KR101051747B1 - Method for manufacturing non-oriented electrical steel sheet having excellent magnetic properties - Google Patents

Abstract

The present invention relates to an electric steel sheet having excellent magnetic properties used as an iron core of an electric device such as a motor and a transformer, and a method of manufacturing the same.

In the present invention, C: 0.005% or less, Si: 4.0% or less, P: 0.1% or less, S: 0.001% or less, Mn: 0.1 to 1.0%, Al: 0.45 to 1.5%, Cu: 0.01 to 0.3 by weight% %, N: 0.003% or less, Ti: 0.005% or less, and depending on the Al content is characterized in that it contains Sn as shown in the following [Formula 1].

800> Sn (ppm)> 285 x Al (wt%)-125

The present invention can reduce the energy loss by using the iron core of the motor by reducing the iron loss by optimizing the amount of Sn and the amount of Sn according to the dew point and Al content during final annealing in high-quality non-oriented electrical steel sheet.

Description

Method for manufacturing non-oriented electrical steel sheets having excellent magnetic property

The present invention relates to a method of manufacturing an electrical steel sheet having excellent magnetic properties used as an iron core of an electric device such as a motor and a transformer.

As industrialization continues worldwide, demand for motors and transformers is increasing. In particular, demand for high efficiency, high value-added motors and transformers is gradually increasing as environmental pollution prevention and energy saving are required. Accordingly, efforts have been made to increase the efficiency of electrical steel sheets used as iron core materials for motors and transformers.

In order to increase the efficiency of electrical steel sheet, the increase of the magnetization value and the iron loss due to the excitation current has been reduced by increasing the Si alloy element, and recently, the iron loss by increasing the Al alloy element due to the limitation of Si input due to the inferior rolling property Has been reduced.

However, an increase in Al and a decrease in impurity elements such as S have been found to increase the surface reactivity, thereby producing Al-based nitrides and oxides under the surface layer during final annealing, thereby worsening iron loss. Therefore, in order to prevent the deterioration of iron loss caused by this, a study has been conducted such as adding a trace element, making a surface Al or Si enriched layer, or controlling the content of S.

For example, Japanese Patent Application Laid-Open Nos. 1998-183310 and 2001-140018 disclose techniques for suppressing subsurface nitride by forming a dense Al or Si thick layer of about 1 µm by improving the surface roughness by sufficiently pickling. In addition, Japanese Patent 2006-241563 has an internal steam partial pressure ratio of 0.3 to 0.5 up to 650 degrees, but at a predetermined annealing crack temperature of 650 degrees, the steam hydrogen partial pressure ratio is adjusted to between 0.1 and 0.3 to provide SiO ₂ and 2-20 nm. A technique for improving iron loss by forming an MnO layer to prevent subsurface precipitates is disclosed. In addition, Japanese Patents 1998-317111 and 2000-328207 disclose a technique for preventing subsurface nitriding by adding a trace element according to the content of S. When S is 10 ppm or less, Sb or Sn is added to form Al-based oxides to form nitrides. I tried to improve the iron loss by preventing.

However, when the Al thickening layer is used for the surface layer, nitrogen absorption by the Al thickening layer proceeds, which is likely to infer the adhesion of the coating, and in order to make the thickening layer, Al must be increased. Workability problems are likely to occur. In the early stage of increasing the hydrogen partial pressure ratio of steam, a technique of improving the iron loss by forming a SiO ₂ layer has difficulty in operating a facility by setting a region where the partial pressure is different in a continuous heating zone where hydrogen is introduced. In addition, in the case of the patent using a trace element such as Sb, Sn, there is a problem in the field application because it does not specify the Al content and atmosphere conditions inside the steel, which is the main cause of subsurface nitriding.

The present invention was devised to solve the above problems. In order to prevent magnetic deterioration due to subsurface nitriding and oxides occurring during the final annealing process, the dew point is controlled to be low, and the amount of Sn added is appropriate for the magnetic properties. It is an object to obtain this excellent non-oriented electrical steel sheet.

     The present invention, in order to achieve the above object, by controlling the Sn amount of the non-oriented electrical steel sheet containing Al and the dew point of the final annealing furnace, the non-oriented electrical steel sheet excellent magnetic properties by suppressing the subsurface nitriding and oxide of the final product sheet To get.

delete

delete

delete

delete

The manufacturing method of the present invention, In the method of manufacturing a non-oriented electrical steel sheet which is completed by the reheating and hot rolling of the slab, followed by hot rolling annealing, cold rolling, final annealing,
The slab is more than C: 0% and 0.005% or less, Si: more than 0% and 4.0% or less, P: more than 0% and 0.1% or less, S: more than 0% and less than 0.001%, Mn: 0.1 to 1.0%, Al : 0.45 ~ 1.5%, Cu: 0.01 ~ 0.3%, N: 0% or more and 0.003% or less, Ti: 0% or more and 0.005% or less, and according to Al content, it is composed of a composition containing Sn as shown in Equation 1 below. The final annealing is carried out in an atmosphere consisting of hydrogen and nitrogen, but characterized in that the dew point is managed to be -10 degrees or less. It is done.
800> Sn (ppm)> 285 x Al (wt%)-125
In addition, the maximum value of subsurface nitrogen of the steel sheet is controlled to 5% or less when observed by glow discharge spectroscopy (GDS), and the depth at which surface oxygen is reduced to 50% when observed by GDS is controlled to 0.075 μm or less. Characterized in that.

The present invention can reduce the energy loss by using the iron core of the motor by reducing the iron loss by optimizing the amount of Sn and the amount of Sn according to the dew point and Al content during final annealing in high-quality non-oriented electrical steel sheet.

Hereinafter, the present invention will be described in more detail.

First, look at the reasons for limiting the components of the non-oriented electrical steel sheet of the present invention. The content below is by weight.

[C: 0.005% or less]

C is contained at 0.004% by weight or less because it causes magnetic aging in the final product, and lowers the magnetic properties during use.The lower the content of C, the better the magnetic property. .

[Si: 4.0% or less]

Si is a component that decreases the eddy current loss during iron loss by increasing the specific resistance, and if it is added in excess of 4.0%, it is preferable to limit it to 4.0% or less because cold rolling is poor.

[P: 0.1% or less]

P is added to increase the resistivity, improve the texture, and improve the magnetism. If excessively added, cold rolling is deteriorated, so it is preferable to limit it to 0.1% or less.

[S: 0.001% or less]

S is preferably managed low because it forms fine precipitates MnS and CuS and suppresses grain growth to deteriorate magnetic properties, so the content is limited to 0.001% or less.

[Mn: 0.1-1.0%]

If Mn is present at less than 0.1%, fine MnS precipitates are formed to inhibit grain growth, thereby deteriorating magnetism. Therefore, when 0.1% or more exists, coarse MnS is formed and S component can be prevented from being precipitated by CuS which is a finer precipitate. However, when Mn increases, the magnetic content is decreased, so it is added below 1.0%.

[Al: 0.45-1.5%]

Al is an effective component to lower the eddy current loss by increasing the specific resistance. In the case of less than 0.45%, AlN is finely precipitated to deteriorate the magnetism, and in the case of more than 1.5%, the workability is degraded.

[Cu: 0.01-0.3%]

Cu is an element added to improve the corrosion resistance and to promote the formation of coarse Mn (Cu) S precipitates instead of the fine MnS precipitates to grow grains and to develop a texture favorable for magnetic. If the amount is too small, the effect is insignificant, and if the amount is too large, cracking may occur on the surface of the hot rolled sheet, so it is preferable to limit the amount to 0.01 to 0.3%.

[N: 0.003% or less]

N is formed to contain fine and long AlN precipitate inside the base material to suppress grain growth, so it is contained less, it is preferable to limit to 0.003% or less in the present invention.

[Ti: 0.005% or less]

Ti inhibits grain growth by forming fine TiN and TiC precipitates, and when added in excess of 0.005%, many fine precipitates occur and worsen the magnetic structure.

In addition to the above composition, the remainder consists of Fe and other inevitable impurities.

The slabs having the composition as described above are subjected to hot rolling, winding and hot rolled sheet annealing, followed by pickling and cold rolling, followed by final annealing. At this time, the hot-rolled sheet annealing is performed to improve the texture of the final annealing plate for the high-grade electrical steel sheet without phase transformation, and immediately after the annealing to remove the scale of the surface layer to ensure the surface quality.

After cold rolling, the rolling oil present on the surface is degreased and finally annealed. This process produces the final product, which is annealed in an atmosphere composed of hydrogen and nitrogen because surface quality is important. Since hydrogen is included in the final annealing, Fe or Si-based oxides are mostly reduced, and some Al is oxidized or nitrided. In general, Al oxides are distributed in the surface layer, and Al nitrides are formed in angular agglomerates and in the surface layer and under the surface layer, both of which impede the movement of the magnetic domain, adversely affecting iron loss, and inferior coating adhesion. . In the case of Al oxide, if the dew point is managed low, it is suppressed. Particularly, if the dew point is -10 degrees or less, the oxygen partial pressure is lowered, so that little oxide is generated. However, if the dew point falls below a certain temperature, the possibility of nitride formation due to relative absorption is increased.

In particular, when the dew point is low, the Al content is relatively high, and the S content is low, and the surface reactivity is good, nitrogen penetrates under the surface layer to deteriorate the magnetic properties. Therefore, when the surface precipitation element is added, such as Sn, the surface reactivity may be lowered, and thus, the magnetic property may be improved by preventing further nitriding. When Al is 0.45% or less in the steel, almost no adsorption occurs, and the higher Al is, the lower the surface reactivity is. Therefore, the amount of Sn according to Al should be increased as shown in Equation 1 below. It is effective to secure the magnetism. If the amount of Sn is over 800ppm, the magnetism deteriorates due to delay of grain growth.

 800> Sn (ppm)> 285 x Al (wt%)-125

As a method for analyzing the surface layer in a short time, there is a method of analyzing the content of elements by depth through surface evaporation such as glow discharge spectroscopy (GDS). When the surface layer of the non-oriented electrical steel sheet was observed by the GDS, the maximum nitrogen content of the surface layer was 5% or less when manufactured according to the above conditions. In the case of oxygen, the maximum value is mostly observed at 100% on the surface, and then tends to decrease rapidly with depth. Therefore, it is meaningful how rapidly it decreases with depth rather than the maximum value of oxygen content. When Sn is appropriately added according to Al content according to [Formula 1] and excellent in magnetism, the time when the oxygen content is 50% is 0.075 μm or less.

Hereinafter, the present invention will be described in more detail by way of examples.

By weight, C: 0.0030%, P: 0.012%, S: 0.0006%, N: 0.0013%, Mn: 0.17%, Ti: 0.0015% and the remaining Fe and other unavoidable impurities and Al, Si, Sn as shown in Table 1 The slab was prepared by reheating to 1130 ℃ and hot rolled to 2.3mm to prepare a hot rolled steel sheet. At this time, Al + Si values were kept the same in order to eliminate the iron loss caused by the difference in resistivity. The hot rolled steel sheet was wound at 650 ° C., cooled in air, hot rolled sheet annealed at 1040 ° C. for 2 minutes, and cold rolled to 0.35 mm after pickling, changing the dew point to -40 to -5 degrees. After the final annealing in 20% hydrogen and 80% nitrogen for 10 seconds at 1040 ℃, magnetic and surface analysis was performed. Magnetic measurements were averaged by measuring in the rolling direction and the right angle direction using a 60 × 60 mm ² size plate measuring instrument, and the surface was analyzed the fraction of nitrogen and oxygen according to the depth using GDS.

Table 1 shows the iron loss and surface analysis results according to the dew point and alloy components.

TABLE 1

sample
number dew point Steelmaking component Subsurface Nitrogen Maximum (%) Oxygen 50% penetration depth (μm) Iron loss division Al Si Sn 2 -40 0.46 3.65 120 4 0.047 2.16 Invention 2 3 -40 0.81 3.41 0 10.5 0.051 2.35 Comparative Material 1 4 -40 0.82 3.42 55 9 0.062 2.32 Comparative Material 2 5 -41 0.80 3.38 90 7.5 0.058 2.3 Comparative Material 3 6 -42 0.83 3.40 120 4 0.053 2.19 Invention 3 7 -40 0.82 3.40 200 2.5 0.049 2.12 Invention 4 8 -40 1.21 3.03 150 7 0.051 2.35 Comparative Material 4 9 -40 1.09 3.08 210 3.5 0.047 2.13 Invention 5 10 -40 1.23 3.01 304 3 0.049 2.1 Invention 6 11 -40 1.45 2.66 150 6.5 0.051 2.31 Comparative Material 5 14 -40 1.54 2.70 800 3 0.051 2.31 Comparative Material 6 15 -40 1.50 2.65 1000 3.5 0.050 2.32 Comparative Material7 17 -26 0.80 3.38 90 7 0.070 2.31 Comparative Material 9 18 -22 0.82 3.40 200 2 0.073 2.13 Invention Material 9 19 -23 1.21 3.03 150 6.5 0.069 2.34 Comparative Material 10 20 -18 1.09 3.08 210 4 0.071 2.22 Invention 10 21 -23 1.45 2.66 150 6 0.072 2.33 Comparative Material 11 23 -10 0.45 3.70 0 4 0.180 2.31 Comparative Material 12 24 -8 0.46 3.65 120 2.5 0.170 2.35 Comparative Material 13 25 -4 0.81 3.41 0 4.5 0.160 2.33 Comparative Material14 26 -5 0.80 3.38 90 4 0.180 2.31 Comparative Material 15 27 -5 0.83 3.40 120 3.5 0.170 2.31 Comparative Material 16 28 -5 0.82 3.40 200 2.5 0.180 2.32 Comparative Material17 29 -6 1.21 3.03 150 4.5 0.210 2.35 Comparative Material 18 30 -5 1.09 3.08 210 3 0.180 2.32 Comparative Material 19 31 -2 1.23 3.01 304 2.5 0.170 2.31 Comparative Material 20 32 -8 1.45 2.66 150 4 0.170 2.33 Comparative Material21 33 -6 1.60 2.70 250 4.5 0.200 2.41 Comparative Material 22 34 -5 1.55 2.71 320 3 0.170 2.4 Comparative Material 23 35 -5 1.50 2.65 400 3.5 0.170 2.41 Comparative Material 24

1) Final annealing furnace dew point measured by chilled mirror type dew point meter

2) Maximum nitrogen in the depth distribution graph of nitrogen as measured by GDS

3) Depth at which the fraction of oxygen reaches 50% as measured by GDS

In general, if the dew point is higher than -10 degrees, the amount of nitride decreases as in Comparative Materials 12 to 23, but the oxide loss penetrates deeply and the iron loss worsens. If the dew point is lower than -10 degrees, the iron loss is changed according to the alloy composition. As in Inventive Material 2, when Al is 0.46% and the relative amount of Al is small, the nitrogen value under the surface is low and the iron loss is improved.

This is because most of the nitride is AlN, so if the amount of Al decreases, the probability of forming nitride in the river decreases. In the case where Al is higher than that, the maximum nitrogen value in the surface layer changes according to the amounts of Al and Sn. As the amount of Al increases and the Sn decreases, the nitrogen value in the surface layer increases. When the Al value is 0.8% and the Sn value is 120ppm or more, Al is 1.2% or more, 200ppm or more, Al 1.5% is more than 250ppm magnetism was good. As the amount of Al increases, the amount of the appropriate Sn increases because the absorption is better as the amount of Al increases.

Therefore, Sn has an excellent magnetic property when the value of the larger than 285 x Al (wt%)-125 by custom calculation of the experimental results. In the case of the excellent magnetic material, the maximum subsurface nitrogen was 5 or less, and the oxygen penetration depth was 0.075 μm or less. As in Comparative Materials 6 and 7, Sn tends to deteriorate in the case of more than 800 ppm, which is thought to be because Sn impairs grain growth.

Claims (7)

delete delete delete In the method of manufacturing a non-oriented electrical steel sheet which is completed by the reheating and hot rolling of the slab, followed by hot rolling annealing, cold rolling, final annealing, The slab is more than C: 0% and 0.005% or less, Si: more than 0% and 4.0% or less, P: more than 0% and 0.1% or less, S: more than 0% and less than 0.001%, Mn: 0.1 to 1.0%, Al : 0.45 ~ 1.5%, Cu: 0.01 ~ 0.3%, N: 0% or more and 0.003% or less, Ti: 0% or more and 0.005% or less, and according to Al content, it is composed of a composition containing Sn as shown in Equation 1 below. , The final annealing is carried out in an atmosphere consisting of hydrogen and nitrogen, the manufacturing method of the non-oriented electrical steel sheet having excellent magnetic properties, characterized in that the dew point is managed to be less than -10 degrees. 800> Sn (ppm)> 285 x Al (wt%)-125 5. The method of claim 4, The hot rolled sheet annealing is a method of producing an excellent non-oriented electrical steel sheet, characterized in that the surface of the scale in the pickling bath immediately after annealing. 5. The method of claim 4, A method for producing non-oriented electrical steel sheet having excellent magnetism, characterized in that the maximum value of nitrogen under the surface of the steel sheet is controlled to 5% or less when observed by GDS. 5. The method of claim 4, A method for producing non-oriented electrical steel sheet having excellent magnetism, characterized by controlling the depth at which the oxygen under the surface of the steel sheet is reduced to 50% when observed with GDS.