JP2022061805A - 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 prevent low-temperature cracking while reducing a burden of a preheating work, and can obtain a weld joint so as to be advantageous in terms of work environment and cost, and a flux-cored cut wire used in the same.SOLUTION: There are provided a method for manufacturing a weld joint that includes a flux-cored cut wire welding step of filling at least a part in a groove with a flux-cored cut wire having a flux containing a predetermined fluoride, and welding the groove; and a flux-cored cut wire used in the same, which has a steel sheath and a flux that is made to fill the inside of the steel sheath and contains a fluoride.SELECTED DRAWING: Figure 1

Description

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, in the field of manufacturing large steel structures such as shipbuilding, steel frames, and bridges, the strength of steel sheets has been increasing in order to achieve both weight reduction and high performance. Further, from the viewpoint of improving construction efficiency, submerged arc welding (SAW), which is mainly used for plate joint welding, requires a welding material capable of large heat input welding such as single-sided welding and double-sided single-layer welding.

Generally, the strength of the weld metal is required to be equal to or higher than the strength of the base metal. Therefore, it is necessary to increase the strength of the weld metal as the strength of the steel sheet increases. However, when a high-strength steel plate having a tensile strength of 780 MPa or more is welded, low-temperature cracking at the welded portion becomes a problem. In particular, in the first layer of multi-layer welding of extremely thick high-strength steel with a thick plate, the probability of occurrence is high. Therefore, it is necessary to preheat the welded portion in order to prevent this low temperature cracking, but in the case of an extra-thick steel sheet, the preheating work itself becomes a heavy load.

Since diffusible hydrogen in the weld metal affects this low-temperature cracking, hydrogen ions (H ⁺ ) are converted to fluoride ions (F-) by adding fluoride to the flux ^and welding wire used for submerged arc welding. ), And the hydrogen is discharged to the outside of the arc to reduce the concentration of hydrogen taken into the molten pool.

For example, Patent Document 1 describes a welding wire used for submerged arc welding, in which a flux component filled in the wire contains a fluorine compound having a melting point of 1000 ° C. or lower and a powdery fluorine compound in an amount of 0.1 mass. A flux-cored wire containing% or more and less than 10% by mass is described. Further, in Patent Document 2, in addition to SiO ₂ and the like, CaF ₂ is 9 to 21%, MgF ₂ and one or two of MnF ₂ are 2 to 10%, and Li fluoride is 0.02 to Li equivalent. It is described that 780 MPa high-strength steel is submerged arc welded together with a predetermined wire using a flux containing 1.0%.

However, Patent Document 1 aims at pipe welding of steel pipes such as high-strength pipelines for crude oil transportation, and the thickness of the steel plate used in the embodiment is also 25 mm. That is, when an attempt is made to perform multi-layer welding with a flux-cored wire as in Patent Document 1 for an extremely thick high-strength steel plate having a plate thickness of 50 mm or more, the problem of the working environment due to the generation of fume and spatter becomes remarkable. Moreover, using such a flux-cored wire for all paths leads to high cost.

Further, Patent Document 2 shows an example in which 780 MPa steel having a plate thickness of 80 mm is subjected to multi-layer welding of one layer in two passes in an example, but as is clear from the description in the specification, the preheating temperature. Preheating work at 100 ° C. is required (see paragraph 0044). Further, when submerged arc welding is performed using the flux-cored wire of Patent Document 1 or the flux of Patent Document 2, the fluoride is separated by the arc, the arc becomes unstable, and the bead shape becomes defective. It ends up.

On the other hand, when manufacturing a joint with large heat input in submerged arc welding, a cut wire made by cutting a small diameter steel wire into a predetermined length in order to control high welding efficiency and penetration depth. Is performed in the groove. Further, Patent Document 3 describes a cut wire in which the cut wire strand is covered with a Cu adherend layer and oil is applied to the surface thereof.

In Patent Document 3, the reason for providing the Cu adherend layer is to consider the arc startability due to its high electrical conductivity, and to apply an appropriate amount of oil to the wire surface is the arc startability. This is to improve the rust resistance without damaging the rust resistance, and to prevent the low temperature cracking property from being lowered (see paragraphs 0013 and 0021). That is, the oil amount control of the cut wire in Patent Document 3 can suppress the increase of diffusible hydrogen, but does not reduce it. Therefore, it is difficult to reliably prevent the problem of low-temperature cracking when the strength of steel sheets and weld metals is increasing. As the cut wire to be filled in the groove as described above, the cut wire obtained by cutting the solid wire has been mainly used so far.

Japanese Unexamined Patent Publication No. 2013-123711 Japanese Unexamined Patent Publication No. 5-212583 Japanese Unexamined Patent Publication No. 9-94690

In this way, as the strength of steel sheets increases and the strength of weld metals increases, the present inventors can reduce low-temperature cracking while reducing the burden of preheating work even in the case of extremely thick high-strength steel sheets. As a result of diligent studies on a method that can prevent the problem of the working environment due to fume and spatter as much as possible, a flux-cored cut wire containing a predetermined fluoride is filled in the groove and welded. 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, which can prevent low-temperature cracking while reducing the burden of preheating work, and can obtain a welded joint advantageously in terms of work environment and cost. To do.

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 flux-cored cut wire welding step in which a flux-cored cut wire having a steel outer skin and a flux containing a flux filled inside the steel outer skin is filled and welded to at least a part of the groove. A method of manufacturing a welded joint, which is characterized by being equipped with.
(2) The claim that the fluoride is one or more selected from the group consisting of CaF ₂ , MgF ₂ , LiF, NaF, K ₂ ZrF ₆ , K ₂ SiF ₆ , and Na ₃ AlF ₆ . The method for manufacturing a welded joint according to 1).
(3) The flux-cored cut wire is a mass ratio of the flux-cored cut wire to the total mass.
The fluoride is contained in an F equivalent value of 0.01% by mass or more, and the content of a chemical component consisting of C, Si, Mn, Cu, Ni, Cr, Mo, Nb, V, Ti, Al, B, and Bi. C: 0.120% or less, Si: 2.00% or less, Mn: 3.50% or less, Cu: 5.00% or less, Ni: 5.00 or less, Cr: 5.00% or less, Mo: 5.00% or less, Nb: 0.50% or less, V: 0.50% or less, Ti: 0.50% or less, Al: 1.70% or less, B: 0.020% or less, and Bi: 0 .030% or less, and also
The method for manufacturing a welded joint according to (1) or (2), wherein the content of the impurity element composed of P and S is P: 0.030% or less and S: 0.020% or less.
(4) The flux-cored cut wire welding step comprises any one of (1) to (3), in which the flux-cored cut wire is filled in the groove and welded in one pass. The method for manufacturing a welded joint described in 1.
(5) The flux-cored cut wire welding step is performed by one-layer welding in which the first layer in the groove is filled with the flux-filled cut wire and welded, or in the first layer and the second and subsequent layers in the groove. The welding according to any one of (1) to (3), which comprises multi-layer welding in which the flux-cored cut wire is filled and welded, and is performed until at least the temperature of the base metal reaches the temperature equivalent to preheating. Welding method.
(6) The method for manufacturing a welded joint according to any one of (1) to (5), wherein the welding means is submerged arc welding or gas shielded arc welding.
(7) The method for manufacturing a welded joint according to any one of (1) to (6), wherein the base material is a high-strength steel material having a tensile strength of 780 MPa or more.
(8) The method for manufacturing a welded joint according to any one of (1) to (7), wherein the base material is made of an extra-thick steel material having a thickness of 50 mm or more.
(9) A cut wire for filling the groove provided between the base materials when manufacturing a welded joint, which is a steel outer skin and a flux filled inside the steel outer skin. A flux-cored cut wire for groove filling, characterized in that it has a flux containing.
(10) The fluoride is one or more selected from the group consisting of CaF ₂ , MgF ₂ , LiF, NaF, K ₂ ZrF ₆ , K ₂ SiF ₆ , and Na ₃ AlF ₆ (9). Flux-filled cut wire for groove filling as described in.
(11) At the mass ratio to the total mass of the flux-cored cut wire.
The fluoride is contained in an F equivalent value of 0.01% by mass or more, and the content of a chemical component consisting of C, Si, Mn, Cu, Ni, Cr, Mo, Nb, V, Ti, Al, B, and Bi. C: 0.120% or less, Si: 2.00% or less, Mn: 3.50% or less, Cu: 5.00% or less, Ni: 5.00 or less, Cr: 5.00% or less, Mo: 5.00% or less, Nb: 0.50% or less, V: 0.50% or less, Ti: 0.50% or less, Al: 1.70% or less, B: 0.020% or less, and Bi: 0 .030% or less, and also
The flux-containing cut wire for groove filling according to (9) or (10), wherein the content of the impurity element composed of P and S is P: 0.030% or less and S: 0.020% or less.
(12) The flux-containing cut wire for groove filling according to any one of (9) to (11), wherein the base material is a high-strength steel material having a tensile strength of 780 MPa or more.
(13) The flux-containing cut wire for groove filling according to any one of (9) to (12), wherein the base material is made of an extra-thick steel material having a thickness of 50 mm or more.

According to the present invention, for example, even when welding an extremely thick high-strength steel plate, the burden of preheating work can be reduced to prevent low-temperature cracking, and the work environment due to fume or spatter can be prevented. It becomes possible to manufacture a welded joint advantageously in terms of cost by suppressing the problem as much as possible.

FIG. 1 is an explanatory diagram showing an example of a flux-cored cut wire welding process in the present invention. FIG. 2 is an explanatory diagram showing another example of the flux-cored cut wire welding process in the present invention. FIG. 3 is an explanatory diagram showing a groove shape used for evaluation of low temperature crack resistance and a state of filling a flux-cored cut wire in an embodiment. FIG. 4 is an explanatory diagram showing the groove shape used for evaluating the low temperature crack resistance in the first layer of the groove and the state of filling the flux-cored cut wire in the embodiment.

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, as for the flux-cored cut wire, the flux containing fluoride is used. Fluoride has a function of reducing the amount of diffusible hydrogen in the weld metal and remarkably improving the low temperature crack resistance of the weld metal. This is because the flux melts when the flux-cored cut wire is welded, and the flux (F ⁻ ) in the flux combines with hydrogen (H ⁺ ) to form hydrogen fluoride (HF), and this HF is outside the weld metal. It is presumed that it is released to.

These fluorides are preferably one or more selected from the group consisting of CaF ₂ , MgF ₂ , LiF, NaF, K ₂ ZrF ₆ , K ₂ SiF ₆ , and Na ₃ AlF ₆ . Is good. According to these compounds, Ca, Mg, Li, Na, K, Zr, Si, and Al generated by ionization can all combine with oxygen to reduce the amount of oxygen in the weld metal, resulting in desorption. Acts as an acid element. This is advantageous in improving the toughness and elongation of the weld metal.

As described above, from the viewpoint that the amount of diffusible hydrogen in the weld metal can be sufficiently reduced, the amount of fluorine (F) contained in the fluoride is adjusted to the content of the fluoride in the flux-cored cut wire. If specified by the F conversion value expressed in mass% with respect to the total mass, it is preferable that the flux-cored cut wire is contained in an amount of 0.01% or more, preferably 0.03% or more, in terms of the mass ratio to the total mass. It is better, more preferably 0.05% or more, still more preferably 0.10% or more. This content represents the total amount of fluoride contained in the flux. That is, as long as the total mass ratio of the fluorides contained in the flux is 0.01% or more in terms of F, the lower limit of the content of each fluoride is not particularly limited. Further, since this F conversion value indicates the amount of fluorine (F) contained in the fluoride in mass% with respect to the total mass of the flux-cored wire, the type of fluoride is the fluoride of the above-mentioned preferable example. In some cases, the F conversion value can be obtained from the following equation A.
0.487 x CaF ₂ +0.610 x MgF ₂ +0.732 x LiF +0.452 x NaF +0.402 x K ₂ ZrF ₆ +0.517 x K ₂ SiF ₆ +0.543 x Na ₃ AlF ₆ ...
Here, the chemical formula of the fluoride in the formula A indicates the mass% of the fluoride corresponding to each chemical formula with respect to the total mass of the flux-cored wire. The coefficient of the chemical formula of each fluoride is calculated from the amount of the chemical formula of each fluoride. Assuming that the type of fluoride is these cases, the content at that time is preferably 0.10% or more as a mass ratio to the total mass of the flux-cored cut wire, preferably 0. It is preferably 5% or more, more preferably 1.0% or more, still more preferably 2.0% or more.

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

Further, the flux-containing cut wire in the present invention may contain, for example, an alloy component for controlling the chemical component, carbon equivalent (Ceq), etc. of the weld metal, in addition to the fluoride (these chemical components and alloys). Ingredients are simply referred to as "chemical ingredients"). At that time, for example, the metal powder or the alloy powder melts at the time of welding in the same manner as the steel outer skin. Therefore, chemical components other than the fluoride may be contained in the flux in the form of metal powder or alloy powder, for example, or may be contained in the form of a steel outer skin, and may be contained on the outer surface of the steel outer skin. It may be included as a plating, and both have the same effect. It should be noted that these chemical components other than the fluoride are required to be 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 can be contained in the form of metal powder or alloy powder as described above.

Specifically, the flux-containing cut wire of the present invention contains 0.01% or more of fluoride in terms of F in terms of mass ratio to the total mass of the flux-containing cut wire, and C, Si, Mn, as optional components. It contains any one or more chemical components selected from the group consisting of Cu, Ni, Cr, Mo, Nb, V, Ti, Al, B, and Bi, and the content of these chemical components is C :. 0.120% or less, Si: 2.00% or less, Mn: 3.50% or less, Cu: 5.00% or less, Ni: 5.00 or less, Cr: 5.00% or less, Mo: 5.00 % Or less, Nb: 0.50% or less, V: 0.50% or less, Ti: 0.50% or less, Al: 1.70% or less, B: 0.020% or less, and Bi: 0.030% It is preferable that the content of the impurity element composed of P and S is P: 0.030% or less and S: 0.020% or less, respectively. In the present invention, since the amount of diffusible hydrogen can be reduced without containing any of these arbitrary chemical components by containing the above-mentioned fluoride, the content of each of these arbitrary chemical components can be reduced. The lower limit is 0%.

Of these, among the chemical components as optional components, C in "C: 0.120% or less" is an important element for ensuring the proof stress and tensile strength of the weld metal by solid solution strengthening. However, if the C content in the flux-containing cut wire exceeds 0.120%, the C content in the weld metal becomes excessive, the yield strength and tensile strength of the weld metal increase excessively, and the toughness of the weld metal Decreases. In order to stably secure all of the toughness, proof stress, and tensile strength of the weld metal, it is preferable to set the upper limit of the C content to 0.10%. On the other hand, the lower limit of the C content is 0%, but if necessary, the lower limit of the C content is 0.010%, 0.020%, 0.030%, 0.040%, or 0.050%. May be. Similarly, the upper limit of the C content may be 0.100%, 0.090%, 0.080%, or 0.070%.

Si in "Si: 2.00% or less" 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%.

Mn in "Mn: 3.50% or less" is an element necessary for ensuring the hardenability of the weld metal and increasing the strength of the weld metal, but may be 0%. In order to increase the strength of the weld metal, the lower limit of the Mn content in the flux-cored cut wire may be 0.50%, 0.75%, or 1.0%. On the other hand, when the Mn content exceeds 3.50%, the grain boundary embrittlement sensitivity of the weld metal increases and the toughness of the weld metal deteriorates. Therefore, the upper limit of the Mn content is 3.50%, but the upper limit of the Mn content may be 3.00%, 2.50%, or 2.00%.

Cu in "Cu: 5.00% or less" has an effect of improving the strength and toughness of the weld metal, but may be 0%. Cu may be contained in the plating on the surface of the steel outer skin in the flux-cored cut wire, or may be contained in the flux as a simple substance or as an alloy. This Cu content is the total amount of Cu contained in the steel outer skin and flux and Cu contained in the plating on the surface. When the Cu content exceeds 5.00%, the toughness of the weld metal decreases. The upper limit of the Cu content is preferably 4.00%, 3.00%, or 2.00%. On the other hand, the lower limit of the Cu content is preferably 0.05%, 0.1%, or 0.15%.

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

Since Cr in "Cr: 5.00% or less" is not an essential component, the lower limit of the Cr content in the flux-cored cut wire is 0%. On the other hand, Cr is an element effective for improving the strength of the weld metal because it enhances the hardenability of the weld metal. In order to obtain the effect sufficiently, the Cr content is preferably 0.10% or more. Further, when the Cr content exceeds 5.00%, the weld metal is excessively hardened and the toughness of the weld metal is deteriorated. The upper limit of the Cr content is preferably 4.00%, 3.00%, 2.00%, or 1.00%.

Since Mo in "Mo: 5.00% or less" is not an essential component, the lower limit of the Mo content in the flux-cored cut wire is 0%. On the other hand, Mo has an effect of improving the hardenability of the weld metal, and is therefore an effective element for increasing the strength of the weld metal. In order to obtain the effect, the Mo content is preferably 0.01% or more. However, if the Mo content exceeds 5.00%, the toughness of the weld metal may deteriorate, so the Mo content is set to 5.00% or less. The upper limit of the Mo content is preferably 4.00%, 3.00%, 2.00%, 1.00%, or 0.60%.

Since Nb in "Nb: 0.50% or less" is not an essential component, the lower limit of the Nb content in the flux-cored cut wire is 0%. On the other hand, Nb forms fine carbides in the weld metal, and 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%.

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

Since Ti in "Ti: 0.50% or less" is not an essential component, the lower limit of the Ti content in the flux-cored cut wire is 0%. On the other hand, Ti is a deoxidizing element and has an effect of reducing the amount of oxygen in the weld metal. Further, Ti contained in the flux-cored cut wire remains slightly in the weld metal to fix the solid solution N, and thus has an effect of alleviating the adverse effect of the solid solution N on the toughness of the weld metal. Therefore, the flux-cored cut wire may contain 0.01% or more of Ti. However, if the Ti content exceeds 0.50%, the toughness of the weld metal may deteriorate due to the formation of excessive precipitates. Here, when Ti is contained in the flux-cored cut wire, it is conceivable that ferrotitanium (an alloy of iron and titanium) is contained in the flux. The upper limit of the Ti content is preferably 0.40%, 0.30%, 0.20%, or 0.10%.

Al in "Al: 1.70% or less" 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%.

Since B in "B: 0.020% or less" 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%.

Since Bi in "Bi: 0.030% or less" 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 0.030%, solidification cracks are likely to occur in the weld metal, so the upper limit of the Bi content is 0.030%. The upper limit of the Bi content is preferably 0.025%, 0.020%, or 0.010%.

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.

Further, 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. Is desirable to reduce as much as possible. 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, but contains Fe and impurities in addition to these chemical components and the fluoride and impurity elements. 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.

Further, the flux-containing cut wire in the present invention may contain oxides and carbonates of metal elements other than the above-mentioned fluorides, chemical components, and impurity elements as long as the characteristics are not impaired. .. In this case, these oxides and carbonates are not included in the above-mentioned fluorides, chemical components, impurity elements, and the contents of Fe and impurities. However, these oxides and carbonates do not exclude the case where they are contained. That is, the flux-containing cut wire in the present invention contains the above-mentioned fluoride in a predetermined ratio in terms of F, and the contents of the above-mentioned chemical components and impurity elements are in the predetermined ranges, respectively, and the balance is Fe and impurities. Or, it has a chemical composition consisting of Fe, impurities, and oxides and carbonates thereof. Preferably, the above-mentioned fluoride is contained in a predetermined ratio in terms of F, the contents of the above-mentioned chemical components and impurity elements are each in a predetermined range, and the balance has a chemical composition consisting of Fe and impurities.

Further, the steel outer skin of the flux-containing cut wire according to the present invention is not particularly limited as long as the above-mentioned matters are satisfied. For example, when the steel outer skin is made of a mild steel outer skin, the chemical composition of the outer skin is C: 0. .1% or less, Si: 0.10% or less, Mn: 3.00% or less, P: 0.030% or less, S: 0.020% or less, Al: 0.1% or less, and N: 0. It can be mentioned that it is 030% or less and the balance is iron and impurities.

The flux-cored cut wire in the present invention can be obtained by finely cutting a steel outer skin into a predetermined length in the form of a wire 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.

Above all, in this flux-cored cut wire welding step, it is preferable to fill at least the first layer in the groove with the flux-cored cut wire according to the present invention and perform welding. That is, by filling the first layer in the groove with a high probability of low-temperature cracking with a flux-cored cut wire, the load of preheating work can be surely reduced, for example, the preheating temperature can be lowered to 50 ° C. or lower. Or the preheating work itself can be eliminated.

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. 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.

Here, if the temperatures of the base material 1 and the base material 2 reach the preheating temperature (preheating equivalent temperature) in the case of performing the preheating work by welding in FIG. 1B, for example, if the temperature reaches 100 ° C. Since the risk of low temperature cracking is eliminated, the welded joint may be manufactured without using the flux-cored cut wire of the present invention in the subsequent welding. If the base metal 1 and the base metal 2 have not reached the temperature equivalent to preheating, welding obtained by including the flux-cored cut wire 4 filled in the first layer as shown in FIG. 1 (c). The flux-cored cut wire 4 of the present invention is sprayed again on the metal 7 to fill the groove 3, and the welding wire 6 is arranged to perform welding. After that, this is repeated until the temperatures of the base material 1 and the base material 2 reach the preheating equivalent temperature, the flux-cored cut wire 4 of the present invention is filled and welded, and when the preheating equivalent temperature is reached, the above case Similarly, welding may be performed without using the flux-cored cut wire of the present invention.

An example of the flux-filled cut wire welding process shown in FIG. 1 is one-layer welding in which the first layer in the groove is filled with flux-filled cut wire and welded, or the first layer and two layers in the groove. This is a case of multi-layer welding in which the flux-containing cut wire is filled and welded after the eyes, and the flux-containing cut wire is filled and welded until the temperature of the base metal reaches at least 100 ° C. That is, by using the flux-cored cut wire according to the present invention for the first layer welding in the groove, the amount of diffusible hydrogen in the weld metal can be reduced. Moreover, since the flux-cored cut wire welding process also serves as the preheating work, the preheating work can be eliminated and the burden of the preheating work can be significantly reduced.

Further, as shown in FIG. 2, 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. 2A, after the backing material 5 is attached to the back surfaces of the base materials 1 and 2, in the example of FIG. 2, 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. 2 (b), the welding wire 6 is arranged on the substantially central portion of the filled flux-cored cut wire 4, and an arc is generated for welding, as shown in FIG. 2 (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 process shown in FIG. 2, since the flux-cored cut wire according to the present invention is used in almost all of the grooves, the preheating work is not required and the burden of the preheating work is large. Can be reduced to.

In FIGS. 1 and 2, an example of a so-called V-shaped groove is shown in which the groove between the base materials is a so-called V-shaped groove. , Re-shaped, K-shaped, J-shaped, X-shaped, U-shaped, H-shaped, or the like, or any other shape of the groove may be used. 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 or gas shielded arc welding in order to reliably melt the flux-cored cut wire filled in the groove. It is good to be. 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 it is most effective to be applied in a situation where low temperature cracking becomes a problem and preheating work is burdened. That is, typically, it is welding of a base metal made of a high-strength steel material having a tensile strength of 780 MPa or more and 1500 MPa or less. Further, in the case of an extra-thick steel material having a thickness of 50 mm or more and 250 mm or less, the burden of preheating work becomes particularly large. Therefore, the present invention is particularly applied when an extra-thick high-strength steel material is used as a base material. Can be said to be extremely effective. 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 cut wire containing a flux containing a fluoride is used as a groove filler, it is possible to preferably obtain a welded joint in which the amount of diffusible hydrogen of the weld metal is 1.0 ml / 100 g or less, and in particular, a predetermined one. By using a flux-containing cut wire containing more chemical components, a welded joint having high strength and high toughness can be obtained.

(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-containing cut wires (Sample Nos. 1 to 47) 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. The configurations of these flux-cored cut wires are shown in Tables 1 and 2.

The unit of the content of each fluoride disclosed in Tables 1 and 2, the chemical component as an optional component and iron powder (Fe powder), and each element contained as an impurity element is the mass with respect to the total mass of the flux-filled cut wire. Percentage (% by mass). The F-converted value of the flux-cored cut wire disclosed in the table indicates the amount of fluorine (F) contained in the fluoride in the flux-cored cut wire in mass% with respect to the total mass of the flux-cored cut wire. , The value obtained by the above-mentioned formula A.

Further, the balance in the chemical composition of the flux-cored cut wire (that is, components other than each element disclosed 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 oil is not applied unless otherwise specified in the remarks column. On the other hand, each element contained as a chemical component in the flux-cored cut wire disclosed in Table 2 is contained in the form of a steel outer skin or a metal powder. In the table, the blanks in the table relating to the content of the chemical component or the compound mean that the chemical component or the compound is not intentionally added. In addition, fluoride and chemical components may be inevitably mixed.

The flux-containing cut wires of the invention example and the comparative example were evaluated by the method described below.
First, i) As an evaluation of low temperature crack resistance, welding was performed on a tensile strength 780 MPa class steel having a plate thickness of 50 mm under the welding condition 1 in Table 3, and H-type restraint cracking was performed according to JIS Z3159: 1993. Evaluated in the test. The groove shape is a Y-shape shown in FIG. 3, and the slit length is 300 mm. Further, the spraying thickness of the flux-containing cut wire 4 in the groove 3 was set to 8 mm. Further, NB-250H manufactured by Nippon Steel Welding & Co., Ltd. was used as the welding flux, and Y-80M (wire diameter φ4.8 mm) manufactured by Nippon Steel Welding & Co., Ltd. was used as the welding wire.

Further, ii) As an evaluation of the low temperature crack resistance in the first layer in the groove, welding was performed on the 780 MPa class steel having a tensile strength of 50 mm under the welding condition 2 in Table 3. At that time, the groove shape was V-shaped as shown in FIG. 4, and the spray thickness of the flux-containing cut wire 4 in the groove 3 was 2 mm. Further, Y-82C (wire diameter φ1.2 mm) manufactured by Nippon Steel Welding & Co., Ltd. was used as the welding wire, and SB-41 manufactured by Nippon Steel Welding & Co., Ltd. was used for the backing material 5. Under the welding conditions 1 and 2 in these evaluations, the test was carried out without preheating the base material (steel material) 1 and 2.

In addition, iii) the amount of diffusible hydrogen in the weld metal was evaluated as follows. That is, the welding conditions for evaluating the amount of diffusible hydrogen in the weld metal were the welding conditions 3 shown in Table 3. Further, the flux-cored cut wires of the invention example and the comparative example were sprayed on the test plate and the end tab so as to have a thickness of 2 mm, and then the welding flux was sprayed so as to have a thickness of 10 mm. Here, NB-250H manufactured by Nippon Steel Welding & Co., Ltd. was used as the welding flux, and Y-80M (wire diameter φ4.0 mm) manufactured by Nippon Steel Welding & Co., Ltd. was used as the welding wire. The diffusible hydrogen content of the weld metal was measured by a gas chromatograph method based on JIS Z 3118: 2007 (method for measuring the hydrogen content of steel welds). The flux-cored cut wire having a diffusible hydrogen amount of 1.0 ml / 100 g or less in the weld metal was accepted as a pass for the diffusible hydrogen amount.

Furthermore, after i) H-type weld crack test and ii) evaluation of low temperature crack resistance in the first layer, the height difference of the bead surface unevenness is measured at a bead length of 25 mm pitch to evaluate the bead shape. bottom. At this time, both after i) H-type weld crack test and ii) after evaluation of low temperature crack resistance in the first layer, the case where the surface unevenness of the bead shape is 3 mm or less is regarded as good (○), and the case where it exceeds 3 mm is defective. It was evaluated as (x). Then, ii) regarding the evaluation of low temperature crack resistance and bead shape in the first layer, if there is no crack and the bead shape is good (○), the overall judgment is passed and one or more is defective (×). ), The overall judgment was rejected.

The results of each test evaluated by the above method are shown in Table 4. When welding is performed using the flux-cored cut wire of the invention example, there is no cross-sectional crack in any of the cross-sections of the H-type weld crack test and the evaluation of low-temperature crack resistance in the first layer, even if the steel material is not preheated. (No cross-sectional cracks occurred). That is, it was confirmed that the flux-containing cut wire of the invention example has extremely high low temperature crack resistance. Further, as shown in the test results in Table 4, by using the flux-cored cut wire of the invention example, the bead shape evaluation was passed and good welding workability was shown. On the other hand, when the flux-cored cut wire of the comparative example was used, there was cross-sectional crack in both the H-type weld crack test and the evaluation of the low temperature crack resistance in the first layer (cross-section cracking occurred). )Met.

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

1, 2: Base material (steel material), 3: Groove, 4: Flux-filled cut wire, 5: Backing material, 6: Welding wire, 7: Welded metal.

Claims (13)

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 welding step in which a flux-cored cut wire having a steel outer skin and a flux containing a flux filled inside the steel outer skin is filled and welded to at least a part of the groove. A method of manufacturing a welded joint, which is characterized by being equipped with. The first aspect of the present invention, wherein the fluoride is one or more selected from the group consisting of CaF ₂ , MgF ₂ , LiF, NaF, K ₂ ZrF ₆ , K ₂ SiF ₆ , and Na ₃ AlF ₆ . How to manufacture welded joints. The flux-cored cut wire is a mass ratio of the flux-cored cut wire to the total mass.
The fluoride is contained in an F equivalent value of 0.01% by mass or more, and the content of a chemical component consisting of C, Si, Mn, Cu, Ni, Cr, Mo, Nb, V, Ti, Al, B, and Bi. C: 0.120% or less, Si: 2.00% or less, Mn: 3.50% or less, Cu: 5.00% or less, Ni: 5.00 or less, Cr: 5.00% or less, Mo: 5.00% or less, Nb: 0.50% or less, V: 0.50% or less, Ti: 0.50% or less, Al: 1.70% or less, B: 0.020% or less, and Bi: 0 .030% or less, and also
The method for manufacturing a welded joint according to claim 1 or 2, 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 welded joint according to any one of claims 1 to 3, wherein the flux-cored cut wire welding step comprises a 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. Manufacturing method. The flux-cored cut wire welding step is a one-layer welding in which the first layer in the groove is filled with the flux-filled cut wire and welded, or the first layer in the groove and the second and subsequent layers are filled with the flux. The method for manufacturing a welded joint according to any one of claims 1 to 3, which comprises multi-layer welding in which cut wires are filled and welded, and which is performed at least until the temperature of the base metal reaches a temperature equivalent to preheating. The method for manufacturing a welded joint according to any one of claims 1 to 5, wherein the welding means is submerged arc welding or gas shielded arc welding. The method for manufacturing a welded joint according to any one of claims 1 to 6, wherein the base material is a high-strength steel material having a tensile strength of 780 MPa or more. The method for manufacturing a welded joint according to any one of claims 1 to 7, wherein the base material is made of an extra-thick steel material having a thickness of 50 mm or more. A cut wire for groove filling that is filled in the groove provided between the base materials when manufacturing a welded joint, and is a steel outer skin and a flux that is filled inside the steel outer skin and contains fluoride. A flux-cored cut wire for groove filling, characterized by having. The ninth aspect of the present invention, wherein the fluoride is one or more selected from the group consisting of CaF ₂ , MgF ₂ , LiF, NaF, K ₂ ZrF ₆ , K ₂ SiF ₆ , and Na ₃ AlF ₆ . Flux-filled cut wire for groove filling. By mass ratio to the total mass of the flux-cored cut wire
The fluoride is contained in an F equivalent value of 0.01% by mass or more, and the content of a chemical component consisting of C, Si, Mn, Cu, Ni, Cr, Mo, Nb, V, Ti, Al, B, and Bi. C: 0.120% or less, Si: 2.00% or less, Mn: 3.50% or less, Cu: 5.00% or less, Ni: 5.00 or less, Cr: 5.00% or less, Mo: 5.00% or less, Nb: 0.50% or less, V: 0.50% or less, Ti: 0.50% or less, Al: 1.70% or less, B: 0.020% or less, and Bi: 0 .030% or less, and also
The flux-containing cut wire for groove filling according to claim 9 or 10, 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 flux-containing cut wire for groove filling according to any one of claims 9 to 11, wherein the base material is a high-strength steel material having a tensile strength of 780 MPa or more. The flux-containing cut wire for groove filling according to any one of claims 9 to 12, wherein the base material is made of an extra-thick steel material having a thickness of 50 mm or more.

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