KR100406391B1 - The method of manufacturing non-oriented electrical steel with better core loss at high frequency - Google Patents

Abstract

The present invention relates to a method of manufacturing a non-oriented electrical steel sheet for high frequency, the object of the conventional non-oriented electrical steel sheet by cold-rolled Mn by electroplating method by annealing alloying to diffuse the Mn uniformly into the steel sheet It is to provide a method for producing a large amount of non-oriented electrical steel sheet having excellent high-frequency iron loss characteristics inexpensively.

In the present invention having such an object, in the method for producing a non-oriented electrical steel sheet comprising the step of hot-rolled, cold-rolled silicon steel slab to produce a cold rolled sheet,

The technical gist of the non-oriented electrical steel sheet having excellent high-frequency iron loss characteristics, including electroplating the Mn plated film to 0.05 mm or less on both surfaces of the cold rolled sheet, and then annealing the alloy.

Description

Method for manufacturing non-oriented electrical steel sheet having excellent high-frequency iron loss characteristics {THE METHOD OF MANUFACTURING NON-ORIENTED ELECTRICAL STEEL WITH BETTER CORE LOSS AT HIGH FREQUENCY}

The present invention relates to a method for manufacturing high-frequency non-oriented electrical steel sheet, and more particularly, to a method for manufacturing a high-frequency non-oriented electrical steel sheet with low iron loss at low cost.

Since non-oriented electrical steel has excellent magnetic properties, it has been widely used as iron core material of various motors. Recently, electric energy has become more efficient in terms of energy saving, and the tendency to use it in the high frequency range is increasing for this purpose. Accordingly, excellent high-frequency magnetic properties are required for the electric steel sheet used as the iron core of the motor.

When the steel sheet is magnetized in the high frequency region, the loss of eddy current increases, so the iron loss increases rapidly. Therefore, eddy current loss has been reduced by reducing the thickness of the electrical steel sheet or increasing the resistivity. In other words, high frequency non-oriented electrical steel sheet has been used in high frequency applications in which a large amount of Si + Al is added in terms of increasing the resistivity, and the thickness of the steel sheet is reduced to 0.1-0.25 mm. However, if the Si content is 4% or Al content is more than 3% by weight, the ductility decrease of the steel sheet is remarkable, and it is difficult to cold-roll without causing plate breakage, making it impossible to industrially manufacture the cold rolled plate. For this reason, the magnetic improvement of the electrical steel sheet by the increase of Si or Si + Al content had a limit.

As a prior art for solving such a problem, Unexamined-Japanese-Patent No. 62-227079, Unexamined-Japanese-Patent No. 58-45349, Unexamined-Japanese-Patent No. 7-258863, etc. are mentioned.

Japanese Laid-Open Patent Publication No. 62-227079 proposes a method of continuously manufacturing high silicon steel sheet by a method of immersing a steel strip by vapor phase chemical vapor deposition (CVD) and subsequent diffusion heat treatment in a SiCl ₄ gas atmosphere. Although this method is industrially feasible, it requires a dedicated facility for CVD, and also has a long deposition time, which leads to deterioration in productivity, and thus, SiCl ₄ is a toxic gas and thus has a bad working environment. In addition, since the melting point of Si is high at 1410 ° C., the annealing time is long, which is uneconomical.

Japanese Laid-Open Patent Publication No. 58-45349 proposes a method of obtaining a high silicon steel sheet by thinning a high silicon molten steel containing 5-8% of Si by a quench solidification method. However, this method can produce only a thin thickness of about 30 μm or less, and there is a decisive disadvantage that not only the degree of plate thickness is bad but also the plate width is narrow.

In Japanese Laid-Open Patent Publication No. 7-258863, by weight%, Si: 4% or less, Al: 3% or less, and the sum of Si + Al is 5% or less, C: 0.01% or less, Mn: 1% or less, and the rest. Alloying annealing after forming an Al plating film having a thickness of 0.1 mm or less or an Al-Mn alloy coating film having a thickness of 0.1 mm or less having a Mn content of 50% or less by an electroplating method or a molten salt electroplating method on an electrical steel sheet made of Fe and unavoidable impurities. A method for producing a non-oriented electrical steel sheet is described. However, Al has a melting point of 660 ° C, a melting point of 800 ° C for 90% Al-10% Mn alloys, a melting point of 950 ° C for 70% Al-30% Mn alloys and a 50% Al-50% Mn alloy. Since the melting point is only about 1100 ° C., it is impossible to anneal in the range of 1050-1200 ° C., which is a typical alloying annealing temperature. Therefore, this prior art has a fatal problem that it cannot be applied to a continuous line of mass production.

The present inventors have continuously studied to develop a method for producing a large amount of non-oriented electrical steel sheet having a high frequency iron loss characteristic equivalent to that of high silicon steel sheet at low cost while improving the problems of the prior art and based on the experimental results. It came to propose invention.

The present invention is to inexpensively manufacture a large amount of non-oriented electrical steel sheet having excellent high frequency iron loss characteristics by performing Mn plating on a cold rolled sheet, which is a conventional non-oriented electrical steel sheet, by electroplating, and then annealing alloys to uniformly diffuse Mn into the steel sheet. To provide a method, the purpose is.

Non-oriented electrical steel sheet manufacturing method of the present invention for achieving the above object,

The non-oriented silicon steel slab for non-oriented electrical steel sheet is hot rolled and cold rolled to make a cold rolled sheet, and the surface of the cold rolled sheet is electroplated so that the Mn plating film is 0.05 mm or less, followed by alloy annealing. .

Hereinafter, the present invention will be described in detail.

In general, low iron loss when magnetizing high frequency non-oriented electrical steel sheet (about 0.1-0.25mm thickness) in the frequency range of hundreds to thousands of kHz is mainly determined by eddy current loss. This is because the eddy current loss is proportional to the square of the frequency, while the hysteresis loss simply increases with the frequency. Therefore, it is effective to reduce the eddy current loss in order to improve the high frequency iron loss characteristics, and the eddy current loss is inversely proportional to the square of the electrical resistivity, so it must contain a large amount of alloying element to increase the electrical resistivity.

Representative alloying elements that increase the electrical resistivity are Si, Al, Mn, etc., but many non-oriented electrical steel sheets containing a large amount of these alloying elements are manufactured through a conventional blast furnace-steel-hot rolling-cold rolling process. Difficulties follow That is, in the case of Si and Al, when Si is about 4.0% or more and Al is about 3.0% or more, breakage occurs during cold rolling, which makes cold rolling difficult. On the other hand, when a large amount of Mn is added, excessive temperature decrease occurs during steelmaking, greatly reducing workability, and a large amount of Mn oxide is formed in the hot rolling process, thus deteriorating pickling properties. In a conventional manufacturing method, it is impossible or impossible to manufacture a product containing a large amount of such alloying elements.

For this reason, the present inventors investigated a method for solving the above problems by using a cold rolled sheet of non-oriented electrical steel sheet using an existing plating facility and annealing facility. It was found that the melting point of the plated layer was higher than the normal alloying annealing temperature, but the smaller the difference was, the more effective it was to plate these alloy elements and then spread them uniformly into the steel sheet in a short time. Since Si is difficult to coat by hot-dip galvanizing or electroplating, it is proposed to anneal the alloy by annealing in SiCl ₄ atmosphere by vapor chemical vapor deposition, but this method has a long deposition time, which leads to deterioration of productivity and working environment. Not only is it very bad, but the melting point of Si is 1410 ° C., so the annealing time is long, which is uneconomical. When Al is plated, plating may be performed by hot dip plating, but since Al has a low melting point of 660 ° C., alloying annealing itself at a high temperature is impossible and cannot be used industrially. Therefore, the inventors have conducted studies and experiments on various elements that can reduce the iron loss by increasing the electrical resistivity as in Si, and can be diffused very easily without melting in the range of alloy annealing temperature of 1050-1200 ° C. As a result, Mn was found to be an ideal element suitable for these conditions. In particular, since Mn has a melting point of 1245 ° C., diffusion has a much faster diffusion rate in the alloy annealing temperature range of 1050-1200 ° C. compared with Si having a melting point of 1410 ° C. In addition, since the melting point of Mn is significantly higher than that of Al, plating is difficult by the hot dip plating method, but not only is possible by the electroplating method, but also close to the normal alloying annealing temperature of the steel plate which is not plated, and thus it is uniformly spread in a short time.

The present invention completed on the basis of the results of the research, characterized in that the alloying annealing after forming the Mn plating film by the electroplating method on both sides of the cold-rolled sheet which is a non-oriented electrical steel sheet of a conventional composition. The cold rolled sheet applied to the present invention is a conventional non-oriented electrical steel sheet silicon steel slab is produced through the usual hot rolling, cold rolling.

As a conventional silicon steel slab, in weight%, C: 0.01% or less, Si: 4.0% or less, Al: 0.1-3.0% or less, Mn: 2.0% or less, P: 0.2% or less, S: 0.007% or less, N A component system containing less than 0.005% may be exemplified. The reason for limitation of this component is as follows.

Since the C is limited in spontaneous decarburization in the manufacturing process, if it is contained in an amount of 0.01% or more, the iron loss is rapidly increased during use of the electric equipment, so the amount of addition is made 0.01% or less.

The Si reduces the iron loss by increasing the resistivity, if more than 4.0% is cold rolling is limited to less than 4.0%.

Al increases the resistivity as much as Si, and reduces iron loss. It is necessary to add 0.1% or more in order to prevent the precipitation of fine AlN, which hinders the movement of magnetic domains. Therefore, it is preferable to set it in the range of 0.1-3.0%.

The Mn not only improves the hot workability but also improves the resistivity, thereby reducing the iron loss, but when it exceeds 2.0%, the pickling property of the hot rolled plate is rapidly deteriorated, so it is preferable to limit the Mn to 2.0% or less.

The P also increases the resistivity and contributes to the improvement of iron loss, but if it is 0.2% or more, the cold rolling property becomes poor, so it is limited to 0.2% or less.

S is limited to 0.007% or less because it forms a fine emulsion and degrades magnetic properties.

N is also limited to 0.005% or less since it forms fine AlN and degrades magnetic properties.

The silicon steel slab formed as described above is usually manufactured as a cold rolled plate through hot rolling, hot rolled sheet annealing, cold rolling, and the present invention is electroplated and alloyed with Mn on the cold rolled sheet. At this time, the thickness of the cold rolled sheet applied to the present invention can be adjusted by subtracting the thickness increased by the electroplating from the thickness of the final product.

A method of plating Mn according to the present invention on the cold rolled plate will be described.

First, plating of Mn on a cold rolled plate is performed on both surfaces thereof by the electroplating method. This is because Mn has a high melting point of 1245 ° C, which makes it difficult to plate by the hot dip plating method. Furthermore, when Mn is plated on only one side of a cold rolled plate, plating on both sides is much more diffused under the same conditions. The reason for this is that the time required for alloying annealing can be reduced because it occurs easily.

The thickness of the Mn plating film by electroplating should be less than 0.05mm. If the thickness of the plating film is more than 0.05mm, it will not be possible to obtain a film of uniform thickness. This is because it is difficult to cause.

The electroplating method of Mn may be performed by a method known in the electroplating field. In other words, in a plating cell using an insoluble anode (TiO ₂ or Pb) and the cathode consisting of non-oriented electrical steel sheet, MnSO ₄ · 2H ₂ O 50-200 g / l, (NH ₄ ) ₂ SO ₄ to 3.0-5.5, current density It may be plated with a thickness of 0.05 mm or less under the condition of 20-100 A / dm 2.

After the Mn plated films are formed on both sides of the cold rolled sheet by electroplating, annealing is performed to make Mn in the plated film mutually diffuse with Fe of the base steel sheet to make the composition inside the steel sheet the same. Since Mn is easily oxidized at the time of annealing, the heat treatment atmosphere is preferably a non-oxidizing component. Since annealing of Mn in the coating film must be uniformly diffused into the steel sheet, the conditions of annealing should be selected so that this object can be sufficiently achieved. The alloy annealing varies depending on the thickness of the cold rolled steel sheet, the thickness of the plated coating, and the composition of the coating, but is preferably treated at 1050-1200 ° C. for 10 seconds to 10 minutes, and there is no particular limitation on the cooling rate thereafter.

The alloy annealing temperature is a conventional alloy annealing temperature in the case of a steel plate which is not plated, and in the present invention, it is possible to perform annealing at the alloy annealing temperature by electroplating Mn in an appropriate range.

Hereinafter, the present invention will be described in detail through examples.

Example 1

A silicon steel slab consisting of Si: 3.12%, Al: 0.38%, C: 0.0043%, Mn: 0.25%, P: 0.026%, S: 0.0037%, and N: 0.0022% by weight of the remaining Fe at 1160 ° C. After reheating for a period of time and hot rolled to a thickness of 2.1mm it was wound up at 680 ℃. It was pickled and cold-rolled so that thickness might be 0.168 mm and 0.20 mm, respectively. The cold rolled sheet having a thickness of 0.168 mm was cleaned by degreasing and pickling, and then subjected to Mn plating of 0.016 mm on both sides by electroplating under the following conditions so that the final thickness was 0.20 mm.

The electroplating condition at this time,

Insoluble anode: TiO ₂

Plating bath composition: MnSO ₄ 2H ₂ O 120g / ℓ, (NH ₄ ) ₂ SO ₄ 80g / ℓ, NH ₄ CNS 60g / ℓ

-Current density: 60 A / dm 2.

The electroplated steel sheet was alloyed and annealed by continuous annealing at 1150 ° C. for 5 minutes in a non-oxidizing atmosphere. In addition, the steel sheet cold rolled to a thickness of 0.20mm was continuously annealed under the same conditions. Table 1 shows the results of measuring the magnetic properties of the electrical steel sheet thus obtained in the form of a ring having an inner diameter of 33 mm and an outer diameter of 45 mm.

division Manufacture process Final plate thickness Iron hand (w / kg) Cold Rolled Sheet Thickness Mn Electroplating Annealing Condition W _10/400 W _5/1000 W _2/5000 Comparative material 1 0.20mm radish 1150 ℃ x 5 minutes 0.20mm 11.8 12.3 27.2 Invention 1 0.168 mm U 7.9 8.1 18.3 Comparative material 2 6.5% Si steel (precipitating, alloy annealing) 8.1 8.4 19.0 W _10/400 (w / kg): Loss value at magnetic flux density 1.0Tesla, frequency _{400Hz.W 5/1000} (w / kg): Loss value at magnetic flux density 0.5Tesla, frequency _{1000Hz.W 2/5000} (w / kg): Iron loss value at magnetic flux density 0.2Tesla, frequency 5000Hz.

As shown in Table 1, Invention 1 is not only superior to the high frequency iron loss compared to the comparative material 1 of the conventional 3% Si steel sheet, it can be seen that shows the same or better iron loss than 6.5% high silicon steel sheet Can be.

As described above, the present invention is composed of a cold-rolled sheet of a non-oriented electrical steel sheet produced by a conventional method as a base material, and is formed by a method of performing annealing of an alloy after plating Mn on both sides by an electroplating method. Facilities and annealing facilities can be utilized. Therefore, according to the present invention, by producing a large amount of non-oriented electrical steel sheet having excellent high-frequency iron loss characteristics at low cost, it is effective in contributing to increase the efficiency of the electric equipment.

Claims (3)

In the manufacturing method of the non-oriented electrical steel sheet comprising the step of producing a cold rolled sheet by hot-rolled, cold-rolled silicon steel slab, Mn plated film on both sides of the cold rolled sheet to be electroplated so as to be 0.05mm or less, and then annealing annealing, characterized in that the high-frequency iron loss characteristics excellent manufacturing method of the non-oriented electrical steel sheet. The method of claim 1, wherein the silicon steel slab is by weight, C: 0.01% or less, Si: 4.0% or less, Al: 0.1-3.0% or less, Mn: 2.0% or less, P: 0.2% or less, S: 0.007 Method for producing a non-oriented electrical steel sheet having excellent high-frequency iron loss characteristics characterized in that less than, N: 0.005% or less. The method of claim 1, wherein the annealing is performed for 10 seconds to 10 minutes at a temperature of 1050-1200 ° C. 6.