JP2021016884A - Ferritic heat-resistant dissimilar steel weld joint and method for producing the same - Google Patents

Abstract

To provide a dissimilar material weld joint having high creep strength and solidification crack resistance.SOLUTION: The present invention provides a weld joint 10, wherein, a ferritic heat-resistant steel 1 welded to a dissimilar material through a weld metal 3 contains in mass%, C: 0.04-0.12%, Si: 0.05-0.60%, Mn: 0.10-0.80%, P: 0.020% or less, S: 0.010% or less, Cr: 8.0-10.0%, Co: 2.0-4.0%, Mo+W: 2.0-4.0%, Nb+Ta: 0.02-0.18%, V: 0.05-0.40%, B: 0.005-0.020%, Al: 0.030% or less, N: 0.002-0.025%, O: 0.020% or less, Nd: 0-0.06%, Ni: 0-0.4%, Cu: 0-1.0%, Ti: 0-0.30%, Ca: 0-0.050%, Mg: 0-0.050%, with the balance being Fe and impurities, and B of an initial layer part of the weld metal satisfies 0.1×([%BBM1]+[%BBM2])/2≤[%BWM]≤0.005.SELECTED DRAWING: Figure 1

Description

The present invention relates to a ferritic heat-resistant steel dissimilar welded joint and a method for manufacturing the same.

In recent years, in thermal power generation, in order to improve thermal efficiency, high temperature and high pressure steam conditions have been promoted. In the future, it is planned to operate under ultra-supercritical pressure conditions of 650 ° C and 350 atm. Ferritic heat-resistant steels are cheaper than austenitic heat-resistant steels and Ni-based heat-resistant steels. Ferritic heat-resistant steel further has an advantage as a heat-resistant steel having a small coefficient of thermal expansion. Therefore, ferritic heat-resistant steels are widely used in high-temperature and high-pressure environments.

In addition, ferritic heat-resistant steel may be welded and used as a welded joint in a structure. In this case, the creep strength of the weld heat-affected zone (hereinafter referred to as "HAZ") of the welded joint may decrease. Therefore, Patent Documents 1 to 3 propose ferritic heat-resistant steels that suppress a decrease in creep strength in HAZ.

The ferrite-based heat-resistant steel disclosed in Patent Document 1 contains 0.003 to 0.03% by mass of B, thereby suppressing granulation in HAZ. As a result, the decrease in creep strength in HAZ is suppressed. The ferrite-based heat-resistant steel disclosed in Patent Documents 2 and 3 contains a large amount of B, and the C content is adjusted according to the welding heat input or the B content. As a result, the decrease in strength in HAZ is suppressed, and liquefaction cracking during welding is suppressed.

When welding ferritic heat-resistant steel containing a large amount of B, a welding material is generally used. As a welding material used at the time of welding, for example, Patent Document 4 describes creep strength by containing 0.0005% to 0.006% of B and adjusting (Mo + W) / (Ni + Co) to a predetermined range. Welding materials for ferritic heat-resistant steel that achieve both toughness and toughness have been proposed.

Further, Patent Document 5 optionally contains 0.0005% to 0.006% of B, and in addition to (Mo + W) / (Ni + Co) and (0.5 × Co + 0.5 × Mn + Ni), Cr equivalent amount. Welding materials for ferritic heat-resistant steels have been proposed in which both creep strength and toughness are achieved by adjusting the above.

Further, Patent Document 6 contains B: 0.007% to 0.015%, and is excellent by adjusting (Cr + 6Si + 1.5W + 11V + 5Nb + 10B-40C-30N-4Ni-2Co-2Mn) to a predetermined range. Welding materials for ferritic heat-resistant steel that have both creep strength and toughness are disclosed.

Japanese Unexamined Patent Publication No. 2004-300532 JP-A-2010-7094 International Publication No. 2008/149703 Japanese Unexamined Patent Publication No. 8-187592 Japanese Unexamined Patent Publication No. 9-308989 International Publication No. 2017/104815

By the way, a welding material for a Ni-based heat-resistant alloy may be used for welding a ferrite-based heat-resistant steel containing a large amount of B because stable and excellent creep strength can be obtained. In addition, ferritic heat-resistant steel and stainless steel or Ni-based alloy may be welded. However, when welding dissimilar materials containing a ferrite-based heat-resistant steel containing such a large amount of B, solidification cracks may occur in the weld metal.

An object of the present invention is to solve the above problems and to provide a ferritic heat-resistant steel dissimilar welded joint having excellent solidification crack resistance in addition to high creep strength and a method for manufacturing the same.

The present invention has been made to solve the above problems, and the gist of the present invention is the following ferrite-based heat-resistant steel dissimilar welded joint and a method for manufacturing the same.

(1) A ferritic heat-resistant steel dissimilar welded joint in which a ferritic heat-resistant steel and stainless steel or a Ni-based alloy are welded with different materials via a weld metal.
The chemical composition of the ferritic heat-resistant steel is mass%.
C: 0.04 to 0.12%,
Si: 0.05 to 0.60%,
Mn: 0.10 to 0.80%,
P: 0.020% or less,
S: 0.010% or less,
Cr: 8.0-10.0%,
Co: 2.0-4.0%,
Mo + W: 2.0-4.0% in total,
Nb + Ta: 0.02 to 0.18% in total,
V: 0.05 to 0.40%,
B: 0.005 to 0.020%,
Al: 0.030% or less,
N: 0.002-0.025%,
O: 0.020% or less,
Nd: 0-0.06%,
Ni: 0-0.4%,
Cu: 0-1.0%,
Ti: 0 to 0.30%,
Ca: 0 to 0.050%,
Mg: 0 to 0.050%,
Remaining: Fe and impurities,
The B content contained in the ferrite heat-resistant steel, the stainless steel or the Ni-based alloy, and the initial layer portion of the weld metal satisfies the following formula (i).
Ferritic heat-resistant steel dissimilar welded joint.
0.1 × ([% B _BM1 ] + [% B _BM2 ]) / 2 ≦ [% B _WM ] ≦ 0.005 ・ ・ ・ (i)
However, [% B _BM1 ] in the formula (i) is the B content (mass%) contained in the ferrite heat-resistant steel, and [% B _BM2 ] is the B content (mass%) contained in the stainless steel or Ni-based alloy. ), [% B _WM ] is the B content (mass%) contained in the initial layer portion of the weld metal.

(2) The chemical composition of the weld metal is mass%.
C: 0.005 to 0.180%,
Si: 0.02 to 1.20%,
Mn: 0.02 to 4.00%,
P: 0.040% or less,
S: 0.010% or less,
Cr: 8.0-25.0%,
Mo: 0 to 12.0%,
Co: 0 to 15.0%,
Cu: 0-4.0%,
W: 0-6.0%,
Nb + V + Ti + Ta: 0-4.50% in total,
Fe: 0.01-5.00%,
B: 0.005% or less,
Al: 1.80% or less,
N: 0.30% or less,
O: 0.020% or less,
Nd: 0-0.06%,
Ca: 0 to 0.050%,
Mg: 0 to 0.050%,
Remaining: Ni and impurities,
The ferrite-based heat-resistant steel dissimilar welded joint according to (1) above.

(3) The chemical composition of the stainless steel or the Ni-based alloy is mass%.
Ni: 5.0 to 70.0%, and Cr: 15.0 to 30.0%.
The ferrite-based heat-resistant steel dissimilar welded joint according to (1) or (2) above.

(4) The chemical composition of the stainless steel or the Ni-based alloy is mass%.
C: 0.04 to 0.12%,
Si: 0.02-1.00%,
Mn: 0.02 to 4.00%,
P: 0.040% or less,
S: 0.010% or less,
Ni: 5.0-70.0%,
Cr: 15.0 to 30.0%,
Co: 0-4.0%,
Cu: 0-4.0%,
Mo: 0-2.0%,
W: 0-8.0%,
Nb: 0-1.0%,
V: 0-1.0%,
Ti: 0-1.0%,
B: 0 to 0.006%,
Al: 1.00% or less,
N: 0-0.30%,
O: 0.020% or less,
Nd: 0-0.05%,
Ca: 0 to 0.050%,
Remaining: Fe and impurities,
The ferrite-based heat-resistant steel dissimilar welded joint according to (3) above.

(5) A method for manufacturing a ferritic heat-resistant steel dissimilar welded joint including a multi-layer welding process in which a ferrite-based heat-resistant steel and stainless steel or a Ni-based alloy are welded in multiple layers with a welding material for a Ni-based heat-resistant alloy.
The chemical composition of the ferritic heat-resistant steel is mass%.
C: 0.04 to 0.12%,
Si: 0.05 to 0.60%,
Mn: 0.10 to 0.80%,
P: 0.020% or less,
S: 0.010% or less,
Cr: 8.0-10.0%,
Co: 2.0-4.0%,
Mo + W: 2.0-4.0% in total,
Nb + Ta: 0.02 to 0.18% in total,
V: 0.05 to 0.40%,
B: 0.005 to 0.020%,
Al: 0.030% or less,
N: 0.002-0.025%,
O: 0.020% or less,
Nd: 0-0.06%,
Ni: 0-0.4%,
Cu: 0-1.0%,
Ti: 0 to 0.30%,
Ca: 0 to 0.050%,
Mg: 0 to 0.050%,
Remaining: Fe and impurities,
In the multi-layer welding step, the total area of the molten ferrite heat-resistant steel, the stainless steel or the Ni-based alloy, and the area of the weld metal in the cross section of the welded portion after the first layer welding and before the second layer welding. The first layer welding is performed under the condition that the following equation (ii) is satisfied in relation to the B content contained in the ferrite heat-resistant steel and the stainless steel or the Ni-based alloy.
A method for manufacturing ferrite-based heat-resistant steel dissimilar welded joints.
0.1 ≤ [S _BM ] / [S _WM ] ≤ -65 x ([% B _BM1 ] + [% B _BM2 ]) _/2+1.2 ... (ii)
However, in equation (ii), [ _SBM ] is the total area of molten ferritic heat-resistant steel and stainless steel or Ni-based alloy, [ _SWM ] is the area of weld metal, and [% B _BM1 ] is ferrite. The B content (% by mass) and [% B _BM2 ] contained in the heat-resistant steel are the B content (mass%) contained in the stainless steel or Ni-based alloy.

(6) The chemical composition of the stainless steel or the Ni-based alloy is mass%.
Ni: 5.0 to 50.0%, and Cr: 15.0 to 30.0%.
The method for manufacturing a ferritic heat-resistant steel dissimilar welded joint according to (5) above.

(7) The chemical composition of the stainless steel or the Ni-based alloy is mass%.
C: 0.04 to 0.12%,
Si: 0.02-1.00%,
Mn: 0.02 to 4.00%,
P: 0.040% or less,
S: 0.010% or less,
Ni: 5.0-70.0%,
Cr: 15.0 to 30.0%,
Co: 0-4.0%,
Cu: 0-4.0%,
Mo: 0-2.0%,
W: 0-8.0%,
Nb: 0-1.0%,
V: 0-1.0%,
Ti: 0-1.0%,
B: 0 to 0.006%,
Al: 1.00% or less,
N: 0-0.30%,
O: 0.020% or less,
Nd: 0-0.05%,
Ca: 0 to 0.050%,
Remaining: Fe and impurities,
The method for manufacturing a ferritic heat-resistant steel dissimilar welded joint according to (6) above.

(8) The chemical composition of the welding material for Ni-based heat-resistant alloy is mass%.
C: 0.005 to 0.180%,
Si: 0.02 to 1.20%,
Mn: 0.02 to 4.00%,
P: 0.020% or less,
S: 0.010% or less,
Cr: 16.0 to 25.0%,
Mo: 0 to 12.0%,
Co: 0 to 15.0%,
Cu: 0-0.80%,
Nb + Ta: 0-4.50% in total,
Ti: 0-1.00%,
Fe: 0-6.00%,
N: 0.050% or less,
Al: 0.002 to 1.800%,
O: 0.020% or less,
Remaining: Ni and impurities,
The method for manufacturing a ferritic heat-resistant steel dissimilar welded joint according to any one of (5) to (7) above.

According to the present invention, it is possible to obtain a ferrite-based heat-resistant steel dissimilar welded joint having excellent solidification crack resistance in addition to high creep strength.

It is the schematic which shows an example of the cross section in the welded part of the ferritic heat-resistant steel dissimilar material welded joint. It is the schematic which shows the cross section of the welded part of the ferritic heat resistant steel dissimilar material welded joint after the first layer welding and before the second layer welding. It is schematic cross-sectional view which shows the shape of the plate material which performed the groove processing in an Example.

As a result of repeated studies by the present inventors on a method for improving the solidification crack resistance of the weld metal, the following findings have been obtained.

B is an element indispensable for improving creep strength, but on the other hand, it is also an element that deteriorates solidification crack resistance. When a ferrite-based heat-resistant steel containing a large amount of B and stainless steel or a Ni-based alloy are welded using a welding material for a Ni-based heat-resistant alloy, B contained in the ferrite-based heat-resistant steel flows into the weld metal. As a result, the solidification crack resistance of the weld metal is lowered.

Therefore, when welding multiple layers of dissimilar materials, the B content in the weld metal is controlled by appropriately controlling the welding conditions, especially during the first layer welding, and limiting the amount of B flowing into the weld metal from the ferritic heat-resistant steel. Can be reduced. As a result, the occurrence of solidification cracks in the weld metal can be suppressed.

The present invention has been made based on the above findings. Hereinafter, each requirement of the present invention will be described in detail.

1. 1. Overall Configuration FIG. 1 is a schematic view showing an example of a cross section (hereinafter, also referred to as “cross section”) perpendicular to one direction in a welded portion of a ferritic heat-resistant steel dissimilar material welded joint according to the present invention. As shown in FIG. 1, the ferritic heat-resistant steel dissimilar welded joint 10 is formed by welding a ferritic heat-resistant steel 1 and a stainless steel or a Ni-based alloy 2 through a weld metal 3 extending in one direction. is there.

2. 2. Chemical Composition of Ferritic Heat-Resistant Steel The ferrite-based heat-resistant steel according to the present invention has the following chemical composition. The reasons for limiting each element are as follows. In the following description, "%" for the content means "mass%".

C: 0.04 to 0.12%
Carbon (C) is an effective element for obtaining a martensite structure. C further produces fine carbides when used at high temperatures, increasing the creep strength of the base metal. If the C content is too low, these effects cannot be obtained. However, unlike the weld metal, the base metal is suppressed from solidification segregation and is used after being tempered. Therefore, even if the C content is lower than that of the weld metal, the above effect can be obtained. On the other hand, if the C content is too high, the effect of improving the creep strength is saturated. Therefore, the C content is 0.04 to 0.12%. The C content is preferably 0.06% or more, and preferably 0.10% or less.

Si: 0.05 to 0.60%
Silicon (Si) has the effect of deoxidizing steel. Si further enhances the water vapor oxidation resistance of the base metal. If the Si content is too low, these effects cannot be obtained. However, unlike the weld metal, the base metal is suppressed from solidification segregation and is used after being tempered. Therefore, even if the Si content is lower than that of the weld metal, the above effect can be obtained. On the other hand, if the Si content is too high, the creep ductility and toughness of the base metal will decrease. Therefore, the Si content is 0.05 to 0.60%. The Si content is preferably 0.10% or more, and preferably 0.40% or less.

Mn: 0.10 to 0.80%
Manganese (Mn), like Si, has the effect of deoxidizing steel. Mn further promotes martensitic formation of the base metal structure. If the Mn content is too low, these effects cannot be obtained. However, unlike the weld metal, the base metal is suppressed from solidification segregation and is used after being tempered. Therefore, even if the Mn content is lower than that of the weld metal, the above effect can be obtained. On the other hand, if the Mn content is too high, creep embrittlement is likely to occur. Therefore, the Mn content is 0.10 to 0.80%. The Mn content is preferably 0.20% or more, and preferably 0.70% or less.

P: 0.020% or less Phosphorus (P) is an element contained in steel as an impurity. If the P content is too high, the creep ductility will decrease. Therefore, the P content is 0.020% or less. The P content is preferably 0.018% or less, and preferably as low as possible. However, from the viewpoint of material cost, the P content is preferably 0.0005% or more.

S: 0.010% or less Sulfur (S) is an element contained in steel as an impurity. If the S content is too high, the creep ductility will decrease. Therefore, the S content is 0.010% or less. The S content is preferably 0.005% or less, and preferably as low as possible. However, from the viewpoint of material cost, the S content is preferably 0.0002% or more.

Cr: 8.0-10.0%
Chromium (Cr) enhances water vapor oxidation resistance and corrosion resistance of the base metal at high temperatures. Cr further precipitates as carbides during use at high temperatures, increasing the creep strength of the base metal. If the Cr content is too low, these effects cannot be obtained. However, unlike the weld metal, the base metal is suppressed from solidification segregation and is used after being tempered. Therefore, even if the Cr content is lower than that of the weld metal, the above effect can be obtained. On the other hand, if the Cr content is too high, the stability of the carbide is lowered and the creep strength of the base metal is lowered. Therefore, the Cr content is 8.0 to 10.0%. The Cr content is preferably 8.5% or more, and preferably 9.5% or less.

Co: 2.0-4.0%
Cobalt (Co) is effective in increasing the creep strength by forming the structure of the base material into a martensite structure. If the Co content is too low, this effect cannot be obtained. However, unlike the weld metal, the base metal is suppressed from solidification segregation and is used after being tempered. Therefore, even if the Co content is lower than that of the weld metal, the above effect can be obtained. On the other hand, if the Co content is too high, the creep strength and creep ductility of the base metal will decrease. Further, since Co is an expensive element, the material cost is high. Therefore, the Co content is 2.0-4.0%. The Co content is preferably 2.5% or more, and preferably 3.5% or less.

Mo + W: 2.0-4.0% in total
Molybdenum (Mo) and tungsten (W) are dissolved in the matrix or precipitated as an intermetallic compound during long-term use, increasing the creep strength at high temperatures. If the Mo and / or W content is too low, this effect will not be obtained. However, unlike the weld metal, the base metal is suppressed from solidification segregation and is used after being tempered. Therefore, even if the content of these elements is lower than that of the weld metal, the above effect can be obtained. On the other hand, if the content of Mo and / or W is too high, the above effect will be saturated. Therefore, the total content of Mo and W is 2.0-4.0%. The total content of Mo and W is preferably 2.5% or more, and preferably 3.5% or less.

Nb + Ta: 0.02 to 0.18% in total
Niobium (Nb) and tantalum (Ta) precipitate in the grains as fine carbonitrides during use at high temperatures, increasing creep strength. If the content of Nb and / or Ta is too low, this effect cannot be obtained. However, unlike the weld metal, the base metal is suppressed from solidification segregation and is used after being tempered. Therefore, even if the content of these elements is lower than that of the weld metal, the above effect can be obtained. On the other hand, if the content of Nb and / or Ta is too high, a large amount of coarse carbonitride is precipitated, and the creep strength and creep ductility are lowered. Therefore, the total content of Nb and Ta is 0.02 to 0.18%. The total content of Nb and Ta is preferably 0.05% or more, and preferably 0.12% or less.

V: 0.05 to 0.40%
Vanadium (V), like Nb and Ta, precipitates in the grains as fine carbonitrides during use at high temperatures, increasing creep strength. If the V content is too low, this effect cannot be obtained. However, unlike the weld metal, the base metal is suppressed from solidification segregation and is used after being tempered. Therefore, even if the V content is lower than that of the weld metal, the above effect can be obtained. On the other hand, if the V content is too high, a large amount of coarse carbonitride is precipitated, and the creep strength and creep ductility are lowered. Therefore, the V content is 0.05 to 0.40%. The V content is preferably 0.10% or more, and preferably 0.30% or less.

B: 0.005 to 0.020%
Boron (B) is effective in enhancing hardenability and obtaining a martensite structure. B further finely disperses carbides at the former austenite boundary and the martensitic lath boundary during use at high temperatures to suppress tissue recovery and increase creep strength. If the B content is too low, this effect cannot be obtained. However, unlike the weld metal, the base metal is suppressed from solidification segregation and is used after being tempered. Therefore, even if the B content is lower than that of the weld metal, the above effect can be obtained. On the other hand, if the B content is too high, the toughness decreases. Therefore, the B content is 0.005 to 0.020%. The B content is preferably 0.007% or more, and preferably 0.015% or less.

Al: 0.030% or less Aluminum (Al) has the effect of deoxidizing steel. However, if the Al content is too high, the cleanliness of the base material is lowered and the workability is lowered. If the Al content is too high, the creep strength is further reduced. Therefore, the Al content is 0.030% or less. The Al content is preferably 0.010% or less. Considering the production cost, the Al content is preferably 0.001% or more. In the present specification, the Al content is sol. It means Al (acid-soluble Al).

N: 0.002-0.025%
Nitrogen (N) finely precipitates in the grains as fine nitrides during use at a high temperature to increase creep strength. If the N content is too low, this effect cannot be obtained. However, unlike the weld metal, the base metal is suppressed from solidification segregation and is used after being tempered. Therefore, even if the N content is lower than that of the weld metal, the above effect can be obtained. On the other hand, if the N content is too high, the nitride becomes coarse and the creep ductility decreases. Therefore, the N content is 0.002 to 0.025%. The N content is preferably 0.005% or more, and preferably 0.015% or less.

O: 0.020% or less Oxygen (O) is an element contained in steel as an impurity. If the O content is too high, the processability of the base metal will decrease. Therefore, the O content is 0.020% or less. The O content is preferably 0.010% or less. Considering the production cost, the O content is preferably 0.001% or more.

Nd: 0 to 0.06%
Neodymium (Nd) may be contained if necessary in order to improve the creep ductility of the base material. However, if the Nd content is too high, the hot workability is lowered. Therefore, the Nd content is 0 to 0.06%. The Nd content is preferably 0.05% or less. When the above effect is desired, the Nd content is preferably 0.01% or more.

Ni: 0-0.4%
Nickel (Ni) is effective in obtaining a martensite structure, and may be contained if necessary. However, if the Ni content is too high, the above effects will be saturated. Therefore, the Ni content is 0 to 0.4%. The Ni content is preferably 0.2% or less. When the above effect is desired, the Ni content is preferably 0.05% or more, and more preferably 0.1% or more.

Cu: 0-1.0%
Copper (Cu), like Co and Ni, is effective in forming a martensite structure, and may be contained if necessary. However, if the Cu content is too high, the creep ductility will decrease. Therefore, the Cu content is 0 to 1.0%. The Cu content is preferably 0.8% or less, more preferably 0.6% or less. When the above effect is desired, the Cu content is preferably 0.05% or more, and more preferably 0.1% or more.

Ti: 0 to 0.30%
Titanium (Ti), like Nb, Ta and V, precipitates in the grains as fine carbonitrides during use at high temperatures and contributes to the improvement of creep strength, and therefore may be contained as necessary. .. However, if the Ti content is too high, a large amount of carbonitride is precipitated coarsely, resulting in a decrease in creep strength and creep ductility. Therefore, the Ti content is 0 to 0.30%. The Ti content is preferably 0.20% or less. When the above effect is desired, the Ti content is preferably 0.02% or more, and more preferably 0.04% or more.

Ca: 0 to 0.050%
Calcium (Ca) has an effect of improving hot workability at the time of production, and may be contained if necessary. However, if the Ca content is too high, Ca binds to oxygen, which significantly reduces cleanliness and, on the contrary, deteriorates hot workability. Therefore, the Ca content is 0 to 0.050%. The Ca content is preferably 0.030% or less, and more preferably 0.020% or less. When the above effect is desired, the Ca content is preferably 0.0005% or more, and more preferably 0.001% or more.

Mg: 0 to 0.050%
Magnesium (Mg), like Ca, has the effect of improving hot workability during production, and may be contained as necessary. However, if the Mg content is too high, Mg binds to oxygen, which significantly reduces cleanliness and, on the contrary, deteriorates hot workability. Therefore, the Mg content is 0 to 0.050%. The Mg content is preferably 0.030% or less, more preferably 0.020% or less. When the above effect is desired, the Mg content is preferably 0.0005% or more, more preferably 0.001% or more.

In the chemical composition of the base material of the present invention, the balance is Fe and impurities. Here, the "impurity" is a component mixed with raw materials such as ore and scrap and various factors in the manufacturing process when steel is industrially manufactured, and is allowed as long as it does not adversely affect the present invention. Means something.

3. 3. Chemical Composition of Welding Metal As described above, even when welding a ferrite-based heat-resistant steel containing a large amount of B and stainless steel or a Ni-based alloy using a welding material for a Ni-based heat-resistant alloy, the weld metal is used. In order to suppress the occurrence of solidification cracks, it is necessary to limit the amount of B flowing into the weld metal from the ferrite heat-resistant steel.

Therefore, specifically, the B content contained in the initial layer portion of the weld metal is limited to 0.005% or less in terms of mass%. On the other hand, when the B content in the weld metal is extremely low in relation to the B content contained in the ferrite heat-resistant steel and the stainless steel or Ni-based alloy, fusion failure, back wave failure, etc. occur. Weld defects are more likely to occur.

From the above viewpoint, in the present invention, the B content contained in the initial layer portion of the weld metal is as follows (i) in relation to the B content contained in the ferritic heat-resistant steel and the stainless steel or Ni-based alloy. ) Satisfy the equation.
0.1 × ([% B _BM1 ] + [% B _BM2 ]) / 2 ≦ [% B _WM ] ≦ 0.005 ・ ・ ・ (i)
However, [% B _BM1 ] in the formula (i) is the B content (mass%) contained in the ferrite heat-resistant steel, and [% B _BM2 ] is the B content (mass%) contained in the stainless steel or Ni-based alloy. ), [% B _WM ] is the B content (mass%) contained in the initial layer portion of the weld metal.

The chemical composition of the entire weld metal is not particularly limited, but from the viewpoint of improving the creep strength of the weld metal, the weld metal can be used.
By mass%
C: 0.005 to 0.180%,
Si: 0.02 to 1.20%,
Mn: 0.02 to 4.00%,
P: 0.040% or less,
S: 0.010% or less,
Cr: 8.0-25.0%,
Mo: 0 to 12.0%,
Co: 0 to 15.0%,
Cu: 0-4.0%,
W: 0-6.0%,
Nb + V + Ti + Ta: 0-4.50% in total,
Fe: 0.01-5.00%,
B: 0.005% or less,
Al: 1.80% or less,
N: 0.30% or less,
O: 0.020% or less,
Nd: 0-0.06%,
Ca: 0 to 0.050%,
Mg: 0 to 0.050%,
Remaining: It is preferable to have a chemical composition of Ni and impurities.

Among the above, the C content is preferably 0.01 to 0.150%, the Si content is preferably 0.03 to 1.00%, and the Mn content is 0.05 to 3 It is preferably .50%, the P content is preferably 0.030% or less, and the S content is preferably 0.007% or less.

The Cr content is preferably 10.0 to 23.0%, the Mo content is preferably 0.001 to 10.0%, and the Co content is 0.001 to 13.0%. The Cu content is preferably 0.001 to 3.0%, and the W content is preferably 0.001 to 5.0%.

The total content of Nb, V, Ti and Ta is preferably 0.01 to 4.00%, the Fe content is preferably 0.02 to 4.50%, and the B content. Is preferably 0.003% or less, the Al content is preferably 1.50% or less, and the N content is preferably 0.20% or less.

The O content is preferably 0.010% or less, the Nd content is preferably 0.0001 to 0.05%, and the Ca content is 0.0001 to 0.030%. The Mg content is preferably 0.0001 to 0.030%.

The chemical composition of the weld metal is determined by the inflow ratio of the base material (ferritic heat-resistant steel and stainless steel or Ni-based alloy) and the welding material at the time of welding. The suitable chemical composition of the stainless steel or Ni-based alloy used for producing the welded joint according to the present invention and the welding material will be described below.

4. Chemical composition of stainless steel or Ni-based alloy As described above, in the ferrite-based heat-resistant steel dissimilar material welded joint of the present invention, the ferrite-based heat-resistant steel having the above-mentioned chemical composition and the stainless steel or Ni-based alloy are welded different materials. It is a thing. The chemical composition of the stainless steel or Ni-based alloy is not particularly limited, and examples thereof include those containing Ni: 5.0 to 70.0% and Cr: 15.0 to 30.0% in mass%. Be done.

The chemical composition of the chemical composition of stainless steel or Ni-based alloy will be described. The reasons for limiting each element are as follows. In the following description, "%" for the content means "mass%".

C: 0.04 to 0.12%
C is an austenite-forming element and is an element effective for enhancing the stability of the austenite structure when used at a high temperature. In order to obtain the effect, it is preferable to contain C in an amount of 0.04% or more. However, if it is contained in an excessive amount, coarse carbides may be generated during use at a high temperature, which may rather reduce the creep strength. Therefore, the C content is preferably 0.12% or less. The C content is preferably 0.06% or more, and preferably 0.10% or less.

Si: 0.02-1.00%
Since Si has a deoxidizing effect, it is preferably contained in an amount of 0.02% or more. Excessive reduction of the Si content does not provide a sufficient deoxidizing effect, increases the cleanliness of the steel, lowers the cleanliness, and increases the manufacturing cost. However, the Si content is preferably 1.00% or less because excessive content may reduce toughness. The Si content is preferably 0.1% or more, and preferably 0.8% or less.

Mn: 0.02 to 4.00%
Since Mn has a deoxidizing effect like Si, it is preferably contained in an amount of 0.02% or more. Excessive reduction of the Mn content does not provide a sufficient deoxidizing effect, increases the cleanliness of the steel, lowers the cleanliness, and increases the manufacturing cost. However, if it is contained in an excessive amount, embrittlement may occur. Therefore, the Mn content is preferably 4.00% or less. The Mn content is preferably 0.1% or more, and preferably 3.0% or less.

P: 0.040% or less P is contained as an impurity, and if the P content is excessive, the creep ductility may be lowered and the liquefaction cracking resistance of the weld heat affected zone may be lowered. Therefore, the P content is preferably 0.040% or less. The P content is more preferably 0.035% or less. The lower limit of the P content is not particularly set, that is, the content may be 0%, but the extreme reduction significantly increases the manufacturing cost. Therefore, the P content is preferably 0.005% or more.

S: 0.010% or less S is contained as an impurity like P, and if the S content is excessive, the creep ductility is lowered and the liquefaction cracking resistance of the weld heat affected zone is lowered. Therefore, the S content is preferably 0.010% or less, and more preferably 0.005% or less. The lower limit of the S content is not particularly set, that is, the content may be 0%, but the extreme reduction significantly increases the manufacturing cost. Therefore, the S content is preferably 0.0002% or more.

Ni: 5.0-70.0%
Ni is an element that is effective for obtaining an austenite structure, and is also an element that is effective for ensuring structure stability during long-term use and obtaining creep strength. In order to obtain the effect, it is preferable to contain 5.0% or more of Ni. However, Ni is an expensive element, and excessive content causes an increase in cost. Therefore, the Ni content is preferably 70.0% or less. The Ni content is preferably 7.0% or more, and preferably 60.0% or less.

Cr: 15.0 to 30.0%
Since Cr is an element effective for ensuring oxidation resistance and corrosion resistance at high temperatures, it is preferable to contain Cr in an amount of 15.0% or more. However, if the Cr content is excessive, the stability of the austenite structure during high-temperature use may deteriorate, and the creep strength may decrease. Therefore, the Cr content is preferably 30.0% or less. The Cr content is preferably 16.0% or more, and preferably 28.0% or less.

Co: 0-4.0%
Co does not necessarily have to be contained in stainless steel or Ni-based alloy, but like Ni, it is an austenite-forming element and is contained because it enhances the stability of the austenite structure and contributes to the improvement of creep strength. You may let me. However, since it is an extremely expensive element, excessive Co content increases the cost significantly. Therefore, the Co content is preferably 4.0% or less. Further, the Co content is more preferably 3.5% or less. When the above effect is desired, the Co content is preferably 0.5% or more.

Cu: 0-4.0%
Cu does not necessarily have to be contained in the stainless steel or Ni-based alloy, but it contributes to maintaining the stability of the austenite structure of the weld metal when used at a high temperature, and is precipitated as a Cu-enriched phase to increase the creep strength. Since it is an effective element to obtain, it may be contained. However, if it is contained in an excessive amount, it is excessively precipitated and causes embrittlement. Therefore, the Cu content is preferably 4.0% or less. Further, the Cu content is more preferably 3.6% or less. When the above effect is desired, the Cu content is preferably 0.5% or more.

Mo: 0-2.0%
Mo is not necessarily contained in the stainless steel or Ni-based alloy, but it may be contained because it is an element that dissolves in the matrix and contributes to the improvement of creep strength at high temperature. However, if Mo is contained in an excessive amount, the stability of the austenite structure is lowered, resulting in a decrease in creep strength. Therefore, the Mo content is preferably 2.0% or less. Further, the Mo content is more preferably 1.5% or less. When the above effect is desired, the Mo content is preferably 0.3% or more.

W: 0-8.0%
W does not necessarily have to be contained in the stainless steel or Ni-based alloy, but it may be contained because it is an element that dissolves in the matrix and greatly contributes to the improvement of creep strength and tensile strength at high temperatures. Good. However, even if W is excessively contained, the above effect is saturated, and in some cases, the creep strength may be lowered. Further, since W is an expensive element, excessive inclusion of W causes an increase in cost. Therefore, the W content is preferably 8.0% or less. Further, the W content is more preferably 7.8% or less. When the above effect is desired, the W content is preferably 1.0% or more.

Nb: 0-1.0%
Nb does not necessarily have to be contained in stainless steel or Ni-based alloy, but it is contained in stainless steel or Ni-based alloy because it is an element that precipitates in grains as fine carbonitride during use at high temperature and improves creep strength. You may. However, if Nb is excessively contained, a large amount and coarsely precipitates as a nitride, resulting in a decrease in creep strength and creep ductility. Therefore, the Nb content is preferably 1.0% or less. Further, the Nb content is more preferably 0.8% or less. When the above effect is desired, the Nb content is preferably 0.1% or more.

V: 0-1.0%
V is not necessarily contained in stainless steel or Ni-based alloy, but like Nb, it is an element that precipitates in the grains as fine carbonitride during use at high temperature to improve creep strength. Therefore, it may be contained. However, if V is excessively contained, a large amount and coarsely precipitates as a nitride, resulting in a decrease in creep strength and creep ductility. Therefore, the V content is preferably 1.0% or less. Further, the V content is more preferably 0.8% or less. When the above effect is desired, the V content is preferably 0.1% or more.

Ti: 0-1.0%
Ti does not necessarily have to be contained in stainless steel or Ni-based alloys, but like Nb and V, it is an element that precipitates in the grains as fine carbonitrides during use at high temperatures to improve creep strength. Therefore, it may be contained. However, if Ti is excessively contained, a large amount and coarsely precipitates as a nitride, resulting in a decrease in creep strength and creep ductility. Therefore, the Ti content is preferably 1.0% or less. Further, the Ti content is more preferably 0.8% or less. When the above effect is desired, the Ti content is preferably 0.1% or more.

B: 0 to 0.006%
B is not necessarily contained in the stainless steel or Ni-based alloy, but creeps by precipitating at the grain boundaries during use at a high temperature to strengthen the grain boundaries and finely dispersing the grain boundary carbides. Since it is an element that improves strength, it may be contained. However, if B is excessively contained, the liquefaction crackability of the weld heat affected zone is lowered. Therefore, the B content is preferably 0.006% or less. Further, the B content is more preferably 0.005% or less. When the above effect is desired, the B content is preferably 0.001% or more.

Al: 1.00% or less Al is contained as a deoxidizing material during the production of the base metal, but if it is contained in a large amount, the cleanliness of the steel deteriorates and the hot workability deteriorates. Therefore, the Al content is preferably 1.00% or less. The Al content is more preferably 0.8% or less. The lower limit of the Al content is not particularly set, that is, the content may be 0%, but the extreme reduction significantly increases the manufacturing cost. Therefore, the Al content is preferably 0.01% or more.

N: 0-0.30%
N does not necessarily have to be contained in the stainless steel or Ni-based alloy, but it may be contained because it stabilizes the austenite structure and precipitates as a solid solution or a nitride, which contributes to the improvement of high-temperature strength. Good. However, if N is excessively contained, a large amount of fine nitrides are precipitated in the grains during long-term use, resulting in a decrease in creep ductility and toughness. Therefore, the N content is preferably 0.30% or less. Further, the N content is more preferably 0.25% or less. When the above effect is desired, the N content is preferably 0.05% or more.

O: 0.020% or less O is present as an impurity, but when it is contained in a large amount, the workability is lowered. Therefore, the O content is preferably 0.020% or less. The O content is preferably 0.018% or less, more preferably 0.015% or less. The lower limit of the O content is not particularly set, that is, the content may be 0%, but the extreme reduction significantly increases the manufacturing cost. Therefore, the O content is preferably 0.002% or more.

Nd: 0-0.05%
Nd does not necessarily have to be contained in the stainless steel or Ni-based alloy, but may be contained because it is an element that contributes to the improvement of creep ductility at high temperatures. However, when Nd is excessively contained, it binds to oxygen, which significantly reduces cleanliness and reduces ductility. Therefore, the Nd content is preferably 0.05% or less. Further, the Nd content is more preferably 0.045% or less. When the above effect is desired, the Nd content is preferably 0.005% or more.

Ca: 0 to 0.050%
Since Ca has an effect of improving hot workability during production, it may be contained if necessary. However, if the Ca content is too high, Ca binds to oxygen, which significantly reduces cleanliness and, on the contrary, deteriorates hot workability. Therefore, the Ca content is preferably 0.050% or less. The Ca content is more preferably 0.030% or less, and further preferably 0.020% or less. When the above effect is desired, the Ca content is preferably 0.0005% or more, and more preferably 0.001% or more.

5. Chemical Composition of Welding Material The chemical composition of the welding material used in manufacturing the ferritic heat-resistant steel dissimilar welded joint according to the present invention is not particularly limited, but it is preferable to use a welding material for Ni-based heat-resistant alloys. .. The suitable chemical composition of the welding material for Ni-based heat-resistant alloys will be described. The reasons for limiting each element are as follows. In the following description, "%" for the content means "mass%".

C: 0.005 to 0.180%
C is an austenite-forming element and is an element effective for enhancing the stability of the austenite structure when the weld metal is used at a high temperature. In order to obtain the effect, it is preferable to contain C in an amount of 0.005% or more. However, if it is contained in an excessive amount, it may be precipitated in a large amount as a carbide, which may reduce creep ductility and corrosion resistance at high temperature. Therefore, the C content is preferably 0.180% or less. The C content is preferably 0.008% or more, and more preferably 0.010% or more. The C content is preferably 0.150% or less, more preferably 0.120% or less.

Si: 0.02 to 1.20%
Si is added as an antacid, but is an element effective for the steam oxidation resistance of the weld metal. In order to obtain the effect, it is preferable to contain 0.02% or more of Si. However, if it is excessively contained, the susceptibility to solidification and cracking of the weld metal may be increased. Therefore, the Si content is preferably 1.20% or less. The Si content is preferably 0.05% or more, more preferably 0.10% or more. Further, the Si content is preferably 1.00% or less, and more preferably 0.80% or less.

Mn: 0.02 to 4.00%
Mn, like Si, is added as an antacid, but is an effective element for enhancing the structural stability of the weld metal at high temperatures. In order to obtain the effect, it is preferable to contain 0.02% or more. However, if it is excessively contained, embrittlement may occur. Therefore, the Mn content is preferably 4.00% or less. The Mn content is preferably 0.05% or more, and more preferably 0.08% or more. The Mn content is preferably 3.50% or less, more preferably 3.00% or less.

P: 0.020% or less P is contained as an impurity, which increases the susceptibility to solidification and cracking during solidification of the weld metal and causes a decrease in creep ductility. Therefore, the P content is preferably 0.020% or less. The P content is more preferably 0.018% or less, and further preferably 0.016% or less. It should be noted that the smaller the P content, the better, that is, the content may be 0%, but the extreme reduction significantly increases the material cost. Therefore, the P content is preferably 0.0005% or more, and more preferably 0.001% or more.

S: 0.010% or less S is contained as an impurity like P, and increases the susceptibility to solidification and cracking during solidification of the weld metal and causes a decrease in creep ductility. Therefore, the S content is preferably 0.010% or less. The S content is more preferably 0.008% or less, and further preferably 0.005% or less. It should be noted that the smaller the S content, the better, that is, the content may be 0%, but the extreme reduction significantly increases the manufacturing cost. Therefore, the S content is preferably 0.0001% or more, and more preferably 0.0002% or more.

Cr: 16.0 to 25.0%
Cr is an element effective for steam oxidation resistance and corrosion resistance of weld metals at high temperatures. In addition, it precipitates as carbide during use at high temperature, which also contributes to the improvement of creep strength. In order to obtain these effects, it is preferable to contain 16.0% or more. However, if it is excessively contained, the tissue stability at high temperature may be lowered and the creep strength may be lowered. Therefore, the Cr content is preferably 25.0% or less. The Cr content is preferably 16.5% or more, and more preferably 17.0% or more. The Cr content is preferably 24.5% or less, more preferably 24.0% or less.

Mo: 0 to 12.0%
Mo does not necessarily have to be contained in the welding material, but it may be contained because it is an element that dissolves in the matrix and contributes to ensuring the creep strength of the weld metal at a high temperature. However, if it is contained in an excessive amount, the tissue stability at high temperature is lowered, and the creep strength is rather lowered. Therefore, the Mo content is preferably 12.0% or less. The Mo content is more preferably 11.5% or less, and even more preferably 11.0% or less. When the above effect is desired, the Mo content is preferably 0.02% or more, more preferably 0.05% or more.

Co: 0 to 15.0%
Co does not necessarily have to be contained in the welding material, but it may be contained because it is an element effective for stabilizing the structure of the weld metal at high temperature and improving the creep strength. However, if it is contained in an excessive amount, the creep strength and creep ductility are rather lowered. In addition, it is a very expensive element, which increases material costs. Therefore, the Co content is preferably 15.0% or less. The Co content is more preferably 14.5% or less, and even more preferably 14.0% or less. When the above effect is desired, the Co content is preferably 0.02% or more, more preferably 0.05% or more.

Cu: 0-0.80%
Like Co, Cu does not necessarily have to be contained in the welding material, but it may be contained because it is an element effective for stabilizing the structure of the weld metal at high temperature and improving the creep strength. However, if it is contained in an excessive amount, the creep ductility is rather lowered. Therefore, the Cu content is preferably 0.80% or less. The Cu content is more preferably 0.60% or less, and even more preferably 0.50% or less. When the above effect is desired, the Cu content is preferably 0.02% or more, and more preferably 0.05% or more.

Nb + Ta: 0-4.50% in total
Nb and Ta may be contained in one or both of them because they are precipitated in the grains as fine carbonitrides during use at a high temperature and contribute to the improvement of the creep strength of the weld metal. However, if the content is excessive, a large amount and coarse precipitation may occur, which may lead to a decrease in creep strength and creep ductility. Therefore, the total content of Nb and Ta is preferably 4.50% or less. The total content of Nb and Ta is more preferably 4.20% or less, and further preferably 4.00% or less. When the above effect is desired, the total content of Nb and Ta is preferably 0.02% or more, and more preferably 0.05% or more.

Ti: 0-1.00%
Like Nb and Ta, Ti does not necessarily have to be contained in the welding material, but it precipitates in the grains as fine carbonitride during use at high temperature, which contributes to the improvement of the creep strength of the weld metal. Therefore, it may be contained. However, if the content is excessive, a large amount and coarse precipitation may occur, which may lead to a decrease in creep strength and creep ductility. Therefore, the Ti content is preferably 1.00% or less. The Ti content is more preferably 0.90% or less, and further preferably 0.80% or less. When the above effect is desired, the Ti content is preferably 0.02% or more, and more preferably 0.05% or more.

Fe: 0-6.00%
Fe does not necessarily have to be contained in the welding material, but it may be contained because it has an effect of improving the deformability in heat during the production of the welding material. However, if it is contained in excess, the coefficient of thermal expansion of the alloy increases and the steam oxidation resistance may deteriorate. Therefore, the Fe content is preferably 6.00% or less. The Fe content is more preferably 5.50% or less, and even more preferably 5.00% or less. When the above effect is desired, the Fe content is preferably 0.01% or more, and more preferably 0.02% or more.

N: 0.050% or less N is an element effective for improving weld metal structure stability at high temperature, but if it is contained in excess, it causes precipitation of a large amount of nitride during use at high temperature. It is preferably 0.050% or less in order to reduce toughness and ductility. The N content is more preferably 0.030% or less, and further preferably 0.010% or less. The lower limit of the N content is not particularly set, that is, the content may be 0%, but it is preferably 0.0005% or more, and more preferably 0.001% or more.

Al: 0.002 to 1.800%
Al binds to Ni and finely precipitates in the grains as an intermetallic compound, which contributes to improving the creep strength of the weld metal. In order to obtain this effect, it is preferable to contain 0.002% or more. On the other hand, excessive content causes excessive precipitation of the intermetallic compound phase and lowers toughness. Therefore, the Al content is preferably 1.800% or less. The Al content is preferably 0.005% or more, and more preferably 0.010% or more. Further, the Al content is preferably 1.600% or less, and more preferably 1.500% or less.

O: 0.020% or less O is contained as an impurity, but when it is contained in a large amount, the ductility of the weld metal is lowered. Therefore, the O content is preferably 0.020% or less. The O content is more preferably 0.015% or less, and further preferably 0.010% or less. The O content is preferably reduced as much as possible, i.e. the content may be 0%, but the extreme reduction leads to an increase in material cost. Therefore, the O content is preferably 0.0005% or more, and more preferably 0.001% or more.

6. Method for manufacturing welded joint The ferrite-based heat-resistant steel dissimilar material welded joint according to the present invention includes a multi-layer welding process in which a ferrite-based heat-resistant steel and stainless steel or a Ni-based alloy are welded in multiple layers with a welding material for a Ni-based heat-resistant alloy. Manufactured by the method.

Here, in the multi-layer welding process, the welding conditions at the time of initial layer welding are appropriately controlled according to the B content contained in the ferrite heat-resistant steel and the B content contained in the stainless steel or Ni-based alloy. , The amount of B flowing into the weld metal from the ferrite heat-resistant steel can be limited, and the B content in the weld metal can be within the above range.

Specifically, the ratio of the total area of the molten ferrite heat-resistant steel and stainless steel or Ni-based alloy to the area of the weld metal in the cross section of the welded portion after the first layer welding and before the second layer welding is In relation to the B content contained in the ferrite heat-resistant steel and the stainless steel or Ni-based alloy, it is preferable to perform the initial layer welding under the condition satisfying the following equation (ii).

0.1 ≤ [S _BM ] / [S _WM ] ≤ -65 x ([% B _BM1 ] + [% B _BM2 ]) _/2+1.2 ... (ii)
However, in equation (ii), [ _SBM ] is the total area of molten ferritic heat-resistant steel and stainless steel or Ni-based alloy, [ _SWM ] is the area of weld metal, and [% B _BM1 ] is ferrite. The B content (% by mass) and [% B _BM2 ] contained in the heat-resistant steel are the B content (mass%) contained in the stainless steel or Ni-based alloy.

The present inventors conducted tests using various ferritic heat-resistant steel base materials having different B contents, and investigated the relationship between the ratio [ _SBM ] / [ _SWM ] and the presence or absence of solidification cracks. It was experimentally derived that solidification cracking can be suppressed when the ratio [S _BM ] / [S _WM ] is [-65 × ([% B _BM1 ] + [% B _BM2 ]) / 2 + 1.2] or less.

If the ratio [S _BM ] / [S _WM ] is [-65 × ([% B _BM1 ] + [% B _BM2 ]) / 2 + 1.2] or less, B is the weld metal from the base metal during the initial layer welding. It is considered that the decrease in the solidification temperature can be suppressed because the amount of B that is concentrated in the residual liquid phase of the final solidification portion is reduced even if it flows into the water. As a result, solidification cracking in the first layer weld metal is suppressed.

Suppressing the melting of the ferritic heat-resistant steel base material is effective in suppressing stable solidification cracks, but when the melting of the base material is extremely suppressed, welding defects such as fusion defects or back wave defects are likely to occur. .. Then, in order to suppress this, it is effective to control the initial layer welding so that the ratio [ _SBM ] / [ _SWM ] is 0.1 or more. The ratio [ _SBM ] / [ _SWM ] is preferably 0.2 or more.

The ratio [ _SBM ] / [ _SWM ] appropriately controls the welding conditions at the time of first layer welding, such as welding heat input, welding material supply speed, groove shape, gap, welding method and shield gas type. This can be within a predetermined range.

Further, [ _SBM ] and [ _SWM ] are obtained as follows. That is, the cross section of the welded portion after the first layer welding and before the second layer welding is revealed. For example, the exposed cross section is as shown in FIG. With respect to this cross section, the total area [S _WM ] of the weld metal (first layer weld metal) 3, the molten ferritic heat-resistant steel 1 melted from the original groove shape, and the stainless steel or Ni-based alloy 2 [S]. _BM ] can be obtained by image analysis.

In addition, the appearance of the cross section cuts the stationary portion in the welded portion after the first layer welding and before the second layer welding, that is, the portion where the welding bead is stably formed except for the arc start portion and the crater portion. Do it by.

Specifically, the image analysis of the cross section is performed as follows. From the image data of the cross section of the welded portion that appears above, the three weld metal portions, that is, the region corresponding to the area [ _SWM ] are color-coded in order to distinguish them from the other regions. Further, from the geometric information at the time of groove processing on the image data, the portion of the ferritic heat-resistant steel 1 and the stainless steel or Ni-based alloy 2 melted during the initial layer welding, that is, the area corresponding to the area [ _SBM ]. Is similarly color coded to distinguish it from other areas. Then, the area of each color-coded region is measured using commercially available image analysis processing software.

7. Applications The welded structure having a ferritic heat-resistant steel dissimilar welded joint according to the present invention is used for equipment used at high temperatures, such as a boiler for power generation. Examples of welded structures used at high temperatures include boiler pipes for coal-fired power plants, oil-fired power plants, waste incineration power plants, biomass power plants, etc., decomposition pipes for petrochemical plants, and the like. .. Here, the "use at high temperature" in the present embodiment includes, for example, an embodiment of use in an environment of 350 to 700 ° C. (further, 400 to 650 ° C.).

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

After the ingots in which the materials of steel grades A to E having the chemical compositions shown in Table 1 are melted and cast in a laboratory, heat treatment is performed by hot forging and hot rolling to form, quench, and temper. It was processed into a plate material having a plate thickness of 12 mm, a width of 50 mm, and a length of 200 mm, and produced for welding base material 1 (ferritic heat-resistant steel). Further, the materials of steel types F and G having the chemical compositions shown in Table 2 were prepared for the welding base material 2 (stainless steel) on the different material side in the same process.

Using the above-mentioned welding base material 1 and welding base material 2, the U groove of FIG. 3 is processed in the longitudinal direction, and then abutted to obtain a molten material No. 1 having an outer diameter of 1.2 mm and having the chemical composition shown in Table 3. Using the welding materials for Ni-based heat-resistant alloys 1 to 3, the first layer was welded by automatic gas tungsten arc welding with Ar as the shield gas, and two 45 types of welded joints shown in Table 4 were produced. At the time of welding, as shown in Table 4, the heat input was varied from 6 to 10 kJ / cm and the supply rate of the welding material was varied from 0.8 to 13.3 mm / s.

Using one of the two welded joints obtained, a penetrant inspection test was performed on the weld metal surface to confirm the presence or absence of cracks. Then measure the cross section of the weld current out by the method described above, in the weld cross section after initial layer welding by the melted area of the base material [S _BM] and the area of the weld metal [S _WM] image processing Then, the ratio [ _SBM ] / [ _SWM ] was calculated. Further, the presence or absence of back wave formation was visually observed, and the welded joint in which there was no crack instruction pattern in the penetrant inspection test and the back wave was formed was evaluated as "pass".

Of the two welded joints obtained, the other was laminated and welded by automatic gas tungsten arc welding with a heat input of 6 kJ / cm and a supply speed of the welding material of 8.3 mm / s. Then, the cross section of the welded portion was exposed and mirror-polished, and corroded with a virera reagent (picric acid 1 g, hydrochloric acid 5 ml, ethanol 100 ml) for about 30 seconds to 2 minutes. Then, the first layer portion was identified from the observation with an optical microscope, and the B content [% B _WM ] contained in the first layer portion of the weld metal was measured. Table 5 shows the results of measuring the chemical composition of the entire weld metal.

Further, for some of the passed welded joint codes, a round bar creep test piece having a weld metal in the center of the parallel portion was collected from the welded joint. Then, a creep rupture test was conducted under the conditions of 650 ° C. and 127 MPa, and those having a rupture time exceeding 1000 hours were regarded as "passed". Table 6 shows [ _SBM ] / [ _SWM ], [% _BWM ], and the test results together.

Test No. In order to satisfy all the provisions of the present invention, 1 to 4, 7 to 10, 12 to 15, 17 to 23, 25 to 29, 34 to 39, 41 to 45 are used in a deep penetration test, a back wave observation, and a creep test. It showed good results.

Test No. In Nos. 6, 11, 16, 31, 32, and 33, the B content in the first layer weld metal exceeded 0.005, and the equation (ii) was not satisfied, so that the weld metal crack occurred.

Test No. In No. 30, the B content in the weld metal was lower than the value calculated from the B content contained in the welding base material 1 and the welding base material 2, and the equation (i) was not satisfied. became. In addition, the test No. In 5 and 40, (i) addition to not satisfy the _equation, because below the _{[S BM] / [S WM} ] 0.1 became penetration failure.

Test No. In No. 24, since the B content contained in the welding base material 1 was less than the specified range, the creep rupture test failed.

According to the present invention, it is possible to obtain a ferrite-based heat-resistant steel dissimilar welded joint having excellent solidification crack resistance in addition to high creep strength.

1. 1. Ferritic heat resistant steel 2. Stainless steel or Ni-based alloy 3. Welded metal 10. Ferritic heat-resistant steel dissimilar welded joint

Claims (8)

A ferritic heat-resistant steel dissimilar welded joint in which a ferritic heat-resistant steel and stainless steel or a Ni-based alloy are welded with different materials via a weld metal.
The chemical composition of the ferritic heat-resistant steel is mass%.
C: 0.04 to 0.12%,
Si: 0.05 to 0.60%,
Mn: 0.10 to 0.80%,
P: 0.020% or less,
S: 0.010% or less,
Cr: 8.0-10.0%,
Co: 2.0-4.0%,
Mo + W: 2.0-4.0% in total,
Nb + Ta: 0.02 to 0.18% in total,
V: 0.05 to 0.40%,
B: 0.005 to 0.020%,
Al: 0.030% or less,
N: 0.002-0.025%,
O: 0.020% or less,
Nd: 0-0.06%,
Ni: 0-0.4%,
Cu: 0-1.0%,
Ti: 0 to 0.30%,
Ca: 0 to 0.050%,
Mg: 0 to 0.050%,
Remaining: Fe and impurities,
The B content contained in the ferrite heat-resistant steel, the stainless steel or the Ni-based alloy, and the initial layer portion of the weld metal satisfies the following formula (i).
Ferritic heat-resistant steel dissimilar welded joint.
0.1 × ([% B _BM1 ] + [% B _BM2 ]) / 2 ≦ [% B _WM ] ≦ 0.005 ・ ・ ・ (i)
However, [% B _BM1 ] in the formula (i) is the B content (mass%) contained in the ferrite heat-resistant steel, and [% B _BM2 ] is the B content (mass%) contained in the stainless steel or Ni-based alloy. ), [% B _WM ] is the B content (mass%) contained in the initial layer portion of the weld metal. The chemical composition of the weld metal is mass%.
C: 0.005 to 0.180%,
Si: 0.02 to 1.20%,
Mn: 0.02 to 4.00%,
P: 0.040% or less,
S: 0.010% or less,
Cr: 8.0-25.0%,
Mo: 0 to 12.0%,
Co: 0 to 15.0%,
Cu: 0-4.0%,
W: 0-6.0%,
Nb + V + Ti + Ta: 0-4.50% in total,
Fe: 0.01-5.00%,
B: 0.005% or less,
Al: 1.80% or less,
N: 0.30% or less,
O: 0.020% or less,
Nd: 0-0.06%,
Ca: 0 to 0.050%,
Mg: 0 to 0.050%,
Remaining: Ni and impurities,
The ferrite-based heat-resistant steel dissimilar welded joint according to claim 1. The chemical composition of the stainless steel or the Ni-based alloy is mass%.
Ni: 5.0 to 70.0%, and Cr: 15.0 to 30.0%.
The ferrite-based heat-resistant steel dissimilar welded joint according to claim 1 or 2. The chemical composition of the stainless steel or the Ni-based alloy is mass%.
C: 0.04 to 0.12%,
Si: 0.02-1.00%,
Mn: 0.02 to 4.00%,
P: 0.040% or less,
S: 0.010% or less,
Ni: 5.0-70.0%,
Cr: 15.0 to 30.0%,
Co: 0-4.0%,
Cu: 0-4.0%,
Mo: 0-2.0%,
W: 0-8.0%,
Nb: 0-1.0%,
V: 0-1.0%,
Ti: 0-1.0%,
B: 0 to 0.006%,
Al: 1.00% or less,
N: 0-0.30%,
O: 0.020% or less,
Nd: 0-0.05%,
Ca: 0 to 0.050%,
Remaining: Fe and impurities,
The ferrite-based heat-resistant steel dissimilar welded joint according to claim 3. A method for manufacturing a ferritic heat-resistant steel dissimilar welded joint including a multi-layer welding process in which a ferrite-based heat-resistant steel and stainless steel or a Ni-based alloy are welded in multiple layers with a welding material for a Ni-based heat-resistant alloy.
The chemical composition of the ferritic heat-resistant steel is mass%.
C: 0.04 to 0.12%,
Si: 0.05 to 0.60%,
Mn: 0.10 to 0.80%,
P: 0.020% or less,
S: 0.010% or less,
Cr: 8.0-10.0%,
Co: 2.0-4.0%,
Mo + W: 2.0-4.0% in total,
Nb + Ta: 0.02 to 0.18% in total,
V: 0.05 to 0.40%,
B: 0.005 to 0.020%,
Al: 0.030% or less,
N: 0.002-0.025%,
O: 0.020% or less,
Nd: 0-0.06%,
Ni: 0-0.4%,
Cu: 0-1.0%,
Ti: 0 to 0.30%,
Ca: 0 to 0.050%,
Mg: 0 to 0.050%,
Remaining: Fe and impurities,
In the multi-layer welding step, the total area of the molten ferrite heat-resistant steel, the stainless steel or the Ni-based alloy, and the area of the weld metal in the cross section of the welded portion after the first layer welding and before the second layer welding. The first layer welding is performed under the condition that the following equation (ii) is satisfied in relation to the B content contained in the ferrite heat-resistant steel and the stainless steel or the Ni-based alloy.
A method for manufacturing ferrite-based heat-resistant steel dissimilar welded joints.
0.1 ≤ [S _BM ] / [S _WM ] ≤ -65 x ([% B _BM1 ] + [% B _BM2 ]) _/2+1.2 ... (ii)
However, in equation (ii), [ _SBM ] is the total area of molten ferritic heat-resistant steel and stainless steel or Ni-based alloy, [ _SWM ] is the area of weld metal, and [% B _BM1 ] is ferrite. The B content (% by mass) and [% B _BM2 ] contained in the heat-resistant steel are the B content (mass%) contained in the stainless steel or Ni-based alloy. The chemical composition of the stainless steel or the Ni-based alloy is mass%.
Ni: 5.0 to 70.0%, and Cr: 15.0 to 30.0%.
The method for manufacturing a ferritic heat-resistant steel dissimilar welded joint according to claim 5. The chemical composition of the stainless steel or the Ni-based alloy is mass%.
C: 0.04 to 0.12%,
Si: 0.02-1.00%,
Mn: 0.02 to 4.00%,
P: 0.040% or less,
S: 0.010% or less,
Ni: 5.0-70.0%,
Cr: 15.0 to 30.0%,
Co: 0-4.0%,
Cu: 0-4.0%,
Mo: 0-2.0%,
W: 0-8.0%,
Nb: 0-1.0%,
V: 0-1.0%,
Ti: 0-1.0%,
B: 0 to 0.006%,
Al: 1.00% or less,
N: 0-0.30%,
O: 0.020% or less,
Nd: 0-0.05%,
Ca: 0 to 0.050%,
Remaining: Fe and impurities,
The method for manufacturing a ferritic heat-resistant steel dissimilar welded joint according to claim 6. The chemical composition of the welding material for Ni-based heat-resistant alloy is mass%.
C: 0.005 to 0.180%,
Si: 0.02 to 1.20%,
Mn: 0.02 to 4.00%,
P: 0.020% or less,
S: 0.010% or less,
Cr: 16.0 to 25.0%,
Mo: 0 to 12.0%,
Co: 0 to 15.0%,
Cu: 0-0.80%,
Nb + Ta: 0-4.50% in total,
Ti: 0-1.00%,
Fe: 0-6.00%,
N: 0.050% or less,
Al: 0.002 to 1.800%,
O: 0.020% or less,
Remaining: Ni and impurities,
The method for manufacturing a ferritic heat-resistant steel dissimilar welded joint according to any one of claims 5 to 7.

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