JP2022061826A - Method for manufacturing weld joint, and flux-cored cut wire for groove filling - Google Patents

Abstract

To provide a method for manufacturing a weld joint which can obtain a weld joint excellent in fatigue resistance characteristics, and a flux-cored cut wire used in the same.SOLUTION: There are provided a method for filling any one of an initial layer, a final layer and a weld bead toe in a groove with a flux-cored cut wire having a steel sheath and a flux that is made to fill the inside of the steel sheath, and welding the groove in which the flux contains a Ms point low temperature element (C, Mn, V, Cr, Ni, Cu and Mo), a Ni content is less than 50 mass% in a mass ratio of the flux-cored cut wire to the total mass, and the Ms point is 450°C or lower; and a flux-cored cut wire used in the same.SELECTED DRAWING: None

Description

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

In recent years, the demand for safety of structural materials has become more and more stringent. The requirements include, for example, mechanical properties (tensile strength and toughness) and fatigue resistance properties. The fatigue resistance property is a fracture resistance property against repeated stress and is evaluated by fatigue strength. Fatigue strength is the upper limit of the stress amplitude that does not break even when stress is applied an infinite number of times when stress is repeatedly applied to the material, and is obtained by a fatigue test. Materials with high fatigue resistance are suitable for structures that are regularly exposed to violent vibrations.

Generally, the welded part of the structure (the weld metal, which is a metal melted and solidified during welding, and the mother whose structure, metallurgical properties, mechanical properties, etc. have changed due to welding heat but have not melted and solidified. The fatigue resistance of the part including the heat-affected zone, which is the part of the material) tends to be lower than that of the base material, and therefore the welded part tends to be the starting point of fatigue failure. Techniques as disclosed in Patent Documents 1 and 2 have been proposed in order to improve the fatigue resistance of the welded portion.

In Patent Document 1, Ni is added to the flux-cored wire and N and C are positively added from the flux, and a low oxygen MAG or MIG welding method is adopted, whereby the phase transformation temperature (Ms point) of the weld metal is obtained. A wire containing a high Ni flux is disclosed for the purpose of obtaining a welded portion having excellent fatigue strength by reducing the amount of the wire (see claim 1 and paragraph 0022, etc.). In welding using this weld wire, whether the weld metal is subjected to martensite transformation in a low temperature range and the volume expansion during this transformation is used to generate compressive residual stress in the weld to reduce the tensile residual stress in the weld. Alternatively, the fatigue strength of the weld is improved by applying compressive residual stress to the weld.

Patent Document 2 discloses a flux-cored wire that reduces oxygen in a weld metal by adding CaF ₂ to a wire containing a high Ni flux, 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 material of the above-mentioned prior art is used only in a place where fatigue cracks occur (for example, a weld bead toe), it takes time and effort to switch the welding wire, and the construction efficiency deteriorates. There's a problem.

For the reasons described above, the industrial world is required to develop a method for manufacturing a welded joint having high efficiency and excellent fatigue resistance and a welding material.

Japanese Unexamined Patent Publication No. 2007-296535 Japanese Unexamined Patent Publication No. 2014-050882

Therefore, as a result of diligent studies on a method capable of efficiently improving the fatigue strength of the welded portion, the present inventors fill the groove with a flux-cored cut wire containing a predetermined element and perform welding. By doing so, it was found that the above-mentioned problems could be solved, and the present invention was completed.

Therefore, an object of the present invention is to provide a method for manufacturing a welded joint capable of efficiently improving the fatigue strength of the welded portion.
Another object of the present invention is to provide a flux-cored cut wire used in such a method for manufacturing 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 in a groove provided between base materials and welded.
A method in which a flux-cored cut wire having a steel outer skin and a flux filled inside the steel outer skin is filled in any of the first layer, the final layer, and the toe of the weld bead in the groove and welded. And
The flux contains one or more Ms point cooling elements selected from the group consisting of C, Mn, V, Cr, Ni, Cu, and Mo as a metal and / or an alloy, and also contains the Ni. The amount is less than 50% by mass as a mass ratio 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 x [C] -64 x [Mn] -32 x [V] -18 x [Cr] -15 x [Ni] -9 x [Cu] -5 x [Mo] ... Equation 1
[However, the element symbol enclosed in square brackets in Equation 1 is the content represented by the mass ratio (mass%) to the total mass of the flux-containing cut wire. ]
(2) The flux-cored cut wire is a mass ratio of the flux-cored cut wire to the total mass.
The total content of the Ms point lowering element is 0.10% or more, and the content of the chemical component composed of Si, Nb, Al, B, and Bi is Si: 2.00% or less, Nb: 0. Selected from the group consisting of 50%, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less, and Ca, Mg, Ti, Zr, and REM. The total content of strongly deoxidized elements is 5.00% or less, and
The method for manufacturing a welded joint according to (1) above, wherein the content of the impurity element composed of P and S is P: 0.030% or less and S: 0.020% or less.
(3) The above-mentioned (1) or (2), wherein the flux-cored cut wire is filled in the first layer in the groove, and then the solid cut wire cut from the solid wire is filled and welded. How to manufacture welded joints.
(4) The method for manufacturing a welded joint according to any one of (1) to (3) above, wherein the welding is submerged arc welding or gas shielded arc welding.

(5) A cut wire for groove filling that fills the groove provided between the base materials to manufacture a welded joint.
It has a steel husk and a flux filled inside this steel husk,
The flux contains one or more Ms point cooling elements selected from the group consisting of C, Mn, V, Cr, Ni, Cu, and Mo as a metal and / or an alloy, and also contains the Ni. The amount is less than 50% by mass as a mass ratio to the total mass of the flux-cored cut wire.
A flux-containing cut wire for groove filling, wherein the martensitic transformation temperature (Ms point) calculated by the following formula 1 is 450 ° C. or lower.
Ms = 613-406 x [C] -64 x [Mn] -32 x [V] -18 x [Cr] -15 x [Ni] -9 x [Cu] -5 x [Mo] ... Equation 1
[However, the element symbol enclosed in square brackets in Equation 1 is the content represented by the mass ratio (mass%) to the total mass of the flux-containing cut wire. ]
(6) The flux-cored cut wire is a mass ratio of the flux-cored cut wire to the total mass.
The total content of the Ms point cooling element is 0.10% or more, and the content of the chemical component composed of Si, Nb, Al, B, and Bi is Si: 2.00% or less, Nb: 0. Selected from the group consisting of 50%, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less, and Ca, Mg, Ti, Zr, and REM. The total content of strongly deoxidized elements is 5.00% or less, and
The flux-containing cut wire for groove filling according to (5) above, wherein the content of the impurity element composed of P and S is P: 0.030% or less and S: 0.020% or less.
(7) The above-mentioned (5) or (6), wherein the first layer, the last layer, and the toe of the weld bead in the groove provided between the base materials are filled and used. Flux-filled cut wire for groove filling.

According to the present invention, a welded joint having excellent fatigue resistance can be manufactured efficiently and easily.
Further, 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 the welded portion.

FIG. 1 is an explanatory diagram showing an example of a flux-cored cut wire welding process in the present invention (when applied only to the first layer). FIG. 2 is an explanatory diagram showing another example (when applied only to the final layer) of the flux-cored cut wire welding process in the present invention. FIG. 3 is an explanatory diagram showing still another example (when applied to one pass) of the flux-cored cut wire welding process in the present invention. FIG. 4 is an explanatory diagram showing still another example of the flux-cored cut wire welding process in the present invention (when applied to an additional bead at the toe of a weld bead). FIG. 5 is an explanatory diagram showing how the groove shape and the flux-cored cut wire used for the evaluation of fatigue resistance are filled in the groove in the embodiment. FIG. 6 is an explanatory diagram showing a test piece prepared for evaluation of fatigue resistance in Examples.

The present invention uses a flux-cored cut wire having a steel outer skin and a flux filled inside the steel outer skin, and the flux is contained in at least a part of the groove provided between the base materials. A welded joint is manufactured so as to include a flux-cored cut wire welding process for filling and welding the cut wire.
Hereinafter, the flux-cored cut wire according to the present invention will be described, and a method for manufacturing a welded joint using the cut wire will be described.

[Cut wire with flux]
First, with respect to the flux-cored cut wire, as the flux, one or more Ms point cooling elements selected from the group consisting of C, Mn, V, Cr, Ni, Cu, and Mo are used as metals and / or. Use what is included as an alloy. These elements for lowering the temperature of the Ms point have the function of lowering the temperature of the Ms point of the weld metal and remarkably improving the fatigue resistance of the welded portion. This causes the weld metal to undergo martensite transformation in the low temperature range, and the volume expansion during this martensite transformation is used to generate compressive residual stress in the weld, thereby reducing the tensile residual stress in the weld. By applying compressive residual stress to the welded portion, the fatigue strength of the welded portion is improved. Here, the Ms point is calculated by the following equation 1.
Ms = 613-406 x [C] -64 x [Mn] -32 x [V] -18 x [Cr] -15 x [Ni] -9 x [Cu] -5 x [Mo] ... Equation 1
[However, the element symbol enclosed in square brackets in Equation 1 is the content represented by the mass ratio (mass%) to the total mass of the flux-containing cut wire. ]

As described above, the above-mentioned elements for lowering the temperature of the Ms point (C, Mn, V, Cr, Ni, Cu, and Mo) lower the temperature of the Ms point in the weld metal. The total content of the Ms point cooling element with respect to the total mass of the above can be specified by the Ms point. In the case of the flux-containing cut wire of the present invention, the Ms point calculated from the total mass thereof is preferably 450 ° C. or lower, preferably 400 ° C. or lower, and more preferably 300 ° C. or lower. It is preferable that the temperature is 250 ° C. or lower. That is, as long as the mass ratio of the Ms point cooling element contained in the flux is 450 ° C. or less, the lower limit of the content of each Ms point cooling element is not particularly limited. Regarding the Ms point calculated by the above equation 1, Ni promotes high temperature cracking and the alloy cost is high, so the upper limit is preferably less than 50%, and other Ms point lowering. Regarding the amount of the elements C, Mn, V, Cr, Cu, and Mo added, the Ms point may be 450 ° C. or lower, and the upper limit thereof is not specified.

Further, in the flux-containing cut wire in the present invention, in addition to the Ms point cooling element, for example, an alloy component for controlling the chemical component, carbon equivalent (Ceq), etc. of the weld metal (hereinafter, these chemical components and alloy components). Is simply referred to as a “chemical component”), and may further contain a strongly deoxidizing element. Here, since the chemical component is an alloy component and melts in the same manner as the steel outer skin during welding, it may be included in the flux in the form of metal powder or alloy powder, for example, and the steel outer skin may be included. It may be contained in the form or may be contained as a plating on the outer surface of the steel outer skin, both of which have the same effect. It should be noted that these chemical components other than the Ms point low temperature element are in the state of oxides and carbonates because arc stability and omnidirectional weldability are not required as in the case of flux-filled wires that are not cut wires. It does not have to be, and can be contained in the form of the metal powder or alloy powder as described above. As for the strongly deoxidizing element, for example, one or more of Ca, Mg, Ti, Zr, and REM [Rare Earth Metals] are used as oxides and / or alloys to cut with flux. It is preferably added to the wire, preferably as an alloy iron or oxide. By using it as an oxide and / or an alloy, the oxide is spherical and the alloy is easily deformed, so that it is difficult to break when manufacturing a flux-cored cut wire, especially when the wire is drawn. .. Here, the REM refers to 15 elements having atomic numbers 57 to 71 and a total of 17 elements including two elements Sc and Y, and any one of them, or a mixture of two or more kinds can be used. The content of REM is the total content of the 17 elements.

Specifically, the flux-containing cut wire of the present invention is a group consisting of C, Mn, V, Cr, Ni, Cu, and Mo, which are elements for lowering the temperature at the Ms point, in terms of mass ratio to the total mass of the flux-containing cut wire. Contains any one or more selected from the above as a metal and / or alloy in a total ratio of 0.10% or more, and the Ni content is the mass ratio to the total mass of the flux-containing cut wire. From less than 50% and, as optional components, one or more chemical components selected from the group consisting of Si, Nb, Al, B, and Bi, and Ca, Mg, Ti, Zr, and REM. Contains one or more strongly deoxidizing elements selected from the above group, and the content of each of the chemical components is 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, and the total content of the strongly deoxidizing element is 5.00% or less, and from P and S. Contains P: 0.030% or less and S: 0.020% or less, respectively.
In the present invention, by including the above-mentioned Ms point lowering element, it is possible to improve the fatigue characteristics without containing the chemical component and the strongly deoxidizing element as the above-mentioned optional components. The lower limit of the respective contents of the chemical component and the strongly deoxidizing element is 0%.

Hereinafter, the chemical composition and the strongly deoxidizing element as the above optional components will be described.
Regarding the chemical component as an optional component, "Si: 2.00% or less", Si is a deoxidizing element and has a function of reducing the amount of oxygen in the weld metal and increasing the cleanliness of the weld metal. When the Si content in the flux-cored cut wire exceeds 2.00%, Si deteriorates the toughness of the weld metal. In order to stably secure 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 the fine carbides cause precipitation strengthening in the weld metal, so that Nb improves the tensile strength of the weld metal. In order to obtain the effect sufficiently, the Nb content is preferably 0.005% or more. However, it is not preferable that the Nb content exceeds 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 an effect of improving the cleanliness of the weld metal. When the Al content in the flux-cored cut wire exceeds 1.70%, Al forms nitrides, oxides and the like, and reduces 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, since B is combined with the solid solution N in the weld metal to form a BN, it has an effect of reducing the adverse effect of the solid solution N on the toughness of the weld metal. Further, B has an effect of improving the strength of the weld metal because it enhances the hardenability of the weld metal. Therefore, the flux-cored cut wire may contain 0.0005% or more of B. However, when the B content exceeds 0.020%, B in the weld metal becomes excessive, forming coarse BN and B compounds such as Fe ₂₃ (C, B) ₆ and deteriorating the toughness of the weld metal. It is not preferable because it causes 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 peelability of slag. In order to sufficiently obtain the effect, the Bi content is preferably 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 cracks are likely to occur in the weld metal, so the upper limit of the Bi content is 0.020%. The upper limit of this Bi content is preferably 0.015%, 0.010%, or 0.005%.

Further, the total content of Ca, Mg, Ti, Zr, and REM contained as the above-mentioned optional components as the strongly deoxidizing elements is 5.00% or less, and each of the strongly deoxidizing elements has a total content of 5.00% or less. The content is preferably 2.00% or less. Since these strongly 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 strongly deoxidizing elements are elements that improve high temperature crack resistance. In order to sufficiently obtain the effect, the total content of these strongly deoxidizing elements is preferably 0.005% or more, 0.010% or more, or 0.012% or more. On the other hand, if the total content of these strongly deoxidizing elements exceeds 5.00%, the oxides in the weld metal aggregate and the toughness tends to deteriorate, so the upper limit is 4.90%. This upper limit is preferably 4.80%, more preferably 4.70%, and further 4.6%, 4.5%, 4.0%.

Further, since P in "P: 0.030% or less" existing as the impurity element lowers the toughness of the weld metal, it is necessary to reduce the P content in the flux-cored cut wire as much as possible. Therefore, the lower limit of the P content is 0%. Further, when the P content is 0.030% or less, the adverse effect on the toughness of P is within an acceptable range. More preferably, the P content is 0.020% or less, 0.015% or less, or 0.010% or less in order to prevent solidification cracking of the weld metal.

If S in "S: 0.020% or less" existing as the impurity element is excessively present in the weld metal, both the toughness and ductility of the weld metal are deteriorated. Therefore, the S content in the flux-cored cut wire is as much as possible. It is desirable to reduce it. Therefore, the lower limit of the S content is 0%. Further, when 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.

The flux-containing cut wire in the present invention may or may not contain the above-mentioned chemical components and strongly deoxidizing elements, but these chemical components, the strongly deoxidizing elements, the Ms point lowering element, and the elements may be contained. Other than the impurity element, Fe and impurities. Of these, Fe may contain iron powder in addition to the steel outer skin. That is, iron powder may be contained in the flux, if necessary, in order to adjust the packing rate of the flux in the flux-containing cut wire or to improve the welding efficiency. The content of this iron powder is not particularly limited, but it is possible that the oxygen adhering to the surface layer of the iron powder increases the oxygen content of the weld metal and lowers the toughness. The mass ratio to total mass should be 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, since iron powder is not essential in the flux-cored cut wire according to the present invention, the lower limit of the iron powder content is 0%.

Impurities are components derived from raw materials or mixed due to various factors in the manufacturing process when the flux-cored cut wire is industrially manufactured. These are meant to be permissible as long as they do not adversely affect the flux-cored cut wire according to the present invention.

In the flux-containing cut wire of the present invention, the above-mentioned Ms point cooling element, chemical component, strongly deoxidizing element, and fluorides, oxides, carbonates, and the like of other metal elements other than the impurity element are also the characteristics thereof. May be contained within a range that does not impair. In this case, the fluorides, oxides, and carbonates of the other metal elements are included in the contents of the above-mentioned Ms point lowering element, chemical component, strongly deoxidizing element, and impurity element, as well as Fe and impurities. It shall not be possible. However, it means that the case where these other metal elements such as fluorides, oxides and carbonates are contained is not excluded. That is, the flux-containing cut wire in the present invention contains the above-mentioned Ms point lowering element in a predetermined ratio, and the contents of the above-mentioned chemical component, strongly deoxidizing element, and impurity element are each in a predetermined range. The balance has a chemical composition of Fe and impurities, or Fe, impurities, and fluorides, oxides, and carbonates of these other metal elements. Preferably, the above-mentioned Ms point lowering element is contained in a predetermined ratio, and the contents of the above-mentioned chemical component, strongly deoxidizing element, and impurity element are each in a predetermined range, and the balance is a chemistry consisting of Fe and impurities. Has a composition.

Further, as long as the above-mentioned 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 is made of a mild steel outer skin, the chemical composition of the outer skin is, for example. , 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 may be iron and impurities.

The flux-cored cut wire in the present invention can be obtained by finely cutting the wire into a predetermined length in the form of a wire in which the inside of the steel outer skin is filled with flux. There is no particular limitation on the shape of the cut wire containing flux, and the small-diameter steel wire can be cut into small pieces to a predetermined length to make it similar to a general cut wire having a circular cross section. However, considering that the flux is filled, the diameter thereof 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-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.

Further, 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% as a mass ratio to the total mass of the flux-cored cut wire. Further, 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, the amount of hydrogen contained in the flux-cored cut wire is preferably 12 ppm or less with respect to the total mass of the flux-cored cut wire. This amount of hydrogen invades during the manufacture of the flux-cored cut wire and may increase due to the intrusion of moisture during storage of the flux-cored cut wire. Therefore, the period from the manufacture of the cut wire to its use is long. In some cases, it is desirable to store it while preventing the ingress of moisture.

In manufacturing the flux-cored cut wire in the present invention, the procedure and the like are not particularly limited, but the following example can be shown as a method for manufacturing the wire filled with the flux before cutting.
First, as a method for manufacturing a seamlessly shaped flux-containing cut wire in which the seam of the steel outer skin is welded and there is no slit-shaped gap, a step of preparing the flux so that the fluoride and chemical components are within a predetermined range. In addition, a process of forming a U-shaped open tube by forming it using a forming roll while feeding the steel strip in the longitudinal direction, a process of supplying flux into the open tube through the opening of the open tube, and a process of supplying flux to the open tube. The process of butt-welding the opposing edges of the openings to obtain a seamless tube, the process of drawing a seamless tube to obtain a flux-containing wire having a predetermined wire diameter, and the process of drawing a wire are in the middle or completed. It is later provided with a step of quenching the flux-containing wire. Then, by cutting the wire to a predetermined length, a flux-cored cut wire can be obtained.

Here, the butt welding is performed by electric stitch welding, laser welding, TIG welding, or the like. Further, during the wire drawing process or after the wire drawing process is completed, annealing is performed to remove water in the wire. Preferably, the annealing temperature is 650 ° C. or higher and the annealing time is 4 hours or longer so that the H content contained in the wire is 12 ppm or less. However, in order to prevent deterioration of the flux, the annealing temperature is set to 900 ° C. or lower. Even if the gaps in the steel outer skin are brazed instead of the butt welding, a wire having no slit-shaped gaps can be obtained.

Further, it is also possible to obtain a flux-cored cut wire having a slit-shaped gap without welding the seam of the steel outer skin. In that case, instead of the process of butt-welding the ends of the open pipes to obtain a seamless pipe, the process of forming an open pipe and butt-butting the ends of the open pipes to obtain a pipe with a slit-shaped gap is performed. It is the same as the method for manufacturing a wire having a seamless shape except that the wire has a seamless shape. The method of manufacturing a wire having a slit-like gap may further include a step of crimping the end of the abutted open tube. In the method of manufacturing a wire having a slit-shaped gap, the pipe is drawn with the slit-shaped gap.

As described above, the flux-containing cut wire according to the present invention may be a wire having a seamless shape in which the seam of the steel outer skin is welded and has no slit-shaped gap, and the seam of the steel outer skin may be cut. A wire having a slit-shaped gap may be cut without being welded, but a flux-containing cut wire obtained by cutting a wire having no slit-shaped gap in a steel outer skin is preferable. .. H (hydrogen) that invades the welded portion during welding diffuses into the weld metal and the material to be welded, accumulates in the stress concentration portion, and causes low-temperature cracking. There are various sources of H, but if the cleanliness of the weld and the welding conditions are strictly controlled, the moisture (H ₂ O) contained in the flux-cored cut wire can be the source of H. Therefore, the amount of this water may affect the amount of diffusible hydrogen in the welded joint. Therefore, it is desirable to cut a seamlessly shaped wire without a slit-shaped gap, but if the wire having a slit-shaped gap is cut, for example, it is vacuum-packed and stored or dried. The flux-packed cut wire may be stored in a container that can hold the state.

Further, the flux-cored cut wire in the present invention may have an oil (lubricant) coated on its surface. The lubricant applied to the surface of the filler has the effect of suppressing the generation of rust during storage. As such a lubricant, various kinds (for example, vegetable oil such as palm oil) can be used, but in order to suppress low temperature cracking of the weld metal, a perfluoropolyether oil containing no H (hydrogen) is used. It is preferable to use (PFPE oil). When the flux-cored cut wire has plating on its surface, the lubricant is applied to the surface of the plating.

[Manufacturing method of welded joint]
Next, in manufacturing a welded joint using the above-mentioned flux-cored cut wire, in the present invention, at least a part of the groove provided between the base materials is filled with the flux-cored cut wire and welded. Provide a wire welding process. 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 metal and welded in any one or more of one pass to the final pass. If there is only one pass for welding, the flux-cored cut wire of the present invention is used in that one pass.

In particular, in this flux-cored cut wire welding step, at least one of the first layer, the final layer, and the toe of the weld bead in the groove is filled with the flux-cored cut wire according to the present invention and welded. Is preferable. When applied to the toe of the weld bead, an additional bead may be used. That is, by filling the welded portion at the boundary between the weld bead and the base metal, which has a high probability of generating fatigue cracks, with a flux-cored cut wire, the fatigue resistance characteristics of the welded portion can be improved.

1 and 2 show an example of a flux-cored cut wire welding process in the present invention, respectively.
Of these, FIG. 1 is an example in which a flux-cored cut wire 4 is filled in a part of the groove 3 provided between the base material 1 and the base material 2 and welded. )-(C) show the case where the flux-cored cut wire 4 of the present invention is used only for the first layer, and in FIGS. 1 (a)-(c), the flux of the present invention is used only for the first layer. The case where the insert cut wire 4 is used is shown.

First, as shown in FIG. 1A, the backing material 5 is attached to the back surfaces of the base materials 1 and 2, and then the first layer in the groove 3 is filled with the flux-containing cut wire 4 according to the present invention. do. Next, as shown in FIG. 1 (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 to perform welding to obtain the weld metal 7. After that, as shown in FIGS. 1 (c) and 1 (d), the welding wire 6 is arranged and welded on the weld metal 7 formed in the initial layer without filling the flux-cored cut wire 4. Is performed to form the weld metal 8, and this operation is continuously repeated until the final layer to complete the welding.

Next, FIGS. 2 (a) to 2 (c) show the case of multi-layer welding in which the flux-containing cut wire 4 of the present invention is filled only in the final layer and welded. As shown, after the backing material 5 is attached to the back surfaces of the base materials 1 and 2, the welding wire 6 is arranged and welded to form the weld metal 8 without filling the flux-containing cut wire 4. Then, as shown in FIG. 2 (b), the same operation is continuously repeated as many times as necessary to form the weld metal 8, and then, as shown in FIG. 2 (c), the present invention is applied to the final layer in the groove 3. The flux-containing cut wire 4 according to the above is filled, a welding wire 6 is arranged on a substantially central portion of the filled flux-containing cut wire 4, an arc is generated to perform welding, and a weld metal 7 as a final layer is obtained. Form.

Further, as shown in FIG. 3, the flux-cored cut wire welding process according to the present invention comprises flux-cored cut wire filling 1-pass welding in which the flux-filled cut wire is filled in the groove and welded in one pass. You may do it.
That is, as shown in FIG. 3A, after the backing material 5 is attached to the back surfaces of the base materials 1 and 2, in the example of FIG. 3, almost all of the groove 3 is, for example, a groove. The flux-containing cut wire 4 according to the present invention is sprayed so as to fill about 80% of the inner height. Next, as shown in FIG. 3 (b), the welding wire 6 is placed on the substantially central portion of the filled flux-cored cut wire 4, and an arc is generated for welding, as shown in FIG. 3 (c). As described above, the welded joint is manufactured by the weld metal 7 including the flux-cored cut wire 4.
In the example of the flux-cored cut wire welding step shown in FIG. 3, the flux-cored cut wire according to the present invention is used in almost all of the grooves.

Further, as shown in FIG. 4, the flux-cored cut wire welding step according to the present invention may be applied to welding when an additional bead is applied to the toe of the weld bead after the main welding is completed.
That is, as shown in FIG. 4 (a), the flux-containing cut wire 4 according to the present invention is sprayed on the weld bead toe of the weld metal 7 formed after the main welding, and then FIG. 4 (b). As shown in FIG. 4, the weld metal 7 is arranged as shown in FIG. 4 (c) by arranging the welding wire 6 on the substantially central portion of the sprayed flux-containing cut wire 4 and generating an arc for welding. An additional weld metal 9 is provided at the toe of the weld bead of the above, and a welded joint is manufactured.

In FIGS. 1 to 4, the groove between the base materials is an example of so-called V-shaped groove butt welding, but in the present invention, the groove shape and the joint shape are not limited, and the V-shaped groove is used. In addition to the above, for example, a groove shape such as I-type, Les-type, K-type, J-type, X-type, U-type, H-type, or any other shape may be used. The joint shape may be any joint shape other than these, such as a T-shaped joint, a square turning joint, and the like, in addition to the butt joint. Further, in the present invention, single-sided welding may be used, and double-sided welding may be applicable. Further, in the case of multi-layer welding as in the example of FIG. 1, each layer may be divided into two or more passes for welding.

The welding method (welding means) used in the present invention is not particularly limited, but is preferably Submerged Arc Welding (SAW) in order to reliably melt the flux-containing cut wire filled in the groove. Alternatively, it may be gas shielded arc welding. However, in vertical welding or upward welding, it may be difficult to fill the groove with the flux-cored cut wire, so it is desirable that the welding posture is downward or sideways.

Further, in the method for manufacturing a welded joint in the present invention, the type and shape of the base metal are not particularly limited, but the most effective application is in a joint shape in which it is important to ensure fatigue resistance. That is, it is typically welding of a load non-transmission type cross joint. The combination of the base materials forming the groove is arbitrary, and the base materials of the same type may be used, or the base materials may be different from each other.

Further, in general, in the method of manufacturing a welded joint, a welded joint including a base metal plate (base material) and a welded portion composed of a weld metal and a welded heat-affected portion can be obtained. Since a flux-filled cut wire containing an element for lowering the temperature of the Ms point is used as a groove filler, a welded joint having excellent fatigue resistance can be obtained by using a flux-filled cut wire further containing a predetermined chemical component. Will be.

(Example)
Next, the present invention will be described more specifically based on examples and the like. However, the following examples do not have the property of limiting the present invention, and it is within the technical scope of the present invention to change the design only for the purposes of the preceding and the following.

The flux-cored cut wires (samples of wire numbers 1 to 44) of the present invention example and the comparative example were manufactured by the following method.
First, a U-shaped open pipe was obtained by molding using a forming roll while feeding the steel strip in the longitudinal direction. Flux was supplied into the open pipe through the opening of the open pipe, and the opposing edges of the opening of the open pipe were butt-welded to obtain a seamless pipe. This seamless tube was drawn to obtain a flux-cored wire having no slit-shaped gap. However, at that time, some of the samples were made into a tube having a slit-shaped gap without seam welding, and the wire was drawn to form a wire. In this way, a wire containing a flux having a final filler diameter of φ2.0 mm was prototyped.
In the middle of the wire drawing work of these wires, the flux-cored wire was annealed in the temperature range of 650 to 950 ° C. for 4 hours or more. After the trial production, a lubricant was applied to the surface of some wires. Then, the produced flux-cored wire was cut to a length of 2.0 mm, and each sample of the flux-cored cut wire was prepared.
Then, in preparing the above flux, the Ms point cooling elements shown in Table 1 are used as the metal (alloy) powder for each element of C, Mn, V, Cr, Ni, Cu, and Mo. Further, regarding the chemical components shown in Table 2, each element of Si, Nb, Al, B, and Bi is used as the metal powder thereof, and the strongly deoxidizing elements shown in Table 2 are Ca, Mg, and Ti. Was used as a metal (alloy) powder, and each element of Ce and La, which are REM elements, was used as an oxide thereof. In addition, Tables 1 and 2 show the mass ratio of each element.
The configurations of these flux-cored cut wires are shown in Tables 1 and 2.

Ms point cooling elements (C, Mn, V, Cr, Ni, Cu, and Mo) disclosed in Tables 1 and 2, and chemical components as optional components (Si, Nb, Al, B, and Bi). The unit of content of each element contained as strongly deoxidizing elements (Ca, Mg, Ti, Zr, Ce, and La), iron powder (Fe powder), and impurity elements (P and S) is cut with flux. The mass ratio (% by mass) to the total mass of the wire. Further, the Ms point of the flux-cored cut wire disclosed in Table 1 is a value obtained by the above-mentioned formula 1.

Further, the balance in the chemical composition of the flaked cut wire of the present invention (that is, components other than the elements shown in Tables 1 and 2) is iron (including intentionally added Fe powder) and impurities. be. The wire structure of each flux-cored cut wire is as shown in Table 1, and oil is not applied unless otherwise specified in the remarks column. On the other hand, each element contained in the flux-cored cut wire disclosed in Table 2 is contained in the steel outer skin in the form of an alloy, or in the form of a metal powder or an oxide. In Tables 1 and 2, the blanks in the table relating to the contents of the Ms point lowering element, the chemical component, the strongly deoxidizing element, and the Fe powder are the Ms point lowering element, the chemical component, and the strongly deoxidizing element. It means that no element and Fe powder are intentionally added. In addition, Ms point low temperature element, chemical component, and strong deoxidizing element may be inevitably mixed.

The flux-cored cut wires (wire numbers 1 to 44) of the invention example and the comparative example were evaluated by the method described below.
The SM490A having a plate thickness of 20 mm was subjected to SAW welding in one pass under the welding conditions shown in Table 3. At that time, the groove shape was V-shaped as shown in FIG. Flux-containing cut wire 4 was sprayed on the first layer and the final layer in the groove 3. The spray thickness was 18 mm. Furthermore, NF-60 manufactured by Nippon Steel & Sumikin Welding & Co., Ltd. was used as the welding flux, and Y-DS (wire diameter φ4.8 mm) manufactured by Nippon Steel & Sumikin Welding & Co., Ltd. was used as the welding wire. The weld wire was installed perpendicular to the steel plate.

The fatigue test was carried out under the conditions of a stress ratio of 0.1, a stress range of 200 MPa, and a frequency of 10 Hz for the test piece with a surplus shown in FIG. Was measured and evaluated, and the case where N was 5 × ¹⁰⁶ or more and did not break was regarded as acceptable. At the time of the fatigue test, a fatigue load was applied in the direction perpendicular to the welding line direction.

The results of each test evaluated by the above method are shown in Table 4. When welding was performed using the flux-cored cut wire of the invention example, all the fatigue tests passed. That is, it was confirmed that having the flux-containing cut wire of the invention example has extremely high fatigue resistance.

As described above, according to the present invention, a welded joint having excellent fatigue resistance can be easily manufactured at low cost.

1, 2 ... Base material (steel material), 3 ... Groove, 4 ... Flux-filled cut wire, 5 ... Backing material, 6 ... Welding wire, 7, 8 ... Welding metal, 9 ... Addition welding metal.

Claims (7)

It is a method of manufacturing a welded joint in which a cut wire is filled in a groove provided between base materials and welded.
A flux-cored cut wire having a steel outer skin and a flux filled inside the steel outer skin is filled and welded to at least one of the first layer, the final layer, and the toe of the weld bead in the groove. Is the way
The flux contains one or more Ms point cooling elements selected from the group consisting of C, Mn, V, Cr, Ni, Cu, and Mo as a metal and / or an alloy, and also contains the Ni. The amount is less than 50% by mass as a mass ratio 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 x [C] -64 x [Mn] -32 x [V] -18 x [Cr] -15 x [Ni] -9 x [Cu] -5 x [Mo] ... Equation 1
[However, the element symbol enclosed in square brackets in Equation 1 is the content represented by the mass ratio (mass%) to the total mass of the flux-containing cut wire. ] The flux-cored cut wire is a mass ratio of the flux-cored cut wire to the total mass.
The total content of the Ms point lowering element is 0.10% or more, and the content of the chemical component composed of Si, Nb, Al, B, and Bi is Si: 2.00% or less, Nb: 0. Selected from the group consisting of 50%, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less, and Ca, Mg, Ti, Zr, and REM. The total content of strongly deoxidized elements is 5.00% or less, and
The method for manufacturing a welded joint according to claim 1, wherein the content of the impurity element composed of P and S is P: 0.030% or less and S: 0.020% or less. The method for manufacturing a welded joint according to claim 1 or 2, wherein the flux-cored cut wire is filled in the first layer in the groove, and then the solid cut wire in which the solid wire is cut is filled and welded. The method for manufacturing a welded joint according to any one of claims 1 to 3, wherein the welding is submerged arc welding or gas shielded arc welding. A cut wire for groove filling that fills the groove provided between the base materials to manufacture a welded joint.
It has a steel husk and a flux filled inside this steel husk,
The flux contains one or more Ms point cooling elements selected from the group consisting of C, Mn, V, Cr, Ni, Cu, and Mo as a metal and / or an alloy, and also contains the Ni. The amount is less than 50% by mass as a mass ratio to the total mass of the flux-cored cut wire.
A flux-containing cut wire for groove filling, wherein the martensitic transformation temperature (Ms point) calculated by the following formula 1 is 450 ° C. or lower.
Ms = 613-406 x [C] -64 x [Mn] -32 x [V] -18 x [Cr] -15 x [Ni] -9 x [Cu] -5 x [Mo] ... Equation 1
[However, the element symbol enclosed in square brackets in Equation 1 is the content represented by the mass ratio (mass%) to the total mass of the flux-containing cut wire. ] The flux-cored cut wire is a mass ratio of the flux-cored cut wire to the total mass.
The total content of the Ms point lowering element is 0.10% or more, and the content of the chemical component composed of Si, Nb, Al, B, and Bi is Si: 2.00% or less, Nb: 0. Selected from the group consisting of 50%, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% or less, and Ca, Mg, Ti, Zr, and REM. The total content of strongly deoxidized elements is 5.00% or less, and
The flux-containing cut wire for groove filling according to claim 5, wherein the content of the impurity element composed of P and S is P: 0.030% or less and S: 0.020% or less. The groove filling according to claim 5 or 6, wherein the filler is used by filling at least one of the initial layer, the final layer, and the toe of the weld bead provided between the base materials. Flux-filled cut wire.

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