JP2006274405A - Method for manufacturing grain-oriented electromagnetic steel sheet causing high magnetic-flux density - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent adhesion between steel sheets at the end of a final-finish-annealed coil, which becomes a problem in the manufacture of a grain-oriented electromagnetic steel sheet containing Cr. <P>SOLUTION: In a process of placing a coil of a cold-rolled sheet containing, by mass%, 2.5-4.5% Si, 0.01-0.50% Cr and an inhibitor-forming element such that an axis of the coil stands straight and subjecting it to final finish annealing including purification treatment at 1,100°C or higher for three hours or longer, this manufacturing method comprises: controlling a dew point of an atmosphere in a temperature range of 900°C or higher during the final finish annealing to 20°C or lower; controlling a heating rate in a temperature range of 900°C or higher to 15°C/h or lower; and making a region having no secondary recrystallization exist in a 1 mm or inner area from the side end in a sheet width direction, at least in one place in a longitudinal direction of the coil which has been final-finish-annealed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a high magnetic flux density grain-oriented electrical steel sheet that is suitably used as an iron core for a transformer, a generator, etc., and in particular, stably produces a low iron loss and high magnetic flux density electrical steel sheet containing Cr. It is intended to provide technology.

  A grain-oriented electrical steel sheet containing Si and having a crystal orientation of {110} <001>, that is, a so-called Goss orientation, exhibits excellent soft magnetic properties, so that it can be used as an iron core for transformers and generators. It is used.

  A fundamentally important characteristic of such an electrical steel sheet is a low iron loss value. In addition, magnetic steel sheets with high magnetic flux density have low iron loss, are advantageous for downsizing transformers, and can produce low noise transformers. Along with this, the usage is increasing year by year. Against this background, development of grain-oriented electrical steel sheets with higher magnetic flux density is also desired.

  In general, in order to reduce the iron loss of electrical steel sheets, a method of increasing the electric resistance by increasing the Si content effective for reducing eddy current loss, a method of reducing the steel sheet thickness, and reducing the crystal grain size of the product And a method for improving the magnetic flux density by increasing the degree of integration of crystal orientations are known. However, if Si is excessively contained, the rollability and workability deteriorate, so the method of increasing the Si content has reached its limit, and the method of reducing the thickness of the steel sheet and the crystal grain size of the product are reduced. However, the current method has reached a limit because it causes an extreme increase in manufacturing costs.

  On the other hand, as a method for improving the magnetic flux density, research is mainly conducted to increase the degree of accumulation of the Goss orientation of secondary recrystallized grains by selecting the type of precipitates called inhibitors and controlling the form of the precipitates. .

  This precipitate plays a role of promoting the rapid growth of the secondary recrystallized grains by preventing the movement of the grain boundaries in the high-temperature heat treatment and suppressing the growth of the primary recrystallized grains. It is known that the growth suppression force of primary recrystallized grains due to precipitates is generally given by the Zener equation, and the smaller the volume fraction of precipitates, the smaller the volume fraction that becomes the same. The more it is dispersed and precipitated, the stronger the inhibitory power.

  Therefore, it is important that the inhibitor is uniformly and finely dispersed. Therefore, conventionally, in slab heating before hot rolling, high temperature heating is used to completely dissolve the inhibitor-forming components, and this inhibitor is finely dispersed in the process from hot rolling to secondary recrystallization. The method of making it take is taken.

Examples of the inhibitor include sulfides, selenides, and nitrides such as Cu ₂ -xS, MnS, Cu ₂ -xSe, MnSe, AlN, and BN. Generally, a substance having extremely low solubility in steel is used. It has been.

  On the other hand, it is well known that not only the above-mentioned precipitates but also elements segregating at the grain boundaries have an inhibitory action. This effect is due to a mechanism that segregates at the grain boundaries and reduces grain boundary energy to suppress grain boundary movement. Regarding the use of this segregating element, for example, Patent Document 1 discloses a method of adding Cu or Sn into steel, Patent Document 2 discloses a method of adding Sb or Mo, Patent Document 3, Patent Document 4, and Patent Document. 5 and Patent Document 6 each propose a method of adding Bi. Since these elements do not have a great effect of suppressing grain growth due to the segregation effect, they are not single, but precipitates and segregation of segregation elements such as MnSe and Sb, AlN and Sb, and AlN and Sn. Often uses a complex action. This combined use method has not only the grain boundary segregation effect of the segregation element but also the action that the segregation element segregates also at the precipitate interface and suppresses the Ostwald growth of the precipitate.

  In general, it is considered that the higher the degree of orientation accumulation, the stronger the inhibitor and the stronger the suppression of normal grain growth. Therefore, usually, a plurality of types of inhibitor forming elements are used. In addition, since grain growth becomes more noticeable at higher temperatures, it is important to increase the suppression at high temperatures.

  In particular, it is known that Bi acts effectively as a suppressing force in a high temperature region in the final finish annealing (see, for example, Patent Document 7). Therefore, using Bi as an inhibitor is effective in improving orientation accumulation.

  However, since the inhibitor that segregates at the grain boundaries segregates not only at the grain boundaries but also at the steel sheet surface, the forsterite that forms on the steel sheet surface during the final finish annealing after applying the annealing separator mainly composed of MgO It has a great influence on the properties of the coating. Usually, when a segregation type inhibitor is added, the film appearance of the product and the adhesion of the insulating coating tend to deteriorate.

  Here, in order to improve the characteristic defect of the forsterite film, it is effective to improve the structure of the subscale generated by decarburization annealing by containing Cr in the steel as disclosed in Patent Document 8. It is. This method is particularly effective for improving the coating when Bi is contained in the steel.

However, when a grain-oriented electrical steel sheet containing Cr was manufactured, a problem was caused that the steel sheets were in close contact with each other at the end of the electrical steel sheet coil during final finish annealing. When the steel plate and the steel plate are brought into close contact with each other in this way, coil rewinding becomes difficult in the next step, particularly at the start and end, and the plate passing property is deteriorated, for example, the steel plate meanders due to a shape defect. When adhesion occurs remarkably, the coil cannot be rewound by a normal method, which is a very serious problem in manufacturing.
Japanese Patent Publication No. 60-48886 Japanese Patent Laid-Open No. 2-115319 Japanese Patent Laid-Open No. 49-119817 Japanese Patent Publication No.59-30771 Japanese Examined Patent Publication No. 56-18044 Japanese Patent Publication No. 56-21331 Japanese Patent Laid-Open No. 11-335736 JP 2000-96149 A

  The object of the present invention is to prevent adhesion at the end of the coil after final finish annealing, which is a problem in the production of grain-oriented electrical steel sheets containing Cr, and has both low iron loss and high magnetic flux density. The present invention intends to provide a technique for stably producing an electromagnetic material.

  In the manufacture of grain-oriented electrical steel sheets containing Cr, the inventors have proposed that in the region of 1 mm or more in the width direction end portion of the coil after final finish annealing, in order to prevent adhesion at the coil end portion after final finish annealing. The inventors have found that it is effective to suppress secondary recrystallization and to control the dew point of the atmosphere at 900 ° C. or higher and the temperature increase rate at 900 ° C. or higher in the final finish annealing, and have completed the present invention. It was.

  That is, the gist configuration of the present invention is as follows.

1. After heating a steel slab containing Si: 2.5-4.5%, Cr: 0.01-0.50% and an inhibitor-forming element in mass%, it is hot-rolled and then at least accompanied by an annealing treatment After the final plate thickness is obtained by one cold rolling, decarburization annealing is performed, and then the annealing separator is applied to the surface of the steel sheet and then wound on the coil, and the final finish is made with the coil shaft upright. In a method for producing a grain-oriented electrical steel sheet, comprising a series of steps for annealing, wherein the final finish annealing includes a purification treatment of 1100 ° C. or more and 3 hours or more,
The dew point of the atmosphere in the temperature range of 900 ° C. or more of the final finish annealing is 20 ° C. or less, and the temperature rising rate in the temperature range of 900 ° C. or more is 15 ° C./h or less. A method for producing a high magnetic flux density grain-oriented electrical steel sheet in which at least one region in the direction has a region that is not secondary recrystallized by 1 mm or more from the end in the plate width direction.

  2. Heating of the steel slab is performed at 1350 ° C or higher in an atmosphere in which the oxygen concentration is controlled to 0.01 to 2% by volume%, and the high magnetic flux density grain-oriented electrical steel sheet according to the above 1, Production method.

  3. When heating the steel slab, the surface temperature of the steel slab at the position corresponding to the end in the plate width direction at the time of final finish annealing is lower by 5 ° C. or more than the surface temperature of the center of the width, A method for producing a high magnetic flux density grain-oriented electrical steel sheet according to 1 or 2.

  4). There is a soaking step between the hot rolling and the final finish annealing, and in the soaking step, the surface temperature at the position corresponding to the end portion in the plate width direction at the time of the final finish annealing is set to the surface at the width center portion. The method for producing a high magnetic flux density grain-oriented electrical steel sheet according to any one of the above 1 to 3, wherein the temperature is higher by 5 ° C or more than the temperature.

  5. 5. The method for producing a high magnetic flux density grain-oriented electrical steel sheet according to 4 above, wherein the annealing treatment accompanying the cold rolling includes the soaking step.

  6). The method for producing a high magnetic flux density grain-oriented electrical steel sheet according to any one of 1 to 5 above, wherein the steel slab further contains Bi: 0.0005 to 0.100% by mass.

  7). The steel slab is further mass%, C: 0.03 to 0.10%, Mn: 0.050 to 1.5%, S and / or Se in total 0.010 to 0.040%, Sol . Al: 0.015 to 0.050% and / or B: 0.001 to 0.01%, and N: 0.005 to 0.015%, characterized in that 1 to 6 above The manufacturing method of the high magnetic flux density directionality electrical steel plate in any one.

  8). The steel slab is further mass%, Ni: 0.05 to 0.5%, Cu: 0.05 to 0.5%, Sn: 0.005 to 0.5%, Sb: 0.005 to 0 .10%, As: 0.005 to 0.10%, Mo: 0.005 to 0.10%, Te: 0.005 to 0.10% and P: 0.005 to 0.10% The method for producing a high magnetic flux density grain-oriented electrical steel sheet according to any one of 1 to 7 above, which comprises one or more selected types.

  According to this invention, in the manufacture of grain-oriented electrical steel sheets containing Cr, it is possible to prevent close contact of the coil ends after the final finish annealing. Therefore, the grain-oriented electrical steel sheets having low iron loss and high magnetic flux density can be stably produced. Can be manufactured.

  Below, the investigation and experimental results that form the basis of the present invention will be described. Unless otherwise specified, the composition is expressed in mass%.

  A plurality of coils after final finish annealing of a grain-oriented electrical steel sheet having a final thickness of 0.23 mm from a steel slab containing Si: 3%, Bi: 0.004% and Cr: 0.25% according to a known method. Individually manufactured. In addition, according to a conventional method, an annealing separator mainly composed of MgO was applied to the steel plate before the final finish annealing. Further, during the final finish annealing, the coil was placed in the heating furnace so that its axis was upright.

  A schematic diagram of the coil after final finish annealing thus obtained is shown in FIG. As a result of investigating the adhesion between the steel plates of the coil 1 after the final finish annealing, as shown by reference numeral 2 in FIG. 1, in some coils, the lower end of the coil 1, that is, the plate on the side that became the lower surface during annealing. Although the width direction edge part was not full length, it was contact | adhered partially.

  Adhesion was particularly remarkable in the region from the outermost winding side to the 30th winding and from the innermost winding side to the 30th winding. As a result of investigating the crystal grains of the coil, it was found that the coil in which secondary recrystallization did not occur at the end portion in the plate width direction of the coil was lightly adhered.

  The reason why adhesion is difficult to occur unless secondary recrystallization occurs at the end in the plate width direction of the coil, in other words, the reason why secondary recrystallization grains tend to adhere is considered as follows. Since the secondary recrystallized grains accumulate in the Goss orientation, the orientations of the different secondary recrystallized grains are very close, so that when the secondary recrystallized grains of different steel plates contact at high temperature, the rearrangement of atoms easily occurs. It is thought that it adheres easily.

  In addition, the reason why the contact between the outermost winding portion and the innermost winding portion of the coil becomes conspicuous is that the outermost winding portion and the innermost winding portion are unsteady portions when winding on the coil in the process immediately before the final finish annealing. Therefore, it is considered that sufficient winding tension cannot be obtained, and that the coil is deformed by thermal expansion during the final finish annealing, so that the coil is loosened at the unsteady portion in the outermost winding and the innermost winding portion. That is, it is considered that the lack of the annealing separator (described later) becomes remarkable in the outermost winding and the innermost winding portion.

  However, it has been found that even in the coil where the secondary recrystallization does not occur at the plate width end portion of the coil, there is still a close contact portion. In order to elucidate the cause of such adhesion, the cross section of the adhesion part was observed with a scanning electron microscope and analyzed by energy dispersive X-ray spectroscopy (EDX). An example of the cross section of the contact portion is shown in FIG.

  FIG. 3 shows the result of the EDX analysis. From this analysis result, it is found that the composition 2 which is judged to be an Fe—Cr alloy having a composition that is clearly different from that of the base iron 7 and the coating 6 exists in the adhesion portion 2. There was found. This Fe—Cr alloy 8 is considered to be formed by the formation of oxides of Fe and Cr at the initial stage of final finish annealing and reduced during the purification process of final finish annealing. It is unknown whether this Fe and Cr oxide is a composite oxide or mixture of Fe oxide and Cr oxide, or a mixture of both. The product is called an Fe-Cr oxide.

  Further, it has been found that the Fe—Cr alloy in the close contact portion does not contain Mg, which is the main component of the annealing separator, and the annealing separator is missing. That is, the close contact lacks the annealing separation agent at the lower end of the coil during final finish annealing, the lower side of the coil is deformed by its own weight, and the force due to its own weight becomes uneven at the lower end of the coil. It is considered that a strong force was partially exerted between the steel sheets at the lower end of the coil, and was generated by sandwiching the Fe—Cr alloy between the steel sheets. It is highly possible that this Fe—Cr alloy is involved in the occurrence of adhesion, and therefore it has been estimated that adhesion can be prevented by reducing or eliminating the Fe—Cr alloy between the steel plates.

  In view of this, the inventors have studied a method in which an Fe—Cr alloy is not generated in order to prevent adhesion in the coil. That is, it was studied to suppress the formation of Fe—Cr-based oxides that are the basis of Fe—Cr alloys.

Usually, on the steel plate before final finish annealing, a slurry in which a substance mainly composed of MgO is suspended in water is applied to the steel plate as an annealing separator (usually both sides but one side is also possible), and then wound on a coil. Is customary. The slurry applied to the steel sheet retains physically adsorbed H ₂ O even after being dried, and partly hydrates and changes to Mg (OH) ₂ . Therefore, H ₂ O is released during the final finish annealing. It is known that the surface of the steel sheet is oxidized during the final finish annealing by this H ₂ O.

In general, the oxidation reaction rate becomes more prominent at higher temperatures. On the other hand, a Cr-based oxide, that is, an oxide containing Cr as a composition changes to a reduction reaction at a high temperature in the same oxygen potential atmosphere. For example, the following reaction is converted to a reverse reaction at about 1150 ° C. in a 1 atmosphere H ₂ atmosphere with a dew point of −13 ° C., as calculated by the standard free energy of oxide formation.
1 / 2Fe + Cr + O ₂ → 1 / 2FeCr ₂ O ₄

From the above, in order to suppress the formation of Fe—Cr-based oxides, it is considered effective not to cause an oxidation reaction between H ₂ O released from the annealing separator and the steel sheet surface in a high temperature range. It is done. That is, it is considered that the oxidation of Cr on the surface of the steel sheet can be suppressed by reducing the oxidation of the atmosphere in the region where the temperature during the final finish annealing is 900 ° C. or higher, particularly in the region of about 900 to 1100 ° C.

  Further, when the coil is deformed due to non-uniform thermal expansion in the coil, the coil's own weight is locally concentrated in the lower part of the coil, so that it is considered that adhesion is promoted. Therefore, it is considered that reducing the temperature increase rate to reduce the temperature difference in the coil suppresses adhesion, and in particular, slowing the temperature increase rate in a high temperature range where the strength of the steel sheet is reduced suppresses adhesion. It is thought that it is effective.

  Therefore, the following experiment was conducted to confirm the above points.

That is, C: 0.06%, Si: 3.3%, Mn: 0.06%, Cu: 0.1%, Se: 0.02%, N: 0.008%, Al: 0.03% The steel slab containing Bi: 0.01% was hot rolled into a hot-rolled sheet having a thickness of 2.4 mm, and then annealed at 1000 ° C. for 30 seconds. Then, after finishing to a thickness of 1.5 mm by cold rolling, an intermediate annealing was performed at 1130 ° C. for 40 seconds, and then cold rolling was performed to a final thickness of 0.23 mm. Further, after performing decarburization annealing at 820 ° C. for 150 seconds, an annealing separator comprising 3% TiO ₂ and 2% SrSO ₄ by mass% is applied to MgO, wound on a coil, and removed. Several carbon annealed plate coils were manufactured. At that time, in order to prevent secondary recrystallization at the end in the plate width direction of the coil after the final finish annealing, the temperature at the end in the plate width direction during intermediate annealing is set to the temperature 1130 of the width center (that is, the center in the plate width direction). The temperature was set to 1150 ° C., which is 20 ° C. higher than that.

  Thereafter, as final finish annealing, the temperature was raised to 850 ° C. at a rate of 8 ° C./h in a nitrogen atmosphere, and then heated to 1200 ° C. in an atmosphere of nitrogen: 25% and hydrogen: 75% in volume%. A purification treatment was performed in a hydrogen atmosphere at 1200 ° C. for 5 hours. Here, in the temperature increase to 850 to 1200 ° C., the temperature range of 900 to 1100 ° C. is controlled to various temperature increase rates of 5, 10, 15, 20, and 30 ° C./h, and 1200 ° C. after 1100 ° C. In order to prevent overshooting to an excessively high temperature, the heating rate was set lower than these heating rates. Moreover, the dew point in the temperature range of 900 ° C. or higher of the final finish annealing was changed to 0, 10, 20, 30, 40 ° C. for each temperature increase rate condition.

  In the coil obtained under the above conditions, the adhesion of the steel plate at the lower end was investigated for an area of about 100 m in length for 30 turns of the outermost winding part. The degree of adhesion was evaluated based on the number of locations within 30 windings of the outermost winding portion, with the adhesion strength being three stages of weak, medium and strong. Here, the adhesion force is evaluated by the length of a crack that extends in the plate width direction when the adhesion portion is peeled off, and the case where the length of the crack is 10 mm or more is strong, and the case where it is less than 10 mm is in close contact. The case where no cracking occurred was considered weak.

  The results are shown in Table 1. From Table 1, when the temperature rise temperature between 900-1100 ° C. is 15 ° C./h or less and the dew point of 900 ° C. or more is 20 ° C. or less, the steel plate and the steel plate at the lower end of the coil after final finish annealing It became clear that the adhesion of was light.

Next, the present invention will be described in detail in the order of the manufacturing process.
First, the component composition of the steel slab used as the raw material for the steel plate will be specifically described.

Si: 2.5-4.5%
Si is a component effective for increasing the specific resistance of the steel sheet and reducing iron loss, but if the content exceeds 4.5%, the cold rolling property is impaired. On the other hand, when the content is less than 2.5%, not only the specific resistance is lowered, but also the crystal orientation is randomized by α-γ transformation during the final finish annealing for secondary recrystallization and purification. Occurs, and a sufficient iron loss reduction effect cannot be obtained. Therefore, the Si content is limited to a range of 2.5 to 4.5%.

Cr: 0.01 to 0.50%
Cr has an action of promoting the formation of a forsterite film. In particular, when Bi is added, it becomes difficult to form a forsterite film, so it is effective to add Cr for improvement. If the effect is less than 0.01%, it is not sufficient. On the other hand, if it exceeds 0.50%, the effect is saturated and the cost is increased. For this reason, the range of Cr shall be 0.01 to 0.50%. Of course, even when Bi is not added, the addition of Cr is effective in improving the forsterite film.

  In addition to the above two elements, a component composition containing an inhibitor forming element is defined as a basic composition. This inhibitor-forming element will be specifically described later, but it is also possible to add the following components as required in addition to the above two elements.

C: 0.03-0.10%
The C content is preferably 0.03 to 0.10%. That is, if it exceeds 0.10%, the amount of γ transformation becomes excessive, which results in inhibiting the uniform dispersion of inhibitors such as MnSe and MnS precipitated during hot rolling, which is harmful. Moreover, the load of decarburization annealing increases and it becomes easy to generate | occur | produce a decarburization defect. On the other hand, if it is less than 0.03%, the effect of improving the structure cannot be obtained, the secondary recrystallization is incomplete, and the magnetic characteristics are similarly deteriorated. Therefore, C is preferably in the range of 0.03 to 0.10%.

Mn: 0.050 to 1.5%
Mn is preferably added in an amount of at least about 0.050% in order to prevent hot brittleness. However, if the Mn content is too large, the magnetic properties are deteriorated, so the upper limit may be 1.5%. desirable.

  Moreover, as an inhibitor forming element, the following elements are preferably added.

Bi: 0.0005 to 0.100%
The addition of Bi is effective in improving the degree of orientational integration of secondary recrystallized grains, that is, improving magnetic properties. If Bi is less than 0.0005%, the expected effect cannot be obtained. On the other hand, if it exceeds 0.100%, it is difficult to disperse uniformly. Therefore, when it contains Bi, it is set as 0.0005 to 0.100% of range.

  Note that the application of the present invention is particularly effective when Bi is added, since adhesion in the coil after the final finish annealing is particularly noticeable when Bi is added.

Sol. Al: 0.015-0.050% and / or B: 0.001-0.01%
When the final cold rolling reduction is 80% or more, the secondary recrystallization temperature becomes very high. Therefore, it is necessary to contain an inhibitor-forming element that is stable at a high temperature in the steel. A combination of N, Al and / or B and N is suitable.

  That is, Al is sol. It is preferable to contain 0.015 to 0.050% as Al (acid-soluble Al). That is, when the Al content is less than 0.015%, the amount of precipitated AlN is insufficient, and good secondary recrystallization cannot be obtained. On the other hand, if it exceeds 0.050%, it is difficult to uniformly disperse into a size that functions as an inhibitor, which is not preferable.

  On the other hand, B preferably contains 0.001 to 0.01%. That is, when the B content is less than 0.001%, the amount of precipitated BN is insufficient, and a good secondary recrystallization cannot be obtained. Conversely, if it exceeds 0.01%, it is difficult to uniformly disperse it to a size that functions as an inhibitor, which is not preferable.

N: 0.005 to 0.015%
N is a component constituting AlN and / or BN serving as an inhibitor. For this purpose, N must be contained in an amount of 0.005% or more. However, if it exceeds 0.015%, it may cause problems such as gasification in steel and swelling of the steel sheet surface. Therefore, it is preferable that N has a content of 0.005 to 0.015%.

  When BN is used alone as an inhibitor, in other words, when Al is not used as an inhibitor-forming element, it is preferable to limit the Al content to 0.012% or less. That is, when the Al content increases, there is an aspect that it is difficult to generate subscales in decarburization annealing and forsterite generation in finish annealing. Therefore, when Al is not used as an inhibitor forming element, it is preferable to limit the Al content as an impurity to 0.012% or less in order to improve the forsterite film.

S and / or Se in total 0.010 to 0.040%
As an inhibitor component, S and Se can be contained alone or in combination. These components are precipitated in the steel as Mn compounds or Cu compounds, but in order to maintain the effect of suppressing grain growth, 0.010% or more in total of any one or two of them is required. On the other hand, if it exceeds 0.040%, it cannot be completely dissolved even by high-temperature slab heating, resulting in coarse precipitates. Therefore, when it contains these, it is preferable to set it as the range of 0.010-0.040% in total of any 1 type or 2 types.

  When adding S and / or Se, if Mn / (Se + S) (calculated in% by mass) is less than 2.5, grain boundary cracking and ear roughness increase significantly during hot rolling, so Mn / ( It is practically preferable to add each element so that Se + S) ≧ 2.5.

  Further, in order to strengthen the function of the above-described inhibitor forming elements, addition of the following respective elements is preferable. That is, Ni, Cu, Sn, Sb, As, Mo, Te, P and the like have an auxiliary function of strengthening the inhibitory power of known inhibitors, and thus are preferably added to steel as necessary. As for the preferable addition amount necessary to exert this effect, Ni and Cu are 0.05 to 0.5%, Sn is 0.005 to 0.5%, Sb, As, Mo, Te and P are each Each is 0.005 to 0.10%. In any case, if the amount is less than the lower limit, the effect of suppressing the growth of normal grains is not exhibited. On the other hand, if the upper limit is exceeded, the coating properties are deteriorated.

  As for other additive elements, for example, addition of Ge or Co has an effect of improving the surface properties of the steel sheet, and therefore can be appropriately contained. The contents at that time are preferably Ge: 0.02 to 0.30% and Co: 0.02 to 0.30%.

  Next, manufacturing conditions will be specifically described.

  The molten steel adjusted to the above-described preferred components is usually made into a slab (steel slab) by a continuous casting method or an ingot-bundling method.

  Then, after this slab is heated, it is formed into a hot-rolled coil by hot rolling. At this time, the slab is heated at a high temperature to dissolve the inhibitor-forming elements in the steel. At that time, it is preferable to heat in an atmosphere in which the heating temperature is 1350 ° C. or more and the oxygen concentration is adjusted to 0.01 to 2% by volume%. This is because if the slab heating temperature is less than 1350 ° C., the inhibitor is not sufficiently dissolved, and fine and uniform dispersion precipitation of Mn (Se, S), BN, etc. cannot be obtained.

  However, when the slab containing Cr is heated at a high temperature, the adhesion at the lower end of the coil in the final finish annealing in the subsequent process tends to be increased. Since there is no step of heating to a temperature higher than the final finish annealing after the slab heating and before the final finish annealing, the increase in adhesion is caused by some reaction with the atmosphere during the high temperature heating of the slab containing Cr. It is thought that the change in the surface layer remained without being eliminated by the process before the final finish annealing.

  On the other hand, when Cr is sufficiently oxidized in a high temperature atmosphere containing oxygen of 0.01% by volume or more during slab heating, the amount of Cr in the surface layer immediately below the scale decreases, and the change in the slab surface layer described above occurs. As a result of being suppressed, adhesion in the final finish annealing can be reduced, and therefore, the oxygen concentration in the atmosphere is preferably 0.01% by volume. On the other hand, when the oxygen concentration exceeds 2% by volume, the scale loss due to the generation of melt scale increases, so the oxygen concentration is preferably in the range of 0.01 to 2% by volume.

  The slab heating at 1350 ° C. or higher is more suitable for an electric heating furnace with easy atmosphere control than for a gas combustion heating furnace. Considering costs such as fuel costs, it is preferable to heat to about 1200 ° C. with a gas combustion type heating furnace and then heat to 1350 ° C. or more with an atmosphere control type electric heating furnace.

  Regarding hot rolling, it is possible to appropriately add known techniques such as thickness reduction processing and width reduction processing for homogenizing the structure before and after slab heating.

  Next, about a cold rolling process, at least 1 time of cold rolling accompanying an annealing process is performed. Specifically, any one of the cold rolling method and the cold rolling method may be used. Here, the cold rolling one-time method is a method of obtaining the final sheet thickness by one cold rolling after the hot-rolled sheet annealing, and the cold-rolling two-time method is hot rolling sheet annealing as necessary. After the application, the final thickness is obtained by performing cold rolling at least twice with intermediate annealing.

  About the rolling reduction of cold rolling, it is preferable to set it as a conventionally well-known range. For example, in the case of the first rolling in the cold rolling method, the content is preferably about 15 to 60%. This is because when the rolling reduction is less than 15%, the rolling recrystallization mechanism does not work, so that the crystal structure cannot be made uniform. On the other hand, when the rolling reduction exceeds 60%, the texture is accumulated. This is because the rolling effect cannot be obtained.

  Furthermore, the rolling reduction of the final rolling is preferably about 80 to 90%. This is because when the rolling reduction exceeds 90%, secondary recrystallization becomes difficult, whereas when the rolling reduction is less than 80%, good secondary recrystallization grain orientation cannot be obtained, and the magnetic flux density of the product decreases. is there.

  In addition, when the annealing temperature is excessively low in hot-rolled sheet annealing or intermediate annealing, (110) grains ((110) crystal planes parallel to the plate surface are cores of secondary recrystallization in the recrystallized structure after rolling. The number of crystal grains) is insufficient, and a secondary recrystallized structure with good orientation cannot be obtained. In order to obtain a sufficient number of (110) grains, it is necessary to coarsen the crystal structure after hot-rolled sheet annealing to a certain size or more. For this purpose, it is preferable to raise the temperature to a temperature of 800 ° C. or higher. . On the other hand, the upper limit of the annealing temperature is preferably set to 1200 ° C. or lower because it is important to avoid re-solution or Ostwald growth of finely precipitated inhibitors such as Mn (Se, S) and BN.

  In addition, about the cooling process of such hot-rolled sheet annealing or intermediate annealing, although it does not restrict | limit, in order to increase the solid solution C in steel after annealing, a rapid cooling process is performed, or in steel Performing a quenching and low-temperature holding treatment in order to precipitate fine carbide is effective in improving the magnetic properties of the product. In addition, means for decarburizing the steel sheet surface layer portion by increasing the oxidizability of the annealing atmosphere also works effectively.

  Further, as is well known in cold rolling, the final cold rolling can be performed by warm rolling at 100 to 350 ° C. or by adding an aging treatment between passes at 100 to 350 ° C. for 10 to 60 minutes. The recrystallization texture can be further improved. In addition, after the final cold rolling, it is possible to perform a treatment such as providing a linear groove on the steel plate surface for magnetic domain fragmentation.

  Next, after the steel sheet having the final thickness is subjected to decarburization annealing by a known method, generally, an annealing separator mainly composed of MgO is applied to the steel sheet surface, and then wound on a coil for final finishing annealing. In this case, it is preferable to add a Ti compound or to contain Ca or B in the annealing separator because it has the effect of further improving the magnetic properties.

Furthermore, after the primary recrystallization annealing and until the start of the secondary recrystallization, the nitriding treatment in which N is contained in the steel in a mass ppm range of 550 ppm or less can also be used to suppress the normal grain growth in the steel. It is appropriate if it is weak and does not interfere with the application of this technology. As a nitriding method, a method of heat-treating a steel sheet in an atmosphere containing NH ₃ after primary recrystallization annealing, a method of containing a decomposable nitride in an annealing separator, and the like are suitable, but are not limited thereto. It is not something.

Final finish annealing consists of secondary recrystallization annealing and purification annealing.In the first half of secondary recrystallization annealing, secondary recrystallization occurs in the steel sheet, and then the purification annealing is performed in a higher temperature region. As the purification proceeds, desired magnetic characteristics can be obtained. At this time, in order to sufficiently purify the steel plate, the region of 1100 ° C. or higher needs to be 3 hours or longer. Further, it is preferable that the purification annealing is performed in an atmosphere of a reducing gas such as hydrogen gas, an inert gas such as Ar, He, Ne, N ₂ gas, or a mixed gas thereof.

The iron loss value and magnetic flux density that can be achieved by the above composition and production conditions depend on the product thickness and the presence or absence of magnetic domain refinement treatment, for example, a product having a thickness of 0.30 mm that is not subjected to magnetic domain refinement treatment. Then, W _17/50 can be 1.1 W / kg or less, and B ₈ can be 1.88 T or more.

  Since the final finish annealing is a long-time process, the steel plate is placed in the heating furnace in a coil state as described above. From the viewpoint of workability, when mounting, as shown in FIG. 1, the coil axis is in an upright direction, that is, the coil axis is in the vertical direction, and the end portions in the plate width direction are the upper and lower surfaces. Placed in. It goes without saying that the coil axis does not have to be strictly vertical.

  Here, it is also possible to set the dew point of the atmosphere in the temperature range of 900 ° C. or higher of the final finish annealing to 20 ° C. or lower, and the temperature increase rate in the temperature range of 900 ° C. or higher to 15 ° C./h or lower. Is a requirement. That is, by lowering the dew point of the atmosphere in a temperature range of 900 ° C. or higher where Cr oxide is likely to be generated to 20 ° C. or lower, the generation of Cr oxide generated between steel sheets in the coil is suppressed, and subsequent purification annealing is performed. In this case, Fe—Cr alloy produced by reduction of Cr oxide is reduced, and adhesion between the steel plates under the coil is prevented.

  Further, by slowing the rate of temperature rise in the temperature range of 900 ° C. or higher to 15 ° C./h or less, the temperature gradient in the coil in the high temperature range where the coil is likely to be deformed is reduced, and the coil's own weight under the coil is reduced. As a result, the force applied to the lower part of the coil is prevented from concentrating locally, and as a result, it is possible to prevent the steel sheet below the coil from sticking.

  Note that the rate of temperature increase V is V = (t = t1, t2 (t1 <t2) when the time is 5 hours or more away in the heating process of final finish annealing, and T1 and T2 are the temperatures at each time. T2-T1) / (t2-t1). Making the temperature rising rate in the temperature range of 900 ° C. or higher 15 ° C./h or less means that V ≦ 15 ° C./h is always satisfied under the conditions satisfying T1, T2 ≧ 900 ° C. In addition, the maximum V under the conditions satisfying T1 and T2 ≧ 900 ° C. is defined as the maximum value of the heating rate at 900 ° C. or higher.

  In order to set the dew point of the furnace atmosphere to 20 ° C. or less, a method by adjusting the flow rate of gas passing into the furnace or adjusting the particle size of the particles sealing the lower end of the inner cover part can be applied. It is not limited to these methods.

  Here, it is important to make it difficult for secondary recrystallization from the width center portion of the end portion in the plate width direction on the lower side of the coil at the time of final finish annealing. Specifically, it is one of the requirements of the present invention that at least one portion in the longitudinal direction in the coil after the final finish annealing has a region that is not recrystallized by 1 mm or more from the end in the plate width direction. One. That is, since the secondary recrystallized grains are accumulated in the Goss orientation, the crystal orientations of the different secondary recrystallized grains are close to each other, and thus are easily adhered. Therefore, in order to prevent the coil from adhering in the final finish annealing, it is necessary not to recrystallize a region having a width of 1 mm or more at the end in the plate width direction at least at one position in the longitudinal direction of the coil.

  The reason why the width of the region not subjected to secondary recrystallization is set to 1 mm or more in at least one place in the longitudinal direction of the coil is as follows.

  As illustrated in FIG. 2, the close contact occurs at about 0.5 mm from the end in the width direction of the plate, and practically, secondary recrystallization must be performed in an area of about 0.5 mm at the end in the width direction of the plate. It is enough. Here, considering that the process conditions that the end in the plate width direction does not change significantly in the region of one coil, empirically, at least one region in the longitudinal direction has a region where the secondary recrystallization is not performed at a width of 1 mm. If it is above, it can be presumed that secondary recrystallization is not performed in other portions as much as 0.5 mm in width. Further, even if the other part is secondary recrystallized, if the above condition is satisfied, the start of secondary recrystallization is sufficiently delayed in the region of at least 1 mm width at the end in the plate width direction, thereby preventing adhesion. The effect works. That is, it is not necessary to set the width of the region not secondary recrystallized to 1 mm or more over the entire length of the coil. In addition, since the region not subjected to secondary recrystallization is eventually discarded, it is preferable that the width of the region not subjected to secondary recrystallization is 1 mm or more in order to improve the yield.

  In addition, if the thickness is 1 mm or more, the structure can be visually observed, and the evaluation is easy. Whether or not it is a secondary recrystallized grain can be easily determined by the size of the crystal grain. If it is ambiguous, the crystal grain orientation analysis is performed and compared with the central portion of the width.

  When judging the structure visually, it is not necessary to investigate the entire longitudinal direction of the coil. Although there is no particular limitation on the investigation location, from the viewpoint of the occurrence frequency of adhesion and workability, 30 turns of the outer winding portion and / or inner winding portion of the coil, or from the end portion of the coil in the longitudinal direction from the end portion in the longitudinal direction of the coil. It is preferable to investigate the area up to a position of 100 m. As an example of another method, the acceptance level is set to be about 10 mm or more from the end in the plate width direction, and the instrument is measured (for example, the crystal orientation distribution measurement method using ultrasonic waves described in JP-A-1-229996). Thus, a region that is not secondary recrystallized online may be detected.

  In addition, as a method of suppressing secondary recrystallization at the plate width direction end, when heating the steel slab, the surface temperature at the position corresponding to the plate width direction end at the time of final finish annealing of the steel slab, A method of lowering the surface temperature by 5 ° C. or more from the surface temperature at the center of the width can be considered. As another method, or a method that can be used in combination with the above method, in the heat treatment of the steel plate between hot rolling and final finish annealing (ie, hot-rolled plate annealing, intermediate annealing, etc.), particularly in the soaking step, There is a method in which the surface temperature at the position corresponding to the end portion in the plate width direction at the time of final finish annealing is higher by 5 ° C. or more than the surface temperature at the width center portion. All of these methods suppress secondary recrystallization by weakening the suppressive force of normal grain growth at the end in the plate width direction.

  Here, “the position corresponding to the end portion in the plate width direction at the time of final finishing annealing” is defined in consideration of the fact that the end portion in the plate width direction may be cut off during the process. That is, after the heat treatment including the slab heating or the soaking step, in the intermediate process until the final finish annealing, when the plate width direction end portion is cut off by a slitter or the like, the cut-off width (one side) is Xmm, The position corresponding to the end portion in the plate width direction at the time of final finish annealing is a position inside Xmm from the end portion in the plate width direction.

  In addition, it is sufficient to implement these methods at the end portions in the plate width direction at the 30th winding portion on the outermost winding side and the innermost winding side of the coil at the time of final finish annealing. However, the upper and lower sides of the coil may be reversed depending on the number of processes, and the position of the outermost winding part and the innermost winding part at the time of final finish annealing changes depending on the amount of cutting in the longitudinal direction in the intermediate process. . Therefore, industrially, it is easy and preferable to carry out at both ends in the plate width direction over the entire length of the coil in consideration of ease of control of the heating furnace.

The reason for the surface temperature is that temperature measurement is easy. The reason why the steel slab is lowered by 5 ° C. or more and the steel plate at the time of soaking in the heat treatment is raised by 5 ° C. or more is that a sufficient effect cannot be obtained unless there is a difference of 5 ° C. or more from the width center. These temperature differences are immediately after exiting the heating furnace for steel slabs. In addition, when heating steel slab using two or more heating furnaces, it is set as the temperature difference immediately after coming out of the heating furnace where the temperature of steel slab becomes the highest. In the case of soaking of a steel plate, it may be ensured not only at all times during soaking but at any time during soaking. Here, soaking means that the temperature at the center of the width is within the range of T _max −50 ° C. to T _{max when} the maximum temperature at the center of the width is T _max in one heat treatment step. To do.

  An electric heating furnace is suitable for controlling the temperature in the slab width direction when heating the steel slab.

  After the final finish annealing, after removing the unreacted annealing separator, an insulating coating is applied to the surface of the steel sheet to obtain a product. However, the surface of the steel sheet may be mirrored before applying the coating if necessary. A coating having a tension imparting effect may be used as the insulating coating. Furthermore, the coating baking process may be combined with the flattening process.

  In order to further reduce the iron loss, the steel sheet after the secondary recrystallization is subjected to a known magnetic domain refinement process, that is, a plasma jet or laser irradiation is linearly provided, or a linear dent region is provided by a protruding roll. Processing can also be performed.

  Naturally, after the final finish annealing, the region not subjected to secondary recrystallization at the end in the plate width direction is cut off with a slitter or the like.

  In mass%, Cr: 0.15%, Bi: 0.008%, C: 0.07%, Si: 3.38%, Mn: 0.07%, Cu: 0.1%, Se: 0.00. A plurality of steel slabs with a thickness of 250 mm were cast, containing 02%, N: 0.0081% and Al: 0.025%, the balance being substantially iron and inevitable impurities. These steel slabs were charged into a gas heating furnace, heated in an atmosphere having an oxygen concentration of 7% by volume at 1140 ° C. for 80 minutes, and then in an atmosphere having an oxygen concentration of 0.2% by volume by an induction heating furnace. The center part was heated to 1380 ° C. Then, subsequent to rough rolling, finish rolling was performed to obtain a hot rolled sheet having a thickness of 2.2 mm. At this time, the temperature in the width direction of the steel slab is controlled in the induction heating furnace, and the surface temperature at the position corresponding to the end portion in the sheet width direction at the time of final finish annealing is half of the one set to 1370 ° C. or higher and 1375 ° C. or lower, A half of 1376 ° C. to 1385 ° C. was prepared.

  This hot-rolled sheet was cut off by 200 mm on both sides of the sheet width end with a slitter. Thereafter, the hot-rolled sheet was annealed at 1000 ° C. for 45 seconds, quenched at a rate of 35 ° C./s, pickled, and finished to a thickness of 1.5 mm by the first cold rolling. Subsequently, intermediate annealing was performed at 1100 ° C. for 70 seconds, quenched at a rate of 35 ° C./s, and then finished to a thickness of 0.22 mm by warm rolling at 240 ° C.

Thereafter, after degreasing treatment, decarburization annealing was performed in an atmosphere at 830 ° C. for 100 seconds, a dew point of 58 ° C., a hydrogen concentration of 52% by volume and a nitrogen concentration of 48% by volume, and MgO was subjected to Sr (OH) _2. Was applied to both sides of the steel sheet with a coating amount of 7 g / m ^{2 on} both sides of the steel plate. 2% by mass of TiO ₂ , 8% by mass of TiO ₂ and 1% by mass of SrSO ₄ were added. Thereafter, the steel plate was wound around a coil.

Then, as the final finish annealing, at a rate of 30 ° C./h in N ₂ gas up to 850 ° C., and from 850 ° C. to 1050 ° C. in a mixed gas of N ₂ : 25 vol% and H ₂ : 75 vol%, Thereafter, the temperature was raised to 1200 ° C. in H ₂ gas, held at 1200 ° C. for 8 hours, lowered to 1000 ° C., and then lowered to room temperature in Ar gas. The coil was subjected to final finish annealing with the axial direction upright.

  For each coil, in the steel slab after heating, the surface temperature at the position corresponding to the end in the plate width direction at the time of final finish annealing, the region where the secondary recrystallization of the end in the plate width direction after the final finish annealing is not performed. The relationship between the maximum width, the maximum value of the dew point of the atmosphere in the temperature range of 900 ° C. or higher in the final finish annealing, the maximum value of the temperature increase rate in the same temperature range, and the adhesion between the steel plates below the coil was examined. The adhesion was investigated over 30 m of the outermost winding, that is, about 100 m in length from each longitudinal end, and the adhesion of the steel sheet was investigated. The degree of adhesion was evaluated based on the number of locations within 30 volumes of the outermost winding portion, with the adhesion strength being three levels of weak, medium and strong. The close contact of the innermost winding part in 30 turns was almost the same as that of the outermost winding part.

  The results are shown in Table 2. As shown in Table 2, in the example according to the present invention, the adhesion is mild at the lower part of the coil.

  Steel slabs having a thickness of 220 mm and a width of 1300 mm were cast from the molten steel having the composition shown in Tables 3 and 4 by continuous casting. These steel slabs were heated at 1125 ° C. for 80 minutes in an atmosphere having an oxygen concentration of 5% by volume in a gas heating furnace, and then the slab width was reduced to 1100 mm under the width of the press, and the slab thickness was increased to 200 mm by horizontal reduction. . Subsequently, it heated at 1400 degreeC in the atmosphere whose oxygen concentration is 0.2 volume% with the induction heating furnace.

  Thereafter, a sheet bar having a thickness of 40 mm was obtained by rough rolling, followed by finish rolling to obtain a hot rolled sheet having a thickness of 2.4 mm. This hot-rolled sheet was cut off by 20 mm on both sides of the sheet width end with a slitter.

  Furthermore, these steel sheets were annealed at 1000 ° C. for 50 seconds, quenched at a rate of 30 ° C./s, pickled, finished to a thickness of 1.7 mm by the first cold rolling, and then at 1100 ° C. The intermediate annealing was performed for 75 seconds, and quenched at a rate of 40 ° C./s. Then, after finishing the sheet thickness to 0.22 mm by warm rolling at 250 ° C. and performing a degreasing treatment, an atmosphere having a dew point of 59 ° C., a hydrogen concentration of 60% by volume and a nitrogen concentration of 40% by volume at 830 ° C. for 2 minutes. Decarburization annealing was performed inside.

Next, an annealing separator containing 2% by mass of Sr (OH) ₂ , 5% by mass of TiO ₂ and 2% by mass of SrSO ₄ in MgO was applied to both sides of the steel sheet at a coating amount of 6 g / m ^{2 on} one side. And wound on a coil. After placing in the furnace with the coil axis upright, as final finish annealing, 25 volumes of N ₂ from 850 ° C. to 1050 ° C. at a rate of 30 ° C./h in N ₂ gas up to 850 ° C. %, In a mixed gas containing 75% by volume of H ₂ at a rate of temperature increase of 12.0 ° C./h, after that, the temperature was increased to 1200 ° C. in H ₂ gas and held at 1200 ° C. for 8 hours. The temperature was lowered in H ₂ gas to 0 ° C., and the temperature was lowered in Ar gas from 1000 ° C.

  At this time, in the steel plate at the time of soaking in the intermediate annealing, the surface temperature at the position corresponding to the end portion in the plate width direction at the final finish annealing is 1110 ° C., and the plate width with respect to the longitudinal direction of the coil after the final finish annealing One or more locations where the width of the region not subjected to secondary recrystallization at the end in the direction is 1 mm or more are secured. Further, the dew point in the temperature range of 900 ° C. or higher in the final finish annealing was 10 ° C. or lower, and the rate of temperature increase at 900 ° C. or higher was 12.0 ° C./h or lower at the maximum.

  With respect to the coil after the final finish annealing thus obtained, the state of adhesion between the steel plates under the coil was examined. As a result, all the steel plates obtained according to the present invention had a slight adhesion at the bottom of the coil. That is, there was no adhesion with strong adhesion. In addition, adhesion was investigated over 30 m of the outermost winding part and 30 winding parts of the innermost winding part, that is, about 100 m in length from each longitudinal end, and the adhesion of the steel sheet was investigated. The degree of adhesion was evaluated in three levels: weak, medium and strong adhesion.

  As described above, according to the present invention, adhesion can be lightened, and a directional electrical steel sheet having a high magnetic flux density can be stably produced.

  A steel slab having a thickness of 220 mm was cast by continuous casting from the molten steel having the composition of symbol 2 shown in Tables 3 and 4. These steel slabs were heated in an atmosphere having an oxygen concentration of 5% by volume in a gas heating furnace at 1180 ° C. for 70 minutes, and then heated to 1380 ° C. in an induction heating furnace. At that time, it was performed in atmospheres having various oxygen concentrations shown in Table 5.

  Thereafter, a sheet bar having a thickness of 40 mm was obtained by rough rolling, followed by finish rolling to obtain a hot rolled sheet having a thickness of 2.2 mm. This hot-rolled sheet was cut off by 10 mm at the end in the sheet width direction with a slitter, pickled, and finished to a sheet thickness of 1.5 mm by the first cold rolling. Next, intermediate annealing was performed at 1110 ° C. for 70 seconds, quenched at a rate of 36 ° C./s, and then finished to a sheet thickness of 0.22 mm by cold rolling. Thereafter, after degreasing treatment, decarburization annealing was performed at 840 ° C. for 1 minute in an atmosphere having a dew point of 58 ° C., a hydrogen concentration of 50% by volume, and a nitrogen concentration of 50% by volume.

Next, an annealing separator containing 2% by mass of Sr (OH) ₂ , 5% by mass of TiO ₂ and 2% by mass of SrSO ₄ in MgO was applied to both sides of the steel sheet at a coating amount of 7 g / m ^{2 on} one side. And wound on a coil. After axis of the coil is placed on the furnace in a direction in which an upright, as a final finish annealing, at a heating rate of 20 ° C. / h in N ₂ gas to 850 ° C., also from 850 ° C. to 1050 ° C. N _2: 20% by volume and H ₂ : 80% by volume in a mixed gas at a rate of temperature increase of 10 ° C./h, then heated to 1200 ° C. in H ₂ gas, held at 1200 ° C. for 4 hours, and then 1000 ° C. The temperature was lowered in H ₂ gas until the temperature was lowered from 1000 ° C. in Ar gas.

  At this time, in the steel plate at the time of soaking in the decarburization annealing, the surface temperature at the position corresponding to the end portion in the plate width direction at the final finish annealing is 850 ° C., and at least one place in the longitudinal direction of the coil after the final finish annealing. The width of the region not subjected to secondary recrystallization at the end in the plate width direction was set to 1 mm or more. Further, the dew point of the atmosphere in the temperature range of 900 ° C. or higher in the final finish annealing was set to 15 ° C. or lower, and the temperature rising rate at 900 ° C. or higher was set to 10 ° C./h or lower at the maximum.

  About the coil after the final finish annealing thus obtained, the outermost winding part 30 and the innermost winding part 30, that is, the length of about 100 m from the end in the longitudinal direction, respectively, the adhesion of the steel plate Investigated. The degree of adhesion was evaluated according to the number of locations in volume 60, with the adhesion strength being three levels of weak, medium and strong. As shown in Table 5, the results of examining the adhesion between the steel sheets below the coil were mild except for the coil of symbol 1 in which the atmospheric oxygen concentration in the induction heating furnace was 0.005% by volume. In addition, the adhesion of the lower part of the coil indicated by symbol 1 is at a level where the adhesion is weak and relatively easy to peel because the region where the secondary recrystallization at the end in the plate width direction and the final finish annealing conditions are within the scope of the present invention. It was.

  Thus, adhesion at the lower part of the coil can be prevented by setting the oxygen concentration of the atmosphere in the slab heating at 1350 ° C. or more to 0.01% by volume or more. Considering an increase in scale loss due to slab heating, the oxygen concentration of the atmosphere in slab heating at 1350 ° C. or higher is preferably in the range of 0.01 to 2% by volume.

  % By mass, C: 0.08%, Si: 3.4%, Mn: 0.06%, Sol. Al: 0.020%, N: 0.0083%, S: 0.02%, Cr: 0.06%, the balance is made of molten steel consisting of iron and inevitable impurities. A 1200 mm steel slab was cast. These steel slabs were heated at 1200 ° C. for 80 minutes in an atmosphere with an oxygen concentration of 5% by volume in a gas heating furnace, and then heated at 1360 ° C. for 20 minutes in an atmosphere with an oxygen concentration of 0.05% by volume by an induction heating furnace. did.

  Thereafter, a sheet bar having a thickness of 45 mm was obtained by rough rolling, followed by finish rolling to obtain a hot-rolled sheet having a thickness of 2.3 mm. This hot-rolled sheet was cut off by 15 mm at the end in the sheet width direction with a slitter. Then, this hot-rolled sheet was annealed at 1000 ° C. for 30 seconds, quenched at a rate of 30 ° C./s, pickled, and finished to a sheet thickness of 0.28 mm by cold rolling. Thereafter, after degreasing treatment, decarburization annealing was performed at 840 ° C. for 2 minutes in an atmosphere having a dew point of 60 ° C., a hydrogen concentration of 50% by volume, and a nitrogen concentration of 50% by volume.

Next, an annealing separator in which 5% by volume of TiO ₂ was added to MgO was applied to both sides of the steel sheet at a coating amount of 6 g / m ^{2 on} one side and wound around a coil. After placing in the furnace with the coil axis standing upright, as final finish annealing, the temperature was raised to 850 ° C. at a rate of 20 ° C./h in N ₂ gas, held for 20 hours, and then 850 ° C. To 1150 ° C. in a mixed gas of N ₂ : 20% by volume and H ₂ : 80% by volume at a rate of temperature increase of 12 ° C./h, and then heated up to 1200 ° C. in H ₂ gas at 1200 ° C. After holding for 5 hours, the temperature was lowered to 1000 ° C. in H ₂ gas, and from 1000 ° C., the temperature was lowered in Ar gas.

  At this time, in the steel sheet at the time of soaking of hot-rolled sheet annealing, the surface temperature at the position corresponding to the sheet width end at the time of final finish annealing is 1030 ° C., and at least one place in the longitudinal direction of the coil after the final finish annealing. The width of the region not subjected to secondary recrystallization at the end in the plate width direction was set to 1 mm or more. Moreover, the dew point of the atmosphere in the temperature range of 900 ° C. or higher in the final finish annealing was set to 15 ° C. or lower.

  With respect to the coil after the final finish annealing thus obtained, when the adhesion state between the steel plates under the coil was examined, the adhesion at the lower part of the coil was mild. That is, there was no adhesion with strong adhesion. The close contact was investigated over a length of about 100 m from the 30 outermost winding part and the 30 innermost winding part, that is, the respective end portions in the longitudinal direction. The degree of adhesion was evaluated in three levels: weak, medium and strong adhesion.

  According to this invention, in the manufacture of grain-oriented electrical steel sheets containing Cr, it is possible to prevent adhesion of the lower part of the coil after the final finish annealing, and thus stably produce the grain-oriented electrical steel sheets having low iron loss and high magnetic flux density. can do.

It is a schematic diagram which shows the coil after final finishing annealing with the direction in annealing. It is a cross-sectional photograph of the coil lower part after final finish annealing. It is a figure which shows the measurement result of energy dispersive X-ray spectroscopy (EDX).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coil 2 Close_contact | adherence part 3 Plate | board width direction 4 Coil lower side 5 Thickness direction 6 Coating 7 Base iron 8 Fe-Cr alloy 9 Crevice

Claims (8)

After heating a steel slab containing Si: 2.5-4.5%, Cr: 0.01-0.50% and an inhibitor-forming element in mass%, it is hot-rolled and then at least accompanied by an annealing treatment After the final plate thickness is obtained by one cold rolling, decarburization annealing is performed, and then the annealing separator is applied to the surface of the steel sheet and then wound on the coil, and the final finish is made with the coil shaft upright. In a method for producing a grain-oriented electrical steel sheet, comprising a series of steps for annealing, wherein the final finish annealing includes a purification treatment of 1100 ° C. or more and 3 hours or more,
The dew point of the atmosphere in the temperature range of 900 ° C. or more of the final finish annealing is 20 ° C. or less, and the temperature rising rate in the temperature range of 900 ° C. or more is 15 ° C./h or less. A method for producing a high magnetic flux density grain-oriented electrical steel sheet in which at least one region in the direction has a region that is not secondary recrystallized by 1 mm or more from the end in the plate width direction.   2. The high magnetic flux density grain-oriented electrical steel sheet according to claim 1, wherein heating of the steel slab is performed at 1350 ° C. or higher in an atmosphere in which the oxygen concentration is controlled to 0.01 to 2% by volume%. Manufacturing method.   When heating the steel slab, the surface temperature of the steel slab at a position corresponding to the end portion in the plate width direction at the time of final finish annealing is lower by 5 ° C. or more than the surface temperature of the width center portion. Item 3. The method for producing a high magnetic flux density grain-oriented electrical steel sheet according to Item 1 or 2.   There is a soaking step between the hot rolling and the final finish annealing, and in this soaking step, the surface temperature at the position corresponding to the end portion in the plate width direction at the time of the final finish annealing is determined by the surface at the center of the width. The method for producing a high magnetic flux density grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the temperature is higher by 5 ° C or more than the temperature.   The said annealing process accompanying the said cold rolling includes the said soaking process, The manufacturing method of the high magnetic flux density directionality electrical steel plate of Claim 4 characterized by the above-mentioned.   The method for manufacturing a high magnetic flux density grain-oriented electrical steel sheet according to any one of claims 1 to 5, wherein the steel slab further contains Bi: 0.0005 to 0.100% by mass.   The steel slab is further mass%, C: 0.03 to 0.10%, Mn: 0.050 to 1.5%, S and / or Se in total 0.010 to 0.040%, Sol . 7. Al: 0.015 to 0.050% and / or B: 0.001 to 0.01%, and N: 0.005 to 0.015%. The manufacturing method of the high magnetic flux density directionality electrical steel plate in any one of these.   The steel slab is further mass%, Ni: 0.05 to 0.5%, Cu: 0.05 to 0.5%, Sn: 0.005 to 0.5%, Sb: 0.005 to 0 .10%, As: 0.005-0.10%, Mo: 0.005-0.10%, Te: 0.005-0.10% and P: 0.005-0.10% The method for producing a high magnetic flux density grain-oriented electrical steel sheet according to any one of claims 1 to 7, comprising one or two or more selected ones.