JP2009262180A - Gas shielded arc welding method for thin steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas shielded arc welding method for a thin steel sheet, by which a stable penetration amount can be secured and a satisfactory weld bead with a high bead width can be obtained without causing any burn through upon welding even if a wire target position is varied in the case particularly a lap joint part and a T joint part are welded at a high speed. <P>SOLUTION: Welding is performed using a solid wirecontaining 0.2 to 0.7% C, 0.05 to 0.2% Si and 0.2 to 0.5% Mn while applying a pulse in which pulse peak current Ip is 380 to 600A, pulse base current Ib is 30 to 80A, and the pulse peak current Ip[A] and the pulse peak time Tp[ms] satisfy inequality (1): 120≤Ip×Tp≤380 (1). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a high-speed gas shielded arc welding method for a thin steel plate. More specifically, the welding speed is 0.8 m when welding a lap joint portion or a T joint portion of a thin steel plate having a thickness of 1.2 to 4.5 mm. Consumable electrode gas shielded arc welding (hereinafter referred to as pulsed MAG welding) with pulse welding applied under conditions of at least / min, excellent arc stability even when the wire target position changes and the arc length changes, and the weld metal This relates to a high-speed gas shielded arc welding method for a thin steel plate in which a good weld metal part can be obtained even when the groove gap of the weld part (hereinafter referred to as a gap) is large.

The gas shielded arc welding method using solid wire is easy to automate the welding, and can be widely applied to the welding of thin steel plates because it has high efficiency, good mechanical properties and good bead metal properties. Has been. In addition, the joint part of the welded structure is mainly composed of Ar gas as a shielding gas for the purpose of reducing the amount of spatter generated due to quality characteristics and reducing adhesion to the member and ensuring high-speed weldability. In recent years, pulse MAG welding methods using a gas in which CO ₂ is mixed and further O ₂ gas is mixed are increasing. Since the pulse MAG welding method can weld with a low average current, it can improve the burn-out resistance in the welding of thin steel plates, and it is constructed under high-speed welding conditions, so it is highly productive and has good quality. Is obtained.

  Pulse MAG welding is a welding method in which a peak current that is higher than the average current value as a welding current and a base current that is lower than the average current value are periodically passed. As a result, the welding wire that is being fed constantly during the peak current period is melted and made into a droplet state by the action of electromagnetic pinch force, etc., and this droplet is stably transferred to the molten pool during the base current period. Even when the arc voltage inside becomes low, the droplets can be transferred to the molten pool without short-circuiting the molten pool.

  In this way, by applying the pulse welding power source, a droplet generation amount corresponding to the melting energy composed of the product of the peak current, the peak time, and the arc voltage is obtained in the pulse MAG welding. That is, one droplet is generated at the time of one pulse peak current, and the droplet is melted smoothly by setting a pulse condition of 1 pulse-1 drop transition for transferring the droplet to the molten pool during the base current period. The amount of spatter generated is reduced by moving to a pond. For this reason, in the welding power source, the frequency of the pulse changes from several tens of Hz to about 300 Hz corresponding to the feeding speed of the welding wire.

  On the other hand, if the energy to melt the wire, which is the product of peak current, peak time, and arc voltage, becomes imbalanced with the wire feed rate, droplet formation will become the base current period, or droplet formation will occur during the peak current period. The droplets completed at the initial stage cannot be smoothly transferred and are scattered as spatter. In addition, the droplet transfer timing occurs discontinuously during the base current period and the peak current period, resulting in not only scattering as spatter but also a non-uniform bead shape.

  In particular, high-speed welding in gas shielded arc welding is likely to cause undercut, and as a method of suppressing this, it is common to employ welding conditions with a low arc voltage, but the arc spread Since it becomes small, the bead width is also narrowed, and it becomes difficult to form a good joint with a wide bead width. In addition, the shape of the structure of the thin steel plate is complicated, and the shape of the joint part is also complicated in the welded part, and the precision of the aiming of the welding is required. This is a cause of frequent spatters due to deterioration of the stability of the steel and poor bead shape.

  FIG. 1A, FIG. 1B, FIG. 1C, FIG. 1D, and FIG. 1E show an example of a bead formation state when there is a gap in the lateral orientation of the lap joint portion of a thin steel plate. In the figure, 1 is a front plate, 2 is a rear plate, 3 is a weld metal, and G is a gap. FIG. 1 (a) shows an example in which a good weld metal 3 having a large bead width W without melt-through, bead dripping and undercut is obtained. 1B is an example in which an undercut 4 occurs, FIG. 1C is an example in which molten metal hangs down to the front plate 1, FIG. 1D is an example in which a steel plate is melted, FIG. (E) shows an example in which the molten metal drips into the gap G between the front plate 1 and the rear plate 2.

  FIG. 1B occurs when the arc voltage is high. FIG. 1C is likely to occur when the wire aiming position 6 shown in FIG. 2 is the front side 61 of the front plate 1. FIG. 1D is likely to occur when the wire aiming position 6 shown in FIG. FIG. 1D tends to occur when the gap G is large. Thus, when the wire aiming position fluctuates, not only does the molten metal sag and the steel plate on the rear plate side melt, but if the gap of the lap joint is large, the molten metal cannot be cross-linked and is good. There was a problem that it was difficult to form a weld bead.

  Conventionally, as a method for welding thin steel sheets, for example, in Japanese Patent Laid-Open No. 56-80377 (Patent Document 1), as a first stage welding, a welding wire is short-circuited with a base material to cause red hot, fusing, and short-time stubbing. After welding for a certain period of time according to welding conditions in which arc generation is repeated, the gap is filled, and then welding with a stable steady-state arc is performed as the second stage welding. A thin plate welding method has been proposed that enables welding while filling the gap stably even when there is a gap. However, this welding method is not practical in terms of efficiency, for example, a large amount of spatter is generated when welding in a stubbed state, and it is not suitable for high-speed welding.

  Japanese Patent Application Laid-Open No. 2001-321985 (Patent Document 2) proposes a gas shielded arc welding wire and a pulse MAG welding method that are excellent in crosslinkability and excellent in crack resistance even if the gap of the welding member is large. . However, when this welding method is applied to the welding of a lateral lap joint, it is difficult to apply the molten metal due to dripping.

Japanese Patent Laid-Open No. 8-243749 (Patent Document 3) uses a wire of a predetermined chemical component for a thin steel plate having a thickness of 1.2 to 1.6 mm, and contains 3 to 7% by volume of Ar. There has been disclosed a welding method that prevents melt-down and enables high-efficiency welding by pulse MAG welding using a shielding gas mixed with O ₂ . However, this method allows high-efficiency gas shield arc welding even in a steel plate having a relatively small thickness by limiting the shielding gas component, but the gap in the lap joint portion of the thin steel plate is particularly large. In some cases, the weld metal drips and is difficult to apply.

  Furthermore, Japanese Patent Laid-Open No. 9-206984 (Patent Document 4) discloses a welding method for ensuring gap resistance in pulse MAG welding with a thin steel plate using a steel wire for gas shielded arc welding. However, it is difficult to apply lap joints of thin steel plates to high-speed welding, and it is impossible to ensure the dripping resistance and wide beads of molten metal.

As described above, various investigations such as means for preventing burn-off in thin steel plate welding, various wire compositions, shield gas compositions, etc. have been made. It has not yet improved sag resistance, wide bead securing and gap resistance.
JP-A-56-80377 JP 2001-321985 A Japanese Patent Laid-Open No. 8-243749 JP-A-9-206984

  The present invention provides a high-speed gas shield arc welding method for thin steel plates, particularly when welding lap joints and T joints at high speeds, and by adding appropriate pulse conditions, even if the wire aiming position fluctuates, it melts away. An object of the present invention is to provide a welding method capable of obtaining a good weld bead having a wide bead width even when a proper penetration characteristic is obtained and a gap between members is large.

The gist of the present invention is that, in a method of gas shielded arc welding of a thin steel plate having a thickness of 1.2 to 4.5 mm at a welding speed of 0.8 m / min or more, C: 0.2 to 0.7. %, Si: 0.05-0.2%, Mn: 0.2-0.5%, and further contains at least one of Al: 0.10% or less and Ti: 0.10% or less as required. , P: 0.03% or less, S: 0.03% or less, with the balance being a solid wire made of Fe and inevitable impurities, with pulse peak current Ip: 380-600 A, pulse base current Ib: 30-80 A And the pulse peak current Ip [A] and the pulse peak time Tp [ms] are welded while applying a pulse satisfying the following formula (1): .
120 ≦ Ip × Tp ≦ 380 (1)

  According to the high-speed gas shielded arc welding method for a thin steel sheet of the present invention, particularly when a lap joint part or a T joint part is welded at a high speed, even if the wire aiming position fluctuates, the steel sheet does not melt, and the gap Even when it is large, molten metal does not sag and a good wide weld bead can be obtained with high efficiency.

In order to solve the above-mentioned problems, the inventors made a thin steel plate into a lap joint, welded at various welding conditions at a welding speed of 0.8 m / min or more using various components of solid wire, The following findings were obtained as a result of detailed investigations regarding the presence or absence of burn-through during target position fluctuation, penetration characteristics, and sagging resistance and gap resistance of molten metal.
(1) The wire composition reduces the amount of Si and Mn and increases the amount of C to refine the molten steel, improve the stability of the arc, increase the amount of wire melting, optimize the viscosity and surface tension of the molten metal, Welding with a small amount of spatter can be performed with a wide bead, and a weld metal part with good penetration characteristics and a good bead appearance can be obtained.
(2) By using a wire with the above wire composition in a region where the pulse condition is 1 pulse-1 drop droplet transfer, the droplet is short-circuited with the molten pool even if the arc voltage is lowered by high-speed welding. Therefore, a wide bead without undercut is obtained even in high-speed welding with less spatter generation.

Hereinafter, the reasons for limiting the wire composition, its content, and pulse conditions in the present invention will be described.
[C: 0.2 to 0.7% by mass]
C has the effect of ensuring the strength of the weld metal and making the droplets finer, but in the present invention, the amount of Si and Mn, which are deoxidizing elements, is reduced for the purpose of obtaining finer molten steel and obtaining a wide bead. The deoxidation of the molten metal is mainly performed by C. If C is less than 0.2% by mass (hereinafter referred to as “%”), deoxidation is insufficient, making it difficult to refine the molten steel, making the arc unstable and the bead width nonuniform. In addition, a large amount of spatter is generated, and molten metal sags. On the other hand, if it exceeds 0.7%, the viscosity of the molten metal is inferior and the sag resistance cannot be ensured. Further, not only the spatter generation amount increases, but also the weld metal is remarkably hardened and the crack resistance is deteriorated.

[Si: 0.05 to 0.2%]
Si is an element having a great effect of optimizing the viscosity and surface tension of the molten metal. Further, the droplets are made finer and a wide bead is obtained, and even when the arc voltage is lowered, the droplets are hardly short-circuited, which can contribute to the expansion of voltage conditions. As a result, the steel sheet can be prevented from being melted even when the wire aiming position of the welded joint is changed, and the penetration characteristics can be stably secured. However, if Si is less than 0.05%, the above effect cannot be obtained. On the other hand, if the content exceeds 0.2%, the droplets become large, so that short-circuiting is likely to occur, and this causes spatter when the wire aiming position changes. Also, the molten metal in the molten pool cannot follow the welding speed and tends to be a humping bead. Further, there is a problem that the molten slag increases.

[Mn: 0.2 to 0.5%]
Mn has the effect of optimizing the viscosity and surface tension of the molten metal. If Mn is less than 0.2%, the effect cannot be obtained, and pore defects such as blowholes are likely to occur, and the viscosity and surface tension of the molten metal deteriorate, so that the molten metal droops and the bead shape is inferior. A sufficient gap resistance cannot be obtained. On the other hand, if Mn exceeds 0.5%, the droplets become large and short-circuiting easily occurs, which causes spattering when the wire aiming position changes.

  In addition, since S makes the familiarity of a bead toe part favorable, it is preferable to contain 0.005% or more. However, if S and P exceed 0.030%, the crack resistance of the weld metal deteriorates. Moreover, at least one of Al and Ti can be contained in the range of 0.10% or less for the purpose of adjusting the viscosity of the molten metal as other components.

  Furthermore, as a result of examining the optimum pulse condition range in which the bead width is wide and does not sag, it is difficult to cause a short circuit in the region where the pulse peak current Ip and the pulse peak time Tp are one pulse and one drop region. The optimum pulse condition range was found to obtain a wide bead even when the wire aiming position fluctuated.

[Pulse peak current Ip: 380 to 600 A]
When the pulse peak current Ip is less than 380 A, the droplets are not released smoothly due to the electromagnetic pinch effect, the arc is unstable, and the amount of spatter is increased. Further, since the transfer of the droplets becomes unstable, the melting characteristics become unstable, and further, the bead spreads unevenly and becomes a convex bead. On the other hand, if it exceeds 600 A, the thin steel plate tends to melt off due to the arc force, and the molten pool tends to sag.

[Pulse base current Ib: 30-80A]
The pulse base current Ib requires a current value that can hold the arc in the base period. If it is less than 30 A, the arc becomes unstable, and the amount of generated patch is large, and the bead width becomes non-uniform. On the other hand, when the current exceeds 80 A, the droplets are not detached quickly, the droplet transfer becomes unstable, the arc is unstable, and the amount of spatter generated increases. Further, the bead width is non-uniform, and the bead does not spread and becomes a convex bead.

[120 ≦ Ip × Tp ≦ 380]
In addition to the aforementioned pulse peak current Ip and pulse base current Ib, the value obtained by the product Ip × Tp of the pulse peak current Ip [A] and the pulse peak time Tp [ms] expressed by the following equation (1) is limited. As a result, short-circuiting of the droplets occurs at the base and the molten metal does not easily sag, and a wide weld bead can be obtained and a good weld joint can be obtained even when the target position of the wire fluctuates.
120 ≦ Ip × Tp ≦ 380 (1)

  If the product Ip × Tp of the pulse peak current Ip [A] and the pulse peak time Tp [ms] is less than 120, the energy for forming droplets is insufficient during the peak current period, and sufficient droplets cannot be formed. In some cases, the width is narrow, the amount of spatter generated increases, and the penetration depth becomes unstable, resulting in burnout. On the other hand, if it exceeds 380, the wire feed amount and the droplet generation amount become unbalanced, and the excessively grown droplets are likely to short-circuit, and the molten pool is blown away by the arc force at the time of re-ignition. At the same time, melt-off easily occurs and the gap resistance deteriorates.

In the present invention, in order to obtain a stable bead, the wire diameter is set to 1.2 mm (nominal diameter), and the wire feeding speed is set to 7 m / min or more. If the wire feed speed is less than 7 m / min, the molten metal is in a humped state and a stable bead cannot be obtained.
Hereinafter, the present invention will be described specifically by way of examples.

A transverse direction in which a thin steel plate having a thickness of 2.3 mm and a length of 500 mm having the components shown in Table 1 is sandwiched between the rear plate 2 and the front plate 1 with a spacer 5 shown in FIG. A lap joint was used and welded under various welding conditions shown in Table 3 using solid wires of various components shown in Table 2 having a wire diameter of 1.2 mm. As shown in FIG. 2, the welding was started with the wire aiming position 6 being the front side end 61 of the front plate 1, and the rear plate side end 62 of the front plate 1 was set at the end of welding. The torch angle θ was 30 °, the tip-base metal distance was 15 mm, and the shielding gas was Ar-20% CO ₂ for welding.

  For each condition, the penetration amount L and the bead width W shown in FIG. 1A in the center of the weld length were examined, and the weld operability in the weld metal sag in the vicinity of the welding start portion and the entire weld length was investigated. In the evaluation, the penetration amount L was 20% or more of the steel plate thickness of 0.46 mm or more, and the weld metal bead width W was 7 mm or more. The survey results are summarized in Table 4.

In Tables 3 and 4, test no. 1-9 are examples of the present invention, Test No. 10 to 21 are comparative examples.
Test No. which is an example of the present invention. Nos. 1 to 9 have appropriate wire components and appropriate pulse conditions, so that the welding workability is good, and even when the wire target position fluctuates, there is no dripping or melting of the molten metal, and a penetration amount L is ensured. The results were extremely satisfactory, such as good bead characteristics due to the wide bead width.

Test No. in Comparative Examples. In No. 10, since the pulse peak current Ip was low, the arc was unstable and the amount of spatter generated was large. Moreover, the amount of penetration L and bead width W were small, and it became a convex bead.
Test No. In No. 11, since the pulse peak current Ip was high, the molten metal drooped in the vicinity of the welding start portion. In addition, welding was stopped because it melted down to the rear plate side at the center of the welding length.

Test No. In No. 12, since the pulse base current Ib was low, the arc was unstable, the amount of spatter was large, and the bead width W was non-uniform.
Test No. In No. 13, since the pulse base current Ib was high, the arc was unstable and the amount of spatter generated was large. Moreover, the bead width was uneven and became a convex bead.

Test No. In No. 14, the product Ip × Tp of the pulse peak current Ip and the pulse peak time Tp was low, so that the amount of spatter was large. In addition, the bead did not spread and the bead width W was narrowed, and burnout occurred in the vicinity of the welding end portion.
Test No. No. 15, because the product Ip × Tp of the pulse peak current Ip and the pulse peak time Tp was high, the amount of spatter was large, and it melted down to the rear plate side at the center of the weld length, so welding was stopped.

Test No. In No. 16, since the Mn of the wire symbol W8 is low, the molten metal dripped in the vicinity of the welding start portion. There was also a pit.
Test No. In No. 17, since the Si of the wire symbol W9 is low, the molten metal dripped near the welding start portion. Further, the bead width W was narrow.

Test No. No. 18 had high Si of the wire symbol W10, and had a large amount of spatter generation. It became a humping bead.
Test No. No. 19 had a large amount of spatter because the Mn of the wire symbol W11 was high.

Test No. In No. 20, since the C of the wire symbol W12 was high, the amount of spatter was large, and dripping of the molten metal also occurred in the vicinity of the welding start portion.
Test No. In No. 21, since the C of the wire symbol W13 was low, the arc was unstable and the amount of spatter generated was large. Further, the bead width W was not uniform, and molten metal sagging occurred near the welding start portion.

(A) thru | or (e) is a figure which shows the example of a bead formation state in case there exists a gap in the horizontal orientation of the lap joint part of a thin steel plate, respectively. The figure which shows the wire aim position of the horizontal lap joint part in the Example of this invention. The figure which shows the test plate of the horizontal lap joint used for the Example of this invention.

Explanation of symbols

1 Front plate 2 Rear plate 3 Weld metal 4 Undercut 5 Spacer 6, 61, 62 Target position 7 Torch θ Torch angle W Bead width L Penetration depth G Gap

Claims (2)

In a method of gas shielded arc welding of a thin steel plate having a thickness of 1.2 to 4.5 mm at a welding speed of 0.8 m / min or more, C: 0.2 to 0.7%, Si: 0.00. A solid wire containing 0.05 to 0.2%, Mn: 0.2 to 0.5%, P: 0.03% or less, S: 0.03% or less, the balance being Fe and inevitable impurities is used. The pulse peak current Ip is 380 to 600 A, the pulse base current Ib is 30 to 80 A, and the pulse peak current Ip [A] and the pulse peak time Tp [ms] are applied to satisfy the following expression (1). A high-speed gas shielded arc welding method for a thin steel sheet, characterized in that welding is carried out.
120 ≦ Ip × Tp ≦ 380 (1) 2. The high-speed gas shielded arc welding method for a thin steel sheet according to claim 1, wherein the solid wire further contains at least one of Al: 0.10% or less and Ti: 0.10% or less.

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