KR102733213B1 - Flux for submerged arc welding, method for submerged arc welding, and method for manufacturing flux for submerged arc welding - Google Patents

Abstract

Provides a flux for submerged arc welding with excellent slag detachment properties while suppressing the occurrence of iron or fork marks, regardless of construction conditions. A flux used for submerged arc welding, comprising a fluoride and an oxide, wherein the oxides are composed of a high-melting-point oxide having a melting point of 1800°C or higher and a low-melting-point oxide having a melting point of less than 1800°C, and wherein the high-melting-point oxide comprises an oxide containing Ca, and the low-melting-point oxide comprises an oxide containing Mn, wherein the content with respect to the total mass of the flux is such that the Mn equivalent value in MnO is 2 to 8 mass%, and further, the MnO equivalent value, the CaF ₂ equivalent value of F, the CaO equivalent value of Ca, and CO ₂ satisfy the relationship 1.6≤{CaF ₂ equivalent value/(MnO equivalent value+CaO equivalent value+CO ₂ )}, and the ratio of the content of the sum of the high-melting-point oxides to the content of the sum of the oxides (sum of high-melting-point oxides/sum of oxides) is 0.56 or more.

Description

Flux for submerged arc welding, method for submerged arc welding, and method for manufacturing flux for submerged arc welding

The present invention relates to a flux used in submerged arc welding, and more specifically, to a flux for submerged arc welding having excellent welding workability, particularly excellent slag detachment property. In addition, the present invention relates to a submerged arc welding method using the flux and a method for manufacturing the flux.

Submerged arc welding is a welding method in which granular flux is sprayed along the welding area in advance, the welding wire is continuously fed into the flux, and an arc is generated between the welding material and the tip of the welding wire while covered with the flux.

Various studies are being conducted with the aim of improving welding workability in submerged arc welding.

For example, Patent Documents 1 and 2 disclose that by specifying the content of components constituting the flux and setting the ratio of the MgO content and the total content of Al ₂ O ₃ , CaF ₂ equivalents and TiO ₂ within a specific range, welding workability is improved regardless of whether the welding current is AC or DC. Furthermore, Patent Documents 1 and 2 disclose that the amount of diffusible hydrogen in the weld metal can be reduced, and Patent Document 2 discloses that the moisture absorption amount of the flux can be reduced.

Japanese Patent Publication No. 2015-112633 Japanese Patent Publication No. 2016-140889

However, in welding that is particularly difficult to construct, such as narrow-line improvement welding, the bead tends to have a convex shape, making it difficult to secure slag detachability, especially at the weld joint.

Regarding this, the inventor of the present invention focused on the element called Mn and found that the more Mn is added, the more the slag detachability is improved. On the other hand, the addition of Mn causes the occurrence of iron grain protrusions (hereinafter simply referred to as "iron grains") or pock marks, and thus there remains a problem in terms of welding workability, such as bead appearance or surface defects.

The present invention has been made in light of the above circumstances, and aims to provide a flux for submerged arc welding having excellent slag detachment properties while suppressing the occurrence of surface defects such as iron grains or fork marks regardless of construction conditions.

According to one aspect of the present invention, a flux is used for submerged arc welding, and contains a fluoride and an oxide, wherein the oxide is composed of a high-melting-point oxide having a melting point of 1800°C or higher and a low-melting-point oxide having a melting point of less than 1800°C, and contains an oxide containing Ca as the high-melting-point oxide, and an oxide containing Mn as the low-melting-point oxide, and the content with respect to the total mass of the flux is such that the Mn equivalent value in MnO is 2 to 8 mass%, and further, the MnO equivalent value, the CaF ₂ equivalent value of F, the CaO equivalent value of Ca, and CO ₂ satisfy the relationship of 1.6≤{CaF ₂ equivalent value/(MnO equivalent value+CaO equivalent value+CO ₂ )}, and the ratio of the content of the sum of the high-melting-point oxides to the content of the sum of the oxides (content of the sum of the high-melting-point oxides/content of the sum of the oxides) is 0.56 or more. It is a flux for submerged arc welding.

In the above flux for submerged arc welding, the high-melting-point oxide includes at least one of MgO and TiO ₂ , and the content with respect to the total mass of the flux may be such that the Mg equivalent value of Mg is 25 mass% or less, and the Ti equivalent value of TiO ₂ is 9 mass% or less, and the ratio of the content of the sum of the MgO equivalent value and the TiO ₂ equivalent value to the content of the total of the high-melting-point oxides {(MgO equivalent value + TiO ₂ equivalent value) / content of the sum of the high-melting-point oxides} may be 0.430 or more.

Furthermore, in the above-described submerged arc welding flux, the content of the high-melting-point oxide with respect to the total mass of the flux may be such that the CaO conversion value is 10 mass% or less, the Al ₂ O ₃ conversion value of Al is 25 mass% or less, and further, the MgO conversion value, the TiO ₂ conversion value, the CaO conversion value, and the Al ₂ O ₃ conversion value satisfy the relationship of 30≤(MgO conversion value + 0.67TiO ₂ conversion value + 0.92CaO conversion value + 0.74Al ₂ O ₃ conversion value)≤50.

In the above flux for submerged arc welding, the content of the low melting point oxide with respect to the total mass of the flux may be such that the SiO ₂ conversion value of Si may be 20 mass% or less, the FeO conversion value of Fe may be 5 mass% or less, the B ₂ O ₃ conversion value of B may be 1 mass% or less, and the alkali metal oxide conversion value of the alkali metal element may be 5.0 mass% or less.

In addition, in the above flux for submerged arc welding, the alkali metal oxide conversion value may be a value converted into at least one oxide selected from the group consisting of Na ₂ O, K ₂ O, and Li ₂ O.

In the above flux for submerged arc welding, the content relative to the total mass of the flux may be 20 mass% or more in terms of the CaF ₂ , and may also be 6.0 mass% or less of the CO ₂ .

A welding method according to one aspect of the present invention is a submerged arc welding method for performing arc welding using a flux, wherein the flux contains a fluoride and an oxide, and the oxide is composed of a high-melting-point oxide having a melting point of 1800°C or higher and a low-melting-point oxide having a melting point of less than 1800°C, and includes an oxide containing Ca as the high-melting-point oxide, and an oxide containing Mn as the low-melting-point oxide, and the content with respect to the total mass of the flux is such that the Mn equivalent value in MnO is 2 to 8 mass%, and further, the MnO equivalent value, the CaF ₂ equivalent value of F, the CaO equivalent value of Ca, and CO ₂ satisfy the relationship of 1.6≤{CaF ₂ equivalent value/(MnO equivalent value+CaO equivalent value+CO ₂ )}, and the ratio of the content of the sum of the high-melting-point oxides to the content of the sum of the oxides (content of the sum of the high-melting-point oxides/sum of the oxides) Use one with a content of 0.56 or higher.

In the above submerged arc welding method, the material to be welded may be processed to have a U-shaped or V-shaped improvement, and the improvement angle may be 10 to 60°.

A method for manufacturing a flux according to one aspect of the present invention is a method for manufacturing a flux used in submerged arc welding, comprising a step of firing a granulated product derived from a raw material at 400 to 950°C, wherein the flux after the firing step contains a fluoride and an oxide, wherein the oxide is composed of a high-melting-point oxide having a melting point of 1800°C or higher and a low-melting-point oxide having a melting point of less than 1800°C, and includes an oxide containing Ca as the high-melting-point oxide, and an oxide containing Mn as the low-melting-point oxide, wherein the content with respect to the total mass of the flux is such that the Mn equivalent value in MnO is 2 to 8 mass%, and further, the MnO equivalent value, the CaF ₂ equivalent value of F, the CaO equivalent value of Ca, and CO ₂ satisfy the relationship of 1.6≤{CaF ₂ equivalent value/(MnO equivalent value+CaO equivalent value+CO ₂ )}, A method for manufacturing a flux for submerged arc welding, wherein the ratio of the content of the sum of the high-melting-point oxides to the content of the sum of the above oxides (content of the sum of the high-melting-point oxides/content of the sum of the oxides) is 0.56 or more.

According to the present invention, it is possible to provide a flux for submerged arc welding that has excellent slag detachability while suppressing the occurrence of iron spots or fork marks. By performing submerged arc welding using this flux, it is possible to achieve both excellent slag detachability and a good bead appearance with few surface defects regardless of the construction conditions.

Hereinafter, a form for implementing the present invention (the present embodiment) will be described in detail. In addition, the present invention is not limited to the embodiment described below, and can be implemented by arbitrarily changing it within a scope that does not deviate from the gist of the present invention.

＜Flux＞

A flux for submerged arc welding according to the present embodiment (hereinafter, sometimes simply referred to as “flux”) contains a fluoride and an oxide, wherein the oxide is composed of a high-melting-point oxide having a melting point of 1800°C or higher and a low-melting-point oxide having a melting point of less than 1800°C, and includes an oxide containing Ca as the high-melting-point oxide and an oxide containing Mn as the low-melting-point oxide.

The content with respect to the total mass of the flux satisfies the relationship that the Mn equivalent value of Mn is 2 to 8 mass% in MnO conversion, and further, the MnO equivalent value, the CaF ₂ equivalent value of F, the CaO equivalent value of Ca, and CO ₂ 1.6≤{CaF ₂ equivalent value/(MnO equivalent value+CaO equivalent value+CO ₂ )}. Furthermore, the ratio of the content of the sum of high-melting-point oxides to the content of the sum of oxides (content of the sum of high-melting-point oxides/content of the sum of oxides) is 0.56 or more.

Examples of high-melting point oxides include MgO, TiO ₂ , CaO, Al ₂ O ₃ , ZrO ₂ , and BaO.

In addition to the above, the flux may also contain low melting point oxides having a melting point of less than 1800°C, for example, MnO, MnO ₂ , Mn ₂ O ₃ , SiO ₂ , B ₂ O ₃ , FeO, Fe ₂ O ₃ , Fe ₃ O ₄ , alkali metal oxides, etc.

Hereinafter, the content of each component in the flux according to the present embodiment will be described. In addition, the content in the present embodiment means mass% with respect to the total mass of the flux unless otherwise specified. In addition, some of the components constituting the flux have the content converted into oxides or fluorides based on the amount of each element obtained by analysis, based on JIS Z 3352:2017, etc. Therefore, the sum of the content of each component with respect to the total mass of the flux may exceed 100 mass%.

[MnO equivalent of Mn: 2-8 mass%]

The MnO conversion value is the value converted from the total Mn content of the flux to MnO. The measured total Mn content may include components other than MnO, such as MnO ₂ and Mn ₂ O ₃ , but since these components have almost the same effect, the MnO conversion value of the total Mn should be within the above-mentioned range.

MnO is an essential component that affects the viscosity and solidification temperature of slag and is effective in improving slag detachability. Among the oxide forms such as MnO, MnO ₂ and Mn ₂ O ₃ , its usefulness is demonstrated especially when added in the form of MnO or MnO ₂ .

As such, the higher the MnO content, the better the slag detachability. On the other hand, it was found that when the MnO content increases, iron grains and fork marks are more likely to occur.

The mechanism of iron formation is thought to be as follows. First, iron in the flux coagulates in the molten slag and settles to form large metal particles. At that time, if the bead surface is in a molten state, the metal particles become weld metal as they are, but if the bead surface is in a solidified state, the metal particles adhere to the bead surface and become iron particles.

That is, when metal particles settle in the slag in a molten state, the occurrence of iron particles can be suppressed if the bead surface is in a molten state. A method for making the bead surface in a molten state is to raise the solidification temperature of the slag.

Regarding this, the melting point of MnO is about 1785℃ and it is not a high-melting point oxide. Therefore, it is thought that if the content of MnO is too high, iron grains are likely to form.

On the other hand, it is presumed that if the solidification temperature of the slag is too high, it becomes difficult for the bubbles that are formed to escape, making it easy for fork marks to occur. In addition, fork marks are also likely to occur when the moisture content in the slag is high.

In addition, it is thought that hygroscopicity can also be a factor in the occurrence of pokmarks, and since MnO has high hygroscopicity, it is thought that if the content of MnO is excessively high, pokmarks become more likely to occur.

For the above reasons, the content of Mn in terms of MnO in the present embodiment is 2 mass% or more, preferably 2.5 mass% or more, and more preferably 3 mass% or more. In addition, the content in terms of MnO is 8 mass% or less, preferably 7.5 mass% or less, and more preferably 7 mass% or less.

[F's CaF ₂ conversion value]

The CaF ₂ conversion value is the total F amount of the flux converted to CaF ₂ . The total F amount measured may include fluorides other than CaF ₂ , such as AlF ₃ or MgF _{2 .} However, regardless of the form, since they have almost the same effect as CaF ₂ as fluorides, the CaF ₂ conversion value of the total F amount should be within the above-mentioned range.

Fluoride is a component that suppresses the occurrence of fork marks and increases the electrical conductivity and fluidity of slag. On the other hand, as for the action related to fluidity, it is proportional to the amount of its existence, like CaO described later, and is one of the components that affects the high-temperature viscosity of slag.

In the present embodiment, the content of F in terms of CaF ₂ is preferably 20 mass% or more, more preferably 25 mass% or more, and even more preferably 27 mass% or more, from the viewpoint of promoting the discharge of gas from molten slag and thereby suppressing the occurrence of fork marks. On the other hand, if it is too much, the fluidity of the slag becomes too high, and the bead shape deteriorates. Therefore, the content of CaF ₂ in terms of CaF 2 is preferably 35 mass% or less, and more preferably 33 mass% or less.

[MgO conversion of Mg]

The MgO conversion value is the total amount of Mg in the flux converted to MgO.

MgO is a high-melting-point oxide with a melting point of 2800°C, and greatly contributes to improving the slag detachability. In order to obtain this effect, the content of Mg in terms of MgO is preferably 15 mass% or more, more preferably 16 mass% or more, and even more preferably 17 mass% or more. On the other hand, if it is too much, the bead shape deteriorates, slag entrapment, poor fusion, etc. easily occur, and undercuts and the like easily occur. In addition, there is a concern that the solidification temperature of the slag becomes too high, making it easy for fork marks to occur. Therefore, the MgO conversion value is preferably 25 mass% or less, more preferably 24 mass% or less, and even more preferably 23 mass% or less.

[TiO ₂ conversion of Ti]

The TiO ₂ conversion value is the total Ti content of the flux converted to TiO ₂ .

TiO ₂ is a high-melting-point oxide with a melting point of 1870°C, and is an effective component for improving slag detachability, and also has the effect of improving the bead appearance by adding an appropriate amount. In addition, some of the TiO ₂ becomes Ti by a reduction reaction during welding and is added to the weld metal, which also contributes to improving the toughness. In order to obtain this effect, the content of Ti in terms of TiO ₂ is preferably more than 0 mass%, more preferably 0.1 mass% or more, and further preferably 0.2 mass% or more. On the other hand, if it is too much, there is a concern that the bead shape may deteriorate, or the solidification temperature of the slag may become too high, making it easy for pockmarks to occur. Therefore, the TiO ₂ conversion value is preferably 9 mass% or less, more preferably 4 mass% or less, and further preferably 3.5 mass% or less.

[Ca to CaO conversion]

The CaO conversion value is the value converted to CaO by deducting the Ca amount included in the CaF ₂ conversion value, which is converted from the total F amount, from the total Ca amount of the flux.

CaO is a high-melting-point oxide with a melting point of 2572℃, and it is a component that increases the basicity of slag, thereby increasing the cleanliness of the weld metal, and also affects the fluidity of the slag. This effect is proportional to its presence, and the lower limit of the content of Ca in terms of CaO is not particularly limited, but, for example, 0.5 mass% or more is preferable. On the other hand, if CaO is too much, the fluidity of the molten slag may become excessive, which may deteriorate the appearance and shape of the bead. In addition, since CaO, like MnO, has high hygroscopicity, if the CaO content is too much, there is also a concern that pockmarks may easily occur. Therefore, the CaO conversion value is preferably 10 mass% or less, more preferably 9.5 mass% or less, and even more preferably 9 mass% or less.

[ _Al2O3 conversion of Al _]

_{The Al2O3} conversion value is the total amount of Al in the flux converted _{to Al2O3} .

_Al2O3 is a high-melting-point _oxide with a melting point of 2072℃, and is a component that adjusts the viscosity and melting point of slag, and has the effect of raising the solidification temperature of slag and improving the bead shape during welding. In order to obtain this effect, the content of _Al in terms of _Al2O3 is preferably 10 mass% or more, more preferably 12 mass% or more, and even more preferably 15 mass% or more. On the other hand, if it is too much, the melting point of the slag may rise excessively, which may cause deterioration of the bead shape during welding. Therefore, _{the Al2O3} conversion value is preferably 25 mass% or less, and more preferably 20 mass% or less.

[ZrO ₂ conversion of Zr]

The ZrO ₂ conversion value is the total Zr content of the flux converted to ZrO ₂ .

ZrO ₂ is a high-melting-point oxide with a melting point of 2715°C, and is a component that adjusts the viscosity and melting point of slag, and has the effect of raising the solidification temperature of slag and improving the bead shape during welding. This effect is proportional to the amount present, and is an arbitrary component, and the lower limit of the content of Zr in terms of ZrO ₂ is not particularly limited, but when it is desired to impart a useful effect, it is preferably 0.5 mass% or more, for example. On the other hand, if there is too much ZrO ₂ , the melting point of the molten slag may become excessive, and there is a concern that the bead appearance and bead shape may deteriorate. Therefore, the ZrO ₂ conversion value is preferably 5 mass% or less, and more preferably 3 mass% or less.

[BaO conversion of Ba]

The BaO conversion value is the total Ba content of the flux converted to BaO.

BaO is a high-melting-point oxide with a melting point of 1923℃, and is a component that increases the basicity of slag, thereby increasing the cleanliness of the weld metal, and also affects the fluidity of the slag. This effect is proportional to its presence, and is an arbitrary component, and the lower limit of the content of Ba in terms of BaO is not particularly limited, but when it is desired to impart a useful effect, for example, 0.5 mass% or more is preferable. On the other hand, if BaO is too much, the fluidity of the molten slag may become excessive, which may deteriorate the bead appearance and bead shape. Therefore, the BaO conversion value is preferably 5 mass% or less, and more preferably 3 mass% or less.

[High melting point oxide]

The flux according to the present embodiment contains high-melting-point oxides having a melting point of 1800°C or higher. Among the high-melting-point oxides, the higher the ratio of MgO and TiO ₂ , the better the slag detachability becomes. Therefore, the ratio of the content of the sum of the MgO equivalent and the TiO ₂ equivalent to the content of the sum of the high-melting-point oxides, expressed by {(MgO equivalent + TiO ₂ equivalent) / content of the sum of the high-melting-point oxides}, is preferably 0.430 or higher, and more preferably 0.450 or higher. On the other hand, if this ratio is too high, it contributes to an excessive solidification point, and therefore, this ratio is preferably 0.600 or lower, and more preferably 0.545 or lower.

If the total content of the MgO equivalent, the TiO ₂ equivalent, the CaO equivalent, and the Al ₂ O ₃ equivalent, which means the content of the sum of high-melting-point oxides, is too small, iron grains are likely to occur. In addition, when the flux contains ZrO ₂ or BaO, the content of Zr in ZrO ₂ equivalent and Ba in BaO equivalent are also included in the content of the sum of the high-melting-point oxides.

On the other hand, if the content of the sum is too high, the solidification temperature of the slag becomes too high, making it easy for fork marks to occur. Therefore, the content thereof is preferably 30 or more, more preferably 32 or more, as expressed by the formula (converted value for MgO + converted value for 0.67TiO ₂ + converted value for 0.92CaO + converted value for 0.74Al ₂ O ₃ ). In addition, the value is preferably 50 or less, more preferably 45 or less.

In the above formula, each coefficient multiplied by the content of each high-melting-point oxide is a weighted coefficient using the ratio of melting points based on the melting point of 2800°C of MgO. For example, the coefficient 0.67 multiplied by the TiO ₂ conversion value is a value calculated by dividing the melting point of 1870°C of TiO ₂ by the melting point of 2800°C of MgO.

The ratio of the total content of high-melting-point oxides having a melting point of 1800°C or higher to the total content of all oxides, expressed as (content of total high-melting-point oxides/content of total oxides), is 0.56 or more. By setting this ratio to 0.56 or more, the slag solidification temperature can be raised, thereby suppressing the occurrence of iron grains. In addition, although the upper limit is not particularly limited, by setting this ratio to 0.80 or less, the slag solidification temperature can be prevented from becoming unnecessarily high, thereby suitably suppressing the occurrence of fork marks.

The value expressed as (content of the sum of high-melting-point oxides/content of the sum of oxides) is preferably 0.57 or more. In addition, it is preferable that this value is 0.75 or less.

Meanwhile, the content of the total oxide means the sum of the oxide conversion values of elements forming high-melting-point oxides having a melting point of 1800°C or higher and the oxide conversion values of elements forming low-melting-point oxides having a melting point of less than 1800°C. Low-melting-point oxides having a melting point of less than 1800°C include MnO, MnO ₂ , Mn ₂ O ₃ , SiO ₂ , FeO, Fe ₂ O ₃ , Fe ₃ O ₄ , B ₂ O ₃ , alkali metal oxides, etc.

[ _SiO2 equivalent of Si]

The _SiO2 conversion value is the total Si content of the flux converted to _SiO2 .

_SiO2 is a component that mainly improves the bead appearance and bead shape by providing appropriate viscosity to molten slag. In order to obtain this effect, the content of Si in terms of _SiO2 is preferably 8 mass% or more, and more preferably 11 mass% or more. On the other hand, if it is too much, the viscosity of the slag becomes excessive, which causes the slag detachability to deteriorate, and there is a concern that the slag baking may become intense. Therefore, the _SiO2 conversion value is preferably 20 mass% or less, more preferably 19 mass% or less, and even more preferably 17 mass% or less.

In addition, although there is SiO ₂ derived from alloys and SiO ₂ derived from minerals and _water glass, the converted SiO ₂ value from alloys such as Fe-Si is preferably 4 mass% or less in terms of securing good mechanical performance, and the total of the converted SiO ₂ values from minerals and water glass is preferably 16 mass% or less in terms of slag detachability.

[FeO conversion of Fe]

The FeO conversion value is the value converted from the total Fe content of the flux to FeO. The measured total Fe content may include components other than Fe added as metal powder, such as FeO, Fe ₂ O ₃ and Fe ₃ O ₄ , but the FeO conversion value of the total Fe content is sufficient as long as it is within the above-mentioned range. An example of Fe added as metal powder is Fe-Si, and it mainly has the effect of promoting the deoxidation phenomenon of the weld metal.

FeO has the effect of increasing the pockmark resistance. This effect is proportional to its amount, and the FeO conversion value of Fe has no particular lower limit, but is preferably 0.5 mass% or more, for example. On the other hand, if it is too much, it may affect the solidification temperature of the slag, and there is a risk that the bead appearance, bead shape, and slag detachability may deteriorate. Therefore, the FeO conversion value is preferably 5 mass% or less, and more preferably 4 mass% or less.

[ _B2O3 conversion of B _]

_{The B2O3} conversion value is the total amount of B in the flux _converted to _B2O3 .

B ₂ O ₃ has the effect of improving the toughness of the weld metal. When B is included, the content of B in terms of B ₂ O ₃ is preferably 0.1 mass% or more. On the other hand, if it is too much, the molten metal hardens and the toughness rather decreases, so the B ₂ O ₃ conversion value is preferably 1 mass% or less, and more preferably 0.5 mass% or less.

[Conversion of alkali metal elements to alkali metal oxides]

Alkali metal elements are components that mainly affect the arc stability during welding and the moisture absorption characteristics of the flux, and this effect is proportional to the amount present. The total amount of the alkali metal oxide equivalent of the alkali metal element has no particular lower limit, but when it is desired to impart a useful effect, it is preferably 1 mass% or more. On the other hand, if the total amount of the alkali metal oxide equivalent is excessive, the moisture absorption characteristics of the flux deteriorate, and the arc becomes too strong and unstable, and there is a concern that the bead appearance and bead shape deteriorate. Therefore, the total amount of the alkali metal oxide equivalent is preferably 5.0 mass% or less, and more preferably 4.5 mass% or less.

As the alkali metal element, it is preferable to include at least one element selected from the group consisting of Na, K, and Li, and when Na is included, the content is specified in terms of Na ₂ O, when K is included, the content is specified in terms of K ₂ O, and when Li is included, the content is specified in terms of Li ₂ O. That is, it is preferable that the alkali metal oxide conversion value is a value converted into at least one oxide selected from the group consisting of Na ₂ O, K ₂ O, and Li ₂ O.

The _Na2O conversion, _K2O conversion and _Li2O conversion are all values obtained by converting the total Na, K or Li amount including the binder origin of the flux obtained in accordance with JIS M 8852:1998 into _Na2O , _K2O or _Li2O , respectively. The measured total _Na , K or Li amount may include _NaAlSi3O8 , _KAlSi3O8 or _LiAlSi3O8 , but since it has the same effect, the total of the _Na2O conversion, _K2O conversion and _{Li2O conversion} should be within the above _- mentioned range.

Among the above, it is more preferable to additionally include at least one of the elements of Na and K. In this case, the total amount of the Na ₂ O equivalent and the K ₂ O equivalent is preferably 1 mass% or more, further preferably 5.0 mass% or less, and more preferably 4.5 mass% or less.

［CO ₂ ］

_CO2 is a component mainly derived from carbonates such as _CaCO3 and _BaCO3 , and refers to _CO2 gas generated by decomposition of carbonates during welding. _CO2 gas is an effective component for preventing intrusion into the weld metal because it shields the weld zone from the outside air and reduces the partial pressure of impurity gases such as _H2 gas and _N2 gas, and this effect is proportional to its presence. It is an arbitrary component, and the lower limit of the _CO2 content is not particularly limited, but when it is desired to impart a useful effect, it is preferably 0.5 mass% or more. On the other hand, if it is too much, it may cause the occurrence of pockmarks, and there is a concern that the pockmark resistance may deteriorate. Therefore, the _CO2 content is preferably 6.0 mass% or less, more preferably 5.0 mass% or less, and still more preferably 4.5 mass% or less.

[Other ingredients]

Components other than those mentioned above in the flux according to the present embodiment are unavoidable impurities such as P and S, and since they affect the welding quality, it is preferable to regulate P and S to 0.05 mass% or less each.

In addition, other elements may be included within a range that does not impair the effects of the present invention. Examples of other elements include Ni, Cr, Mo, Nb, V, and C. It is preferable that the total amount of these other elements is 5.0 mass% or less.

That is, the sum of the above components, excluding inevitable impurities and other elements, is usually 90 mass% or more, and preferably 95 mass% or more.

［CaF ₂ equivalent / (MnO equivalent + CaO equivalent + CO ₂ )］

In the flux according to the present embodiment, Mn, expressed in terms of MnO, is a component that improves slag detachability, but causes the occurrence of pock marks due to its hygroscopicity. Similarly, CaO and CO ₂ are components that tend to cause the occurrence of pock marks. On the other hand, fluoride, expressed in terms of CaF ₂ , is a component that suppresses the occurrence of pock marks.

Therefore, by setting the content ratio expressed as {CaF ₂ equivalent value/(MnO equivalent value+CaO equivalent value+CO ₂ )} to 1.6 or more, the occurrence of pockmarks is suitably suppressed.

It is desirable that this ratio be 1.8 or higher. On the other hand, if the value is too high, the fluidity of the slag may become excessively high, which may deteriorate the bead shape, so the value is desirable to be 9.0 or lower, and more preferably 7.0 or lower.

The flux according to the present embodiment is preferably a high-temperature calcined flux in which the raw material-derived assembly is calcined at 400 to 950°C.

＜Method for manufacturing flux＞

When manufacturing a flux according to the present embodiment, the process includes, for example, a step of mixing raw material components so as to have the composition described in the above <Flux> and mixing them together with a binder, a step of assembling them, and a step of firing an assemblage derived from the obtained raw material, in this order.

As a binder in the mixing process, for example, polyvinyl alcohol or water glass can be used.

The assembly method in the assembling process is not particularly limited, but a method using an electric assembly machine or an extrusion assembly machine is preferable.

It is preferable that the assembled flux undergoes particle size treatment such as dust removal and coarse particle disintegration to reduce the particle size to 2.5 mm or less.

Firing after assembly can be performed in a rotary kiln, a stationary batch furnace, a belt-type kiln, etc. The firing temperature at that time is preferably 400 to 950°C from the viewpoint of the moisture absorption characteristics of the flux, and more preferably 450°C or higher.

The flux according to the present embodiment obtained above has excellent slag detachability while suppressing the occurrence of iron grains or fork marks because the content of each component is within a specific range.

Meanwhile, the composition of the flux of the present embodiment is suitable as a high-temperature sintering flux, but it does not completely exclude application as a molten flux.

＜Welding method using flux＞

The welding method according to the present embodiment is a submerged arc welding method that performs arc welding using a flux that satisfies the composition range described in the above <Flux>.

This welding method is very useful for improved welding, especially narrow improved welding, which is one of the welding methods that is difficult to perform. That is, the shape of the improved shape of the workpiece to be welded, called the parent material or workpiece, is not particularly limited, but it is more preferable that it be processed into a U-shaped or V-shaped shape.

When the weld material is a U-shaped improvement or V-shaped improvement that has undergone U-shaped improvement or V-shaped improvement processing, the improvement angle is preferably 10° or more, and more preferably 15° or more. In addition, the improvement angle is preferably 90° or less, more preferably 60° or less, and more preferably 20° or less.

The depth of improvement is preferably 20 mm or less, and more preferably 15 mm or less, from the viewpoint of preventing oxidation of the weld material.

In U-shaped improvement, the root radius of the U improvement is preferably R2 or more from the viewpoint of preventing welding defects, and more preferably R5 or more. In addition, the root radius is preferably R10 or less from the viewpoint of welding efficiency, and more preferably R8 or less. Root radius is a welding term defined in JIS Z 3001-1:2018.

Example

Hereinafter, the contents of the present invention will be specifically described using test examples.

Fluxes according to Test Examples 1 to 18 were produced by mixing raw materials to obtain the compositions described in Tables 1 and 2, kneading them with water glass as a binder, assembling them, pre-drying them at 150 to 250°C (actual temperature), and then firing them at 450 to 550°C (actual temperature) using a rotary kiln and adjusting the particle size. Meanwhile, fluxes according to Test Examples 1 to 19 are examples, and fluxes according to Test Examples 20 to 29 are comparative examples.

In addition, in Table 1, the notation "-" in _CO2 means 0.5 mass% or less, and the notation "-" in _{the B2O3 conversion} value of B means 0.1 mass% or less.

In the table, the numerical value of each component represents the content, and is expressed as mass% with respect to the total mass of the flux. "R" represents an alkali metal element, but alkali metal elements other than Li, Na, and K were not included in any test example. "RO conversion value" represents the content of the sum of the alkali metal oxide conversion values of alkali metal elements, but since alkali metal elements other than Li, Na, and K are not included in any test example, it means the sum of the values converted to at least one oxide selected from the group consisting of Na ₂ O, K ₂ O, and Li ₂ O. "High-melting-point oxide" represents the content of the sum of oxide conversion values of elements forming high-melting-point oxides having a melting point of 1800° C. or higher, and in this example, since ZrO ₂ and BaO are not included, it is the sum of the MgO conversion value, the TiO ₂ conversion value, the CaO conversion value, and the Al ₂ O ₃ conversion value. "Low _- melting-point oxide" means the sum of the oxide-converted content of elements forming oxides having a melting point of less than 1800°C. However, even when _Fe2O3 or _Fe3O4 is included, the total Fe amount is converted to FeO, and even when _MnO2 or _Mn2O3 is included, the total _Mn amount is converted to MnO. Therefore, "low-melting-point _oxide " means the sum of the MnO-converted value, the _SiO2- converted value, the FeO-converted value, the _{B2O3 -} converted value, and the alkali metal oxide-converted value. The sum of "oxides" means the sum of the high-melting-point oxides and low-melting-point oxides, but if the sum deviates from the sum of the contents described in the high-melting-point oxides and low-melting-point oxides, as in Test Example 11, this is due to significant figures. Likewise, for example, in Test Example 1, the sum of the "SiO ₂ equivalent of Si" deviates from the sum of the contents described in the alloy origin and the mineral origin due to significant figures. Although the total content of all components may exceed 100 mass%, this is because the total amount of each element obtained by analysis is converted into oxide or fluoride and used as the content.

Using the obtained flux, submerged arc welding was performed using a steel plate as a weld material. The weld material, the wire used for welding, and the welding conditions are as shown below.

[Welding material]

Steel plate: C 0.16 mass%, Si 0.30 mass%, Mn 1.30 mass%, P 0.007 mass%, S 0.001 mass%, balance Fe and inevitable impurities

Plate thickness: 25mm

Improvement Depth: 15mm

Root gap: 0mm

Improved shape: U-shaped improvement

Improvement angle: 16°

Root Radius: R8

[Wire]

Wire type: Conforms to JIS Z 3351:2012 YS-S6

Wire diameter: 4.0mm

[Welding conditions]

Welding current: 650A

Welding voltage: 30V

Welding speed: 65 cm/min

Lamination method: 1 layer, 1 pass

For submerged arc welding using each flux, slag detachability and the occurrence of iron and pock marks were evaluated.

The evaluation methods and evaluation criteria are as follows. In the comprehensive evaluation, if any one of the evaluation results of slag detachability, iron grain, and fork mark fails, it is judged to be outside the scope of application as a flux and fails.

＜Slag peelability＞

Slag detachability is evaluated as follows with respect to the ease of slag removal, with A and B being acceptable and C being unacceptable. The results are shown in “Slag detachment” in Table 2.

A: The welding slag is naturally exfoliated immediately after welding.

B: When the slag is hit with a jig such as a hammer, the welding slag is peeled off.

C: Even if the slag is struck with a jig such as a hammer, the welding slag does not peel off, and a small amount of welding slag remains on the bead.

＜Incidence of iron fractures＞

The occurrence of iron grains on the bead surface was visually confirmed. The occurrence rate was evaluated as follows, with A and B being acceptable, and C and D being unacceptable. The results are shown in “Iron grains” in Table 2.

A: There is no occurrence of iron particles on the bead surface.

B: The number of iron grains occurring per 750 mm of welding length on the bead surface is 1 or 2.

C: The number of iron grains per 750 mm of welding length on the bead surface is 3 or more and 9 or less.

D: The number of iron grains occurring per 750 mm of welding length on the bead surface is 10 or more.

＜Forkmark occurrence rate＞

The occurrence of fork marks on the bead surface was visually confirmed. The occurrence rate was evaluated as follows, with A to C being passable and D being failable. The results are shown in “Fork Mark” in Table 2.

A: There are no fork marks on the bead surface.

B: The number of fork marks per 750 mm of welding length on the bead surface is 1 or 2.

C: The number of fork marks per 750 mm of welding length on the bead surface is 3 or more and 5 or less.

D: The number of fork marks per 750 mm of welding length on the bead surface is 6 or more.

As shown in Table 2, the fluxes according to Test Examples 1 to 19 had excellent slag detachment properties and a low incidence of iron grains and fork marks.

In particular, for test examples 1 to 6, 10 to 12, and 14 to 16, two or more of the evaluation items of slag detachability, iron grain, and fork mark were evaluated as A, indicating that the flux was very good for use in submerged arc welding.

From the above results, it was confirmed that by using the flux according to the present invention in submerged arc welding, both excellent slag detachability and good bead appearance with few surface defects can be achieved even in difficult-to-construct welding such as narrow-line welding.

Above, although various embodiments have been described with reference to the drawings, it goes without saying that the present invention is not limited to these examples. It is clear that those skilled in the art can devise various modifications or alterations within the scope described in the patent claims, and it is understood that these also naturally fall within the technical scope of the present invention. In addition, each component in the above embodiments may be arbitrarily combined within the scope that does not deviate from the spirit of the invention.

Meanwhile, this application is based on Japanese patent application (Special Application No. 2019-166576) filed on September 12, 2019 and Japanese patent application (Special Application No. 2020-117993) filed on July 8, 2020, the contents of which are incorporated by reference in this application.

Claims (9)

As a flux used in submerged arc welding,
Contains fluorides, oxides and carbonates,
The above oxide is composed of a high melting point oxide having a melting point of 1800°C or higher and a low melting point oxide having a melting point of less than 1800°C.
It includes an oxide containing Ca as the high melting point oxide and an oxide containing Mn as the low melting point oxide,
The content of the total mass of the flux is,
The MnO equivalent of Mn is 2–8 mass%,
_CO2 derived from carbonate is 0.5 mass% or more, and
The above MnO conversion value, F's CaF ₂ conversion value, Ca's CaO conversion value and CO ₂ satisfy the relationship of 1.6≤{CaF ₂ conversion value/(MnO conversion value+CaO conversion value+CO ₂ )},
A flux for submerged arc welding, wherein the ratio of the content of the sum of the high-melting-point oxides to the content of the sum of the above oxides (content of the sum of the high-melting-point oxides/content of the sum of the oxides) is 0.56 or more. In paragraph 1,
The above high melting point oxide comprises at least one of MgO and TiO ₂ ,
The content of the total mass of the flux is,
The MgO equivalent of Mg is less than 25 mass%, and
The conversion value of TiO ₂ is 9 mass% or less,
A flux for submerged arc welding, wherein the ratio of the content of the sum of the MgO equivalent and the TiO ₂ equivalent to the content of the sum of the high-melting-point oxides {(MgO equivalent + TiO ₂ equivalent) / content of the sum of the high-melting-point oxides} is 0.430 or more. In the second paragraph,
The content of the high melting point oxide relative to the total mass of the flux is
The above CaO conversion value is 10 mass% or less,
The Al ₂ O ₃ conversion value of Al is 25 mass% or less, and
A flux for submerged arc welding, wherein the above MgO conversion value, the above TiO ₂ conversion value, the above CaO conversion value, and the above Al ₂ O ₃ conversion value satisfy the relationship of 30≤(MgO conversion value + 0.67TiO ₂ conversion value + 0.92 CaO conversion value + 0.74Al ₂ O ₃ conversion value)≤50. In any one of claims 1 to 3,
The content of the low melting point oxide relative to the total mass of the flux is
The _SiO2 equivalent of Si is 20 mass% or less,
FeO conversion value of Fe is 5 mass% or less,
_{The B2O3 conversion} value of B is less than 1 mass%, and
A flux for submerged arc welding having an alkali metal oxide equivalent of 5.0 mass% or less of alkali metal elements. In paragraph 4,
A flux for submerged arc welding, wherein the alkali metal oxide conversion value is a value converted into at least one oxide selected from the group consisting of Na ₂ O, K ₂ O, and Li ₂ O. In any one of claims 1 to 3,
The content of the total mass of the flux is,
The above CaF ₂ conversion value is 20 mass% or more, and
A flux for submerged arc welding, wherein the _CO2 content is 6.0 mass% or less. A submerged arc welding method that performs arc welding using flux,
The above flux is,
Contains fluorides, oxides and carbonates,
The above oxide is composed of a high melting point oxide having a melting point of 1800°C or higher and a low melting point oxide having a melting point of less than 1800°C.
It includes an oxide containing Ca as the high melting point oxide and an oxide containing Mn as the low melting point oxide,
The content of the total mass of the flux is,
The MnO equivalent of Mn is 2–8 mass%,
_CO2 derived from carbonate is 0.5 mass% or more, and
The above MnO conversion value, F's CaF ₂ conversion value, Ca's CaO conversion value and CO ₂ satisfy the relationship of 1.6≤{CaF ₂ conversion value/(MnO conversion value+CaO conversion value+CO ₂ )},
A submerged arc welding method, which utilizes a ratio of the content of the sum of the high-melting-point oxides to the content of the sum of the above oxides (content of the sum of the high-melting-point oxides/content of the sum of the oxides) of 0.56 or more. In paragraph 7,
A submerged arc welding method in which the weld material is processed to be improved by U improvement or V improvement, and the improvement angle is 10 to 60°. A method for manufacturing a flux used in submerged arc welding,
Includes a process of calcining an assembly derived from raw materials at 400 to 950°C.
The flux after the above firing process is
Contains fluorides, oxides and carbonates,
The above oxide is composed of a high melting point oxide having a melting point of 1800°C or higher and a low melting point oxide having a melting point of less than 1800°C.
It includes an oxide containing Ca as the high melting point oxide and an oxide containing Mn as the low melting point oxide,
The content of the total mass of the flux is,
The MnO equivalent of Mn is 4–8 mass%,
_CO2 derived from carbonate is 0.5 mass% or more, and
The above MnO conversion value, F's CaF ₂ conversion value, Ca's CaO conversion value and CO ₂ satisfy the relationship of 1.6≤{CaF ₂ conversion value/(MnO conversion value+CaO conversion value+CO ₂ )},
A method for manufacturing a flux for submerged arc welding, wherein the ratio of the content of the sum of the high-melting-point oxides to the content of the sum of the oxides (content of the sum of the high-melting-point oxides/content of the sum of the oxides) is 0.56 or more.