JP7827554B2 - One-sided submerged arc welding method, supporting flux and backing flux - Google Patents

Description

The present invention relates to a single-sided submerged arc welding method for welding to steel plates from one side, as well as a support flux and a backing flux used in this welding method.

Single-sided submerged arc welding, which involves welding from one side of a steel plate, is a highly efficient welding method that is used in a wide range of fields, primarily in shipbuilding, as a plate joint welding. In this type of welding method, a backing flux is placed on the back side of the groove formed in the steel plate to obtain a good back bead.

For example, Patent Document 1 discloses a fused backing flux for one-sided welding, which contains flux raw materials and a thermosetting resin and has a bulk density of 1.20 to 1.45 (g/cm ³ ). The patent document also describes that the flux raw materials contain, based on the total weight of the flux raw materials, 5.0 to 20.0 wt % of CaF ₂ , 5.0 to 25.0 wt % of ZrO ₂ , 20.0 to 40.0 wt % of MgO, 30.0 to 50.0 wt % of _{SiO 2} , 1.0 to 5.0 wt % of TiO 2 , 0.5 to 5.0 wt % of MnO, 0.3 to 5.0 wt % of CaO, and 0.3 to 5.0 wt % of Al ₂ O ₃ , with the balance consisting of trace components and unavoidable impurities totaling 1 wt % or less.
Furthermore, when the contents of _CaF2 , _ZrO2 , _TiO2 , and MnO are expressed in weight percent as [ _CaF2 ], [ _ZrO2 ], [ _TiO2 ], and [MnO], respectively, the formula A = ([ _CaF2 ] + [ _ZrO2 ])/([ _TiO2 ] + [MnO]) is calculated to be 2.0 to 9.0 weight percent, and the thermosetting resin is contained in an amount of 0.5 to 15 weight percent based on the total weight of the backing flux.

Japanese Patent Application Publication No. 10-314983

However, in recent years, the steel plates to be welded have become thicker in order to improve efficiency and strength, and the thicker the plate, the greater the heat input required, which tends to cause instability in the back bead height due to the effects of heat.
Even when the backing flux described in Patent Document 1 is used, it is difficult to obtain a sufficiently good back bead shape when welding thick steel plates, and there is an increasing demand for a welding method that can obtain a more stable back bead height.

The present invention was made in consideration of these issues, and aims to provide a single-sided submerged arc welding method, support flux, and backing flux that can achieve a stable back bead height and a good back bead appearance, even when welding thick plates.

The inventors of the present invention have conducted extensive research into a single-side submerged arc welding method for obtaining a stable back bead height and a good back bead appearance. As a result, they have found that the above-mentioned problems can be solved by using a two-layer structure instead of the conventional backing flux, in which an easily melting resin-coated flux is used as the upper layer and a resin-coated flux that is difficult to melt or, even if it melts to some extent, produces a highly viscous molten slag as the lower layer.
The present invention was made based on these findings.

The above object of the present invention is achieved by the following configuration [1] relating to a single-sided submerged arc welding method.

[1] A single-sided submerged arc welding method in which a pair of steel plates are butted together to form a groove, a backing flux is placed in contact with the back side of the groove, and welding is performed from the front side of the groove,
The backing flux has a slag-forming flux constituting an upper layer and a supporting flux constituting a lower layer,
Both the slag-forming flux and the supporting flux contain a resin,
The slag-forming flux contains one or more of an acidic oxide having a melting point of 1600°C or higher and containing only one metal element, and an amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element in a total content of less than 43% by mass (including 0%);
a supporting flux containing 43 mass% or more in total of one or more of an acidic oxide having a melting point of 1600°C or higher and containing only one metal element, and an amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element.

Furthermore, preferred embodiments of the present invention relating to the one-sided submerged arc welding method relate to the following [2] to [8].

[2] When the total amount of slag-forming fluxes having a particle size of 400 μm or more is F _U400 (mass%) and the total amount of slag-forming fluxes having a particle size of 212 μm or less is F _U212 (mass%),
The value calculated by F _U400 /F _U212 is 0.30 or less,
When the total amount of the supporting flux having a particle size of 400 μm or more is F _L400 (mass%) and the total amount of the supporting flux having a particle size of 212 μm or less is F _L212 (mass%) relative to the total mass of the supporting flux,
The single-side submerged arc welding method according to [1], wherein the value calculated by F _L400 /F _L212 is 0.50 or more and 3.80 or less.

[3] The single-sided submerged arc welding method described in [1] or [2], wherein the slag-forming flux contains 1.0 mass% or more and 5.0 mass% or less of resin based on the total mass of the slag-forming flux.

[4] A single-sided submerged arc welding method according to any one of [1] to [3], wherein the supporting flux contains 1.0 mass% or more and 5.0 mass% or less of resin relative to the total mass of the supporting flux.

[5] The thickness of the upper layer in a direction parallel to the thickness direction of the steel plate is 1 mm or more and 7 mm or less,
The single-sided submerged arc welding method according to any one of [1] to [4], wherein the thickness of the lower layer in a direction parallel to the plate thickness direction of the steel plate is 3 mm or more and 20 mm or less.

[6] A single-sided submerged arc welding method described in any one of [1] to [5], using a flux backing method.

[7] A single-sided submerged arc welding method according to any one of [1] to [6], wherein the thickness of the steel plate is greater than 20 mm.

[8] A single-sided submerged arc welding method according to any one of [1] to [7], wherein the total amount of support flux having a particle size of 850 μm or more is 18 mass% or less relative to the total mass of the support flux.

The above object of the present invention is achieved by the following configuration [9] related to the supporting flux.

[9] A support flux used in a one-sided submerged arc welding method in which a pair of steel plates are butted together substantially horizontally to form a groove and welding is performed from the upper side of the groove, the support flux being arranged below the slag-forming flux constituting the upper layer of a backing flux having an upper layer and a lower layer arranged on the back side of the groove, and supporting the slag-forming flux,
The slag-forming flux contains a resin and is disposed below a slag-forming flux containing one or more of an acidic oxide having a melting point of 1600°C or higher and containing only one metal element and an amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element in a total content of less than 43 mass%;
A supporting flux containing a resin and containing a total of 43 mass% or more of one or more of an acidic oxide having a melting point of 1600°C or higher and containing only one metal element and an amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element.

The above object of the present invention is achieved by the following configuration [10] related to backing flux.

[10] A backing flux used in a one-sided submerged arc welding method in which a pair of steel plates are butted together substantially horizontally to form a groove and welding is performed from the upper side of the groove, and the backing flux is placed on the back side of the groove,
A slag-forming flux is disposed in contact with the back surface side of the groove, and a supporting flux is disposed below the slag-forming flux,
Both the slag-forming flux and the supporting flux contain a resin,
The slag-forming flux contains one or more of an acidic oxide having a melting point of 1600°C or higher and containing only one metal element and an amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element in a total content of less than 43 mass%;
The supporting flux is a backing flux containing one or more of an acidic oxide having a melting point of 1600°C or higher and containing only one metal element, and an amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element, in a total amount of 43 mass% or more.

The present invention provides a single-sided submerged arc welding method, support flux, and backing flux that can achieve a stable back bead height and a good back bead appearance, even when welding thick plates.

FIG. 1 is a cross-sectional view schematically showing a single-side submerged arc welding method according to an embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing a conventional one-side submerged arc welding method using backing flux. FIG. 3 is a schematic diagram showing how one-sided submerged arc welding according to this embodiment is performed using the flux backing method.

Embodiments of the present invention will now be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and can be modified and implemented as desired without departing from the spirit and scope of the present invention.

[Single-sided submerged arc welding method]
1 is a cross-sectional view schematically illustrating a single-sided submerged arc welding method according to an embodiment of the present invention. First, a pair of steel plates 1a and 1b are butted together horizontally to form a groove, and backing flux 10 is placed in contact with the back side of the groove.
In this embodiment, the backing flux 10 is composed of a slag-forming flux 2 constituting an upper layer and a supporting flux 3 constituting a lower layer.

The supporting flux 3 that makes up the lower layer is a flux that is difficult to melt or, even if it does melt somewhat, produces a highly viscous molten slag, and contains resin. The slag-forming flux 2 that makes up the upper layer is a flux that melts more easily than the supporting flux 3 that makes up the lower layer, and, like supporting flux 3, contains resin. Supporting flux 3 and slag-forming flux 2 will be described in more detail below.

Furthermore, underlay flux 4 is placed under backing flux 10, and top flux (not shown) is sprayed onto the groove.
Thereafter, a welding wire is fed from the upper side of the groove into the front flux, and an arc is generated between the steel plates 1a, 1b and the welding wire.

At this time, the area of the backing flux 10 that is affected by the heat of the molten metal is thermally decomposed into molten slag, which covers the molten metal on the back side of the weld. The molten metal and molten slag then cool and solidify, forming the weld metal 5 and slag 6.

For comparison with this embodiment, a conventional one-side submerged arc welding method using backing flux will now be described with reference to the drawings.
A conventional single-sided submerged arc welding method using backing flux is shown in Fig. 2. As shown in Fig. 2, a pair of steel plates 11a and 11b are butted together horizontally to form a groove, and backing flux 12 is placed in contact with the back side of the groove.
Furthermore, an underlay flux 14 is placed under the backing flux 12, and a top flux (not shown) is sprayed on the groove.
Thereafter, a welding wire is fed into the surface flux scattered in the groove, and an arc is generated between the steel plates 1a, 1b and the welding wire, thereby performing one-side submerged arc welding.

In this way, even in conventional welding methods, the area of the backing flux that is affected by the heat of the molten metal becomes molten slag, and the molten metal and molten slag cool, forming weld metal 15 and slag 16.

However, when welding thick steel plates 11a and 11b using conventional welding methods, a large heat input is required, which causes a large amount of melted backing flux 12 and increases the amount of molten slag produced. As a result, molten metal flows into the space where the backing flux 12 is melted, causing the height of the back bead 15a to exceed the desired height and making the height of the back bead 15a unstable.
Furthermore, if a backing flux 12 that is difficult to melt is used to suppress the increase in the amount of molten slag produced, the backing flux 12 will not melt very much, and only a small amount of molten slag will be produced. As a result, there will be no space for the molten metal to flow into, which will result in problems such as an insufficient formation of the back bead 15a, a lack of melting of the back groove, incomplete fusion, and a poor appearance of the back bead 15a.

On the other hand, the welding method according to this embodiment shown in Figure 1 uses two types of flux: a slag-forming flux to improve the appearance of the back bead 5a, and a support flux to keep the height of the back bead 5a constant, thereby achieving a good back bead appearance and a stable back bead height.

In the present invention, there are no particular limitations on the method for placing the backing flux 10 in contact with the backside of the steel sheets 1a and 1b. For example, the flux backing method and copper backing method described below can be used.

3 is a schematic diagram showing how one-sided submerged arc welding according to this embodiment is performed using the flux backing method. In FIG. 3, parts that are the same as or equivalent to those in FIG. 1 are given the same reference numerals, and their description will be omitted or simplified.
As shown in Figure 3, a pair of steel plates 1a, 1b are arranged approximately horizontally to form a groove, and a backing flux 10 consisting of a slag-forming flux 2 and a supporting flux 3 is placed below the groove. The backing flux 10 is pressed against the backsides of the steel plates 1a, 1b by the pressure of gas in an air hose 20 via an underlay flux 4 filled in an irregular bag-like container 8.
The air hose 20 and the underlay flux 4 filled in the bag-shaped container 8 are housed in a metal case 9 with an open top.

In this way, using the flux backing method, the air hose 20 can hold the slag-forming flux 2 and supporting flux 3 in place and reliably press them against the backside of the steel plates 1a and 1b.

As another method for placing the backing flux 10 in contact with the backside of the steel sheets 1a and 1b, a copper backing method can also be used.
Although not shown in the figures, the copper backing method is a method in which the underlying flux in the flux backing method shown in Figure 3 is replaced with a copper plate, and the backing flux 10 is pressed against the back side of the steel sheets 1a and 1b to perform welding.

The flux backing method, which uses only flux, has the advantage that even when there is a difference in thickness of the steel sheet or an unevenness, the backing flux and the underlay flux can be arranged along the step that occurs on the back surface of the steel sheet, and therefore welding is possible regardless of whether there is a difference in thickness of the steel sheet or an unevenness.
On the other hand, the flux copper backing method has the advantage that the height of the back bead can be easily stabilized because a copper plate is placed under the backing flux.

In the single-side submerged arc welding method according to this embodiment, the backing flux 10 is made up of an upper layer of slag-forming flux 2 and a lower layer of supporting flux 3, and the molten metal can be held down by the supporting flux 3. Therefore, the height of the back bead can be stabilized without using a copper plate.
Furthermore, by using the flux backing method, it is possible to stabilize the back bead height and obtain a good back bead appearance even when there are differences in the thickness of the steel plate or when there are misalignments.
Therefore, in this embodiment, the application of the flux backing method is particularly preferable because it is possible to obtain the advantages of both the flux backing method and the copper backing method at the same time.

In the single-sided submerged arc welding method according to this embodiment, there are no particular restrictions on the welding conditions other than the use of the specific backing flux 10, and the conditions used in ordinary single-sided submerged arc welding methods can be used. Regarding the electrode, either a method using a single electrode or a method using two or more electrodes can be selected.

The backing flux 10, as well as the slag-forming flux 2 and supporting flux 3 that make up the backing flux 10, will be described in more detail below.

[1. Backing Flux]
The backing flux 10 has a slag-forming flux 2 constituting an upper layer and a supporting flux 3 constituting a lower layer. In this embodiment, the slag-forming flux 2 is disposed in contact with the back surface side of the groove, and the supporting flux 3 is disposed in contact with the lower side of the slag-forming flux 2. For example, a flux having another function may be disposed below the supporting flux 3.

[1-1. Supporting Flux]
The supporting flux in the lower layer is required to have the effect of obtaining a stable back bead height. In order to obtain a back bead of stable height, it is considered important that the supporting flux itself is difficult to melt, or that even if the supporting flux melts to some extent, the viscosity of the molten slag is high. It was assumed that if the viscosity of the molten slag is high, it will not penetrate deep below the lower layer constituting the supporting flux 3, but will remain at the top of the lower layer and turn into slag.

Therefore, after extensive investigations, the inventors focused on viscosity and melting point and concluded that acidic oxides with melting points of 1600°C or higher and containing only one metal element, and amphoteric oxides with melting points of 2000°C or higher and containing only one metal element, are promising materials that meet the requirements for a support flux.
That is, the inventors have found that a back bead with a stable height can be obtained by using a support flux in which the total content of one or more of an acidic oxide having a melting point of 1600°C or higher and containing only one metal element and an amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element is adjusted to 43 mass% or more.

In this embodiment, the support flux contains a total of 43 mass% or more of one or more of the following: an acidic oxide having a melting point of 1600°C or higher and containing only one metal element; and an amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element. This allows for a stable back bead height. As the acidic oxide having a melting point of 1600°C or higher and containing only one metal element, it is preferable to use _SiO2 , for example. As the amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element, it is preferable to use _Al2O3 or _{ZrO2 ,} for example.

The remainder of the support flux is not particularly limited and may include compounds having a melting point below 1600°C and containing only one metal element, composite compounds having a melting point below 1600°C and containing multiple metal elements, basic oxides having a melting point of 1600°C or higher and containing only one metal element, amphoteric oxides having a melting point of 1600°C or higher but less than 2000°C and containing only one metal element, composite compounds having a melting point of 1600°C or higher and containing multiple metal elements, powders of one or more metals such as Fe, Si, Mn, and Ti, and unavoidable impurities.

Examples of compounds having a melting point of less than 1600°C and containing only one metal element include _CaF2 , _MnO2 , _Na2O , _K2O , FeO, _{and Fe2O3} . Examples of composite compounds having a melting point of less than 1600°C and containing multiple metal elements include CaO-MgO- _SiO2 molten fluxes. Examples of basic oxides having a melting point of 1600°C or higher and containing only one metal element include MgO, CaO, BaO, and MnO. Examples of amphoteric oxides having a melting point of 1600°C or higher and lower than 2000°C and containing only one metal element include _TiO2 . Examples of composite compounds having a melting point of 1600° _C or higher and containing multiple metal elements include _BaTiO3 , _CaTiO3 , and _MgAl2O4 .

If the total content of one or more of the acidic oxides containing only one metal element and having a melting point of 1600°C or higher and amphoteric oxides containing only one metal element and having a melting point of 2000°C or higher is less than 43 mass%, the supporting flux 3 melts more easily and the viscosity of the molten slag decreases. As a result, the molten slag and molten metal generated by the slag-forming flux (described below) cannot be contained at the top of the supporting flux 3 (lower layer). As a result, the molten slag and molten metal may penetrate into the middle or lower part of the supporting flux 3 layer, causing the height of the back bead 5a to become unstable.

Therefore, the total content of one or more of the acidic oxides having a melting point of 1600°C or higher and containing only one metal element and the amphoteric oxides having a melting point of 2000°C or higher and containing only one metal element is 43% by mass or more, preferably 55% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. The total content may be 90% by mass or more, 93% by mass or more, or 95% by mass or more. The upper limit is 100% by mass, but is preferably 99% by mass or less, and more preferably 97% by mass or less. The supporting flux 3 contains a resin.

There are no particular restrictions on the form of acidic oxides in the flux that have a melting point of 1600°C or higher and contain only one metal element. They may be crushed from the acidic oxide alone, or from a mineral ore containing the acidic oxide. Similarly, there are no particular restrictions on the form of amphoteric oxides in the flux that have a melting point of 2000°C or higher and contain only one metal element. They may be crushed from the amphoteric oxide alone, or from a mineral ore containing the amphoteric oxide.

Here, the acidic oxide, amphoteric oxide, and composite oxide in this embodiment will be described in more detail.
Oxides are classified into three types based on their reactivity: acidic oxides that react with bases, basic oxides that react with acids, and amphoteric oxides that react with both acids and bases. Examples of acidic oxides containing only one metal element include _SiO2 , _MoO3 , and _V2O5 , while examples of acidic oxides with a melting point of 1600°C or _higher and containing only one metal element include _SiO2 .

Examples of amphoteric oxides containing only one metal element include Al ₂ O ₃ , TiO ₂ , B ₂ O ₃ , ZrO ₂ , Fe ₂ O ₃ , and Cr ₂ O _{3 .} Examples of amphoteric oxides having a melting point of 2000°C or higher and containing only one metal element include Al ₂ O ₃ , ZrO ₂ , and Cr ₂ O ₃ .
A composite oxide is a type of composite compound. A composite oxide is an oxide made up of multiple metal elements and oxygen (O). For example, a CaO-MgO- _SiO2 molten flux is a composite oxide.

(Thickness of the lower layer made of supporting flux: 3 mm or more and 20 mm or less)
In this embodiment, the melting point of the molten slag formed by the supporting flux is relatively high, so that the height of the back bead can be controlled so that it does not become too high.
If the thickness of the lower layer made of the supporting flux is 3 mm or more, the height of the back bead can be stabilized, and therefore, the thickness of the lower layer is preferably 3 mm or more.
On the other hand, the thickness of the lower layer is not particularly limited, but is preferably 20 mm or less in practical use. The thickness of the lower layer refers to the thickness in a direction parallel to the thickness direction of the steel sheet.

<1-1-1. Resin contained in supporting flux>
In this embodiment, the supporting flux 3 has a resin on its surface. This resin may contain a thermosetting resin and have the property of melting once and then hardening due to heat. When the supporting flux contains such a resin, the resin melts due to the heat of the molten metal or molten slag on the welding direction side of the welding torch, then hardens, bonding the supporting fluxes 3 together. As a result, the fluidity of the supporting flux 3 can be reduced, and the fluidity of the molten metal can be reduced. In particular, the resin contained in the supporting flux 3 can reduce the fluidity of the molten metal in the vertical direction, i.e., the vertical direction, relative to the welding direction. Therefore, the resin contained in the supporting flux 3 can maintain a constant height of the back bead 5a.

Specific examples of the resin that can be used include phenol-based resins, furan-based resins, epoxy resins, urea-based resins, and xylene-based resins.
In addition, a method for obtaining the above-mentioned supporting flux includes adding the raw material flux and the above-mentioned resin together with a solvent such as ethanol, methanol, or acetone, kneading them, and then drying them at a temperature below the melting point of the resin. Note that, as the supporting flux, a flux in which the raw material flux is coated with a resin can be used, but it is not necessary for the resin to coat the entire surface of the raw material flux, as long as it is attached to at least a part of the surface.

(Resin content: 1.0% by mass or more and 5.0% by mass or less)
When the amount of resin contained in the supporting flux, i.e., the resin content in the supporting flux, is 1.0 mass% or more, the powdery flux can be properly hardened during welding, and the effect of improving the back bead appearance can be obtained as described above. Therefore, the resin content in the supporting flux is preferably 1.0 mass% or more, more preferably 1.5 mass% or more, even more preferably 2.0 mass% or more, and particularly preferably 2.5 mass% or more.
On the other hand, if the amount of resin contained in the supporting flux is 5.0 mass% or less, the degree of hardening of the powdery flux during welding can be appropriately adjusted, and the back bead appearance can be improved as described above. Therefore, the resin content relative to the total mass of the supporting flux is preferably 5.0 mass% or less, more preferably 4.5 mass% or less, even more preferably 4.0 mass% or less, and particularly preferably 3.5 mass% or less.

[1-2. Slag-forming flux]
As described above, the slag-forming flux 2 is a flux that melts more easily than the supporting flux 3 that constitutes the lower layer, and the content of flux components that are difficult to melt or that produce a highly viscous molten slag even if they melt to some extent, which are contained in the supporting flux 3 at 43% by mass or more, is restricted to less than 43% by mass. Specifically, the total content of one or more of the acidic oxides having a melting point of 1600°C or higher and containing only one metal element and the amphoteric oxides having a melting point of 2000°C or higher and containing only one metal element is restricted to less than 43% by mass.

In other words, the slag-forming flux 2 contains a total of 57% by mass or more of one or more of the following: a compound having a melting point below 1600°C and containing only one metal element; a composite compound having a melting point below 1600°C and containing multiple metal elements; a basic oxide having a melting point of 1600°C or higher and containing only one metal element; an amphoteric oxide having a melting point of 1600°C or higher but less than 2000°C and containing only one metal element; a composite compound having a melting point of 1600°C or higher and containing multiple metal elements; metal powder; and a resin. The total content of these components is preferably 60% by mass or more, more preferably 65% by mass or more, and even more preferably 70% by mass or more. The upper limit is 100% by mass, but is preferably 99% by mass or less, more preferably 97% by mass or less. Like the supporting flux 3, the slag-forming flux 2 also contains resin on its surface. The remainder may contain unavoidable impurities.
The basic oxide having a melting point of 1600° C. or higher and containing only one metal element is preferably a basic oxide having a melting point of 1600° C. or higher and 2900° C. or lower and containing only one metal element. The composite compound having a melting point of 1600° C. or higher and containing multiple metal elements is preferably a composite compound having a melting point of 1600° C. or higher and 2900° C. or lower and containing multiple metal elements.

When the total content of one or more of the acidic oxides containing only one metal element and having a melting point of 1600°C or higher, and the amphoteric oxides containing only one metal element and having a melting point of 2000°C or higher, exceeds 43% by mass, the resulting composition is similar to that of the support flux 3 described above, making it difficult to melt, or even if it does melt somewhat, the molten slag will have a high viscosity. As a result, a sufficient amount of molten slag cannot be produced, resulting in a poor appearance of the back bead. Furthermore, because it becomes difficult to melt below the slag-forming flux, the molten metal does not flow below the back surfaces of the steel sheets 1a and 1b, preventing the grooves of the steel sheets from melting and resulting in poor fusion.

By limiting the total content of one or more of the acidic oxides having a melting point of 1600°C or higher and containing only one metal element, and the amphoteric oxides having a melting point of 2000°C or higher and containing only one metal element, to less than 43% by mass, the molten slag can be converted to molten slag even below the slag-forming flux 2, producing a sufficient amount of molten slag. As a result, the molten slag can adequately cover the molten metal, improving the appearance of the back bead. The total content of one or more of the acidic oxides having a melting point of 1600°C or higher and containing only one metal element, and the amphoteric oxides having a melting point of 2000°C or higher and containing only one metal element, is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. The lower limit is not particularly limited and may be 0% by mass.

In slag-forming flux 2, if the total content of one or more of the acidic oxides containing only one metal element and having a melting point of 1600°C or higher and amphoteric oxides containing only one metal element and having a melting point of 2000°C or higher is limited to less than 43 mass%, then backing fluxes used in submerged arc welding can be used. Backing fluxes for submerged arc welding include molten fluxes, sintered fluxes, bonded fluxes, and mixed fluxes. Mixtures of molten fluxes and bonded fluxes, and mixtures of molten fluxes and sintered fluxes can also be used.

(Thickness of the upper layer made of slag-forming flux: 1 mm or more and 7 mm or less)
In this embodiment, the melting point of the molten slag produced by the slag-forming flux is relatively low, so that a back bead of a more desired height can be obtained by appropriately adjusting the thickness of the upper layer formed by the slag-forming flux, where the thickness of the upper layer refers to the thickness in the direction parallel to the thickness direction of the steel sheet.
If the thickness of the upper layer is 1 mm or more, the height of the molten metal flow and the amount of slag become appropriate, resulting in a better back bead appearance. On the other hand, if the thickness of the upper layer is 7 mm or less, the height of the back bead can be kept more constant.
Therefore, the thickness of the upper layer is preferably 1 mm or more and 7 mm or less, and more preferably 1.5 mm or more and 5 mm or less.

<1-2-1. Resin contained in slag-forming flux>
In this embodiment, the slag-forming flux 2 also has a resin on its surface. This resin may be any resin that melts and then hardens due to heat. When the slag-forming flux contains such a resin, the resin melts due to the heat of the molten metal or molten slag on the welding torch's welding direction side and then hardens, bonding the slag-forming fluxes 2 together. This reduces the fluidity of the slag-forming flux 2 and the fluidity of the molten metal. In particular, the resin contained in the slag-forming flux 2 reduces the fluidity of the molten metal in the direction transverse to the welding direction, i.e., the left-right direction. Therefore, the resin contained in the slag-forming flux 2 and the resin contained in the support flux have a synergistic effect, allowing the height of the back bead 5a to be maintained constant.

The type of resin, the method for obtaining the slag-forming flux, and the form in which the resin is contained are the same as those for the supporting flux described above.

(Resin content: 1.0% by mass or more and 5.0% by mass or less)
When the amount of resin contained in the slag-forming flux, i.e., the resin content in the slag-forming flux, is 1.0 mass % or more, the powdery flux can be properly hardened during welding, and the effect of improving the back bead appearance can be obtained as described above. Therefore, the resin content relative to the total mass of the slag-forming flux is preferably 1.0 mass % or more, more preferably 1.5 mass % or more, even more preferably 2.0 mass % or more, and particularly preferably 2.5 mass % or more.
On the other hand, if the amount of resin contained in the slag-forming flux is 5.0 mass% or less, the degree of hardening of the granular flux during welding can be appropriately adjusted, and the back bead appearance can be improved as described above. Therefore, the resin content relative to the total mass of the slag-forming flux is preferably 5.0 mass% or less, more preferably 4.5 mass% or less, even more preferably 4.0 mass% or less, and particularly preferably 3.5 mass% or less.

<1-2-2. Composition of slag-forming flux>
In this embodiment, the composition of the slag-forming flux is not particularly limited as long as it satisfies the conditions described in [1-2. Slag-forming flux]. It may contain one or more of CaF ₂ , SiO ₂ , TiO ₂ , ZrO ₂ , and MgO. It may also contain one or more metal powders of Fe, Si, Mn, Ti, etc.

In this embodiment, _CaF2 is a compound having a melting point of less than 1600°C and containing only one metal element. In this embodiment, _SiO2 is an acidic oxide having a melting point of 1600°C or higher and containing only one metal element. In this embodiment, _TiO2 is an amphoteric oxide having a melting point of 1600°C or higher and lower than 2000°C and containing only one metal element. In this embodiment, MgO is a basic oxide having a melting point of 1600°C or higher and containing only one metal element. In this embodiment, _ZrO2 is an amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element.

[2. Underlayment Flux]
In this embodiment, the underlay flux 4 is placed under the backing flux 10, but the underlay flux 4 is not necessarily required in the present invention. For example, even if a copper plate is placed under the backing flux 10, the same effect as that of the underlay flux 4 can be obtained.
When using underlay flux, the raw material may be one that has excellent moisture absorption resistance.

[3. Other conditions]
<3-1. Grain size composition of slag-forming flux and supporting flux>
(Value calculated by F _U400 /F _U212 : 0.30 or less)
If the total mass of the slag-forming flux is F _U400 (mass%), where F U400 is the total mass of the slag-forming flux with a particle size of 400 μm or more, and F _U212 is the total mass of the slag-forming flux with a particle size of 212 μm or less, and the value calculated by F _U400 /F _U212 is 0.30 or less, the gaps between the particles of the slag-forming flux will be large, resulting in a low density. Furthermore, in this embodiment, the slag-forming flux is made of a material that melts relatively easily, so the apparent volume of the slag-forming flux that becomes molten slag is large, and the void space created by the molten slag also becomes large. Molten metal then flows into the resulting ample void space, resulting in an appropriate back bead height.
Therefore, the value calculated from F _U400 /F _U212 is preferably 0.30 or less. Although there is no particular lower limit, the value calculated from F _U400 /F _U212 is preferably 0.01 or more.

(Value calculated by F _L400 /F _L212 : 0.50 or more and 3.80 or less)
If the total mass of the supporting flux is F _L400 (mass%), where F _L212 (mass%) is the total mass of the supporting flux with a particle size of 400 μm or more, and F L212 (mass%) is the total mass of the supporting flux with a particle size of 212 μm or less, and the value calculated by F _L400 /F _L212 is 0.50 to 3.80, the gaps between the supporting flux particles are reduced and the density is increased. Furthermore, in this embodiment, the supporting flux is made of a material that is relatively difficult to melt, so the apparent volume of the supporting flux that becomes molten slag is reduced, and no large voids are formed even when the supporting flux becomes molten slag. As a result, the height of the lower layer composed of the supporting flux does not change significantly, and the positions of the molten slag and molten metal do not change significantly, thereby more stabilizing the back bead height.
Therefore, the value calculated by F _L400 /F _L212 is preferably 0.50 or more, more preferably _0.55 or more, _and is preferably 3.80 or less.

(Total amount of supporting flux with a particle size of 850 μm or more: 18 mass% or less (including 0 mass%))
As described above, in order to reduce the gaps between the particles of the support flux and increase the density of the support flux, it is important to mix a support flux having a large particle size (F _L400 ) and a support flux having a small particle size (F _L212 ) in a balanced manner.
Furthermore, by suppressing the amount of coarse particles to a certain level or less, the gaps between particles can be reduced more stably, and as a result, the height of the back bead can be made more stable.
Therefore, the total amount of supporting flux having a particle size of 850 μm or more is preferably 18% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less, based on the total mass of the supporting flux. In addition, the total amount of supporting flux having a particle size of 850 μm or more is particularly preferably 0% by mass.

(Steel plate thickness: over 20 mm)
As described above, with conventional single-sided submerged arc welding methods, the thicker the plate, the greater the heat input required, and the thermal effects tended to cause the back bead height to become unstable. In this embodiment, even when welding thick plates, the back bead height can be stabilized and a good back bead appearance can be obtained. Therefore, the thickness of the steel plate to be welded is not particularly limited, but the method can also be suitably used for steel plates with a thickness of more than 20 mm, for example. The upper limit of the thickness of the steel plate to be welded is preferably 55 mm or less, for example.

The supporting flux according to this embodiment is as described above in [1-1. Supporting Flux].
The backing flux according to this embodiment is as described above in [1. Backing Flux].

(Method for manufacturing slag-forming flux and supporting flux)
The slag-forming flux and supporting flux according to the present embodiment can be manufactured by a conventional method, for example, by blending raw material powders to have the above-described composition and kneading them with a resin.
The method for adjusting the particle size of the supporting flux and the slag-forming flux to the desired size is not particularly limited, and the following methods can be used, for example: a method using raw material powder whose particle size has been adjusted in advance by sieving, a method in which the particle size distribution is adjusted by sieving the kneaded flux, or the like.

The present invention will be explained in detail below using examples and comparative examples, but the present invention is not limited to these.

[One-sided submerged arc welding]
Two 25 mm thick steel plates were prepared as the workpieces, and four electrodes (electrodes 1 to 4) were prepared. Slag-forming fluxes and supporting fluxes with different components and particle size configurations were also prepared.
Next, the prepared steel plate, front flux, slag-forming flux, and support flux were arranged so as to be applicable to the flux backing method shown in FIG. 3, and single-sided submerged arc welding was carried out at a welding speed of 800 (mm/min).
The welding currents and arc voltages of the first to fourth electrodes, and the wire diameters of the wires used in these electrodes are shown below.

(First electrode) Welding current: 1400 A, arc voltage: 35 V, wire diameter: 4.0 mm
(Second electrode) Welding current: 1000 A, arc voltage: 32 V, wire diameter: 4.8 mm
(Third electrode) Welding current: 1200 A, arc voltage: 44 V, wire diameter: 4.8 mm
(Fourth electrode) Welding current: 1150 A, arc voltage: 44 V, wire diameter: 6.4 mm

[evaluation]
The weld metals obtained were evaluated for back bead height stability and back bead appearance.

(Method and criteria for evaluating back bead height stability)
Measurements were taken at intervals of 0.10 mm over a range of 600 mm to 900 mm from the starting end of the steel plate using a laser displacement meter, and the standard deviation was calculated to evaluate the height stability of the back bead.
The evaluation criteria were as follows: a standard deviation of less than 0.55 mm was rated as ⊚ (excellent); a standard deviation of 0.55 mm or more but less than 1.00 mm was rated as ◯ (good); and a standard deviation of 1.00 mm or more was rated x (poor).

(Method and criteria for evaluating the appearance of the back bead)
The appearance of the back bead was evaluated by visually observing the back bead.
The evaluation criteria were as follows: good was marked with ◯, and poor was marked with ×.

The type and composition of the steel plate used as the welded material are shown in Table 1 below. The composition of the wire used is shown in Table 2 below. The composition of the flux is shown in Table 3 below. The compositions of the slag-forming flux and supporting flux of the inventive examples are shown in Tables 4 and 5 below, respectively, and the compositions of the slag-forming flux and supporting flux of the comparative examples are shown in Tables 6 and 7 below. Furthermore, the particle size distribution is shown in Table 8 below, and the particle size composition, resin content (mass%), and spray height (mm) of the slag-forming flux and supporting flux, as well as the evaluation results, are shown in Table 9 below. In Tables 4 to 7, numerical values indicate compositions intentionally contained in the slag-forming flux and supporting flux. A "-" in Tables 4 to 7 indicates that the slag-forming flux and supporting flux are not intentionally contained. The remainder of the totals in Tables 4 to 7 represents unavoidable impurities not intentionally contained in the slag-forming flux and supporting flux. The unavoidable impurities include trace amounts of one or more of the following: basic oxides that have a melting point of 1600°C or higher and contain only one metal element, amphoteric oxides that have a melting point of 1600°C or higher but less than 2000°C and contain only one metal element, compounds that have a melting point of less than 1600°C and contain only one metal element, composite compounds that have a melting point of less than 1600°C and contain multiple metal elements, and metal powders that contain at least one of Fe, Ti, Mn, and Si, which are not intentionally added.

As shown in Tables 4 to 9, in Examples 1 to 18, single-sided submerged arc welding was performed using a backing flux containing a resin and having the specific properties specified in the present invention as the upper layer, and a support flux containing a resin and having the specific properties specified in the present invention as the lower layer. Therefore, the back bead height was stable and a back bead with a good appearance was obtained. In particular, in Examples 1 to 15 and 17 and 18, the particle size composition (F _L400 /F _L212 ) of the support flux was greater than the more preferable lower limit specified in the present invention, resulting in even more stable back bead height.

On the other hand, in Comparative Examples 1 to 4, the total content of one or more of the acidic oxides containing only one metal element and having a melting point of 1600°C or higher and the amphoteric oxides containing only one metal element and having a melting point of 2000°C or higher in the supporting flux shown in Table 7 falls outside the range specified in the present invention. In particular, as shown in Tables 6 and 7, Comparative Example 1 uses the same supporting flux as the slag-forming flux, resulting in a single-layer structure. Therefore, in all cases, the height of the back bead became unstable and the appearance of the back bead was poor.
In addition, in Comparative Examples 5 to 7, the total content of one or more of the acidic oxides containing only one metal element and having a melting point of 1600°C or higher and the amphoteric oxides containing only one metal element and having a melting point of 2000°C or higher in the slag-forming flux shown in Table 6 was outside the range specified by the present invention. In particular, Comparative Example 6 used the same slag-forming flux as the supporting flux, resulting in a single-layer structure. Therefore, the appearance of the back bead was poor.

1a, 1b, 11a, 11b Steel plate 2 Slag-forming flux 3 Supporting flux 4, 14 Underlaying flux 5, 15 Weld metal 6, 16 Slag 10, 12 Backing flux

Claims (8)

A single-sided submerged arc welding method in which a pair of steel plates are butted together to form a groove, a backing flux is placed in contact with the back side of the groove, and welding is performed from the front side of the groove,
The backing flux has a slag-forming flux constituting an upper layer and a supporting flux constituting a lower layer,
The thickness of the upper layer in a direction parallel to the thickness direction of the steel plate is 1 mm or more and 7 mm or less,
The thickness of the lower layer in a direction parallel to the thickness direction of the steel plate is 3 mm or more,
The slag-forming flux and the supporting flux each contain a resin that is melted by heat and then hardened ,
The slag-forming flux contains 1.0 mass % or more and 5.0 mass % or less of the resin that is melted by heat and then hardened, relative to the total mass of the slag-forming flux;
The supporting flux contains the resin that is melted by heat and then hardened in an amount of 1.0 mass % or more and 5.0 mass % or less relative to the total mass of the supporting flux,
The slag-forming flux contains one or more of an acidic oxide having a melting point of 1600°C or higher and containing only one metal element, and an amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element in a total content of less than 43% by mass (including 0%);
a supporting flux containing 43 mass% or more in total of one or more of an acidic oxide having a melting point of 1600°C or higher and containing only one metal element, and an amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element. When the total amount of slag-forming fluxes having a particle size of 400 μm or more is F _U400 (mass%) and the total amount of slag-forming fluxes having a particle size of 212 μm or less is F _U212 (mass%) relative to the total mass of the slag-forming fluxes,
The value calculated by F _U400 /F _U212 is 0.30 or less,
When the total amount of the supporting flux having a particle size of 400 μm or more is F _L400 (mass%) and the total amount of the supporting flux having a particle size of 212 μm or less is F _L212 (mass%) relative to the total mass of the supporting flux,
The single-side submerged arc welding method according to claim 1, wherein the value calculated by F _L400 /F _L212 is 0.50 or more and 3.80 or less. 3. The single-side submerged arc welding method according to claim 1, wherein the thickness of the lower layer in a direction parallel to the thickness direction of the steel plate is 3 mm or more and 20 mm or less. The single-sided submerged arc welding method according to claim 1 or 2, which uses a flux backing method. The single-sided submerged arc welding method according to claim 1 or 2, wherein the steel plate has a thickness of more than 20 mm. The single-sided submerged arc welding method according to claim 1 or 2, wherein the total amount of support flux having a particle size of 850 μm or more is 18 mass% or less of the total mass of the support flux. A single-sided submerged arc welding method is used in which a pair of steel plates are butted together to form a groove and welding is performed from the upper side of the groove, and a backing flux having an upper layer and a lower layer is placed on the back side of the groove. The backing flux is a supporting flux that constitutes the lower layer and is placed below the slag-forming flux that constitutes the upper layer, supporting the slag-forming flux,
The thickness of the upper layer in a direction parallel to the thickness direction of the steel plate is 1 mm or more and 7 mm or less,
The thickness of the lower layer in a direction parallel to the thickness direction of the steel plate is 3 mm or more,
The slag-forming flux contains a resin that melts once by heat and then hardens in an amount of 1.0 mass % to 5.0 mass % based on the total mass of the slag-forming flux, and is disposed below a slag-forming flux containing less than 43 mass % of one or more of an acidic oxide having a melting point of 1600°C or higher and containing only one metal element and an amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element;
A support flux containing 1.0 mass% or more to 5.0 mass% or less of a resin that melts once due to heat and then hardens , relative to the total mass of the support flux, and containing 43 mass% or more in total of one or more of the following: an acidic oxide having a melting point of 1600°C or more and containing only one metal element; and an amphoteric oxide having a melting point of 2000°C or more and containing only one metal element. A backing flux having an upper layer and a lower layer is used in a one-sided submerged arc welding method in which a pair of steel plates are butted together to form a groove and welding is performed from the upper side of the groove, and is placed on the back side of the groove,
A slag-forming flux is disposed in contact with the back surface side of the groove, and a supporting flux is disposed below the slag-forming flux,
the upper layer being composed of the slag-forming flux;
the lower layer is composed of the supporting flux;
The thickness of the upper layer in a direction parallel to the thickness direction of the steel plate is 1 mm or more and 7 mm or less,
The thickness of the lower layer in a direction parallel to the thickness direction of the steel plate is 3 mm or more,
The slag-forming flux and the supporting flux each contain a resin that is melted by heat and then hardened ,
The slag-forming flux contains 1.0 mass % or more and 5.0 mass % or less of the resin that is melted by heat and then hardened, relative to the total mass of the slag-forming flux;
The supporting flux contains the resin that is melted by heat and then hardened in an amount of 1.0 mass % or more and 5.0 mass % or less relative to the total mass of the supporting flux,
The slag-forming flux contains one or more of an acidic oxide having a melting point of 1600°C or higher and containing only one metal element and an amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element in a total content of less than 43 mass%;
The supporting flux is a backing flux containing one or more of an acidic oxide having a melting point of 1600°C or higher and containing only one metal element, and an amphoteric oxide having a melting point of 2000°C or higher and containing only one metal element, in a total amount of 43 mass% or more.