JP4283533B2 - Manufacturing method of unidirectional electrical steel sheet - Google Patents

Description

【００３３】
（実施例２）
Ｓｉ：３．２％、Ｃ：０．０５％、酸可溶性Ａｌ：０．０２７％、Ｎ：０．００８％、Ｍｎ：０．２０％、Ｓ：０．０７％、Ｃｒ：０．１２％、Ｃｕ：０．００８〜０．０７１％含む珪素鋼スラブを１２００℃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０．３ｍｍ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。
【００３４】

【００３５】
（実施例３）
Ｓｉ：３．３％、Ｃ：０．０６％、酸可溶性Ａｌ：０．０２７％、Ｎ：０．００８％、Ｍｎ：０．１％、Ｓ：０．００８％、Ｃｒ：０．１２％、Ｓｎ：０．０６％、Ｃｕ：０．０１３％及び０．０４８％を含む珪素鋼スラブを１２００℃に加熱し、板厚２．３ｍｍに熱延した。この熱延板を１１２０℃で焼鈍を施した後０．２８ｍｍに冷間圧延した。この冷延板を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０．０２１％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。
一次再結晶焼鈍前の冷延板の化学分析値、及び製品の特性値を表３に示す。
【００３６】

【００３７】
【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Ｃｕ量の影響を示す図である。
【図２】Ｃｕ量がそれぞれ（ａ）Ｃｕ＝０．００５％、（ｂ）Ｃｕ＝０．０５４％である試料の脱炭焼鈍後の一次再結晶粒組織を示した写真である。[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 a {110} <001> orientation 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 composed of crystal grains accumulated in the {110} <001> orientation as described above, and usually has a thickness of 0.1 to 0.4 mm containing Si of 4.8% or less. It is a steel plate. 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, and as typical precipitates, MFLittmann has the following Patent Document 1, JETurnbull has MnS in Non-Patent Document 1, Taguchi et al. Presents MnSe in Patent Document 3 and Komatsu et al. Present (Al, Si) N in Patent Document 4.
On the other hand, Saito presents Pb, Sb, Nb, Ag, Te, Se, S, etc. as grain boundary segregation type elements in Non-Patent Document 2, but industrially all are precipitate type inhibitors. It is only used as an auxiliary to.
[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 Document 4) are considered as follows. .
(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]
As a method for controlling the precipitation size and dispersion state of these inhibitors, for example, in Patent Document 2 and Patent Document 5, precipitates such as MnS, AlN, and MnSe are completely dissolved at the time of slab heating before hot rolling. A method of precipitating in a hot rolling process or a cooling process during 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.
[0008]
[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,
44 (1980), 419/424 [Patent Document 5]
Japanese Patent Publication No. 53-13469 [0009]
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. When the slab heating temperature is lowered, the amount of precipitates functioning as an inhibitor is lowered and the secondary recrystallization is destabilized. Therefore, it is necessary to strengthen the inhibitor by some method.
[0010]
Patent Document 6 below 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, and Patent Document 7 discloses Al. In addition, there is disclosed a method of 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, and Mo. Patent Document 4 and Patent Document 8 disclose a method in which slab heating temperature is reduced to 1280 ° C. or less by performing nitriding after decarburization annealing to form (Al, Si) N precipitates and function as an inhibitor. ing.
[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 5]
A. Kussmann, B. Scharrow, WSMesskin: Stahlund 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 inventors of the present invention have investigated the variation factors of product characteristics in a method of manufacturing a grain-oriented electrical steel sheet by low-temperature slab heating. As a result, it has been found that Cu, which has been increasing in recent years due to scrap recycling among the impurity elements, has become a major fluctuation factor. If Cu is present in a certain amount or more among the impurities in the component, it influences the grain structure of primary recrystallization and destabilizes secondary recrystallization. Therefore, in order to stabilize the magnetic characteristics: magnetic flux density (B8 value) of the product, it is important to control the amount of Cu in the impurities to a certain level or less.
[0017]
The experimental results are specifically shown below.
By mass: Si: 3.3%, C: 0.05%, acid-soluble Al: 0.027%, N: 0.008%, Mn: 0.1%, S: 0.006%, Cr: 0.00. A silicon steel slab containing 12%, Sn: 0.05%, Cu: 0.005 to 0.054%, and the balance Fe and inevitable impurities are heated at 1200 ° C. and then hot-rolled to 2.3 mm. A thick hot-rolled sheet was used. Then, after annealing at 1120 ° C., it was cold-rolled to a thickness of 0.22 mm and decarburized and annealed at 840 ° 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.
[0018]
The result is shown in FIG. From FIG. 1, it can be seen that a product having a stable secondary recrystallization and a high magnetic flux density (B8) is stably obtained when Cu as an impurity is 0.04% or less, preferably 0.02% or less. I understand.
FIG. 2 shows the grain structure of the primary recrystallized sample of these products (a) Cu = 0.005% and (b) Cu = 0.054%. Sample (b), in which secondary recrystallization is unstable and the magnetic flux density (B8) of the product is low, is finer and coarser than the sample (a). It can be seen that the grain structure is non-uniform.
When the cause was investigated, it was found that a large amount of fine copper sulfide was deposited on the cold-rolled sheet having a large amount of Cu as an impurity. Since copper sulfide is thermally unstable compared to manganese sulfide, this thermally unstable fine copper sulfide decomposes during annealing and mixes the primary recrystallized structure, thereby causing secondary recrystallization. It is presumed that the crystal is unstable.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described.
As a component which a slab contains in this invention, by mass%, Si: 0.8-4.8%, C: 0.003-0.1%, acid-soluble Al: 0.012-0.05%, N ≦ 0.012%, Mn ≦ 0.8%, S ≦ 0.015%, and Mn / S ≧ 4.0 are required.
[0020]
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%, γ transformation occurs during finish annealing, the crystal orientation is impaired, and improvement in iron loss characteristics cannot be expected.
[0021]
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.
[0022]
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.
[0023]
If N exceeds 0.012%, voids in the steel plate called blisters are generated, so 0.012% is made the upper limit.
[0024]
S is 0.015% or less, preferably 0.007% or less. Since MnS is not used as an inhibitor in this production method, it is preferable that S is rather small.
[0025]
Mn fixes solute S in steel and prevents hot cracking due to S segregation. When 0.08 or more is added, MnS is coarsely precipitated 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%.
[0026]
Sn is an element effective 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.
[0027]
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, containing a trace amount of B, Bi, Se, Pb, Ti, Mo, V, etc. in the steel does not impair the gist of the present invention.
[0028]
Among impurity elements, Cu tends to increase in recent years due to scrap recycling. It is a point of the present invention that the amount of Cu is defined. Cu is finely precipitated as copper sulfide after hot-rolling and hot-rolled sheet annealing, and part of it decomposes during decarburization annealing to mix the primary recrystallized structure and make secondary recrystallization unstable. It is necessary to regulate the amount of Cu in the steel to 0.04% or less, preferably 0.02% or less.
[0029]
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. After this slab is hot-rolled, the final thickness is obtained by combining annealing and cold rolling. 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 is performed in a humid atmosphere gas, which also serves to remove C in the steel. In the stage before the primary recrystallization, the thermally unstable copper sulfide regulates the amount of Cu in the steel to prevent the primary recrystallized structure from becoming mixed.
[0030]
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 includes a method of performing in an nitriding atmosphere gas such as ammonia, a method of nitriding during 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 so that the ratio is 2/3 or more.
[0031]
【Example】
Hereinafter, the present invention will be described in detail by way of specific examples.
Example 1
Si: 3.3%, C: 0.06%, acid-soluble Al: 0.028%, N: 0.007%, Mn: 0.14%, S: 0.003-0.008%, Cu: A silicon steel slab containing 0.010 to 0.062%, Cr: 0.11%, Sn: 0.05% was heated to 1150 ° C, and then hot rolled to a sheet thickness of 2.3 mm. . This hot-rolled sheet was annealed at 1100 ° C. for 30 seconds. Thereafter, it was cold-rolled to 0.22 mm and subjected to primary recrystallization annealing at 850 ° C. for 3 minutes. After annealing in an ammonia-containing atmosphere to reduce the nitrogen amount to 0.022%, 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.
[0032]

[0033]
(Example 2)
Si: 3.2%, C: 0.05%, acid-soluble Al: 0.027%, N: 0.008%, Mn: 0.20%, S: 0.07%, Cr: 0.12% The silicon steel slab containing Cu: 0.008 to 0.071% was heated to 1200 ° C. and hot rolled to a plate thickness of 2.3 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 0.3 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.
[0034]

[0035]
(Example 3)
Si: 3.3%, C: 0.06%, acid-soluble Al: 0.027%, N: 0.008%, Mn: 0.1%, S: 0.008%, Cr: 0.12% The silicon steel slab containing Sn: 0.06%, Cu: 0.013% and 0.048% was heated to 1200 ° C. and hot rolled to a plate thickness of 2.3 mm. The hot-rolled sheet was annealed at 1120 ° C. and then cold-rolled to 0.28 mm. The cold-rolled sheet was decarburized and annealed at 850 ° C. for 3 minutes, and then annealed in an ammonia-containing atmosphere to make the nitrogen amount 0.021%. 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 3 shows the chemical analysis value of the cold-rolled sheet before the primary recrystallization annealing and the characteristic value of the product.
[0036]

[0037]
【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 effect of Cu content on the magnetic flux density (B8) of a product.
FIG. 2 is a photograph showing a primary recrystallized grain structure after decarburization annealing of a sample in which the amounts of Cu are (a) Cu = 0.005% and (b) Cu = 0.054%, respectively.

Claims (3)

% By mass
Si: 0.8 to 4.8%,
C: 0.003-0.1%,
Acid-soluble Al: 0.012-0.05%
N ≦ 0.012%,
Mn ≦ 0.8%,
S ≦ 0.015%,
Mn / S ≧ 4.0 ,
Cr: 0.03-0.2%
After the silicon steel slab containing the balance Fe and inevitable impurities is heated at a temperature of 1280 ° C. or less, it is formed into a hot-rolled sheet by hot rolling, as it is or after hot-rolled sheet annealing, once or in the middle In the manufacturing method of grain-oriented electrical steel sheet, the final thickness is obtained by cold rolling at least twice with annealing, followed by decarburization annealing, nitriding treatment, and then applying annealing separator, and then performing the final annealing. Among the elements, a method for producing a unidirectional electrical steel sheet, wherein the Cu content is controlled in mass% within the range of the following formula (1).
Cu (%) ≦ 0.04 (1) % By mass
Si: 0.8 to 4.8%,
C: 0.003-0.1%,
Acid-soluble Al: 0.012-0.05%
N ≦ 0.012%,
Mn ≦ 0.8%,
S ≦ 0.015%,
Mn / S ≧ 4.0 ,
Cr: 0.03-0.2%
After the silicon steel slab containing the balance Fe and inevitable impurities is heated at a temperature of 1280 ° C. or less, it is formed into a hot-rolled sheet by hot rolling, as it is or after hot-rolled sheet annealing, once or in the middle In the manufacturing method of grain-oriented electrical steel sheet, the final thickness is obtained by cold rolling at least twice with annealing, followed by decarburization annealing, nitriding treatment, and then applying annealing separator, and then performing the final annealing. Among the elements, the Cu content is controlled by mass% within the range of the following formula (2), and a method for producing a unidirectional electrical steel sheet, comprising:
Cu (%) ≦ 0.02 (2) % By mass
Sn: 0.03-0.15%
It contains, The manufacturing method of the unidirectional electrical steel sheet of Claim 1 or 2 characterized by the above-mentioned.

Images