JP2017164768A - HIGH Ni FLUX-CORED WIRE FOR GAS SHIELDED ARC WELDING AND METHOD OF MANUFACTURING WELDED JOINT - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high Ni flux-cored wire for gas shielded arc welding, excellent in cold cracking resistance and generating less spatter and capable of providing a weld zone excellent in toughness, fatigue strength and tensile strength.SOLUTION: The high Ni flux-cored wire for gas shielded arc welding comprises a flux which includes fluorides of 0.20% or more in total in terms of F and oxides of 0.3% or more but less than 3.50%, the fluorides being one or more selected from the group consisting of CaF, MgF, NaAlF, NaF and KZrF. The contents of CaF, Ti oxide, CaO and iron powder are less than 1.00%, 0.10% or more but less than 2.50%, less than 0.2% and less than 10.0%, respectively. An X value is 3.0% or less and besides, the chemical components excluding fluorides, oxides and carbonates are in a prescribed range.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a flux-cored wire and a method for manufacturing a welded joint.

  In recent years, there has been an increasing demand for larger and higher-rise building structures such as buildings and bridges. Accordingly, the amount of high-strength steel having a tensile strength of 780 MPa (tensile strength of 780 MPa or higher) or higher is increasing.

  By using these high-strength steels as material for members, the amount of steel for obtaining the strength required for the members can be reduced. By reducing the amount of steel used, the cost of steel and the cost of transporting steel are reduced, and the weight of the structure is further reduced. This facilitates the handling of the steel material and reduces the welding amount, so that it is expected to shorten the construction period and the construction cost.

  When manufacturing welded structures such as automobile parts and bridges that require mechanical properties such as high strength and high toughness, the weld metal is also required to have high strength and high toughness. As a welding wire used for manufacturing such a welded structure, a high Ni flux-cored wire containing 5% or more of Ni is known (for example, see Patent Document 1). Ni is an effective element for improving both the strength and toughness of the weld metal because it has less adverse effects on toughness than other hardenability enhancing elements. The high Ni flux-cored wire is a welding wire having a high total amount of Ni contained in the steel sheath and the flux constituting the flux-cored wire. Accordingly, a flux-cored wire in which the flux does not contain Ni and the steel outer sheath contains Ni is also referred to as a high Ni flux-cored wire.

  Further, in a welded structure manufactured by welding high-strength steel, it is required to reduce the tensile residual stress of the welded portion. This is because the tensile residual stress of the welded portion reduces the fatigue strength of the welded portion. In order to satisfy this requirement, it is effective to contain Ni in the flux-cored wire. Ni is an austenite former and is also an element that lowers the phase transformation temperature. A high Ni flux-cored wire intended to obtain a welded portion having excellent fatigue strength by utilizing this property is also known (see, for example, Patent Document 2). In welding using this welding wire, the weld metal can be martensitic transformed in a low temperature region. During the martensitic transformation, the weld metal expands. By utilizing the volume expansion during this transformation, compressive residual stress is generated in the weld, reducing the tensile residual stress in the weld or by applying compressive residual stress to the weld. Strength can be improved.

Furthermore, in welding performed in the bridge and shipbuilding fields, etc., preheating work is performed to release diffusible hydrogen out of the weld joint in order to avoid low temperature cracks due to diffusible hydrogen in the weld metal. Reduction of is demanded. This is because the preheating work has a large work load and leads to an increase in manufacturing cost. In order to reduce the preheating work load (no preheating or lower the preheating temperature), it is necessary to reduce the diffusible hydrogen in the weld metal. Patent Document 3 is an epoch-making technology in which the amount of diffusible hydrogen contained in a weld metal is reduced and cold cracking resistance is improved by adding a fluoride mainly composed of CaF ₂ to a flux-cored wire. .

However, it is not easy to obtain a high Ni flux cored wire excellent in cold cracking resistance. In order to develop a high Ni flux cored wire excellent in cold cracking resistance, the present inventors refer to Patent Document 3 and Patent Document 2, and CaF ₂ is 2% by mass with respect to the total mass of the flux cored wire. A super-added high Ni flux-cored wire was prototyped and welded. As a result, a welded joint having good welds with respect to strength, toughness, fatigue strength and low temperature cracking resistance was obtained. However, when the above-mentioned flux-cored wire is used for welding work in which the shielding gas is 100% CO ₂ gas, there is a problem that spatter frequently occurs and workability is extremely poor. Since 100% CO ₂ shielding gas is less expensive than Ar—CO ₂ mixed shielding gas, it is required to provide a flux-cored wire applicable to welding using 100% CO ₂ shielding gas.

JP 2008-168312 A JP 2007-296535 A Patent No. 5440744

  It is an object of the present invention to provide a method for manufacturing a flux-cored wire and a welded joint, in which a weld metal having excellent toughness, fatigue strength, and tensile strength is obtained, low-temperature crack resistance is excellent, and spatter generation is small. It is.

  The gist of the present invention is as follows.

(1) A high Ni flux-cored wire for gas shielded arc welding according to an aspect of the present invention includes a steel outer sheath and a flux filled in the steel outer sheath, and the flux is CaF ₂ , MgF. ₂ , Na ₃ AlF ₆ , NaF, and K ₂ ZrF _6, one or two or more fluorides selected from the group consisting of F, and the total F converted value with respect to the total mass of the flux-cored wire is 0. 20% or more of fluoride, 0.3% or more and less than 3.50% of oxide by mass with respect to the total mass of the flux-cored wire, and 0% or more of 10% by mass with respect to the total mass of the flux-cored wire. wherein the iron powder is less than 2.0%, the content of the CaF ₂ contained in the fluoride is less than 1.00% by mass% relative to the total weight of the flux-cored wire, the oxide The content of Ti oxide contained in the flux is 0.10% or more and less than 2.50% by mass% with respect to the total mass of the flux-cored wire, and the content of the CaO contained in the oxide is the flux. Less than 0.2% by mass% with respect to the total mass of the cored wire, the X value calculated by the formula 1 is 3.0% or less, and further, excluding the fluoride, the oxide, and the carbonate The chemical component is mass% with respect to the total mass of the flux-cored wire, C: 0.003 to 0.080%, Si: 0.21 to 2.00%, Mn: 0.81 to 3.50%, P : 0.020% or less, S: 0.010% or less, Ni: 5.0 to 15.0%, with the balance being Fe and impurities.
X = [Na ₃ AlF ₆ ] + [NaF] + [MgF ₂ ] + 1.5 × ([K ₂ ZrF ₆ ]) + 3.5 × ([CaF ₂ ]) (Formula 1)
However, the chemical formula with parentheses in Formula 1 represents the content of the fluoride according to the chemical formula in mass% with respect to the total mass of the flux-cored wire, and the content of the fluoride not contained is Consider 0.
(2) The high Ni flux-cored wire for gas shielded arc welding as described in (1) above is further mass% with respect to the total mass of the flux-cored wire, Cu: 0.80% or less, Cr: 5.0% In the following, one or more selected from the group consisting of Mo and 2.0% or less may be contained.
(3) The high Ni flux cored wire for gas shielded arc welding described in (1) or (2) above is further mass% with respect to the total mass of the flux cored wire, Al: 0.400% or less, Ti: One or more selected from the group consisting of 0.30% or less, Nb: 0.05% or less, and B: 0.0100% or less may be contained.
(4) The high Ni flux-cored wire for gas shielded arc welding according to any one of the above (1) to (3) is further mass% with respect to the total mass of the flux-cored wire, and Mg: 0.80 % Or less, Ca: 0.500% or less, and REM: 0.0100% or less may be included.
(5) In the high-Ni flux-cored wire for gas shielded arc welding according to any one of (1) to (4), the flux further includes CaCO ₃ , Na ₂ CO ₃ , and MgCO _3. One or two or more of the carbonates selected from the group may be contained in a total of 2.00% or less by mass% with respect to the total mass of the flux-cored wire.
(6) The high Ni flux-cored wire for gas shielded arc welding described in any one of (1) to (5) above may have a shape in which the steel outer skin has no slit-like gap.
(7) The high Ni flux-cored wire for gas shielded arc welding described in any one of (1) to (5) above may have a shape in which the steel outer skin has a slit-like gap.
(8) The high Ni flux-cored wire for gas shielded arc welding according to any one of the above (1) to (7) further includes perfluoropolyether oil applied to the surface of the flux-cored wire. Also good.
(9) In the method for manufacturing a welded joint according to another aspect of the present invention, the high Ni flux-cored wire for gas shielded arc welding according to any one of (1) to (8) is used.

The present invention can provide a weld metal having high strength and high toughness and excellent fatigue strength, excellent low-temperature cracking resistance, and low Ni sputtering for gas shield arc welding. A method for manufacturing a cored wire and a welded joint can be provided. In particular, the present invention relates to welding of high-strength steel of 780 MPa or more used for members (for example, bridges, shipbuilding, automobiles, buildings, and gas tanks) that require fatigue strength and toughness, and shielding gas is 100%. High Ni flux cored wire and welded joints for gas shielded arc welding that have excellent cold cracking resistance, low spatter generation, and can be welded with high welding efficiency even when applied to welding with CO ₂ A manufacturing method can be provided.

It is a graph which shows the relationship between X value and a sputtering amount. It is a photograph of a cross section of (a) a wire made by butting an edge surface, (b) a wire made by butting the edge surface, and (c) a wire made by crimping the edge surface. It is a figure which shows the collection position of the test piece for evaluation of an Example. It is a figure which shows the test body used for a fatigue test.

The present inventors experimented by changing various slag component amounts in a high Ni flux-cored wire for gas shielded arc welding containing 5% or more of Ni. As a result, the present inventors can improve cold cracking, which is a problem when a thick steel plate is welded using a high Ni flux-cored wire containing 5.0 to 15.0% of Ni, and Furthermore, the inventors have found the types and addition amounts of fluorides that can suppress the amount of spatter generated even when used in welding where the shielding gas is 100% CO ₂ gas.

The present invention has been made as a result of the above studies. Hereinafter, the flux cored wire according to the present embodiment will be described separately for a slag component and an alloy component. In addition, content of the component in description about a welding wire represents the mass% with respect to the total mass of a flux cored wire unless there is particular notice.
Initially, the slag component inserted in the steel outer skin of a wire is demonstrated.

(Total of F converted value with respect to the total mass of the flux-cored wire of fluoride: 0.20% or more)
(Type of fluoride: including one or more selected from the group consisting of CaF ₂ , MgF ₂ , Na ₃ AlF ₆ , NaF, and K ₂ ZrF ₆ )
The flux-cored wire according to the present embodiment includes at least one fluoride selected from the group consisting of CaF ₂ , MgF ₂ , Na ₃ AlF ₆ , NaF, and K ₂ ZrF _{6 with} respect to the total mass of the flux-cored wire. Containing 0.20% or more in total converted value. The F-converted value with respect to the total mass of the flux-cored wire indicates the amount of fluorine (F) contained in the fluoride as a mass% with respect to the total mass of the flux-cored wire. For example, if the CaF ₂ of n% in percentage by weight relative to the total weight of the flux cored wire is included in the flux cored wire, F converted value of CaF ₂ is determined by Equation 2 below.
(F converted value of CaF ₂ ) = n × (19.00 × 2 / 78.08) (Formula 2)
In the above formula 2, “19.00” is the atomic weight of F, “2” is the number of F atoms contained in one CaF ₂ , and “78.08” is the molecular weight of CaF ₂ It is. For fluorides other than CaF ₂ , F conversion values can be calculated in the same manner. When a plurality of types of fluorides are included in the flux, the total value of F converted values of the respective fluorides is regarded as the F converted value of the fluorides included in the flux.

  Fluoride can reduce the amount of diffusible hydrogen in the weld metal. When the total F converted value of fluoride is less than 0.20%, the amount of diffusible hydrogen in the weld metal can be stably reduced, and the low temperature crack resistance cannot be satisfied. In order to further reduce the amount of diffusible hydrogen in the weld metal, the lower limit of the total F converted value of fluoride may be 0.30%, 0.40%, or 0.50%.

  When the content of fluoride is excessive, the amount of spatter during welding increases. However, in the flux-cored wire according to this embodiment, it is not necessary to determine the upper limit value of the F-converted value of fluoride. This is because the inventors have found that the upper limit value of the fluoride content should be limited using a sputter generation index X (X value) described later. The F-converted value of fluoride can be appropriately selected as long as the X value is within the range described below.

(CaF ₂ : less than 1.00% with respect to the total mass of the flux-cored wire)
CaF ₂ generates a larger amount of spatter in gas shielded arc welding using 100% CO ₂ gas than MgF ₂ , Na ₃ AlF ₆ , NaF, and K ₂ ZrF ₆ . Therefore, it is preferable not to add CaF ₂ to the flux-cored wire according to this embodiment. However, CaF ₂ may be contained in the flux raw material. In that case, the CaF ₂ content is limited to less than 1.00%. If the CaF ₂ content is limited to less than 1.00%, the problem of sputtering can be ignored. In order to further reduce the amount of spatter generated, the upper limit of the CaF ₂ content may be set to 0.75% or 0.50%. Since the flux cored wire according to the present embodiment does not require the CaF _2, the lower limit of the content of CaF ₂ is 0%.

(X value: 3.0% or less)
As described above, in gas shielded arc welding in which the shielding gas is 100% CO ₂ gas, CaF ₂ increases spatter. Furthermore, the present inventors made a large number of 1.2 mmφ wires containing various fluorides, having no slit-like gaps in the steel hull, and having vegetable oil applied to the steel hull. The sputter characteristics were investigated. In a copper collection box, on a steel plate, on a bead-on-plate, with a welding current of 280 A, a voltage of 27 V, a welding speed of 25 cm / min, a shielding gas of 100% CO ₂ (25 l / min), and no preheating. Weld beads were prepared for 1 minute using various flux-cored wires. Spatter scattered in the box during the production of the weld bead and spatter adhering to the steel plate were collected, and the total weight of those having a diameter of more than 1.0 mm was measured. As a result of multi-dimensional analysis of the spatter generation amount, the type of fluoride, and the content of each fluoride, a good value shown in FIG. 1 is obtained between the X value calculated using Equation 1 and the spatter generation amount. It was found that there was a correlation.
X = [Na ₃ AlF ₆ ] + [NaF] + [MgF ₂ ] + 1.5 × ([K ₂ ZrF ₆ ]) + 3.5 × ([CaF ₂ ]) (Formula 1)
In the formula 1, the chemical formula with parentheses represents the content of the compound (fluoride) according to the chemical formula in mass% with respect to the total mass of the flux-cored wire. The content of fluoride not contained in the flux is zero. By setting the X value defined by Equation 1 to 3.0% or less, the amount of spatter when welding is performed under the above conditions can be reduced to 5 g / min or less, and even if welding is performed under various conditions. It was found that the amount of spatter can be suppressed to a range where there is no problem. In the flux cored wire according to the present embodiment, it is not necessary to determine the lower limit value of the X value of fluoride. This is because the lower limit of the fluoride content is defined using the above-described F converted value.

As described above, in the flux-cored wire according to the present embodiment, by selecting the type and amount of fluoride so that the X value and the F-converted value are within the above-described range, Both spatter suppression in welding under 100% CO ₂ shielding gas can be achieved. This is the most important technical idea of the present invention.

  The reason why fluoride reduces the amount of diffusible hydrogen is not necessarily clear, but fluoride was decomposed by a welding arc, and the generated fluorine was combined with hydrogen and dissipated into the atmosphere as HF gas, or It is thought that hydrogen is fixed as HF in the weld metal as it is. Further, although the reason why the amount of spatter generated varies depending on the type of fluoride is not necessarily clear, the present inventors have found that the metal element chemically bonded to fluoride has an influence on the sputter formation for some reason. I guess that.

(Total of oxides: 0.30% or more and less than 3.50% with respect to the total mass of the flux-cored wire)
The flux cored wire according to the present embodiment contains a total of 0.30% or more and less than 3.50% of oxides.
The oxide can improve the shape of the weld bead. When the total oxide content is less than 0.30%, the shape of the weld bead may be deteriorated. In order to improve the shape of the weld bead, the lower limit of the total oxide content may be 0.50% or 0.70%. Moreover, when the total content of oxides is 3.50% or more, the toughness of the weld may be lowered. In order to improve the toughness of the weld zone, the upper limit of the total oxide content may be 3.00%, 2.50%, or 1.50%. Note that the oxide necessarily includes a Ti oxide within a numerical range described later, and is arbitrarily selected from the group consisting of Ca oxide, Si oxide, Zr oxide, Mg oxide, and Al oxide. 1 type or 2 types or more are further included. Oxides other than these contained in a binder used for flux granulation may be contained in the flux-cored wire. “Total value of oxide content” means a binder used for granulation of flux in addition to the total amount of Ti oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, etc. Including the content of oxides contained in the above. In addition, regarding the content of Ti oxide and CaO contained in the oxide mentioned above, another rule mentioned later is combined and performed.

(Ti oxide: 0.10% or more and less than 2.50% with respect to the total mass of the flux-cored wire)
If the Ti oxide is less than 0.10%, the weld bead shape may be deteriorated. Ti oxide also has a function as an arc stabilizer. In order to obtain a good weld bead shape, the lower limit of the Ti oxide content may be 0.30%, 0.50%, or 0.70%. Further, if the Ti oxide content is 2.50% or more, the toughness of the welded portion may be lowered. In order to improve the toughness of the weld zone, the upper limit of Ti oxide may be 2.40%, 2.00%, 1.50%, 1.00%, 0.90%, or 0.80%. .

  In the flux-cored wire according to the present embodiment, the toughness of the weld zone is increased by increasing the Ni content, but the toughness can be stably increased by keeping the oxide content within the above range. Can be improved.

(CaO: less than 0.2% with respect to the total mass of the flux-cored wire)
CaO generates a lot of spatter in shielded arc welding using 100% CO ₂ gas. When the flux-cored wire contains 0.2% or more of CaO, it becomes difficult to apply to shielded arc welding using 100% CO ₂ gas. Therefore, the CaO content is less than 0.2%. The lower limit of the CaO content is 0%.

(Total content of carbonate: 2.00% or less with respect to the total mass of the flux-cored wire)
(Type of carbonate: including one or more selected from the group consisting of CaCO ₃ , Na ₂ CO ₃ , and MgCO ₃ )
The flux cored wire according to the present embodiment does not need to contain carbonate. Therefore, the lower limit of the carbonate content is 0%. However, the flux-cored wire according to the present embodiment further contains one or more carbonates selected from the group consisting of MgCO ₃ , Na ₂ CO ₃ , and CaCO ₃ in total of 2.00% or less. It is preferable to do.

The carbonate is ionized by the arc and generates CO ₂ gas. The CO ₂ gas generated from the carbonate lowers the hydrogen partial pressure and reduces the amount of diffusible hydrogen in the weld metal. In order to obtain this effect, when carbonate is added to the flux-cored wire, the total content of carbonate is preferably 0.30% or more. In order to further reduce the amount of diffusible hydrogen in the weld metal, the total lower limit of the carbonate content may be set to 0.50% or 1.00%. Further, if the total content of carbonate exceeds 2.00%, welding fume is excessively generated. In order to avoid welding fume generation, the upper limit of the total carbonate content may be 1.80%, 1.50%, or 1.30%.

  Next, the steel outer shell constituting the flux-cored wire according to the present embodiment, and the alloy component and metal deoxidation component contained in the flux will be described. In the flux-cored wire according to the present embodiment, the alloy component and the metal deoxidation component are components that do not constitute fluoride, oxide, and carbonate. The alloy component may be included in the flux in the form of metal powder or alloy powder, may be included in the steel outer shell, or may be plated on the steel outer shell.

(C: 0.003-0.080%)
C is an element that improves the strength of the weld metal, and is contained in the flux-cored wire according to the present embodiment in a range of 0.080% or less depending on the required strength of the weld metal. When the C content of the alloy component exceeds 0.080%, the weld metal is hardened, which is not preferable for the toughness of the weld metal. From the viewpoint of joint strength and decarburization cost in the production of steel, the lower limit of the C content is set to 0.003%.

(Si: 0.21-2.00%)
Si is a deoxidizing element. The flux cored wire according to the present embodiment needs to contain 0.21% or more of Si in order to reduce the amount of O of the weld metal and increase the cleanliness. However, if Si is contained exceeding 2.00%, the toughness of the weld metal is deteriorated. Therefore, the Si content is 0.21 to 2.00%. In order to ensure the toughness of the weld metal stably, the lower limit of the Si content may be 0.30% or 0.40%, and the upper limit of the Si content is 1.20%, 1.00. % Or 0.80%.

(Mn: 0.81 to 3.50%)
Mn is an element that increases the strength by securing the hardenability of the weld metal, and is included in the flux-cored wire according to the present embodiment in a range of 3.50% or less depending on the required strength of the weld metal. . 3. If Mn is contained exceeding 50%, the grain boundary embrittlement susceptibility of the weld metal increases, and the toughness of the weld metal deteriorates. Since the wire according to the present embodiment contains 5.0% or more of Ni, the Mn content may be small. However, Mn also has an effect of fixing S as MnS and preventing the occurrence of hot cracking. In order to obtain this effect, the lower limit of the Mn content is desirably 0.81%. The lower limit value of the Mn content may be 1.00%, 1.10%, or 1.20%. The upper limit value of the Mn content may be 3.40%, 3.30%, or 3.20%.

(P: 0.020% or less)
P is an impurity element and needs to be reduced as much as possible in order to inhibit the toughness of the weld metal. However, the P content is set to 0.020% or less as an allowable range of adverse effects on toughness. In order to further improve toughness, the upper limit of P may be limited to 0.010%.

(S: 0.010% or less)
S is also an impurity element, and if it is excessively present, it deteriorates both the toughness and ductility of the weld metal, so it is preferable to reduce it as much as possible. The S content is 0.010% or less as a range in which the adverse effects on the toughness and ductility of the weld metal can be tolerated. In order to further improve the toughness of the weld metal, the upper limit of S may be limited to 0.005%.

(Ni: 5.0-15.0%)
Ni is the only element that can improve the toughness of a weld metal having any structure and composition by solid solution toughening (an effect of increasing toughness by solid solution). In particular, Ni is an element effective for increasing the toughness of a high strength weld metal having a tensile strength of 650 MPa or more. Ni has a function of lowering the phase transformation temperature on the low temperature side such as the bainite phase and martensite phase of the weld metal. When the phase transformation temperature on the low temperature side is lowered and the weld metal structure is bainite or martensite, compressive residual stress is generated in the weld using the volume expansion during the bainite transformation or martensite transformation. The fatigue strength can be increased. Therefore, Ni is an effective element for improving the fatigue strength of the welded joint. Furthermore, Ni has the effect of improving the corrosion resistance of the weld metal. In order to obtain these effects sufficiently, the Ni content of the alloy component of the wire needs to be 5.0% or more.

  The higher the Ni content, the better the toughness of the weld metal. However, if the Ni content exceeds 15.0%, the effect is saturated and the manufacturing cost of the welding wire becomes excessive, which is not preferable. For this reason, content of Ni shall be 5.0-15.0%. In addition, since Ni is an expensive element and is also an element that increases the hot cracking susceptibility of the weld metal, the upper limit may be set to 12.0%.

  The flux-cored wire according to the present embodiment includes, as an alloy component or a metal deoxidation component, Cu, Cr, depending on the strength level of the steel plate to be welded and the required toughness of the welded portion, in addition to the basic components described above. One or two or more selected from the group consisting of Mo, and one or two or more selected from the group consisting of Al, Ti, Nb, and B can be contained. However, even when Cu, Cr, Mo, Al, Ti, Nb, and B are not included, the flux-cored wire according to this embodiment can solve the problem, so the lower limit of the content of these elements is 0%. is there.

(Cu: 0.80% or less)
Cu is added to the steel outer sheath of the wire, the surface of the steel outer sheath, and the flux as a simple substance or an alloy, and has the effect of enhancing the hardenability of the weld metal. In order to fully obtain this effect, when adding, it is preferable to contain 0.10% or more of Cu. On the other hand, if the content exceeds 0.80%, the toughness decreases. Therefore, content in the case of containing Cu shall be 0.80% or less. In addition, about content of Cu, in addition to the content contained in steel outer skin itself or a flux, when the copper plating is carried out on the surface of the steel outer skin of a wire, the content is also included.

(Cr: 5.0% or less)
Cr is an element effective for increasing the strength by enhancing the hardenability of the weld metal. In order to acquire the effect, when adding, it is good to contain 0.1% or more of Cr. On the other hand, when Cr is excessively contained exceeding 5.0%, bainite and martensite are hardened unevenly and toughness is deteriorated. Therefore, when Cr is contained, the Cr content is 5.0% or less.

(Mo: 2.0% or less)
Mo is an element for improving the hardenability of the weld metal, and is an element that forms fine carbides and improves the tensile strength of the weld metal by precipitation strengthening. In order to exhibit these effects, when added, it is preferable to contain 0.1% or more of Mo even in consideration of combined effects with other elements having similar effects. On the other hand, if Mo exceeds 2.0% and Mo is contained in the welding wire, coarse precipitates are generated and the toughness of the weld metal is deteriorated. Therefore, the content when Mo is contained is 2.0% or less.

(Al: 0.400% or less)
Al is a deoxidizing element and, like Si, has the effect of reducing the amount of O in the weld metal and improving the cleanliness of the weld metal. When adding in order to exhibit the effect, it is good to contain 0.001% or more of Al. On the other hand, when Al is contained exceeding 0.400%, Al forms Al nitride and Al oxide and inhibits the toughness of the weld metal. Therefore, the Al content is set to 0.4% or less. Further, in order to sufficiently obtain the effect of improving the toughness of the weld metal, the lower limit of the Al content may be 0.004%, and the upper limit of the Al content is suppressed in order to suppress the formation of coarse oxides. , 0.200%, 0.100%, or 0.080%.

(Ti: 0.300% or less)
Ti, like Al, is effective as a deoxidizing element and has the effect of reducing the amount of O in the weld metal. Ti is also effective for fixing solute N and mitigating the adverse effect on toughness. When adding in order to exhibit these effects, it is good to contain 0.005% or more of Ti. However, if the Ti content in the welding wire exceeds 0.300% and excessive, deterioration of the toughness of the weld metal due to the formation of coarse Ti oxides and deterioration of the toughness of the weld metal due to excessive precipitation strengthening may occur. The potential for occurrence is great. Therefore, the content when Ti is contained is 0.300% or less.

(Nb: 0.05% or less)
Nb forms fine carbides and improves the tensile strength of the weld metal by precipitation strengthening. When adding in order to obtain these effects, it is preferable to contain 0.01% or more of Nb even in consideration of combined effects with other elements having similar effects. On the other hand, if Nb exceeds 0.05%, Nb excessively contained in the weld metal forms coarse precipitates and deteriorates the toughness of the weld metal. Therefore, the Nb content when Nb is contained is 0.05% or less.

(B: 0.0100% or less)
When an appropriate amount of B is contained in the weld metal, it has an effect of forming a BN in combination with the solid solution N and reducing the adverse effect on the toughness of the solid solution N. B also has the effect of enhancing hardenability and contributing to strength improvement. When adding in order to acquire these effects, it is preferable that B content in a welding wire shall be 0.0003% or more. On the other hand, when the B content exceeds 0.0100%, B in the weld metal becomes excessive, and coarse B compounds such as BN and Fe ₂₃ (C, B) ₆ are formed, and the toughness of the weld metal is reversed. It is not preferable because it deteriorates. Therefore, the B content when B is contained is 0.0100% or less.

  In the flux-cored wire according to the present embodiment, in addition to the above components, 1 is selected from the group consisting of Mg, Ca, and REM as necessary for the purpose of adjusting the ductility and toughness of the weld metal. Species or two or more can be included in the wire within the following ranges. However, even when Mg, Ca, and REM are not included, the flux-cored wire according to the present embodiment can solve the problem, so the lower limit of the content of these elements is 0%.

(Mg: 0.80% or less)
Mg is a strong deoxidizing element, reduces the amount of O in the weld metal, and improves the ductility and toughness of the weld metal. When adding in order to acquire this effect, it is good to contain 0.10% or more of Mg. However, if the Mg content in the welding wire exceeds 0.80%, Mg forms a coarse oxide in the weld metal, leading to a toughness reduction that cannot be ignored. On the other hand, if the Mg content in the welding wire exceeds 0.80%, the stability of the arc during welding deteriorates, and the bead shape deteriorates. Therefore, when it contains Mg, the content shall be 0.80% or less.

(Ca: 0.500% or less)
(REM: 0.0100% or less)
Both Ca and REM are effective in improving the ductility and toughness of the weld metal by changing the sulfide structure and reducing the size of the sulfide and oxide in the weld metal. When adding in order to acquire the effect, Ca content may be 0.100% or more, and REM content may be 0.0020% or more. On the other hand, when Ca and REM are excessively contained, sulfides and oxides are coarsened, and the ductility and toughness of the weld metal are deteriorated. Moreover, when Ca and REM are contained excessively, the possibility of deterioration of the weld bead shape and weldability also occurs. Therefore, the upper limit of Ca content is 0.500%, and the upper limit of REM content is 0.0100%.

  The content of elements contained as the above alloy components or metal deoxidation components does not include the content when these elements are contained as fluorides, oxides or carbonates. These elements do not necessarily have to be pure substances, and there is no problem even if they are contained in the form of an alloy such as Cu-Ni. Moreover, even if these elements are contained in the steel outer shell or contained as a flux, the effect is the same, and therefore, they may be contained in either the steel outer shell or the flux.

(Iron powder: less than 10%)
Iron powder may be included as necessary for adjusting the filling rate of the flux in the flux-cored wire or for improving the welding efficiency. However, since the surface layer of the iron powder is oxidized, if the flux contains excessive iron powder, the oxygen content of the weld metal may be increased and the toughness may be lowered. Therefore, it is not necessary to contain iron powder. When iron powder is included for adjusting the filling rate, the iron powder content is set to less than 10% in order to ensure the toughness of the weld metal.

  The above is the reason for limitation regarding the component composition of the flux-cored wire according to this embodiment, but the other remaining components are Fe and impurities. The Fe component includes Fe in the steel outer shell, iron powder added in the flux, and Fe in the alloy component.

Subsequently, the form of the flux-cored wire will be described.
FIG. 2 shows a cut surface of the flux-cored wire. FIG. 2 (a) shows a flux-cored wire made by butting the edge surfaces and welding, FIG. 2 (b) shows a flux-cored wire made by joining the edge surfaces, and FIG. 2 (c) shows the edge surface. The flux-cored wire made by caulking is shown. Thus, the flux-cored wire has a wire without a slit-like gap in the steel outer shell as shown in FIG. 2 (a), and a slit in the steel outer shell as shown in FIGS. 2 (b) and 2 (c). It can be roughly divided into wires having a gap in a shape. In the flux-cored wire according to the present embodiment, any cross-sectional structure can be adopted, but in order to suppress low temperature cracking of the weld metal, a wire having no slit-like gap (also referred to as a seamless wire) is used. Is preferred.

  Hydrogen entering the weld during welding diffuses in the weld metal and on the steel material side, accumulates in the stress concentration part, and causes cold cracking. This hydrogen source is the water | moisture content which a welding material holds, the water | moisture content mixed from air | atmosphere, and the rust and scale which adhered to the steel surface. Under welding where the cleanliness of the weld and the gas shield conditions are well controlled, the hydrogen of moisture contained in the wire is the main source of diffusible hydrogen in the weld joint.

  For this reason, it is desirable that the steel outer shell is a tube having no slit-like gap, and that the penetration of hydrogen in the atmosphere from the steel outer shell to the flux is suppressed after the wire is manufactured and used. When the steel outer shell is a tube with slit-like gaps (seams), moisture in the atmosphere easily enters the flux from the slit-like gaps in the outer skin, so that hydrogen sources such as moisture can not penetrate. It cannot be prevented. If the steel outer skin has slits and the period after manufacture is long, it is desirable to vacuum-wrap the entire wire or store it in a container that can keep the wire dry.

  Further, in order to improve the wire feedability, lubricating oil may be applied to the wire surface. In order to reduce diffusible hydrogen, the lubricating oil applied to the wire surface is preferably an oil containing no hydrogen content such as perfluoropolyether oil (PFPE).

The flux cored wire according to the present embodiment can be manufactured by the same manufacturing process as that of a normal flux cored wire manufacturing method.
That is, first, a steel strip as an outer skin, and a flux containing fluoride, alloy components, oxides, carbonates and the like so as to have a predetermined content are prepared. The steel strip is formed into an open pipe (U-shaped) by a forming roll while feeding in the longitudinal direction to form a steel outer shell. During this molding, flux is supplied from the opening of the open pipe. The opposing edge surfaces of the opening are abutted and a slit-shaped gap is welded. The welding method is, for example, electric seam welding, laser welding, TIG welding, or the like. A slitless gap-free tube obtained by welding is drawn and annealed during or after the drawing process to obtain a slit-like gapless wire having a desired wire diameter. In addition, by not welding the slit-shaped gap after abutting the facing edge surfaces of the opening, the steel outer shell is made into a tube with a slit-shaped gap, and by drawing it, it has a slit-shaped gap. Get a wire.

  FIG. 2A shows a cross section of a butt seam welded wire having no slit-like gap. In this cross section, no weld marks are observed unless polished and etched. Therefore, a wire without a slit-like gap as described above may be referred to as a seamless wire. For example, “New Edition Introduction to Welding and Joining Technology” edited by the Japan Welding Society (2008); In 111, a wire having no slit-like gap is described as a seamless type wire.

  FIG. 2 (b) shows an example of a wire that abuts the edge surface of the steel strip, and FIG. 2 (c) shows an example of a wire that crimps the edge surface of the steel strip. Even if the gap is brazed as shown in Fig. 2 (b), or the gap is brazed as shown in Fig. 2 (c), then the gap-free wire is obtained. It is done. In addition, the wires shown in FIGS. 2B and 2C have a slit-like gap when the gap is not brazed.

  The high Ni flux cored wire according to the present embodiment can be applied to any type of steel plate. For example, the high Ni flux-cored wire according to the present embodiment can be used for gas shield arc welding of a steel plate having a tensile strength of about 490 to 1080 MPa and a plate thickness of 6 to 32 mm.

The high Ni flux cored wire according to the present embodiment is applicable to welding in which any kind of shield gas is used. The shield gas has a lower oxygen content in the weld metal, suppresses the generation of fumes, and ensures the stability of the welding arc. For example, a mixed gas of Ar and 3 to 20 vol% CO ₂ , Ar And a mixed gas of 1 to 10 vol% O ₂ , 100% CO ₂ gas, and the like can be used. The flux-cored wire according to the present embodiment generates little spatter even when these shielding gases are used. In particular, the flux-cored wire according to the present embodiment can suppress the amount of spatter generated even when 100% CO ₂ gas, which is likely to cause spattering according to the prior art, is used for welding.

In the method for manufacturing a welded joint according to this embodiment, the high Ni flux-cored wire for gas shielded arc welding according to this embodiment described above is used. In the method for manufacturing a welded joint according to the present embodiment, a preheating operation for preventing low temperature cracking is unnecessary, or the preheating operation can be remarkably reduced, and the amount of spatter generated can be reduced. The type of shield gas and the type of steel plate used in the method for manufacturing a welded joint according to the present embodiment are not particularly limited. However, when the shielding gas is 100% CO ₂ gas and the steel plate is a high strength steel of 780 MPa or more, the method for manufacturing a welded joint according to the present embodiment is compared with the method for manufacturing a welded joint according to the prior art, Since the spatter generation amount can be remarkably reduced and the cold cracking resistance can be remarkably improved, the welding workability can be improved. Also, in this case, the welded joint manufacturing method according to the present embodiment improves the fatigue strength of the welded part by reducing the tensile residual stress of the welded part, as compared with the welded joint manufacturing method according to the prior art. be able to.

  Next, the feasibility and effects of the present invention will be described in more detail with reference to examples.

  The steel strip is formed into an open tube by a forming roll while feeding the steel strip in the longitudinal direction, the flux is supplied from the opening of the open tube during the forming, and the opposing edge surfaces of the opening are butt-seamed and welded to form the steel strip. A seamless core pipe was annealed during the drawing process of the piped wire, and a flux-cored wire with a final wire diameter of φ1.2 mm was made as a prototype. Further, a flux-cored wire having a wire diameter of φ1.2 mm was made by drawing a seamed tube without seam welding. Table 1 and Table 2 show the composition of the components of the prototype flux-cored wire.

  The steel strip that is the steel outer shell has C: 0.002%, Si: 0.02%, Mn: 0.1%, P: 0.002%, S: 0.002%, and Al: 0.00. A soft steel plate containing 005% and the balance being iron and impurities was used. Here, all% means mass% when the mass of only the outer skin is 100%. In addition, the component% described in Table 1 and Table 2 means the component mass% with respect to the total mass of the wire (including all the outer skin and the flux). Therefore, for example, the Ni content described in Table 2 is contained in the flux as Ni powder, not as a steel shell.

  No. Only No. 2 was a seamed flux-cored wire as shown in FIG. 2 (C) where the seam was caulked and not brazed. Until just before the welding work, No. The entire two flux-cored wires were vacuum packaged. In other examples, a steel core was seam-welded, and a flux-cored wire with a seamless steel shell was used. No. Only 3 was coated with perfluoropolyether oil on the surface of the flux-cored wire. Vegetable oil was applied to the other wires.

Using these flux-cored wires, a steel plate 1 having a plate thickness of 20 mm is abutted at a root gap of 12 mm and a groove angle of 45 ° as shown in FIG. 3, and using a backing metal 2, a welding current of 280 A, a voltage of 27 V, Welding was performed under the welding conditions of a welding speed of 25 cm / min, a shielding gas of 100% CO ₂ (25 l / min), no preheating, and an interpass temperature of 100 to 150 ° C. Although the steel plate 1 and the backing metal 2 are SM490A, the grooved surface of the steel plate 1 and the surface of the backing metal 2 are made of buttering of 2 layers or more and 3 mm or more using a flux-cored wire to be tested. Carried out. The obtained welded joint has a low temperature cracking resistance of 0 ° C. in accordance with JIS Z 3157 (U-shaped welding weld cracking test) using a steel sheet with a thickness of 50 mm of a high strength steel sheet for welded structure shown in Table 4. -It was evaluated by a test under a constant atmosphere control of 60% humidity. Forty-eight hours after the creation of the test bee degree, the flux-cored wire applied to the sample having no cracks in the surface and cross section in the welded portion was judged to be acceptable with respect to low temperature crack resistance.

In addition, Ti oxide, Si oxide, Zr oxide, Mg oxide, and Al oxide were TiO ₂ , SiO ₂ , ZrO ₂ , MgO, and Al ₂ O ₃ , respectively.

  From the weld metal of the obtained weld metal (weld bead 3), as shown in FIG. 3, an A1 tensile test piece (round bar) 5 in accordance with JIS Z3111-2005 “Method of tensile and impact test of weld metal” A No. 4 Charpy test piece (2 mmV notch) 4 was collected, and a mechanical property test was performed on each test piece to measure the weld metal tensile strength and Charpy absorbed energy of each test piece. The flux-cored wire applied to the weld metal having a tensile strength of 780 MPa or more at room temperature was judged to be acceptable with respect to the tensile strength. The flux wire related to the weld metal having a breaking elongation of 12% or more at room temperature was judged to be acceptable with respect to elongation. In the Charpy impact test at 0 ° C., the flux-cored wire related to the weld metal having an absorption energy of 60 J or more was determined to be acceptable in terms of toughness.

Further, the fatigue test was performed by creating a cross welded joint test body shown in FIG. 4 using a prototyped flux wire. The fatigue test was performed under the conditions of a stress ratio of 0.1, a stress range of 100 MPa, and a frequency of 10 Hz, and the fatigue life was evaluated by measuring the number N of repeated life. The flux-cored wire according to the specimen that does not break when N is 6 × 10 ⁶ or more was determined to pass the fatigue life. Moreover, the welding workability | operativity of the flux cored wire was judged from arc stability, slag peelability, and bead shape.

The amount of spatter generated on each flux cored wire was measured by the following means. Test in copper collection box, on steel plate, with bead on plate, welding current 280A, voltage 27V, welding speed 25cm / min, shielding gas 100% CO ₂ (25l / min), and no preheating A weld bead was produced for 1 minute using the target flux-cored wire. Spatter scattered in the box during the production of the weld bead and spatter adhering to the steel plate were collected, and the total weight of those having a diameter of more than 1.0 mm was measured. The measurement results are shown in Table 3 in units of g / min. A flux-cored wire having a sputter generation amount of 5 g / min or less was judged to be acceptable with respect to sputtering suppression performance.

  Table 3 shows the evaluation results of each flux-cored wire. As shown in the test results of Table 3, the wire numbers 1 to 15, which are examples of the present invention, are all excellent in strength, toughness, fatigue characteristics, U-shaped crack test results, and low spatter generation amount. The overall judgment was acceptable.

  On the other hand, since the wire numbers 16-30 which are comparative examples do not satisfy the requirements prescribed in the present invention for at least one of the flux composition and the alloy component, they cannot satisfy at least one of strength, toughness, and fatigue characteristics. Because of the reasons mentioned above, or because the characteristics could not be evaluated due to poor welding workability or the occurrence of cracks in the U-shaped crack test, etc., both were determined to be unacceptable in the overall judgment.

According to the present invention, the preheating work for preventing the cold cracking is unnecessary, the preheating work can be remarkably reduced, and the amount of spatter generated can be reduced. In particular, when the present invention is applied to the welding of high-strength steel of 780 MPa or more and the welding where the shielding gas is 100% CO ₂ , the welding work efficiency can be remarkably improved as compared with the prior art. The value in the industry is extremely high.

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Backing metal 3 Weld bead 4 2mmV notch Charpy impact test piece 5 Round bar tensile test piece

Claims (9)

A high Ni flux-cored wire for gas shielded arc welding comprising a steel outer sheath and a flux filled in the steel outer shell,
The flux is
One or two or more fluorides selected from the group consisting of CaF ₂ , MgF ₂ , Na ₃ AlF ₆ , NaF, and K ₂ ZrF ₆ , and having an F conversion value with respect to the total mass of the flux-cored wire. Fluorides totaling 0.20% or more;
An oxide of 0.30% or more and less than 3.50% by mass% with respect to the total mass of the flux-cored wire,
Iron powder of 0% or more and less than 10.0% by mass% with respect to the total mass of the flux-cored wire,
Including
The content of the CaF ₂ contained in the fluoride is less than 1.00% by mass% with respect to the total mass of the flux-cored wire,
The content of Ti oxide contained in the oxide is 0.10% or more and less than 2.50% in mass% with respect to the total mass of the flux-cored wire,
The content of CaO contained in the oxide is less than 0.2% by mass% with respect to the total mass of the flux-cored wire,
X value calculated by Formula 1 is 3.0% or less,
Further, the chemical components excluding the fluoride, the oxide, and the carbonate are in mass% with respect to the total mass of the flux-cored wire,
C: 0.003-0.080%,
Si: 0.21 to 2.00%,
Mn: 0.81 to 3.50%,
P: 0.020% or less,
S: 0.010% or less,
Ni: 5.0 to 15.0%,
A high-Ni flux-cored wire for gas shielded arc welding, wherein the balance is Fe and impurities.
X = [Na ₃ AlF ₆ ] + [NaF] + [MgF ₂ ] + 1.5 × ([K ₂ ZrF ₆ ]) + 3.5 × ([CaF ₂ ]) (Formula 1)
However, the chemical formula with parentheses in Formula 1 represents the content of the fluoride according to the chemical formula in mass% with respect to the total mass of the flux-cored wire, and the content of the fluoride not contained is Consider 0. The flux-cored wire is further in mass% with respect to the total mass of the flux-cored wire,
Cu: 0.80% or less,
The high Ni for gas shielded arc welding according to claim 1, comprising one or more selected from the group consisting of Cr: 5.0% or less and Mo: 2.0% or less. Flux-cored wire. The flux-cored wire is further in mass% with respect to the total mass of the flux-cored wire,
Al: 0.400% or less,
Ti: 0.30% or less,
3. The gas shielded arc welding according to claim 1, comprising one or more selected from the group consisting of Nb: 0.05% or less and B: 0.0100% or less. High Ni flux cored wire. The flux-cored wire is further in mass% with respect to the total mass of the flux-cored wire,
Mg: 0.80% or less,
It contains 1 type or 2 or more types selected from the group which consists of Ca: 0.500% or less and REM: 0.0100% or less, The any one of Claims 1-3 characterized by the above-mentioned. High Ni flux cored wire for gas shielded arc welding. The flux is further
1 type or 2 types or more of the carbonates selected from the group consisting of CaCO ₃ , Na ₂ CO ₃ , and MgCO ₃ are contained in a total of 2.00% or less in mass% with respect to the total mass of the flux-cored wire. The high Ni flux-cored wire for gas shielded arc welding according to any one of claims 1 to 4.   The high Ni flux-cored wire for gas shielded arc welding according to any one of claims 1 to 5, wherein the steel outer shell has a slit-like shape without gaps.   The high Ni flux cored wire for gas shielded arc welding according to any one of claims 1 to 5, wherein the steel outer shell has a shape having a slit-like gap.   The high Ni flux-cored wire for gas shielded arc welding according to any one of claims 1 to 7, further comprising perfluoropolyether oil applied to the surface of the flux-cored wire.   A method for producing a welded joint, comprising using the high-Ni flux-cored wire for gas shielded arc welding according to any one of claims 1 to 8.