JP5066378B2 - Copper plated solid wire for pulse MAG welding of hot dip galvanized steel sheet - Google Patents

Description

  The present invention relates to a copper-plated solid wire for pulse MAG welding of a hot dip galvanized steel sheet, and in particular, in high-speed welding, the arc is stable and the amount of spatter generation is small. The present invention relates to a copper-plated solid wire for pulse MAG welding of a hot-dip galvanized steel sheet in which a good bead shape is obtained without the occurrence of sagging.

A gas shielded arc welding method using a solid wire is highly efficient and widely applied to welding of thin plates because a weld metal with good mechanical performance and a good bead shape can be obtained. In recent years, pulse MAG welding methods that use shielding gas mainly composed of Ar gas mixed with CO ₂ and further O ₂ gas mixed have increased in order to reduce spatter generation and secure high-speed weldability. is doing. These welds are constructed under high-speed and high-current welding conditions to improve productivity, and form a good weld bead to produce a sound welded joint.

  Pulse MAG welding is a welding method in which a peak current that is higher than the average welding current and a base current that is lower than the average current are periodically added by a pulse power source. In this way, by melting the wire in the peak current period and transferring the droplet to the molten pool in the base current period, the droplet is transferred without short-circuiting the molten pool even when the average arc voltage is low. be able to. In pulse MAG welding, one droplet is generated at the time of one pulse peak current according to the wire feed speed by making the melting energy of the wire consisting of the product of peak current, peak voltage and peak time appropriate. The droplets are transferred during the base current period. Under such a pulse condition of 1 pulse-1 drop transition, the droplet smoothly moves to the molten pool, and the amount of spatter generated is reduced.

  However, in the welding of a zinc-based plated steel sheet coated with zinc or a zinc alloy for the purpose of improving the corrosion resistance, the arc in the vicinity of the welded portion evaporates and the arc becomes unstable even in pulse MAG welding. In particular, this tendency is remarkable in the hot-dip galvanized steel sheet because the plating layer is thicker than the electrogalvanized steel sheet. For this reason, the droplet transfer timing occurs discontinuously in the base current period and the peak current period, and the droplet transfer is not performed smoothly but scattered as spatter.

  As shown in FIGS. 1 (a) and 1 (b), particularly in the case of horizontal fillet welding of a lap joint where the upper plate 1 and the lower plate 2 of a thin steel plate are in close contact with each other, zinc vapor is welded. There is a problem that pores such as the pits 4 and the blowholes 5 remain easily in the metal 3.

  From such a background, as a pulse MAG welding wire for galvanized steel sheet with less pores such as pits and blowholes and generation of spatter, a technique in which Bi is added to Japanese Patent Laid-Open No. 1-309796 (Patent Document 1) JP-A-4-135088 (Patent Document 2) discloses a technique in which the sum and ratio of Si and Mn are limited, and JP-A-5-329682 (Patent Document 3) discloses a technique in which Ti and Nb are added. There is disclosure. In addition, as a pulse MAG welding method for galvanized steel sheets, Japanese Patent Laid-Open No. 8-309533 (Patent Document 4) describes the number of pulses and the unit time at which one pulse per one short-circuit droplet transfer is performed along with the pulse conditions. There is a disclosure of a technique in which the ratio of the number of hits per pulse is limited. However, these conventional techniques have some effects on the porosity resistance and low spattering, but the arc becomes unstable and the droplet transfer is not performed smoothly, and spattering is still likely to occur.

Moreover, the example of a bead formation state in case there exists the gap 6 in the horizontal attitude | position welding of the lap joint part of a thin steel plate to FIG. 2 (a), (b), (c) is shown. In the figure, 7 is a front plate and 8 is a rear plate. FIG. 2A shows an example in which a good weld metal 3 is obtained without undercut or dripping of molten metal. 4B shows an example in which an undercut 9 has occurred, and FIG. 4C shows an example in which a dripping 10 of molten metal has occurred on the front plate 7 side. In the prior art described above, there is a problem that undercut or molten metal sag is likely to occur when there is a gap in the transverse posture welding of the lap joint of thin steel plates as shown in FIGS. 2 (b) and 2 (c).
Japanese Patent Laid-Open No. 1-309796 Japanese Patent Laid-Open No. 4-135088 JP-A-5-329682 JP-A-8-309533

  In the present invention, in pulse MAG welding of hot dip galvanized steel sheet, the arc is stable, the droplets are transferred stably and regularly, the bead shape is good, the generation of pores such as pits and blowholes, and the generation of spatter An object of the present invention is to provide a copper-plated solid wire for pulse MAG welding of a hot-dip galvanized steel sheet in which the amount is extremely small and undercut and dripping of molten metal do not occur.

The gist of the present invention is that in a copper-plated solid wire for pulse MAG welding of a hot dip galvanized steel sheet, C: 0.02 to 0.12 mass%, Si: 0.25 to 1.20 mass%, Mn: 0.00. 4 to 1.5% by mass, Nb: 0.1 to 1.2% by mass, Al: 0.002 to 0.020% by mass, copper plating thickness: 0.3 to 1.1 μm In addition, the surface of the wire has 0.3 to 1.5 g of lubricating oil that is liquid at room temperature and 0.004 to 0.25 g of potassium at a room temperature, and the others are P: 0.025% by mass or less. , S: 0.025% by mass or less, O: 0.010% by mass or less , the balance being Fe and inevitable impurities, and more preferably Si, Mn and Nb are Si + Mn + 2Nb 2.2-4. It is 6 mass%.

  According to the copper-plated solid wire for pulse MAG welding of hot dip galvanized steel sheet according to the present invention, the arc is stable and the droplets are transferred stably and regularly, and the generation of pores such as pits and blowholes and spattering are performed. Pulse MAG welding of galvanized steel sheets with excellent welding efficiency such as generation of extremely small amounts and no occurrence of undercut or bead sag is possible.

Hereinafter, the copper-plated solid wire for pulse MAG welding of the hot dip galvanized steel sheet of the present invention will be described in detail.
The material to be welded by the solid wire of the present invention is a hot dip galvanized steel sheet, because the plating layer is thicker than the electrogalvanized steel sheet, and the problems of pores such as pits and blowholes and spattering are prominent. is there. The hot dip galvanized steel sheet includes, for example, zinc-based alloy plating in which zinc contains several percent of Al. Also included is an alloyed hot-dip galvanized steel sheet, generally called a galvanized steel sheet, which is heat-treated after hot-dip galvanizing and converted to an alloy layer containing about 10% iron and has excellent paint adhesion. It has the features such as.

  In order to solve the above-mentioned problems, the inventors made trial wires with different components and different wire surface states, and welded hot-dip galvanized steel sheets at a high speed of 1.5 m / min or more under pulse conditions. As a result of conducting a detailed investigation on the arc state, the bead shape and the spatter generation state, the following knowledge was obtained.

(1) By adjusting the amount of C and Al in the wire composition, the amount of copper plating on the surface of the wire, the amount of lubricating oil, and the amount of potassium, the arc is stabilized and the amount of spatter generated is reduced even in an atmosphere in which zinc evaporates.
(2) By adjusting the Nb amount of the wire composition and the amount of lubricating oil on the wire surface, generation of pores such as pits and blowholes in horizontal fillet welding of lap joints is suppressed.
(3) By adjusting the amounts of C, Si, Mn, Nb and Al in the wire composition, and the potassium amount on the wire surface, a good bead shape can be obtained particularly in the transverse posture welding of the lap joint.
(4) By having potassium on the surface of the wire, the droplets are made uniform and small, so that the transition of 1 pulse to 1 drop is not disturbed, the arc is further stabilized, the amount of spatter is extremely reduced, and undercut occurs. It becomes difficult. In addition, since the droplets are small, the peak voltage time can be shortened, so that higher-speed welding is possible.

Hereinafter, the reasons for limiting the wire composition and the lubricating oil and potassium on the wire surface in the present invention will be described.
[C: 0.02 to 0.12% by mass]
C has the effect of stabilizing the arc and making the droplets finer. If it is less than 0.02% by mass (hereinafter referred to as “%”), the droplets become large and the arc becomes unstable, resulting in a large amount of spatter generation. An undercut occurs in the lateral orientation welding of the lap joint. On the other hand, if it exceeds 0.12%, the viscosity of the molten metal is inferior, and in particular, the molten metal drips in the lateral posture welding of the lap joint, resulting in a poor bead shape. Further, not only the spatter generation amount increases, but also the weld metal is remarkably hardened and the crack resistance is deteriorated.

[Si: 0.25 to 1.20%]
Si is an indispensable element as a main deoxidizer for weld metal, and is an element having a large effect of increasing the electric resistance of the wire to increase the amount of melting of the wire and further increasing the viscosity and surface tension of the molten metal. This makes it possible to form a weld bead that is wide and does not sag even in the transverse posture welding of the lap joint. However, if it is less than 0.25%, the above effect cannot be obtained. On the other hand, if it exceeds 1.20%, the surface tension of the molten metal excessively increases, so that the molten metal cannot follow the high welding speed, and tends to be a humping bead.

[Mn: 0.4 to 1.5%]
Mn acts as a deoxidizer together with Si, and has the effect of increasing the viscosity and surface tension of the molten metal. If it is less than 0.4%, the viscosity and surface tension of the molten metal are lowered, so that the molten metal drips in the lateral posture welding of the lap joint and the bead shape becomes poor. On the other hand, if Mn exceeds 1.5%, the viscosity and surface tension of the molten metal increase excessively, and a wide bead cannot be obtained.

[Nb: 0.1 to 1.2%]
Nb fixes nitrogen and suppresses generation of pores such as pits and blowholes due to shielding failure and zinc vapor in high-speed welding. Moreover, there exists an effect | action which improves a bead shape. If Nb is less than 0.1%, pits and blowholes are likely to occur particularly in horizontal fillet welding of lap joints. On the other hand, if Nb exceeds 1.2%, the viscosity and surface tension of the molten metal are lowered, so that the molten metal drips in the lateral posture welding of the lap joint and the bead shape becomes poor.

[Si + Mn + 2Nb: 2.2 to 4.6%]
Si, Mn, and Nb are contained within the above ranges, and more preferably, Si + Mn + 2Nb is 2.2 to 4.6%. If the Si + Mn + 2Nb is less than 2.2%, the viscosity and surface tension of the molten metal are lowered, so that the molten metal drips in the lateral orientation welding of the lap joint and the bead shape tends to be poor. On the other hand, if Si + Mn + 2Nb exceeds 4.6%, the hardness of the weld metal increases rapidly and high temperature cracking is likely to occur.

[Al: 0.002 to 0.020%]
Al stabilizes the arc during high-speed welding and reduces the amount of spatter generated. If it is less than 0.002%, the arc becomes unstable and a large amount of spatter is generated, and further, undercut occurs in the lateral posture welding of the lap joint. On the other hand, if it exceeds 0.020%, the viscosity and surface tension of the molten metal are lowered, so that the molten metal drips in the lateral posture welding of the lap joint and the bead shape becomes poor.

[Copper plating thickness: 0.3 to 1.1 μm]
Copper plating on the surface of the wire improves the electrical conductivity between the wire and the chip and stabilizes the arc. When the copper plating thickness is less than 0.3 μm, the electrical conductivity between the wire and the chip is partially non-uniform, and the arc becomes unstable due to fluctuations in the arc length, resulting in a large amount of spatter generation. Undercut occurs in the horizontal posture welding. On the other hand, if the copper plating thickness on the wire surface exceeds 1.1 μm, the copper content of the weld metal increases and the crack resistance deteriorates.

[Lubricating oil liquid at normal temperature on the wire surface: 0.3 to 1.5 g per 10 kg of wire]
Lubricating oil, which is liquid at normal temperature, forms a film on the wire surface and stabilizes the arc by keeping the wire feeding speed constant during wire feeding. Further, potassium described later can be uniformly dispersed on the wire surface. If the lubricating oil is less than 0.3 g per 10 kg of wire (hereinafter referred to as g / 10 kgW), potassium cannot be uniformly dispersed on the surface of the wire, and the size of the droplet does not become uniform, and one pulse −1 Disturbing drop transition increases spatter generation. On the other hand, if it exceeds 1.5 g / 10 kgW, pits and blowholes are generated in the weld.

  The lubricating oil may be animal or vegetable oil, mineral oil or synthetic oil. Palm oil, rapeseed oil, castor oil, pig oil, cow oil, fish oil, etc. can be used as animal and vegetable oils, and machine oil, turbine oil, spindle oil, etc. can be used as mineral oils. As the synthetic oil, hydrocarbon type, ester type, polyglycol type, polyphenol type, silicone type and fluorocarbon type can be used.

[Potassium: 0.004 to 0.25 g / 10 kgW]
Since potassium on the surface of the wire is made into uniform and small droplets, the transition of 1 pulse-1 drop is not disturbed, the arc is stabilized, and the amount of spatter generated is extremely reduced. That is, since the peak time can be shortened, high-speed welding is possible, and there is no undercut or dripping of molten metal, and the bead shape is good. If potassium is less than 0.004 g / 10 kgW, the effect is not obtained, the droplets are largely irregular, disturb the transition of 1 pulse-1 drop, the arc becomes unstable, and the amount of spatter generated is large. Undercut occurs in the horizontal posture welding. On the other hand, if it exceeds 0.25 g / 10 kgW, the bead shape becomes concave, and the molten metal drips in the lateral posture welding of the lap joint, resulting in a poor bead shape.

  As potassium, compounds such as potassium stearate, potassium carbonate, potassium citrate and the like are used. If these fine powders are mixed in the lubricating oil, potassium is preferably dispersed on the surface of the wire when applied after finishing wire drawing at the time of wire production. Moreover, what added the ionized potassium in lubricating oil can also be used.

S is preferably contained in an amount of 0.005% or more in order to improve the familiarity of the bead toe. However, when S and P each exceed 0.025%, the crack resistance of the weld metal deteriorates.
On the other hand, if O exceeds 0.010%, the wire surface is cracked during wire production, and the copper plating on the wire surface is peeled off during welding, and chip clogging is likely to occur. Therefore, O is set to 0.010% or less.
Hereinafter, the effect of the present invention will be specifically described with reference to examples.

  A solid wire with a wire diameter of 1.2 mm was prepared by applying copper plating to the wire surfaces of various components shown in Table 1 and applying various lubricating oils and potassium.

JIS G3131 SPHC plate thickness 2.6 mm, length 500 mm, and galvanized steel sheet with a basis weight of 45 g / m ² , as shown in FIG. As a joint, horizontal fillet welding was performed under the welding conditions A shown in Table 2. The welding power source can adjust the wire feed speed to increase or decrease the welding current (average current of peak current and base current) and can set the peak current and peak time. The pulse peak current value and the pulse peak time were set so that pulse MAG welding of one pulse and one drop transition could be performed for each prototype wire, although the pulse frequency was 300 Hz. Welding, as shown in FIG. 3, a corner portion of the wire aiming position 12 lap joint, the angle theta ₁ of the torch 13 was performed in 60 °.

Further, as shown in FIG. 4, the spacer 11 was sandwiched between the rear plate 8 and the front plate 7, and the lap joint lateral posture was set such that the gap G of the gap 6 was 2.5 mm, and welding was performed under the welding condition B shown in Table 2. As shown in FIG. 4, welding was performed with the wire aiming position 12 being the center of the steel plate thickness on the front plate 7 side and the angle θ _{2 of the} torch 13 being 30 °. Note that the pulse peak current value and the pulse peak time were set so that each prototype wire had 1 pulse-1 drop.

  Each wire was examined for arc stability, pore generation, bead shape and spatter generation. The amount of pores such as pits and blowholes was investigated by lap joint horizontal fillet welding shown in FIG. The number of pits generated was examined by appearance survey, and the state of blowholes was checked by X-ray transmission tests. The number of pits generated was 3 or less and the number of blowholes generated was 10 or less.

The spatter generation amount was calculated by calculating the spatter generation amount per minute by performing welding five times by lap joint lateral orientation welding shown in FIG. 4 using a copper collection box. As a result, the amount of spatter generated was 1 g / min or less. Arc stability and bead shape were investigated for both lap joint horizontal fillet welding and lap joint lateral orientation welding. The results are summarized in Table 3.

In Tables 1 and 3, wire symbols W1 to W10 are examples of the present invention, and wire symbols W11 to W20 are comparative examples.
Since the wire symbols W1 to W10 according to the present invention have appropriate wire components and copper plating thicknesses, and the lubricating oil and potassium applied to the wire surface are also appropriate, both the lap joint horizontal fillet welding and the lateral orientation welding are performed. The results were very satisfactory because the arc was stable, there was no dripping or undercutting of the molten metal, the bead shape was good, the amount of pits, blowholes and spatter was small, and there were no hot cracks.

In the comparative example, the wire symbol W11 had a high C, so that a large amount of spatter was generated, and the molten metal was dripped by the lap joint lateral orientation welding, resulting in a poor bead shape. Moreover, hot cracking occurred in the crater part.
Since the wire symbol W12 had a low C, the arc was unstable and the amount of spatter was large in both the lap joint horizontal fillet welding and the lateral orientation welding. In addition, undercuts occurred in the lap joint lateral orientation welding. Furthermore, since Si + Mn + 2Nb was high, the molten metal dripped during the lap joint lateral orientation welding, and the bead shape was poor.

Since the wire symbol W13 is high in Si, both the lap joint horizontal fillet welding and the lateral posture welding became humping beads.
In the wire symbol W14, since the potassium on the surface of the wire was low, the arc was unstable in both the lap joint horizontal fillet welding and the lateral posture welding. In addition, undercuts occurred in the lap joint lateral orientation welding. Furthermore, since Si was low, molten metal was dripped by lap joint lateral orientation welding, and the bead shape was poor.

Since the wire symbol W15 has a high Mn, both the lap joint horizontal fillet welding and the lateral posture welding became convex beads. Moreover, since Si + Mn + 2Nb was high, high temperature cracking occurred in the crater portion by lap joint lateral orientation welding.
In the wire symbol W16, since a large amount of lubricating oil was applied to the surface of the wire, pits and blowholes were frequently generated by lap joint horizontal fillet welding. Moreover, since Mn was low, the molten metal was dripped by the lap joint lateral orientation welding, and the bead shape was poor.

In the wire symbol W17, the amount of spatter generated increased because of less lubricant applied to the wire surface. Moreover, since Nb was high, the molten metal was dripped by the lap joint lateral orientation welding, and the bead shape was poor.
Since the wire symbol W18 has a low Nb, the occurrence of pits and blowholes increased during lap joint horizontal fillet welding. Moreover, since Al was high, the molten metal was dripped by the lap joint lateral orientation welding, and the bead shape was poor.

  In the wire symbol W19, since Al is low, the arc is unstable and the amount of spatter is large in both the lap joint horizontal fillet welding and the lateral orientation welding. In addition, undercuts occurred in the lap joint lateral orientation welding. Furthermore, since the copper plating thickness was thick, hot cracking occurred in the crater portion by lap joint lateral orientation welding.

  In the wire symbol W20, since the copper plating thickness was thin, the arc was unstable and the amount of spatter was large in both the lap joint horizontal fillet welding and the lateral orientation welding. Moreover, since potassium on the surface of the wire was high, the molten metal dripped during the lap joint lateral posture welding, and the bead shape was poor.

In lap joint horizontal fillet welding, (a) is a diagram showing an example in which pits (b) have blowhole pores. (A), (b), (c) is a figure which shows the example of the bead formation state in lap joint lateral attitude welding, respectively. It is a figure which shows the wire aim position of the lap joint horizontal fillet welding used for the Example of this invention. It is a figure which shows the wire aim position of the lap joint sideways attitude | position meat welding used for the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Upper plate 2 Lower plate 3 Weld metal 4 Pit 5 Blow hole 6 Gap 7 Front plate 8 Rear plate 9 Undercut 10 Molten metal dripping 11 Spacer 12 Wire aim position 13 Torch θ ₁ , θ ₂ Torch angle

Claims (2)

In copper-plated solid wire for pulse MAG welding of hot-dip galvanized steel sheet, C: 0.02 to 0.12 mass%, Si: 0.25 to 1.20 mass%, Mn: 0.4 to 1.5 mass %, Nb: 0.1-1.2% by mass, Al: 0.002-0.020% by mass, having a copper plating thickness: 0.3-1.1 μm, and on the wire surface The amount per 10 kg of wire is 0.3 to 1.5 g of lubricating oil which is liquid at room temperature and 0.004 to 0.25 g of potassium, and the others are P: 0.025 mass% or less, S: 0.025 A copper-plated solid wire for pulse MAG welding of a hot-dip galvanized steel sheet, characterized in that it is not more than mass%, O: not more than 0.010 mass% , and the balance is made of Fe and inevitable impurities. Furthermore, Si, Mn, and Nb are Si + Mn + 2Nb and are 2.2-4.6 mass%, The copper plating solid wire for pulse MAG welding of the hot dip galvanized steel plate of Claim 1 characterized by the above-mentioned.

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