Method for manufacturing a welded joint and flux-containing cut wire for groove filling

Abstract

To provide a method for manufacturing a weld joint which can prevent low-temperature cracking while reducing a burden of a preheating work, and can obtain a weld joint so as to be advantageous in terms of work environment and cost, and a flux-cored cut wire used in the same.SOLUTION: There are provided a method for manufacturing a weld joint that includes a flux-cored cut wire welding step of filling at least a part in a groove with a flux-cored cut wire having a flux containing a predetermined fluoride, and welding the groove; and a flux-cored cut wire used in the same, which has a steel sheath and a flux that is made to fill the inside of the steel sheath and contains a fluoride.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a welded joint by filling a cut wire into a groove provided between base materials and welding, and a flux-containing cut wire for groove filling used therefor.

Background Art

[0002] In recent years, in the field of manufacturing large steel structures such as shipbuilding, steel structures, and bridges, in order to achieve both weight reduction and high performance, the strength of steel plates has been increasing. Further, from the viewpoint of improving construction efficiency, in submerged arc welding (SAW) mainly adopted for fillet welding, welding materials capable of coping with high heat input welding such as single-sided welding and double-sided single-layer welding are required.

[0003] Generally, it is required that the strength of the weld metal be equal to or higher than that of the base material. Therefore, with the increase in the strength of steel plates, it is necessary to increase the strength of the weld metal as well. However, when welding high-strength steel plates with a tensile strength of 780 MPa or more, cold cracking in the welded part becomes a problem. In particular, in the first layer of multi-layer build-up welding of extremely thick high-strength steel with a large plate thickness, the occurrence probability becomes high. Therefore, in order to prevent this cold cracking, preheating work of the welded part is required, but in the case of extremely thick steel plates, the preheating work itself becomes a great load.

[0004] Regarding this cold cracking, since diffusible hydrogen in the weld metal has an influence, by adding fluoride to the flux and welding wire used for submerged arc welding, hydrogen ions (H + ) are combined with fluoride ions (F - ) and discharged outside the arc to reduce the hydrogen concentration taken into the molten pool.

[0005] For example, Patent Document 1 describes a welding wire used for submerged arc welding. In the flux component filled in the wire, a flux-containing wire is described that contains a powdery fluorine compound with a melting point of 1000°C or lower and 0.1% by mass or more and less than 10% by mass. Further, Patent Document 2 describes that, in addition to SiO2, etc., a flux containing 9 to 21% of CaF2, one or two of MgF2 and MnF2 in an amount of 2 to 10%, and 0.02 to 1.0% of Li fluoride in terms of Li is used to perform submerged arc welding on 780 MPa high-tensile steel together with a predetermined wire.

[0006] However, in the above Patent Document 1, it is intended for pipe welding of steel pipes such as high-strength pipelines for crude oil transportation, and the plate thickness of the steel plate used in its examples is also 25 mm. That is, when attempting to perform multi-layer welding with a flux-containing wire like that in Patent Document 1 on an extremely thick high-strength steel plate with a plate thickness of 50 mm or more, problems with the working environment due to the generation of fumes and spatter become prominent. Moreover, using such a flux-containing wire for all passes will result in high costs.

[0007] In addition, Patent Document 2 shows an example of multi-layer welding of a 780 MPa steel with a plate thickness of 80 mm in two passes and one layer in its examples. However, as is clear from the description in its specification, preheating work at a preheating temperature of 100°C is required (see paragraph 0044). Furthermore, when performing submerged arc welding using the flux-containing wire of Patent Document 1 or the flux of Patent Document 2, fluorides are separated by the arc, causing the arc to become unstable and the bead shape to become defective.

[0008] On the other hand, when manufacturing joints with a large heat input in submerged arc welding, in order to control high welding efficiency and penetration depth, a cut wire obtained by finely cutting a thin-diameter steel wire into a predetermined length is filled into the groove. And Patent Document 3 describes a cut wire in which the cut wire strand is covered with a Cu coating layer and oil is applied to its surface.

[0009] In Patent Document 3, the reason for providing the Cu coating layer is to consider the arcing start property due to its high electrical conductivity. Also, applying oil with an appropriate oil content on the wire surface improves the rust resistance without impairing the arcing start property and is for preventing the reduction of low-temperature cracking property (see paragraphs 0013 and 0021). That is, in the oil quantity control of the cutting wire in Patent Document 3, although an increase in diffusible hydrogen can be suppressed, reduction cannot be achieved. Therefore, when the strength of steel plates and welded metals increases, it is difficult to surely prevent the problem of low-temperature cracking. Note that, as the cutting wire filled in the groove as described above, mainly the one obtained by cutting a solid wire has been used so far.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0011] Thus, as the strength of steel plates and welded metals increases, the inventors have earnestly studied a method that can prevent low-temperature cracking while reducing the burden of preheating work even in the case of extremely thick high-strength steel plates, and moreover, can suppress the problems of the working environment due to fumes and spatter as much as possible. As a result, it has been found that the above problems can be solved by filling a groove with a cutting wire containing a predetermined fluoride flux and performing welding, and the present invention has been completed.

[0012] Accordingly, an object of the present invention is to provide a method for manufacturing a welded joint that can prevent low-temperature cracking while reducing the burden of preheating work, and can advantageously obtain a welded joint in terms of working environment and cost.

[0013] Another object of the present invention is to provide a flux-cored wire used in such a method for manufacturing a welded joint.

Means for Solving the Problems

[0014] That is, the gist of the present invention is as follows. (1) A method for manufacturing a welded joint in which a cut wire is filled into a groove provided between base materials and welded, characterized by comprising a flux-cored wire welding step of filling at least a part of the groove with a flux-cored wire having a steel outer skin and a flux containing a fluoride filled inside the steel outer skin, and welding. (2) The method for manufacturing a welded joint according to claim (1), wherein the fluoride is one or more selected from the group consisting of CaF2, MgF2, LiF, NaF, K2ZrF6, K2SiF6, and Na3AlF6. (3) The flux-cored wire contains, in terms of mass ratio to the total mass of the flux-cored wire, the fluoride in terms of F conversion value of 0.01% by mass or more, and the contents of chemical components consisting of C, Si, Mn, Cu, Ni, Cr, Mo, Nb, V, Ti, Al, B, and Bi are C: 0.120% or less, Si: 2.00% or less, Mn: 3.50% or less, Cu: 5.00% or less, Ni: 5.00 or less, Cr: 5.00% or less, Mo: 5.00% or less, Nb: 0.50% or less, V: 0.50% or less, Ti: 0.50% or less, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less, and the contents of impurity elements consisting of P and S are P: 0.030% or less and S: 0.020% or less. The method for manufacturing a welded joint according to (1) or (2). (4) The method for manufacturing a welded joint according to any one of (1) to (3), wherein the flux-containing cut wire welding step consists of flux-containing cut wire filling and one-pass welding by filling the flux-containing cut wire into the groove. (5) The method for manufacturing a welded joint according to any one of (1) to (3), wherein the flux-containing cut wire welding step consists of single-layer welding by filling the flux-containing cut wire into the first layer in the groove and welding, or multi-layer welding by filling the flux-containing cut wire into the first layer and the subsequent layers in the groove and welding, and is performed at least until the temperature of the base material reaches a temperature equivalent to preheating. (6) The method for manufacturing a welded joint according to any one of (1) to (5), wherein the welding means is submerged arc welding or gas shielded arc welding. (7) The method for manufacturing a welded joint according to any one of (1) to (6), wherein the base material is made of a high-strength steel material having a tensile strength of 780 MPa or more. (8) The method for manufacturing a welded joint according to any one of (1) to (7), wherein the base material is made of an extra-thick steel material having a thickness of 50 mm or more. (9) A cut wire for groove filling used for filling a groove provided between base materials when manufacturing a welded joint, characterized by having a steel outer skin and a flux containing fluoride filled inside the steel outer skin. (10) The cut wire with flux for groove filling according to (9), wherein the fluoride is one or more selected from the group consisting of CaF2, MgF2, LiF, NaF, K2ZrF6, K2SiF6, and Na3AlF6. (11) By mass ratio with respect to the total mass of the cut wire with flux The fluoride is contained in an amount of 0.01% by mass or more in terms of F conversion value, and the contents of chemical components consisting of C, Si, Mn, Cu, Ni, Cr, Mo, Nb, V, Ti, Al, B, and Bi are as follows: C: 0.120% or less, Si: 2.00% or less, Mn: 3.50% or less, Cu: 5.00% or less, Ni: 5.00 or less, Cr: 5.00% or less, Mo: 5.00% or less, Nb: 0.50% or less, V: 0.50% or less, Ti: 0.50% or less, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less. Also, The content of impurity elements consisting of P and S is P: 0.030% or less and S: 0.020% or less. The flux-containing cut wire for groove filling according to (9) or (10). (12) The base material is made of a high-strength steel material with a tensile strength of 780 MPa or more. The flux-containing cut wire for groove filling according to any one of (9) to (11). (13) The base material is made of an extremely thick steel material with a thickness of 50 mm or more. The flux-containing cut wire for groove filling according to any one of (9) to (12).

Advantages of the Invention

[0015] According to the present invention, for example, even when welding an extremely thick high-strength steel plate, the burden of preheating work can be reduced, preventing cold cracking. Moreover, problems in the working environment caused by fumes and spatter can be minimized as much as possible, and welded joints can be manufactured advantageously in terms of cost performance.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention uses a flux-containing cut wire having a steel outer skin and a flux filled inside the steel outer skin, and fills at least a part of the groove provided between the base materials with this flux-containing cut wire and welds it to provide a flux-containing cut wire welding step, thereby manufacturing a welded joint. Hereinafter, the flux-containing cut wire according to the present invention will be described, and a method for manufacturing a welded joint using the same will be described.

[0018] 〔Flux-containing cut wire〕 First, regarding the flux-containing cut wire, as the flux, one containing fluoride is used. Fluoride has the function of reducing the amount of diffusible hydrogen in the weld metal and significantly improving the low-temperature cracking resistance of the weld metal. This is presumably because when the flux-containing cut wire is welded, the flux melts, and fluorine (F - ) in the flux combines with hydrogen (H + ) to form hydrogen fluoride (HF), and this HF is released outside the weld metal.

[0019] Regarding these fluorides, preferably, it is one or more selected from the group consisting of CaF2, MgF2, LiF, NaF, K2ZrF6, K2SiF6, and Na3AlF6. According to these compounds, Ca, Mg, Li, Na, K, Zr, Si, and Al generated by ionization can all combine with oxygen to reduce the amount of oxygen in the weld metal and act as deoxidizing elements. This is advantageous in improving the toughness and elongation of the weld metal.

[0020] As described above, from the viewpoint that fluoride can sufficiently reduce the amount of diffusible hydrogen in the weld metal, regarding the content of this fluoride, if the content of fluoride is defined by the F conversion value expressed as the mass % of the amount of fluorine (F) contained in the fluoride with respect to the total mass of the flux-cored wire, it is preferably contained in a mass ratio of 0.01% or more with respect to the total mass of the flux-cored wire, more preferably 0.03% or more, still more preferably 0.05% or more, and even more preferably 0.10% or more. This content represents the total amount of fluoride contained in the flux. That is, as long as the total mass ratio of the fluoride contained in the flux is 0.01% or more in terms of the F conversion value, the lower limit value of the content of each fluoride is not particularly limited. Further, since this F conversion value indicates the mass % of the amount of fluorine (F) contained in the fluoride with respect to the total mass of the flux-cored wire, when the type of fluoride is the fluoride of the above-mentioned preferred example, the F conversion value can be obtained from the following formula A. 0.487×CaF2 + 0.610×MgF2 + 0.732×LiF + 0.452×NaF + 0.402×K2ZrF6 + 0.517×K2SiF6 + 0.543×Na3AlF6 … … Formula A Here, the chemical formula of the fluoride in Formula A indicates the mass % of the fluoride corresponding to each chemical formula with respect to the total mass of the flux-cored wire. The coefficient of each chemical formula of the fluoride is calculated from the chemical formula weight of each fluoride. Assuming that the type of fluoride is these cases, the content at that time is preferably contained in a mass ratio of 0.10% or more with respect to the total mass of the flux-cored wire, more preferably 0.5% or more, still more preferably 1.0% or more, and even more preferably 2.0% or more.

[0021] Here, in the flux-containing cut wire of the present invention, since the flux is filled inside (the inner side) of the steel outer skin, even if a large amount of fluoride is contained, the amount of spatter during welding does not increase. Therefore, from the viewpoint of reducing the amount of diffusible hydrogen, the upper limit of the mass ratio of fluoride is not particularly limited. However, considering the presence of the steel outer skin and the filling of the flux thereby, it can be said that the upper limit of the mass ratio of fluoride is 71.80% in terms of F conversion value. Also, this upper limit may be 60% in terms of F conversion value, may be 55% in terms of F conversion value, or may be 50% in terms of F conversion value.

[0022] Further, the flux-containing cut wire of the present invention may contain, in addition to fluoride, for example, alloy components for controlling the chemical composition of the weld metal, carbon equivalent (Ceq), etc. (these chemical compositions and alloy components are simply referred to as "chemical compositions"). At that time, for example, metal powder and alloy powder melt in the same manner as the steel outer skin during welding. Therefore, chemical compositions other than fluoride may be included in the flux in the form of, for example, metal powder or alloy powder, may be included in the form of the steel outer skin, or may be included as plating on the outer surface of the steel outer skin, and all have the same effect. Note that these chemical compositions other than fluoride do not require arc stability and all-position weldability as in the case of a flux-containing wire that is not a cut wire, so they do not need to be in the state of oxides or carbonates, and can be contained in the form of metal powder or alloy powder as described above.

[0023] Specifically, the flux-containing cutting wire of the present invention contains fluoride in a mass ratio to the total mass of the flux-containing cutting wire of 0.01% or more in terms of F conversion value, and contains, as optional components, any one or more chemical components selected from the group consisting of C, Si, Mn, Cu, Ni, Cr, Mo, Nb, V, Ti, Al, B, and Bi. The contents of these chemical components are C: 0.120% or less, Si: 2.00% or less, Mn: 3.50% or less, Cu: 5.00% or less, Ni: 5.00 or less, Cr: 5.00% or less, Mo: 5.00% or less, Nb: 0.50% or less, V: 0.50% or less, Ti: 0.50% or less, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less. Also, it is preferable that the contents of impurity elements consisting of P and S are P: 0.030% or less and S: 0.020% or less, respectively. In the present invention, by containing the above-mentioned fluoride, it is possible to reduce the diffusible hydrogen content without containing any of these optional chemical components. Therefore, the lower limit value of the content of each of these optional chemical components is 0%.

[0024] Among these, in the chemical components as optional components, C in "C: 0.120% or less" is an important element for ensuring the yield strength and tensile strength of the weld metal by solid solution strengthening. However, when the C content in the flux-containing cutting wire exceeds 0.120%, the C content in the weld metal becomes excessive, the yield strength and tensile strength of the weld metal increase excessively, and the toughness of the weld metal decreases. In order to stably ensure all of the toughness, yield strength, and tensile strength of the weld metal, it is preferable to set the upper limit value of this C content to 0.10%. On the other hand, although the lower limit of the C content is 0%, if necessary, the lower limit of the C content may be set to 0.010%, 0.020%, 0.030%, 0.040%, or 0.050%. Similarly, the upper limit of the C content may be set to 0.100%, 0.090%, 0.080%, or 0.070%.

[0025] Si in "2.00% or less" is a deoxidizing element and has the function of reducing the oxygen content in the weld metal and enhancing the cleanliness of the weld metal. When the Si content in the flux cored wire exceeds 2.00%, Si deteriorates the toughness of the weld metal. To stably ensure the toughness of the weld metal, the upper limit of this Si content may be 1.90%, 1.80%, 1.70%, or 1.50%. On the other hand, the lower limit of the Si content is 0%, but if necessary, the lower limit of the Si content may be 0.01%, 0.02%, 0.03%, or 0.04%.

[0026] Mn in "3.50% or less" is an element necessary to ensure the hardenability of the weld metal and increase the strength of the weld metal, but it may also be 0%. To increase the strength of the weld metal, the lower limit value of the Mn content in the flux cored wire may be 0.50%, 0.75%, or 1.0%. On the other hand, when this Mn content exceeds 3.50%, the intergranular embrittlement susceptibility of the weld metal increases and the toughness of the weld metal deteriorates. Therefore, the upper limit value of the Mn content is 3.50%, but the upper limit value of the Mn content may be 3.00%, 2.50%, or 2.00%.

[0027] Cu in "5.00% or less" has the effect of improving the strength and toughness of the weld metal, but it may also be 0%. Cu may be included in the plating on the surface of the steel sheath in the flux cored wire, or may be included in the flux alone or as an alloy. This Cu content is the total amount of Cu contained in the steel sheath and flux and the Cu contained in the surface plating. When this Cu content exceeds 5.00%, the toughness of the weld metal decreases. The upper limit value of the Cu content is preferably 4.00%, 3.00%, or 2.00%. On the other hand, the lower limit value of the Cu content is preferably 0.05%, 0.1%, or 0.15%.

[0028] Since Ni in "Ni: 5.00% or less" is not an essential component, the lower limit of the Ni content in the flux-cored wire is 0%. Also, when this Ni content exceeds 5.00%, solidification cracking is likely to occur. The upper limit of the Ni content is preferably 4.00%, 3.00%, or 2.00%. On the other hand, the lower limit of the Ni content is preferably 0.05%, 0.1%, or 0.15%.

[0029] Since Cr in "Cr: 5.00% or less" is not an essential component, the lower limit of the Cr content in the flux-cored wire is 0%. On the other hand, Cr is an element effective for improving the strength of the weld metal because it enhances the hardenability of the weld metal. To sufficiently obtain its effect, it is preferable to set the Cr content to 0.10% or more. Also, when the Cr content exceeds 5.00%, the weld metal becomes excessively hardened and the toughness of the weld metal deteriorates. The upper limit of the Cr content is preferably 4.00%, 3.00%, 2.00%, or 1.00%.

[0030] Since Mo in "Mo: 5.00% or less" is not an essential component, the lower limit of the Mo content in the flux-cored wire is 0%. On the other hand, Mo is an element effective for increasing the strength of the weld metal because it has the effect of improving the hardenability of the weld metal. To obtain its effect, it is preferable to set the Mo content to 0.01% or more. However, when this Mo content exceeds 5.00%, the toughness of the weld metal may deteriorate, so the Mo content is set to 5.00% or less. The upper limit of the Mo content is preferably 4.00%, 3.00%, 2.00%, 1.00%, or 0.60%.

[0031] Since Nb in "Nb: 0.50% or less" is not an essential component, the lower limit of the Nb content in the flux-cored cut wire is 0%. On the other hand, Nb forms fine carbides in the weld metal, and these fine carbides cause precipitation strengthening in the weld metal, so Nb improves the tensile strength of the weld metal. In order to fully obtain this effect, it is preferable that the Nb content be 0.005% or more. However, if this Nb content exceeds 0.50%, Nb forms coarse precipitates in the weld metal and deteriorates the toughness of the weld metal, which is not preferable. The upper limit of the Nb content is preferably 0.40%, 0.30%, 0.20%, or 0.10%.

[0032] Since V in "V: 0.500% or less" is not an essential component, the lower limit of the V content in the flux-cored cut wire is 0%. On the other hand, V improves the hardenability of the weld metal, so it is an element effective for increasing the strength of the weld metal. In order to fully obtain this effect, it is preferable that the V content be 0.010% or more. When this V content exceeds 0.500%, the precipitation amount of V carbides in the weld metal becomes excessive, the weld metal is excessively hardened, and the toughness of the weld metal deteriorates. The upper limit of the V content is preferably 0.400%, 0.300%, 0.200%, or 0.100%.

[0033] Since Ti in "Ti: 0.50% or less" is not an essential component, the lower limit of the Ti content in the flux-cored cutting wire is 0%. On the other hand, Ti is a deoxidizing element and has the effect of reducing the amount of oxygen in the weld metal. Also, Ti contained in the flux-cored cutting wire slightly remains in the weld metal and fixes the dissolved N, so it has the effect of mitigating the adverse effect of dissolved N on the toughness of the weld metal. Therefore, the flux-cored cutting wire may contain 0.01% or more of Ti. However, if the Ti content exceeds 0.50%, there is a risk of toughness deterioration due to excessive precipitate formation in the weld metal. Here, when adding Ti to the flux-cored cutting wire, it is conceivable to contain ferro-titanium (an alloy of iron and titanium) in the flux. The upper limit of the Ti content is preferably 0.40%, 0.30%, 0.20%, or 0.10%.

[0034] Al in "Al: 1.70% or less" is a deoxidizing element, and like Si, it has the effect of reducing the amount of oxygen in the weld metal and improving the cleanliness of the weld metal. When the Al content in the flux-cored cutting wire exceeds 1.70%, Al forms nitrides and oxides, etc., and reduces the toughness of the weld metal. Therefore, the upper limit of the Al content in the flux-cored cutting wire is set at 1.70%. This upper limit is preferably 1.60%, 1.50%, 1.40%, or 1.30%. The lower limit of the Al content is preferably 0.005%, 0.010%, 0.050%, 0.100%, 0.150%, or 0.200%.

[0035] Since B in "B: 0.020% or less" is not an essential component, the lower limit of the B content in the flux-cored cutting wire is 0%. On the other hand, B combines with dissolved N in the weld metal to form BN, so it has the effect of reducing the adverse effect of dissolved N on the toughness of the weld metal. Also, B enhances the hardenability of the weld metal, so it also has the effect of improving the strength of the weld metal. Therefore, the flux-cored cutting wire may contain 0.0005% or more of B. However, when this B content exceeds 0.020%, the B in the weld metal becomes excessive, and coarse BN and Fe 23Forming a B compound such as (C, B)6 deteriorates the toughness of the weld metal, which is not preferable. The upper limit of the B content is preferably 0.015%, 0.010%, 0.005%, 0.003%, or 0.001%.

[0036] Since Bi in "Bi: 0.030% or less" is not an essential component, the lower limit of the Bi content in the flux-cored wire is 0%. On the other hand, Bi is an element that improves the slag detachability. In order to sufficiently obtain its effect, it is preferable that the Bi content is 0.005% or more, 0.010% or more, or 0.012% or more. On the other hand, when the Bi content exceeds 0.030%, solidification cracking is likely to occur in the weld metal, so the upper limit of the Bi content is 0.030%. This upper limit of the Bi content is preferably 0.025%, 0.020%, or 0.010%.

[0037] Also, P in "P: 0.030% or less" which exists as the impurity element reduces the toughness of the weld metal, so the P content in the flux-cored wire needs to be reduced as much as possible. Therefore, the lower limit of the P content is 0%. Also, if this P content is 0.030% or less, the adverse effect of P on the toughness is within an acceptable range. In order to prevent solidification cracking of the weld metal, more preferably, this P content is 0.020% or less, 0.015% or less, or 0.010% or less.

[0038] Also, S in "S: 0.020% or less" which exists as the impurity element deteriorates both the toughness and ductility of the weld metal if it exists excessively in the weld metal, so it is desirable to reduce the S content in the flux-cored wire as much as possible. Therefore, the lower limit of this S content is 0%. Also, if the S content is 0.020% or less, the adverse effect of S on the toughness and ductility of the weld metal is within an acceptable range. More preferably, it is 0.010% or less, 0.008% or less, 0.006% or less, or 0.005% or less.

[0039] The flux-containing cut wire in the present invention may or may not contain the chemical components as described above. However, in addition to these chemical components, the fluoride and impurity elements, it contains Fe and impurities. Among these, as Fe, in addition to the steel outer skin, iron powder may be included. That is, for adjusting the filling rate of the flux in the flux-containing cut wire or for improving the welding efficiency, iron powder may be contained in the flux as necessary. The content of this iron powder is not particularly limited. However, since it is conceivable that the oxygen adhering to the surface layer of the iron powder increases the oxygen amount of the weld metal and reduces the toughness, at most, it should be less than 90.0% by mass ratio with respect to the total mass of the flux-containing cut wire, preferably less than 80.0%. The upper limit value of the content of iron powder may be limited to 8.0%, 6.0%, 4.0%, 2.0%, or 1.0%. Of course, since iron powder is not essential in the flux-containing cut wire according to the present invention, the lower limit value of the content of iron powder is 0%.

[0040] Also, regarding impurities, they are components that are derived from raw materials or mixed due to various factors in the manufacturing process when the flux-containing cut wire is industrially manufactured. These mean those that are allowed within the range that does not adversely affect the flux-containing cut wire according to the present invention.

[0041] Furthermore, the flux-containing cut wire in the present invention may also contain oxides, carbonates, etc. of other metal elements other than the fluorides, chemical components, and impurity elements described above, as long as their properties are not impaired. In this case, these oxides and carbonates shall not be included in the contents of the fluorides, chemical components, impurity elements, Fe, and impurities described above. However, this indicates that the case of containing these oxides and carbonates is not excluded. That is, the flux-containing cut wire in the present invention contains the aforementioned fluoride in a predetermined ratio in terms of the F conversion value, the contents of the aforementioned chemical components and impurity elements are respectively within a predetermined range, and the balance consists of Fe and impurities, or has a chemical composition consisting of Fe, impurities, and these oxides and carbonates. Preferably, it contains the aforementioned fluoride in a predetermined ratio in terms of the F conversion value, the contents of the aforementioned chemical components and impurity elements are respectively within a predetermined range, and the balance consists of Fe and impurities.

[0042] Furthermore, as long as the above-described matters are satisfied, the steel outer skin of the flux-containing cut wire according to the present invention is not particularly limited. For example, when the steel outer skin consists of a mild steel outer skin, the chemical composition of the outer skin is C: 0.1% or less, Si: 0.10% or less, Mn: 3.00% or less, P: 0.030% or less, S: 0.020% or less, Al: 0.1% or less, and N: 0.030% or less, and the balance is iron and impurities.

[0043] The flux-containing cut wire in the present invention can be obtained by finely cutting a wire-shaped state in which a flux is filled in a steel outer skin into a predetermined length. There is no particular limitation on the shape of the cut flux-containing cut wire, and it can be made comparable to a general cut wire with a circular cross-section by finely cutting a thin steel wire into a predetermined length. However, considering that the flux is filled, its diameter is preferably φ1.0 to φ3.0 mm. Incidentally, the diameter of the conventional cut wire is about φ1.0 to φ2.0 mm. On the other hand, the length of the flux-containing cut wire is preferably 0.5 to 3.5 mm. In the case of a general cut wire, its length corresponds to 0.5 to 2.0 times the wire diameter.

[0044] Also, the filling rate of the flux is not particularly limited as long as the above-mentioned conditions are satisfied. For example, the lower limit value of the filling rate of the flux may be 10% or 12% in terms of the mass ratio to the total mass of the flux-containing cut wire. Also, the upper limit value of the filling rate of the flux may be 80% or 90%.

[0045] Here, in order to reduce the diffusible hydrogen amount of the weld metal, preferably, the hydrogen amount contained in the flux-containing cut wire is 12 ppm or less with respect to the total mass of the flux-containing cut wire. This hydrogen amount may increase not only when it enters during the manufacture of the flux-containing cut wire but also when moisture enters during the storage of the flux-containing cut wire. Therefore, when the period from after the manufacture of the cut wire to its use is long, it is desirable to store it while preventing the intrusion of moisture.

[0046] In manufacturing the flux-containing cut wire in the present invention, the procedure and the like are not particularly limited, but as a method for manufacturing the flux-filled wire before cutting, the following examples can be shown. First, as a method for manufacturing a seamless flux-embedded cut wire in which the joints of the steel outer skin are welded and there are no slit-shaped gaps, in addition to the step of preparing the flux so that fluoride, chemical components, etc. are within a predetermined range, while feeding the steel strip in the longitudinal direction, a step of forming it using a forming roll to obtain a U-shaped open tube, a step of supplying the flux into the open tube through the opening of the open tube, a step of butt-welding the opposing edge portions of the opening of the open tube to obtain a seamless tube, a step of drawing the seamless tube to obtain a flux-embedded wire having a predetermined wire diameter, and a step of annealing the flux-embedded wire during or after the drawing process are provided. Thereafter, by cutting the wire to a predetermined length, a flux-embedded cut wire can be obtained.

[0047] Here, the butt-welding is performed by electric seam welding, laser welding, TIG welding, or the like. Also, annealing is performed during or after the drawing process to remove moisture in the wire. Preferably, in order to make the H content contained in the wire 12 ppm or less, the annealing temperature is 650°C or higher and the annealing time is 4 hours or longer. However, in order to prevent the flux from deteriorating, the annealing temperature is 900°C or lower. Note that instead of butt-welding, even if the gaps in the steel outer skin are brazed, a wire without slit-shaped gaps can be obtained.

[0048] Also, it is possible to obtain a flux-embedded cut wire having slit-shaped gaps without welding the joints of the steel outer skin. In that case, it is the same as the method for manufacturing a wire having a seamless shape except that, instead of the step of butt-welding the ends of the open tube to obtain a seamless tube, there is a step of forming the open tube and butting the ends of the open tube to obtain a tube having slit-shaped gaps. The method for manufacturing a wire having slit-shaped gaps may further include a step of caulking the butted ends of the open tube. In the method for manufacturing a wire having slit-shaped gaps, the tube is drawn in a state having slit-shaped gaps.

[0049] As described above, the flux-embedded cut wire according to the present invention may be obtained by cutting a seamless wire in which the seam of the steel outer skin is welded and there is no slit-like gap, or may be obtained by cutting a wire having a slit-like gap without welding the seam of the steel outer skin. Preferably, it is a flux-embedded cut wire obtained by cutting a wire without a slit-like gap in the steel outer skin. H (hydrogen) that penetrates into the welded part during welding diffuses into the weld metal and the base metal to be welded, accumulates at the stress concentration part, and causes low-temperature cracking. Although there are various sources of H, if the cleanliness of the welded part and the welding conditions are strictly controlled, the moisture (H2O) contained in the flux-embedded cut wire can be a source of H, and the amount of this moisture may affect the diffusible hydrogen amount of the welded joint. Therefore, it is desirable to cut a seamless wire without a slit-like gap. However, when cutting a wire having a slit-like gap, for example, it may be vacuum-packed and stored, or the flux-embedded cut wire may be stored in a container that can maintain a dry state.

[0050] Further, the flux-embedded cut wire in the present invention may have oil (lubricant) applied to its surface. The lubricant applied to the surface of the filler has the effect of suppressing rust generation during storage. As such a lubricant, various types (for example, vegetable oils such as palm oil) can be used. However, in order to suppress low-temperature cracking of the weld metal, it is preferable to use perfluoropolyether oil (PFPE oil) that does not contain H (hydrogen). When the flux-embedded cut wire has plating on its surface, the lubricant is applied to the surface of the plating.

[0051] 〔Method for manufacturing welded joint〕 Next, when manufacturing a welded joint using the flux-cored cutting wire described above, in the present invention, a flux-cored cutting wire welding step is provided in which the flux-cored cutting wire is filled and welded to at least a part of the groove provided between the base materials. That is, when manufacturing a welded joint, in any one or more of the first pass to the final pass, the flux-cored cutting wire according to the present invention is filled into the groove of the base material and welded. When the welding is only one pass, the flux-cored cutting wire of the present invention is used in that one pass.

[0052] Among them, for this flux-cored cutting wire welding step, it is preferable to fill the flux-cored cutting wire according to the present invention into at least the first layer in the groove and perform welding. That is, by filling the flux-cored cutting wire into the first layer in the groove where the probability of cold cracking is high, for example, the load of the preheating operation can be surely reduced, such as reducing the preheating temperature to 50°C or lower, or the preheating operation itself can be made unnecessary.

[0053] FIG. 1 and FIG. 2 each show an example of the flux-cored cutting wire welding step in the present invention. Among these, FIG. 1 is an example in which the flux-cored cutting wire 4 is filled into a part of the groove 3 provided between the base material 1 and the base material 2 and welding is performed. First, as shown in FIG. 1(a), after attaching the backing material 5 to the back surfaces of the base materials 1 and 2, the flux-cored cutting wire 4 according to the present invention is filled into the first layer in the groove 3. Next, as shown in FIG. 1(b), the welding wire 6 is disposed on the substantially central portion of the filled flux-cored cutting wire 4, and an arc is generated to perform welding.

[0054] Here, if the temperatures of the base material 1 and the base material 2 reach the preheating temperature (equivalent preheating temperature) in the case of performing preheating work by welding in FIG. 1(b), for example, if they reach 100°C, the risk of cold cracking is eliminated. Therefore, in subsequent welding, a welded joint may be manufactured without using the flux-cored wire of the present invention. If the base material 1 and the base material 2 have not reached the equivalent preheating temperature, as shown in FIG. 1(c), the flux-cored wire 4 of the present invention is again sprayed onto the weld metal 7 obtained by including the flux-cored wire 4 filled in the first layer, filled into the groove 3, the welding wire 6 is arranged, and welding is performed. Thereafter, this is repeated until the temperatures of the base material 1 and the base material 2 reach the equivalent preheating temperature. The flux-cored wire 4 of the present invention is filled and welded. When the equivalent preheating temperature is reached, welding may be performed without using the flux-cored wire of the present invention as in the previous case.

[0055] The example of the flux-cored wire welding process shown in FIG. 1 consists of single-pass welding in which the flux-cored wire is filled and welded in the first layer in the groove, or multi-pass welding in which the flux-cored wire is filled and welded in the first layer and the subsequent layers in the groove. At least until the temperature of the base material reaches 100°C, the flux-cored wire is filled and welded. That is, by using the flux-cored wire according to the present invention for the first-layer welding in the groove, the amount of diffusible hydrogen in the weld metal can be reduced. Moreover, since this flux-cored wire welding process also serves as a preheating operation, the preheating operation can be made unnecessary or the burden of the preheating operation can be significantly reduced.

[0056] Also, as shown in FIG. 2, the flux-cored cut wire welding process according to the present invention may be composed of a flux-cored cut wire filling and one-pass welding in which the flux-cored cut wire is filled into the groove and welded in one pass. That is, as shown in FIG. 2(a), after attaching the backing material 5 to the back surfaces of the base materials 1 and 2, in the example of FIG. 2, the flux-cored cut wire 4 according to the present invention is sprayed so as to fill substantially all of the groove 3, for example, about 80% of the height inside the groove. Next, as shown in FIG. 2(b), the welding wire 6 is disposed on the substantially central portion of the filled flux-cored cut wire 4, and an arc is generated for welding, whereby, as shown in FIG. 2(c), a weld joint is manufactured by the weld metal 7 including the flux-cored cut wire 4.

[0057] In the example of the flux-cored cut wire welding process shown in FIG. 2, since the flux-cored cut wire according to the present invention is used for substantially all of the inside of the groove, it is possible to eliminate the need for preheating work or significantly reduce the burden of preheating work.

[0058] In FIGS. 1 and 2, an example of a so-called V-shaped groove between the base materials is shown, but in the present invention, there is no limitation on this groove shape, and in addition to the V shape, for example, groove shapes such as I shape, groove shape, K shape, J shape, X shape, U shape, H shape, etc., and grooves of any other shape may be used. Further, in the present invention, it may be a case of single-sided welding or applicable to a case of double-sided welding. Furthermore, in the case of multi-layer welding as in the example of FIG. 1, each layer may be divided into two or more passes for welding.

[0059] The welding method (welding means) used in the present invention is not particularly limited, but in order to surely melt the flux-cored cut wire filled in the groove, preferably, it is submerged arc welding or gas shielded arc welding. However, in the case of vertical welding or uphill welding, it may be difficult to fill the flux-cored cut wire into the groove, so the welding posture is preferably downward or horizontal.

[0060] In addition, in the method for manufacturing a welded joint according to the present invention, the type, shape, etc. of the base material are not particularly limited, but it is most effective to apply it in a situation where cold cracking is a problem and the preheating work is burdensome. That is, typically, it is welding of a base material made of high-strength steel having a tensile strength of 780 MPa or more and 1500 MPa or less. Further, in the case of an extremely thick steel material having a thickness of 50 mm or more and 250 mm or less, the burden of preheating work becomes particularly large. Therefore, it can be said that it is extremely effective to apply the present invention particularly when an extremely thick high-strength steel material is used as the base material. Note that the combination of base materials for forming the groove is arbitrary, and they may be base materials of the same type or different base materials from each other.

[0061] Also, generally, in the method for manufacturing a welded joint, a welded joint including a base material steel plate (base material) and a welded portion composed of a weld metal and a heat-affected zone of welding is obtained. In the present invention, since a flux-cored wire containing a predetermined fluoride is used as the groove filler, preferably, a welded joint having a diffusible hydrogen content of the weld metal of 1.0 ml / 100 g or less can be obtained. In particular, by using a flux-cored wire further containing a predetermined chemical composition, a high-strength and high-toughness welded joint can be obtained.

[0062] (Example) Next, the present invention will be described more specifically based on examples and the like. However, the following examples are not of a nature to limit the present invention, and any design changes in accordance with the gist of the foregoing and following are included in the technical scope of the present invention.

[0063] The flux-cored wires (sample numbers 8 ~47) of the present invention examples and comparative examples were manufactured by the following method. First, while feeding the steel strip in the longitudinal direction, it was formed using a forming roll to obtain a U-shaped open tube. Flux was supplied into the open tube through the opening of the open tube, and the opposing edge portions of the opening of the open tube were butt-welded to obtain a seamless tube. This seamless tube was drawn to obtain a wire filled with flux without a slit-like gap. However, at that time, some samples were made into tubes with a slit-like gap without seam welding, and those were drawn into wires. In this way, a wire filled with flux with a final filler diameter of φ2.0 mm was prototyped. Incidentally, during the wire drawing operation of these wires, the wire filled with flux was annealed at a temperature range of 650 to 950 °C for 4 hours or more. After prototyping, a lubricant was applied to the surface of some of the wires. Then, the manufactured wire filled with flux was cut to a length of 2.0 mm to prepare each sample of the wire filled with flux cut wire. The configurations of these wires filled with flux cut wire are shown in Table 1 and Table 2. Among these, the sample number 35 corresponds to the reference example.

[0064]

Table 1

[0065]

Table 2

[0066] The units of the contents of each fluoride, chemical components as optional components, iron powder (Fe powder), and each element contained as an impurity element disclosed in Tables 1 and 2 are mass ratios (mass %) with respect to the total mass of the wire filled with flux cut wire. The F conversion value of the wire filled with flux cut wire disclosed in the table indicates the amount of fluorine (F) contained in the fluoride in the wire filled with flux cut wire in terms of mass % with respect to the total mass of the wire filled with flux cut wire, and it is the value obtained by the above-described formula A.

[0067] In addition, the balance in the chemical composition of the flux-containing cut wire (i.e., components other than the elements disclosed in Tables 1 and 2) is iron (including intentionally added Fe powder) and impurities. Also, the wire structure of each flux-containing cut wire is as shown in Table 1, and furthermore, unless otherwise specified in the remarks column, no oil is applied. On the other hand, each element contained as a chemical component in the flux-containing cut wire disclosed in Table 2 is contained in the form of a steel outer skin or metal powder. In the table, a blank in the table regarding the content of chemical components, compounds, etc. means that the chemical components, compounds, etc. are not intentionally added. Also, fluorides and chemical components may be unavoidably mixed in.

[0068] The flux-containing cut wires of the invention examples and comparative examples were evaluated by the method described below. First, i) as an evaluation of low-temperature crack resistance, welding was performed on a 780 MPa grade steel with a plate thickness of 50 mm under the welding condition 1 in Table 3, and the evaluation was carried out by an H-type restraint crack test in accordance with JIS Z3159:1993. The groove shape was the Y-type shown in FIG. 3, and the slit length was 300 mm. Also, the spraying thickness of the flux-containing cut wire 4 in the groove 3 was 8 mm. Furthermore, NB-250H manufactured by Nippon Steel Welding & Engineering Co., Ltd. was used as the welding flux, and Y-80M (wire diameter φ4.8 mm) manufactured by Nippon Steel Welding & Engineering Co., Ltd. was used as the welding wire.

[0069] Also, ii) as an evaluation of low-temperature crack resistance in the first layer in the groove, welding was performed on a 780 MPa grade steel with a plate thickness of 50 mm under the welding condition 2 in Table 3. At that time, the groove shape was the V-type shown in FIG. 4, and the spraying thickness of the flux-containing cut wire 4 in the groove 3 was 2 mm. Furthermore, Y-82C (wire diameter φ1.2 mm) manufactured by Nippon Steel Welding & Engineering Co., Ltd. was used as the welding wire, and SB-41 manufactured by Nippon Steel Welding & Engineering Co., Ltd. was used as the backing material 5. In these evaluations, under the welding conditions 1 and 2, the test was carried out without performing preheating work on the base materials (steel materials) 1 and 2.

[0070]

Table 3

[0071] In addition, iii) the diffusible hydrogen content of the weld metal was evaluated as follows. That is, the welding conditions for evaluating the diffusible hydrogen content of the weld metal were the welding conditions 3 described in Table 3. Further, the flux-cored wire of the inventive example and the comparative example was sprayed onto the test plate and the end tab so as to have a thickness of 2 mm, and then the welding flux was sprayed so as to have a thickness of 10 mm. Here, NB-250H manufactured by Nippon Steel Welding & Engineering Co., Ltd. was used as the welding flux, and Y-80M (wire diameter φ4.0 mm) manufactured by Nippon Steel Welding & Engineering Co., Ltd. was used as the welding wire. The measurement of the diffusible hydrogen content of the weld metal was carried out by a gas chromatography method conforming to JIS Z 3118:2007 (Method for Measuring Hydrogen Content in Steel Welded Joints). The flux-cored wire with a diffusible hydrogen content of 1.0 ml / 100 g or less in the weld metal was judged to be qualified with respect to the diffusible hydrogen content.

[0072] Furthermore, i) after the H-type weld cracking test and ii) after the evaluation of the low-temperature crack resistance in the first layer, the unevenness of the bead surface was measured at a pitch of 25 mm in bead length to evaluate the bead shape. At this time, in both cases of i) after the H-type weld cracking test and ii) after the evaluation of the low-temperature crack resistance in the first layer, when the surface unevenness of the bead shape was 3 mm or less, it was evaluated as good (○), and when it exceeded 3 mm, it was evaluated as bad (×). And for the evaluation of the low-temperature crack resistance and the bead shape in the ii) first layer, when there was "no crack" and the bead shape was good (○), it was judged to be qualified in the comprehensive judgment, and when it was evaluated as bad (×) in one or more items, the comprehensive judgment was judged to be unqualified.

[0073] Each test result evaluated by the above method is shown in Table 4. When welding was performed using the flux-cored cutting wire of the invention example, even without preheating the steel material, there was no cross-sectional cracking (no cross-sectional cracking occurred) in any cross-section of the H-type welding crack test or the evaluation of low-temperature crack resistance in the first layer. That is, it was confirmed that the flux-cored cutting wire of the invention example has extremely high low-temperature crack resistance. Also, as shown in the test results of Table 4, by using the flux-cored cutting wire of the invention example, the bead shape evaluation was qualified, indicating good welding workability. On the other hand, when using the flux-cored cutting wire of the comparative example, there was cross-sectional cracking (cross-sectional cracking occurred) in any cross-section of the H-type welding crack test or the evaluation of low-temperature crack resistance in the first layer.

[0074]

Table 4

[0075] As described above, according to the present invention, even when welding an extremely thick high-strength steel plate, the burden of preheating work can be reduced, and low-temperature cracking can be prevented. Moreover, while suppressing the problems of the working environment caused by fumes and spatter as much as possible, welding with a good bead shape can be performed, and a welded joint can be manufactured advantageously in terms of cost.

Explanation of Reference Signs

[0076] 1, 2: Base material (steel material), 3: Groove, 4: Flux-cored cutting wire, 5: Backup material, 6: Welding wire, 7: Weld metal.

Claims

1. A method for manufacturing a welded joint by filling a cut wire into a groove provided between base materials and then welding, comprising: a flux-embedded cut wire welding step of filling at least a part of the groove with a flux-embedded cut wire having a steel outer skin and a flux filled inside the steel outer skin, and then welding; The flux contains one or more fluorides selected from the group consisting of CaF ２ , MgF ２ , LiF, NaF, K ２ ZrF ６ , K ２ SiF ６ , and Na ３ AlF ６ , and the content of the fluoride is 4.02% or more and 71.80% or less in terms of the F conversion value expressed as the mass% of the amount of fluorine contained in the fluoride with respect to the total mass of the flux-containing cut wire. Also, in the flux-embedded cut wire, the content of the chemical component composed of C is 0.010% or more and 0.120% or less in terms of mass ratio to the total mass of the flux-embedded cut wire, and in terms of mass ratio to the total mass of the flux-embedded cut wire, the contents of the chemical components composed of Si, Mn, Cu, Ni, Cr, Mo, Nb, V, Ti, Al, B, and Bi are Si: 2.00% or less, Mn: 3.50% or less, Cu: 5.00% or less, Ni: 5.00% or less, Cr: 5.00% or less, Mo: 5.00% or less, Nb: 0.50% or less, V: 0.50% or less, Ti: 0.50% or less, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less. Also, the contents of the impurity elements composed of P and S are P: 0.030% or less and S: 0.020% or less, and the balance is Fe. A method for manufacturing a welded joint, characterized by the above.

2. The method for manufacturing a welded joint according to claim 1, wherein the flux-embedded cut wire welding step consists of a one-pass welding with the flux-embedded cut wire filled into the groove.

3. The method for manufacturing a welded joint according to claim 1, wherein the flux-embedded cut wire welding step consists of a single-layer welding in which the flux-embedded cut wire is filled and welded in the first layer of the groove, or a multi-layer welding in which the flux-embedded cut wire is filled and welded in the first layer and the subsequent layers of the groove, and is performed at least until the temperature of the base material reaches a preheating equivalent temperature.

4. The method for manufacturing a welded joint according to any one of claims 1 to 3, wherein the welding means is submerged arc welding or gas shielded arc welding.

5. The method for manufacturing a welded joint according to any one of claims 1 to 4, wherein the base material is made of a high-strength steel material having a tensile strength of 780 MPa or more.

6. The method for manufacturing a welded joint according to any one of claims 1 to 5, wherein the base material is made of an extra-thick steel material having a thickness of 50 mm or more.

7. A cut wire for groove filling provided in a groove provided between base materials when manufacturing a welded joint, comprising a flux-containing cut wire having a steel outer skin and a flux filled inside the steel outer skin. wherein the flux contains one or more fluorides selected from the group consisting of CaF ２ , MgF ２ , LiF, NaF, K ２ ZrF ６ , K ２ SiF ６ , and Na ３ AlF ６ , and the content of the fluoride is 4.02% or more and 71.80% or less in terms of the F conversion value expressed as the mass% of the amount of fluorine contained in the fluoride with respect to the total mass of the cut wire containing the flux. Also, In the flux-containing cut wire, the content of the chemical component composed of C is 0.010% or more and 0.120% or less in terms of the mass ratio to the total mass of the flux-containing cut wire, and in terms of the mass ratio to the total mass of the flux-containing cut wire, the content of the chemical components composed of Si, Mn, Cu, Ni, Cr, Mo, Nb, V, Ti, Al, B, and Bi is Si: 2.00% or less, Mn: 3.50% or less, Cu: 5.00% or less, Ni: 5.00 or less, Cr: 5.00% or less, Mo: 5.00% or less, Nb: 0.50% or less, V: 0.50% or less, Ti: 0.50% or less, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less. Also, the content of the impurity elements composed of P and S is P: 0.030% or less and S: 0.020% or less, and further, the balance is Fe. A flux-containing cut wire for groove filling, characterized by the above.

8. The flux-containing cut wire for groove filling according to claim 7, wherein the base material is made of a high-strength steel material having a tensile strength of 780 MPa or more.

9. The flux-containing cut wire for groove filling according to claim 7 or 8, wherein the base material is made of an extremely thick steel material having a thickness of 50 mm or more.

Images