KR100276328B1 - The manufacturing method for non oriented electric steelsheet with low hysterisis - Google Patents

Abstract

PURPOSE: A method for manufacturing fully-processed non-oriented electrical steel sheets having low iron loss is provided to reduce electricity loss of iron core material for small scaled rotators adopted in motor and transformer by adding Cr and controlling final annealing condition/skin pass rolling condition properly. CONSTITUTION: In the manufacturing method of fully-processed non-oriented electrical steel sheets where a silicone steel slab comprising C 0.01wt.% or less, Si 0.1-1.5wt.%, Mn 0.5wt.% or less, Al 1.0wt.% or less, S 0.010wt.% or less, N 0.01wt.% or less, P 0.15wt.% or less, a balance of Fe, and inevitable impurities undergoes hot rolling, annealing, cold rolling, process annealing, and final annealing, the present invention is characterized in that Cr 0.05-1.0wt.% is contained in the silicone steel slab, and also the final continuous annealing is performed in the transformation temperature of 875 to Ac1 for 10sec-30min after temper rolling.

Description

Manufacturing method of pulley process non-oriented electrical steel sheet with low iron loss

The present invention relates to a method for producing a pulley process non-oriented electrical steel sheet used as an iron core material of electric machines such as various motors and small transformers, and more particularly, to a method for manufacturing a pulley process non-oriented electrical steel sheet having low iron loss.

Recently, according to the trend of increasing the efficiency of electrical equipment in terms of energy conservation, the demand for products with low iron loss is gradually increasing even in electrical steel sheets which are iron core materials. Iron loss of non-oriented electrical steel is composed of hysteresis loss and eddy current loss. Hysteresis loss is affected by crystal orientation, purity, and internal stress of iron core material, while eddy current loss is related to thickness, specific resistance, and structure of magnetic core material. Is affected. In addition, since the hysteresis loss accounts for 70-80% of the total iron loss, the reduction of the hysteresis loss is one of the important requirements for lowering the iron loss. This hysteresis loss is inversely proportional to the grain size. You lose. In order to increase the grain size, it is effective to anneal the steel sheet at a high temperature for a long time in the final annealing process, but it is economically disadvantageous, and since it is continuously annealed, it is virtually impossible to anneal it for a long time.

In addition, the iron loss of the non-oriented electrical steel sheet is also affected by the texture, the more the <100> direction of the magnetization axis is parallel to the plate surface, the more favorable the magnetic properties and lower the hysteresis loss by lowering the hysteresis loss. Therefore, making iron core materials with more (100) and (110) planes than the (111) and (211) planes that do not contain a magnetizing biaxial axis is a method of increasing energy efficiency by lowering iron losses.

On the other hand, non-oriented electrical steel sheet is a semi-prosessed material that must be subjected to stress relief annealing after the demand, and a fully-prosessed material that does not require stress relief annealing. It can be largely divided into. The semi-processed products are shipped in a modified state in the manufacturing process of steelmaking → continuous casting → hot rolling → hot rolled sheet annealing → cold rolling → annealing → skin pass rolling → insulation coating. Therefore, after purchasing the product with high demand and processing the product into the desired shape, it is necessary to perform stress relief annealing in order to obtain magnetic properties suitable for the product. In general, the stress relief annealing is performed for a long time of about 4 to 13 hours at the crack temperature of about 800 ° C because the adhesion of the insulation coating is deteriorated when the cracking temperature is higher than 800 ° C, thereby deteriorating the characteristics of the electric equipment.

The pulley process products are shipped in a state where deformation is solved through the manufacturing process of steelmaking → continuous casting → hot rolling → hot rolled sheet annealing → cold rolling → final annealing → insulation coating, so that the demand can be used without stress relief annealing. This product has merit.

Until now, in order to reduce the iron loss of the pulley process non-oriented electrical steel sheet, special elements have been added, clean steel with less impurities, a method of controlling annealing conditions, and the like. A typical example of the addition of a special element is the method disclosed in Japanese Patent Application Laid-open No. 56-54370, which is a method of adding Sb to a non-oriented electrical steel sheet.

According to the above method, the reduction of iron loss can be expected a little due to the increase in magnetic flux density due to the improvement of the aggregate structure. However, since Sb segregates at grain boundaries and interferes with grain growth, there is a limit to lowering the iron loss. As an example of controlling the annealing conditions, there is a method disclosed in Japanese Patent Application Laid-Open No. 59-8049, which inhibits the formation of an internal oxide layer that inhibits the movement of magnetic domains at the time of final annealing and increases iron loss, and crystal grains. In order to grow large, the final annealing is performed for a short time in the range of 3-60 seconds at a temperature of 1050 ℃ or more to obtain excellent magnetic properties. However, the above method is effective because the phase transformation zone does not exist when the Si content is high as 2.5%. However, when the Si content is lower than 1.5%, the ferrite-austenite phase transformation occurs during annealing, and thus the grain size is reduced. There is a problem with this increase.

Meanwhile, semi-process non-oriented electrical steel, which is another production method of non-oriented electrical steel, has been used to control the cooling rate during annealing and to add special elements to improve magnetic properties. For example, the method of Unexamined-Japanese-Patent No. 63-255323, Unexamined-Japanese-Patent No. 59-100217, and Unexamined-Japanese-Patent No. 61-3371 is mentioned. However, all of the above methods have disadvantages in that they do not escape the problem of semi-process products, which require stress relief annealing after processing in order to obtain desired magnetic properties.

Therefore, the present inventors have conducted research and experiment on a method for reducing iron loss by reducing hysteresis loss by growing grains at the time of final annealing and suggesting the present invention based on the results. A method for producing a non-oriented electrical steel sheet having low iron loss by a pulley process by adding Cr to steel grades and appropriately combining skin pass rolling with a short final annealing condition to grow the grains very effectively and uniformly by growth of strained organic grains. Its purpose is to provide it.

The present invention for achieving the above object by weight, C: 0.01% or less, Si: 0.1-1.5%, Mn: 0.5% or less Al: 1.0% or less, S: 0.010% or less, N: 0.01% or less : A method for producing a pulley process non-oriented electrical steel sheet in which a silicon steel slab comprising 0.15% or less and remaining Fe and inevitably contained impurities is hot rolled, hot rolled sheet annealed, cold rolled, intermediate annealed, or annealed. The slab contains 0.05-1.0% of Cr, and after the intermediate annealing of the cold-rolled steel sheet, the skin pass rolled to 1-9%, and the iron loss was finally annealed for 30 seconds to 10 minutes at a temperature of 875 ° C to Ac ₁ transformation point. This low pulley process relates to a method of manufacturing non-oriented electrical steel sheet.

Hereinafter, the present invention will be described.

The present inventors have studied various conditions that can greatly reduce the iron loss by growing the grains in the final continuous annealing, and as a result, it is possible to grow the grains largely by causing strain organic grain growth by a proper combination of the skin pass rolling and the final annealing conditions. It was found that the grains do not grow uniformly but exist in a mixed state. It has also been found that grain growth by strained organic grain growth occurs at a much higher temperature than conventional grain growth in a short time continuous annealing. From these facts, it was found that it is important to increase the ferrite-austenite transformation temperature and facilitate the movement of grain boundaries in order to obtain large and uniform grains by strained organic grain growth. In the present invention, Cr is properly added to the steel slab for this action, and the Cr is not only excellent in increasing the ferrite-austenite transformation temperature, but also segregated in the grain boundary during the final continuous annealing after skin pass rolling. There is a feature of the present invention to control the addition amount and the production method of Cr so as to easily move the grain boundaries and grow the grains very large and uniformly by strained organic grain growth, so that such action occurs effectively.

First, the component range of the additional element in the present invention will be described.

When the content of C exceeds 0.01%, it causes self aging and deteriorates iron loss, so the content of C is preferably 0.01% or less.

The Si is an element that contributes to the improvement of iron loss by increasing the specific resistance, but if the content is less than 0.1% or more than 1.5%, the iron loss improvement effect by skin pass rolling is reduced, so the addition content is in the range of 0.1-1.50%. desirable.

The Mn is an effective element for improving the iron loss, but if it exceeds 0.5%, the ferrite-austenite transformation temperature is lowered and the iron loss is deteriorated, so the addition content is preferably 0.5% or less.

Al, like silicon, contributes to the improvement of iron loss, but if the content exceeds 1.0%, the cold rolling is worse, so that the addition range is 1.0% or less.

Since the S and N form inclusions harmful to iron loss improvement and hinder grain growth during annealing, the lower the addition range, the more preferably the limit of 0.01% or less.

The P is an element necessary for securing mechanical strength, but if the content is more than 0.15%, cold rolling is worse, so it is 0.15% or less.

The Cr content should be 0.05% or more to easily move the grain boundaries during the final continuous annealing after skin pass rolling, and to uniformly and greatly grow the grains. Since it lowers, it is preferable to make the addition range into 0.05-1.0% range.

After reheating the silicon steel slab of the composition as described above, hot rolling, annealing the hot rolled plate, cold rolling, and then performing an intermediate annealing to obtain the final thickness by skin pass rolling. Then the cold rolled plate is finally annealed.

In the present invention, the hot rolled sheet annealing and intermediate annealing may be carried out at a recrystallization temperature or higher, and the hot rolled sheet annealing may be omitted.

The skin pass rolling preferably has a rolling rate of 1-9%. The reason is that when the rolling rate is less than 1%, the grain growth driving force is weak, so that no deformation organic grain growth occurs during final annealing, and the rolling rate is 9%. If this is exceeded, new nucleation occurs at the time of final annealing, so it is impossible to expect the effect of reducing iron loss due to strained organic grain growth.

In addition, even when the skin pass rolling rate is in the range of 1-9%, if the final annealing temperature is lower than 875 ° C. or the annealing time is less than 30 seconds, only normal grain growth, not strain organic grain growth, or strain organic grain growth occurs. This does not happen completely, but the iron loss is increased due to the formation of a mixed tissue. In addition, if the final annealing temperature is higher than the Ac ₁ transformation point, ferrite-austenite transformation occurs and the grains become finer, resulting in higher iron loss. Even if the final annealing time is longer than 10 minutes, the iron loss due to grain growth is small and the magnetic properties are improved. Harmful oxides are produced, resulting in higher iron losses and uneconomics. Therefore, the final annealing condition is preferably carried out for 30 seconds to 10 minutes at the temperature of 875 ℃ to Ac ₁ transformation point.

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

Example 1

By weight, C: 0.0043%, Si: 0.82%, Mn: 0.27%, Al: 0.28%, S: 0.0027%, N: 0.0018%, P: 0.025%, and Cr were added as shown in Table 1, respectively. The silicon steel slab consisting of the remaining Fe and the impurities contained inevitably was reheated at 1180 ° C., hot rolled to 2.3 mm in thickness, and pickled to remove scale. The hot rolled sheet was cold rolled and annealed at 750 ° C. for 2 minutes, and then rolled to a final thickness of 0.50 mm at a skin pass rolling rate of 3%. The skin pass rolling plate was finally annealed at 900 ° C. for 3 minutes to measure magnetic properties, and the results are shown in Table 1 below.

TABLE 1

As shown in Table 1, the invention material (1-2) satisfying the Cr content range of the present invention was found to reduce the iron loss compared to the comparative material (1) without addition of Cr.

In addition, in the case of the comparative material (2) having a Cr content of 1.32%, which is outside the scope of the present invention, iron loss was similar to that of the inventive material (2), but the magnetic flux density was lowered.

Example 2

By weight, C: 0.0038%, Si: 0.76%, Mn: 0.31%, Al: 0.28%, S: 0.0042%, N: 0.0021%, P: 0.024%, Cr: 0.17%, remaining Fe and inevitably contained The silicon steel slab made of impurities was reheated at 1180 ° C., hot rolled to a thickness of 2.0 mm, and then pickled to remove scale. The hot rolled sheet was cold rolled to a final thickness of 0.50 mm by changing rolling conditions under the conditions shown in Table 2, and then the cold rolled sheet was finally annealed at 900 ° C. for 3 minutes to measure magnetic properties. 2 is shown.

TABLE 2

As shown in Table 2, the invention material (3-4) is a large grain growth is low compared to the comparative material (3) obtained by the conventional manufacturing method, the iron loss is low, the skin pass rolling rate does not belong to the scope of the present invention It was found that the comparative material 4-5 had almost no improvement in iron loss characteristics compared with the conventional comparative material 3 produced.

Example 3

By weight, C: 0.0029%, Si: 0.85%, Mn: 0.21%, Al: 0.20%, S: 0.0051%, N: 0.0021%, P: 0.025%, Cr: 0.45%, remaining Fe and inevitably contained The silicon steel slab made of impurity was reheated at 1180 ° C., hot rolled to 2.2 mm in thickness, and then pickled to remove scale. The hot rolled sheet was cold rolled and annealed at 770 ° C. for 2 minutes, and then rolled to a final thickness of 0.50 mm at a skin pass rolling rate of 4%. After the final annealing under the conditions shown in Table 3 to measure the magnetic properties, the results are shown in Table 3.

TABLE 3

As shown in Table 3, the comparative annealing material (6) having a final annealing temperature of 720 ° C. and a comparative material (7) having a final annealing temperature higher than 1015 ° C., which is Ac ₁ transformation point of the present component system, were compared to the inventive material (5-6). The iron loss is high. In addition, the final annealing temperature is within the scope of the present invention, but it was also found that the iron loss was higher in the case of the comparative material 8 having a shorter annealing time of 5 seconds or the comparative material 9 having a longer 20 minutes than the invention material.

As described above, the present invention can provide a pulley process non-oriented electrical steel sheet having lower iron loss compared to conventional materials by adding an appropriate amount of Cr in steel and appropriately controlling the skin pass rolling and final continuous annealing conditions, Oriented electrical steel sheet has a useful effect that can be applied to the field of electrical equipment manufacturing, such as various motors that require excellent energy efficiency.

Claims (1)

(Correction) By weight%, C: 0.01% or less, Si: 0.1-1.5%, Mn: 0.5% or less, Al: 1.0% or less, S: 0.010% or less, N: 0.01% or less and P: 0.15% or less In the method for producing a pulley process non-oriented electrical steel sheet for hot rolling, hot rolled sheet annealing, cold rolling, intermediate annealing, and final annealing of silicon steel slab made of Fe and inevitable impurities, Cr is 0.05- 1.0%, and after the intermediate annealing of the cold-rolled steel sheet, the skin pass rolling to 1-9%, and then low iron loss, characterized in that the final continuous annealing for 30 seconds-10 minutes at a temperature of 875 ℃ ~ Ac ₁ transformation point Method for manufacturing pulley process non-oriented electrical steel sheet.