KR100940677B1 - Local Heatsink Welding Torch, Device and Method for Excellent Low Temperature Toughness - Google Patents

Abstract

The present invention includes a welding wire and a protective gas nozzle which is installed on the outer periphery of the welding wire to eject a protective gas, wherein the protective gas nozzle comprises a room temperature protective gas nozzle and a cryogenic protective gas nozzle. A welding apparatus including a welding torch and a welding method for welding a steel sheet by such welding apparatus.

When welding and cooling are performed according to the present invention, the weld can be quenched efficiently and quickly to obtain a weld structure having excellent toughness.

Cryogenic Protection Gas, Welding Wire, Quenching, Welding Torch

Description

Local Heatsink Welding Torch, Device and Method for Excellent Low Temperature Toughness}

The present invention relates to a welding method for forming a welded joint having excellent properties during melt welding of two steels, and more specifically, torch nozzles for spraying a protective gas in a conventional melt welding process are divided back and forth, and the welding progress direction. While maintaining the function of protecting the arc and the molten area by supplying the existing room temperature protection gas at the front end of the, while in the rear end by quenching the cryogenic protection gas, the steel exposed to high temperature immediately after welding to refine the weld structure It relates to a welding method for improving the characteristics.

In general, when two welded steels are melt welded to form a welded joint, the steel is exposed to high temperature for a predetermined time by the welding heat source. In terms of metallography, such high temperature exposed sites tend to coarse grains, and after transformation, phase transformation may occur due to poor toughness, resulting in deterioration of quality characteristics compared to the base metal. Therefore, overcoming the grain coarsening of the weld heat affected zone and improving the weld properties have been one of the major challenges in the steel fabrication and welding processing industry.

Conventionally known as a means to solve this problem, there was a method of suppressing grain growth by reducing the exposure time at high temperature through a low heat input multilayer welding construction. However, this method has the disadvantage of having to weld several times, there is a disadvantage that the productivity is not good. In recent years, efforts have been made to suppress the grain coarsening of the weld heat affected zone to the maximum by means of forming a welded joint using a high density heat source such as a laser or an electron beam and increasing a cooling rate. Expensive equipment is required to apply, and there are many limitations in widespread commercialization.

On the other hand, in this regard, there is known a technique for improving the low temperature toughness of the welded part by rapidly cooling the welded part by spraying the coolant onto the steel to be welded immediately after welding. There is a problem in that hydrogen mixing may occur in the hot welding portion by the cooled cooling water.

In addition, there is also known a technique to prevent welding deformation of thin thin steel by spraying the cryogenic liquid CO ₂ with a predetermined interval behind the preceding arc torch, but due to the gap between the torch and the cooling nozzle is cold-treated immediately after welding Inevitably, they are exposed to high temperature for a certain period of time, and this technique also has the possibility of scattering and explosion of liquid phase without expensive equipment such as high pressure chamber and shielding for liquid CO ₂ injection treatment. There is a concern that there is a problem in terms of worker safety.

Thus, a method of cooling the weld heat affected zone by gas injection instead of liquid has emerged. However, in order to use the gas injection method in the process, a separate cooling nozzle is required, and there is a certain gap between the arc torch (welding heat source) and the cooling nozzle. Due to this, as soon as the welding is made, it is impossible to perform the cold-cooling process, and the problem still remains that the heat affected zone of the welding is inevitably exposed at a high temperature for a certain time.

Therefore, there is a need for a method capable of miniaturizing the structure by cooling the weld heat affected zone stably and quickly without expensive equipment.

In order to solve the above problems, the torch nozzle for spraying the protective gas in the conventional melt welding process is divided back and forth, and the arc and molten paper by supplying the conventional room temperature protective gas at the front end of the welding progress direction. In addition, while maintaining a protective function, at the rear end by spraying a cryogenic protective gas to quench the steel exposed to high temperature immediately after welding to refine the weld structure and improve its characteristics.

The present invention includes a welding wire and a protective gas nozzle which is installed on the outer periphery of the welding wire and sprays a protective gas, wherein the protective gas nozzle comprises a room temperature protective gas nozzle and a cryogenic protective gas nozzle. A welding device comprising a welding torch.

Further, the present invention includes a welding wire and a protective gas nozzle which is installed on the outer periphery of the welding wire to eject a protective gas, wherein the protective gas nozzle comprises a room temperature protective gas nozzle and a cryogenic protective gas nozzle. In the welding method for welding two steel materials using a welding method, a room temperature protection gas injection step of injecting a room temperature protection gas from the room temperature protection gas nozzle, a welding step of performing welding with the welding wire and in the cryogenic protection gas nozzle It relates to a welding method comprising a welding part quenching step of injecting a low temperature protective gas.

Hereinafter, the present invention (water invention) will be described in detail.

The present inventors conducted a thorough examination through literature studies and systematic experiments on the development of a welding method that significantly improves the properties of welded joints, which inevitably deteriorate compared to the base metal, and have completed the present invention.

During welding, the welded joint is rapidly heated by the welding heat source, and the temperature is raised to a maximum of 1450 ℃ or more, and then cooled. At this time, the grains of austenite structure grow vigorously in the high temperature region of 1450 ~ 800 ℃. And coarsened to a size of 200 μm or more. In particular, in the case of C-Mn carbon steels transforming in a solid phase, coarse austenite does not transform into fine ferrite during cooling, but rather, grain boundary ferrite, upper bainite and martensite. ), Resulting in deterioration of properties such as fracture toughness.

Therefore, it is essential to suppress the coarsening of the austenitic grains in order to improve the characteristics of the welding heat affected zone. For this purpose, the present inventors minimize the exposure time in the high temperature region of 1450 to 800 ° C. or more immediately after the coarsening of the grains. As a method of suppressing grain growth, the inventors focused on using a protective gas that generally suppresses chemical reactions in the heat affected zone during welding.

In general, during welding of steel, a filler metal (welding wire) is supplied to the center of the arc torch to generate arcs, which are heat sources of welding, on the surface of the steel, and at the same time protect these arcs. In order to suppress chemical reactions such as oxidation of the weld heat affected zone having high reactivity by heat, a protective gas made of an inert gas is radially sprayed on the outer surface of the arc torch.

Therefore, if the protective gas is cooled to a cryogenic temperature of -50 ℃ or less, the fact that the weld heat affected zone characteristics can be improved through quenching immediately after welding without the need for additional equipment such as shileding and the present invention Came to.

In addition, when the cryogenic protective gas is simply sprayed on the entire welded portion, the quenching effect can be obtained only at the trailing portion (area that is quenched immediately after the arcing point) in the arc welding direction. Rather, after quenching immediately before welding, the welding proceeds, so that a low temperature crack is generated as it is in the weld metal or the heat affected zone of the welding. Therefore, the present inventors inject a protective gas as shown in FIG. 1 to solve this problem. The method of dividing the cooling nozzle into two parts was used.

As shown in FIG. 1, the nozzle is divided, and the front end nozzle ejects a room temperature protective gas which performs only a general protective gas function, and the rear end nozzle ejects a cryogenic protective gas having a cooling function. In the arc and the molten pool to protect only to perform a function, the end of the welding was completed to quench the steel exposed to high temperature immediately after welding. That is, while maintaining the function of the protective gas to protect the arc at the same time it is possible to further refine the physical properties of the portion by miniaturizing the structure of the weld heat affected zone.

The torch used in the welding method of the present invention, when referring to Figure 1, is composed of a welding gas 11 of the center and a protective gas nozzle which is installed on the outer periphery of the welding wire 11 to eject the protective gas. Here, the protective gas nozzle is divided into a room temperature protection gas nozzle 12 for ejecting a protection gas at room temperature and a cryogenic protection gas nozzle 13 for ejecting a cryogenic protection gas.

In this case, the room temperature protection gas nozzle 12 is located in the welding travel direction, that is, the front end of the cooling nozzle, and the low temperature protection gas nozzle 13 is located at the rear end of the cooling nozzle. In addition, when considering the cross-sectional area of the entire nozzle, as shown in Figure 1, the cross-sectional area of the low temperature protection gas nozzle 13 has a cross-sectional area smaller or equal to that of the room temperature protection gas nozzle 12. If the cross-sectional area of the low temperature protection gas nozzle 13 is larger, since the low temperature protection gas is injected to the front end of the welding progress direction, cooling may be performed before welding is performed, which may not be good for weld properties.

Referring to Fig. 2, as the welding proceeds, a torch composed of a welding wire 21 for generating an arc and a cooling nozzle 21 surrounding the welding wire is moved along a portion that requires welding of the steel plate surface. In this case, the welding proceeding direction, that is, the front end of the cooling nozzle, ejects the welding protective gas at room temperature to protect the arc and the melt and allow welding to occur effectively.

On the other hand, in the opposite direction of the welding process, that is, at the rear end of the cooling nozzle, the cryogenic welding protective gas is ejected to perform the function of the welding protective gas and to rapidly cool the welding heat affected zone, thereby miniaturizing the structure of the welding portion. .

In this case, the cryogenic welding protective gas may generally use a protective gas used for welding, and the type is not particularly limited. However, the cryogenic welding protective gas is appropriately ejected to a temperature of -50 ℃ or less. If the temperature exceeds -50 ° C, the rapid quenching effect of the hot welding heat affected zone cannot be provided.

In addition, it is generally preferable to perform welding and cooling while moving the torch at a speed of 30 to 50 cm / min. This is because, if the speed is less than 30 cm / min, the welding speed is too low to reduce productivity, and if the speed exceeds 50 cm / min, cooling is not performed properly.

It is preferable that quenching by this welding method is made to 800 degreeC. It is an area where phase transformation can occur from a temperature below 800 ° C., since it is continuously made even at a temperature after quenching, martensite or upper bainite structure, which is weak in toughness, may be formed, thereby deteriorating physical properties.

When welding and cooling are performed by this process, the structure of the welded portion can be quenched efficiently and quickly to obtain a structure having excellent toughness of the welded portion.

When welding and cooling are performed by the present invention, the welds can be quenched efficiently and quickly to obtain a weld structure of excellent toughness.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings and examples.

The target steel is a thick plate of EH36-TM, and a thickness of 20 mm was used. The experiment was introduced to the concept of the welding method of Figs. 1 and 2 of the present invention, but the heat cycle reproducing test to reproduce the situation that the steel is subjected to heat effect when welding the steel using such a system, without using a direct system Verification was carried out.

The thermal cycle was reproduced over time in vacuum using a small test piece (10 mm in width x 10 mm in length x 55 mm in length). The welding condition was the submerged arc welding method, and the heat input was 30kJ / cm, and the target area was the coarse grain heat affected zone (CGHAZ) near the weakest melting line. The low temperature toughness was examined through the Charpy impact toughness test, and the absorbed energy value obtained by imposing a V notch on the grain coarsening area and applying a hammer impact to the rear surface was selected. The test temperature was tested at four temperatures (0, -20, -40 and -60 ℃) of 0 ~ -60 ℃. The results of the experiment is shown in Table 1 below.

division Conduct number Cooling rate (℃ / s) CGHAZ Microstructure Charpy impact toughness test results 1450 ~ 800 ℃ 800 ~ 20 ℃ Test temperature (℃) Absorbed energy (J)    Foot honor One      120      10    Fine Acicular ferrite + Bainite  0278 278 2 212 3 225 4  -20 242 5 195 6 185 7  -40 121 8 59 9 82 10  -60 33 11 9 12 15    Comparative Example 13      30      7.6    Coarse grain boundary ferrite + upper bainite  0 67 14 146 15 189 16  -20 91 17 51 18 83 19  -40 20 20 10 21 17 22  -60 18 23 15 24 7

As shown in Table 1, when the quenching method of dividing the protective gas according to the present invention is applied (Examples 1 to 12), CGHAZ showed a fine Acicular ferrite and bainite structure, even in a low temperature region of -40 ℃ The Charpy impact toughness value was found to be quite excellent characteristics about 87J on average.

On the other hand, in the conventional welding process without applying the protection gas split quenching method (Comparative Examples 13-24), CGHAZ is a weak upper part with coarse grain boundary ferrite and large amount of martensite precipitated at the lath interface in the mouth. It can be seen that it consists of bainite tissue. The Charpy impact toughness value was only about 16J at -40 ° C due to these metallographic factors, and all of them showed a lower value than the impact toughness value of the present invention over the test temperature.

In addition, in the conventional process, the exposure time of the high temperature region of 1450 to 800 ° C., which is the highest temperature, was long as about 22 seconds (cooling rate 30 ° C./sec). It can be seen that it can be considerably shortened (within ℃ / sec).

Figure 3 shows the result of comparing the microstructure of the representative weld heat affected zone according to the application of the present invention. In FIG. 3 (a), which is the result of welding according to the present invention, cooling was performed at the maximum temperature immediately after welding, and remarkably fine grains, that is, fine Acicular ferrite and bainite structure were realized. On the other hand, looking at Figure 3 (b) by the existing process, it can be seen that the microstructure of the weld heat affected zone is a mixture of coarse grain boundary ferrite and a weak upper bainite structure.

The above results explain well the configuration and the reason for the limitation of the present invention, and show that the welded joint having excellent characteristics can be formed by the welding method of the present invention.

1 is a cross-sectional view of a welding torch designed for protection gas division according to the present invention.

2 is a schematic view showing a welding step according to the present invention.

Figure 3 is a photograph of the specimen comparing the microstructure of the weld heat affected zone according to the embodiment and comparative example of the present invention

● Explanation of symbols for main parts of drawing

11: welding wire

12: room temperature protection gas nozzle

13: cryogenic protective gas nozzle

14: protective gas nozzle dividing boundary

21: room temperature protection gas

22: low temperature protection gas

23: welding plate

Claims (7)

delete delete delete delete A welding gas and a protective gas nozzle installed at an outer circumference of the welding wire to eject a protective gas, wherein the protective gas nozzle comprises a normal temperature protective gas nozzle and a cryogenic protective gas nozzle. A room temperature protection gas injection step of injecting a room temperature protection gas from the room temperature protection gas nozzle; A welding step of performing welding with the welding wire; And A welding part quenching step of injecting a low temperature protective gas from the cryogenic protective gas nozzle, The temperature of the low temperature protective gas injected from the cryogenic protective gas nozzle is -50 ℃ or less. The method according to claim 5, And a time interval between the welding step and the welding part quenching step is within 5 seconds. delete

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