JP7606071B2 - Manufacturing method of welded joint and flux-cored cut wire for filling groove - Google Patents

Description

The present invention relates to a method for manufacturing a welded joint in which a groove provided between base materials is filled with a cut wire and welded, and to a flux-cored cut wire for filling the groove used in this method.

In recent years, safety requirements for structural materials have become increasingly stringent. These requirements include, for example, mechanical properties (tensile strength and toughness) and fatigue resistance. Fatigue resistance refers to the ability to resist destruction under repeated stress, and is evaluated by fatigue strength. Fatigue strength refers to the upper limit of stress amplitude at which a material will not break even if it is repeatedly subjected to stress an infinite number of times, and is determined by fatigue testing. Materials with high fatigue resistance are suitable for structures that are regularly exposed to severe vibrations.

In general, the fatigue resistance of welds in structures (a general term that includes the weld metal, which is metal that melts and solidifies during welding, and the heat-affected zone, which is the part of the base material that has undergone changes in structure, metallurgical properties, and mechanical properties due to the welding heat but has not melted and solidified) tends to be lower than that of the base material, and therefore welds are likely to become the starting point of fatigue fracture. In order to improve the fatigue resistance of welds, technologies such as those disclosed in Patent Documents 1 and 2 have been proposed.

Patent Document 1 discloses a high-Ni flux-cored wire that aims to lower the phase transformation temperature (Ms point) of the weld metal and obtain a weld with excellent fatigue strength by adding Ni to the flux-cored wire and actively adding N and C from the flux and adopting a low-oxygen MAG or MIG welding method (see claim 1 and paragraph 0022, etc.). In welding using this welding wire, the weld metal is transformed into martensite at a low temperature, and the volume expansion during this transformation is used to generate compressive residual stress in the weld, reducing the tensile residual stress in the weld or imparting compressive residual stress to the weld, thereby improving the fatigue strength of the weld.

Patent Document 2 discloses a flux-cored wire in which _CaF2 is added to a high Ni flux-cored wire to reduce oxygen in the weld metal, thereby improving the fatigue strength of the weld and the toughness of the weld metal (see claim 1 and paragraph 0005, etc.).

However, when the welding materials of the above-mentioned prior art are used only in areas where fatigue cracks occur (e.g., the toes of the weld bead), the welding wire needs to be switched, which reduces the efficiency of the work.

For the reasons stated above, the industrial sector is in need of developing a highly efficient manufacturing method for welded joints with excellent fatigue resistance, as well as welding materials.

JP 2007-296535 A JP 2014-050882 A

Therefore, the inventors conducted extensive research into methods for efficiently improving the fatigue strength of welds, and discovered that the above-mentioned problems could be solved by filling the groove with a cut wire that contains flux containing a specified element and welding, thereby completing the present invention.

Therefore, an object of the present invention is to provide a method for manufacturing a welded joint that can efficiently improve the fatigue strength of a welded portion.
Another object of the present invention is to provide a flux-cored cut wire for use in the method for producing such a welded joint.

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 between base materials and welded,
The method includes filling at least one of a first layer or a final layer in the groove , or a weld bead toe in or outside the groove, with a flux-cored cut wire having a steel sheath and flux filled inside the steel sheath , and welding the weld bead in or outside the groove,
the flux contains one or more Ms point lowering elements selected from the group consisting of C, Mn, V, Cr, Ni, Cu, and Mo as a metal and/or alloy, and the Ni content is less than 50 mass% relative to the total mass of the flux-cored cut wire;
A method for manufacturing a welded joint, characterized in that the martensitic transformation temperature (Ms point) calculated by the following formula 1 is 450°C or lower.
Ms=613-406×[C]-64×[Mn]-32×[V]-18×[Cr]-15×[Ni]-9×[Cu]-5×[Mo]…Formula 1
(Note that the element symbols enclosed in square brackets in formula 1 represent the contents expressed as mass percentages (mass%) relative to the total mass of the flux-cored cut wire.)
(2) The flux-cored cut wire has a mass ratio to the total mass of the flux-cored cut wire of:
the total content of the Ms point lowering elements is 0.10% or more, the contents of the chemical components consisting of Si, Nb, Al, B, and Bi are Si: 2.00% or less, Nb: 0.50%, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less, and the content of the strong deoxidizing elements selected from the group consisting of Ca, Mg, Ti, Zr, and REM is 5.00% or less in total, and
The method for manufacturing a welded joint according to (1) 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.
(3) A method for manufacturing a welded joint as described in (1) or (2) above, characterized in that after the flux-cored cut wire is filled into the initial layer in the groove, a solid cut wire obtained by cutting a solid wire is filled and welded.
(4) The method for manufacturing a 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.

(5) A cut wire for groove filling, which is used to fill a groove between base materials to manufacture a welded joint,
A flux-cored cut wire having a steel sheath and flux filled inside the steel sheath,
the flux contains one or more Ms point lowering elements selected from the group consisting of C, Mn, V, Cr, Ni, Cu, and Mo as a metal and/or alloy, and the Ni content is less than 50 mass% relative to the total mass of the flux-cored cut wire;
A flux-cored cut wire for groove filling, characterized in that the martensitic transformation temperature (Ms point) calculated by the following formula 1 is 450°C or lower.
Ms=613-406×[C]-64×[Mn]-32×[V]-18×[Cr]-15×[Ni]-9×[Cu]-5×[Mo]…Formula 1
(Note that the element symbols enclosed in square brackets in formula 1 represent the contents expressed as mass percentages (mass%) relative to the total mass of the flux-cored cut wire.)
(6) The flux-cored cut wire has a mass ratio to the total mass of the flux-cored cut wire of:
the total content of the Ms point lowering elements is 0.10% or more, the contents of the chemical components consisting of Si, Nb, Al, B, and Bi are Si: 2.00% or less, Nb: 0.50%, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less, and the content of the strong deoxidizing elements selected from the group consisting of Ca, Mg, Ti, Zr, and REM is 5.00% or less in total, and
The flux-cored 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) A flux-cored cut wire for groove filling as described in (5) or (6) above, characterized in that it is used by filling at least one of the first or final layer in a groove provided between base materials, or the toe of a weld bead inside or outside the groove .

According to the present invention, a welded joint having excellent fatigue resistance can be produced efficiently and simply.
Furthermore, according to the present invention, it is possible to provide a flux-cored cut wire for groove filling that can efficiently improve the fatigue strength of a weld.

FIG. 1 is an explanatory diagram showing an example of a flux-cored cut wire welding process according to the present invention (applied only to the first layer). FIG. 2 is an explanatory diagram showing another example of the flux-cored cut wire welding process according to the present invention (applied only to the final layer). FIG. 3 is an explanatory diagram showing yet another example of the flux-cored cut wire welding process according to the present invention (applied to one pass). FIG. 4 is an explanatory diagram showing still another example of the flux-cored cut wire welding process of the present invention (applied to an additional bead at the toe of a weld bead). FIG. 5 is an explanatory diagram showing the groove shape used in the evaluation of fatigue resistance in the examples and the state in which the flux-cored cut wire is filled into the groove. FIG. 6 is an explanatory diagram showing a test specimen prepared for evaluating fatigue resistance in the examples.

The present invention uses a flux-cored cut wire having a steel outer skin and flux filled inside the steel outer skin, and includes a flux-cored cut wire welding process in which the flux-cored cut wire is filled into at least a portion of a groove provided between base materials and welded, thereby manufacturing a welded joint.
Hereinafter, the flux-cored cut wire according to the present invention will be described, along with a method for manufacturing a welded joint using the same.

[Flux-cored cut wire]
First, for the flux-cored cut wire, the flux used contains one or more Ms point lowering elements selected from the group consisting of C, Mn, V, Cr, Ni, Cu, and Mo as metals and/or alloys. These Ms point lowering elements lower the Ms point of the weld metal and significantly improve the fatigue resistance of the weld. This is done by transforming the weld metal into martensitic at a low temperature range and using the volume expansion during this martensitic transformation to generate compressive residual stress in the weld, thereby reducing the tensile residual stress in the weld or imparting compressive residual stress to the weld, thereby improving the fatigue strength of the weld. Here, the Ms point is calculated by the following formula 1.
Ms=613-406×[C]-64×[Mn]-32×[V]-18×[Cr]-15×[Ni]-9×[Cu]-5×[Mo]…Formula 1
(Note that the element symbols enclosed in square brackets in formula 1 represent the contents expressed as mass percentages (mass%) relative to the total mass of the flux-cored cut wire.)

As described above, the above Ms point lowering elements (C, Mn, V, Cr, Ni, Cu, and Mo) lower the Ms point in the weld metal, so the total content of the Ms point lowering elements relative to the total mass of the flux-cored cut wire can be defined as the Ms point. In the case of the flux-cored cut wire of the present invention, the Ms point calculated from the total mass is preferably 450°C or less, preferably 400°C or less, more preferably 300°C or less, and even more preferably 250°C or less. In other words, as long as the mass ratio of the Ms point lowering elements contained in the flux is 450°C or less, the lower limit of the content of each Ms point lowering element is not particularly limited. Regarding the Ms point calculated by the above formula 1, since Ni promotes hot cracking and has high alloying costs, the upper limit should be less than 50%. Furthermore, the amount of other Ms point lowering elements C, Mn, V, Cr, Cu, and Mo added is sufficient as long as the Ms point is 450°C or lower, and there is no upper limit specified.

In addition, the flux-cored cut wire of the present invention may contain, in addition to the Ms point lowering element, for example, alloy components for controlling the chemical composition and carbon equivalent (Ceq) of the weld metal (hereinafter, these chemical components and alloy components are simply referred to as "chemical components"), and even strong deoxidizing elements. Here, the chemical components are alloy components that melt in the same way as the steel sheath during welding, so they may be included in the flux in the form of, for example, metal powder or alloy powder, or in the form of the steel sheath, or as plating on the outer surface of the steel sheath, all of which have the same effect. Note that, unlike the case of a flux-cored wire that is not a cut wire, these chemical components other than the Ms point lowering element do not need to be in the form of oxides or carbonates, and can be included in the form of metal powder or alloy powder as described above, since arc stability and all-position weldability are not required. As for the strong deoxidizing elements, for example, one or more of Ca, Mg, Ti, Zr, and REM (rare earth metals) may be added to the flux-cored cut wire as oxides and/or alloys, preferably as ferroalloys or oxides. By using them as oxides and/or alloys, the oxides are spherical, and the alloys are easily deformed, so that the flux-cored cut wire is less likely to break during production, especially when drawing the wire. Here, REM refers to a total of 17 elements, including 15 elements with atomic numbers 57 to 71, and two elements Sc and Y, and any one of these elements or a mixture of two or more of them may be used. The REM content is the total content of the 17 elements.

Specifically, the flux-cored cut wire of the present invention contains, as a metal and/or alloy, one or more of the Ms point lowering elements selected from the group consisting of C, Mn, V, Cr, Ni, Cu, and Mo in a total amount of 0.10% or more by mass relative to the total mass of the flux-cored cut wire, the content of Ni is less than 50% by mass relative to the total mass of the flux-cored cut wire, and the flux-cored cut wire further contains, as an optional component, one or more of the Ms point lowering elements selected from the group consisting of Si, Nb, Al, B, and Bi. and one or more strong deoxidizing elements selected from the group consisting of Ca, Mg, Ti, Zr, and REM, and the contents of the chemical components are Si: 2.00% or less, Nb: 0.50% or less, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less, respectively, the total content of the strong deoxidizing elements is 5.00% or less, and the impurity elements consisting of P and S are P: 0.030% or less and S: 0.020% or less, respectively.
In the present invention, since the inclusion of the above-mentioned Ms point lowering elements makes it possible to improve fatigue properties without including the above-mentioned optional chemical components and strong deoxidizing elements, the lower limit of each of the contents of these optional chemical components and strong deoxidizing elements is 0%.

The optional chemical components and strong deoxidizing elements will be described below.
Regarding the optional chemical components, "Si: 2.00% or less", Si is a deoxidizing element and has the function of reducing the amount of oxygen in the weld metal and increasing the cleanliness of the weld metal. If the Si content in the flux-cored cut wire exceeds 2.00%, Si deteriorates the toughness of the weld metal. In order to stably ensure the toughness of the weld metal, the upper limit of the 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%.

Regarding "Nb: 0.50% or less", since Nb 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, it is not preferable for the Nb content to exceed 0.50%, because Nb forms coarse precipitates in the weld metal and deteriorates the toughness of the weld metal. The upper limit of the Nb content is preferably 0.40%, 0.30%, 0.20%, or 0.10%.

Regarding "Al: 1.70% or less", Al is a deoxidizing element, and like Si, it reduces the amount of oxygen in the weld metal and has the effect of improving the cleanliness of the weld metal. If the Al content in the flux-cored cut wire exceeds 1.70%, Al forms nitrides and oxides, etc., reducing the toughness of the weld metal. Therefore, the upper limit of the Al content in the flux-cored cut wire is set to 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%.

Regarding "B: 0.020% or less", since B is not an essential component, the lower limit of the B content in the flux-cored cut wire is 0%. On the other hand, B combines with solute N in the weld metal to form BN, and therefore has the effect of reducing the adverse effect of solute N on the toughness of the weld metal. In addition, B also has the effect of improving the strength of the weld metal by increasing the hardenability of the weld metal. Therefore, the flux-cored cut wire may contain 0.0005% or more of B. However, if the B content exceeds 0.020%, the B in the weld metal becomes excessive, forming coarse BN and B compounds such as _Fe23 (C,B) ₆ , which deteriorates the toughness of the weld metal, and this is not preferable. The upper limit of the B content is preferably 0.015%, 0.010%, 0.005%, 0.003%, or 0.001%.

Regarding "Bi: 0.020% or less", since Bi is not an essential component, the lower limit of the Bi content in the flux-cored cut wire is 0%. On the other hand, Bi is an element that improves the removability of slag. To fully obtain this effect, it is preferable that the Bi content be 0.005% or more, 0.010% or more, or 0.012% or more. On the other hand, if the Bi content exceeds 0.020%, solidification cracks are more 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%.

In addition, the total content of Ca, Mg, Ti, Zr, and REM contained as the optional strong deoxidizing elements is preferably 5.00% or less, and each of the strong deoxidizing elements is preferably 2.00% or less. Since these strong deoxidizing elements (Ca, Mg, Ti, Zr, and REM) are not essential components, the lower limit of the content of these elements in the flux-cored cut wire is 0%. On the other hand, these strong deoxidizing elements are elements that improve hot cracking resistance. In order to fully obtain this effect, it is preferable that the total content of these strong deoxidizing elements is 0.005% or more, 0.010% or more, or 0.012% or more. On the other hand, if the total content of these strong deoxidizing elements exceeds 5.00%, oxides in the weld metal will aggregate and the toughness will be easily deteriorated, so the upper limit is 4.90%. This upper limit is preferably 4.80%, more preferably 4.70%, and even 4.6%, 4.5%, and 4.0%.

In addition, P in the "P: 0.030% or less" impurity element reduces the toughness of the weld metal, so the P content in the flux-cored cut wire must be reduced as much as possible. Therefore, the lower limit of the P content is 0%. Furthermore, if the P content is 0.030% or less, the adverse effect of P on toughness falls within an acceptable range. To prevent solidification cracking of the weld metal, the P content is more preferably 0.020% or less, 0.015% or less, or 0.010% or less.

The S content in the "S: 0.020% or less" impurity element mentioned above deteriorates both the toughness and ductility of the weld metal if it is present in excess in the weld metal, so it is desirable to reduce the S content in the flux-cored cut wire as much as possible. Therefore, the lower limit of the S content is 0%. Furthermore, if the S content is 0.020% or less, the adverse effect of S on the toughness and ductility of the weld metal falls 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.

The flux-cored cut wire of the present invention may or may not contain the above-mentioned chemical components and strong deoxidizing elements, but in addition to these chemical components, strong deoxidizing elements, Ms point lowering elements, and impurity elements, it also contains Fe and impurities. Among these, Fe may be included in addition to the steel outer sheath. That is, in order to adjust the flux filling rate in the flux-cored cut wire or to improve the welding efficiency, iron powder may be included in the flux as necessary. The content of this iron powder is not particularly limited, but since oxygen attached to the surface layer of the iron powder may increase the oxygen content of the weld metal and reduce the toughness, it is preferable that the mass ratio of the total mass of the flux-cored cut wire is less than 90.0%, preferably less than 80.0%. The upper limit of the iron powder content may be limited to 8.0%, 6.0%, 4.0%, 2.0%, or 1.0%. Of course, iron powder is not essential for the flux-cored cut wire of the present invention, so the lower limit of the iron powder content is 0%.

In addition, impurities are components that are mixed in during the industrial production of flux-cored cut wire, either from the raw materials or due to various factors in the manufacturing process. These are acceptable to the extent that they do not adversely affect the flux-cored cut wire of the present invention.

In the flux-cored cut wire of the present invention, fluorides, oxides, carbonates, etc. of other metal elements other than the above-mentioned Ms point lowering elements, chemical components, strong deoxidizing elements, and impurity elements may be contained within a range that does not impair the characteristics. In this case, the fluorides, oxides, and carbonates of the other metal elements are not included in the above-mentioned Ms point lowering elements, chemical components, strong deoxidizing elements, and impurity elements, as well as the content of Fe and impurities. However, this does not mean that the fluorides, oxides, and carbonates of these other metal elements are contained. In other words, the flux-cored cut wire of the present invention has a chemical composition that contains the above-mentioned Ms point lowering elements in a predetermined ratio, and the contents of the above-mentioned chemical components, strong deoxidizing elements, and impurity elements are each within a predetermined range, with the remainder being Fe and impurities, or Fe, impurities, and fluorides, oxides, and carbonates of these other metal elements. Preferably, the chemical composition contains the aforementioned Ms point lowering elements in a specified ratio, and the contents of the aforementioned chemical components, strong deoxidizing elements, and impurity elements are each within a specified range, with the balance being Fe and impurities.

Furthermore, as long as the above-mentioned conditions are met, there are no particular limitations on the steel sheath of the flux-cored cut wire according to the present invention. For example, when the steel sheath is made of a mild steel sheath, the chemical composition of the sheath can be, for example, by mass percentage, 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, with the remainder being iron and impurities.

The flux-cored cut wire of the present invention can be obtained by cutting the wire into a predetermined length while the steel sheath is filled with flux. There is no particular restriction on the shape of the cut flux-cored cut wire, and the thin steel wire can be cut into a predetermined length to produce a shape similar to that of a general cut wire with a circular cross section. However, taking into account the fact that the wire is filled with flux, the diameter is preferably φ1.0 to φ3.0 mm. Incidentally, the diameter of a conventional cut wire is about φ1.0 to φ2.0 mm. On the other hand, the length of the flux-cored cut wire is preferably 0.5 to 3.5 mm. The length of a general cut wire is equivalent to 0.5 to 2.0 times the wire diameter.

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

Here, in order to reduce the amount of diffusible hydrogen in the weld metal, it is preferable that the amount of hydrogen contained in the flux-cored cut wire is 12 ppm or less relative to the total mass of the flux-cored cut wire. This amount of hydrogen enters during the manufacture of the flux-cored cut wire, and may increase due to moisture entering the wire during storage. Therefore, if the period between the manufacture of the cut wire and its use is long, it is desirable to store the wire while preventing moisture from entering.

The procedure for producing the flux-cored cut wire of the present invention is not particularly limited, but the following example can be given as a method for producing flux-filled wire before cutting.
First, a method for producing a seamless flux-cored cut wire in which the seam of the steel sheath is welded and there are no slit-like gaps includes the steps of preparing the flux so that the fluoride and chemical components are within a predetermined range, forming the steel strip using a forming roll while feeding the steel strip in the longitudinal direction to obtain a U-shaped open tube, supplying the flux into the open tube through the opening of the open tube, butt-welding the opposing edges of the opening of the open tube to obtain a seamless tube, drawing the seamless tube to obtain a flux-cored wire having a predetermined wire diameter, and annealing the flux-cored wire during or after the drawing step. The wire is then cut to a predetermined length to obtain the flux-cored cut wire.

Here, the butt welding is performed by electric resistance welding, laser welding, TIG welding, or the like. In addition, annealing is performed during the wire drawing process or after completion of the wire drawing process to remove moisture from the wire. Preferably, the annealing temperature is 650°C or higher and the annealing time is 4 hours or longer to reduce the H content in the wire to 12 ppm or less. However, in order to prevent deterioration of the flux, the annealing temperature is 900°C or lower. Note that instead of butt welding, wire without slit-shaped gaps can also be obtained by brazing the gaps in the steel sheath.

It is also possible to obtain a flux-cored cut wire with slit-shaped gaps without welding the seams of the steel sheath. In that case, the method is the same as the method for manufacturing a wire having a seamless shape, except that instead of the process of butt-welding the ends of an open tube to obtain a seamless tube, a process of forming an open tube and butting the ends of the open tube to obtain a tube with slit-shaped gaps is included. The method for manufacturing a wire with slit-shaped gaps may further include a process of crimping the butted ends of the open tube. In the method for manufacturing a wire with slit-shaped gaps, a tube is drawn while having slit-shaped gaps.

As described above, the flux-cored cut wire according to the present invention may be a wire cut from a seamless shape in which the seam of the steel sheath is welded and there is no slit-shaped gap, or a wire cut from a wire having a slit-shaped gap without welding the seam of the steel sheath. However, it is preferable that the flux-cored cut wire is a wire cut from a steel sheath having no slit-shaped gap. H (hydrogen) that penetrates the welded part during welding diffuses into the weld metal and the welded material, accumulates at the stress concentration part, and causes low-temperature cracking. There are various sources of H, but if the cleanliness of the welded part and the welding conditions are strictly controlled, the moisture (H ₂ O) contained in the flux-cored cut wire can be a source of H, and the amount of this moisture may affect the amount of diffusible hydrogen in the welded joint. Therefore, a wire cut from a seamless shape without slit-shaped gaps is preferable, but if the wire has slit-shaped gaps, the flux-cored cut wire may be stored, for example, in a vacuum package or in a container that can maintain a dry state.

The flux-cored cut wire of the present invention may have an oil (lubricant) applied to its surface. The lubricant applied to the filler surface has the effect of suppressing rust generation during storage. Various types of lubricants (e.g. vegetable oils such as palm oil) can be used as such lubricants, but 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). Note that, if the flux-cored cut wire has a plating on its surface, the lubricant is applied to the plating surface.

[Method of manufacturing welded joints]
Next, in manufacturing a welded joint using the above-mentioned flux-cored cut wire, the present invention includes a flux-cored cut wire welding process in which at least a part of a groove provided between base materials is filled with flux-cored cut wire and welded. That is, in manufacturing a welded joint, the flux-cored cut wire according to the present invention is filled in the groove of the base materials and welded in one or more of the first pass to the final pass. When welding is performed in only one pass, the flux-cored cut wire according to the present invention is used in that one pass.

In particular, for this flux-cored cut wire welding process, it is preferable to fill at least one of the first layer, the final layer, and the weld bead toe in the groove with the flux-cored cut wire of the present invention and perform welding. When applied to the weld bead toe, an additional bead may be added. In other words, by filling the weld at the boundary between the weld bead and the base material, where the probability of fatigue cracking is high, with flux-cored cut wire, the fatigue resistance properties of the weld can be improved.

1 and 2 each show an example of a flux-cored cut wire welding process according to the present invention.
Of these, Figure 1 shows an example of welding in which a flux-cored cut wire 4 is filled into a portion of a groove 3 provided between base materials 1 and 2, and Figures 1(a) to (c) show a case in which the flux-cored cut wire 4 of the present invention is used only for the first layer, and Figures 1(a) to (c) show a case in which the flux-cored cut wire 4 of the present invention is used only for the first layer.

First, as shown in FIG. 1(a), a backing material 5 is attached to the back surface of the base materials 1 and 2, and the first layer in the groove 3 is filled with the flux-cored cut wire 4 according to the present invention. Next, as shown in FIG. 1(b), a welding wire 6 is placed approximately at the center of the filled flux-cored cut wire 4, and an arc is generated to perform welding to form the weld metal 7. After that, as shown in FIG. 1(c) and (d), a welding wire 6 is placed on the weld metal 7 formed in the first layer without filling it with the flux-cored cut wire 4, and welding is performed to form the weld metal 8, and this operation is then repeated sequentially up to the final layer to complete the welding.

Next, Fig. 2(a) to Fig. 2(c) show cases of multi-layer welding in which the flux-cored cut wire 4 of the present invention is filled only in the final layer and welded. As shown in Fig. 2(a), after attaching a backing material 5 to the back surface of the base materials 1 and 2, a welding wire 6 is placed and welding is performed to form a weld metal 8 without filling the flux-cored cut wire 4, and then, as shown in Fig. 2(b), the same operation is repeated the necessary number of times to form the weld metal 8, and then, as shown in Fig. 2(c), the flux-cored cut wire 4 of the present invention is filled in the final layer in the groove 3, the welding wire 6 is placed approximately in the center of the filled flux-cored cut wire 4, an arc is generated, and welding is performed to form a weld metal 7 as the final layer.

As shown in FIG. 3, the flux-cored cut wire welding process according to the present invention may be performed by flux-cored cut wire filling one-pass welding in which a flux-cored cut wire is filled in the groove and welding is performed in one pass.
That is, as shown in Fig. 3(a), a backing material 5 is attached to the back surface of the base materials 1 and 2, and then the flux-cored cut wire 4 according to the present invention is dispersed so as to fill almost the entire groove 3, for example, about 80% of the height of the groove in the example of Fig. 3. Next, as shown in Fig. 3(b), a welding wire 6 is placed approximately on the center of the filled flux-cored cut wire 4, and an arc is generated to perform welding, thereby producing a welded joint by a weld metal 7 containing the flux-cored cut wire 4, as shown in Fig. 3(c).
In the example of the flux-cored cut wire welding process shown in FIG. 3, the flux-cored cut wire according to the present invention is used in almost the entire groove.

Furthermore, as shown in FIG. 4, the flux-cored cut wire welding process according to the present invention may be applied to welding when forming an additional bead on the toe of a weld bead after the main welding is completed.
That is, as shown in FIG. 4(a), the flux-cored cut wire 4 according to the present invention is scattered on the toe of the weld bead of the weld metal 7 formed after the main welding is completed, and then, as shown in FIG. 4(b), a welding wire 6 is placed approximately at the center of the scattered flux-cored cut wire 4 and an arc is generated to perform welding, thereby providing an additional weld metal 9 on the toe of the weld bead of the weld metal 7 as shown in FIG. 4(c), thereby producing a welded joint.

In these Figures 1 to 4, an example of butt welding with a so-called V-shaped groove between the base materials is shown, but in the present invention, there is no limitation on the groove shape or joint shape, and the groove shape may be, other than V-shaped, for example, I-shaped, L-shaped, K-shaped, J-shaped, X-shaped, U-shaped, H-shaped, or any other shape. The joint shape may be, other than a butt joint, any other joint shape such as a T-shaped joint or a corner joint. Furthermore, the present invention can be applied to both one-sided welding and double-sided welding. Furthermore, in the case of multi-layer welding as in the example of Figure 1, each layer may be welded in two or more passes.

The welding method (welding means) used in the present invention is not particularly limited, but in order to reliably melt the flux-cored cut wire filled in the groove, it is preferable to use submerged arc welding (SAW) or gas-shielded arc welding. However, since it may be difficult to fill the groove with the flux-cored cut wire in vertical welding or overhead welding, the welding position is preferably downward or sideways.

In addition, the manufacturing method of the welded joint in the present invention is not particularly limited in terms of the type or shape of the base material, but it is most effective when applied to joint shapes in which ensuring fatigue resistance is important. In other words, a representative example is the welding of a non-load-carrying cruciform joint. The combination of base materials forming the groove is arbitrary, and may be the same type of base material or different types of base materials.

Furthermore, while a typical method for manufacturing a welded joint produces a welded joint that includes a base steel plate (base material) and a welded joint that is composed of a weld metal and a weld heat-affected zone, the present invention uses a flux-cored cut wire that contains a specified Ms point lowering element as the groove filler, and by using a flux-cored cut wire that also contains a specified chemical component, a welded joint with excellent fatigue resistance can be produced.

(Example)
Next, the present invention will be described in more detail based on examples, etc. However, the following examples are not intended to limit the present invention, and any design changes that are made in accordance with the spirit described above and below are within the technical scope of the present invention.

The flux-cored cut wires of the present invention and comparative examples (samples with wire numbers 1 to 44) were produced by the following method.
First, a steel strip was fed in the longitudinal direction and 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 edges of the opening of the open tube were butt-welded to obtain a seamless tube. This seamless tube was drawn to obtain a flux-cored wire without slit-shaped gaps. However, at that time, some samples were made into tubes with slit-shaped gaps without seam welding, and these were drawn to obtain wire. In this way, a flux-cored wire with a final filler diameter of φ2.0 mm was experimentally produced.
During the wire drawing process, the flux-cored wires were annealed for 4 hours or more at a temperature range of 650 to 950°C. After the prototypes were produced, a lubricant was applied to the surface of some of the wires. The produced flux-cored wires were then cut to a length of 2.0 mm to prepare samples of flux-cored cut wires.
In preparing the flux, the elements C, Mn, V, Cr, Ni, Cu, and Mo shown in Table 1 were used as their respective metal (alloy) powders, and the chemical components shown in Table 2 were used as their respective metal powders, and the strong deoxidizing elements shown in Table 2 were used as their respective metal (alloy) powders, and the REM elements Ce and La were used as their respective oxides. Tables 1 and 2 show the mass proportions of each element.
The compositions of these flux-cored cut wires are shown in Tables 1 and 2.

The units of the content of each element contained as the Ms point lowering elements (C, Mn, V, Cr, Ni, Cu, and Mo), optional chemical components (Si, Nb, Al, B, and Bi), strong deoxidizing elements (Ca, Mg, Ti, Zr, Ce, and La), iron powder (Fe powder), and impurity elements (P and S) disclosed in Tables 1 and 2 are the mass percentage (mass%) relative to the total mass of the flux-cored cut wire. The Ms point of the flux-cored cut wire disclosed in Table 1 is the value calculated using the above-mentioned formula 1.

The remainder in the chemical composition of the flux-cored cut wire of the present invention (i.e., components other than the elements listed in Tables 1 and 2) is iron (including intentionally added Fe powder) and impurities. The wire structure of each flux-cored cut wire is as shown in Table 1, and unless otherwise specified in the remarks column, no oil is applied. On the other hand, each element contained in the flux-cored cut wire disclosed in Table 2 is contained in the steel sheath in the form of an alloy, or in the form of metal powder or oxide. In Tables 1 and 2, the blanks in the tables relating to the content of the Ms point lowering element, chemical component, strong deoxidizing element, and Fe powder mean that the Ms point lowering element, chemical component, strong deoxidizing element, and Fe powder are not intentionally added. In addition, the Ms point lowering element, chemical component, and strong deoxidizing element may be unavoidably mixed in.

The flux-cored cut wires (wire numbers 1 to 44) of the invention and comparative examples were evaluated by the method described below.
SAW welding was performed in one pass on SM490A with a plate thickness of 20 mm under the welding conditions in Table 3. The groove shape was a V-shape as shown in Figure 5. Flux-cored cut wire 4 was spread in the first and last layers in the groove 3. The spread thickness was 18 mm. Furthermore, NF-60 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 set perpendicular to the steel plate.

A fatigue test was carried out on the specimen with the excess weld shown in Fig. 6 prepared as described above under the conditions of a stress ratio of 0.1, a stress range of 200 MPa, and a frequency of 10 Hz, and the number of repeated cycles N was measured and evaluated. A specimen that did not break when N was 5 x ¹⁰⁶ or more was deemed to have passed. During the fatigue test, a fatigue load was applied in the direction perpendicular to the weld line direction.

The test results evaluated using the above-mentioned methods are shown in Table 4. When welding was performed using the flux-cored cut wire of the invention, all fatigue tests passed. In other words, it was confirmed that the flux-cored cut wire of the invention has extremely high fatigue resistance.

As described above, the present invention makes it possible to manufacture welded joints with excellent fatigue resistance at low cost and easily.

1, 2...base material (steel material), 3...groove, 4...flux-cored cut wire, 5...backing material, 6...welding wire, 7, 8...weld metal, 9...additional weld metal.

Claims (7)

A method for manufacturing a welded joint in which a cut wire is filled into a groove provided between base materials and welded,
The method includes filling at least one of a first layer or a final layer in the groove, or a weld bead toe in or outside the groove, with a flux-cored cut wire having a steel sheath and flux filled inside the steel sheath , and welding the weld bead in or outside the groove,
the flux contains one or more Ms point lowering elements selected from the group consisting of C, Mn, V, Cr, Ni, Cu, and Mo as a metal and/or alloy, and the Ni content is less than 50 mass% relative to the total mass of the flux-cored cut wire;
A method for manufacturing a welded joint, characterized in that the martensitic transformation temperature (Ms point) calculated by the following formula 1 is 450°C or lower.
Ms=613-406×[C]-64×[Mn]-32×[V]-18×[Cr]-15×[Ni]-9×[Cu]-5×[Mo]…Formula 1
(Note that the element symbols enclosed in square brackets in formula 1 represent the contents expressed as mass percentages (mass%) relative to the total mass of the flux-cored cut wire.) The flux-cored cut wire has a mass ratio relative to the total mass of the flux-cored cut wire of:
the total content of the Ms point lowering elements is 0.10% or more, the contents of the chemical components consisting of Si, Nb, Al, B, and Bi are Si: 2.00% or less, Nb: 0.50%, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less, and the content of the strong deoxidizing elements selected from the group consisting of Ca, Mg, Ti, Zr, and REM is 5.00% or less in total, and
2. The method for manufacturing a welded joint according to claim 1, characterized in that the contents of the impurity elements P and S are P: 0.030% or less and S: 0.020% or less. The method for manufacturing a welded joint according to claim 1 or 2, characterized in that after the flux-cored cut wire is filled into the first layer in the groove, a solid cut wire cut from a solid wire is filled and welded. The method for manufacturing a welded joint according to any one of claims 1 to 3, characterized in that the welding is submerged arc welding or gas shielded arc welding. A cut wire for groove filling that fills a groove between base materials to manufacture a welded joint,
A flux-cored cut wire having a steel sheath and flux filled inside the steel sheath,
the flux contains one or more Ms point lowering elements selected from the group consisting of C, Mn, V, Cr, Ni, Cu, and Mo as a metal and/or alloy, and the Ni content is less than 50 mass% relative to the total mass of the flux-cored cut wire;
A flux-cored cut wire for groove filling, characterized in that the martensitic transformation temperature (Ms point) calculated by the following formula 1 is 450°C or lower.
Ms=613-406×[C]-64×[Mn]-32×[V]-18×[Cr]-15×[Ni]-9×[Cu]-5×[Mo]…Formula 1
(Note that the element symbols enclosed in square brackets in formula 1 represent the contents expressed as mass percentages (mass%) relative to the total mass of the flux-cored cut wire.) The flux-cored cut wire has a mass ratio relative to the total mass of the flux-cored cut wire of:
the total content of the Ms point lowering elements is 0.10% or more, the contents of the chemical components consisting of Si, Nb, Al, B, and Bi are Si: 2.00% or less, Nb: 0.50%, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less, and the content of the strong deoxidizing elements selected from the group consisting of Ca, Mg, Ti, Zr, and REM is 5.00% or less in total, and
6. The flux-cored cut wire for groove filling according to claim 5, characterized in that the contents of impurity elements P and S are P: 0.030% or less and S: 0.020% or less. 7. The flux-cored cut wire for groove filling according to claim 5 or 6, characterized in that the flux- cored cut wire is used by filling at least one of a first layer or a final layer in a groove provided between base materials, or a toe of a weld bead inside or outside the groove.

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