KR20010056389A - A Method of Flash Butt Welding for High Carbon Steel - Google Patents
A Method of Flash Butt Welding for High Carbon Steel Download PDFInfo
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- KR20010056389A KR20010056389A KR1019990057839A KR19990057839A KR20010056389A KR 20010056389 A KR20010056389 A KR 20010056389A KR 1019990057839 A KR1019990057839 A KR 1019990057839A KR 19990057839 A KR19990057839 A KR 19990057839A KR 20010056389 A KR20010056389 A KR 20010056389A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/04—Flash butt welding
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K11/00—Resistance welding; Severing by resistance heating
- B23K11/24—Electric supply or control circuits therefor
- B23K11/241—Electric supplies
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2103/00—Materials to be soldered, welded or cut
- B23K2103/02—Iron or ferrous alloys
- B23K2103/04—Steel or steel alloys
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Abstract
Description
본 발명은 열연 고탄소강 생산라인의 코일용접 등의 분야에 적용할 수 있는 플래쉬 버트 용접방법에 관한 것이다.The present invention relates to a flash butt welding method that can be applied to fields such as coil welding of hot rolled high carbon steel production lines.
일반적으로 플래쉬 버트(flash butt)용접은 저항용접에 있어서 대표적인 맞대기 압접방법이다. 서로 용접하기 위한 단면을 적절한 속도로 국부적인 접촉부를 발생시킴으로서, 이 접촉부가 높은 전류밀도의 단락전류로 인하여 저항발열하게 된다. 이에 따라, 접촉부는 용융파단되며 아크가 발생하여 그 부근이 가열된다. 이 아크에 의하여 용융된 금속은 비산하게 된다. 이것을 플래쉬라고 하는데, 이 플래쉬가연속적으로 발생하여 용접단면을 가열하게 된다. 이 용접단면이 균일하게 가열된 상태에서 가압하여 접합하게 되는데, 이것은 업셋(upset)과정이라고 한다.In general, flash butt welding is a typical butt welding method for resistance welding. By generating localized contact portions at appropriate speeds in the cross sections for welding with each other, the contact portions generate resistance heat due to the high current density short-circuit current. As a result, the contact portion melts and the arc is generated and the vicinity thereof is heated. The molten metal is scattered by this arc. This is called a flash, and this flash is generated continuously to heat the weld cross section. The weld end face is pressurized in a uniformly heated state, which is called an upset process.
한편, 플래쉬 과정에서 형성된 산화물은 플래쉬와 함께 비산되거나, 업셋과정에서 용융금속과 함께 외부로 방출하게 된다. 따라서, 플래쉬 과정에서 가열된 양쪽 부분이 건전한 용접부를 형성하게 된다. 그러나, 0.45%정도 이상의 탄소를 함유한 고탄소강은 열을 받은 부분 즉, 열영향부가 경도가 높은 취성의 조직으로 변태하여 용접부가 매우 취약하게 되는 문제가 있다. 이와 같은 고경도의 용접부는 파단의 주요 원인으로 작용한다.On the other hand, the oxide formed during the flash is scattered with the flash, or is released to the outside with the molten metal in the upset process. Thus, both parts heated in the flash process form a healthy weld. However, high carbon steel containing about 0.45% or more of carbon has a problem in that the welded part becomes very vulnerable because the heat-affected part, that is, the heat affected part, is transformed into a brittle structure having high hardness. Such high hardness welds act as a major cause of fracture.
이에, 본 발명자들은 상기 용접부가 취약해지는 문제점을 해결하기 위해 연구와 실험을 거듭하고 그 결과에 근거하여 본 발명을 제안하게 된 것으로, 본 발명은 고탄소강의 플래쉬 버트 용접시 플래쉬과정과 업셋과정의 조건을 적절히 제어하고, 용접후 적정조건의 전류에 의해 열처리를 행함으로서, 용접성이 향상되고 건전한 용접부가 형성되는 용접방법을 제공하고자 하는데, 그 목적이 있다.Accordingly, the present inventors have repeatedly conducted research and experiments to solve the problem of weakening the welded part and propose the present invention based on the results, and the present invention provides a flash process and an upset process during the flash welding of high carbon steel. It is an object of the present invention to provide a welding method in which weldability is improved and a healthy welded portion is formed by appropriately controlling the conditions and performing heat treatment by a current of appropriate conditions after welding.
도 1은 열처리전후 굽힘시험결과 나타나는 용접부의 균열비율을 보이는 그래프Figure 1 is a graph showing the crack ratio of the weld portion appearing before and after the heat treatment bending test
도 2는 플래쉬 버트 용접에 의한 용접부의 열처리 전후 경도를 보이는 그래프Figure 2 is a graph showing the hardness before and after heat treatment of the weld portion by flash butt welding
상기 목적을 달성하기 위한 본 발명은 탄소함량이 0.45%이상인 고탄소강으로 구성되는 소재를 맞대어 플래쉬 버트 용접하는 방법에 있어서, 용접에 의해 소멸되는 상기 소재의 전체 길이를 15-20mm로 하고, 1차 플래쉬 시간을 20-25초로 하고, 2차플래쉬에 의한 이동거리를 5-8mm로 하고, 업셋에 의한 이동거리를 3-5mm로 하여 용접을 행한 다음, 용접부에 2500-3000A의 전류를 6초이상 통전시키는 것을 특징으로 하는 고탄소강의 플래쉬 버트 용접방법에 관한 것이다.In order to achieve the above object, the present invention provides a method for butt welding a material composed of high carbon steel having a carbon content of 0.45% or more, wherein the total length of the material to be extinguished by welding is 15-20 mm, and The welding time is 20-25 seconds, the travel distance by the secondary flash is 5-8mm, the travel distance by the upset is 3-5mm, and the welding is made with a current of 2500-3000A for 6 seconds or more. It relates to a high carbon steel flash butt welding method characterized in that the current.
이하, 본 발명을 상세히 설명하는데, 먼저 플래쉬와 업셋에 의한 용접조건을 설명한 다음, 이어서 열처리 조건에 대하여 설명한다.Hereinafter, the present invention will be described in detail. First, welding conditions by flash and upset will be described, and then heat treatment conditions will be described.
일반적으로, 플래쉬 버트 용접에 있어서 산화물 형성을 억제하고 완전한 용접부를 얻기 위해서는 플래쉬 과정에서 용접단면의 가열정도가 균일하여야 하며, 업셋 압력 또는 거리도 적절하게 적용하여야 한다. 플래쉬와 업셋에 의하여 용접모재가 용융소멸되는 거리를 언클램프(unclamp)거리라고 한다. 플래쉬 과정은 1,2차로 구분하여 1차 플래쉬 과정에서 미세한 플래쉬를 발생시켜 용융층을 균일하게 할 필요가 있으며, 2차 플래쉬 과정은 가속도에 의한 업셋 이전단계가 된다.In general, in the flash butt welding, in order to suppress oxide formation and obtain a complete weld, the heating degree of the welding section must be uniform during the flash process, and an upset pressure or distance should be appropriately applied. The distance that the weld base material melts away by flash and upset is called the unclamp distance. The flash process needs to be divided into 1st and 2nd stages to generate a fine flash in the 1st flash process to make the molten layer uniform, and the 2nd flash process becomes the step before the upset by the acceleration.
한편, 업셋시 빠른 속도로 가압하여야 한다. 그렇지 않으면 용접단면에 산화물이 형성하여 문제가 된다. 플래쉬 직후 가압시 산화물 형성을 억제하기 위하여 초기 업셋은 2차 플래쉬과정과 같은 가속도로 실시하며, 최종적으로 높은 전류와 함께 순간적으로 가압하게 된다.On the other hand, it must be pressurized at high speed during upset. Otherwise, oxides are formed on the welded end face, which is a problem. In order to suppress oxide formation during pressurization immediately after the flash, the initial upset is carried out at the same acceleration as the secondary flash process and finally pressurized instantaneously with high current.
본 발명에서는 용접에 의해 소멸되는 소재의 전체 길이 즉 언클램프의 거리가 15-20mm인 것이 바람직하다.In the present invention, the total length of the material disappeared by welding, that is, the distance between the unclamps is preferably 15-20 mm.
상기 언클램프의 거리가 15mm미만인 경우는 가열되어 소멸되는 양이 적으므로 충분한 가압변형이 되지 못하고 냉접과 같은 결과를 초래하게 되는 문제가 있고, 그 거리가 20mm를 초과하는 경우는 많은 양이 소멸되어야 하지만 가압시 가열/용융된 부분이 완전히 배출되지 못하여 용접부에 용융금속이 잔존하여 결함을 유발할 가능성이 매우 높기 때문이다.If the unclamp distance is less than 15mm, the amount of heat dissipation is small, so there is a problem that it is not sufficiently pressurized and results in cold welding. If the distance exceeds 20mm, a large amount must be dissipated. However, when pressurized, the heated / melted part is not completely discharged, and there is a high possibility of causing a defect due to molten metal remaining in the welded part.
또한, 본 발명에서는 1차 플래쉬 시간을 20-25초로 하는 것이 바람직하다.In the present invention, it is preferable to set the primary flash time to 20-25 seconds.
상기 1차 플래쉬는 용융층을 균일하게 행하는 것으로, 그 시간이 20초 미만인 경우는 충분히 가열되지 않고, 25초를 초과하는 경우는 가열영역이 너무 커서 가열되고 밀린 후 남는 부분이 용접부 결함으로 작용하기 때문에 20-25초로 한다.The primary flash is a uniformly molten layer. If the time is less than 20 seconds, the primary flash is not sufficiently heated. If it is more than 25 seconds, the heating zone is too large to be heated and pushed to act as a weld defect. Therefore, 20-25 seconds.
또한, 본 발명에서는 2차 플래쉬에 의한 이동거리가 5-8mm인 것이 바람직하다.In the present invention, it is preferable that the moving distance by the secondary flash is 5-8 mm.
상기 2차 플래쉬는 가속도에 의해 행해지는 과정으로서, 그 이동거리가 5mm미만이거나 8mm를 초과하는 경우는 가열된 영역에 알맞는 이동이 행해지지 않는 것이다.The secondary flash is a process performed by acceleration, and when the moving distance is less than 5 mm or more than 8 mm, the movement appropriate to the heated area is not performed.
또한, 본 발명에서는 업셋에 의한 이동거리가 3-5mm인 것이 바람직하다.In addition, in the present invention, it is preferable that the moving distance by the upset is 3-5 mm.
상기 업셋은 빠른 속도로 가압하는 것으로, 가압시 산화물 형성을 억제하기 위하여 초기 업셋은 가속도로 실시하며, 최종적으로 높은 전류와 함께 가압하게 된다. 이때, 업셋은 3-5mm의 이동거리로 행하는 것이 바람직하며, 초기 업셋은 1-2mm, 이후는 2-3mm가 바람직하다.The upset is pressurized at a high speed. In order to suppress the formation of oxide during the pressurization, the initial upset is accelerated and finally pressurized with a high current. At this time, the upset is preferably carried out with a moving distance of 3-5mm, the initial upset is preferably 1-2mm, after 2-3mm is preferred.
일반적으로, 고탄소강의 경우는 열영향부의 취약성으로 인한 판파단으로, 조업에 많은 지장을 초래하고 있다. 예를 들면, 탄소함량이 0.45%이상인 고탄소강을 열간압연하고 표면의 산화물을 제거한 후 피막을 입히는 공정에서, 연속작업을 위하여 플래쉬 버트 용접을 실시하는데, 이 경우에도 열영향부가 취약하다는 문제가 있다. 이에, 본 발명에서는 용접후 열처리를 행하여 이같은 열영향부의 취약성을 저감시키는 것이다.In general, high carbon steel is a breakage due to the fragility of the heat affected zone, causing a lot of trouble in the operation. For example, in the process of hot rolling high carbon steel having a carbon content of 0.45% or more, removing oxides from the surface, and coating the film, flash butt welding is performed for continuous operation. . Therefore, in the present invention, the heat treatment after welding is to reduce the fragility of such a heat affected zone.
본 발명에서는 용접과정에서 업셋이 완료된후 언클램핑(unclamping)하고 다시 클램핑(clamping)하여 2500-3000A의 전류를 6초이상 통전시킨다.In the present invention, after the upset is completed in the welding process, it is unclamped (clamped) and clamped again (clamping) to energize the current of 2500-3000A for 6 seconds or more.
상기 전류가 2500A미만이면 열처리온도에 달하지 못하는 문제가 있고, 3000A를 초과하면 너무 고온이 되어 열화되는 문제가 있기 때문에, 2500-3000A의 범위로 행하는 것이 바람직하다.If the current is less than 2500A, there is a problem that the heat treatment temperature cannot be reached. If the current is more than 3000A, there is a problem that the temperature becomes too high and deteriorates. Therefore, the current is preferably in the range of 2500-3000A.
상기 전류는 6초이상 통전시키는 것이 바람직한데, 6초미만인 경우에는 열처리효과가 미미하여 연성이 충분히 회복되기 어렵기 때문이다.The current is preferably energized for 6 seconds or more, because in the case of less than 6 seconds, the heat treatment effect is insignificant and the ductility cannot be sufficiently recovered.
이하, 실시예를 통하여 본 발명을 보다 상세히 설명한다.Hereinafter, the present invention will be described in more detail with reference to Examples.
실시예 1Example 1
탄소 함량이 0.46%인 고탄소강을 하기 표1과 같은 용접조건으로 각각 2개의 플래쉬버트용접을 행하여, 용접조건별로 2개씩의 시험편을 준비하였다.High-carbon steels with a carbon content of 0.46% were subjected to two flash-butt welding, respectively, under welding conditions as shown in Table 1 below, to prepare two test specimens for each welding condition.
상기 표2의 조건에 의한 용접실시 후, 얻어진 시험편 중에서 1개씩은 2700A의 전류를 10초씩 통전하여 열처리를 행하고, 나머지 1개는 열처리를 행하지 않았다. 얻어진 시험편에 대한 용접부의 건전성 및 성형성 평가를 위하여 굽힘시험을 실시하였으며, 그 결과 용접부에 발생한 균열의 길이를 굽힘시험편 폭에 대한 비율을 측정하여 그 결과를 도 1에 나타내었다.After welding under the conditions of Table 2, one of the obtained test pieces was subjected to heat treatment by applying a current of 2700 A for 10 seconds, and the other one was not subjected to heat treatment. A bending test was conducted to evaluate the integrity and formability of the welded part of the obtained test piece. As a result, the length of the crack generated in the welded part was measured by a ratio to the width of the bend test piece, and the result is shown in FIG. 1.
도 1에서 알 수 있는 바와 같이, 열처리를 행하지 않은 시험편들은 모두 용접부에 존재하는 산화물에 의한 파단 뿐만아니라 열영향부의 경화성으로 용접후 굽힘시험결과 100% 파단이 일어났으나, 열처리를 행한 경우에는 연성이 회복되어 그러한 파단은 없었으나, 다만 용접조건이 본 발명의 범위를 벗어난 경우(비교예 1,2,4,5)는 용접부의 산화물에 의한 균열을 일으키고 있었다.As can be seen in Figure 1, all the test pieces that were not subjected to heat treatment were not only broken by the oxides present in the weld, but also 100% of the fracture test results after welding due to the hardenability of the heat affected zone. This recovery did not cause such breakage, but only when the welding conditions were outside the scope of the present invention (Comparative Examples 1, 2, 4, 5), cracks were caused by oxides in the welded portions.
실시예 2Example 2
상기 실시예 1에서 발명예(3)의 조건으로 용접한 후, 2700A의 전류를 하기 표2와 같은 통전시간으로 열처리를 행하여 용접하였다.After welding under the conditions of Inventive Example (3) in Example 1, the current of 2700A was subjected to a heat treatment with a current carrying time as shown in Table 2 below.
얻어진 용접부에 대한 인장강도 및 최고경도(Hv)를 측정하여 그 결과를 하기 표2에나타내었다.Tensile strength and maximum hardness (Hv) of the obtained welds were measured, and the results are shown in Table 2 below.
상기 표2에서 알 수 있는 바와 같이, 통전시간을 6초이상 행한 발명재(3-5)의 경우는 최고경도가 500Hv이하의 값을 보였는데, 이는 회복이 일어나 충분히 연성이 회복되었음을 의미하는 것이다.As can be seen in Table 2, in the case of the invention material (3-5) which performed the energization time for 6 seconds or more, the maximum hardness value was less than 500 Hv, which means that recovery occurred and sufficient ductility was recovered. .
이에 반하여, 통전시간을 6초미만으로 행한 비교재(1-2)의 경우는 최고경도가 500Hv이상의 값을 보였다.On the contrary, in the case of the comparative material (1-2) having the energization time of less than 6 seconds, the maximum hardness showed a value of 500 Hv or more.
상기 발명재(5)에 의한 용접부와 열처리를 행하지 않은 용접부에 있어, 용접중심선으로 부터 거리에 따른 경도를 각각 측정하여 그 결과를 도 2에 나타내었다.In the welded part by the said invention material 5, and the welded part which did not heat-process, the hardness according to the distance from the welding center line was measured, respectively, and the result is shown in FIG.
도 2에서 알 수 있는 바와 같이, 본 발명의 전류에 의한 열처리를 행함으로서, 용접부의 인성이 회복되는데 특히 용접중심부의 회복이 우수하였다.As can be seen from Figure 2, by performing the heat treatment by the current of the present invention, the toughness of the weld portion is recovered, in particular, the recovery of the weld center portion was excellent.
한편, 열처리시 전류를 2500A미만으로 6초 행하고, 3000A를 초과하여 6초 행하는 실험을 하였는데, 2500A미만인 경우에는 열처리온도가 550℃미만을 보여 그 효과가 미미하였고, 3000A를 초과하는 경우에는 열화되는 문제가 있었다.On the other hand, an experiment was performed for 6 seconds at a current of less than 2500 A for 6 seconds and more than 3000 A for 6 seconds. When the temperature was less than 2500 A, the heat treatment temperature was lower than 550 ° C., and the effect was insignificant. There was a problem.
상술한 바와 같은 본 발명에 의하면, 기존 조건에 의한 용접에 비하여 용접부 결함비율이 10배 이상 낮아졌으며, 열처리에 의해 성형성이 매우 우수한 용접부가 얻어진다는 효과 있다.According to the present invention as described above, the weld defect ratio is 10 times lower than that of the welding under the existing conditions, the heat treatment is excellent in the formability of the weld can be obtained.
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US20150020373A1 (en) * | 2002-06-28 | 2015-01-22 | Weatherford Canada Partnership | Method of manufacturing continuous sucker rod |
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