Electroslag welding flux and electroslag welding-flux cored tire

Abstract

To provide an electroslag welding flux that can increase toughness of a weld metal part and an HAZ part while maintaining good bead shape.SOLUTION: An electroslag welding flux comprises by mass% to a total mass: SiO2 of 20 to 30%; CaO of 15 to 40%; MnO of 10 to 30%; MgO of 5 to 15%; Al2O3 of 5 to 20%; CaF2 of 3 to 10%; TiO2 of 0.5 to 4%; a total of FeO and FeO conversion value of metal Fe of 0.1 to 3%; a total of NiO and a NiO conversion value of metal Ni of 0 to 2%; B2O3 of 0 to 2%; BaO of 0 to 0.1%; Na2O of 0 to 0.1%; K2O of 0 to 0.1%; Li2O of 0 to 0.1%; ZrO2 of 0 to 0.1%; oxides other than the above of 0 to 5% in total; fluorides other than the above of 0 to 3% in total; carbonates of 0 to 0.5% in total; and the reminder comprising impurities.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to an electroslag welding flux and an electroslag welding flux-cored wire. [Background technology]

[0002] Electroslag welding is a method in which flux is filled into a groove surrounded by steel plates, a welding wire is inserted, and the flux is melted by Joule heating, causing the welding wire to melt continuously in the molten slag, filling the groove with molten metal and continuously welding steel plates together in a vertical position. Electroslag welding has the advantage of being able to weld thick steel plates efficiently by increasing the heat input, and is less affected by wind because the welding wire melts in the molten slag.Furthermore, unlike arc welding, which melts the wire using arc heat, electroslag welding melts the wire using Joule heat, so there is no arc light and no spatter. Electroslag welding is widely used in the construction industry, for example, for diaphragm welding of large four-sided box columns, and is known as a highly efficient welding method for thick steel plates. In recent years, its application as a vertical welding method for block joints in the shipbuilding industry has also been considered as an alternative welding technique to electrogas arc welding.

[0003] For example, Patent Document 1 describes a flux used in electroslag welding as "containing, by mass%, SiO2: 0-35%, CaO: 5-60%, CaF2: 3-50%, BaF2: 0-20%, MgO: 0-20%, Al2O3: 0-65%, MnO: 0-20%, TiO2: 0-10%, ZrO2: 0-10%, FeO: 0-5%, Na2O: 0-10%, K2O: 0-10%, BaO: 0-20%." and satisfying the following formula (5) ((CaO + CaF2 + BaF2 + MgO + BaO + Na2O + K2O) / (SiO2 + 0.5(Al2O3 + TiO2 + ZrO2 + MnO + FeO)) ≥ 1.00 (however, if none of SiO2, Al2O3, TiO2, ZrO2, MnO, and FeO is contained, the formula is set to > 100)). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-043288 Summary of the Invention [Problem to be solved by the invention]

[0005] However, because electroslag welding requires a large amount of electrical energy, the penetration of the steel plate (i.e., base material) during welding increases, resulting in excessive heat input and reduced toughness in the weld metal and heat-affected zone (HAZ). For example, with conventional electroslag welding, when welding a diaphragm on a four-sided box column, if the steel plate (base material) is 60 mm thick, the heat input can be about 1 million J / cm, and the penetration of the steel plate (base material) can be as little as 15 mm from the groove face of the base material before welding.

[0006] Therefore, an object of the present disclosure is to provide an electroslag welding flux that can maintain a good bead shape, reduce penetration of the steel plate (i.e., base material) during electroslag welding, and increase the toughness of the weld metal and HAZ, and a flux-cored wire for electroslag welding that has this electroslag welding flux inside a steel sheath. [Means for solving the problem]

[0007] The gist of the present disclosure for solving the above problems is as follows. <1> Mass % of the total flux mass SiO2: 20-30%, CaO: 15-40%, MnO: 10-30%, MgO: 5-15% Al2O3: 5-20% CaF2: 3-10%, TiO2: 0.5-4.0%, Sum of FeO and metallic Fe converted to FeO: 0.1 to 3.0% The sum of NiO and metallic Ni converted into NiO: 0 to 2.0% B2O3: 0-2.0% BaO: 0 to 0.10% Na2O: 0-0.10% K2O: 0~0.10%, Li2O: 0 to 0.10%, ZrO2: 0-0.10% Total of oxides other than those mentioned above: 0 to 5.0% Total of fluorides other than those mentioned above: 0 to 3.0% Total carbonates: 0 to 0.50%, and Remainder: impurities A flux for electroslag welding comprising: <2> The basicity BL represented by the following formula 1 is 1.0 to 2.3. <1> The electroslag welding flux according to claim 1. BL=([CaO]+[MgO]+[BaO]+[Na2O]+[K2O]+[Li2O]+[CaF2]+0.5[MnO]+0.5[FeO]) / ([SiO2]+0.5[Al2O3]+0.5[TiO2]+0.5[ZrO2])...Equation 1 (In Equation 1, [CaO] is the CaO content (mass%) relative to the total mass of the flux, [MgO] is the MgO content (mass%) relative to the total mass of the flux, [BaO] is the BaO content (mass%) relative to the total mass of the flux, [Na2O] is the Na2O content (mass%) relative to the total mass of the flux, [K2O] is the K2O content (mass%) relative to the total mass of the flux, [Li2O] is the Li2O content (mass%) relative to the total mass of the flux, and [CaF2] is the CaF2 content (mass%) relative to the total mass of the flux. (MnO] represents the MnO content (mass%) relative to the total mass of the flux, [FeO] represents the total content (mass%) of FeO and the FeO-equivalent value of metallic Fe relative to the total mass of the flux, [SiO2] represents the SiO2 content (mass%) relative to the total mass of the flux, [Al2O3] represents the Al2O3 content (mass%) relative to the total mass of the flux, [TiO2] represents the TiO2 content (mass%) relative to the total mass of the flux, and [ZrO2] represents the ZrO2 content (mass%) relative to the total mass of the flux.) <3> The ratio ([CaO] / [CaF]) of the CaO content (% by mass) to the CaF content (% by mass) is 2.0 to 9.0. <1> or <2> The electroslag welding flux according to claim 1. <4> A steel skin and a material filled inside the steel skin <1> ~ <3> and a flux-cored wire for electroslag welding, the flux being defined in any one of claims 1 to 4. [Effects of the Invention]

[0008] According to the present disclosure, there are provided an electroslag welding flux that can maintain a good bead shape, reduce penetration of the steel plate (i.e., base metal) during electroslag welding, and increase the toughness of the weld metal and HAZ, and an electroslag welding flux-cored wire that has this electroslag welding flux inside a steel sheath. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating an embodiment of an electroslag welding apparatus for performing electroslag welding using a flux according to the present disclosure. FIG. [Figure 2] 1A is a side view showing a welding test plate assembled for welding performed in the examples, and FIG. 1B is a plan view showing the welding test plate. [Figure 3] FIG. 2 is a schematic cross-sectional view for explaining an undercut occurring in a weld metal. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, the flux for electroslag welding (sometimes simply referred to as "flux" in this disclosure) and the flux-cored wire for electroslag welding according to the present disclosure will be described.

[0011] The present inventors have conducted detailed studies on the chemical composition of a flux that can reduce penetration of steel sheets during electroslag welding and increase the toughness of the weld metal and HAZ. As a result, they have discovered that it is important to adjust the chemical composition of the flux to increase the electrical and thermal conductivity of the molten slag (flux melted).

[0012] First, they discovered that increasing the electrical conductivity of the molten slag can reduce the amount of penetration into the steel plate (i.e., base material) during welding. This is because the high electrical conductivity of the molten slag means that only the area near the welding electrode inserted in the molten slag becomes a high-temperature heat-generating area, which narrows the high-temperature area in the molten slag. This prevents the molten slag near the base material from becoming too hot, and therefore reduces penetration into the steel plate (base material).

[0013] Therefore, in the flux according to the present disclosure, the electrical conductivity of the molten slag is increased by increasing the content of CaO, CaF2, MgO, etc. and decreasing the content of SiO2, etc. (preferably by further increasing the basicity). In addition, the electrical conductivity of the molten slag is increased by increasing the content of MnO, TiO2, FeO, NiO, etc.

[0014] They also found that increasing the thermal conductivity of the molten slag can reduce the amount of penetration into the steel plate (base material) during welding. This is thought to be because the high thermal conductivity of the molten slag makes it easier for the molten slag itself to dissipate heat, preventing the molten slag near the base material from becoming too hot due to heat dissipation by the base material, thereby suppressing penetration into the steel plate (base material). Therefore, in the flux according to the present disclosure, the thermal conductivity of the molten slag is increased by increasing the content of Al2O3, etc. Furthermore, it is preferable to increase the ratio of the CaO content to the CaF2 content ([CaO] / [CaF2]), which can further increase the thermal conductivity of the molten slag.

[0015] As described above, the flux according to the present disclosure reduces penetration of steel sheets during electroslag welding and improves the toughness of the weld metal and HAZ. In addition, by reducing penetration of steel sheets during welding and reducing heat input, the welding speed can also be improved.

[0016] The components of the flux according to the present disclosure and the reasons for limiting the composition thereof will be described below. The content of each component is expressed as mass % relative to the total mass of the flux, and the mass % is simply expressed as %. In addition, in the present disclosure, a numerical range expressed using "to" means a range that includes these numerical values ​​as the lower limit and upper limit. In addition, in the numerical ranges described in stages in this specification, the upper limit of a certain numerical range may be replaced by the upper limit of another numerical range described in stages, or may be replaced by a value shown in an Example. Furthermore, the lower limit of a certain numerical range may be replaced by the lower limit of another numerical range described in stages, or may be replaced by a value shown in an Example. The content (%) of "0 or more" means that the component is an optional component and does not need to be contained. Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

[0017] In addition, in this disclosure, the content of "SiO" includes the amount of Si oxides other than SiO, in which case it is the amount of Si oxides in terms of SiO. In other words, when referring to the content of "SiO" in this disclosure, it means the content of "the total amount of Si oxides in terms of SiO." Similarly, the "CaO" content is the "sum of Ca oxides converted to CaO" content, the "MnO" content is the "sum of Mn oxides converted to MnO" content, the "MgO" content is the "sum of Mg oxides converted to MgO" content, the "Al2O3" content is the "sum of Al oxides converted to Al2O3" content, the "TiO2" content is the "sum of Ti oxides converted to TiO2" content, and the "B2O3" content is the "sum of B oxides converted to B The "BaO" content means the "sum of Ba oxides converted into BaO values", the "Na2O" content means the "sum of Na oxides converted into Na2O values", the "K2O" content means the "sum of K oxides converted into K2O values", the "Li2O" content means the "sum of Li oxides converted into Li2O values", and the "ZrO2" content means the "sum of Zr oxides converted into ZrO2 values". Furthermore, in the present disclosure, the content of "the sum of FeO and the FeO equivalent value of metallic Fe" includes the amount of Fe oxides other than FeO, in which case it is the amount of Fe oxide in terms of FeO equivalent. In other words, in the present disclosure, the content of "the sum of Fe oxide in terms of FeO and the FeO equivalent value of metallic Fe" means the content of "the sum of Fe oxide in terms of FeO and the FeO equivalent value of metallic Fe." Similarly, the content of "the sum of NiO and the NiO equivalent value of metallic Ni" means the content of "the sum of Ni oxide in terms of NiO and the NiO equivalent value of metallic Ni." In addition, in this disclosure, "the total of oxides other than the above" refers to the total content of oxides other than SiO2, CaO, MnO, MgO, Al2O3, TiO2, FeO, NiO, BO3, BaO, Na2O, KO, Li2O, and ZrO2. Similarly, "the total of fluorides other than the above" refers to the total content of fluorides other than CaF2. Furthermore, "the total of carbonates" refers to the total content of carbonates.

[0018] Here, for example, the total TiO2 equivalent value of Ti oxides refers to the mass % of TiO2 relative to the total mass of the flux when all Ti oxides contained in the flux (for example, TiO2, Ti2O3, Ti3O5, etc., added as rutile, titanium oxide, titanium slag, ilmenite, sodium titanate, potassium titanate, etc.) are converted into TiO2. The total TiO2 equivalent value of Ti oxides can be determined by analyzing the mass of Ti present as oxide in the flux using an X-ray analyzer. For example, if TiO2, Ti2O3, and Ti3O5 are detected by analysis, the total TiO2 equivalent value of Ti oxides can be determined by adding the TiO2 equivalent values ​​of Ti2O3 and Ti3O5 to the amount of TiO2.

[0019] Other oxides, namely, Si oxide, Ca oxide, Mn oxide, Mg oxide, Al oxide, B oxide, Fe oxide, Ni oxide, Ba oxide, Na oxide, K oxide, Li oxide, Zr oxide, and oxides other than those mentioned above, can be determined in the same manner. Representative oxides detected by analysis are listed below. Si oxides; SiO, SiO2, Si2O3, Si2O4 Calcium oxide; CaO, CaO2 Manganese oxides; MnO, Mn2O, MnO2 Magnesium oxide; MgO, Mg2O Al oxides: AlO, Al2O3, Al3O5 B oxide; B2O3 Fe oxides: FeO, Fe2O4, FeO3 Ni oxide; NiO Ba oxide; BaO Sodium oxide; Na2O Potassium oxide; K2O Lithium oxide; Li2O Zr oxide; ZrO2 Oxides other than those mentioned above: PbO, Nb2O5, Bi2O3, Cr2O3, SnO, SrO, B2O3, P2O5, and V2O5, etc.

[0020] The CaF2 content is also determined by analyzing the mass of Ca present in the flux as fluorides using an X-ray analyzer. Other fluorides can also be determined in the same manner. The carbonate content is also determined using an X-ray analyzer. Representative examples of fluorides and carbonates other than those mentioned above that may be detected by analysis are listed below. Fluorides other than those mentioned above: MgF2, AlF3, LiF, NaF Carbonates: CaCO3, BaCO3, MgCO3, Li2CO3

[0021] [SiO2: 20-30%] SiO2, derived from silica sand, wollastonite, and other materials, adjusts the viscosity of the molten slag, shaping the bead and reducing its electrical conductivity. If the SiO2 content is less than 20%, the slag viscosity decreases, resulting in poor bead shape. On the other hand, if the SiO2 content exceeds 30%, the slag viscosity increases, reducing the electrical conductivity of the molten slag. This increases the penetration of the steel plate during electroslag welding, coarsening the crystal grains in the metal structure, and reducing the toughness of the weld metal and HAZ. Therefore, the SiO2 content is set to 20 to 30%. The lower limit of SiO2 is preferably 22% or 24%. The upper limit of SiO2 is preferably 28% or 26%.

[0022] [CaO: 15-40%] CaO, derived from calcium oxide and other raw materials, adjusts the viscosity of the molten slag, shaping the bead and increasing electrical conductivity. It also reduces the oxygen content of the weld metal. If the CaO content is less than 15%, the slag viscosity increases, resulting in poor bead shape and a high oxygen content in the weld metal, preventing low-temperature toughness. Furthermore, the electrical conductivity of the molten slag decreases, increasing penetration of the steel sheet during electroslag welding and coarsening the crystal grains in the metal structure, resulting in reduced toughness of the weld metal and HAZ. On the other hand, if the CaO content exceeds 40%, the viscosity of the molten slag decreases, resulting in undercutting and poor bead shape. Therefore, the CaO content is set to 15 to 40%. The lower limit of CaO is preferably 17%, 20%, or 22%. The upper limit of CaO is preferably 35%, 30%, or 28%.

[0023] Here, "undercut" will be explained using Fig. 3. The welded joint 400 shown in Fig. 3 has two steel plates 20C and 20D, which are base materials, and a weld metal 40 formed in a groove 4 between the steel plates 20C and 20D. Undercuts 112 and 114 have occurred in the weld metal 40. In other words, the undercuts 112 and 114 refer to a state in which the side surfaces of the weld metal 40 do not reach the height of the surfaces of the steel plates 20C and 20D, which are base materials, and the width of the weld metal 40 does not reach the width of the groove 4.

[0024] [MnO: 10-30%] MnO, derived from manganese oxide, roasted manganese, etc., adjusts the viscosity of the molten slag, shaping the bead and increasing electrical conductivity. If the MnO content is less than 10%, the viscosity of the molten slag increases, resulting in poor bead shape. Furthermore, the electrical conductivity of the molten slag decreases, increasing penetration of the steel sheet during electroslag welding and coarsening the crystal grains in the metal structure, resulting in reduced toughness of the weld metal and HAZ. On the other hand, if the MnO content exceeds 30%, the viscosity of the molten slag decreases, resulting in undercutting and poor bead shape. Therefore, the content of MnO is set to 10 to 30%. The lower limit of MnO is preferably 12%, 15%, or 17%. The upper limit of MnO is preferably 28%, 25%, or 23%.

[0025] [MgO: 5-15%] MgO, derived from magnesia clinker and other raw materials, adjusts the viscosity of the molten slag, shaping the bead and increasing electrical conductivity. If the MgO content is less than 5%, the molten slag will have insufficient viscosity, resulting in undercutting and poor bead shape. Furthermore, the electrical conductivity of the molten slag will decrease, increasing penetration of the steel sheet during electroslag welding and coarsening the crystal grains in the metal structure, resulting in reduced toughness in the weld metal and HAZ. On the other hand, if the MgO content exceeds 15%, the viscosity of the molten slag will increase, resulting in poor bead shape. Therefore, the MgO content is set to 5 to 15%. The lower limit of MgO is preferably 6% or 8%. The upper limit of MgO is preferably 14% or 12%.

[0026] [Al2O3: 5-20%] Al2O3, derived from alumina and other raw materials, is an effective component for adjusting the viscosity of molten slag. If the Al2O3 content is less than 5%, the viscosity of the molten slag will be low, resulting in undercutting and poor bead shape. Furthermore, the thermal conductivity of the molten slag will decrease, resulting in greater penetration of the steel plate during electroslag welding, and the grain size of the metal structure will increase, reducing the toughness of the weld metal and HAZ. On the other hand, if the Al2O3 content exceeds 20%, the viscosity of the molten slag will be too high, resulting in poor bead shape. Therefore, the Al2O3 content is set to 5 to 20%. The lower limit of Al2O3 is preferably 6% or 8%. The upper limit of Al2O3 is preferably 13%, 15%, or 18%.

[0027] [CaF2: 3-10%] CaF2, derived from fluorite and other raw materials, adjusts the viscosity of the molten slag, shaping the bead and increasing electrical conductivity. It also reduces the oxygen content of the weld metal, improving toughness. If the CaF2 content is less than 3%, the slag viscosity increases, resulting in poor bead shape. Furthermore, the high oxygen content in the weld metal prevents low-temperature toughness from being achieved. Furthermore, the reduced electrical conductivity of the molten slag increases the penetration of the steel sheet during electroslag welding, causing the crystal grains in the metal structure to become coarse, resulting in reduced toughness in the weld metal and HAZ. On the other hand, if the CaF2 content exceeds 10%, the slag viscosity decreases, resulting in poor fluidity, undercutting, and poor bead shape. Therefore, the CaF2 content is set to 3 to 10%. The lower limit of CaF2 is preferably 3.5% or 4%. The upper limit of CaF2 is preferably 6% or 8%.

[0028] [TiO2: 0.5-4.0%] TiO2, derived from raw materials such as rutile and titanium oxide, adjusts the viscosity of the molten slag, shaping the bead and increasing its electrical conductivity. If TiO2 is less than 0.5%, the viscosity of the molten slag increases, resulting in poor bead shape. Furthermore, the electrical conductivity of the molten slag decreases, increasing penetration of the steel sheet during electroslag welding and coarsening the crystal grains in the metal structure, resulting in reduced toughness in the weld metal and HAZ. On the other hand, if TiO2 exceeds 4.0%, the viscosity of the molten slag decreases, causing undercutting and poor bead shape. Therefore, the TiO2 content is set to 0.5 to 4.0%. The lower limit of TiO2 is preferably 1.0% or 1.5%. The upper limit of TiO2 is preferably 3.5%, or 3.0%.

[0029] [Total of FeO and metallic Fe converted to FeO: 0.1 to 3.0%] FeO, which is made from mill scale and other raw materials, adjusts the viscosity of the molten slag, shapes the bead, and increases electrical conductivity. Note that even if metallic Fe is included in the flux, it will oxidize during welding to form Fe oxide, which has the same effect. If the total of FeO and the FeO-equivalent value of metallic Fe is less than 0.1%, the viscosity of the molten slag increases, resulting in poor bead shape. Furthermore, the electrical conductivity of the molten slag decreases, increasing penetration of the steel sheet during electroslag welding, resulting in coarsening of the crystal grains in the metal structure and reduced toughness of the weld metal and HAZ. On the other hand, if the total of FeO and the FeO-equivalent value of metallic Fe exceeds 3.0%, the viscosity of the molten slag decreases, causing undercutting and poor bead shape. Therefore, the total of FeO and the FeO-equivalent value of metallic Fe is set to 0.1 to 3.0%. The lower limit of the total of FeO and the FeO-equivalent value of metallic Fe is preferably 0.3%, 0.5%, or 0.8%. The upper limit of the total of FeO and the FeO-equivalent value of metallic Fe is preferably 2.5%, 2.0%, or 1.5%.

[0030] [Total of NiO and metallic Ni converted to NiO: 0 to 2.0%] NiO, which is made from nickel oxide and other raw materials, adjusts the viscosity of the molten slag, shapes the bead, and increases electrical conductivity. Note that even if metallic Ni is included in the flux, it will oxidize during welding to form Ni oxide, which has the same effect. The total of NiO and the NiO-equivalent value of metallic Ni may be 0%. However, from the viewpoint of obtaining the effect of increasing the electrical conductivity of the molten slag, it is preferable to set it to 0.01% or more. On the other hand, if the total of NiO and the NiO-equivalent value of metallic Ni exceeds 2.0%, the viscosity of the molten slag decreases, undercutting occurs, and the bead shape becomes poor. Therefore, the total of NiO and the NiO-equivalent value of metallic Ni is set to 0 to 2.0%. The lower limit of the total of NiO and the NiO-equivalent value of metallic Ni is preferably 0.01%, 0.05%, or 0.1%. The upper limit of the total of NiO and the NiO-equivalent value of metallic Ni is preferably 1.8%, 1.5%, or 1.3%.

[0031] [B2O3: 0-2.0%] B2O3, which is made from raw materials such as borax and boron oxide, has a lower melting point and boiling point than other oxides, so it exists on the molten slag and bead surface and has the effect of improving slag removal. B2O3 may be 0%. However, from the viewpoint of obtaining the effect of slag removal, it is preferable to set it to 0.01% or more. On the other hand, if B2O3 exceeds 2.0%, the melting point of the molten slag will be low and the bead shape will be poor. Therefore, the B2O3 content is set to 0 to 2.0%. The lower limit of B2O3 is preferably 0.01%, 0.05%, or 0.1%. The upper limit of B2O3 is preferably 1.8%, 1.5%, or 1.0%.

[0032] [BaO: 0-0.10%] BaO, derived from barium oxide and other raw materials, is a component that adjusts the viscosity of the molten slag. BaO may be 0%. However, from the perspective of adjusting the viscosity of the molten slag, it is preferable to set the BaO content at 0.01% or more. On the other hand, if BaO exceeds 0.10%, the viscosity of the molten slag decreases, causing undercuts and poor bead shape. Therefore, the BaO content is set to 0 to 0.10%. The lower limit of BaO is preferably 0.01%. The upper limit of BaO is preferably 0.08%.

[0033] [Na2O: 0-0.10%] Na2O, derived from sodium carbonate and other raw materials, is a component that adjusts the viscosity of the molten slag. Na2O may be 0%. However, from the perspective of adjusting the viscosity of the molten slag, it is preferable to set it to 0.01% or more. On the other hand, if Na2O exceeds 0.10%, the viscosity of the molten slag will be insufficient, resulting in a poor bead shape. Therefore, the Na2O content is set to 0 to 0.10%. The lower limit of Na2O is preferably 0.01%. The upper limit of Na2O is preferably 0.08%.

[0034] [K2O: 0~0.10%] KO, derived from potassium carbonate and other raw materials, is a component that adjusts the viscosity of the molten slag. KO may be 0%. However, from the perspective of adjusting the viscosity of the molten slag, it is preferable to set the KO content at 0.01% or more. On the other hand, if the KO content exceeds 0.10%, the viscosity of the molten slag will be insufficient, resulting in a poor bead shape. Therefore, the content of K2O is set to 0 to 0.10%. The lower limit of K2O is preferably 0.01%. The upper limit of K2O is preferably 0.08%.

[0035] [Li2O: 0-0.10%] Li2O, derived from lithium fluoride or other raw materials, is a component that adjusts the viscosity of the molten slag. The Li2O content may be 0%. However, from the viewpoint of adjusting the viscosity of the molten slag, it is preferable to set the Li2O content to 0.01% or more. On the other hand, if the Li2O content exceeds 0.10%, the viscosity of the molten slag will be insufficient, resulting in a poor bead shape. Therefore, the Li2O content is set to 0 to 0.10%. The lower limit of Li2O is preferably 0.01%. The upper limit of Li2O is preferably 0.08%.

[0036] [ZrO2: 0-0.10%] ZrO2, derived from zircon sand and other raw materials, is a component that affects the melting point and viscosity of the molten slag. ZrO2 may be 0%. However, from the perspective of adjusting the melting point and viscosity of the molten slag, it is preferable to set the ZrO2 content to 0.01% or more. On the other hand, if the ZrO2 content exceeds 0.10%, the viscosity increases, making slag entrapment more likely to occur. Therefore, the ZrO2 content is set to 0 to 0.10%. The lower limit of ZrO2 is preferably 0.01%. The upper limit of ZrO2 is preferably 0.08%.

[0037] [Total of oxides other than those listed above: 0-5.0%] Oxides other than those mentioned above (hereinafter also referred to as "other oxides") affect the viscosity of the molten slag. The other oxides may be 0%. However, from the viewpoint of adjusting the melting point and viscosity of the molten slag, it is preferable to set the other oxides to 0.1% or more. On the other hand, if the other oxides exceed 5.0%, the viscosity of the molten slag decreases, undercutting occurs, and the bead shape becomes poor. Therefore, the content of other oxides is set to 0 to 5.0%. The lower limit of the other oxides is preferably 0.1%. The upper limit of other oxides is preferably 4.0%.

[0038] [Total of fluorides other than those listed above: 0-3.0%] Fluorides other than those mentioned above (hereinafter also referred to as "other fluorides") affect the viscosity of the molten slag. The other fluorides may be 0%. However, from the viewpoint of adjusting the melting point and viscosity of the molten slag, it is preferable to set the other fluorides to 0.1% or more. On the other hand, if the other fluorides exceed 3.0%, the viscosity of the molten slag decreases, undercut occurs, and the bead shape becomes poor. In addition, fluoride gas is generated during welding, making the welding unstable. Therefore, the other fluorides are set to 0 to 3.0%. The lower limit of other fluorides is preferably 0.1%. The upper limit of other fluorides is preferably 2.0%.

[0039] [Total carbonate: 0-0.50%] Carbonates made from raw materials such as CaCO3, BaCO3, and MgCO3 are added to stir the molten pool. The carbonate content may be 0%. However, in order to stir the molten pool, it is preferable to set the content at 0.01% or more. On the other hand, if the carbonate content exceeds 0.50%, gas generation can cause welding to become unstable, leading to poor bead shape. Therefore, the carbonate content should be 0 to 0.5%. The lower limit of carbonate is preferably 0.01%. The upper limit for carbonate is preferably 0.50%.

[0040] [Remainder: impurities] The remainder of the electroslag welding flux according to the present disclosure is impurities contained in trace amounts in the raw materials. Examples of impurities include C, P, and S. The total content of these impurities may be 2% or less.

[0041] [Basicity BL: 1.0-2.3] The basicity BL, expressed by the following formula 1, adjusts and increases the viscosity of the molten slag, thereby reducing the oxygen content in the weld metal and improving the toughness of the weld metal. Increasing the basicity BL also increases the electrical conductivity of the molten slag, further reducing penetration of the steel sheet during electroslag welding and preventing coarsening of the crystal grains in the metal structure, thereby improving the toughness of the weld metal and HAZ. A basicity BL of 1.0 or higher reduces the oxygen content in the weld metal and improves toughness. On the other hand, a basicity BL of 2.3 or less reduces the viscosity of the slag, improving slag removability. Therefore, the basicity BL represented by the following formula 1 is preferably set to 1.0 to 2.3. The lower limit of the basicity BL is more preferably 1.2 or 1.4. The upper limit of the basicity BL is more preferably 2.0 or 1.8.

[0042] BL=([CaO]+[MgO]+[BaO]+[Na2O]+[K2O]+[Li2O]+[CaF2]+0.5[MnO]+0.5[FeO]) / ([SiO2]+0.5[Al2O3]+0.5[TiO2]+0.5[ZrO2])...Equation 1 (In Equation 1, [CaO] is the CaO content (mass%) relative to the total mass of the flux, [MgO] is the MgO content (mass%) relative to the total mass of the flux, [BaO] is the BaO content (mass%) relative to the total mass of the flux, [Na2O] is the Na2O content (mass%) relative to the total mass of the flux, [K2O] is the K2O content (mass%) relative to the total mass of the flux, [Li2O] is the Li2O content (mass%) relative to the total mass of the flux, and [CaF2] is the CaF2 content (mass%) relative to the total mass of the flux. (MnO] represents the MnO content (mass%) relative to the total mass of the flux, [FeO] represents the total content (mass%) of FeO and the FeO-equivalent value of metallic Fe relative to the total mass of the flux, [SiO2] represents the SiO2 content (mass%) relative to the total mass of the flux, [Al2O3] represents the Al2O3 content (mass%) relative to the total mass of the flux, [TiO2] represents the TiO2 content (mass%) relative to the total mass of the flux, and [ZrO2] represents the ZrO2 content (mass%) relative to the total mass of the flux.)

[0043] [[CaO] / [CaF2]:2.0~9.0] Increasing the ratio ([CaO] / [CaF2]) of the CaO content (mass%) to the CaF2 content (mass%) can increase the thermal conductivity of the molten slag, further reducing penetration of the steel sheet during electroslag welding and preventing coarsening of the crystal grains in the metal structure, thereby further improving the toughness of the weld metal and HAZ. A [CaO] / [CaF2] ratio of 2.0 or higher achieves this effect, improving the toughness of the weld metal and HAZ. On the other hand, a [CaO] / [CaF2] ratio of 9.0 or less increases the viscosity of the molten slag, suppressing undercut. Therefore, it is preferable that [CaO] / [CaF2] is 2.0 to 9.0. The lower limit of [CaO] / [CaF2] is more preferably 2.5 or 3.0. The upper limit of [CaO] / [CaF2] is more preferably 8.5 or 8.0.

[0044] [Electroslag welding] The flux according to the present disclosure is used in electroslag welding. Electroslag welding is a method in which flux is filled into a groove surrounded by steel plates, a welding wire is inserted, and the flux is melted by Joule heating, causing the welding wire to melt continuously in the molten slag, filling the groove with molten metal and continuously welding steel plates together in a vertical position. Electroslag welding is widely used in the construction industry, for example, for diaphragm welding of large four-sided box columns, and is known as a highly efficient welding method for thick steel plates. In recent years, its application as a vertical welding method for block joints in the shipbuilding industry has also been considered as an alternative welding technique to electrogas arc welding.

[0045] [Electroslag welding equipment] 1 is a diagram showing a schematic configuration of an embodiment of an electroslag welding apparatus for performing electroslag welding using a flux according to the present disclosure, where hatched portions indicate cross sections.

[0046] The electroslag welding apparatus 1 includes a fixed water-cooled copper plate 2, which is an example of a fixed plate, and a sliding water-cooled copper plate 3, which is an example of a sliding plate. The fixed water-cooled copper plate 2 corresponds to a backing metal. Note that a ceramic backing material or the like can be used as the fixed plate instead of the fixed water-cooled copper plate. The sliding water-cooled copper plate 3 faces the fixed water-cooled copper plate 2 and is disposed at a distance from the fixed water-cooled copper plate 2. The sliding water-cooled copper plate 3 is configured to be movable in the vertical direction (Z direction). Both the fixed water-cooled copper plate 2 and the sliding water-cooled copper plate 3 have a structure that allows cooling water to flow through them, and during welding, they are cooled to a temperature that does not melt the molten slag (for example, 1200 to 1450°C). Note that the weld metal can be more easily cooled by expanding the water-cooled area by increasing the number of locations where water-cooled copper plates are used. 1, a copper plate is used as the fixed plate, but this is not limited to copper plates and, for example, ceramic plates with high heat resistance can also be used. Similarly, the sliding plate is not limited to copper plates and can be made of other metals. However, if metal plates with a melting point lower than the molten slag temperature are used as the fixed plate or sliding plate, a cooling means such as a water-cooled structure must be applied to prevent the metal plate from dissolving in the molten slag.

[0047] The electroslag welding apparatus 1 includes a carriage 5, a rail 6 extending in the vertical direction along which the carriage 5 travels, and a control unit 100, as an example of a movement mechanism for moving the sliding water-cooled copper plate 3 up and down. The sliding water-cooled copper plate 3 is fixed to the carriage 5, and when the carriage 5 rises, for example, the sliding water-cooled copper plate 3 slides vertically upward by the same amount as the movement of the carriage 5. The sliding water-cooled copper plate 3 is also configured to be movable in the Y direction by adjusting a screw-type slider (not shown).

[0048] A welding torch 7 is attached to the carriage 5 above the attachment point of the sliding water-cooled copper plate 3. Because the sliding water-cooled copper plate 3 and the welding torch 7 are fixed to the same carriage 5, they can move vertically while always maintaining the same relative positional relationship with each other.

[0049] A contact tip 8 is attached to the tip of welding torch 7. Welding wire 9 fed from a wire feeder (not shown) passes through the inside of welding torch 7 and is fed out from the tip of contact tip 8. Welding torch 7 is connected to a welding power source (not shown), and welding current is supplied to welding wire 9 via contact tip 8.

[0050] The welding torch 7 can be moved by itself in the X direction and vertical direction (Z direction) using a screw-type slider (not shown), allowing adjustment of its position relative to the carriage 5. Also, for example, by moving the welding torch 7 in the Z direction, the length (dry extension) of the welding wire 9 from the lower end of the contact tip 8 to the slag bath surface can be changed. Note that although a single-electrode welding device using one welding torch 7 is exemplified in this embodiment, the welding device may also be a multi-electrode device using two or more welding torches.

[0051] During welding, the groove 4 contains a slag bath 10 formed by melting flux supplied from a flux supply nozzle 33, a molten metal 11 pooling at the bottom of the slag bath 10, and a bead 12 formed by the molten metal 11 cooling and solidifying. During welding, the tip of a welding wire 9 is immersed in the slag bath 10, and electricity flows through the slag bath 10 via the welding wire 9. A welding current flows through the slag bath 10, generating resistance heat in the slag bath 10. This resistance heat melts the welding wire 9 and the base material (not shown) to be welded. This forms the molten metal 11, which accumulates on the bead 12. The molten metal 11 then gradually cools from the bottom, solidifying the cooled portion and welding the base materials together. The electroslag welding system 1 also includes a slag bath detector 20 for detecting the surface of the slag bath 10. The slag bath detector 20 is a detector that detects the bath surface of the slag bath 10. When the detector is not in contact with the slag bath 10, the absence of a bath surface detection signal input to the control unit 100 triggers the spraying of flux from the flux supply nozzle 33. This raises the bath surface of the slag bath 10, allowing the slag bath 10 to be maintained at an appropriate position.

[0052] The flux according to the present disclosure can be used as the flux to be filled in a groove surrounded by steel plates in electroslag welding. Also, a flux-cored wire for electroslag welding having a steel sheath and flux filled inside the steel sheath can be used as the welding wire to be inserted into the flux filled in the groove, and the flux according to the present disclosure can be used as the flux filled inside the steel sheath of this wire. [Example]

[0053] The effects of the flux for electroslag welding according to the present disclosure will be specifically described below using examples.

[0054] Example 1 Fluxes having the component compositions shown in Tables 1-1 to 1-6 were prepared as prototypes. In Tables 1-1 to 1-6, "other oxides" refers to "oxides other than those mentioned above" in the present disclosure, "other fluorides" refers to "fluorides other than those mentioned above" in the present disclosure, and "balance" refers to impurities. In addition, a welded test plate was assembled from two steel plates 20A and 20B as shown in Figures 2(A) and 2(B), using steel plates with the chemical compositions shown in Table 2 and the sizes shown in Table 3, with a gap of 10 mm. Figure 2(A) is a side view of the welded test plate, and (B) is a plan view of the welded test plate. Welding was performed using a solid wire with the chemical composition shown in Table 4 under the welding conditions shown in Table 5. The weld length was 1000 mm.

[0055] (Steel plate penetration (before welding)) After welding, macro test pieces were taken, and the penetration of the groove at the center of the plate thickness was evaluated using the surface of the base metal groove before welding. A penetration of 7 mm or less was considered pass, and a penetration of more than 7 mm was considered fail.

[0056] (Toughness (impact test -20℃)) Three impact test pieces (JIS Z 2242:2020, V-notch test pieces) were taken from each of the weld metal and HAZ parts at the center of the plate thickness after welding, and a Charpy impact test was performed at -20°C. A specimen with an average value of 60J or more was deemed to have passed, and a specimen with an average value of less than 60J was deemed to have failed.

[0057] (Bead shape) On the weld bead surface after welding, if an undercut of 1 mm or more occurred at the bead toe, it was rated as poor, and if no undercut of 1 mm or more occurred, it was rated as good.

[0058] (Arc state) When the arc was unstable during welding and spatter was continuously generated, the welding result was rated as poor, and when the arc was stable and continuous spatter generation was suppressed, the welding result was rated as good.

[0059] (comprehensive evaluation) When the evaluations of the steel sheet penetration amount, toughness, bead shape, and arc state were all "pass" or "good," the test was judged as "A (○)," and when any one of them was "fail" or "poor," the test was judged as "B (×)." These results are summarized in Tables 6-1 to 6-3.

[0060] [Table 1-1]

[0061] [Table 1-2]

[0062] [Table 1-3]

[0063] [Table 1-4]

[0064]

Table 1-5

[0065]

Table 1-6

[0066]

Table 2

[0067]

Table 3

[0068]

Table 4

[0069]

Table 5

[0070]

Table 6-1

[0071]

Table 6-2

[0072]

Table 6-3

[0073] As shown in Tables 6-1 to 6-3, in Comparative Example 2, in which the SiO content exceeded 30%, Comparative Example 3, in which the CaO content was less than 15%, Comparative Example 5, in which the MnO content was less than 10%, Comparative Example 7, in which the MgO content was less than 5%, Comparative Example 11, in which the CaF content was less than 3%, Comparative Example 13, in which the TiO content was less than 0.5%, and Comparative Example 15, in which the FeO content was less than 0.1%, the steel sheet penetration was large and the toughness of at least one of the weld metal and the HAZ was poor. Furthermore, in all Comparative Examples except Comparative Example 2, the bead shape was poor. Furthermore, in Comparative Example 25, in which the total of other fluorides exceeded 3.0%, and Comparative Example 26, in which the total of carbonates exceeded 0.50%, the arc condition was poor. On the other hand, in Examples 1 to 40, the steel sheet penetration was suppressed and both the weld metal and HAZ had excellent toughness. Furthermore, in Examples 1 to 40, both the bead shape and the arc state were good. [Explanation of symbols]

[0074] 1. Electroslag welding equipment 2 Fixed water-cooled copper plate 3 Sliding water-cooled copper plate 4 Bevel 5 carts 6 Rail 7. Welding torch 8 Contact Tips 9 Welding Wire 10 Slag bath 11 Molten Metal 12 beads 20 Slag bath detector 20A, 20B, 20C, 20D steel plate 33 Flux supply nozzle 40 Weld Metal 100 control section 112, 114 Undercut 400 Welded Joints

Claims

1. Mass % of the total mass of the flux Yes ２ :20~30%, CaO: 15-40%, MnO: 10-30%, MgO: 5-15%, <h2 style=";text-align:left;direction:ltr">Al<h2 style=";text-align:left;direction:ltr"> ２ <h2 style=";text-align:left;direction:ltr"> O<h2 style=";text-align:left;direction:ltr"> ３ <h2 style=";text-align:left;direction:ltr"> :5~20%、 CaF ２ :3~10%、 TO ２ :0.5~4.0%、 Sum of FeO and metallic Fe converted into FeO: 0.1 to 3.0% Sum of NiO and metal Ni converted into NiO: 0 to 2.0% B ２ O ３ :0~2.0%、 BaO: 0 to 0.10%, Na ２ O:0~0.1%%、 K ２ O:0~0.10%、 Li ２ O:0~0.10%、 ZrO ２ :0~0.10%、 Total of oxides other than those mentioned above: 0 to 5.0% Total of fluorides other than those mentioned above: 0 to 3.0% Total carbonates: 0-0.50%, and Remainder: impurities A flux for electroslag welding comprising:

2. The flux for electroslag welding according to claim 1, wherein the basicity BL represented by the following formula 1 is 1.0 to 2.

3. BL = ([CaO] + [MgO] + [BaO] + [Na ２ O] + [K ２ O] + [Li ２ O] + [CaF ２ + 0.5[MnO] + 0.5[FeO]) / ([SiO ２ + 0.5[Al ２ O ３ + 0.5[TiO ２ + 0.5[ZrO ２ )···Formula 1 (In formula 1, [CaO] is the CaO content (% by mass) relative to the total mass of the flux, [MgO] is the MgO content (% by mass) relative to the total mass of the flux, [BaO] is the BaO content (% by mass) relative to the total mass of the flux, and [Na ２ O] is the ratio of Na to the total mass of the flux ２ The content of O (mass%) is ２ O] is the K relative to the total mass of the flux ２ The content of O (mass%) is calculated by [Li ２ O] is the ratio of Li to the total mass of the flux ２ The O content (mass%) was calculated by [CaF ２ ] is the CaF relative to the total mass of the flux ２ [MnO] is the content (mass%) of MnO relative to the total mass of the flux, [FeO] is the total content (mass%) of FeO and metallic Fe converted into FeO relative to the total mass of the flux, and [SiO ２ ] is the SiO ２ The content (mass%) of [Al ２ O ３ ] is the Al content relative to the total mass of the flux ２ O ３ The content (mass%) of [TiO ２ ] is the ratio of TiO to the total mass of the flux ２ The content (mass%) of [ZrO ２ ] is the ratio of ZrO to the total mass of the flux ２ The content (mass%) of

3. The CaO content (mass%) and the CaF ２ The ratio of the content (mass%) of [CaO] / [CaF ２ 2. The electroslag welding flux according to claim 1, wherein the saturation coefficient (μm) of the flux is 2.0 to 9.

0.

4. A flux-cored wire for electroslag welding, comprising: a steel sheath; and the flux according to any one of claims 1 to 3, filled inside the steel sheath.

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