JP2018111114A - Pulse mag welding method for high-strength steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pulse MAG welding method for a high-strength steel sheet, wherein, the arc is stable, the fit of a toe part is good, a weld bead that is wide can be obtained, there are no weld defects, and excellent weld metal mechanical performance can be obtained.SOLUTION: A pulse MAG welding method uses a solid wire that contains, in mass% based on the total wire mass, C: 0.02-0.15%, Si: 0.30-0.60%, Mn: 1.20-1.90%, Ni: 2.0-4.0%, Cr: 0.30-0.70%, Mo: 0.40-0.80%, the total of Cr and Mo : 0.75-1.15%, Ti: 0.02-0.07%, and Cu: 0.10-0.40%, with S: 0.03% or less and P: 0.03% or less, having pulse peak current (Ip): 440-600A and pulse base current (Ib): 30-80A, the pulse peak current (Ip) and pulse peak time (Tp) satisfying the following formula: 415≤Ip(A)×Tp(msec)≤780.SELECTED DRAWING: None

Description

  The present invention relates to a pulse MAG welding method for a high strength thin steel sheet having a tensile strength of 780 MPa or more, and particularly to arc welding when welding a lap joint or a T joint of a high strength thin steel sheet having a thickness of 1.2 to 3.2 mm. This makes it possible to obtain a weld bead with a wide bead width even when the gap of the welded portion is large, no weld defects, and excellent mechanical performance of the weld metal. The present invention relates to a pulse MAG welding method for a high-strength thin steel sheet suitable for obtaining a highly efficient and high-quality weld.

  In recent years, from the viewpoint of global environmental conservation, improving the fuel efficiency of automobiles has become an important issue, and the use of thinner steel sheets has been promoted in order to increase the strength of car body materials. For example, Patent Document 1 discloses a steel sheet for automobiles that is a high-strength steel sheet having a maximum tensile strength of 780 MPa or more and that is excellent in impact absorption at the time of collision. Patent Document 2 discloses a steel sheet for automobiles having a high strength steel sheet having a tensile strength of 980 MPa or more and excellent in formability.

Welding thin steel sheets for automobiles uses Ar as a shielding gas for the purpose of reducing the amount of spatter generated by reducing the amount of spatter generated from the aspect of quality characteristics of the joint using solid wires and ensuring high-speed weldability. In recent years, pulse MAG welding methods using a gas mainly composed of gas, mixed with CO ₂ gas, and further mixed with O ₂ gas have been increasing. The pulse MAG welding method can weld with a low average current, so it can improve the melt-off 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. Part 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, which is constantly fed during the peak current period, is melted into a droplet state by an action such as an electromagnetic pinch force, and this droplet is stably transferred to the molten pool during the base current period. Even when the arc voltage during welding becomes low in order to suppress undercut during high-speed welding, the droplets can be smoothly transferred to the molten pool without short-circuiting with the molten pool.

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

  On the other hand, if the energy for melting the wire, which is the product of peak current, peak time, and arc voltage, becomes unbalanced with the wire feed amount, droplet formation becomes the base current period, and droplet formation occurs at the beginning of the peak current period. The finished droplets cannot move smoothly and scatter 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.

  Particularly in high-speed welding in gas shielded arc welding, undercut is likely to occur. As a method for suppressing this, it is common to employ welding conditions with a reduced arc voltage, but the arc spread is reduced. As a result, the bead width is also narrowed, making it 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 portion is also complicated in the welded part, so that the accuracy of the aiming of the welding is required. This causes frequent spatters due to stability deterioration and bead shape defects.

  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. The rear plate 2 is positioned on the rear side with respect to the front plate 1, and the weld metal 3 is formed on each of the front plate 1 and the rear plate 2. A gap G is formed between the front plate 1 and the rear plate 2. 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. FIG. 1B shows an example in which an undercut 4 has occurred. FIG. 1C shows an example in which the molten metal 3 hangs down to the front plate 1 side. FIG.1 (d) shows the example which the steel plate (rear plate 2) melted away. FIG. 1 (e) shows an example in which the molten metal 3 has dropped into the gap G between the front plate 1 and the rear plate 2.

  The undercut 4 shown in FIG. 1B occurs when the arc voltage is high. The dripping of the molten metal 3 shown in FIG. 1C toward the front plate 1 side is likely to occur when the wire aiming position 6 shown in FIG. 2 is the front side 61 of the front plate 1. The steel plate (rear plate 2) shown in FIG. 1 (d) is likely to be melted when the wire aiming position 6 shown in FIG. The dripping of the weld metal 3 into the gap G shown in FIG. 1 (e) is likely to occur when the gap G itself is large. In this way, when the wire aiming position fluctuates, not only does the molten metal 3 droop and the steel plate on the rear plate 2 side melts, but if the gap G of the lap joint is large, the molten metal 3 moves forward. There was a problem that it was impossible to bridge between the plate 1 and the rear plate 2 and it was difficult to form a good weld bead.

  For example, in Patent Document 3, a solid wire for welding of a high-strength thin steel sheet has a carbon equivalent derived from the wire composition and a toe portion having an appropriate curvature radius by limiting the welding voltage, and the fatigue strength There is a disclosure of a technique that an excellent weld can be obtained. However, welding is MAG welding, and in the case of high-speed welding, the amount of spatter generated increases. Further, the strength and toughness of the weld metal are not satisfactory.

  On the other hand, as a pulse MAG welding wire for high-strength steel plates, Patent Document 4 welds a thin high-tensile steel plate (690 MPa steel grade) with limited wire components, shielding gas composition and pulse application conditions, and mechanically welds the metal. A technique has been disclosed in which properties can be improved and the amount of spatter generated is small and welding workability is excellent. However, even in the technique disclosed in Patent Document 4, even when the arc is stable, the bead width is wide, the bead toe is well-fitted, and the gap is large, a good weld metal cannot be obtained. There was a problem that the strength of the metal was also lowered.

Japanese Patent Laying-Open No. 2015-175061 JP-A-2015-175051 Japanese Patent Laid-Open No. 8-25080 JP-A-8-99175

  Therefore, the present invention has been devised in view of the above-described problems, and is a lap joint or T joint of a high strength thin steel plate having a plate thickness of 1.2 to 3.2 mm and a tensile strength of 780 MPa or more. When welding parts, the arc is stable, the toe end fits well, and even when the weld gap is large, a weld bead with a wide bead width can be obtained, and there are no weld defects and an excellent weld metal machine. It is an object of the present invention to provide a pulse MAG welding method for a high-strength thin steel sheet, which can obtain a high-quality welded portion with high efficiency, such as a high performance.

The gist of the present invention is that, in the pulse MAG welding method of a high-strength thin steel sheet having a thickness of 1.2 to 3.2 mm, C: 0.02 to 0.15%, Si: 0 with respect to the total mass of the wire. .30 to 0.60%, Mn: 1.20 to 1.90%, Ni: 2.0 to 4.0%, Cr: 0.30 to 0.70%, Mo: 0.40 to 0.80 %, And the total of Cr and Mo: 0.75 to 1.15%, Ti: 0.02 to 0.07%, Cu: 0.10 to 0.40%, S: 0.03% or less , P: 0.03% or less, the balance using a solid wire made of Fe and inevitable impurities, pulse peak current (Ip): 440-600A, pulse base current (Ib): 30-80A, and the pulse A pulse whose peak current (Ip) and pulse peak time (Tp) satisfy the following formula (1): In the pulse MAG welding method of the high strength thin steel sheet, which comprises welding by pressurizing.
415 ≦ Ip (A) × Tp (msec) ≦ 780 (1)

  According to the pulse MAG welding method of a high strength steel sheet of the present invention, an arc is generated when welding a lap joint part or a T joint part of a high strength thin steel sheet having a plate thickness of 1.2 to 3.2 mm and a tensile strength of 780 MPa or more. Stable, good fit at the toe, and a wide weld bead even when the weld gap is large, no weld defects, and excellent weld metal mechanical performance, etc. High quality and high quality welds can be obtained.

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

  In order to solve the above-mentioned problems, the inventors made thin steel plates into lap joints, welded at various welding conditions at a welding speed of 0.6 m / min or more using solid wires of various components, and arcs. As a result of evaluating the stability of the weld, the bead width, the conformability of the weld toe, the presence or absence of weld defects, and examining the strength and low temperature toughness of the weld metal in detail, the following knowledge was obtained.

  (1) The wire composition is sputtered with a wide bead by optimizing the Mn content and Si content to make the droplets finer, improve the stability of the arc, and optimize the viscosity and surface tension of the molten metal. Welding with a small amount of generation is possible, and a weld metal having a good bead appearance and no welding defects can be obtained. In addition, by optimizing the C content, Cr content and Mo content and adding Ni, Ti and Cu, a weld metal having high strength and stable toughness can be obtained.

  (2) Even if the arc voltage is lowered by welding at a high speed of 60 cm / min or more by using the wire having the above composition, the pulse condition is set to a region in which the pulse condition is 1 pulse-1 drop droplet transfer. Can be transferred without short-circuiting with the molten pool, and the amount of spatter is small and a wide bead can be obtained even in high-speed welding.

  Hereinafter, the reason for limitation of the pulse MAG welding method of the high strength thin steel sheet of the present invention will be described.

  First, the wire component composition will be described. In addition, the content rate of each component shall be represented by the mass% with respect to the total mass of a wire, and the description regarding the mass% is only described as%.

[C: 0.02 to 0.15%]
C is an element that ensures the strength of the weld metal. It also has the effect of stabilizing the arc and making the droplets finer. If C is less than 0.02%, the strength of the weld metal cannot be obtained. Further, it is difficult to make the droplets finer, the arc is unstable, and the amount of spatter generated increases. Furthermore, dripping of molten metal occurs in the transverse lap joint welding, and the bead appearance is deteriorated. On the other hand, when C exceeds 0.15%, not only the amount of spatter generated increases, but also the strength of the weld metal increases and the crack resistance deteriorates. Moreover, the melt of the molten metal is inferior due to the transverse lap joint welding, and the sag resistance cannot be secured. Therefore, C is 0.02 to 0.15%.

[Si: 0.30 to 0.60%]
Si is an essential element as a main deoxidizer for weld metal. In addition, there is an effect that the electric resistance of the wire is increased to increase the melting amount of the wire, and further the viscosity and surface tension of the molten metal are increased. As a result, dripping of the molten metal in the lateral lap joint welding is reduced, and the gap resistance is obtained. However, if Si is less than 0.30%, the above-mentioned effects cannot be obtained, and the molten metal sag is produced by the transverse lap joint welding, so that sufficient gap resistance cannot be obtained. On the other hand, when Si exceeds 0.60%, the surface tension of the molten metal is excessively increased, so that the molten metal cannot follow the welding speed and tends to be a humping bead. Further, the arc is unstable, and the amount of spatter generation and slag generation increases. Therefore, Si is 0.30 to 0.60%.

[Mn: 1.20 to 1.90%]
Mn acts as a deoxidizer together with Si, and also has an effect of increasing the viscosity and surface tension of the molten metal. If Mn is less than 1.20%, the above-mentioned effects cannot be obtained, and the viscosity and surface tension of the molten metal are lowered. On the other hand, when Mn exceeds 1.90%, the amount of spatter generated increases. In addition, since the viscosity and surface tension of the molten metal increase excessively, sufficient gap resistance cannot be obtained by transverse lap joint welding. Therefore, Mn is 1.20 to 1.90%.

[Ni: 2.0 to 4.0%]
Ni is an element that refines the structure of the weld metal and improves toughness. However, if Ni is less than 2.0%, the effect cannot be obtained, and the toughness of the weld metal decreases. On the other hand, when Ni exceeds 4.0%, the strength of the weld metal increases, crack resistance deteriorates, and the amount of spatter generated increases. Therefore, Ni is set to 2.0 to 4.0%.

[Cr: 0.30 to 0.70%]
Cr is an element that refines the structure of the weld metal and improves toughness. If Cr is less than 0.30%, the effect cannot be obtained, and the toughness of the weld metal decreases. On the other hand, if Cr exceeds 0.70%, the weld metal is markedly hardened and the toughness is lowered, and the amount of spatter generated is increased. Therefore, Cr is 0.30 to 0.70%.

[Mo: 0.40 to 0.80%]
Mo, like Cr, is an element that refines the structure of the weld metal and improves toughness. If Mo is less than 0.40%, the effect cannot be obtained, and the toughness of the weld metal decreases. On the other hand, if Mo exceeds 0.80%, the weld metal is markedly hardened and the toughness is lowered, and the amount of spatter generated is increased. Therefore, Mo is set to 0.40 to 0.80%.

[Total of Cr and Mo: 0.75 to 1.15%]
The total of Cr and Mo is added to improve the strength of the weld metal. If the total of Cr and Mo is less than 0.75%, the strength of the weld metal cannot be obtained. On the other hand, if the total of Cr and Mo exceeds 1.15%, the strength of the weld metal increases and the crack resistance deteriorates. Therefore, the total of Cr and Mo is set to 0.75 to 1.15%.

[Ti: 0.02 to 0.07%]
Ti improves the toughness of the weld metal by generating a fine oxide of Ti in the weld metal together with the effect of stabilizing the arc. If Ti is less than 0.02%, the effect cannot be obtained, the toughness of the weld metal is lowered, and the arc becomes unstable. On the other hand, if Ti exceeds 0.07%, the solid solution Ti in the weld metal increases and the toughness decreases. In addition, a large amount of slag is generated and the bead appearance is deteriorated. Therefore, Ti is made 0.02 to 0.07%.

[Cu: 0.10 to 0.40%]
Cu has the effect of refining the structure of the weld metal and stabilizing the toughness. If Cu is less than 0.10%, stable toughness cannot be obtained. On the other hand, if Cu exceeds 0.40%, precipitation embrittlement occurs and the toughness decreases. Also, hot cracking is likely to occur. Therefore, Cu is 0.10 to 0.40%.

[P: 0.03% or less]
P is an impurity, and an increase in P causes cracking of the weld metal, so 0.03% or less. Preferably it is 0.02% or less.

[S: 0.03% or less]
S is an impurity, and an increase in S causes cracking of the weld metal, so 0.03% or less. Preferably it is 0.02% or less.

  Furthermore, as a result of examining the optimum pulse MAG condition range in which the bead width is wide and the molten metal is difficult to sag under high-speed welding conditions of 60 cm / min or more, the pulse peak current Ip and the pulse peak time which are one pulse-1 drop region In the region of Tp, the optimum pulse MAG condition range was found in which short-circuiting is difficult and the amount of spatter generated is small, and a wide bead can be obtained even when the wire aiming position fluctuates.

[Pulse peak current (Ip): 440 to 600 A]
When the pulse peak current (Ip) is less than 440 A, the droplets are not released smoothly due to the electromagnetic pinch effect, resulting in uneven convex beads. Further, the arc is unstable and the amount of spatter generated increases. On the other hand, when the pulse peak current (Ip) exceeds 600 A, the molten metal tends to sag due to the arc force. Therefore, the pulse peak current (Ip) is set to 440 to 600A.

[Pulse base current (Ib): 30-80A]
The pulse base current (Ib) requires a current value that can hold the arc in the base period. When the pulse base current (Ib) is less than 30 A, the arc becomes unstable, the amount of spatter generated is large, and the bead appearance deteriorates. On the other hand, when the pulse base current (Ib) exceeds 80 A, the droplets are not released quickly, the arc is unstable, and the amount of spatter generated increases. Therefore, the pulse base current (Ib) is 30 to 80A.

[415 ≦ Ip (A) × Tp (msec) ≦ 780]
Even when the arc voltage is high in the region where the peak time is short, by limiting the value obtained by the product (Ip × Tp) of the pulse current (Ip) and the pulse peak time (Tp) represented by the following formula (1), The short circuit of the droplets occurs moderately at the peak and at the base, and the dripping of the molten metal hardly occurs, and a wide bead is obtained. If the product (Ip × Tp) of the pulse peak current (Ip) and the pulse peak time (Tp) is less than 415, the energy for forming the droplet is insufficient during the peak current period, and sufficient droplet formation is not possible. Sufficient gap resistance cannot be obtained. Further, when Ip × Tp is less than 415, the molten metal tends to sag. On the other hand, if the product of the pulse peak current (Ip) and the pulse peak time (Tp) exceeds 780, the excessively grown droplets are likely to be short-circuited, and the molten ground is blown away by the arc force at the time of re-ignition. However, the amount of spatter generated becomes unstable and the molten metal tends to sag, and sufficient gap resistance cannot be obtained. Therefore, Ip × Tp is set to a range represented by the following formula (1).
415 ≦ Ip (A) × Tp (msec) ≦ 780 (1)

  Hereinafter, the effects of the present invention will be described more specifically with reference to examples.

  First, Table 1 shows chemical components of the trial wire that was prepared by vacuum melting the raw steel, forging, rolling, wire drawing, annealing, copper plating, wire drawing to a wire diameter of 1.2 mm, and winding on a spool.

  Using the prototype wires shown in Table 1, a gap resistance test was conducted on the lap fillet joint in a lateral orientation by pulse MAG welding, and the gap width capable of crosslinking was investigated. The test specimen used was a 980 MPa class high-strength thin steel sheet having chemical components shown in Table 2, a plate thickness of 1.6 mm, and a weld length of 500 mm. In the gap resistance test, a spacer 5 was sandwiched between the front plate 1 and the rear plate 2 as shown in FIG. 2 to form a joint having a test piece length of 500 mm. At this time, welding was performed so that the gap length G1 = 1 mm increased to G2 = 3 mm. Welding was started from the gap length G1 = 1 mm side under the pulse MAG welding conditions shown in Tables 3 and 4 until the weld metal could not be cross-linked. As shown in FIG. 3, the welding was performed with the angle on the front plate 1 and the rear plate 2 side set as a target position and the angle θ of the welding torch 7 being 30 °. The weldable gap at this time was measured, and a weldable gap of 2.5 mm or more was evaluated as good. Further, the arc state, spatter generation amount, slag generation amount, and bead shape were sensory, and the presence or absence of hot cracking was visually evaluated.

  In addition, in order to evaluate the strength and toughness of the weld metal using the trial wire shown in Table 1, a weld metal test was conducted according to JIS Z 3111. In addition, the used steel plate is a high strength thin steel plate of 980 MPa class shown in Table 2. The welding conditions were as shown in Table 3, and a tensile test piece (JIS Z 2241 No. 10) and a Charpy impact test piece (JIS Z 2242 V notch test piece) were collected around the center of the steel plate thickness of the weld specimen. . The tensile test was evaluated as good when the tensile strength was 780 to 980 MPa. In the evaluation of the impact test, a Charpy impact test at −40 ° C. was performed, and the average of the three absorbed energy was 47 J or more. These results are summarized in Table 4.

  Test No. in Table 4 1-No. 12 is an example of the present invention, test no. 13-No. Reference numeral 25 is a comparative example. Test No. which is an example of the present invention. 1-No. No. 12, since the wire symbols W1 to W12 are within the respective component ranges defined in the present invention and the pulse MAG welding conditions are appropriate, the arc of the lap fillet joint welding in a lateral orientation by pulse MAG welding is stably generated. The amount of molten metal and the amount of slag generation are low, the viscosity and surface tension of the molten metal are appropriate, the molten metal does not sag, the weldable gap is wide, the bead appearance is good, and the tensile strength and absorbed energy are good even in the weld metal. The result was very satisfactory.

  Test No. in the comparative example. In No. 13, since the C of the wire symbol W13 was small, the arc was unstable, the amount of spatter was large, the molten metal melted and the bead appearance was poor. In the weld metal test, the tensile strength of the weld metal was low. Further, since the amount of Ni is small, the absorbed energy of the deposited metal is low.

  Test No. No. 14 had a lot of C in the wire symbol W14, so that the amount of spatter was large, crater cracking occurred, dripping of the molten metal occurred, and the bead appearance was poor. In the weld metal test, the tensile strength of the weld metal was high. Furthermore, since there is little Cr, the absorbed energy of the weld metal was low.

  Test No. In No. 15, since the Si of the wire symbol W15 was small, dripping of the molten metal occurred, the bead appearance was poor, and the weldable gap was narrow. Moreover, since there was much Ni, spatter generation amount was large and the crater crack generate | occur | produced. Furthermore, in the weld metal test, the tensile strength of the weld metal was high.

  Test No. No. 16 was a humping bead due to the large amount of Si of the wire symbol W16, the arc was unstable, and the amount of spatter generation and slag generation was large. Moreover, since there is little Mo, the absorbed energy of the weld metal was low in the weld metal test.

  Test No. In No. 17, since the Mn of the wire symbol W17 was small, dripping of the molten metal occurred, the bead appearance was poor, and the weldable gap was narrow. Further, since there is a large amount of Cr, a lot of spatter was generated, and in the weld metal test, the absorbed energy of the weld metal was low.

  Test No. No. 18 had a large amount of Mn in the wire symbol W18, so that a large amount of spatter was generated and the weldable gap was narrow. Furthermore, since the total of Cr and Mo is small, in the weld metal test, the tensile strength of the weld metal was low.

  Test No. No. 19 has a large amount of Mo of the wire symbol W19, so that the amount of spatter generated was large, and in the weld metal test, the absorbed energy of the weld metal was low. Moreover, since the pulse peak current (Ip) was high, dripping of the molten metal occurred and the bead appearance was poor.

  Test No. No. 20 had a large sum of Cr and Mo of the wire symbol W20, and crater cracking occurred. In the weld metal test, the tensile strength of the weld metal was high. Furthermore, since the pulse peak current (Ip) was low, the arc was unstable, the amount of spatter generated was large, and the bead appearance was poor.

  Test No. In No. 21, since the Ti of the wire symbol W21 was small, the arc was unstable. In the weld metal test, the absorbed energy of the weld metal was low.

  Test No. In No. 22, since the Ti of the wire symbol W22 is large, the amount of slag generated is large and the bead appearance is poor. In the weld metal test, the absorbed energy of the weld metal was low. Further, since the product Ip × Tp of the pulse peak current Ip and the peak time Tp was low, the amount of spatter generated was large, dripping of the molten metal occurred, and the weldable gap was narrow.

  Test No. No. 23 had less Cu of the wire symbol W23, so the absorbed energy of the weld metal was low in the weld metal test. Further, since the pulse base current (Ib) was low, the arc was unstable, the amount of spatter was large, and the bead appearance was poor.

  Test No. In No. 24, crater cracking occurred because of the large amount of Cu of the wire symbol W24. In the weld metal test, the absorbed energy of the weld metal was low. Furthermore, since the pulse base current (Ib) is high, the arc is unstable and the amount of spatter generated is large.

  Test No. 25, the wire symbol W6 is within the range of each component defined in the present invention, but the product Ip × Tp of the pulse peak current Ip and the peak time Tp is high. The bead appearance was poor and the weldable gap was narrow.

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

Claims (1)

In the pulse MAG welding method of a high-strength thin steel plate having a plate thickness of 1.2 to 3.2 mm,
% By mass relative to the total mass of the wire
C: 0.02 to 0.15%,
Si: 0.30 to 0.60%,
Mn: 1.20 to 1.90%,
Ni: 2.0 to 4.0%,
Cr: 0.30 to 0.70%,
Mo: 0.40 to 0.80%,
And the total of Cr and Mo: 0.75 to 1.15%,
Ti: 0.02 to 0.07%,
Cu: 0.10 to 0.40% is contained,
P: 0.03% or less,
S: 0.03% or less,
The remainder uses a solid wire made of Fe and inevitable impurities,
Pulse peak current (Ip): 440 to 600 A,
Pulse base current (Ib): 30-80A,
A pulse MAG welding method for high-strength thin steel sheets, wherein the pulse peak current (Ip) and the pulse peak time (Tp) are welded by applying a pulse satisfying the following formula (1).
415 ≦ Ip (A) × Tp (msec) ≦ 780 (1)

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