JPH10273720A - Method for annealing plate welded zone in continuos pickling line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a weld zone excellent in weld strength in a short time by mixing the air in fuel gas, heating the front surface and back surface of plate at weld zone with the flame of a burner, using a built-in computing element to obtain relation between plate thickness and the heating time, setting the heating time for each plate thickness and annealing the weld zone. SOLUTION: The combustion time is controlled with a timer 8. The relation between the plate thickness and the heating time is before-hand inputted in the computing element of a CPU, etc., and the information of the passing plate is transported to the timer 8 to control the combustion of the burner 9 needed to the annealing. The direct heating with the flame of gas combustion burner is executed to apply the heat treatment of the welded part in a short time. Further, the fuel gas having not so high combustion temp., e.g. natural gas is used by beforehand mixing the air to easily adjust the optimum annealing temp. Many holes in the burner 9 are arranged in the width direction so as to be able to execute the uniform annealing. Further, the upper surface annealing burner 9a and the lower surface annealing burner 9b are arraigned to execute the annealing from both surfaces of the plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for annealing a weld after welding a preceding material and a following material in a continuous pickling line.

[0002]

2. Description of the Related Art In a continuous pickling line, when a steel sheet is passed, a tail part of a preceding material and a tip part of a following material are first welded and joined. At that time, if the high carbon steel is left as it is, a martensite structure is generated, the strength of the weld becomes uneven, and the brittleness increases depending on the amount of carbon. Therefore, in order to equalize the joint strength of the weld, heat treatment is performed by tempering after welding. Conventional heat treatment methods after welding include a method using high-frequency induction heating outside the welding machine and a heat treatment method using a welding power supply. Was adopted.

[0003]

Since the conventional annealing method is configured as described above, there are the following problems.
That is, in the case of the high-frequency induction heating, the heating time is long and the productivity is reduced. If the heating time is to be shortened, a large-capacity facility is required. Also,
When a welding power source is used, unevenness of the heat treatment temperature in the width direction occurs due to the influence of the plate shape, and a portion higher than the A1 transformation point may occur at a high place. In such a case, the target annealing temperature Was difficult to set. Further, in the heat treatment, a portion heated to a high temperature (above the A1 transformation point) during welding and then cooled is tempered to a portion below the A1 transformation point (about 650 ° C.) by cooling, and the martensite structure is tempered and sorbite structure (softened It is important that the tempering temperature rises to the A1 transformation point or higher. After cooling, the martensite structure is formed again and the hardness becomes higher. When it was received, there was a risk that the weld might break.

[0004] The present invention has been made to solve the above-mentioned problems. In particular, a fuel gas is premixed with air to produce fuel, and a gas burner provided with a number of flame holes in the width direction is used. Provided is a method and an apparatus for annealing an interconnected line plate joint in which a welded portion is heated from above and below, an annealing time is set for each sheet thickness, and annealing is performed to obtain a welded portion having excellent joint strength in a short time. The purpose is to do.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for annealing a welded part in which a preceding material and a succeeding material are connected in a continuous pickling line. While heating with a burning fire from the front and back of the board,
This is a method of performing the annealing by setting the heating time for each sheet thickness using an arithmetic unit having a built-in relationship between the sheet thickness and the heating time. In addition, the combustion gas is a natural gas, LPG, LNG, or a sub-gas generated in a steel mill. Using raw gas or a mixed gas of at least two kinds selected from the above gases, and welding a welded part connecting a preceding material and a following material in a continuous pickling line with a welding machine,
In the annealing apparatus of the inter-acid line plate joint welded so as to be annealed by the annealing apparatus, the burner of the annealing apparatus is an upper surface,
It is composed of a lower-surface annealing burner, and the plate width of the welded portion and the width of the burner substantially match.

[0006]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an embodiment of a method and an apparatus for annealing an interconnected steel plate joint weld according to the present invention. FIG. 1 is a diagram showing an example of a schematic configuration of equipment to which the method of the present invention is applied. In FIG. 1, the leading end of the following material 2 sent out by the tension reel T and the leading material 1
And a tail end thereof are connected by a flash butt type welding machine 3, and the connected welded portion 20 is annealed by an annealing device 4. FIG. 2 is a diagram showing a schematic configuration of the annealing device 4. The gas is sent from the fuel gas storage facility 6 to the mixing device 7 via the pipe 10 and the blower 5 is provided as a device for sending air. The air is sent to the mixing device 7 to mix the fuel gas and air. It is sent to the burner 9. The mixing ratio between the fuel gas and air is a mixing ratio at which an optimum combustion state is obtained, and the combustion time is controlled by the timer 8. The relationship between the previously determined sheet thickness and the heating time is input to an arithmetic unit (not shown) such as a CPU, and a signal is sent from the information on the passing sheet to the timer 8 to control the combustion of the burner 9 required for heating annealing. Will be In order to perform annealing of the welded portion 20 from both sides of the plate, an upper surface annealing burner 9a and a lower surface annealing burner 9b of the burner 9 are provided. In this embodiment, since the LPG is a liquefied gas, the collecting device is provided with a heating device for vaporizing, though not shown. Further, the width of the burner 9 and the plate width of the welded portion 20 are substantially equal to each other. Next, as a method of performing heat treatment of the welded portion in a short time, direct heating by the flame of the gas combustion burner is performed. This gas is
If the fuel gas is O ₂ mixed, the combustion temperature is too high (2200-200)
2700 ° C.), it is difficult to adjust to the optimum annealing temperature (600 to 650 ° C.).
(0 ° C) using air premixing. The fuel gas may be natural gas, LPG, LNG, or a by-product gas generated in steel works. Further, a mixed gas obtained by mixing the above gases may be used. The calorific value of the fuel gas or the amount of air to be mixed may be controlled so as to obtain an optimum flame temperature, and the heating and burning time may be determined in advance. Regarding the distance between the plate and the burner, when heating with a flame, it is better to be as close as possible to the plate because the flame surface temperature is higher because the heating capacity is higher, but if it is too close, there is concern about contact with the plate. Is done. Therefore, since the flame surface temperature is high up to about 50 mm, the distance between the plate and the burner 9 is suitably 50 mm.

The condition for annealing the welded portion is that annealing is completed uniformly and within a target time. For this purpose, the combustion width, that is, the flame width is 20 to 30 mm, and the width direction (1500 mm) of the plate is simultaneously heated from the front and back surfaces of the plate, and the combustion temperature is 1000 to 1200 ° C. or less. With the above-described burner configuration, the burner 9 is provided with a large number of holes in the width direction, and if the welding capability becomes uniform, the target temperature can be set and the constant annealing can be always performed. Since the thickness of the pickling board changes and the thickness of the weld changes accordingly, the heating time to the optimum temperature changes. Therefore, the heat annealing time by the flame is set in advance in the calculation unit for each sheet thickness, and annealing is performed with the preset heat annealing time.

[0008]

Next, the welding device 20 was actually used by using the above-described apparatus.
The case where annealing is performed will be described. In this embodiment, FIG.
A burner 9 having a large number of flame holes 9A as shown in FIG.
The welded portion was uniformly heated with a flame of 00 mm, and the LPG gas was flowed at a flow rate of 40 Nm ³ / hr with a flame injection width of about 20 mm and mixed with air to burn.

After welding the tail end of the preceding material 1 and the tip end of the following material 2 in FIG. 1 in the welding machine 3, the welding portion 20 is heated to 650 ° C. in the annealing device 4. At this time, the heating time is changed and set according to the plate thickness. FIG.
LPG gas was flowed at a constant flow rate of 40 Nm ³ / hr using the burner 9, mixed with air, burned by using the burner 9, and heated from the front and back surfaces of the plate. . The distance from the surface of the plate to the flame outlet of the burner was set to 50 mm. As a result, as shown in FIG. 4, a linear relationship between the plate thickness and the temperature rise at 650 ° C. was recognized.

Therefore, based on the relationship shown in FIG. 4, a steel material Sk5 was used as a test material, and a hot-rolled strip steel having a width of 1200 mm and a thickness of 6 mm was connected by flash butt welding to obtain a relationship shown in FIG. In the same manner as above, the heating and burning time was set to 70 seconds, and the distance from the joint surface after annealing and the cross-sectional hardness (Hv)
Shows the relationship. The line a in the figure is the result of measuring the hardness at the center of the plate at 1 mm intervals, and the line b is 50 mm from the edge of the plate.
It was measured at intervals of 1 mm in the same place as the above, and the hardness was uniform at both the central portion and the edge portion, and the heat annealing was satisfactory.

[0011]

Since the method of the present invention is configured as described above, it takes a shorter time and a shorter time than the method performed by the conventional method.
Variations in the tempering effect in the sheet width direction can be eliminated, and the joining strength of the welded portion can be made uniform. Therefore, it is possible to prevent a breakage accident of the plate joint during operation of the continuous line beforehand, and it is possible to prevent a decrease in productivity due to a stop of the line and an increase in cost required for re-welding.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an example of a schematic configuration of equipment to which the method of the present invention is applied.

FIG. 2 is a schematic configuration diagram of the annealing apparatus of FIG.

FIG. 3 is a characteristic diagram showing a relationship between a plate thickness and a heating time up to 650 ° C. in the present invention.

FIG. 4 is a diagram illustrating a relationship between a distance from a bonding surface and a sectional hardness in the present invention.

FIG. 5 is a diagram showing a sectional hardness.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lead material 2 Trailing material 3 Welding machine 4 Annealing device 9 Burner 9a Upper surface annealing burner 9b Lower surface annealing burner 20 Welded part

Claims (3)

[Claims] 1. A preceding material (1) and a following material in a continuous pickling line
In the method of annealing the welded part (20) connected to (2), the air is mixed with the fuel gas and the welded part (20) is mixed with the burner (9).
Heating with a combustion fire from the front and back surfaces of the plate, and performing annealing by setting the heating time for each plate thickness using an arithmetic unit having a built-in relationship between the plate thickness and the heating time. Annealing method for joint welds. 2. The combustion gas is natural gas, LPG, LN.
2. The method of annealing a seam welded joint of a tandem acid line according to claim 1, wherein the gas is a by-product gas generated in an ironworks or a mixed gas of at least two kinds of the gases. 3. A preceding material (1) and a following material in a continuous pickling line
(2) is connected to the welded part (20) is welded by a welding machine (3), in an annealing apparatus for a steel strip joint welding part so as to be annealed by an annealing apparatus (4), the annealing apparatus (4) The burner (9) consists of upper and lower annealing burners (9a, 9b),
An annealing apparatus for a seam joint weld of a joint acid line, wherein the plate width of (0) and the width of the burner (9) are substantially the same.