JPH05140649A - Manufacture of now-oriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PURPOSE:To stably manufacture a non-oriented silicon steel sheet excellent in magnetic properties by heating a steel slab having a specified compsn. contg. Si, Al, N, S, C, Mn, Ti, Zr, Nb, V and P to a specified temp. and executing hot rolling. CONSTITUTION:Steel constituted of, by weight, 1.0 to 4.O% Si, 0.001 to 2.0% Al, <=0.0020% N, <=0.0020% S, <=0. 0030% C, 0.1 to 2.0% Mn, 0.003 to 0.010% Ti, <=0.0050% Zr, <=0.0050% Nb, <=0.0050% V, <=0.2% P and the balance Fe with inevitable impurities is melted by a converter and is subjected to continuous casting. The obtd. slab is heated at 1125 to 1300 deg.C in the surface temp. soaked, and thereafter, subjected to hot rolling to a prescribed thickness. The obtd. hot rolled steel strip is, as rolled or after annealing at about 900 to 1000 deg.C, subjected to pickling. Next, the steel strip is subjected to cold rolling for one time or >= two times including a process annealing to regulate its sheet thickness into a final one. The cold rolled steel sheet is subjected to finish annealing at about 1000 to 1100 deg.C. In this way, the non-oriented silicon steel sheet of the highest grade can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a non-oriented electrical steel sheet having an extremely low iron loss, and in particular, it produces an ultra-high purity slab at the stage of melting and casting of steel and uses this as a starting material. The present invention relates to a method for manufacturing a non-oriented electrical steel sheet.

[0002]

2. Description of the Related Art In recent years, demands for improving the characteristics of non-oriented electrical steel sheets as magnetic core materials for large rotating machines have become stronger and stronger from the viewpoint of energy saving. In order to meet this requirement, the steel manufacturers that manufacture non-oriented electrical steel sheets are also conducting research and development to improve the properties of non-oriented electrical steel sheets, and industrially, JIS 35A230, J
High grade non-oriented electrical steel sheets such as IS 50A270 are manufactured. It is known that it is effective to increase the Si and Al contents in the steel in order to improve the properties of the non-oriented electrical steel sheet, and especially to improve the iron loss characteristics (reduction of iron loss).

However, if the contents of Si and Al in steel are increased, the material becomes brittle, the workability deteriorates, and the manufacturing becomes difficult, and also when the product is punched by the customer. It causes problems such as cracking. Therefore, there is a limit in increasing the contents of Si and Al in steel. Therefore, if the products have the same iron loss value level, it is better that the contents of Si and Al in the steel are as low as possible. Further, if the contents of Si and Al in the steel are reduced, the magnetic flux density of the product can be increased. As described above, by reducing the contents of Si and Al in the steel, the production of the non-oriented electrical steel sheet can be facilitated, and the magnetic properties and the workability (punching etc.) of the product can be improved.

[0004]

DISCLOSURE OF THE INVENTION The present invention relates to S in steel.
Stable production of products with characteristics (iron loss, magnetic flux density, workability) that exceed the grade levels stipulated in the current JIS without increasing the i and Al contents to the conventional levels. The purpose is to provide a method that can.

[0005]

In order to achieve the above object, the present invention provides, as weight%, Si: 1.0 to 4.0%, Al: 0.001 to 2.0%, N: ≤0. .0020%, S: ≤ 0.0020%, C: ≤ 0.0030% Mn: 0.1-2.0%, Ti: 0.003-0.010%, Zr: ≤ 0.0050%, Nb. : ≤ 0.0050%, V: ≤ 0.0050%, P: ≤ 0.2%, a slab consisting of the balance Fe and unavoidable impurities is heated to a temperature range of 1125 to 1300 ° C at the surface temperature, and hot. A magnetic property characterized by being rolled into a hot rolled steel strip, pickled, then cold-rolled once or twice with intermediate annealing to obtain a final plate thickness, and then finish-annealed. Is a method for manufacturing an excellent non-oriented electrical steel sheet. Further, in the above invention, another aspect is that the hot rolled steel strip is annealed, then pickled, and then cold rolled and finish rolled in the same manner as in the above invention.

The present invention will be described in detail below. The inventors of the present invention have conducted many experiments on technical means for improving the properties of non-oriented electrical steel sheets such as iron loss, magnetic flux density and workability without increasing the Si and Al contents in the steel. I went. As a result, in order to manufacture the highest grade non-oriented electrical steel sheet having a very low iron loss value without increasing the Si and Al contents in the steel, it is extremely effective to highly refine the steel. I found that.

The inventors consider the reason as follows. That is, the iron loss of the non-oriented electrical steel sheet is higher than that of the grain-oriented electrical steel sheet in that the ratio of the hysteresis loss is higher than the eddy current loss, which is 60 to 80% of the total iron loss. It is inversely proportional to the grain size of the product. Therefore, accelerating the growth of normal grains in the recrystallization process in finish annealing in the manufacturing process is an effective means for reducing the iron loss value of the product.

On the other hand, impurities that become precipitates and inclusions not only hinder the growth of normal grains during the recrystallization process in finish annealing in the manufacturing process of non-oriented electrical steel sheets, but also the precipitates and inclusions themselves. Is a bottleneck that reduces the hysteresis loss by hindering the movement of the domain wall in the product by the pinning effect.
As for these impurities, conventionally, S, N and Mn, Al
Although it is known that MnS and AlN are bound to each other, the inventors have found that not only Mn and Al but also Zr and
Ti, Nb, and V also form compounds with N and S, and these compounds are finely deposited mainly as nitrides, and these are used as nuclei for Si, Fe, Mg, Al, and C.
The inventors have newly found that a composite precipitate containing u, Ti, etc. is produced.

Among these impurities, Zr, Nb, and V can be removed by strengthening the sorting control of scrap as a steelmaking raw material and by improving the material of the refractory material of the ladle. It is possible to prevent mixing into steel. However, it is not easy to reduce the content of Ti because the source is Ti iron charging in the ironmaking process for stabilizing the blast furnace operation and alloy iron in the steelmaking process.

The inventors found that, when the magnetism of the non-oriented electrical steel sheet was continuously measured in the rolling direction after the finish annealing in the manufacturing process, there were periodic portions with poor iron loss. .. As a result of diligent research on the cause,
The parts with inferior iron loss characteristics (high iron loss values) should correspond to the skid position of the heating furnace during the slab heating stage. It was clarified that this phenomenon occurs when the Ti content in steel is high. That is,
Ti as an impurity element is finely precipitated in the form of TiN or TiC in a portion of the slab that is in contact with the skid of the heating furnace and has a relatively low temperature during the slab heating stage. Was found to be coarse and harmless.

This skid mark disappeared when the slab heating temperature was raised. Fig. 1 shows an example of continuous iron loss measurement recording after finish annealing. In the case of Fig. 1 (a) in which the slab is heated normally (around 1100 ° C), the iron loss at the skid mark portion is deteriorated. In the case of FIG. (B) heated at 1200 ° C., the skid mark disappears. However, when the slab heating temperature is increased, if other impurities such as N and S are large, MnS, AlN, etc. are partially re-dissolved and finely precipitated during hot rolling, and recrystallized grains grow during finish annealing. In addition to the above, the fine precipitates themselves impede the movement of the domain wall in the product due to the pinning effect and deteriorate the iron loss characteristics.

Therefore, in the present invention, in the manufacturing process of the non-oriented electrical steel sheet, the impurity elements other than Ti, such as C, N, S, Zr, V and Nb, are reduced to an extremely low level in the steel melting stage. In addition to solving the problems of skid marks by eliminating the above-mentioned adverse effects when heating the slabs at high temperatures and by heating the slabs to a temperature sufficient to erase the skid marks manifested by the inclusion of Ti. , The problem of magnetic deterioration of the product when the slab is heated at high temperature is solved.

The reasons for limiting the components in the present invention will be explained below. C forms ZrC, VC, TiC, NbC, and these fine precipitates not only hinder the growth of normal grains in the recrystallization process of steel during finish annealing, but also in the product due to the pinning effect of the fine precipitates themselves. It impedes the movement of the domain wall and impairs the iron loss characteristics. On the other hand, the application of the highest grade non-oriented electrical steel sheet is the core of a large rotating machine such as a generator, so it is required to endure long-term use, and the magnetic properties deteriorate during use (magnetic aging). It is indispensable not to cause. Therefore, and in order not to form the above-mentioned carbides, the C content must be 0.0030% or less. In order to satisfy this requirement, it is conceivable to decarburize the steel sheet (strip) in the middle of the manufacturing process. When the decarburization treatment of the steel sheet is performed in the hot-rolled sheet annealing step, the steel sheet is thick at this stage, so that the treatment time becomes long and the productivity is reduced. Further, when the steel sheet is subjected to a decarburizing treatment in the intermediate annealing step in cold rolling, an oxide layer is formed on the steel sheet surface, not only contaminating the rolling oil in the subsequent cold rolling stage, but also a flaw on the rolling roll, As a result, surface defects occur on the steel sheet. After the intermediate annealing, it is possible to pickle the steel sheet to remove the oxide layer on the surface, but this raises the manufacturing cost and is not realistic. Further, it is also possible to decarburize the steel sheet in the finish annealing step,
It has been implemented. However, also in this case, the iron loss characteristics in the high magnetic field of the product may be deteriorated due to the oxide layer formed on the surface of the steel sheet. As described above, it is not preferable to decarburize the steel sheet in the intermediate stage after hot rolling to reduce the C content from the viewpoint of manufacturing cost and product quality. Therefore, in the steel melting stage, the C content is 0.0030% or less,
Preferably it is 0.0010% or less. If the content of S is large, it partially re-dissolves in the slab heating stage and forms precipitates such as MnS and CuS during hot rolling, and these precipitates cause the growth of recrystallized grains during finish annealing. Also, the pinning effect of the precipitate prevents the movement of the domain wall in the product,
Deteriorate iron loss characteristics. Therefore, in order to minimize the formation of precipitates such as MnS and CuS, the S content is
It must be 0.0030% or less. When the S content is reduced to 0.0010% or less, the absolute amount of precipitates is sufficiently reduced, the slab heating temperature can be increased up to 1300 ° C., and there is no restriction on the slab heating temperature in terms of product quality.

Like S, when N is large in content, it partially re-dissolves in the slab heating stage, and AlN and T are added during hot rolling.
Precipitates such as iN, ZrN, Fe ₄ N, Si ₃ N ₄ , and VN are formed, and these precipitates prevent the growth of recrystallized grains during finish annealing, and the pinning effect of the precipitates causes the domain wall movement in the product. And iron loss characteristics are deteriorated. Therefore, the N content must be 0.0030% or less. Furthermore, when the content of N is 0.0010% or less, the absolute amount of precipitates is sufficiently reduced, and there is no restriction on the slab heating temperature from the aspect of quality, and the slab heating temperature in the hot rolling process is up to 1300 ° C. Can be higher. If the slab heating temperature can be raised to 1300 ° C., there are advantages such as that the shape (flatness) of the rolled material can be improved in the hot rolling stage.

Ti is added in the form of iron sand in order to stabilize the operation of the blast furnace, and is mixed into the steel from the ferroalloy at the melting stage of the steel. Ti reacts with N and C in the steel in the steps of casting molten steel and heating the slab, and TiN, TiC
To form. When the Ti content exceeds 0.0050%,
Under normal slab heating conditions, the steel sheet (strip) part corresponding to the slab part corresponding to the skid position of the slab heating furnace inhibits the growth of recrystallized grains during the finish annealing process, resulting in iron loss of the product. It becomes a so-called skid mark whose value is inferior to other parts. However, increasing the slab heating temperature can eliminate skid marks.
Further, in the refining process in the normal steelmaking process, the amount of Ti inevitably mixed in the steel is 0.010%.
The above skid mark has a Ti content of 0.003
If it is less than%, it will not occur. Therefore, preferably 0.0
It is less than 03%. O (oxygen) does not exist in a free state itself but exists as an oxide.
For example, SiO ₂ , Al ₂ O ₃ , Zr ₂ O ₃ , TiO
_It exists as ₂ , V ₂ O ₃ . Therefore, when the content of O is reduced, oxide-based inclusions can be reduced. Among the inclusions, SiO ₂ and Al ₂ O ₃ are
It can be sufficiently reduced by appropriate treatment conditions in the steel melting stage. In addition, Zr ₂ O ₃ ,
Inclusions such as TiO ₂ and V ₂ O ₃ can be reduced by reducing the content of elements such as Zr, Ti and V.

Zr is a basic refractory lining of a ladle when the Al content in the steel is high at the melting stage of the steel, especially when producing the highest grade non-oriented electrical steel sheet as in the present invention. Is an impurity that enters the steel by reducing Zr oxide and replacing it with Al. Thus, using a neutral refractory material is one of the effective means for preventing Zr from entering the steel. Zr forms precipitates of N, C and ZrN, ZrC, etc. in the steel during the casting stage of molten steel or the slab heating stage, and these deposits serve as nuclei for complex precipitates. Zr is 0.0050% or less, preferably 0.003% or less in order to reduce the influence of these precipitates to a level without actual harm.
Must be 0% or less.

Nb and V form precipitates with N and C in the steel, and these precipitates prevent the growth of normal grains in the recrystallization process in the finish annealing step, and prevent the movement of the magnetic domain wall in the product, and Since it deteriorates the loss characteristics, it should be 0.0050% or less, preferably 0.0030% or less.

Si is added to increase the specific resistance of the non-oriented electrical steel sheet and reduce eddy current loss. If Si is added in excess of 4.0%, the workability is extremely deteriorated and cold rolling becomes difficult. On the other hand, in the case of a medium to low grade product of less than 2.0%, it is possible to easily obtain a product having characteristics satisfying the grade quality without using the present invention.
In the present invention, good results are obtained when the Si content is 2.5 to 4.0%.

Al, like Si, increases the specific resistance of the non-oriented electrical steel sheet and reduces the eddy current loss. In the case of low-grade products whose content is less than 0.10%, it is possible to easily obtain products having characteristics satisfying the grade quality without using the present invention. On the other hand, when Al is added at the same time as Si, the atomic radii of Si and Al are such that Fe is sandwiched between Al and Al.
Since they exist in the order of>Fe> Si, the strain of the lattice is relaxed, the risk of brittleness is extremely reduced, and even if added up to 2.0%, there is no problem in cold rolling. Mn is
If the content is less than 0.1%, the workability of the steel sheet deteriorates. On the other hand, if the content exceeds 2.0%, the magnetic flux density of the product is significantly deteriorated. Mn content is 0.1
At 0.4%, good results are obtained.

P is added within the range of 0.2% or less in order to improve the punching property of the non-oriented electrical steel sheet. If added over 0.2%, the magnetic properties of the product will be impaired. Preferably, the P content is 0.1% or less.

Next, the manufacturing process will be described. The highest grade non-oriented electrical steel sheet of the present invention is melted in a converter. At this stage, C, N, S, Ti, Zr, Nb,
The V content is reduced to the level specified in the present invention to achieve high purity. The obtained molten steel is continuously cast into a slab or is poured into a mold to form a steel ingot, which is soaked and slab-rolled into a slab. The slab has a thickness of 100 to 300 mm, and usually has a unit weight of 10 tons or more. Therefore, when heating the slab prior to hot rolling, the temperature varies depending on the part of the slab. In the present invention, the lower limit is 1125 ° C. necessary for hot rolling, and the upper limit is 1300 ° C. from the viewpoint of refractory material cost of heating furnace and heating energy cost.

After heating, the slab is hot rolled to a thickness of 1.5 to 2.5 mm. The slab heating temperature defined in the present invention is the average surface temperature when the slab is soaked sufficiently for hot rolling and extracted from the heating furnace.

Then, the hot-rolled sheet is rolled or 900-1.
Annealing is performed for 30 seconds to 3 minutes in a temperature range of 000 ° C., followed by pickling and cold rolling to a final sheet thickness of 0.2 to 0.7 mm. The final sheet thickness may be obtained by performing cold rolling once from the hot rolled sheet, or may be obtained by performing cold rolling twice or more with intermediate annealing. When the final plate thickness is obtained by cold rolling twice, the intermediate plate thickness after the first cold rolling is 0.5 to 1.0 mm. After that, 1000-11
Finish annealing is performed for 20 to 200 seconds in a temperature range of 00 ° C.

[0024]

【Example】

(Embodiment 1) FIG. 2 shows the weight percentage of Si: 2.85 to 3.1.
5%, Al: 0.50 to 0.70%, S: 0.0005
To 0.0020%, N: 0.0005 to 0.0020
%, C: 0.0005 to 0.0025%, V: 0.00
20-0.0040%, Nb: 0.0020-0.00
40%, Zr: 0.0010 to 0.0040%, T
i: 0.0040 to 0.0080%, Mn: 0.1
A silicon slab consisting of 0.3%, P: 0.01 to 0.05%, the balance Fe and unavoidable impurities is 1200 at the surface temperature.
It shows the state of generation of skid marks when heated and soaked at ℃ and 1100 ℃. After hot rolling the slab,
The hot-rolled sheet was annealed, pickled, cold-rolled to 0.35 mm, and then finish-annealed in a dry atmosphere.

The horizontal axis represents the height of the skid mark, and in the case of heating at 1200 ° C., the generation of skid marks is extremely reduced as compared with the case of heating at 1100 ° C. or,
The average iron loss in each case is W1 at 1200 ° C heating
0/50 = 1.001 W / kg (n number = 81 coils), 1
W100 / 50 = 0.986 W / kg (n
(Number = 71 coils), the difference is extremely small, and the effect of high purification appears.

[0026]

According to the present invention, the highest grade non-oriented electrical steel sheet can be stably manufactured without adding a large amount of alloying elements such as Si and Al.
Further, by refining the steel to a high degree, it is possible to eliminate the skid mark, which is unavoidable due to the influence of Ti mixed in, by increasing the slab heating temperature.

[Brief description of drawings]

1 is a continuous iron loss measurement record after finish annealing in the case of Example, (a) is a normal (1100 ° C.) slab heating, and (b) is a 1200 ° C. iron loss value (skid mark) Presence / absence).

FIG. 2 is a diagram showing the occurrence of skid marks when the slab having the component composition in Example 1 of the present invention was heated to 1100 ° C. and 1200 ° C. and soaked in relation to iron loss.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Fujino 1-1, Toibata-cho, Tobata-ku, Kitakyushu, Fukuoka Prefecture New Nippon Steel Corporation Yawata Works

Claims (2)

[Claims] 1. As weight%, Si: 1.0 to 4.0%, Al: 0.001 to 2.0%, N: ≤ 0.0020%, S: ≤ 0.0020%, C: ≤ 0.0030% Mn: 0.1 to 2.0%, Ti: 0.003 to 0.010%, Zr: ≤ 0.0050%, Nb: ≤ 0.0050%, V: ≤ 0.0050%, P: ≤0.2%, the slab consisting of the balance Fe and unavoidable impurities is heated to a temperature range of 1125 to 1300 ° C at the surface temperature, hot rolled into a hot rolled steel strip, and pickled, Next, a method for producing a non-oriented electrical steel sheet having excellent magnetic properties, which comprises performing final annealing after cold rolling one or more times with intermediate annealing sandwiched between them to obtain a final sheet thickness. 2. As weight%, Si: 1.0 to 4.0%, Al: 0.001 to 2.0%, N: ≤ 0.0020%, S: ≤ 0.0020%, C: ≤ 0.0030% Mn: 0.1 to 2.0%, Ti: 0.003 to 0.010%, Zr: ≤ 0.0050%, Nb: ≤ 0.0050%, V: ≤ 0.0050%, P: ≦ 0.2%, the slab consisting of the balance Fe and unavoidable impurities is heated to a temperature range of 1125 to 1300 ° C. at the surface temperature and hot rolled into a hot rolled steel strip, which is annealed and then acidified. A method for producing a non-oriented electrical steel sheet having excellent magnetic properties, which comprises washing and then cold rolling one or more times with intermediate annealing to obtain a final sheet thickness, followed by finish annealing.