JP2007030015A - Steel plate connection welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel plate connection welding method in which steel plates are butted to each other like the coil connection welding used in manufacturing a spiral steel tube, the butted portion of the steel plates is submerged-arc welded only from one face side to perform the connection welding, a welding bead (penetration bead) can be generated to back sides of the steel plates, and any repair welding (corrective welding) of the back side of the welding bead becomes unnecessary, e.g., after forming the steel tube. <P>SOLUTION: Steel plates 1, 1 are butted to each other, a butted portion 2 of the steel plates 1, 1 is submerged-arc welded only from one face side. In such a condition, while a backing 4 is abutted on a back side opposite to welding torches, a coil 5 for induction heating is arranged ahead in the advancing direction of welding torches 3a, 3b, the butted portion 2 is heated in advance, and the submerge-arc welding is performed using two electrodes (the welding torches 3a, 3b). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for welding a steel plate, and more particularly to a method useful when applied to a plate in a spiral steel pipe production line.

Coil joint welding in spiral steel pipes is submerged arc welding (SAW) only from one side of the coil, so even if the welding conditions (speed, current, voltage, etc.) are variously changed, a complete weld bead (back) Wave beads are not generated. Therefore, the unwelded part on the back side of the coil must be reworked (repair welding) by offline work after it becomes a steel pipe, which obstructs process waste and line flow.
Further, if the back surface of the coil where the back bead is not formed is roll-formed as it is, the forming of the portion becomes insufficient, resulting in a rounded shape without roundness, and the roundness of the steel pipe is poor, which is not preferable in terms of quality. Therefore, it is necessary to adjust so that the coil joint portion does not come to the tube end portion, and the coil joint portion causes the yield deterioration.

On the other hand, butt welding using laser, plasma, etc., tends to increase for the purpose of high productivity and yield improvement in plate joint welding in continuous lines of steel plates (cold rolling, annealing, pickling, etc.) Patent Document 1 proposes a method of welding while pre-ripening the weld at 200 to 250 ° C. for the purpose of preventing weld cracking of high carbon steel in such welding.
Japanese Patent Laid-Open No. 6-312285

  However, the steel plate joint welding method of Patent Document 1 is a method of irradiating a laser (or plasma) beam, and the steel plate to be welded has a thickness of about 1 mm or less to several mm such as a cold-rolled steel plate. It is a thin steel plate, and is not applicable to a hot rolled steel plate having a thickness of 9 to 30 mm, which is a material of a spiral steel pipe targeted by the present invention.

  The present invention has been made in view of such circumstances, and, as in coil joint welding used in the manufacture of spiral steel pipes, etc., the steel plates are butt-matched, and the butt portion of the steel plates is submerged only from one side. It is possible to generate weld beads (backside bead) up to the back side of the steel sheet in the plate-welding method, where the plate is welded and welded. It is an object of the present invention to provide a method for joint welding of steel plates that becomes unnecessary.

  As a result of extensive experiments under various conditions, the present inventors have butted steel plates, and in a joint welding method for joining plates by performing submerged arc welding of the butt portion of the steel plates only from one surface side, By preheating the butt and performing the submerged arc welding with two electrodes, the amount of molten metal is increased, the penetration width and the bead width are widened, and the back bead is likely to occur, and the present invention is completed. It came to do.

That is, the method of joining the steel plates according to claim 1 is a method of joining the steel plates, in which the steel plates are butt-joined, and the butt portions of the steel plates are joined by submerging arc welding only from one surface side. The submerged arc welding is performed with two electrodes.
In the first aspect of the present invention, since the two-electrode submerged arc welding is performed after the butt portion is heated in advance, the penetration width and the bead width are widened, and a weld bead can be generated up to the back surface side of the steel sheet. Therefore, for example, in coil joint welding in a spiral steel pipe production line, complete reverse wave welding of the coil transverse portion can be realized. As a result, offline welding (repair welding) and grinder care of the spiral steel pipe coil joint can be reduced or eliminated (part of the manufacturing process of the spiral steel pipe is omitted). Moreover, the yield improvement by commercialization of the pipe end coil joint part of a spiral steel pipe can be expected.

According to a second aspect of the present invention, in the invention according to the first aspect, the steel plate is welded so that the temperature of the steel plate surface on the opposite side to the surface to be submerged arc welded in the butt portion is 300 ° C. or higher. It is characterized by doing.
In the invention described in claim 2, a complete weld bead is formed up to the back surface side by heating so that the temperature of the steel sheet surface on the opposite side to the surface side to be subjected to submerged arc welding at the butt portion becomes 300 ° C. or higher. It becomes possible.

According to a third aspect of the present invention, in the invention according to the first or second aspect, the steel sheet has a thickness of 9 to 30 mm.
In the invention according to claim 3, although the thickness of the steel plate is applied to the plate-welding of 9 to 30 mm, the plate-welding of such a plate thickness can form a weld bead to the back side, Suitable for use in the manufacture of spiral steel pipes.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the two-electrode welding method according to the thickness of the butt portion of the steel plate where the two-electrode submerged arc welding is performed. It is characterized by optimizing the heat input condition of each electrode of the electrode submerged arc welding.
That is, in submerged arc welding, the total heat input of the two electrodes is 25 to 165 kJ / cm, and the relationship between the heat input by the preceding electrode and the heat input by the subsequent electrode satisfies the following relationship: .
−0.3 × t + 1.2 ≦ R ≦ −0.3 × t + 1.5
Here, R is a ratio of heat input by the following electrode and heat input by the preceding electrode (R = heat input by the following electrode / heat input by the preceding electrode), and t is the thickness of the butt portion of the steel sheet. To express.
In invention of Claim 4, even if the plate | board thickness of a steel plate butt | matching part changes variously, by setting appropriately the heat input of each of the preceding electrode and the succeeding electrode of submerged arc welding using two electrodes, Always good bead shape is realized.

  In addition, in the Japanese Patent Application No. 2004-311748, the present applicants also disclosed an invention relating to a steel plate joining method characterized in that submerged arc welding is performed by preheating the butt portion of the steel plate in advance. However, this application is characterized by performing two-electrode submerged arc welding in order to further improve the efficiency of welding.

According to the steel plate joint welding method of the present invention, it is possible to form a weld bead (back wave bead) up to the back surface side of the steel plate, and therefore, it is not necessary to make repair welding (repair welding) on the back surface side after welding. Is possible.
In addition, even if the thickness of the steel plate butt changes, the bead shape is always achieved by appropriately setting the heat input of each of the leading and trailing electrodes of submerged arc welding using two electrodes. can do.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a perspective view for explaining a steel plate joining method according to an embodiment of the present invention.
As shown in the figure, in the steel plate joint welding method of the present embodiment, the steel plates 1 and 1 are butted together, and welding torches (submerged arc welding torches) 3a and 3b at the butt portion 2 of the steel plates 1 and 1 are shown. In the state where the backing metal (backing plate) 4 is in contact with the back surface on the opposite side, a coil 5 for high frequency induction heating is arranged in front of the welding rods 3a and 3b in the advancing direction, and the butt 2 is predetermined. Submerged arc welding (SAW) is performed while heating in advance so as to reach a temperature of 5 mm. The distance between the preceding welding torch 3a and the coil 5 is, for example, about 100 mm, and the coil 5 is also moved in the same direction at the same speed as the welding torch 3a as the welding torch 3a progresses. As shown in FIG. 2, a groove having a predetermined groove angle α (°) is formed in the steel plate 1 as necessary, and a predetermined route gap r (mm) is provided between the steel plates 1 and 1 as necessary. ).

  At this time, the flux disposed close to the front side in the moving direction of the welding torch 3a on the surface side (welding torch 3a, 3b side) of the butt portion 2 of the steel plates 1, 1 as in the case of normal submerged arc welding. While the flux is dispersed from the supply hose 6, the flux is supplied to the upper surface of the backing metal 4 on the back surface side of the butt portion 2 before starting welding. As a method of supplying the flux to the upper surface of the backing metal 4, a manual operation or a supply device may be used. It is also possible to make a through hole in the backing metal 4 and supply the flux to the upper surface of the backing metal 4 through the through hole. As the type of the flux, it is desirable to use a sintered flux having a relatively high melting point on both the front surface side and the back surface side of the steel plates 1 and 1 in terms of stabilizing the back bead shape.

  Although not shown in FIG. 1, in order to stabilize the submerged arc welding at both ends in the width direction of the butt portion 2 of the steel plates 1 and 1, a cut plate called a tab is temporarily attached to both ends in advance. It is desirable to start from the welding of the butt portion of the cut plate and end the series of submerged arc welding processes by welding the butt portion of the cut plate.

The heating state (temperature distribution) of the butt portion 2 of the steel plates 1 and 1 varies depending on the amount of power supplied to the high frequency induction heating coil 5 and the thickness of the steel plates 1 and 1.
As shown in FIG. 3, the steel plates 1, 1 are butted together, and a high frequency induction heating coil 5 is arranged on one surface (surface) of the butting portion 2 of the steel plates 1, 1, and the high frequency output (electric power) and steel plate The thickness of 1 was changed, high frequency induction heating of the butt 2 was performed, and a heating test was performed to measure the temperature of the back surface of the butt 2. The output frequency of the high frequency power supply is 50 kHz. The high frequency induction heating coil 5 was moved at a speed of 500 mm / min along the butt portion 2 of the steel plates 1 and 1. As a steel plate 1 as a test material, SS400, a general structural rolled steel material, was used. The test results are shown in FIG.

  From FIG. 4, the temperature of the back surface (surface opposite to the high-frequency induction heating coil 5) of the butt 2 of the steel plates 1 and 1 having a high-frequency output (electric energy) in the range of 36 to 48 kW and a thickness of 30 mm or less. It turns out that it can heat so that it may become 300 degreeC or more. It can also be seen that when the high-frequency output (power consumption) is 22 kW, the temperature of the back surface of the butt portion 2 of the steel plates 1 and 1 having a thickness of 14 mm or less is 300 ° C. or higher. In addition, the influence on the groove shape of the butt | matching part 2 of the steel plates 1 and 1 shown in FIG. 2 and the heating temperature of the root gap r was hardly recognized.

FIG. 5 shows an analysis of results obtained through a huge experiment on two-electrode submerged arc welding under high-frequency induction heating on the butt portion 2 of the steel plates 1 and 1 performed by the present inventors. It is the figure which represented typically the influence which the balance of the leading electrode 3a and the succeeding electrode 3b in submerged arc welding has on the butt welding quality of the steel plates 1 and 1.
In the figure, the upper side of the bead represents the welding torch (electrodes 3a, 3b) side (the surface side of the steel plate 1), and the lower side of the bead represents the opposite side of the welding torch (the back side of the steel plate 1).
Generally, when high-frequency induction heating is performed on a steel plate 1 having a relatively small thickness, the temperature difference between the front and back surfaces of the steel plate 1 is small, but the temperature difference between the front and back surfaces of the steel plate tends to increase as the thickness of the thick steel plate 1 is increased. There is.
In general, when submerged arc welding using two electrodes is performed, the leading electrode 3a uses a DC power source, so the penetration shape tends to become deeper in the thickness direction, and the trailing electrode 3b uses an AC power source because it uses an AC power source. There is a tendency that the embossed shape becomes shallower and wider in the thickness direction.

From these findings and experimental results under various conditions, the following findings were obtained as schematically shown in FIG.
(1) When submerged arc welding is performed on a relatively thin steel plate with two electrodes, setting the subsequent electrode heat input to the same level as the preceding electrode heat input leads to stabilization of the bead shape.
On the other hand, if the heat input from the trailing electrode is larger than the heat input from the preceding electrode, if the difference in heat input by both electrodes is relatively small, the back bead is small and the front bead is large, and further, the difference in heat input by both electrodes is large. When the weight of the front bead becomes excessive, and the weight of the entire bead eventually exceeds the surface tension of the back surface, the phenomenon that the molten metal melts is observed. Conversely, if the heat input from the trailing electrode is smaller than the heat input from the preceding electrode, the back bead is formed excessively, the weight of the back bead becomes excessive, and eventually the surface tension of the back surface is exceeded, which also melts off the bead. Leads to.
(2) When submerged arc welding is performed on a relatively thick steel plate with two electrodes, setting the subsequent electrode heat input smaller than the preceding electrode heat input leads to stabilization of the bead shape.
On the other hand, if the trailing electrode heat input is slightly less than the leading electrode heat input, the back bead is small and the front bead is large, and if the trailing heat input is increased to the same level as the leading electrode heat input, As a result, the weight of the entire bead exceeds the surface tension of the back surface, so that the molten metal melts.

FIG. 6 is a graph showing the relationship between the thickness of the steel plate butt 2 and the heat input by the trailing electrode 3b and the heat input by the preceding electrode 3a in the two-electrode submerged arc welding according to the present invention. The inventors have organized the results of performing two-electrode submerged welding while preheating with a high-frequency induction heating coil using steel plates 1 of various plate thicknesses.
The vertical axis of FIG. 6 represents the ratio R of heat input by the trailing electrode 3b and heat input by the leading electrode 3a (= heat input by the trailing electrode ÷ heat input by the leading electrode), and the horizontal axis represents the butt of the steel plates 1 and 1. The thickness of the part 2 is represented.
From FIG. 6, the present inventors have obtained the following knowledge and completed the present invention.
(1) There is a clear correlation between the ratio R of the heat input by the trailing electrode and the heat input by the leading electrode to obtain a good weld bead shape (marked with a circle in the figure) and the thickness of the steel sheet. However, it is necessary to set R to be smaller as the thickness of the steel sheet is smaller, and to be smaller as the thickness of the steel sheet is larger.
(2) As a result of regressing the relationship between the R and the thickness of the steel plate at the joint, a good weld bead shape (marked with a circle in the figure) is obtained when performing two-electrode submerged welding while preheating with a high-frequency induction heating coil. In order to achieve this, it is effective to set R within the following range. Here, t represents the thickness of the butt portion of the steel plate.
−0.3 × t + 1.2 ≦ R ≦ −0.3 × t + 1.5

Next, the present invention will be described more specifically with reference to examples.
In this example, the steel plate joint welding method of the present invention was applied to a plate joint in a spiral steel pipe production line.
The steel plate used as the material for the spiral steel pipe is SS400, which is a rolled steel plate for general structure whose width is 1100 to 1600 mm.
When jointing steel plates, the pipe making line is temporarily stopped and the steel plate is stationary, and then the end of the preceding material (pipe making hot coil) and the succeeding material (following the preceding material) In order to make the tip of each hot coil flat, a crop of a predetermined length was cut with a shear. Thereafter, the abutting portion of the preceding material and the succeeding material is moved to the standby position of the backing metal, the welding torch and the high-frequency heating coil. Submerged arc welding was performed in a state where the material was butted.

The thickness of the steel plate was 9-30 mm. The groove shape of the plate joint portion was a groove on both sides of α = 0 to 10 °, and the root gap r was 0 mm. Heating (preheating) by the high-frequency heating coil 5 was performed with an electric energy of 32.5 to 36.4 kW, and the back surface temperature of the butt portion of the steel sheet was 300 to 350 ° C. The total heat input in submerged arc welding using two electrodes is 25 to 165 kJ / cm, and the ratio R of heat input by the succeeding electrode and heat input by the preceding electrode (= heat input by the succeeding electrode divided by the preceding electrode) The heat input was set to fall within the following range.
−0.3 × t + 1.2 ≦ R ≦ −0.3 × t + 1.5
Here, t represents the thickness of the butt portion of the steel plate. In the submerged arc welding of the butt portion of the steel plate, a sintered type flux was supplied to the butt portion from the welding torch side and the backing metal side.

As a comparative example, the heat input by the preceding electrode and the heat input by the succeeding electrode were set so that the R did not satisfy the above range, and plate joint welding was performed in the same manner.
The results are shown in Table 1. In addition, the quality of the welded portion in Table 1 represents the properties of the bead on the back side, and the ○ mark, △ mark, and x mark in the evaluation section are levels that require no or almost no care for the back surface of the welded part, This indicates a level that requires only grinder care and a level that requires overlay welding repair due to the occurrence of a burn-out.

  As can be seen from Table 1, in any comparative example in which the ratio R of heat input by the trailing electrode and heat input by the preceding electrode deviates from the above range regardless of the thickness of the steel plate, the shape of the bead -According to the steel plate joint welding method in which the ratio R of the heat input by the succeeding electrode and the heat input by the preceding electrode is set within the prescribed range of the present invention, compared with the case where the quality is poor and the rear surface of the welded portion is required. Good back bead was generated, and repair welding and grinder care of the welded part were at a level unnecessary or almost unnecessary.

It is a perspective view for demonstrating the plate-welding method of the steel plate which concerns on embodiment of this invention. It is a longitudinal cross-sectional view which shows the butt | matching part of a steel plate. It is a perspective view for demonstrating the high frequency induction heating test method of the butt | matching part of a steel plate. It is a figure which shows the relationship between the thickness of the steel plate by high frequency induction heating, and the temperature of the back surface of the butt | matching part of a steel plate. It is a figure for qualitatively explaining the influence which the balance of the preceding electrode and the succeeding electrode in the two-electrode submerged arc welding according to the present invention has on the butt welding quality of the steel sheet. It is a figure for demonstrating the relationship between the thickness of the steel plate butt | matching part in 2 electrode submerged arc welding which concerns on this invention, and the ratio of the heat input by a succeeding electrode, and the heat input by a preceding electrode. It is a figure for demonstrating the relationship between the thickness of the butt | matching part of a steel plate in the two-electrode submerged arc welding which concerns on this invention, and total heat input.

Explanation of symbols

1 Steel plate 2 Butt part 3a Welding torch (leading electrode)
3b Welding torch (following electrode)
4 Backing plate 5 High frequency induction heating coil 6 Flux supply hose α Groove angle r Route gap

Claims (4)

In the plate joint welding method in which steel plates are butted together, and the butt portion of the steel plate is joined by submerging arc welding only from one side,
A method of joining steel sheets, wherein the butt portion is heated in advance and the submerged arc welding is performed with two electrodes.   2. The method of joining steel sheets according to claim 1, wherein heating is performed so that the temperature of the steel sheet surface opposite to the surface side to be subjected to submerged arc welding in the butt portion is 300 ° C. or higher.   3. The steel sheet joint welding method according to claim 1, wherein the steel sheet has a thickness of 9 to 30 mm. In the submerged arc welding, the total heat input of the two electrodes is 25 to 165 kJ / cm, and the relationship between the heat input by the preceding electrode and the heat input by the subsequent electrode satisfies the following relationship. A method for joint welding of steel sheets according to any one of claims 1 to 3.
−0.3 × t + 1.2 ≦ R ≦ −0.3 × t + 1.5
Here, R is a ratio of heat input by the following electrode and heat input by the preceding electrode (R = heat input by the following electrode / heat input by the preceding electrode), and t is the thickness of the butt portion of the steel sheet. To express.

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