KR100345706B1 - Non oriented electrical steel sheet having superior magnetic properties and manufacturing process thereof - Google Patents

Abstract

PURPOSE: A method for manufacturing non-oriented electrical steel sheets having superior magnetic properties is provided. CONSTITUTION: The method includes the steps of reheating a steel slab comprising 0.02 wt.% or less of C, 1.0 wt.% or less of Si, 0.5 wt.% or less of Mn, 0.15 wt.% or less of P, 0.02 wt.% or less of S, 0.005 wt.% or less of Sol-Al, 0.006 wt.% or less of N, Sn 0.03 to 0.30 wt.%, B 0.0004 to 0.0030 wt.%, a balance of Fe and incidental impurities at 1100 to 1250°C, wherein B/N is 0.1 to 0.5; hot rolling the steel slab; coiling the hot rolled steel sheet at less than 750 deg.C, followed by pickling and cold rolling; annealing the cold rolled steel sheet at 700 to 1050°C; and stress relief annealing.

Description

Non oriented electrical steel sheet having superior magnetic properties and manufacturing process

The present invention relates to a non-oriented electrical steel sheet used for iron cores of electrical equipment such as small and medium-sized motors and small transformers, and a method for manufacturing the same. More specifically, the non-oriented electrical steel sheet with low iron loss, high magnetic flux density and permeability; It relates to a manufacturing method.

In general, non-oriented electrical steel sheet is used in a motor for generating power by converting electrical energy into rotational energy or a transformer for reducing or boosting an input voltage, and most of the power generation is consumed for the above purposes.

Therefore, the magnetic properties of non-oriented electrical steel sheet are directly related to energy loss, and are important in terms of energy saving. In particular, iron loss, magnetic flux density, and permeability among magnetic properties are important. Magnetic properties of the steel sheet can be compared by comparing iron loss and / or permeability at a given magnetic flux density.

On the other hand, non-oriented electrical steel sheet is also classified by the content of Si, according to this, can be classified into the material with the Si content of less than 1.0% and the material with more than 1.0%, high Si content can increase the specific resistance can be low iron loss However, the magnetic flux density and permeability will be lowered.

Iron loss among magnetic characteristics means energy loss and can be classified into history loss and eddy current loss. Vortex losses are determined by the composition and thickness of the material, and hysteresis losses are mainly determined by the impurity element and its manufacturing method. Since the hysteresis loss accounts for a large percentage of iron losses, it is necessary to reduce the hysteresis loss by controlling the manufacturing method.

As a method of reducing hysteresis loss and increasing permeability, it is known to reduce impurities such as S, N and O. This method imposes a lot of time and manufacturing cost in the steel making process in order to contain as few of these elements as possible. Doing.

In particular, when the content of Si is less than 1.0%, it is necessary to reduce the influence of N. Furthermore, by growing the grains and developing the aggregation coarse {200} <hkl> and {110} <wxy> which are favorable for magnetism, Magnetic properties can be improved.

Japanese Laid-Open Patent Publication No. 63-33518 discloses a method of improving magnetic properties by containing 1.0% to 1.5% of Mn. This method has a problem in that rollability is reduced and manufacturing cost increases due to addition of Al.

In addition, European Patent Publication 0084980 discloses a method for managing B and N by adding Sn and B, so that the ratio of B / N is 0.5-1.5. However, this method has a high B / N ratio, so that the amount of B added is large, and Al must be added.

On the other hand, many efforts have been made to improve the manufacturing process in order to reduce hysteresis loss and increase the permeability. For example, hot roll annealing after hot rolling, and cold pass annealing (skin pass), etc. Can be mentioned.

However, in the case of the above-described manufacturing method, the process is added, there is a problem that the demand must be subjected to stress annealing, and the plate shape after light rolling is bad.

Accordingly, the present inventors have studied in various angles to solve the problems of the prior art, and as a result, AlN or AlN or Al by adding only Al for deoxidation, is managed more actively than the N contained inevitably. It was confirmed that the precipitation of B precipitates harmful to other magnetism is suppressed and the magnetic properties are improved, and the present invention is proposed based on this.

An object of the present invention is to provide a non-oriented electrical steel sheet having a low iron loss, high magnetic flux density, and high permeability, and a method of manufacturing the same.

Another object of the present invention is to provide a non-oriented electrical steel sheet having excellent permeability by controlling the precipitates of B and N while controlling the ratio of B and N appropriately, and a method of manufacturing the same.

Therefore, in the present invention, by weight%, C: 0.02% or less, Si: 1.0% or less, Mn: 0.5% or less, P: 0.15% or less, S: 0.02% or less, Sol.Al: 0.005% or less, N: 0.006 The present invention relates to a non-oriented electrical steel sheet having excellent magnetic properties, including% or less, Sn: 0.03-0.30%, B: 0.0004-0.003%, balance Fe and unavoidable impurities, and satisfying a B / N ratio of 0.1 to 0.5.

In the present invention, by weight%, C: 0.02% or less, Si: 1.0% or less, Mn: 0.5% or less, P: 0.15% or less, S: 0.02% or less, Sol.Al: 0.005% or less, N: 0.006 % Or less, Sn: 0.03-0.30%, B: 0.0004-0.003%, balance Fe and unavoidable impurities, after reheating and hot rolling a steel slab with a B / N ratio of 0.1 to 0.5 After winding to a temperature of, the hot rolled sheet is annealed or pickled without hot rolled sheet annealing, and then cold rolled, the cold rolled sheet is annealed at a temperature of 700-1050 ℃ to produce a non-oriented electrical steel sheet having excellent magnetic properties It is about a method.

Hereinafter, the present invention will be described in detail.

The present invention is to provide a method of improving the magnetic properties by reducing the content of N as much as possible with respect to the steel of the component having a Si content of 1.0% or less.

N generally deteriorates the magnetism by inhibiting grain growth by precipitating as AlN, a fine and linear precipitate in the final product.

In order to minimize the influence of N, the addition of Sn, the segregation element of the grain boundary, and the addition of B, which has a high bonding force, can enhance the magnetism by effectively suppressing N in steelmaking and N in rolling and annealing. Can be.

In steels with a Si content of 1.0% or less, N is fine and precipitation of grains is mainly suppressed by linear AlN to suppress grain growth.

Therefore, N and Al should be suppressed as much as possible.

B is an element that binds to N in the material and forms BN, which is coarse boron precipitate instead of fine AlN, which acts more advantageously for grain growth.

However, when the amount of B is excessively added, precipitation of B ₂ O ₃ and FeB results in an increase in impurities in the steel. Therefore, it is most important not to add B other than the amount of binding with BN as much as possible.

Accordingly, the inventors have investigated the method of adding an amount of B which is arbitrarily adjustable rather than the amount of N inevitably contained, and found that the permeability is the highest in the range of B / N ratio lower than 0.5 and higher than 0.1.

In addition, in the steel containing 1.0% or less of Si, it was found that the Al element was not added as much as possible compared to the steel added up to 0.005% to 0.015%. In detail, the AlN precipitated as linear precipitates suppresses grain growth and lowers magnetic properties. Thus, AlN is added as little as possible or Al5 is added in an amount of 0.15% or more in a manner that does not precipitate AlN. It is preferable to form a large and round shape, but considering that Al is expensive, it is advantageous not to add as much as possible.

Therefore, in the present invention, Al is not added except inevitably added for deoxidation in steelmaking.

That is, in the present invention, the content of Soluble Al (Sol.Al), which is soluble Al, is limited to 0.005% or less, and preferably, the content of Al is limited to 0.005% or less.

Hereinafter, the steel composition of the present invention and the reason for limitation thereof will be described.

Since C causes magnetic aging to lower magnetic properties during use, its content is limited to 0.02% or less, preferably 0.02% or less in slabs, and 0.003% or less in final products.

In order to lower the C to 0.003% or less, decarburization may be performed during final annealing.

Si is an element that lowers iron loss by increasing specific resistance, but is preferably limited to 1.0% or less in consideration of improving permeability.

Mn is an effective element for improving iron loss, but if it exceeds 0.5%, the iron loss is deteriorated and the magnetic flux density is also lowered, so it is preferable to limit it to 0.5% or less.

P is an element that forms an advantageous texture for magnetic properties, but if it exceeds 0.15%, cold rolling is deteriorated, so it is preferable to limit it to 0.15% or less.

The S is advantageously managed as low as possible by forming a fine precipitate MnS to suppress grain growth, in the present invention is managed up to 0.02%.

Since Al suppresses grain growth by forming fine linear AlN precipitates, in the present invention, Al is added only for deoxidation in the steelmaking step, and it is preferable not to be contained in steel as much as possible, at most 0.005% in steel. May contain up to.

In addition, in the present invention, the content of Al may be limited to 0.005% or less in the form of Sol.Al.

Here, Sol.Al is Al in atomic state without Al compounds such as AlN and Al ₂ O ₃ in total aluminum, and means soluble Al (soluble Al).

The N needs to be suppressed as much as possible by forming fine and long AlN precipitates, and in the present invention, the content is limited to 0.006% or less.

The Sn segregates at grain boundaries to suppress the diffusion of N and to suppress the texture of the (222) plane, which is disadvantageous to magnetism. To this end, Sn needs to be added at least 0.03%. It is preferable that the content is limited to 0.03-0.30% because it worsens and the shape of the hot rolled sheet becomes poor.

B is an element that binds to N in the material and forms BN, which is coarse boron precipitate instead of fine AlN, and acts more advantageously for grain growth. To this end, it is necessary to add more than 0.0004%, but when the amount is increased, Lower permeability allows up to 0.003% addition.

In the present invention, in order to more appropriately form coarse BN precipitates instead of AlN, it is necessary to adjust the ratio of B / N to 0.1-0.5. If the ratio of B / N is less than 0.1, the amount of B is small and N is likely to be precipitated as AlN, and grain growth can be suppressed. If the ratio of B / N exceeds 0.5, the content of B is relatively large and B is B. Precipitation with ₂ O ₃ and FeB can lead to increased impurities in the steel.

That is, in the present invention, when the ratio of B / N is adjusted to 0.1-0.5, the BN precipitates are formed appropriately, the grains are coarsened, and the formation of precipitates such as B ₂ O ₃ and FeB is prevented. The magnetic properties of, in particular, the permeability can be significantly improved. Hereinafter, the manufacturing process of this invention is demonstrated.

The steel slab formed as described above is charged to a heating furnace and heated at a temperature of 1250 ° C. or lower, and then hot rolled in a conventional manner. At this time, if the heating temperature is too high, the impurity element precipitated in the slab may be re-dissolved and finely precipitated.

However, if the heating temperature is too low, hot rolling may be difficult due to uneven temperature distribution in the slab.

Therefore, in the present invention, the slab heating temperature is preferably selected to 1100-1250 ℃.

After hot rolling as above, the hot rolled hot rolled sheet is wound up. At this time, the coiling temperature is preferably selected to 750 ℃ or less to improve pickling properties.

The hot rolled sheet wound as described above may be annealed as necessary. When annealing the hot rolled sheet, the annealing temperature is preferably in the temperature range of 800-1100 ° C., and the annealing time is preferably limited to 5 minutes or less.

Such hot-rolled sheet annealing grows fine precipitates in the hot-rolled sheet coarsely, improves the overall characteristics of the material by making the structure uniform, and also serves to form a grain structure favorable for magnetism and to greatly increase the grain size.

The hot rolled sheet is pickled in a conventional pickling solution, followed by cold rolling to obtain a cold rolled sheet, and then final annealing.

The final annealing at this time is preferably annealed in a continuous process for a time of 30 seconds or more and 5 minutes or less at a temperature of 700-1050 ℃. This is because recrystallization is insufficient when the final annealing temperature is less than 700 ° C., and an oxide layer may be generated on the surface when the final annealing temperature is lower than 1050 ° C. If the final annealing time is less than 30 seconds, the residual stress of the cold rolled sheet may be excessively low, and the permeability may be lowered. If the final annealing time is more than 5 minutes, the shape of the annealing plate may be poor.

After the final annealed cold rolled plate as described above is shipped to the demand price, it is punched into the desired shape. At this time, if necessary, the punched material can be stress-annealed. Stress relieving annealing is preferably performed at a temperature of 700-850 ° C. for at least 10 minutes in a non-oxidizing atmosphere.

Through such stress relief annealing, residual stress generated during punching can be removed, so the permeability is particularly improved. If the stress relief annealing temperature is less than 700 ℃, the annealing time is too long, if it exceeds 850 ℃ can damage the insulating film.

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

Example 1

Steel slabs having the components shown in Table 1 below were heated to the temperature conditions as shown in Table 2 below, and hot rolled to a thickness of 2.0 mm, followed by winding the hot rolled plates at the temperature shown in Table 2, followed by pickling and cold rolling. The plate was annealed under the temperature and time conditions shown in Table 2 below.

At this time, the thickness of the cold rolled sheet was 0.5 mm, cold roll annealing was carried out in a mixed atmosphere of 20% hydrogen and 80% nitrogen.

The iron loss, magnetic flux density and permeability of the non-oriented electrical steel sheet manufactured as described above are shown in Table 2 below.

In Table 2, the iron loss represents the iron loss value generated when magnetizing at 1.5 Tesla at 50 Hz, the magnetic flux density represents the magnetic flux density induced when magnetizing at 5000 A / m, and the magnetic permeability (μ _1.5 ) is the magnetic flux of _1.5 Tesla. Permeability when the magnetic field is induced by density.

Steel grade Chemical composition (% by weight) C Si Mn P Al S N Sn B B / N Invention steel a 0.005 0.55 0.34 0.04 0.002 0.005 0.0035 0.09 0.0009 0.25 b 0.006 0.57 0.27 0.07 0.001 0.005 0.0037 0.10 0.0010 0.27 Comparative steel a 0.004 0.55 1.15 0.04 0.005 0.004 0.0030 0.11 0.0010 0.33 b 0.006 0.56 0.35 0.07 0.027 0.005 0.0020 0.10 0.0020 0.74

Sample Number Steel grade Slab reheating temperature (℃) Hot Rolled Sheet Winding Temperature (℃) Cold Rolled Annealing _Iron loss (W _15/50 ) W / kg Magnetic flux density (B ₅₀ ) Permeability (μ _1.5 ) Temperature (℃) Time (sec) Invention 1 Inventive Steel a 1200 700 950 90 3.62 1.79 4200 Invention 2 Inventive Steel a 1150 600 1000 30 3.50 1.79 4500 Comparative Material 1 Inventive Steel a 1280 800 950 90 3.90 1.76 3500 Comparative Material 2 Inventive Steel a 1200 700 850 10 4.12 1.75 3200 Invention 3 Inventive Steel b 1200 600 1000 60 3.52 1.80 4700 Comparative Material 3 Comparative Steel a 1200 700 950 60 3.74 1.75 2800 Comparative Material 4 Comparative Steel b 1200 700 950 60 3.98 1.76 3100 Comparative Material 5 Comparative Steel b 1200 800 950 60 4.08 1.75 2900

As shown in Table 2 above, the inventive material (1-3) manufactured with the steel composition and manufacturing conditions in accordance with the present invention is a comparative material prepared with emphasis and / or manufacturing conditions outside the scope of the present invention (1--1). Compared to 5), it is excellent in iron loss, magnetic flux density and permeability.

Example 2

C: 0.003%, Si: 0.95%, Mn: 0.25%, P: 0.025%, S: 0.003%, Al: 0.0005%, N: 0.003%, Sn: 0.08%, B: 0.0009%, and the rest of Fe and others. The steel slab composed of unavoidable impurities was heated to a temperature condition as shown in Table 3, followed by hot pressing. The hot rolled sheet was wound at a temperature condition as shown in Table 3, and then pickled.

The plate pickled as described above was cold rolled to a thickness of 0.50 mm, and then the cold rolled plate was annealed at 1000 ° C. for 1 minute in a dry atmosphere containing 20% hydrogen and 80% nitrogen for grain growth.

Iron loss, magnetic flux density, magnetic permeability and grain size of the steel sheet manufactured as described above were investigated, and the results are shown in Table 3 below.

Sample Number Slab reheating temperature (℃) Hot Rolled Sheet Winding Temperature (℃) Cold Rolled Annealing _Iron loss (W _15/50 ) W / kg Magnetic flux density (B ₅₀ ) Permeability (μ _1.5 ) Crystal grain size (㎛) Temperature (℃) Time (sec) Invention 4 1200 700 1000 60 3.21 1.77 4100 75 Comparative Material 6 1280 800 1000 60 3.71 1.74 3200 45

As shown in Table 3 above, the inventive material (4) manufactured with the steel composition and manufacturing conditions in accordance with the present invention is compared with the comparative material (6) manufactured with emphasis and / or manufacturing conditions outside the scope of the present invention. It is excellent in iron loss, magnetic flux density, and permeability.

In addition, it can be seen that the grain size of the invention material 4 was significantly increased as compared with that of the comparative material 6.

Example 3

Steel slabs having the components shown in Table 4 below were heated to 1200 ° C., hot rolled to a thickness of 2.1 mm, then wound up at 730 ° C., and cooled. The cooled hot rolled sheet was subjected to hot roll annealing or hot rolled sheet annealing under the conditions as shown in Table 5 below, followed by cold rolling to a final thickness of 0.50 mm after pickling, followed by final annealing in a mixed atmosphere of hydrogen and nitrogen. Then, after heating for 90 minutes at 800 ℃ after the stress relief annealing to quench, the magnetic permeability and texture were measured and the results are shown in Table 5 below.

In Table 5 below, the magnetic permeability (μ _1.5 ) indicates the magnetic permeability when the magnetic field is induced at a magnetic flux density of _1.5 Tesla, and the collective strength of the collective structure of the {200} plane and {110} plane, which is advantageous for magnetism, is shown. Intensity was measured.

Steel grade Chemical composition (% by weight) C Si Mn Al Sol.Al P S N Sn B B / N Invention steel c 0.003 0.25 0.21 0.0012 0.0007 0.081 0.003 0.0026 0.10 0.0008 0.30 d 0.002 0.23 0.23 0.0016 0.0010 0.080 0.004 0.0035 0.15 0.0012 0.34 Comparative steel c 0.003 0.24 0.22 0.0027 0.0023 0.082 0.003 0.0026 0.12 0.0028 1.07 d 0.004 0.21 0.24 0.0061 0.0055 0.079 0.004 0.0026 0.12 0.0032 1.23

Sample Number Steel grade Hot Rolled Annealing Temperature (℃) Final annealing Demand stress relief annealing Permeability (μ _1.5 ) Texture strength (P110 + P200) Temperature (℃) Time (sec) Invention 5 Invention steel c Not carried 850 60 practice 5860 3.2 Invention 6 Not carried 800 90 Not carried 4850 2.9 Comparative Material7 Not carried 600 60 Not carried 3610 2.1 Invention 7 Invention 950 900 90 practice 6200 3.4 Invention Material 8 850 950 90 practice 5620 3.0 Comparative Material 8 Comparative Steel c 850 950 90 practice 3840 2.3 Comparative Material 9 Comparison 850 950 90 practice 3250 1.9

As shown in Table 5, in the case of the comparative material (8-9) made of a comparative steel (c-d) of more than 0.5 ratio of B / N it can be seen that the permeability and texture strength is low.

On the contrary, in the case of the inventive material (5-8) made of the inventive steel (c-d) satisfying the conditions of the present invention, the steel component and the ratio of B / N are high in permeability and excellent in texture strength. In addition, it can be seen that the magnetic properties of the hot-rolled sheet annealing (invention material 7-8) are superior to those of the inventive material without the hot-rolling sheet annealing (invention material 5-6).

The same was true of demand stress annealing. However, it can be seen that the magnetic permeability and the texture strength of the comparative material (7) in which the present invention steel (c) was finally annealed at 600 ° C.

Example 4

C: 0.003%, Si: 0.62%, Mn: 0.32%, P: 0.069%, S: 0.003%, Al: 0.0006% (Sol.Al: 0.0003%), N: 0.0028%, Sn: 0.07%, B: A steel slab composed of 0.0011% and B / N in a ratio of 0.39 and the remaining Fe and other unavoidable impurities were heated to 1150 ° C., and then hot rolled to a rolling finishing temperature of 900 ° C., followed by winding at 650 ° C., followed by cooling. Next, it was pickled and cold rolled to a final thickness of 0.50 mm. The cold rolled sheet was finally annealed at a temperature of 1000 ° C. in an atmosphere of 20% hydrogen and 80% nitrogen. After the cutting process, the annealing was performed at 790 ° C. for 90 minutes under stress relieving annealing.

The material thus prepared had an iron loss (W _15/50 ) of 3.31 W / kg and a permeability (μ _1.5 ) of 5670. As a result of testing the properties of the material, the grain size was 70 µm, and the sum of the texture strengths of the {200} and {110} planes by the Horta equation was 3.9.

As described above, the present invention has the effect of providing a non-oriented electrical steel sheet having a low iron loss and excellent magnetic flux density and permeability.

In addition, the present invention is easy to magnetize due to the high permeability, thereby reducing the amount of copper wire used in the iron core can reduce the ratio of copper loss, and also skin pass rolling after the final annealing to secure magnetic properties It is possible to secure excellent magnetic properties without going through the effect that the manufacturing process is shortened.

Claims (6)

By weight%, C: 0.02% or less, Si: 1.0% or less, Mn: 0.5% or less, P: 0.15% or less, S: 0.02% or less, Sol.Al: 0.005% or less, N: 0.006% or less, Sn: Non-oriented electrical steel sheet containing 0.03-0.30%, B: 0.0004-0.0030%, balance Fe and unavoidable impurities, and having excellent magnetic properties satisfying a B / N ratio of 0.1-0.5. By weight%, C: 0.02% or less, Si: 1.0% or less, Mn: 0.5% or less, P: 0.15% or less, S: 0.02% or less, Sol.Al: 0.005% or less, N: 0.006% or less, Sn: The steel slab containing 0.03-0.30%, B: 0.0004-0.0030%, balance Fe and unavoidable impurities and satisfying the B / N ratio of 0.1-0.5 was reheated, hot rolled, and wound up to a temperature of 750 ° C or lower. Next, the method of producing a non-oriented electrical steel sheet having excellent magnetic properties after pickling the hot rolled sheet, followed by cold rolling, annealing at a temperature of 700-1050 ℃. The method of claim 2, wherein the heating temperature of the slab is 1100-1250 ℃. The method for manufacturing a non-oriented electrical steel sheet according to claim 2, wherein the cold rolled sheet is annealed and then processed, followed by stress relief annealing. By weight%, C: 0.02% or less, Si: 1.0% or less, Mn: 0.5% or less, P: 0.15% or less, S: 0.02% or less, Sol.Al: 0.005% or less, N: 0.006% or less, Sn: The steel slab containing 0.03-0.30%, B: 0.0004-0.0030%, balance Fe and unavoidable impurities and satisfying the B / N ratio of 0.1-0.5 was reheated, hot rolled, and wound up to a temperature of 750 ° C or lower. Next, after annealing the hot rolled sheet, pickling, followed by cold rolling, and then annealing at a temperature of 700-1050 ° C excellent non-oriented electrical steel sheet manufacturing method. The method of manufacturing a non-oriented electrical steel sheet according to claim 5, wherein the cold rolled sheet is annealed, processed, and then stress-annealed.