KR20240035904A - Bond fluxes and weld metals for submerged arc welding - Google Patents

Abstract

A bond flux for submerged arc welding of high-Cr ferritic heat-resistant steel that can obtain weld metal with excellent tensile strength and toughness after PWHT is provided. Bond flux for submerged arc welding of high-Cr ferritic heat-resistant steel is, in mass % relative to the total mass of the flux, MgO: 25.0% to 36.0%, Ca: 7.0% to 18.0%, F: 4.5% to 12.0%, Al ₂ O ₃ : 9.5% to 21.7%, SiO ₂ : 8.0% to 20.0%, CO ₂ : 1.0% to 8.0%, Na: 0.5% to 4.0%, ZrO ₂ : 4.0% or less, Al: 0.80% Hereinafter, when C: 0.12% or less and the contents of MgO, F, and CO ₂ in the flux are respectively [MgO], [F], and [CO ₂ ], equation (1): ([MgO] + 2.055 × The value obtained by [F])/([CO ₂ ]) is 6.0 to 45.0.

Description

Bond fluxes and weld metals for submerged arc welding

The present invention relates to a bond flux and weld metal for submerged arc welding suitable for welding high Cr ferritic heat-resistant steel.

Since thermal power generation boilers, turbines, pressure vessels for oil refining, and various heat-resistant and pressure-resistant steel pipes are used in high-temperature and high-pressure environments, various heat-resistant steel sheets are used depending on the usage environment. For example, pressure vessel alloy steel sheets include A387Gr.91, which is specified in ASTM (American Society for Testing and Materials) standards and ASME (American Society of Mechanical Engineers) standards. . And, many proposals have already been made regarding welding materials used for such heat-resistant steels.

For example, Patent Document 1 discloses a submerged arc welding method for 9Cr-1Mo steel. The welding method described in Patent Document 1 is a method of welding by combining wire and flux with controlled content of components, and it is described that cracking can be prevented and excellent high-temperature strength and toughness can be obtained.

Japanese Patent Publication No. 1-258894

However, in recent years, further improvement in the mechanical performance of the weld metal has been required, and even if the welding method described in Patent Document 1 is used, the required mechanical performance cannot be satisfied. Specifically, there is a demand for a welding material that can produce a weld metal with superior tensile strength and toughness after PWHT (Post Weld Heat Treatment).

The present invention was made in consideration of the above-mentioned situation, and provides a bond flux for submerged arc welding of high-Cr ferritic heat-resistant steel that can obtain a weld metal with excellent tensile strength and toughness after PWHT, and excellent tensile strength and toughness. The purpose is to provide a weld metal having

The above object of the present invention is achieved by the following configuration [1] related to a bond flux for submerged arc welding.

[1] A bond flux for submerged arc welding for high Cr ferritic heat-resistant steel,

For the total mass of flux,

MgO: 25.0 mass% or more and 36.0 mass% or less,

Ca: 7.0 mass% or more and 18.0 mass% or less,

F: 4.5 mass% or more and 12.0 mass% or less,

Al ₂ O ₃ : 9.5 mass% or more and 21.7 mass% or less,

SiO ₂ : 8.0 mass% or more and 20.0 mass% or less,

CO ₂ : 1.0 mass% or more and 8.0 mass% or less,

Na: Contains 0.5 mass% or more and 4.0 mass% or less,

ZrO ₂ : 4.0% by mass or less,

Al: 0.80% by mass or less,

C: 0.12% by mass or less,

The MgO content in the flux is set to [MgO] as a mass% with respect to the total mass of the flux, the F content in the flux is set to [F] as a mass% with respect to the total mass of the flux, and the _CO2 content in the flux is set to mass with respect to the total mass of the flux. A bond flux for submerged arc welding, characterized in that when [CO ₂ ] is expressed in %, the value obtained by the following equation (1) is 6.0 or more and 45.0 or less.

Equation (1): ([MgO]+2.055×[F])/([CO ₂ ])

Preferred embodiments of the present invention related to bond flux for submerged arc welding relate to the following [2] to [5].

[2] Additionally, for the total mass of flux,

The bond flux for submerged arc welding according to [1], characterized in that it contains Mn: 0.5 mass% or more and 2.5 mass% or less.

[3] Additionally, for the total mass of flux,

The bond flux for submerged arc welding according to [1] or [2], characterized in that it contains K: 0.5 mass% or more and 3.0 mass% or less.

[4] Additionally, for the total mass of flux,

The bond flux for submerged arc welding according to any one of [1] to [3], characterized in that it contains Li: 0.05 mass% or more and 0.20 mass% or less.

[5] Used with wire for submerged arc welding,

The wire for submerged arc welding is, with respect to the total mass of the wire,

C: 0.030 mass% or more and 0.080 mass% or less,

Si: 0.05 mass% or more and 0.30 mass% or less,

Mn: 0.50 mass% or more and 2.20 mass% or less,

Ni: 0.30 mass% or more and 1.00 mass% or less,

Cr: 8.00 mass% or more and 10.50 mass% or less,

Mo: 0.80 mass% or more and 1.20 mass% or less,

V: 0.10 mass% or more and 0.40 mass% or less,

Nb: 0.020 mass% or more and 0.095 mass% or less,

N: Contains 0.016 mass% or more and 0.065 mass% or less,

P: 0.015% by mass or less,

S: 0.010% by mass or less,

The bond flux for submerged arc welding according to any one of [1] to [4], wherein the balance is Fe and inevitable impurities.

The above object of the present invention is achieved by the following configuration [6] related to weld metal.

[6] A weld metal formed using the bond flux for submerged arc welding according to any one of [1] to [5].

According to the present invention, a bond flux for submerged arc welding of high Cr ferritic heat-resistant steel can be obtained after PWHT, and a weld metal with excellent tensile strength and toughness can be provided. .

Hereinafter, modes for carrying out the present invention will be described in detail. Meanwhile, the present invention is not limited to the embodiments described below, and can be implemented with any modification without departing from the gist of the present invention.

The present inventors conducted an intensive study on a bond flux for submerged arc welding to obtain a weld metal excellent in both tensile strength and toughness after PWHT. As a result, it was found that it is effective to appropriately control the contents of each component in the flux, especially MgO, Ca, F, CO ₂ , Al, and C, and to control parameters using the contents of MgO, F, and CO ₂ did.

Hereinafter, the bond flux for submerged arc welding according to the present embodiment will be described in detail as to the reason for adding its components and the reason for limiting its composition.

[One. Bond flux for submerged arc welding]

The bond flux for submerged arc welding according to the present embodiment is a bond flux suitable for welding high Cr ferritic heat-resistant steel, and may contain the following elements as essential components or as optional components.

<MgO: 25.0 mass% or more and 36.0 mass% or less>

MgO is a slag additive and is a component that has the effect of improving the fluidity of slag and adjusting the bead shape. In addition, MgO is also a component that has the effect of reducing the amount of oxygen in the weld metal and ensuring toughness.

If the MgO content in the flux is less than 25.0% by mass, the effect of reducing the amount of oxygen in the weld metal is insufficient, and the toughness decreases and the bead appearance deteriorates. Therefore, the MgO content relative to the total mass of the flux is set to 25.0 mass% or more, preferably 25.5 mass% or more, and more preferably 26.0 mass% or more.

On the other hand, if the MgO content in the flux exceeds 36.0% by mass, slag inclusion increases and welding workability deteriorates. Therefore, the MgO content relative to the total mass of the flux is set to 36.0 mass% or less, preferably 35.5 mass% or less, and more preferably 35.0 mass% or less.

Meanwhile, in this embodiment, the MgO content means the value obtained by converting all Mg contained in the flux into MgO.

<Ca: 7.0 mass% or more and 18.0 mass% or less>

Ca is a component that acts as a deoxidizer and has the effect of reducing the amount of oxygen in the weld metal.

If the Ca content in the flux is less than 7.0% by mass, sufficient deoxidation effect due to Ca cannot be obtained, and toughness decreases and the bead appearance deteriorates. Therefore, the Ca content relative to the total mass of the flux is 7.0 mass% or more, preferably 8.0 mass% or more, and more preferably 9.0 mass% or more.

On the other hand, when the Ca content in the flux exceeds 18.0 mass%, the slag peelability decreases. Therefore, the Ca content relative to the total mass of the flux is set to 18.0 mass% or less, preferably 17.5 mass% or less, and more preferably 17.0 mass% or less.

Meanwhile, Ca is contained in the flux in the form of fluoride and carbonate.

<F: 4.5 mass% or more and 12.0 mass% or less>

F is a component that has the effect of reducing the amount of diffusible hydrogen in the weld metal and improving low-temperature cracking resistance, as well as controlling the amount of oxygen in the weld metal and adjusting the bead shape.

If the F content in the flux is less than 4.5% by mass, the amount of oxygen in the weld metal increases and the toughness decreases. Therefore, the F content relative to the total mass of the flux is 4.5 mass% or more, preferably 5.2 mass% or more, and more preferably 5.8 mass% or more.

On the other hand, if the F content in the flux exceeds 12.0% by mass, the arc becomes unstable, and the bead shape and slag peelability deteriorate. Therefore, the F content relative to the total mass of the flux is set to 12.0 mass% or less, preferably 11.5 mass% or less, and more preferably 11.0 mass% or less.

<Al ₂ O ₃ : 9.5 mass% or more and 21.7 mass% or less>

Al ₂ O ₃ is a slag additive and is a component that has the effect of improving the fluidity of slag and adjusting the bead shape.

If the Al ₂ O ₃ content in the flux is less than 9.5 mass%, the bead shape deteriorates. Therefore, the Al ₂ O ₃ content relative to the total mass of the flux is 9.5 mass% or more, preferably 11.0 mass% or more, and more preferably 11.5 mass% or more.

On the other hand, if the Al ₂ O ₃ content in the flux exceeds 21.7% by mass, slag inclusion increases and welding workability decreases. Therefore, the Al ₂ O ₃ content relative to the total mass of the flux is set to 21.7 mass% or less, preferably 21.0 mass% or less, and more preferably 20.5 mass% or less.

<SiO ₂ : 8.0 mass% or more and 20.0 mass% or less>

SiO ₂ is a component that has the effect of improving the fluidity of slag and adjusting the bead shape.

If the SiO ₂ content in the flux is less than 8.0 mass%, the bead shape deteriorates. Therefore, the SiO ₂ content relative to the total mass of the flux is 8.0 mass% or more, preferably 9.0 mass% or more, and more preferably 10.0 mass% or more.

On the other hand, when the SiO ₂ content in the flux exceeds 20.0% by mass, slag inclusion increases and welding workability decreases. Therefore, the SiO ₂ content relative to the total mass of the flux is set to 20.0 mass% or less, preferably 19.0 mass% or less, and more preferably 18.5 mass% or less.

Meanwhile, in this embodiment, the content of SiO ₂ means the value obtained by converting all Si contained in the flux into SiO ₂ . Additionally, SiO ₂ in the flux also includes SiO ₂ derived from water glass used as a binder.

<CO ₂ : 1.0 mass% or more and 8.0 mass% or less>

CO ₂ is a component that has the effect of reducing the amount of diffusible hydrogen in the weld metal and improving low-temperature cracking resistance, as well as controlling the amount of oxygen in the weld metal.

If the CO ₂ content in the flux is less than 1.0 mass%, low-temperature cracking occurs. Therefore, the CO ₂ content relative to the total mass of the flux is set to 1.0 mass% or more, and is preferably 1.2 mass% or more.

On the other hand, when the CO ₂ content in the flux exceeds 8.0% by mass, the amount of oxygen in the weld metal increases and the toughness decreases. Therefore, the CO ₂ content relative to the total mass of the flux is set to 8.0 mass% or less, preferably 7.0 mass% or less, and more preferably 6.0 mass% or less.

On the other hand, CO ₂ is contained in the flux in the form of metal carbonate. Examples of metal carbonates include CaCO ₃ , BaCO ₃ , and MgCO ₃ . If the conversion value of these metal carbonates into CO ₂ is within the above range, similar effects can be obtained.

<Na: 0.5 mass% or more and 4.0 mass% or less>

Na is a component that has the effect of improving arc stability.

If the Na content in the flux is less than 0.5% by mass, arc stability decreases and welding defects occur. Therefore, the Na content relative to the total mass of the flux is 0.5 mass% or more, preferably 1.0 mass% or more, and more preferably 1.5 mass% or more.

On the other hand, when the Na content in the flux exceeds 4.0% by mass, the moisture absorption of the flux increases, the amount of hydrogen in the weld metal increases, and low-temperature cracking occurs. Therefore, the Na content relative to the total mass of the flux is set to 4.0 mass% or less, preferably 3.6 mass% or less, and more preferably 3.2 mass% or less.

<ZrO ₂ : 4.0 mass% or less (including 0 mass%)>

ZrO ₂ is a slag additive and is a component that has the effect of improving the fluidity of slag and adjusting the bead shape, but it does not necessarily need to be contained in the flux.

When ZrO ₂ is contained in the flux, the ZrO ₂ content relative to the total mass of the flux is preferably 0.01 mass% or more, and more preferably 0.1 mass% or more.

On the other hand, if the ZrO ₂ content in the flux exceeds 4.0% by mass, slag inclusion increases and welding workability decreases. Therefore, the ZrO ₂ content relative to the total mass of the flux is set to 4.0 mass% or less, preferably 3.5 mass% or less, and more preferably 3.0 mass% or less.

Meanwhile, in this embodiment, the content of ZrO ₂ means the value obtained by converting all Zr contained in the flux into ZrO ₂ .

<Al: 0.80 mass% or less (including 0 mass%)>

Al combines with N to form AlN, and is a component that reduces the amount of carbonitride precipitates of Cr, Nb, and V, which are essential for ensuring creep strength, and deteriorates creep strength. Therefore, Al in the flux should be kept as low as possible. It is desirable to reduce it.

If the Al content in the flux exceeds 0.80% by mass, the beads are baked and the slag removability deteriorates. Additionally, because the yield of elements in the weld metal improves and the strength increases, toughness deteriorates. Therefore, the Al content relative to the total mass of the flux is set to 0.80 mass% or less, preferably 0.75 mass% or less, and more preferably 0.70 mass% or less.

Meanwhile, Al, defined here as 0.80% by mass or less, is contained in the flux in the form of Al alone and Al alloy, and does not include the form of oxide.

<C: 0.12 mass% or less (including 0 mass%)>

Since C is a component that increases susceptibility to high-temperature cracking, it is desirable to reduce C in the flux as much as possible.

If the C content in the flux exceeds 0.12% by mass, the susceptibility to high-temperature cracking increases, and cracking becomes easy to occur, especially in submerged arc welding within a narrow groove. Additionally, the amount of carbide precipitated increases, significantly increasing the strength of the weld metal and deteriorating toughness. Therefore, the C content relative to the total mass of the flux is preferably 0.12 mass% or less, and preferably 0.11 mass% or less.

<Formula (1): 6.0 or more and 45.0 or less>

The following equation (1) parameterizes the deoxidizing power of the flux component to the weld metal. If the value obtained by equation (1) increases, the deoxidation power by the flux increases and the oxygen content of the weld metal decreases, so toughness can be improved. However, if it becomes excessively high, the slag viscosity at each temperature becomes too high. Therefore, welding workability deteriorates. That is, by appropriately controlling the value obtained by equation (1), both improvement in toughness and improvement in welding workability can be achieved.

If the value obtained by equation (1) is less than 6.0, the deoxidation power becomes weak and the toughness of the weld metal decreases. Therefore, the value obtained by equation (1) is 6.0 or more, preferably 11.0 or more, and more preferably 15.0 or more.

On the other hand, if the value obtained by equation (1) exceeds 45.0, the shape of the weld bead is deteriorated, such as the central part of the bead becoming a convex bead shape. Therefore, the value obtained by equation (1) is set to 45.0 or less, preferably 40.0 or less, and more preferably 35.0 or less.

Equation (1): ([MgO]+2.055×[F])/([CO ₂ ])

Meanwhile, in the above formula (1), [MgO] is the value expressed as the MgO content in the flux expressed as mass% based on the total mass of the flux, and [F] is the F content expressed in the flux expressed as mass% based on the total mass of the flux. It is a value, and [CO ₂ ] is a value expressing the CO ₂ content in the flux as a mass percent based on the total mass of the flux.

The bond flux for submerged arc welding according to the present embodiment preferably contains the following components in a predetermined content in addition to the above components.

<Mn: 0.5 mass% or more and 2.5 mass% or less>

Mn is a component that has a deoxidizing effect.

When Mn is included in the flux, if the Mn content is 0.5% by mass or more, a deoxidizing power is exerted and the weld metal becomes hypoxic, so toughness can be improved. Therefore, the Mn content relative to the total mass of the flux is preferably 0.5 mass% or more, more preferably 0.6 mass% or more, and even more preferably 0.7 mass% or more.

On the other hand, if the Mn content in the flux is 2.5% by mass or less, the strength and toughness of the weld metal can be well balanced. Therefore, the Mn content relative to the total mass of the flux is preferably 2.5 mass% or less, more preferably 2.3 mass% or less, and even more preferably 2.1 mass% or less.

<K: 0.5 mass% or more and 3.0 mass% or less>

K is an arc stabilizer and is a component contained in the flux to improve arc stability.

When K is included in the flux, if the K content is 0.5% by mass or more, arc stability is improved and welding workability can be improved. Therefore, the K content relative to the total mass of the flux is preferably 0.5 mass% or more, and more preferably 0.6 mass% or more.

On the other hand, if the K content in the flux is 3.0% by mass or less, the moisture absorption of the flux is suppressed and the amount of hydrogen in the weld metal is reduced, thereby suppressing the occurrence of low-temperature cracking. Therefore, the K content relative to the total mass of the flux is preferably 3.0 mass% or less, more preferably 2.7 mass% or less, and even more preferably 2.4 mass% or less.

<Li: 0.05 mass% or more and 0.20 mass% or less>

Li is an arc stabilizer and is a component contained in the flux to improve arc stability.

When Li is included in the flux, if the Li content is 0.05% by mass or more, arc stability is improved and welding workability can be improved. Therefore, the Li content relative to the total mass of the flux is preferably 0.05 mass% or more, and more preferably 0.06 mass% or more.

On the other hand, if the Li content in the flux is 0.20% by mass or less, the moisture absorption of the flux is suppressed and the amount of hydrogen in the weld metal is reduced, thereby suppressing the occurrence of low-temperature cracking. Therefore, the Li content relative to the total mass of the flux is preferably 0.20 mass% or less, more preferably 0.18 mass% or less, and even more preferably 0.17 mass% or less.

<Total content of essential ingredients>

In the bond flux for submerged arc welding according to the present embodiment, the total content of MgO, Ca, F, Al ₂ O ₃ , SiO ₂ , CO ₂ , Na, ZrO ₂ , Al, and C is the total content of the flux. It is preferably 88% by mass or more, more preferably 91% by mass or more, and even more preferably 93% by mass or more.

<Remaining balance>

The bond flux for submerged arc welding according to the present embodiment may contain, in addition to the above components, for example, Fe, Mo, W, Cu, etc., within a range that does not interfere with the effect of the present invention. Meanwhile, these components may exist as a single substance or as a compound.

[2. Wire for submerged arc welding]

The bond flux for submerged arc welding according to this embodiment is used with a wire for submerged arc welding. Hereinafter, the wire that is preferably used with the bond flux for submerged arc welding according to the present embodiment will be described in detail as to the reason for adding the component and the reason for limiting the composition.

<C: 0.030 mass% or more and 0.080 mass% or less>

C is a component that has a significant influence on the hardenability and precipitation amount of carbonitride in the weld metal, and also functions as an austenite stabilizing element and has the effect of suppressing the residual of the δ ferrite phase in the weld metal.

If the C content in the wire is less than 0.030% by mass, the C content in the weld metal becomes too small, and the amount of carbide precipitated becomes insufficient. Additionally, the δ ferrite phase remains, making it impossible to obtain the desired creep strength. Therefore, the C content with respect to the total mass of the wire is 0.030 mass% or more, and is preferably 0.032 mass% or more.

On the other hand, when the C content in the wire exceeds 0.080% by mass, the susceptibility to high-temperature cracking increases, and cracking becomes easy to occur, especially in submerged arc welding within a narrow groove. Additionally, the amount of carbide precipitated increases, significantly increasing the strength of the weld metal and deteriorating toughness. Therefore, the C content with respect to the total mass of the wire is 0.080 mass% or less, preferably 0.075 mass% or less, and more preferably 0.070 mass% or less.

<Si: 0.05 mass% or more and 0.30 mass% or less>

Si is a component that has the effect of improving the adhesion of the weld bead and functioning as a deoxidizer to improve the strength and toughness of the weld metal.

If the Si content in the wire is less than 0.05% by mass, the Si content in the weld metal becomes too small, and welding workability (for example, weld bead affinity and fusion) deteriorates, and toughness and creep strength also deteriorate. Therefore, the Si content with respect to the total mass of the wire is 0.05 mass% or more, and is preferably 0.06 mass% or more.

On the other hand, if the Si content in the wire exceeds 0.30% by mass, the strength of the weld metal increases significantly and the toughness deteriorates. Therefore, the Si content with respect to the total mass of the wire is 0.30 mass% or less, preferably 0.25 mass% or less, and more preferably 0.21 mass% or less.

<Mn: 0.50 mass% or more and 2.20 mass% or less>

Mn, like Si, is a component that functions as a deoxidizer and has the effect of improving the toughness of the weld metal. In addition, Mn is also a component that functions as an austenite stabilizing element and has the effect of suppressing the residual of the δ ferrite phase in the weld metal. Furthermore, as will be described later, Mn also has the effect of alleviating the adverse effects of S on high-temperature cracking properties.

If the Mn content in the wire is less than 0.50% by mass, the Mn content in the weld metal becomes too small, making it impossible to obtain the desired toughness, and the soft δ ferrite phase remains in the weld metal, causing the creep strength to deteriorate. Moreover, it becomes difficult to suppress high-temperature cracking caused by S. Therefore, the Mn content with respect to the total mass of the wire is 0.50 mass% or more, preferably 0.55 mass% or more, and more preferably 0.60 mass% or more.

On the other hand, when the Mn content in the wire exceeds 2.20% by mass, the Mn content in the weld metal becomes too large, the carbonitride becomes unstable, and the creep strength decreases. Therefore, the Mn content with respect to the total mass of the wire is set to 2.20 mass% or less, preferably 2.00 mass% or less, and more preferably 1.50 mass% or less.

<Ni: 0.30 mass% or more and 1.00 mass% or less>

Ni is a component that is dissolved in solid solution in the matrix of the weld metal and has the effect of improving the toughness of the ferrite itself.

If the Ni content in the wire is less than 0.30% by mass, the effect of improving the toughness of ferrite cannot be obtained. Therefore, the Ni content with respect to the total mass of the wire is 0.30 mass% or more, preferably 0.34 mass% or more, and more preferably 0.38 mass% or more.

On the other hand, when the Ni content in the wire exceeds 1.00% by mass, Ni is concentrated in the final solidified portion during welding, the solidification completion temperature is lowered, and the susceptibility to hot cracking increases. Additionally, the size of the carbonitride becomes coarse during creep deformation, and the creep strength decreases. Therefore, the Ni content with respect to the total mass of the wire is 1.00 mass% or less, preferably 0.90 mass% or less, and more preferably 0.85 mass% or less.

<Cr: 8.00 mass% or more and 10.50 mass% or less>

Cr is a component that forms carbonitrides during PWHT and has the effect of improving the creep strength of the weld metal.

If the Cr content in the wire is less than 8.00% by mass, the amount of carbonitride precipitated is insufficient, and the desired creep strength cannot be obtained. Therefore, the Cr content with respect to the total mass of the wire is 8.00 mass% or more, preferably 8.10 mass% or more, and more preferably 8.20 mass% or more.

On the other hand, if the Cr content in the wire exceeds 10.50% by mass, the solidification completion temperature decreases, the high-temperature cracking susceptibility increases, and the δ ferrite phase remains in the weld metal, thereby reducing creep strength and toughness. Additionally, slag peelability is significantly deteriorated. Therefore, the Cr content with respect to the total mass of the wire is set to 10.50 mass% or less, preferably 10.00 mass% or less, and more preferably 9.60 mass% or less.

<Mo: 0.80 mass% or more and 1.20 mass% or less>

Mo is a component that is dissolved in Cr-based carbide or in the parent phase during PWHT and has the effect of improving the creep strength of the weld metal.

If the Mo content in the wire is less than 0.80 mass%, the desired creep strength cannot be obtained. Therefore, the Mo content with respect to the total mass of the wire is 0.80 mass% or more, preferably 0.82 mass% or more, and more preferably 0.85 mass% or more.

On the other hand, when the Mo content in the wire exceeds 1.20% by mass, the solid solution capacity in the Cr-based carbide and the base phase increases excessively, the strength of the weld metal significantly increases, and the toughness deteriorates. Therefore, the Mo content with respect to the total mass of the wire is 1.20 mass% or less, preferably 1.15 mass% or less, and more preferably 1.10 mass% or less.

<V: 0.10 mass% or more and 0.40 mass% or less>

V is a component that forms carbonitride during PWHT and has the effect of improving the creep strength of the weld metal.

If the V content in the wire is less than 0.10% by mass, the desired creep strength cannot be obtained. Therefore, the V content with respect to the total mass of the wire is 0.10 mass% or more, preferably 0.14 mass% or more, and more preferably 0.18 mass% or more.

On the other hand, when the V content in the wire exceeds 0.40% by mass, the amount of carbonitride precipitated significantly increases, the strength of the weld metal increases, and the toughness deteriorates. Therefore, the V content with respect to the total mass of the wire is 0.40 mass% or less, preferably 0.35 mass% or less, and more preferably 0.30 mass% or less.

<Nb: 0.020 mass% or more and 0.095 mass% or less>

Nb, like V, is a component that forms carbonitride during PWHT and has the effect of improving the creep strength of the weld metal.

If the Nb content in the wire is less than 0.020% by mass, the desired creep strength cannot be obtained. Therefore, the Nb content with respect to the total mass of the wire is 0.020 mass% or more, preferably 0.040 mass% or more, and more preferably 0.060 mass% or more.

On the other hand, when the Nb content in the wire exceeds 0.095% by mass, the amount of carbonitride precipitated increases significantly, the strength of the weld metal increases, and the toughness deteriorates. Additionally, the slag removability is significantly deteriorated. Therefore, the Nb content with respect to the total mass of the wire is preferably 0.095 mass% or less, and preferably 0.093 mass% or less.

<N: 0.016 mass% or more and 0.065 mass% or less>,

N is a component that combines with Cr, V, Nb, etc. during PWHT to form carbonitride and has the effect of improving the creep strength of the weld metal.

If the N content in the wire is less than 0.016% by mass, the desired creep strength cannot be obtained. Therefore, the N content with respect to the total mass of the wire is 0.016 mass% or more, preferably 0.025 mass% or more, and more preferably 0.035 mass% or more.

On the other hand, when the N content in the wire exceeds 0.065% by mass, the amount of carbonitride precipitated significantly increases, the strength of the weld metal increases, and the toughness deteriorates. Additionally, N ₂ gas generated during the welding process tends to remain in the molten metal, resulting in blow holes. Therefore, the N content with respect to the total mass of the wire is 0.065 mass% or less, preferably 0.063 mass% or less, and more preferably 0.061 mass% or less.

<P: 0.015 mass% or less (including 0 mass%)>

P is a component that not only forms a low-melting point compound in the final solidified portion during welding and increases high-temperature cracking susceptibility, but also embrittles the weld metal and deteriorates toughness. Therefore, it is desirable to reduce P in the wire as much as possible. .

If the P content in the wire exceeds 0.015% by mass, high-temperature cracks are likely to occur and toughness deteriorates. Therefore, the P content with respect to the total mass of the wire is 0.015 mass% or less, preferably 0.012 mass% or less, and more preferably 0.009 mass% or less.

<S: 0.010 mass% or less (including 0 mass%)>

S is a component that combines with Fe during welding and forms a low-melting point eutectic of Fe-FeS in the final solidified portion, which not only increases high-temperature cracking properties but also embrittles the weld metal and deteriorates toughness. , it is desirable to reduce S in the wire as much as possible.

If the S content in the wire exceeds 0.010% by mass, high-temperature cracks are likely to occur and toughness deteriorates. Therefore, the S content with respect to the total mass of the wire is preferably 0.010 mass% or less, and preferably 0.009 mass% or less.

<Remaining balance>

In the wire that is preferably used with the bond flux for submerged arc welding according to the present embodiment, the balance is Fe and inevitable impurities. Examples of inevitable impurities include Sn, As, Sb, Pb, and Bi. Among these impurities, Sn, As, and Sb are each preferably, for example, 0.005% by mass or less, and preferably 0.015% by mass or less in total, relative to the total mass of the wire.

In addition, it is preferable that Pb and Bi are each, for example, 0.001% by mass or less with respect to the total mass of the wire. Additionally, elements other than those listed as the above inevitable impurities may be contained in the wire as inevitable impurities as long as they are 0.10% by mass or less relative to the total mass of the wire, and are preferably 0.08% by mass or less, and are preferably 0.06% by mass or less. It is more preferable that it is % or less.

[3. weld metal]

The weld metal according to this embodiment has the above [1. This is a weld metal formed using the bond flux described in [Bond flux for submerged arc welding].

Meanwhile, in the weld metal according to the present embodiment, various welding conditions other than using the bond flux for submerged arc welding according to the present embodiment are not particularly limited, and include the type of base material, welding voltage, welding current, For welding posture, etc., normal conditions in the submerged arc welding method can be used.

Example

Below, the content of the present invention will be described in detail with reference to invention examples and comparative examples showing the effects of the present invention.

[Submerged arc welding]

First, a wire with a diameter of 4 mm was prepared, and bond fluxes with various chemical components were prepared. The chemical components in the wire and their content are shown in Table 1 below, and the chemical components in the flux and their content are shown in Table 2 below.

On the other hand, the remainder of the chemical components in the wire shown in Table 1 below are Fe and inevitable impurities. In addition, in the chemical components of the bond flux shown in Table 2 below, Al is a component that is not actively added, so it was set as “<0.80” (less than 0.80).

Next, submerged arc welding was performed using the wire and bond flux, and then post-welding heat treatment (PWHT) was performed under two types of conditions. Welding conditions and PWHT conditions are shown below.

(welding conditions)

Base material: ASTM A387 Gr.91

Plate thickness of base material: 25mm

Improvement angle, shape: 10°, V-shaped

Root spacing: 20mm

Polarity: AC (Alternating Current)

Wire diameter: 4.0mm

Welding posture: downward

Current: 450∼550A

Voltage: 30∼32V

Welding speed: 30∼36cm/min

Temperature between preheating and passes: 250∼300℃

Stacking method: 5 to 7 layers, 10 to 14 passes

(PWHT conditions)

A: 750∼765℃, 40∼44hr

B: 735∼750℃, 9∼10hr

[evaluation]

After the submerged arc welding, heat treatment was performed under the PWHT conditions, and the obtained weld metal was evaluated for room temperature strength and toughness. The specific temperature (°C) and time (hr) of the PWHT conditions and the evaluation results of each test are shown in Table 3 below.

<Room temperature strength>

For the welded metal after PWHT under condition A, a tensile test was conducted at room temperature in accordance with the tensile and impact test methods for welded metal specified in JIS Z3111:2005, and the yield stress (YS) and tensile strength were measured at 0.2%. (TS: Tensile Strength) was measured. On the other hand, those that achieved the same level of strength as the base material, A387 Gr.91, were considered acceptable. Specifically, with respect to TS, those that were 585 to 760 MPa were considered to be passed, and those that were less than 585 MPa or more than 760 MPa were judged to be failed. In addition, regarding YS, those that were 415 MPa or more were judged as passing, and those that were less than 415 MPa were judged to be failed.

<Toughness>

Three test specimens were taken from the weld metal after PWHT under condition B, and a Charpy impact test was performed at 0°C in accordance with the Charpy impact test method for metal materials specified in JIS Z2242. Then, the average value of the absorbed energy vE(J) of each measured test material was calculated to evaluate toughness. On the other hand, those with an average value of absorbed energy obtained by measurement of 54 J or more were judged as passing, and those with an average value of less than 54 J were judged as failing.

As shown in Tables 2 and 3, Invention Example No. 1 to 6, since the content of chemical components in the bond flux for submerged arc welding is within the scope of the present invention, as a result of submerged arc welding using these fluxes, it has excellent tensile strength and toughness after PWHT. Weld metal could be obtained.

Meanwhile, Comparative Example No. In 1 to 3, the room temperature strength and toughness decreased because the value calculated by equation (1) based on the MgO, F, and CO ₂ contents in the flux was below the lower limit of the range of the present invention. In particular, Comparative Example No. 1 and 2 were Comparative Example No. 2 because the CO ₂ content in the flux exceeded the upper limit of the range of the present invention. Compared to 3, the toughness became lower.

Although various embodiments have been described above, it goes without saying that the present invention is not limited to these examples. It is clear to those skilled in the art that various changes or modifications can be made within the scope described in the claims, and it is understood that they naturally fall within the technical scope of the present invention. Additionally, each component in the above embodiment may be arbitrarily combined without departing from the spirit of the invention.

Meanwhile, this application is based on the Japanese patent application (Japanese patent application 2021-145758) filed on September 7, 2021, the contents of which are incorporated by reference in this application.

Claims (9)

As a bond flux for submerged arc welding for high Cr ferritic heat-resistant steel,
For the total mass of flux,
MgO: 25.0 mass% or more and 36.0 mass% or less,
Ca: 7.0 mass% or more and 18.0 mass% or less,
F: 4.5 mass% or more and 12.0 mass% or less,
Al ₂ O ₃ : 9.5 mass% or more and 21.7 mass% or less,
SiO ₂ : 8.0 mass% or more and 20.0 mass% or less,
CO ₂ : 1.0 mass% or more and 8.0 mass% or less,
Na: Contains 0.5 mass% or more and 4.0 mass% or less,
ZrO ₂ : 4.0% by mass or less,
Al: 0.80% by mass or less,
C: 0.12% by mass or less,
The MgO content in the flux is set to [MgO] as a mass% with respect to the total mass of the flux, the F content in the flux is set to [F] as a mass% with respect to the total mass of the flux, and the _CO2 content in the flux is set to mass with respect to the total mass of the flux. A bond flux for submerged arc welding, characterized in that when [CO ₂ ] is expressed in %, the value obtained by the following equation (1) is 6.0 or more and 45.0 or less.
Equation (1): ([MgO]+2.055×[F])/([CO ₂ ]) According to claim 1,
Additionally, for the total mass of flux,
Mn: A bond flux for submerged arc welding, characterized in that it contains 0.5 mass% or more and 2.5 mass% or less. The method of claim 1 or 2,
Additionally, for the total mass of flux,
K: A bond flux for submerged arc welding, characterized in that it contains 0.5 mass% or more and 3.0 mass% or less. The method of claim 1 or 2,
Additionally, for the total mass of flux,
A bond flux for submerged arc welding, characterized in that it contains Li: 0.05 mass% or more and 0.20 mass% or less. According to claim 3,
Additionally, for the total mass of flux,
A bond flux for submerged arc welding, characterized in that it contains Li: 0.05 mass% or more and 0.20 mass% or less. The method of claim 1 or 2,
Used with wire for submerged arc welding,
The wire for submerged arc welding is, with respect to the total mass of the wire,
C: 0.030 mass% or more and 0.080 mass% or less,
Si: 0.05 mass% or more and 0.30 mass% or less,
Mn: 0.50 mass% or more and 2.20 mass% or less,
Ni: 0.30 mass% or more and 1.00 mass% or less,
Cr: 8.00 mass% or more and 10.50 mass% or less,
Mo: 0.80 mass% or more and 1.20 mass% or less,
V: 0.10 mass% or more and 0.40 mass% or less,
Nb: 0.020 mass% or more and 0.095 mass% or less,
N: Contains 0.016 mass% or more and 0.065 mass% or less,
P: 0.015% by mass or less,
S: 0.010% by mass or less,
A bond flux for submerged arc welding, characterized in that the balance is Fe and inevitable impurities. According to claim 3,
Used with wire for submerged arc welding,
The wire for submerged arc welding is, with respect to the total mass of the wire,
C: 0.030 mass% or more and 0.080 mass% or less,
Si: 0.05 mass% or more and 0.30 mass% or less,
Mn: 0.50 mass% or more and 2.20 mass% or less,
Ni: 0.30 mass% or more and 1.00 mass% or less,
Cr: 8.00 mass% or more and 10.50 mass% or less,
Mo: 0.80 mass% or more and 1.20 mass% or less,
V: 0.10 mass% or more and 0.40 mass% or less,
Nb: 0.020 mass% or more and 0.095 mass% or less,
N: Contains 0.016 mass% or more and 0.065 mass% or less,
P: 0.015% by mass or less,
S: 0.010% by mass or less,
A bond flux for submerged arc welding, characterized in that the balance is Fe and inevitable impurities. According to claim 4,
Used with wire for submerged arc welding,
The wire for submerged arc welding is, with respect to the total mass of the wire,
C: 0.030 mass% or more and 0.080 mass% or less,
Si: 0.05 mass% or more and 0.30 mass% or less,
Mn: 0.50 mass% or more and 2.20 mass% or less,
Ni: 0.30 mass% or more and 1.00 mass% or less,
Cr: 8.00 mass% or more and 10.50 mass% or less,
Mo: 0.80 mass% or more and 1.20 mass% or less,
V: 0.10 mass% or more and 0.40 mass% or less,
Nb: 0.020 mass% or more and 0.095 mass% or less,
N: Contains 0.016 mass% or more and 0.065 mass% or less,
P: 0.015% by mass or less,
S: 0.010% by mass or less,
A bond flux for submerged arc welding, characterized in that the balance is Fe and inevitable impurities. A weld metal formed using the bond flux for submerged arc welding according to claim 1 or 2.