JPH11335743A - Slow cooling method for wire rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for applying slow cooling to a wire rod after hot rolling uniformly in a width direction. SOLUTION: In a method of slow cooling for wire rod where slow cooling is applied to a wire rod after hot finish rolling on a Stelmor type conveyor, the coiling density of the wire rod is regulated to (30 to 50)turns/m to apply air-blast cooling to the transverse end until the starting of slow cooling, and, in the course of slow cooling, the coiling density of the wire rod is made to (80 to 150)turns/m within a heat insulating cover 6 and at least either of the application of air-blast cooling to the transverse end and the application of heating to the central part is performed. It is further desirable to evacuate the upper part within the heat insulating cover.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cooling a wire in a wire manufacturing process, and more particularly to a method for uniformly cooling a steel wire on a stealmore type conveyor.

[0002]

2. Description of the Related Art Heat treatment after finishing rolling of a hot wire is performed by winding a wire with a laying head in a steel wire rolling line having a stellmore type conveyor, and winding the wire on a conveyor installed behind the wire. The loosened bundle is continuously developed and cooled while being transported.

In recent years, when a hot-rolled wire is drawn, a softened wire that does not require annealing before working is required. To obtain this, a heat insulating cover is provided on the upper part of the conveyor, and direct heat treatment by slow cooling is performed. Have been done.

When the cooling is performed, the solid solution structure becomes a softened structure of ferrite and pearlite. However, if the cooling rate is too high, bainite is formed and the structure becomes ferrite + pearlite + bainite structure and hardens. If the temperature of the material becomes too low before the slow cooling starts, bainite is formed to form a hardened structure. Therefore, it is necessary to secure a predetermined temperature or more at the time of starting the slow cooling. If the temperature at the time of exiting the heat retaining cover (slow cooling end temperature) is too high, it will be rapidly cooled thereafter, and will also have a hardened structure. Therefore, the slow cooling start temperature, slow cooling speed, and slow cooling end temperature are the main control points. Normal softened wire (wire diameter 9
~ 14 mm), the slow cooling start temperature is 720-630 ° C, the slow cooling rate is 0.15-0.5 ° C / s, and the slow cooling end temperature is 600.
The upper limit, the lower limit or the upper and lower limits are determined from the chemical composition of the wire and the wire diameter.

Various techniques relating to slow cooling have been disclosed.
For example, Japanese Patent Publication No. 60-45252 discloses that as a uniform slow cooling measure in the width direction of a wire, a conveyor is divided, and when the wire is transferred to the next conveyor, a step is provided to loosen the wire, and a wire coil is formed. A method is disclosed in which air is blown to both side ends while compensating and heating the supercooled part.

Japanese Unexamined Patent Publication (Kokai) No. 3-64420 discloses a method of keeping a wire at a temperature of 650 ° C. ± 10 ° C. for at least 3 minutes as a measure for preventing supercooling, and a method of heating the wire to achieve the above condition. I have.

[0007]

SUMMARY OF THE INVENTION The aforementioned Japanese Patent Publication No. 60-45.
In the method disclosed in Japanese Patent Publication No. 252, there is a possibility that the cooling speed in the width direction varies due to variations in the loosening method when blowing the cool air and restrictions on the transit time when moving on the conveyor. In addition, there are problems that the equipment becomes large and the operation becomes complicated.

In the method disclosed in JP-A-3-64420, a heating means is shown as a countermeasure for supercooling. Things have not been revealed.

[0009] An object of the present invention is to secure a predetermined slow cooling start temperature and a slow cooling end temperature, particularly on a steermore type conveyor, in a heat treatment after rolling of a wire rod, to secure a required slow cooling rate, and It is an object of the present invention to provide a means for uniformly cooling wires in a width direction and a height direction.

[0010]

Means for Solving the Problems The present inventors have studied a method of uniformly cooling a bundle of wires in the width direction (hereinafter, also simply referred to as the width direction), and have conducted various tests. Quantitatively clarify the relationship between winding density and cooling rate,
By changing the winding density and the cooling method of the wire before and during the slow cooling, optimum cooling conditions were found for each of the width end and the width center. Furthermore, when it tried to cool the width end part by blowing, it turned out that the cooling of the downstream side becomes inadequate compared with the upstream side of cold air. The following findings were obtained from these studies.

(A) Until the slow cooling is started, the temperature is lowered to the slow cooling start temperature as soon as possible in order to increase the efficiency and shorten the length of the conveyor. Therefore, the winding density is reduced and forced cooling is performed. The forced cooling is mainly performed at the width end portion where the cooling rate is slow, so that the temperature distribution in the width direction at the start of slow cooling is made uniform, and the lower limit of the slow cooling start temperature is secured. Under forced cooling at the width end, there is an appropriate winding density at which the cooling rate is high and a uniform temperature distribution is easily obtained in the width direction.

(B) During slow cooling, the slow cooling rate must be lower than the upper limit of the slow cooling rate. Therefore, it is covered with a heat insulating cover to increase the winding density and reduce the heat dissipation area. However, in order to increase efficiency and shorten the length of the conveyor, forced cooling is performed within a range not exceeding the upper limit of the slow cooling rate. The forced cooling is performed on the width end where the cooling rate is slow. In addition, if the slow cooling rate becomes higher than the specified value even after covering with the heat retaining cover, heating is required. Heating is performed at the center of the width where the cooling rate is high. At the end of the slow cooling (when the thermal insulation cover is removed), the temperature of the wire must be lower than or equal to the upper limit of the above-mentioned slow cooling end temperature, and if it exceeds this, the wire is rapidly cooled by the rear conveyor, and a softened structure cannot be obtained. . During slow cooling, there is an appropriate winding density at which an appropriate slow cooling rate can be obtained under the width edge cooling and a uniform temperature distribution in the width direction can be easily obtained.

(C) However, it may be difficult to uniformly cool the overlapped wires in the height direction in the case of item (b).
This is because when the cool air blown from the lower surface of the wire passes upward through the gap of the overlapped wire bundle, it does not reach the uppermost part but escapes partly in the width direction of the wire. This is due to the variation of

(D) As a countermeasure, by providing an exhaust port above the width end of the wire bundle in the slow cooling cover and forcibly exhausting the atmosphere, a uniform cooling rate in the height direction can be secured.

(E) No special heat treatment is required after leaving the heat insulating cover. The wire may be forcibly cooled to reduce the length of the conveyor or to facilitate handling after winding.

The gist of the present invention completed on the basis of the above findings is as follows (1) and (2). (1) In the method of gradually cooling a wire after hot finish rolling on a stellmore type conveyor, the winding density of the wire is set to 30 to 50 / m until the slow cooling is started. The width end is subjected to blast cooling, and during slow cooling, the winding density of the wire is set to 80 to 150 turns / m in the heat retaining cover, and the blast cooling of the width end of the wire and / or the heating of the central portion are performed. Method for slowly cooling wire.

(2) The method of blast cooling of the width end of the wire during slow cooling is a method of blowing cold air from the lower surface of the conveyor, and forcibly exhausting air from an exhaust port provided above the width end of the wire in the heat retention cover. The method for slowly cooling a wire according to the above (1), which is characterized in that:

Here, the width end of the wire is 0.7 to 0.7 mm from the center of the width of the wire bundle unfolded and spread on the conveyor.
The portion of 1.1R (R is the winding radius), and the center of the wire is a portion within 0.5R from the center of the width of the wire bundle. Also,
The impingement cooling refers to a cooling method of forcibly blowing air using a blower or the like.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a graph of a cooling rate for each part of a wire in a width direction. The figure shows a wire diameter of 9.0 mm, a winding diameter D (twice the radius R) of 1250 mm, and a winding density of 30 mm.
The cooling rate at the time of spontaneous cooling (cooling) from 650 ° C. to 600 ° C. while changing at １８０180 / m is shown.

As described above, the object of the present invention is to provide uniform cooling in the width direction. In order to make the quality of the width end and the center of the wire bundle uniform, it is necessary to make the annealing temperature uniform. It is necessary to make the slow cooling rate uniform.

As shown in FIG. 1, since the cooling speed is small at the width end of the wire in natural cooling, it is conceivable to cool the width end or heat the center in order to make this uniform. .

Before the start of slow cooling, the cooling rate may be high, so that the winding density is reduced and the width end is cooled to obtain a uniform cooling rate. At this time, if necessary, the central portion may be subjected to blast cooling. The winding density at this stage is determined by conditions that increase the cooling rate at the width end and easily obtain a uniform temperature distribution in the width direction.

During the slow cooling, the winding density is increased so that the cooling rate in the central portion is equal to or lower than the upper limit of the cooling rate, while the width end portion having a lower cooling rate than the central portion is forcibly cooled.
It is necessary to make the cooling rate uniform. If the slow cooling rate at the center is too high even if the winding density is increased, it is desirable to heat the center. The winding density at this stage is determined by the condition of the winding density at which the cooling rate in the central portion is equal to or lower than the upper limit of the cooling rate and a uniform temperature distribution is easily obtained in the width direction by forced cooling.

FIG. 2 is a schematic side view showing an apparatus for gradually cooling a wire rod for carrying out the method of the present invention. In FIG. 2, a wire 1 is discharged by a laying head 2 into a ring shape on a front conveyor 3 and cooled. At the exit of the front conveyor 3, a slow cooling conveyor 4 covered with a heat insulating cover 6 is installed. After the wire 1 is gradually cooled on the slow cooling conveyor 4,
After being transferred to the rear conveyor 5 and further cooled on the rear conveyor 5, it is dropped on the winding tab 10 to be a product. The wire is supplied by the front blower 7 through the cool air duct 15 in the front conveyor 3 and the cold air duct 1 in the slow cooling conveyor 4.
The cooling air is cooled by a slow cooling blower 8 through a cooling air duct 6 and a rear blower 9 through a cooling air duct 17 in the rear conveyor 5.

The conveying speed of the front conveyor 3 is set to be higher than that of the slow cooling conveyor, and the wire 1 is cooled in a state where the winding density is small (thin winding). The conveying speed of the slow cooling conveyor 4 is lower than that of the front conveyor 3, and the wire material has a high winding density (thick winding) on the slow cooling conveyor 4. Since the conveying speed of the rear conveyor 5 is set to be higher than that of the slow cooling conveyor 4, the winding density becomes thin again and cooling is promoted.

FIG. 3 is a sectional view taken along the line AA of FIG. In the figure, the cool air supplied by the front blower 7 is blown onto the thinly wound wire 1 through dampers 11a to 11c installed near the front conveyor 3 and a cool air duct 15 divided into three in the width direction. Can be As shown in the figure, in the case of the method of the present invention, the damper 11b for the central portion is fully closed to half open, and the dampers 11a and 11c for the width end are fully open. The central portion of the wire 1 is allowed to cool, while the width end portion is subjected to blast cooling. Since the bulk end has a higher bulk density than the center, the temperature difference between the width end and the center at the outlet of the front conveyor 3 is as small as possible.

FIG. 4 is a sectional view taken along the line BB of FIG. 4, the cool air supplied by the slow cooling blower 8 (see FIG. 2) is supplied to the damper 1 installed near the slow cooling conveyor 4.
Cold air duct 1 divided into 3 in 2a to 12c and width direction
After passing through 6, the wire 1 is sprayed on the thickly wound wire 1. As shown in the figure, in the case of the method of the present invention, the damper 12b for the center portion is fully closed, and the damper 12b for the width end portion.
The openings a and 12c are fully opened or the opening is adjusted so that a required air volume can be obtained. The winding density at the center is smaller than that at the width end, and the cooling rate tends to be higher. However, in a thick winding state, a sufficiently slow cooling rate can be obtained by keeping the heat by the heat retaining cover 6. However, when the internal temperature of the heat retaining cover 6 is low, such as immediately after the start of operation, when the diameter of the wire is small, or when it is desired to prevent the cool air blown to the width end from wrapping around and prevent the center of the wire from being overcooled. It is desirable to provide a heater 14 for heating only the central portion between the rolls of the slow cooling conveyor 4. By providing appropriate cooling / heating conditions to these devices, the rate of slow cooling in the wire width direction can be made substantially equal.

FIG. 5 is a sectional view taken along the line CC in FIG. In FIG. 5, the cold air supplied by the rear blower 9 (see FIG. 2) is supplied to the damper 1 installed near the rear conveyor 5.
Through the cold air duct 17 divided into three sections 3a to 13c and in the width direction, the wire 1 is blown onto the thinly wound wire 1 and cooled to near room temperature. In the cooling stage of the rear conveyor 5, it is not necessary to control the cooling speed in the width direction. Therefore, as shown in the figure, all the dampers 13a to 13c may be opened for cooling, and The air volume may be preferentially distributed.

By the above method, the temperature difference in the width direction at the outlet of the front conveyor 3 and the slow cooling conveyor 4 is reduced, and uniform slow cooling in the width direction can be realized.

The position of the width end and the center in the blast cooling or the center heating will be described below. In FIG. 1 described above, the shape of the graph is a portion having a relatively high cooling rate from the center to 0.5R (R is a winding radius), 0.8 to 1.
There is a part with a low cooling rate of 0R and a slope part connecting it. Therefore, when the wire is cooled by the blast, the range of 0.8 to 1.0 R at the width end may be cooled, and when keeping the temperature, the range of the center to 0.5 R may be heated. Considering that the wire material slightly varies from side to side on the conveyor, it is preferable to cool the width end portion in the range of 0.7 to 1.1R (the range indicated by the dotted line in FIG. 1).

Of the three divided widths of the cool air duct 15 and the cool air duct 16 shown in FIGS. 3 and 4, the position of the duct at the width end is in the range of 0.7R to 1.1R as described above. Is good. In FIG. 4, the width of the heater 14 is preferably in the range of about ± 0.5R.

The winding density on the front conveyor before slow cooling is 3
0 to 50 (lines / m). For winding densities in this range,
Normal softening wire rolling end temperature (about 800 to 750 ° C), slow cooling start temperature (about 720 to 630 ° C) and normal cooling time (determined by front conveyor length / conveyor speed in about 50 to 80 s) This is because it is easy to obtain a uniform temperature distribution under the condition that the width end is subjected to blast cooling, and it is possible to secure the upper and lower limits of the temperature before the start of the predetermined slow cooling.

The winding density on the front conveyor is 50 (books /
If m) is exceeded, the slow cooling start temperature at the width end becomes higher than the target slow cooling start temperature, and even if it is subjected to blast cooling in the slow cooling conveyor, it cannot be cooled below the upper limit of the slow cooling end temperature. As a result, after leaving the slow cooling conveyor, it is quenched by the rear conveyor and a bainite structure is generated.

When the winding density is less than 30 (lines / m),
The temperature of the wire at the central portion before the slow cooling becomes lower than the lower limit of the slow cooling start temperature, and bainite is also generated. Also, in terms of equipment, if the winding density is smaller than this, the conveyor length becomes longer. More preferably, 35-4
5 (books / m).

The winding density during slow cooling is 80 to 150 (book /
m). When the winding density is within this range, when gradually cooling at a predetermined cooling rate from the slow cooling start temperature to the slow cooling end temperature in the heat insulating cover, the blast cooling of the width end portion (the width if necessary) is performed. It is easy to obtain a uniform temperature in the width direction under the condition that the central part is also heated).

When the winding density in the slow cooling conveyor exceeds 150 (lines / m), the width end portion is not cooled to the upper limit of the slow cooling end temperature in the slow cooling conveyor, and exits the slow cooling conveyor. After that, it is quenched by a rear conveyor to form a bainite structure. When the winding density is less than 80 (lines / m), the cooling rate at the center of the wire becomes larger than the upper limit, and a bainite structure is also generated. More preferably 90 to 140
(Book / m).

The winding speed of the wire can be adjusted by changing the speed of the conveyor. V (m / s) of finishing rolling speed,
The winding density is n (lines / m), and the winding diameter of the wire is D (m, D
= 2R), and assuming that the speed of the conveyor is v (m / s), n
= V / (π · D · v), the conveyor speed v may be adjusted according to the required winding density.

Even if the above measures are taken, there may be a case where the quality varies greatly depending on the position of the overlapping height of the wire rod end. In the slow cooling conveyor, since the cool air is blown from the lower surface, for example, the wire diameter is large, and in the case of relatively thick winding, the ventilation resistance of the cool air is large, the speed of the cool air is reduced, or the cool air escapes in the width direction of the wire. That's why.

In such a case, it is preferable to forcibly evacuate the atmosphere near the width end by the slow cooling conveyor. Due to the forced exhaust, the pressure difference in the vertical direction of the heat retaining cover increases, and the cool air is sufficiently supplied also to the upper portion of the width end portion, and the variation in quality depending on the height position is reduced.

FIG. 6 is a schematic side view showing a slow cooling device for implementing the method of forcibly exhausting the inside of the slow cooling cover according to the present invention. In the figure, reference numeral 18 denotes an exhaust blower, and 19 denotes an exhaust duct.

FIG. 7 is a sectional view taken along the line DD in FIG. 4, the same parts as those in FIGS. 4 and 6 are denoted by the same reference numerals.

In FIG. 7, the structure of the cool air duct 16 and the dampers 12a to 12c on the lower surface of the slow cooling conveyor 4 and the method of setting the damper opening are as described in FIG. Exhaust ports 20 a and 20 b are provided above the width end of the wire 1, and the atmosphere at the width end of the wire 1 is sucked by the exhaust blower 18 through the dampers 21 a and 21 b and the exhaust duct 19.

It is preferable that the width of the exhaust ports 20a, 20b substantially correspond to the width of the cold air duct on the lower surface. That is, it is preferable to exhaust air at a position in the range of 0.7 to 1.1R with respect to the winding radius R of the wire. In order to efficiently suck the cool air from the lower surface, it is better that the distance between the exhaust ports 20a and 20b and the wire 1 is narrower. However, depending on the wire diameter and winding density,
It would be even more desirable if the height of the exhaust port could be changed as the height changed. Exhaust port 20a, 20b
When the height of the wire is fixed, it is preferable that the maximum height of the overlap of the wire is about +50 mm in consideration of the fact that the wire jumps or swells for some reason. Exhaust port 2
If the distance between the 0a and 20 bt wires exceeds 300 mm, the exhaust effect is significantly reduced and should be avoided.

[0044]

(Embodiment 1) In this embodiment, an apparatus shown in FIG. 2 was used. To perform a softening treatment of SCM435 having a wire diameter of 9 mm, wind the wire with a laying head at 800 ° C.
On a stealmore type front conveyor, cool in a thin wound state, cool to a target temperature of 650 ° C or more and 720 ° C or less, gradually change to a thick winding state, gradually cool in a heat insulation cover, and finish cooling. The target temperature was set to 600 ° C. or less. Thereafter, the lower surface was forcibly cooled by a conveyor having an open top, and cooled to near normal temperature.

Comparative tests were carried out under conditions different from the method of the present invention and the scope of the present invention. Table 1 shows the results.

[0046]

[Table 1]

In the examples of the present invention of Test Nos. 1 and 2, the temperatures of the central part and the edge part before the start of the slow cooling and after the slow cooling satisfy predetermined conditions, and the structure of the product is a good structure of ferrite + pearlite. was gotten.

The following test is a comparative example. Test No. 3
The winding density before slow cooling was less than the lower limit of the present invention, the slow cooling start temperature at the center could not be secured, and a bainite-mixed structure was obtained, and the softening treatment failed.

In Test No. 4, the winding density before slow cooling exceeded the upper limit of the present invention, and the slow cooling start temperature was excessive.
Although a good structure was obtained at the width end by forced cooling, the center part was gradually cooled with insufficient cooling, and rapidly cooled by a rear conveyor, so that the structure was a mixture of bainite.

In Test No. 5, the winding density during the slow cooling was less than the lower limit of the present invention, and although the material was heated during the slow cooling, it was rapidly cooled on the slow cooling conveyor to form a structure containing bainite.

In Test No. 6, the winding density during slow cooling exceeded the upper limit of the present invention, and the slow cooling end temperature was high at both the center and the end of the width, and the roll was rapidly cooled by the rear conveyor. became.

In Test No. 7, the width end was not cooled before slow cooling. As a result, the slow cooling start temperature was high, the slow cooling end temperature was high even if the forced cooling was performed during slow cooling, and the structure was rapidly cooled by the rear conveyor to form a bainite-mixed structure.

Test No. In No. 8, the width end was not cooled during slow cooling. As a result, the temperature at the end of the slow cooling was high, and the structure was rapidly cooled by the rear conveyor, and the structure was mixed with bainite.

Example 2 In this example, the apparatus shown in FIG. 6 was used. A softening treatment of SCM435 having a wire diameter of 12 mm was performed. The wire is wound up with a laying head at 800 ° C., cooled with a front conveyor, and the target temperature for slow cooling start is set at 650.
The temperature was set to about 720 ° C., and the mixture was put into a slow cooling conveyor. The slow cooling end temperature was targeted at 600 ° C. or lower. After gradual cooling, the product was cooled to near room temperature by a rear conveyor and dropped on a winding tab to obtain a product.

In the apparatus shown in FIG. 6, the case where the slow cooling cover 6 according to the second invention of the present invention is evacuated (Example A of the present invention) and the condition shown in FIG. The case where the exhaust of the slow cooling cover 6 is not performed (Example B of the present invention) was compared. Table 2 shows the test results.

[0056]

[Table 2]

As shown in Test Nos. 11 and 12 in Table 2, the temperature when the slow cooling cover was exited (slow cooling end temperature) was 600 ° C. or higher above the overlap of the wires at the width end. There was a part, and the structure of bainite mixture was seen in the product.

On the other hand, in Test Nos. 9 and 10 according to the second invention of the present invention, when the atmosphere at the width end was exhausted, there was little variation in the slow cooling end temperature depending on the height position of the width end. And a good structure of ferrite and pearlite was obtained.

As described above, in addition to the blast cooling of the wire width end from the lower part of the slow cooling conveyer, it was found that the combination of the wire upper part exhaust and the case where the wire diameter is large and the case where the winding density is high can be handled. .

[0060]

According to the present invention, it is easy to equalize the slow cooling start temperature, the average slow cooling rate and the slow cooling end temperature in the width direction and in the vertical direction of the wire overlap. Therefore, the precision of the slow cooling control can be improved without significantly modifying or newly installing the equipment, and a great effect can be exerted on the improvement of the quality and yield of the softened wire.

[Brief description of the drawings]

FIG. 1 is a graph of a cooling rate for each position in a width direction of a wire.

FIG. 2 is a schematic side view showing a wire rod slow-down device for implementing the method of the present invention.

FIG. 3 is a sectional view taken along the line AA of FIG. 2;

FIG. 4 is a sectional view taken along the line BB of FIG. 2;

FIG. 5 is a sectional view taken along the line CC in FIG. 2;

FIG. 6 is a schematic side view showing a slow cooling device for performing the method of forcibly exhausting the inside of the slow cooling cover according to the present invention.

FIG. 7 is a sectional view taken along the line DD in FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wire rod 2 Raying head 3 Front conveyor 4 Slow cooling conveyor 5 Rear conveyor 6 Heat insulation cover 7 Front blower 8 Slow cooling blower 9 Rear blower 10 Winding tab 11a-11c Damper 12a-12c Damper 13a-13c Damper 14 Heater duct 16 Cold air duct 17 Cold air duct 18 Exhaust blower 19 Exhaust duct 20a, 20b Exhaust port 21a, 21b Damper

Continued on the front page (72) Inventor Naoki Suetomi 1 Konomi-cho, Kokurakita-ku, Kitakyushu-shi Sumitomo Metal Industries, Ltd. Inside the Kokura Works (72) Inventor Yutaka Neishi 4-5-33 Kitahama, Chuo-ku, Osaka-shi Sumitomo Metal Industries Inside the corporation

Claims (2)

[Claims] 1. A wire cooling method in which a wire after hot finish rolling is gradually cooled on a stellmore type conveyor, wherein the winding density of the wire is 30 to 50 wires / m until the slow cooling is started. The width end of the wire is subjected to blast cooling, and during slow cooling, the winding density of the wire is set to 80 to 150 windings / m in the heat retaining cover, and the blast cooling of the width end of the wire and / or the heating of the central portion are performed. Characteristic method of slowly cooling wire. 2. The method of blast cooling the end of the width of the wire during slow cooling is a method of blowing cold air from the lower surface of the conveyor, and forcibly exhausting air from an exhaust port provided above the end of the width of the wire in the heat retaining cover. The method for gradually cooling a wire according to claim 1.