KR20000041270A - Method of manufacturing non-oriented electrical sheet excellent in magnetism - Google Patents

Abstract

PURPOSE: A method of manufacturing a non-oriented electrical sheet is provided to enhance magnetic characteristic by inducing growth of crystals without annealing a hot-rolled sheet. CONSTITUTION: A silicon steel slab consists of, by weight %: not more than 0.01% of C, not more than 1.0% of Si, 0.10-1.0% of Al, not more than 0.3% of Mn, not more than 0.03% of P, not more than 0.01% of S, not more than 0.0060% of N, 0.01-0.1% of REM, 0.005-0.25% of Sn, Fe and incidental impurities. The silicon steel slab is hot-rolled and pickled without passing through annealing of the hot-rolled sheet. After decarbonization-annealing, the slab is cold-rolled once for up to the final thickness.

Description

Method for manufacturing non-oriented electrical steel sheet with excellent magnetic properties

The present invention relates to a non-oriented electrical steel sheet used as an iron core of a motor, and more particularly, to a method for manufacturing a non-oriented electrical steel sheet excellent in magnetic properties while improving productivity by omitting hot-rolled sheet annealing.

Non-oriented electrical steel sheet is widely used for iron core materials such as electric motors, generators, and small transformers. Iron core materials used for large rotary machines such as large turbines and generators must have low iron loss in order to reduce power loss and heat generation. High magnetic flux density is required for miniaturization.

Iron loss of non-oriented electrical steel is classified into hysteresis loss and vortex loss. Of these, hysteresis losses account for 60-80%. The hysteresis loss is inversely proportional to the grain size, and the larger the grain, the lower the loss. Vortex losses are lower with higher resistivity in the material and thinner material. In addition, the magnetic properties of the non-oriented electrical steel sheet is greatly affected by the texture of the aggregate. In order to reduce the iron loss and increase the magnetic flux density, it is necessary to increase the degree of integration of the (100) and (110) planes with respect to the rolling surface of the crystal structure forming the material.

In general, the manufacturing process of non-oriented electrical steel sheet consists of a series of processes of hot-rolling silicon steel slab and hot-rolled sheet annealing, cold pickling once or twice to the final thickness after pickling. Through such a series of steps, C (carbon), N (nitrogen) and the compound remain in the steel in the steel sheet immediately before the final annealing. These all hinder the growth of grains during final annealing, which prevents them from growing to sufficient size. In addition, the impurities in the final product are damaging to the magnetic properties. This interferes with the movement of the magnetic domain and increases the iron loss. Among these impurities, C may be removed in the decarburization process, but nitrogen and sulfur compounds may remain.

Japanese Laid-Open Patent Publication No. 9-316535 (hereinafter referred to as 'prior art') includes REM in components of C: 0.01% by weight, Si: 1.0% by weight, Al: 0.2-1.5% by weight, and P: 0.3% by weight. A method of improving iron loss by removing S (sulfur) or AlN (aluminum nitride), which are impurities in steel, by adding 0.0002-0.0080 wt% has been proposed. In this prior art, impurities are removed by REM (rare earth metal: atomic number: 57-71), and the limited reason of addition amount is less than 0.0002% by weight, and the effect of removing impurities is less than 0.0080% by weight. Rather, the reason for the deterioration of magnetism is revealed. In addition, the manufacturing process, the molten steel formed as described above is made into slabs by continuous casting, hot-rolled annealing at 900 ℃ for 2 minutes after hot rolling, and made into 0.5mm thickness through pickling and cold rolling. After the final annealing for 15 seconds at 800 ℃ and coated with an insulating film to make a product. However, in the prior art, there is a problem in that the hot rolled sheet annealing is always performed, resulting in low productivity.

Accordingly, an object of the present invention is to provide a method for producing a non-oriented electrical steel sheet having excellent magnetic properties by appropriately inducing grain growth and texture formation while omitting hot rolled sheet annealing.

1 is a graph showing the change in magnetic properties according to the final annealing temperature.

The present invention for achieving the above object, in weight%, C: 0.01% or less, Si: 1.0% or less, Al: 0.10-1.0%, Mn: 0.3% or less, P: 0.03% or less, S: 0.01% or less , Hot rolled silicon steel slab consisting of N: 0.0060% or less, REM: 0.01% -0.1%, Sn: 0.005-0.25%, and the remaining Fe and inevitable impurities, followed by hot-rolled sheet annealing, followed by pickling. Decarbonization followed by cold rolling once to final thickness followed by continuous annealing.

Hereinafter, the present invention will be described in detail.

Features of the present invention,

First, the hot rolled sheet annealing is omitted during the manufacturing process.

Second, to prevent the ungrowth of crystal grains by adjusting the amount of REM added,

Third, Sn is added to compensate for the deterioration of magnetism due to the addition of REM.

The role of hot-rolled sheet annealing in the manufacturing process of non-oriented electrical steel sheet is an important part to give the final magnetic properties of the steel sheet. In particular, it is more important with respect to the formation of aggregates that are advantageous for grain growth and magnetic properties. Therefore, when hot-rolled sheet annealing is omitted for the purpose of productivity improvement, (1) the grain size should be large and (2) the aggregate structure should be advantageously formed.

(1) In the present invention, the hot rolled sheet annealing can be omitted by removing impurities that are obstacles to grain growth by adding REM as much as possible. C (carbon), N (nitrogen), and the compound remaining in the steel sheet immediately before the final annealing are obstacles to the growth of the grains, which prevents the grains from growing to a sufficient size. In addition, impurities in the final product can cause fatal damage to magnetic properties, which impedes the movement of magnetic domains and increases iron loss.

Among these impurities, C can be removed in the decarburization process, but nitrogen and sulfur compounds remain. Therefore, it must be removed sufficiently to induce grain growth, and thus hot-rolled sheet annealing can be omitted. In the present invention, REM is sufficiently added for this purpose. REM (rare earth metal: rare earth metal: atomic number 57-71) is 1.5 times larger than that of Fe, and reacts well with sulfur, oxygen and nitrogen compounds, so it is a good means to remove impurities. The prior art limits the REM to a maximum of 0.008% by weight, because the REM serves to remove impurities, but if too much, the REM itself damages the magnetic properties of the steel sheet. However, in order to omit hot-rolled sheet annealing, it is necessary to remove a larger amount of impurities, which requires a larger amount of REM than that disclosed in the above-mentioned prior art. Therefore, it is necessary to solve the problem of aggregates generated by removing impurities by inserting a large amount of REM.

(2) The present invention improves the problem of texture by adding Sn in large amounts of REM. That is, the REM lowers the degree of integration of the (100) and (110) planes, which are advantageous for the magnetism of the steel sheet, and increases the degree of integration of the (111) planes, which is disadvantageous for the magnetic. On the other hand, since Sn has a property of segregating at the grain boundary, it not only inhibits the development of the (111) plane preferentially nucleated at the grain boundary but also promotes the development of the (110) plane by promoting nucleation in the mouth. Therefore, when REM and Sn are added at the same time, it is possible to prevent deterioration of the texture due to the addition of REM.

Silicon steel slab of the present invention designed according to this principle is composed of C, Si, Al, Mn, P, S, N in addition to REM, Sn, when explaining the reasons for the limitation of these components are as follows.

The C is decarburized about 0.005% naturally during the hot rolling and annealing process, and if it is contained in the final product more than 0.005%, the magnetic deterioration is taken into consideration so that the steel slab is contained less than 0.01%.

The Si is better to put a lot to reduce the iron loss due to the increase in the resistivity, but the present invention is less than 1.0% in terms of the medium-low grade non-oriented electrical steel sheet of about 1.0% or less.

The Al is in the range of 0.01% to 1.0% to increase the specific resistance to lower the iron loss and to remove the shape in which grain growth is suppressed by fine AlN precipitation.

Since Mn is easy to form non-metallic inclusions such as emulsions, conventionally, Mn has not been used to improve the magnetic properties of non-oriented electrical steel sheets, but with the development of steelmaking technology, high-purity steel manufacturing technology becomes possible, and thus its use is possible. Mn not only decreases iron loss by increasing resistivity, but also increases the degree of integration of (100) and (110) planes, which are beneficial to magnetic properties, while Mn greatly reduces the density of (111) planes, which is disadvantageous to magnetic properties, and increases grain size. It works. However, if excessively contained will destroy the action of Sn, so less than 0.3%.

The P is for improving the punchability, and when the content of alloying elements such as Si and Al is large, the amount of P is large and wu brittleness is increased, so it is limited to 0.03% or less.

S and N are less than 0.01% and less than 0.006%, respectively, because they produce non-metallic inclusions that are harmful to magnetism.

The REM removes elements that interfere with grain growth, including sulfides, nitrides, and oxides, which are present as impurities of steel grades. The amount of addition is preferably in the range of 0.01-0.1%, which is less than 0.01%, and the effect is less than 0.1%. These REMs can also be a mismetal, which is a mixture of cerium rare earth elements and is a reflection of the refining process. The component usually contains Ce: 40-50%, La: 20-40%, and may also contain Nd: 15-20% and Pr: 3-6%. Such a metal is cheaper than a rare earth element because it is a reflection of the refining process. In particular, the rare earth element has a high affinity with oxygen, which can cause a large recovery loss due to the oxidation and evaporation of the melt. However, since the metal is a semi-finished product in the refining process, it is chemically stable and easy to manage the composition of the steelmaking process.

Since Sn has a property of segregating at the grain boundary, it not only inhibits the development of the (111) plane preferentially nucleated at the grain boundary but also promotes the development of the (110) plane by promoting nucleation in the mouth. To achieve this effect, 0.005% or more is required, but even if 0.25% or more, the effect is not only saturated, but also breakage occurs during cold rolling and manufacturing cost increases, so Sn is suitable in the range of 0.005-0.25%.

Hereinafter, the manufacturing method of the present invention will be described.

The slab formed as described above is hot rolled by a conventional method, and the finish rolling temperature at this time can be performed at about 900 ° C or more. In this manner, hot rolling and winding are performed. The winding temperature at this time may be 650 ° C. or higher as usual, but preferably high temperature winding, that is, at a temperature of 700-800 ° C. After hot winding, the rolled sheet annealing is omitted and subjected to pickling to form a final thickness through one cold rolling. The cold rolled sheet having the final thickness is decarbonized and continuously annealed (final annealed) to obtain the final product.

The magnetic properties of the final product change with the final annealing temperature. In general, the final annealing temperature is made between 800-1000 ℃, the higher the annealing temperature, the better the magnetic properties. This is because the higher the annealing temperature, the more grains are formed and the texture is advantageously formed. More preferably, it is continuous annealing at a temperature of 950-1100 ° C. for 30 seconds to 10 minutes in a non-oxidizing atmosphere. If the annealing temperature is less than 950 ℃ grain growth is somewhat inadequate and higher than 1100 ℃ grain growth is large, but the annealing temperature is developed adversely to the magnetic properties, so the annealing temperature range of 950-1100 ℃ is appropriate. In addition, even if the annealing temperature is properly maintained, if the annealing time is less than 30 seconds, the grain growth is insufficient. If the annealing time is longer than 10 minutes, the grain size becomes large, but the texture is rather disadvantageous to magnetic properties, so the annealing time is preferably 30 seconds to 10 minutes.

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

Example 1

The silicon steel slab having the components shown in Table 1 below was heated at 1200 ° C., hot rolled to a thickness of 2.0 mm, and wound up at a temperature of 800 ° C. Subsequently, cold rolling was performed once with a thickness of 0.5 mm without pickling after hot roll annealing. After the final heat treatment was performed for 5 minutes at 950 ℃ to produce a final product. At this time, REM was used as a rare earth metal (misch matal), which is composed of the main component Ca: 49% by weight, La: 25% by weight, Nb: 18% by weight, Pr: 5.4% by weight.

Magnetic properties of the specimens prepared as described above were measured and shown for W _15/50 and B ₅₀ . The value shown is the average value of the rolling direction of a steel plate and a rolling right direction.

Lecture number Chemical composition in steel (% by weight) Magnetic properties Crystal grain size (㎛) Remarks C Si Al Mn P S REM Sn W _15/50 B ₅₀ One 0.005 0.82 0.23 0.26 0.026 0.008 - - 4.474 1.682 46.5 Comparative material 2 0.003 0.81 0.24 0.25 0.027 0.006 0.03 - 4.281 1.675 48.1 Comparative material 3 0.004 0.82 0.25 0.25 0.026 0.008 0.06 - 4.139 1.671 67.6 Comparative material 4 0.003 0.80 0.24 0.25 0.027 0.009 0.09 - 4.102 1.689 75.5 Comparative material 5 0.003 0.80 0.24 0.24 0.026 0.005 0.12 - 4.504 1.671 49.8 Comparative material 6 0.003 0.80 0.25 0.25 0.025 0.005 0.06 0.1 4.020 1.760 46.8 Invention * W _15/50 : Magnetic flux density at magnetic flux density of 1.5 Tesia and frequency of 50 Hz * B ₅₀ : Magnetic flux density at magnetic field strength of 5000 A

As shown in Table 1, it can be seen that all the grains of REM-added steels are larger than those without REMs, and iron loss is also lowered. In case of steel 4 added with 0.09% REM, grain size was the largest and iron loss was the lowest. However, the magnetic flux density was lower than that of the comparative material. This is because the formation of the (100) and (110) surfaces favorable to the magnetism is insufficient due to the omission of the hot rolled sheet annealing.

Inventive material ten times in Table 1 is the addition of 0.1% by weight of Sn to the addition of 0.06% by weight of REM. The magnetic flux density is much better than the others, and the iron loss is also lowered.

Example 2

By weight C: 0.003%, Si: 0.80%, Al: 0.25%, Mn: 0.25%, P: 0.025%, S: 0.005%, N: 0.0050% and REM: 0.0061%, Sn: 0.1% and the remaining Fe And reheating and hot rolling the silicon steel slab made of impurities which are inevitably added at a temperature of 1200 ° C., followed by winding at a temperature of 730 ° C., omitting the hot rolled sheet annealing, and cold rolling once to the final thickness after pickling. It carried out for 5 minutes to -1000 degreeC. Magnetic properties of the specimens prepared as described above are shown in FIG. 1. The value shown is the average value of the rolling direction of a steel plate and a rolling right direction.

As shown in FIG. 1, the higher the final annealing temperature, the better the magnetic properties. However, the magnetic properties are expected to worsen above 1100 ℃.

As described above, the present invention has the effect that the magnetic properties can be maintained at a level equal to or higher than that of the prior art in which the hot rolled sheet annealing is performed even if the hot rolled sheet annealing is omitted.

Claims (3)

By weight%, C: 0.01% or less, Si: 1.0% or less, Al: 0.10-1.0%, Mn: 0.3% or less, P: 0.03% or less, S: 0.01% or less, N: 0.0060% or less and REM: 0.01 Hot-rolled silicon steel slab consisting of% -0.1%, Sn: 0.005-0.25% and the remaining Fe and inevitable impurities, followed by hot-rolled sheet annealing, pickling, decarbonization annealing, and then cold once to final thickness Method for producing a non-oriented electrical steel sheet excellent in magnetic properties formed by continuous annealing after rolling. The method of claim 1, wherein the REM is a mischmetal including Ce: 40-50% and La: 20-40%. The method of claim 1, wherein the continuous annealing is performed for 30 seconds to 10 minutes at a temperature of 950-1100 ° C.