KR960014510B1 - Method for manufacturing non-oriented electro magnetic steel plates with excellent magnetic characteristic - Google Patents

Abstract

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Description

Method for manufacturing non-oriented electrical steel sheet having excellent magnetic properties by controlling hot rolling conditions

The present invention relates to a method for manufacturing non-oriented electrical steel sheet used as iron core material of electric machines such as various motors and small transformers, and more particularly, to manufacture non-oriented electrical steel sheet having low iron loss and high magnetic flux density by controlling hot rolling conditions. It is about a method.

The main magnetic properties required for non-oriented electrical steel are iron loss, magnetic flux density and permeability. Among these magnetic properties, iron loss and magnetic flux density are generally higher than Si depending on the Si content. Therefore, when the Si content is increased, the iron loss is lowered, but the magnetic flux density is also lowered. Because of these characteristics, demanders have taken the method of selecting economical materials according to the more important magnetization and use, but they are insufficient to satisfy both iron loss and magnetic flux density as requirements. For example, in the case of small motors or home electronics materials that are used for a short time, the increase in iron loss had to be tolerated by lowering the Si content to make the magnetic flux density more important. Therefore, the development of a method for manufacturing non-oriented electrical steel sheet that can satisfy the requirements of iron loss and magnetic flux density at the same time was required.

As an example of the development of non-oriented electrical steel sheet having such magnetic properties, in the early 80's, Nippon Steel Co., Ltd. developed a high efficiency non-oriented electrical steel sheet named New Core. This material was developed by lowering the S component of steel, adding 0.1% Sn and 10% or more of Mn. The material has excellent iron loss of less than 3.0w / Kg in terms of electromagnetic properties, but its magnetic flux density is less than 1.69 Tesla. It was insufficient in cotton.

In comparison, RSM 27, which has high magnetic flux density, high permeability, and low iron loss, was developed by Kawasaki Steel in the mid-80s, which is 0.05% for Sb, which develops (100) and (110) crystal surfaces, which favor grain size and magnetism. It was the steel plate which contained about. This product is made of semi-process containing 2.1% of Si. It is a high-quality radish with a demand of 2.8w / Kg iron loss, 1.72Tesla and magnetic permeability of 2500 or higher after heat treatment. It is a oriented steel sheet.

Since then, Nippon Steel has developed M 43, which is made of Fully-Process with iron loss of 2.9w / Kg and magnetic flux density of 1.69Tesla, but the permeability is still inconsistent with New Core mentioned above. .

As described above, in order to produce magnetic properties, it is necessary to have an appropriate grain size that can exhibit the maximum characteristics and to develop a texture structure that is advantageous for intellect, especially the (200) or (110) plane. Among the methods, a method of adding Si or Al, which is an element that lowers specific resistance and reduces iron loss, has been mainly used.

In addition, there is a method of adding Sn in addition to Si and Al. As a representative technique, Japanese Patent Laid-Open No. 63-23262 uses 0.02-0.20% by weight of Sn and 0.1-1.0% by weight of Cu. How to lower iron loss and increase magnetic flux density?

However, in the method for producing a non-oriented electrical steel sheet containing such a component element, there is a disadvantage that the magnetic flux density is not high even if the iron loss is low when the grain growth suppression by Sn and the hot-rolling winding temperature are lower than 750 ° C.

As mentioned above, the methods for improving the iron loss and the magnetic properties were mainly based on the development of the component system by the addition of alloying elements, and there was no particular discussion on the manufacturing conditions in the manufacturing process, in particular, the hot rolling conditions.

Therefore, the present invention, unlike the manufacturing method of the non-oriented electrical steel sheet to improve the magnetic properties by only adding the alloying elements, appropriately select the component system of the non-oriented electrical steel sheet to which the alloying elements such as Sn is added, and controls the hot rolling conditions Therefore, to provide a non-oriented electrical steel sheet having a low magnetic loss and high magnetic flux density, the purpose is to.

Hereinafter, the present invention will be described.

In the present invention, by weight%, C: 0.15% or less, Si: 1.50% or less, Mn: 0.50% or less, P: 0.05-0.10%, S: 0.01% or less, N: 0.008% or less, Cu: 0.05-0.50% Steel slab composed of not more than 0.5% Al, 0.05-0.30% Sn, residual Fe and other unavoidable impurities, after reheating in the temperature range of 1150-1250 ° C., followed by a two-phase coexistence zone of austenite and ferrite in the hot rolling step The non-oriented electrical steel sheet having excellent magnetic properties by controlling hot rolling conditions, which must be subjected to two-pass rolling at 0, followed by finishing hot rolling in a ferritic zone, followed by ordinary hot rolled sheet annealing, pickling, cold rolling and final annealing. It relates to a manufacturing method of.

EMBODIMENT OF THE INVENTION Hereinafter, the numerical limitation of the steel component and composition of this invention is demonstrated in detail.

The C austenite phase is widened in accordance with the increase of the C content in the Si-C composition, so that the austenite phase exists even in a high Si content range, but if the C content is high, a separate decarburization process must be performed. It is an element that affects the range of the mixed phase zone where two phases coexist in the boundary region of austenite phase and ferrite phase depending on the C content. It is a harmful component that raises the iron loss and causes self-aging. In order to achieve this, the amount is preferably 0.015% or less.

The Si is an element mainly to lower the specific resistance to reduce the iron loss, the iron loss is advantageous as the Si content of the steel is increased, but the magnetic flux density is lowered at the same time, it is preferable to limit the content to 1.5% or less.

The Mn is to prevent brittle fracture at the time of hot rolling, to compensate for the intrinsic resistance of the steel due to the decrease in Al content, but to reduce the iron loss, but when the product manufacturing cost is increased to 0.50% or more, the Mn is preferably 0.5% or less.

The P is a major element that increases the resistivity to reduce the iron loss, but when less than 0.05%, it is disadvantageous in forming the aggregate, and if it exceeds 0.10%, cold rolling is difficult and the grain growth is impaired, so the range is 0.05-0.10%. This is preferred.

S is preferably 0.01% or less in order to contain a suitable amount of Mn to maintain the heating temperature at a relatively low temperature when reheating the slab to form MnS harmless to grain growth.

The N is good to lower the amount contained in the steelmaking step, but it is difficult to manage the nitrogen content level of the silicon steel to 10 ppm or less, and usually exceeds 30 ppm, so it is 0.008% or less.

The Cu is an element that develops texture that is beneficial to corrosion resistance and magnetism and increases specific resistance. By forming fine precipitates, Cu is precipitated in the form of coarse CuS that inhibits grain growth and development of texture that is good for magnetism. It shows the effect of improving the magnetism, but the content of Cu is preferably 0.05% -0.50% because the magnetic content is low at 0.05% or less, and the surface cracks may occur before hot rolling at 0.5% or more. Al is an important element to reduce iron loss by lowering specific resistance like Si, but it combines with N in steel to form AlN, so the Al content is limited to 0.50% or less so that AlN precipitates in a form harmless to crystal growth when reheated. desirable.

Sn is an important element that reduces the hysteresis loss during iron loss by inhibiting the development of (111) planes, which are disadvantageous to the magnetic properties preferentially nucleated at the grain boundary during annealing, and promoting the development of (110) planes that are favorable to the magnetic properties. The above effect can be obtained, but if it exceeds 0.3%, the magnetic property effect is saturated, the cold rolling property is lowered, and the manufacturing cost is also increased, so it is preferable to be in the range of 0.05-0.30%.

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

In general, a non-oriented electrical steel sheet exhibits a loop-shaped unusual phase region covering the austenite phase in Si-C state diagram according to the silicon content, and the range of the mixed phase in which the austenite phase region coexists according to the carbon content changes. Will also change.

Therefore, if the Si content is less than 1.5% by weight (hereinafter, referred to as%), the hot rolling will necessarily pass through the two-phase zone, and the orientation distribution of the grains formed will depend on how it passes through this zone, which is advantageous for magnetic properties. The development of the collective will be affected.

In other words, during hot rolling, the deformation starts in the austenite region, and when the austenite crystals uniformly refined by dynamic recrystallization pass through the phase transformation temperature section as the temperature decreases, the mixed phase of the uniform fine austenite and the transformed ferrite coexists in the two phase region. It is necessary to allow a typical rolled structure of ferrite, which is advantageous for magnetism, to retain a large number of ferrites having a component of the crystal orientation of {200} 110.

Therefore, the present invention is carried out by hot rolling of two passes in the temperature range of the two-phase zone, the mixed structure of the ferrite and the modified ferrite, respectively, as the fine uniform austenite and the transformed ferrite formed in the two-phase is further lowered in temperature. It is characterized by a manufacturing method for improving the magnetic properties by developing a crystal orientation component of {200} 110 when present.

When reheating the steel slab having the above-mentioned composition, the reheating temperature is preferably in the temperature range of 1150-1250 ° C. The reason is that when the reheating temperature is 1150 ° C or lower, the second pass rolling section is carried out in the mixed zone of austenite and ferrite phases. This is because it is difficult to match and since it forms fine CuS when it heats 1250 degreeC or more, it has a bad influence on a magnetism.

Hot rolling is generally performed in four passes, but in the present invention, two-pass hot rolling is performed in the two-phase coexistence zone. In this case, the temperature of the two-phase coexistence zone is changed depending on the content of C and Si. Typically it can be in the temperature range of 1030-975 ° C.

The hot rolling can be carried out in the usual hot rolling temperature range to allow the {200} 100 texture, which is a typical hot rolled structure of ferrite, to be developed, but after finishing rolling in the ferrite single phase region, that is, in the 800-900 ° C temperature range, It is more preferable to wind up in the temperature range of 700-750 degreeC.

After the hot rolled sheet is wound, conventional hot rolled sheet annealing may be performed, more preferably, hot rolled sheet annealing at 870-970 ° C. for 3-5 minutes.

After the hot-rolled sheet annealing treatment and pickling, cold rolling, cold rolling is preferably performed once or two times cold rolling including the intermediate annealing at 800-950 ℃.

After the cold rolling treatment, the final cold rolled sheet annealing can be carried out in a conventional cold rolled sheet annealing, more preferably annealing for 10 minutes or less at 800-970 ℃ to grow the grains and develop the texture.

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

Example 1

By weight, C: 0.005%, Si: 0.1%, Mn: 0.30%, P: 0.005%, S: 0.003%, N: 0.002%, Cu: 0.07%, Al: 0.28%, Sn: 0.07%, Balance After reheating the steel slab composed of Fe and other unavoidable impurities at 1230 ° C., 1200 ° C. and 1150 ° C., the steel slabs were hot rolled to a thickness of 2 mm with different deformation orders for each hot rolling temperature section as shown in Table 1 below. In order to obtain the coiling temperature effect, the mixture was maintained at 700 ° C. in a dry nitrogen atmosphere for 1 hour and then cooled by furnace.

After annealing the hot rolled sheet for 5 minutes in a dry nitrogen atmosphere at 910 ° C., pickling and cold rolling to a thickness of 0.5 mm, followed by 150 seconds at 870 ° C. and 90 seconds at 910 ° C. as a mixed gas atmosphere of hydrogen and nitrogen. Continuous annealing was performed. Next, iron loss and magnetic flux density were measured for the manufactured cold rolled steel sheet, and grain size and (200) plane strength were measured, and the results are shown in Table 2 below.

As shown in Table 2, the iron loss and the magnetic flux density are excellent in the case of the invention material (c) lower than that of the invention material (a) having a high reheating temperature, because the solid phase in the molten state at the low reheating temperature is low. The lack of coarse precipitates does not dissolve, making grains more coarse and iron loss improving.

In the case of the invention material (b) and the comparative materials (d) and (e) having the same reheating temperature, the invention material (b) subjected to two passes of hot rolling in the temperature range passing through the two-phase zone as in the present invention is 1 It can be seen that the magnetic properties are improved compared to the comparative materials (d) and (e) which were passed.

Example 2

By weight%, C: 0.005%, Si: 0.50%, Mn: 0.30%, P: 0.05%, S: 0.003%, N: 0.002%, Cu: 0.07%, Al: 0.28%, Sn: 0.07%, balance The steel slab composed of Fe and other unavoidably added impurities is reheated at a temperature of 1150 ° C. and 1200 ° C., and is manufactured according to the same method as Example 1, except that the cold rolled steel sheet is changed with different hot rolling temperatures as shown in Table 3 below. After the preparation, magnetic properties, grain size, and (200) plane strength were measured in the same manner as in Example 1, and the results are shown in Table 4 below.

As shown in Table 4, as in Example 1, the invention material (g) having a low reheating temperature was excellent in magnetic properties, and in the result of the hot rolling method, the hot rolling method according to the present invention was performed. In the case of phosphorus invention material (fg), iron loss is low compared with the case of comparative material (hi) which performed only one pass in the 2-phase area | region.

As described above, the present invention, unlike the conventional method for producing non-oriented electrical steel sheet by the addition of alloying elements, appropriately select the components of the conventional non-oriented electrical steel sheet, hot rolling to perform two-pass rolling in the two-phase zone By controlling the zinc conditions, it is effective to provide a non-oriented electrical steel sheet having a low iron loss and high magnetic flux density.

Claims (1)

By weight%, C: 0.015% or less, Si: 1.50% or less, Mn: 0.50% or less, P: 0.05-0.10%, S: 0.01% or less, N: 0.008% or less, Cu: 0.05-0.50%, Al: After reheating the steel slab composed of 0.5% or less, Sn: 0.05-0.30%, balance Fe and other unavoidable impurities in the temperature range of 1150-1200 ° C., in the two-phase coexistence zone of austenite and ferrite in the hot rolling step, After the pass rolling, finish hot rolling in a ferritic zone, and then a method for producing a non-oriented electrical steel sheet having excellent magnetic properties by controlling the hot rolling conditions characterized by the usual hot rolled sheet annealing, pickling, cold rolling and annealing .