JPH0866792A - Metal flux cored wire for galvanized steel sheet and gas shield arc welding method - Google Patents

Abstract

PURPOSE: To provide the gas shield arc welding method to reduce defect of pit, blow hole, etc., due to zinc vapor for a steel sheet having wide difference in kind and deposit quantity of galvanization. CONSTITUTION: A zinc or zinc alloy galvanized steel sheet is subjected to gas arc welding using pure Ar or the gas in which <=30vol% CO2 is mixed to Ar. Further, the metal flux cored wire having a composition consisting of, by weight for the whole wire, 0.05-0.10% C, 0.10-0.60% Si, 0.20-1.00% Mn, 0.20-0.90% total of one kind or more out of Nb, V, in which SiO2 or a silicate acid compound satisfies <=0.30% in term of SiO2 , in which an oxygen content 0wt.% for plating deposit quantity Xg/m<2> satisfies 0.43.logX-0.2<=0<=0.43.logX, is used.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a flux-cored wire for galvanized steel sheet, which can obtain a sound weld metal in which defects such as pits and blow holes are hard to occur when gas-shielded arc welding of zinc or zinc alloy-plated steel sheet is performed. And a gas shielded arc welding method.

[0002]

2. Description of the Related Art Generally, a galvanized steel sheet is a hot-rolled or cold-rolled steel surface coated with zinc for the purpose of rust prevention. It is widely used in a wide range of fields such as building materials, parts for household appliances, and automobile bodies. Therefore, there are many types of steel sheets depending on the galvanizing method and the amount of coating adhered. For example, in the classification of the plating method, JIS G 33
"Hot-dip galvanized steel sheets and strips" in 02 is JIS
In addition to “electrogalvanized steel sheets and strips” specified in G 3313, there are various galvannealed steel sheets and the like. Also, the method for measuring the amount of plating adhered is JIS H 0
401 "Hot dip galvanizing test method", and the coating amount of steel sheet is also defined in JIS G, for example.
40-for 3302 "hot dip galvanized steel sheet and strip"
In the range of 600 g / m ² , JIS G3313 “electrogalvanized steel sheet and steel strip” defines the range of 10 to 50 g / m ² .

[0003] These galvanized steel sheets are usually processed by arc welding like ordinary steel materials. However, when galvanized steel sheets are arc-welded, their boiling points are lower than the melting point of iron due to the influence of welding heat. Zinc having a temperature of (906 ° C) penetrates into the molten pool as air bubbles, causing pore defects such as pits (pores open on the weld bead surface) and blow holes (pores not open on the weld bead surface). It is a frequent issue and is an important issue in welding construction.

As a method of reducing these defects such as pits and blow holes as much as possible, various welding wires and welding methods have been proposed. In particular, the gas shield arc welding method in which the welding wire is a metal-based flux-cored wire and the mixed gas in which Ar is mixed with CO ₂ is 1.5 m longer than the combination with a solid wire or pure CO ₂ gas. Since the welding arc is stable even in high-speed welding of 1 / min, spatter is less likely to occur, and due to the shallow bead shape of the flux-cored wire, the amount of zinc evaporated due to the effect of welding heat can be reduced. This is an advantageous method for welding galvanized steel sheets.

A flux-cored wire for galvanized steel sheets and a gas shielded arc welding method using the flux-cored wire are characterized in that the amounts of C and O in all the wires are specified in JP-A-64-31569. A flux-cored wire that can be used is disclosed in Japanese Patent Laid-Open No. 3-146295.
The flux-cored wire in which the amount of i, Mn, Nb, and V and the amount of potential hydrogen are specified is also disclosed in Japanese Patent Publication No. 4-557.
No. 97 discloses a flux-cored wire in which the amounts of C, P, Zr, Ti and Nb are specified. Each of these wires is a gas shielded arc welding wire that uses a combination of CO ₂ , pure Ar or Ar-CO ₂ mixed gas and a metal flux-cored wire, and each has a specific wire component and a specific plating adhesion amount. The effect of reducing the pore defects is obtained only for the galvanized steel sheet having.

[0006]

As described above, pure Ar is used.
Alternatively, in gas shielded arc welding using a combination of metal-based flux-cored wires with Ar-CO ₂ mixed gas as a shield gas, a gas shielded arc welding method using a wire of a specific metal component has been proposed. The gas shielded arc welding method using the above wire was a gas shielded arc welding method effective only for a galvanized steel sheet having a specific coating amount. Therefore, when the coating amount of the plating is small, excess hydrogen may penetrate into the weld metal, or the additive elements of zinc and uncombined may deteriorate the performance of the weld metal. However, there is a problem that the effect of reducing pore defects cannot be obtained by the conventional method.

Further, a method of controlling the influence of metallic elements in the wire by adding an oxidizing component to the shield gas can be considered. However, if an oxidizing component is added to the shield gas, the arc becomes unstable. Therefore, there is a possibility that the arc stability itself, which is a characteristic of using pure Ar or an Ar—CO ₂ mixed gas, may be impaired because it may occur or a large amount of spatter may occur.

The present invention is not possible with the conventional gas shielded arc welding method in gas shielded arc welding using a combination of metal flux-cored wires with pure Ar or Ar-CO ₂ mixed gas as a shield gas. For a wide range of galvanized steel sheets with different types of galvanizing and coating weight, it has excellent arc stability during high-speed welding and contains flux for galvanized steel sheets that reduces pore defects such as pits and blowholes caused by zinc vapor. It is an object of the present invention to provide a wire and a gas shielded arc welding method.

[0009]

First, the inventors of the present invention used a conventional metal flux-cored wire by an arc welding phenomenon analyzer capable of observing a welding current, an arc voltage and a welding arc image at high speed and with high accuracy. The arc welding phenomenon of the previously galvanized steel sheet was observed in detail, and the following (1)-
I found the characteristic of (3). (1) In combination with a metal-based flux-cored wire, arc stability is good with pure Ar or a mixed gas containing 30 vol% or less of CO ₂ , but CO ₂
When the mixing ratio exceeds 30 vol%, the arc becomes unstable, and even in droplet transfer, short circuit or unstable droplet shape transfer is likely to occur, and the amount of spatter generated remarkably increases. (2) The galvanized steel sheet having a large amount of coating adhered has a large amount of gas generated from the molten pool and a large amount of pore defects. (3) When a small amount of slag is generated in the vicinity of the solidification interface behind the molten pool and the slag has a high viscosity and a large thickness, pore defects frequently occur.

In order to reduce the porosity defects of the galvanized steel sheet, the following actions (a) to (c) are considered to be necessary, and welding is performed with a metal flux-cored wire having various wire components adjusted, A gas shielded arc welding method that has good stability and reduces porosity defects in the weld metal was studied. (A) The deoxidizing element in the wire is limited, and the amount of oxygen in the wire is appropriately controlled with respect to the amount of plating on the steel sheet to oxidize the zinc attached to the steel sheet to reduce the amount of zinc vapor released. Suppress. (B) By increasing the oxygen potential of the molten pool,
It lowers the viscosity of the molten metal and facilitates the release of zinc vapor by the stirring action. (C) The slag composition of the double oxide containing ZnO and the oxide of the deoxidizing metal element is made to have a low melting point and a low viscosity to facilitate the release of bubbles in the vicinity of the solidification interface on the surface of the molten pool.

As a result, there is an optimum combination for the relationship between the coating weight and the wire composition, and the occurrence of pore defects can be effectively reduced by controlling the properties of a small amount of slag generated during welding. We have invented a flux-cored wire and a gas shielded arc welding method. That is, the gist of the present invention is to use zinc or zinc alloy plated steel sheet in pure Ar or Ar with 30 vol% or less of C.
In gas shielded arc welding using a shield gas mixed with O ₂ , C: 0.0
5 to 0.10 wt%, Si: 0.10 to 0.60 wt
%, Mn: 0.20 to 1.00 wt%, the sum of one or more kinds of Nb and V: 0.20 to 0.90 wt%, and SiO ₂ or a silicate compound is converted to SiO ₂ and is 0 for the entire wire. Oxygen content O with respect to the coating amount X (g / m ² ) on the welded surface of the steel plate
(Wt%) is 0.43 · logX for the whole wire
The metal-based flux-cored wire and the gas shield arc welding method are characterized in that −0.2 ≦ O ≦ 0.43 · logX.

[0012]

The operation of the flux-cored wire for galvanized steel sheet and the gas shielded arc welding method of the present invention will be described in detail below. First, in the welding method of the present invention, zinc or zinc alloy-plated steel sheet is pure Ar or Ar in an amount of 30 v.
The reason is limited to the gas shielded arc welding method performed by using a combination of a shield gas mixed with ol% or less of CO ₂ and a metal-based flux-cored wire. It is characterized by controlling the oxidation of zinc vapor and metal components in the inside, and its effect is exhibited only in the combination of the shield gas composition and the wire component described below. It is an important requirement that it not grow and that the stability of the arc be good.

Therefore, the shield gas is, as described above,
Pure Ar or a mixed gas in which 30 vol% or less of CO ₂ is mixed with Ar is required. CO ₂ mixing ratio is 30 vol%
When it exceeds the limit or when an oxidizing component such as O ₂ is added,
The effect due to the combination with the wire composition described later cannot be exerted, the arc becomes unstable, and even in droplet transferability, short-circuiting or transfer with an unstable droplet shape easily occurs, and the amount of spatter generated also significantly increases. To do. In addition, the flux-cored wire and welding method of the present invention have a coating amount of 300
It is applied when g / m ² or less.

Further, the fact that the flux-cored wire of the present invention is a metal-based flux-cored wire is that the arc-corrosion of the flux-cored wire is much better than that of the solid wire, and the tolerance to welding conditions is large. For a slag-based flux-cored wire containing a large amount of slag component, a large amount of slag is generated during welding, and it is difficult to release zinc vapor and other gas components.

Next, the reasons for limiting the composition of C, Si, Mn, Nb and V of the flux-cored wire of the present invention will be described. The flux-cored wire of the present invention is characterized by containing a wire oxygen amount in a specific range with respect to a specific coating amount of the galvanized steel sheet, and C in the wire secures the strength of the weld metal. In gas shielded arc welding, it is a component that bonds best with oxygen in the welding arc atmosphere, and when the amount of C added exceeds 0.10 wt%, the balance of the amount of oxygen in the wire for oxidizing zinc in the plating is lost. . Furthermore, since it is easy to cause cold cracking of the weld metal due to the balance with other metal components, 0.10 wt%
Must be limited to: On the other hand, if it is less than 0.05 wt%, it cannot be used because the blowhole increases due to the insufficient stirring effect of the molten pool and the strength of the weld metal becomes insufficient. Therefore, C in the wire is 0.05-0.10w
It is necessary to limit the range to t%.

Both Si and Mn in the wire secure the mechanical performance of the weld metal, and a part of them is combined with oxygen in the wire, which will be described later, to form an oxide film or slag having a complex oxide composition. Is. When these components are added excessively, the oxidation effect of zinc is suppressed, and the amount of slag generated in the vicinity of the solidification interface on the surface of the molten pool becomes excessive and the effect of reducing pore defects cannot be exhibited.
Must be limited to 0.60 wt% or less and Mn to 1.00 wt% or less. However, when Si is reduced to less than 0.10 wt% and Mn is reduced to less than 0.20 wt%, deoxidation becomes insufficient and conversely, pore defects are likely to occur. Therefore, the appropriate amount of Si in the wire is 0.10 to 0.60 wt%,
The appropriate amount of Mn in the wire is limited to the range of 0.20 to 1.00 wt%.

Next, the action of Nb and V in the wire will be described. Generally, in metal-based flux-cored wires, there are oxides such as alkali silicates that are inevitably present as a surface oxide film in powder raw materials such as iron powder and arc stabilizers or pretreatment agents for powder raw materials. Exists. These oxide components, S in the wire by welding
SiO ₂ —ZnO— is formed on the surface of the molten pool due to the oxidation of i and Mn, and ZnO produced by the oxidation of zinc in the plating.
MnO-FeO slag is generated, but if the viscosity of this slag and the interfacial tension with the molten metal are large,
Due to the convection of the molten metal, a thick slag with poor wettability is formed near the solidification interface. This thick slag hinders the release of bubbles, which causes the formation of pits and blowholes having large pore diameters.

A part of Nb and V in the wire is combined with nitrogen in the air mixed in the shield gas to prevent the generation of pores due to the nitrogen gas, but most are generated in the welding method of the present invention. It acts to reduce the viscosity of slag. Nb and V are oxidized by oxygen in the wire, which will be described later, and act on the slag as Nb ₂ O ₅ and V ₂ O ₅ to reduce the viscosity of the slag and facilitate the release of bubbles. In order to obtain this effect, the amount of Nb and V in the wire must be 0.20 wt% or more in total for one or more types.
If the total amount of one or more of Nb and V exceeds 0.90 wt%, the alloy is excessively alloyed in the weld metal, and the weld metal becomes excessively strong and cracks easily occur.
Is limited to 0.20 to 0.90 wt%.

As described above, the metal-based flux-cored wire has an oxide component such as an alkali silicate used as an arc stabilizer or a pretreatment agent for powder raw materials. ₂ has a great effect on the amount and viscosity of slag even in a small amount, and when the amount of SiO ₂ or silicate compound contained in the wire converted to SiO ₂ exceeds 0.30 wt% with respect to the entire wire. However, the amount of slag generated is too large and thick, and particularly in the case of a steel sheet having a large amount of plating adhered, bubbles such as zinc vapor and excess oxidizing gas are less likely to be discharged from the slag. Accordingly, the wire in the SiO ₂ amount of SiO ₂ or silicic acid compound in terms of SiO ₂ has to be limited so as to be less 0.30 wt% relative to the total wire.

Further, as a reason for limiting the amount of oxygen in the wire, the inventors of the present invention, as described above, are required to reduce the porosity defects of various galvanized steel sheets having a wide range of coating deposits. It was considered effective to control the amount of oxygen in the wire appropriately with respect to the amount of plating on the steel sheet and oxidize zinc attached to the steel sheet to suppress the amount of zinc vapor released. Then, with respect to galvanized steel sheets having various coating adhesion amounts, as a result of investigating the porosity defect resistance when performing a welding test using metal flux-cored wires having different amounts of oxygen in the wire, the adhesion of the plating on the steel sheet The relationship between the amount and the range of the appropriate oxygen amount in the wire is a logarithmic function, and the range is the oxygen content O with respect to the coating adhesion amount X (g / m ² ) on the steel plate weld surface.
(Wt%) is 0.43 · logX for the whole wire
The range was −0.2 ≦ O ≦ 0.43 · logX.

In the flux-cored wire of the present invention, P, S, Ni, Cr, Mo, Cu, Ti and Z in the wire are used.
Other components such as r and RE metal are not specified, but may be added within a range that does not deteriorate the pore defect resistance. Also, the shape of the wire is preferably a seamless type in which oxygen can be easily controlled, but it may be a type that uses a hoop for the outer cover, and the metal component and oxygen can be added as a single substance or as a compound in the flux. It may be added to the outer metal. Furthermore, the welding power source and other welding peripheral devices used in the welding method of the present invention are not particularly limited,
Even better effects can be obtained by using together a power source having an inverter type pulse waveform.

[0022]

EXAMPLE An example of the present invention will be described with reference to the results of a welding test using a trial wire. Table 1 shows the composition of the metal-based flux-cored wire that was prototyped and the results of comparison of the amount of pore defects generated by performing lap fillet welding of a galvanized steel sheet using the wire. The test plate used for this welding test is JI
A material equivalent to SG 3302 SGC400 and having a plating deposition amount of 44.6 g / m ² was used. The dimensions were plate thickness 2.0 mm × width 50 mm × length 300 mm, and the welding wire had a wire diameter of 1. It is 2 mm. Welding test is 8
Using the 0% Ar-20% mixed gas of CO ₂ welding current 2
Overlap fillet welding was performed under the conditions of 00 A, welding voltage 24 V, and welding speed 20 mm / sec. The porosity defect rate was determined by calculating the percentage of the cross-sectional area of the porosity defect with respect to the cross-sectional area of the weld bead from the X-ray transmission test photograph of the test plate after the welding test. The evaluation by the porosity defect rate of the welded part of the galvanized steel sheet considers static strength and fatigue strength of the welded part, and
Less than 0% was judged as good and 10% or more was judged as bad.

As is clear from Table 1, C and S in the wire
Total of one or more of i, Mn, Nb and V, Si in wire
Any of the comparative examples welded using the wires of W4 to W12 in which O ₂ is outside the range of the present invention has a high porosity defect rate and cannot be used. In particular, when Mn is too low in W8, arc instability is caused, and in the wire of W11 having too high Nb + V and W12 having too high SiO ₂ , the slag amount becomes excessive and the defect rate becomes 30%.
% Or more. However, when the wires of Examples W1 to W3 of the present invention were used for welding, the porosity defect rate was less than 10%, and good effects were observed.

Further, FIG. 1 shows the galvanized steel sheet having a thickness of 2.0 mm and having the adhesion amount of the five kinds of plating shown in Table 2, C, Si, Mn, Nb, V, and SiO ₂ in Table 1 and W3.
Porosity defect resistance when lap fillet welding is performed using a metal-based flux-cored wire in which the amount of oxygen in the wire is adjusted to 0.27 to 1.06 wt% by adjusting the amount of oxygen in the wire as it is Is the result of the investigation. The amount of plating deposited on each steel sheet was measured by the film thickness test method of JIS H0401. The welding conditions are the same as the welding conditions in Table 1, and the evaluation of the pore defect resistance is the same as the method of Table 1 with a defect rate of less than 10%.
Those with a defect rate of 10% or more are shown as having poor pore defect resistance.

From FIG. 1, a range between two straight lines in the figure, which is the range of the present invention, that is, an oxygen content O (wt%) with respect to a coating adhesion amount X (g / m ² ) on a steel plate welding surface. Is 0.43 · logX−0.2 ≦ O for the entire wire
Compared with the case of ≦ 0.43 · logX, when it is out of the range of the present invention, the pore defect resistance is poor, and the effect of the present invention can be seen.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

As described above, according to the flux-cored wire and the gas shielded arc welding method of the present invention, a wide range of types of zinc plating and the amount of coating adhered, which are impossible with the conventional gas shielded arc welding method, are different. It is possible to perform gas shielded arc welding on a steel sheet to reduce pit defects such as pits and blow holes due to zinc vapor.

[Brief description of drawings]

FIG. 1 is a diagram showing an influence of a coating amount of a steel sheet and oxygen in a wire on a pore defect in welding a galvanized steel sheet.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiro Miura 3-5-4 Tsukiji, Chuo-ku, Tokyo Inside Nippon Steel Welding Industry Co., Ltd. (72) Inventor Ichiro Suda 3-5, Tsukiji, Chuo-ku, Tokyo No. 4 Inside the Nippon Steel Welding Industry Co., Ltd. (72) Inventor Ryuichi Shimura 3-5-4 Tsukiji, Chuo-ku, Tokyo Inside the Nippon Steel Welding Industry Co., Ltd. research laboratory

Claims (2)

[Claims] 1. C: 0.05 to the whole wire.
0.10 wt%, Si: 0.10 to 0.60 wt%, M
n: 0.20 to 1.00 wt%, the total of one or more of Nb and V: 0.20 to 0.90 wt%, and the SiO ₂ or silicate compound converted to SiO ₂ is 0.30 with respect to the entire wire.
Oxygen content O (wt%) with respect to the amount X (g / m ² ) of plating adhered to the welded surface of the steel plate, satisfying wt% or less
Is 0.43 · logX−0.2 ≦ for the entire wire
A metal-based flux-cored wire for galvanized steel sheet, wherein O ≦ 0.43 · logX. 2. A zinc or zinc alloy-plated steel sheet is pure A
Gas shield arc welding performed by using a shielding gas in which r or Ar is mixed with 30 vol% or less of CO ₂ , wherein the metal-based flux-cored wire according to claim 1 is used for welding. Arc welding method.