JPH01224169A - Method for removing oxide of flash butt welding method - Google Patents

Abstract

PURPOSE:To effectively remove an oxide produced at the time of welding by setting the flash voltage specifically and further, holding applied current density between steels in the specific range and in addition, limiting the upset force. CONSTITUTION:The process to impress the flash voltage between the steels is divided into the preceding period and the latter period and the preceding period and the latter period are limited in the ranges of 7.5-11.0V and 4.0-6.0V respectively and further, the applied current density between the steels in the upset process is held in the range of 1-20A/mm<2> and in addition, the upset force is limited in the range of 2-6kg f/mm<2>. By this method, the oxide produced on the joining surface at the time of performing flash butt welding is fined and dispersed uniformly and can be removed effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for removing oxides in flash butt welding, and more specifically, for removing saponified substances and the like that are generated in welds or joints during flash butt welding. Furthermore, it effectively removes these oxides by applying an extremely high upsetting force, especially for large diameter steel pipes, rails, etc.
Tensile strength 50kgf/ for high tension chains, thick plates, etc.
This invention relates to a method for removing oxides from welds and joints that allow flash butt welding, which produces welds with excellent tensile strength, bending properties, etc., of steel materials of Grade 2 or higher.

Conventional technology In general, butt welding is used for welding thin materials such as M-class steel pipes and small diameter steel pipes. On the other hand, so-called thick materials such as large diameter steel pipes, thick plates, rails, high tension chains, etc.
Due to the lack of passion for butt welding, flash
Butt welding is used. The flash butt welding method consists of a flash process and an upset process. In the flash process, a flash is generated between a pair of steel materials to melt the joint surface of the steel materials, and in the subsequent upset process, this steel material is melted. Steel materials are joined together under pressure by bringing their joining surfaces into close contact with each other. However, in the flash butt welding method, the austenite grains in the welded area or joint area become coarse due to the high temperature heating during welding. When the surfaces are melted, oxidation tends to occur (this oxide remains in the joint even during the upsetting process, which has the disadvantage of impairing the properties and strength of the resulting weld).

To explain in more detail, flash butt welding allows for high efficiency welding by increasing the penetration depth under a large current, and for this reason, it is possible to weld stably even with thick steel materials with a large joint surface area. For this reason, it is widely used for welding rails, high-tension chains, large-diameter steel pipes, etc. However, the joints obtained by flash butt welding cannot be tested in tensile tests. However, when a bending test is performed, it has the disadvantage that it breaks at the joint.If we examine the causes of this, we can point to the following two reasons.

(1) In the flash process, in particular, thickening the penetration with a large current (this promotes the formation of oxides on the joint surface, and this oxide remains during the upset process, causing oxides to form in the joint or weld. (2) Mild heat during flash butt welding causes austenite grains in the joint to coarsen, impairing the properties and strength of the weld. For some time, it has been proposed to improve the quality of welded parts by flash butt welding, as shown in Japanese Patent Laid-Open No. 60-96378.

In this flash butt welding method, the flash process is divided into the first and second stages. In the first stage, the material to be welded is heated to a predetermined temperature determined by the material to be welded. In the second stage, the flash voltage is lowered from the flash voltage of the first stage to cover the entire joint surface. Generates a stable and fine flash over an extended period of time. In addition, in the upsetting process of the bond, the power supply to the steel material is stopped, and in this state, an upsetting force slightly larger than the deformation resistance near the recrystallization temperature is applied to the steel material to press the molten joint surface.

However, this flash butt welding method uses even thin materials such as thin plates as materials to be welded, and the upset force is, for example, 5 to 7 k (1/CI'
If the force is increased to a certain degree, buckling will occur during butt, so the upset force is less than 5 to 7 klJ/CI2 (only a very low force is applied, and for this reason, the oxide remaining in the joint during the upset process is is finely dispersed and cannot be removed.
It has the disadvantage that it breaks at the joint during tensile and bending tests. In short, although the flash butt welding method has disadvantageous effects due to oxides present in the weld, no effective means to overcome this problem has yet been developed.

Problems to be Solved by the Invention The present invention aims to solve the above-mentioned drawbacks, and specifically, it provides large diameter steel pipes, rails, and rails suitable for flash butt welding.
This paper proposes a method for improving the properties and mechanical properties of welded parts by refining, dispersing, and removing intervening oxides during welding of high-tension chains and the like.

Means for Solving the Problems and Their Effects First, the method of the present invention involves a flash process in which a flash is generated between a pair of steel materials to melt the joining surfaces of these steel materials, and then, in the subsequent upsetting process, the steel materials are fused and joined. This is a flash butt welding method in which surfaces are brought close together and pressure-welded, and moreover, during this welding, oxides present in the weld between steel materials are effectively removed.

In addition, in the method of the present invention, the flash step is divided into an early stage and a latter stage, and preferably, the former stage and the latter stage are divided at a ratio of 1:1 or close to that, and the flash voltage at this time is set to 1:1 in the early stage.
．． 5-11.0v% In addition to setting it at 4.0-6.0V in the chronic phase, an upsetting force of 2-6kgf/III' is applied during the upsetting process, and a current is passed between the steel materials to increase the current density to 1-6.0V. Keep in the range of 20A/llI2. Therefore,
Oxides present in the weld zone are finely dispersed and can be effectively removed.

Therefore, the configuration of these means and their functions will be specifically explained as follows.

First, the flashing process is divided into an early stage and a latter stage. Preferably, the first stage and the latter stage are divided, for example, at a ratio of 1:1 or close to that, and a predetermined flash voltage is applied to each in the winter season, and the flashing process is performed between the joint surfaces of the steel materials. Generates flash and melts.

That is, the flash voltage in the first period is applied, as is the usual method, for the purpose of melting the entire butt joint surface of the steel material of the workpiece. In this case, if it is less than 7.5V, not only will the entire surface be melted, but the melting speed will not be able to keep up with the approaching speed of the steel material to be welded, and freezing will occur. Also, the flash voltage is 11. If it is larger than OV, the electric energy will be excessive, flash will be generated excessively, extremely uneven parts will be generated on the joint surface of the welded materials, and oxides remaining on the uneven parts of the joint surface will be generated. remains even after the upsetting process, adversely affecting the mechanical properties of the resulting joint.

In addition, in the latter half, the flash voltage is lowered from the flash voltage in the first half to 4.0 to 6. Set within the range of Ov. The reason for this is that the unevenness of the bonding surface caused in the flashing process in the first stage is smoothed out in the latter stage, so that oxides can be smoothly discharged in the upsetting process. To explain in more detail, even if the flash voltage is maintained within the above-mentioned appropriate range in the first stage, as long as the entire joint surface is melted, uneven parts will inevitably be generated, although there are differences in degree.
If these uneven portions remain as they are, oxides often stick to and remain in the recessed portions. For this purpose, in the latter stage, the occurrence of flash is adjusted, the unevenness that occurred in the first stage is smoothed, and the oxide is attached to the smoothed joint surface, and a predetermined upsetting force is applied in the upsetting process described later. In addition, it allows oxides to be excreted. For this reason, the flash voltage in the second half was lowered from the first half to 4.0 to 6.
．． Make it an OV. In other words, the flash voltage in the latter half is 6
．． If it is higher than Ov, the uneven portion will remain until the upset, and 4. Below OV, the melting rate becomes less than the platen movement rate and freezing occurs.

Next, after passing through the flashing process as described above, in the upsetting process, a large upsetting force of, for example, 2 to 6 klJf/-2 is applied to expel the oxides generated during the flashing process. In addition, in the upset process, current is passed between the steel materials of the workpiece to reduce the current density to 1.
~20 A/-2 to make the oxides generated during the flashing process finer so that they can be easily expelled by the foregoing upsetting force.

In other words, the bonding surfaces of a pair of steel materials and the oxides generated thereon in the flashing process are adjusted as described above, and then,
In the upsetting process, both joining surfaces are butted and joined, and at this time, by applying a large upsetting force,
Remove oxides and obtain welded joints familiar with mechanical properties, etc.

When the upset force is less than 2kQf/kaku2,
The oxides generated on the abutting surfaces are discharged to the outside and remain at the joint, adversely affecting tensile, bending, Charpy, etc.

On the other hand, if it is larger than 6klJr/-2, a cold welded part of the joint surface, that is, a solid phase joint, will be generated, and the resulting welded joint will have welding defects and will not show good results.

Further, the reason why electricity is applied during the upset process is to make the oxide finer and promote the discharge of the oxide.

From this point, the current density must be 1 A/mm2 or more, but if it exceeds 20 A/mm2, the capacity of the welding machine will be affected. (In addition, when the cross-sectional area of the steel butt surfaces is extremely large, the current density is set to be thicker than 10 A/mm2 (then, the capacity of the welding machine l1tf - extremely thick (
I don't like it.

Example First, a high-tensile steel plate (thickness: 18 mm x width: 100 mm x length: 500 mm) having the chemical composition shown in Table 1 was prepared, and flash butt welding was performed using the method of the present invention under the following conditions. Then, it was cooled to room temperature (cooled naturally).

Welding conditions〉 First period Second period Flash voltage 7.5~it, 0(V) 4.0~
6.0 (Vl flash time 50 (seconds) Flash distance 25 (■) Upset force (per unit cross-sectional area of sample) 2 to 6 (k124/I+112)
Upset current density 1.0-20.0 (A/m2)
Next, the residual portion at the welded part was removed using a grinder, and a round rod tensile test piece with a diameter of 10 mm was cut out from the center of the plate thickness and subjected to a tensile test. In addition, the bending test is 18tX12
．． The test was carried out using a side bend specimen of 5WX200j. The results are shown in Table 2.

In Table 2, A to F are those welded by the method of the present invention, while 6 to 6 are welded by the comparative example (i.e., G%
H indicates a high upsetting force, ■ indicates a high flash voltage in the first period, and J indicates a low flash voltage in the first period. ).

As is clear from Table 2, the tensile and bending properties of the welded joints obtained by the method of the present invention are good, but as in Comparative Examples E and G, the upsetting force is 9.0.11,0 kq.
f/a2 value, heat affected zone metal 70 in bending test
In the tensile test, cracks occurred at the joint, and the strength of the joint was lower than that of the base metal. In addition, as in Comparative Example 1, when the flash voltage in the first period is high, there is a large amount of oxide generated, which causes fracture at the joint in the tensile test. Even when the voltage was low, the joints similarly broke due to insufficient penetration of the joint surfaces.

Figure 1 (a) shows an example of the macrostructure of a typical weld cross section when the upsetting force is changed during the upsetting process to perform low upsetting force and high upsetting force.
) and (b). As shown in Fig. 1+11), when the forge force is high, the closer the metal 70- is to the joint, the more rapidly it rises, and no white molten layer is observed at the joint itself. In this method, when a flash voltage is applied between a pair of steel materials to be welded during the flash process, the flash process is divided into an early stage and a latter stage, and the flash voltage for the early stage is set at 7.5 to 11.0 (V), and the flash voltage for the latter stage is set at 7.5 to 11.0 (V). Flash voltage 4.0-6. Furthermore, in the upsetting process, electricity is applied between the steel materials of a pair of workpieces, and the W1 load density at that time is maintained at 1 to 20 (A/2), and in conjunction with this, the upsetting Power 2-6 (ktlf/閤2)
range.

Therefore, the oxides generated on the joint surface during this flash-butt are made fine and uniformly dispersed, and furthermore, these oxides can be effectively removed. Therefore, even when welding large diameter steel pipes, the mechanical properties of the welded portion can be greatly improved. In other words, by performing flash butt welding using the method of the present invention and removing the oxides generated during this process, a welded part of high-strength steel with excellent joint tensile properties and joint bending properties that are the same as the mechanical properties of the base metal can be obtained. 1q can be obtained.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are micrographs showing the cross-sectional structures of welded parts when welding was performed with low upsetting force and high upsetting force.

Claims (1)

[Claims] 1) A flash process in which a flash is generated between a pair of steel materials to melt the joint surfaces of these steel materials, and then in a subsequent upsetting process, the molten joint surfaces of the steel materials are brought close together and pressure-welded. When removing oxides present in the weld between the steel materials using the butt welding method, the flashing process is divided into an early stage and a latter stage, and the flash voltage at this time is 7.5 to 11.0 V in the first stage and 7.5 to 11.0 V in the latter stage. So 4.
In addition to setting it to 0 to 6.0V, 2V is set in the upset process.
Adding upsetting force of ~6kgf/mm^2,
A current is passed between the steel materials at a current density of 1 to 20 A/mm.
A method for removing oxides in a flash butt welding method, which is characterized by maintaining the oxides within a range of ^2.