JP2010149138A - Heat-keeping device for preventing crack in steel material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-keeping device for preventing cracks in a steel material, which device prevents cracks to be caused by rapid cooling from being generated in a high-temperature steel material after being rolled before charging the steel material into an annealing furnace in the next step. <P>SOLUTION: In the heat-keeping device for preventing cracks in a steel material, there is arranged a heat-keeping device for preventing cracks to be caused by rapid cooling from being generated in the steel material during a step of directly sending the material to an annealing furnace after rolling. The heat-keeping device for preventing cracks in a steel material comprises a mechanism for keeping a material temperature that can be housed in a charge table. Further, the steel material treated in the heat-keeping device is a bar steel of martensitic stainless steel, tool steel, or heat-resistance steel. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a heat retaining device for preventing cracking of a steel material for preventing a high-temperature steel material after rolling from being rapidly cooled before being charged into an annealing furnace of the next process.

  Conventionally, as shown in FIG. 5 (a), steel materials are gradually cooled by pits after rolling, then heat treated in an annealing furnace and then straightened, and then transported to the next step. However, when performing slow cooling in the pits after rolling, a large bend (about 20 mm / m) occurred due to uneven heat during air cooling. Therefore, in order to prevent a large bend, as shown in FIG. 5 (b), the process was changed to a process of eliminating the slow cooling at the pits after the rolling and sending it directly to the annealing furnace. At that time, in a furnace having a relatively short furnace length, the steel material must be heat-treated with sufficient time, so the steel material is transported in the furnace at a low speed.

  Moreover, since it is not a serialization line, the steel material is transported from the previous process by a truck or the like, and stored in the steel material arrangement frame in the factory until the annealing furnace is charged. On the other hand, the amount of steel material that can be transported per hour is determined in the annealing furnace, and when the steel material transported into the annealing furnace is fully loaded, the charging of the steel material into the annealing furnace is awaited in turn. For this reason, it often occurs that it takes a long time after the target steel material is transported into the factory until it is transported into the annealing furnace.

  On the other hand, it has been confirmed that cracking is likely to occur particularly in steel materials such as martensitic stainless steel, tool steel, and heat resistant steel when the steel material is rapidly cooled to a predetermined temperature. When a crack occurs, non-conforming parts that cannot be sent to the next process are cut off, and scrapping is performed as non-conforming materials. Therefore, when performing temporary placement for a long period of time, a heat retaining device is required immediately before the annealing furnace in order to prevent the steel material temperature from being lowered due to the rapid cooling of the steel material.

  Thus, as disclosed in, for example, Japanese Patent Application Laid-Open No. 7-80533 (Patent Document 1), a method for conveying the inside of a heat insulating device made of steel that surrounds a steel material passing portion has been proposed. Further, as disclosed in Japanese Patent Laid-Open No. 5-123731 (Patent Document 2), in order to prevent heat dissipation at the end of the high temperature steel and correct the temperature difference between the center and the end of the steel, A heat insulating plate that can be moved in the width direction according to the width is suspended, and the heat insulating plate is heated to a temperature equal to the end temperature when the steel material enters the heat insulating cover, and is heated from outside the heat insulating device with a heating wire or the like. There has been proposed a method for preventing a temperature drop in the apparatus by heating and preventing rapid cooling of the steel material.

In this case, when the apparatus for keeping the temperature is installed as fixed, it encloses the passing portion of the steel material transport table, so that it is necessary to install a relatively long transport table in order to secure a space for loading the steel material. . In addition, when the heating type is used, there is a problem that costs are increased.
Japanese Patent Laid-Open No. 7-80533 Japanese Patent Laid-Open No. 5-123731

  As described above, in the heat treatment process from rolling to pit annealing, a large bending of the steel material occurs, and thus a correction process is required in the next process. In addition, the method of directly feeding to the annealing furnace without the slow cooling of the pits has a problem that the steel material is cracked due to rapid cooling while waiting for the furnace to be charged. Therefore, the present invention provides a heat retaining device for the purpose of preventing steel material cracking due to rapid cooling when performing a direct heat treatment process from rolling to pit annealing. This heat retaining device is a detachable and non-heating type. In the conventional fixed heat retaining apparatus, the upper part of the transport table is enclosed, and a space for loading steel materials is required. In addition, the heating method is expensive during normal operation.

  As a result of diligent development, the inventors have installed a retractable steel heat insulation device to prevent cracking due to rapid cooling of the steel material in the process of being sent directly to the annealing furnace after rolling. An object of the present invention is to provide a heat insulating device for preventing cracking of a steel material that maintains the heat insulation without interfering with the continuous furnace by a heat insulation mechanism that does not contact the steel material.

The gist of the invention is that
(1) A heat retaining device for preventing cracking of a steel material, wherein a heat retaining device for preventing cracking of the steel material due to rapid cooling is provided in the step of directly feeding the steel material to an annealing furnace after rolling.
(2) A heat retaining device for preventing cracking of a steel material, wherein the heat retaining device according to (1) includes a material heat retaining mechanism that is housed in a charging table.
(3) The steel material according to (1) or (2) is a heat retention device for preventing cracking of a steel material, characterized by being a martensitic stainless steel, tool steel, or heat-resistant steel bar.

  According to the present invention, it is possible to prevent the occurrence of cracks in the steel material due to rapid cooling in the state of waiting for the steel material in the process of direct annealing to the furnace after rolling. The effect is particularly excellent for martensitic stainless steel, tool steel, and heat-resistant steel bars.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a view showing a flow sheet in which a heat retaining device is introduced after rolling according to the present invention and before charging an annealing furnace. As shown in FIG. 1, in the process of sending directly to the annealing furnace after rolling, cracks frequently occurred particularly in those that took 12 hours or more from rolling to charging the annealing furnace. As a result of measuring the steel material surface temperature of the sample of the same conditions in order to grasp | ascertain the frequent occurrence situation, it turned out that each is 100 degrees C or less. As a result, in order to prevent cracking, it was found that it is necessary to keep the surface temperature of the steel material at 100 ° C. or higher within the time from rolling to charging in the annealing furnace. A countermeasure based on this will be described in detail below.

  FIG. 2 is a view showing a heat retaining device according to the present invention. FIG. 2A is a diagram showing a state in which the heat retaining device according to the present invention is stored, and FIG. 2B is a diagram showing a state in which the heat retaining device according to the present invention is used. As shown in this figure, the heat retaining device 1 includes a steel framework 3 for standing a protective cover 2 made of fabric having excellent heat resistance and heat insulation, an upper openable deck 4 that can store the protective cover 2, and a protective cover. 2 is a heat retaining device composed of a take-up roller 5 that gives tension to 2.

  After loading the steel material 7 on the table 6, the steel framework 3 is erected, and the protective cover 2 with the steel pipe 8 serving as a bone attached to the tip is taken out from the inside of the adjacent winding roller 5, and the upper part of the table 6 Pass through. Thereafter, the steel pipe 8 is hooked on the hook 9 attached to the steel framework 3 on the opposite side across the table 6. After that, the protective cover 2 is tensioned by the take-up roller 5 installed on the rear end side of the protective cover 2 and stretched relatively horizontally. The fabric is a device that can adjust its position by an adjustable pin structure attached to the take-up roller 5 so that the tension can be adjusted in accordance with the tension.

In particular, in the above, as shown in FIG. 2 (a), because it has a structure that can be stored in the take-up roller 5 adjacent to the dough for heat insulation, when a heat retention mechanism such as steel loading is not necessary, It is housed in the adjacent winding roller 5.
FIG. 3 is a plan view showing a state in which the heat retaining device is used. The steel material 7 is completely protected between the upper opening / closing deck 4 and the take-up roller 5 by the protective cover 2, so that the heat insulation of the steel material 7 can be maintained.

Hereinafter, the present invention will be specifically described with reference to examples.
FIG. 4 is a graph showing a temperature drop on the steel material surface over time. As shown in this figure, the horizontal axis represents elapsed time, and the vertical axis represents material surface temperature. The surface temperatures of the steel materials at 180 ° C. and 192 ° C. at the time of charging were confirmed for 8 hours in a state without a heat retaining device and a state with a heat retaining device, respectively. In the state without a heat retention device, the steel surface temperature fell below 100 ° C in about 4 hours, while in the state with a heat retention device, the steel surface temperature could be maintained at 100 ° C or higher even after 8 hours. It is possible to prevent cracking of the steel material.

  As described above, when the high-temperature steel material rolled in the rolling process is placed in the annealing furnace, it is exposed to room temperature, and when the time is long, in order to prevent end cracking from the temperature difference, at least By arranging a protective cover to keep the temperature above 100 ° C, it is possible to prevent end cracking of the steel material after annealing, and to reduce the generation of flaws and defective materials in the subsequent processes and improve yield. It has an extremely excellent effect.

It is the flow sheet which introduced the heat retention apparatus after the rolling by this invention and before annealing furnace charging. It is a figure which shows the heat retention apparatus which concerns on this invention. It is a top view which shows the state which is using the heat retention apparatus. It is the graph which showed the temperature fall of the steel material surface by time passage. It is the flow sheet of the conventional process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat retention apparatus 2 Protective cover using the fabric excellent in heat resistance and heat insulation 3 Steel framework 4 Upper opening / closing type deck 5 Rewind-type roller 6 Table 7 Steel material 8 Steel pipe 9 Hook


Patent Applicant Sanyo Special Steel Co., Ltd.
Attorney: Attorney Shiina

Claims (3)

A heat insulating device for preventing cracking of a steel material, characterized in that a heat insulating device for preventing cracking of the steel material due to rapid cooling is disposed in a process of directly feeding the steel material to an annealing furnace after rolling. A heat retaining device for preventing cracking of a steel material, wherein the heat retaining device according to claim 1 comprises a material heat retaining mechanism that is housed in a charging table. A heat insulating device for preventing cracking of a steel material, wherein the steel material according to claim 1 or 2 is a martensitic stainless steel, a tool steel, or a heat-resistant steel bar.

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