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 secure corrosion resistance of weld metal, 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 corrosion-resistant element; and a flux-cored cut wire used in the same, in which the flux-cored cut wire is composed of a steel sheath and a flux containing a predetermined corrosion-resistant element that is made to fill the inside of the steel sheath as metal and / or an alloy.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, the requirements for the safety of structural materials have become increasingly strict. Such requirements include, for example, mechanical properties (tensile strength and toughness) and corrosion resistance. Materials with high corrosion resistance are suitable for structures exposed to severe corrosion environments.

[0003] For oil tanks of crude oil tankers transporting crude oil and oil tanks storing crude oil above or below ground, welded structural steel excellent in strength and weldability is used. The steel oil tank is exposed to a corrosion environment caused by moisture, salt, corrosive gas components, etc. contained in the crude oil. In particular, the inner surface of the oil tank of a crude oil tanker becomes a unique corrosion environment due to volatile components in the crude oil, salt in the mixed seawater and oilfield brine, and dew condensation due to daily temperature fluctuations. In particular, the welded part of the steel plate is thinned by corrosion. The most effective method for preventing general corrosion and local corrosion is to apply a heavy coating on the surface to block it from the corrosion environment. However, the painting work has a huge area to be painted, and repainting is required due to deterioration of the paint film, resulting in huge costs for inspection and painting.

[0004] Therefore, conventionally, technologies for improving the corrosion resistance of the welded part of steel plates have been proposed. For example, Patent Documents 1 to 3 disclose that the corrosion resistance of the welded part is improved by controlling the ratio of Cu, Mo, or W in the weld metal and the steel plate. Also, Patent Documents 4 to 5 propose flux-containing wires for gas shielded arc welding having excellent corrosion resistance.

[0005] However, generally, elements that ensure corrosion resistance deteriorate the high-temperature crack resistance and toughness of the weld metal. Also, corrosion resistance is mainly required for the surface of the joint, and there is little need to ensure corrosion resistance up to the inside of the joint. Furthermore, it is assumed that the corrosion environment may differ between the front and back surfaces of the joint. However, all of the techniques described in Patent Documents 1 to 5 above assume that a predetermined welding material is used throughout the joint. For this reason, in many cases, there is a problem that it takes time to change the welding material and excessive manufacturing costs are incurred.

[0006] Therefore, in the technology for improving the corrosion resistance of the welded part of the steel plate, a technology for easily changing the type of corrosion-resistant element is required so that the necessary corrosion-resistant element can be supplied to the necessary part of the welded joint and an appropriate corrosion-resistant treatment can be performed. Also, from the viewpoint of improving construction efficiency, in submerged arc welding (SAW), which is mainly adopted in fillet welding, a welding material capable of coping with high-heat-input welding such as single-sided welding and double-sided single-layer welding is required.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0008] In view of the various problems in the above-described method for manufacturing a welded joint, the inventors of the present invention have diligently studied a method for manufacturing a welded joint that can supply necessary corrosion-resistant elements to necessary locations of the welded joint to perform appropriate corrosion resistance treatment, easily obtain a welded joint excellent in corrosion resistance, and further cope with high heat input welding. As a result, it has been found that the above problems can be solved by filling a groove with a flux-containing cut wire containing a predetermined corrosion-resistant element and performing welding, and the present invention has been completed.

[0009] Accordingly, an object of the present invention is to provide a method for manufacturing a welded joint that can supply necessary corrosion-resistant elements to necessary locations of the welded joint to perform appropriate corrosion resistance treatment, easily obtain a welded joint excellent in corrosion resistance, and further cope with high heat input welding.

[0010] Another object of the present invention is to provide a flux-containing cut wire used in such a method for manufacturing a welded joint.

Means for Solving the Problems

[0011] That is, the gist of the present invention is as follows. (1) A method for manufacturing a welded joint in which a groove provided between base materials is filled with a cut wire and welded, wherein a flux-containing cut wire having a steel outer skin and a flux filled inside the steel outer skin is filled and welded in any one or two or more layers from the first layer to the final layer in the groove, and the flux contains one or more corrosion-resistant elements selected from the group consisting of Cr, Mo, Cu, W, Sn, and Sb as a metal and / or an alloy, and is characterized by a method for manufacturing a welded joint. (2) The flux-containing cut wire is, by mass ratio with respect to the total mass of the flux-containing cut wire, The total content of the corrosion-resistant elements is 0.05% or more and 98.00% or less, and the contents of the chemical components consisting of C, Si, Mn, Ni, Nb, V, Ti, Al, B, and Bi are C: 0.120% or less, Si: 2.00% or less, Mn: 3.50% or less, Ni: 5.00% or less, Nb: 0.50% or less, V: 0.500% 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 method for manufacturing the welded joint according to (1) above, characterized in that the contents of the impurity elements consisting of P and S are P: 0.030% or less and S: 0.020% or less. (3) The method for manufacturing the welded joint according to (1) or (2) above, characterized in that after filling the flux-containing cut wire into the first layer in the groove, a solid cut wire obtained by cutting a solid wire is filled and welded. (4) The method for manufacturing the welded joint according to any one of (1) to (3) above, characterized in that the welding is submerged arc welding or gas shielded arc welding.

[0012] (5) A cut wire for groove filling for manufacturing a welded joint by filling it into a groove provided between base metals, having a steel outer skin and a flux filled inside the steel outer skin, The flux-containing cut wire for groove filling, characterized in that the flux contains one or more corrosion-resistant elements selected from the group consisting of Cr, Mo, Cu, W, Sn, and Sb as a metal and / or an alloy. (6) In terms of the mass ratio to the total mass of the flux-containing cut wire, The total content of the corrosion-resistant elements is 0.05% or more and 98.00% or less, and the contents of the chemical components consisting of C, Si, Mn, Ni, Nb, V, Ti, Al, B, and Bi are C: 0.120% or less, Si: 2.00% or less, Mn: 3.50% or less, Ni: 5.00% or less, Nb: 0.50% or less, V: 0.500% 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 flux-containing cut wire for groove filling according to (5) above, characterized in that the contents of impurity elements consisting of P and S are P: 0.030% or less and S: 0.020% or less. (7) The flux-containing cut wire for groove filling according to (5) or (6) above, characterized in that it is used by being filled in any one or two or more layers from the first layer to the last layer in the groove provided between base materials.

Advantages of the Invention

[0013] According to the present invention, for example, even when a steel plate is subjected to submerged arc welding, it is possible to supply necessary corrosion-resistant elements to necessary portions of the welded joint and perform appropriate corrosion-resistant treatment, and it is possible to easily manufacture a welded joint excellent in corrosion resistance. In addition, it can also cope with high heat input welding.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0015] The present invention uses a flux-filled cut wire having a steel outer skin and a predetermined flux filled inside the steel outer skin, and fills the flux-filled cut wire into any one or two or more layers from the first layer to the last layer (corresponding to the outermost layer of the groove surface) in the groove provided between the base materials and welds it, so as to include a flux-filled cut wire welding process for manufacturing a welded joint. Hereinafter, the flux-filled cut wire according to the present invention will be described, and a method for manufacturing a welded joint using the same will be described.

[0016] 〔Flux-filled cut wire〕 First, for the flux-filled cut wire, one or more corrosion-resistant elements selected from the group consisting of Cr, Mo, Cu, W, Sn, and Sb are used as a metal and / or an alloy. These corrosion-resistant elements have the function of significantly improving the corrosion resistance of the weld metal, but are also elements that can impair the high-temperature crack resistance and toughness of the weld metal. Therefore, regarding the content of these corrosion-resistant elements in the flux-filled cut wire, it is desirable to specify it within a predetermined range in order to ensure the corrosion resistance of the weld metal without deteriorating the high-temperature crack resistance and toughness of the weld metal. Here, the reason for using the corrosion-resistant element as a metal and / or an alloy is that it melts and solidifies during welding and effectively contributes to the manifestation of corrosion resistance as a part of the weld metal.

[0017] From the above viewpoints, the total content of corrosion-resistant elements (Cr, Mo, Cu, W, Sn, and Sb) in the flux-containing cutting wire is preferably 0.05% or more and 98.00% or less in terms of the mass ratio to the total mass of the flux-containing cutting wire. Here, for the lower limit value, it is preferably 0.10% or more, more preferably 0.20% or more, and still more preferably 0.30% or more. For the upper limit value, it may be 95.00%, 90.00%, or 80.00%. The total content of these corrosion-resistant elements represents the total amount of corrosion-resistant elements contained in the steel outer skin constituting the flux-containing cutting wire and the flux filled therein. As long as the total mass ratio of each corrosion-resistant element (Cr, Mo, Cu, W, Sn, or Sb) contained in the flux is 0.05% or more and 98.00% or less, the content of each corrosion-resistant element is not particularly limited within the range of 0.00% to 98.00% and can be determined by the following formula 1. 0.05% ≤ [Cr] + [Mo] + [Cu] + [W] + [Sn] + [Sb] ≤ 98.00%... Formula 1 〔However, the element symbols with square brackets in Formula 1 represent the mass ratio (mass%) to the total mass of the flux-containing cutting wire for the elements corresponding to the respective element symbols in the chemical composition of the flux-containing cutting wire.〕 In addition, the addition of the above corrosion-resistant elements to the flux-containing cutting wire can be performed on either one or both of the steel outer skin of the flux-containing cutting wire and the flux because the entire flux-containing cutting wire melts and solidifies during welding to become a part of the weld metal.

[0018] Here, to ensure the corrosion resistance of the weld metal, it is desirable that the total content of corrosion-resistant elements (Cr, Mo, Cu, W, Sn, and Sb) is 0.05% or more. Also, although there is no particular upper limit for the total content of corrosion-resistant elements, in the flux-cored wire of the present invention, since the flux is filled inside the steel outer skin, it is substantially 98.00%. That is, even if a large amount of corrosion-resistant elements are contained in the flux-cored wire of the present invention, since most of the weld metal is occupied by welding materials other than the flux-cored wire [for example, the flux and wire in submerged arc welding (SAW)], it does not affect the deterioration of toughness. Therefore, from the viewpoint of improving corrosion resistance, the upper limit of the mass ratio of corrosion-resistant elements is not particularly limited.

[0019] In addition to the metals and / or alloys of the above corrosion-resistant elements (Cr, Mo, Cu, W, Sn, and Sb), the flux-cored wire of the present invention may contain alloying components for controlling, for example, the chemical composition of the weld metal and the carbon equivalent (Ceq), etc. (hereinafter, these chemical compositions and alloying components are simply referred to as "chemical compositions"). When adding such chemical compositions into the flux-cored wire, if the added chemical composition is in the form of metal or alloy powder, it melts in the same way as the steel outer skin during welding. Therefore, the addition of chemical compositions other than corrosion-resistant elements may be added to the flux in the form of metal powder or alloy powder, or 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. In any case, the same effect can be achieved. In the case of the present invention, different from the case of the flux-cored wire that is not a conventional cut wire, the chemical compositions other than corrosion-resistant elements are not required to have arc stability and all-position weldability, and do not need to be in the state of oxides or carbonates. Therefore, the chemical compositions other than the above corrosion-resistant elements can be contained in the form of metal powder or alloy powder.

[0020] Specifically, the flux-containing cutting wire of the present invention contains a corrosion-resistant element contained as a metal and / or an alloy in a mass ratio of 0.05% or more and 98.00% or less with respect to the total mass of the flux-containing cutting wire, and contains any one or more chemical components selected from the group consisting of C, Si, Mn, Ni, Nb, V, Ti, Al, B, and Bi as optional components. The content of each chemical component is C: 0.120% or less, Si: 2.00% or less, Mn: 3.50% or less, Ni: 5.00% or less, Nb: 0.50% or less, V: 0.500% or less, Ti: 0.50% or less, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less, respectively. Also, the content of impurity elements consisting of P and S is preferably P: 0.030% or less and S: 0.020% or less, respectively. In the present invention, by containing the above-described corrosion-resistant element, the corrosion resistance can be improved without containing the chemical components as the optional components. Therefore, the lower limit value of the content of each of these chemical components is 0%.

[0021] 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%.

[0022] Si in "Si: 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%.

[0023] Mn in "Mn: 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 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 susceptibility to intergranular embrittlement 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%.

[0024] Ni in "Ni: 5.00% or less" is not an essential component, so the lower limit value of the Ni content in the flux cored wire is 0%. Also, when this Ni content is too high, solidification cracking is likely to occur. Therefore, the upper limit value of the Ni content is preferably 4.00%, 3.00%, or 2.00%. The lower limit value of the Ni content is preferably 0.05%, 0.1%, or 0.15%.

[0025] Since Nb in "Nb: 0.50% or less" is not an essential component, the lower limit of the Nb content in the flux-added 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 is 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%.

[0026] Since V in "V: 0.500% or less" is not an essential component, the lower limit of the V content in the flux-added 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 is 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%.

[0027] 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, the 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 the flux-cored cutting wire contains Ti, 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%.

[0028] Al in "Al: 1.70% or less" is a deoxidizing element and, like Si, 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, 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%.

[0029] 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 increases 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 the B content exceeds 0.020%, the B in the weld metal becomes excessive, and coarse BN and Fe23 Forming B compounds 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%.

[0030] Since Bi in "Bi: 0.020% 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 0.020%, solidification cracking is likely to occur in the weld metal, so the upper limit of the Bi content is 0.020%. This upper limit of the Bi content is preferably 0.015%, 0.010%, or 0.005%.

[0031] Also, P in "P: 0.030% or less" present as the impurity element reduces the toughness of the weld metal, so it is necessary to reduce the P content in the flux-cored wire 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 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.

[0032] When S in "S: 0.020% or less" present as the impurity element is excessively present in the weld metal, it deteriorates both the toughness and ductility of 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.

[0033] The flux-containing cut wire in the present invention may or may not contain the chemical components as described above. However, except for these chemical components, the corrosion-resistant elements, and the impurity elements, they are 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, the mass ratio to the total mass of the flux-containing cut wire is less than 90.0%, 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%.

[0034] Also, regarding impurities, they are components that are derived from raw materials or mixed in 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.

[0035] In the flux-containing cut wire of the present invention, fluorides, oxides, carbonates, etc. of other metal elements other than the above-described corrosion-resistant elements, chemical components, and impurity elements may also be contained as long as their properties are not impaired. In this case, the fluorides, oxides, and carbonates of the other metal elements shall not be included in the contents of the above-described corrosion-resistant elements, chemical components, impurity elements, as well as Fe and impurities. However, this indicates that the case where these fluorides, oxides, and carbonates of other metal elements are contained is not excluded. That is, the flux-containing cut wire in the present invention contains the above-described corrosion-resistant elements at a predetermined ratio, and the contents of the above-described chemical components and impurity elements are respectively within a predetermined range, and the balance consists of Fe and impurities, or a chemical composition consisting of Fe, impurities, and these fluorides, oxides, and carbonates of other metal elements. Preferably, it contains the above-described corrosion-resistant elements at a predetermined ratio, and the contents of the above-described chemical components and impurity elements are respectively within a predetermined range, and the balance consists of Fe and impurities.

[0036] 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, by mass ratio, 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 consists of iron and impurities.

[0037] 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 to be about the same as 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, etc., 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.

[0038] Also, regarding the filling rate of the flux, as long as the above-described conditions are satisfied, there is no particular limitation. 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%.

[0039] Here, in the production and storage of the flux-containing cut wire of the present invention, in order to reduce the amount of diffusible hydrogen in the weld metal and prevent the problem of cold cracking, preferably, appropriate measures described later are taken during production and storage so that the amount of hydrogen contained in the flux-containing cut wire becomes 12 ppm or less with respect to the total mass of the flux-containing cut wire. This amount of hydrogen not only enters during the production of the flux-containing cut wire, but may also increase due to the intrusion of moisture during the storage of the flux-containing cut wire. When the period from after the production of the cut wire to its use is long, it is desirable to store it while preventing the intrusion of moisture.

[0040] In manufacturing the flux-containing cut wire in the present invention, its procedure and the like are not particularly limited, but as a method for manufacturing the wire filled with the flux 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 corrosion-resistant elements, 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.

[0041] 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 gap of the steel outer skin is brazed, a wire without slit-shaped gaps can be obtained.

[0042] Also, it may be 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 manufacturing method of 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 manufacturing method of a wire having slit-shaped gaps may further include a step of caulking the butted ends of the open tube. In the manufacturing method of a wire having slit-shaped gaps, the tube is drawn with the slit-shaped gaps.

[0043] As described above, the flux-containing cut wire according to the present invention may be obtained by cutting a seamless wire in which the joints of the steel outer skin are welded and there are no slit-like gaps, or by cutting a wire having slit-like gaps without welding the joints of the steel outer skin. Preferably, it is a flux-containing cut wire obtained by cutting a wire without slit-like gaps 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 stress concentration parts, 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-containing 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 slit-like gaps. However, when cutting a wire having slit-like gaps, for example, it may be vacuum-packed and stored, or stored in a container that can maintain a dry state.

[0044] Further, the flux-containing 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-containing cut wire has plating on its surface, the lubricant is applied to the surface of the plating.

[0045] 〔Method for manufacturing welded joint〕 Next, when manufacturing a welded joint using the flux-cored cutting wire described above, the present invention provides a flux-cored cutting wire welding step of filling at least a part of the groove provided between the base materials with the flux-cored cutting wire and performing welding. 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.

[0046] Among them, for this flux-cored cutting wire welding step, it is preferable to fill at least the first layer or the final layer (the outermost layer of the groove surface) in the groove with the flux-cored cutting wire according to the present invention and perform welding. That is, by filling the flux-cored cutting wire on the surface of the welded part where corrosion resistance is required, the corrosion resistance of the welded part can be improved.

[0047] FIG. 1 and FIG. 2 each show an example of the flux-cored cutting wire welding step in the present invention. Among them, 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. And when corrosion resistance is required only for the surface on the first layer side, in the subsequent welding, without using the flux-cored cutting wire of the present invention, as shown in FIG. 1(b), the welding wire 6 is disposed on the filled flux-cored cutting wire 4, and the welded joint may be manufactured.

[0048] Also, if the welding amount is insufficient with only the first layer, or if corrosion resistance is required for the entire thickness, as shown in Fig. 1(c), on the welded metal 7 obtained by including the flux-cored cut wire 4 filled in the first layer, the flux-cored cut wire 4 of the present invention is again sprayed and filled into the groove 3, the welding wire 6 is arranged, and welding is performed. Thereafter, this is repeated, and when the required welding amount is reached, welding may be performed without using the flux-cored cut wire of the present invention.

[0049] And, if corrosion resistance is required only in the final layer (the outermost layer on the groove surface) in the groove, as shown in Fig. 1(d), after attaching the backing material 5 to the back surfaces of the base materials 1 and 2, the operation of arranging the welding wire 6 in the groove 3 and generating an arc for welding is repeated the necessary number of times. As shown in Fig. 1(e), it is joined with a plurality of welded metals 8 not including the flux-cored cut wire of the present invention (here, an example in which about 80% of the height inside the groove is joined with three welded metals 8 is shown). Thereafter, the flux-cored cut wire 4 of the present invention is sprayed and filled on this welded metal 8. Then, as shown in Fig. 1(f), the welding wire 6 is arranged on the substantially central portion of the filled flux-cored cut wire 4, and an arc is generated for welding, thereby manufacturing a welded joint having the final layer 9 including the flux-cored cut wire 4 of the present invention.

[0050] 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 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 inside 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 arranged on the substantially central portion of the filled flux-cored cut wire 4, and an arc is generated for welding, thereby manufacturing a welded joint with the welded metal 7 including the flux-cored cut wire 4 as shown in Fig. 2(c). In the example of the flux-cored cut wire welding process shown in this Figure 2, since the flux-cored cut wire according to the present invention is used for almost all of the groove, the weld portion can ensure corrosion resistance over the entire plate thickness.

[0051] In these Figures 1 and 2, the groove between the base materials shows an example of a so-called V-groove, but in the present invention, there is no limitation to this groove shape. In addition to the V-groove, for example, groove shapes such as I-groove, L-groove, K-groove, J-groove, X-groove, U-groove, H-groove, etc., or grooves of any other shape may be used. Also, in the present invention, it may be a case of single-sided welding or applicable to double-sided welding. Furthermore, in the case of multi-layer welding as in the example of Figure 1, each layer may be welded by dividing it into two or more passes.

[0052] 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 vertical welding or uphill welding, it may be difficult to fill the flux-cored cut wire in the groove, so the welding posture is preferably downward or horizontal.

[0053] Also, in the method for manufacturing a welded joint in the present invention, the type and shape of the base material are not particularly limited, but it is most effective for application in scenes where corrosion is a problem. That is, typically, it is welding of oil tanks for transporting or storing crude oil, such as oil tanks of crude oil tankers or above-ground or underground crude oil tanks for storing crude oil.

[0054] (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 all included in the technical scope of the present invention.

[0055] The flux-cored cut wires (sample numbers 7 ~44) of the present invention example and the comparative example 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 this 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 with flux and no slit-like gaps. However, at that time, some samples were made into tubes with slit-like gaps without seam welding, and those were drawn into wires. In this way, a wire with flux having a final filler diameter of φ2.0 mm was prototyped. In addition, during the wire drawing operation of these wires, the wires with flux were 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 wires with flux were cut to a length of 2.0 mm to prepare each sample of the cut wire with flux. And when preparing the above flux, regarding the corrosion-resistant elements shown in Table 1, for each element of Cr and Mo, they were used as ferrochrome alloy powder and ferromolybdenum alloy powder respectively, and for each element of Cr, W, Sn, and Sb, they were used as their metal powders respectively. Also, in Tables 1 and 2, they are shown in terms of the mass ratio of each element. The compositions of these cut wires with flux are shown in Tables 1 and 2.

[0056]

Table 1

[0057]

Table 2

[0058] The units of the corrosion-resistant elements, chemical components as optional components, iron powder (Fe powder), and the content of each element contained as impurity elements disclosed in Tables 1 to 2 are mass ratios (mass %) with respect to the total mass of the cut wire with flux.

[0059] 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 included as a chemical component in the flux-containing cut wire disclosed in Table 2 is included in the form of a steel outer skin or metal powder. In Tables 1 and 2, the blanks in the table regarding the corrosion-resistant elements, chemical components, and the content of Fe powder mean that the corrosion-resistant elements, chemical components, and Fe powder are not intentionally added. Also, the corrosion-resistant elements and chemical components may be unavoidably mixed in.

[0060] The flux-containing cut wires of the inventive examples and comparative examples were evaluated by the method described below. For SM490A with a plate thickness of 20 mm, SAW welding was performed in one pass under the welding conditions shown in Table 3. At that time, the groove shape was a V shape shown in Figure 3, and the spraying thickness of the flux-containing cut wire 4 in the groove 3 was 18 mm. Furthermore, NF-100 manufactured by Nippon Steel & Sumitomo Metal Welding Co., Ltd. was used as the welding flux, and Y-DS (wire diameter φ4.8 mm) manufactured by Nippon Steel & Sumitomo Metal Welding Co., Ltd. was used as the welding wire. The welding wire was installed perpendicular to the steel plate.

[0061] (Evaluation of the Corrosion Resistance of the Weld Metal) (1) General Corrosion Test To evaluate the corrosion resistance against general corrosion on the inner surface of the tanker upper deck, a rectangular piece with a width of 15 mm × a length of 60 mm × a thickness of 5 mm (corrosion test piece 11 for corrosion resistance evaluation) that was only the weld metal was cut out from the cut-out position A of the joint for evaluation shown in Figure 4 manufactured under the welding conditions shown in Table 3, and its surface was polished with 600-grit emery paper. The back surface and end faces were sealed with tape so as not to corrode, and a general corrosion test was performed using the corrosion test apparatus shown in Figure 5.

[0062] This corrosion test apparatus is composed of a corrosion test tank 12 and a temperature control plate 13. Water 16 maintained at a temperature of 36°C is injected into the corrosion test tank 12. Further, a mixed gas (introduced gas 14) consisting of 4 vol% O2, 13 vol% CO2, 0.01 vol% SO2, 0.05 vol% H2S, and the balance N2 is introduced into the water 16 to fill the inside of the corrosion test tank 12 with supersaturated water vapor, reproducing the corrosion environment on the back of the upper deck of the crude oil tank. Then, a temperature change with a cycle of 25°C × 3 hours + 50°C × 21 hours is repeatedly applied for 180 days to the corrosion test piece 11 set on the upper and lower surfaces of this test tank via the temperature control plate 13 incorporating a heater and a cooling device, causing condensed water to form on the surface of the corrosion test piece 11 to cause general corrosion. In FIG. 5, 15 indicates the exhaust gas from the test tank.

[0063] After the above test, the rust on the surface of each corrosion test piece was removed, and the mass reduction amount due to corrosion was obtained from the mass change before and after the test and converted into the plate thickness reduction amount (corrosion rate on one side) per year. As a result, when the corrosion rate was 0.10 mm / y or less and no pitting corrosion was observed, the general corrosion resistance was evaluated as good.

[0064] (2) Pitting corrosion test To evaluate the corrosion resistance against pitting corrosion in the bottom plate of the tanker oil tank section, a rectangular small piece (corrosion resistance test piece 17) with a width of 15 mm × a length of 60 mm × a thickness of 5 mm was cut out from the cut-out position A of the joint for evaluation in FIG. 4 manufactured under the welding conditions in Table 6 so as to be only the weld metal, and the entire surface was polished with 600-grit emery paper.

[0065] Next, a test solution was prepared by adjusting a 10 mass% NaCl aqueous solution to a Cl ion concentration of 10 mass% and a pH of 0.85 using concentrated hydrochloric acid. The test piece was suspended through a tegus into a 3 mmφ hole opened at the upper part of the corrosion test piece and immersed in 2 L of the test solution for 168 hours for a corrosion test. The test solution was pre-heated and maintained at 30°C and exchanged with a new test solution every 24 hours.

[0066] The apparatus used in the above corrosion test is shown in Fig. 6. This corrosion test apparatus is a double-layered apparatus consisting of a corrosion test tank 18 and a thermostatic bath 19. The test solution 20 is placed in the corrosion test tank 18, and the corrosion test piece 17 is suspended and immersed in it by tags 21. The temperature of the test solution 20 is maintained by adjusting the temperature of the water 22 placed in the thermostatic bath 19.

[0067] After the above corrosion test, after removing the rust generated on the surface of the corrosion test piece, the mass difference before and after the test was obtained, and this difference was divided by the total surface area to obtain the reduction in plate thickness per year (corrosion rate on both sides). As a result, when the corrosion rate was 0.50 mm / y or less, it was evaluated that the resistance to local corrosion was good.

[0068]

Table 3

[0069] Each test result evaluated by the above method is shown in Table 4. When welding was performed using the flux-cored cut wire of the example of the present invention, the corrosion resistance was good, and all the weld metals passed, and a weld metal having excellent corrosion resistance could be manufactured. On the other hand, the comparative example had insufficient corrosion resistance and failed. When welding was performed using the flux-cored cut wire of the example of the present invention, hot cracks did not occur. Also, using the No. 4 Charpy test piece cut out from the weld metal 7, as a result of the Charpy impact test conducted in accordance with JIS Z3111:2005, the Charpy absorption energy at -20 °C was 45 J or more, and there was no problem with low-temperature toughness.

[0070]

Table 4

[0071] As described above, according to the present invention, a welded joint having excellent corrosion resistance can be produced, and it can be advantageously constructed in terms of cost performance.

Explanation of Reference Numerals

[0072] 1, 2: Base material (steel material), 3: Groove, 4: Flux-cored cutting wire, 5: Backup material, 6: Welding wire, 7, 8: Weld metal, 9: Final layer (the outermost layer of the groove surface), 11, 17: Corrosion test piece, 12, 18: Corrosion test tank, 13: Temperature control plate, 14: Introduced gas, 15: Exhaust gas, 16, 22: Water, 19: Constant temperature bath, 20: Test solution, 21: Tags, A: Cutting position of the corrosion test piece.

Claims

1. A method for manufacturing a welded joint by filling a groove provided between base materials with a cutting wire and then welding, wherein a flux-containing cutting wire having a steel outer skin and a flux filled inside the steel outer skin is filled and welded in any one or two or more layers from the first layer to the final layer in the groove, the flux contains one or more corrosion-resistant elements selected from the group consisting of Cr, Mo, Cu, W, Sn, and Sb as a metal and / or an alloy, in the flux-containing cutting wire, the total content of the corrosion-resistant elements is 0.05% or more and 98.00% or less by mass ratio with respect to the total mass of the flux-containing cutting wire, in the flux-containing cutting wire, by mass ratio with respect to the total mass of the flux-containing cutting wire, the contents of chemical components consisting of C, Si, Mn, Ni, Nb, V, Ti, Al, B, and Bi are C: 0.120% or less, Si: 2.00% or less, Mn: 3.50% or less, Ni: 5.00% or less, Nb: 0.50% or less, V: 0.500% 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, 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, characterized in that after filling the flux-containing cutting wire into the layer in the groove, a solid cutting wire obtained by cutting a solid wire is filled and welded.

3. The method for manufacturing a welded joint according to claim 1 or 2, characterized in that the welding is submerged arc welding or gas shielded arc welding.

4. A cutting wire for groove filling for manufacturing a welded joint by filling and welding in a groove provided between base materials, which is a flux-containing cutting wire having a steel outer skin and a flux filled inside the steel outer skin, the flux contains one or more corrosion-resistant elements selected from the group consisting of Cr, Mo, Cu, W, Sn, and Sb as a metal and / or an alloy, and the total content of the corrosion-resistant elements is 0.05% or more and 98.00% or less by mass ratio with respect to the total mass of the flux-containing cutting wire, and also, by mass ratio with respect to the total mass of the flux-containing cutting wire, The content of the chemical components consisting of C, Si, Mn, Ni, Nb, V, Ti, Al, B, and Bi is such that C: 0.120% or less, Si: 2.00% or less, Mn: 3.50% or less, Ni: 5.00% or less, Nb: 0.50% or less, V: 0.500% 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 consisting 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.

5. The flux-containing cut wire for groove filling according to claim 4, characterized in that it is used by being filled in any one or two or more layers from the first layer to the last layer in the groove provided between base materials.

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