JPH11320104A - Flash-butt welding equipment and welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize flash-butt welding to improve the quality of a weld zone by controlling hardening of the weld zone. SOLUTION: With this flash-butt welding equipment equipped with gas discharge ports 2 to supply combustible gas to upper and lower sides of the welded portion of the material to be flash-butt-welded, a system to supply the combustible gas to the gas discharge ports 2 is equipped with an adjusting means 6 for the type and flow rate of the combustible gas. Multiple gas discharge ports for the combustible gas are arranged in the width direction of the welded material, and the combustible gas supply system is provided with a means to control the flow rate and quantity of input heat of the combustible gas to be supplied to the gas discharge ports in the width direction of the welded material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a carbon steel (mild steel),
The present invention relates to a flash butt welding apparatus and a welding method used for welding alloy steel, high-strength steel, heat-resistant steel, and the like.

[0002]

2. Description of the Related Art Flash butt welding is a process in which a material to be welded is clamped, and a voltage is applied to both ends of the material to make the butt end faces approach at an appropriate speed to form a local contact portion. The end face is locally concentratedly heated by resistance heat generated by a short-circuit current having a high current density flowing through the wire and an arc generated by melting and breaking of the contact short-circuit portion. At this time, a process in which the molten metal on the end face is scattered by the arc [flash process]. When the temperature of the entire end face is raised by this flushing, and a substantially uniform molten layer is formed on the entire face of the butted end face, it is rapidly increased. This is a welding method that consists of a process of pressing and deforming [upset process].

[0003] In a steel sheet production line, the steel sheets are often joined by flash butt welding. In a production line such as a cold rolling, a welded portion is subjected to the same treatment as that of a base material portion. Therefore, when the strength of the welded portion is not sufficiently obtained, a break occurs in the production line. When a fracture occurs, a significant decrease in production efficiency and a large increase in production cost due to damage to equipment such as a rolling roll due to a fractured material cause a decrease in the strength of the welded portion.

[0004] The following two points can be cited as the main causes of such a decrease in strength. When welding a steel sheet containing an alloy component that easily forms oxidized inclusions such as Si, Mn, and Al, the inclusions remain at the weld interface, and cracks occur therefrom as a starting point, thereby lowering the strength of the welded portion. In high carbon steel, alloy steel, etc., the vicinity of the weld interface hardens,
Since the toughness deteriorates, the strength of the weld decreases.

[0005] In order to prevent a decrease in the strength of the welded portion, how to prevent the inclusions from remaining on the welding interface for the following factors and how to suppress the hardening of the welded portions for the other factors. Is important.

[0006] As a method of avoiding the inclusions remaining at the welding interface, the formation of inclusions during welding, in particular, the formation of oxides which are most easily generated among the inclusions, is suppressed, and the inclusions are avoided. A method has been proposed. JP-A-49-96
Japanese Patent No. 947 discloses a method of shutting off oxygen in the atmosphere by burning a gas containing a reducing gas in the vicinity of a welded portion. Japanese Patent Application Laid-Open No. 50789/1981 discloses a method of hermetically sealing a butt-welded portion and shielding it with an inert gas. A way to do that has been proposed.

In Japanese Patent Application Laid-Open No. Sho 59-118282, a protective gas generating material such as a carbon polymer, an organic compound, an organosilicon compound, zinc, zinc powder-containing material, calcium, magnesium alloy or the like is provided near a welded portion. , JP 62
Japanese Patent Application Laid-Open No. 275581/1995 proposes a method in which grease is applied to the vicinity of a welded portion to generate a protective gas by heat during welding, and Japanese Patent Application Laid-Open No. 63-203281 proposes a method of applying the same.

As a method of suppressing the hardening of the welded portion, measures such as lowering the cooling rate after welding or softening the welded portion by performing a pre-heat treatment and a post-heat treatment before and after welding are taken. The pre-heat treatment includes, for example, a method of electrically heating the material to be welded by repeatedly contacting and separating the material to be welded before the flash process. For post-heat treatment, there is a method of heating a welded portion by high-frequency heating or by directly energizing using a power source of a welding machine. For example, JP-A-55-36017, JP-A-55-36018
Japanese Patent Application Laid-Open Publication No. H11-15064 proposes a method of performing a post heat treatment in a welding machine using a welding power source.

[0009]

However, the conventional methods have the following problems. First, there is the following problem regarding the method of suppressing inclusions at the interface.

Japanese Patent Application Laid-Open No. 49-96947 is relatively effective in suppressing inclusions, but the effect of suppressing quenching of a welded portion by combustion of a gas containing a reducing gas alone is small, and the quality of the welded portion is low. Can often not be improved. JP-A-56-5
No. 0789 has a problem that the cost is increased due to the modification and operation of the equipment due to hermeticity, and the maintenance work around the butted portion which requires fine adjustment by attaching these equipment to the welding machine is hindered. JP-A-59-
The methods disclosed in JP-A-118282, JP-A-62-275581, and JP-A-63-203281 increase the number of steps of applying grease or the like to a steel sheet, resulting in a decrease in efficiency and equipment cost. Cause an increase.

When these methods are used, grease adheres and remains on a welding machine or the like, so that spatter or the like easily adheres. When the spatter adheres to the electrode surface, the contact between the electrode and the steel plate becomes localized, and a welding defect such as diburn is generated. Further, if spatter falls onto the steel sheet during the passing of the steel sheet, the surface of the steel sheet is damaged, so that complicated cleaning for removing grease or the like must be performed.

Further, there are the following problems regarding the pre-heat treatment and the post-heat treatment of the welded portion. In the pre-heat treatment method of electrically heating the material to be welded by repeatedly contacting and separating the material to be welded before the flashing process, the contact and separation are repeatedly performed while applying a voltage, so that it is difficult to control the temperature and the stable heat treatment is performed. Heat treatment cannot be performed. Also, Japanese Patent Laid-Open No. 55-36
No. 017, JP-A-55-36018, the post-heat treatment method only controls the voltage on the primary side while clamping the welded portion with the electrode. However, heat generation cannot be accurately controlled.

Furthermore, in the case of a steel sheet, the electrode is wider than the steel sheet and the current-carrying point extends over the entire width of the steel sheet in the above-described electric heating, so that the temperature at both ends of the steel sheet is significantly higher than that in the center. There is. This is due to the effect of heat conduction such as heat reflection on the current path and the end of the steel plate,
In the above-mentioned method, it is not possible to suppress the high temperature of both ends of the steel sheet, and there is a problem that a difference occurs in the structure and strength of the welded portion between the end and the inside.

In order to solve such a problem, Japanese Unexamined Patent Publication No. Hei 8-118034 discloses that in order to solve such a problem, only the output electrode is unclamped after flash butt welding, and a metal plate having a width smaller than that of the steel plate is connected to the output electrode. A method has been proposed in which a temperature distribution in the width direction of a steel sheet is made uniform by inserting a current between the steel sheets to conduct electricity. However, this method requires a device for inserting a metal plate, which not only complicates the equipment, but also deteriorates the metal plate during continuous use and deteriorates the electrical conductivity. Have.

An object of the present invention is to provide a flash butt welding apparatus and a welding method capable of suppressing the hardening of a welded portion and improving the quality of the welded portion in consideration of the above problems.

[0016]

The gist of the present invention for solving the above problems is as follows.

(1) In a flash butt welding apparatus having a gas discharge port for supplying a flammable gas above and below a portion to be welded of a material to be subjected to flash butt welding by butt welding, the flammable gas supplied to the gas discharge port is provided. A flash butt welding apparatus characterized in that a supply system for a flammable gas is provided with means for adjusting the type and flow rate of a flammable gas.

(2) In the above (1), a plurality of gas discharge ports for flammable gas are divided in the width direction of the material to be welded, and a plurality of gas discharge ports are provided in the supply system for the flammable gas. A flash butt welding apparatus, comprising: means for controlling a flow rate of a combustible gas supplied to a port and a heat input.

(3) When performing the flash butt welding with the materials to be welded against each other, in the process from the end of the clamping of the material to the end of the upset or the end of the post-heat treatment, the flammability near the joint of the material to be welded is determined. A flash butt welding method, wherein a gas is burned to shield a portion to be welded from atmospheric oxygen and perform a post-heat treatment or a pre-heat treatment after completion of clamping.

(4) The flash butt welding method according to the above (3), wherein when combustible gas is burned, the kind and flow rate of the combustible gas supplied in each step are adjusted.

(5) In the above (3) or (4), in the post heat treatment after the flash butt welding, in addition to the combustion of the combustible gas, the welding section is directly energized by using a welding power source. And flash butt welding method.

(6) In the above (3) to (5), a plurality of gas discharge ports for supplying a combustible gas are arranged in the width direction of the material to be welded, and the width of the material to be welded is changed according to the width of the material to be welded. A flash butt welding method comprising controlling a flow rate of a combustible gas supplied to a gas discharge port in a direction.

According to the present invention, the gas is burned in the vicinity of the welded portion during, after, or before welding, thereby isolating the welded portion from oxygen in the atmosphere and reducing the temperature of the steel sheet in the vicinity of the welded portion. It is possible to suppress the hardening of the welded part by raising the upset amount easily by raising it, and also by performing the post-heat treatment of the welded part efficiently and appropriately using the combustion gas, thereby suppressing the hardening of the welded part. And the quality of the welded portion can be remarkably improved. Alternatively, the pre-heat treatment temperature can be optimized by efficiently and appropriately performing the pre-heat treatment of the welded portion using the combustion gas before welding, so that the above-described effect can be further improved.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

FIG. 1 is a view showing a cross section of a main part of a clamp die assembly at the time of clamping a steel plate in a flash butt welding apparatus according to an embodiment of the present invention. FIG. 2 is a view showing a clamp die and gas supply in the apparatus of FIG. It is a figure showing an example of a connection state of a device. 1 and 2, 1 is a clamp die, 2 is a gas discharge port (gas discharge port), 3 is an electrode, 4 is a steel plate, 5a and 5b are shielding valves, 6 is a flammable gas flow control valve, and 7 is air. Reference numeral 8 denotes a combustible gas supply pipe, and reference numeral 9 denotes an air supply pipe.

In the present apparatus, a plurality of gas discharge ports 2 are provided in the width direction of the steel sheet on the welding portion side of the clamp die 1. The flammable gas supplied from the flammable gas supply pipe 8 and the combustion air supplied from the air supply pipe 9 are used to adjust the flammable gas flow rate based on a command from a flash butt welding machine controller (not shown). The mixed gas is adjusted to a predetermined flow rate by the valve 6 and the air flow adjusting valve 7 and mixed. The mixed gas is sent to the gas discharge ports 2 arranged in the width direction of the steel sheet through the air-fuel mixture pipe 11 and the branch pipe 12, The fuel is injected from the gas outlet 2 and burned.

In addition, based on a command from a control device of a flash butt welding machine (not shown), the control valve is provided to each of the air-fuel mixture pipes 11 in accordance with the width of the steel strip and to the shielding valve 5a and each of the branch pipes 12. By opening and closing the provided shielding valve 5b, the injection width of the mixed gas injected from the gas discharge port 2, that is, the combustion width can be adjusted.

Further, based on a command from a control device of a flash butt welding machine (not shown), a flammable gas flow rate and a combustion air flow rate when the steel plate 4 is preheated in the vicinity of the joint after the steel plate 4 is clamped, and a flash process, The flammable gas flow rate and the combustion air flow rate in the upset process, and the flammable gas flow rate and the combustion air flow rate in the subsequent post heat treatment can be individually controlled.

After the steel plate 4 is clamped by the upper and lower electrodes 3 and 3 at a predetermined initial interval (d) using the present apparatus, a voltage is applied between the upper and lower electrodes 3 and 3 and the ends of the steel strip are butted. Welding is performed through a flash process and an upset process, and a post heat treatment is performed. If necessary, a pre-heat treatment is performed after the clamping and before the flash process. In each of the above steps, the supply and combustion of the combustible gas are performed as follows.

In the flash process, a combustible gas is burned near the butt weld to form a reducing atmosphere around the weld. As a result, inclusions that become cracks such as oxides remaining at the bonding interface are reduced. Further, the heat input to the steel sheet during gas combustion can be used to raise the temperature of the steel sheet near the joining interface, thereby increasing the upset amount in the upset process. As a result, the bonding interface expands, the density of inclusions is further reduced, and defects serving as crack starting points are greatly reduced.

Further, after the upset process, the combustible gas is burned to perform post-heat treatment near the weld interface, to suppress hardening and toughness deterioration near the weld interface, and to reduce the notch sensitivity, thereby reducing the notch sensitivity. Even if expanded to some extent, they will not be connected to each other and eventually lead to a large crack. As described above, the effect of improving the mechanical properties of the welded portion by the method combining the shielding with the combustion gas and the heat treatment has a remarkably large effect as compared with the case where these are not used.

Here, there are several methods for heat treatment of the welded portion.
Can be classified. Broadly speaking, one is aus
Tenite transformation point (A_ThreeAnnealing)
The other method is 200 ° C or higher A₁Below the transformation point
This is a tempering treatment performed at a temperature of. In both these methods,
Each has advantages and disadvantages. High temperature in annealing
After holding for a fixed period of time, it is necessary to
Yes, long cooling time to keep final tissue hardness low
Need. In the case of tempering, the unstable phase
Decomposition of rutensite into ferrite and carbide
Although the hardness of the weld is reduced, the cooling rate after heating is
There is no need to manage. Also, the processing temperature is A ₁Below the transformation point
Since the annealing is performed, the annealing can be performed at a lower temperature.

However, depending on the component system, the tempering treatment may not be sufficient or it may take a long time, and it is preferable that the processing method can be freely selected depending on the component system. For example, the power supply capacity required for the flash process is smaller than that required for heat treatment by direct energization, and when the board thickness is large or the board width is large, the capacity may be insufficient,
As described above, there is a case where a difference occurs in the temperature distribution in the width direction of the sheet, so that an appropriate heat treatment cannot be performed.

According to the present invention, the temperature and time of the post heat treatment can be freely selected. In addition, by combining the direct energization using a welding power source and the heat treatment by gas combustion, efficient and stable heat treatment is possible.

In the present invention, the pre-heat treatment of the welded portion is performed by using the combustion gas before the flashing process, so that the temperature of the pre-heat treatment can be optimized, so that the above effect can be further improved.

In the present invention, by controlling the type and flow rate of the combustion gas in each step, a gas containing a reducing gas is supplied in the flashing process to the upsetting process to shield the bonding interface, and the pre-heat treatment and post-heating are performed. During the heat treatment, a gas having a high combustion efficiency is supplied, and the heat treatment can be performed efficiently in a short time.

In the flashing process to the upsetting process, the combustible gas must be continuously burned in order to enhance the shielding effect. However, in the pre-heat treatment or the post-heat treatment, if the required heating can be performed, it is intermittent. May burn.

In the present invention, the combustion gas discharge port is divided in the plate width direction to adjust the flow rate of the combustion gas and to control the amount of heat input, so that the heating by gas combustion is performed only at the central portion of the steel plate and the temperature at the edge portion is reduced. Since the difference can be corrected, a more appropriate heat treatment can be performed by making the temperature distribution in the plate width direction uniform.

The method described above does not need to be performed in all cases, and may be applied as needed.

[0040]

EXAMPLES In weight%, C: 0.08%, Si: 1.5
%, Mn: Sheet thickness 5.0m containing 1.7% as a main component
A welding test was performed on a carbon steel hot-rolled steel sheet having a thickness of 1600 mm and a width of 1600 mm and a tensile strength of 800 MPa using the flash butt welding apparatus shown in FIGS. 1 and 2. The gas discharge ports have a diameter of 3 mm and are arranged at a pitch of 30 mm in the plate width direction.

At the time of the welding test, a test is performed for the case where the combustible gas specified in the present invention is burned or not burned in each of the pre-heat treatment, the flash process to the upset process, and the post-heat treatment. The test was also performed with and without direct energization. In this example, the flammable gas is burned using all the gas discharge ports for the pre-heat treatment, the flash process to the upset process, and the flammable gas is burned within 50 mm from both ends of the steel plate for the post-heat treatment. Burned gas.

The welding conditions were set to the optimum conditions when each processing method was applied. Based on the crack length ratio of the welded portion in the bending test and the time required for welding (required welding time), the performance of the welded portion and the welding time were determined. The efficiency was evaluated. Propane was used as the combustion gas, and only propane was used during shielding, and air that was 20 times as much as propane was mixed during the heat treatment and burned.

Regarding the bending test, 30 test pieces having a width of 50 mm were taken out from the welded portion having a width of 1600 mm, and a 180 ° bending test was performed with a 6R punch. The length of a crack generated in the weld after the test was measured. The ratio of the length to the total length of the welded portion is calculated as the crack length ratio (%, crack length (mm) /
50 × 100). From the empirical knowledge so far, if the crack length is 10% or less, no break occurs during line passing, so that 10% or less was judged to be a good weld. The time required for welding was defined as the time from the start of clamping to the end of the welding process (including heat treatment).

Table 1 summarizes the welding test conditions, the required welding time, and the performance of the welded parts. In Table 1, "presence / absence" of the pre-heat treatment is defined as the presence / absence of the pre-heat treatment by combustible gas combustion defined in the present invention, and "presence / absence" of the gas shield is defined in the present invention in a flash process to an upset process. The presence or absence of a seal due to a reducing atmosphere near the joint due to combustible gas combustion is shown.

[0045]

[Table 1]

When the gas shield is not performed, and when the gas shield is performed and the post-processing is not performed (Comparative Examples 1 to 3),
The crack length ratio is extremely poor. Even if the gas shield is performed, when the post heat treatment is performed by the conventional direct energization (Comparative Example 4), the performance of the welded portion is still insufficient. FIG. 3 shows Comparative Example 4
3 shows the temperature change during the post heat treatment. As shown in this figure, in the conventional post-heat treatment method in which post-heat treatment is performed by direct energization, the temperature rise in the width direction of the steel sheet is not uniform, and the temperature rise in the central portion is insufficient compared with the end portion. The reason why sufficient welded part performance cannot be obtained is due to such uneven heating.

On the other hand, when post-heat treatment is performed by a gas shield and gas heating specified in the present invention (Inventive Examples 1 to 3)
Has good weld performance. FIG. 4 shows a temperature change at the time of the post heat treatment of Invention Example 2. By the gas heating, the temperature rise of the welded portion can be efficiently performed and the entire width of the steel strip can be uniformly heated as compared with the direct energization, and as a result, the performance of the welded portion is excellent.

Further, by simultaneously performing the direct energization and heating by gas combustion, the required time for welding is further reduced (Invention Example 2). Furthermore, the above-mentioned effect can be further improved by performing a pre-heat treatment by gas combustion immediately after clamping (Invention Example 3).

[0049]

As described in detail above, according to the present invention,
Welding that is efficient and has excellent weld performance can be performed even on difficult-to-weld materials.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross section of a main part of a clamp die assembly when a steel plate is clamped in a flash butt welding apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a connection state between a clamp die and a gas supply device in the flash butt welding apparatus according to the embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a temperature distribution in a width direction and an energizing time during a post heat treatment according to a conventional method.

FIG. 4 is a diagram showing the relationship between the temperature distribution in the width direction and the energization time during the post heat treatment according to the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Clamp die 2 Gas discharge port (gas discharge port) 3 Electrode 4 Steel plate 5a, 5b Shut-off valve 6 Flammable gas flow control valve 7 Air flow control valve 8 Flammable gas supply pipe 9 Air supply pipe 11 Mixture pipe 12 Branch pipe

Continuing from the front page (72) Inventor Kiyofumi Shibuya 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Yasutoshi Nakayama 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Stock In company

Claims (6)

[Claims] 1. A flash butt welding apparatus having a gas discharge port for supplying a flammable gas above and below a portion to be welded of a material to be subjected to flash butt welding by butt welding, wherein a flammable gas supplied to the gas discharge port is provided. A flash butt welding apparatus comprising a gas supply system having means for adjusting the type and flow rate of combustible gas. 2. A flammable gas gas discharge port is divided into a plurality of pieces in the width direction of the material to be welded, and a plurality of flammable gas supply ports are provided to a gas discharge port in the width direction of the material to be welded to a flammable gas supply system. The flash butt welding apparatus according to claim 1, further comprising means for controlling a flow rate and a heat input. 3. When performing the flash butt welding by abutting the materials to be welded, in the process from the end of the clamping of the material to the end of the upset or the end of the post heat treatment, a flammable gas is present in the vicinity of the joint of the materials to be welded. A flash butt welding method characterized in that a portion to be welded is shielded from atmospheric oxygen and post-heat-treated, or pre-heat treatment is performed after clamping is completed, by burning the material. 4. The flash butt welding method according to claim 3, wherein when burning the combustible gas, the kind and flow rate of the combustible gas supplied in each step are adjusted. 5. The post-heat treatment after the flash butt welding, wherein in addition to the burning of the combustible gas, a current is directly supplied to the welded portion by using a welding power source. Flash butt welding method. 6. A plurality of gas discharge ports for supplying a flammable gas in a width direction of a material to be welded, and a flammable gas to be supplied to the gas discharge port in a width direction of the material to be welded according to the width of the material to be welded. The flash butt welding method according to any one of claims 3 to 5, wherein a flow rate is controlled.