JPS6234811B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cooling device for steel strip (hereinafter referred to as "strip") in a continuous annealing line. Recently, batch annealing has been replaced by continuous annealing in the heat treatment (annealing) of cold-rolled steel sheets for processing used in automobile steel plates, etc., and this method has already been adopted domestically and internationally and is already in practical use. The continuous furnace, which forms the main part of this continuous annealing equipment, generally consists of a heating zone, a soaking zone, a primary cooling zone, an overaging zone, and a secondary cooling zone. Among these, it has been introduced in various literature that the cooling rate control technology in the primary cooling zone is an important factor that influences the workability of cold rolled steel sheets. In order to improve the overall workability of a steel plate, it is necessary to make the crystal grain size of the steel plate sufficiently large and to minimize the amount of solid solution C contained in the steel plate.
Furthermore, for deep drawing processing, it is preferable that the average plastic strain ratio value is large. As an example of cooling rate control that takes these into consideration, JP-A-55-104430 states that if the initial cooling after annealing is too early, the crystal grains will become finer due to γ-α transformation and the value will also decrease. , the first cooling after annealing is performed at a cooling rate of less than 35°C/sec,
A cooling method is disclosed in which slow cooling is stopped at a temperature Tθ of 600° C. or higher, rapid cooling is performed at 50° C./second or higher, and overaging treatment is performed. Note that this rapid cooling treatment is effective in suppressing dissolution of carbides during annealing, and in shortening the time required for overaging by increasing the degree of supersaturation of C.
A cooling method in which the cooling rate is controlled to change from gradual cooling to rapid cooling as described above is called a shoulder cooling method, and is one of the known techniques for obtaining a cold-rolled steel sheet with excellent workability. A typical thermal cycle is schematically shown in FIG. 2 by a solid line. The area between AB is the slow cooling area, and the area between BC is the rapid cooling area. Also, in the same figure, a shoulder cooling method for high-tensile steel plates is schematically shown by broken lines. The area between A'B' is the slow cooling area, and the area between B'C' is the rapid cooling area. Through this slow cooling between A′B′, alloy components such as C and Mn are concentrated into the austenite phase, and through the next rapid cooling between B′C′, the austenite phase is effectively hardened and transformed into a structure containing martensite. do. At the same time, the ferrite phase of the matrix is purified by reducing the alloying components due to the previous slow cooling, so it has high ductility. That is, by this shoulder cooling method, a high tensile strength steel plate having sufficient strength and good workability can be manufactured using an inexpensive material having a small alloy component. Currently, the well-known liquid immersion method, gas cooling method,
Furthermore, the above-mentioned shoulder cooling method is applied using the four methods of cooling using a gas-liquid injection device (Japanese Patent Application No. 135680-1983) and a liquid injection device (Japanese Patent Application No. 18837-1983), for which the present applicant has previously applied for a patent. However, there are advantages and disadvantages as shown in Table 1, and there is nothing that can be recommended.

[Table] That is, the liquid immersion method is suitable for the rapid cooling range of primary cooling, but when carrying out the shoulder cooling control, the cooling capacity is too large and slow cooling operation is difficult. Moreover, when overaging treatment is required, since there is no cooling controllability, it is necessary to lower the temperature and reheat to the overaging treatment temperature, which is uneconomical. On the other hand, when using the gas cooling method, although it is suitable in the slow cooling region, in the rapid cooling region the cooling capacity is insufficient compared to the liquid immersion method, and the length of the effective cooling equipment inevitably needs to be longer. , it is undesirable that a large amount of alloy must be added when manufacturing high-strength steel sheets. On the other hand, the cooling method using a gas-liquid injection device and a liquid injection device previously proposed by the present applicant for the purpose of eliminating the drawbacks of the former two methods is useful because it can perform the above-mentioned shoulder cooling control to a certain degree. However, the former gas-liquid injection method is inferior to the liquid immersion method and the gas cooling method described above in terms of cooling rate controllability in the rapid cooling region, and the latter liquid injection method in the slow cooling region. This point will be explained in detail as follows. That is,
In the case of the gas-liquid injection method, the cooling capacity in the quenching region is insufficient, or even if the cooling capacity is sufficient, it is necessary to circulate a large amount of gas to atomize a large amount of liquid, which increases equipment costs and costs. There is a problem that operating costs increase. On the other hand, in the case of the liquid injection method, as a result of restricting the cooling capacity and therefore the liquid flow rate in the slow cooling region, atomization becomes insufficient and the shape (flatness) of the steel strip tends to be poor due to uneven cooling. Furthermore, in some cases, the force of the liquid flow may be insufficient, resulting in a problem that the liquid does not reach the steel strip and cooling itself is not performed. In order to eliminate the above-mentioned problems, the inventors of the present invention,
As a result of repeated research on the cooling method, we have developed so-called shoulder cooling, which requires slow cooling for the first stage of primary cooling, by connecting the gas-liquid injection device and the liquid injection device, which we have already proposed. For processing, a gas-liquid injection device is installed independently, and a liquid injection device is installed to control the end point of rapid cooling to a desired temperature, and by disassembling the cooling function, a cooling system that can handle complex cooling control is created. This is what I found out that it can be obtained. That is, the gist of the present invention is that in a cooling device installed in a continuous strip heat treatment facility,
A gas-liquid injection cooling device that first injects a gas-liquid mixed fluid created by mixing a gas flow and a liquid flow onto the front and back surfaces of a high-temperature strip that runs vertically, and a liquid jet cooling device that injects only liquid alone. This is a strip cooling device characterized by having a strip cooling device connected with a strip cooling device. Hereinafter, embodiments of the cooling device according to the present invention will be described in detail with reference to the drawings. FIG. 1 is an example in which the cooling device of the present invention is applied to a primary cooling treatment step in a continuous annealing step for producing cold rolled steel sheets. For convenience of explanation, the structure and operation will be described mainly focusing on the primary cooling process. A strip 1 is heated and soaked at a high temperature in a continuous annealing furnace and moves from top to bottom between a soaking zone 2 and a passage 3 in the continuous annealing furnace. A cooling chamber consisting of one type of cooling means is usually interposed between the continuous annealing furnace soaking zone 2 and the passage 3 to cool and control the strip to a desired temperature. However, the cooling device of the present invention is composed of two cooling chambers, a first cooling chamber 4 and a second cooling chamber 5, and each cooling chamber has a different cooling means. That is, an air/water injection cooling device 6 (hereinafter referred to as a fog spray device) is installed in the first cooling chamber 4, and a water injection cooling device 7 (hereinafter simply referred to as a spray device) is installed in the second cooling chamber 5 in the direction of advance of the steel strip. and parallel to the width direction of the strip, facing each other in multiple stages. On the outlet side of each cooling chamber, a spray device 8, 8' for removing water adhering to the surface of the strip is provided. As the fog spray device 6 provided in the first cooling chamber, the fog spray device previously proposed by the present applicant in Japanese Patent Application No. 135680/1988 can be used. That is,
Inert gas (hereinafter referred to as "gas") is supplied from the gas supply header 9 and from the water or water supply header pipe 10, and is externally mixed at each tip, so that the air and water are mixed slightly upwardly with respect to the strip in the direction of the arrow. It is sprayed in a stream. If this fog spray direction is horizontal to the strip,
The fog that was injected in advance interferes with the fog that follows, and as a result, the fog is scattered on the surface of the strip and its vicinity, causing a water film to form on the surface of the strip, or creating an atmosphere where it is easy to form, resulting in uneven cooling. Otherwise, it tends to occur, which makes efficient cooling and cooling control difficult. By injecting the fog in an upward direction relative to the horizontal direction, cooling is performed evenly and efficiently. The fog is usually sprayed onto the strip at a speed of 40 to 100 m/sec. Splashed water sprayed onto the strip from the fog spray device 6 bounces off the strip, travels on the water guide plate 11 provided on the fog spray device, and is led to the drain main 121 from the drain ports 12, 12' provided at the bottom. It is discharged from the system. Note that the water guide plate 11 is structured to be tilted backward so as not to return to the strip. The gas in the first cooling chamber is guided from the exhaust port 13 to the exhaust main pipe 131 and exhausted to the outside of the system. The first cooling chamber is a fog spray device 6 as described above.
If configured as follows, the primary cooling initial slow cooling (usually less than 35°C/sec) necessary to obtain a cold-rolled steel sheet with good workability,
So-called shoulder cooling can be easily performed.
If the strip is slowly cooled to the overaging temperature (300 to 500℃), carbon will not precipitate sufficiently during the overaging treatment and will remain in the steel, causing problems in terms of aging.
After stopping slow cooling at the above temperature Tθ, rapid cooling is performed at a cooling rate of 50°C/second or more to form a solid solution of carbon in the steel to a certain degree of supersaturation.If overaging treatment is performed, carbon The precipitation of is promoted, and a cold-rolled steel sheet of good quality with satisfactory workability and aging resistance can be obtained. In the cooling device of the present invention, in order to cope with this rapid cooling process, a second cooling chamber 5 dedicated to the rapid cooling process is provided adjacent to the first cooling chamber 4. Second cooling chamber 5
In the rapid cooling process, it is necessary to stop the strip at a predetermined overaging temperature, so in this embodiment, spray cooling was used as a cooling means capable of controlling the cooling end point. The type of spray treatment is not particularly important, but the applicant has already filed a patent application
Since the spray device proposed in No. 57-18837 is effective for cooling with end point temperature control, this spray device was adopted in this example. This spray device is designed with special attention to the orientation of the spray nozzles 14, with the topmost spray nozzle facing downwards relative to the strip, the second stage spray nozzles horizontally, and the third and subsequent stages all facing upwards. It is provided. By orienting the uppermost spray nozzle downward, the jetted cooling water can prevent the backflow phenomenon on the strip surface and form an impingement zone of uniform droplet flow on the strip. By oriented the second stage nozzle horizontally, the uniform droplet flow obtained by the top stage spray nozzle is prevented from being scattered. Next, the amount of water dripping onto the strip can be reduced by orienting all the spray nozzles provided in the third and subsequent stages upward. 15 and 15'
is connected to the drain main pipe 121 at a drain port in the second cooling chamber. In addition, the fog spray in the first cooling chamber and the second
In order to uniformly cool the surface of the strip, the water sprays in the cooling chamber are preferably arranged so that they do not overlap on the front and back surfaces of the strip, and are staggered vertically, horizontally, or both. This arrangement allows cooling without deteriorating the shape of the strip. A guide roll 16 for preventing the strip from shaking is disposed between the first cooling chamber and the second cooling chamber.
17, 17', and 17'' are steering rolls, one in the soaking zone 2 of the annealing furnace and two in the passage 3. A drain 18 is provided at the bottom of the passage 3 and is connected to the main drainage pipe 121. The strip is made to be able to remove accumulated water in the passage.The strip is gradually cooled in the first cooling chamber, rapidly cooled in the second cooling chamber, and then stopped at the overaging temperature (300 to 500℃) through passage 3. Then, although not shown, the continuous annealing process is completed in an overaging zone and a secondary cooling zone, and finally, the sheet is reduced by 1 to 2% in a temper rolling mill and wound into a coil to become a cold rolled steel sheet. If the cooling device of the invention is applied to the above-mentioned primary cooling zone, the cooling capacity will be higher than that of water-only spray cooling for so-called shoulder cooling, which requires slow cooling in the early stage of cooling, which was difficult to control with conventional single cooling means. The first cooling chamber is equipped with a gradual fog spray cooling system, and when the process is subsequently transferred to rapid cooling, water spray cooling is used, which has a greater cooling capacity than fog spray cooling and can control the end point temperature. By performing rapid cooling treatment in the second cooling chamber containing the device,
Complex cooling control can be easily performed. Therefore, it is an optimal cooling device for producing cold-rolled steel sheets for deep drawing, which require shoulder cooling treatment and have good workability and little aging deterioration. In addition, this cooling device is suitable for producing inexpensive high-strength steel sheets with good workability that can be effectively subjected to shoulder cooling treatment. The shoulder cooling treatment of cold-rolled steel sheets for deep drawing and high-strength cold-rolled steel sheets is performed as shown on the thermal cycle in Figure 2.
The slow cooling area (between AB and A'B') is treated with a fog spray indicated by the symbol FS, and the rapid cooling area (between BC and A'B') is
B′C′) is cooled with a water spray represented by the symbol S. Note that if shoulder cooling is not required for primary cooling, the fog spray device in the first cooling chamber can be stopped and cooling can be performed only with the water spray device in the second cooling chamber. As detailed above, in any case, the cooling device of the present invention, which combines gas-liquid injection cooling suitable for gradual cooling and liquid injection cooling suitable for rapid cooling, can provide a wide range of cooling with low equipment costs and operating costs. A remarkable effect of control can be achieved.

[Brief explanation of the drawing]

Fig. 1 shows an embodiment of the present invention, which is a schematic diagram applied to the primary cooling zone of a continuous annealing furnace, and Fig. 2 shows an embodiment of the present invention on a thermal cycle of a deep drawing steel plate and a high-strength steel plate. It is something that 1: Strip, 2: Annealing furnace soaking zone, 3: Passage, 4: First cooling chamber, 5: Second cooling chamber, 6: Fog spray device, 7: Water spray device, 8: Draining spray device, 9: Gas Supply header, 1
0: Water supply header pipe, 11: Water guide plate, 12,
15, 18: Drain port, 13: Exhaust port, 14: Spray nozzle.

Claims (1)

[Claims] 1 In a cooling device installed in a continuous heat treatment facility for steel strips, gas-liquid injection cooling injects a gas-liquid mixed fluid created by mixing a gas flow and a liquid flow onto the top and bottom surfaces of a steel strip running in the vertical direction. 1. A cooling device for steel strip, characterized in that the device and a liquid jet cooling device for injecting only liquid alone are connected to the lower part of the gas-liquid jet cooling device.