JP4585144B2 - Method for producing unidirectional electrical steel sheet with excellent magnetic properties - Google Patents

Description

【００５０】
【表２】

【００５１】
【発明の効果】
本発明により、二次再結晶の不均一性を解消して、優れた磁気特性を有する一方向性電磁鋼板を、工業的に生産することが可能となる。
【図面の簡単な説明】
【図１】熱延加熱温度と析出物インヒビター完全溶体化温度の差、及び、ＢからＮ当量差し引いた量（＝Ｂ−０．７７１×Ｎ）に対する、磁気特性の関係を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a unidirectional electrical steel sheet mainly used as an iron core such as a transformer.
[0002]
[Prior art]
Various techniques for stably producing unidirectional electrical steel sheets having excellent magnetic properties with a magnetic flux density B8 (magnetic flux density in a magnetic field of 800 A / m) exceeding 1.9 T have been proposed. In general, it can be classified into the following three categories.
The first technique is to heat the slab to its heating temperature for a sufficient amount of time to heat the slab from 1350 ° C to an ultra-high temperature of up to 1450 ° C and uniformly throughout the slab (soaking). It is a method of holding. This method is for completely dissolving a substance having inhibitor ability such as MnS, AlN and the like to function as an inhibitor necessary for secondary recrystallization, and this complete solution treatment is performed simultaneously with a slab site. In this respect, the above method makes sense for realizing stable production.
[0003]
However, in the case of the above-described method, the heating temperature necessary for completely dissolving the substance having the inhibitor ability, that is, the complete solution temperature becomes an extremely high temperature. In actual production, the amount of the inhibitor necessary for secondary recrystallization. In order to ensure this, it is heated at a temperature equal to or higher than the complete solution temperature (ultra high temperature), and thus various problems are included in actual production.
[0004]
For example, 1) In hot rolling, it becomes difficult to ensure a required hot rolling temperature, and when the temperature cannot be ensured, a deviation in the slab of inhibitor strength occurs, and therefore secondary recrystallization failure occurs. 2) Coarse grains are produced during hot rolling heating, and the coarse grains cannot be recrystallized secondary, resulting in linear secondary recrystallization failure. 3) The slab surface is melted and becomes noro for maintenance of the heating furnace. A large amount of labor is required. 4) Problems such as a large edge crack occurring in the steel strip after hot rolling and a decrease in yield occur.
[0005]
As an improvement technique of this technique, an attempt is made to stabilize the secondary recrystallization by performing nitriding after the primary recrystallization based on the above method as disclosed in JP-A-1-168817. Although the method is known, the problem that can be solved by this method is only the problem 1), and there are still difficulties in solving the problems 2) to 4) in actual production.
[0006]
The second technique uses AlN as an inhibitor and slab heating at 1280 ° C. as disclosed in JP 59-56522 A, JP 5-1112827 A, JP 9-118964 A, and the like. This is a combination of a nitriding process after decarburization annealing and before the start of secondary recrystallization. In such a method, for example, as shown in JP-A-2-182866, the average particle size of primary recrystallized grains after decarburization annealing is controlled within a certain range, usually within a range of 18 to 35 μm. This is very important for good secondary recrystallization.
[0007]
Furthermore, Japanese Patent Application Laid-Open No. 5-295443 discloses that the amount of solid solution in a steel having an inhibitor ability such as solid solution nitrogen during hot rolling heating determines the grain growth property of primary recrystallization. A method is disclosed in which components are adjusted so as to keep the dissolved nitrogen and the like during hot rolling heating low so that the size of the crystal grains is uniform.
However, in this method, no matter how precisely the components are adjusted, there is a deviation in the slab such as the amount of dissolved nitrogen, and the difference in the inhibitor capacity in the slab, that is, the difference in the primary recrystallized grain size in the slab. It is impossible to eliminate it strictly. As a result, there is a problem that it may be difficult to make the secondary recrystallization uniform in the slab, and the above method is not an industrially extremely stable production method. .
[0008]
As disclosed in JP-A-6-322443 and the like, the third technique is Cu as an inhibitor._xS (x = 1.8 or 2) is used, and the slab heating temperature is set to Cu._xThis is a method of setting the solution temperature to be not less than the complete solution temperature of S and not more than the complete solution temperature of MnS. The feature of this method is that an additional step such as nitriding treatment adopted in the second technique is not required after the slab heating temperature is lowered.
[0009]
However, the above method has a problem similar to the problem of the second technique because the slab heating temperature is not more than the complete solution temperature of MnS, and it is also an industrially extremely stable production method. is not. In the first place, Cu_xAlthough S is known as an inhibitor for controlling secondary recrystallization, it is not particularly suitable for the production of a high magnetic flux density unidirectional electrical steel sheet having a final cold rolling rate exceeding 80% (“Iron and Steel”). P.2049, N0.15, Vol.70, N0.1984).
[0010]
In addition to the above, JP-A-51-73922, JP-A-51-145422, etc. disclose a method using B addition. Since the N affinity of B is stronger than that of Al, it is considered that BN was used as an inhibitor that is stable up to a higher temperature than that of AlN. However, it seems difficult to secure an amount for industrially stabilizing secondary recrystallization, Currently, industrial production is not carried out by this method.
[0011]
[Problems to be solved by the invention]
In general, whether or not secondary recrystallization with good magnetic properties can be achieved is mainly determined by the primary recrystallization grain size and the secondary inhibitor that controls the secondary recrystallization. Although the primary recrystallized grain size in the first technique is about 10 μm, while that in the second technique is 18 to 35 μm, each primary recrystallized grain size is greatly different. In addition, it is possible to realize a good secondary recrystallization by any method. The primary recrystallization necessary for realizing a secondary recrystallization with a well-equipped Goss orientation ({110} <001> orientation). This indicates that the combination of recrystallized particle size and secondary inhibitor is not necessarily unique.
[0012]
Therefore, the present inventors have the idea that, by adjusting the secondary inhibitor, secondary recrystallization with well-aligned Goss orientation can be realized regardless of the primary crystal grain size. , Have been researching. Based on the above idea, the present inventors, from the viewpoint of establishing a stable production method, for the inhibitor essential to the production of the unidirectional electrical steel sheet, the primary reactivation is performed by the stage of exerting its function. It was classified into a primary inhibitor that controls the crystal grain size and a secondary inhibitor that controls the secondary recrystallized grain size, and the production of unidirectional electrical steel sheets with excellent magnetic properties was studied.
[0013]
By the way, although the combination of the primary recrystallization grain size and the secondary inhibitor necessary for realizing secondary recrystallization with well-aligned Goss orientation is not unique, for example, the primary crystal grain size is the entire slab (coil). If the secondary inhibitor strength is not properly controlled for each slab site, a good secondary recrystallization orientation cannot be obtained. Therefore, a production method in which both the primary recrystallization particle size and the secondary recrystallization particle size do not vary throughout the slab is a stable production method.
[0014]
Further, since the primary crystal grain size is determined by the primary inhibitor strength and the temperature of decarburization annealing for performing primary recrystallization, it is desirable that the primary inhibitor strength does not vary throughout the slab. That is, from the viewpoint of establishing a stable production method, the biggest problem is how to build both the primary inhibitor and the secondary inhibitor without fluctuation over the entire slab.
[0015]
In this regard, each of the first to third techniques has the following problems.
In the first technique, it is necessary to heat the slab in a very narrow temperature range that is not less than the complete solution temperature of the inhibitor and not more than the coarse grain formation temperature during hot rolling heating that causes instability of secondary recrystallization. In addition, it is very difficult to ensure both the strength of the inhibitor necessary for the secondary recrystallization and the industrially stable quality.
[0016]
In the second technique, it is easy to secure the secondary inhibitor strength by nitriding between decarburization annealing and secondary recrystallization during finish annealing, but in terms of uniformity of primary inhibitor strength A finite amount of solute nitrogen and the like are unevenly distributed in the slab (coil), which causes fluctuations in the primary recrystallized grain size. In this case, since the primary inhibitor also acts as a secondary inhibitor, the fluctuation of the primary inhibitor throughout the slab (coil) also leads to the fluctuation of the secondary inhibitor.
[0017]
In the third technique, MnS is not subjected to a complete solution treatment, and since it is a production method in which 60% or more of AlN is precipitated after hot rolling, as in the second technique, in the slab (coil) of the primary inhibitor. The secondary inhibitor does not change from the primary inhibitor, and the secondary inhibitor varies from slab site to industrial site. It is difficult to ensure stable quality. Furthermore, as mentioned above, Cu_xAlthough S is known as an inhibitor for controlling secondary recrystallization, it is not particularly suitable for producing a high magnetic flux density unidirectional electrical steel sheet having a final cold rolling rate exceeding 80%.
[0018]
That is, the present invention was invented in view of the above-described circumstances, and a method capable of extremely stably producing a unidirectional electrical steel sheet having excellent magnetic properties by making secondary recrystallization even more complete. The purpose is to provide.
[0019]
[Means for Solving the Problems]
  The present invention has been made to solve the above problems, and the gist thereof is as follows.
(1) A slab for a unidirectional electrical steel sheet containing Al is heated at a temperature of 1200 ° C. or higher and then hot-rolled to form a hot-rolled sheet, which is then annealed or not subjected to 1 In the method for producing a unidirectional electrical steel sheet, which is subjected to cold rolling at least twice with intermediate or intermediate annealing, then decarburized annealing, then applied with an annealing separator and subjected to finish annealing, the slab has a mass %: C: 0.025-0.10%, Si: 2.5-4.0%, acid-soluble Al (solAl): 0.01-0.10%, N: 0.0054% or less, Mn : 0.02 to 0.20%, Seq = S + 0.406 × Se: 0.003 to 0.05%, B: 0.0005 to 0.0070%Sn: 0.02-0.3%, Cr: 0.02-0.3%The balance is composed of Fe and inevitable impurities, and [] represents the mass% of the component elements in [],
  [B] ≧ 0.771 × [N]
And the heating of the slab is expressed by the following formula:
  T1 = 10062 / (2.72−log ([solAl] × [N])) − 273,
  T2 = 14855 / (6.82-log ([Mn] × [S]))-273, and
  T3 = 10733 / (4.08-log ([Mn] × [Se]))-273,
Secondary recrystallization of finish annealing after decarburization annealing is performed at a slab heating temperature Ts (° C) higher than the maximum temperature among T1 (° C), T2 (° C) and T3 (° C) defined by It is characterized by nitriding the steel sheet before the start.RuichiA method for producing grain-oriented electrical steel sheets.
[0020]
  (2) The slab further contains, by mass%, Cu: 0.01 to 0.30%, and the slab is heated by the following formula (where [] is a component element in []). Mass%), T4 = 43091 / (25.09-log ([Cu] × [Cu] × [S]))-273, T4 (° C.), T1 (° C.), T2 (° C.) T3 ( (1), which is performed at a slab heating temperature Ts (° C) higher than the maximum temperature inOneA method for producing grain-oriented electrical steel sheets.
[0021]
  (3) The heating of the slab is performed at a temperature of 1350 ° C. or less, as described in (1) or (2)OneA method for producing grain-oriented electrical steel sheets.
  (4) The average particle size of the primary recrystallized grains after completion of the decarburization annealing is 7 μm or more and less than 18 μm, according to any one of (1) to (3)OneA method for producing grain-oriented electrical steel sheets.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
The inventors have taken the starting point that, when a slab is heated, complete solution of a substance having inhibitor ability is the optimum method for uniformizing the primary inhibitor in the slab (coil) to the limit. When the concentration in the slab of the substance having the ability is lower than that of the conventional method, attention is paid to the fact that the complete solution temperature is lowered. As a technique for achieving complete solution of an inhibitor during hot rolling heating, there is the first technique described above. However, in this technique, when the concentration in the slab of the substance having inhibitor ability is lowered, secondary recrystallization occurs due to a decrease in inhibitor strength. Was not established as a stable industrial production technology.
[0023]
The inventors have conducted research and experiments based on the belief that the secondary recrystallization instability can be avoided by performing nitriding after the first recrystallization until the start of the secondary recrystallization. It has been found that by containing at least N equivalents of B as a component, it is possible to make the strength of the primary inhibitor uniform over the entire slab and to introduce a secondary inhibitor that exhibits an inhibitor effect up to a higher temperature than AlN.
[0024]
That is, by containing B as a slab component in an amount equal to or more than N equivalents, first, regarding the fluctuation of the primary inhibitor strength in the slab (coil), it was caused by non-uniform precipitation of AlN during hot rolling. By adding B having a stronger N affinity to N equivalents or more, it is possible to minimize solute N that can become AlN. Furthermore, BN existing from the above process (hot rolling) is more stable than AlN, so it has been found that it can function strongly as a secondary inhibitor up to high temperature.
[0025]
On the other hand, it was also found that sulfide and selenide inhibitors do not affect as much as nitride inhibitors in the homogenization of inhibitors in the hot rolling process, and as primary inhibitors, mainly sulfides and selenides. It has also been found effective to use inhibitors.
Although the cause of the difference in the action effect of this nitride inhibitor and sulfide or selenide inhibitor is not clear, the solubility of AlN is greatly different between the α phase and the γ phase, and during hot rolling, It is considered that the cause is that AlN precipitates non-uniformly when the matrix phase transitions from the γ phase in which AlN is easily dissolved to the α phase in which it is difficult to dissolve. Similarly to AlN, BN is considered to have a difference in solubility in the α phase and γ phase. However, since the N affinity of B is larger than that of Al, the precipitation of BN starts at a higher temperature than that of AlN. It is believed that the precipitates are deposited before reaching the late stage of hot rolling, where the temperature difference due to is large, and the uniformity of precipitation due to the sites is not as bad as that of AlN.
[0026]
By the above method (reduction of the nitrogen concentration in the slab component), the difference in primary inhibitor ability (strength) between slab (coil) sites can be extremely reduced, while it is excellent in secondary recrystallization. In order to obtain a sharp Goss orientation with magnetic properties, in addition to sulfide and selenide, an inhibitor that is stable up to high temperature is necessary. In the present invention, in addition to BN, AlN is formed by nitriding treatment. Secure by doing.
[0027]
That is, the present invention reduces the complete solution temperature of the inhibitor by lowering the concentration of the substance having inhibitor ability in the slab component as compared with the conventional method, and raises the slab heating temperature above that temperature. Nitrogen treatment between decarburization annealing and start of secondary recrystallization after decarburization annealing, due to uniform primary inhibitor strength regardless of site and lowering inhibitor component concentration By applying nitride (AlN, Si_ThreeN_Four, MnN, etc. alone or composite precipitates) and function as an inhibitor to compensate, thereby enabling stable production of a unidirectional electrical steel sheet with good magnetic properties.
[0028]
In other words, the object of the present invention is to metallurgically separate the function exhibiting stages of inhibitors that have a large role in the production of unidirectional electrical steel sheets, and to express their functions using different substances at each function exhibiting stage. To provide a very stable production method.
Moreover, since the temperature of decarburization annealing in which primary recrystallization is performed in the production of unidirectional electrical steel sheets is generally as low as 930 ° C. or less, at this stage, it is as powerful as that formed by high-temperature hot rolling in the conventional method. Inhibitors are not required. In the present invention, since sulfide or selenide is mainly used as the primary inhibitor, the temperature dependence of primary recrystallization grain growth is extremely small, and the primary recrystallization annealing (actually decarburization annealing) temperature is greatly changed. There is no need. As a result, the constituent composition of the primary oxide layer and the nitriding amount in the subsequent nitriding treatment are remarkably stabilized, and the effect of drastically reducing the primary film defects can be obtained.
[0029]
Next, the reasons for limiting the component composition of the slab in the present invention will be described.
When C is less than 0.025%, the primary recrystallization texture becomes unsuitable, and when it exceeds 0.10%, decarburization becomes difficult and unsuitable for industrial production.
If Si is less than 2.5%, good iron loss cannot be obtained, and if it exceeds 4.0%, cold rolling becomes extremely difficult and is not suitable for industrial production.
[0030]
Acid-soluble Al (solAl) combines with N to form AlN, and mainly functions as a secondary inhibitor. This AlN includes both those formed before nitriding and those formed at the time of high-temperature annealing after nitriding, and 0.01 to 0.10% is necessary to secure the amount of both AlN. When it is less than 0.01%, the function as a secondary inhibitor becomes insufficient, and secondary recrystallized grains having good Goss orientation cannot be stably obtained, and when it exceeds 0.10% In this case, the amount of nitriding required in the subsequent process increases, and the film is seriously damaged.
[0031]
If N exceeds 0.0054%, it causes non-uniform precipitation during hot rolling, so the upper limit was made 0.0054%. More preferably, it is 0.0030% or less.
S and Se combine with Mn and Cu and mainly act as primary inhibitors. The S and Se contents are limited to Seq = S + 0.406 × Se, but if Seq exceeds 0.05%, it is not preferable because the time required for purification by final finish annealing becomes too long. Moreover, since the effect as a primary inhibitor will become weak when it is less than 0.003%, it is necessary to make a minimum into 0.003%.
[0032]
  If Mn is less than 0.02%, cracks are likely to occur in the hot-rolled steel strip, and the yield decreases. On the other hand, if it exceeds 0.20%, MnS and MnSe increase too much, the degree of solid solution becomes uneven depending on the location, and stable production becomes difficult, so the upper limit is made 0.2%.
  When B is less than 0.0005%, the inhibitor effect as BN is not exhibited, and when it exceeds 0.007%, the amount of nitridation required when forming an inhibitor by nitriding becomes too large. As a result, primary film defects in which the ground iron is exposed frequently occur. Furthermore, it is one of the main points of the present invention that B is N equivalent (= 0.711 × N mass%) or more. B has a stronger N affinity than Al, and by containing more than N equivalents of B, it is possible to reduce the precipitation of AlN, which causes precipitation differences depending on the coil position, particularly during the hot rolling stage, until the primary recrystallization is completed. It becomes possible. Furthermore, adjusting the B and N of the slab components and the slab heating temperature so as to completely dissolve BN during slab heating prior to hot rolling works more effectively because it increases the uniformity of the primary inhibitor.
  Sn, Cr is advantageously suitable as an inhibitor-forming component. The preferred addition range of these components is 0.02 to 0.3%, respectively.
[0033]
When hot rolling is performed under the conditions of the present invention in which the slab is heated at 1200 ° C. or higher, Cu forms fine precipitates together with S and Se and exhibits a primary inhibitor effect. The precipitates also serve as precipitation nuclei that make the dispersion of AlN more uniform, and also play the role of a secondary inhibitor, and this effect makes secondary recrystallization good. If the content is less than 0.01%, the above effect is reduced and stable production becomes difficult. If the content exceeds 0.30%, the above effect is saturated, and it causes surface flaws such as “copper lashes” during hot rolling.
[0034]
Furthermore, about each content of Al, N, S, Se, Mn, and Cu, it is 1400 even if one of T1 (degreeC)-T4 (degreeC) defined by the following formula calculated | required from the component density | concentration in those slabs. If it is higher than ° C., it is necessary to make the slab heating temperature Ts (° C.) very high in order to completely dissolve these components. There is.
[0035]
T1 = 10062 / (2.72−log ([solAl] × [N])) − 273
T2 = 14855 / (6.82-log ([Mn] × [S]))-273
T3 = 10733 / (4.08-log ([Mn] × [Se]))-273
T4 = 43091 / (25.09-log ([Cu] * [Cu] * [S]))-273
Here, [] in the formula represents mass% of the component elements in [].
[0036]
  As described above, in the present invention, primary recrystallized grains are controlled mainly using sulfide or selenide as the primary inhibitor, and N in the slab component needs to be reduced as much as possible. The following is desirable. However, this alone is insufficient to control the secondary recrystallization, so that a nitriding treatment described later is required.
  In addition, as an inhibitor formation component, the above-mentioned Al, N, S, Se, Mn, Cu, B, Sn, CrOther, Sb, P, Mo, Cd, Ge, Te, Bi, etc. are also advantageously adapted, and since Ni has a significant effect on the uniform dispersion of precipitates as primary and secondary inhibitors, each can be included in small amounts. .
[0037]
  The preferred range of addition of the above components is, Sb and P: 0.02-0.3%, Mo and Cd: 0.008-0.3%, Ge, Te and Bi: 0.005-0.1%, and Ni: 0.03-0.3% Each of these components can be used alone or in combination.
  Next, the reason for limiting the conditions relating to the manufacturing process in the present invention will be described.
[0038]
Regarding the average particle size of primary recrystallized grains after completion of decarburization annealing, for example, in JP-A-7-252532, the average particle size of primary recrystallized grains is set to 18 to 35 μm. By making the average particle size of the grains 7 μm or more and less than 18 μm, the magnetic properties (particularly iron loss) can be further improved.
That is, if the primary recrystallized grain size is small, it means that the number of primary recrystallized grains existing in the unit volume increases. Furthermore, when the primary recrystallized grains are small in size, the volume fraction of Goss-oriented grains that become the nucleus of secondary recrystallization at the primary recrystallization stage increases from the viewpoint of grain growth (“Materials Science Forum” Vol. .204-206, Part2: pp: 631).
[0039]
As a result, the absolute number of Goss orientation grains is about five times as large as the average grain size of primary recrystallized grains, for example, from 18 to 35 μm. As a result, the iron loss is remarkably improved.
In addition, if the average grain size of the primary recrystallized grains is small, the driving force of secondary recrystallization will increase, and secondary recrystallization should be started during the final finish annealing at an early stage (at a lower temperature) of the temperature raising stage. Can do. In the present situation where final finish annealing is performed in a coil shape, the temperature difference at each point of the coil (temperature history difference) increases as the temperature increases, so the temperature history at each point of the coil is reduced by lowering the secondary recrystallization temperature described above. Can be recrystallized in a temperature region where the temperature is more uniform (the rate of temperature rise at each point of the coil is constant), and the non-uniformity between the coil parts is remarkably reduced and the magnetic characteristics are extremely stable.
[0040]
However, when the average grain size of the primary recrystallized grains is less than 7 μm, the secondary recrystallization temperature is considered to be too low due to the large driving force for grain growth, but from the Goss orientation of the secondary recrystallized grain orientations. Increases the dispersion of the magnetic flux density.
It is essential in the present invention that the steel sheet is subjected to nitriding treatment after decarburization annealing and before the start of secondary recrystallization. As the method, there are a method of mixing nitride (CrN, MnN, etc.) with an annealing separator at the time of finish annealing, and a method of nitriding in an atmosphere containing ammonia under the condition of running the strip after decarburization annealing. . Either method may be adopted, but the latter method is industrially stable.
[0041]
The amount of nitrogen increased by this nitriding treatment (nitrogen increase) is limited to 0.001 to 0.03% by mass. However, if it is less than 0.001%, secondary recrystallization becomes unstable. When it exceeds, the primary film defect in which the ground iron is exposed frequently occurs. A preferable nitrogen increase is 0.003 to 0.025%.
The slab heating temperature prior to hot rolling is an important point of the present invention. If the slab heating temperature is less than 1200 ° C., the primary inhibitor, which is the key point of the present invention, is not sufficiently produced, causing problems such as a large variation in the primary recrystallized grain size with respect to the decarburization annealing temperature.
[0042]
On the other hand, by making the slab heating temperature higher than the complete solution temperature of the substance having inhibitor ability, the difference in strength of the primary inhibitor at each slab site can be made extremely small. However, when the slab heating temperature is set immediately above the complete solution temperature of the inhibitor, the time required to hold the heating temperature for the solution of the inhibitor becomes longer, so at least about 20 ° C. from the viewpoint of productivity. The above is preferably set high. Note that heating at an ultrahigh temperature exceeding 1400 ° C. is extremely difficult in industrial production and should be avoided.
[0043]
On actual production, the slab heating temperature is 1200 to 1350 ° C., which is easy to hot-roll and excellent in the shape (crown) of the hot-rolled steel strip, and is not accompanied by actual harm related to melting of the slab surface layer and occurrence of mineralization preferable.
In the method of the present invention, first, a slab having an initial thickness of 150 mm to 300 mm, preferably 200 mm to 250 mm, is manufactured by a known continuous casting method. Instead of this slab, a so-called thin slab having an initial thickness of about 30 mm to 70 mm may be used. In this case, when manufacturing a hot-rolled steel strip, there is an advantage that it is not necessary to perform rough processing to an intermediate thickness. There is. Moreover, it is also possible to manufacture a unidirectional electrical steel sheet by the method of the present invention using a slab or steel strip having a thinner initial thickness produced by steel strip casting.
[0044]
In addition, on industrial production, a normal gas heating method may be used as a heating method for hot rolling, but in addition to this method, it is desirable to use induction heating and direct current heating in terms of uniform annealing, In these special heating methods, there is no problem even if the ingot slab is subjected to ingot rolling in order to ensure the required shape. Moreover, when heating temperature becomes 1300 degreeC or more, the texture may be improved by this partial rolling and the amount of C may be reduced. These are within the scope of the prior art.
[0045]
If the final cold rolling reduction in cold rolling is less than 80%, it is difficult to obtain a desired orientation accumulation degree in the Goss orientation grains in the primary recrystallization texture, and it is difficult to ensure a high magnetic flux density. On the other hand, if the final cold rolling reduction exceeds 95%, the number of Goss orientation grains in the primary recrystallization texture becomes extremely small, and secondary recrystallization becomes unstable.
[0046]
The annealing of the hot-rolled steel strip is mainly performed to remove the unevenness of the structure / inhibitor dispersion in the steel strip that has occurred during hot-rolling. Annealing in a hot-rolled steel strip may be sufficient, and annealing before the last cold rolling may be sufficient. That is, before the final cold rolling, it is desirable to perform at least one annealing in order to eliminate non-uniformity due to the difference in temperature history during hot rolling.
The final cold rolling may be performed at room temperature, but if at least one pass is maintained at a temperature of 100 to 300 ° C. for 1 minute or longer, the primary recrystallization texture is improved and the magnetic properties are extremely good.
[0047]
【Example】
[Example 1]
Table 1 shows the results of the molten steel components melted by the usual method, the production conditions, and the product characteristics.
Hot-rolled sheet annealing was held at 1100 ° C. for 50 seconds for cooling. The plate was pickled and cold-rolled, and then decarburized and annealed at 850 ° C. for 90 to 150 seconds. Thereafter, nitridation annealing was performed in a mixed gas of hydrogen, nitrogen, and ammonia at 750 ° C. for 30 seconds, and the total nitrogen content of the steel sheet after nitriding was adjusted to around 200 ppm. Next, MgO, TiO₂After applying an annealing separation agent mainly composed of No. 1 and heating to 1200 ° C. at a rate of temperature increase of 15 ° C./hour, finish annealing was performed at 1200 ° C. for 20 hours. Thereafter, a generally used insulating tension coating was applied and planarized. The results are shown in Table 2.
[0048]
From Table 1, the difference between the hot rolling heating temperature (Ts) and the precipitate inhibitor complete solution temperature (maximum value of T1 to T4) and the amount obtained by subtracting N equivalents from B (= B−0.771 × N) FIG. 1 shows an extracted relationship between the magnetic characteristics in the coil.
From the slab belonging to the component composition of the present invention, it can be seen that when manufactured according to the process conditions of the present invention, excellent magnetic properties are stably obtained over the entire length of the product coil.
[0049]
[Table 1]

[0050]
[Table 2]

[0051]
【The invention's effect】
According to the present invention, it is possible to industrially produce a unidirectional electrical steel sheet having excellent magnetic properties by eliminating non-uniformity of secondary recrystallization.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between magnetic properties with respect to the difference between hot rolling heating temperature and precipitate inhibitor complete solution temperature, and the amount obtained by subtracting N equivalents from B (= B−0.771 × N).

Claims (4)

A slab for a unidirectional electrical steel sheet containing Al is heated at a temperature of 1200 ° C. or higher and then hot-rolled to form a hot-rolled sheet, which is then annealed or not applied once or in the middle. In the manufacturing method of the unidirectional electrical steel sheet, which is cold-rolled twice or more sandwiching annealing, then decarburized annealing, then applying an annealing separator and performing finish annealing, the slab is in mass%,
C: 0.025 to 0.10%,
Si: 2.5-4.0%
Acid-soluble Al (solAl): 0.01 to 0.10%,
N: 0.0075% or less
Mn: 0.02 to 0.20%,
Seq = S + 0.406 × Se: 0.003 to 0.05%,
B: 0.0005~0.0100%,
Sn: 0.02-0.3%,
Cr: 0.02-0.3%
The balance is composed of Fe and inevitable impurities, and [] represents the mass% of the component elements in [],
[B] ≧ 0.771 × [N]
And the heating of the slab with the following formula (where [] is the mass% of the component elements in []),
T1 = 10062 / (2.72−log ([solAl] × [N])) − 273,
T2 = 14855 / (6.82-log ([Mn] × [S]))-273,
as well as,
T3 = 10733 / (4.08-log ([Mn] × [Se]))-273,
Secondary crystallization of finish annealing after decarburization annealing is performed at slab heating temperature Ts (° C) higher than the maximum temperature among T1 (° C), T2 (° C) and T3 (° C) defined by until the start, manufacturing method of an oriented electrical steel sheet you and performing a nitriding treatment of the steel sheet. The slab according to claim 1 further contains Cu: 0.01 to 0.30% by mass%, and the slab is heated according to the following formula (where [] is in []. % By weight of component elements)
T4 = 43091 / (25.09-log ([Cu] * [Cu] * [S]))-273
In definition to T4 (° C.) and T1 (℃), T2 (℃ ) T3 according to claim 1, characterized in that the largest high slab heating temperature Ts than the temperature in (℃) (℃) manufacturing method of an oriented electrical steel sheet. Manufacturing method of an oriented electrical steel sheet according to claim 1 or 2 heating of the slab, and performing at 1350 ° C. or lower. Characterized by an average particle size of the primary recrystallization grains after the completion of decarburization annealing less than 7μm or 18 [mu] m, the manufacturing method one oriented electrical steel sheet according to any one of claims 1 to 3, wherein .

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