JPH08164481A - Welding method of high cr ferritic heat resistant steel - Google Patents

Abstract

PURPOSE: To prevent the low temperature crack during the welding by preheating the groove surface before the welding and keeping the preheated condition, and heating the weld zone under the prescribed condition before the weld zone is cooled, and keeping the heated condition in a method where the ferritic heat resistant steel is arc welded to obtain the weld metal with the Cr equivalent calculated by the prescribed formula being in the prescribed range. CONSTITUTION: The ferritic heat resistant steel is arc welded to provide the weld metal whose Cr equivalent obtained by the formula is 4-13. The groove surface is preheated at 150-300 deg.C before the welding, and the temperature between each welding pass is kept at 150-300 deg.C. After the welding is completed, and before the weld zone is cooled below 300 deg.C, the weld zone is heated at 150-300 deg.C and this condition is kept for >=10 minutes and <=2 hours per 25mm of the base metal thickness. The reliability of the weld zone can be greatly improved in applying the high Cr ferritic heat resistant steel of high strength to the energy plant of high temperature and high efficiency. Each term in the formula indicates the weight % of each element of the weld metal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding method for welding a high-strength, high-Cr ferritic heat-resistant steel using a welding material whose strength is compatible with that of a base material.

[0002]

2. Description of the Related Art In recent years, along with the demand for high-temperature and high-efficiency energy plants, high strength ferritic steels with extremely high creep strength and less risk of stress corrosion cracking as seen in austenitic stainless steels as plant steels. Heat-resistant steel has been developed and is being put to practical use.

Joining by welding is indispensable for construction of such a plant. For example, JP-A-5-177384, JP-A-5-261589, or JP-A-5-261589.
A welding material having excellent creep characteristics and toughness, as seen in Japanese Patent No. 28591, has also been developed and used together with a steel material. However, the weld metal obtained from these welding materials has a perfect martensitic structure, and the hardness immediately after welding is extremely high at about 500 Vickers hardness. For this reason,
The susceptibility to cold cracking due to hydrogen contained in weld metal and residual stress is extremely high, which makes welding extremely difficult.

However, changing the composition of the welding material to lower the hardness immediately after welding and lower the crack susceptibility, on the other hand, lowers the strength for a short time and thus the creep strength, which greatly impairs practical performance. Further, since the Cr equivalent of the weld metal is limited to 13 or less from the viewpoint of toughness, it is difficult to further change the composition. Therefore, when welding
Cracks are only reduced by reducing the hydrogen content, such as drying the welding material and reducing the humidity in the welding environment.

[0005]

SUMMARY OF THE INVENTION In view of the above situation, the present invention provides a welding method for preventing cold cracking when welding high strength high Cr ferritic heat resistant steel without impairing the mechanical properties of the weld metal. The purpose is to provide.

[0006]

Means for Solving the Problems That is, the gist of the present invention is as follows. (1) Arc welding of ferritic heat-resistant steel
In a method of obtaining a weld metal having a Cr equivalent of 4 to 13 obtained from the formula, the welding groove surface is 150 ° C. to 300 ° C. before welding.
Preheat to ℃, and the temperature between each welding pass is 150 ℃ ～ 30
Hold at 0 ℃, and after welding is completed, the weld will be 300 ℃
Heating temperature of the weld before cooling to below: 150 ° C-30
0 ℃, holding time: 10 minutes or more per 25mm thickness of base material 2
It is a welding method for high Cr ferritic heat resistant steel characterized by heating and holding for less than a time, and Cr equivalent = Cr% + 6Si% + 4Mo% + 1.5W% + 11V% + 5Nb% + 12Al% -40C% -30N % -4Ni% -2Mn% -Cu% -2Co (1) (Each item on the right side is the weight% of each element of the weld metal) , C: 0.02 to 0.20%, S
i: 0.001-0.4%, Mn: 0.05-2.0
%, Cr: 7.5 to 13.0%, Mo: 0.5 to
2.5%, W: 0.2 to 2.0%, Ni:
0.01-1.0%, Nb: 0.02-0.12
%, V: 0.04-0.40%, N: 0.01
The method for welding high Cr ferritic heat-resistant steel according to (1) above, which comprises arc-welding the high Cr ferritic heat-resistant steel containing 0.06% to 0.06% of the balance iron and unavoidable impurities. And (3) arc welding using a coated arc welding rod, which is the method for welding high Cr ferritic heat-resistant steel according to (1) or (2), and (4) coated arc welding rod. C: 0.0 based on the total weight
1 to 0.15%, Si: 0.2 to 1.5%, Mn:
0.8-2.0%, Cr: 5.5-13.0
%, W: 0.8 to 2.0%, Mo: 0.2 to
0.7%, Ni: 0.01 to 1.0%, V:
0.08 to 0.45%, Nb: 0.01 to 0.12%,
N: 0.02 to 0.07%, with the balance being iron and unavoidable impurities, steel core wire, metal carbonate, metal fluoride, arc stabilizer, slag generator, deoxidizer, binder The covering material containing 20% to 20% of the total weight of the welding rod.
The welding method for high Cr ferritic heat-resistant steel according to the above (1) or (2), characterized in that arc welding is performed using a coated arc welding rod applied so as to have a content of 40%. % By weight, C: 0.02-0.13%, S
i: 0.005 to 0.35%, Mn: 0.2 to 1.6
%, Cr: 7.5 to 13.0%, W: 0.5
~ 3.5%, Mo: 0.3-1.8%, Ni:
0.04 to 1.3%, V: 0.03 to 0.40
%, Nb: 0.01 to 0.15%, N: 0.01
~ 0.08% contained in the balance, TIG welding using a solid wire consisting of iron and unavoidable impurities TIG welding, characterized in that the high Cr ferritic heat-resistant steel welding method according to (1) or (2) And (6) the solid wire is in a weight% of C: 0.03 to
0.25%, Si: 0.05-0.30%, Mn:
0.2-3.0%, Cr: 7.5-13.0
%, W: 0.5 to 2.5%, Mo: 0.1
1.5%, Ni: 0.04 to 1.3%, V:
0.05-0.6%, Nb: 0.01-0.15%,
N: 0.01 to 0.10%, flux is wt%, CaF ₂ : 10 to 35%, CaO or MgO.
At least one of: 10 to 45%, Al ₂ O ₃ : 10 to 10%
45%, SiO ₂ : 5 to 30% is contained, and the remainder of the solid wire and the flux is iron and inevitable impurities. Submerged arc welding is performed by the combination of the solid wire and the flux, (1) Alternatively, it is the method of welding high Cr ferritic heat resistant steel according to (2).

[0007]

The present invention controls the microstructure during welding by performing the optimum heat treatment on the welded portion during welding, and further promotes the diffusion of hydrogen in the weld metal from the weld metal. Prevents low temperature cracking.

Cold cracking occurs due to the combined action of diffusible hydrogen in the weld metal, hardness and residual stress. Of these, the residual stress is greatly influenced by the shape of the welded structure, and therefore it is difficult to reduce it unconditionally. Therefore, the amount of diffusible hydrogen in the weld metal and the hardness are reduced. Since the amount of hydrogen contained in the welding material has already been reduced to the limit, the improvement effect that can be expected is small. Therefore, it was found that diffusible hydrogen in the weld metal diffuses into the base metal by slowing the cooling rate after welding. Further, softening of the tissue can be realized by decreasing the cooling rate.

The reason why the ferritic heat-resistant steel is limited here is that low temperature cracking is a particular problem in the steel type, and the reason for limiting the arc welding method is that low temperature cracking is a problem in the welding method. . Furthermore, the reason why the steel type is limited to claim 2 is that the component system is particularly sensitive to cold cracking and must be solved in welding work. Further, in the present steel type, it is desirable to weld with a common metal type welding material in terms of use characteristics, so that the welding material is limited as in claims 4, 5 and 6.

The present invention will be specifically described below. The reason why the Cr equivalent of the weld metal is limited to 4 to 13 is that if the Cr equivalent is less than 4, heat resistance and oxidation resistance are reduced. On the other hand, if it exceeds 13, δ ferrite is generated in the weld metal and the toughness is reduced.

Next, the welding method will be described. First, before performing welding, the welding groove surface is heated to 150 ° C. or higher and 300 ° C. or lower to make the temperature uniform, and then welding is performed.
The heating method is not limited as long as the temperature of the weld groove surface becomes uniform, and for example, heating with a burner or insertion into a soaking furnace can be considered. Considering the construction efficiency, the simplest method is preferable. Here, the lower limit temperature of 150 ° C. is the minimum preheating temperature required to prevent cold cracking by the method of the present invention, and if it is lower than this, cold cracking after welding occurs. If the upper limit temperature of 300 ° C is higher than this, if welding is started, the cooling rate immediately after welding will be small,
Hot cracking occurs.

After the temperature of the weld groove surface reaches uniform, welding is carried out. As the welding condition, an appropriate value of the welding material used is used. After the completion of the welding of the first layer, when the temperature of any position on the surface of the weld bead and the groove surface on which the next weld bead is placed reaches the temperature range of 150 ° C to 300 ° C, the next weld bead is Put. The grounds for the temperature range are the same as for the preheat temperature range above. When the temperature of the weld bead surface or the groove face on which the next weld bead is placed is out of the temperature range of 150 ° C to 300 ° C due to a problem such as a long welding length, partial heating is performed by a burner or the like. Keep within temperature range. After that, each time each welding bead is placed, the next welding bead is placed while the temperature of the groove surface is within the range of 150 ° C to 300 ° C. In this way, the temperature between welding passes is from 150 ° C to
Welding is carried out by holding at 300 ° C.

After placing the final weld bead, the weld is 30
Before cooling to 0 ° C., the weld metal and weld heat affected zone of the weld are heated and held at 150 ° C. to 300 ° C. The holding time is 10 minutes or more and 2 hours or less per 25 mm plate thickness of the base material. Here, the lower limit temperature, 150 ° C., is the lowest immediate hot temperature required to prevent cold cracking by the method of the present invention, and if it is less than this, cold cracking after welding cannot be prevented. Maximum temperature of 3
It may be difficult to maintain the temperature of 00 ° C. at a temperature higher than this, and the effect of preventing cold cracking is not significantly improved. The lower limit of holding time is 1 per 25 mm of the base metal.
When the holding time is shorter than 0 minute, the cold crack cannot be prevented. In addition, 2 per 25 mm of base metal plate thickness
No improvement in the effect of preventing low temperature cracking is observed even when heated for over a period of time.

Here, the reason why the composition of the high Cr ferritic heat resistant steel is limited as in claim 2 will be explained. C: 0.02 to 0.20% C needs to be 0.02% or more to secure hardenability and strength, but on the contrary, 0.20% is the upper limit from the viewpoint of weldability. Si: 0.001 to 0.4% Si is an element that improves the oxidation resistance. for that reason,
It is necessary to add 0.001% or more, but if it exceeds 0.4%, toughness is deteriorated, so 0.4% is the upper limit.

Mn: 0.05 to 2.0% Mn is a component necessary for maintaining strength, and is required to be 0.05% or more. The upper limit is set to 2.0% because if it exceeds this, the toughness is reduced. Cr: 7.5-13.0% Since Cr is a very important element for securing the oxidation resistance and hardenability, it is necessary to have at least 7.5%, but if it exceeds 13%, δ ferrite will be formed. Since it precipitates and the toughness deteriorates remarkably, 13% is the upper limit.

Mo: 0.5 to 2.5% Since Mo is an element that remarkably enhances high temperature strength by solid solution strengthening, it is added for the purpose of raising the operating temperature and pressure, but when a large amount is added, δ ferrite is added. Since it precipitates, the toughness is lowered. Therefore, 2.5% is the upper limit. On the other hand, 0.5% or more is effective in improving the high temperature strength when coexisting with W, so 0.5% is the lower limit. W: 0.2 to 2.0% W is the most excellent element as a solid solution strengthening element that contributes to the creep strength of the ferritic heat resistant alloy. In particular, the effect of improving the creep rupture strength at high temperature for a long time is extremely large. However, if it is less than 0.2%, the effect cannot be exhibited in the coexistence with Mo, so the lower limit was set to 0.2%. In addition, δ ferrite is precipitated by excessive addition,
In particular, 2.0% is the upper limit because it lowers the toughness of the weld heat affected zone. Ni: 0.01 to 1.0% Ni is an element that improves toughness, but is also an element that lowers high temperature creep strength. Therefore, from the viewpoint of ensuring the toughness, the lower limit is 0.01% and the upper limit is 1.0%. Nb: 0.02 to 0.12% In addition to precipitating as Nb carbonitride to secure the strength, it is also important as an element for refining crystal grains to give toughness, so at least 0.02% is necessary, If it exceeds 0.12%, the effect is saturated. Therefore, 0.12% is the upper limit.

V: 0.04 to 0.40% V is required to be at least 0.04% to secure strength by precipitating as carbonitride like Nb. On the other hand, if it exceeds 0.40%, strength is rather increased. The upper limit is 0.40 because it will decrease
%. N: 0.01 to 0.06% N is required to be at least 0.01% because it contributes as a remarkable creep resistance even if it forms a solid solution in the matrix or precipitates as a nitride. If it exceeds 0.06%, a large amount of nitride precipitates, which causes a problem such as a decrease in toughness.
The upper limit is 0.08%. Other impurities include A
1 can be contained in 0.06% or less, and P and S can be contained in 0.03% or less, respectively.

Since the coated arc welding rod is particularly sensitive to hydrogen cracking, measures against cold cracking are important. Next, the reason why the chemical composition of the coated arc welding rod is limited as in claim 4 will be explained. C: 0.01 to 0.15% C is required to be 0.01% or more to secure hardenability and strength, but 0.15% is the upper limit from the viewpoint of crack resistance. Si: 0.2 to 1.5% Although Si is added as a deoxidizing agent in an amount of 0.2% or more, it is also an element that improves the oxidation resistance. However, if it exceeds 1.5%, the toughness is lowered, so 1.5% is the upper limit.

Mn: 0.8 to 2.0% Mn is a component required not only for deoxidation but also for maintaining strength. The upper limit is 2.0% because if it exceeds this, toughness is reduced, and the lower limit is 0.8% as the amount required for deoxidation. Cr: 5.5 to 13.0% Since Cr is a very important element for securing the oxidation resistance and hardenability, at least 5.5% is required, but if it exceeds 13%, crack resistance is high. At the same time, δ-ferrite is precipitated and toughness is significantly deteriorated, so 13% is the upper limit.

W: 0.8 to 2.0% W is the most excellent element as a solid solution strengthening element that contributes to the creep strength of the ferritic weld metal. In particular, the effect of improving the creep rupture strength at high temperature for a long time is extremely large. However, if less than 0.8%, the effect cannot be exhibited in the coexistence with Mo, so the lower limit was set to 0.8%. In addition, δ ferrite is precipitated by excessive addition,
Since the toughness of the weld metal is reduced and the welding workability is also deteriorated, 2.0% is the upper limit. Mo: 0.2 to 0.7% Since Mo is an element that significantly enhances high temperature strength by solid solution strengthening, it is added for the purpose of raising the operating temperature and pressure, but if added in a large amount, the weldability is impaired, and Since δ ferrite is precipitated, the toughness is lowered. Therefore, 0.7% is the upper limit. On the other hand, in the coexistence with W, it is 0.2% or more that is effective in improving the high temperature strength.
The lower limit is 0.2%.

Ni: 0.01 to 1.0% Ni is an element that improves toughness, but is also an element that lowers high temperature creep strength. Therefore, the lower limit is 0.01% from the viewpoint of improving the toughness, and the upper limit is 1.0% from the viewpoint of ensuring high temperature creep strength. V: 0.08 to 0.45% V is required to be at least 0.08% in order to precipitate carbonitride to secure the strength, but on the other hand, if it exceeds 0.45%, the strength is rather lowered, so that it is 0. 45% is the upper limit.

Nb: 0.01 to 0.12% Nb is precipitated as a carbonitride similar to V to secure the strength, and is also important as an element which gives the toughness by refining the crystal grains, so that Nb is at least 0. 01% required, but 0.12%
If it exceeds, not only the effect is saturated but also the weldability is deteriorated. Therefore, 0.12% is the upper limit. N: 0.02 to 0.07% N contributes as a remarkable creep resistance even if it forms a solid solution in the matrix or precipitates as a nitride, so at least 0.02% is required. If it exceeds 0.07%, a large amount of nitride precipitates, which causes a problem such as a decrease in toughness.
The upper limit is 0.07%.

Examples of metal carbonates, metal fluorides, arc stabilizers, slag generators, and deoxidizers contained in the coating material include lime, alumina, fluorite, iron powder, alkaline components, rutile and the like. Examples of the binder include water glass containing sodium silicate and potassium silicate. The range of the weight% of the coating material with respect to the total weight of the coated arc welding rod is 20 to 40%, but if it is less than 20%, the function as a protective cylinder becomes insufficient, so that spatter is often generated or slag is insufficient. On the other hand, if it exceeds 40%, the amount of slag becomes too large and defects such as slag entrapment occur.

The reason why the chemical composition of the TIG welding wire is limited as in claim 5 will be described below. C: 0.02 to 0.13% C is required to be 0.02% or more in order to secure hardenability and strength, but 0.13% is the upper limit from the viewpoint of crack resistance. Si: 0.005 to 0.35% Si is added as a deoxidizing agent in an amount of 0.005% or more, and is also an element that improves oxidation resistance. However, if it exceeds 0.35%, the toughness decreases, so 0.35
% Is the upper limit.

Mn: 0.2-1.6% Mn is a component necessary not only for deoxidation but also for strength retention. The upper limit is set to 1.6% because if it exceeds this, toughness is reduced, and the lower limit is 0.2% as the amount required for deoxidation. Cr: 7.5-13.0% Since Cr is a very important element for securing the oxidation resistance and hardenability, it is necessary to have at least 7.5%, but if it exceeds 13%, crack resistance is high. At the same time, δ-ferrite is precipitated and toughness is significantly deteriorated, so 13% is the upper limit.

W: 0.5 to 3.5% W is the most excellent element as a solid solution strengthening element that contributes to the creep strength of the ferritic weld metal. In particular, the effect of improving the creep rupture strength at high temperature for a long time is extremely large. However, if less than 0.5%, the effect cannot be exhibited in the coexistence with Mo, so the lower limit was set to 0.5%. In addition, δ ferrite is precipitated by excessive addition,
Since the toughness of the weld metal is reduced and the welding workability is also deteriorated, 3.5% is the upper limit. Mo: 0.3 to 1.8% Since Mo is an element that remarkably enhances high temperature strength by solid solution strengthening, it is added for the purpose of raising the operating temperature and pressure, but if added in a large amount, the weldability is impaired, and Since δ ferrite is precipitated, the toughness is lowered. Therefore, the upper limit is 1.8%. On the other hand, in the coexistence with W, 0.3% or more is effective in improving the high temperature strength.
The lower limit is 0.3%.

Ni: 0.04 to 1.3% Ni is an element that improves the toughness, but is also an element that lowers the high temperature creep strength. Therefore, the lower limit is 0.04% from the viewpoint of improving the toughness, and 1.3 is the upper limit from the viewpoint of ensuring high temperature creep strength. V: 0.03 to 0.40% V is required to be at least 0.03% in order to precipitate as carbonitride to secure the strength, but on the other hand, when it exceeds 0.40%, the strength is rather lowered, so that it is 0. The upper limit is 40%.

Nb: 0.01 to 0.15% Nb is precipitated as a carbonitride similar to V to secure the strength, and is also important as an element which gives the toughness by refining the crystal grains, so that at least 0. 01% required, but 0.15%
If it exceeds, not only the effect is saturated but also the weldability is deteriorated. Therefore, 0.15% is the upper limit. N: 0.01 to 0.08% N is required as a minimum 0.01% because it contributes as a remarkable creep resistance even if it forms a solid solution in the matrix or precipitates as a nitride. If it exceeds 0.08%, a large amount of nitride precipitates, and conversely, there arises a problem that the toughness deteriorates.
The upper limit is 0.08%.

The reason why the chemical composition of the submerged arc welding solid wire and the flux is limited as in claim 6 will be described below. C: 0.03 to 0.25% C is required to be 0.03% or more to secure hardenability and strength, but 0.25% is the upper limit from the viewpoint of crack resistance. Si: 0.05 to 0.30% Although Si is added as a deoxidizing agent in an amount of 0.05% or more, it is also an element that improves oxidation resistance. However, if it exceeds 0.30%, the toughness decreases, so 0.30
% Is the upper limit.

Mn: 0.2-3.0% Mn is a component required not only for deoxidation but also for maintaining strength. The upper limit is 3.0% because if it exceeds this, the toughness is reduced, and the lower limit is 0.2% as the amount required for deoxidation. Cr: 7.5-13.0% Since Cr is a very important element for securing the oxidation resistance and hardenability, it is necessary to have at least 7.5%, but if it exceeds 13%, crack resistance is high. At the same time, δ-ferrite is precipitated and toughness is significantly deteriorated, so 13% is the upper limit.

W: 0.5 to 2.5% W is the most excellent element as a solid solution strengthening element that contributes to the creep strength of the ferritic weld metal. In particular, the effect of improving the creep rupture strength at high temperature for a long time is extremely large. However, if less than 0.5%, the effect cannot be exhibited in the coexistence with Mo, so the lower limit was set to 0.5%. In addition, δ ferrite is precipitated by excessive addition,
Since the toughness of the weld metal is reduced and the welding workability is also deteriorated, 2.5% is the upper limit. Mo: 0.1 to 1.5% Since Mo is an element that remarkably enhances high temperature strength by solid solution strengthening, it is added for the purpose of raising the operating temperature and pressure, but if added in a large amount, the weldability is impaired, and Since δ ferrite is precipitated, the toughness is lowered. Therefore, the upper limit is 1.5%. On the other hand, in the coexistence with W, 0.1% or more is effective in improving the high temperature strength.
The lower limit is 0.1%.

Ni: 0.04 to 1.3% Ni is an element that improves the toughness, but is also an element that lowers the high temperature creep strength. Therefore, the lower limit is 0.04% from the viewpoint of improving the toughness, and 1.3 is the upper limit from the viewpoint of ensuring high temperature creep strength. V: 0.05 to 0.60% V is required to be at least 0.05% in order to be precipitated as carbonitride to secure the strength, but on the other hand, when it exceeds 0.60%, the strength is rather lowered, so that it is not preferable. The upper limit is 60%.

Nb: 0.01 to 0.15% Nb is precipitated as a carbonitride similar to V to secure strength, and is also important as an element which gives toughness by refining crystal grains, so that Nb is at least 0. 01% required, but 0.15%
If it exceeds, not only the effect is saturated but also the weldability is deteriorated. Therefore, 0.15% is the upper limit. N: 0.01 to 0.10% N contributes as a remarkable creep resistance even if it forms a solid solution in the matrix or precipitates as a nitride, so 0.01% is necessary at the minimum. If it exceeds 0.10%, a large amount of nitride precipitates, and conversely the toughness deteriorates.
The upper limit is 0.10%. Next, the reason for limiting the flux will be described below. CaF _2: 10~35% CaF ₂ is raised basicity of slag is effective to improve significantly reduced toughness oxygen in the weld metal. Further, it lowers the melting point of the slag to make the penetration shallow, thereby improving the peelability of the slag and improving the bead shape and appearance. 10
If it is less than%, there is no effect, and if it exceeds 35%, the fluidity of the slag becomes excessive and the bead shape and appearance deteriorate. Therefore, the upper limit of CaF ₂ is 35% and the lower limit is 10%.

At least one of CaO and MgO: 10
~ 45% CaO and MgO are both strongly basic components and CaF ₂
It is also effective in reducing oxygen in the weld metal. Also, Ca
O and MgO are highly refractory components and have a low melting point of C.
It is effective for adjusting the melting characteristics of the flux containing aF ₂ and adjusting the bead shape. If it is less than 10%, there is no effect, and if it exceeds 45%, the flux is difficult to melt,
The shape of the bead surface deteriorates. Therefore CaO or Mg
At least one of O is limited to 10 to 45%.

Al ₂ O ₃ : 10 to 45% Al ₂ O ₃ has a high melting point and is effective in adjusting the fluidity of the slag and adjusting the bead shape. To obtain this effect, at least 10% is required, and if it exceeds 45%, slag entrapment and undercutting are likely to occur.

SiO ₂ : 5 to 30% SiO ₂ is effective in adjusting the viscosity of the slag and improving the bead appearance, but if it is less than 5%, there is no effect and 30%.
If it exceeds, viscosity increases and slag entrapment occurs. Therefore, the range is limited to 5 to 30%.

[0037]

EXAMPLE FIG. 1 shows the results of the oblique Y-type restraint crack test when the preheating temperature was changed to 60 to 350 ° C. and the heat temperature immediately after welding was 150 ° C. to 250 ° C. The heat immediately after welding is the heating / holding process immediately after welding according to the present invention. The temperature between each pass was 150 to 300 ° C.

In this embodiment, the temperature is kept at 150 to 250 ° C. for 1 hour. The horizontal axis represents the preheating temperature, and the vertical axis represents the ratio of the crack length to the throat thickness in the weld bead cross section. The smaller this value, the smaller the tendency of crack generation. In FIG. 1, the average value of 5 cross sections is shown.

The oblique Y-type constrained cracking test is a test for evaluating the low temperature cracking sensitivity defined in JIS.Z.3158. Figure 2
Shows its shape. The base material used is 9Cr-1.8W high-strength ferritic heat-resistant steel having a chemical composition shown in Table 1 and a thickness of 50 mm. Further, the welding rod used was a 9Cr-1.5W-based co-metal coated arc welding rod having the chemical composition shown in Table 2. As the welding method, covered arc welding was used in this embodiment, but TIG welding and SAW welding can also be applied. Table 3 shows the welding conditions. Further, Table 4 shows the chemical composition and Cr equivalent of the weld metal.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

As shown in FIG. 1, when the immediate heating temperature is 150 ° C. or higher and 250 ° C. or lower, low temperature cracking can be prevented even if the preheating temperature is 150 ° C. When the preheating temperature is higher than 300 ° C, high temperature cracking occurs. FIG. 3 also shows the results of the oblique Y-shaped restraint crack test when the heat immediately after the heating was 100 ° C. or higher and lower than 150 ° C. In this case, cracking could not be prevented at a preheating temperature of 150 degrees.

[0045]

According to the welding method of the present invention, when welding high Cr ferritic heat-resistant steel, it is possible to carry out welding without generation of cold cracks. When applied to an energy plant, the reliability of the welded portion can be greatly improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between heat immediately after welding and a crack rate according to the present invention.

FIG. 2 is a test piece shape of an oblique Y-type constrained cracking test used in Examples, (a) is a plan view of a welded portion of the test piece, (b) is a sectional view taken along line AA, and (c) is B-. The B section is shown.

FIG. 3 is a diagram showing a relationship between heat immediately after welding and a crack rate in a comparative example.

[Explanation of symbols]

 1 Restrained weld bead 2 Groove for test bead

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B23K 35/30 320 E 330 A 35/362 310 C C22C 38/00 302 Z 38/48 (72) Inventor Noritaka Yurioka 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd.

Claims (6)

[Claims] 1. A method of arc-welding a ferritic heat-resistant steel to obtain a weld metal having a Cr equivalent of 4 to 13 determined by the following formula (1), wherein the weld groove surface is 150 ° C. before welding.
Preheat to ~ 300 ° C and keep the temperature between each welding pass at 150
C. to 300.degree. C., and after the welding is completed, before heating the weld to less than 300.degree. C., heating temperature of the weld is 150.
C-300 C, holding time: 10 per 25 mm thickness of base material
High C, characterized by heating and holding for at least 2 minutes but no less than 2 minutes
r Welding method for ferritic heat resistant steel. Cr equivalent = Cr% + 6Si% + 4Mo% + 1.5W% + 11V% + 5Nb% + 12Al% -40C% -30N% -4Ni% -2Mn% -Cu% -2Co ... .. (1) (Each item on the right side is the weight% of each element of the weld metal) 2. By weight%, C: 0.02 to 0.20%, Si: 0.001 to 0.4%, Mn: 0.05 to 2.0%, Cr: 7.5 to 13. 0%, Mo: 0.5 to 2.5%, W: 0.2 to 2.0%, Ni: 0.01 to 1.0%, Nb: 0.02 to 0.12%, V: 0 2. A high Cr ferritic heat-resisting steel containing 0.04 to 0.40%, N: 0.01 to 0.06%, and the balance being iron and inevitable impurities, is arc-welded. Welding method for high Cr ferritic heat-resisting steel. 3. The method for welding high Cr ferritic heat resistant steel according to claim 1, wherein arc welding is performed using a covered arc welding rod. 4. C: 0.01 to 0.15%, Si: 0.2 to 1.5%, Mn: 0.8 to 2.0%, Cr: to the total weight of the covered arc welding rod. 5.5-13.0%, W: 0.8-2.0%, Mo: 0.2-0.7%, Ni: 0.01-1.0%, V: 0.08-0. 45%, Nb: 0.01 to 0.12%, N: 0.02 to 0.07%, with the balance being iron and inevitable impurities, steel core wire, metal carbonate, metal fluoride, arc Covering rate of 20-40% based on the total weight of the welding rod with a coating material containing a stabilizer, slag generator, deoxidizer and binder.
The method for welding high Cr ferritic heat-resistant steel according to claim 1 or 2, wherein arc welding is performed using a coated arc welding rod applied so that 5. By weight%, C: 0.02-0.13%, Si: 0.005-0.35%, Mn: 0.2-1.6%, Cr: 7.5-13. 0%, W: 0.5 to 3.5%, Mo: 0.3 to 1.8%, Ni: 0.04 to 1.3%, V: 0.03 to 0.40%, Nb: 0. 0.01 to 0.15%, N: 0.01 to 0.08%, and the balance is iron and inevitable impurities. TIG welding is performed using a solid wire. High Cr
Welding method for ferritic heat resistant steel. 6. The solid wire is, by weight, C: 0.03 to 0.25%, Si: 0.05 to 0.30%, Mn: 0.2 to 3.0%, Cr: 7.5. ~ 13.0%, W: 0.5-2.5%, Mo: 0.1-1.5%, Ni: 0.04-1.3%, V: 0.05-0.6%, Nb: 0.01 to 0.15%, N: 0.01 to 0.10% are contained, and the flux is by weight, CaF ₂ : 10 to 35%, at least one of CaO and MgO: 10 to 45%. , Al ₂ O ₃ : 10 to 45%, SiO ₂ : 5 to 30%, and the balance of the solid wire and flux is iron and inevitable impurities. Submerged arc welding with a combination of solid wire and flux. A method for welding high Cr ferritic heat resistant steel according to claim 1 or 2, .