JP4495060B2 - Welded joints for refractory structures with excellent high-temperature strength and toughness - Google Patents

Description

  The present invention relates to a welded joint for a refractory structure which is mainly applied to a construction steel structure and has excellent fire resistance particularly at a temperature of 700 to 800 ° C. In addition, this joint is applied to the weld joint of welding heat input 10-200 kJ / cm irrespective of a welding method.

  Conventionally, in order to ensure the safety of steel structures in the event of fire, steel materials used in buildings and the like have fire resistance standards set so that the steel surface temperature during fires is 350 ° C or lower. It was necessary to apply fireproof coating such as rock wool on the steel surface. However, in the construction of building steel structures, there is a growing demand for reducing the cost of fireproof coating on the surface of steel materials, omitting the construction process, and the need to completely eliminate the fireproof coating from the viewpoint of the landscape. .

  Based on this background, in response to the achievements of fire prevention and fire prevention professionals in 1987 (according to Article 38 certification), it becomes possible to design building steel structures that take into account the fire resistance performance of steel materials, The necessity of fireproof coating was determined in consideration of the load applied to the actual building steel structure, and in some cases it was possible to use steel with fireproof coating.

  Under these circumstances, a steel material excellent in fire resistance (hereinafter, sometimes referred to as 600 ° C. refractory steel) having a high temperature yield strength at 600 ° C. of 2/3 or more at normal temperature has been developed (see, for example, Patent Document 1). ). In addition, steel materials excellent in fire resistance that guarantee high-temperature yield strength at 700 ° C. or 800 ° C. (sometimes referred to as 700 ° C. fire resistant steel or 800 ° C. fire resistant steel) have also been proposed (see, for example, Patent Documents 2 and 3). ). In general, with 600 ° C refractory steel, the range that can be used with non-fireproof coating is limited to multilevel parking lots and external steel frames with relatively small amounts of combustibles, so in order to expand the range of use to architectural steel structures in the future, Furthermore, the practical use of 700 ° C. and 800 ° C. refractory steel is desired.

  On the other hand, when constructing a building structure using 700 ° C and 800 ° C refractory steel, the welded portion of the steel structure is also used for the welded portion (welded metal and welded heat affected zone) to ensure safety. High high temperature yield strength is required.

  In the conventional conventional refractory steel, the refractory performance is determined so that the high-temperature yield strength is 2/3 of that at normal temperature, and this standard is also applied to a welded joint of 700 ° C. refractory steel. However, in the case of 800 ° C. refractory steel, it is necessary to determine the high temperature yield strength standard of the welded joint in consideration of the actual design of the steel structure. In fireproof design, it is only necessary to maintain high strength within the fire duration, and it is not necessary to consider long-time strength unlike conventional heat-resistant steel. Further, in the 800 ° C. refractory steel, a welded portion is provided in a portion having a small acting stress in a steel structure. Taking these into consideration, the high-temperature yield strength of the welded joint (welded metal and weld heat affected zone) is specifically 217 MPa or more at 700 ° C. and 70 MPa at 800 ° C. in a relatively short time of about 30 minutes. It is considered sufficient if the above high temperature yield strength can be maintained.

  Moreover, when ensuring the safety | security of a steel structure, high toughness is requested | required with the said high temperature yield strength as a welded joint. In the case of a general structure, the absorption energy (vE0) of the 2 mmV notch Charpy impact test at 0 ° C. is required to be 27 J or more, but it is preferable to have 70 J or more in consideration of the earthquake resistance.

  In order to ensure the high temperature strength of the above-mentioned 700 ° C. or 800 ° C. refractory steel, a method of adding an alloy element such as Cr or Mo is generally used. However, in order to ensure the fire resistance at 700 ° C. or 800 ° C. only with such a steel material component design, in order to sufficiently suppress the structural transformation at high temperature and the coarsening or disappearance of precipitates such as carbides, Compared to 600 ° C. refractory steel, it is necessary to add a large amount of alloying elements, resulting in problems such as poor weldability and exceeding the upper limit of room temperature yield strength defined by steel for building structures. Under such circumstances, 400MPa class steel and 490MPa class steel having a fireproof performance that can be designed with a fireproof coating up to 800 ° C have not been put into practical use, but recently, alloy elements, By optimizing hot rolling conditions and improving the Ac1 transformation temperature, high-temperature fire-resistant building structural steels having excellent fire resistance even at high temperatures up to 700 ° C. and further to 800 ° C. are being put into practical use.

  On the other hand, when constructing a steel structure for fireproof building structure using 700 ° C or 800 ° C fireproof steel, high toughness is required as a welded joint property in addition to high high-temperature yield strength similar to steel materials. The

  Conventionally, many welding materials such as arc welding wires, welding rods, and fluxes have been developed and proposed for obtaining welds having excellent fire resistance when welding 600 ° C. refractory steel (for example, Patent Documents 4 to 12). ,reference). In recent years, a method of submerged arc welding of 800 ° C. refractory steel and a welding wire and flux for the method have been proposed (see, for example, Patent Document 13).

  The welded portion is composed of a weld metal formed by melting and solidifying the steel material and the weld material, and a heat-affected zone of the steel material whose structure has been changed by welding heat input. In order to ensure high temperature yield strength in steel materials and weld metals, elements that are harmful to toughness, such as alloy elements such as Mo, Nb, V, etc., are contained in large quantities, so that toughness is maintained while maintaining high temperature yield strength. It was difficult to improve. Further, in the heat-affected zone of 700 or 800 ° C. refractory steel, the structure is changed by welding heat input, so that there is a possibility that the high-temperature yield strength is also reduced as compared with the steel material. Further, since the weld metal of 700 or 800 ° C. refractory steel contains a large amount of alloy elements such as Mo, Nb, and V, the grain boundary of the weld metal becomes brittle at around 700 ° C. and the ductility is extremely reduced. The problem of embrittlement or reheat embrittlement is also likely to occur.

  As described above, in order to ensure the safety of a steel structure for a fireproof building structure at 700 or 800 ° C., as a welded joint, a high temperature yield strength of 217 MPa or more at 700 ° C. and 70 MPa or more at 800 ° C. is maintained, In addition, it is desired to develop general-purpose and comprehensive technologies that can secure 70 J or more in the absorbed energy (vE0) of the 2 mmV notch Charpy impact test at 0 ° C.

Japanese Patent Laid-Open No. 2-77523 JP-A-9-209077 JP-A-10-68015 Japanese Patent Laid-Open No. 2-52196 JP-A-2-217195 JP-A-2-205298 JP-A-2-274394 Japanese Patent Laid-Open No. 2-63698 JP-A-2-274394 JP-A-2-75494 Japanese Patent Laid-Open No. 2-200393 JP-A-2-268994 Japanese Patent Laid-Open No. 2003-311477

  The present invention provides a welded joint for a refractory structure that has excellent fire resistance at a temperature of 700 to 800 ° C. as a whole and has high toughness that can ensure the safety of the structure, regardless of the welding method. For the purpose. More specifically, the present invention relates to a joint property of refractory steel, in which both the weld metal and the weld heat-affected zone have high high-temperature strength of 217 MPa or higher at 700 ° C. and 70 MPa or higher at 800 ° C., and 2 mm V notch Charpy. The object is to have an excellent toughness of 70 J or more in the absorbed energy (vE0) of the impact test.

  The weld joint is composed of a steel plate (base material), and a welded portion including a weld heat affected zone (HAZ) and a weld metal (WM). The present inventors investigated in detail the refractory characteristics and the controlling factors of toughness and composition of each part in the entire welded joint. As a result, (a) As for the high temperature strength and toughness of the base material and the heat affected zone, the performance is almost determined by the composition of the steel material itself, but the weld metal is a solidified structure, so the base material, HAZ In order to ensure both high temperature strength and toughness of the weld metal, it is difficult to ensure high temperature strength as compared to (b) Mo, W, Nb, V, Ta, It was newly found out that not only the individual contents of Zr but also the total amount thereof is defined, and in particular, Nb and V must also strictly define the solid solution amounts at the same time.

  The present invention has been accomplished based on the above findings, and the gist thereof is as follows.

(1) In mass%,
C: 0.005 to 0.15%,
Si: 0.005 to 1%
Mn: 0.1 to 2%,
P: 0.02% or less,
S: 0.01% or less,
O: 0.01% or less,
Al: 0.002 to 0.1%,
N: 0.001 to 0.01%
Including,
Mo: 0.1 to 1%,
W: 0.01 to 1%
Nb: 0.005 to 0.2 %,
T a: 0.005 to 0.5%, and
Zr: 0.005 to 0.5%
1 or 2 types of the above, and the remainder is a welded joint for a fireproof structure comprising a steel for a fireproof structure composed of Fe and inevitable impurities, and a welded portion,
The weld metal formed in the weld is in mass%,
C: 0.01 to 0.15%,
Si: 0.1 to 1%,
Mn: 0.3 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%,
O: 0.005 to 0.06%
Including
Nb: 0.01~0.5%,
Contain,
further,
Mo: 0.02 to 2%,
W: 0.02 to 2%,
Ta: 0.01 to 0.5%, and
Zr: 0.01 to 0.5%
1 or more of them, the total content of C and N in the weld metal is 0.01 to 0.06%, and the Nb equivalent defined by the following formula (3) is 0. 0.05 to 1% is satisfied, the solid solution Nb content is 0.005 to 0.1%, and the relationship between the total content of C and N in the weld metal and the Nb content is as follows ( 4) A welded joint for a refractory structure excellent in high-temperature strength and toughness, characterized by satisfying the formula and the balance being Fe and inevitable impurities.
Nb equivalent = Nb% + 0.47 Mo% + 0.25 W% + 0.4 Ta% + 0.2 Zr% (3)
However, said Nb%, Mo%, W%, Ta%, Zr% shows content (mass%) of Nb, Mo, W, Ta, Zr in a weld metal, respectively.
0.3 ≦ (Nb%) / (C% + N%) ≦ 5 (4)
However, the above “Nb%”, “C%”, and “N%” indicate the contents (mass%) of Nb, C, and N, respectively, in the weld metal.
(2) By mass%
C: 0.005 to 0.15%,
Si: 0.005 to 1%
Mn: 0.1 to 2%,
P: 0.02% or less,
S: 0.01% or less,
O: 0.01% or less,
Al: 0.002 to 0.1%,
N: 0.001 to 0.01%
Including,
Mo: 0.1 to 1%,
W: 0.01 to 1%
Nb: 0.005 to 0.2%,
V: 0.01-0.5%
Ta: 0.005 to 0.5%, and
Zr: 0.005 to 0.5%
1 or 2 types of the above, and the remainder is a welded joint for a fireproof structure comprising a steel for a fireproof structure composed of Fe and inevitable impurities, and a welded portion,
The weld metal formed in the weld is in mass%,
C: 0.01 to 0.15%,
Si: 0.1 to 1%,
Mn: 0.3 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%,
O: 0.005 to 0.06%
Including
Nb: 0.01-0.5%
V: 0.01 to 0.7%
Containing
further,
Mo: 0.02 to 2%,
W: 0.02 to 2%,
Ta: 0.01 to 0.5%, and
Zr: 0.01 to 0.5%
1 or more of them, the total content of C and N in the weld metal is 0.01 to 0.06%, and the Nb equivalent defined by the following formula (1) is 0. 0.05 to 1%, and the total amount of solute Nb and solute V is 0.005 to 0.1%, and the total content of C and N in the weld metal and Nb And a total content of V satisfy the following formula (2), and the balance consists of Fe and inevitable impurities, a weld joint for refractory structures with excellent high temperature strength and toughness.
Nb equivalent = Nb% + 0.47 Mo% + 0.25 W% + 0.65 V% + 0.4 Ta%
+ 0.2Zr% (1)
However, said Nb%, Mo%, W%, V%, Ta%, Zr% shows content (mass%) of Nb, Mo, W, V, Ta, Zr in a weld metal, respectively.
0.3 ≦ (Nb% + V%) / (C% + N%) ≦ 5 (2)
However, the above “Nb%”, “V%”, “C%”, and “N%” indicate the contents (mass%) of Nb, V, C, and N in the weld metal, respectively.

( 3 ) The steel material is further in mass%,
Cu: 0.005 to 1.5%,
Ni: 0.01-6%,
Co: 0.01 to 6%
Cr: 0.005 to 1.5%,
Ti: 0.002~0.1%,
C a: 0.0005 to 0.005%,
REM: 0.0005 to 0.01%, and
Mg: 0.0002 to 0.005%
1 or 2 types of these, The weld joint for fireproof structures excellent in the high temperature strength and toughness as described in said (1) or (2 ) characterized by the above-mentioned.

(4) The weld metal is further Cu: 0.005 to 1.5% by mass,
Ni: 0.01-6%,
Co: 0.01 to 6%
Cr: 0.002 to 0.5%,
Ti: 0.002~0.1%,
Ca : 0.0005 to 0.005%,
REM: 0.0005 to 0.01%, and
Mg: 0.0002 to 0.005%
1 or 2 types or more of these, The weld joint for fireproof structures excellent in the high temperature strength and toughness in any one of said (1)-(3) characterized by the above-mentioned .

( 5 ) The refractory structure excellent in high-temperature strength and toughness according to any one of claims 1 to 4 , wherein the weld metal is formed under conditions of a welding heat input of 10 kJ / cm to 200 kJ / cm. Welded joints.

  According to the present invention, it is possible to provide a welded joint having excellent high-temperature strength and toughness useful in a high-temperature fire-resistant structure excellent in fire resistance at temperatures from 700 to 800 ° C., and having few welding defects. It is remarkable.

  In order to ensure the overall characteristics of the welded joint, it is particularly necessary to ensure both the characteristics of the weld metal and the characteristics of the weld heat affected zone (HAZ). In order to ensure the characteristics of the weld heat affected zone of the steel material, it can be achieved by limiting the chemical composition of the steel material. On the other hand, since the weld metal is formed by melting and solidifying the weld material and the steel material, it is necessary to consider not only the component composition of the weld material but also the dilution from the chemical composition of the steel material. Generally, since the dilution ratio of the weld metal from the chemical composition of the steel material changes depending on the welding method, and the amount of O in the weld metal also greatly changes from several tens of ppm to several hundred ppm, the welding method The composition of the welding material is adjusted every time.

  According to the examination results by the present inventors' confirmation test, when welding under conditions of welding heat input of 10 to 200 kJ / cm, regardless of the welding method, Mo, which is an element exhibiting high-temperature strength in the weld metal, Confirm that the content of W, Nb, V, Ta, and Zr can be optimized, and the solid solution amount of Nb and V that are important for securing both high-temperature strength and toughness of the weld metal can be optimized. did. As a result, it is possible to sufficiently improve the characteristics of both the high temperature strength and toughness of the weld heat affected zone and the weld metal, which has been difficult in the conventional 700 or 800 ° C. refractory steel. It has become possible to improve the safety of welded joints.

  That is, the welded joint for fireproof structure of the present invention is a welded joint for fireproof structure having a component composition described later and having a high temperature yield strength of 700 to 800 ° C. as a base material, The weld metal formed in the welded portion has the component composition shown below. The welded joint for fireproof structure means a welded joint in which at least one base material is a fireproof steel of 700 to 800 ° C.

That is, in the welded joint for fireproof structure of the present invention, the component composition of the weld metal is mass%, C: 0.01 to 0.15%, Si: 0.1 to 1%, Mn: 0.3 to 2. 0.5%, P: 0.02% or less, S: 0.01% or less, Al: 0.001-0.1%, N: 0.001-0.015%, O: 0.005-0. Including 06%, Nb: 0.01-0.5%, or Nb: 0.01-0.5% and V: 0.01-0.7% ,
further,
Mo: 0.02 to 2%,
W: 0.02 to 2%,
Ta: 0.01 to 0.5%, and
Zr: 0.01 to 0.5%
1 or more of them, the total content of C and N in the weld metal is 0.01 to 0.06%, and the Nb equivalent defined by the following formula (1) is 0. 0.05 to 1%, and the total amount of solute Nb and solute V is 0.005 to 0.1%, and the total content of C and N in the weld metal and Nb And the total content of V satisfy the following formula (2), the balance consists of Fe and inevitable impurities, and Cu: 0.005 to 1.5%, Ni: 0 as necessary. 0.01 to 6%, Co: 0.01 to 6%, Cr: 0.002 to 0.5%, Ti: 0.002 to 0.1% , Ca : 0.0005 to 0.005%, REM: One or two or more of 0.0005 to 0.01% and Mg: 0.0002 to 0.005% are included. Thus, the welding heat input regardless of the welding method if conditions 10~200kJ / cm, Ru can be achieved welded joint having a weld metal having both excellent high-temperature strength and toughness.
N b eq = Nb% + 0.47Mo% + 0.25W % + 0.65V% + 0.4Ta%
+ 0.2Zr% (1)
However, said Nb%, Mo%, W%, V%, Ta%, Zr% shows content (mass%) of Nb, Mo, W, V, Ta, Zr in a weld metal, respectively. In addition, when V does not exist (V0%), the following equation (3) is obtained.
Nb equivalent = Nb% + 0.47 Mo% + 0.25 W% + 0.4 Ta% + 0.2 Zr%
(3)
0.3 ≦ (Nb% + V%) / (C% + N%) ≦ 5 (2)
However, “Nb%”, “V%”, “C%”, and “N%” indicate the contents (mass%) of Nb, V, C, and N in the weld metal, respectively. In addition, when V does not exist (V0%), the following equation (4) is obtained.
0.3 ≦ (Nb%) / (C% + N%) ≦ 5 (4)
In addition, in order for the above-mentioned weld metal to reliably exhibit a reliable effect as a joint for a refractory structure, any welding method can be used. It is preferable to be within.

  Below, the reason for limitation of the component composition of the steel materials and weld metal which comprise the welded joint for fireproof structures of this invention is demonstrated in detail.

  First, the reasons for limiting the chemical composition of the welded joint steel for fireproof structure (700 to 800 ° C fireproof steel) will be described.

Note that “%” shown below means “% by mass” unless otherwise specified.
C is the most effective element for securing the room temperature strength of the steel material. In order to exhibit this effect, it is necessary to contain 0.005% or more in the steel material. On the other hand, if the content exceeds 0.15%, the weldability deteriorates and it becomes difficult to ensure the toughness of the base material and the HAZ. Also, if the C content in the steel material is more than 0.15%, depending on the welding method, the amount of C in the weld metal becomes excessive, which may adversely affect the toughness and high temperature characteristics of the weld metal, It is not preferable.
Si is a deoxidizing element, and in order to maintain the soundness of steel, it is necessary to contain at least 0.005% or more. However, if it is excessively contained in excess of 1%, the HAZ is hardened to deteriorate the toughness and low-temperature cracking property of the HAZ. Therefore, in the present invention, the Si content is 0.005 to 1%. limit.

  Mn is an essential element for steel materials in order to ensure hardenability and increase strength, and if it is within a certain amount, it is effective in improving the toughness by refining the structure. In order to reliably exhibit the effect of improving the strength and refining the structure, it is necessary to contain 0.1% or more in the steel material. On the other hand, if the content exceeds 2%, the grain boundary embrittlement susceptibility increases and the possibility of deterioration in toughness and weld crack resistance increases, so in the present invention, the Mn content in the steel material is 0.1 to 0.1%. Limited to 2%.

  P is an impurity element and needs to be reduced as much as possible in order to inhibit toughness. However, if the content in the steel sheet is 0.02% or less, adverse effects on toughness can be tolerated. Therefore, in the present invention, the P content in the steel sheet Is 0.02% or less.

S is also an impurity element, and if it is excessively present in the steel sheet, it deteriorates both toughness and ductility, so it is preferable to reduce it as much as possible. If the content in the steel sheet is 0.01% or less, adverse effects on toughness and ductility can be tolerated. Therefore, in the present invention, the S content in the steel sheet is 0.01% or less.
O is also an impurity element in steel materials, and if it exceeds 0.01% and is excessively contained in the steel material, ductility and toughness are deteriorated, so in the present invention, the O content in the steel material. Is 0.01% or less.

  Al is also a deoxidizing element. Like Si, it is an effective element for reducing the oxygen content of steel and ensuring soundness. For that purpose, it is necessary to contain 0.002% or more. On the other hand, if the content exceeds 0.1% excessively, a coarse oxide may be formed in the steel material and the toughness may be hindered. Therefore, in the present invention, the Al content is 0.002 to 0. Limited to 1%.

  In a small amount, N forms fine nitrides when the steel slab is heated to refine the heated austenite grain size and contribute to toughness. For that purpose, 0.001% or more is necessary as content in steel. On the other hand, if the content exceeds 0.01%, the nitride becomes coarse, or the amount of solute N increases and the toughness is deteriorated. Therefore, in the present invention, the N content in the steel material is set to 0.0. It is limited to 001 to 0.01%.

  In order to express the high temperature strength, one or more of Mo, W, Nb, V, Ta, and Zr, which are effective in improving the high temperature strength in a solid solution or / and in a precipitated state, are further included in the steel material. It is an essential requirement to contain in the following range.

  Mo is one of the elements that play the most important role in expressing the fire resistance characteristics of steel. In the solid solution and precipitation state, the movement of dislocations at a high temperature is hindered to increase the high temperature strength. However, in order to exert the effect, it is necessary to contain 0.1% or more. On the other hand, if the content exceeds 1%, the toughness in the base material and the HAZ is greatly deteriorated. Therefore, in the present invention, the Mo content in the steel material is limited to 0.1 to 1%.

  W has substantially the same effect as Mo on the mechanical properties of steel. Therefore, the limited range of the W content in the present invention is also 0.01 to 1%, similar to Mo.

  Nb is an element that can improve the high-temperature strength in a relatively small amount. When contained in the steel material used in the present invention, 0.005% or more is necessary for improving high-temperature strength, particularly high-temperature strength at 700 ° C. or higher. On the other hand, if it exceeds 0.2% and is contained excessively in the steel material, a coarse precipitate portion is formed, the effect of improving the high-temperature strength is saturated, and the toughness of the base material and HAZ is remarkably deteriorated. Therefore, in this invention, Nb content in steel materials shall be 0.005-0.2%.

  V is also an element similar to Nb, but in order to exert its effect, it is necessary to contain 0.01% or more in the steel material, and if it exceeds 0.5%, the toughness deterioration becomes remarkable. When V is contained in the steel material, the content is limited to 0.01 to 0.5%.

  Ta is an element similar to Nb and V, and is effective in improving the high-temperature strength. When it is contained in the steel material, 0.005% or more is necessary for exhibiting the effect, and the upper limit needs to be 0.5% in order not to significantly deteriorate the toughness.

  Zr is also an element similar to Nb, V, and Ta, and is effective in improving the high temperature strength. When it is contained in the steel material, 0.005% or more is necessary for exhibiting the effect, and the upper limit needs to be 0.5% in order not to significantly deteriorate the toughness.

The above are the limiting requirements for the basic components of the 700 to 800 ° C. refractory steel material used for the welded joint in the present invention, ensuring high temperature yield strength at 700 to 800 ° C., and particularly room temperature yield strength as a steel material for steel structures. Steel material with sufficient basic properties such as toughness.
Further, in the present invention, among the basic characteristics intended by the present invention, especially for the purpose of adjusting the strength and toughness and improving the ductility, Cu, Ni, Co, Cr, Ti, B, Ca are further added as necessary. , REM, and Mg can be contained in one kind or two or more kinds.

  Cu has the effect of improving the hardenability of the steel material and improving the strength by precipitation strengthening. Although it is a preferable element in that the toughness deterioration is not remarkable for the strengthening margin, in order to exert the effect, it is necessary to contain 0.005% or more in the steel material. On the other hand, if the content exceeds 1.5%, hot cracking of the steel slabs or toughness deterioration becomes clear, which is not preferable.

  Ni is the only element that has the effect of improving hardenability and strength, and at the same time improving toughness, and is very effective for steel for applications that emphasize toughness. Needs to be contained in an amount of 0.01% or more. However, if it is contained in a large amount exceeding 6%, the Ac1 transformation point will be extremely lowered and reverse transformation will occur to the extent that it cannot be ignored at 700 ° C. or higher. From the viewpoint of Therefore, in the present invention, when Ni is contained in the steel material, the content is limited to 0.01 to 6%.

  If Co is contained when the amount of other alloy elements is large and the hard phase is produced and the toughness is deteriorated, it is effective in increasing the transformation point and suppressing the formation of the hard phase to prevent the deterioration of the toughness. In order to exhibit this effect, it is necessary to contain at least 0.01%. On the other hand, even if the content exceeds 6%, the effect is saturated, and on the contrary, the structure becomes coarse and the toughness may be deteriorated. Therefore, in the present invention, the upper limit when Co is contained in the steel material is 6 %.

  Cr is an element effective for increasing the strength and improving the corrosion resistance. In order to exert the effect, it is necessary to contain 0.005% or more. On the other hand, if over 1.5%, the toughness deteriorates, such being undesirable. Therefore, in this invention, the range of Cr amount when making it contain in steel shall be 0.005-1.5%.

  Ti is an element which is effective in improving the toughness by refining the steel structure. Although it is weak due to precipitation strengthening, it also has an effect of improving high-temperature strength. In order to exert these effects, it is necessary to contain 0.002% or more in the steel material. However, if the content exceeds 0.1%, coarse nitrides and oxides are formed, which may cause a steel plate flaw and a toughness deterioration of the base material and the HAZ. Therefore, in this invention, when Ti is contained in steel materials, it is set as 0.002 to 0.1% of range.

  Further, in the present invention, in addition to the above-described steel material components, Ca: 0.0005 to 0.005%, REM in mass%, if necessary, for the purpose of improving the ductility of the steel material and improving the HAZ toughness. : 0.0005 to 0.01%, and Mg: 0.0002 to 0.005%, or one or more of them can be contained.

  Ca, REM, and Mg all have almost the same effect, and Ca and REM must be contained in 0.0005% or more, and Mg must be contained in 0.0002% or more in order to exert the effect reliably. There is. The upper limit is determined from the content that forms coarse inclusions and degrades both ductility and toughness. In the present invention, the upper limit of Ca and Mg content is 0.005%, the content of REM The upper limit is 0.01%.

  The above is the reason for limiting the chemical composition of the steel material (700 to 800 ° C. refractory steel) constituting the welded joint for fireproof structure of the present invention.

  Next, the reason for limitation of the component composition of the weld metal formed in the welded portion of the welded joint using 700 to 800 ° C. refractory steel having the above component composition as a base material will be described in detail below.

  First, the C content in the weld metal is set to 0.01 to 0.15%. If the C content is less than 0.01%, the strength of the weld metal is not sufficient. On the other hand, if the C content exceeds 0.15%, the weld metal is cured, and the toughness and crack resistance are increased. Is deteriorated, and a large amount of carbides are formed, so that the amount of solid solution Nb and V becomes too small to ensure high temperature strength.

  Si is a deoxidizing element, and is an essential element for ensuring the cleanliness of the weld metal. It also has the effect of increasing strength through solid solution strengthening. If the Si content in the weld metal is less than 0.1%, deoxidation is not sufficient, and defects may occur in the weld metal, such being undesirable. On the other hand, if the Si content in the weld metal exceeds 1%, the hardened structure and coarse oxides in the weld metal increase, which deteriorates the toughness of the weld metal. Therefore, in this invention, Si content of a weld metal is limited to 0.1 to 1%.

  Mn is a preferable element in terms of improving both strength and toughness within a range that contributes to refinement of the structure by increasing the hardenability of the weld metal. In order to exhibit the effect when contained in the weld metal, it is necessary to contain 0.3% or more in the weld metal. However, if the weld metal is contained excessively in excess of 2.5%, the weld metal is excessively cured and the toughness and cold cracking properties are deteriorated, which is not preferable. Therefore, in the present invention, the Mn content in the weld metal is limited to 0.3 to 2.5%.

  P is an impurity element that greatly deteriorates the toughness of the weld metal, and is preferably reduced as much as possible. However, if it is 0.02% or less, the toughness deterioration is acceptable, so in the present invention, The P content is limited to 0.02% or less.

  S is also an impurity element that greatly deteriorates the toughness and ductility of the weld metal, and it is preferable to reduce it as much as possible. However, if it is 0.01% or less, the deterioration of toughness is acceptable, so in the present invention, welding is performed. The S content in the metal is limited to 0.01% or less.

  Al is a strong deoxidizing element and is important for preventing the oxygen content of the weld metal from becoming excessive and maintaining the cleanliness of the weld metal. In order to exert the effect, it is necessary to be 0.001% or more, but if it is excessively contained exceeding 0.1%, coarse inclusions are formed to inhibit toughness. The Al content is limited to 0.001 to 0.1%.

  If N is a trace amount, it can contribute to the improvement of toughness by forming a nitride with Ti or Al to refine the austenite grain size. For that purpose, it is necessary to make it contain in 0.001% or more in a weld metal. However, an excessive content exceeding 0.015% is not preferable because the nitride becomes coarse and becomes a starting point of fracture, and the solid solution N increases to deteriorate toughness. Therefore, in the present invention, the N content in the weld metal is limited to 0.001 to 0.015%.

  O is inevitably contained in the weld metal, and its content range is limited to some extent for each welding method. In order to ensure the characteristics of the weld metal regardless of the welding method by satisfying the requirements regarding the chemical composition of the weld metal, it is necessary to limit the amount of O within a certain range. It is difficult to reduce the amount of O in the weld metal as much as the base metal, and if the amount of O is too small, the number of acicular ferrite formation nuclei effective for refining the structure is extremely reduced, which is harmful to toughness. Is not preferable. If the amount of O in the weld metal is 0.005% or more, the minimum necessary amount of acicular ferrite can be generated regardless of the welding method and welding heat input, so the lower limit of the amount of O is 0.005%. To do. On the other hand, if the amount of O in the weld metal exceeds 0.06%, the oxide amount increases and becomes coarse, and even if other requirements are satisfied, the deterioration of the weld metal toughness is unavoidable. In this case, the upper limit of the amount of O in the weld metal is 0.06%. Therefore, a welding method in which the amount of O in the weld metal cannot be made 0.06% or less is out of the scope of the present invention.

Nb and V are elements important for high temperature strength expression of the weld metal in the present invention, and contain one kind of Nb or two kinds of Nb and V in the following ranges.
Nb is an element that can improve the high-temperature strength by being contained in a relatively small amount in the weld metal, and is an important element for the high-temperature strength expression of the weld metal in the present invention. In order to sufficiently improve the high temperature strength of the weld metal, particularly 700 ° C. to 800 ° C., with Nb alone, it is necessary to contain 0.01% or more of Nb in the weld metal. On the other hand, if Nb is excessively contained in the weld metal in excess of 0.5%, a coarse precipitate is formed in the weld metal and the effect of improving the high-temperature strength is saturated, and the toughness of the base material and HAZ is remarkably increased. Since it degrades, it is not preferable. Therefore, in the present invention, the Nb content in the weld metal is set to 0.01 to 0.5%.

  As will be described later, in order to achieve both high temperature strength and toughness at 700 ° C. to 800 ° C. of the weld metal, the total amount of solute Nb and solute V is 0.005 to 0.1%. In order to ensure the high temperature strength and toughness of the weld metal in a relatively wide weld heat input range of 10 to 200 kJ / cm, regardless of the welding method, all Nb in the weld metal It is preferable to adjust the balance between Nb precipitates and solid solution Nb in the range of 0.01 to 0.5%.

V has an effect similar to that of Nb, and is an important element for expressing the high temperature strength of the weld metal in the present invention. In order to sufficiently improve the high temperature strength of the weld metal by V alone, particularly at 700 ° C. to 800 ° C., it is necessary to contain 0.01% or more of V in the weld metal. On the other hand, if V is excessively contained in the weld metal in excess of 0.7%, a coarse precipitate portion is formed in the weld metal and the effect of improving the high temperature strength is saturated, and the toughness of the base material and the HAZ is remarkably increased. Since it degrades, it is not preferable. Therefore, in the present invention, the V content in the weld metal is set to 0.01 to 0.7%.
V, like Nb, as described later, in order to achieve both high-temperature strength and toughness at 700 ° C. to 800 ° C. of the weld metal, the total amount of solid solution Nb and solid solution V is 0.005 to It must be 0.1% regardless of the solid solution amount of V proper amount welding process, and high-temperature strength of the weld metal welding heat input at a relatively wide welding heat input range of 10~200kJ / cm In order to ensure toughness, it is preferable to adjust the balance between V precipitates and solid solution V in the range of 0.01 to 0.7% of the total V amount in the weld metal.

  In the present invention, Mo, W, Ta, and Zr in the weld metal are less effective than Nb and V, but are elements that act on the high temperature strength of the weld metal as in the case of Nb and V. is there. In the present invention, since these elements are contained in the 700 ° C. or 800 ° C. refractory steel material, they are inevitably mixed into the weld metal due to dilution of the refractory steel components even if these elements are not contained in the welding material. However, in order to exert the effect of increasing the high-temperature yield strength at 700 ° C. to 800 ° C. in the presence of Nb equivalent, solid solution Nb, and solid solution V defined by the formula (1) as in the present invention. In the case where one or more of Mo, W, Ta, Zr, and Mo are contained in the weld metal, the content must be limited as shown below.

Mo, like refractory steel, is one of the elements that plays the most important role in the development of refractory properties in weld metals.
Mo in the weld metal has an effect of preventing the movement of dislocations at a high temperature in a solid solution and a precipitated state and stably increasing the high temperature yield strength, and particularly Nb defined by the formula (1) as in the present invention. In order to exhibit the effect of increasing the high-temperature yield strength in the presence of equivalent conditions and solid solution Nb and solid solution V, Mo needs to be contained in the weld metal in an amount of 0.02% or more. On the other hand, if Mo is contained in the weld metal in excess of 2%, the weld metal is excessively hardened, and the toughness and cold cracking resistance are remarkably deteriorated. Therefore, in the present invention, the Mo content in the weld metal Is limited to 0.02 to 2%.

  W has substantially the same effect as Mo on the mechanical properties of the weld metal. Therefore, the limited range in the present invention is also set to 0.02 to 2% like Mo.

  Ta is also an effective element for increasing the high temperature strength by precipitation strengthening in the weld metal. When contained in the weld metal, 0.01% or more is necessary for improving the high-temperature strength at 700 ° C. or more. However, if the content exceeds 0.5%, the toughness of the weld metal deteriorates significantly. In the present invention, when Ta is contained in the weld metal, the range is 0.01 to 0.5%. Limited to.

  Zr, like Ta, is an effective element for increasing the high temperature strength by precipitation strengthening. When contained in the weld metal, 0.01% or more is necessary for improving the high-temperature strength at 700 ° C. or more. However, if the content exceeds 0.5%, the toughness of the weld metal is significantly deteriorated. Therefore, in the present invention, when Zr is contained in the weld metal, the range is 0.01 to 0.5%. Limited to.

In the present invention, one or more of Nb and V that play an important role in the manifestation of high-temperature yield strength of the weld metal, and further, one or more of Mo, W, Ta, and Zr are included in the above ranges, respectively. In order to improve the toughness while maintaining the high-temperature yield strength, the total amount of Nb equivalent defined by the following formula (1), the solid solution Nb and the solid solution V amount is limited as follows: There is a need to.
That is, in the present invention, in order to achieve both high-temperature yield strength and toughness of the weld metal, the contents of Nb, V, Mo, W, Ta, and Zr in the weld metal are set to the high-temperature yield strength and toughness of these alloy elements. It is necessary to limit the Nb equivalent defined by the following formula (1) considering the degree of contribution to 0.05 to 1%.
Nb equivalent = Nb% + 0.47 Mo% + 0.25 W% + 0.65 V% + 0.4 Ta%
+ 0.2Zr% (1)
However, said Nb%, Mo%, W%, V%, Ta%, Zr% shows content (mass%) of Nb, Mo, W, V, Ta, Zr in a weld metal, respectively.
When the Nb equivalent defined by the above formula (1) is less than 0.05% due to the contents of Nb, V, Mo, W, Ta, and Zr in the weld metal, the contents of the individual elements are as described above. Even within the scope of the invention, it is difficult to sufficiently improve the high-temperature yield strength of the weld metal at 700 ° C to 800 ° C. On the other hand, even if the content of each element is within the range of the present invention, if the Nb equivalent defined by the above formula (1) exceeds 1%, the degree of toughness deterioration of the weld metal becomes unacceptable. Therefore, in the present invention, in addition to limiting the contents of Nb, V, Mo, W, Ta, and Zr, the Nb equivalent defined by the formula (1) is limited to 0.05 to 1%.

  In addition, as a result of examinations by the present inventors such as confirmation tests, all of the above Nb, V, Mo, W, Ta, and Zr are elements that have the effect of increasing the high temperature strength by solid solution or precipitation strengthening in the weld metal. On the other hand, it has been found that the toughness of the weld metal is greatly deteriorated when these elements, particularly Nb and V, are present in the weld metal in the form of Nb precipitates and V precipitates. Therefore, in the present invention, when one or two of Nb and V are contained in the weld metal, Nb and V in the weld metal are secured in order to increase the high-temperature yield strength of the weld metal and at the same time ensure toughness. In this case, it is necessary to suppress the precipitation of Nb and the total amount of solute Nb and solute V to be in the range of 0.005 to 0.1%.

  If the total amount of solute Nb and solute V in the weld metal is less than 0.005%, is the content of each of Nb and V and / or the Nb equivalent defined by the above formula (1) reduced? Alternatively, most of Nb and V in the weld metal are present as precipitates, and the high-temperature yield strength is lowered (in the former case) or the toughness is significantly deteriorated (in the latter case).

  On the other hand, if the total amount of solute Nb and solute V in the weld metal exceeds 0.1%, from the heat history of the weld metal if the normal welding heat input is 10 to 200 kJ / cm, Along with the solid solution Nb and the solid solution V, the amounts of Nb precipitates and V precipitates are inevitably excessive, and thus a significant deterioration in toughness is inevitable.

  Therefore, in the present invention, in order to achieve both high-temperature strength and toughness of the weld metal, the total amount of solute Nb and solute V is set to 0.005 to 0.1%.

  In the present invention, the amount of solid solution Nb and the amount of solid solution V in the weld metal are, for example, the amount of Nb precipitation and the amount of V precipitation measured by a nonaqueous solvent electrolysis method, and the total amount of Nb contained in the weld metal. , And defined as an amount obtained by subtracting the Nb precipitation amount and the V precipitation amount from the total V amount.

  The effect of improving both the high-temperature yield strength and toughness characteristics of the weld metal by defining the solid solution Nb and the solid solution V amount in the weld metal is exhibited regardless of the welding method and conditions. In order to ensure that the total amount of dissolved Nb and solute V is within the scope of the present invention, the total content of C and N that has a great influence on the precipitation of Nb and V carbonitrides in the weld metal. Is preferably limited to 0.01 to 0.06%. When the total content of C and N is less than 0.01%, the precipitation amount of elements that develop high temperature strength by precipitation strengthening is not sufficient, and it is not easy to ensure high temperature strength stably. On the other hand, if the total content of C and N is more than 0.06%, the precipitation amount of Nb and V may be excessive and the toughness may be deteriorated, and the toughness deterioration due to C and N itself is also large. Therefore, it is not preferable.

Further, it is preferable that the contents of C and N in the weld metal satisfy the following formula (2) from the relationship between the total Nb amount and the total V amount.
0.3 ≦ (Nb% + V%) / (C% + N%) ≦ 5 (2)
However, the above “Nb%”, “V%”, “C%”, and “N%” indicate the contents (mass%) of Nb, V, C, and N in the weld metal, respectively.

In the above formula (2), (Nb% + V%) / (C% + N%), which is the ratio of the total content of C and N in the weld metal and the total content of Nb and V, If it is less than 0.3, Nb and V easily form carbonitrides in the weld metal, and it becomes difficult to secure and control solid solution Nb and solid solution V. On the other hand, when (Nb% + V%) / (C% + N%) exceeds 5, and Nb and V are excessive compared to C and N, solid solution Nb and solid solution V become excessive, which causes the weld metal This is not preferable because the toughness is deteriorated.
Therefore, in the present invention, since the necessary and sufficient solid solution Nb and solid solution V can be secured more stably in the weld metal, the total content of C and N and the content of Nb and V in the weld metal It is preferable that the relationship with the total satisfies the above formula (2).

  More preferably, the welding heat input is limited to 10 kJ / cm to 200 kJ / cm in order to ensure that the total amount of the solute Nb and the solute V amount of the weld metal is within the scope of the present invention. More preferred.

  If the welding heat input is less than 10 kJ / cm, each weld bead is subjected to relatively high-temperature reheating by the previous welding pass by multi-layer welding, so that it is difficult to secure the amounts of solute Nb and V. On the other hand, when the welding heat input exceeds 200 kJ / cm, the cooling rate after solidification of the weld metal becomes small, and when the total amount of Nb and V is large, the total amount of solute Nb and solute V is excessive. Occurs. Further, if the welding heat input exceeds 200 kJ / cm, the microstructure of the weld metal becomes excessive and it is not easy to ensure toughness, which is not preferable.

In the present invention, in addition to the above basic components of the weld metal, Cu, Ni, Cr, Co, Cr, Ti , C a as necessary for the purpose of adjusting the strength of the weld metal, improving ductility, and the like. , REM, and Mg can be selectively contained in the following ranges.

  Cu has the effect of increasing the hardenability of the weld metal and improving the strength by precipitation strengthening. Although it is a preferable element in that the toughness deterioration is not remarkable for the strengthening margin, in order to exert the effect, it is necessary to contain 0.005% or more in the steel material. On the other hand, if the content exceeds 1.5%, hot cracking of the weld metal occurs or toughness deterioration becomes clear, which is not preferable.

  Ni is the only element that has the effect of improving hardenability and strength, and at the same time improving toughness, and has a great effect of improving toughness. In order to exhibit this effect, it is necessary to contain 0.01% or more. However, if it exceeds 6% and excessively contained, the Ac1 transformation point will be extremely lowered, reverse transformation will occur to the extent that it cannot be ignored at 700 ° C. or higher, and the high temperature strength of the weld metal may be significantly reduced. It is not preferable from the viewpoint of ensuring fire resistance. Therefore, in the present invention, when Ni is contained in the weld metal, the content is limited to 0.01 to 6%.

  If Co is contained when the amount of other alloy elements is large and the hard phase is produced and the toughness is deteriorated, it is effective in increasing the transformation point and suppressing the formation of the hard phase to prevent the deterioration of the toughness. There is also an effect of suppressing toughness deterioration due to unstable retained austenite. In order to exhibit this effect, it is necessary to contain at least 0.01%. On the other hand, even if the content exceeds 6%, the effect is saturated, and on the contrary, the structure becomes coarse and the toughness may be deteriorated. Therefore, in the present invention, the upper limit when Co is contained in the steel material is 6 %.

  Cr is an element effective for increasing the strength and improving the corrosion resistance. In order to exert the effect, it is necessary to contain 0.002% or more. On the other hand, if over 0.5%, the toughness deteriorates, such being undesirable. Therefore, in this invention, the range of Cr amount when making it contain in steel shall be 0.005-0.5%.

  When Ti is present in an appropriate amount in the weld metal, its oxides and nitrides become intragranular transformation nuclei, and fine acicular ferrite is generated and contributes to the refinement of the structure, thus contributing to the improvement of the toughness of the weld metal. In order to exert this effect, it is necessary to contain 0.002% or more in the weld metal. On the other hand, when the content in the weld metal exceeds 0.1%, oxides and nitrides are coarsened to deteriorate toughness. Therefore, in the present invention, the Ti content in the weld metal is 0.002 to 0. Limited to 1%.

  When an appropriate amount of Ca is contained in the weld metal, the structure is refined by controlling the form of the inclusions, which is effective in improving toughness and ductility. In order to exhibit this effect, when Ca is contained in the weld metal, it is necessary to contain 0.0005% or more. On the other hand, if the content exceeds 0.005%, a coarse oxide is formed and the toughness is deteriorated. Therefore, in the present invention, the content when Ca is contained in the weld metal is limited to 0.0005 to 0.005%.

  REM has the same effect as Ca, and it is necessary to contain 0.005% or more in order to clarify the toughness and ductility improvement of the weld metal. However, if it is excessively contained in excess of 0.01%, coarse oxides and sulfides are formed and the mechanical properties are impaired. Therefore, when REM is included in the weld metal, 0.0005 to 0.005. A range of 01% is preferable.

  Mg also contributes to refinement of the microstructure of the weld metal in a small amount. When Mg is contained in the weld metal, if it is 0.0002% or more, the effect of improving toughness and ductility becomes clear. On the other hand, when the content in the weld metal is more than 0.005%, coarse oxides and sulfides are formed to inhibit the mechanical properties. Therefore, when Mg is contained in the weld metal, 0.0002% It is preferable to make it into the range of -0.005%.

The above-described effects and operations of the present invention will be described in more detail with reference to examples. Although the basic effect of the present invention does not depend on the welding method or welding heat input, in the examples, submerged arc welding and Ar + 5% CO ₂ welding were used as welding methods.

Table 1 shows the chemical composition and base material characteristics of the steel sheet used for the joint. The plate thickness of the steel plate is constant at 25 mm, and the manufacturing method is variously changed according to the composition to manufacture the steel plate. Steel plates Nos. 1 to 3 and 5 to 6 have not only room temperature strength but also high strength at 700 and 800 ° C. and high toughness because the chemical composition of the steel plates satisfies the present invention. Steel plates 4 and 7 are reference examples. On the other hand, since the chemical compositions of the steel plates 8 to 11 do not satisfy the present invention, the properties of the welded joint described later are also inferior, but the properties of the steel plate itself are also inferior to those of the present invention.

  That is, the steel plate number 8 is inferior in the toughness of the steel plate (base material) because the amount of C in the steel plate is excessive. Further, the heat transformation point is lowered, and the high-temperature strength at 800 ° C. is also low.

  In steel plate number 9, since the amount of P in the steel plate is excessive, deterioration of the toughness of the steel plate is particularly remarkable.

  Steel plate number 10 is inferior in toughness of the steel plate (base material) because the amount of Mn in the steel plate is excessive. Further, the heat transformation point is lowered, and the high-temperature strength at 800 ° C. is also low.

  Steel plate No. 11 does not contain any high-temperature strength-expressing element, so the high-temperature strength of the steel plate is low at both 700 ° C. and 800 ° C., and is not preferable as a refractory steel for 700 ° C. and 800 ° C.

For Ar + 5% CO ₂ welding, a welding wire shown in Table 2 was used, and under the welding conditions shown in Table 3, joints were produced by combining various steel plates, welding wires, and welding heat input.

For submerged arc welding, a welding wire shown in Table 4 and a flux shown in Table 5 were used, and under the welding conditions shown in Table 6, various types of steel plates, welding wires, flux, and welding heat input were used to produce joints. Both Ar + 5% CO ₂ welding and submerged arc welding were multilayered and welded in the groove shape shown in FIG.

  Table 7 shows the chemical composition of the welded joint. The solid solution Nb and V amounts were obtained by subtracting the precipitation amount obtained by extraction residue analysis of the same region from the average content of the portion excluding the excess portion of the weld metal.

  Table 8 shows the mechanical properties of the weld joint of Table 7. As the mechanical properties, room temperature to high temperature tensile properties and 2 mmV notch Charpy impact properties were investigated. As shown in Fig. 2, the tensile property is a round bar tensile test piece, one from the center of the steel plate thickness is perpendicular to the longitudinal direction of the weld bead, the parallel part is the base material, the weld heat affected zone (HAZ), and the weld The sample was collected so as to include all of the metal (for joint tensile property investigation), and the other was collected parallel to the longitudinal direction of the weld bead (for weld metal property investigation). As shown in FIG. 3, the 2 mm V notch Charpy impact test piece was sampled perpendicularly to the longitudinal direction of the weld bead from the center of the steel plate thickness. For the joint evaluation, a notch was introduced into the fusion line, and for the weld metal evaluation, a notch was introduced in the center of the weld metal.

Among Table 8, joints A1, A3, A5, A8 to A14, A16, and A17 are joints that satisfy the requirements of the present invention, and have sufficient high-temperature strength as welded joints for 700 ° C and 800 ° C refractory steel structures. At the same time, all joint toughnesses can stably achieve 100 J or more with an absorbed energy of 0 ° C. According to the present invention, extremely good characteristics can be obtained as a welded joint for a fire resistant structure for 700 ° C. and 800 ° C. Is clear. Incidentally, A2, A4, A6, A 7, A15 and A18 are reference examples.

  On the other hand, in Table 8, since the joints B1 to B11 are joints that do not satisfy the requirements of the present invention, the characteristics as joints are not sufficient for 700 ° C and 800 ° C fireproof structures.

  That is, since the joint B1 has an excessive C content in the steel sheet, the toughness of the base metal is not only inferior as described above, but also the toughness of the weld heat affected zone is extremely low. The high temperature strength at is low.

  In the joint B2, since the P content of the steel sheet is excessive, the toughness of the base metal is inferior as described above, and the toughness of the weld heat affected zone is extremely low, which is not preferable.

  In the joint B3, since the Mn content of the steel plate is excessive, the toughness of the base metal is inferior as described above, and the toughness of the weld heat affected zone is also low. The high temperature strength at is low.

  Joints B4 and B11 are comparative examples of Ar + 5% CO2 welding and submerged arc welding, respectively, and all of Mo, W, Nb, Ta, V, and Zr, which are high-temperature strength developing elements, are in the steel plate as well. Since it is not contained in the weld metal, the base metal, the weld heat-affected zone, the weld metal, and all joint sites have low high-temperature strengths of 700 ° C. and 800 ° C., which is insufficient as a weld joint for fireproof structures.

  The joint B5 contains all of Mo, W, Nb, Ta, V, and Zr, which are high-temperature strength expressing elements, in the chemical composition of the weld metal, but the content is too small and the Nb equivalent However, since it is below the lower limit of the present invention, the high temperature strength of the weld metal is not sufficient, and as a result, the high temperature strength of the joint is also low due to the influence of the weld metal, which is not preferable.

  In the joint B6, although Mo, Nb, and V are contained in the weld metal at the lower limit or more of the present invention, since the Nb equivalent is too small, the high temperature strength in the weld metal is inferior to that of the present invention, and 700 ° C. , It is insufficient as a welded joint for a fireproof structure for 800 ° C.

  In the joint B7, the content and Nb equivalent of the high temperature strength expressing element in the weld metal satisfy the present invention, but the total amount of the solute Nb and the solute V is too small. The high-temperature strength at 800 ° C. is low and the toughness of the weld metal is low although the high-temperature strength is low, which is not preferable.

  In the joints B8 and B9, since the Mo content in the weld metal is excessive and the Nb equivalent is also excessive, the toughness of the weld metal is greatly inferior to that of the present invention.

  In the joint B10, since the Nb content in the weld metal is excessive and the Nb equivalent is also excessive, the toughness of the weld metal is greatly inferior to that of the present invention.

   From the results of the above examples, according to the present invention, the weld joint as a whole has excellent fire resistance at temperatures from 700 to 800 ° C. and has toughness that can ensure the safety of the structure. It is clear to provide a joint.

It is a schematic diagram which shows the welding groove shape used for the Example of this invention. It is a schematic diagram for demonstrating the tensile test piece collection point from a welded joint. It is a schematic diagram for demonstrating the tensile test piece collection point from a welded joint.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Groove 3 Back metal 4 Weld bead 5 Weld metal tensile test piece 6 Joint tensile test piece 7 2mmV notch Charpy impact test piece

Claims (5)

% By mass
C: 0.005 to 0.15%,
Si: 0.005 to 1%
Mn: 0.1 to 2%,
P: 0.02% or less,
S: 0.01% or less,
O: 0.01% or less,
Al: 0.002 to 0.1%,
N: 0.001 to 0.01%
Including,
Mo: 0.1 to 1%,
W: 0.01 to 1%
Nb: 0.005 to 0.2 %,
T a: 0.005 to 0.5%, and
Zr: 0.005 to 0.5%
A welded joint for refractory structure comprising one or two or more of the above, and the balance being a refractory structural steel made of Fe and inevitable impurities, and a weld,
The weld metal formed in the weld is in mass%,
C: 0.01 to 0.15%,
Si: 0.1 to 1%,
Mn: 0.3 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%,
O: 0.005 to 0.06%
Including
Nb: 0.01~0.5%,
Contain,
further,
Mo: 0.02 to 2%,
W: 0.02 to 2%,
Ta: 0.01 to 0.5%, and
Zr: 0.01 to 0.5%
1 or 2 or more of them, the total content of C and N in the weld metal is 0.01 to 0.06%, and the Nb equivalent defined by the following formula (3) is 0. 0.05 to 1% is satisfied, the solid solution Nb content is 0.005 to 0.1%, and the relationship between the total content of C and N in the weld metal and the Nb content is as follows ( 4) A welded joint for a refractory structure excellent in high-temperature strength and toughness, characterized by satisfying the formula and the balance being Fe and inevitable impurities.
Nb equivalent = Nb% + 0.47 Mo% + 0.25 W% + 0.4 Ta% + 0.2 Zr% (3)
However, said Nb%, Mo%, W%, Ta%, Zr% shows content (mass%) of Nb, Mo, W, Ta, Zr in a weld metal, respectively.
0.3 ≦ (Nb%) / (C% + N%) ≦ 5 (4)
However, the above “Nb%”, “C%”, and “N%” indicate the contents (mass%) of Nb, C, and N in the weld metal, respectively. % By mass
C: 0.005 to 0.15%,
Si: 0.005 to 1%
Mn: 0.1 to 2%,
P: 0.02% or less,
S: 0.01% or less,
O: 0.01% or less,
Al: 0.002 to 0.1%,
N: 0.001 to 0.01%
Including,
Mo: 0.1 to 1%,
W: 0.01 to 1%
Nb: 0.005 to 0.2%,
V: 0.01-0.5%
Ta: 0.005 to 0.5%, and
Zr: 0.005 to 0.5%
1 or 2 types of the above, and the remainder is a welded joint for a fireproof structure comprising a steel for a fireproof structure composed of Fe and inevitable impurities, and a welded portion,
The weld metal formed in the weld is in mass%,
C: 0.01 to 0.15%,
Si: 0.1 to 1%,
Mn: 0.3 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%,
O: 0.005 to 0.06%
Including
Nb: 0.01-0.5%
V: 0.01 to 0.7%
Containing
further,
Mo: 0.02 to 2%,
W: 0.02 to 2%,
Ta: 0.01 to 0.5%, and
Zr: 0.01 to 0.5%
1 or more of them, the total content of C and N in the weld metal is 0.01 to 0.06%, and the Nb equivalent defined by the following formula (1) is 0. 0.05 to 1%, and the total amount of solute Nb and solute V is 0.005 to 0.1%, and the total content of C and N in the weld metal and Nb And a total content of V satisfy the following formula (2), and the balance consists of Fe and inevitable impurities, a weld joint for refractory structures with excellent high temperature strength and toughness.
Nb equivalent = Nb% + 0.47 Mo% + 0.25 W% + 0.65 V% + 0.4 Ta%
          + 0.2Zr% (1)
However, said Nb%, Mo%, W%, V%, Ta%, Zr% shows content (mass%) of Nb, Mo, W, V, Ta, Zr in a weld metal, respectively.
0.3 ≦ (Nb% + V%) / (C% + N%) ≦ 5 (2)
However, the above “Nb%”, “V%”, “C%”, and “N%” indicate the contents (mass%) of Nb, V, C, and N in the weld metal, respectively. The steel material is further Cu: 0.005 to 1.5% by mass%,
Ni: 0.01-6%,
Co: 0.01 to 6%
Cr: 0.005 to 1.5%,
Ti: 0.002~0.1%,
Ca : 0.0005 to 0.005%,
REM: 0.0005 to 0.01%, and
Mg: 0.0002 to 0.005%
The welded joint for refractory structures having excellent high-temperature strength and toughness according to claim 1 or 2 , wherein one or more of them are included. The weld metal is further Cu: 0.005 to 1.5% by mass%,
Ni: 0.01-6%,
Co: 0.01 to 6%
Cr: 0.002 to 0.5%,
Ti: 0.002~0.1%,
Ca : 0.0005 to 0.005%,
REM: 0.0005 to 0.01%, and
Mg: 0.0002 to 0.005%
The weld joint for refractory structures excellent in high-temperature strength and toughness according to any one of claims 1 to 3, wherein one or more of them are included. 5. The weld joint for a refractory structure excellent in high-temperature strength and toughness according to any one of claims 1 to 4 , wherein the weld metal is formed under conditions of a welding heat input of 10 kJ / cm to 200 kJ / cm. .

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