JPH0382716A - Heat treatment method for wire rod coil and heat treatment furnace thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat treatment method and apparatus for uniform rapid heating that significantly shortens the annealing time of a wire coil and makes the quality uniform.

[Prior art] In annealing treatment, typically spheroidizing annealing, steel is heated to an appropriate temperature to once dissolve carbides in the structure, and then cooled at an appropriate rate to dissolve the carbides in the structure. Heat treatment that improves the shape and improves the plastic workability and rigidity of the material. At this time, in order to make the quality of the processed material uniform,
It is necessary to uniformize the state of progress of solid solution formation by limiting the temperature for solid solution formation to a narrow temperature range of 10° C. or less and reducing the time difference during which the temperature is maintained within that temperature range.

However, continuous annealing furnaces generally used for annealing wire rod coils are equipped with atmospheric heating that performs indirect heating using a radiant tube 20 that circulates high-temperature combustion gas through the tube as a heat source, as shown in Figure 1O (d). method is adopted. In this method, the outer periphery of the wire coil is heated by direct radiation, so the temperature rises relatively quickly depending on the ambient temperature.
The inside of the wire coil mainly undergoes heat conduction from the outer periphery, so it takes a long time to raise the temperature. Therefore, the temperature difference due to the temperature increase rate difference is large in the entire wire coil. In addition, when the target temperature range for soaking is narrow, such as in annealing,
Not only does the treatment time become long, but there is also a large difference in the holding time at the holding temperature, resulting in large variations in the solid solution state. In order to make a uniform spheroidal structure from a coil in such a state, it is necessary to hold the coil in the carbide precipitation temperature range for a long time, or to perform slow cooling at a rate of 10°C/hr or less to reduce the temperature during precipitation. The organization must be made uniform. For this reason, spherical annealing of a wire coil usually takes about 20 hours.

For this reason, it has been a long-standing challenge to develop a technique to uniformly and rapidly heat the entire wire coil to shorten the spheroidizing annealing time. Improvement measures taken so far include JP-A-60-1, an improvement of steel materials by refining the pearlite structure before annealing by reduction during hot rolling, controlled cooling, etc.
52627 and JP-A No. 60-255922, and on the other hand, Japanese Patent Publication No. 60-22050 describes a method of forming a wire coil into a strand, rapidly heating it with a special heating device, and then winding it into a coil again. , and Japanese Patent Publication No. 61-15930, and Japanese Patent Publication No. 51-33053 proposes a method of improving productivity by bringing spheroidizing annealing online to hot rolling.

A known document related to the invention of pond water is the Japanese Patent Publication No. 57-2 in which a stirring fan was installed in the furnace to create convection of the atmosphere inside the furnace.
No. 00526 also discloses a blast heat treatment method used for heat treatment, especially cooling, of wire coils in JP-A-55-1095.
No. 15 discloses a method for supplying air blast to a wire coil, and Japanese Patent Application Laid-Open No. 57-203724 discloses a method for supplying air blast to a wire coil.

[Problems to be Solved by the Invention] However, the techniques of the above-mentioned JP-A-60-152627 and JP-A-60-255922 involve rapid cooling after rolling of the steel material to form fine ferrite parvalite and bainite or marten. It has a mixed structure of sites, which speeds up the spheroidization speed of cementite. However, in such a method, the cementite is excessively fine and the hardness is considerably higher than that in the conventional method, so that the intended purpose of spheroidizing annealing cannot be achieved. Furthermore, with regard to shortening the annealing time, if heat treatment is performed using the current atmosphere heating method, the heating time of the wire coil itself remains the same and cannot be a fundamental solution, so a significant time reduction cannot be expected.

Next, Special Publication No. 60-22050 and Special Publication No. 61-'1
The method of heat treatment in which the strands are once formed into a strand as disclosed in Japanese Patent No. 5930 not only requires modification of equipment such as special heating equipment, but also has problems in practical application because productivity is significantly reduced.

In addition, Japanese Patent Publication No. 5]-33053 discloses a processing furnace in which a hot-rolled wire rod in the form of a non-concentric ring is placed on a conveyor and transferred through a spheroidizing processing furnace to perform a spheroidizing process, which improves productivity. However, since there is no way to uniformly and rapidly heat the material, there is considerable variation in the material (it has not yet reached the level of quality achieved by conventional long-time annealing). Furthermore, it is not possible to uniformly heat the tight wire coils to which the present invention is applied in a short period of time, and thus cannot be applied.

Furthermore, in JP-A-57-200526, a stirring fan is installed in the furnace to create convection in the atmosphere in the furnace to shorten the annealing time, but the effect of promoting heat transfer to the wire coil is small.
A significant reduction in annealing time, which is the objective of the present invention, cannot be expected.

Furthermore, JP-A-55-109515 is strongly related to the blast heat treatment method C of the present invention, which involves closing one end of the wire coil and introducing gas into the inner circumference of the wire coil from the other end. This is a blast heat treatment method in which the wire is fed and passed through the gap between the wires to perform heat treatment. This heat treatment method has many embodiments as a method for cooling a wire rod coil after hot rolling. However, with this heat treatment method, the amount of blast air that passes through is locally uneven due to variations in the density characteristic of wire coils, so temperature variations are unavoidable. There are no examples of it being used.

In addition, JP-A-57-20:1724 related to blast heat treatment
The publication discloses a method for passing blast air through the gap between wire coils using a hood connected to a heat transfer medium through an air blast supply duct, in which blast air is supplied from the outer periphery of the wire coil and extracted from the inner periphery. This is to reduce temperature variations. This is because the flow velocity passing through a unit cross section decreases as the blast moves from the center of the concentric circle toward the outer circumference, so the heat transfer coefficient is smaller at the outer circumference of the wire coil than at the inner circumference of the wire coil. be. However, since the blast temperature can be increased on the outer periphery side of the wire coil where the heat transfer coefficient is low, although this is advantageous for uniform heating, it is insufficient for the uniform rapid heating that is the objective of the present invention, and on the contrary, The problem remains that the temperature rise is delayed.

As described above, all of the conventional techniques for shortening the spheroidizing annealing time have problems and have not been put into practical use.Furthermore, the conventional blast heat treatment techniques, which are closely related to the present invention, still require improvement. Therefore, it cannot be applied to the uniform rapid heat treatment of the entire wire rod coil in a short period of time, which is the object of the present invention.

[Means for Solving the Problems] The present invention has been made in view of the problems of the prior art described above with respect to the problem of shortening the spheroidizing annealing treatment time, and its gist is (1) wire rod In order to eliminate extremely small areas in the coil where the local filling factor (true volume of the steel material/apparent volume of the coil and gap) is 0.2 or less, the wire rod is Press with a load of 1/5 or more of the coil unit weight.

(When passing high-temperature gas through the gap between two wire coils, the apparent speed of the gas is set to 1.5 m to prevent channeling phenomenon that causes temperature variations.
/sec or more -E.

(3) In order to further reduce temperature variations within the wire coil, as a method of supplying blast air to the wire coil, alternately combine the wire coil from the inner circumferential side to the outer circumferential side and from the outer circumferential side to the inner circumferential side. A blast of wind. At this time, by setting the time periods of each combination at an appropriate ratio, it is possible to contribute to shortening the heating time.

(4) It is to provide a heat treatment apparatus for carrying out the invention of the spheroidizing annealing treatment method having the above-mentioned constituent features.

Hereinafter, specific contents of the present invention will be explained in detail based on the drawings.

First, the C component targeted by the present invention is 0. As is already well known, the heat treatment procedure for spheroidizing annealing of mechanical structural carbon steels, cold heading carbon steels, low alloy steels, etc. containing 0.6% to 0.6% is as well known. ), the carbides in the structure are once dissolved into solid solution, and the solid solution is adjusted by holding for a certain period of time. After that, the carbide in the structure is solidified by slow cooling at a cooling rate of 40°C/hr or less until just below the Ar transformation temperature (near 650°C). The process is to precipitate the molten carbide into spherical shapes, and then bring it to room temperature by cooling with air or the like. There is no restriction at all on the time and speed of heating to dissolve the carbide, but when the solid solution carbide is precipitated, the material will become hard if the cooling rate exceeds the above, so slow cooling at 40°C/hr or less is mandatory. Must be protected.

Therefore, the most important point in shortening the spheroidizing annealing treatment time of the present invention is how to uniformly heat the entire wire coil to a predetermined holding start temperature.

This will be explained using an example of a spheroidizing annealing heat pattern of a JIS, 545G wire coil by heating in a conventional atmospheric furnace as shown in FIG. Here, region a in the figure is called heating, and is the time range until the temperature of the - part (outer circumference A) of the wire coil reaches a predetermined temperature, and region b is called soaking, which is the time range when the temperature inside C of the wire coil reaches the specified temperature. This is the time range until the temperature approximates the predetermined temperature of the outer peripheral part A. The a region is called retention, and is the time range required for uniformly dissolving carbides, and the d region is called slow cooling, which is the time range required to uniformly dissolve carbides. is the time range required for spheroidization precipitation, and region e is called cooling, and is the time range such as air cooling from the completion of spheroidization precipitation to room temperature. Further, the line A is the outer circumference of the wire coil, and the broken line C is the heat pattern at each position inside the coil.

As can be seen from the diagram, the temperature of the outer part A increases relatively quickly because it is directly radiated, but the temperature of the inner part C is mainly due to radiation and heat conduction between the wires, so it reaches the target holding temperature. The time it takes to do so is several hours later than at position A. Therefore, it is necessary to extend the soaking time until the entire wire coil is uniformly heated to a predetermined temperature and the retention time of the carbide solid solution, which is an obstacle to shortening the heat treatment time. Furthermore, the extension of the soaking and holding time causes variations in the state of solid solution of carbides, and in order to eliminate the variations in solid solution, as is clear from the figure, long-term cooling (between Ac and ^r1) is required. It is essential to homogenize the structure during carbide precipitation by slow cooling (lower than 10° C./Hr), and this also has a large effect on the time required for heat treatment. The spheroidizing annealing time in this example required approximately 19 hours.

In this way, in spheroidizing annealing using the atmosphere heating method, a temperature difference inevitably occurs between the outer circumference and the inside of the wire coil, and adjustment time is always required to eliminate this temperature difference, making it impossible to shorten the heat treatment time. there were.

Therefore, the present invention has devised a heat treatment method based on the blast heating method, in which high-temperature gas is passed as a heat transfer medium through the gap between the wire coils, instead of this atmosphere heating method. The basic structure of this blast heat treatment has been described above, but it cannot be applied as it is to the uniform rapid heating of the entire wire coil, which is the object of the present invention. In other words, as a characteristic of a normal wire coil, there are local variations in the density of the wire, and even if a high-temperature blast is sent to a wire coil with large variations, the pressure loss will increase as the blast passes through the gaps between the wires. The flow concentrates only in areas with a small filling rate, and areas with a large filling rate have an extremely small amount of blast, resulting in a delay in temperature rise. Fig. 3 (a) and (b) show a normal wire coil (wire diameter: 10 mm, coil outer diameter: 1.4 m, inner diameter: ], Om, axial height + 1. 3
A schematic diagram in which air was blasted at an average flow rate of 3 m/sec on a specimen (unit weight: 2 t) and the results of an investigation of the air volume distribution at that time are shown.

From this result, the local apparent velocity is 1 to 8 m/sec.
Even if high-temperature air is sent in this state, it is not possible to achieve a uniform temperature throughout the wire coil. For this reason, we discovered the pressing of wire rod coils, which is one of the constituent elements of the present invention, and attempted to make the coil filling rate uniform.

Figure 4 shows the effect of pressing, and (a)
The schematic diagram shows the above-mentioned densely uneven wire rod coil being coil pressed through the blast hood 4 in the coil press machine II under a load of 400 kg, which is one-fifth of the unit weight of the wire rod 1, 2 tons, and then filled. This figure shows a uniform wire coil state in which there are no parts where the rate is extremely low, and (b) of the same figure shows the air volume distribution when the press coil is blown at the same average speed of 3 m/sec as described above. From the results shown in this figure, the local apparent speed of the blast is reduced to a range of 1.5 to 4.0 m/sec, and the effect of the press is recognized.

In addition, in the investigation of Figures 3 and 4, the relationship between the filling rate of the wire coil and the apparent blast velocity (hereinafter referred to as blast velocity) was determined and shown in Figure 6. In the normal wire coil without coil press shown in Fig. 3, the local filling factor within the coil is in the range of 0.1 to 0.5, and the blast velocity at the region with a filling factor of 0.1 and less density is Ull/ sec, whereas in a region with a dense packing rate of 0.5, it is 1
It is about III/sec.

On the other hand, the wire rod coil subjected to the coil press shown in Fig. 4 is
The filling rate is 0 because the filling area is less than 0.2 from 40.1.
．． Axis/sec at part 2, 1.5 at part with filling rate 0.5
The blast speed was +i/sec, and it can be seen that the variation in blast speed is significantly reduced by pressing.

In addition, the relationship between the coil press load and the variation in blast speed and air volume was investigated, and the results are shown in FIG. As is clear from the figure, the larger the press load is, the smaller the variation in air volume in the blast speed becomes.In order to reduce this variation in air volume, the press load should be set to one-fifth (0,2) of the coil unit weight. It is necessary to do so. However, if too much press load is applied, problems such as bending or breaking may occur depending on the material of the wire coil, so it is preferable to limit the press load to 15 times the amount of the coil alone.

Next, in order to find the appropriate blast speed for this pressed wire coil, we used a room-temperature pressed wire coil under the same conditions as in Figure 4 above, and injected a high-temperature gas heat transfer medium (750°C) into the gap between the coils. The influence of the blast speed on the time required to heat the hot water to a soaking temperature of 740°C ± 5°C was investigated by varying the blast speed. Figure 7 shows the results. As is clear from the figure, the heating time until uniform heating can be shortened by increasing the blast speed, but if it is less than 1.5o+/sec, a so-called channeling phenomenon occurs in which the air volume varies within the wire coil, and the entire wire coil It was found that it took a long time to equalize the temperature. For this reason, it has become possible to significantly shorten the heating time until the end of soaking by blowing air at a speed of 1.5 m/sec or higher.

Furthermore, we investigated the method of supplying this blast. As mentioned above, the conventional blast supply method is a method in which the blast 26 is sent from the inner periphery of the wire coil 1 as shown in FIG. 8(b), passes through the gap between the coils, and flows toward the outer periphery of the wire coil. ,or,
The opposite method, shown in FIG. 8(a), is to flow the wire from the outer circumferential side to the inner circumferential side of the wire coil. Of the two, as mentioned above, the latter is more advantageous in terms of uniform heating, but it is not always satisfactory for uniform rapid heating, which is the objective of the present invention. As a result of various experimental investigations, it was found that combining the two methods and adjusting the blast supply time to an appropriate ratio can further contribute to shortening the processing time for uniform rapid heating.

FIG. 9 shows the optimal range of the ratio between the ratio of the heating time of A to the total blast heating time (A+B) and the heating time until the soaking temperature is reached. Here, A represents the blast time from the outer circumferential side of the coil to the inner circumferential side, and B represents the blast time from the inner circumferential side to the outer circumferential side. As is clear from this figure, A/
If A and B are alternately combined and blasted so that the ratio (A + B) is between more than 0.5 and less than 1.0, it is possible to further contribute to shortening the uniform rapid heating time.

In this way, the present invention corrects the density variation in the wire coil by adjusting the coil filling rate by pressing, passes the blast through the coil gap at a speed higher than a predetermined amount that does not cause the channeling phenomenon, and further improves the blast supply method. This is a blast heating method that combines wire coils from the outer circumferential side or from the inner circumferential side at an appropriate ratio. Figure 1 satisfies these configuration requirements,
This is an example of a heat pattern in which a wire coil having the components shown in Table 1 was subjected to spheroidizing annealing treatment in a blast furnace.

The heat treatment conditions and the like are as shown in symbol 12) in Table 2, which will be described in the Examples section below.

As is clear from the figure, the temperature at position C inside the wire coil uniformly follows the temperature at position A on the outer periphery in almost the same time, and it takes 0.8 hours to reach the holding start temperature, and carbide precipitation occurs. The total processing time to complete the process up to 650°C was 4.0 hours, which was a significant reduction.

Next, a heat treatment furnace of the present invention for implementing the above-described method of the present invention will be described.

First, when constructing heat treatment furnace equipment, it is necessary to fully consider not only the productivity of heat treatment and the quality obtained, but also the equipment costs including running costs. Carbon steel for machine structures, carbon steel for cold heading, which the present invention targets;
Low alloy steel, etc. C: In the spheroidizing annealing treatment at 0.1!6 to 0.6 $@, there are no restrictions on the heating and soaking time and temperature increase rate as described above, but the carbide solid solution The cooling rate of slow cooling to precipitate is fast (40℃/hr
(super), the hardness of the material to be heat treated becomes hard and the desired softening cannot be achieved.

Considering the special circumstances of spheroidizing annealing, we compare the equipment costs and running costs between a blast furnace and a conventional atmosphere furnace. It will be about 2 to 5 times the size of the furnace. Also, in terms of running costs, blast furnaces are worse, mainly because the electricity cost per unit time for blowing air is about 5 to 20 times higher.

However, as mentioned above, with the blast furnace heating method, it is easy to uniformly and rapidly heat the entire wire coil, so productivity can be increased several times as much as heating with an atmospheric furnace, and quality can be made more uniform. Therefore, the equipment cost (equipment cost per unit furnace length (yen/l1
1) × Furnace length (m)) On the contrary, a blast furnace can be a cheaper equipment, and the running cost of electricity per unit (yen/T) is almost the same as an atmospheric furnace. become.

In any case, when constructing the optimal heat treatment furnace equipment, it is important to make a comprehensive decision that takes into consideration productivity, quality, equipment costs, running costs, and minimizing the installation site area. Based on this, as a result of researching and considering heat treatment furnaces for the special spheroidizing annealing heat treatment of the wire rod coil of the present invention, it was found that heating and soaking with emphasis on uniform rapid heating are performed in a blast furnace, and there are restrictions on the cooling rate including retention. For slow cooling, we devised a heat treatment furnace that combines a conventional atmosphere furnace with a blast furnace and an atmosphere furnace in a directly connected system. In particular, if you have an existing atmosphere furnace, you can directly connect it by simply installing a new blast furnace, and you can expect a significant cost reduction.

The heat treatment furnace of the present invention was developed based on this reason. That is, in order to economically shorten the spheroidizing annealing time of the wire coil, a blower device for blowing a high-temperature gas heat transfer medium, a heat compensator for controlling the medium temperature, and a wire coil are pressed. A blast supply device consisting of a press drive device to equalize the filling rate in the coil.
This heat treatment furnace is constructed by directly connecting and integrating a blast furnace with at least one blast furnace, an atmospheric furnace consisting of a plurality of radiant tubes serving as a radiant heat source, and a plurality of stirring fans for causing convection of the atmosphere inside the furnace. Furthermore, when the wire coil is transported in the furnace, a convector plate is installed on the carrier for transport, and the structure is such that conductive heat loss due to contact of the lower end surface of the wire coil with the carrier for transport is reduced.

These will be further explained in detail based on the drawings.

FIG. 10 shows an example of a heat treatment furnace in which the spheroidizing annealing method of the present invention can be carried out, and FIG. 10(a) is a schematic diagram showing the overall configuration. In addition, (b) and (c) in Fig. 10 are views showing details of the blast furnace blast supply device, (b) is a side view, and (c) is a side view.
is a front view. In the figure, 1 is a wire coil of the material to be heat treated;
2 is a carrier for transporting the wire coil 1; 3 is a transport roller; 14 is a convector plate for reducing conduction heat loss due to contact between the lower end surface of the wire coil 1 and the transport carrier 2; 6 is a blast supply device 17; The blast furnace with multiple units (three in this example) is mainly used for heating and uniform heating, and is also capable of holding and slow cooling, while the number 7 is a conventional atmosphere furnace, which is mainly used for holding and slow cooling, but also capable of heating and uniform heating. , 5.5' is a blast furnace 6 and an atmospheric furnace 7 in which a reducing gas (e.g. hydrogen, explosive gas such as carbon oxide) is
is used, a purge chamber is provided for purging with inert gas (for example, N, etc.), 12 is a blast duct through which the blast is guided by 1°, and 4 is connected to the blast duct 12 at its end surface. A blast foot 11 connects to the lifting duct bellows 8 and closes the upper end of the wire coil 1 on one end.
a press drive device for elevating and lowering the wire coil 1 through the 1 m hood to equalize the filling rate of the coil;
13 is a vertically movable partition door for easily changing the processing in each furnace chamber, that is, the temperature, pressure inside the furnace, amount of air blast, direction of air blast, etc., and 9 is installed in the system of the air blast duct 12. IO is a blower device that blows a heat transfer medium and changes the blast direction by changing the rotation direction;
26 is a WR wind for indicating the wind direction.

FIG. 10(d) is a front view showing details of the conventional atmosphere furnace 7 shown in FIG. 10(a). In the figure, 21 is a high-temperature combustion gas, 20 is a plurality of radiant tubes installed above and below the furnace that circulate the combustion gas of 21 and emit it as a radiant heat source, and 23 is a drive motor that causes convection of the atmosphere inside the furnace. This is a stirring fan.

FIG. 11 is a plan view of the convector plate 14 shown in FIG. 10. As shown in the figure, the convector plate 14 has radial holes 15 installed through girders 16 so that blast air can pass between the lower end surface of the wire coil 1 and the carrier 2 for transportation. It may be integrated or may be separated. Due to the empty space in the conhector plate, the contact area of the lower end surface of the wire coil with the carrier is reduced, and conductive heat loss can be prevented by passing the blast through the flow path of the groove I5.

FIG. 12 shows the temperature rise at the lower end surface of the wire coil depending on whether the convector plate is empty or not. In the figure, the dotted line a is the average temperature of the wire coil, the line b is the temperature of the lower end surface of the wire coil with a convector plate installed, and the broken line C is the wire coil when there is no convector plate and only a carrier flat plate. This is the temperature of the lower end surface. As is clear from the figure, the temperature rise at the lower end surface of the wire coil without a convector plate is significantly delayed compared to the average temperature rise, but by providing a convector plate, this delay is improved, and the temperature rise at the lower end surface of the coil It can be seen that heat transfer is reduced by conduction.

[Function] The heat treatment furnace of the present invention is a blast furnace equipped with a plurality of blast supply devices that are advantageous for rapidly and uniformly heating the entire wire rod coil that is the material to be heat treated, and an atmosphere furnace that is advantageous in terms of economy in equipment costs and running costs. This is a combination structure in which the functions are divided into holding and slow cooling, and this heat treatment significantly shortens the spheroidizing annealing processing time, and the quality of the wire rod coil is also the same as that of the conventional method.

The operation of the heat treatment furnace described above will be described below.

The wire coil 1 of the material to be heat-treated is placed on the convector plate 14 on the conveyance carrier 2 and transferred to the purge chamber 5 by the conveyance roller 3.
If an explosive reducing gas is used in the next blast furnace, it is purged with an inert gas such as N in the purge chamber, and then sent to blast furnace 6. The wire coil 1 transported into the furnace is stopped at a predetermined position directly under the blast hood 4,
The blast hood 4 is lowered by the press drive device 11 and pressed with a predetermined load to equalize the filling rate within the wire coil 1. Next, with the wire coil still in the pressed state, the blower
is operated to perform blast heating so that the temperature of the wire coil reaches 740°C directly above Ac, but at this time, by alternating the direction of the blast inside the wire coil, the heating inside the coil becomes more uniform. Therefore, the rotation of the blower device is changed according to the predetermined directional ratio described above.

The gas used as a heat transfer medium for blast heating is composed of a single substance or a mixture of two or more of nitrogen, hydrogen, oxygen, carbon dioxide, hydrocarbon gas, inert gas, etc. A certain gas is controlled to a desired temperature by a heat compensator 9 disposed within the blast duct 12 system. There are two types of heat compensation devices: a direct heating method using combustion heat, and an indirect heating method using a heat exchanger, but there is no problem in using either method.

In the example of the blast furnace 6 shown in FIG. 1O, there are three blast supply devices 1.
7 is arranged, but when a large number of wire coils are sequentially conveyed and subjected to blast heating treatment in this blast furnace, it is more efficient to perform blast heating on the same wire coil with three blast supply devices. As for the heating time, the time required for heating and uniform heating is divided into 173 steps, and continuous blast heating is performed by intermittent conveyance. When heat treating a small number of wire coils, there is no need to operate all three units, and if holding and slow cooling in an atmosphere furnace is advantageous in terms of running costs, the entire heat pattern can be achieved using only a blast furnace. There is no harm in doing so.

The operational diagram of the blast supply device shown in FIG. 10(b) is No.
1 presses the wire rod coil through the blast foot 4 by operating the press drive device 11 to equalize the filling rate in the wire rod coil, and heats the wire rod by passing the blast air 26 from the outer circumference to the inner circumference of the coil. In NO12, the blast hood 4 is raised while waiting for the wire coil to be carried in, in NO12, the blast hood 4 is raised, and in NO003
is the same as No. 091, but represents a state in which the blast air 26 passes from the inner circumference of the wire coil to the outside and heats it.

In addition, since the heat treatment methods in the blast supply apparatus furnaces of No., 1xNo., and No. 3 are different for the partition doors 13, all the partition doors are in a closed state.

Heat treatment corresponding to the above-mentioned conditions is performed in the blast furnace, and the wire rod coil that has been heated and soaked is then transferred to the atmosphere furnace 7.
It is then sent to a storage facility for retention and slow cooling.

Since the temperature inside the atmosphere furnace is maintained at the inlet side, the temperature range of the furnace length is such that the temperature of the wire rod coil can be maintained at 740°C just above Ac for a predetermined time, and the temperature beyond that is Ar, which is the final discharge temperature. Cooling rate 40℃/hr up to direct temperature 650℃
The radiant heat from the radiant tube is controlled within the following furnace length range. When the retention and slow cooling are completed in this way, the spheroidization of the solute carbides is completed, but if an explosive reducing gas is used in the atmosphere furnace, the purge chamber 5' provided at the rear of the atmosphere furnace 7 The wire coil is sent, purged with an inert gas such as N, and carried out. All that is left to do is to cool it using an appropriate method such as air cooling.

[Example] Hereinafter, the method of the present invention (
An example in which a wire rod coil was subjected to spheroidizing annealing heat treatment is shown below.
This will be explained together with a conventional method and a comparative example.

The material to be heat treated is 545G mechanical structural steel specified by JIS with the components shown in Table 1, and the finishing temperature is 700.
After being rolled to 10mmφ at ~1000°C, the material was cooled at a prescribed cooling rate, with an outer diameter of 1.4m and an inner diameter of 1.0m.
It is a wire coil wound into a coil shape with a height (axial direction) of 1.3a+ and a unit weight of 2 tons.

Table 2 also shows the heat treatment conditions and material evaluation results when the wire coil was subjected to spheroidizing annealing heat treatment. Material evaluation is based on hardness of spheroidized wire coil and JIS
Two points of the degree of spheroidization defined in G35:119 were examined. The material achievement target for spheroidizing annealing is a hardness Hv of 10.
5x (Desk + *Si/3 + %Mn/6 + !k
cr/19) +72.6 (points) or less, and the degree of spheroidization is NO12 or less.

Symbols 1 to 12 in the table are examples of the present invention, where symbol 1 is the blast velocity which is the lower limit of the present invention], 5n+/sec, symbol 2 is where the blast velocity is increased to 10 m/sec, Symbol 3 has a slow cooling rate of 9°C/hr for 10 hours, and symbols 4 and 5 have a large coil press load, 20 tons and 2, respectively, which are 10 times the coil unit weight.
Although it is a large load of 40 tons, which is 0 times, the symbol 5
Although the material of the wire with a 40 ton load was good, the wire had significant bending distortion and was unsuitable as a product. symbol 6
Symbol 7 is the one in which blast heating is performed with the blast direction constant from the outer circumference to the inner circumference of the coil, and symbol 7 is the opposite of symbol 6, in which the blast direction is constant from the inner circumference to the outer circumference of the coil. Symbol 6 is the one in which the blast direction is 1:1 and the ratio of the blast direction is from the outer periphery of the coil to that from the inner periphery for the same blast time. Items 8 to 8 required an extra 0.1 hour of soaking time than the others.

This shows that the ratio range of the present invention in the blast direction contributes to a considerable reduction in processing time.

Symbol 9 is a case in which only heating was performed in a blast furnace, and the soaking process was performed in an atmospheric furnace, but the soaking time was 11 times longer than in a blast furnace.
．． It took an extra 7 hours. Symbol 10 is the heat treatment performed under the most ideal conditions of the present invention, symbol 11 is the heat treatment performed from heating, soaking, and holding in a blast furnace, and only slow cooling is performed in an atmosphere furnace, and symbol 12 is the heat treatment from heating to slow cooling. The entire heat pattern was processed using only the blast furnace.

In all of the above embodiments of the method of the present invention, materials with satisfactory hardness and degree of spheroidization after spheroidizing annealing were obtained as desired.

Next, symbols 13 to 20 are comparative examples. Symbol 13 has a short annealing time of 2 hours and a fast cooling rate of 45°C/hr, symbol 16 has no coil pressing at all, and symbol 17
Symbol 18 is one in which blast heating is performed while the coil press load is 0.2 tons, which is less than the unit weight of the coil of the present invention, which is 175 or more (0.4 tons or more for a 2-ton coil).
and No. 19 were blast-heated with the blast direction constant from the outer circumferential side of the coil to the inner circumferential side or from the inner circumferential side of the coil to the outer circumferential side of the coil, but the soaking time was the same in this case. In code 10.11, soaking time is required to be 0.4 hours, but in case of code 20, soaking time is completed faster at 0.3 hours.
In this case, a wire coil was placed on a flat plate and heat treated without using a convector plate. Even in the comparative examples that attempted to shorten the spheroidization annealing time, there were cases in which the annealing speed was faster than the specified one, the heating blast speed was slower, the coil press load was reduced, and the heating was soaked in the direction of the blast. If the time is insufficient, the optimum shape of the carbide will not be spheroidized, and therefore the hardness will be too hard and the desired softness will not be obtained. In addition, when a convector plate is not used, the lower end of the wire coil is not sufficiently heated and the target quality is not obtained.

Symbols 21 and 22 are those in which spheroidizing annealing heat treatment was performed in an atmospheric furnace using a conventional method. Symbol 21 has a total processing time of 18
Since the process is time consuming and sufficient, the material quality after annealing is equivalent to that of the method of the present invention. However, the processing time is about five times that of the present invention. In code 22, in order to shorten the annealing time, the soaking and slow cooling times are shortened, and the total processing time is 13,
Although the heating time was set to 5 hours, the desired material quality was not obtained due to insufficient local temperature rise, which resulted in uneven heating of the entire wire coil, resulting in insufficient spheroidization.

[Effects of the Invention] As explained above, the present invention solves the long-standing problem of shortening the heat treatment time for spheroidizing annealing of wire rods as they are by using a uniform rapid heating blast method that is stable in terms of quality. The processing time was reduced to approximately 115 minutes.

In addition, this blast furnace that performs blast heating can be directly connected to a conventional atmosphere furnace, and the heat treatment process part in the heat pattern can be distributed to the furnace that matches the superior characteristics of each part.Energy saving of equipment costs and running costs. We have discovered a heat treatment furnace that takes the above effects into consideration, and it has extremely high industrial utility value.

[Brief explanation of drawings]

FIG. 1 shows an example of a heat pattern for spheroidizing annealing according to the present invention.
Figure 2 is an example of the heat pattern of spheroidizing annealing using a conventional atmosphere furnace, Figure 3 (a) is a schematic diagram of a normal wire coil being blasted with densely uneven conditions, and Figure 3 (b) is the case. Figure 4 (a) is a schematic diagram showing the air flow distribution of 8I in a state where it is pressed into a normal wire coil.
b) is a diagram showing the air volume distribution at that time, Figure 5 is a diagram showing the relationship between the coil press load and the blast air volume variation, and Figure 6 is a diagram showing the relationship between the local filling rate in the wire coil and the blast speed. ,
Figure 7 is a diagram showing the relationship between the blast speed and the time required for heating and soaking, and Figure 8 is a diagram showing the relationship between the blast velocity and the time required for heating and soaking.
, or a schematic diagram showing the blast method from the inner circumferential side (b), Figure 9 is a diagram showing the relationship between blast direction ratio and heating time, Figure 1
Figure 0 shows an example of the heat treatment furnace of the present invention.
) is a schematic diagram showing the overall configuration, (b) is a side view showing details of the blast supply device of the blast furnace, (C) is a front view thereof, and (d) is a diagram showing details of a conventional atmosphere furnace. FIG. 11 is a schematic diagram of an example of installing a convector board, and FIG. 12 is a diagram showing the effect of increasing the temperature on the lower end face of a wire coil by installing a convector board. 1...Wire coil, 2...Transportation carrier, 3.
...Conveyance roller, 4...Blast hood, 5,5'...
Purge chamber, 6... Blast furnace, 7... Atmosphere furnace, 8...
・Elevating duct bellows, 9... Heat compensation device, 10...
・Air blower, 11...Press drive device, 12...Blast duct, 13...Partition door, l4...Convector board, 17...Blast supply device, 20...Radiant tube , 23... Stirring fan, 25... Furnace wall, 26
...Blast of wind

Claims (1)

[Claims] 1. In an annealing heat treatment method for a wire coil, the wire coil is pressed in the axial direction with a load of one-fifth or more of the unit weight of the wire coil, and high-temperature gas is transmitted into the gap between the wire coils. A blast as a heating medium is passed through, and the apparent velocity of the blast is set to 1.5.
A method for heat treatment of a wire coil, characterized in that the heat treatment is performed at m/sec or more. 2. The direction of the blast is A from the outer circumference to the inner circumference of the wire coil, and B is from the inner circumference to the outer circumference, and the total time of the blast (
A time ratio A/(A+B) to A+B) is 0.5
2. The method for heat treatment of a wire coil according to claim 1, wherein A and B are alternately combined and blasted at a blowing rate of less than 1.0. 3. A shock absorber consisting of a blower device that blows a high-temperature gas heat transfer medium, a heat compensation device that controls the medium temperature, and a press drive device that presses the wire coil to equalize the filling rate in the coil. A blast furnace equipped with one or more air supply devices, an atmosphere furnace consisting of a plurality of radiant tubes serving as a radiant heat source, and a plurality of stirring fans that create convection in the atmosphere inside the furnace are combined in a directly connected and integrated configuration. Heat treatment furnace. 4. The heat treatment furnace according to claim 3, wherein a convector plate is installed on a carrier for transportation when the wire rod coil is transported in the furnace, and the wire rod coil is placed on the convector plate.