KR20060000490A - Manufacturing method for non-oriented electrical steel sheet having low core loss and high magnetic induction - Google Patents

Abstract

The present invention improves the texture of the steel sheet by adding Si, Al, Mn and Sn in an appropriate amount, and controlling the cracking temperature of the steel sheet at the appropriate temperature during hot rolling annealing and recrystallization annealing, thereby reducing the iron loss and high magnetic flux density. It relates to a method of manufacturing electrical steel sheet.

The present invention is by weight, C: 0.005% or less, S: 0.005% or less, N: 0.005% or less, Si: 1.2 to 2.3%, Al: 0.5 to 1.5%, Mn: 0.3 to 1.2%, Sn: 0.03 to Steel slab composed of 0.10%, remaining Fe and other impurities is reheated at 1050-1250 ℃, hot rolled to 1.8 ~ 3.0mm thickness, wound at 650 ~ 800 ℃, and hot rolled sheet at 800 ~ 1050 ℃ After annealing and pickling, cold rolling is performed once at 0.2 ~ 0.65mm thickness, heating at a temperature rising rate of 5 ° C./sec or more, and recrystallization annealing at 900-1100 ° C. for 30 to 300 seconds. This technical summary relates to a method for producing a non-oriented electrical steel sheet having a low magnetic flux density.

Non-oriented electrical steel sheet, magnetic flux density, iron loss, hot rolling, hot rolled sheet annealing, recrystallization annealing

Description

Manufacturing method for non-oriented electrical steel sheet having low core loss and high magnetic induction}

The present invention relates to a method for producing a non-oriented electrical steel sheet having a low iron loss and high magnetic flux density characteristics, and more particularly, a non-oriented electrical steel sheet having a low iron loss and a high magnetic flux density without adding Sb harmful to the human body. It relates to a method of manufacturing.

Since non-oriented electrical steel has excellent magnetic properties, it is widely used as an iron core material for electric machines such as various motors, small transformers, and ballasts, and is classified into two types. These include semi-process products, which must be subjected to stress relief annealing after demand processing, and fully-process products, which do not require stress relief annealing. The semi-process products are usually shipped in a modified state in the manufacturing process of steelmaking → continuous casting → slab reheating → hot rolling → winding → hot rolled sheet annealing → cold rolling → annealing → skin-pass rolling → insulation coating After purchasing a thin product and processing the product into the desired shape, stress relief annealing must be performed to obtain magnetic properties suitable for the product. On the other hand, pulley process products are shipped from the steelmaking process → continuous casting → slab reheating → hot rolling → winding → hot rolled sheet annealing → cold rolling → recrystallization annealing → insulation coating. It has the advantage that it can be used without.

In recent years, as the energy efficiency of electric devices has been increased and miniaturized, the demand for products having low iron loss and high magnetic flux density has been gradually increased even for electric steel sheets which are iron core materials. In general, the iron loss is expressed in W / kg as electrical loss (Watt) per weight (kg) of the iron core, that is, electrical energy loss caused by heat generation at a specific magnetic flux density and frequency. Therefore, the iron core material having a low iron loss is more preferable for manufacturing high-efficiency electric equipment. Accordingly, various methods have been proposed to provide a non-oriented electrical steel sheet having high magnetic flux density and low iron loss. US Pat. No. 4,204,890 proposes a method for producing a non-oriented electrical steel sheet having excellent magnetic properties such as high magnetic flux density and low iron loss containing Si, Al, Mn, Sb and the like. However, since the non-oriented electrical steel sheet is required to add Sb harmful to the human body, there is a disadvantage that a separate additional equipment is required in the steelmaking process.

The present invention is to manufacture a non-oriented electrical steel sheet having excellent low magnetic loss and high magnetic flux density characteristics according to a more simplified method after recrystallization annealing as described above, Sb harmful to the human body in the case of a pulley process material non-oriented electrical steel sheet It is an object of the present invention to provide a method for producing a non-oriented electrical steel sheet having a low iron loss and high magnetic flux density after recrystallization annealing without addition of a.

Low iron loss and high magnetic flux density according to the present invention for achieving the above object is a method for producing a non-oriented electrical steel sheet, by weight, C: 0.005% or less, S: 0.005% or less, N: 0.005% or less, Si : 1.2 ~ 2.3%, Al: 0.5 ~ 1.5%, Mn: 0.3 ~ 1.2%, Sn: 0.03-0.20%, Steel slab composed of remaining Fe and other impurities is reheated at 1050 ~ 1250 ℃, 1.8 ~ 3.0mm Hot rolled to thickness and wound at 650 ~ 800 ℃, hot rolled sheet annealed and pickled at 800 ~ 1050 ℃, cold rolled once to 0.2 ~ 0.65mm thickness, and heated at a temperature increase rate of 5 ℃ / sec. Recrystallization annealing for 30 to 300 seconds at 900 ~ 1100 ℃ temperature.

Hereinafter, the present invention will be described in detail.

The present inventors add Sn in an appropriate amount instead of adding Sb, and simultaneously control the cracking temperature during hot rolling annealing and the cracking temperature during recrystallization annealing, thereby facilitating grain growth during recrystallization annealing. The iron loss is low and the magnetic flux density of the non-oriented electrical steel sheet can be produced through research and experiments to complete the present invention.

The present invention is largely divided into steel slab composition step, hot rolling step, hot rolled sheet annealing step, cold rolling step and recrystallization annealing step. By controlling the process conditions in each step to provide a non-oriented electrical steel sheet having a low iron loss and high magnetic flux density after recrystallization annealing, the operation effect in each step will be described in detail.                     

[Steel slab composition stage]

Prior to the component composition step for steel slab production, steelmaking, molten steel and ingot or continuous casting process are usually preceded. First, in the steelmaking step, the content of C, N, S in the molten steel is controlled low, and an appropriate amount of Si, Al, Mn, Sn, etc. is added. Subsequently, the steel slab containing an appropriate amount of components is manufactured by performing a molten steel in the ingot or continuous casting process. Among the components of the slab steel of the present invention, C, N, and S are elements that interfere with grain growth, so it is necessary to control the content in the steelmaking step at a low level, and Si, Al, and Mn lower the iron loss and at the same time increase the magnetic flux density. In an appropriate ratio, a suitable amount is added into the steel, and Sn is added for the purpose of forming a grain structure of grains in the preferred direction during recrystallization annealing. The reason for limiting the composition range is as follows.

C: 0.005% or less

When C is excessively contained, slabs are formed during the manufacturing of the electrical steel sheet of the present invention, thereby inhibiting grain growth, and also causing magnetic aging during use as an iron core of an electric device. It is preferable to contain in a steel so that it may have a composition of 0.005% or less.

N: 0.005% or less

N tends to react with Al during the steel sheet manufacturing process of the present invention to form AlN precipitates, thereby suppressing grain growth, so that it has a minimum amount as much as possible. Therefore, the content of N is preferably 0.005% or less. .

S: 0.005% or less                     

In addition to C and N, S tends to react with Mn to form MnS, which is a fine precipitate, to suppress grain growth, so it is important to have a minimum amount as much as possible. desirable.

Si: 1.2 to 2.3%

If the Si content is less than 1.2wt%, the resistivity of the steel is small and the iron loss characteristics are not preferable. If the Si content is more than 2.30wt%, the excellent magnetic flux density is not obtained and the punchability is deteriorated. Not good to increase

Al: 0.5-1.5%

When the acid-soluble Al is less than 0.5wt%, the specific resistance of the steel is small, the iron loss characteristics are deteriorated, and if it is more than 1.5wt%, the cold rolling property is deteriorated.

Mn: 0.3 ~ 1.2%

Mn is also less than 0.3 wt% is not preferable because the specific resistance of the steel is small to deteriorate the iron loss characteristics, and if it is more than 1.2wt% roll load is increased to deteriorate cold rolling property.

Sn: 0.03-0.20%

Sn added to steel during steelmaking is an element that reduces (111) surface strength, which is harmful to magnetic properties.If the added amount is less than 0.03wt%, the effect of improving the magnetic flux density after recrystallization annealing is insignificant. Since there is no effect and only raises a raw material cost, it is preferable to add Sn in the quantity of 0.3-0.20 wt% in this invention.                     

In addition to the above components, the steel contains Fe and other unavoidable impurities. In the present invention, it is important not to add Sb. In order to add Sb that is harmful to human body, it is necessary not only to have a separate molten steel Sb input facility during steelmaking, but even if the magnetic flux density is improved by adding Sb, in the clean steel where C and N are extremely controlled, Sb is grain boundary This is because the hysteresis loss is increased due to excessive segregation and decrease of grain growth rate during recrystallization annealing, which can not take advantage of clean steel manufacturing.

[Hot Rolling Step]

The steel slab is charged into a heating furnace and reheated as a pretreatment step of the hot rolling step performed after the composition step. In this case, in order to facilitate hot rolling, the reheating temperature of the steel slab should be 1050 ° C. or higher, but if it exceeds 1250 ° C. Precipitates, which are harmful to iron loss characteristics such as AlN and MnS, are re-dissolved and tend to cause excessive generation of fine precipitates after hot rolling. Such fine precipitates are undesirable because they hinder grain growth and deteriorate iron loss characteristics. Therefore, in the case of the present invention, it is preferable to heat to a temperature of 1050 ~ 1250 ℃.

The hot rolling is performed as described above, and the operating conditions are performed according to a conventional method. In this case, in order to prevent excessive generation of an oxide layer of the hot rolled sheet, the finishing rolling temperature is preferably adjusted to 800 to 950 ° C. If the thickness of the hot rolled sheet is less than 1.8 mm, the shape of the hot rolled sheet becomes poor, which is not preferable. If the thickness of the hot rolled sheet exceeds 3.0 mm, a good texture cannot be obtained, and the magnetic flux density deteriorates.                     

Subsequently, the hot rolled sheet winding may be performed at a temperature of 800 ° C. or lower so as not to excessively generate an oxide layer in the hot rolled sheet, but at a temperature of 650 ° C. or higher for grain growth of the hot rolled sheet. After cooling in air in a coil state, or more preferably furnace cooling.

[Hot Rolled Sheet Annealing Step]

Subsequently, the hot rolled sheet is subjected to hot rolled sheet annealing so as to recrystallize the stretched grains in the center portion and to obtain a uniform grain distribution in the steel plate thickness direction. At this time, if the annealing temperature is lower than 800 ℃, the uniform grain distribution is not obtained, and thus the effect of improving the magnetic flux density and iron loss is insufficient. If the annealing temperature is higher than 1050 ℃, the (111) plane texture which is unfavorable to magnetic Increasing magnetic flux density deteriorates.

[Cold rolling stage]

Subsequently, the hot rolled sheet annealing plate is subjected to cold rolling after pickling. In this case, when rolling at a reduction ratio of less than 64%, rolling productivity is reduced, so it is preferable to roll once at a reduction ratio of 64% or more. At this time, if the cold rolling thickness is less than 0.20mm, the strength of the (111) plane, which is an unfavorable texture after annealing, is not preferable because the magnetic flux density decreases. If the thickness exceeds 0.65mm, the eddy current loss is increased with the increase of the plate thickness. This is not good because (eddy current loss) increases and total iron loss increases.

[Recrystallization Annealing Step]

In the recrystallization annealing step performed according to the above method, the annealing temperature is lower than 900 ℃, the crystal growth rate is low after recrystallization, the iron loss is deteriorated, if higher than 1100 ℃, the surface oxide layer increase rather than the advantage of crystal growth The iron loss and magnetic flux density characteristics are deteriorated due to the harmful effects, and therefore, it is preferable to anneal at 900 to 1100 ° C. At this time, the temperature increase rate influences the strength of the (200) plane, which is an advantageous structure in the steel sheet, to influence the iron loss characteristics and the magnetic flux density values. In order to improve these characteristics, the temperature increase rate is controlled at 5 ° C / sec or more. Preferably, the annealing time is adjusted to 30 to 300 seconds.

The steel sheet annealed in the recrystallization annealing step is processed immediately with organic, inorganic and organic-inorganic composite coatings or coated with other insulating coatings without going through the skin-pass rolling step. Punch into the desired product.

Hereinafter, although this invention is demonstrated more concretely, this invention is not limited only to these examples.

Example 1

To prepare a steel slab having the components shown in Table 1, the steel slab was heated at a temperature of 1160 ℃ and hot-rolled under the finish rolling temperature conditions of 890 ℃ to make a hot rolled plate to a thickness of 2.5mm, then 740 ℃ After winding up at temperature, it was cooled in air. The cold rolled hot rolled plate was subjected to hot rolled sheet annealing as shown in Table 2, followed by pickling, followed by cold rolling to a thickness of 0.35 mm, and then recrystallized annealing as shown in Table 2 below. The hot-rolled sheet annealing atmosphere was air, but may be an inert gas atmosphere such as nitrogen or argon. The recrystallization annealing atmosphere was atmosphere of 20% hydrogen and 80% nitrogen. The recrystallized annealing plate was coated with an insulating film of organic / inorganic composite, and then the magnetic properties, grain size, and (200) surface strength after cutting were investigated and the results are shown in Table 2 below. At this time, iron loss and W15 / 50 are energy loss consumed by heat when inducing magnetic flux density of 1.5 Tesla to iron core at AC of 50Hz, magnetic flux density, B50 is induced value at excitation force of 5000A / m, After the recrystallized annealing cross section of the specimen was etched with 3% nital (Nital) was measured by an Image Analyzer (Image Analyzer). The surface strength is represented by the aggregate structure strength according to the Horta equation. As the (200) surface strength increases or the (111) surface strength decreases, the magnetization becomes easier and the magnetic properties are improved.

Table 1

Steel grade Ingredient (% by weight) C Si Al Mn S N Sn Sb Invention steel A 0.003 1.2 0.7 0.5 0.003 0.002 0.05 0.00 B 0.005 1.5 0.6 0.6 0.003 0.003 0.06 0.00 C 0.003 1.8 0.5 0.6 0.005 0.002 0.07 0.00 D 0.002 1.7 0.5 0.7 0.004 0.002 0.05 0.00 E 0.003 1.6 0.6 0.8 0.003 0.003 0.06 0.00 F 0.004 1.7 0.5 0.7 0.003 0.003 0.07 0.00 G 0.003 1.5 0.7 0.6 0.003 0.002 0.05 0.00 Comparative steel A 0.006 ^* 1.8 0.5 0.6 0.003 0.003 0.06 0.00 B 0.003 1.0 ^* 0.7 0.6 0.003 0.002 0.07 0.00 C 0.003 2.5 ^* 0.7 0.6 0.003 0.002 0.05 0.00 D 0.003 1.7 0.3 ^* 0.7 0.003 0.002 0.06 0.00 E 0.003 1.5 0.6 0.2 ^* 0.003 0.003 0.05 0.00 F 0.003 1.6 0.5 0.7 0.006 ^* 0.003 0.06 0.00 G 0.003 1.7 0.8 0.6 0.003 0.006 ^* 0.07 0.00 H 0.003 1.7 0.8 0.6 0.003 0.003 0.21 ^* 0.00 I 0.003 1.7 0.8 0.8 0.003 0.003 0.02 ^* 0.00 J 0.002 1.7 0.8 0.8 0.003 0.002 0.00 0.05 ^{* *} : Conditions outside the scope of the present invention

[Table 2]

Sample Number Hot Rolled Plate Annealing Crack Temperature (℃) Recrystallization Annealing Crack Temperature (℃) Iron loss, W15 / 50 (W / kg) Magnetic flux density, B10 (T) Recrystallized Annealed Plate Grain Size (㎛) Recrystallized Annealing Plate (200) Recrystallized Annealing Plate (111) Surface Strength Steel grade Invention 1 1025 1025 2.32 1.74 160 1.58 4.52 Inventive Steel A Invention 2 800 900 2.35 1.73 150 1.56 4.56 Inventive Steel B Invention 3 950 950 2.30 1.74 152 1.59 4.57 Invention Steel C Invention 4 900 900 2.34 1.72 156 1.51 4.51 Inventive Steel D Invention 5 1050 1100 2.28 1.75 159 1.62 4.65 Inventive Steel E Invention 6 1030 1030 2.33 1.73 158 1.53 4.53 Inventive Steel F Invention 7 900 900 2.31 1.74 153 1.55 4.58 Invention Steel G Comparative Material 1 1070 ^* 1025 2.37 1.69 ^* 168 1.23 8.58 ^* Inventive Steel F Comparative Material 2 780 ^* 1025 3.12 ^* 1.67 ^* 156 0.38 ^* 4.69 Inventive Steel F Comparative Material 3 1025 1120 ^* 2.92 ^* 1.69 ^* 176 1.18 4.92 Inventive Steel F Comparative Material 4 1025 880 ^* 3.02 ^* 1.72 90 1.50 4.53 Inventive Steel F Comparative Material 5 1000 1000 3.30 ^* 1.73 85 ^* 1.55 0.55 Comparative Steel A Comparative Material 6 1050 1050 3.09 ^* 1.74 152 1.57 0.57 Comparative Steel B Comparative Material7 1000 1000 2.28 1.68 ^* 155 1.56 0.56 Comparative Steel C Comparative Material 8 1000 1000 3.06 ^* 1.74 154 1.55 0.55 Comparative Steel D Comparative Material 9 1030 1030 3.05 ^* 1.74 155 1.56 0.56 Comparative Steel E Comparative Material 10 1000 1000 3.35 ^* 1.73 77 ^* 1.55 0.55 Comparative Steel F Comparative Material 11 900 900 3.34 ^* 1.73 78 ^* 1.55 0.55 Comparative Steel G Comparative Material 12 930 930 3.29 1.75 155 1.62 0.62 Comparative Steel H Comparative Material 13 1000 1000 3.18 ^* 1.69 ^* 153 0.40 ^* 0.40 ^* Comparative Steel I Comparative Material14 1000 1000 3.32 ^* 1.73 88 ^* 1.55 0.55 Comparative Steel J

As shown in Table 1 and Table 2, it was found that the invention material (1-7) is superior in iron loss and magnetic flux density characteristics than the comparative material (1-14). Specifically, in Comparative Material 1, the components and recrystallization annealing conditions are within the scope of the present invention. However, when the hot rolled sheet annealing is excessively cracked, the texture of the (111) plane strongly develops, resulting in increased magnetic flux density. In Comparative Material 2, the crack temperature was insufficient during annealing of the hot rolled sheet. Therefore, high (100) surface strength was not obtained, and thus the magnetic flux density and iron loss deteriorated. In Comparative 3, the composition and hot-rolled sheet annealing conditions are within the scope of the present invention, but the excellent magnetic properties were not obtained because the grain size increased due to excessive crack temperature during recrystallization annealing, but the surface oxide layer was excessively formed. In case of 4, the crack temperature was insufficient during recrystallization annealing, and grain loss was poor, resulting in deterioration of iron loss characteristics. Comparative materials 5, 10, and 11 had C, S, and N contents in the range of the present invention, and the grain growth was low, so that excellent iron loss characteristics were not obtained. Also excellent iron loss characteristics were not obtained because they were added, while Comparative Material 7 was excellent in iron loss characteristics but inferior magnetic flux density when Si was added beyond the scope of the present invention. In addition, excellent iron loss characteristics were not obtained in Comparative Materials 8 and 9 in which Al and Mn were added below the present invention, respectively. Comparative material 12 is excellent in iron loss and magnetic flux density characteristics when the amount of Sn added exceeds the scope of the present invention, but the improvement of the texture due to the reduction of the (111) surface strength due to the addition of Sn no longer appears, thus increasing the manufacturing cost. On the contrary, the iron loss and magnetic flux density improvement effect due to the increase of Sn are saturated and thus not included in the present invention. In Comparative Material 13, when Sn was added below the range of the present invention, excellent magnetic flux density and iron loss characteristics were not obtained as a result of deterioration of the texture. In Comparative Material 14, when Sb was added to steel with extremely low C and N contents, grain growth was poor when recrystallization annealing due to excessive grain boundary segregation of Sb.

As described above, the present invention has an effect of providing an excellent non-oriented electrical steel sheet having low iron loss and high magnetic flux density after stress relief annealing. In addition, the present invention has the effect of ensuring excellent magnetic properties without the need for a separate molten steel Sb injection equipment in order to add Sb harmful to the human body during steelmaking.

Claims (4)

By weight%, C: 0.005% or less, S: 0.005% or less, N: 0.005% or less, Si: 1.2 to 2.3%, Al: 0.5 to 1.5%, Mn: 0.3 to 1.2%, Sn: 0.03 to 0.20%, The steel slab composed of the remaining Fe and other impurities is reheated at a temperature of 1050 to 1250 ° C, hot rolled to a thickness of 1.8 to 3.0mm, wound at a temperature of 650 to 800 ° C, and then annealed and pickled at a temperature of 800 to 1050 ° C. After the cold rolling to a thickness of 0.2 ~ 0.65mm, and recrystallized annealing for 30 to 300 seconds at a temperature of 900 ~ 1100 ℃ low iron loss, high magnetic flux density non-oriented electrical steel sheet manufacturing method. The method of claim 1, The hot rolling is a method of producing a non-oriented electrical steel sheet having a low iron loss and high magnetic flux density, characterized in that the finish rolling at 800 ~ 950 ℃. The method of claim 1, The cold rolling is a method of producing a non-oriented electrical steel sheet having a low iron loss and high magnetic flux density, characterized in that the rolling once with a rolling reduction of 64% or more. The method of claim 1, The recrystallization annealing is a method for producing a non-oriented electrical steel sheet having a low iron loss and high magnetic flux density, characterized in that the heating is performed at a temperature increase rate of 5 ° C / sec or more.