steel sheet, the best orientation for magnetism is the {100} orientation, followed by {110} and the {111} is worst. The more the {100} orientations are arranged parallel to the rolling direction of the steel strip, the better the magnetic properties of the steel strip.

In the case of a steel sheet in which the content of Si and Al is 1.6% or more and has no phase transformation, the non-oriented electrical steel sheet according to the prior art has more {110} orientation than the {100} orientation.

Therefore, research is needed to improve the magnetism by changing the texture.

An object of the present invention is to provide a non-oriented electrical steel sheet having a low iron loss and excellent magnetic properties by controlling the alloying elements of steel, texture, annealing conditions and the like, and a manufacturing method thereof.

A method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention comprises: 1.5 to 4.0% of Si, 0.005% or less (including 0%) of C, 0.1 to 3.0% of Al, : 0.01 to 0.6%, S: 0.001 to 0.005, the balance being Fe and other inevitably incorporated impurities; Preparing a hot-rolled steel sheet by reheating the slab and then hot-rolling the slab; Cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet; A final annealing step of heating the cold-rolled steel sheet including a heating step and a cracking step; Wherein the temperature rise time from the temperature of 650 ° C to the temperature of cracking is equal to or longer than the cracking time of the cracking step.

The heating rate may be 3 to 25 ° C / sec in the heating step.

The cracking temperature in the cracking step may be 900 to 1070 캜.

The cracking time in the cracking step may be 10 to 60 seconds.

The slab may further contain Sn: 0.01 to 0.2% by weight.

The non-oriented electrical steel sheet to which the final annealing has been completed has F _{100} > F _{110} can be satisfied.

Where F _{100} is the volume fraction of crystal grains having an angle of {100} with the rolled surface of not more than 15 ° F _{110} is the volume fraction of grains having an angle of {110} Percentage fraction.)

The inevitably added impurities include Ti, N, and P, and Ti, N, and P may be 0.005% or less by weight, N: 0.005% or less, and P: 0.2% or less by weight.

The reheating may be performed at 1200 ° C or lower.

After the step of producing the hot-rolled steel sheet, annealing the hot-rolled steel sheet at 900 to 1200 ° C.

The non-oriented electrical steel sheet according to one embodiment of the present invention comprises 1.5 to 4.0% of Si, 0.005% or less of C (does not include 0%), 0.1 to 3.0% of Al, 0.6%, S: 0.001 to 0.005, the balance including Fe and other inevitably incorporated impurities, F _{100} ≥ F _{110} .

Where F _{100} is the volume fraction of crystal grains having an angle of {100} with the rolled surface of not more than 15 ° F _{110} is the volume fraction of grains having an angle of {110} Percentage fraction.)

The non-oriented electrical steel sheet may further contain Sn in an amount of 0.01 to 0.2% by weight.

The inevitably added impurities include Ti, N, and P, and Ti, N, and P may be 0.005% or less by weight, N: 0.005% or less, and P: 0.2% or less by weight.

The nonoriented electric steel sheet according to the present invention improves the aggregate structure by optimally managing the annealing conditions, so that the fraction of {100} aggregate structure is larger than that of the {110} aggregate structure, to provide.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described in detail below.

However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims.

The non-oriented electrical steel sheet according to one embodiment of the present invention comprises 1.5 to 4.0% of Si, 0.005% or less of C (does not include 0%), 0.1 to 3.0% of Al, 0.6%, S: 0.001 to 0.005, the remainder comprising Fe and other inevitably incorporated impurities,

F _{100} ≥ F _{110} .

Where F _{100} is the volume fraction of crystal grains having an angle of {100} with the rolled surface of not more than 15 ° F _{110} is the volume fraction of grains having an angle of {110} Percentage fraction.)

The non-oriented electrical steel sheet may further contain Sn in an amount of 0.01 to 0.2% by weight.

The inevitably added impurities include Ti, N and P, and Ti, N and P may be 0.005% or less by weight, N: 0.005% or less, and P: 0.2% or less by weight.

The reason for limiting the content of the components in the present invention is as follows.

Si is an element that increases the resistivity and lowers eddy current loss during iron loss.

If the Si content is excessive, brittleness may occur and sheet breakage may occur. Therefore, it is preferable to add Si at a content of 4.0% or less. In the present invention, Si is added in an amount of 1.5% or more based on a composition in which no solid phase transformation is present in the entire temperature range.

Al is an element that decreases the eddy loss by increasing the resistivity.

When the Al content is less than 0.1%, AlN and Al oxides are excessive and phase transformation occurs, and when the Al content is more than 3.0%, the magnetism is opened due to the formation of coarse material.

C causes magnetic aging to degrade the magnetic properties, and therefore it is preferable to control it to 0.005% or less.

S forms MnS and CuS which are fine precipitates and suppresses crystal grain growth, and therefore, it is preferable to add S to 0.005% or less.

However, in the present invention, S is added in an amount of 0.001% or more in order to inhibit invasion of elements such as N, O and the like through the grain boundaries during the heating time and to form an atmosphere easy to form {100} desirable.

In addition to the alloying elements, Mn may be further added. Since Mn plays a role in developing the texture, it is preferable to add Mn by 0.01% or more. However, the saturation magnetic flux density decreases as the addition amount increases, and in order to satisfy the range that does not cause the solid phase transformation in the present invention, it is preferably added in an amount of 0.6% or less.

The balance consists of Fe and other inevitably added impurities.

The inevitably added impurities may include N, Ti, and P, and Ti, N, and P may be 0.005% or less by weight, N: 0.005% or less, and P: 0.2% or less by weight.

N is formed to contain fine and long AlN precipitates so as to suppress the growth of crystal grains, and therefore it is preferably contained in a small amount, and in the present invention, it is preferably limited to 0.005% by weight or less

Ti forms precipitates such as fine carbides and nitrides to suppress grain growth, and therefore, Ti is 0.005% or less.

P is added because it increases the resistivity to lower the iron loss, but when P is excessive, it is preferable to limit the cold rolling property to 0.2 wt% or less.

Hereinafter, a method of manufacturing the non-oriented electrical steel sheet according to the present invention will be described.

The steel sheet according to any one of claims 1 to 3, wherein the content of Si is 1.5 to 4.0%, the content of C is 0.005% or less (excluding 0%), the content of Al is 0.1 to 3.0%, the content of Mn is 0.01 to 0.6%, the content of S is 0.001 to 0.005, A slab containing impurities inevitably incorporated is reheated and hot rolled to produce a hot-rolled steel sheet.

The slab may further contain Sn: 0.01 to 0.2% by weight.

The inevitably added impurities include Ti, N, and P,

Ti, N, and P may be contained in an amount of 0.005% or less, 0.005% or less, and 0.2% or less in terms of% by weight.

The reheating temperature may be 1200 ° C or less.

Hot rolling is rough rolling and finish rolling, and finishing rolling of finish rolling can be finished on the ferrite. Also, the final reduction can be less than 30% for the plate shape calibration.

After the step of producing the hot-rolled steel sheet, the hot-rolled sheet annealing may be performed at 900 to 1200 ° C.

The hot-rolled steel sheet is cold-rolled.

If necessary, the steel can be subjected to a secondary cold rolling through an intermediate annealing step after the primary cold rolling, and the final rolling reduction can be in the range of 50 to 95%.

The cold-rolled steel sheet is subjected to final annealing.

The final annealing includes a step of raising the temperature of the cold-rolled steel sheet from room temperature to the cracking temperature, and a cracking step of keeping the heated steel plate at a constant temperature for a certain period of time.

As a result of repeated experiments, the inventors of the present invention have studied conditions for making the volume fraction of the {100} plane larger than the volume fraction of the {110} plane, which is an aggregation structure favorable to magnetism in the final annealing step.

During the final annealing step, the structure of the material changes constantly. That is, around 650 ° C, recrystallization nuclei begin to form, grow, grow, and are replaced by new grains. When the cracking temperature is reached according to the content of the material, a new recrystallization occurs only at the grain growth rather than the nucleation, and the growth is slowed down and stopped.

In this annealing process, {100} is well developed in the texture, but it is found that the fraction of {110} rather than {100} increases with the increase of the time at the cracking stage where recrystallization stops.

Also, it is advantageous for {100} to develop well to increase the temperature rise time over the crack time.

It is preferable that the temperature rise time from the temperature rising step to the cracking temperature is longer than the cracking time in the temperature raising step of the steel type in which the Si and Al contents without phase transformation are 1.6 wt% or more.

The temperature raising rate is preferably 3 to 25 DEG C / sec. The {100} production fraction was less when heated at less than 3 ℃ / sec and the energy consumption was more than 25 ℃ / sec and its effect decreased.

In addition, when S was added in the amount of 0.001 to 0.005%, {100} texture was favorable for development.

This is because S is segregated in grain boundaries and suppresses the invasion of N or O through the grain boundaries during the heating step to provide an atmosphere that is easy to form {100} texture.

The cracking temperature is preferably 900 to 1070 占 폚. When the temperature is less than 900 ° C, the grain growth is insufficient, and when the temperature exceeds 1070 ° C, the crystal grains are excessively grown and the texture structure {110} can be generated more than {100}.

The cracking time is preferably 10 to 60 seconds. In less than 10 seconds, grain growth is insufficient, and {110} may be overproduced in over 60 seconds.

The electric steel sheet after completion of the final annealing may be subjected to an insulating coating treatment.

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

[Example 1]

A slab having the composition shown in Table 1 was heated at 1,150 占 폚, hot-rolled at a thickness of 2.3 mm, and wound at 650 占 폚.

The hot-rolled steel sheet cooled in air was annealed at 1,050 ° C for 3 minutes, pickled, and then cold-rolled to a thickness of 0.35 mm.

The cold-rolled steel sheet was finally annealed under the conditions shown in Table 2.

The final temperature of the heating zone during heating was the same as the cracking temperature.

Steel grade C Si Mn P S Al N Ti Sn Comparative River 1 0.0025 1.2 0.15 0.05 0.0062 0.11 0.0013 0.0021 0.05 Inventive Steel 1 0.0023 1.6 0.17 0.05 0.0011 0.28 0.0018 0.0018 0.02 Invention river 2 0.0031 2.1 0.12 0.02 0.0021 0.35 0.0015 0.0012 0.05 Invention steel 3 0.0031 2.5 0.05 0.02 0.0035 0.25 0.0015 0.0014 0.04 Comparative River 2 0.0026 2.4 0.16 0.01 0.0007 0.28 0.0013 0.0015 0.07 Comparative Steel 3 0.0025 2.6 0.25 0.02 0.0055 0.31 0.0019 0.0011 0 Inventive Steel 4 0.0031 2.5 0.21 0.02 0.0015 0.45 0.0021 0.0013 0 Invention steel 5 0.0022 2.7 0.15 0.05 0.0031 0.32 0.0015 0.0013 0.04 Invention steel 6 0.0025 2.5 0.51 0.01 0.0026 0.75 0.0011 0.0012 0.05 Invention steel 7 0.0023 2.8 0.02 0.05 0.0021 0.72 0.0020 0.0013 0 Comparative Steel 4 0.0025 3.1 0.65 0.01 0.0005 1.3 0.0016 0.0011 0.03 Inventive Steel 8 0.0024 3.5 0.09 0.06 0.0021 1.5 0.0011 0.0015 0.05

In Table 1, the unit of component content is wt%

In the above table, the inventive steel satisfies the compositional range of the invention. Comparative steel 1 is low in Si, phase transformation occurs, S is added to 0.0061% excessively, and Comparative steel 2 is low in S content. The comparative steel 3 was added with a high S content, and the comparative steel 4 was added with the Mn content exceeding the range of the invention, and the S content was low.

For each specimen, the texture was examined using Electron Backscatter Diffraction (EBSD), and the iron loss and magnetic flux density were measured using a magnetometer. The results are shown in Table 2 below.

division Steel grade Heating
Speed (° C / sec) 650 ℃ to crack temperature
Temperature rise time (sec) crack
Temperature (℃) crack
Time (sec) {100} volume fraction (%) {110} volume
Fraction
(%) Iron loss
W _15/50
(W / kg) Magnetic flux density B ₅₀
(Tesla) Comparison 1 Comparative River 1 5 50 900 40 18 29 5.2 1.73 Inventory 1 Inventive Steel 1 4 62.5 900 40 31 15 4.3 1.82 Inventory 2 Inventive Steel 1 10 25 900 40 25 17 4.1 1.84 Comparative material 2 Inventive Steel 1 28 8.9 900 40 17 25 4.6 1.74 Inventory 3 Invention river 2 8 41.3 980 20 25 14 2.7 1.78 Invention 4 Invention steel 3 10 35 1000 20 29 19 2.8 1.79 Comparative material 3 Comparative River 2 10 35 1000 20 18 25 2.9 1.71 Comparison 4 Comparative Steel 3 10 35 1000 20 15 25 2.8 1.72 Invention Article 5 Inventive Steel 4 5 70 1000 30 28 15 2.4 1.78 Inventions 6 Invention steel 5 10 35 1000 30 29 13 2.3 1.79 Invention 7 Invention steel 6 14 25 1000 30 27 15 2.1 1.77 Invention 8 Invention steel 7 10 37 1020 30 26 12 1.9 1.77 Invention 9 Inventive Steel 8 4 100 1050 50 29 12 1.82 1.79 Comparative material 5 Inventive Steel 8 2 215 1080 70 20 26 2.1 1.65 Comparative material 6 Inventive Steel 8 30 14.4 1081 20 18 25 2.2 1.66

1) _Iron loss (W _15/50 ) is the average loss (W / kg) in the rolling direction and the rolling direction perpendicular to the magnetic flux density of 1.5 Tesla at 50 Hz frequency.

2) The magnetic flux density (B ₅₀ ) is the magnitude of the flux density (Tesla) induced when a magnetic field of 5000 A / m is added.

As shown in Table 2, the inventive electrical steel sheet according to an embodiment of the present invention was found to have good magnetism in comparison with the comparative material. In addition, the inventive material has a higher {100} plane fraction {110} plane parallel to the plane and superior magnetic properties.

In comparative material 1, comparative steel 1 had poor magnetic properties although the annealing condition of the comparative material was within the scope of the invention. It is explained that the excessively high value of S has adversely affected the formation of aggregate structure.

In comparison material 2, though it was an inventive steel, it was found that the heating rate was excessively high and the magnetic properties were poor.

The comparative material 3 or 4 was excessively high in the comparative steels 2 and 3.

The comparative materials 5 and 6 were inventive steel 8, but the heating rate was too slow or too fast, and the {100} fraction was low.

[Example 2]

0.008% of C, 3.1% of Si, 0.15% of Mn, 0.015% of P, 0.0015% of S, 0.91% of Al, 0.0013% of N, 0.0012% of Ti and the balance of Fe and other unavoidable impurities Was reheated to 1,150 占 폚 and then hot rolled to obtain a hot-rolled steel sheet having a thickness of 2.5 mm, rolled at 650 占 폚 and cooled in air.

The hot-rolled sheet was continuously annealed for 5 minutes, pickled, and cold-rolled to a thickness of 0.5 mm.

The cold-rolled sheet was finally annealed under the conditions shown in Table 3 at 70% nitrogen and 30% hydrogen. The final temperature of the heating zone during heating was equal to the cracking temperature.

For each specimen, EBSD (Electron Backscatter Diffraction) was used to calculate the mean grain size with the highest frequency of grain size as a representative value. The texture of the grains was measured and the {100} and {110} The fractions were measured. The iron loss and the magnetic flux density were measured using a magnetometer, and the results are shown in Table 3 below.

division Heating rate (° C / sec) 650 ℃ or higher
Heating time (sec) crack
Temperature (℃) crack
Time (sec) {100}
Fraction (%) {110}
Fraction (%) Iron loss
W _15/50
(W / kg) Magnetic flux density B ₅₀
(Tesla) Inventory 1 5 80 1050 50 28 15 2.06 1.74 Inventory 2 10 40 1050 30 30 14 2.06 1.75 Inventory 3 15 26.7 1050 20 32 12 2.08 1.76 Invention 4 20 21 1070 18 29 15 2.13 1.74 Comparison 1 3 133.3 850 80 17 28 2.41 1.67 Comparative material 2 30 13.3 1050 30 18 23 2.51 1.65

Inventive materials worked within the scope of the invention, the {100} fraction was higher than the {110} fraction, and the magnetic properties were also good.

The comparative material 1 was found to be heated at a slow rate due to the low cracking temperature, and the cracking time was also increased to heat the magnetism.

The heating time of the comparative member 2 was shortened by heating at a high speed, and the heating time was excessively fast during the subsequent cracking time. That is, although the cracking time is short, the heating rate is excessively fast, and the stagnation time in the cracking zone becomes relatively longer, and accordingly, the change in the material is considered to be a condition of longer cracking time.

While the present invention has been described in connection with certain exemplary embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (17)

The steel sheet according to any one of claims 1 to 3, wherein the content of Si is 1.5 to 4.0%, the content of C is 0.005% or less (excluding 0%), the content of Al is 0.1 to 3.0%, the content of Mn is 0.01 to 0.6%, the content of S is 0.001 to 0.005, Providing a slab comprising impurities that are inevitably incorporated;
Preparing a hot-rolled steel sheet by reheating the slab and then hot-rolling the slab;
Cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet;
A final annealing step of heating the cold-rolled steel sheet including a heating step and a cracking step; / RTI >
Wherein the temperature rise time from the temperature of 650 ° C to the crack temperature in the final annealing step is equal to or longer than the cracking time of the cracking step. The method according to claim 1,
Wherein the heating rate in the heating step is 3 to 25 DEG C / sec. 3. The method of claim 2,
Wherein the cracking temperature in the cracking step is 900 to 1070 占 폚. The method of claim 3,
Wherein the cracking time is 10 to 60 seconds in the cracking step. 5. The method of claim 4,
Wherein the slab further comprises 0.01 to 0.2% Sn in terms of% by weight. 6. The method according to any one of claims 1 to 5,
The non-oriented electrical steel sheet having completed the final annealing,
F _{100} ≥ F _{110} .
Where F _{100} is the volume fraction of crystal grains having an angle of {100} with the rolled surface of not more than 15 ° F _{110} is the volume fraction of grains having an angle of {110} Percentage fraction.) The method according to claim 6,
The inevitably added impurities include Ti, N, and P,
Wherein the Ti, N and P are 0.005% or less of Ti, 0.005% or less of N, and 0.2% or less of P by weight. 8. The method of claim 7,
Wherein the step of reheating the slab is performed at a temperature of 1200 DEG C or less. 9. The method of claim 8,
Further comprising the step of annealing the hot-rolled steel sheet at 900 to 1200 ° C after the step of manufacturing the hot-rolled steel sheet. The steel sheet according to any one of claims 1 to 3, wherein the content of Si is 1.5 to 4.0%, the content of C is 0.005% or less (excluding 0%), the content of Al is 0.1 to 3.0%, the content of Mn is 0.01 to 0.6%, the content of S is 0.001 to 0.005, Contains impurities that are inevitably incorporated,
F _{100} ≥ F _{110} .
Where F _{100} is the volume fraction of crystal grains having an angle of {100} with the rolled surface of not more than 15 ° F _{110} is the volume fraction of grains having an angle of {110} Percentage fraction.) 11. The method of claim 10,
The non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet further contains 0.01 to 0.2% Sn by weight, 12. The method of claim 11,
The inevitably added impurities include Ti, N, and P,
Wherein the Ti, N and P are 0.005% or less of Ti, 0.005% or less of N, and 0.2% or less of P by weight%. The steel sheet according to any one of claims 1 to 3, wherein the content of Si is 1.5 to 4.0%, the content of C is 0.005% or less (excluding 0%), the content of Al is 0.1 to 3.0%, the content of Mn is 0.01 to 0.6%, the content of S is 0.001 to 0.005, A cold rolled steel sheet is produced by rolling a hot rolled steel sheet by heating and rolling a slab containing impurities inevitably incorporated therein. The cold rolled steel sheet is finally annealed through a temperature elevating step and a cracking step,
In the final annealing step, the heating time from 650 ° C to the cracking temperature is equal to or longer than the cracking time of the cracking step,
F _{100} ≥ F _{110} .
Where F _{100} is the volume fraction of crystal grains having an angle of {100} plane with the rolled surface of not more than 15 ° F _{110} is the volume of grain at an angle of {110} Percentage fraction.) 14. The method of claim 13,
Wherein the temperature raising rate in the temperature raising step is 3 to 25 캜 / sec,
F _{100} ≥ F _{110} . 15. The method of claim 14,
In the cracking step, the cracking temperature is 900 to 1070 占 폚,
F _{100} ≥ F _{110} . 16. The method of claim 15,
Wherein the cracking time in the cracking step is 10 to 60 seconds,
F _{100} ≥ F _{110} . 17. The method of claim 16,
Wherein the slab further comprises 0.01 to 0.2% Sn by weight,
F _{100} ≥ F _{110} .