KR100516464B1 - A method for manufacturing high hardness non-grain oriented silicon steel sheet - Google Patents

Abstract

The present invention relates to a non-oriented electrical steel sheet manufacturing method used as an iron core material for magnetic switch, by controlling the Si content, pre-annealing conditions and final annealing conditions in the steel, for magnetic switches having excellent hardness as well as coercivity and residual magnetic flux density It is an object to manufacture a non-oriented electrical steel sheet.

The present invention for achieving the above object,

By weight%, C: 0.004-0.006%, Si: 2.6-3.0%, Mn: 0.25-0.35%, P: ≤0.01%, S: ≤0.003%, Al: 0.4-0.5%, N: 0.005% or less, The silicon steel slab composed of the balance Fe and unavoidable impurities is reheated at 1230-1290 ° C, hot rolled and wound up, preannealed at 1000-1100 ° C, and then cold-rolled at a temperature rising rate of 15-16 ° C / sec. The technical gist of the manufacturing method of the high hardness non-oriented electrical steel sheet which includes heating to 900 degreeC and carrying out the final annealing which hold | maintains at this temperature is made into the technical summary.

Description

Manufacturing method of high hardness non-oriented electrical steel sheet {A METHOD FOR MANUFACTURING HIGH HARDNESS NON-GRAIN ORIENTED SILICON STEEL SHEET}

The present invention relates to a method for producing an non-oriented electrical steel sheet used as an iron core material for a magnetic switch, and more particularly, to a method for manufacturing a non-oriented electrical steel sheet having low iron loss and high Vickers hardness.

The non-oriented electrical steel sheet is a material used for iron core materials such as various motors and generators, and the magnetic properties required here include core loss and magnetic induction.

The iron loss is classified into hysteresis loss and eddy current loss. This hysteresis loss is an energy loss due to the irreversible movement of the magnetic domain wall, and is affected by crystal orientation, purity (impurity, snow), and internal stress of iron core material. On the other hand, the eddy current loss is the energy loss due to the eddy current caused by the magnetic flux change accompanying the magnetic domain movement, and in the nondirectional direction, it is almost determined by the thickness of the iron core material.

In general, the iron loss of non-oriented electrical steel sheet is largely dependent on the silicon content and the plate thickness, which greatly increases the resistivity, but if they are the same, it mainly depends on grain size and texture. In other words, as the grain size increases, the hysteresis loss decreases due to the reduction of the grain boundary area that impedes the movement of the magnetic domain wall, while the magnetic domain width increases, and the eddy current loss increases due to the increase of the moving speed of the magnetic domain wall. Increases. Therefore, there is an appropriate grain size for minimizing iron loss, which is known to vary depending on the silicon content, plate thickness and alloying elements.

On the other hand, the magnetic flux density is known to vary significantly depending on the texture, although it is mostly determined by the silicon content. Therefore, in order to reduce the iron loss of the non-oriented electrical steel sheet and increase the magnetic flux density, the grains are grown to an appropriate size, and the grains include the {200} and {110} directions containing the <100> direction of the magnetization axis. It is important to have a face.

Among the factors affecting the magnetism of non-oriented electrical steel sheet, the effects of Si content, impurities and thickness and the obstacles to the movement of the magnetic domain walls during the magnetization process are as follows.

* Si content: The most important role of Si among the various components of non-oriented electrical steel sheet is to increase the resistivity, reduce the eddy current loss, widen the heat treatment range as ferrite expansion element, and give the strength needed to be used as iron core material of rotating equipment. .

* Impurities (C, S, O, N): Impurities such as C, S, O, N form precipitates like MnS and AlN during hot rolling, which hinders grain growth during annealing and makes the movement of domains difficult and recrystallization Aggregates form adversely to the magnetism, which adversely affects the magnetism.

* Thickness: As the iron loss decreases as the thickness becomes thinner and then increases again when it is less than a certain thickness, it can be seen that there is a minimum thickness of the iron loss. This phenomenon occurs because the hysteresis loss and the eddy current loss constituting the iron loss change opposite to each other depending on the thickness. In other words, the thinner the thickness, the hysteresis loss increases while the eddy current loss decreases. The reason why hysteresis loss and complete flow loss change as the thickness becomes thinner is that the grain size decreases as the thickness becomes thinner, which increases the grain boundary area which hinders the movement of the magnetic domain wall and is disadvantageous for magnetization {222} This is because the density of the magnetic flux decreases due to the increased degree of integration of the {211} plane. On the other hand, the reason why the eddy current loss decreases is because the thickness becomes thin and the path through which the eddy current flows in the material is reduced.

On the other hand, the non-oriented electrical steel sheet, in particular can be used for the magnetic switch, in addition to the above-described characteristics, such as hardness (Hardness), Coercive Force, and residual magnetic flux density (Remanence) also requires additional do. A magnetic switch is a kind of electromagnet used as a switch for opening and closing an electric circuit. Since a control circuit and an operating circuit for opening and closing a switch are electrically separated from each other, an operation circuit is operated even with a weak current in the control circuit. It has the characteristic to control much larger current. Since the control circuit of the switch consists of a core which is coiled and fixed so as to be magnetized and a core which is movable to open and close the circuit, the magnetic core material of the magnetic switch has a contact point of the E-type core. Since they collide frequently with each other, the hardness must be high, and when the current is cut off, the switch must be easy to be broken, so the coercive force and the residual magnetic flux density are low. In addition, it is needless to say that the iron loss is low and the magnetic flux density is high.

However, until now, the non-oriented electrical steel sheet having a Si content of 2.1% and a thickness of 0.50 mmt was used as the magnetic switch material as described above. Thus, there is a problem that the competitiveness of the product is deteriorated because it is greatly disadvantageous in terms of productivity and wear resistance. there was.

Accordingly, the inventors of the present invention have repeatedly studied and experimented to solve the above problems, and proposed the present invention based on the results. The present invention controls the Si content, pre-annealing condition and final annealing condition in steel. It is an object of the present invention to manufacture a non-oriented electrical steel sheet for magnetic switches having excellent hardness as well as coercive force and residual magnetic flux density.

The present invention for achieving the above object,

By weight%, C: 0.004-0.006%, Si: 2.6-3.0%, Mn: 0.25-0.35%, P: ≤0.01%, S: ≤0.003%, Al: 0.4-0.5%, N: 0.005% or less, The silicon steel slab composed of the balance Fe and unavoidable impurities is reheated at 1230-1290 ° C, hot rolled and wound up, preannealed at 1000-1100 ° C, and then cold-rolled at a temperature rising rate of 15-16 ° C / sec. It relates to a method for producing a high hardness non-oriented electrical steel sheet comprising heating to 900 ℃ and the final annealing to maintain at this temperature.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The inventors of the present invention, in view of the fact that the hardness of the non-oriented electrical steel sheet is generally affected by the Si content and the pre-annealed, the grain size of the final annealing plate, the inventors and experiments to find the optimum conditions for these As a result, the present invention has been completed.

That is, in the present invention, components other than Si and their content ranges were used in the manufacture of non-oriented electrical steel sheet, and were used in general, and only the content of Si, which is a characteristic element of the present invention, was set to an optimal value.

The Si is a substitutional element, the hardness increases as the content is increased, and the iron loss is improved, which is advantageous in terms of energy efficiency. However, when excessively added, the saturation magnetic flux density is lowered, so that the magnetic flux density is thermally deteriorated, and there is a problem in that the cost burden is increased due to the material cost increase. Therefore, the content range of the Si is preferably set to 2.6 ~ 3.0%.

The steel slabs thus formed are made of a non-oriented electrical steel sheet after reheating, hot rolling and winding, followed by cold rolling according to a conventional method, in which the present invention is carried out after winding with a coil after hot rolling. It is characterized by appropriately controlling the temperature conditions of the final annealing after pre-annealing and cold rolling. As described above, in order to increase the hardness, the grains in the final annealing plate should be refined because the increase in grain size increases the possibility of cracking at grain boundaries. Therefore, in order to increase the hardness by controlling the grain size under the appropriate Si content conditions, it is advantageous to lower the annealing temperature and short the ashing time. However, if grain growth is too low at this time, hysteresis loss increases and eddy current loss decreases, but iron loss is inferior because hysteresis loss increases far more than eddy current loss, and accordingly, non-directional magnetic switch is used. There is a problem of increasing coercivity and residual magnetic flux density, which are important characteristics required for electrical steel sheet.

In the present invention, in order to prevent the crystal grains from becoming too fine after the final annealing and inferior to the required level, the pre-annealing temperature carried out after hot rolling and hot rolling is set to 1000 to 1100 ° C. That is, the pre-annealing serves to create conditions for growth of the granules into the proper grains, when the pre-annealing temperature is less than 1000 ℃ is insufficient for proper grain growth, if the precipitate is excessively high above 1100 ℃ It is not preferable because it may inhibit fine grain growth in final annealing as it precipitates finely again in the cooling process afterwards.

In addition, the cold-rolled steel sheet cooled to room temperature after the cold rolling is finally annealed, in which case it is preferably carried out by heating to 870 to 900 ℃ at a temperature rising rate of 15 to 16 ℃ / sec and maintained at this temperature. The reason is that the annealing time is longer than necessary when the temperature increase rate is less than 15 ° C / sec. As a result, the hardness may not satisfy the required level due to excessive grain growth. This is because magnetic properties may be inferior by miniaturization. In addition, the reason for heating the steel sheet to 870 ~ 900 ℃ during the final annealing is, because the annealing temperature is higher than 900 ℃ difficult to secure the hardness due to grain growth, if less than 870 ℃ magnetic properties are inferior due to grain refinement to be. The holding time at the annealing temperature usually takes about 40 to 50 seconds.

The non-oriented electrical steel sheet thus produced has a Vickers hardness of 180 or more, measured at a load of 1 kg, and is a suitable material for magnetic switches.

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

(Comparative Example 1)

By weight, it contains C: 0.005%, Mn: 0.29%, P: 0.009%, S: 0.0028%, Al: 45%, N: 0.0012%, balance Fe and other unavoidable impurities, and the content of Si is shown in the following table. The steel slab changed as described above was reheated at 1270 ° C. and then hot rolled to a thickness of 1.8 mmt, and not preannealed or carried out at 1100 ° C. Thereafter, the product was cold rolled to 0.70 mmt, heated to 760 ° C at a temperature rising rate of 13.5 ° C / sec, and then subjected to final annealing to be maintained at this temperature.

The mechanical and magnetic properties of the materials thus prepared were investigated, and the results are shown in Table 1 below. Here, the magnetic properties are measured by the magnetic flux density (B ₅₀ ) induced in the specimen under the magnetic field of 5000 A / m and the iron loss value measured under 1.5 Tesla, 50 Hz.

division Si content (wt%) Preliminary Annealing _Iron loss (W _15/50 ) Magnetic flux density (B ₅₀ ), Tesla Hardness (load 1 kg) Coercive force (A / m) Comparative Material 1 2.1 O 5.548 1.718 154 96 Comparative Material 2 2.1 X 6.427 1.692 156 112 Comparative Material 3 2.6 O 5.335 1.683 189 124 Comparative Material 4 2.6 X 5.928 1.662 183 133 Comparative Material 5 3.0 O 4.977 1.664 202 105 Comparative Material 6 3.0 X 5.624 1.649 207 127

As shown in Table 1, in the case of the comparative materials (2), (4), and (6) in which preliminary annealing was omitted, a tendency for the magnetic properties to be inferior is large, which is not suitable as a magnetic switch material. I could confirm it.

In addition, in the case of the comparative material (1) having a small content of Si, which enhances the solid solution strengthening effect, even when the final annealing temperature was lowered as much as possible, it was found that it was difficult to satisfy the required hardness characteristics.

On the other hand, in the case of the comparative materials (3) and (5), the content of Si and pre-annealing conditions are within the scope of the present invention, and the Vickers hardness when the load is 1 kg satisfies all 180 or more, but the final annealing conditions Outside the scope of the present invention, it can be seen that the coercive force is very inferior to all 75A / m or more.

Therefore, in order to satisfy the conditions of Vickers hardness of 180 or more and coercive force of 75 A / m or less, which are characteristics suitable for use for the magnetic switch, it is required that all Si content, preannealing and final annealing conditions must satisfy the present invention conditions. Able to know.

(Example 2)

By weight, it contains C: 0.005%, Mn: 0.29%, P: 0.009%, S: 0.0028%, Al: 45%, N: 0.0012%, balance Fe and other unavoidable impurities, and the content of Si is shown in the following table. After reheating the steel slab changed as shown in 2 and hot-rolled to 1.8mmt thickness, pre-annealed at 1100 ° C and cold-rolled, the final annealing conditions were different as shown in Table 2 below. .

Then, the mechanical properties and magnetic properties of the steel sheet were investigated and the results are shown in Table 2 below. Here, the magnetic properties are measured magnetic flux density (B ₅₀ ) induced in the specimen under the magnetic field of 5,000A / m and iron loss value (W _15/50 ) measured under 1.5 Tesla, 50Hz.

division Si content Temperature rise rate (℃ / sec) Annealing Temperature (℃) _Iron loss (W _15/50 ) Magnetic flux density (B ₅₀ ), Tesla Hardness Coercive force (A / m) Comparative Example 1 2.4 14.7 830 5.622 1.647 172 102 Comparative Example 2 15.5 870 5.324 1.663 169 86 Comparative Example 3 15.8 890 5.067 1.679 154 57 Comparative Example 4 16.3 920 4.776 1.689 122 45 Comparative Example 5 2.6 14.7 830 5.321 1.662 186 88 Inventive Example 1 15.5 870 4.955 1.674 187 74 Inventive Example 2 15.8 890 4.718 1.688 181 56 Comparative Example 6 16.3 920 4.344 1.702 175 42 Comparative Example 7 3.0 14.7 830 4.972 1.683 205 105 Inventive Example 3 15.5 870 4.485 1.692 187 72 Inventive Example 4 15.8 890 4.218 1.704 182 65 Comparative Example 8 16.3 920 3.945 1.718 174 48

As shown in Table 2, in the case of Comparative Examples (1) to (4) having a low Si content, it was difficult to secure the desired hardness due to insufficient solidifying effect, and the comparative material (6) having a high annealing temperature, In the case of (8), it can be seen that it is difficult to secure hardness due to excessive grain growth.

On the other hand, in the case of Inventive Examples (1) to (3) of the present invention, it is understood that the Vickers hardness when measured under a load of 1 kg is superior to the magnetic properties while being equal to or greater than that of the comparative example.

According to the present invention as described above, a high hardness non-oriented electrical steel sheet having a Vickers hardness of 180 or more and a coercive force of 75 A / m or less can be produced, which has an effect that can be applied for a magnetic switch.

Claims (2)

By weight%, C: 0.004-0.006%, Si: 2.6-3.0%, Mn: 0.25-0.35%, P: ≤0.01%, S: ≤0.003%, Al: 0.4-0.5%, N: 0.005% or less, The silicon steel slab composed of the balance Fe and unavoidable impurities is reheated at 1230-1290 ° C, hot rolled and wound, and then preannealed at 1000-1100 ° C, and then cold-rolled at a temperature rising rate of 15-16 ° C / sec. Method for producing a high hardness non-oriented electrical steel sheet comprising heating to 900 ℃ and the final annealing maintained at this temperature The method of claim 1, wherein the non-oriented electrical steel sheet is a high hardness non-oriented electrical steel sheet, characterized in that Vickers hardness of 180 or more measured by a load of 1kg.