JP4767592B2 - Submerged arc welding method for refractory structural steel - Google Patents

Description

  The present invention relates to a submerged arc welding method for a steel plate (hereinafter referred to as refractory steel or refractory structural steel) having excellent fire resistance used in various structures such as buildings and bridges, and in particular, 700 to 800 ° C. of a weld metal. The present invention relates to a submerged arc welding method for refractory steel having excellent proof stress, elongation (high temperature embrittlement resistance) and low temperature toughness.

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.
As a result of the achievement of the fire prevention and fire prevention professionals in 1987 (according to Article 38 certification), it became possible to design a performance type. As a result, how much fire resistance depends on the high temperature strength of the steel and the load actually applied to the building. It became possible to determine whether a coating was necessary, and in some cases, it was possible to use steel with a non-fireproof coating.
Under these circumstances, a steel material having a high-temperature yield strength at 600 ° C. of 2/3 or more at normal temperature, that is, a 600 ° C. refractory steel was developed. In addition, recently, techniques relating to 700 ° C. refractory steel and 800 ° C. refractory steel that guarantee high-temperature yield strength at 700 ° C. or even 800 ° C. are being disclosed.

Even in the structure using refractory steel as described above, a welded structure is mainly used, and a welded joint having a property equal to or higher than that of a weld metal is required according to each refractory strength. A method is needed.
For example, a submerged arc welding method as shown in Patent Document 1 described below is disclosed for 600 ° C. fire resistance, and a submerged arc welding method as shown in Patent Document 2 described below is also disclosed for 800 ° C. fire resistance. Yes. With any of these techniques, Mo, Nb, V and Cr are contained in the weld metal to enhance the high temperature characteristics.
JP-A-9-225682 Japanese Patent Laid-Open No. 2003-311477

However, even with the techniques described in the above-mentioned patent documents, particularly for 700 to 800 ° C. refractory applications that require more severe high temperature characteristics, a large amount of alloy elements are required to ensure high temperature characteristics. Therefore, there was a problem in securing toughness. In addition, when a large amount of elements such as Mo, Nb, and V that increase the hardenability and increase the strength by precipitation strengthening are contained in the weld metal, the grain boundary becomes brittle and the ductility is extremely lowered at around 700 ° C. The problem of high temperature embrittlement or reheat embrittlement also occurred, and there was a problem as a welding method for producing a welded joint having sufficient safety for a structure.
The present invention relates to a submerged arc welding method used for a fireproof structural steel excellent in fire resistance up to 800 ° C. in view of the above-mentioned problems of the prior art, and not only high temperature strength but also toughness and high temperature embrittlement resistance. It is another object of the present invention to provide a submerged arc welding method capable of obtaining an excellent weld metal.

The present invention achieves the above object, and the gist thereof is as follows.
(1) In the present invention, when submerged arc welding is performed on a refractory structural steel, each of them is contained in either or both of a welding wire and a flux and excluding those present as oxides and fluorides in the flux The total content of the components is mass% except for Fe and inevitable impurities , C: 0.01 to 0.15%, Si: 0.1 to 2%, Mn: 0.2 to 5%, Mo: Welding wire and flux that are 0.1 to 2%, Nb: 0.023 to 0.5%, Al: 0.002 to 7%, Ti: 0.01 to 5%, Cr: less than 0.01% Are used in combination.
(2) In the present invention, the total amount of the welding wire and the flux excluding the oxides and fluorides existing in the flux described above is expressed by mass%, Cu: 0.01 to 3%, Ni : 0.01-6%, W: 0.05-3%, V: 0.002-0.5%, Ta: 0.002-0.5%, B: 0.0002-0.005% 1 type or 2 types or more are included.
(3) In the present invention, the total amount of the welding wire and the flux excluding the oxides and fluorides existing in the flux described above is expressed by mass%, Ca: 0.0002 to 0.1%. , Mg: 0.0002 to 0.1%, REM: 0.0002 to 0.1%, or one or more thereof.

(4) The present invention is characterized in that the fireproof structural steel is applied to a steel having a high temperature yield strength at 800 ° C. of 0.4 or more as a lower limit ratio to a room temperature yield strength.
(5) The present invention is characterized by being applied to a steel having a yield strength of 70 MPa or more at 800 ° C. as the fireproof structural steel.
(6) The present invention is characterized in that the fireproof structural steel is applied to a steel having Charpy absorbed energy at 0 ° C. of 100 J or more.

  According to the present invention, it relates to a submerged arc welding method used for a refractory structural steel excellent in fire resistance up to 800 ° C., and obtains a weld metal excellent not only in high temperature strength but also in toughness and high temperature embrittlement resistance. Therefore, it is possible to provide a submerged arc welding method that can be applied, and the industrial effect is extremely large.

The present invention will be described in detail below based on the best mode.
In fireproof design of building steel structures, it is only necessary to maintain high high-temperature strength within the duration of the fire, 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 refractory steel, the performance is determined so that the yield strength at high temperature is 2/3 or more at normal temperature, but the actual design range of the steel structure is 0.2 to 0.4, which is the lower limit of normal temperature yield strength. Based on the idea that it can be used if the room temperature yield strength lower limit ratio is 0.4 or more, the lower limit ratio to room temperature yield strength should be 0.4 or more as a guideline for 800 ° C high temperature strength. Can do. That is, the target value of 800 ° C. yield strength is 94 MPa for 400 MPa steel and 130 MPa for 490 MPa.

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 the 800 ° C yield strength of the welded part is one of the target 800 ° C yield strength of the base material. The inventors have confirmed that it is sufficient to obtain 70 MPa with a yield strength target of 800 ° C. even if it is assumed to be used as / 2, that is, 490 MPa steel. For the same reason, the yield strength target at 700 ° C. is about 220 MPa.
Therefore, the inventors of the present invention, as a welding material for high-temperature refractory structural steel up to 800 ° C., have yield strengths of 700 MPa and 800 ° C. of 220 MPa and 70 MPa, respectively, and with regard to toughness, safety is further improved. Emphasizing, Charpy absorbed energy at 0 ° C is 100 J or more, and has high temperature embrittlement resistance that does not cause high temperature embrittlement cracking due to load stress or welding residual stress when exposed to high temperature. We investigated the submerged arc welding materials and welding methods from which weld metals can be obtained.

As a result, for fire resistance, it is essential to contain Mo and Nb in the weld metal, and addition of W, V, and Ta is also effective, but generally improves high-temperature strength and creep strength. Cr, which is considered to be effective, has almost no effect on the fire resistance at 700 ° C. or higher, while the adverse effect on toughness is remarkably larger than other strengthening elements. The present inventor newly found out that Cr is regarded as an impurity element when considered for fireproofing, and that it is preferable not to substantially contain Cr in order to achieve both high-temperature strength and toughness.
Moreover, in order to achieve high toughness such that the Charpy absorbed energy at 0 ° C. is 100 J or more while the high temperature strength is maintained, the inventor of the present application includes Ti in the weld metal together with an appropriate combination of alloy compositions. I also found that is essential.
Based on the knowledge newly found out as described above, the present inventors, in the submerged arc welding method for a refractory structural steel, have any of welding wires and fluxes except those existing as oxides and fluorides in the flux. It was found that the above problems can be solved by limiting the element content of the total content of either or both, and the present invention has been achieved.

That is, the present invention relates to submerged arc welding of a refractory structural steel, which is contained in either or both of a welding wire and a flux, and each component except those present as oxides and fluorides in the flux. The total content is mass%, C: 0.01 to 0.15%, Si: 0.1 to 2%, Mn: 0.2 to 5%, Mo: 0.1 to 2%, Nb : 0.005 to 0.5%, Al: 0.002 to 7%, Ti: 0.01 to 5%, and a combination of a welding wire and a flux with Cr less than 0.01% are used. The present invention relates to a submerged arc welding method for refractory structural steel.
In addition to the above composition, the present invention includes Cu: 0.01 to 3%, Ni: 0.01 to 6%, W: 0.05 to 3%, V: 0.002 to 0 as necessary. 0.5%, Ta: 0.002-0.5%, B: 0.0002-0.005%, or two or more of them may be included, and if necessary, Ca: 0 A welding wire and a flux having a composition containing one or more of 0002 to 0.1%, Mg: 0.0002 to 0.1%, and REM: 0.0002 to 0.1% are used in combination. The present invention relates to a submerged arc welding method for refractory structural steel.

The reason for limiting the total content of either or both of the welding wire and flux of each element will be described in more detail below. In addition, the following component content is the mass% with respect to what remove | excluded the oxide which contains in a flux, and the component which exists as a fluoride.
C requires 0.01% in the wire and flux in order to obtain the strength of the weld metal at room temperature, but if it exceeds 0.15%, the toughness decreases, so either the wire or the flux The total amount contained in one or both is limited to 0.01% or more and 0.15% or less.
Since Si reduces the oxygen content in the weld metal and improves toughness, it is necessary to add 0.1% or more in combination with the wire and the flux. However, if it exceeds 2%, the normal temperature strength becomes too high and the weld metal toughness is also lowered, so the total amount contained in either or both of the wire and the flux is limited to 0.1% or more and 2% or less.
Mn has the effect of reducing the oxygen content of the weld metal and improving toughness in the same way as Si, so 0.3% is necessary. However, if excessively contained, Mn is 800 ° C. in order to lower the Ac1 transformation temperature. Since it is harmful to high-temperature strength, it is limited to 5.3% or less. Therefore, the Mn content is set to 0.3 to 5% in the total amount contained in one or both of the wire and the flux.

Mo is a basic element that enhances the high-temperature strength of the weld metal in a solid solution state and a precipitated state, and is an essential element in the combination of the wire and flux of the present invention. In order to reliably increase the high-temperature strength up to 800 ° C, the total amount contained in one or both of the wire and the flux needs to be 0.2% or more. Since it becomes too high and the weld metal toughness may be lowered, the Mo content is 0.2% or more and 2% or less in terms of the total amount contained in one or both of the wire and the flux.
Nb is an element that can increase the high-temperature strength mainly in a precipitated state, and is an essential element in the combination of the wire and the flux of the present invention. In order to increase the 800 ° C. high temperature strength, the total amount contained in one or both of the wire and the flux needs to be 0.005% or more. However, if the content exceeds 0.5%, the weld metal toughness is lowered, and high temperature embrittlement becomes remarkable, which is not preferable. Therefore, the total amount contained in one or both of the wire and the flux is 0.005% or more and 0.5% or less.

Al, like Si, reduces the oxygen content of the weld metal and improves toughness. For that purpose, 0.002% or more of the total amount contained in one or both of the wire and the flux is necessary. However, if the content exceeds 7%, welding workability such as slag peelability is remarkably lowered, which is not preferable. Therefore, Al is 0.002% or more and 7% or less in the total amount contained in one or both of the wire and the flux.
Ti, like Al and Si, is a deoxidizing element and has the effect of reducing the oxygen content of the weld metal and improving the toughness. In addition to this, it exists as a Ti oxide and nitride, so that weld metal In order to achieve high toughness such that the Charpy absorbed energy at 0 ° C. is 100 J or more, as is the object of the present invention, particularly for improving the toughness of steel, it is conventionally used for refractory structures of 700 ° C. or higher. It is essential to contain Ti which is not used in steel. In order to exhibit these effects, the Ti content needs to be 0.01% or more in terms of the total amount contained in one or both of the wire and the flux. On the other hand, if the Ti content exceeds 5%, there is a greater concern about the formation of coarse Ti inclusions in the weld metal to deteriorate the toughness. Therefore, in the present invention, either or both of the wire and the flux are used. Ti is 0.01% or more and 5% or less in the total amount contained in the steel.

While Cr is an element that greatly reduces the toughness while being hardly effective in improving the high-temperature strength at 700 ° C. or higher, it is very important not to contain Cr substantially for 700 ° C. fire resistance. It is. If the total amount contained in one or both of the welding wire and the flux is less than 0.01%, the content in the weld metal hardly causes toughness deterioration. If the total amount contained in either one or both is less than 0.01%, it is considered that Cr is not substantially contained.
The above is the reason for limiting the essential elements in the total amount contained in either or both of the welding wire and the flux in the present invention, but for the adjustment of the strength and toughness of the weld metal and the improvement of the welding workability. As needed, 1 type, or 2 or more types of Cu, Ni, W, V, Ta, and B can be contained.

Cu is an austenite stabilizing element and is an element effective for improving the strength by increasing the hardenability of the weld metal. In order to reliably improve the hardenability of the weld metal, 0.01% or more is required in the total amount contained in one or both of the welding wire and the flux. On the other hand, if the total amount contained in one or both of the welding wire and the flux exceeds 3%, hot cracking tends to occur, which is not preferable. Therefore, in this invention, Cu is limited to 0.01 to 3% by the total amount contained in any one or both of a welding wire and a flux. When Cu is contained in the welding wire, it may be contained uniformly throughout, or / and may be present as a plating on the surface.
Ni is a very effective element for improving the toughness due to the solid solution toughening effect. In order to increase the weld metal toughness, 0.01% or more is required in the total amount contained in one or both of the welding wire and the flux. However, if excessively contained, the Ac1 transformation temperature is lowered, and 800% Since reverse-transformed austenite is generated at 0 ° C. and the high-temperature strength may be reduced, in the present invention, the upper limit is 6% in the total amount contained in one or both of the welding wire and the flux.

W is contained in the weld metal in order to increase the strength of the weld metal mainly by solid solution strengthening and precipitation strengthening. In order to exert a clear strength improvement effect, the total amount contained in one or both of the welding wire and the flux requires 0.05% or more, but if it exceeds 3%, the toughness of the weld metal is remarkably increased. In order to deteriorate, when W is used, the total amount contained in one or both of the welding wire and the flux is set to 0.05 to 3%.
V is contained in the weld metal in order to increase the strength of the weld metal mainly by precipitation strengthening. In order to exert a clear strength improvement effect, the total amount contained in one or both of the welding wire and flux requires 0.002% or more, but if it exceeds 0.5%, the toughness of the weld metal When V is used, the total amount contained in one or both of the welding wire and the flux is set to 0.002 to 0.5%.
Ta is also contained in the weld metal in order to increase the strength of the weld metal mainly by precipitation strengthening. In order to exert a clear strength improvement effect, the total amount contained in one or both of the welding wire and flux requires 0.002% or more, but if it exceeds 0.5%, the toughness of the weld metal When V is used, the total amount contained in one or both of the welding wire and the flux is set to 0.002 to 0.5%.

  B is an element effective for increasing the strength of weld metal by increasing the hardenability in a small amount. In order to clearly exhibit the effect of improving hardenability, 0.0002% or more is required in the total amount contained in one or both of the welding wire and the flux. On the other hand, if the total amount contained in one or both of the welding wire and the flux exceeds 0.005%, the hot metal cracking susceptibility of the weld metal is increased and the toughness is likely to deteriorate. When B is used, the total amount contained in one or both of the welding wire and the flux is 0.0002 to 0.005%.

Furthermore, for the purpose of adjusting the ductility and toughness of the weld metal, one or more of Ca, Mg, and REM can be contained in the weld metal as necessary.
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 0.0002% in the total amount contained in one or both of the welding wire and the flux. On the other hand, excessive content causes coarsening of sulfides and oxides, leading to deterioration of ductility and toughness. Also, there is a possibility of deterioration of weld bead shape and weldability. And the total amount contained in either or both of the flux and 0.01%.

The effects of the constituent elements in the above welding wire and flux are generally valid for weld metals formed by submerged arc welding. If the welding heat input is in the range of 150 kJ / cm or less, the effect is small. Even if the welding conditions change from heat to large heat input, and even if the type and composition of the steel plate vary, the effect of the present invention is not impaired.
In the present invention, for the reasons described above, the fire resistance performance and toughness of the target weld metal are ensured by defining the components by the total amount contained in one or both of the wire and the flux during the submerged arc welding. be able to.
In addition, when adding said metal component to a weld metal using a flux, the said metal component (X) addition form, such as an alloy with metal (X), iron, or another metal (Fe-X ), etc. in a flux It is preferable to add at.

Further, in the present invention, the following metal oxide, metal fluoride or metal carbonate may be contained in the flux in order to further improve welding workability and the like.
TiO ₂ improves the bead shape but deteriorates the slag removability. Particularly when it exceeds 8%, slag sticking occurs on the bead surface, and the slag removability is extremely deteriorated. Therefore, it is preferably limited to 8% or less. .
SiO ₂ increases the viscosity of the slag and is a very effective component to form a weld bead with a good fit at the toe, and has a tendency to make the slag vitreous, which makes it easy to break. It is possible to generate slag with good properties. Such an effect of SiO ₂ can be obtained by addition of 10% or more with respect to the total weight of the flux, but if added over 16%, the melting point of the slag is lowered, the surface of the weld bead is disturbed, The amount of oxygen in the weld metal is increased and the toughness of the weld metal is deteriorated. Therefore, it is preferable to add 10 to 16% of SiO ₂ with respect to the total weight of the flux.
CaO is highly basic and is a composition necessary for reducing the amount of oxygen in the weld metal, and improves toughness. Such an effect of CaO can be obtained by adding 3% or more based on the total weight of the flux. However, if added over 20%, the beads become uneven and the appearance becomes poor. Therefore, it is preferable to add 3 to 20% of CaO with respect to the total weight of the flux.

ZrO ₂ is a very effective component for forming a bead with a wide bead width and can be obtained by addition of 1% or more. On the other hand, if it exceeds 9%, the amount of slag increases. In addition, seizure occurs at the toe end of the bead. Therefore ZrO ₂ is preferably added 1-9%.
Al ₂ O ₃ can be added in an amount of 8% or more in order to narrow the bead width and improve the slag peelability. However, if it exceeds 18%, the oxygen content of the weld metal increases and the toughness deteriorates. Therefore, it is preferable to add 8 to 18% of Al ₂ O ₃ with respect to the total weight of the flux.
MgO is an effective component for increasing the bead holding force and widening the bead width to form a weld bead having a familiar end of the toe, so that it can be added in an amount of 10% or more based on the total weight of the flux. However, if added over 23%, the amount of slag increases, the slag becomes difficult to break, and the slag peelability deteriorates. Therefore, it is preferable to add 10 to 23% of MgO with respect to the total weight of the flux.

Metal fluorides such as CaF ₂ can be obtained by addition of 1% or more with respect to the total weight of the flux in order to reduce the oxygen content of the weld metal and improve toughness, but if added over 18% The arc phenomenon becomes unstable, an avatar is generated on the surface of the weld bead, and the bead shape becomes poor. Therefore, it is preferable to add 1 to 18% of CaF ₂ with respect to the total weight of the flux.
Metal carbonates such as CaCO ₃ and BaCO ₃ dissociate into CO ₂ gas in the arc cavity during welding, lower the hydrogen partial pressure in the arc cavity, lower the amount of hydrogen transferred to the weld metal, and the amount of diffusible hydrogen Has the effect of reducing. When the metal carbonate is less than 3% in terms of CO ₂ in terms of CO ₂ , the amount of diffusible hydrogen in the weld metal does not decrease, and low temperature cracking due to hydrogen tends to occur. On the other hand, if it exceeds 6%, the amount of gas generated becomes excessive, the arc is blown up, and the bead shape becomes poor. Therefore, it is preferable to contain 3 to 6% of metal carbonates such as CaCO ₃ and BaCO _{3 with} respect to the total weight of the flux in terms of CO ₂ .
Since Li ₂ O ₃ , LiF, etc. have a very high moisture absorption preventing effect, the flux absorbs moisture in the atmosphere, increases the partial pressure of hydrogen during welding, and suppresses increasing the diffusible hydrogen of the weld metal. . In particular, this tendency is strong in the bond flux containing water glass. In order to obtain this effect, 0.04 or more can be added in terms of Li. On the other hand, if it exceeds 0.5% in terms of Li, an avatar is generated on the surface of the weld bead and the bead shape becomes poor. _Therefore, Li ₂ O 3, LiF, etc. relative to the total weight of the flux is preferably added from 0.04 to 0.5 percent by Li terms.

  Fe increases welding efficiency and improves welding work efficiency. Since the bulk weight of the flux increases due to the inclusion of Fe, there is an effect of increasing the penetration of the weld metal, so that it is possible to obtain the necessary penetration even in a narrow groove. In order to obtain such an effect, it is necessary to add 1% or more in the flux. However, if it is added in excess of 35%, the amount of slag forming agent is insufficient, so that the bead forming ability is deteriorated, the wavy surface of the bead surface becomes rough, and protrusions are easily generated on the bead surface, which is preferable in terms of appearance. Absent. Therefore, the addition amount of Fe is preferably 1 to 35%. In addition, it is preferable to use iron powder and an iron alloy for the addition form of Fe.

The effects of the present invention will be described in more detail with reference to examples.
Several types of 700-800 ° C. refractory steel sheets 1 having a chemical composition shown in Table 1 and having a thickness of 16 mm were grooved into grooves 2 having the dimensions shown in FIG. 1 and subjected to welding. The backing metal 3 was also a thick plate similar to the steel plate 1.
Welding was performed under the conditions shown in Table 2, and multi-layer welding was performed using submerged arc welding of one layer and two passes. Table 3 shows the chemical composition of the welding wire used in this welding, and Table 4 shows the chemical composition of the flux. Table 5 shows the total amount of welding wire content and flux content for each element. In addition, content of each element of Table 4 is the mass% about the part added with forms other than an oxide and a fluoride with respect to the whole flux. The flux was prepared by mixing and mixing raw materials, granulating water glass as a fixing material, firing at 550 ° C. for 2 hours, and sizing to 12 to 100 mesh.

  Submerged arc welding was performed by various combinations of the steel plates in Table 1, the wires and fluxes in Tables 3 and 4 as shown in Table 5. 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 test temperature of the tensile test was 700 ° C. and 800 ° C., and the 2 mmV notch Charpy impact test was performed at 0 ° C. The test results are shown in Table 6. The tensile test was performed with 2 repetitions and 2 mmV notch Charpy repetitions, and the average values are shown in Table 6.

As shown in Table 5, joints JA1 to JA14 are examples that satisfy the conditions of the present invention, and joints JB1 to JB16 are comparative examples that do not satisfy the conditions of the present invention.
As shown in Table 6, each of the joints JA1 to JA14 of the present invention has a high temperature strength of 0.2% proof stress, more than 250 MPa at 700 ° C., more than 100 MPa at 800 ° C., and more than 220 MPa at 700 ° C., 800 ° C. Is sufficiently satisfied.
In addition, although embrittlement at high temperature is reflected in the ductility value of the high temperature tensile test, in the examples of the present invention, the drawing value of the tensile test is sufficiently high at 700 ° C. and 800 ° C., and high temperature embrittlement does not occur. Furthermore, the toughness has a high level of all absorbed energy at 0 ° C. exceeding 100 J. That is, in the welded joint according to the present invention, it is apparent that the weld metal has a very good level of high-temperature strength, toughness, and high-temperature embrittlement resistance.

On the other hand, since the joints JB1 to JB16 of the comparative example do not satisfy the requirements of the present invention, at least any of the high temperature strength, toughness, and high temperature embrittlement resistance is extremely inferior to the present invention.
That is, the joint JB1 has an excessive Mo content in the total of the content of the welding wire and the flux excluding those present as oxides and fluorides in the flux, so the toughness of the weld metal is higher than that of the present invention. Greatly inferior.
The joint JB2 does not contain Ti in either the flux or the welding wire, and the toughness improving effect by Ti is not exhibited, so the toughness of the weld metal is greatly inferior to that of the present invention.
The joint JB3 contains neither Mo nor Nb, which are essential for high-temperature strength expression, in either the flux or the welding wire. Therefore, the high-temperature strength at 700 ° C. and 800 ° C. is extremely low as compared with the present invention, and is used for fire resistance. Not suitable for.
In the joint JB4, the Mo content is excessive due to the total content of the welding wire and the flux excluding those present as oxides and fluorides in the flux, so the toughness of the weld metal is greatly inferior to that of the present invention. .
In the joint JB5, since the Mo content is excessive as the sum of the contents of the welding wire and the flux excluding those present as oxides and fluorides in the flux, the toughness of the weld metal is greatly inferior to that of the present invention. .

In the joint JB6, the total content of the welding wire and the flux excluding those present as oxides and fluorides in the flux has an excessive Cr content, so the toughness of the weld metal is greatly inferior to that of the present invention. .
In the joint JB7, since the V content is excessive as the sum of the contents of the welding wire and the flux excluding those present as oxides and fluorides in the flux, the toughness of the weld metal is greatly inferior to that of the present invention. .
In the joint JB8, the total content of the welding wire and the flux excluding those present as oxides and fluorides in the flux has an excessive B content, so that the toughness of the weld metal is greatly inferior to that of the present invention. . Further, as is clear from the fact that the aperture value is low, high temperature embrittlement is clearly generated, which is not preferable.
In the joint JB9, since the Si content is excessive as the sum of the contents of the welding wire and the flux excluding those present as oxides and fluorides in the flux, the toughness of the weld metal is greatly inferior to that of the present invention. .
In the joint JB10, since the Al content is excessive as the sum of the contents of the welding wire and the flux excluding those present as oxides and fluorides in the flux, the toughness of the weld metal is greatly inferior to that of the present invention. . Moreover, since Mo is not contained, high temperature strength is also inferior.

In the joint JB11, since the Ti content is excessive as the sum of the contents of the welding wire and the flux excluding those present as oxides and fluorides in the flux, the toughness of the weld metal is greatly inferior to that of the present invention. .
In the joint JB12, the Mo content is excessive due to the total content of the welding wire and the flux excluding those present as oxides and fluorides in the flux, so the toughness of the weld metal is greatly inferior to that of the present invention. .
In the joint JB13, since the Nb content is excessive as the sum of the contents of the welding wire and the flux excluding those present as oxides and fluorides in the flux, the toughness of the weld metal is greatly inferior to that of the present invention. . Further, as is clear from the fact that the aperture value is low, high temperature embrittlement is clearly generated, which is not preferable.
In the joint JB14, the Mo content is too small in the total content of the welding wire and the flux excluding those present as oxides and fluorides in the flux, so the high-temperature strength of the weld metal is inferior to that of the present invention. .
In the joint JB15, the total content of the welding wire and the flux excluding those present as oxides and fluorides in the flux and the Nb content are too small, so the high temperature strength of the weld metal is inferior to that of the present invention. .

In the joint JB16, the total content of the welding wire and the flux excluding those present as oxides and fluorides in the flux is too small in Ti content, so the toughness of the weld metal is greatly inferior to that of the present invention. .
From the above examples, according to the present invention, the submerged arc welding method used for the refractory structural steel having excellent fire resistance up to 700 ° C. to 800 ° C., the high temperature strength is sufficiently high, and the toughness and high temperature brittleness are also high. It is clear that it is possible to obtain a weld metal having excellent crystallization characteristics.
More specifically, from the test results shown in Table 6, those having a 0.2% yield strength at 700 ° C. of 257 MPa or more can be specifically obtained, and at a 0.2% yield strength at 800 ° C. of 105 MPa or more. I was able to get something concrete. Moreover, the thing of 101J or more was specifically obtained in the Charpy absorbed energy in 0 degreeC.

FIG. 1 is a diagram showing an example of a groove shape applied in the present invention. FIG. 2 is a diagram showing test piece collection positions applied in the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Thickness 2 ... Groove 3 ... Back metal 4 ... High temperature tensile test piece 5 ... Charpy impact test piece

Claims (6)

In the method of submerged arc welding of refractory structural steel, the content of each component excluding those contained in either or both of the welding wire and the flux and existing as oxides and fluorides in the flux. The total amount is mass% except for Fe and inevitable impurities .
C: 0.01 to 0.15%,
Si: 0.1 to 2%,
Mn: 0.2 to 5%
Mo: 0.1 to 2%,
Nb: 0.023 to 0.5%,
Al: 0.002 to 7%,
Ti: 0.01 to 5%,
Cr: less than 0.01%,
A method of submerged arc welding of refractory structural steel, characterized by using a combination of a welding wire and a flux. As a total amount in the welding wire and flux excluding those present as oxides and fluorides in the flux,
Cu: 0.01 to 3%,
Ni: 0.01-6%,
W: 0.05-3%,
V: 0.002 to 0.5%,
Ta: 0.002 to 0.5%,
B: 0.0002 to 0.005%,
1 or 2 types or more of these are included, The submerged arc welding method of the refractory structural steel of Claim 1 characterized by the above-mentioned. As a total amount in the welding wire and flux excluding those present as oxides and fluorides in the flux,
Ca: 0.0002 to 0.1%,
Mg: 0.0002 to 0.1%,
REM: 0.0002 to 0.1%
1 or 2 types of these are included, The submerged arc welding method of the refractory structural steel of Claim 1 or 2 characterized by the above-mentioned.   The refractory structural steel according to any one of claims 1 to 3, wherein the refractory structural steel is applied to a steel having a high temperature yield strength at 800 ° C of 0.4 or more with respect to a room temperature yield strength. Submerged arc welding method for steel.   The submerged arc welding method for a refractory structural steel according to any one of claims 1 to 3, wherein the refractory structural steel is applied to a steel having a yield strength of 70 MPa or more at 800 ° C.   The submerged arc welding method for a refractory structural steel according to any one of claims 1 to 5, wherein the refractory structural steel is applied to a steel having a Charpy absorbed energy at 0 ° C of 100 J or more.

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