KR100890812B1 - A electrical steel sheet manufacturing method having low iron loss and high magnetic property - Google Patents

Abstract

The present invention relates to the production of electrical steel sheet, more specifically, Si, Al, Mn and P is added in an appropriate amount, the hot rolled sheet annealing and recrystallization annealing by controlling the cracking temperature of the steel sheet at an appropriate temperature texture of the steel sheet The purpose of the present invention is to provide a method for manufacturing non-oriented electrical steel sheet having low iron loss and high magnetic flux density,

In order to achieve the above object, by weight%, C: 0.005% or less, S: 0.005% or less, N: 0.005% or less, Si: 1.5 to 3.0%, Al: 0.5 to 1.5%, Mn: 0.3 to 1.2%, P: 0.03 ~ 0.14%, Si + 20 * P <4.5 and steel slabs composed of remaining Fe and other impurities are reheated at 1050 ~ 1250 ℃, hot rolled to 1.8 ~ 3.0mm thickness and wound at 650 ~ 800 ℃ Then, after hot-rolled sheet annealing and pickling at 900 ~ 1050 ℃ temperature, cold rolling once to 0.2 ~ 0.65mm thickness, heated at a temperature rising rate of 10 ℃ / sec ~ 50 ℃ / second 30 ~ at 900 ~ 1100 ℃ temperature Recrystallization annealing for 300 seconds.

Non-oriented electrical steel sheet, high magnetic flux density, low iron loss, non-oriented electrical steel sheet of pulley process material, P, proper component system design, recrystallization annealing

Description

A electrical steel sheet manufacturing method having low iron loss and high magnetic property

The present invention relates to the production of electrical steel sheet, more specifically, Si, Al, Mn and P is added in an appropriate amount, the hot rolled sheet annealing and recrystallization annealing by controlling the cracking temperature of the steel sheet at an appropriate temperature texture of the steel sheet By improving the low iron loss and high magnetic flux density relates to a method for producing a non-oriented electrical steel sheet.

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 are semi-process products that must be subjected to stress relief annealing after demand processing and fully-process products that 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 the product is purchased and processed into the desired shape, stress relief annealing must be performed to obtain the magnetic properties 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 of the prior art as described above is required to add Sb harmful to the human body has a problem that a separate additional equipment is required in the steelmaking process.

Therefore, the present invention is to solve the problems of the prior art described above, to manufacture a non-oriented electrical steel sheet having excellent low magnetic loss and high magnetic flux density characteristics after recrystallization annealing in the production of non-oriented electrical steel sheet according to a more simplified method In the case of a non-oriented electrical steel sheet of pulley process material, a low component and high magnetic flux density are required to produce non-oriented electrical steel sheet having low iron loss and high magnetic flux density after recrystallization annealing through the design of an appropriate component system in which P is added to steel. It is an object of the present invention to provide a method for producing non-oriented electrical steel sheet.

The method for producing a non-oriented electrical steel sheet having a low iron loss and high magnetic flux density according to the present invention for achieving the above object is, in weight%, C: 0.005% or less, S: 0.005% or less, N: 0.005% or less, Si: A steel slab composed of 1.5 to 3.0%, Al: 0.5 to 1.5%, Mn: 0.3 to 1.2%, P: 0.03 to 0.14%, Si + 20 * P <4.5, and the remaining Fe and other impurities was formed at 1050 to 1250 ° C. Re-heated at 1.8 ~ 3.0mm, hot rolled and wound at 650 ~ 800 ℃, hot rolled annealed and pickled at 900 ~ 1050 ℃, cold rolled once at 0.2 ~ 0.65mm thickness, 10 ℃ / It is characterized by consisting of recrystallization annealing for 30 to 300 seconds at a temperature of 900 ~ 1100 ℃ by heating at a temperature increase rate of seconds ~ 50 ℃ / second.

In the process of the present invention described above, the hot rolling is characterized in that the finish rolling is carried out at 800 ~ 950 ℃, the cold rolling is characterized in that rolling once with a rolling reduction of 64% to 85%.

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

In the present invention, by adding an appropriate amount of P, simultaneously controlling the cracking temperature during hot rolling annealing and the cracking temperature during recrystallization annealing, grain growth is facilitated during recrystallization annealing, and an iron structure is low due to the development of a texture that is advantageous for magnetism. The non-oriented electrical steel sheet with high magnetic flux density can be manufactured.

The present invention described above is largely composed of the 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 a high magnetic flux density after recrystallization annealing, the effect of each step will be described in detail below.

[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, P, 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. At this time, C, N, S among the components of the slab steel of the present invention is an element that prevents grain growth, it is necessary to control the content already in the steelmaking step, Si, Al, and Mn to lower the iron loss and at the same time the magnetic flux density In order to increase, it adds in a suitable quantity steel in a suitable ratio, and P is used for the purpose of forming the grain structure of a grain in a preferable direction at the time of recrystallization annealing. The reason for limiting the composition range is as follows.

C: 0.005 wt% or less

When C is excessively contained, carbides are formed during the manufacturing process of the electrical steel sheet of the present invention, thereby inhibiting grain growth. Also, C tends to lower magnetic properties by causing magnetic aging during use as an iron core of electrical equipment. It is preferable to contain in slab steel so that it may have a composition of 0.005 weight% or less.

N: 0.005% by weight or less

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

S: 0.005% by weight or less

In addition to the 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. It is preferable.

Si: 1.5-3.0 weight%

If the content of Si is less than 1.5% by weight, the specific resistance of the steel is small and the iron loss characteristics are deteriorated, and if it is more than 3.0% by weight, the excellent magnetic flux density is not obtained and the punchability is deteriorated, so the demand for mold wear rate is high. Not good to increase

Al: 0.5-1.5 wt%

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

Mn: 0.3 ~ 1.2 wt%

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

P: 0.03-0.14 wt%

P added in steel during steelmaking is an element that reduces (111) surface strength, which is harmful to magnetic properties.If the added amount is less than 0.03% by weight, the effect of improving the magnetic flux density after recrystallization annealing is insignificant. It is preferable to add P in an amount of 0.03 to 0.14% by weight in the present invention because there is no effect and only increases the raw material cost and cold rolling property is deteriorated.

Si + 20 * P <4.5

The content of Si and P in the range satisfying the content of each component should satisfy the above formula. If the Si + 20 * P value is 4.5 or higher, the cold rolling property is deteriorated due to the high hardness of the material. Therefore, the stress is concentrated inside the material during cold rolling, thereby developing the {111} aggregate structure, which is disadvantageous to magnetism during final annealing.

In addition to the above components, the steel contains Fe and other unavoidable impurities.

[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 detrimental to iron loss characteristics such as AlN and MnS, are redissolved 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 plate is less than 1.8 mm, the shape of the hot rolled plate becomes poor, which is not preferable. If the thickness of the hot rolled plate exceeds 3.0 mm, a good texture is not 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 coiled state, or more preferably furnace cooled.

[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 900 ℃, 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 is unfavorable to the magnetic. Increasing magnetic flux density deteriorates.

[Cold rolling stage]

Subsequently, the hot rolled sheet annealing plate is subjected to cold rolling after pickling. At this time, it is preferable to cold-roll once with the reduction ratio of 64%-85%. When rolling with a rolling reduction of less than 64%, the rolling productivity decreases and rolling with a rolling reduction of 85% or more reduces the stress density in the cold rolled sheet, increasing the strength of the {111} plane, which is detrimental to the magnetic properties after annealing, thereby decreasing the magnetic flux density. . 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 according to the increase of the plate thickness. This is not good because the loss increases, resulting in an increase in total iron loss.

[Recrystallization Annealing Step]

In the recrystallization annealing step performed according to the above method, the annealing temperature is lower than 900 ℃ when the annealing temperature is lower than the crystal growth rate after recrystallization deteriorated iron loss, higher than 1100 ℃ to increase the surface oxide layer rather than the advantage of crystal growth Due to the deterioration caused by the iron loss and magnetic flux density characteristics deteriorate, the annealing time at 900 ~ 1100 ℃ temperature is preferably adjusted to 30 to 300 seconds. The temperature increase rate up to the cracking temperature is preferably limited to 10 ° C./sec to 50 ° C./sec, thereby improving the magnetic properties of the material. When the heating rate is lower than 10 ℃ per second, when heated {222}, {112} aggregated tissue is deteriorated, the magnetism deteriorates. If the temperature rise rate is higher than 50 ℃ per second, the plate shape of the product worsens and excessive development of Goss tissue Magnetic anisotropy increases.

The steel sheet annealed in the recrystallization annealing step is treated with organic, inorganic and organic / inorganic composite film or coated with other insulating film without any skin-pass rolling step, and then shipped at demand price. Squeeze into the desired product to go.

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 at the finish rolling temperature conditions of 890 ℃ to make a hot rolled plate to a thickness of 2.0mm, 700 ℃ After winding at temperature, it was cooled in air. The cold rolled hot rolled sheet was subjected to hot rolled sheet annealing at 1000 ° C. for 5 minutes, followed by pickling, followed by cold rolling to a thickness of 0.35 mm, followed by recrystallization annealing at 1000 ° C. for 100 seconds. 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 the organic-inorganic composite, and the magnetic properties and grain size after the cutting were investigated. 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 under 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).

Steel grade C Si Al Mn S N P Invention steel A 0.003 1.6 0.7 0.8 0.003 0.003 0.12 B 0.004 1.8 1.1 0.6 0.003 0.002 0.1 C 0.003 2.0 0.7 0.6 0.005 0.003 0.09 D 0.002 1.9 0.8 0.7 0.003 0.004 0.08 E 0.003 2.0 0.9 0.5 0.004 0.002 0.09 F 0.004 2.4 0.7 0.5 0.002 0.003 0.05 Comparative steel A 0.006 * 1.9 0.8 0.7 0.002 0.003 0.07 B 0.003 1.0 * 0.7 0.5 0.003 0.002 0.12 C 0.003 3.5 * 0.7 0.6 0.003 0.002 0.05 D 0.002 1.9 0.3 * 0.6 0.003 0.003 0.09 E 0.003 1.8 0.6 0.2 * 0.002 0.003 0.08 F 0.003 2.0 0.8 0.7 0.006 * 0.003 0.07 G 0.002 2.2 1.0 0.7 0.002 0.006 * 0.07 H 0.002 2.0 0.9 0.8 0.003 0.002 0.01 * I 0.003 1.9 1.0 0.8 0.002 0.003 0.17 * J 0.002 2.5 0.7 0.6 0.003 0.002 0.12 *: Conditions outside the invention, J: Si + 20 * P> 4.5

As shown in Table 1 and Table 2, it was found that the invention material (1-6) is superior in iron loss and magnetic flux density characteristics than the comparative material (1-10).

Specifically, the comparative materials 1, 6, and 7 have C, S, and N contents in the range of the present invention, and the grain growth during recrystallization annealing was poor, so that excellent iron loss characteristics were not obtained. Since the content was added below the range of the present invention, also excellent iron loss characteristics were not obtained, while Comparative Material 3 was excellent in iron loss characteristics but inferior magnetic flux density when Si was added beyond the range of the present invention. In addition, excellent iron loss characteristics were not obtained in Comparative Material 4 and Comparative Material 5 in which Al and Mn were added below the present invention, respectively. In Comparative Material 8, when the P addition amount was less than the scope of the present invention, excellent magnetic flux density and iron loss characteristics were not obtained as a result of deterioration of the texture. Comparative material 9 was excellent in iron loss, but inferior in cold rolling property when P exceeded the scope of the present invention, and the effect of improving the texture by reducing {111} surface strength was no longer exhibited. Comparative Material 10 was inferior in cold rolling with Si + 20 * P value of 4.5 or higher and inferior in magnetic flux density.

Iron loss Magnetic flux density Crystal grain size (㎛) Steel grade Invention 1 2.33 1.72 148 Inventive Steel A Invention 2 2.31 1.71 153 Inventive Steel B Invention 3 2.34 1.71 139 Invention Steel C Invention 4 2.29 1.70 146 Inventive Steel D Invention 5 2.28 1.70 151 Inventive Steel E Invention 6 2.21 1.69 149 Inventive Steel F Comparative Material 1 2.85 * 1.70 96 Comparative Steel A Comparative Material 2 2.96 * 1.73 134 Comparative Steel B Comparative Material 3 2.15 1.67 * 153 Comparative Steel C Comparative Material 4 2.74 * 1.71 141 Comparative Steel D Comparative Material 5 2.69 * 1.71 137 Comparative Steel E Comparative Material 6 2.98 * 1.69 88 Comparative Steel F Comparative Material7 2.93 * 1.69 92 Comparative Steel G Comparative Material 8 2.35 1.68 * 133 Comparative Steel H Comparative Material 9 2.38 1.67 * 145 Comparative Steel I Comparative Material 10 2.45 1.66 * 138 Comparative Steel J

Example 2

Steel slabs having the same components as the inventive steels B and F were prepared, and the steel slabs were heated at a temperature of 1160 ° C. and hot rolled at a finish rolling temperature of 890 ° C. to produce hot rolled plates having a thickness of 2.0 mm. After winding up at a temperature of C, it was cooled in air. The cold rolled hot rolled plate was subjected to hot rolled sheet annealing at 1000 ° C. for 5 minutes, followed by pickling. Then, cold rolled to a thickness of 0.35 mm. 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 and shape were examined after cutting. The results are shown in Table 3 below. At this time, iron loss, W15 / 50 is the energy loss consumed by heat when inducing magnetic flux density of 1.5 Tesla to the iron core at 50 Hz alternating current, magnetic flux density B50 is induced at an excitation force of 5000 A / m, and the grain size is The cross section of the recrystallized annealed specimen was polished and then etched with 3% nital and measured with an image analyzer.

number Temperature rise rate Iron loss Magnetic flux density shape Steel grade Comparative Material 1 5 2.52 1.79 Good Inventive Steel B Invention 1 15 2.31 1.71 Good Inventive Steel B Invention 2 30 2.29 1.71 Good Inventive Steel B Comparative Material 2 60 2.49 1.70 Bad Inventive Steel B Comparative Material 3 5 2.45 1.67 Good Inventive Steel F Invention 3 15 2.21 1.69 Good Inventive Steel F Invention 4 30 2.23 1.70 Good Inventive Steel F Comparative Material 4 60 2.39 1.67 Bad Inventive Steel F

As shown in Table 3, it was found that the invention material (1-4) is superior to the iron loss, magnetic flux density and shape characteristics compared to the comparative material (1-4). Specifically, the comparative materials 1 and 3 had a temperature rise rate of less than or equal to the range of the present invention, and the development of the aggregate structure during recrystallization annealing was poor, so that excellent magnetic properties were not obtained. Therefore, excellent magnetic and shape characteristics were not obtained.

That is, the present invention described above allows the production of a non-oriented electrical steel sheet having excellent magnetic properties by suppressing nucleation of {111} aggregates, which is disadvantageous to magnetism at the time of final annealing due to the control of components and hot rolling conditions.

The present invention as described above provides an effect of easily producing excellent non-oriented electrical steel sheet having a low iron loss and high magnetic flux density in the production of non-oriented electrical steel sheet.

Claims (3)

By weight%, C: 0.005% or less, S: 0.005% or less, N: 0.005% or less, Si: 1.5 to 3.0%, Al: 0.5 to 1.5%, Mn: 0.3 to 1.2%, P: 0.03 to 0.14%, Reheat the steel slab with Si + 20 * P <4.5% and the remaining Fe and other impurities at 1050-1250 ℃ and finish-roll at 800 ~ 950 ℃ to hot roll to 1.8 ~ 3.0mm thickness and 650 ~ 800 ℃ After hot-rolled at 900∼1050 ℃, hot rolled sheet annealing and pickling, and then rolled once with a reduction ratio of 64% ~ 85%, cold rolled to a thickness of 0.2 ~ 0.65mm, of 10 ℃ / second ~ 50 ℃ / second A method of manufacturing a non-oriented electrical steel sheet having low iron loss and high magnetic flux density, comprising heating and heating at an elevated rate to recrystallize annealing at a temperature of 900 to 1100 ° C. for 30 to 300 seconds. delete delete