JP6083157B2 - Rapid heating apparatus and rapid heating method for continuous annealing equipment - Google Patents

Description

The present invention relates to a rapid heating apparatus in a continuous annealing facility for steel sheets, and specifically relates to a rapid heating apparatus and a rapid heating method in a continuous annealing facility suitable for primary recrystallization annealing of a grain-oriented electrical steel sheet.

  In recent years, the heating rate when annealing a cold-rolled steel sheet tends to be rapidly heated as described in Patent Document 1, and in particular, the directionality used as a material such as an iron core of a transformer or electrical equipment. Rapid heating is becoming common in primary recrystallization annealing of magnetic steel sheets. Its main purpose is that, in addition to improving production efficiency by shortening the heating time, rapid heating is expected to improve magnetic properties by developing specific textures as described below. .

  In general, in the primary recrystallization process of the cold-rolled cold-rolled steel sheet, the <111> // ND orientation having a high accumulated strain energy preferentially recovers or recrystallizes. As a result, at a temperature increase rate of about 10 ° C./s as in the conventional case, the recrystallization texture after the primary recrystallization is mainly in the <111> // ND orientation. On the other hand, if the rate of temperature rise is made higher than the above rate, it is heated to a high temperature causing recrystallization before the <111> // ND orientation recovers, and thus it is difficult to recrystallize <110>. // ND orientation also causes primary recrystallization. As a result, the <110> // ND orientation and thus the Goth orientation ({110} <001>) in the product plate after the secondary recrystallization increase, and at the same time, the grain size becomes finer and the iron loss characteristics are improved.

  However, in the rapid heating as described above, it is necessary to strictly control the heating conditions such as the heating temperature and the heating time. This is because if the temperature distribution in the steel sheet varies during the heating of the primary recrystallization annealing, the texture after the primary recrystallization annealing changes in the steel sheet, and this is the secondary recrystallization texture after the finish annealing. This is because the dispersion of magnetic properties in the steel sheet of the grain-oriented electrical steel sheet is increased.

  Furthermore, when the temperature unevenness in the steel sheet, especially the temperature unevenness in the width direction of the sheet increases, when passing through the annealing equipment, vertical wrinkles and warpage occur in the steel sheet, the product shape deteriorates, or the transport roll in the furnace This is because, when the steel sheet is wound, narrowing occurs, and in the worst case, a serious operational trouble such as the steel sheet breaking in the furnace is caused.

  As a technique for strictly managing the temperature in the steel plate, for example, in Patent Document 2, a heating compensation member made of a conductive material is disposed at a connection portion between each coil case of two or more induction heating devices, There has been disclosed a method for minimizing heating interruption between induction heating devices by effectively using leakage magnetic flux from the induction heating coil.

Japanese Patent Laid-Open No. 01-290716 JP 2008-266727 A

  However, even with the technique disclosed in Patent Document 2, in the case of rapid heating such as induction heating, the actual situation is that temperature unevenness is likely to occur in the steel plate, particularly in the plate width direction. As a result, in the case of rapid heating, not only the shape change in the steel strip, the occurrence of shape defects due to it, the operation troubles, etc., but also the variation of the magnetic properties in the product coil, It was a cause of quality degradation.

The present invention has been developed to solve the above-described problems of the prior art, and the purpose thereof is in the steel plate, particularly in the width direction, even when the steel plate is rapidly heated by an induction heating device. The present invention provides a rapid heating apparatus in a continuous annealing facility that can achieve uniform quality distribution and improve quality such as steel plate shape and magnetic properties, and propose a rapid heating method using the apparatus .

  In order to solve the above-mentioned problems, the inventors have made various studies by paying attention to the configuration and arrangement of the induction heating device that constitutes the heating zone of the continuous annealing equipment. As a result, two or more induction heating devices are disposed in the first half of the heating zone, and a gradual heating section is provided between them in order to achieve a uniform temperature distribution in the steel sheet. The present invention has been found by finding it effective.

That is, the present invention is a rapid heating apparatus for continuous annealing equipment for a final cold-rolled material of an electromagnetic steel sheet containing Si: 8.0 mass% or less , comprising a heating zone, a soaking zone, and a cooling zone , Two or more induction heating devices are arranged in series in the first half portion, and a gradual heating section is provided in a temperature range in which the steel plate temperature between the two or more induction heating devices is 250 to 600 ° C. Is a rapid heating apparatus characterized by

  The rapid heating apparatus of the present invention is characterized by having a heating apparatus in the above-mentioned slow heating section that makes the temperature rising rate of the steel sheet exceed 0 ° C./s and not more than 10 ° C./s.

  Moreover, the rapid heating apparatus of this invention is characterized by the length of the said slow heating area being 1-30 m.

  Moreover, the rapid heating apparatus of the present invention is characterized in that the temperature increase rate in the induction heating apparatus installation section is 50 ° C./s or more.

Moreover, this invention proposes the rapid heating method of the electrical steel sheet containing Si: 8.0 mass% or less characterized by heating using the rapid heating apparatus of any one of Claims 1-4. To do.

  According to the present invention, two or more induction heating devices are arranged in series in the first half of the heating zone of the continuous annealing equipment, and a 1-30 m slow heating section is provided between the two or more induction heating devices. In this slow heating section, the temperature in the steel strip is made uniform to reduce the temperature unevenness in the plate width direction due to rapid heating. The unevenness of the magnetic characteristics can be greatly reduced. Furthermore, according to the present invention, by providing the slow heating section in the middle of heating, an appropriate amount of accumulated strain energy of <111> // ND orientation is released, and <111> // ND orientation in the primary recrystallized structure. Since the abundance ratio of <110> // ND orientation with respect to can be relatively increased, the effect of improving magnetic characteristics by rapid heating can be further enhanced as compared with the prior art.

It is a schematic diagram explaining the structure of the conventional continuous annealing equipment. It is a schematic diagram explaining the conventional rapid heating apparatus using an induction heating apparatus. It is a schematic diagram explaining the rapid heating apparatus of this invention using the induction heating apparatus. It is a schematic diagram explaining the heating pattern of the Example using the rapid heating apparatus of this invention.

Hereinafter, the case where the rapid heating apparatus of the present invention is applied to a continuous annealing facility for primary recrystallization annealing of a grain-oriented electrical steel sheet will be described as an example.
FIG. 1 shows a continuous annealing equipment used for primary recrystallization annealing on a grain-oriented electrical steel sheet cold-rolled to the final thickness (product thickness) or primary recrystallization annealing also serving as decarburization annealing. The example of a general structure of a furnace part is shown typically. The furnace section of the continuous annealing equipment is usually composed of a heating zone 2 with a radiant tube heating system, a soaking zone 3 with an electric heater heating system, and a cooling zone 4, and the furnace starts from the heating zone 2 entry side (left side in FIG. 1). The steel plate 1 transported inside is heated to a soaking temperature in the heating zone 2, maintained at a predetermined soaking temperature in the soaking zone 3 for a predetermined time, and then cooled to near room temperature in the cooling zone 4 and outside the furnace ( It is carried out to the right side of FIG. FIG. 1 shows a state in which a steel plate is conveyed in the horizontal direction in the furnace, imitating a horizontal furnace, but the steel plate is conveyed via conveying rolls arranged vertically or horizontally in the furnace. Of course, it may be heat-treated while reciprocating in the furnace. Moreover, steel plate temperature is managed by the plate | board thermometers 51-53 etc. which were installed in the exit side of each belt | band | zone, for example.

  In FIG. 2, an induction heating device 21 capable of rapid heating is disposed in front of the heating zone 20 by the radiant tube heating method, rapidly heating from room temperature to a predetermined temperature at once, and then the soaking temperature in the radiant tube. 2 shows a heating zone of the prior art that heats up to.

  The reason why the magnetic properties are improved by rapid heating using the induction heating apparatus as described above is that, as described above, by rapid heating, the core of secondary recrystallization is <110> // ND. This is because the generation of the Goth orientation ({110} <001> orientation) in the medium can be promoted, and as a result, the secondary recrystallized structure is refined and the magnetic properties can be improved.

  However, as described above, in the steel plate heating using the induction heating apparatus as shown in FIG. 2 in the heating zone, the temperature increase rate of the steel plate is high, and therefore the temperature distribution in the steel plate, particularly in the plate width direction, becomes non-uniform. For example, the temperature difference (maximum temperature-minimum temperature) in the plate width direction measured by the plate thermometer 61 installed on the exit side of the induction heating device 21 shown in FIG. As a result, vertical wrinkles, warpage, etc. occur in the steel sheet and the product shape deteriorates.When the steel sheet is wound around the transport roll in the furnace, narrowing occurs, or in the worst case, the steel sheet breaks in the furnace. Cause serious operational troubles.

  Therefore, in order to solve the above problems, the present invention divides the induction heating device 21 of FIG. 2 into two parts 21a and 21b as shown in FIG. 3, and separates them through the duct part 21c. Thus, a gradual heating section is provided in the middle of rapid heating. The duct portion 21c serving as the slow heating section has, for example, a heating device 21d capable of gradually heating the steel plate at a temperature rising rate of 0 ° C./s to 10 ° C./s on the front and back surfaces of the steel plate. It is preferable that they are arranged to face each other. By providing this heating device, it is possible to more effectively reduce the temperature unevenness in the steel sheet, particularly in the plate width direction, as compared with the case where there is no heating device. As a result, the temperature non-uniformity in the steel plate, particularly in the plate width direction, is further reduced to improve the shape defect, and the variation in magnetic characteristics can be further reduced.

The inventors consider the mechanism for improving the temperature unevenness by installing such a heating device as follows.
First, in the case where a constant heating section having a certain length is provided between the induction heating devices, which is one of the constituent elements of the present invention, the induction heating section is caused by thermal diffusion while the steel plate passes through the slow heating section. The temperature unevenness in the steel plate formed by is reduced. Furthermore, when a heating means such as a heater, which is another constituent element of the present invention, is disposed in the slow heating section, in addition to the thermal diffusion in the steel plate, the heating means in the plate width direction by these heating means Since the temperature equalizing effect is added, the temperature increase allowance of the high temperature portion in the steel sheet is small, the temperature increase allowance of the low temperature portion is large, and heating can be performed while actively mitigating temperature unevenness. As a result, temperature unevenness can be further reduced as compared with the case where no heating means is provided.

  In addition, there is no restriction | limiting in particular about the heating means of the said heating apparatus 21d, Any means may be used if it can reduce the temperature nonuniformity in a steel plate, such as an electric heater, a radiant tube, and high temperature gas spraying.

  Here, the reason that the magnetic characteristics are further improved by providing the duct portion 21c, that is, the slow heating section, compared to the conventional rapid heating is that by providing the slow heating section in the middle of heating, <111> // ND The amount of accumulated strain energy in the orientation can be released in an appropriate amount, and the abundance ratio of the <110> // ND orientation with respect to the <111> // ND orientation in the primary recrystallized structure can be further increased as compared with the prior art. Because it can.

  In order to obtain the improvement effect, the duct portion 21c is preferably provided in a temperature range in which the steel plate temperature is 250 ° C to 600 ° C. This is because the present invention reduces the recrystallization superiority of <111> // ND by gradually heating for a short time in a temperature range in which dislocation density is reduced and recrystallization does not occur. It is a technical idea. Therefore, the above effect cannot be obtained at a temperature lower than 250 ° C. at which dislocation migration is hardly expected. On the other hand, recrystallization of <111> // ND begins to occur at a temperature higher than 600 ° C. This is because the generation of the {110} <001> orientation cannot be promoted.

  Moreover, it is preferable that the length of the said duct part 21c, ie, the length of a slow heating area, shall be the range of 1-30 m. If it is less than 1 m, the time for gradual heating is too short, temperature uniformity in the steel sheet is not sufficient, and the effect of improving the shape and magnetic properties cannot be obtained. On the other hand, if it exceeds 30 m, the slow heating time becomes longer, and the recovery of the rolling structure proceeds excessively, which may cause secondary recrystallization failure. Incidentally, it is preferable that the time for the above-described slow heating (the time required for the steel plate to pass through the duct portion 21c) is in the range of 1 to 10 seconds.

  In order to obtain the effect of improving the magnetic characteristics, it is preferable that the section for rapid heating by the induction heating device is between room temperature and at least 700 ° C. The reason why the upper limit is 700 ° C. is that the temperature at which <111> // ND is preferentially recrystallized is 700 ° C. or less, and not only the effect of improving the magnetic properties is saturated even when rapidly heated to a temperature exceeding 700 ° C., This is because the energy required for heating increases, which is not preferable.

  In addition, in order to obtain the effect of improving the magnetic characteristics, it is preferable that the temperature increase rate in the induction heating device installation section is 50 ° C./s or more. This is because the effect of improving the magnetic properties is not sufficient at less than 50 ° C./s. However, even if rapid heating is performed at 200 ° C./s or more, the effect of improving magnetic properties is saturated, so the upper limit is preferably about 200 ° C./s.

  In addition, in the said description, although the induction heating apparatus 21 was divided | segmented into two, 21a and 21b, the induction heating apparatus of 21a and 21b may be one each, and may be comprised from multiple units | sets. Good. Moreover, when comprised from multiple units | sets, the induction heating apparatus by the side of the duct part 21c of 21a and 21b can be moved to the conveyance direction of a steel plate, for example, the induction heating apparatus which comprised 21a is made 21b side. You may make it change the position of the duct part 21c, ie, the temperature range used as a slow heating area, by moving or moving the induction heating apparatus which comprised 21b to the 21a side.

  In addition, as described above, the rapid heating apparatus of the present invention can be applied to continuous annealing of a steel sheet subjected to rapid heating, thereby improving the steel sheet shape and also controlling the texture after recrystallization. , For primary recrystallization annealing that also serves as primary recrystallization annealing and decarburization annealing for the final cold-rolled sheet of grain-oriented electrical steel sheet containing Si by 8.0 mass% or less, or for the final cold-rolled sheet of non-oriented electrical steel sheet It is effective to apply to annealing.

  C: 0.070 mass%, Si: 3.35 mass%, Mn: 0.10 mass%, Al: 0.025 mass%, N: 0.012 mass%, S: 0.01 mass%, Se: 0.02 mass%, Sb : 0.02 mass% and Sn: 0.02 mass%, the remainder of the grain-oriented electrical steel sheet cold rolled to a final thickness of 0.3 mm manufactured from a slab composed of Fe and inevitable impurities, A primary recrystallization annealing furnace that also serves as decarburization annealing was applied in a continuous annealing furnace composed of the tropics and cooling zone. As shown in FIG. 3, the heating zone of the continuous annealing furnace is provided with an induction heating device 21 in front of the heating zone 20 by the radiant tube heating method. Further, the induction heating device 21 is composed of 21a and 21b. A duct part 21c having a heating device 21d that can be gradually heated between 21a and 21b is provided, which is composed of two parts and is relatively movable in the conveying direction of the steel sheet. Is designed.

Heating using the above heating equipment was performed in two heating patterns as described in FIG. 4 and below.
Pattern A: A duct portion (gradual heating section) 21c of about 2.5 m is provided between the induction heating devices 21a and 21b, and the first 21a is heated from room temperature (20 ° C.) to 500 ° C. at 75 ° C./s. The duct portion 21c is gradually heated at a temperature rising rate of 2.0 ° C./s for 2.0 seconds, and the subsequent 21b is heated up to 700 ° C. at 75 ° C./s, and then is heated at 850 ° C. with a radiant tube. Heating pattern of the present invention for heating up to an average heating rate of 15 ° C./s until pattern B: Pattern B: 700 ° C. from room temperature (20 ° C.) without providing duct part (gradual heating section) 21c between induction heating devices 21a and 21b Up to 75 ° C./s at a stroke, and then heated to a soaking temperature of 850 ° C. with a radiant tube at an average heating rate of 15 ° C./s.

  At this time, the temperature distribution in the plate width direction of the steel sheet is measured with plate thermometers 61a, 61c and 61b installed on the exit side of the induction heating device 21a, the exit side of the duct portion 21c and the exit side of the induction heating device 21b. At the same time as obtaining the difference between the maximum temperature and the minimum temperature, the shape of the steel plate on the exit side of the induction heating device 21b was measured using a laser displacement meter to determine the steepness.

The steel sheet subjected to primary recrystallization annealing that also serves as decarburization annealing with the above heating pattern is then coated with an annealing separator on the steel sheet surface according to a conventional method, dried, subjected to finish annealing, A flattened annealing that combines baking and shape correction was performed to obtain a product sheet of grain-oriented electrical steel sheet.
Test pieces were collected from the coil tip of the product plate thus obtained, the positions 1/4, 2/4 and 3/4 from the tip of the total length of the coil, and the coil tail end in a total of five locations, and the magnetic flux density B ₈ The iron loss W _17/50 was measured according to the Epstein method defined in JIS C2550, and the inferior magnetic flux density B ₈ and the iron loss W _17/50 were _taken as guaranteed values in the coil.

  The results are shown in Table 1. From this result, by using the annealing equipment of the present invention, the temperature difference in the sheet width direction in the steel sheet during heating is greatly reduced, and as a result, the steel sheet shape is stable and the plateability to the annealing equipment is improved. In addition, it can be seen that the variation in the magnetic properties in the steel sheet can be reduced and the guaranteed value in the coil can be improved.

  As described above, the rapid heating apparatus of the present invention can make the texture of the steel sheet preferable according to the required characteristics through the control of the recrystallization behavior. Therefore, the present invention is not limited to the field of grain-oriented electrical steel sheets, and also requires texture control, for example, non-oriented electrical steel sheets and thin steel sheets for automobiles that require deep drawability, The present invention can also be applied to fields such as thin steel sheets that require anisotropic control.

1: Steel plate (steel strip)
2: Heating zone 20: Radiant tube heating part 21, 21a, 21b: Induction heating device 21c: Slow heating section (duct part)
21d: Slow heating device 3: Soaking zone 4: Cooling zone 51, 52, 53: Plate thermometer 61a, 61b, 61c: Plate thermometer in induction heating section

Claims (5)

A rapid heating apparatus for continuous annealing equipment of a final cold-rolled material of an electrical steel sheet containing Si: 8.0 mass% or less, comprising a heating zone, a soaking zone and a cooling zone,
The heating zone comprises two or more induction heating devices arranged in series in the first half part, and
A rapid heating apparatus comprising a gradual heating section in a temperature range in which a steel plate temperature between the two or more induction heating apparatuses is 250 to 600 ° C. 2. The rapid heating apparatus for a steel sheet according to claim 1, further comprising a heating apparatus that sets a temperature rising rate of the steel sheet to 0 ° C./s to 10 ° C./s in the slow heating section. The rapid heating apparatus according to claim 1 or 2 , wherein the length of the slow heating section is 1 to 30 m. The rapid heating apparatus according to any one of claims 1 to 3 , wherein a temperature increase rate of the steel sheet in the induction heating apparatus installation section is set to 50 ° C / s or more. Heating using the rapid heating apparatus of any one of Claims 1-4, The rapid heating method of the electrical steel sheet containing Si: 8.0 mass% or less characterized by the above-mentioned.

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