JPH09201697A - Flux-cored wire for gas shielded arc welding - Google Patents

Abstract

(57) Abstract: Ar-CO ₂ mixed gas shielded arc welding having good welding workability and excellent low temperature toughness and pore defect resistance in posture welding, especially in upward and horizontal welding. To provide a flux-cored wire for use. In a flux-cored wire for gas shielded arc welding in which a steel shell is filled with flux, TiO is added to the total weight of the wire in the filled flux.
₂ , containing Si, Mn, Mg, and further Al and Ti
A is contained in a ratio satisfying the following formula:
Flux-cored wire for r-CO ₂ mixed gas shielded arc welding. 0.2 ≦ (Al + Ti) ≦ −0.8 Mg + 0.7

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flux-cored wire for gas shielded arc welding, which uses an Ar--CO ₂ mixed gas as a shielding gas. More specifically, it has good welding workability in upward and horizontal welding. The present invention relates to a flux-cored wire for gas shielded arc welding, which has excellent low temperature toughness and pore defect resistance.

[0002]

2. Description of the Related Art A gas shielded arc welding flux cored wire using a titania-based flux as a filler and a single or mixed gas such as carbon dioxide, argon, helium or the like as a shielding gas has an excellent bead appearance,
It is widely used for structures of mild steel and high-strength steel of 50 kg class because it can improve the workability and the welding efficiency while obtaining the shape.

Conventionally, it has been known that the weld metal obtained by the titania-based flux-cored wire has a low low-temperature toughness, while having good welding workability.
Various methods for reducing the oxygen content in the weld metal and improving the low temperature toughness have been studied by adding a strong deoxidizer represented by g to the wire.

However, if the degree of deoxidation of the weld metal increases,
While the nitrogen solubility of the molten metal is increased, the nitrogen solubility of the solidified metal is reduced, the fluidity of the molten metal and molten slag is reduced, and the release of gas is hindered, so that pores are likely to occur in the weld metal. Are known.

Further, when an Ar-CO ₂ mixed gas is used as the shield gas, the oxygen content of the molten metal is lowered, so that the above phenomenon is further promoted, and especially in the case of single-sided welding using a solid backing material. When it is difficult to release the gas, such as a corrugated bead, there is a drawback that pore defects such as gas grooves and avatars are likely to occur.

For improving the low temperature toughness by studying a deoxidizing agent, for example, in JP-B-59-44159, Mg, Ti, and B are added in combination to reduce the amount of oxygen in the weld metal. Proposed a flux-cored wire for gas shielded arc welding with improved low temperature toughness, but no improvement has been made regarding pore defect resistance.

Furthermore, in Japanese Patent Publication No. 6-47191,
Limits the amount of potential hydrogen in the wire, and further slag forming agents, metal fluorides and deoxidizing agents (Si, Mn, Al, M
A flux-cored wire for gas shielded arc welding having few welding defects such as pits, gas grooves, and blow holes in high-speed fillet welding of a primer-coated steel sheet has been proposed by adding a certain amount of (g, Ti, etc.). But,
In high speed fillet welding, this is Al, M in the wire.
By adding a strong deoxidizing agent such as g and Ti, it is possible to suppress excessive formation of MnO having a low melting point and a function of lowering the viscosity of slag, and obtain good pit resistance and bead shape. It is difficult to secure the weldability and the low temperature toughness at the same time.

[0008]

The present invention solves the above problems,
It is intended to provide a flux-cored wire for gas shielded arc welding, which has good welding workability in posture welding, particularly upward and horizontal welding, and has excellent low temperature toughness and pore defect resistance.

[0009]

The gist of the present invention is to provide a flux-cored wire for gas shielded arc welding in which a steel shell is filled with a flux of TiO 2 in the filled flux with respect to the total weight of the wire. ₂ ; 4.0-7.5% Si; 0.2-1.0% Mn; 1.5-3.0% Mg; 0.10-0.35%, and further Al and T
i; Al; 0.05 to 0.40% Ti; 0.05 to 0.40%, and contained in a proportion satisfying the formula, for Ar-CO ₂ mixed gas shielded arc welding Located on the flux-cored wire.

0.2 ≦ (Al + Ti) ≦ −0.8Mg + 0.7

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, although low temperature toughness is improved by adding Mg to a titania-based flux-cored wire to reduce the amount of oxygen in the weld metal, Ar
One-sided welding using a —CO ₂ mixed gas as a shield gas has a drawback that pore defects such as gas grooves and avatars are likely to occur in the back bead.

Therefore, as a result of various investigations by the present inventors regarding the addition amount of the deoxidizing agent and the generation of pore defects, the present invention has made it possible to limit the addition amount of Mg to a low level so that even when an Ar—CO ₂ mixed gas is used. , It has been found that the occurrence of pore defects can be prevented.

Further, as a result of further research to improve the deterioration of low temperature toughness by limiting the amount of Mg, a specific amount of deoxidizing element such as Si, Mn, Al and Ti was added in combination with Mg. By doing so, without generating pore defects,
It was clarified that good low temperature toughness can be obtained.

The reasons for limiting the components in the present invention will be described below.

TiO ₂ ; 4.0-7.5% TiO ₂ is a main component of the titania-based flux-cored wire, and has excellent bead encapsulation and slag releasability not found in other slag forming agents. , Is an essential component as an arc stabilizer. However, if it is less than 4.0%, the molten metal cannot be held in all position welding, and the bead shape is deteriorated or the metal drips. Also,
If it exceeds 7.5%, the amount of slag generated becomes excessive, and slag entrainment easily occurs in the groove, so 4.0 to 4.0.
It was set to 7.5%.

Si: 0.2 to 1.0% Si is used as a deoxidizer and is effective in reducing the amount of oxygen in the weld metal. However, if it is less than 0.2%, the deoxidizing power is insufficient and blowholes are generated, and if it exceeds 1.0%, the yield amount in the weld metal becomes excessive, and the crystal grains become coarse and the low temperature toughness deteriorates. To do.

Mn: 1.5-3.0% Mn improves the fluidity of the molten metal, improves the bead shape, promotes deoxidation of the weld metal, and yields the weld metal, It has the effect of increasing strength. In order to obtain these effects, it is necessary to add 1.5% or more, but if it exceeds 3.0%, the yield amount to the weld metal becomes excessive, the strength increases, and cracks occur. It will be easier.

Mg; 0.10 to 0.35% Mg reacts with oxygen in a high temperature arc, and a deoxidation reaction is carried out at the stage of droplets at the tip of the wire. As a result, for example, deoxidation products such as MgO do not remain in the molten pool, and further, deoxidation reaction by Si and Mn reacting in the molten pool is assisted to reduce the amount of oxygen in the weld metal. . However, the object of the present invention is Ar-CO ₂
In order to obtain the porosity defect resistance in single-sided welding using a mixed gas, it is necessary to limit the content to 3.50% or less, and in order to obtain the deoxidizing effect, 0.10% or more is added. is necessary.

In order to obtain a sufficient deoxidizing effect, M
As a g source, in addition to metallic Mg, Al-Mg, Mg-Si, N
A Mg alloy such as i-Mg is used.

Al: 0.05 to 0.40% Al is a strong deoxidizer added to prevent the deterioration of the low temperature toughness by limiting the amount of Mg added. In order to obtain a sufficient deoxidizing effect, it is necessary to add 0.05% or more, but when it exceeds 0.40%, Al oxides rapidly increase, forming Ti oxides and large complex oxides. As a result, the low temperature toughness deteriorates, so the addition of Al is 0.05 to 0.4.
0%.

In order to obtain a sufficient deoxidizing effect, A
In addition to metallic Al, an Al alloy such as Fe-Al or Al-Mg is used as the l source.

Ti: 0.05 to 0.40% Ti is a strong deoxidizing agent that is added to prevent low temperature toughness due to the limitation of the amount of addition of Mg like Al.
If it is less than 0.05, the above effect cannot be obtained, and 0.40
%, The solid solution Ti increases, the weld metal excessively hardens, and the toughness decreases. Therefore, the addition of Ti is 0.0
It was set to 5 to 0.40%.

In order to obtain a sufficient deoxidizing effect, a Ti alloy such as Fe-Ti or the like is used as the Ti source in addition to Ti.

Further, the inventors of the present application decided to further study the optimum addition amounts of Al and Ti in order to achieve both the low temperature toughness of the weld metal and the welding workability.

In the flux-cored wire whose components were adjusted for Ar-CO ₂ mixed gas shielded arc welding, trial wires were prepared in which the amounts of deoxidizing agents Mg, Al, and Ti were changed, and the wires were placed in an upward position. Fig. 1 shows the results of an investigation of the welding workability and the low temperature toughness of the weld metal. It was found that good low temperature toughness can be obtained without causing pore defects in the back bead within the range of the conditions where the mark “◯” in FIG. 1 exists. This range is expressed as a formula.

0.2 ≦ (Al + Ti) ≦ −0.8Mg + 0.7 In the formula, if (Al + Ti) is less than 0.20, the effect of improving low temperature toughness cannot be obtained, and (−0.8Mg +) on the right side is not obtained.
If it exceeds 0.7), a large composite oxide of Al and Ti is formed, so that the low temperature toughness deteriorates.

Although the above are the essential components of the present invention, other slag agents, arc stabilizers, alloying elements and the like can be used in combination within the range where the above requirements can be satisfied.

For example, as the slag agent, SiO ₂ , A
l ₂ O ₃ , MnO, and FeO are N as an arc stabilizer.
Conventionally known are a ₂ O and K ₂ O. However, if a metal fluoride or the like that has the effect of lowering the slag viscosity is added,
Since it is difficult to secure a good bead shape in upward and horizontal welding, it is desirable not to use them together.

Further, CO in Ar-CO ₂ mixed gas ₂
The mixing ratio is preferably in the range of 5 to 35% by volume in combination with the wire of the present invention.

There is no limitation on the cross-sectional shape of the wire, and when the wire has a small diameter of 2.0 mm or less, it is generally a relatively simple cylindrical shape. Also, in the case of a seamless wire, by subjecting the surface to Cu plating,
In addition to obtaining the rust preventive effect of the wire, the electric conductivity of the wire surface is improved, which is also effective in improving the stability of the arc.

[0031]

EXAMPLES Table 1 shows a steel outer shell (C: 0.05%, Si:
0.01%, Mn: 0.30%, P: 0.003%,
S: 0.003%), and 15% based on the total weight of the wire
2 shows a flux-cored wire manufactured by filling flux with the filling rate of. Each of the wires has a diameter of 1.2 mm and contains iron, iron oxide and inevitable impurities derived from iron powder / ferroalloy in addition to the chemical components shown in Table 1.

Table 2 shows the results obtained by welding the above wire under the following groove and welding conditions, and examining the bead shape, the presence or absence of pore defects in the back bead, and the impact characteristics of the weld metal.

As for the impact property, a product having a Charpy absorbed energy at -20 ° C. of 47 J or more was accepted.

<Groove conditions> Steel plate: JIS G 3106 SM490B (plate thickness;
20mm) ・ Groove: 45 ° V type (root interval; 5mm) <Welding condition> ・ Welding position: Upward (semi-automatic) ・ Welding condition: 230A-24V ・ Shield gas: Ar-20% CO ₂ (flow rate: 25l) /
min) ・ Others: Use solid backing material

[0035]

[Table 1]

[0036]

[Table 2] In Table 1 and Table 2, No. With the wires 1 to 5 of the present invention, good pore defect resistance and low-temperature toughness were obtained in single-sided welding using an Ar—CO ₂ mixed gas in an upward posture.

On the other hand, in No. 6 and no. In No. 11, since TiO ₂ which is a slag forming agent was out of the scope of the present invention, No. 11 was used. In No. 6, the molten metal could not be held in the upward welding, resulting in a convex bead. In No. 11, on the contrary, the amount of slag produced was excessively large, so that slag inclusion occurred.

No. In No. 7, since Mg was excessively added, the fluidity of the molten metal and the molten slag was deteriorated, and gas release from the weld metal was hindered, so that gas grooves were generated in the back bead.

No. 8 and No. In No. 12, the amounts of Al and Ti added to assist the deoxidizing effect of Mg deviate from the (Al + Ti) amount within the range of the present invention. 8
In No. 2 since a large complex oxide of Al and Ti was formed in the weld metal. In No. 12, since the above-mentioned toughness improving effect was not obtained, the low temperature toughness failed in all cases.

No. In No. 9, the Mn was as high as 3.7%, which exceeds the range of the present invention, so the weld metal was excessively hardened and cracking occurred.

No. In No. 10, since both Si and Mg were small, the weld metal was excessively deoxidized, and blowholes were generated.

Although the present embodiment describes only the upward welding, the wire of the present invention can also be used in the horizontal welding.
Good pore defect resistance and low temperature toughness are obtained under almost the same conditions.

[0043]

As described above, with the wire of the present invention, good welding workability can be obtained and excellent low-temperature toughness and resistance can be obtained for the first time in single-sided welding in all positions using Ar-CO ₂ mixed gas. Pore defectivity can be secured.

Therefore, it is possible to reduce the rework of the welding bead,
This greatly contributes to improving the reliability of the welded portion and improving the welding efficiency.

[Brief description of drawings]

FIG. 1 is a diagram showing the effect of the addition amounts of Mg and (Al + Ti), which are deoxidizers, on the low temperature toughness of weld metal.

Claims (1)

[Claims] 1. A flux-cored wire for gas shielded arc welding, comprising a steel outer shell filled with flux, in weight% with respect to the total weight of the wire (hereinafter, all% are weight%).
In the illustrated), TiO _2; contains 0.10~0.35%,; 4.0~7.5% Si; 0.2~1.0% Mn; 1.5~3.0% Mg further, Al and Ti, Al; 0.05 to 0.40% Ti; at 0.05 to 0.40% range, and characterized in that it contains a proportion satisfying formula, Ar-CO ₂ Flux-cored wire for mixed gas shielded arc welding. 0.2 ≦ (Al + Ti) ≦ −0.8Mg + 0.7 ...