KR20000031656A - Process for preparing non-directional electric steel plate which has good magnetic property and low magnetic-bi-directional property - Google Patents

Abstract

PURPOSE: A process for preparing a non-directional electric steel plate is provided to have good magnetic property and low magnetic-bi-directional property. CONSTITUTION: The process is comprised of heat-rolling, heat-soft plate-rolling, cold-rolling the following defined slab at desired thickness, and annealing the thus-obtained materials. The slab is characterized by comprising 0.04% or less of C, 2.0% or less of Si, 1.0% or less of Al, 0.1 to 1.0% of Mn, 0.010% or less of S, 0.01% or less of N, 0.010% or less of O, and the remainder being consisted of Fe and inevitable impurities. The process is characterized that the latter rolling step is performed at temperatures less than those of the phase deterioration of Ar1, and its final annealing rate is increased in rates of 10 to 50°C/sec.

Description

Manufacturing method of non-oriented electrical steel sheet with excellent magnetic properties and small magnetic anisotropy

The present invention relates to a method for producing a non-oriented electrical steel sheet suitable for iron core materials, such as small and medium-sized motor, more specifically, hot rolling conditions and final annealing of silicon steel slab containing less than Si: 2.0%, Al: 1.0% or less The present invention relates to a method of manufacturing a non-oriented electrical steel sheet having excellent magnetic properties as well as small magnetic anisotropy by controlling the temperature rising rate of the battery.

Important magnetic properties required for non-oriented electrical steel sheet include iron loss and magnetic flux density. By the way, iron loss and magnetic flux density change in opposition with Si content. In other words, if the Si content is high, the iron loss is low, the magnetic flux density is also low. Due to these characteristics, demands have been used to select a product suitable for the purpose of an electric apparatus using iron core material. For example, a small motor or a motor for home appliances uses a high magnetic flux density, while a short time instantaneous use uses a product with a high magnetic flux density. Has been used. However, according to the recent trend to increase the efficiency and miniaturization of such electrical equipment in terms of energy saving, there is an increasing demand for development of products having low magnetic loss and high magnetic flux density even in electrical steel sheets which are iron core materials.

In addition, since the magnetization occurs in various directions due to the characteristics of the rotating machine, it is preferable that the difference in magnetic properties of the iron core material is small depending on the direction. The magnetic properties of non-oriented electrical steel sheet are represented by the average value between the rolling direction and the rolling right angle direction. In the manufacturing process, cold rolling and continuous annealing are performed in one direction. In particular, the magnetic anisotropy tends to increase as the iron loss is low, which is a part that must be overcome in order to upgrade the iron core material for a rotating machine. Until now, the development of non-oriented electrical steel sheets used as iron core materials for rotating machines has been focused on improving magnetic properties, while neglecting magnetic anisotropy. However, recently, due to the high quality and precision of electrical equipment, the magnetic anisotropy receives attention. It became. However, no significant progress has been made on the reduction of magnetic anisotropy.

The magnetic properties of non-oriented electrical steel sheets vary with the grain size of the core material and the degree of development of the texture. Iron loss of non-oriented electrical steel sheet is classified into hysteresis loss and eddy current loss. Hysteresis loss decreases as the grain size increases, while eddy current loss increases, so that there is a proper grain size that minimizes iron loss in general. In addition, the magnetic properties of non-oriented electrical steel sheet is significantly affected by the texture of the texture, and in general, the more grains parallel to the plane of the <100> axis, the better. Since the crystal plane containing the most <100> axes is the {100} plane, the aggregate must be well developed so that the {100} plane is parallel to the plate plane. However, the {100} plane is relatively slower to be recrystallized than the {110} plane or {111} plane during recrystallization annealing, so the actual production of conventional non-oriented electrical steel sheet is {110} plane {110} parallel to the plate plane. It is a product having an aggregate. Since the steel sheet having the {110} assembly structure contains the <100> axis in the {110} plane only in one direction, usually in the rolling direction, it shows excellent magnetic properties when magnetized in this direction, but also includes the <111> axis in the back surface. Magnetic properties show great anisotropy in the steel sheet. Therefore, in order to have excellent magnetic properties and to reduce anisotropy in the steel sheet, it is necessary to sufficiently develop the {100} texture.

As a method for improving the magnetic properties of non-oriented electrical steel sheet, a method for controlling special element addition and hot rolling conditions such as Sb and Sn during the production of electrical steel sheet has been proposed. 56732 and Japanese Patent Laid-Open No. Hei 6-192731.

In Japanese Laid-Open Patent Publication No. 58-56732, Sn was added to reduce iron loss. In order to maximize the effect of adding Sn, the cooling rate was decreased during hot annealing and the heating rate during final annealing was less than 50 ° C. per minute. To reduce iron loss. However, this method is not only economically inconvenient to be applied to the continuous annealing plant, but is also economical.

In Japanese Laid-Open Patent Publication No. 6-192731, in order to improve magnetic properties, hot rolling is terminated at a temperature above the Ar ₃ transformation point during hot rolling, and then the average cooling rate is continued in the section from the Ar ₃ transformation point to the Ar ₁ transformation point. Working below 5 ° C / sec. However, in order to end the hot rolling at a temperature above the Ar ₃ transformation point, the slab heating temperature must be increased. However, when the slab heating temperature is high, fine MnS, AlN, etc. precipitate in the hot rolled plate, thereby degrading the magnetic properties of the final product.

Meanwhile, Korean Patent Registration No. 97-122173, which is filed and published by the present inventors, has a weight% of C: less than 0.040%, Si: 2.0-4.0%, Al: 0.5-2.0%, Mn: 0.1-2.0%, and S. : Silicon steel slab consisting of 0.010% or less, N: 0.010% or less, O: 0.010% or less, remaining Fe and inevitably contained impurities, including hot rolling, hot rolled sheet annealing, one time or final annealing. In the manufacturing method of the non-oriented electrical steel sheet which is cold rolled and final annealed more than once, the final cold rolling rate is 60% or more and the high magnetic anisotropy is characterized in that the temperature increase rate at the time of final annealing is 30 to 80 ° C / sec. A method for producing non-oriented electrical steel sheet has been proposed.

However, in this method, since the Si is 2.0 to 4.0% and Al is 0.5 to 2.0%, the iron loss is very low but the magnetic flux density is also lowered, which is suitable for iron core materials of large motors, but high magnetic flux density is required. It is not suitable for iron core materials of small and medium sized motors and home appliances. Accordingly, the present inventors have conducted a number of studies and experiments to produce a non-oriented electrical steel sheet suitable for iron core materials of small and medium-sized motors not only excellent in magnetic properties but also small in magnetic anisotropy, and have come to propose the present invention based on the results.

The present invention is characterized by controlling the hot rolling and final annealing conditions for silicon steel slabs in which the steel system is adjusted to less than 2.0% and less than 1.0% for Al to be suitable as iron core materials for small and medium-sized motors or motors for home appliances. To provide a non-oriented electrical steel sheet having excellent magnetic anisotropy as well as excellent, the object is.

The present invention for achieving the above object, in weight%, C: 0.04% or less, Si: 2.0% or less, Al: 1.0% or less, Mn: 0.1-1.0%, S: 0.010% or less, N: 0.010% or less In the method for producing a non-oriented electrical steel sheet, which is hot rolled, hot rolled sheet annealing, or final annealing of silicon steel slab composed of remaining Fe and inevitably contained impurities, O: 0.010% or less, the hot rolled sheet. The test finish rolling was carried out at a temperature below the Ar ₁ transformation point, and the temperature increase rate during the final annealing was 10 to 50 ° C / sec.

Hereinafter, the present invention will be described in detail.

When a large amount of Si or Al is added to the non-oriented electrical steel sheet, it is possible to reduce the iron loss because the electrical resistivity increases and the eddy current loss is reduced, but the decrease in the magnetic flux density due to the decrease in the saturation magnetic flux density is inevitable. Small and medium-sized motors or motors for home appliances are more important to reduce the size of the device by improving the magnetic flux density at the expense of iron loss to some extent, the present inventors sought to limit the Si and Al content to less than 2.0%, 1.0%, respectively . However, since Si is an element extending the ferrite region, if the content is about 2.0% or more, the phase transformation zone does not exist from the melting point to room temperature, whereas if it is 2.0% or less, the phase transformation zone exists. That is, in the hot rolling operation, the slab heating temperature is about 1200 ° C, but the austenitic single phase region is changed to become a ferrite single phase region through the two-phase region of (austenite + ferrite) according to the temperature decrease. In the electrical steel sheet having the composition of phase transformation zone, the conditions of hot rolling change the grain size and texture, so what temperature, ie, what phase is in the region, changes the grain size and texture. Will affect.

Therefore, the present inventors have studied various process conditions affecting magnetic properties and magnetic anisotropy in silicon steel slabs of Si 2.0% or less and Al 1.0% or less suitable as iron core materials for small and medium-sized motors and home appliance motors. It was found that the final rolling temperature during hot rolling and the rate of temperature increase during final annealing are important variables. When the finish rolling during hot rolling is performed in the ferrite region below the Ar ₁ transformation point, the grains of the hot rolled sheet are coarsened and the magnetic structure is advantageous. Therefore, the iron loss of the final product is low as well as the magnetic anisotropy is reduced. While the finish rolling to the above Ar ₃ transformation point austenite region or Ar ₁ transformation point or more than Ar ₃ transformation point (austenite + ferrite) When carried out in two-phase region of the hot-rolled sheet is the iron loss of the final product consists of fine recrystallized grains without deformation Was higher and the magnetic anisotropy was larger than that of the finish rolled in the ferrite region.

In the case of finish rolling in the ferrite region, the iron loss of the final product was lower than that in the austenite region or in the two-phase region of (austenite + ferrite), but the magnetic flux density deteriorated. Many experiments have shown that this problem can be solved by controlling the aggregates. That is, it was possible to change the crystal orientation of the crystal grains to be recrystallized by controlling the temperature increase rate during the final annealing. When the temperature increase rate at the time of final annealing was slower than 10 ° C./sec, the {110} or {111} planes, which are relatively fast in nucleation, developed rapidly, not only increasing magnetic anisotropy but also excellent magnetic properties. On the other hand, if the temperature increase rate is higher than 50 ° C./sec, the {211} plane including the <111> axis, which is difficult to magnetize, is developed, but the magnetic anisotropy is not great, but the magnetic properties are greatly deteriorated.

Hereinafter, the reason for the numerical limitation in the base metal and the processing conditions used in the production method of the present invention will be described.

If C is contained more than 0.04%, decarburization will occur, which will deteriorate the magnetic properties of the final product.

Si needs to be added to reduce the iron loss due to the increase of the resistivity, but when it is more than 2.0%, the saturation magnetic flux density is lowered, and the magnetic flux density is lowered.

Al is required for iron loss reduction like Si, but if it is more than 1.0%, cold rolling is not only worsened, but the saturation magnetic flux density is lowered, so the magnetic flux density is lowered.

If Mn is less than 0.1%, the hot workability is bad, and if it exceeds 1.0%, Mn forms a surface oxide layer during final annealing, thereby deteriorating magnetic properties and lowering magnetic flux density.

S, O, N is limited to a maximum of 0.010% or less because the content of the S, O, N is formed to interfere with the movement of the magnetic domain.

In hot rolling of the silicon steel slab, in the present invention, it is preferable to finish-roll in a ferrite region having a temperature below the Ar ₁ transformation point, for the following reason.

When the finish rolling during hot rolling is performed in the ferrite region below the Ar ₁ transformation point, the grains of the hot rolled sheet are coarse and the aggregate structure which is favorable for the magnetic anisotropy is developed, so that the iron loss of the final product is low and the magnetic anisotropy is also small. While the finish rolling to the above Ar ₃ transformation point austenite region or Ar ₁ transformation point or more than Ar ₃ transformation point (austenite + ferrite) When carried out in two-phase region of the hot-rolled sheet is the iron loss of the final product consists of fine recrystallized grains without deformation This is because it is higher and the magnetic anisotropy is larger than the case of finish rolling in the ferrite region. In the hot rolling of the present invention, the lower limit of the finish rolling temperature is preferably set in consideration of the rolling property of the raw material and the rolling equipment, and may be performed at about 800 ° C. or more in consideration of the usual rolling equipment.

After hot rolling as described above, the hot rolled sheet annealing is cold rolled to the final thickness. In the present invention, the hot rolled sheet annealing may be performed at a temperature of 700 ° C. or higher, and may be omitted.

In addition, the present invention is the final annealing of the cold-rolled silicon steel slab as described above, the temperature increase rate is preferably in the range of 10 ~ 50 ℃ / sec, the reason is as follows. If the temperature increase rate at the time of final annealing is slower than 10 ° C./sec, the {110} or {111} planes which rapidly generate nucleation during recrystallization are rapidly developed to increase magnetic anisotropy and not have excellent magnetic properties. On the other hand, if the temperature increase rate is higher than 50 ℃ / sec, because the {211} plane including the <111> axis difficult to magnetize is developed, the magnetic anisotropy is not large, but the magnetic properties are greatly deteriorated.

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

EXAMPLE

By weight percent, a silicon steel slab consisting of C: 0.0045%, Si: 0.78%, Al: 0.22%, Mn: 0.15%, S: 0.0051%, N: 0.0024%, O: 0.0035%, and the remaining Fe at 1210 ° C. After reheating, the finish rolling temperature was changed as shown in Table 1, hot rolled to a thickness of 2.1 mm, and wound at 660 ° C. The phase transformation temperature of this silicon steel was Ar ₁ at 920 ° C and Ar ₃ at 1002 ° C. After pickling the hot rolled plate, the scale was removed and cold rolled to a final thickness of 0.50 mm. After cold-rolled sheet was changed to the conditions shown in Table 1 and finally annealed, the magnetic properties and magnetic anisotropy were measured, and the results are shown in Table 1 together.

division Hot Rolling Condition Final Annealing Condition Magnetic anisotropy Magnetic properties Finish rolling temperature (℃) Temperature (℃) Temperature rise rate (℃ / sec) W _{15/50, R} / W _{15/50, C} B _{50, R} / B _{50, C Iron} loss (W _15/50 , w / kg) Magnetic flux density (B ₅₀ , Tesla) Comparative Material 1 1035 840 7 0.95 1.014 5.95 1.702 Comparative Material 2 960 840 7 0.96 1.012 5.76 1.688 Comparative Material 3 880 840 7 0.97 1.008 5.43 1.694 Comparative Material 4 1035 945 7 0.94 1.021 5.32 1.697 Comparative Material 5 960 945 7 0.96 1.019 5.09 1.691 Comparative Material 6 880 945 7 0.96 1.018 4.87 1.693 Invention 1 880 945 20 0.98 1.014 4.70 1.704 Invention 2 880 945 30 0.97 1.014 4.63 1.706 Invention 3 880 945 40 0.97 1.016 4.57 1.709 Comparative Material7 880 945 65 0.98 1.012 4.95 1.692 W _15/50, w / kg: magnetic flux density of 1.5T, the iron loss value at a frequency of 50Hz B _50, Tesla: magnetic flux density value of the intensity of the magnetic field 5000A / m when _{W 15/50, R / W} 15/50, C : The iron loss ratio in the rolling direction to the iron loss in the rolled steel direction. The closer to 1, the smaller the magnetic anisotropy. Where subscript R denotes rolling direction and C denotes rolling direction. B _{50, R} / B _{50, C} : represents magnetic flux density ratio of rolling direction to magnetic flux density in rolling direction. Low magnetic anisotropy.

As shown in Table 1, Comparative material 3 and Comparative 6 rolled in the ferrite region has lower iron loss and lower magnetic anisotropy, but magnetic flux density compared to Comparative Material 1, Comparative Material 2 and Comparative Material 4 and Comparative Material 5, respectively. There is a problem of being lowered.

On the contrary, Invention 1, Inventive Material 2, and Inventive Material 3, which are finish-rolled in a ferrite region and the temperature increase rate at the time of final annealing, fall within the scope of the present invention, are the comparative materials 3 whose temperature increase rate at the time of final annealing is later than the range of the present invention. It can be seen that the magnetic properties are superior and the magnetic anisotropy is smaller than that of the comparative material 6 and. However, Comparative Material 7, which was finish-rolled in the ferrite region but whose temperature rise rate was higher than the range of the present invention at the time of final annealing, was shown to have low magnetic anisotropy but deteriorated magnetic properties.

As described above, the present invention controls the finishing rolling conditions during hot rolling and the temperature rising rate during final annealing of silicon steel slabs having Si: 2.0% or less and Al: 1.0% or less suitable as iron core materials for small and medium-sized motors and motors for home appliances. Therefore, the non-oriented electrical steel sheet having excellent magnetic properties as well as small magnetic anisotropy has the effect of increasing the efficiency and miniaturization of the rotating machine and increasing the precision.

Claims (1)

By weight%, C: 0.04% or less, Si: 2.0% or less, Al: 1.0% or less, Mn: 0.1-1.0%, S: 0.010% or less, N: 0.010% or less, O: 0.010% or less, remaining Fe and In the manufacturing method of the non-oriented electrical steel sheet which hot-rolled, hot-rolled sheet annealing and the final thickness of the silicon steel slab which consists of an impurity contained unavoidably, the finish rolling at the time of hot rolling is carried out at the temperature below Ar ₁ transformation point. The method for producing a non-oriented electrical steel sheet having excellent magnetic properties and small magnetic anisotropy, which is carried out in the above and characterized in that the temperature increase rate at the time of final annealing is 10 to 50 ° C / sec.