Heat-retention vessel for intermediate annealing and intermediate annealing method for hot processed steel material

Abstract

To provide a heat-retention vessel for intermediate annealing having no heat source and having a structure capable of reducing heat extraction from hot processed steel material and preventing time for intermediate annealing from being unnecessarily long, and to provide an intermediate annealing method.SOLUTION: A heat-retention vessel for intermediate annealing having no heat source used for the intermediate annealing of hot processed steel material 2 after a hot process, comprises a placing table 21 on which the hot processed steel material is placed, and a heat-retention cover 11 installed on the placing table to form a heat-retention chamber to keep the hot processed steel material hot by covering it. A placing table heat insulating material 21 is arranged on the placing table, the heat-retention chamber has a plurality of vent holes 12 in communication with outdoor air to decrease temperature in the heat-retention chamber, the vent holes are openable / closable and arranged on a top side and a side surface side of the heat-retention chamber, at least one of the vent holes is openable / closable and arranged on the side surface side of the heat-retention chamber, and a vent hole 13 arranged on the side surface side is provided with a fan mechanism for sending the outdoor air into the heat-retention chamber.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an intermediate annealing heat retention tank and a method for intermediate annealing hot-worked steel material. [Background technology]

[0002] Regarding intermediate annealing between hot working steps, there is a proposal in the applicant's International Publication No. WO2007 / 119722 (Patent Document 1) to perform intermediate annealing on hot-worked steel material after working without using a heating furnace. This invention is targeted at semi-finished steel materials such as hot die steels, whose pearlite nose transformation completion point is 30 minutes or more, and utilizes the heat after the completion of hot working in the previous process. Specifically, the hot-worked steel material (semi-finished steel material) is placed in a heat retention tank at the appropriate time to restore the temperature of the hot-worked steel material, and the transformation latent heat generated when the hot-worked steel material transforms into pearlite is used to complete the intermediate annealing, which is a groundbreaking proposal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. WO2007 / 119722 Brochure Summary of the Invention [Problem to be solved by the invention]

[0004] The aforementioned Patent Document 1 discloses an intermediate annealing heat-retaining tank that does not have a heating source. This intermediate annealing heat-retaining tank adjusts the hot-worked steel material to a pearlite structure by combining the heat of the hot-worked steel material after hot working and the transformation latent heat. However, there are problems with heat removal due to contact between the hot-worked steel material and the placement table, and the temperature in the intermediate annealing heat-retaining tank during intermediate annealing is difficult to decrease, resulting in a long intermediate annealing time. In addition, the intermediate annealing heat-retaining tank is required to reduce the heat removal from the hot-worked steel material to the placement table on which the hot-worked steel material is placed. In this respect, the intermediate annealing heat-retaining tank shown in Patent Document 1 has room for improvement. An object of the present invention is to provide an intermediate annealing heat retention tank having no heat source, which is structured so as not to prolong the intermediate annealing time more than necessary, and which is capable of reducing heat removal from hot-worked steel material, and an intermediate annealing method using said intermediate annealing heat retention tank. [Means for solving the problem]

[0005] The present invention has been made in view of the above-mentioned problems. That is, the present invention relates to an intermediate annealing heat retention tank having no heat source for intermediate annealing of hot-worked steel after hot working, the intermediate annealing heat retention tank having a placement table for placing the hot-worked steel, and a heat retention lid that is placed on the placement table to form a heat retention chamber that covers the hot-worked steel and keeps it warm, placement table insulation is arranged on the placement table, the heat retention chamber has a plurality of vents that communicate with outside air to lower the temperature inside the heat retention chamber, the vents are openable and closed and are provided on the ceiling side of the heat retention chamber, at least one of the vents is openable and closed and is provided on a side side of the heat retention chamber, and the vent provided on the side side is equipped with a blower mechanism for blowing outside air into the heat retention chamber. Preferably, the intermediate annealing heat retention tank is provided with a seal material at a portion where the mounting table and the heat retention lid come into contact with each other, the seal material being deformed by the weight of the heat retention lid. The present invention also provides a method for intermediate annealing hot-worked steel material, in which the hot-worked steel material after hot working is intermediate-annealed using the above-mentioned intermediate annealing heat-retaining tank. Effect of the Invention

[0006] The intermediate annealing heat retention tank of the present invention, which does not have a heat source, is capable of appropriately controlling the intermediate annealing time and reducing the amount of heat removed from the hot-worked steel material. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a schematic diagram showing an example of a state in which hot-worked steel material after hot working is introduced into a thermal insulation tank for intermediate annealing. [Diagram 2] FIG. 2 is a schematic diagram showing an example of a state in which hot-worked steel material is being placed in an intermediate annealing thermal insulation tank. [Diagram 3] FIG. 2 is a schematic cross-sectional view of an intermediate annealing heat retention tank while hot-worked steel is being fed. [Figure 4] FIG. 2 is a schematic diagram showing an example of placement of hot-worked steel material using a spacer. [Diagram 5] FIG. 11 is a schematic diagram showing another example of placing hot-worked steel material using a spacer. [Figure 6] FIG. 2 is a schematic cross-sectional view showing an example of the internal structure of an insulation lid. [Figure 7] 10 is a schematic cross-sectional view showing an example of a state in which a sealing material provided on an insulation table is deformed due to the weight of the insulation lid. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] First, the terms used in the present invention will be explained. In the present invention, "intermediate annealing" refers to annealing of hot-worked steel (semi-finished steel) performed between the previous hot working process and the next hot working process. Hot-worked steel usually weighs 500 kg or more. The metal structure of hot-worked steel that has been intermediately annealed (sometimes called intermediate annealed steel) becomes pearlite. Therefore, the steel targeted in the present invention refers to a type of steel that can be transformed from austenite to pearlite. The "heat-retaining tank for intermediate annealing" transforms the hot-worked steel into pearlite by the heat of the hot-worked steel and the transformation latent heat generated by the hot-worked steel itself. During intermediate annealing, the tank does not have any heat source such as gas, oil, or electricity to heat the inside of the tank. Moreover, the term "hot working" includes, for example, plastic working in the austenite region, such as hot forging and hot extrusion.

[0009] Next, the present invention will be described with reference to the drawings, together with an intermediate annealing method. As a representative example, hot working is assumed to be hot forging, and the material of the hot-worked steel material to be intermediately annealed is assumed to be JIS-SKD61, a hot die steel. 1 and 2 are schematic diagrams showing the state when a hot-worked steel material 2 after hot working is introduced into an intermediate annealing heat retention tank 1. Fig. 3 is a schematic cross-sectional view of the hot-worked steel material 2 when it is introduced into the intermediate annealing heat retention tank 1. A hot-forged SKD61 steel ingot is prepared as the hot-worked steel material 2. The hot-forging temperature may be set to an appropriate temperature range depending on the material, and for SKD61, a temperature of 1100 to 1280° C. is preferable. The prepared hot-worked steel material 2 is transported and placed on the placement table 31. 1, the mounting table 31 is further covered with a mounting table insulation material 21. This prevents the hot-worked steel material 2 from coming into direct contact with the mounting table 31. The reason for this is to prevent or reduce heat loss caused by direct contact between the hot-worked steel material 2 and the mounting table 31. Since the intermediate annealing heat retention tank 1 of the present invention does not have a heating source, there is no problem of temperature drop due to heat transfer from the hot-worked steel 2, which is not particularly considered in normal heating furnaces. If there is a large amount of heat transfer from the hot-worked steel 2 to the mounting table 31, the temperature of the hot-worked steel 2 will drop at the part of the hot-worked steel 2 that contacts the mounting table and its surroundings. This will cause a temperature difference in the hot-worked steel 2, which may result in large variations in the structure and hardness after intermediate annealing. In order to prevent this problem, it is preferable to cover the mounting table 31 with mounting table insulation material 21. The material of the mounting table insulating material 21 for preventing heat loss can be selected from, for example, heat-resistant bricks, heat-resistant sheets made of glass fiber or ceramic fiber, heat-resistant boards made of plate-shaped glass fiber or ceramic fiber, etc. Of course, for example, heat-resistant bricks and heat-resistant sheets may be used in combination.

[0010] In Fig. 1, the hot-worked steel 2 is placed directly on the mounting table insulation 21 on the mounting table 31, but to more reliably prevent heat loss from the hot-worked steel 2, a spacer 22 can be used as shown in Figs. 4 and 5. When using a spacer 22, it is preferable to provide a spacer insulation 23 at the portion that comes into contact with the hot-worked steel 2 to prevent direct contact between the hot-worked steel 2 and the spacer 22. When the hot-worked steel is transported by a crane, the hot-worked steel is suspended by a chain. When the hot-worked steel is transported onto the mounting table, the spacer can provide a space for removing the chain, improving safety. The use of the spacer 22 is particularly effective when the hot-worked steel material 2 has a rectangular columnar shape as shown in Fig. 4 or Fig. 5. If the hot-worked steel material 2 has a rectangular columnar shape, the entire specific surface will be in contact with the mounting table insulation material 21 on the mounting table 31. Although the mounting table insulation material 21 is provided, there is a risk of some heat dissipation, so it is preferable to prevent heat dissipation from the hot-worked steel material 2 by using the spacer 22 with the spacer insulation material 23 arranged thereon. The material of the spacer insulation material 23 can be selected from heat-resistant sheets made of glass fiber or ceramic fiber, heat-resistant boards made of plate-shaped glass fiber or ceramic fiber, etc. Of course, for example, a heat-resistant sheet and a heat-resistant board may be used in combination. Since hot-worked steel products often weigh more than 500 kg, it is preferable to place a metal bar or plate (not shown) at the position where the spacer is placed to prevent the spacer from sinking into the mounting table 31.

[0011] After the hot-worked steel material 2 is placed on the placing table 31, the hot-worked steel material 2 is covered with the heat-insulating lid 11 and kept warm. To cover the hot-worked steel material 2 with the heat-insulating lid 11 shown in Fig. 1 to create the intermediate annealing heat-insulating tank 1 shown in Fig. 2, the heat-insulating lid 11 may be transported by hoisting it with a crane or the like, and then the heat-insulating lid 11 may be placed on the hot-worked steel material 2. In this case, if a guide member 32 is provided around the placing table 31, the heat-insulating lid 11 can be prevented from shifting from its original position and set at a predetermined position. As described in the above-mentioned Patent Document 1, the timing for covering with the heat-insulating lid 11 shown in Fig. 2 (timing for inserting the material) is such that the maximum temperature of the surface of the hot-worked steel material 2 is within a range of from the pearlite nose transformation end point plus 100°C to the pearlite nose transformation end point minus 200°C. A preferable timing for covering with the heat-insulating lid 11 is such that the maximum temperature of the surface of the hot-worked steel material 2 is within a range of from the pearlite nose transformation end point plus 50°C to the pearlite nose transformation end point minus 150°C, and more preferably from the pearlite nose transformation end point plus 50°C to the pearlite nose transformation end point minus 100°C. If the hot-worked steel material 2 is covered with the heat-insulating lid 11 within this temperature range, the hot-worked steel material 2 is reheated in the heat-insulating chamber 4, and the metal structure is maintained as austenite. 3 is a schematic cross-sectional view of the intermediate annealing thermal insulation tank 1 when the hot-worked steel material 2 is covered with a thermal insulation lid 11. The hot-worked steel material 2 is subjected to intermediate annealing in the thermal insulation chamber 4.

[0012] During the period from when the heat-retaining lid 11 is placed over the hot-worked steel material 2 until the pearlite transformation is completed, the only heat source within the heat-retaining chamber 4 is the heat retained by the hot-worked steel material 2 itself. To make the most of this retained heat, it is necessary to be able to appropriately control the temperature inside the heat-retaining chamber 4 while maintaining the airtightness inside the heat-retaining chamber 4. To achieve this, it is important to ensure the heat-retaining properties of the heat-retaining lid 11, ensure the airtightness of the heat-retaining chamber 4, and prevent the intermediate annealing time from being longer than necessary. In order to ensure the heat retention of the heat-retaining lid 11, it is preferable that the heat-retaining lid 11 itself has a structure that has heat retention. FIG. 6 shows a schematic cross-sectional view of the internal structure of the heat-retaining lid 11. Symbol 11A is the outside, 11B is the inside (inside the heat-retaining chamber), and 11C is the heat-retaining table side. As shown in FIG. 6(A), the heat-retaining lid 11 may be structured to be provided with a heat-retaining lid insulation material 14 throughout the inside, or as shown in FIG. 6(B), a space 15 may be provided to form an air layer for insulation. Since the heat-retaining lid 11 may be transported by a crane, it is better to reduce the weight of the heat-retaining lid 11 itself, and the heat-retaining lid insulation material may be selected from heat-resistant sheets made of glass fiber or ceramic fiber, heat-resistant boards made of plate-shaped glass fiber or ceramic fiber, and the like. Of course, for example, a heat-resistant sheet and a heat-resistant board may be used in combination. In addition, the outer side 11A, the warming base side 11C, and the inner side 11B of the heat-retaining lid 11 can be separate parts. By making them separate parts, they can be made of different metallic materials, and deteriorated heat-retaining lid insulating material can be easily replaced.

[0013] In the intermediate annealing heat retention tank 1 which does not have a heat source, it is important to prevent unintended intrusion of outside air as much as possible in order to maintain the heat retention effect until the pearlite transformation is completed. In order to ensure the airtightness of the heat retention chamber 4, it is preferable to provide a seal material 24 which deforms under the weight of the heat retention lid 11 at the portion where the mounting table and the heat retention lid come into contact. FIG. 7 is a schematic cross-sectional view showing the state when the seal material 24 provided on the heat-retaining table 31 is deformed by the weight of the heat-retaining lid 11. The seal material 24 deforms to prevent the intrusion of outside air and ensure the airtightness of the heat-retaining chamber. The seal material is preferably a heat-resistant sheet made of glass fiber or ceramic fiber and arranged with a certain thickness. The thickness of the seal material should be 1 mm or more. Since an excessively thick seal material rarely increases the effect, it is sufficient to arrange the seal material with a thickness of about 100 mm as the upper limit. Of course, for example, a heat-resistant sheet and a heat-resistant board may be used in combination. It is also possible to extend the mounting table insulation material 21 to the portion where the sealing material 24 is to be disposed, so that part of the mounting table insulation material 21 also serves as the sealing material 24. In that case, it is preferable that the portion that is to function as the sealing material 24 is provided with a heat-resistant sheet of an appropriate thickness in the portion that comes into contact with the heat-retaining lid 11.

[0014] The hot-worked steel material 2 covered with the thermal insulation lid 11 is reheated in the thermal insulation tank, and then the temperature gradually drops. As the temperature drops, the metal structure of the hot-worked steel material 2 transforms from austenite to pearlite, generating transformation latent heat in the process. The transformation latent heat causes the hot-worked steel material 2 to self-heat, and the hot-worked steel material 2 completes its pearlite transformation in the thermal insulation chamber 4. The hot-worked steel material 2 that has completed its pearlite transformation is then subjected to intermediate annealing, and an intermediate annealed material with reduced cracking can be obtained. The reheating of the hot-worked steel material 2 covered with the heat-retaining lid 11 may cause the temperature to become too high, or the effects of the reheating and transformation latent heat may continue too long, resulting in an excessively long time until the pearlite transformation is completed. In such cases, the temperature inside the heat-retaining chamber 4 can be lowered by using the vents shown in Figures 1 to 3. The ventilation openings are provided by arranging one or more upper ventilation openings 12 on the ceiling side of the heat-retaining chamber and one or more side ventilation openings 13 on the side of the heat-retaining chamber. As shown in Figs. 1 to 3, it is preferable to provide the side ventilation openings 13 closer to the mounting base 31 side of the heat-retaining lid 11. This is in consideration of the flow of outside air that has entered the chamber when opening both the upper ventilation openings 12 and the side ventilation openings 13 to take in outside air and lower the temperature inside the heat-retaining chamber 4. It is preferable to provide the side ventilation openings 13 at a low height (a height close to the mounting base 31 side) that is 1 / 3 or less of the height of the heat-retaining lid 11. Since the ventilation openings are provided for the purpose of lowering the temperature inside the heat-retaining chamber 4, it is preferable to provide a structure that allows them to be opened and closed freely. Furthermore, at least one each of the upper vent 12 and side vent 13 is required, but there is no particular upper limit. When the weight of the hot-worked steel material to be kept warm is on the order of several tons, it is acceptable to provide multiple upper vents 12 or multiple side vents 13. Also, as shown in Figures 1 to 3, by providing multiple upper vents 12 (three in the drawings) and multiple side vents (a total of eight in the drawings), it is possible to select the optimum combination of vents for efficiently lowering the temperature inside the warming chamber. By opening the vents in an appropriate combination at the temperature and time when the pearlite transformation is completed, it is possible to shorten the intermediate annealing time. As shown in FIG. 2, the air from the air blower 41, which is an air blowing mechanism, can be blown into the heat-retaining chamber 4 through the duct 42 to the air vent 13 provided on the side of the heat-retaining chamber. By providing multiple air vents on the side of the heat-retaining chamber, the installation location of the air blowing mechanism can be selected, and multiple air blowing mechanisms can also be provided. In order to confirm the completion of the pearlite transformation, a measurement hole (not shown) for measuring the temperature of the hot-worked material during intermediate annealing may be provided in part of the heat-retaining lid.

[0015] The intermediate annealing heat retention tank having no heat source according to the present invention described above is capable of appropriately controlling the intermediate annealing time and reducing the amount of heat removed from the hot-worked steel material. By using the intermediate annealing heat retention tank of the present invention, it becomes easy to control the temperature inside the heat retention chamber, and it becomes possible to shorten the intermediate annealing time by approximately one hour or more compared to a case in which openable and closable air vents are not provided on the ceiling and side surfaces of the heat retention chamber. [Explanation of symbols]

[0016] 1. Thermal insulation tank for intermediate annealing, 2. Hot-worked steel, 4. Thermal insulation chamber, 11. Thermal insulation lid, 12. Upper air vent, 13. Side air vent, 14. Thermal insulation lid insulation, 15. Space, 21. Mounting table insulation, 22. Spacer, 23. Spacer insulation, 24. Sealing material, 31. Mounting table, 32. Guide member, 41. Blower, 42. Duct

Claims

1. An intermediate annealing heat retention tank having no heat source for intermediate annealing of hot-worked steel material after hot working, The intermediate annealing heat-retaining tank has a placement table on which the hot-worked steel material is placed, and a heat-retaining lid that is placed on the placement table to form a heat-retaining chamber that covers the hot-worked steel material and keeps it warm, A mounting table heat insulating material is disposed on the mounting table, The heat-retaining chamber has a plurality of vents communicating with outside air to lower the temperature inside the heat-retaining chamber, the vent openings are openable and closable and are provided on the ceiling side of the heat-retaining chamber, at least one of the vent openings is openable and closable and is provided on a side surface of the heat-retaining chamber, and the vent opening on the side surface is equipped with a blower mechanism for blowing outside air into the heat-retaining chamber.

2. 2. The intermediate annealing heat retention tank according to claim 1, further comprising a seal member at a portion where the mounting table and the heat retention lid come into contact with each other, the seal member being deformed by the weight of the heat retention lid.

3. 3. A method for intermediate annealing hot-worked steel material, comprising intermediate annealing hot-worked steel material after hot working, using the intermediate annealing heat retention tank according to claim 1 or 2.

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