JP4267320B2 - Manufacturing method of unidirectional electrical steel sheet - Google Patents

Description

【００３６】
（実施例２）
Ｓｉ：３．２％、Ｃ：０．０５％、酸可溶性Ａｌ：０．０２８％、Ｎ：０．００８％、Ｍｎ：０．１５％、Ｓ：０．００７％、Ｃｒ：０．１２％、Ｓｎ：０．０４％を含む珪素鋼スラブ（１３００〜１１００℃の温度域の冷却速度０．０１℃／秒）を、１１００℃、１１５０℃、１２００℃、１２５０℃に加熱し、板厚２．３ｍｍに熱延した。この熱延板を１１２０℃で２分間焼鈍した後９００℃まで１０秒で冷却し、次いで１００℃湯冷した。
その後０．２２ｍｍに冷間圧延し、８５０℃で３分間脱炭焼鈍を施した後、アンモニア含有雰囲気で焼鈍して窒素量を０．０２４％とした。この脱炭焼鈍板にＭｇＯを主成分とする焼鈍分離剤を塗布した後、１２００℃で２０時間仕上げ焼鈍を施した。
製品の特性値を表２に示す。
【００３７】

【００３８】
【発明の効果】
本発明により、二次再結晶を行わせるために必要な、一次再結晶粒組織の調整を安定して達成することが可能となり、工業的に高磁束密度の一方向性電磁鋼板を安定して製造することができる。
【図面の簡単な説明】
【図１】製品の磁束密度（Ｂ8 ）に及ぼすスラブの１３００〜１１００℃の温度域の冷却速度の影響を示す図である。
【図２】製品の磁束密度（Ｂ8 ）に及ぼす鋼中のＭｎ量とスラブ加熱温度の影響を示した図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a so-called grain-oriented electrical steel sheet in which crystal grains are accumulated in {110} <001> orientations with a Miller index. This steel plate is used as an iron core of electrical equipment such as a transformer as a soft magnetic material.
[0002]
[Prior art]
The grain-oriented electrical steel sheet is a steel sheet having a thickness of 0.1 to 0.4 mm, which is composed of crystal grains accumulated in the {110} <001> orientation as described above and usually contains 4.8% or less of Si. It is. This steel sheet is required to have excitation characteristics and iron loss characteristics as magnetic characteristics, and in order to meet these requirements, it is important to align the crystal orientation at a high level. This integration of crystal orientation is achieved by utilizing a catastrophic grain growth phenomenon called secondary recrystallization.
[0003]
In order to control this secondary recrystallization, (1) adjustment of the primary recrystallization structure before secondary recrystallization, and (2) adjustment of fine precipitates or grain boundary segregation elements called inhibitors are carried out. is necessary. This inhibitor has a function of suppressing the growth of general grains in the primary recrystallization structure and preferentially growing only specific orientation grains.
[0004]
Numerous studies have been made on inhibitors. As typical precipitates, MFLittmann (Patent Document 1) and JETurnbull (Non-Patent Document 1) use MnS, Taguchi et al. (Patent Document 2) use AlN, Middle (Patent Document 3) presents MnSe and Komatsu et al. (Patent Document 4) presents (Al, Si) N.
On the other hand, Saito (Non-Patent Document 2) presents Pb, Sb, Nb, Ag, Te, Se, S, etc. as grain boundary segregation type elements. It is only used as a supplement to inhibitors.
[0005]
[Patent Document 1]
Japanese Patent Publication No. 30-3651 [Non-Patent Document 1]
Trans.Met.Soc.AIME, 212 (1958) 769/781 [Patent Document 2]
Japanese Patent Publication No. 40-15644 [Patent Document 3]
Japanese Patent Publication No. 51-13469 [Patent Document 4]
Japanese Patent Publication No.62-45285 [Non-patent Document 2]
Journal of the Japan Institute of Metals, 27 (1963), 186/195 [0006]
The necessary conditions for these precipitates to function as inhibitors are not necessarily clear, but the results of Matsuoka (Non-patent Document 3), Kuroki et al. (Non-patent Documents 4 and 5) are summarized as follows. Can be considered.
(1) Presence of sufficient amount of fine precipitates to suppress the growth of primary recrystallized grains before secondary recrystallization.
(2) The precipitate is thermally stable and should not be weakened suddenly during secondary recrystallization.
[0007]
[Non-Patent Document 3]
Iron and Steel, 53 (1967), 1007/1023 [Non-Patent Document 4]
Journal of the Japan Institute of Metals, 43 (1979), 175/181 [Non-patent Document 5]
Journal of the Japan Institute of Metals, 44 (1980), 419/424 [0008]
As a method for controlling the precipitation size and dispersion state of these inhibitors, for example, in Patent Document 2 and Patent Document 5 below, precipitates such as MnS, AlN, and MnSe are completely dissolved at the time of slab heating before hot rolling, The method of making it precipitate in the subsequent hot rolling process and the cooling process at the time of hot-rolled sheet annealing is disclosed. In order to completely dissolve the inhibitor necessary for the secondary recrystallization, it is necessary to insert the slab into a furnace at about 1400 ° C. for a long time. This is about 200 ° C higher than the slab heating temperature of ordinary steel, requires a dedicated high-temperature slab heating furnace, has a high energy intensity of the heating furnace, has a large amount of melting scale, and increases the maintenance cost of the heating furnace. Occurs.
[0009]
[Patent Document 5]
Japanese Patent Publication No. 53-13469 [0010]
In order to solve such problems, a technique for producing grain-oriented electrical steel sheets by slab heating similar to that of ordinary steel has been studied. If the slab heating is lowered, the amount of precipitates functioning as an inhibitor is reduced, and secondary recrystallization is destabilized. Therefore, it is necessary to strengthen the inhibitor by some method.
The following Patent Document 6 discloses a method of bringing the slab heating temperature to a range of 1050 to 1350 ° C. by adding grain boundary segregation elements such as As, Bi, and Sb into the steel. In addition to Al, a method for reducing the slab heating temperature to a range of 1100 to 1260 ° C. by adding a nitride forming element such as Zr, Ti, B, Nb, Ta, V, Cr, or Mo is disclosed. . Moreover, in the said patent document 4 and the following patent document 8, a slab heating temperature shall be 1280 degrees C or less by performing a nitriding process after decarburization annealing, forming (Al, Si) N precipitate, and functioning as an inhibitor. A method is disclosed.
[0011]
[Patent Document 6]
Japanese Patent Publication No. 54-24685 [Patent Document 7]
JP 52-24116 A [Patent Document 8]
Japanese Examined Patent Publication No. 8-3125 [0012]
As for the influence of Cu on the magnetic properties of electromagnetic steel sheets, there is a study by A. Kussmann et al. According to this, the magnetic properties deteriorate when Cu is mixed, but the deterioration allowance is small up to about 0.7%, and it has been reported that it can be contained up to this amount. On the other hand, Patent Document 9 and Patent Document 10 below disclose that when Cu is added together with Mn, Se, and S, it functions as a secondary recrystallization inhibitor as manganese copper selenide or manganese copper sulfide. Has been. Thereafter, the following Patent Document 11, Patent Document 12, Patent Document 13 and the like disclose a method for producing a grain-oriented electrical steel sheet using copper sulfide as an inhibitor.
[0013]
[Non-Patent Document 6]
A. Kussmann, B. Scharrow, WSMesskin: Stahl und Eisen, 50 (1930), p1194
[Patent Document 9]
Japanese Patent Publication No. 58-43443 [Patent Document 10]
Japanese Patent Publication No. 58-43444 [Patent Document 11]
JP-A-6-322443 [Patent Document 12]
JP-A-6-145803 [Patent Document 13]
JP-A-8-277421 [0014]
[Problems to be solved by the invention]
In the method for producing a grain-oriented electrical steel sheet by low-temperature slab heating disclosed in Patent Document 4, Patent Document 8 and the like, the inhibitor is formed by nitriding after decarburization annealing, so that the primary recrystallized structure in the previous stage It is important to control. For example, the inventors point out the importance of Patent Document 14 and Patent Document 15 below.
An object of the present invention is to provide a technology for producing grain-oriented electrical steel sheets that are controlled industrially and have excellent magnetic properties by controlling the grain structure of primary recrystallization.
[0015]
[Patent Document 14]
Japanese Patent Publication No. 8-32929 [Patent Document 15]
JP-A-6-49543 [0016]
[Means for Solving the Problems]
The present inventors investigated the influence of various production conditions on the primary recrystallization structure. As a result of this investigation, it became clear that the cooling rate of the slab and the slab heating temperature have a significant effect on the primary recrystallized grain structure, and by controlling these factors, products with high magnetic flux density can be manufactured stably. .
[0017]
Specific experimental results are shown below.
By mass: Si: 3.3%, C: 0.06%, acid-soluble Al: 0.027%, N: 0.008%, Mn: 0.1%, S: 0.006%, Cr: 0.00. In the process of continuously casting a steel containing 12%, Sn: 0.05%, and the balance Fe and inevitable impurities, the cooling rate in the temperature range of 1300 ° C to 1100 ° C is 10 ° C / second, 1 ° C / second , And controlled to 0.01 ° C./second and cooled to room temperature. The silicon steel slab was heated at 1150 ° C. and then hot rolled to obtain a hot-rolled sheet having a thickness of 2.3 mm.
Then, after annealing at 1120 ° C., it was cold-rolled to a thickness of 0.22 mm and decarburized and annealed at 850 ° C. for 90 seconds. After decarburization annealing, annealing was performed in an ammonia-containing atmosphere, and after the nitrogen content was 0.020 to 0.024%, finish annealing was performed.
[0018]
The result is shown in FIG. FIG. 1 shows that when the cooling rate of the silicon steel slab is 1 ° C./second or less, a secondary recrystallization is stable and a product having a high magnetic flux density (B8) is stably obtained. When the precipitates and grain structure of these decarburized and annealed plates were investigated, it was found that when the cooling rate was as fast as 10 ° C./second, the size of the sulfide was small and the grain structure was non-uniform.
[0019]
Based on this result, the silicon steel slab in which Mn was changed in the range of 0.05 to 0.25% in the above component system, the cooling rate in the temperature range of 1300 ° C. to 1100 ° C. was 0.01 ° C./second. And cooled to room temperature. The silicon steel slab was heated in a temperature range of 1050 ° C. to 1280 ° C. and then hot rolled to obtain a hot-rolled sheet having a thickness of 2.3 mm. Then, after annealing at 1120 ° C., it was cold-rolled to a thickness of 0.22 mm and decarburized and annealed at 850 ° C. for 90 seconds. After decarburization annealing, annealing was performed in an ammonia-containing atmosphere, and the amount of nitrogen was adjusted to 0.020 to 0.024%, and then finish annealing was performed.
[0020]
The result is shown in FIG. By controlling the slab heating temperature to the range of the following formula (1), preferably the formula (2) with respect to the Mn content of the steel sheet, it is possible to stably produce a high magnetic flux density unidirectional electrical steel sheet from FIG. I understand.
T (° C.) ≦ 250 · log {Mn (%)} + 1440 (1)
T (° C.) ≦ 250 · log {Mn (%)} + 1410 (2)
[0021]
In these cases as well, when the precipitates and grain structure of the decarburized annealed plate were investigated, secondary recrystallization was unstable, and under the conditions of low magnetic flux density, the sulfide size was small and the grain structure was unsatisfactory. It was confirmed to be uniform.
Accordingly, the sulfide precipitation size depends not only on the cooling conditions of the slab but also on the slab heating conditions. In the slab heating, the heating temperature is managed according to the amount of Mn, and the dispersion state of the sulfide can be controlled. It is considered important.
[0022]
From the above results, the present inventors consider this secondary recrystallization stabilization mechanism as follows.
Regarding sulfides, so far, (1) MnS is not used as an inhibitor in the present production method, so it is preferable that S is rather small, and (2) Mn and S are used to prevent hot cracking due to S segregation. It is disclosed that the ratio of Mn / S ≧ 4.0 is necessary.
This result suggests that further coarse precipitation of sulfide is important for secondary recrystallization stabilization. First, by setting the cooling rate of the slab to 1 ° C./second or less in a temperature range of 1300 to 1100 ° C. where MnS precipitates, precipitation is promoted and coarse precipitates are formed. Then, by limiting the temperature of slab heating, re-solution of the coarse MnS precipitate is suppressed, and the coarse state is maintained before the primary recrystallization annealing. Coarse MnS is thermally stable and does not change during annealing, so primary recrystallized grains grow uniformly to form a sized structure, and secondary recrystallization stabilizes, so high magnetic flux density is unidirectional. It is considered that electrical steel sheets can be manufactured.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described.
As a component which a slab contains in this invention, Si: 0.8-4.8% by mass, acid-soluble Al: 0.012-0.05%, N: 0.004-0.012% are required. is there.
When Si is added in an increased amount, the electrical resistance is increased and the iron loss characteristics are improved. However, if it exceeds 4.8%, the material is easily cracked during cold rolling, and rolling becomes difficult. On the other hand, if it is less than 0.8%, the γ transformation occurs during finish annealing, the crystal orientation is impaired, and improvement in iron loss characteristics cannot be expected.
[0024]
If C remains, it causes a decrease in product characteristics (iron loss), so it is necessary to suppress it to 0.003% or less at the product stage. However, if the amount of C is lowered in the steelmaking stage, coarse {100} elongated grains are present in the crystal structure of the hot-rolled sheet, which adversely affects secondary recrystallization. Also from the viewpoint of controlling precipitates and primary recrystallization texture, C must be added to some extent in the steelmaking stage. Therefore, it is desirable to add 0.003% or more, preferably 0.02% or more, at which the α / γ transformation occurs in the steelmaking stage. Even if more than 0.1% is added, the above-mentioned influence on the crystal structure, precipitates, etc. is almost saturated, and the time required for decarburization becomes longer, so 0.1% is made the upper limit.
[0025]
In the present invention, acid-soluble Al is an essential element for binding to N and precipitating as AlN to function as an inhibitor. The limited range is 0.012 to 0.050% where the magnetic flux density increases.
[0026]
If N exceeds 0.012%, voids in the steel plate called blisters are produced, so the upper limit is 0.12%. From the viewpoint of the quantity of AlN, 0.004% is made the lower limit.
[0027]
S is 0.015% or less, preferably 0.007% or less. Since MnS is not used as an inhibitor in the production method of the present invention, it is preferable that S is rather small.
[0028]
Mn fixes solute S in steel and prevents hot cracking due to S segregation. When 0.08% or more is added, MnS coarsely precipitates and secondary recrystallization is stabilized. On the other hand, if the amount of Mn exceeds 0.8%, the magnetic flux density of the product is lowered, which is not preferable. Therefore, the upper limit is set to 0.8%.
[0029]
Sn and Sb are effective elements for stably producing a product having a high magnetic flux density by segregating on the surface of the steel sheet to suppress decomposition of the inhibitor during finish annealing. It is desirable to add 0.03 to 0.15%. If it is less than this lower limit value, the inhibitor decomposition suppressing effect is small, and a substantial magnetic flux density improving effect cannot be obtained. If this upper limit is exceeded, nitriding into the steel sheet becomes difficult and secondary recrystallization may become unstable.
[0030]
Cr is an element that improves the oxide layer of decarburization annealing and is effective for glass coating formation. It is desirable to add 0.03 to 0.2%.
In addition, the inclusion of a small amount of B, Bi, Cu, Se, Pb, Ti, Mo, V, etc. in the steel does not impair the gist of the present invention.
[0031]
The silicon steel slab is obtained by melting steel with a converter or an electric furnace, vacuum-degassing the molten steel as necessary, and then performing continuous casting or ingot forming and then batch rolling. Controlling the cooling rate of the slab is one point of the present invention.
When the slab is hot-rolled, it is another point of the present invention to define the slab heating temperature according to the amount of Mn.
[0032]
Thereafter, annealing and cold rolling are combined to obtain the final thickness. At that time, in order to adjust the texture, the cold rolling may be performed at a final cold rolling reduction of 80% or more as disclosed in Patent Document 2.
Thereafter, primary recrystallization annealing that also serves as decarburization is performed in a humid atmosphere gas that also serves to remove C in the steel. It is a constituent factor of the present invention to prevent the primary recrystallized structure from becoming mixed by controlling the cooling rate of the slab and the slab heating temperature before the primary recrystallization annealing.
[0033]
Thereafter, after applying an annealing separator mainly composed of MgO, finish annealing is performed. At that time, in order to secure an inhibitor amount necessary for performing the secondary recrystallization, it is necessary to perform a nitriding treatment before the secondary recrystallization occurs. The method of nitriding is not particularly limited, and there are a method of performing in an nitriding atmosphere gas such as ammonia, a method of nitriding at the time of finish annealing by adding a nitride additive in an annealing separator. The amount of nitriding may be 0.005% or more, preferably N / acid-soluble Al is 2/3 or more.
[0034]
【Example】
Example 1
Si: 3.3%, C: 0.06%, acid-soluble Al: 0.026%, N: 0.007%, Mn: 0.1%, S: 0.008%, Cr: 0.11% , After heating a silicon steel slab containing Sn: 0.05% (cooling rate 0.01 ° C./second in a temperature range of 1300 to 1100 ° C.) to 1100 ° C., 1150 ° C., 1200 ° C. and 1250 ° C. A hot-rolled sheet having a thickness of 2.0 mm was obtained by rolling. This hot-rolled sheet was annealed at 1100 ° C. for 30 seconds.
Thereafter, it was cold-rolled to 0.19 mm and subjected to primary recrystallization annealing at 850 ° C. for 3 minutes. After annealing in an ammonia-containing atmosphere to make the amount of nitrogen 0.024%, finish annealing was performed at 1200 ° C. for 20 hours.
Table 1 shows the chemical analysis value of the cold-rolled sheet before the primary recrystallization annealing and the characteristic value of the product.
[0035]

[0036]
(Example 2)
Si: 3.2%, C: 0.05%, acid-soluble Al: 0.028%, N: 0.008%, Mn: 0.15%, S: 0.007%, Cr: 0.12% , Sn: A silicon steel slab containing 0.04% (cooling rate 0.01 ° C./second in a temperature range of 1300 to 1100 ° C.) is heated to 1100 ° C., 1150 ° C., 1200 ° C., and 1250 ° C. to obtain a plate thickness of 2 Hot rolled to 3 mm. The hot-rolled sheet was annealed at 1120 ° C. for 2 minutes, cooled to 900 ° C. in 10 seconds, and then cooled at 100 ° C. with hot water.
Thereafter, it was cold-rolled to 0.22 mm, decarburized and annealed at 850 ° C. for 3 minutes, and then annealed in an ammonia-containing atmosphere to make the amount of nitrogen 0.024%. After applying an annealing separator mainly composed of MgO to the decarburized annealing plate, finish annealing was performed at 1200 ° C. for 20 hours.
Table 2 shows the product characteristic values.
[0037]

[0038]
【The invention's effect】
According to the present invention, it is possible to stably achieve the adjustment of the primary recrystallized grain structure necessary for performing secondary recrystallization, and industrially stable unidirectional electrical steel sheet with high magnetic flux density. Can be manufactured.
[Brief description of the drawings]
FIG. 1 is a graph showing the influence of the cooling rate of a slab in the temperature range of 1300 to 1100 ° C. on the magnetic flux density (B 8) of a product.
FIG. 2 is a graph showing the influence of the amount of Mn in steel and the slab heating temperature on the magnetic flux density (B8) of the product.

Claims (2)

% By mass
Si: 0.8 to 4.8%,
C: 0.003-0.1%,
Acid-soluble Al: 0.012-0.05%
N: 0.004 to 0.012%,
Mn ≦ 0.8%,
S ≦ 0.015%,
Mn / S ≧ 4.0 ,
Cr: 0.03-0.2%,
Sn: 0.03-0.15%
The steel comprising the balance Fe and inevitable impurities is made into a slab, and the slab is heated at a temperature of 1280 ° C. or less, and then hot-rolled by hot rolling, as it is or after hot-rolled sheet annealing, In a method for producing a grain-oriented electrical steel sheet in which a final sheet thickness is obtained by cold rolling at least twice with intermediate or intermediate annealing, followed by decarburization annealing, nitriding, and finish annealing, cooling is performed from 1300 ° C to 1100 ° C after slab formation. A method for producing a unidirectional electrical steel sheet, characterized by controlling the slab heating temperature to a range of the following formula (1) with respect to the Mn content of the steel sheet while controlling the speed to 1 ° C./second or less.
T (° C.) ≦ 250 · log {Mn (%)} + 1440 (1) % By mass
Si: 0.8 to 4.8%,
C: 0.003-0.1%,
Acid-soluble Al: 0.012-0.05%
N: 0.004 to 0.012%,
Mn ≦ 0.8%,
S ≦ 0.015%,
Mn / S ≧ 4.0 ,
Cr: 0.03-0.2%,
Sn: 0.03-0.15%
The steel comprising the balance Fe and inevitable impurities is continuously cast to form a slab, the slab is heated at a temperature of 1280 ° C. or less, and then hot-rolled by hot rolling, as it is or hot-rolled After annealing, in the manufacturing method of grain-oriented electrical steel sheet, which is subjected to final rolling thickness by cold rolling at least once with intermediate or intermediate annealing, followed by decarburization annealing, nitriding treatment, finish annealing, from 1300 ° C after slab formation Production of a unidirectional electrical steel sheet characterized by controlling the cooling rate at 1100 ° C. to 1 ° C./second or less and controlling the slab heating temperature within the range of the following formula (2) with respect to the Mn content of the steel sheet. Method.
T (° C.) ≦ 250 · log {Mn (%)} + 1410 (2)

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