JP6939574B2 - Flux-cored wire for gas shielded arc welding and welding joint manufacturing method - Google Patents

Description

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

Ferritic heat-resistant steels and austenitic heat-resistant steels are well known as high-temperature materials used for heat-resistant and pressure-resistant pipes in thermal power generation boilers, petrochemical refining equipment, and the like. Ferritic heat-resistant steel is characterized by containing several% to 12% of Cr and several% of Mo. Since the coefficient of thermal expansion is smaller and cheaper than that of austenitic heat-resistant steel, various ferrite-based heat-resistant steels are used in large quantities depending on the usage environment.

When these ferritic heat-resistant steels are used, they are generally assembled by welding to form a structure. At the time of welding, a welding material for ferritic heat-resistant steel, which has an alloy component similar to that of the base material ferrite-based heat-resistant steel and can form a similar structure, is widely used.

By the way, when welding is performed using these welding materials for ferritic heat-resistant steel, for example, as described in Non-Patent Document 1, it is widely known that low-temperature welding cracking becomes a problem. In order to prevent this, as shown in Non-Patent Document 1, work is taken to preheat the portion to be welded before welding.

Further, in Patent Document 1, in order to prevent low-temperature cracking of high Cr ferrite heat-resistant steel, preheating is performed at 150 to 300 ° C. regardless of welding methods such as coated arc welding, TIG welding, and submerged arc welding. The specific method is shown. Further, in Patent Document 1, in order to prevent low-temperature cracking in welding, the welded portion is heated to a temperature of 150 to 300 ° C. per 25 mm of the base metal thickness before the welded portion is cooled to less than 300 ° C. after the completion of welding. It is stated that heat is required immediately after holding for minutes or more and 2 hours or less.

However, since the preheating operation shown in these documents heats the welded portion to a high temperature, the welding efficiency is significantly impaired and the welding cost is increased. Therefore, it is desired to omit the preheating work or lower the preheating temperature. In addition, it is desirable to omit the heat immediately after welding because it is necessary to heat and maintain the welded portion at a high temperature before the welded portion is cooled after welding.

Regarding the welding material that enables the omission of preheating and immediate heat, for example, Patent Document 2 states that the amount of alloying elements such as C is adjusted, and Cr and Mo are 0.8 to 1.5% and 0, respectively. TIG welding materials containing 4 to 1.2% have been proposed. However, the technique proposed here originally relates to a solid wire used for TIG welding in which low temperature cracking is less likely to be a problem, and cannot be applied to a flux-cored wire whose application range is expanding in recent years.

On the other hand, Patent Document 3 discloses a steel material for welding materials containing 0.1 to 10.0% of Co as an essential element and optionally 0.1 to 3.0% of Mo. Patent Document 3 states that preheating can be omitted by using a shielded metal arc welding material or a flux-cored wire manufactured by using the above-mentioned steel material for welding material in which Co is indispensable. Further, Patent Document 4 proposes a 490-780 MPa class high-tensile flux-cored wire having improved low-temperature cracking resistance by containing V in the outer skin or flux. However, the welding material proposed in Patent Document 3 is not preferable for industrial use in that it requires the inclusion of expensive Co. In Patent Document 4, no consideration is given to the strength of the weld metal at a high temperature.

Patent Document 5 discloses an epoch-making technique in which the amount of diffusible hydrogen contained in the weld metal is reduced and the low temperature crack resistance is improved by adding a fluoride mainly composed _{of CaF 2} to the flux-containing wire. doing. However, Patent Document 5 does not study the means for ensuring the high temperature strength of the weld metal.

As a result of investigating to solve the above-mentioned problems, the present inventors have managed the amount of flux in the flux in the flux-cored wire within an appropriate range to reduce the amount of diffusible hydrogen in the weld metal. It was found that the amount of reduction can be reduced, the preheating work can be simplified, and that the required high temperature strength can be achieved at the same time by setting the alloy component of the entire wire within a predetermined range.

As a result, a welded joint having a welded portion having good high temperature strength and low temperature crack resistance was obtained. However, when the above-mentioned flux-cored wire is used for the welding work in which the shield gas is 100% CO _{2 gas, there is a problem that spatter occurs frequently and the workability is remarkably poor.} Since 100% CO ₂ shield gas is _{cheaper than Ar-CO 2} mixed shield gas, it is required to provide a flux-cored wire applicable to welding using _{100% CO 2 shield gas.}

Welding Technology System <Volume 14> Welding of heat-resistant steel and heat-resistant materials, Sanpo Publishing Co., Ltd. (1980), P.M. 55-58

Japanese Unexamined Patent Publication No. 8-164481 JP-A-2002-1579 Japanese Unexamined Patent Publication No. 2006-9070 Japanese Unexamined Patent Publication No. 8-257785 Japanese Unexamined Patent Publication No. 2015-27700

The subject of the present invention is a method for manufacturing a flux-cored wire and a welded joint, which can obtain a weld metal having excellent low-temperature cracking resistance and high-temperature strength, a small amount of spatter, and other good welding workability. Is to provide.

The gist of the present invention is as follows.

(1) The flux-containing wire for gas shielded arc welding according to one aspect of the present invention includes a steel outer skin and a flux filled in the steel outer skin, and is an alloy in mass% with respect to the total mass of the flux-containing wire. As components, C: 0.003 to 0.150%, Si: 0.05 to 2.00%, Mn: 0.40 to 3.50%, P: 0.020% or less, S: 0.020% Hereinafter, Cr: 1.50 to 13.00% and Mo: 0.10 to 2.50% are contained, and further, in mass% with respect to the total mass of the flux-filled wire, in terms of fluoride: F conversion value. The total is more than 0.10% and 0.30% or less, Si oxide: _{0.01 to 0.40% in terms of SiO 2} , and Na compound and K compound: 0 in total of Na conversion value and K conversion value. It contains 06 to 0.35%, and the balance is composed of Fe and impurities in the form of any one or more of the steel outer skin, iron powder, and iron alloy powder.
(2) The flux-cored wire for gas shielded arc welding according to (1) above further has V: 0.5000% or less and Nb: 0.50% or less in mass% with respect to the total mass of the flux-cored wire. , Ti: 0.50% or less, and Ta: 0.50% or less may contain one or more selected from the group.
(3) The flux-cored wire for gas shielded arc welding according to the above (1) or (2) further has Cu: 1.00% or less and Ni: 3 in mass% with respect to the total mass of the flux-cored wire. It may contain one or more selected from the group consisting of 0.0% or less, Co: 5.00% or less, and B: 0.0200% or less.
(4) The flux-cored wire for gas shielded arc welding according to any one of (1) to (3) above has a mass% of the total mass of the flux-cored wire, W: 4.00% or less. It may be contained.
(5) The flux-welded wire for gas shielded arc welding according to any one of (1) to (4) above has Ca: 0.500% or less in mass% with respect to the total mass of the flux-welded wire. It may contain one or more selected from the group consisting of REM: 0.0100% or less, Mg: 0.80% or less, and Al: 0.400% or less.
(6) The flux-welded wire for gas shielded arc welding according to any one of (1) to (5) above is further, in mass% with respect to the total mass of the flux-welded wire, and is 0 in terms of Zr compound: Zr. It may contain ~ 0.30%.
(7) The flux-cored wire for gas shielded arc welding according to any one of (1) to (6) above may have a steel outer skin having a slit-like shape without gaps.
(8) The flux-cored wire for gas shielded arc welding according to any one of (1) to (6) above may have a shape in which the steel outer skin has a slit-shaped gap.
(9) The flux-cored wire for gas shielded arc welding according to any one of (1) to (8) above further comprises a feed lubricant on the outer surface of the steel outer skin, and the feed lubricant of the feed lubricant. The amount per 10 kg of the flux-cored wire may be 0.25 to 1.00 g.
(10) In another method of manufacturing a welded joint according to another aspect of the present invention, a steel material is welded using the flux-cored wire for gas shielded arc welding according to any one of (1) to (9) above.

INDUSTRIAL APPLICABILITY According to the present invention, a weld metal having excellent high-temperature strength can be obtained, low-temperature cracking resistance is excellent, and a flux-cored wire and a welded joint for gas shielded arc welding with a small amount of spatter generation and good welding workability can be obtained. A manufacturing method can be provided. In particular, the present invention has low temperature crack resistance even when applied to welding ferrite-based heat-resistant steel used for members requiring high-temperature strength and welding in which the shield gas is 100% CO _2. It is possible to provide a method for manufacturing a flux-filled wire for gas shielded arc welding and a welded joint, which are excellent, generate less spatter, and can be welded with high welding efficiency.

It is sectional drawing of the wire which concerns on this embodiment.

The present inventors conducted experiments by changing the amounts of various slag components in a flux-cored wire for gas shielded arc welding, which requires high-temperature strength. As a result, the present inventors can improve low-temperature cracking, which is a problem when a steel material is welded using a flux-cored wire containing 1.50 to 13.00% of Cr, and the shield gas can be used. We have found a component system that can suppress the amount of spatter generated even when used for welding, which 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 the slag component and the alloy component. Unless otherwise specified, the content of the component in the description of the flux-cored wire is mass% with respect to the total mass of the flux-cored wire.
The flux-cored wire for gas shielded arc welding according to the present embodiment has a steel outer skin and a flux wrapped in the steel outer skin. The flux filled inside the steel outer skin contains a slag component such as a fluoride and an oxide, and an alloy component such as a metal powder and an alloy powder. In addition, the flux may contain iron powder for adjusting the filling rate. First, the flux inserted inside the steel skin of the wire will be described.

[Fluoride: Total F conversion value is more than 0.10% and 0.30% or less]
The flux-cored wire according to the present embodiment contains fluoride, and the content thereof is controlled by the F conversion value. The "F-converted value of the fluoride in the flux-cored wire" means the content of F contained in the fluoride in the flux-filled wire in mass% with respect to the total mass of the flux-filled wire. That is, the F conversion value of the flux-cored wire is the F content of the flux-cored wire. The contents of the K compound, Na compound, and Zr compound, which will be described later, are also controlled by the K conversion value, the Na conversion value, and the Zr conversion value. That is, the "K conversion value of the K compound in the flux-containing wire", the "Na conversion value of the Na compound in the flux-containing wire", and the "Zr conversion value of the fluoride in the flux-containing wire", which will be described later, are similarly applied. , The content of K contained in the K compound contained in the flux-filled wire, Na contained in the Na compound, and Zr contained in the Zr compound in mass% with respect to the total mass of the flux-filled wire.

F is _{contained in the flux-filled wire as a fluoride of CaF 2} , NaF, LiF, MgF ₂ , K ₂ SiF ₆ , K ₂ ZrF _6, Na ₃ AlF _{6 , AlF 3,} etc., and reduces the amount of diffusible hydrogen in the weld metal. It has the effect of reducing and preventing low temperature cracking. When the F content is 0.10% or less, low temperature cracking cannot be sufficiently suppressed. Further, NaF, Na ₃ AlF ₆ , AlF ₃ , K ₂ SiF ₆ , MgF _2, etc. also have a function as an arc stabilizer if the content is appropriate. On the other hand, fluoride has a function of increasing spatter, and particularly when the F content exceeds 0.30%, the arc becomes rough and unstable, and the spatter generation amount exceeds the allowable upper limit. Therefore, the F content is set to more than 0.10% and 0.30% or less. The lower limit of the F content may be 0.11% or 0.12%. The upper limit of the F content may be 0.25% or 0.27%.

[Si oxide: 0.01 to 0.40% in terms of _{SiO 2]}
When Si is contained in the flux of the flux-cored wire as a Si oxide such as silica sand (SiO ₂ ), zircon sand (ZrSiO ₄ ), sodium silicate (Na ₂ SiO ₃ ), and potassium silicate (K ₂ SiO _3). It has a function of increasing the viscosity of the molten slag to improve the slag encapsulation property, improving the familiarity of the bead toe, and improving the appearance and shape of the bead.

In view of the above circumstances, in the flux-cored wire according to the present embodiment, the amount of Si oxide is in the range of 0.01 to 0.40% in terms of _{SiO 2.} If the amount of Si oxide is _{less than 0.01% in terms of SiO 2} , the fit of the bead toe of the weld bead will be poor, and the bead appearance and bead shape will be poor. When the amount of Si oxide _{exceeds 0.40% in terms of SiO 2} , the amount of slag generated during welding increases, and welding defects such as slag entrainment are likely to occur. The lower limit of the Si oxide content may be 0.02% or 0.05% in terms _{of SiO 2.} The upper limit of the Si oxide content may be 0.35% or 0.30% in terms _{of SiO 2.}

Note that "SiO ₂ converted value of Si oxide in the flux-cored wire", in the case of Si contained in the Si oxide in the flux cored wire is considered that all of the SiO _2, the SiO ₂ flux cored It means the content in mass% with respect to the total mass of the wire. _{For the SiO 2} conversion value of the Si oxide in the flux-containing wire, the amount of Si constituting the Si oxide contained in the flux-containing wire is obtained, and 2.14 (= (28.1 + 16.0 × 2) / 28.1 and 28.1 are the atomic weights of Si, and 16.0 is the atomic weight of oxygen).

[Na compound and K compound: 0.06 to 0.35% in total of Na conversion value and K conversion value]
Na contained in the flux-cored wire as an oxide of _{Na 2} O and Na ₂ SiO ₃ , and K contained in the flux-cored wire as an oxide of _{K 2 O and K 2} SiO _{3 and the like cause an arc.} It has the function of stabilizing and suppressing the amount of spatter. Further, when Na is contained as a fluoride such as NaF described later and K is _{contained as a fluoride such as K 2} SiF ₆ described later, it has a function of stabilizing an arc. In addition, Na fluoride and K fluoride also contribute to the reduction of the amount of diffusible hydrogen, which is understood as the effect of F described later. The Na compound and the K compound can be contained in the form of powders such as _{K 2} SiO ₃ , Na ₂ SiO ₃ , NaF, and K ₂ SiF _{6, which} are solid components of water glass composed of sodium silicate and potassium silicate.

In order to obtain the above effects, in the flux-cored wire according to the present embodiment, the total content (Na + K) of the Na compound and the K compound shall be 0.06% or more in total of the Na conversion value and the K conversion value. There is a need. On the other hand, when the total of the Na conversion value and the K conversion value exceeds 0.35%, the arc becomes too strong and the spatter amount increases. Further, when the total of the Na conversion value and the K conversion value exceeds 0.35%, the familiarity of the bead toe portion becomes poor, and the bead appearance and the bead shape become poor. Further, when the total of the Na conversion value and the K conversion value exceeds 0.35%, the amount of generated slag increases, and welding defects such as slag entrainment are likely to occur. Therefore, the total value of the Na conversion value and the K conversion value is set to 0.35%. The lower limit of the total of the Na conversion value and the K conversion value may be 0.08% or 0.10%. Further, the upper limit of the total of the Na conversion value and the K conversion value may be 0.25% or 0.30%.

[Zr compound: 0 to 0.30% in terms of Zr]
The flux-cored wire according to this embodiment does not necessarily contain the Zr compound. Therefore, the lower limit of the content of the Zr compound is 0%. However, when the Zr compound is contained in the flux-cored wire, it has a deoxidizing effect, which reduces the amount of oxygen in the weld metal. In addition, the Zr compound has the effect of improving the shape of the bead toe. Therefore, 0.06% or more of Zr compound may be contained. On the other hand, when the content of the Zr compound exceeds 0.30%, the amount of slag produced increases and welding defects such as slag entrainment are likely to occur. Therefore, the upper limit of the content of the Zr compound is 0.30%. The upper limit of the content of the Zr compound may be 0.20% or 0.25%. The Zr compound is contained as _{ZrSiO 4} or K ₂ ZrF _6.

Although ZrSiO ₄ is an oxide of Zr and also an oxide of Si, when ZrSiO ₄ is contained in the flux-filled wire, _{the content of ZrSiO 4 is} the content of the Zr compound (Zr conversion value). And Si oxide content (SiO ₂ conversion value) shall be included in both. Similarly, when K ₂ ZrF ₆ is contained in the flux-cored wire, _{the content of K 2} ZrF ₆ is set to either the content of Zr compound (Zr conversion value) or the content of fluoride (F conversion value). Is also included. _{The content of other components (K 2} SiF _6, etc.) that can be classified into two or more kinds of compounds is also treated in the same manner.

Next, the alloy component of the flux-cored wire according to the present embodiment will be described.

(C: 0.003 to 0.150%)
C is an essential additive element because it forms carbides, contributes to ensuring the high temperature strength of the weld metal, and is effective in obtaining bainite and martensite structures, and is in the range of 0.150% or less. It is contained in the flux-containing wire according to the present embodiment. When the C content of the alloy component exceeds 0.150%, the weld metal is excessively hardened, which is not preferable for the toughness of the weld metal. The upper limit of the C content may be 0.090%, 0.080%, or 0.070%. From the viewpoint of joint strength and decarburization cost during steel production, the lower limit of C content is set to 0.003%. The lower limit of the C content may be 0.015% or 0.020%.

(Si: 0.05 to 2.00%)
Si is a deoxidizing element. The flux-cored wire according to the present embodiment needs to contain 0.05% or more of Si in order to reduce the amount of O in the weld metal and improve the cleanliness. However, if Si is contained in excess of 2.00%, the creep ductility and toughness of the weld metal are lowered and spatter is also increased. Therefore, the Si content is set to 0.05 to 2.00%. Further, in order to stably secure the toughness of the weld metal, the lower limit of the Si content may be 0.10%, 0.20%, or 0.21%. The upper limit of the Si content may be 1.80%, 1.60% or 1.40%.

(Mn: 0.40 to 3.50%)
Mn is an element that secures the hardenability of the weld metal and enhances the strength, and is contained in the flux-containing wire according to the present embodiment in a range of 3.50% or less depending on the required strength of the weld metal. When Mn is contained in excess of 3.50%, the grain boundary embrittlement sensitivity of the weld metal increases, the toughness of the weld metal deteriorates, and spatter also increases. However, Mn also has the effect of immobilizing S as MnS and preventing the occurrence of high temperature cracks. In order to obtain this effect, the lower limit of the Mn content is set to 0.40%. The lower limit of the Mn content may be 0.60%, 0.80%, 0.90%, or 1.00%. The upper limit of the Mn content may be 3.40%, 3.30%, or 3.20%.

(P: 0.020% or less)
Since P is an impurity element and inhibits the toughness of the weld metal, it is necessary to reduce it as much as possible. However, the P content is 0.020% or less within an allowable range of adverse effects on the toughness. The upper limit of P may be limited to 0.015% for further improvement of toughness.

(S: 0.020% or less)
S is also an impurity element, and if it is present in an excessive amount, both the toughness and ductility of the weld metal are deteriorated, so it is preferable to reduce it as much as possible. The S content shall be 0.020% or less within an acceptable range for adverse effects on the toughness and ductility of the weld metal. The upper limit of S may be limited to 0.010% in order to further improve the toughness of the weld metal.

(Cr: 1.50 to 13.00%)
Cr is an essential element for ensuring oxidation resistance and high-temperature corrosion resistance in heat-resistant steel, and for stably obtaining the bainite and martensite structures of the weld metal matrix. In order to obtain the effect, it is necessary to contain 1.50% or more of Cr. However, if Cr is excessively contained, the stability of the carbide is lowered due to the formation of a large amount of Cr carbide during use at a high temperature, the creep strength of the weld metal is lowered, and the toughness of the weld metal is also deteriorated. Therefore, the Cr content needs to be 13.000% or less. The desired range of Cr content is 1.60 to 12.50%, and the more desirable range is 1.80 to 12.00% or 2.00 to 11.00%.

(Mo: 0.10 to 2.50%)
Mo is an element that solid-solves and strengthens the weld metal matrix and contributes to the improvement of creep strength. In order to obtain this effect, the flux-cored wire according to the present embodiment needs to contain 0.10% or more of Mo. However, if Mo is contained in an amount of more than 2.50%, the effect is saturated and coarse carbides are generated, resulting in a decrease in the toughness of the weld metal. The desirable range of Mo content is 0.30 to 2.20%, and the more desirable range is 0.50 to 2.00%.

The flux-containing wire according to the present embodiment has V, Nb as an alloy component or a metal deoxidizing component, in addition to the above basic components, depending on the strength level of the steel material to be welded and the required degree of toughness of the welded portion. , Ti, Ta, Cu, Ni, Co, B, W, Ca, REM, Mg, and Al. Can be contained instead of. However, even when these optional elements are not contained, 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%.

(V: 0.5000% or less, Nb: 0.50% or less, Ti: 0.50% or less, Ta: 0.50% or less)
The flux-cored wire according to the present embodiment is one or more selected from the group consisting of V: 0.5000% or less, Nb: 0.50% or less, Ti: 0.50% or less, and Ta: 0.50% or less. May be optionally contained. All of these combine with carbon and nitrogen during use at high temperatures and precipitate as carbonitrides, which contributes to the creep strength of the weld metal. Therefore, even if the flux-filled wire according to the present embodiment contains these elements. good. However, if these elements are excessively contained, a large amount of the above-mentioned carbonitride is precipitated, which causes a decrease in the toughness of the weld metal. Therefore, when the flux-cored wire contains V, Nb, Ti, and Ta, the upper limit of any of the elements is within the above range. The content of each of these elements is preferably 0.40% or less, more preferably 0.30% or less. Further, in order to stably obtain the effects of these elements, it is desirable that each of these elements is contained in an amount of 0.03% or more, more preferably 0.04% or more. Further, Ti is preferably 0.05% to 0.30%.

(Cu: 1.00% or less, Ni: 3.0% or less, Co: 5.00% or less, B: 0.0200% or less)
The flux-cored wire according to the present embodiment is one or more selected from the group consisting of Cu: 1.00% or less, Ni: 3.0% or less, Co: 5.00% or less, and B: 0.0200% or less. May be contained. Since all of these are elements effective for enhancing the hardenability of the weld metal and obtaining a bainite structure or a martensite structure, the flux-filled wire according to the present embodiment may contain these elements. However, when these elements are excessively contained, the creep ductility of the weld metal is lowered. Therefore, when the flux-cored wire contains these elements, the upper limit is 1.00% for Cu, 3.0% for Ni, 5.00% for Co, and 0.0200% for B. Desirably, Cu is 0.80% or less, Ni is 2.0% or less or 1.5% or less, Co is 4.50% or less, and B is 0.0180% or less. More preferably, Cu and Ni are 0.60% or less, Co is 4.00% or less, and B is 0.0150% or less. Further, in order to stably obtain these effects, it is desirable that Cu, Ni and Co are 0.10% or more, B is 0.0005% or more, and Cu, Ni and Co are 0.20. It is desirable that% or more and B be 0.001% or more.

(W: 4.00% or less)
Since W is an element that solid-solves and strengthens the matrix of the weld metal and contributes to the improvement of creep strength, the flux-cored wire according to the present embodiment may contain W. However, when W is excessively contained, W produces a coarse intermetallic compound, which causes a decrease in the toughness of the weld metal. Therefore, when W is contained, the upper limit is 4.00%. The W content is preferably 3.80% or less, and more preferably 3.50% or less. Further, in order to obtain a stable effect, it is desirable that W is contained in an amount of 0.10% or more, more preferably 0.20% or more.

(Mg: 0.80% or less, Ca: 0.500% or less, REM: 0.010% or less, Al: 0.400% or less)
Mg is a strongly deoxidizing element, which reduces the amount of O in the weld metal and improves the ductility and toughness of the weld metal. When it is contained in order to obtain this effect, it is preferable to contain 0.10% or more of Mg. However, if the Mg content in the flux-cored wire exceeds 0.80%, Mg forms a coarse oxide in the weld metal, resulting in a non-negligible decrease in toughness. Further, if the Mg content in the flux-cored wire exceeds 0.80%, the stability of the arc during welding deteriorates, which also causes the bead shape to deteriorate. Therefore, when Mg is contained, the content thereof is set to 0.80% or less.

Both Ca and REM are effective in improving the ductility and toughness of the weld metal by changing the structure of the sulfide in the weld metal and reducing the size of the sulfide and the oxide in the weld metal. When it is contained in order to obtain the effect, the Ca content may be 0.100% or more, and the REM content may be 0.0020% or more. On the other hand, excessive content of Ca and REM causes coarsening of sulfides and oxides, resulting in deterioration of ductility and toughness of the weld metal. Further, if Ca and REM are excessively contained, there is a possibility that the shape of the weld bead is deteriorated and the weldability is deteriorated. Therefore, the upper limit of the Ca content is 0.500%, and the upper limit of the REM content is 0.0100%. The term "REM" refers to a total of 17 elements composed of Sc, Y and lanthanoids, and the above-mentioned "content of REM" means the total content of these 17 elements.

Al is a deoxidizing element, and like Si, it has the effect of reducing the amount of O in the weld metal and improving the cleanliness of the weld metal. When it is contained in order to exert its effect, it is preferable to contain 0.001% or more of Al. On the other hand, when Al is contained in excess of 0.400%, Al forms Al nitrides and Al oxides, and inhibits the toughness of the weld metal. Therefore, the Al content is set to 0.400% 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 set to 0.004%, and the upper limit of the Al content may be set to suppress the formation of coarse oxides. , 0.200%, 0.100% or 0.080%.

The element does not necessarily have to be a pure substance, and there is no problem even if it is contained in the form of an alloy such as Cu—Ni. Further, these elements may be contained in either the steel outer skin or the flux because the effect is the same regardless of whether they are contained in the steel outer skin or as a flux. Further, Cu and the like may be contained in the plating of the outer surface of the steel outer skin.

[Remaining: Fe and impurities]
The balance of the components of the flux-cored wire for gas shielded arc welding according to this embodiment is Fe and impurities. Fe is contained in the flux-cored wire as any one or more forms selected from the group consisting of a steel outer skin, iron powder for adjusting the filling rate, and iron alloy powder for controlling the amount of alloying elements. The type of iron powder is not particularly limited, but atomized iron powder is desirable in order to suppress an increase in the amount of oxygen in the weld metal. Impurities are components that are mixed due to various factors in the raw material or the manufacturing process when the flux-containing wire according to the present embodiment is industrially manufactured, and adversely affect the flux-containing wire according to the present embodiment. Means something that is acceptable to the extent that it does not exist. For example, Al, which can be contained as an impurity during steelmaking of a steel outer skin, is preferably small because it forms non-metal inclusions in the weld metal and reduces toughness as described above, but it is preferable with respect to the total mass of the flux-filled wire. If the mass% is 0.400% or less, it is acceptable. P and S reduce the toughness of the weld metal as described above, but are acceptable as long as they are 0.020% or less in mass% with respect to the total mass of the flux-cored wire. N impairs the toughness of the weld metal when it is contained in the weld metal as a solid solution N, but it is acceptable if it is 0.01% or less in mass% with respect to the total mass of the flux-filled wire.

In the flux-cored wire according to the present embodiment, the flux filling rate (ratio of the total mass of the flux to the total mass of the flux-filled wire) is not particularly limited, but is preferably 8 to 20% from the viewpoint of productivity.

Subsequently, the form of the flux-cored wire will be described.
FIG. 1 shows a cut surface of a flux-cored wire. FIG. 1 (a) shows a flux-cored wire made by butt-welding edge surfaces, FIG. 1 (b) shows a flux-cored wire made by butt-butting edge surfaces, and FIG. 1 (c) shows an edge surface. The flux-cored wire made by caulking is shown. As described above, the flux-cored wire includes a wire having no slit-shaped gap in the steel outer skin as shown in FIG. 1 (a) and a slit in the steel outer skin as shown in FIGS. 1 (b) and 1 (c). It can be roughly divided into wires having a similar gap. Any cross-sectional structure can be adopted for the flux-cored wire according to the present embodiment, but in order to suppress low-temperature cracking of the weld metal, a wire having no slit-shaped gap (also referred to as a seamless wire) should be used. Is preferable.

Hydrogen that invades the welded portion during welding diffuses into the weld metal and the steel material side, accumulates in the stress concentration portion, and causes low-temperature cracking. The hydrogen source is moisture contained in the welding material, moisture mixed from the atmosphere, rust and scale adhering to the steel surface, and the like. Under welds where the cleanliness of the weld and the conditions of the gas shield are well controlled, the water hydrogen contained in the wire is the main source of diffusible hydrogen in the weld joint.

For this reason, it is desirable to use a steel outer skin as a pipe without slit-shaped gaps and suppress the invasion of hydrogen in the atmosphere from the steel outer skin into the flux from the time when the wire is manufactured until the time when it is used. When the steel outer skin is a tube with slit-shaped gaps (seam), moisture in the atmosphere easily enters the flux through the slit-shaped gaps in the outer skin, so hydrogen sources such as moisture can enter the wire. It cannot be prevented by the steel hull alone. If the steel crust has slits and has a long time to use after manufacture, it is desirable to vacuum package the entire wire or store it in a container that can keep the wire dry.

The flux-cored wire according to the present embodiment may further include a feed lubricant on the outer surface of the steel outer skin. The feed lubricant on the surface of the flux-cored wire improves the feedability of the flux-cored wire, especially in the case of semi-automatic welding, stabilizes the arc, reduces the amount of spatter, and prevents the occurrence of welding defects. .. The amount of the feed lubricant applied is not particularly limited, but is preferably 0.25 to 1.00 g per 10 kg of wire, for example. If the amount of the feed lubricant on the surface of the flux-cored wire is less than 0.20 g per 10 kg of the wire, the wire feedability may be poor, the arc may be unstable, and the amount of spatter generated may increase. Further, in this case, a slag entanglement defect may easily occur. On the other hand, if the amount of feed lubricant on the surface of the flux-cored wire exceeds 1.00 g per 10 kg of wire, the flux-cored wire may slip at the feed roller portion, the arc may become unstable, and the amount of spatter generated may increase. be. Further, in this case, the amount of diffusible hydrogen in the weld metal may increase and low-temperature cracking may easily occur.

The feed lubricant may be any of animal and vegetable oils, mineral oils and synthetic oils. As the animal and vegetable oil, palm oil, rapeseed oil, castor oil, pig oil, cow oil, fish oil and the like can be used, and as the mineral oil, machine oil, turbine oil, spindle oil and the like can be used. As the synthetic oil, hydrocarbon-based, ester-based, polyglycol-based, polyphenol-based, silicone-based, and fluorocarbon-based oils can be used. Further, a sulfur-containing lubricating oil which is one or more of sulfur-containing fats and oils, sulfide esters, sulfide fatty acids or sulfide olefins in one or more base oils of fats and oils or esters can also be used. The above-mentioned component specification of the flux-cored wire relates to the steel outer skin of the flux-cored wire and the flux, and does not include the component of the feed lubricant. Since the amount of the feed lubricant applied is very small with respect to the mass of the flux-cored wire, the feed lubricant has no substantial effect in defining the components of the flux-cored wire.

The flux-cored wire according to the present embodiment can be manufactured by the same manufacturing process as the usual method for manufacturing a flux-cored wire.
That is, first, a steel strip to be a steel outer skin and a flux in which fluoride, alloy components, oxides and the like are blended so as to have a predetermined content are prepared. The steel strip is formed into an open pipe (U-shape) by a forming roll while being fed in the longitudinal direction to form a steel outer skin. During this molding, flux is supplied from the opening of the open pipe. The opposing edge surfaces of the openings are butted and a slit-shaped gap is welded. The welding method is, for example, electric sewing welding, laser welding, TIG welding, or the like. A slit-shaped gapless tube obtained by welding is drawn and annealed during wire drawing or after the wire drawing process is completed to obtain a slit-shaped gapless wire having a desired wire diameter. Further, by not welding the slit-shaped gap after abutting the opposite edge surfaces of the openings, the steel outer skin is made into a pipe with a slit-shaped gap, and by drawing the wire, the slit-shaped gap is provided. Get the wire.

A cross section of a butt-seam welded wire without slit-shaped gaps is shown in FIG. 1 (a). No weld marks are observed on this cross section unless it is polished and etched. Therefore, a wire having no slit-shaped gap as described above is sometimes called a seamless wire. For example, "Introduction to Welding and Joining Technology" (2008), edited by the Welding Society, Sanpo Publishing, p. In 111, a wire having no slit-shaped gap is described as a seamless type wire.

FIG. 1B shows an example of a wire in which the edge surfaces of the steel strips are butted, and FIG. 1C shows an example of a wire in which the edge surfaces of the steel strips are crimped. Even if the gaps are brazed after abutting as shown in FIG. 1 (b) or the gaps are brazed after crimping as shown in FIG. 1 (c), a wire without slit-shaped gaps is obtained. Will be brazed. Further, the wires of FIGS. 1B and 1C are wires having slit-shaped gaps when the gaps are not brazed.

The flux-cored wire according to this embodiment can be applied to any kind of steel material. For example, the flux-cored wire according to the present embodiment is used for gas shielded arc welding of ferritic heat-resistant steel containing Cr: 1.5 to 13% and Mo: 0.1 to 2.5% and having a plate thickness of 4 mm or more. It can be used, but is not limited to this.

The flux-cored wire according to this embodiment can be applied to welding in which any kind of shield gas is used. In order to lower the oxygen content of the weld metal, suppress the amount of fume generation, and ensure the stability of the welding arc, the shield gas is, for example, a mixed gas of _{Ar and 3 to 20 vol% CO 2, Ar.} A mixed gas of 1 to 10 vol% O _{2 and 100% CO 2} gas can be used, but the present invention is not limited thereto. The flux-cored wire according to the present embodiment is less likely to generate spatter even when these shield 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 prone to spatter according to the prior art, is used for welding as a shield gas.}

In the method for manufacturing a welded joint according to the present embodiment, a steel material is welded using the flux-cored wire for gas shielded arc welding according to the above-described embodiment. In the method for manufacturing a welded joint according to the present embodiment, preheating work for preventing low temperature cracking is unnecessary, or the preheating work can be remarkably reduced, and the amount of spatter generated can be reduced. The type of shield gas and the type of steel material used in the method for manufacturing a welded joint according to the present embodiment are not particularly limited. However, when the shield gas is 100% CO ₂ gas and the steel material is ferritic heat-resistant steel, the method for manufacturing the welded joint according to the present embodiment is remarkable as compared with the method for manufacturing the welded joint by the prior art. Since the amount of spatter generated can be reduced and the low temperature crack resistance can be remarkably improved, the welding workability can be improved. Further, in this case, the method for manufacturing a welded joint according to the present embodiment can improve the high temperature strength of the welded portion as compared with the method for manufacturing a welded joint according to the prior art.

Next, the feasibility and effect of the present invention will be described in more detail by way of examples.

While feeding the steel strip in the longitudinal direction, it is formed into an open tube by a forming roll, flux is supplied from the opening of the open tube during this forming, and the opposite edge surfaces of the opening are abutted and seam welded to form the steel strip. A flux-cored wire having a final wire diameter of φ1.2 mm was prototyped by using a seamless pipe and annealing during the wire drawing work of the pipe-made wire. In addition, a flux-cored wire having a wire diameter of φ1.2 mm was prototyped by drawing a seam-welded pipe without seam welding. The component compositions (flux composition and alloy component or metal deoxidizing component) of the prototyped flux-cored wire are shown in Table 1, Table 2-1 and Table 2-2. Numerical values outside the scope of the present invention are underlined. In addition, the components that were not added were left blank in the table. The prototyped flux-containing wire contains one or more selected from the group consisting _{of CaF 2} , NaF, LiF, MgF ₂ , K ₂ SiF ₆ , K ₂ ZrF _6, Na ₃ AlF ₆ , and AlF _{3 as fluoride.} rice field. The "F-converted value" shown in the table is the total content of the fluoride contained in the flux-cored wire in the F-converted value. _{Further, "SiO 2} " described in the table is the content of Si oxide contained in the flux-cored wire in _{terms of SiO 2} , and "Na + K" is the Na compound and K compound contained in the flux-cored wire. Is the total content of the Na-converted value and the K-converted value, and "Zr" is the content of the Zr compound contained in the flux-cored wire in the Zr-converted value.

The steel strip, which is the steel outer skin, contains C: 0.04%, Si: 0.02%, Mn: 0.1%, P: 0.002%, S: 0.002%, and the balance is A soft steel sheet composed of iron and impurities was used. Here,% means the mass% when the mass of only the outer skin is taken as 100%. In addition, the component% described in the table means the component mass% with respect to the total mass of the wire (including all the steel outer skin and the flux). Therefore, for example, Cr shown in Tables 2-1 and 2-2 is contained in the flux as Cr powder instead of the steel outer skin.

Only wire number 2 was a seamed, unbrazed, flux-cored wire as shown in FIG. 1 (c). Until just before the welding operation, the entire flux-cored wire of wire number 2 was vacuum-packed. In the other example, the steel outer skin was seam welded, and the steel outer skin was made into a seamless flux-cored wire. Only wire number 3 was coated with perfluoropolyether oil as a feed lubricant on the surface of the flux-cored wire. Palm oil was applied to the other wires as a feed lubricant. The amount of the feed lubricant applied was 1.20 g per 10 kg of wire for wire number 6, and 0.20 to 1.00 g per 10 kg of wire for other flux-cored wires.

The low temperature crack resistance is 20 ° C-humidity 60% in accordance with JIS Z 3157 (U-shaped weld crack test method) using a steel plate with a thickness of 20 mm having the chemical composition (steel material component) shown in Table 4. It was evaluated by a test under constant atmosphere control. Forty-eight hours after the test bead was created, the flux-cored wire applied to the sample (the wire whose U-shaped crack test result was "no crack") with no cracks on the surface and cross section of the weld was judged to pass the low temperature crack resistance. Was done. Welding heat input was 17 kJ / cm.

Further, as a result of the welding low temperature crackability evaluation, the wire that passed the welding was welded onto a steel plate having the same chemical composition as the steel plate used in the previous welding low temperature crackability test and having a thickness of 20 mm, a width of 150 mm and a length of 200 mm. A fully welded metal was produced by multi-layer overlay welding under the same welding method and welding conditions as described above by applying the lower limit preheating temperature (preheating temperature shown in Table 3) at which low temperature cracking does not occur.

The high temperature strength was evaluated by performing a creep rupture test on the obtained fully welded metal. Wire numbers 1 to 9 and wire numbers 18 to 27 are subjected to post-weld heat treatment (PWHT) of 740 ° C. × 1 hour, air cooling, and wire numbers 10 to 17, 28 to 32 are 720 ° C. After performing post-weld heat treatment (PWHT) of air cooling for × 1 hour on all weld metals, round bar creep rupture test pieces with a parallel part diameter of 6 mm and a parallel part length of 30 mm are collected, and each welding material is used. A creep rupture test was conducted under stress conditions where the target rupture time of the base metal at 550 ° C was about 1000 hours, and those with a rupture time exceeding 1000 hours were regarded as "passed" in terms of high temperature strength (creep rupture test results). ..

Further, the amount of spatter generated and the state of slag were evaluated by repeating bead-on-plate welding for 30 seconds × 5 times under the slag and spatter test conditions shown in Table 5 using a copper collection box. A welding material having a particle size of 1 mm or more and 1.00 g or less in terms of the amount of spatter generated per minute was judged to be good in terms of spatter suppression ability. Further, a welding material having a good shape of the bead formed after the above-mentioned sputtering test and having no problems such as slag entrainment was judged to be good in terms of welding workability.

A sample that satisfies all of the above test items is described as having a "comprehensive judgment" of "pass", and a sample that fails one or more of the above test items has a "comprehensive judgment" of "failed". It was stated that.

Table 3 shows the results of evaluating the low temperature crackability of welding. Wire numbers 1 to 9 and 18 to 27 were preheated to 50 ° C., and wire numbers 10 to 17 and 28 to 32 were tested at room temperature of 20 ° C. without preheating, and those without cracks were accepted. ..

In addition, Table 3 shows the results of a creep test performed on the flux-cored wire that passed the evaluation of low-temperature crackability in welding after performing multi-layer overlay welding to obtain a fully welded metal.

Wire numbers 27 and 28 did not contain more than the required amount of Cr, and wire numbers 26 did not reach the required creep rupture times because they contained an excess of Cr.
Since the wire number 20 lacked Si oxide, the bead shape was poor and the welding workability was rejected. Since the wire number 21 had an excess of Si oxide, slag was sprinkled in and the welding workability was rejected.
Since the wires numbers 18 and 22 lacked Na + K, the arc became unstable, the penetration was not stable, and the workability was rejected. Since the wire number 23 had an excess of Na + K, the slag increased, and the workability was rejected due to the slag entrainment.
Since the amount of fluoride in wire numbers 24, 25, 29, and 30 was insufficient, the amount of diffusible hydrogen in the weld metal could not be sufficiently reduced, and cracks occurred in the U-shaped crack test. Since the amount of fluoride in wire number 19 was too large, the amount of spatter generated was large, and the welding workability was inferior and the wire number 19 was rejected.
The wire number 31 had an excessive amount of Mn, and there was a lot of spatter, and the workability was unacceptable.
Wire number 32 was rejected in terms of workability because C and Si were excessive, the creep strength was lowered, and there was a lot of spatter.
On the other hand, the flux-cored wires of the examples of wire numbers 1 to 17 suppress the amount of spatter, have good welding workability, suppress low-temperature cracking, and produce a weld metal having the required creep rupture strength. I was able to.

As described above, it can be seen that only the flux-cored wire satisfying the scope of the present invention can have the effect of reducing the preheating work, the welding workability, and the creep rupture strength of the weld metal.

INDUSTRIAL APPLICABILITY According to the present invention, a weld metal having excellent high-temperature strength can be obtained, low-temperature cracking resistance is excellent, the amount of spatter generated is small, and other welding workability is also excellent. Flux-filled wire for gas shielded arc welding. And a method for manufacturing a welded joint can be provided. In particular, the present invention has low temperature crack resistance even when applied to welding ferrite-based heat-resistant steel used for members requiring high-temperature strength and welding in which the shield gas is 100% CO _2. It is possible to provide a method for manufacturing a flux-filled wire for gas shielded arc welding and a welded joint, which are excellent, generate less spatter, and can be welded with high welding efficiency. Therefore, the present invention has high industrial applicability in the field of welding, particularly in the field of welding high-temperature materials used for heat-resistant and pressure-resistant pipes such as thermal power generation boilers and petrochemical refining equipment.

Claims (10)

A flux-cored wire for gas shielded arc welding including a steel outer skin and a flux filled in the steel outer skin.
As an alloy component, in mass% with respect to the total mass of the flux-cored wire
C: 0.003 to 0.150%,
Si: 0.05 to 2.00%,
Mn: 0.40-3.50%,
P: 0.020% or less,
S: 0.020% or less,
It contains Cr: 1.50 to 13.00% and Mo: 0.10 to 2.50%.
Further, by mass% of the total mass of the flux-cored wire,
Fluoride: Total F conversion value is more than 0.10% and 0.30% or less,
Si oxide: _{0.01 to 0.40% in terms of SiO 2} , and Na compound and K compound: 0.06 to 0.35% in total of Na conversion value and K conversion value
Contains,
A flux-cored wire for gas shielded arc welding, wherein the balance is composed of Fe and impurities in the form of any one or more of the steel outer skin, iron powder, and iron alloy powder. Further, by mass% of the total mass of the flux-cored wire,
V: 0.5000% or less,
Nb: 0.50% or less,
The flux-cored wire for gas shielded arc welding according to claim 1, further comprising one or more selected from the group consisting of Ti: 0.50% or less and Ta: 0.50% or less. Further, by mass% of the total mass of the flux-cored wire,
Cu: 1.00% or less,
Ni: 3.0% or less,
The flux-cored wire for gas shielded arc welding according to claim 1 or 2, wherein it contains one or more selected from the group consisting of Co: 5.00% or less and B: 0.0200% or less. .. Further, by mass% of the total mass of the flux-cored wire,
W: The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 3, which contains 4.00% or less. Further, by mass% of the total mass of the flux-cored wire,
Ca: 0.500% or less,
REM: 0.0100% or less,
The gas shield arc according to any one of claims 1 to 4, which contains at least one selected from the group consisting of Mg: 0.80% or less and Al: 0.400% or less. Flux-filled wire for welding. Further, by mass% of the total mass of the flux-cored wire,
Zr compound: 0 to 0.30% in terms of Zr
The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 5, wherein the wire contains. The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 6, wherein the steel outer skin has a slit-like shape without gaps. The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 6, wherein the steel outer skin has a shape having a slit-shaped gap. The outer surface of the steel outer skin is further provided with a feed lubricant.
The flux-cored gas shielded arc welding according to any one of claims 1 to 8, wherein the amount of the feed lubricant per 10 kg of the flux-cored wire is 0.20 to 1.00 g. Wire. A method for manufacturing a welded joint, which comprises welding a steel material using the flux-cored wire for gas shielded arc welding according to any one of claims 1 to 9.

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