JP2018111102A - Mag welding wire for high-strength steel sheet and pulse mag welding method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an MAG welding wire for high-strength steel sheets, wherein, when welding a lap joint part or T joint part of a high-strength steel sheet with a tensile strength of 780 MPa or more, the arc is stable, the amounts of sputtering and slag generation are small, drop of weld metal is prevented even with a large gap, the bead appearance is good, and excellent strength of the weld metal is obtained, and a pulse MAG welding method using the same.SOLUTION: The present invention provides an MAG welding wire for a high-strength steel sheet with a thickness of 1.2-3.2 mm. The MAG welding wire contains, in mass% based on the total wire mass, C: 0.05-0.20%, Mn: 1.5-2.5%, and Mo: 0.4-0.7%, with Si: 0.10% or less, P: 0.03% or less, and S: 0.03% or less, with the balance being Fe and unavoidable impurities.SELECTED DRAWING: None

Description

  The present invention relates to a wire for MAG welding of a high strength thin steel sheet having a tensile strength of 780 MPa or more and a pulse MAG welding method using the same, and particularly to a lap joint portion of a high strength thin steel sheet having a thickness of 1.2 to 3.2 mm. When welding T and T joints, the arc is stabilized, the amount of spatter and slag generated is small, and even when the gap is large, the weld metal does not easily sag, the bead appearance is good, and good welding is achieved. The present invention relates to a wire for MAG welding of a high-strength thin steel sheet suitable for obtaining metal strength and a pulse MAG welding method using the same.

  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.

  On the other hand, a high-strength material is required for the welding wire to be applied to the welding of the high-strength steel plate. For example, in Patent Document 3, a thin high-tensile steel plate (690 MPa steel grade) includes a wire component, an arc voltage, A technique for improving the fatigue strength of a welded joint by limiting welding current, welding speed, and shielding gas is disclosed.

  Patent Document 4 discloses a technique for suppressing low temperature cracking of a welded portion by limiting the penetration depth, the Vickers hardness of the weld metal and the Pcm value of the wire in welding of a high strength thin steel sheet having a tensile strength of 980 MPa or more. Is disclosed.

  However, when a high strength thin steel sheet is MAG welded using the welding wires described in Patent Document 3 and Patent Document 4, the arc is unstable and the weld bead does not spread, and the familiarity of the bead toe becomes poor. There is a problem that it is easy.

  For this reason, pulse MAG welding to which pulses are applied in order to perform welding with a stable arc at a high speed has been proposed.

  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 amount of welding wire fed.

  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 part is also complicated in the welded part, and the accuracy of the aiming of the welding is required. This causes 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. 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 sag of the weld metal 3 to the front plate 1 side shown in FIG. 1C is likely to occur when the wire aiming position 6 shown in FIG. 3 is the front side 61 of the front plate 1. The steel plate (rear plate 2) shown in FIG. 1D 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 is a problem that it becomes impossible to bridge between the plate 1 and the rear plate 2 and it becomes difficult to form a good weld bead.

  Conventionally, as a wire for pulse MAG welding of a high-strength steel plate, for example, in Patent Document 5, a thin high-tensile steel plate (690 MPa steel grade) is welded by limiting the wire component, the shielding gas composition, and the pulse application conditions. A technique that can improve the mechanical properties and has low spatter generation and excellent welding workability is disclosed.

  However, the technique disclosed in Patent Document 5 also has a problem in that the arc is stable, the amount of slag generation is small, a weld metal having a good bead appearance cannot be obtained, and the strength of the weld metal is reduced. It was.

Japanese Patent Laying-Open No. 2015-175061 JP-A-2015-175051 Japanese Patent Laid-Open No. 8-25080 JP 2010-214466 A 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 amount of spatter generation and slag generation is small, and even when the gap is large, the weld metal does not easily sag, the bead appearance is good, and the strength of the weld metal is good. It aims at providing the wire for MAG welding of the high strength thin steel plate from which this is obtained, and the pulse MAG welding method using the same.

The gist of the present invention is as follows.
(1) In a MAG welding wire of a high-strength thin steel sheet having a thickness of 1.2 to 3.2 mm, C: 0.05 to 0.20%, Mn: 1.5 to 2.5%, Mo: 0.4 to 0.7%, Si: 0.10% or less, P: 0.03% or less, S: 0.03% or less, the balance is Fe and inevitable A wire for MAG welding of a high-strength thin steel sheet characterized by comprising impurities.

(2) In the pulse MAG welding method using the MAG welding wire of the high-strength thin steel sheet described in (1), the pulse peak current (Ip) is 400 to 600 A, the pulse base current (Ib) is 30 to 80 A, A pulse MAG welding method, wherein welding is performed by adding a pulse in which the pulse peak current (Ip) and the pulse peak time (Tp) satisfy the following formula (1).
400 ≦ Ip (A) × Tp (msec) ≦ 800 (1)

  According to the wire for MAG welding of a high strength thin steel sheet and a pulse MAG welding method using the same according to the present invention, a lap joint portion 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. When welding T and T joints, the arc is stable, the amount of spatter generation and slag generation is small, even when the gap is large, the weld metal does not sag easily, the bead appearance is good, and the welding is good High-efficiency and high-quality welds such as the strength of the metal 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 a test plate in the horizontal lap joint used for the Example of this invention. It is a figure which shows the wire aim position of the horizontal lap joint in the Example of this invention.

  In order to solve the above-mentioned problems, the present inventors have made a lap joint with a transverse orientation of a thin steel plate, welded at a welding speed of 60 cm / min or more under MAG welding and various pulse conditions using solid wires of various components. As a result of detailed examination of the stability of the arc, the weld bead width, the presence or absence of weld defects, and the hardness of the weld metal, the following knowledge was obtained.

  (1) The wire composition increases the Mn content and reduces the Si content to make the droplets finer, improve the arc stability, optimize the viscosity and surface tension of the molten metal, and use a wide bead. Welding with less spatter generation and slag generation is possible, and a weld metal having a good bead appearance and no weld defects can be obtained. Moreover, a high-strength weld metal can be obtained by optimizing the C content and adding Mo.

  (2) Even if the arc voltage is lowered by welding at a high speed of 80 cm / min or more by using the wire having the above-described composition, the pulse condition is set to a region in which the pulse transition is 1 pulse-1 drop. However, even when the gap is large, the weld metal does not easily sag and a bead with less spatter generation is obtained.

  Hereinafter, the reason for limitation of the wire component composition for MAG welding and pulse MAG welding conditions of the high-strength thin steel sheet of the present invention will be described.

  First, the wire component composition for MAG welding of a high strength thin steel sheet 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: 0.05-0.20%]
C has the effect of securing the strength of the weld metal and making the droplets finer, but in the present invention, the content of Si as a deoxidizing element for the purpose of making the droplets finer and obtaining a wide bead. The deoxidation of the molten metal is mainly performed by C. If C is less than 0.05%, deoxidation is insufficient, making it difficult to make the droplets fine, making the arc unstable and deteriorating the bead appearance. In addition, a large amount of spatter is generated, and dripping of molten metal occurs. On the other hand, when C exceeds 0.20%, 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. Therefore, C is set to 0.05 to 0.20%.

[Mn: 1.5 to 2.5%]
Mn acts as a deoxidizer and has the effect of ensuring the strength of the weld metal and optimizing the viscosity and surface tension of the molten metal. If Mn is less than 1.5%, the effect cannot be obtained, and the viscosity and surface tension of the molten metal deteriorate, so that the molten metal sags and sufficient gap resistance cannot be obtained. In addition, the strength is insufficient. On the other hand, if Mn exceeds 2.5%, the droplets become large and a short circuit is likely to occur, causing a spatter. Furthermore, the weld metal hardens and crack resistance deteriorates. Therefore, Mn is 1.5 to 2.5%.

[Mo: 0.4 to 0.7%]
Mo is an element that refines the structure of the weld metal and improves the strength. Also, by adding Mo, droplet formation is improved, the transition is stable, and the amount of spatter generated is reduced. If Mo is less than 0.4%, the above effect cannot be obtained, and the strength of the weld metal is lowered. In addition, the amount of spatter generated increases. On the other hand, if Mo exceeds 0.7%, the weld metal is hardened and crack resistance is deteriorated, and the droplet formation is poor, the transition becomes unstable, and the amount of spatter generated increases. Therefore, Mo is 0.4 to 0.7%.

[Si: 0.10% or less]
Si is added in a small amount to optimize the viscosity and surface tension of the molten metal. Moreover, even when the droplets are made finer by addition of a small amount and the arc voltage is lowered, the droplets are hardly short-circuited, which can contribute to the expansion of voltage conditions. However, if the Si content exceeds 0.10%, the droplets become large, so that a short circuit is likely to occur, causing spattering. In addition, the molten metal in the molten area cannot follow the welding speed and tends to be a humping bead. Furthermore, a lot of slag is generated, and the bead appearance is deteriorated. Therefore, Si is made 0.10% or less. In addition, although a minimum is not specifically limited, It is preferable that it is 0.005% or more from steelmaking cost.

[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 0.010% 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 0.015% or less.

  Furthermore, as a result of studying the optimum pulse MAG condition range where the bead width is wide and difficult to sag under high-speed welding conditions of 80 cm / min or more, the region of the pulse peak current Ip and the pulse peak time Tp which are one pulse-1 drop region Thus, the optimum pulse MAG condition range in which a wide bead can be obtained even when the wire target position fluctuates because the short-circuiting is difficult and the amount of spatter generated is small.

[Pulse peak current (Ip): 400-600A]
When the pulse peak current (Ip) is less than 400 A, the droplets are not released smoothly due to the electromagnetic pinch effect, the arc is unstable, and the bead width becomes narrow, so that sufficient gap resistance cannot be obtained. On the other hand, when the pulse peak current (Ip) exceeds 600 A, the melted ground tends to sag due to the arc force. Therefore, the pulse peak current (Ip) is 400 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 30A, the arc becomes unstable. When the pulse base current (Ib) exceeds 80A, the detachment of the droplets is not performed quickly, and the arc is unstable and the amount of spatter generated increases. Therefore, the pulse base current (Ib) is 30 to 80A.

[400 ≦ Ip (A) × Tp (msec) ≦ 800]
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. When the product (Ip × Tp) of the pulse peak current (Ip) and the pulse peak time (Tp) is less than 400, the energy for forming the droplets is insufficient in the peak current period, and sufficient droplets cannot be formed. Since the bead width is narrow, sufficient gap resistance cannot be obtained. If Ip × Tp is less than 400, 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 800, the excessively grown droplets are likely to short-circuit, and the molten ground is blown away by the arc force at the time of re-ignition. As the amount generated increases, 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).
400 ≦ Ip (A) × Tp (msec) ≦ 800 (1)

  The balance of the MAG welding wire of the high-strength thin steel plate to which the present invention is applied is Fe and inevitable impurities.

  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 wire shown in Table 1, a weld gap resistance test was conducted on a laterally overlapped fillet joint by MAG welding, and a gap width capable of crosslinking was investigated. The test body used was a high strength thin steel sheet of 980 MPa class 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 under the MAG welding conditions shown in Table 3 from the gap length G1 = 1 mm side, and welding was performed 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 considered good. In addition, the arc state, spatter generation amount, slag generation amount, presence of molten metal sagging, and bead appearance were investigated. Further, after completion of welding, a macro test piece was taken from 200 mm from the start of welding, Vickers hardness was measured according to JISZ2244, and an average value of 10 points was considered to be 250 to 400 Hv. The results are summarized in Table 4.

  Test No. in Table 1 and Table 4 1-No. 7 is an example of the present invention, test no. 8-No. 14 is a comparative example. Test No. which is an example of the present invention. 1-No. No. 7, since the wire symbols W1 to W7 are within the respective component ranges defined in the present invention, the arc of horizontal overlapped fillet joint welding by MAG welding is stable, the amount of spatter generation and slag generation is small, molten metal Viscosity and surface tension were appropriate, there was no dripping of molten metal, a wide weldable gap was obtained, a good bead appearance was obtained, and the Vickers hardness of the weld metal was also appropriate, which was a very satisfactory result.

  Test No. in Comparative Examples. In No. 8, since the C of the wire symbol W8 is small, the arc becomes unstable, the amount of spatter generated is large, dripping of the molten metal occurs near the start of welding, and the bead appearance is poor.

  Test symbol No. No. 9 had a large amount of spatter generated due to the large number C of the wire symbol W9, and the weld metal drooped near the start of welding. Moreover, the hardness of the weld metal was high and crater cracks also occurred.

  Test symbol No. In No. 10, since the Mn of the wire symbol W10 was small, the hardness of the weld metal was low, dripping of the molten metal occurred, the weldable gap was narrow, and the bead appearance was poor.

  Test symbol No. No. 11 had much Mn of the wire symbol W11, so the hardness of the weld metal was high, crater cracking occurred, and the amount of spatter was large.

  Test symbol No. In No. 12, since the Mo of the wire symbol W12 is small, the hardness of the weld metal is low and the amount of spatter generated is large.

  Test symbol No. No. 13 was a humping bead because of the large amount of Si of the wire symbol W13, and the amount of spatter generated was large. Moreover, the amount of slag produced was large and the bead appearance was poor.

  Test symbol No. No. 14 had a large amount of Mo of the wire symbol W14, so the hardness of the weld metal was high, crater cracking occurred, and the amount of spatter generated was large.

  Using the prototype wires shown in Table 1, a gap resistance test of transverse lap fillet joint welding by pulse MAG welding was performed. As the test body, the same test body as in Example 1 was used. For welding, the same welding and evaluation as in Example 1 were performed under the pulse MAG welding conditions shown in Tables 3 and 5. The results are summarized in Table 5.

  Test No. in Table 5 15-No. No. 20 is an example of the present invention, test no. 21-No. 26 is a comparative example. Test No. which is an example of the present invention. 15-No. No. 20, since the wire symbols W1 to W7 are within the respective component ranges defined in the present invention and the pulse MAG welding conditions are appropriate, the arc of transverse overlapped fillet joint welding by pulse MAG welding is stable, and the amount of spatter generated The weld metal has an appropriate viscosity and surface tension, no molten metal sagging, a wide weldable gap, a good bead appearance, and the weld metal has an appropriate Vickers hardness. .

  Test symbol No. in the comparative example. No. 21 was a humping bead due to the large amount of Si of the wire symbol W13, and the amount of spatter generated was also large. Moreover, the amount of slag produced was large and the bead appearance was poor. Furthermore, since the pulse base current Ib was low, the arc was unstable.

  Test symbol No. No. 22 is within the respective component ranges defined by the wire symbol W3 in the present invention, but since the pulse peak current (Ip) is high, welding metal sagging occurred near the start of welding.

  Test symbol No. In No. 23, since the Mn of the wire symbol W11 is large, the hardness of the weld metal is high, crater cracks are generated, and the amount of spatter generated is large. Moreover, since the pulse peak current (Ip) was low, the arc became unstable, the bead appearance was poor, and the weldable gap was narrow.

  Test symbol No. In No. 24, since the Mo of the wire symbol W12 is small, the hardness of the weld metal is low and the amount of spatter generated is also large. Further, since the product Ip × Tp of the pulse peak current Ip and the peak time Tp was low, the weldable gap was narrow, and molten metal sagging occurred near the start of welding.

  Test symbol No. 25, the wire symbol W4 is within the respective component ranges defined in the present invention, but since the pulse base current Ib is high, the arc becomes unstable and the amount of spatter generated is large.

  Test symbol No. No. 26 is within the component ranges defined by the wire symbol W5 in the present invention, but the product Ip × Tp of the pulse peak current Ip and the peak time Tp is high, so that the amount of spatter was large. Furthermore, molten metal dripping occurred near the start of welding, 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 (2)

In the MAG welding wire of a high-strength thin steel sheet having a thickness of 1.2 to 3.2 mm,
% By mass relative to the total mass of the wire
C: 0.05-0.20%,
Mn: 1.5 to 2.5%
Mo: contains 0.4 to 0.7%,
Si: 0.10% or less,
P: 0.03% or less,
S: 0.03% or less,
A MAG welding wire for a high-strength thin steel sheet, characterized in that the balance consists of Fe and inevitable impurities. In the pulse MAG welding method using the MAG welding wire of the high-strength thin steel sheet according to claim 1,
Pulse peak current (Ip): 400-600A,
Pulse base current (Ib): 30-80A,
A pulse MAG welding method, wherein welding is performed by adding a pulse in which the pulse peak current (Ip) and the pulse peak time (Tp) satisfy the following formula (1).
400 ≦ Ip (A) × Tp (msec) ≦ 800 (1)

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