KR20100037705A - Non-oriented electromagnetic steel sheet with low iron loss and adequate workability, and manufacturing method therefor - Google Patents

Abstract

PURPOSE: A non-oriented electrical steel sheet with low iron loss and adequate workability and a method for manufacturing the same are provided to reduce energy loss when used as a motor iron core by controlling the thickness of an AL system nitride and an oxide layer. CONSTITUTION: A non-oriented electrical steel sheet with low iron loss and adequate workability comprises C 0.005 weight%, Si 4.0 weight% or less, P 0.1 weight% or less, S 0.005 weight% or less, Mn 0.1~1.0 weight%, Al 0.6~1.5 weight%, Cu 0.01~0.3 weight%, N 0.003 weight% or less, Ti 0.005 weight% or less, and the remainder consisting of Fe and impurities. The thickening layer exists within 0.2 micron depth from the surface. The thickening layer is composed of Al system nitride and oxide.

Description

Non-oriented electrical steel sheet with excellent workability and manufacturing method thereof {NON-ORIENTED ELECTROMAGNETIC STEEL SHEET WITH LOW IRON LOSS AND ADEQUATE WORKABILITY, AND MANUFACTURING METHOD THEREFOR}

The present invention relates to a non-oriented electrical steel sheet used as an iron core of an electric device such as a motor and a transformer, and a method of manufacturing the same. More particularly, the punching processability is achieved by optimizing the final annealing conditions to form an Al-based concentrated layer on the surface of the base material. An improved non-oriented electrical steel sheet and a method of manufacturing the same.

Recently, the reduction of energy consumption is strongly required from the standpoint of protecting the environment. As for the electric equipment, improvement of the electric consumption of the motor has become an important problem. In particular, many air conditioners and refrigerator compressor motors in continuous operation are required to be highly efficient. The fuel economy improvement is also actively promoted for automobiles, and electric vehicles using a motor as a driving force, and hybrid vehicles using a motor and a gasoline engine or a motor and a diesel engine as a driving force have been put into practical use.

Non-oriented electrical steel sheet is used as a material for the core of the stopper, such as a rotary device of a motor and a generator and a small transformer, and low low iron loss is required to improve the efficiency of the motor. In addition, high dimensional accuracy of each component constituting the motor is required for high rotational accuracy, low torque variation, and low vibration operation. Therefore, research is being conducted to improve workability while maintaining low iron loss to prevent electrical energy loss.

In order to improve the punchability of non-oriented electrical steel sheet, it is effective to have appropriate grains and hardness. Japanese Patent Laid-Open No. 2001-59145 has a technique for improving the workability by adjusting the Si, Al and Mn contents to optimize the hardness. Japanese Patent Laid-Open Publication No. 2002-220643 proposes a manufacturing method for improving processability by optimizing grain size by controlling the size and number of crystal grains of precipitates according to hot-rolled sheet annealing conditions. The method of manufacturing non-oriented electrical steel sheet with excellent punching workability by suggesting proper distribution of oxide inclusions on the surface is proposed, but the method of producing precipitates makes iron loss inferior, making it difficult to apply to high-quality non-oriented electrical steel sheet sensitive to iron loss change. There is.

The present invention is to solve the above problems by controlling the final annealing atmosphere and time of the non-oriented electrical steel sheet by adjusting the Al-based nitride and oxide thickening layer on the surface of the electrical steel sheet, the non-oriented electrical steel sheet with improved punchability without additional cost and Its main purpose is to provide the production method.

The non-oriented electrical steel sheet excellent in punchability according to the present invention for achieving the above object is C: 0.005% or less, Si: 4.0% or less, P: 0.1% or less, S: 0.005% or less, Mn: 0.1 to 1.0%, Al: 0.6 ~ 1.5%, Cu: 0.01 ~ 0.3%, N: 0.003% or less, Ti: 0.005% or less, consisting of residual Fe and other unavoidable impurities, and thickening composed of Al-based nitride and oxide The layer is characterized by being less than 0.2 μm from the surface. In addition, the Al-based oxide of the thickening layer is present in a layer of 0.05 ~ 0.2㎛ thickness, the Al-based nitride is characterized in that present in the Al-based oxide layer in the form of particles. The Al-based nitride is characterized in that it contains 70 to 80% of the total concentrated layer. The surface hardness of the electrical steel sheet is characterized in that Hv 200 ~ 220.

Method for producing a non-oriented electrical steel sheet with improved punching workability according to the present invention by weight% C: 0.005% or less, Si: 4.0% or less, P: 0.1% or less, S: 0.005% or less, Mn: 0.1 ~ 1.0%, Slabs made of Al: 0.6 ~ 1.5%, Cu: 0.01 ~ 0.3%, N: 0.003% or less, Ti: 0.005% or less and residual Fe and other unavoidable impurities are hot rolled, wound, hot rolled sheet annealed, pickled, After the cold rolling, the final annealing was performed at 1000 to 1100 ° C. for 40 to 60 seconds under the furnace atmosphere of Equation 1 to form a concentrated layer made of Al-based nitride and oxide of 0.2 μm or less from the surface.

(Formula 1) 100 × Al (%) + N ₂ > 145 (Al is 0.6 to 1.5%, and N ₂ is the ratio of N _{2 in} the furnace.)

In addition, the Al-based oxide is characterized in that the thickness of 0.05 ~ 0.2㎛ layer, the Al-based nitride is characterized in that present in the Al-based oxide layer in the form of particles. The slab reheating temperature is 1200 ℃ or less, The winding temperature is 700 ℃ or less, the hot rolled sheet annealing temperature is 1000 ~ 1100 ℃, annealing time is characterized in that 1 minute 30 seconds ~ 2 minutes 30 seconds.

The present invention is to properly control the thickness of the Al-based nitride and oxide layer on the surface by appropriately adjusting the final annealing conditions in the high-quality non-oriented electrical steel sheet, which can improve the workability when punching the customer, so that the energy loss when using the motor core It is possible to reduce the energy loss of the motor for the hybrid vehicle, in particular.

Hereinafter, the present invention will be described in detail.

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

[C: 0.005% or less]

C contains less than 0.004% by weight because it causes magnetic aging in the final product and degrades its magnetic properties during use.The lower the content of C, the better the magnetic properties. .

[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: 0.005% or less]

S is preferably managed low because it deteriorates the magnetic properties to suppress grain growth to form fine precipitates MnS and CuS, so the content is limited to 0.0005% or less.

[Mn: 0.1-1.0%]

When Mn is less than 0.1%, fine MnS precipitates are formed, which inhibits crystal 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 decreases, so it is added below 1.0%.

[Al: 0.6-1.5%]

Al is an important component in the present invention, and is an effective component for lowering eddy current loss by increasing specific resistance. If it is less than 0.6%, the Al-based nitride and oxide layers cannot be formed on the surface, and if it is more than 1.5%, the workability is deteriorated, and the magnetic enhancement effect is insignificant compared to the amount added, and therefore it is preferably limited to 1.5% or less.

[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 of addition is too small, the effect is insignificant, and if the amount of addition is too high, cracking may occur on the surface of the hot rolled sheet.

[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.

In order to improve punchability, a concentrated layer made of Al-based nitride and oxide is formed on the surface of the base material in the nitrogen atmosphere of the finish annealing process. This is to suppress the Al-based nitride and oxide as much as possible in the base material to improve iron loss, and to have the Al-based nitride and oxide thickening layer formed on the surface of the electrical steel sheet so as to have an appropriate surface hardness of the electrical steel sheet during punching processing. Preferably present within 0.2 μm from the surface. The iron loss of the steel sheet increases when present in excess of 0.2 μm as the surface.

As for the thickness of the Al type oxide layer formed in the base material surface, 0.05-0.2 micrometer is preferable. If the concentration is less than 0.2 μm, the thickening layer is excessively formed, which adversely affects the magnetism. If the concentration is less than 0.05 μm, it does not have sufficient surface hardness and does not have an effect of improving punchability.

The surface hardness of the steel sheet is preferably Hv 200 to 220. If the surface hardness is less than 200, burrs may occur at the edge of the base material, resulting in poor punching. If the value is greater than 220, burrs may be formed at the edge of the base material due to abrasion of the mold during punching. Burr can occur.

Method for producing a non-oriented electrical steel sheet improved punchability according to the present invention is as follows. The steel slab formed as mentioned above is reheated to 1200 degrees C or less which is normal conditions, and then hot rolled, wound up to 700 degrees C or less, and cooled in air. After the hot rolled sheet annealing process, to release the residual stress remaining in the hot rolled steel sheet, homogenizing the material of the base material. The wound hot rolled sheet is subjected to cold rolling after annealing and pickling.

If the temperature is too high when reheating the slab before hot rolling, the magnetic properties are lowered, so it is carried out at 1200 ° C or less. This is because the coiling temperature is performed at 700 ° C. or lower, but when the temperature is too high, the magnetic properties are lowered. Hot-rolled sheet annealing is performed in order to improve the magnetic property which precedes cold rolling after hot rolling. If the hot rolled sheet annealing temperature is too low, there is no effect. If the hot rolled sheet annealing temperature is too high, the crystal grains become large and the steel sheet breaks during cold rolling, so the hot rolled sheet annealing temperature is preferably 1000 to 1100 ° C., and the annealing time is 1 minute 30 seconds to 2 minutes 30 seconds. .

If the final annealing after cold rolling is less than 0.6% of Al or the amount of nitrogen in the atmosphere is not sufficient, a thick layer of dense nitride and oxide is not formed, and the Al-based oxide layer thickness is 0.2 μm or less under the conditions as shown in [Equation 1]. It is present in the form of a layer of, and the size is embedded in the Al-based oxide layer of the surface portion having an average diameter of 0.5 μm or less. At this time, the Al-based nitride is preferably 80 to 90% of the total concentrated layer. If the content of Al-based nitride is less than 80%, the hardness is low, and the punchability is worsened. If it is more than 90%, the hardness is too high, the punchability is worsened. The Al-based nitride and oxide thickening layer is appropriately formed to obtain the best workability.

100 * Al (%) + N2 (%)> 145 (Al is 0.6% or more, and N2 means the ratio of N2 in the furnace.)

Under the annealing atmosphere as described above, the final annealing is performed at a temperature range of 1000 to 1100 ° C. The reason for limiting the final annealing temperature range is that when the annealing temperature is less than 1000 ° C., the grain growth is insufficient and the magnetism is deteriorated. In addition, the rework time is preferably 40 to 60 seconds. During the final annealing, Al in the furnace and nitrogen in the furnace react in the annealing atmosphere to form a concentrated layer of Al nitride and oxide on the surface of the annealing plate. When the furnace time is less than 40 seconds, the Al nitride and oxide are When the layer is too thin, the surface hardness decreases, resulting in burrs at the edge of the material during processing, which is detrimental to workability. In the case of 60 seconds or more, the thickening layer made of Al-based nitride and oxide is excessively formed. Abrasion of the mold is formed during the punching process, causing burrs at the edges due to abrasion of the mold, causing lamination failure, and a major cause of deterioration of motor properties.

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

Example 1

By weight%, C: 0.0030%, Si: 3.1%, P: 0.008%, S: 0.001%, N: 0.0013%, Mn: 0.2%, Ti: 0.0015% and the Al content ratios of Table 1 below and the remaining Fe and The slabs composed of other unavoidable impurities were reheated to 1150 ° C. and hot rolled to 2.3 mm to prepare hot rolled steel sheets. The hot rolled steel sheet was wound at 700 ° C., cooled in air, subjected to hot roll annealing at 1050 ° C. for 2 minutes, and cold rolled to 0.5 mm after pickling, and the atmosphere shown in Table 1 below at 1050 ° C. for 50 seconds. After the final annealing under the conditions, punching was performed. Electron scanning microscope (SEM) was used to measure the thickness of the Al-based nitride and oxide layers of the surface layer, and Vickers hardness was measured to check the mechanical properties of the surface. The height of the burr was measured using a micrometer.

Sample Number Al content (%) % N2 in furnace 100 * Al (%) + N2 (%) Surface Hardness (Hv1) Al-based oxide / nitride layer thickness (㎛) Burr Height (μm) division One 0.5 95 145 201 0.12 98 Comparative Material 1 2 0.5 90 140 192 0.11 101 Comparative Material 2 3 0.5 80 130 184 0.10 104 Comparative Material 3 4 0.5 70 120 179 0.04 121 Comparative Material 4 5 0.7 95 165 213 0.15 41 Invention 1 6 0.7 80 150 201 0.14 68 Invention 2 7 0.7 75 145 198 0.14 77 Invention 3 8 0.7 50 120 186 0.10 121 Comparative Material 5 9 0.7 20 90 182 0.08 175 Comparative Material 6 10 0.8 80 160 211 0.015 50 Invention 4 11 0.8 70 150 202 0.14 68 Invention 5 12 0.8 50 130 184 0.11 104 Comparative Material7 13 0.8 30 110 174 0.09 139 Comparative Material 8 14 1.2 60 180 221 0.16 14 Invention 6 15 1.2 50 170 215 0.16 30 Invention Material7 16 1.2 30 150 203 0.14 68 Invention Material 8 17 1.2 20 140 198 0.14 86 Comparative Material 9

In the above results, when the Al content is 0.5%, it can be seen that the burr height has a considerably high value near 100 μm regardless of the nitrogen content. The reason for the high burr height is thought to be that Al-based nitride and oxide layers are generated on the surface and the hardness value is lowered. In the case where the Al content is more than 0.7%, it can be seen that as the amount of nitrogen in the annealing atmosphere increases, the thickness of the concentrated layer composed of Al-based nitrides and oxides generally increases, thereby increasing hardness and improving workability accordingly. It was found that the height of the burrs decreased. Therefore, in order to secure proper workability, the Al content must be at least 0.6%, appropriate nitrogen must exist according to the Al content, and the nitrogen ratio in the furnace can satisfy 100 * Al (%) + N2 (%)> 145. It can be seen that the punchability is improved when.

[Example 2]

By weight, C: 0.0030%, Si: 3.2%, P: 0.020%, S: 0.001%, N: 0.0013%, Al: 0.8%, Mn: 0.2%, Ti: 0.0015%, and the rest Fe and other unavoidable The slab composed of impurities was reheated to 1150 ° C. and then hot rolled to 2.3 mm to prepare a hot rolled steel sheet. The hot rolled steel sheet was wound at 700 ° C., cooled in air, and subjected to hot roll annealing at 1050 ° C. for 2 minutes, followed by cold rolling to a thickness of 0.5 mm. The final annealing atmosphere was 80% nitrogen and 20% hydrogen. The annealing temperature and time were adjusted under the conditions of Table 2 below. After the final annealing was cut to 60mm × 60mm to measure the magnetism in the rolling and rolling perpendicular direction. In addition, an electron scanning microscope (SEM) was used to measure the thickness of the thick layer of Al-based nitride and oxide of the surface layer, and Vickers hardness was measured to check the mechanical properties of the surface.

Sample Number Annealing Temperature (℃) Annealing time (seconds) Grain size (㎛) Surface Hardness (Hv1) Thickness of Al-based Oxidation / Nitride Layer (㎛) The iron loss _{(W 15/50; W /} Kg) Remarks One 980 40 130 215 0.14 2.31 Comparative example 2 980 50 133 226 0.15 2.28 Comparative example 3 980 60 135 225 0.16 2.29 Comparative example 4 1030 40 130 205 0.15 2.15 Inventive Example 5 1030 60 133 206 0.16 2.16 Inventive Example 6 1030 80 135 225 0.35 2.13 Comparative example 7 1050 40 153 207 0.17 2.11 Inventive Example 8 1050 50 152 208 0.19 2.1 Inventive Example 9 1050 60 155 210 0.2 2.08 Inventive Example 10 1050 80 176 223 0.32 2.11 Comparative example 11 1110 80 182 235 0.4 2.1 Comparative example 12 1110 90 188 245 0.42 2.13 Comparative example

( _Iron loss (W _15/50 ) is the loss of 1.5Tesla magnetic flux density at 50Hz frequency)

In case of samples No. 6 and 10, the residence time in the furnace was too long, so that the Al-based nitride and oxide layers were formed too thick, the surface hardness was excessively increased. In addition, in the case of Sample Nos. 11 and 12, although the annealing temperature was too high, the concentration of Al-based nitrides and oxides was excessively formed, resulting in inferior machinability. Although the Al-based nitride and oxide layers are formed, the workability is excellent, but the annealing temperature is too low, so that the grain growth does not occur sufficiently, and the magnetism is inferior. As a result, when the annealing temperature is set to 1030 ° C or 1050 ° C and the working time is 40 to 60 seconds, the thickness of the Al-based nitride and oxide layers is appropriate, and the surface hardness favorable to workability is obtained, and the iron loss is maintained. have.

Claims (7)

C: 0.005% or less, Si: 4.0% or less, P: 0.1% or less, S: 0.005% or less, Mn: 0.1 to 1.0%, Al: 0.6 to 1.5%, Cu: 0.01 to 0.3%, N: It is 0.003% or less, Ti: 0.005% or less, and is made of residual Fe and other inevitable impurities, and an enriched layer made of Al-based nitride and oxide exists within 0.2 탆 depth from the surface. Oriented electrical steel sheet. The method of claim 1, The Al-based oxide of the thickening layer is present in a layer of 0.05 ~ 0.2㎛ thickness, Al-based nitride is a non-oriented electrical steel sheet excellent in punchability, characterized in that present in the Al-based oxide layer in the form of particles. The method according to claim 1 or 2, The non-oriented electrical steel sheet excellent in punchability, characterized in that the Al-based nitride contains 70 to 80% of the total concentrated layer. The method of claim 1, The non-oriented electrical steel sheet excellent in punchability, characterized in that the surface hardness of the electrical steel sheet is Hv 200 ~ 220 C: 0.005% or less, Si: 4.0% or less, P: 0.1% or less, S: 0.005% or less, Mn: 0.1 to 1.0%, Al: 0.6 to 1.5%, Cu: 0.01 to 0.3%, N: After reheating the slab which is 0.003% or less, Ti: 0.005% or less, and is made of residual Fe and other inevitable impurities, it is subjected to hot rolling, winding, hot rolled sheet annealing, pickling, and cold rolling, The final annealing at 1000 ~ 1100 ℃ for 40 to 60 seconds to form a concentrated layer of Al-based nitride and oxide at a depth of 0.2 ㎛ or less from the surface of the excellent non-oriented electrical steel sheet manufacturing method characterized in that the punchability. 100 x Al (%) + N ₂ (%)> 145 (Al is 0.6 to 1.5%, and N ₂ is the ratio of N _{2 in} the furnace.) The method of claim 5, The Al-based oxide of the thickening layer is present in a layer of 0.05 ~ 0.2㎛ thickness, the Al-based nitride is produced in the punchable non-oriented electrical steel sheet, characterized in that present in the Al-based oxide layer in the form of particles Way. The method of claim 5, The slab reheating temperature is 1200 ℃ or less, the winding temperature is 700 ℃ or less, the hot rolled sheet annealing temperature is 1000 ~ 1100 ℃, annealing time is 1 minute 30 seconds ~ 2 minutes 30 seconds Method for producing this excellent non-oriented electrical steel sheet.