JP2008195998A - Finish-annealing method for grain-oriented electrical steel sheet, and inner case used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for suppressing uneven distribution of temperature in a coil caused in a heating process and a cooling process after soaking process without being accompanied with a large facility reconstruction and without preventing a transfer of the heat between the side wall in an inner case and the outer part of a coil faced to this side wall, in a finish-annealing of a grain-oriented electrical steel sheet wherein the coil for winding the electrical steel sheet is finish-annealed in a state of covering the inner-case by using a butch-type annealing furnace. <P>SOLUTION: In the method for finish-annealing the grain-oriented electrical steel sheet, the inner case having a cylindrical recessed part faced to the inner winding part of the coil is covered on the upper part of the case while the coil is finish-annealed in the butch-type annealing furnace. And, this inner case for finish-annealing to the grain-oriented electrical steel sheet, has the cylindrical recessed part facing the inner-winding part of the coil at the upper part used for this finish-annealing. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention can shorten the length of a shape defect portion of a grain-oriented electrical steel sheet manufactured through a rewinding process after finish annealing of the grain-oriented electrical steel sheet, and suppress the deterioration margin of the magnetic property of the middle winding of the coil. The present invention relates to a finish annealing method for grain-oriented electrical steel sheets and an inner case used therefor.

  Generally, a grain-oriented electrical steel sheet is manufactured as follows. First, the components are adjusted by steel making, molten steel containing 3% by mass of Si is cast into a steel slab, the steel slab is hot-rolled, and then once or intermediate cold annealing is performed twice or more cold Roll. A magnetic steel sheet containing 3% by mass of Si having a final thickness obtained by cold rolling is subjected to decarburization annealing, and then an annealing separator is applied to the surface, and then wound tightly in a coil shape. As shown in FIG. 2, the coil in which this electromagnetic steel sheet is tightly wound is then placed in the furnace of the batch annealing furnace 1 with the center of the coil vertical, and is annealed by moving the hearth. The 1A is a furnace ceiling, 1B is a furnace wall, and 2 is a burner disposed on the top of the furnace wall 1B.

Next, the coil that has been annealed and formed with the tension coating film is rewound in a subsequent process, and is subjected to various treatments as necessary to obtain a product of grain-oriented electrical steel sheet.
The inner case 3 is generally used for finish annealing of grain-oriented electrical steel sheets. The main role of the inner case 3 is to cover a coil wound with a magnetic steel sheet tightly, and to set a predetermined position in the coil thickness direction in the inner case 3 (for example, the outer winding W1 and the inner winding W2 of the coil in FIGS. 1 and 3). Position) as a temperature management point, a heating step for heating the coil until the temperature at the management point reaches a predetermined soaking temperature, a subsequent soaking step, and then the temperature at the management point reaches a predetermined cooling temperature. A cooling step of cooling to a temperature is to shield the atmosphere in contact with the electromagnetic steel sheet from the furnace atmosphere. In the soaking step, it is particularly important to maintain a predetermined soaking time at a predetermined soaking temperature, for example, 900 to 1200 ° C., in order to secure magnetic properties when the product is a grain-oriented electrical steel sheet.

By the way, when the conventional inner case is used and finish annealing of the grain-oriented electrical steel sheet, it is known that a large non-uniformity is generated in the temperature distribution in the coil in the heating process and the cooling process. As a result, abdominal stretch, shape defects such as “longitudinal wrinkles”, and deterioration of the magnetic properties of the middle winding of the coil occurred.
When the conventional inner case is used, in the heating step, the temperature of the outer winding W1 of the coil becomes higher than any position in the inner winding W2 and the coil thickness direction. In the cooling step of cooling until reaching a predetermined cooling temperature after the soaking step of holding a predetermined soaking time at a predetermined soaking temperature, the temperature of the outer winding W1 of the coil first decreases.

  It has been proposed to use an inner case that prevents overheating and overcooling of the outer winding W1 of the coil (Patent Documents 1 and 2). The inner case of this Patent Document 1 is intended to prevent “vertical wrinkles” of defective shapes, and a heat insulating plate is attached to the inside of the side wall to suppress a temperature difference in the vertical direction of the coil. . Moreover, in order to reduce the temperature difference between the heat source side and the counter heat source side and the radial direction in the strip coil, the inner case of Patent Document 2 is thick on the side facing the annealing furnace heat source and thinly shielded on the counter heat source side. It has a body.

In addition, in order to suppress local cooling during cooling and prevent ear distortion (ear extension), a moving hearth type continuous heat treatment method is also proposed in which a heat treatment cover is placed on a heat treatment product in a predetermined temperature section of the cooling process. (Patent Document 3). This heat-treated product is preferably a strip coil in the inner case and having the axis centered vertically.
JP 2006-257486 A Japanese Utility Model Publication No. 61-043260 JP 05-271790 A

However, when using an inner case that prevents overheating and overcooling of the outer winding W1 of the coil as in the inner cases of Patent Documents 1 and 2, there are the following problems.
In the inner case of Patent Document 1, even if overheating of the upper part of the coil can be prevented, heat transfer between the side wall of the inner case and the outer winding of the coil facing the inner case is hindered by the heat insulating plate.

For this reason, when performing finish annealing of grain-oriented electrical steel sheets, extra time is required in the heating process for heating the coil and the cooling process for cooling until reaching a predetermined cooling temperature after the soaking process. . In the inner case of this Patent Document 1, the coil heating rate and cooling rate may be restricted.
In the case of the inner case of Patent Document 2, since the shield is provided on the side wall, there is a problem similar to that of Patent Document 1. That is, the inner case as disclosed in Patent Documents 1 and 2 cannot be adopted as a countermeasure when the production is tight.

Moreover, the heat insulation cover of patent document 3 is a moving hearth provided with the apparatus which extends | stretches a heat insulation cover to the predetermined location of a cooling zone, and covers it to a to-be-processed goods, and the apparatus which collect | recovers a heat insulation cover in this and another place It is necessary to use a batch-type annealing furnace of the type, and this cannot be adopted because it involves major equipment modifications.
The present invention eliminates the above-mentioned problems of the prior art, and uses a batch-type annealing furnace to greatly modify the equipment in the finish annealing of grain-oriented electrical steel sheets, in which finish annealing is performed with a coil wound with electrical steel sheets covered with an inner case. Temperature distribution in the coil that occurs in the heating process and the cooling process after the soaking process without interfering with heat transfer between the side wall of the inner case and the outer winding of the coil facing the inner case. It aims at providing the technology which suppresses.

  The present invention relates to a finish annealing method for a directional electrical steel sheet in which a coil wound with a magnetic steel sheet is subjected to finish annealing in a state where the coil center is placed vertically in a furnace of a batch annealing furnace. A finish annealing method for grain-oriented electrical steel sheets, characterized in that an inner case having a cylindrical recess facing the inner winding of a coil is placed on the upper part of the case during finish annealing in the furnace.

  In addition, it is an inner case that is used with a coil wound with magnetic steel sheets placed in the furnace of a batch annealing furnace with the center of the coil vertical and covered, and facing the inner winding of the coil at the top of the case An inner case for finish annealing of a grain-oriented electrical steel sheet characterized by having a cylindrical recess.

  According to the present invention, the inner case used for finish annealing of the grain-oriented electrical steel sheet is modified to form an inner case having a shape capable of positively heating and cooling the inner winding side of the coil. That is, while finishing annealing a coil of electromagnetic steel sheet in a furnace of a batch annealing furnace, the temperature distribution in the coil is non-uniform by covering the upper part of the case with an inner case having a cylindrical recess facing the inner winding of the coil. Can be suppressed.

  As a result, it is possible to shorten the length of the defective shape portion caused by the temperature distribution in the coil, and to achieve the soaking time in the middle winding of the coil during finish annealing. It is possible to suppress the deterioration margin of the middle winding magnetic characteristics.

Hereinafter, the background of the present invention will be described. The present inventor does not greatly modify the equipment, and does not hinder the transfer of heat between the side wall of the inner case and the outer winding of the coil facing the coil, and the coil generated in the heating step and the cooling step after the soaking step The technology for suppressing the non-uniformity of the temperature distribution in the inside was intensively studied.
First, a description will be given of what happens to the temperature distribution in the coil when the annealing is performed using the moving hearth type batch annealing furnace shown in FIG. 2 and the conventional inner case 3 is covered with the coil.

  Here, the moving hearth-type batch annealing furnace 1 is provided with a burner 2 for injecting combustion gas to the upper part of the furnace wall 1B along the moving direction of the hearth, and in the inner case 3 placed on the hearth. The coil is heated in sequence with the movement of the hearth until it reaches a predetermined soaking temperature, followed by a soaking step, followed by a cooling step for cooling until the temperature reaches a predetermined cooling temperature. Finish annealing. And the coil which reached | attained predetermined | prescribed cooling temperature is extracted from an extraction port.

  Meanwhile, from the burner 2 using a predetermined position in the coil thickness direction in the inner case 3 (for example, the surface of the outer winding W1 and the inner winding W2 in FIG. 3 and the center position in the coil height direction) as a temperature management point. Combustion control of the combustion gas to be ejected is performed. This burned gas is the atmosphere inside the batch annealing furnace 1. On the other hand, the atmosphere in the inner case 3 is a reducing atmosphere different from the furnace atmosphere. An appropriate gap is provided between the side wall of the inner case 3 and the outer winding W1 of the coil, and a gap in the upper part of the coil and a gap in the central part of the coil pass through the reducing atmosphere. It has become.

  For this reason, transfer of heat to the coil that is subjected to finish annealing with the inner case 3 covered is performed mainly by radiant heat through the side wall of the inner case 3. As shown in FIG. 3, the conventional inner case 3 does not have a cylindrical recess facing the inner winding W2 of the coil at the upper part of the case. On the other hand, the shape of the inner case 3 according to the present invention is shown in FIG. In either case, a heat insulating material or a shield for shielding radiant heat is not provided on the side wall.

  In the case of this conventional inner case 3, between the heating process and the first half of the soaking, the outer winding of the coil facing the side wall first rises in temperature due to the radiant heat from the side wall of the inner case 3. Next, heat is transferred in the radial direction of the coil by heat transfer. Therefore, the temperature in the coil has a temperature distribution in which the outer winding W1 is the highest, the middle winding is next, and the inner winding W2 is the lowest. And in the first half of the heating process, the combustion gas ejected from the burner 2 is strongly cooked into the furnace, so that when the conventional inner case 3 is used as shown in FIG. A large non-uniformity occurs.

  On the other hand, in the cooling step after the soaking step where the soaking time is maintained at a predetermined soaking temperature, the coil is cooled by blowing cooling air from the upper part outside the inner case. For this reason, when the coil reaches the cooling process, the temperature of the side wall of the inner case 3 first decreases, and the temperature of the outer winding W1 of the coil begins to decrease. Then, although the heat flow direction is the reverse of the heating process, heat is transferred in the coil radial direction even in the cooling process, resulting in non-uniform temperature distribution in the coil.

  Since this conventional inner case 3 does not have a cylindrical recess facing the inner winding W2 of the coil in the upper part of the case, there was little transfer of heat to the inner winding W2 of the coil via the inner case 3. Therefore, when finish annealing is performed with the conventional inner case 3 covered on the coil, a heating step of heating the coil until a predetermined soaking temperature is reached, and a predetermined cooling temperature is reached after the soaking step. In the cooling process of cooling, a large non-uniformity occurs in the temperature distribution in the coil. As a result, a shape defect called abdominal stretch and deterioration of the magnetic characteristics of the middle winding of the coil occurred. This deterioration of the magnetic characteristics is because the temperature increase rate of the intermediate winding is slower than the temperature increase rate of the outer winding W1 of the coil, so that the intermediate winding soaking time (in the case of two-stage soaking, the primary soaking time and 2 This was often caused by failure to achieve either or both of the soaking times.

Therefore, in the present invention, the inner case 3 used for finish annealing of the grain-oriented electrical steel sheet is remodeled so that the inner winding W2 side of the coil can be actively heated and cooled as shown in FIG. . The inner case 3 according to the present invention is characterized by having a cylindrical recess 4 facing the inner winding W2 of the coil at the upper part of the case.
The cylindrical recess 4 is made of the same material as that of the inner case, and the bottom of the recess is positioned substantially at the same position as the lower end of the side wall of the inner case 3 or slightly higher. That is, in the inner case 3 according to the present invention, the center of the cylindrical recess 4 is aligned with the center of the coil, and the coil is wound on the coil wound with the electromagnetic steel sheet, and the inner case 3 is covered with the outer winding W1 of the coil. An appropriate gap is formed between them, and the reducing atmosphere flows through the gap between the coil, the upper gap of the coil, and the cylindrical recess 4 inserted into the central part of the coil and the inner winding W2 of the coil. It is like that. The rest is the same as the conventional inner case 3.

The operation of the inner case 3 having the cylindrical recess 4 facing the inner winding of the coil at the upper part of the case is as follows.
Since the inner case 3 according to the present invention has the cylindrical recess 4 facing the inner winding W2 of the coil at the upper part of the case, the radiant heat radiated from the cylindrical recess 4 of the inner case 3 to the inner winding W2 of the coil in the heating process. Thus, the inner winding W2 side of the coil can be positively heated. On the other hand, since the outer winding W1 side of the coil faces the side wall of the inner case 3, it is heated by radiant heat radiated from the side wall of the inner case 3 as in the conventional case. FIG. 4 shows the temperature distribution in the coil thickness direction in the first half of the heating process in which the combustion gas is strongly cooked from the burner 2 into the furnace.

Thus, according to the inner case 3 according to the present invention, in the heating process, the inner winding W2 side of the coil can be heated by the radiant heat like the outer winding W1 side, and the coil is compared with the conventional inner case. The non-uniformity of the temperature distribution inside can be suppressed.
Further, according to the inner case 3 according to the present invention, in the cooling step after the soaking step, the cylindrical recess 4 of the inner case 3 is first cooled, so that the inner winding W2 side of the coil facing it is the outer winding W1 side. As compared with the conventional case, it is possible to suppress the non-uniformity of the temperature distribution in the coil as compared with the conventional inner case.

  Therefore, by using the inner case 3 according to the present invention and finish annealing the grain-oriented electrical steel sheet, it is possible to positively heat and cool the inner winding W2 side of the coil without significant equipment modification. In addition, by changing the shape of the inner case, the length of the defective shape portion caused by the temperature distribution in the coil can be shortened and the finish annealing can be performed as described in the following examples. It is possible to suppress the deterioration of the magnetic characteristics caused by, for example, not achieving the soaking time of the middle winding of the coil.

  A plurality of coils each containing 3% by mass of Si and wound with a magnetic steel sheet having a thickness of 0.3 mm, a width of 1160 mm, and a length of 3000 m were placed in a furnace of a batch annealing furnace and subjected to finish annealing. At that time, with the two types of inner cases covered, the temperature distribution in the coil during finish annealing (however, at the center position in the coil height direction) was measured. Moreover, after finishing annealing, the coil was rewound, various treatments were performed, and the sheet was cut into a sheet to obtain a grain-oriented electrical steel sheet. In the process of rewinding the coil, the length of the defective shape portion was measured. The magnetic properties were evaluated by taking a sample from a grain-oriented electrical steel sheet cut into a magnetic sheet, performing a known Epstein test, and evaluating the loss of iron loss.

Inner case of the present invention example: a case having a cylindrical recess in the upper part of the case (see FIG. 1).
Inner case of the conventional example: a case with no cylindrical recess at the top of the case (see FIG. 3)
Inner case thickness: 25 mm for both the inventive example and the conventional example.
(Finish annealing conditions)
Soaking temperature: 1150 ° C., soaking time: 10 h, atmosphere in the inner case: hydrogen atmosphere, heating rate: 500 to 1000 ° C. in a temperature range of 20 to 30 ° C./h (rapid heating pattern), cooling rate: 1150 A temperature range of ˜500 ° C. is 15 to 20 ° C./h.

  As a result, when finish annealing was performed with the conventional inner case covered on the coil, the temperature distribution in the coil had a maximum temperature difference of 250 ° C. in the coil thickness direction. It was possible to make it small. Therefore, by applying the present invention, it is possible to improve the length of the shape defect portion due to the temperature distribution in the coil as compared with the conventional example as shown in FIG. As shown in Table 1, the cost could be reduced as compared with the conventional example. In the conventional example, the most deteriorated portion of the magnetic characteristics occurred in the middle winding of the coil, and the poorly stretched portion of the belly occurred in the middle winding of the coil in both the inventive example and the conventional example.

(A) which shows the shape of the inner case of this invention is a perspective view including a partial cross section, (b) is the longitudinal cross-sectional view. It is sectional drawing explaining the problem in the heating process when finish-annealing the coil which wound the electromagnetic steel plate with a batch annealing furnace. (A) which shows the shape of the conventional inner case is a perspective view containing a partial cross section, (b) is the longitudinal cross-sectional view. It is a characteristic view explaining the effect | action at the time of using the inner case of this invention compared with the past. It is a characteristic view which compared the effect of the example of this invention with the prior art example.

Explanation of symbols

r Distance from coil center W1 Outer winding W2 Inner winding 1 Batch type annealing furnace 1A Furnace ceiling 1B Furnace wall 2 Burner 3 Inner case 4 Cylindrical dent

Claims (2)

  In the method of finish annealing of directional electrical steel sheets, in which a coil wound with electrical steel sheets is subjected to finish annealing in a state where the coil center is placed vertically in the furnace of a batch annealing furnace, the coils are placed in the furnace of the batch annealing furnace. A finish annealing method for grain-oriented electrical steel sheets, wherein an inner case having a cylindrical recess facing the inner winding of the coil is placed on the upper part of the case during finish annealing.   This is an inner case that is used with a coil wound with magnetic steel sheets placed in the furnace of a batch annealing furnace with the center of the coil vertical and covered, and the upper part of the case is a cylindrical shape facing the inner winding of the coil An inner case for finish annealing of grain-oriented electrical steel sheets, characterized by having a dent.

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