JP2009018316A - Flux-cored welding wire for gas shielded arc welding of fire-resistant steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flux-cored welding wire for gas shielded arc welding which is used for welding a steel for fireproof construction which is excellent in fire resistance at 700 to 800°C. <P>SOLUTION: The welding wire includes, by mass%, 0.002 to 0.2% C, 0.005 to 1% Si, 0.1 to 2.5% Mn, and predetermined amounts of P, S, Al, N with respect to the whole wire. The wire further includes predetermined amounts of one or more elements of Mo, W, Nb, V, Ta, Ti, wherein a Nb equivalent is 0.05 to 0.2%, and includes remainder being Fe and inevitable impurities. A steel outer skin includes 0.002 to 0.2% C, 0.005 to 1% Si, 0.1 to 2.5% Mn, and predetermined amounts of P, S, Al, N, Mo, W, Nb, V, Ta, Ti as the whole outer skin. Filler flux includes predetermined amounts of CaF<SB>2</SB>, TiO<SB>2</SB>, SiO<SB>2</SB>, ZrO<SB>2</SB>, Al<SB>2</SB>O<SB>3</SB>, which are 0.5 to 20% in total, as the whole wire, and remainder being metal powder and inevitable impurities. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a flux-cored welding wire used for gas shielded arc welding of steel having excellent fire resistance (hereinafter also referred to as fireproof steel or fireproof structural steel) used for various structures such as buildings and bridges. In particular, it can be used for Ar + CO ₂ welding and CO ₂ welding, which can obtain a refractory structure excellent in yield strength, elongation (high temperature embrittlement resistance), low temperature toughness of weld metal at 700 to 800 ° C., The present invention relates to a flux-cored welding wire for gas shielded arc welding of refractory steel. The gas shielded arc welding targeted by the present invention is highly versatile because it has good workability and can be welded in all positions.

  For example, in order to ensure safety in the event of a fire, fire resistance standards have been established so that the steel surface temperature during a fire is 350 ° C or lower, and fireproof coating such as rock wool is required. . However, there is a growing demand for fireproof coating to be completely omitted from the viewpoint that the construction cost of fireproof coating is expensive, extra steps are required, and the landscape is also required.

  From 1982 to 1986, the “Development of Fire Prevention Design Law for Buildings” was implemented as a comprehensive project of the former Ministry of Construction. Based on the results, the performance type was approved by the Minister of Construction under Article 38 of the former Building Standard Law. Design became possible. As a result, it has become possible to determine how much fireproof coating is necessary depending on the high-temperature strength of the steel and the load actually applied to the building, and in some cases, it has become possible to use steel with fireproof coating. After that, from 1993 to 1997, “Development of anti-fire and fire resistance evaluation technology” was carried out again as a comprehensive project of the former Ministry of Construction (see Non-Patent Document 1). The revised Building Standard Law, which was promulgated in 2000 and entered into force in 2000, has made it possible to use fire-resistant design for parts using ordinary steel. However, since high-temperature strength is insufficient for application to multistory parking lots, etc., the use of uncoated plain steel is limited except for concrete-filled steel tube columns (CFT (Concrete Filled Steel Tube) columns). ing.

  The necessary fire resistance is that members such as pillars and beams that always support the load against a fire do not collapse. When a steel member is heated during a fire, the member temperature rises and the yield strength decreases. In fireproof design, the steel material temperature is calculated based on the amount of heat flowing into the member (hereinafter also referred to as heat input), and the steel material and member cross-section are selected to ensure the necessary high-temperature strength. . If steel does not have a fireproof coating, the steel is directly subjected to fire heating, so a significant reduction in strength is inevitable, so usually a certified fireproof coating (sprayed rock wool, calcium silicate plate, etc.) is applied, Take measures to reduce the heat input to the steel. However, the use of fire-resistant steel with excellent high-temperature strength is considered to increase the possibility of fire-resistant coating in multi-story parking lots, station buildings, schools, etc. with less combustibles and relatively less fire.

  Under these circumstances, many so-called refractory steels with increased high-temperature strength for a short time have been developed. Initially, a steel material having a high-temperature yield strength at 600 ° C. of 2/3 or more at normal temperature, ie, a 600 ° C. refractory steel, was recently developed, and most recently 700 ° C. or even 800 ° C. guarantees high-temperature yield strength. Techniques relating to ℃ refractory steel and 800 ℃ refractory steel are being disclosed.

  Also in the structure using refractory steel, the weld structure is mainly, and according to the fire resistance strength of each refractory steel member, it is necessary to have a welded joint having the same or better characteristics in the weld metal. A welding method is required.

  For example, Patent Document 1 proposes a submerged arc welding method applied to high-temperature refractory structural steel up to 800 ° C. Patent Documents 2 and 3 disclose a welding wire for 700 to 800 ° C. refractory steel for gas shielded arc welding.

Japanese Patent Laid-Open No. 2003-311477 JP 2005-305460 A JP 2006-289405 A Ministry of Construction Architectural Institute, Japan Building Center: Ministry of Construction Comprehensive Technology Development Project “Development of Technology to Evaluate Prevention and Fireproof Performance”, March 1998

  However, the invention described in Patent Document 1 is the same as the present invention in terms of 700 to 800 ° C. refractory steel, but relates to submerged arc welding with a completely different welding method. Submerged arc welding is generally dedicated to downward welding because of the need to spread the flux in advance, and is not an alternative to gas seal arc welding in all positions.

  Moreover, the welding wire shown by patent document 2 and patent document 3 is related to what is called a solid wire which is a steel solid wire substantially, and is not related to the flux cored wire which this invention makes object. .

  By the way, for gas shielded arc welding, a flux-cored wire in which a component raw material or a deoxidizer is filled in a steel outer shell is often used. Flux-cored wire is preferable from the viewpoint of ease of manufacture because the adjustment of wire components is easier than solid wire, and also has good workability and preferable bead shape. A wire is desired. On the other hand, the flux-cored wire has its own problems such as the yield from the welding wire to the weld metal is changed and the oxygen (O) content is high depending on the selection of the filler. Needs a completely different technique. For this reason, the knowledge of solid wires cannot be directly applied to flux-cored wires. Thus, to date, no flux-cored wire has been proposed for fire-resistant structural steels for high temperature strength and toughness of weld metal for 700 to 800 ° C., and its development is desired.

  In welding wires and welding materials for 700-800 ° C. refractory structural steel, in order to ensure the fire resistance characteristics of the weld metal, that is, the high temperature strength at 700-800 ° C. above a certain level, an element that exhibits high temperature strength, Typically, it is necessary to contain a relatively large amount of precipitation strengthening elements such as Mo, Nb, and V in the weld metal. Such a high-temperature strength-expressing element naturally contributes to solid solution strengthening and precipitation strengthening even at room temperature, and greatly deteriorates toughness accordingly. Therefore, in welding wires and welding materials for 700 to 800 ° C. refractory structural steels. Has a problem that it is difficult to ensure toughness. In particular, in the case of flux-cored wires, there are more impurities in the filler than in solid wires, and the amount of oxygen (O) in the entire welding wire is also high, so high-temperature strength and toughness compared to other welding materials and welding wires. Is more difficult to achieve.

  Therefore, the present invention advantageously solves the above-mentioned problems, and can obtain a weld metal having high-temperature strength equivalent to or higher than that of the base material and at the same time having good toughness, and has fire resistance at 700 to 800 ° C. An object of the present invention is to provide a flux-cored welding wire for gas shielded arc welding of refractory steel, which can be used for welding of refractory structural steel excellent in the above. More specific weld metal targets include 0.2% proof stress at 700 ° C. of about 220 MPa or higher, 0.2% proof stress at 800 ° C. of 70 MPa or higher, and absorption of a 2 mm V notch Charpy impact test at 0 ° C. Target energy is 27J or more.

The present invention solves the above problems, and the gist of the invention is as follows.
(1) In a flux-cored welding wire for gas shielded arc welding of refractory steel with a steel sheath filled with flux,
As a whole welding wire, C: 0.002 to 0.2%, Si: 0.005 to 1% (excluding SiO ₂ in the filling flux), Mn: 0.1 to 2.5% by mass% , P: 0.02% or less, S: 0.01% or less, Al: 0.001 to 0.2% (excluding Al ₂ O ₃ in the filling flux), N: 0.001 to 0.015 In addition, Mo: 0.01 to 2%, W: 0.01 to 2%, Nb: 0.005 to 0.1%, V: 0.005 to 0.5%, Ta: 0 0.005 to 0.5%, Ti: 0.005 to 0.5% (excluding TiO ₂ in the filling flux) or one or more of them are contained, and further represented by the following formula (1) Nb equivalent (Nbeq.) Is 0.05 to 0.2%, the balance has a component composition consisting of Fe and inevitable impurities,
And the said steel outer skin is the mass% with respect to the total mass of outer skin, C: 0.002-0.2%, Si: 0.005-1%, Mn: 0.1-2.5%, P: 0 0.02% or less, S: 0.01% or less, Al: 0.001 to 0.1%, N: 0.001 to 0.015%, Mo: 2% or less (including 0%), W: 2% or less (including 0%), Nb: 0.1% or less (including 0%), V: 0.5% or less (including 0%), Ta: 0.5% or less (0 Containing Ti: 0.2% or less (including 0%), the balance having a component composition consisting of Fe and inevitable impurities,
The filling flux is mass% with respect to the total mass of the wire, CaF ₂ : 5% or less (including 0%), TiO ₂ : 15% or less (including 0%), SiO ₂ : 2% or less (0%) ZrO ₂ : 2% or less (including 0%), Al ₂ O ₃ : 2% or less (including 0%), and the above, CaF ₂ , TiO ₂ , SiO ₂ The total content of ZrO ₂ and Al ₂ O ₃ is 0.5 to 20%, and the balance has a component composition consisting of metal powder and inevitable impurities. Flux-cored welding wire.
Nbeq. = Nb% + V% / 5 + Mo% / 10 + W% / 10 + Ta% / 5
+ Ti% / 5 (1)
However, Nb%, Mo%, W%, Ta%, and Ti% indicate mass% of each component contained in the welding wire, respectively.
(2) Further, as a whole wire, in mass%, Cr: 0.01 to 3%, Ni: 0.01 to 3%, Cu: 0.01 to 1.5%, Co: 0.01 to 6% B: One or more of 0.0005 to 0.015% is contained in one or both of the steel outer shell and the filling flux, and the gas of the refractory steel according to (1) above Flux-cored welding wire for shielded arc welding.
(3) Further, as a whole wire, by mass%, Ca: 0.0002 to 0.1% (excluding CaF ₂ in the filling flux), Mg: 0.0002 to 1%, REM: 0.0002 to 1% or more of 1% is contained in one or both of the steel outer sheath and the filling flux, and the flux for gas shielded arc welding of refractory steel according to (1) or (2) above Cored welding wire.

According to the present invention, in gas-shielded arc welding such as Ar + CO ₂ welding and CO ₂ welding of a fire-resistant structural steel having excellent fire resistance at 700 to 800 ° C., not only high-temperature strength but also excellent toughness is excellent. Therefore, it is possible to provide a flux-cored welding wire for gas shielded arc welding of refractory steel, which can obtain a weld metal, and its industrial effect is extremely great.

  In fire-resistant design of building steel structures, it is only necessary to maintain high high-temperature strength within the fire duration, and for a long time in a high-temperature environment at a high temperature of about 500-600 ° C like heat-resistant steel for pressure vessels such as conventional boilers. There is no need to consider the high-temperature strength at the time of use, as long as the yield strength at a high temperature for a relatively short time can be maintained. For example, if high temperature yield strength can be secured in a short time of about 30 minutes at 800 ° C., it can be sufficiently used as 800 ° C. refractory steel.

  In the conventional 600 ° C refractory steel, the performance was determined so that the yield strength at high temperature was 2/3 or more at room temperature, but the actual design range of the steel structure was 0.2 to 0, which is the lower limit of room temperature yield strength. In consideration of the fact that the lower limit ratio of room temperature yield strength is 0.4 or more, the lower limit ratio to the room temperature yield strength is 0.4 or more as a guideline for 800 ° C high temperature strength. Has been. That is, the target value of 800 ° C. yield strength is 94 MPa or more for 400 MPa class steel and 130 MPa or more for 490 MPa class steel.

  On the other hand, since the welded part at the time of manufacturing the steel column in the building structure is provided at a position where the acting stress is small, the target value of 800 ° C yield strength of the welded part is 1/2 of the target of 800 ° C yield strength of the base material. In other words, the inventors have confirmed that even if it is assumed to be used as a 490 MPa class steel, it is sufficient that 70 MPa or more is obtained with a yield strength target of 800 ° C. On the same basis, the yield strength target at 700 ° C. is 220 MPa or more.

  Therefore, the inventors, as welding materials for high-temperature refractory structural steel up to 800 ° C, have yield strengths of 700 ° C and 800 ° C of 220 MPa or more and 70 MPa or more, respectively, and safety is more important for toughness. Then, a flux-cored welding wire for gas shielded arc welding from which a weld metal having a Charpy absorbed energy at 0 ° C. of 27 J or more was obtained was examined based on detailed experiments.

Prior to this study, the inventors determined that the high-temperature strength at 700 ° C. and 800 ° C. of the welded portion made of solid wire should contain an appropriate amount of Mo, Nb, W, V, or Ta in the weld metal. Each element exhibits almost the same effect on high-temperature strength, but the degree depends on the element, and the effect of these elements on high-temperature strength is defined by the following equation (2) It has already been disclosed in Patent Document 3 that the Nb equivalent (Nbeq.) Is uniformly arranged.
Nbeq. = Nb% + V% / 5 + Mo% / 10 + W% / 10 + Ta% / 5 (2)
However, Nb%, Mo%, W%, and Ta% respectively indicate mass% of each component contained in the welding wire.

As will be described later, the inventors proceeded with the same study on the flux-cored welding wire, and the flux-cored welding wire is uniformly arranged with the same Nb equivalent (Nbeq.) As the Nb equivalent disclosed in Patent Document 3. I found out that However, especially when placing emphasis on all orientation, TiO ₂ is often added to the flux, and the amount of Ti in the weld metal also increases with the flux-cored wire, and the effect of Ti on the high-temperature strength cannot be ignored. Based on the above-described formula (2), an Nb equivalent for the flux-cored welding wire of the formula (1) that takes into account the effect of Ti was obtained.
Nbeq. = Nb% + V% / 5 + Mo% / 10 + W% / 10 + Ta% / 5
+ Ti% / 5 (1)
However, Nb%, Mo%, W%, Ta%, and Ti% indicate mass% of each component contained in the welding wire, respectively.

Below, the inventors will investigate in detail the relationship between the high-temperature strength and the content of the high-temperature strength-expressing element in the weld metal, and an experiment that has led to the above expression (1) will be described. That is, 0.04% C-0.05% Si (excluding SiO ₂ as a flux) -0.25% Mn-0.012% P-0.006% S in mass% with respect to the total mass of the welding wire. −0.008% Al (excluding Al ₂ O ₃ as a flux) −0.15% Cu−0.0035% N−2.5% CaF ₂ −0.2% TiO ₂ −0.35% SiO ₂ based, Mo 0-2%, W 0-2%, Nb 0-0.1%, Ta 0-0.5%, V 0-0.5%, Ti (as flux Of TiO ₂ was added in various amounts and combinations in the range of 0 to 0.5%, and trial manufacture was performed using small laboratory equipment. The welding wire diameter is 1.4 mm, and the filling rate of the entire filling flux is 12%. Mo, W, Nb, Ta, V, and Ti were added in amounts as fillers made of pure metal or master alloy powder.

Of the steel plates having fire resistance at 700 ° C. to 800 ° C. with a plate thickness of 25 mm shown in Table 1 used in the examples described later, the groove 2 as shown in FIG. A welded joint was prepared using a prototype welding wire. The backing metal 3 was also the same steel plate as the steel plate 1. Welding was multi-layered CO ₂ welding with a heat input of 3 kJ / mm, and a high-temperature tensile test piece 4 was taken from the specimen after welding at the position shown in FIG. 2 and examined for high-temperature tensile properties at 700 ° C. Based on the results of this investigation, the influence of each alloy component on the 0.2% yield strength at 700 ° C. was calculated using a multiple regression analysis technique. And the result of normalizing the influence of each calculated component with the influence of Nb is the above-mentioned formula (1). It was found that the coefficient of Ti is 1/5 together with the result that the coefficients of the components other than Ti are equivalent to the expression (2).

FIG. 3 shows that, among the above investigation results, Nb or Ti (as flux) in the welding wire against the 0.2% proof stress at 700 ° C. of the weld metal of the welded joint produced by the welding wire containing no element related to the Nb equivalent. TiO ₂ is excluded.) The relationship between the improvement in 0.2% proof stress at 700 ° C. of the weld metal of welded joints prepared by welding wires each independently added and the content of each element in the welding wire is shown. It is a figure. It can be seen that 0.2% proof stress at 700 ° C. is improved according to the content of both Nb and Ti, but the improvement margin per mass% is about 1/5 smaller than that of Nb. A value equivalent to the regression analysis result was obtained. From the above knowledge, the coefficient of Ti in the Nb equivalent formula is set to 1/5 as in the above formula (1).

  For all the welded joints in this experiment, the relationship between the 0.2% proof stress of the weld metal at 700 ° C. and the new Nb equivalent is shown in FIG. From FIG. 4, the Nb equivalent has a clear correlation with the 0.2% yield strength of the weld metal. If the Nb equivalent is 0.05% or more, the 0.2% yield strength of the weld metal at 700 ° C. It can be seen that the pressure can be 220 MPa or more.

  As for the toughness of the weld metal, it is possible to obtain a desired level by optimizing the Nb equivalent. However, the weld metal using the flux-cored wire is more suitable for the impurity element or oxygen (not the solid weld metal). O) Because of the unavoidable amount, the toughness must be low even at the same high-temperature strength, that is, the same amount of elements exhibiting high-temperature strength, and it is necessary to contain it to the extent that high-temperature strength can be secured. On the other hand, it has also been found that it is necessary to limit to the minimum necessary amount, that is, it is necessary to strictly limit the content range.

  In addition, in order to stably improve the toughness of the weld metal, it is a basic element for developing strength, while forming a carbide or island martensite to inhibit the toughness, and a microstructure of the weld metal It is necessary to optimize the alloying elements such as Si, Mn, Al, Ti, etc., which serve as the base for defining the content. In order to stably control the content of these elements in the weld metal, It was also found that it is necessary to optimize the chemical composition of the steel outer skin as well as the components. Conventionally, component adjustment in a flux-cored wire has been performed from a filler, and general steel such as mild steel has been used for the steel outer sheath, and no special consideration has been given to its composition.

The inventors have further studied influential factors of weld metal toughness due to the flux-cored wire. As a result, the flux filler is also used for controlling workability particularly in terms of securing toughness and in terms of spatter and bead shape. It has also been found that CaF ₂ , TiO ₂ , SiO ₂ , ZrO ₂ , and Al ₂ O ₃ are selectively used and must be contained in appropriate amounts.

  The present invention has been made on the basis of the above-mentioned new findings, and the important elements that need to be strictly controlled and to determine the composition of the steel outer shell and the filler are as follows. By defining the total amount with the steel outer shell, the weld metal can obtain desired characteristics.

  First, the reasons for limiting the chemical composition of the steel shell will be shown. In addition, content of each element in steel outer skin is prescribed | regulated by the mass% with respect to the mass of the whole steel outer shell.

[C of steel outer skin: 0.002 to 0.2%]
C is an element effective in securing strength at room temperature and high temperature through refinement of the structure by improving hardenability and the effect of forming carbides by containing an appropriate amount in the weld metal, but deteriorates the toughness of the weld metal. It is also an element to be made, and since it is necessary to strictly control the content in the weld metal, the content in the steel outer shell is limited. If the C content in the steel outer skin is less than 0.002%, the C content in the weld metal becomes too small, and it becomes difficult to ensure room temperature strength and high temperature strength. On the other hand, when the C content in the steel outer shell exceeds 0.2%, the toughness of the weld metal is greatly deteriorated. Therefore, in the present invention, the C content in the steel outer shell is 0.0002 to 0.00. 2%.

[Si in steel hull: 0.005 to 1%]
Si is an element effective in securing strength at room temperature and high temperature through refinement of the structure by improving hardenability and solid solution strengthening effect by containing a proper amount in the weld metal. Since the element needs to be contained in the metal, the content in the steel outer shell is limited. If the amount of Si in the steel outer shell is less than 0.005%, the above effect is not sufficiently exhibited, and if it exceeds 1%, the weld metal is excessively hardened or island martensite that deteriorates toughness is excessively generated. In the present invention, the Si content in the steel outer skin is limited to 0.005 to 1%.

[Mn of steel outer skin: 0.1 to 2.5%]
Mn is an element that is effective in securing strength at room temperature and high temperature through the refinement of the hardenability and the effect of solid solution strengthening by including an appropriate amount in the weld metal. Since the element needs to be contained in the metal, the content in the steel outer shell is limited. If the amount of Mn in the steel outer shell is less than 0.1%, the above effect is not sufficiently exhibited, and if it exceeds 2.5%, the weld metal is excessively hardened or excessively island martensite that deteriorates toughness is excessive. In the present invention, the Mn content in the steel outer shell is limited to 0.1 to 2.5% because the toughness of the weld metal is remarkably impaired due to the generation.

[P of steel hull: 0.02% or less]
P is an impurity element, and it is preferable to reduce the content in the weld metal as much as possible in order to deteriorate the toughness and hot cracking property of the weld metal. In the present invention, the P content in the steel outer shell is limited because the P content in the weld metal is surely reduced by regulating the content in the steel outer shell. If the P content in the steel shell is 0.02% or less, the adverse effect on the toughness and hot cracking resistance of the weld metal can be tolerated. Therefore, in the present invention, the P content in the steel shell Is 0.02% or less.

[S of steel outer skin: 0.01% or less]
S is also an impurity element, and it is preferable to reduce the content in the weld metal as much as possible in order to degrade the ductility and toughness of the weld metal, and further the high temperature cracking property. In the present invention, the S content in the steel outer skin is limited because the content in the steel outer skin is surely reduced in reducing the S content in the weld metal. If the S content in the steel outer skin is 0.01% or less, the adverse effect on the toughness and hot cracking resistance of the weld metal can be tolerated. Therefore, in the present invention, the S content in the steel outer skin. Is 0.01% or less.

[Al of steel outer skin: 0.001 to 0.1%]
Al is an element necessary for the amount of O in the weld metal not to be excessively increased as a deoxidizing element, and since it is an element that needs to be contained in the weld metal in an appropriate amount, The content of is limited. If the Al content in the steel outer skin is less than 0.001%, the effect is not clear, which is not preferable. On the other hand, if the Al content in the steel outer shell exceeds 0.1%, a coarse oxide is formed in the steel outer shell to inhibit the toughness and ductility of the steel outer shell, thereby inhibiting the wire manufacturability. Therefore, it is not preferable. Therefore, in the present invention, the Al content in the steel outer skin is limited to 0.001 to 0.1%.

[N of steel outer skin: 0.001 to 0.015%]
N is also an impurity element in the weld metal and adversely affects toughness mainly in a solid solution state, so care must be taken so that it is not excessively contained in the weld metal. For this purpose, it is preferable to limit the content in the steel outer shell. However, it is not industrially easy to reduce the N content in the steel to less than 0.001%, and if it is about this level, the adverse effect on the weld metal properties is negligible. Has a lower limit of N content in the steel outer skin of 0.001%. On the other hand, the upper limit of the N content in the steel outer shell is determined as a range in which the adverse effect on the weld metal can be tolerated. In the present invention, the upper limit of the N content in the steel outer shell is set to 0 based on various experimental results. .015%.

  In addition to the elements or impurity elements that are essential to be contained in the above steel outer sheath, it is essential for the entire welding wire, but if the total amount in the steel outer sheath and in the filling flux satisfies the appropriate range Good elements include Mo, W, Nb, V, Ta, and Ti. However, when these elements are contained in the steel outer shell, the content in the steel outer shell is also limited for the following reasons. In addition, about the necessity and appropriate range which contain each element of Mo, W, Nb, V, Ta, and Ti as the whole welding wire, the whole welding wire used as the total amount in the steel outer shell and the filling flux separately. This will be described in detail in the reason for limitation as the content of.

[Mo of steel shell: 2% or less (including 0%)]
When Mo is contained in the steel outer shell, the upper limit is made 2%. This is because if the steel outer shell contains Mo in excess of 2%, the manufacturability of the steel outer shell deteriorates and the strength of the steel outer shell becomes excessively high. This is because the feedability is also hindered.

[W of steel outer skin: 2% or less (including 0%)]
When W is contained in the steel outer shell, the upper limit is made 2%. Like Mo, when steel content exceeds 2% and W is contained, the manufacturability of the steel shell deteriorates and the strength of the steel shell becomes excessively high, and the wire manufacturability, This is because the wire feedability during welding is also hindered.

[Nb of steel outer shell: 0.1% or less (including 0%)]
When Nb is contained in the steel outer shell, the upper limit is made 0.1%. This is because when the steel outer shell contains Nb in an amount exceeding 0.1%, the manufacturability of the steel outer shell deteriorates and the strength of the steel outer shell becomes excessively high. This is because the wire feedability is also hindered.

[V of steel skin: 0.5% or less (including 0%)]
When V is contained in the steel outer shell, the upper limit is made 0.5%. This is because if the steel outer shell contains V exceeding 0.5%, the manufacturability of the steel outer shell deteriorates and the strength of the steel outer shell becomes excessively high, so that the wire manufacturability and This is because the wire feedability is also hindered.

[Ta of steel outer layer: 0.5% or less (including 0%)]
When Ta is contained in the steel outer shell, the upper limit is made 0.5%. This is because when the steel outer shell contains Ta exceeding 0.5%, the manufacturability of the steel outer shell deteriorates and the strength of the steel outer shell becomes excessively high, so that the wire manufacturability and the welding time are reduced. This is because the wire feedability is also hindered.

[Ti of steel hull: 0.2% or less (including 0%)]
When Ti is contained in the steel outer shell, the upper limit is made 0.2%. This is because if the steel shell contains more than 0.2% Ti, the productivity of the steel shell deteriorates and coarse inclusions are formed, or the strength of the steel shell becomes excessively high. This is because, for the reasons described above, wire manufacturability and wire feedability during welding are also hindered.

  The above is the reason for limitation when Mo, W, Nb, V, Ta, and Ti are contained in the steel outer shell. Mo, W, Nb, V, Ta, and Ti are 700 by solid solution strengthening and precipitation strengthening. It is an important element that develops high temperature strength at ˜800 ° C. Since the effects on high temperature strength are similar, it is necessary to contain one or two or more types as wires, and from the viewpoints of ensuring high temperature strength, coexistence with toughness, etc. It is necessary to limit the content of the entire welding wire as the total amount in the medium and the filling flux.

[Mo of the entire welding wire: 0.01 to 2%]
Mo is a basic element that increases the high-temperature strength of the weld metal in a solid solution state and a precipitated state, and is an element effective for improving the fire resistance. When it is contained in the wire in order to exert such an effect clearly, Mo is required to be 0.01% or more in total in the steel outer shell and the filling flux, but in the steel outer shell and in the filling flux. If the total exceeds 2%, the strength at room temperature becomes too high, and the weld metal toughness is likely to be lowered. Therefore, the Mo content is limited to 0.01 to 2% in the steel outer shell and the filling flux. .

[W of the entire welding wire: 0.01 to 2%]
W, like Mo, is an element that can increase the high-temperature strength by solid solution strengthening and precipitation strengthening. Since the effect on the high temperature strength and the adverse effect on the toughness are almost the same as those of Mo, in the present invention, when W is contained in the welding wire, the total amount in the steel outer shell and the filling flux is 0. The range is 0.01 to 2%.

[Nb of entire welding wire: 0.005 to 0.1%]
Nb is effective for securing the fire resistance at a high temperature exceeding 700 ° C. by increasing the high-temperature strength mainly by precipitation strengthening or dispersion strengthening mechanism due to dispersion of Nb carbonitride. When Nb is contained in the welding wire for improving the high temperature strength, 0.005% or more is contained in the total amount in the steel outer shell and the filling flux in order to surely exert the effect of improving the high temperature strength. There is a need. However, Nb is also an element that significantly deteriorates toughness, and the total amount in the steel outer shell and filling flux exceeds 0.1% and excessively contained in the welding wire allows toughness deterioration of the weld metal. Since it becomes impossible, it is not preferable. Further, since high temperature embrittlement is also promoted, in the present invention, when Nb is contained in the welding wire, the total amount in the steel outer sheath and the filling flux is 0.005 to 0.1%. The range.

[V of welding wire as a whole: 0.005 to 0.5%]
V, like Nb, is an element that develops high-temperature strength mainly due to the dispersion of precipitates. When V is contained in the welding wire for improving the high temperature strength, 0.005% or more is contained in the total amount in the steel outer shell and the filling flux in order to surely exert the effect of improving the high temperature strength. There is a need. However, if the total amount in the steel outer shell and the filling flux exceeds 0.5% and is excessively contained in the welding wire, the toughness of the weld metal is greatly deteriorated. When it is contained, the total amount in the steel outer shell and the filling flux is set to a range of 0.005 to 0.5%.

[Ta of the entire welding wire: 0.005 to 0.5%]
Ta, like Nb and V, is an element that exhibits high-temperature strength mainly due to the dispersion of precipitates. When Ta is contained in the welding wire to improve high temperature strength, 0.005% or more is contained in the total amount in the steel outer shell and the filling flux in order to surely exert the effect of improving high temperature strength. There is a need. However, since the total amount in the steel outer shell and the filling flux exceeds 0.5% and excessively contained in the welding wire, the toughness deterioration of the weld metal becomes large. When it is contained, the total amount in the steel outer shell and the filling flux is set to a range of 0.005 to 0.5%.

[Ti of the entire welding wire: 0.005 to 0.5% (excluding TiO ₂ in the filling flux)]
Ti contributes to improved toughness due to the effect of refining the structure, but by forming stable TiN and fixing solute N, other precipitation strengthening elements form coarse nitrides and contribute to high-temperature strength. It is effective to improve the high-temperature strength by preventing the decrease of the strength, or by forming a refined carbide and strengthening by precipitation. For that purpose, it is necessary to contain 0.005% or more in the total amount in the steel outer shell and the filling flux. However, since the total amount in the steel outer shell and the filling flux exceeds 0.5% and is excessively contained in the welding wire, the toughness deterioration of the weld metal increases. When it is contained, the total amount in the steel outer shell and the filling flux is set to a range of 0.005 to 0.5%. Here, Ti as used herein means Ti that can form a carbonitride, and therefore TiO ₂ added as a slag forming agent to be described later is not included here.

As described above, for Mo, W, Nb, V, Ta, and Ti that are important for high-temperature strength development, any of the content in the steel outer shell and the total content of the welding wire that is the total amount in the steel outer shell and the filling flux In addition, in order to reliably achieve the desired high-temperature strength in the weld metal, in the present invention, the formula (1) obtained based on the contribution ratio of each element to the high-temperature strength is determined. Nb equivalent (Nbeq.) Must be within an appropriate range.
Nbeq. = Nb% + V% / 5 + Mo% / 10 + W% / 10 + Ta% / 5
+ Ti% / 5 (1)
However, Nb%, Mo%, W%, Ta%, and Ti% indicate mass% of each component contained in the welding wire, respectively.

  As a result of examining the relationship between the Nb equivalent (Nbeq.) Of the formula (1) and the mechanical properties of the weld metal through detailed experiments, it was confirmed that the 0.2% proof stress at 700 ° C. of the weld metal was 220 MPa or more, 800 In order to ensure that the 0.2% proof stress at 70 ° C. is 70 MPa or more, the Nb equivalent (Nbeq.) In the formula (1) is at least 0.05% on the premise of optimizing other welding wire compositions. It is necessary to. Nbeq. If it is less than 0.05%, the 0.2% proof stress at 700 ° C. and 800 ° C. may be less than 220 MPa and 70 MPa, respectively. Nbeq. However, if it exceeds 0.2%, the strength at room temperature becomes excessively high, the weld crack resistance is deteriorated, and the toughness is also adversely affected. For the above reasons, in the present invention, the Nb equivalent (Nbeq.) Of the formula (1) is limited to 0.05 to 0.2%.

[C, Si, Mn, P, S, Al, N amount of the entire welding wire]
As described above, in the present invention, C, Si, Mn, P, S, Al, and N, which are basic elements that determine the structure and characteristics of steel, are defined as steel outer shell compositions. Can be added to the filling flux and may be contained as an impurity. In the present invention, the content of these elements in the entire wire is also limited.

That is, for C, Si, Mn, P, S, and N, the content of the entire wire is C: 0.002 to 0.2%, Si: 0.005 to 1% (excluding SiO ₂ in the filling flux), Mn: 0.1 to 2.5%, P: 0.02% or less, S: 0.01% or less, Al: 0.001 ˜0.2% (excluding Al ₂ O ₃ in the filling flux), N: 0.001 to 0.015%.

However, with regard to Al, the upper limit is 0.1%, which is the lower upper limit in terms of steel manufacturability, but it is effective as a deoxidizing element and exhibits favorable effects such as reducing the amount of O in the weld metal. Therefore, it can be further contained in the filling flux, and the upper limit of the total amount in the steel outer shell and the filling flux is set to 0.2%. If the total amount in the steel outer shell and in the filling flux exceeds 0.2%, it is not preferable because the wire manufacturability is impaired and the properties of the weld metal are adversely affected. Note that the Al content in the filled flux here is different in the effect, and thus Al ₂ O ₃ is excluded.

[Filling flux]
The above is the reason for limiting the chemical composition of the welding wire that mainly defines the chemical composition of the weld metal. The present invention relates to a flux-cored welding wire, and in order to develop good workability and bead shape, which are characteristics of a flux-cored welding wire, the mass relative to the total mass of the welding wire is included in the filler as necessary. %, CaF ₂ : 5% or less (including 0%), TiO ₂ : 15% or less (including 0%), SiO ₂ : 2% or less (including 0%), ZrO ₂ : 2% It is necessary to contain the following (including 0%), Al ₂ O ₃ : 2% or less (including 0%). In addition, in the use which dislikes slag formation as much as possible, when permitting a slight deterioration of the bead shape and workability, none of the above oxides may be included.

[CaF _{2 of} filling flux: 5% or less (including 0%)]
CaF ₂ has properties as a slag forming agent and a deoxidizing agent. In particular, it is effective in reducing the amount of O in the weld metal and improving toughness. Therefore, it is preferable to add in the case of an application that places importance on ensuring the toughness of the weld metal. However, if the content is more than 5% by mass with respect to the total mass of the welding wire, the slag peelability, bead shape and workability deteriorate, so the upper limit is made 5% in the present invention. When CaF ₂ is less than 0.5%, the effect as a deoxidizer is lost and the effect of improving the toughness is not clear. Therefore, when the effect of improving the toughness of the weld metal is expected, 0.5% or more It is preferable to contain.

[TiO _{2 of} filling flux: 15% or less (including 0%)]
TiO ₂ has a function as a slag forming agent and an arc stabilizer, and is useful when it is necessary to ensure good workability and to improve the bead shape. In addition, TiO ₂ has an effect as a nucleus for forming intragranular ferrite in the metal structure of the weld metal. However, if the mass% with respect to the total mass of the welding wire exceeds 15%, when the ratio (filling rate) of the flux filler is constant, it becomes impossible to contain other fillers, making it difficult to adjust the components, and other fillers. If the amount of TiO ₂ is more than 15%, the filler filling rate becomes excessive and wire manufacturability deteriorates, which is not preferable. In addition, the amount of O in the weld metal and coarse oxides increase and adversely affect the toughness of the weld metal. Therefore, in the present invention, when TiO ₂ is contained in the flux filler, the upper limit is 15% in terms of mass% with respect to the total mass of the welding wire. Note that TiO ₂ is effective for forming a slag that maintains arc stability and has good enveloping properties. In addition, it is preferable to add 0.5% or more of TiO ₂ .

[Filling flux SiO ₂ : 2% or less (including 0%)]
[ZrO _{2 of} filled flux: 2% or less (including 0%)]
Both SiO ₂ and ZrO ₂ have a similar action as TiO ₂ . However, when the mass% with respect to the total mass of the welding wire exceeds 2%, there is a risk that a coarse oxide is formed in the weld metal and the toughness is deteriorated. It is limited to 2% by mass% with respect to the total mass of the welding wire.

[Al ₂ O _{3 of} filling flux: 2% or less (including 0%)]
Al ₂ O ₃ has a strong deoxidation action, and can contribute to improvement of toughness by reducing O in the weld metal. However, when the content of the welding wire exceeds 2% by mass with respect to the total mass of the welding wire, the effect of reducing O is saturated, while coarse Al ₂ O ₃ is formed and conversely deteriorates the toughness of the weld metal. Therefore, in the present invention, when Al ₂ O ₃ is contained in the filling flux, the upper limit is set to 2% in terms of mass% with respect to the total mass of the welding wire.

[Total content of CaF ₂ , TiO ₂ , SiO ₂ , ZrO ₂ , Al ₂ O ₃ ]
The CaF ₂ , TiO ₂ , SiO ₂ , ZrO ₂ , and Al ₂ O ₃ can be selectively used after individually defining the content range for the above reasons. In order to ensure good workability, good bead shape, and secure slag for ensuring all postures, etc., it is necessary to define the upper and lower limits of the total content. That is, when the total content of CaF ₂ , TiO ₂ , SiO ₂ , ZrO ₂ , and Al ₂ O ₃ is less than 0.5% by mass with respect to the total mass of the welding wire, the molten steel is supported during welding, Since the amount of slag that protects from the outside air is not sufficient, there is a risk of characteristic deterioration, bead shape deterioration, and workability deterioration. On the other hand, if the total content of CaF ₂ , TiO ₂ , SiO ₂ , ZrO ₂ , and Al ₂ O ₃ is mass% with respect to the total mass of the welding wire and exceeds 20%, the amount of slag formation is excessive, This is unfavorable because it hinders the properties and deteriorates the wire manufacturability. Therefore, in the present invention, the total content of CaF ₂ , TiO ₂ , SiO ₂ , ZrO ₂ , and Al ₂ O ₃ is limited to 0.5 to 20% in mass% with respect to the total mass of the welding wire.

  In addition, from the viewpoint of ensuring the high temperature strength and toughness of the weld metal that is the object of the present invention, the ratio of the filling flux including the above-mentioned fluorides and oxides, further the metal for adjusting the component, and the alloy, that is, the total mass of the wire The mass% (hereinafter referred to as the filling rate) of the filling flux with respect to is not particularly limited, but the lower limit is 2% from the viewpoint of ensuring the freedom of component adjustment, and the upper limit is 25% from the viewpoint of wire manufacturability. It is preferable to do.

  The above is the limitation reason regarding the essential requirements in the flux-cored welding wire for gas shielded arc welding of the refractory steel of the present invention. In the present invention, for the purpose of adjusting the room temperature strength and high temperature strength of the weld metal, ensuring toughness stability, improving ductility, etc., one kind of Cr, Ni, Cu, Co, B or Two or more kinds, and further, one or more kinds of Ca, Mg, and REM can be contained in the steel outer sheath and / or the filling flux. All the above selected elements may be limited by the total amount of the steel outer shell and the filling flux.

[Cr of welding wire as a whole: 0.01 to 3%]
Cr is an element effective for increasing the room temperature strength. In general, it is an element that also increases the high-temperature strength, but is less effective for high-temperature strength of 700 ° C. or higher. On the other hand, when it contains excessively in a weld metal, it has the bad influence which deteriorates toughness greatly. In order to clearly show the effect when it is contained in the wire for adjusting the room temperature strength of the weld metal, etc., 0.01% or more in the total mass% in the steel outer shell and the filling flux with respect to the total mass of the wire is necessary. On the other hand, if the total mass in the steel outer shell and the filling flux exceeds 3%, the toughness of the weld metal is deteriorated, which is not preferable. Therefore, in the present invention, when Cr is contained in the wire, the total mass% in the steel outer shell and the filling flux with respect to the total mass of the wire is limited to 0.01 to 3%.

[Ni in the entire welding wire: 0.01 to 3%]
Ni is an element that is generally extremely effective for improving the toughness of steel. Also in the present invention, it is possible to contain Ni in the welding wire as necessary. In order to clearly enjoy the toughening effect of Ni, it is necessary to contain 0.01% or more of Ni in the total mass% in the steel outer shell and the filling flux with respect to the total mass of the wire. On the other hand, if the content exceeds 3%, the heating transformation point (Ac1 transformation point) is significantly lowered and austenite is generated at 700 ° C., so that the high-temperature strength at 700 ° C. or more may be greatly reduced. Therefore, in the present invention, when Ni is contained in the wire, the total mass% in the steel outer shell and the filling flux is limited to 0.01 to 3% with respect to the total mass of the wire.

[Cu of welding wire as a whole: 0.01 to 1.5%]
Cu is an element effective for improving the room temperature strength. Also in this invention, it is possible to contain Cu in a welding wire as needed. In order to clearly exhibit the effect of Cu, Cu needs to be contained in an amount of 0.01% or more in the total mass% in the steel outer shell and the filling flux with respect to the total mass of the wire. On the other hand, if the content exceeds 1.5%, the toughness and hot cracking resistance of the weld metal may be deteriorated. Therefore, in the present invention, when Cu is contained in the wire, it is made of steel with respect to the total mass of the wire. The total mass% in the outer skin and the filling flux is limited to 0.01 to 1.5%.

[Co of welding wire as a whole: 0.01 to 6%]
Co is an element that can improve the room temperature strength without greatly lowering the heat transformation point. Also in the present invention, Co can be contained in the welding wire as necessary. In order to clearly exhibit the effect of Co, it is necessary to contain Co in a total mass% of 0.01% or more in the steel outer shell and the filling flux with respect to the total mass of the wire. On the other hand, if the content exceeds 6%, the toughness and hot cracking resistance of the weld metal may be deteriorated. Therefore, in the present invention, when Co is contained in the wire, in the steel outer shell relative to the total mass of the wire. And the total mass% in the filling flux is limited to 0.01 to 6%.

[B of welding wire as a whole: 0.0005 to 0.015%]
B is an element effective in making the weld metal structure fine by increasing the hardenability in a small amount and effective in improving the room temperature strength and toughness. Also in this invention, it is possible to contain B in a welding wire as needed. In order to clearly exhibit the effect of B, it is necessary to contain B in an amount of 0.0005% or more in the total mass% in the steel outer shell and the filling flux with respect to the total mass of the wire. On the other hand, if the content exceeds 0.015%, the toughness and high-temperature ductility of the weld metal may be deteriorated. Therefore, in the present invention, when B is contained in the wire, in the steel outer shell relative to the total mass of the wire. And the total mass% in the filling flux is limited to 0.0005 to 0.015%.

[Ca, Mg, REM amount of the entire welding wire]
Ca, Mg, and REM are all effective in improving ductility and toughness by changing the structure of sulfides and reducing the size of sulfides and oxides in the weld metal. The lower limit content for exhibiting the effect is the total mass% in the steel outer shell and the filling flux with respect to the total mass of the wire, and both are 0.0002%. On the other hand, excessive content causes coarsening of sulfides and oxides, leading to deterioration of ductility and toughness, and also the possibility of deterioration of weld bead shape and weldability. The total mass% in the steel outer shell and the filling flux with respect to the mass is 0.1% for Ca and 1% for Mg and REM. Note that the Ca, there is also one containing as CaF ₂ in the filled flux, CaF ₂ the purpose is the Ca described here in this case, since the effect is different, excluded. Ca may be in any form as long as it is other than CaF ₂ , such as pure Ca, a mother alloy containing Ca, Ca oxide, or the like. Existence of other elements is not limited unless otherwise specified.

  The effects of the present invention will be described in more detail with reference to examples.

Various steel plates 1 having a chemical composition shown in Table 1 and having a thickness of 25 mm and having fire resistance at 700 to 800 ° C. were grooved into a groove 2 having the dimensions shown in FIG. 1 and subjected to welding. The backing metal 3 was also the same steel plate as the steel plate 1. The welding was multi-layered CO ₂ welding with a heat input of 3 kJ / mm.

  The welding wire used was adjusted to the filling rate and composition of the filling flux using the steel outer sheath shown in Table 2 so that the composition of the entire welding wire would be the composition shown in Table 3. Although all the welding wires are so-called seamless types, the effect of the present invention is not changed even if the type of the welding wire is a seamless type or a caulking type.

  In Table 2, skin numbers HA1 to HA9 are steel skins satisfying the present invention, and skin numbers HB1 to HB6 are steel skins as comparative examples not satisfying the present invention. All the welding wires were drawn to a diameter of 1.4 mm and subjected to welding. In Table 3, the wire numbers WA1 to WA15 are welding wires that satisfy the present invention in terms of the outer skin composition and also satisfy the requirements as a whole welding wire, and the wire numbers WB1 to WB16 satisfy the requirements of the present invention. It is a comparative welding wire that has not. Table 3 also shows details of the welding wire, that is, the steel manufactured type, raw material, flux filling rate, chemical composition of the entire welding wire, and wire manufacturability evaluated by the presence or absence of wire breakage during wire drawing.

  A high-temperature tensile test piece 4 and a 2 mmV notch Charpy impact test piece 5 were sampled from the test specimen after welding at the position shown in FIG. 2 and used for each test. The specimen collection position is the center of the weld metal for both specimens. The test temperature of the tensile test was 700 ° C., and the 2 mmV notch Charpy impact test was performed at 0 ° C.

  The test results are shown in Table 4. The tensile test was performed with 2 repetitions and 2 mmV notch Charpy repetitions, and the average values are shown in Table 4. Table 4 also shows the results of investigation of welding workability, bead shape, and the like. Welding workability was evaluated by visual inspection during welding, and the bead shape was evaluated by visual inspection of the joint appearance and cross-sectional macrostructure observation.

  Among Table 4, joints JA1 to JA15 are examples of weld metal of joints produced using the welding wire of the present invention, and joints JB1 to JB16 are produced using welding wires of comparative examples not satisfying the present invention. This is an example of a joint. As is apparent from Table 4, the weld metal of the joints JA1 to JA15 using the welding wire of the present invention has a 0.2% yield strength at 700 ° C. sufficiently higher than about 220 MPa, and the absorbed energy of the Charpy test at 0 ° C. is also from 27J. It is clear that it has a sufficient safety as a structural material together with a fire resistance at 700 ° C. In addition, the weld metal according to the present invention is satisfactory in welding workability and bead shape and has no problem.

  On the other hand, the weld metal of the joints JB1 to JB16 manufactured using the welding wire of the comparative example not satisfying the present invention has one of 700 ° C. strength, Charpy impact characteristics, workability, and bead shape as compared with the present invention. It is clear that it is significantly worse.

  That is, in the joint JB1, the C content in the steel outer shell is excessive, so that the C content in the weld metal increases more than necessary, and the toughness (Charpy absorbed energy at 0 ° C.) of the weld metal is inferior.

  On the other hand, the joint JB2 has an excessively low C content in the steel outer shell, so that the C content in the weld metal is too low and the precipitation of carbides effective for fire resistance is insufficient. Although satisfying the invention, the high temperature strength is insufficient for 700 ° C. fire resistance.

  In the joint JB3, since the Si content of the steel outer shell is excessive, the Si content in the weld metal is increased more than necessary, and the toughness of the weld metal is inferior.

  In the joint JB4, since the Mn content in the steel outer shell is excessive, the Mn content in the weld metal increases more than necessary, and the toughness of the weld metal is inferior. Moreover, since the Mn content in the weld metal is excessive, the 0.2% proof stress at 700 ° C. exceeds the target 220 MPa due to the lower heating temperature. It is relatively low. Furthermore, if Mn is excessively contained, the steel is hardened in the wire drawing process, and wire breakage is likely to occur during wire drawing.

  In the joint JB5, since the P content in the steel outer shell is excessive, the P content in the weld metal is more than necessary, and the toughness of the weld metal is inferior.

  In the joint JB6, since the S content in the steel outer shell is excessive, the S content in the weld metal is increased more than necessary, and the toughness of the weld metal is inferior. Further, if S is excessively contained, the ductility of the steel is remarkably reduced, so that disconnection occurs during wire drawing, and the productivity of the wire is also inferior.

Since the joint JB7 does not contain Mo, W, Nb, V, Ta, and Ti (other than TiO ₂ ) necessary for expressing the high temperature strength in the welding wire, the high temperature strength of the weld metal is the present invention. Therefore, it is not preferable as a welding wire for 700 to 800 ° C. fire resistance.

  In the joint JB8, although an element exhibiting high-temperature strength is contained in the welding wire, the Nb equivalent (Nbeq.) Is too small to deviate from the scope of the present invention, so that the high-temperature strength is insufficient as in the joint JB7. .

Contrary to the joint JB9, the joint JB9 has an Nb equivalent (Nbeq.) Although the contents of Mo, W, Nb, V, Ta, and Ti (other than TiO ₂ ) in the weld metal satisfy the present invention. ) Deviates from the scope of the present invention, so that the high temperature strength of the weld metal is sufficiently high, but the toughness is remarkably inferior, so it is not preferable as a welding wire for structural materials.

The joint JB10 is an example in which the total amount of oxide (TiO ₂ , SiO ₂ , ZrO ₂ , Al ₂ O ₃ ) and CaF ₂ in the wire is too small. In this case, the characteristics as a flux-cored wire cannot be expressed, and the bead shape is inferior to the flux-cored wire of the present invention.

On the contrary, the joint JB11 is an example in which the total amount of oxide (TiO ₂ , SiO ₂ , ZrO ₂ , Al ₂ O ₃ ) and CaF ₂ in the wire is excessive. Also in this case, the bead shape deteriorates and breakage occurs during wire drawing, which is not preferable.

Since the joint JB12 has an excessive amount of CaF ₂ in the wire, the welding workability is remarkably inferior. That is, a large amount of spatter is generated during welding, and the generated slag adheres to the weld bead and is difficult to peel off.

The joint JB13 is an example in which TiO ₂ is excessively contained in the oxide in the wire. This is not preferable because the frequency of occurrence of disconnection during wire drawing increases.

The joint JB14 is an example in which SiO ₂ is excessively contained in the oxide in the wire. In this case, a coarse oxide is formed in the weld metal, which is not preferable because the toughness is remarkably deteriorated.

The joint JB15 is an example in which ZrO ₂ is excessively contained in the oxide in the wire. In this case, a coarse oxide is formed in the weld metal, which is not preferable because the toughness is remarkably deteriorated.

The joint JB16 is an example in which Al ₂ O ₃ is excessively contained in the oxide in the wire. In this case, a coarse oxide is formed in the weld metal, which is not preferable because the toughness is remarkably deteriorated.

It is a figure which shows typically the groove shape of the welded joint used for the Example with sectional drawing. It is a figure which shows typically the extraction | collection point of the high temperature tensile test piece from a welded joint, and a 2 mmV notch Charpy impact test piece. It is the figure which compared the effect of Nb or Ti content in a welding wire with respect to the improvement of 0.2% yield strength in 700 degreeC of a weld metal. It is the figure which showed the correlation with Nb equivalent shown by (1) Formula, and the 0.2% yield strength in 700 degreeC of a weld metal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Groove 3 Backing metal 4 High temperature tensile test piece 5 2mmV notch Charpy impact test piece

Claims (3)

In a flux-cored welding wire for gas shielded arc welding of refractory steel with a steel outer shell filled with flux,
As a whole welding wire,
C: 0.002 to 0.2%,
Si: 0.005 to 1% (excluding SiO ₂ in the filling flux),
Mn: 0.1 to 2.5%
P: 0.02% or less,
S: 0.01% or less,
Al: 0.001 to 0.2% (excluding Al ₂ O ₃ in the filling flux),
N: 0.001 to 0.015%
In addition,
Mo: 0.01-2%
W: 0.01-2%
Nb: 0.005 to 0.1%,
V: 0.005-0.5%
Ta: 0.005 to 0.5%,
Ti: 0.005 to 0.5% (excluding TiO ₂ in the filling flux)
And a component composition comprising Nb equivalent (Nbeq.) Of 0.05 to 0.2% represented by the following formula (1) and the balance of Fe and inevitable impurities: Have
And the steel outer shell is a mass% with respect to the total mass of the outer skin,
C: 0.002 to 0.2%,
Si: 0.005 to 1%
Mn: 0.1 to 2.5%
P: 0.02% or less,
S: 0.01% or less,
Al: 0.001 to 0.1%,
N: 0.001 to 0.015%,
Mo: 2% or less (including 0%),
W: 2% or less (including 0%),
Nb: 0.1% or less (including 0%),
V: 0.5% or less (including 0%),
Ta: 0.5% or less (including 0%),
Ti: 0.2% or less (including 0%)
And the balance has a component composition consisting of Fe and inevitable impurities,
The filling flux is the mass% with respect to the total mass of the wire,
CaF ₂ : 5% or less (including 0%),
TiO ₂ : 15% or less (including 0%),
SiO ₂ : 2% or less (including 0%),
ZrO ₂ : 2% or less (including 0%),
Al ₂ O ₃ : 2% or less (including 0%)
In addition, the total content of CaF ₂ , TiO ₂ , SiO ₂ , ZrO ₂ , and Al ₂ O ₃ is 0.5 to 20%, and the balance is composed of metal powder and inevitable impurities. A flux-cored welding wire for gas shielded arc welding of refractory steel, characterized by having a composition.
Nbeq. = Nb% + V% / 5 + Mo% / 10 + W% / 10 + Ta% / 5
+ Ti% / 5 (1)
However, Nb%, Mo%, W%, Ta%, and Ti% respectively represent mass% of each component contained in the welding wire. Furthermore, as a whole wire,
Cr: 0.01 to 3%,
Ni: 0.01 to 3%,
Cu: 0.01 to 1.5%,
Co: 0.01 to 6%
B: 0.0005 to 0.015%
The flux-cored welding wire for gas shielded arc welding of refractory steel according to claim 1, characterized in that one or more of these are contained in one or both of the steel outer shell and the filling flux. Furthermore, as a whole wire,
Ca: 0.0002 to 0.1% (excluding CaF ₂ in the filling flux),
Mg: 0.0002 to 1%,
REM: 0.0002 to 1%
The flux-cored welding wire for gas shielded arc welding of refractory steel according to claim 1 or 2, wherein one or more of these are contained in one or both of the steel outer shell and the filling flux.

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