JP2022121317A - Wire with flux for gas shield arc-welding - Google Patents

Abstract

To provide a wire with a flux for gas shield arc-welding that is used in horizontal fillet welding for corrosion-resistance steel, which is suitable for horizontal fillet gas shield arc-welding in welding a crude oil tank or the like, is excellent in arc stability and in welding operability including bead formation, and can acquire weld metal with excellent corrosion resistance.SOLUTION: A wire with a flux for gas shield arc-welding, which has an outer film made of steel filled with fluxes and is used in horizontal fillet welding for corrosion-resistance steel, contains TiO2, SiO2, ZrO2, Al2O3, MgO, C, Si, Mn, Mo, Cu, Al, Mg, Na+K and F in respective predetermined ranges, with respect to the total mass of the wire, where the others are made of Fe and inevitable impurities.SELECTED DRAWING: None

Description

The present invention relates to a flux-cored wire for gas-shielded arc welding.

In general, steel for welded structures is used for crude oil tanks, and the strength and toughness of the base material and the strength and toughness of the weld are required. Furthermore, for the reasons described below, corrosion resistance has recently been required in base metals and welds.

For example, it is known that general corrosion occurs on the inner surface of a crude oil tank of a tanker, particularly on the steel material used for the underside of the upper deck and the upper portion of the side wall. The cause of this general corrosion is
(1) Repeated dew condensation and drying (dry and wet) on the surface of the steel sheet due to the temperature difference between day and night,
(2) Inert gas (e.g., about 5 vol% _O2 , about 13 _vol % _CO2 , SO2 is about 0.01% by _volume , the _balance being _N2 .) into the _condensed water,
(3) dissolution of corrosive gases such as H ₂ S volatilizing from crude oil into condensed water;
(4) Residual seawater used to wash crude oil tanks;
etc.
This is because sulfate ions (SO ₄ ^2- ) and chloride ions (Cl ^- ) are detected in strongly acidic condensed water during dock inspections conducted every 2.5 years. can also be seen.

In addition, when H ₂ S is oxidized using iron rust produced by corrosion as a catalyst, solid S is formed in layers in the iron rust, but these corrosion products are easily exfoliated and dropped off, and the crude oil tank is damaged. Sediments on the bottom. Therefore, in the dock inspection, repairing the upper part of the tank and collecting deposits at the bottom of the tank are currently performed at great cost.

On the other hand, the steel material used for the bottom plates of crude oil tanks of tankers does not corrode due to the corrosion-inhibiting action of the crude oil itself and the corrosion-inhibiting action of the crude oil-derived protective coat (oil coat) formed on the inner surface of the crude oil tank. was thought to be However, recent research has revealed that bowl-shaped localized corrosion (pitting corrosion) occurs even in the steel material of the tank bottom plate. The cause of this localized corrosion is
(1) Presence of aggregated water in which salts typified by sodium chloride are dissolved at a high concentration;
(2) Detachment of the oil coat due to excessive washing,
(3) increasing the concentration of sulfides contained in crude oil;
(4) Increasing the concentration of O ₂ , CO ₂ , SO ₂ and the like in the explosion-proof inert gas dissolved in the condensed water.
In fact, high concentrations of chloride ions and sulfate ions were detected in the analysis of water accumulated in crude oil tanks during dock inspections of actual ships.
As the most effective method for preventing general corrosion and localized corrosion as described above, there is a method of applying a heavy coating to the steel material surface to isolate the steel material from the corrosive environment. However, the painting of crude oil tanks requires a huge amount of surface area to be painted, and the deterioration of the paint film requires repainting about once every 10 years. Occur. Furthermore, it has been pointed out that corrosion is accelerated in the corrosive environment of a crude oil tank in a portion where the paint film is heavily coated and damaged.

In general, when the corrosion resistance of the weld metal is inferior to that of the base material (steel), the dissolution of the weld metal is accelerated in a corrosive environment. Therefore, various techniques have been proposed to improve the corrosion resistance of the steel material itself and the welded joints to improve the corrosion resistance of the crude oil tank under the corrosive environment.
For example, in Patent Documents 1 to 3, in submerged arc welding (SAW) and shielded arc welding (SMAW), by adjusting the chemical composition balance of the weld metal and steel material, selective corrosion in the weld zone is suppressed. there is In addition, in Patent Document 4, it can also be applied to gas shielded arc welding (carbon dioxide gas arc welding, _CO2 welding), and by using a welding wire with a composition obtained by obtaining a target composition of corrosion-resistant elements from the base metal dilution rate, , discloses a welding method that suppresses selective corrosion in welds. Furthermore, Patent Literature 5 discloses a welding wire for crude oil tank steel with improved corrosion resistance.

Japanese Unexamined Patent Application Publication No. 2005-21981 Japanese Patent Application Laid-Open No. 2005-23421 JP 2010-43342 A Japanese Patent Application Laid-Open No. 2012-1809 JP 2013-226578 A

However, the inventions described in Patent Documents 1 to 4 limit the components contained in the welded joint, and it is necessary to consider the component contents of the welding material and the welding base metal, making it difficult to adjust them. Met.
In addition, the welding material (flux-cored wire) described in Patent Document 5 aims to improve corrosion resistance by specifying the content of components contained in the wire, but welding workability is sufficient. has not been considered. In particular, when manufacturing crude oil tanks, etc., horizontal fillet gas-shielded arc welding is often used. Good bead shape, spatter yield, slag releasability, and hot crack resistance are required. In order to satisfy not only the corrosion resistance of the weld metal part but also the weldability, it is important to optimize the wire alloy composition and the flux composition.

The present invention has been made in view of the above-described circumstances, and is suitable for horizontal fillet gas shield arc welding when welding crude oil tanks, etc., and has good welding workability such as arc stability and bead shape. It is an object of the present invention to provide a flux-cored wire for gas-shielded arc welding used for horizontal fillet welding of corrosion-resistant steel, capable of obtaining a weld metal having excellent corrosion resistance.

Here, the corrosion-resistant steel refers to steel that satisfies predetermined corrosion resistance performance in corrosion resistance evaluation corrosion tests for crude oil tank bottom plates and crude oil tank top plates specified by the International Maritime Organization (IMO). Specifically, for corrosion-resistant steel for bottom plate, the corrosion rate in the evaluation corrosion test is 1 mm/year or less, and for corrosion-resistant steel for top plate, the estimated corrosion amount after 25 years in the evaluation corrosion test is 2 mm. Refers to steel that is:

A flux-cored wire for gas-shielded arc welding according to one aspect of the present invention is a flux-cored wire for gas-shielded arc welding used for horizontal fillet welding of corrosion-resistant steel, in which a steel outer sheath is filled with flux,
per total wire mass,
TiO ₂ : 1.5% by mass or more and 4.5% by mass or less,
SiO ₂ : 0.3% by mass or more and 1.5% by mass or less,
ZrO ₂ : 0.1% by mass or more and 1.0% by mass or less,
Al ₂ O ₃ : 0.02% by mass or more and 0.30% by mass or less,
MgO: 0.05% by mass or more and 0.30% by mass or less,
C: 0.01% by mass or more and 0.10% by mass or less,
Si: 0.3% by mass or more and 1.5% by mass or less,
Mn: 0.5% by mass or more and 3.5% by mass or less,
Mo: 0.05% by mass or more and 0.4% by mass or less,
Cu: 0.10% by mass or more and 0.5% by mass or less,
Al: 0.05% by mass or more and 0.5% by mass or less,
Mg: 0.1% by mass or more and 0.7% by mass or less,
Na + K: 0.02% by mass or more and 0.30% by mass or less, and F: 0.01% by mass or more and 0.20% by mass or less,
and the balance is composed of Fe and unavoidable impurities.

The flux-cored wire for gas-shielded arc welding further has Ti: 0.05% by mass or more and 0.50% by mass or less, and B: 0.001% by mass or more and 0.020% by mass or less, based on the total mass of the wire. It is preferable to contain at least one selected.

In addition, the flux-cored wire for gas-shielded arc welding further has Sb: 0.01% by mass or more and 0.20% by mass or less, and Sn: 0.01% by mass or more and 0.20% by mass or less, based on the total mass of the wire. It is preferable to contain at least one selected from.

According to the present invention, a weld metal that is suitable for horizontal fillet gas shield arc welding during welding of crude oil tanks and the like, has good welding workability such as arc stability and bead shape, and has excellent corrosion resistance is produced. It is possible to provide a flux-cored wire for gas-shielded arc welding used for horizontal fillet welding of corrosion-resistant steel that can be obtained.

FIG. 1 is a diagram showing a corrosion test apparatus used for the general corrosion test. FIG. 2 is a diagram showing a corrosion test apparatus used for the localized corrosion test.

Hereinafter, a form (this embodiment) for carrying out the present invention will be described in detail. The present invention is not limited to the embodiments described below, and can be arbitrarily modified without departing from the gist of the present invention.

In order to solve the above-mentioned problems, the present inventors diligently studied the contents of various components such as oxide components and metal components in the flux-cored wire. As a result, it is possible to obtain a flux-cored wire for gas-shielded arc welding that has good welding workability such as arc stability and bead shape required in horizontal fillet welding, and that can obtain a weld metal with excellent corrosion resistance. I found out.

That is, the flux-cored wire according to this embodiment has a predetermined content of each chemical component with respect to the total mass of the wire. The flux-cored wire according to this embodiment will be described below.

[1. Flux-cored wire]
The flux-cored wire of the present embodiment has a steel sheath (hoop) filled with flux. Specifically, the flux-cored wire according to the present embodiment is composed of a tubular steel outer sheath and flux filled inside (inside) the outer sheath. In addition, the flux-cored wire may be in any form of a seamless type with no seam on the outer cover, or a seam type with a seam on the outer cover such as a C section, a lapped section, or the like. Moreover, the flux-cored wire may or may not be plated with Cu or the like on the wire surface (outside of the sheath).

The thickness of the steel outer sheath and the wire diameter (diameter) of the flux-cored wire according to this embodiment are not particularly limited, but from the viewpoint of wire feeding stability, the preferred wire diameter is 0.00. 8 to 4.0 mm, and a more preferable wire diameter is 1.2 to 2.4 mm.

Next, the composition of the flux-cored wire according to the present embodiment will be described in detail with respect to the reasons for adding the components and the reasons for limiting the composition. Each element for obtaining the weld metal having the required properties may be added from either the steel skin or the filling flux. Therefore, unless otherwise specified in the following description, the amount of each component in the flux-cored wire is the total amount of the components contained in the steel sheath and the flux, and the total mass of the wire (steel sheath and (total amount of flux).

<TiO ₂ : 1.5% by mass or more and 4.5% by mass or less>
TiO ₂ is a component generally added as a slag forming agent, and has the effect of improving arc stability and uniformly coating the bead surface to improve the bead shape.
If the TiO ₂ content is less than 1.5% by mass, the amount of slag becomes insufficient, and the bead shape deteriorates due to the deterioration of the slag encapsulation property. Therefore, the TiO ₂ content in the wire should be 1.5% by mass or more, preferably 2.0% by mass or more, and more preferably 2.5% by mass or more.
On the other hand, when the TiO ₂ content exceeds 4.5% by mass, the arc stability improves, but the amount of slag increases, resulting in excessive slag formation thickness and poor bead shape. Therefore, the TiO ₂ content in the wire should be 4.5 mass % or less, preferably 4.0 mass % or less, more preferably 3.5 mass % or less.
The TiO ₂ content means a value obtained by converting the content of all Ti compounds contained in the wire into TiO ₂ . For example, the TiO ₂ equivalent value is obtained assuming that all the Ti compounds contained in the wire are TiO ₂ .

<SiO ₂ : 0.3% by mass or more and 1.5% by mass or less>
SiO ₂ is a component that is generally added as a slag forming agent, and has the effect of improving arc stability.
If the SiO ₂ content is less than 0.3% by mass, the arc becomes unstable and the amount of spatter increases. Therefore, the SiO ₂ content in the wire should be 0.3 mass % or more, preferably 0.4 mass % or more, more preferably 0.5 mass % or more.
On the other hand, if the _SiO2 content exceeds 1.5% by mass, the slag becomes hard and the slag releasability deteriorates. Therefore, the SiO ₂ content in the wire should be 1.5 mass % or less, preferably 1.3 mass % or less, more preferably 1.0 mass % or less.
The SiO ₂ content means a value obtained by converting the content of all Si compounds contained in the wire into SiO ₂ .

<ZrO ₂ : 0.1% by mass or more and 1.0% by mass or less>
ZrO ₂ is a component that has the effect of improving bead smoothness.
If the ZrO ₂ content is less than 0.1% by mass, the smoothness of the bead tends to deteriorate in downward and horizontal fillet welding. Therefore, the ZrO ₂ content in the wire should be 0.1 mass % or more, preferably 0.2 mass % or more, more preferably 0.3 mass % or more.
On the other hand, when the ZrO ₂ content exceeds 1.0% by mass, isopodity tends to deteriorate in horizontal fillet welding, and the bead shape in the vertical position approaches a convex shape. Therefore, the ZrO ₂ content in the wire should be 1.0% by mass or less, preferably 0.7% by mass or less, and more preferably 0.5% by mass or less.
The ZrO ₂ content means a value obtained by converting the content of all Zr compounds contained in the wire into ZrO ₂ .

<Al ₂ O ₃ : 0.02% by mass or more and 0.30% by mass or less>
Al ₂ O ₃ is a component that has the effect of raising the slag solidification point.
If the Al ₂ O ₃ content is less than 0.02% by mass, the effect of raising the slag freezing point cannot be obtained, and the molten metal drips. Therefore, the Al ₂ O ₃ content in the wire should be 0.02% by mass or more, preferably 0.05% by mass or more, and more preferably 0.10% by mass or more.
On the other hand, when the Al ₂ O ₃ content exceeds 0.30% by mass, the bead shape deteriorates. Therefore, the Al ₂ O ₃ content in the wire should be 0.30% by mass or less, preferably 0.20% by mass or less, and more preferably 0.15% by mass or less.
The Al ₂ O ₃ content means a value obtained by converting the content of all Al compounds contained in the wire into Al ₂ O ₃ .

<MgO: 0.05% by mass or more and 0.30% by mass or less>
MgO is a component that has the effect of adjusting the solidification temperature and viscosity of slag and improving the bead shape.
If the MgO content is less than 0.05% by mass, the effect of adjusting the solidification temperature and viscosity of the slag and improving the bead shape cannot be obtained. Therefore, the MgO content in the wire should be 0.05% by mass or more, preferably 0.07% by mass or more, and more preferably 0.10% by mass or more.
On the other hand, when the MgO content exceeds 0.30% by mass, the arc becomes too strong and the amount of spatter generation increases. Therefore, the MgO content in the wire should be 0.30% by mass or less, preferably 0.25% by mass or less, and more preferably 0.20% by mass or less.
The MgO content means a value obtained by converting the content of all Mg compounds contained in the wire into MgO.

<C: 0.01% by mass or more and 0.10% by mass or less>
C is a component that has the effect of improving the strength of the weld metal.
If the C content is less than 0.01% by mass, the above effects cannot be sufficiently obtained, and the strength of the weld metal is insufficient and the toughness is lowered. Therefore, the C content in the wire should be 0.01% by mass or more, preferably 0.02% by mass or more, and more preferably 0.03% by mass or more.
On the other hand, if the C content exceeds 0.10% by mass, the arc will be too concentrated and undercut will likely occur. Therefore, the C content in the wire should be 0.10% by mass or less, preferably 0.07% by mass or less, and more preferably 0.05% by mass or less.
As the C source, in addition to those added to the steel outer shell, iron powder and alloy powder with a large carbon content, graphite, graphite, carbon simple substances such as carbon nanotubes, starch, and cornstarch, which are added to the flux. organic matter.

<Si: 0.3% by mass or more and 1.5% by mass or less>
Si is a component that promotes deoxidation and improves bead conformability.
If the Si content is less than 0.3% by mass, pores are generated due to insufficient deoxidation, and the conformability of the bead is deteriorated. Therefore, the Si content in the wire should be 0.3% by mass or more, preferably 0.5% by mass or more, and more preferably 0.7% by mass or more.
On the other hand, when the Si content exceeds 1.5% by mass, intergranular ferrite precipitation is accelerated and the toughness of the weld metal is lowered. Therefore, the Si content in the wire should be 1.5% by mass or less, preferably 1.3% by mass or less, and more preferably 1.0% by mass or less.
The Si content means the sum of the Si content contained in the single metal and alloy contained in the wire. That is, Si contained in compounds such as Si oxides is not included in this Si content.

<Mn: 0.5% by mass or more and 3.5% by mass or less>
Mn is a component that acts as a deoxidizing agent to remove oxygen in the weld metal as slag and has the effect of improving mechanical properties.
If the Mn content is less than 0.5% by mass, the above effects cannot be sufficiently obtained. Therefore, the Mn content in the wire should be 0.5% by mass or more, preferably 1.0% by mass or more, and more preferably 1.5% by mass or more.
On the other hand, if the Mn content exceeds 3.5% by mass, the strength of the weld metal becomes excessive and the toughness decreases. Therefore, the Mn content in the wire should be 3.5% by mass or less, preferably 3.0% by mass or less, and more preferably 2.5% by mass or less.
The Mn content means the total content of Mn contained in the single metal and alloy contained in the wire.

<Mo: 0.05% by mass or more and 0.4% by mass or less>
Mo is a component that has the effect of suppressing not only pitting corrosion of the welded metal portion of the bottom plate of the oil tank of the tanker, but also general corrosion resistance of the welded metal portion of the back surface of the upper deck of the tanker. The reason why Mo has such an effect of improving corrosion resistance is that MoO ₄ ^2- is generated with the corrosion of the steel sheet, and the presence of this MoO ₄ ^2- suppresses the penetration of chloride ions into the steel sheet surface. considered to be from
If the Mo content is less than 0.05% by mass, the above effect cannot be obtained. Therefore, the Mo content in the wire should be 0.05% by mass or more, preferably 0.10% by mass or more, and more preferably 0.15% by mass or more.
On the other hand, when the Mo content exceeds 0.4% by mass, not only do the above effects saturate, but problems such as the occurrence of hot cracks and a decrease in the toughness of the weld metal portion occur. Therefore, the Mo content in the wire should be 0.4% by mass or less, preferably 0.3% by mass or less, and more preferably 0.2% by mass or less.
In addition, Mo content means the total content of Mo contained in the simple substance of the metal contained in a wire, and an alloy.

<Cu: 0.10% by mass or more and 0.5% by mass or less>
Cu is present in rust generated by corrosion and has the effect of enhancing corrosion resistance.
If the Cu content is less than 0.10% by mass, the effect of enhancing the corrosion resistance of the weld metal cannot be obtained. Therefore, the Cu content in the wire should be 0.10% by mass or more, preferably 0.15% by mass or more, and more preferably 0.20% by mass or more.
On the other hand, when the Cu content exceeds 0.5% by mass, not only does the effect of improving the corrosion resistance saturate, but problems such as the occurrence of hot cracks and a decrease in the toughness of the weld metal part occur. Therefore, the Cu content in the wire should be 0.5% by mass or less, preferably 0.4% by mass or less, and more preferably 0.3% by mass or less.

<Al: 0.05% by mass or more and 0.5% by mass or less>
Al is a strong deoxidizing element, and is a component that has the effect of improving the mechanical properties of the weld metal by improving the yield of weld metal components that have an affinity for oxygen. It also has the effect of stabilizing the droplet transfer of the arc.
If the Al content is less than 0.05% by mass, the yield of weld metal components having an affinity for oxygen is low, the denitrification effect is insufficient, and the required toughness cannot be obtained. In addition, arc droplet transfer becomes unstable. Therefore, the Al content in the wire should be 0.05% by mass or more, preferably 0.10% by mass or more, and more preferably 0.15% by mass or more.
On the other hand, if the Al content exceeds 0.5% by mass, the yield of the weld metal components becomes excessive, resulting in a decrease in toughness, or an increase in the slag solidification point, resulting in a decrease in porosity resistance. Therefore, the Al content in the wire should be 0.5% by mass or less, preferably 0.4% by mass or less, and more preferably 0.3% by mass or less.
The Al content means the total content of Al contained in the single metal and alloy contained in the wire.

<Mg: 0.1% by mass or more and 0.7% by mass or less>
Mg is a deoxidizing element and is effective in improving the toughness of the weld metal.
If the Mg content is less than 0.1% by mass, a sufficient deoxidizing effect cannot be obtained, and no improvement in the toughness of the weld metal can be expected. Therefore, the Mg content in the wire should be 0.1% by mass or more, preferably 0.2% by mass or more, and more preferably 0.3% by mass or more.
On the other hand, if the Mg content exceeds 0.7% by mass, the amount of spatter increases and welding workability deteriorates. Therefore, the Mg content in the wire should be 0.7% by mass or less, preferably 0.6% by mass or less, and more preferably 0.5% by mass or less.
The Mg content means the total content of Mg contained in the single metal and alloy contained in the wire.

<Na + K: 0.02% by mass or more and 0.30% by mass or less>
Either one or both of the Na compound and the K compound are added to the flux as arc stabilizers. Here, Na+K means the total content of Na and K in Na compounds and K compounds, respectively.
If the total amount of Na and K contained in the wire is less than 0.02% by mass, the effect of stabilizing the arc is small and the amount of spatter generated increases. Therefore, Na+K in the wire should be 0.02% by mass or more, preferably 0.05% by mass or more, and more preferably 0.10% by mass or more.
On the other hand, if the total amount of Na and K exceeds 0.30% by mass, the bead shape deteriorates. Therefore, Na+K in the wire should be 0.30% by mass or less, preferably 0.20% by mass or less, and more preferably 0.15% by mass or less.

<F: 0.01% by mass or more and 0.20% by mass or less>
Fluoride has the effect of promoting the release of hydrogen gas that has entered the molten pool.
Here, F is a value obtained by converting the fluoride contained in the wire into F. If the F content is less than 0.01% by mass, the above effects are reduced and the amount of diffusible hydrogen in the weld metal increases, so that cold cracking of the weld metal is likely to occur. Therefore, the F content in the wire should be 0.01% by mass or more, preferably 0.03% by mass or more, and more preferably 0.05% by mass or more.
On the other hand, if the F content exceeds 0.20% by mass, the amount of spatters generated increases and welding workability deteriorates. Therefore, the F content in the wire should be 0.20% by mass or less, preferably 0.15% by mass or less, and more preferably 0.10% by mass or less.

<Ti: 0.05% by mass or more and 0.50% by mass or less>
The flux-cored wire according to this embodiment may further contain Ti as an optional component. By including Ti in the wire, the toughness of the resulting weld metal can be improved.
If the Ti content is 0.05% by mass or more, there is an effect of improving the toughness of the weld metal. Therefore, when Ti is contained in the wire, the Ti content in the wire is preferably 0.05% by mass or more, more preferably 0.10% by mass or more, and more preferably 0.15% by mass or more. It is more preferable to
On the other hand, if the Ti content is 0.50% by mass or less, it is possible to prevent excessive solid-solution Ti, excessively increasing the strength of the weld metal, and deteriorating toughness. Therefore, when Ti is contained in the wire, the Ti content in the wire is preferably 0.50% by mass or less, more preferably 0.30% by mass or less, and 0.20% by mass or less. It is more preferable to
Note that the Ti content means the total content of Ti contained in the single metal and alloy contained in the wire. That is, Ti contained in compounds such as Ti oxides is not included in this Ti content.

<B: 0.001% by mass or more and 0.020% by mass or less>
The flux-cored wire according to this embodiment may further contain B as an optional component. By including B in the wire, the toughness of the resulting weld metal can be improved. For example, B is contained in the form of a compound.
If the B content is 0.001% by mass or more, the above effect can be obtained. Therefore, the B content in the wire is preferably 0.001% by mass or more, more preferably 0.003% by mass or more, and even more preferably 0.005% by mass or more.
On the other hand, if the B content is 0.020% by mass or less, it is possible to suppress the deterioration of the hot cracking resistance of the weld metal. Therefore, when B is contained in the wire, the B content in the wire is preferably 0.020% by mass or less, more preferably 0.015% by mass or less, and 0.010% by mass or less. It is more preferable to

<At least one selected from Sb: 0.01% by mass or more and 0.20% by mass or less, and Sn: 0.01% by mass or more and 0.20% by mass or less>
The flux-cored wire according to this embodiment may further contain at least one selected from Sb and Sn as an optional component. Sb and Sn are components that not only suppress pitting corrosion of the welded metal portion of the bottom plate of the tanker oil tank, but also have the effect of suppressing general corrosion resistance of the welded metal portion of the back surface of the upper deck of the tanker. In order to obtain the above effects, it is preferable that at least one selected from Sb and Sn is contained in the wire in a predetermined content.
If one or both of Sb and Sn are contained in the wire within the range of 0.01% by mass or more of Sb or 0.01% by mass or more of Sn, the above effects can be obtained. can be done. Therefore, when Sb is contained in the wire, the Sb content in the wire is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and 0.03% by mass or more. It is more preferable that Further, when Sn is contained in the wire, the Sn content in the wire is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and 0.03% by mass or more. It is more preferable that

On the other hand, if the Sb content is 0.20% by mass or less and the Sn content is 0.20% by mass or less, the above effects are not saturated, and problems such as the occurrence of hot cracks and a decrease in the toughness of the weld metal part occur. can be prevented from occurring. Therefore, when Sb is contained in the wire, the Sb content in the wire is preferably 0.20% by mass or less, more preferably 0.15% by mass or less, and 0.10% by mass or less. It is more preferable that Further, when Sn is contained in the wire, the Sn content in the wire is preferably 0.20% by mass or less, more preferably 0.15% by mass or less, and 0.10% by mass or less. It is more preferable that
The Sb content and the Sn content refer to the Sb and Sn contents contained in the metal Sb and Sn alone and in the Sb and Sn alloy contained in the wire.

<Fe: 85% by mass or more>
Fe is the main component of flux-cored wires. The Fe content in the wire is preferably 85% by mass or more, more preferably 87% by mass or more, and more preferably 90% by mass or more based on the total mass of the wire, considering the amount of welding and other component compositions. It is even more preferable to have Also, the Fe content in the wire is preferably 97% by mass or less, more preferably 95% by mass or less, based on the total mass of the wire.

<Remainder>
The remainder of the flux-cored wire according to this embodiment contains unavoidable impurities.
In addition, in the flux-cored wire according to the present embodiment, it is preferable that the total content of the components and Fe specified above is 95% by mass or more with respect to the total mass of the wire.

<Others: Flux filling rate>
The flux filling rate (=flux mass/total wire mass×100) of the flux-cored wire according to this embodiment is not particularly limited.
However, if the flux filling rate is less than 10% by mass, the stability of the arc deteriorates, the amount of spatter generation increases, and the welding workability may decrease. Therefore, the flux filling rate is preferably 10% by mass or more. and more preferably 12% by mass or more.
On the other hand, if the flux filling rate exceeds 30% by mass, wire breakage may occur, and powder may spill out during flux filling, resulting in reduced productivity. Therefore, the flux filling rate is preferably 30% by mass. or less, more preferably 25% by mass or less.

[2. Manufacturing method of flux-cored wire]
Although the method for manufacturing the flux-cored wire according to the present embodiment is not particularly limited, for example, the method shown below can be mentioned.
First, a steel strip constituting the steel outer skin is prepared, and the steel strip is formed by forming rolls while being fed in the longitudinal direction to form a U-shaped open pipe. Next, the steel sheath is filled with a flux containing various raw materials so as to have a predetermined composition, and then processed to have a circular cross section. Thereafter, the wire is drawn by cold working to form a flux-cored wire having a wire diameter of, for example, 1.2 to 2.4 mm.
Annealing may be performed during cold working. In addition, it is possible to employ either a seamless wire in which the joints of the steel outer skin formed during the manufacturing process are welded, or a wire in which the joints are not welded and are left as gaps.

The flux-cored wire for gas-shielded arc welding according to the present embodiment can be applied to any corrosion-resistant steel materials such as thick steel plates, thin steel plates, and shaped steels that are used as materials for manufacturing crude oil tanks.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these.

[Manufacturing of flux-cored wire]
A flux containing an appropriate blend of raw materials was filled in the steel sheath so that the ratio of the flux to the total weight of the wire was 12 to 25% by mass, thereby producing a flux-cored wire with a wire diameter of 1.4 mm. Tables 1 to 3 below show the contents (% by mass) of the chemical components in the flux-cored wires of the invention examples and comparative examples.
The content of each chemical component shown in Tables 1 to 3 is the content (% by mass) per total mass of the wire. In addition, the balance is unavoidable impurities. Furthermore, in Tables 1 to 3, the notation "-" in each component composition means that it is below the detection limit value in composition analysis.

[Evaluation of flux-cored wire]
Gas-shielded arc welding was performed using the prepared wires under the following welding conditions to evaluate the welding workability and the corrosion resistance and mechanical properties of the obtained weld metal.

(Welding conditions for corrosion resistance evaluation)
Test steel plate: Corrosion-resistant steel for upper deck and corrosion-resistant steel for bottom plate, 25 mm × (200 + 200) mm × 700 mm
Groove shape: 40° V groove, root gap 6 mm
Backing material: Ceramic backing Welding method: Semi-automatic welding Welding position: Downward Current-voltage: 180A-25V (first layer), 280A-34V (second layer and later)

(Welding conditions for mechanical performance evaluation)
Test steel plate: JIS G 3106 SM490A, 20 mm × (120 + 120) mm × 300 mm
Groove shape: 20° V groove, root gap 16mm
Backing material: JIS G 3106 SS400
Welding method: semi-automatic welding Welding position: downward Current-voltage: 280A-34V

<Welding Workability>
≪Porosity resistance≫
Two plate-shaped base materials were used as test plates, and one plate (horizontal plate) was placed on top of the other plate so as to be perpendicular to the other plate. was used to evaluate the porosity resistance by performing horizontal fillet welding of the fillet portion under the above welding conditions.
In addition, porosity resistance is measured by welding two sets of test plates with a length of 600 mm under the same conditions, and then measuring the number of weld defects such as pits or gas grooves generated in the welded part on the side plate side. It was evaluated as good (○) when there was no defect, and as bad (x) when there was a defect.

≪Arc stability≫
Gas-shielded arc welding was performed under the above welding conditions, and arc stability during welding was evaluated. In the evaluation of arc stability, good arc stability was evaluated as "Good", and arc stability was evaluated as "X" (bad).

≪Bead shape≫
After performing gas-shielded arc welding under the above welding conditions, the welded portion obtained was observed to evaluate the bead shape. The bead shape was evaluated by visual inspection, and the bead shape was evaluated as "Good" when the bead shape was smooth and good, and when the bead shape was convex or sagging, and was evaluated as "Poor".

≪Slag removability≫
After performing gas-shielded arc welding under the above welding conditions, the slag releasability was evaluated by observing the welded portion obtained. Regarding the slag removability, the entire weld bead was covered with slag and was extremely easy to remove. was evaluated as "x" (defective).

After that, the corrosion resistance test and mechanical property test described below were carried out on the specimens with good welding workability.
<Corrosion resistance>
A general corrosion test simulating the underside of the upper deck and a local corrosion (pitting corrosion) test simulating the tanker bottom plate environment were conducted in the following manner.

(1) “General corrosion test simulating tanker upper deck environment”
Wire Nos. shown in Tables 1 to 3 were used to evaluate the corrosion resistance to general corrosion on the back surface of the tanker upper deck. A test piece was prepared from a thick steel plate welded joint using No. 1 to 57, and a general corrosion test was performed.
A test piece for general corrosion test was obtained by cutting out a rectangular small piece of width 20 mm × length 20 mm × thickness 5 mm from only the weld metal at a position of 1/4 of the plate thickness of the welded joint of thick steel plate, and polishing the surface with 600-thick emery. It was prepared by polishing with paper and sealing the back surface and end surfaces with tape so as not to corrode.

FIG. 1 shows the corrosion test apparatus used for the general corrosion test.
The corrosion test apparatus is composed of a corrosion test tank 2 and a temperature control plate 3. Water 6 maintained at 36° C. is poured into the corrosion test tank 2. As shown in FIG. The water 6 contains 12% by volume CO ₂ , 5% by volume O ₂ , 0.01% by volume SO ₂ and 0.3% by volume H ₂ S, and the balance is N ₂ . A mixed gas (introduced gas 4) is introduced, exhaust gas 5 is discharged from the upper part of the corrosion test tank 2, and the inside of the corrosion test tank 2 is filled with supersaturated water vapor, thereby reducing the corrosive environment behind the upper deck of the crude oil tank. reproduced.
In the general corrosion test, a corrosion test piece 1 set on the upper and lower surfaces of a corrosion test tank 2 is passed through a temperature control plate 3 with a built-in heater and cooling device at 25°C x 3 hours + 50°C x 21 hours as one cycle. A temperature change was repeatedly applied for 180 days to create an environment in which dew condensation water was generated on the surface of the test piece 1 and general corrosion was caused.

After the general corrosion test, remove the rust on the surface of each test piece, measure the mass before and after the test, determine the amount of decrease in mass due to corrosion, and use this value to determine the amount of decrease in plate thickness per year (corrosion rate of one side ) to evaluate the general corrosion resistance.
It should be noted that, from the knowledge obtained so far, it is known that the general corrosion rate of the base material of the corrosion-resistant steel material for crude oil tanks to be welded using the wire of the present invention is 0.08 mm/year or less. If the conversion value of plate thickness loss was 0.08 mm / year or less, the general corrosion resistance was good (○), and if it exceeded 0.08 mm / year, the general corrosion resistance was poor (×). It was evaluated as If the evaluation result of the general corrosion resistance is good, it is possible to suppress significant corrosion only at the welded portion.

(2) “Local corrosion (pitting) corrosion test simulating the tanker oil tank bottom plate environment”
Wire Nos. shown in Tables 1 to 3 above were used to evaluate the resistance to pitting corrosion of the bottom plate of the tanker oil tank. A test piece was prepared from a thick steel plate welded joint using No. 1 to 57, and a local corrosion (pitting corrosion) test was performed.
The test piece for the local corrosion test was obtained by cutting out a rectangular piece of width 20 mm x length 20 mm x thickness 5 mm from only the weld metal at the position of 1/4 of the plate thickness of the welded joint of thick steel plate. It was made by sanding with paper.

FIG. 2 shows the corrosion test apparatus used for the localized corrosion test.
The corrosion test apparatus is a double-type tank consisting of a corrosion test tank 8 and a constant temperature tank 9, and the corrosion test tank 8 is filled with a test solution 10. A test solution 10 was prepared from a 10% by mass NaCl aqueous solution using concentrated hydrochloric acid so that the Cl ion concentration was 10% by mass and the pH was 0.85. The temperature of the test solution 10 was maintained by adjusting the temperature of the water 12 placed in the constant temperature bath 9 . Then, a hole having a diameter of 3 mm is made in the upper part of the test piece 7 for local corrosion test, and the extremity 11 is passed through this hole and suspended so as to be immersed in the test solution 10, and each test piece is immersed in 2 liters of the test solution for 168 hours. A localized corrosion test was performed by immersion. The test solution 10 was previously heated and held at 30° C. and replaced with a new test solution every 24 hours.

After the above local corrosion test, remove the rust generated on the surface of the test piece, measure the mass before and after the test, divide the amount of decrease in mass due to corrosion by the total surface area of the test piece, and calculate the amount of plate thickness decrease per year ( The local corrosion resistance was evaluated by converting to the corrosion rate of both surfaces).
It should be noted that the local corrosion rate of the base material of the corrosion-resistant steel material for crude oil tanks to be welded using the wire of the present invention is known to be 0.10 mm/year or less from the knowledge obtained so far. If the conversion value of plate thickness loss is 0.10 mm / year or less, the local corrosion resistance is good (○), and if it exceeds 0.10 mm / year, the local corrosion resistance is poor (×). It was evaluated as If the evaluation result of the local corrosion resistance is good, it is possible to suppress significant corrosion only at the welded portion.

<Mechanical Properties>
A test piece was prepared from the weld metal in accordance with JIS Z 3111, the tensile strength (TS) was measured by a tensile test, and the 0°C absorbed energy (vE _0°C ) was measured by an impact test to evaluate the mechanical properties. . A type IA0 test piece was used as the tensile test piece, and a V-notch test piece was used as the impact test piece. A tensile strength TS of 510 MPa or more was evaluated as good (○), and a tensile strength TS of less than 510 MPa was evaluated as poor (x). The 0° C. absorbed energy vE _{0° C.} of 47 J or more was evaluated as good (○), and the one with less than 47 J was evaluated as unsatisfactory (×). The samples with poor welding workability were marked with "-" because their corrosion resistance and mechanical properties were not evaluated.
Evaluation results of the above tests are shown in Tables 4 to 6 below.

As shown in Tables 1 to 6 above, Invention Example No. Nos. 1 to 42 were welded with wires having all the component compositions contained in the wires within the scope of the present invention, so that welding could be performed with good welding workability and corrosion resistance was also excellent. became.

On the other hand, Comparative Example No. In No. 1, the Mo content and Cu content in the wire were less than the lower limits of the ranges of the present invention, so the corrosion resistance decreased.
Comparative example no. 2 to 6, 8, 12 and 14 are TiO ₂ content, SiO ₂ content, ZrO ₂ content, Al ₂ O ₃ content, MgO content, Si content, Al content and Na + K content in the wire. Since one of them was less than the lower limit of the range of the present invention, at least one of the welding workability evaluations was unsatisfactory.

Comparative example no. In Nos. 7, 9, 13 and 15, any one of C content, Mn content, Mg content and F content in the wire was less than the lower limit of the range of the present invention, so the mechanical properties were deteriorated.
Also, Comparative Example No. In Nos. 10 and 11, the Mo content or Cu content in the wire was less than the lower limit of the range of the present invention, so the corrosion resistance decreased.

1, 7 Test pieces 2, 8 Corrosion test chamber 3 Temperature control plate 4 Introduced gas 5 Exhaust gas 6, 12 Water 9 Thermostatic chamber 10 Test solution 11 Tegus

Claims (3)

A flux-cored wire for gas-shielded arc welding used for horizontal fillet welding of corrosion-resistant steel, wherein the steel sheath is filled with flux,
per total wire mass,
TiO ₂ : 1.5% by mass or more and 4.5% by mass or less,
SiO ₂ : 0.3% by mass or more and 1.5% by mass or less,
ZrO ₂ : 0.1% by mass or more and 1.0% by mass or less,
Al ₂ O ₃ : 0.02% by mass or more and 0.30% by mass or less,
MgO: 0.05% by mass or more and 0.30% by mass or less,
C: 0.01% by mass or more and 0.10% by mass or less,
Si: 0.3% by mass or more and 1.5% by mass or less,
Mn: 0.5% by mass or more and 3.5% by mass or less,
Mo: 0.05% by mass or more and 0.4% by mass or less,
Cu: 0.10% by mass or more and 0.5% by mass or less,
Al: 0.05% by mass or more and 0.5% by mass or less,
Mg: 0.1% by mass or more and 0.7% by mass or less,
Na + K: 0.02% by mass or more and 0.30% by mass or less, and F: 0.01% by mass or more and 0.20% by mass or less,
A flux-cored wire for gas-shielded arc welding containing Fe and unavoidable impurities. Furthermore, per total wire mass,
Ti: 0.05% by mass or more and 0.50% by mass or less, and B: 0.001% by mass or more and 0.020% by mass or less,
The flux-cored wire for gas-shielded arc welding according to claim 1, containing at least one selected from. Furthermore, per total wire mass,
Sb: 0.01% by mass or more and 0.20% by mass or less, and Sn: 0.01% by mass or more and 0.20% by mass or less,
The flux-cored wire for gas-shielded arc welding according to claim 1 or 2, containing at least one selected from.

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