JP5888515B2 - Rapid heating method and rapid heating apparatus for steel sheet - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a rapid heating method and a rapid heating apparatus for a steel sheet, and more specifically, a rapid heating method suitable for use in a continuous annealing facility for annealing a raw steel sheet such as a cold-rolled ordinary steel sheet or an electromagnetic steel sheet. The present invention relates to a rapid heating apparatus used for the above.

  The equipment for heat-treating cold-rolled steel sheets is roughly divided into a box-type annealing furnace (also called a batch annealing furnace) in which a steel sheet coil is placed in a cover with controlled atmospheric gas, and a steel sheet coil is wound. There is a continuous annealing furnace in which steel plates are continuously passed through a furnace with controlled atmospheric gas while returning, and heat treatment is performed.At present, continuous annealing equipment with excellent material uniformity and productivity after annealing is the mainstream. It has become.

  The heat treatment in the continuous annealing furnace is performed by continuously passing the steel sheet through a furnace heated by a radiant tube or the like while rewinding the steel sheet coil, heating it to a predetermined temperature, and holding it for a predetermined time. After that, the process is completed by cooling to room temperature and winding it around the coil again. Of the above heating, soaking and cooling processes, the essential process is a soaking process, and the heating and cooling processes are essentially unnecessary steps. From the viewpoint of increasing productivity, the shorter the time, the better. It can be said.

Therefore, for example, in Patent Document 1, an electric current is passed through a cold-rolled steel sheet through an energizing roll, or an induction current is generated in the cold-rolled steel sheet by passing the cold-rolled steel sheet through an annular transformer and passing an alternating current through a reflux transformer A continuous annealing method is disclosed in which electricity is applied by heating and a cold-rolled steel sheet is rapidly heated by Joule heat and then rapidly cooled by a jet of non-oxidizing gas containing H ₂ . This annealing method does not include a soaking process, but discloses a technique effective for shortening the time of the heating and cooling processes.

However, when a cold-rolled steel sheet having a thickness of 0.5 mm or less is rapidly heated to a temperature of 600 to 900 ° C. via an energizing roll, the thermal expansion of the steel sheet is constrained by contact with the energizing roll disposed on the high temperature side. Therefore, there is a problem that a streak-like shape defect occurs in the steel sheet (see, for example, Patent Document 2).
Therefore, as a technique for dealing with such a problem, a method of rapidly heating a steel sheet by induction heating without an energizing roll instead of the above-described energizing heating has been proposed (for example, see Patent Document 3).

Japanese Patent No. 3156108 JP 09-137233 A JP 2009-046727 A

  By adopting the induction heating, it is possible to avoid the shape failure of the steel sheet due to the contact with the energizing roll. However, by induction heating, a new shape defect occurs in the steel plate, and when the steel plate comes into contact with the transport roll, a double problem occurs, and a new problem such as a wrinkle-like or streak-like defect occurs. It became so. This shape defect becomes more prominent as the steel sheet is rapidly heated.

  The present invention has been made in view of the above-described problems of the prior art, and the purpose thereof can effectively prevent a new steel sheet shape defect that occurs when rapid heating is performed using induction heating. It is to propose a rapid heating method and apparatus for a steel plate.

  In order to solve the above-mentioned problems, the inventors made extensive studies by paying attention to the relationship between the change in the steel plate shape during rapid heating and the transport roll. As a result, the steel plate that has been subjected to rapid heating tends to thermally expand in the width direction, but the thermal expansion is restrained by contact with the transport roll to cause wrinkle-like defects, and therefore to prevent the defects. The inventors have found that it is only necessary to impart an upward C-warp to the steel sheet before rapid heating, and to make the point where the steel sheet comes into contact with the transport roll as one point, leading to the development of the present invention.

That is, the present invention provides a method for rapidly heating a steel sheet after cold rolling to a temperature of 600 ° C. or higher with an induction heating device in a horizontal heat treatment furnace equipped with a transport roll in the furnace. A rapid heating method for a thin steel sheet, characterized by imparting an upward C warpage.

The rapid heating method for a thin steel sheet according to the present invention is characterized in that the above-described upward C warpage is imparted by changing the traveling direction of the steel sheet by 90 degrees or more from the upward direction to the horizontal direction with a deflector roll. .

Moreover, the rapid heating method of the thin steel plate of the present invention is characterized in that the above-described upward C warpage is imparted by a transport roll disposed on the upstream side of the induction heating device.

Further, the present invention is a rapid heating apparatus for rapidly heating a steel sheet after cold rolling to a temperature of 600 ° C. or higher in a horizontal heat treatment furnace provided with a transport roll in the furnace, the induction heating apparatus for rapidly heating the steel sheet, A rapid heating apparatus for a thin steel sheet, having means for imparting a C warp that is warped upward to the steel sheet, provided on the upstream side of the induction heating apparatus.

Rapid heating device of a thin steel sheet of the present invention, wherein the means for applying a C warp warped the above is a deflector roll for performing 90 ° or more above direction conversion in the horizontal direction the traveling direction of the steel plate from the upward direction And

Further, in the rapid heating apparatus for thin steel sheets according to the present invention, the means for imparting the C warp that warps upward is disposed on the upstream side of the induction heating apparatus, and the shape of the body portion is a bowl shape or a barrel shape. It is a conveyance roll.

Moreover, rapid heating device of a thin steel sheet of the present invention, the distance between the induction heater and means for applying a C warp warped the above is equal to or less than 10 m.

  According to the present invention, by preliminarily imparting C warpage to the steel plate before rapid heating by induction heating, it is possible to absorb the change in the cross-sectional shape of the steel plate due to thermal expansion associated with rapid heating, and thus be harmless. The shape defect of the steel plate accompanying rapid heating can be prevented. Therefore, according to the present invention, even in a continuous annealing facility that rapidly heats a steel sheet by induction heating, the steel sheet can be stably passed, which greatly contributes to improvement in shape quality and productivity.

It is a figure explaining the continuous annealing equipment provided with the conventional rapid heating apparatus. It is a figure explaining the mechanism in which a wrinkle-like defect generate | occur | produces by rapid heating. It is a figure explaining the mechanism which prevents a wrinkle-like defect by C curvature grant. It is a figure explaining the C curvature generation | occurrence | production mechanism when a steel plate is bending-displaced. It is a figure explaining the C curvature giving to the steel plate by a deflector roll. It is a figure explaining the continuous annealing equipment provided with the rapid heating apparatus of this invention. It is a figure explaining the other method of providing C curvature to a steel plate.

First, the basic technical idea of the present invention will be described.
FIG. 1 shows an excerpt of the entrance equipment and heat treatment furnace of a continuous annealing equipment equipped with a conventional rapid heating apparatus. The rapidly heated steel plate 1 is supplied from an inlet side equipment 6 such as an uncoiler, welder, cleaning equipment, looper, etc. (not shown) and fed linearly into the horizontal heat treatment furnace 3. The heat treatment furnace 3 includes a rapid heating region 4 for heating the steel plate to a predetermined temperature at a heating rate of 100 ° C./s or higher in a short time, and a soaking region for further heating the steel plate to a soaking temperature and holding it for a predetermined time. 5. In addition, the steel plate 1 to be rapidly heated is transported by transport rollers disposed in the traveling direction. The rapid heating region 4 corresponds to a pre-tropical zone or a heating zone of a normal continuous annealing facility, and the soaking zone 5 corresponds to a soaking zone.

  The rapid heating region 4 is usually composed of a plurality of induction heating devices arranged in the traveling direction of the steel sheet, and in order to ensure a predetermined heating rate, it responds to changes in the sheet feeding speed and the dimensions of the steel sheet. Thus, the number and output of induction heating devices can be changed. Moreover, the conveyance roll 7 for conveying a steel plate is arrange | positioned between each induction heating apparatus.

  In the heat treatment furnace having such a configuration, the steel plate 1 fed into the rapid heating region 4 in a flat state is thermally expanded by rapid heating and tends to expand in the plate width direction. However, since the steel plate is constrained by contact with the transport roll, the cross-section in the width direction of the steel plate has a wavy irregular shape in order to absorb the extra width generated by the thermal expansion. Then, as shown in FIG. 2, when the steel sheet reaches the transport roll with the irregular cross-sectional shape, the steel sheet comes into contact at a plurality of points and the movement in the width direction is restricted, and the temperature rises. Combined with the decrease in deformation resistance due to the above, the surplus width portion buckles and plastically deforms to produce streak defects or wrinkle defects.

  Therefore, the inventors have repeatedly studied a method for preventing the generation of streak defects and wrinkle defects accompanying rapid heating by induction heating. As a result, the restraint of the transport roll that generates streak defects or wrinkle defects on the steel sheet is caused by the steel sheet coming into contact with the transport roll at a plurality of points. Therefore, in order to eliminate the restraint, the steel sheet and the transport roll It has been found that it is only necessary to have a single contact point with the steel plate, and in order to realize this, a large C warp should be imparted to the steel plate before rapid heating.

  FIG. 3 shows changes in the cross-sectional shape in the width direction of the steel sheet when the steel sheet is preheated and then rapidly heated. A steel plate to which C warpage is imparted undergoes thermal expansion by rapid heating, but the shape change due to thermal expansion is absorbed by the C warp that has been imparted in advance so that a small wave is absorbed by a large wave. There is no regular change. As a result, the thermally expanded steel sheet contacts with the transport roll only at one point in the center of the sheet width while being warped downward, and can be freely thermally expanded in the width direction without being restricted by the transport roll. Furthermore, the contact area between the thermally expanded steel sheet and the transport roll gradually expands from the center of the sheet width to the left and right, and finally flattenes along the roll. There are no defects.

Next, the inventors examined in advance a method for imparting C warpage to a steel plate before rapid heating.
In general, when bending deformation is applied to a steel sheet, as shown in FIG. 4, the inner surface side of the steel sheet is shrunk in the rolling direction, so that an internal stress that tends to extend in the sheet width direction is present on the outer surface side in the rolling direction. Therefore, an internal stress that tends to shrink in the plate width direction is generated. As a result, it is known that a steel sheet that has undergone bending deformation warps to the outer surface side, and a C warp called a “soaking warp” occurs.

  Therefore, the inventors pay attention to the fact that a large number of deflector rolls for changing the traveling direction of the steel sheet are usually installed in the continuous annealing equipment, and consider using these deflector rolls as a C warp imparting means. did. FIG. 5 shows a change in the shape of a steel plate whose traveling direction is bent by 90 ° by the deflector roll 2. The flat steel plate before being redirected by the deflector roll is given a C warp (upward warpage) in which both width end portions of the steel plate warp upward due to a volume change accompanying bending when the direction is changed.

  FIG. 6 shows an example of the rapid heating apparatus of the present invention in which the above deflector roll is installed in a continuous annealing facility equipped with a conventional rapid heating apparatus. The steel plate 1 before being rapidly heated supplied from the entrance side equipment 6 such as an uncoiler, welder, washing equipment, looper, etc. is changed by 90 ° from the horizontal direction to the upward direction by the deflector roll 2 ′, The deflector roll 2 is turned 90 ° from the upper direction to the horizontal direction, and at the same time, is given a C warp and is conveyed toward the rapid heating region 4 of the horizontal heat treatment furnace 3. The steel sheet fed into the rapid heating region 4 is rapidly heated and thermally expands. However, since the thermal expansion is absorbed by the previously applied C warp, only the magnitude of the C warp is increased. Therefore, the point of contact with the transport roll is basically heated to a high temperature with one point remaining. Thereafter, the entire steel sheet is heated isothermally in the soaking region 5, so that the C warpage is eliminated and the steel plate returns to a flat shape.

  Here, in order to give C curvature, the angle which changes the advancing direction of a steel plate with the deflector roll 2 increases C curvature, so it is preferable to make it 90 degrees or more. This is because if it is less than 90 °, it is difficult to obtain a sufficiently large C warp. Therefore, for example, a 180 ° direction change may be performed.

  The distance L between the deflector roll 2 and the rapid heating region 4 (induction heating device) is preferably 10 m or less. The C warpage imparted by the deflector roll is usually a deformation within the elastic region, and gradually decreases as the distance from the deflector roll increases. When the distance exceeds 10 m, the steel plate becomes flat and the C warp imparting effect is lost. Because it ends up. When rapid heating at 200 ° C./s or more is performed, the shape change due to thermal expansion becomes severe, so it is necessary to increase the C warpage to be applied. The distance L between them is preferably 5 m or less.

  In addition, as a means to provide C curvature to a steel plate, it is not limited to the method by the said deflector roll, You may use another method. For example, as shown in FIG. 7A, a method of imparting C warpage to a steel sheet by making the body shape of the transport roll into a drum shape with a recessed central portion, as shown in FIG. 7B The barrel shape of the transport roll is formed into a barrel shape with a convex central portion, and a method of imparting C warpage to the steel sheet by pressing it, or a combination of the drum shape and the barrel-shaped transport roll are disposed. A method of imparting C warpage to the steel sheet can be used.

  In these methods, when the direction in which the steel sheet is conveyed is the direction opposite to that in FIG. 6, that is, when the steel sheet conveyed from the upper side to the lower side is turned 90 ° by the deflector roll 2, the applied C warpage is applied. In contrast to FIG. 5, both width ends of the steel sheet are sagged downward, so that it is necessary to give a reverse C warp (upward warp), or on the equipment arrangement of annealing equipment, deflector roll It is effective when it is difficult to install

In addition, also when giving C curvature using a conveyance roll, the distance L between the conveyance roll which provides C curvature and a rapid heating area | region (induction heating apparatus) is 10 m or less from the reason mentioned above. preferable.
Of course, the method of applying the C warp by the transport roll and the method of applying the C warp by the deflector roll may be used in combination.

  A cold-rolled steel sheet for an electromagnetic steel sheet containing 3 mass% of Si, having a sheet thickness of 0.3 mm or 0.2 mm, and a sheet width of 1200 mm is imparted with C warpage to the steel sheet with the deflector roll shown in FIG. Using the continuous annealing equipment in which the rapid heating apparatus of the present invention is installed, it is rapidly heated under various conditions shown in Table 1 and continuously annealed, and the shape of the steel plate after the heat treatment is visually inspected for wrinkle-like or streak defects. The occurrence was investigated. In addition, it investigated similarly about the case where the continuous annealing equipment which installed the rapid heating apparatus without a deflector roll shown in FIG. 1 was used as a comparative example.

  The results of the above investigation are also shown in Table 1. From this result, when the conventional rapid heating apparatus was used, defects such as wrinkles were generated under any conditions, whereas the rapid heating apparatus of the present invention that imparts C warpage with a deflector roll was used. Occurrence of defects such as wrinkles has not been confirmed. However, if the distance L between the deflector roll and the rapid heating device exceeds 10 m when the rapid heating rate is 150 ° C./s, and exceeds 5 m when the rapid heating rate is 500 ° C./s. Minor wrinkle defects have been observed.

  The technique of the present invention can be suitably applied to a continuous annealing line (CAL) as well as a line for continuously annealing a steel sheet, such as a continuous hot dip galvanizing line (CGL).

1: Steel plate (steel strip)
2: Deflector roll 3: Heat treatment furnace 4: Rapid heating area 5: Soaking area 6: Entrance equipment 7: Transport roll

Claims (7)

In a method of rapidly heating a steel plate after cold rolling to a temperature of 600 ° C. or higher with an induction heating device in a horizontal heat treatment furnace equipped with a transport roll in the furnace, the C warp warped upward in advance to the steel plate before rapid heating. A method for rapid heating of a thin steel sheet, characterized in that: Rapid heating of the thin steel sheet according to claim 1, characterized in that confer by a C warp warped to the upward and turning over 90 ° in the horizontal direction from the upward direction to the traveling direction deflector roll steel plates Method. The rapid heating method for a thin steel sheet according to claim 1, wherein the C warp warped upward is applied by a conveying roll disposed on the upstream side of the induction heating device. A rapid heating apparatus for rapidly heating a steel sheet after cold rolling to a temperature of 600 ° C. or higher in a horizontal heat treatment furnace equipped with a transport roll in the furnace, the induction heating apparatus for rapidly heating the steel sheet, and the induction heating apparatus A rapid heating apparatus for a thin steel sheet, characterized by comprising means for imparting a C warp upwardly warped to a steel sheet provided on the upstream side. Means for applying a C warp warped the upward, the traveling direction of the steel plate from the upward direction of the thin steel sheet according to claim 4, characterized in that a deflector roll for performing 90 ° or more above direction conversion in the horizontal direction Rapid heating device. The means for imparting the upwardly warped C warp is a transport roll disposed upstream of the induction heating device and having a barrel shape of a bowl shape or a barrel shape. The rapid heating apparatus for thin steel sheets as described. The rapid heating apparatus for a thin steel sheet according to claim 5 or 6, wherein a distance between the means for giving the C warp warped upward and the induction heating apparatus is 10 m or less.

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