The present disclosure relates to a method for manufacturing a ferritic heat resistant steel welded joint.
Background technology
[0002]
In recent years, in thermal power generation, high temperature and high pressure steam conditions have been promoted in order to improve thermal efficiency, and in the future, operations under ultra-supercritical pressure conditions of 650 ° C and 350 atm are planned. Ferritic heat-resistant steels are widely used because they are not only cheaper than austenitic heat-resistant steels or Ni-based heat-resistant steels, but also have an advantage as high-temperature steels having a small coefficient of thermal expansion.
[0003]
Regarding ferritic heat-resistant steel, in order to cope with the severe steam conditions in the future, for example, the contents of W and Mo are optimized as in Patent Document 1 or Patent Document 2, and Co and B are contained. A material with high strength has been proposed. Further, as disclosed in Patent Document 3, various materials having high strength have been proposed by positively utilizing the carbide or the intermetallic compound phase deposited at the interface of the martensitras.
[0004]
Further, recently, ferrite for the purpose of suppressing a decrease in creep strength of a weld heat-affected zone (hereinafter, also simply referred to as “HAZ”) of a welded joint, which is a problem when ferritic heat-resistant steel is used as a welded structure. Various ferritic steels have been proposed. For example, Patent Document 4 discloses a ferrite-based heat-resistant steel capable of suppressing a decrease in creep strength in HAZ by suppressing granulation in HAZ by containing 0.003% to 0.03% of B. ing. Further, Patent Document 5 and Patent Document 6 contain a large amount of B, and by adjusting the C content according to the welding heat input or the B content, the decrease in the strength of HAZ is suppressed and the HAZ strength is suppressed. Ferritic heat-resistant steels that can prevent liquefaction cracking during welding are disclosed.
[0005]
By the way, these ferrite heat-resistant steels containing a large amount of B are generally used by welding. Therefore, as a welding material used at the time of welding, for example, Patent Document 7 contains 0.0005% to 0.006% of B and adjusts (Mo + W) / (Ni + Co) to a predetermined range. Welding materials for ferritic heat-resistant steels that achieve both creep strength and toughness have been proposed. Further, Patent Document 8 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 9 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.
Prior art literature
Patent documents
[0006]
Patent Document 1: Japanese Patent Application Laid-Open No. 4-371551
Patent Document 2: Japanese Patent Application Laid-Open No. 4-371552
Patent Document 3: Japanese Patent Application Laid-Open No. 2002-241903
Patent Document 4: Japanese Unexamined Patent Publication No. 2004-300532
Patent Document 5: Japanese Unexamined Patent Publication No. 2010-7094
Patent Document 6: International Publication No. 2008/149703
Patent Document 7: Japanese Patent Application Laid-Open No. 8-187592
Patent Document 8: Japanese Unexamined Patent Publication No. 9-308989
Patent Document 9: International Publication No. 2017/104815
Outline of the invention
Problems to be solved by the invention
[0007]
By the way, for welding of these ferrite heat-resistant steels containing a large amount of B, a welding material for Ni-based heat-resistant alloys may be used because stable and excellent creep strength can be obtained. However, solidification cracks may occur in the weld metal.
[0008]
The present disclosure has been made in view of the above situation, and stable solidification cracking occurs even when a welding material for a Ni-based heat-resistant alloy is used when multi-layer welding of a ferritic heat-resistant steel base material containing a large amount of B. It is an object of the present invention to provide a method for manufacturing a ferritic heat resistant steel welded joint that can be suppressed.
Means to solve problems
[0009]
As a result of repeated studies based on the above situation, the present inventors have found that the above problems can be solved by the following means.
<1>
It has a multi-layer welding process in which a ferritic heat-resistant steel base material containing 0.006% by mass to 0.023% by mass of B is multi-layer welded with a welding material for Ni-based heat-resistant alloys.
The area [SBM] of the molten ferrite heat-resistant steel base material and the area [SWM] of the weld metal in the cross section of the welded portion after the first layer welding and before the second layer welding in the multilayer welding step. A method for manufacturing a ferrite heat-resistant steel welded joint in which the first layer is welded under the welding conditions satisfying the following formula (1) with respect to the mass% [% B BM] of B contained in the ferrite heat-resistant steel base material. ..
0.1 ≤ [S BM] / [S WM] ≤ -50 x [% B BM] +1.3 ... (1)
<2>
The ferrite-based heat-resistant steel base material is by mass%,
C: 0.04% to 0.15%,
Si: 0.05% to 0.80%,
Mn: 0.10% to 1.00%,
P: 0% to 0.020%,
S: 0% to 0.010%,
Cr: 8.0% to 10.0%,
Total of at least one of Mo and W: 0.5% -4.0%,
Total of at least one of Nb and Ta: 0.02% to 0.30%,
V: 0.05% to 0.40%,
B: 0.006% -0.023%
N: 0.002% to 0.025%,
Al: 0% to 0.030%, and
The method for manufacturing a ferritic heat-resistant steel welded joint according to <1>, wherein O: contains 0% to 0.020% and the balance is Fe and impurities.
<3>
The method for manufacturing a ferrite heat-resistant steel welded joint according to <2>, wherein the ferrite-based heat-resistant steel base material contains at least one element selected from the following group in mass% instead of a part of the Fe. ..
Group Co: 4.0% or less,
Ni: 1.00% or less,
Cu: 1.0% or less,
Ti: 0.30% or less,
Ca: 0.050% or less,
Mg: 0.050% or less,
REM: 0.100% or less
<4>
The welding material for Ni-based heat-resistant alloy is by mass%,
C: 0.005% to 0.180%,
Si: 0.02% to 1.20%,
Mn: 0.02% to 4.00%,
P: 0% to 0.020%,
S: 0% to 0.010%,
Co: 0% to 15.0%,
Cu: 0% to 0.80%,
Cr: 16.0% to 25.0%,
Mo: 0% -12.0%,
Total of at least one of Nb and Ta: 0% to 4.50%,
Ti: 0% to 1.00%,
Fe: 0% to 6.00%,
N: 0% to 0.050%,
Al: 0.002% to 1.800%, and
O: The method for manufacturing a ferritic heat-resistant steel welded joint according to any one of <1> to <3>, which contains 0% to 0.020% and the balance is Ni and impurities.
The invention's effect
[0010]
According to the present disclosure, ferritic heat resistant steel base material containing a large amount of B can be stably suppressed from solidification cracking even when multi-layer welding is performed using a welding material for Ni-based heat resistant alloys. A method for manufacturing a steel welded joint can be provided.
A brief description of the drawing
[0011]
FIG. 1 is a schematic cross-sectional view showing a cross section of a welded portion after first layer welding and before second layer welding in the method for manufacturing a ferritic heat resistant steel welded joint according to the present disclosure.
FIG. 2 is a schematic cross-sectional view showing the shape of a plate material subjected to groove processing in an example.
Embodiment for carrying out the invention
[0012]
Hereinafter, the method for manufacturing a ferrite-based heat-resistant steel welded joint according to the embodiment of the present disclosure will be described in detail.
In the description in this specification, the "%" indication of the content of each element means "mass%".
In the present specification, the numerical range represented by using "-" means a range including the numerical values ​​before and after "-" as the lower limit value and the upper limit value unless otherwise specified. The element whose content is described as "0% to X%" (X is a numerical value) is an optional element and may not contain the element (that is, 0%), and is more than 0% to X%. It means that it may be included in the range.
[0013]
[Manufacturing method of ferritic heat-resistant steel welded joint]
The method for manufacturing a ferritic heat-resistant steel welded joint according to the present disclosure includes a multi-layer welding process in which a ferritic heat-resistant steel base material containing 0.006% to 0.023% of B is multi-layer welded with a welding material for a Ni-based heat-resistant alloy. ..
Then, the area [SBM] of the molten ferrite-based heat-resistant steel base material and the area [SWM] of the weld metal in the cross section of the welded portion after the first layer welding and before the second layer welding in the multilayer welding step. The first layer welding is performed under the welding conditions satisfying the following equation (1) with respect to the mass% [% BBM] of B contained in the ferrite-based heat-resistant steel base material.
0.1 ≤ [S BM] / [S WM] ≤ -50 x [% B BM] +1.3 ... (1)
[0014]
The present inventors conducted a detailed investigation in order to solve the above-mentioned problems. As a result, the following findings were clarified.
(1) When a ferrite heat-resistant steel base material containing 0.006% to 0.023% of B is welded using a welding material for a Ni-based heat-resistant alloy, solidification cracks are likely to occur in the weld metal of the first layer. The reason for this is that B contained in the base metal flows into the weld metal due to the melting of the base metal during welding.
[0015]
(2) In order to suppress solidification cracking that occurs in the first layer weld metal, the amount of melt of the base material in the first layer weld metal is within a predetermined range according to the B content of the base material for ferritic heat-resistant steel. It turns out that it needs to be managed. Specifically, the area of ​​the molten ferritic heat-resistant steel base metal [SBM] and the area of ​​the weld metal (first layer weld metal) [S] in the cross section of the welded portion after the first layer weld and before the second layer weld. The ratio with [WM] needs to be {-50 × [% B BM] +1.3} or less with respect to the amount (% by mass) [% B BM] of B contained in the ferritic heat-resistant steel base material. Revealed that there is.
[0016]
Here, the reason why the upper limit of the ratio [SBM] / [SWM] is defined by the formula {-50 × [% BBM] +1.3} will be described. That is, this relationship was tested using various ferrite heat-resistant steel base materials having different B contents [% B BM], and the relationship between the ratio [SBM] / [SWM] and the presence or absence of solidification cracks was determined. As a result of the investigation, it was experimentally derived that solidification cracking can be suppressed when [SBM] / [SWM] is smaller than {-50 × [% BBM] +1.3}.
[0017]
(3) Suppressing the melting of the ferritic heat-resistant steel base material is effective in suppressing stable solidification cracking, but when the melting of the base material is extremely suppressed, another welding defect, so-called fusion failure or back wave. It turned out that defects are likely to occur. In order to suppress this, the area [SBM] of the molten ferritic heat-resistant steel base material and the weld metal (first layer weld metal) in the cross section of the welded portion after the first layer weld and before the second layer weld. It was also clarified that it is effective to control the initial layer welding so that the ratio of the ferritic stainless steel to the area [SWM] is 0.1 or more.
[0018]
Based on the above findings, the reasons for limiting the manufacturing method of ferritic heat-resistant steel welded joints in this disclosure are as follows.
When a ferrite heat-resistant steel base material containing 0.006% to 0.023% of B is multi-layer welded using a welding material for Ni-based heat-resistant alloy, the crossing of the welded portion after the first layer welding and before the second layer welding. The ratio [SBM] / [SWM] of the area [SBM] of the molten ferrite heat-resistant steel base material and the area [SWM] of the weld metal (first layer weld metal) on the surface is the ferrite heat-resistant steel. It shall be {-50 × [% B BM] +1.3} or less according to the mass% [% B BM] of B contained in the base material.
[0019]
If the ratio [S BM] / [S WM] is {-50 × [% B BM] +1.3} or less, even if B flows into the weld metal from the base metal during the initial layer welding, the final solidified portion It is considered that the decrease in the solidification temperature is suppressed because the amount of B concentrated in the residual liquid phase of the above is reduced. As a result, solidification cracking in the first layer weld metal is suppressed.
When the ratio [SBM] / [SWM] exceeds {-50 × [% BBM] +1.3}, B excessively flows from the base metal into the weld metal during the initial layer welding. Excessive for weld metal It is considered that B that has flowed into the weld metal is concentrated in the residual liquid phase of the final solidified portion when the weld metal is solidified, lowers the solidification temperature, and causes solidification cracking.
[0020]
In order to suppress solidification cracking of the weld metal, the smaller the ratio [SBM] / [SWM] is, the more preferable it is. Wave defects are likely to occur. Therefore, the ratio [SBM] / [SWM] is set to 0.1 or more. More preferably, it is 0.2 or more.
[0021]
For the above reasons, the preferable range of the ratio [SBM] / [SWM] is defined in the following equation (1).
0.1 ≤ [S BM] / [S WM] ≤ -50 x [% B BM] +1.3 ... (1)
[0022]
・ Ratio [SBM] / [SWM] control method
The ratio [SBM] / [SWM] appropriately controls the welding conditions at the time of first layer welding, for example, welding heat input, welding material supply speed, groove shape, gap, welding method, shield gas type, and the like. This can be within a predetermined range.
[0023]
・ Measurement method of [SBM] and [SWM]
[SBM] and [SWM] are required 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. For this cross section, the area [SWM] of the weld metal (first layer weld metal) 4 and the area [SBM] of the ferritic heat-resistant steel base metal melted from the original groove shape can be obtained by image analysis. ..
[0024]
The cross section is a cross section in a direction orthogonal to the butt plane between the butt base materials 2A and 2B. The appearance of the cross section is obtained by cutting the stationary portion in the welded portion after the first layer welding and before the second layer welding, that is, the portion where the weld bead is stably formed except for the arc start portion and the crater portion. Make it appear.
The area [SWM] of the weld metal (first layer weld metal) 4 is the first layer weld of the weld metal 4 (base metal 2A and 2B) in the cross section of the welded portion after the first layer welding and before the second layer welding. Refers to the area (including the part considered to have been melted by).
The area [SBM] of the molten ferrite heat-resistant steel base material refers to the area of ​​the portion of the base materials 2A and 2B that is considered to have been melted by the initial layer welding before the initial layer welding.
[0025]
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 appeared above, the four weld metal parts, that is, the region corresponding to the area [SWM] are color-coded in order to distinguish them from the other regions. From the geometric information at the time of groove processing on the image data, in order to distinguish the portion melted at the time of initial layer welding in the base materials 2A and 2B, that is, the region corresponding to the area [SBM] from other regions as well. Color code. Then, the area of ​​each color-coded region is measured using commercially available image analysis processing software.
[0026]
Next, the chemical composition of the base material for ferritic heat-resistant steel used in the present disclosure is not particularly limited as long as the steel composition has a B content of 0.006% to 0.023%, but is described below. The composition shown is preferable. In the following description, the "%" indication of the content of each element means "mass%".
[0027]
B: 0.006% -0.023%
B is effective for obtaining a martensite structure, and finely disperses carbides at the former austenite boundary and the martensite lath boundary during use at high temperature, suppresses the recovery of the structure, and greatly contributes to the improvement of creep strength. .. It is also an effective element for reducing the decrease in creep strength of the weld heat affected zone. In order to obtain the effect, it is contained in an amount of 0.006% or more. However, if it is contained in an excessive amount, it flows into the weld metal during welding, increasing the susceptibility to solidification and cracking and causing a decrease in toughness. Therefore, the upper limit is 0.023%. The preferred lower limit of the B content is 0.007%, the preferred upper limit is 0.018%, the more preferred lower limit is 0.008%, and the further preferred upper limit is 0.015%.
[0028]
C: 0.04% to 0.15%
C is effective for obtaining a martensite structure and also produces fine carbides when used at a high temperature, which contributes to ensuring creep strength. In order to obtain the sufficient effect, it may be contained in an amount of 0.04% or more. However, if it is contained in excess of 0.15%, the effect of improving creep strength is saturated, so the content is set to 0.15% or less. The preferred lower limit of the C content is 0.05%, and the preferred upper limit is 0.13%. A more preferable lower limit is 0.07%, and a further preferable upper limit is 0.11%.
[0029]
Si: 0.05% to 0.80%
Si is contained as a deoxidizing agent, but is an element effective for water vapor oxidation resistance. In order to obtain the effect, it is contained in an amount of 0.05% or more. However, if it is contained in excess, it causes a decrease in creep ductility and ductility. Therefore, the Si content is set to 0.80% or less. The preferred lower limit of the Si content is 0.10%, and the preferred upper limit is 0.60%. A more preferable lower limit is 0.20%, and a further preferable upper limit is 0.50%.
[0030]
Mn: 0.10% to 1.00%
Mn is an element that is contained as a deoxidizing agent like Si, but is also effective in obtaining a martensite structure. In order to obtain the effect, it is contained in an amount of 0.10% or more. However, if Mn is excessively contained, creep embrittlement is caused, so the Mn content is set to 1.00% or less. The preferred lower limit of the Mn content is 0.20%, and the preferred upper limit is 0.80%. A more preferable lower limit is 0.30%, and a further preferable upper limit is 0.70%.
[0031]
P: 0% to 0.020%
P is contained as an impurity, and if it is contained in excess, creep ductility is lowered. Therefore, the content of P is 0.020% or less. The content of P is preferably 0.018% or less, and more preferably 0.016% or less. The lower the content of P, the better, that is, the content may be 0%, but the extreme reduction significantly increases the material cost. Therefore, the preferable lower limit of the P content is 0.0005%, and the more preferable lower limit is 0.001%.
[0032]
S: 0% to 0.010%
Like P, S is contained as an impurity, and if it is contained in excess, creep ductility is lowered. Therefore, the content of S is 0.010% or less. The S content is preferably 0.008% or less, more preferably 0.005% or less. The lower the content of S, the better, that is, the content may be 0%, but the extreme reduction significantly increases the manufacturing cost. Therefore, the desirable lower limit of the S content is 0.0002%.
[0033]
Cr: 8.0% to 10.0%
Cr is an element effective for ensuring water vapor oxidation resistance and corrosion resistance 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 sufficiently, it is sufficient to contain Cr of 8.0% or more. However, if it is excessively contained, the stability of the carbide is lowered and the creep strength is lowered. Therefore, the Cr content is set to 10.0% or less. The preferred lower limit of the Cr content is 8.3%, and the preferred upper limit is 9.8%. A more preferable lower limit is 8.5%, and a further preferable upper limit is 9.5%.
[0034]
Total of at least one of Mo and W: 0.5% -4.0%
Both Mo and W are elements that dissolve in the matrix or precipitate as intermetallic compounds during long-term use and contribute to ensuring creep strength at high temperatures. In order to obtain this effect, at least one kind may be contained in a total of 0.5% or more. However, if it is contained in excess of 4.0%, the effect of improving creep strength is saturated and the material cost is increased because it is a very expensive element. Therefore, it should be 4.0% or less. The preferred lower limit is 0.8% and the preferred upper limit is 3.8%. A more preferable lower limit is 1.0%, and a further preferable upper limit is 3.5%.
[0035]
Total of at least one of Nb and Ta: 0.02% to 0.30%
Nb and Ta precipitate in the grains as fine carbonitrides during use at high temperatures, contributing to the improvement of creep strength. In order to obtain the effect, at least one kind may be contained in a total of 0.02% or more. However, if the content is excessive, a large amount and coarse precipitation will occur, resulting in a decrease in creep strength and creep ductility. Therefore, the upper limit is 0.30%. The preferred lower limit of the content is 0.04% and the preferred upper limit is 0.25%. A more preferable lower limit is 0.06%, and a further preferable upper limit is 0.20%.
[0036]
V: 0.05% to 0.40%
Like Nb and Ta, V precipitates in the grains as fine carbonitrides during use at high temperatures, and contributes to the improvement of creep strength. In order to obtain the effect, it is contained in an amount of 0.05% or more. However, if the content is excessive, a large amount and coarse precipitation will occur, resulting in a decrease in creep strength and creep ductility. Therefore, the upper limit of the V content is 0.40%. The preferred lower limit is 0.10% and the preferred upper limit is 0.35%. A more preferable lower limit is 0.15%, and a further preferable upper limit is 0.25%.
[0037]
N: 0.002% -0.025%
N finely precipitates in the grains as fine nitrides during use at high temperatures, and contributes to the improvement of creep strength. In order to obtain this effect, it is contained in an amount of 0.002% or more. However, if it is contained in an excessive amount, the nitride will be coarsened and the creep ductility will be lowered. Therefore, the N content is limited to 0.025%. The preferred lower limit is 0.004% and the preferred upper limit is 0.020%. A more preferable lower limit is 0.006%, and a further preferable upper limit is 0.015%.
[0038]
Al: 0% to 0.030%
Al is contained as a deoxidizing agent, but if it is contained in a large amount, the cleanliness is significantly impaired and the processability is deteriorated. It is also not preferable from the viewpoint of creep strength. Therefore, the Al content is 0.030% or less. It is preferably 0.025% or less, more preferably 0.020% or less. The lower limit does not need to be set in particular, that is, the content may be 0%, but the extreme reduction increases the manufacturing cost. Therefore, it may be more than 0%, preferably 0.001% or more. Al here means Sol. Refers to Al (solid solution Al).
[0039]
O: 0% to 0.020%
O exists as an impurity, but when it is contained in a large amount, it lowers workability. Therefore, the content of O is 0.020% or less. It is preferably 0.018% or less, more preferably 0.015% or less. The lower limit does not need to be set in particular, that is, the content may be 0%, but the extreme reduction increases the manufacturing cost. Therefore, it may be more than 0%, preferably 0.001% or more.
[0040]
Further, the base material for ferritic heat-resistant steel used in the present disclosure is at least one element belonging to at least one group from the following groups 1 to 3 below, instead of a part of Fe contained in the base material. May be contained. The reason for the limitation is described below.
[0041]
Group 1 Co: 4.0% or less, Ni: 1.00% or less, Cu: 1.0% or less
Co: 4.0% or less (0% to 4.0%)
The content of Co may be 0%, or it may be contained because it is an element effective for obtaining a martensite structure and improving creep strength. However, if added in excess, creep strength and creep ductility will rather decrease. In addition, since it is a very expensive element, it increases the material cost. Therefore, the Co content is set to 4.0% or less. The preferred upper limit is 3.8%, and the more preferred upper limit is 3.5%. When it is contained, the preferable lower limit is 0.05%, and the more preferable lower limit is 0.1%.
[0042]
Ni: 1.00% or less (0% to 1.00%)
Ni may have a content of 0%, and like Co, it may be contained as needed because it is effective for obtaining a martensite structure. However, the above Co content range In the surroundings, even if it is contained in excess of 1.00%, its effect is saturated and it is an expensive element, so the upper limit is 1.00%. The preferred upper limit is 0.80%, more preferably 0.60% or less. When it is contained, the preferable lower limit is 0.05%, and the more preferable lower limit is 0.10%.
[0043]
Cu: 1.0% or less (0% to 1.0%)
Cu may have a content of 0%, and like Co and Ni, it may be contained as necessary because it is effective in forming a martensite structure. However, if the content exceeds 1.0%, the creep ductility is lowered, so the content is set to 1.0% or less. The preferred upper limit is 0.8%, more preferably 0.6% or less. When it is contained, the preferable lower limit is 0.05%, and the more preferable lower limit is 0.1%.
[0044]
Group 2 Ti: 0.30% or less (0% to 0.30%)
The content of Ti may be 0%, and like Nb, V and Ta, it precipitates in the grains as fine carbonitrides during use at high temperatures, which contributes to the improvement of creep strength, and therefore, if necessary. May be contained. However, if the content is excessive, a large amount and coarse precipitation will occur, resulting in a decrease in creep strength and creep ductility. Therefore, the upper limit is 0.30%. More preferably, it is 0.20% or less. The preferable lower limit of the content is 0.02%, and the more preferable lower limit is 0.04%.
[0045]
Group 3 Ca: 0.050% or less, Mg: 0.050% or less, REM: 0.100% or less
Ca: 0.050% or less (0% to 0.050%)
Ca may have a content of 0% or may be added as needed because it has an effect of improving hot workability during production. However, excessive addition combines with oxygen, significantly lowers cleanliness, and conversely deteriorates hot workability, so the content is set to 0.050% or less. It is preferably 0.030% or less, more preferably 0.020% or less. The preferred lower limit for inclusion is 0.0005%. A more preferable lower limit is 0.001%.
[0046]
Mg: 0.050% or less (0% to 0.050%)
Mg may have a content of 0%, and like Ca, it may be added as needed because it has an effect of improving hot workability during production. However, excessive addition combines with oxygen, significantly lowers cleanliness, and conversely deteriorates hot workability, so the content is set to 0.050% or less. It is preferably 0.030% or less, more preferably 0.020% or less. The preferred lower limit for inclusion is 0.0005%. A more preferable lower limit is 0.001%.
[0047]
REM: 0.100% or less (0% to 0.100%)
The content of REM may be 0%, and like Ca and Mg, it has an effect of improving hot workability during production, and therefore may be added as necessary. However, excessive addition combines with oxygen, significantly lowers the cleanliness, and conversely deteriorates the hot workability, so the content is set to 0.100% or less. It is preferably 0.080% or less, more preferably 0.060% or less. The preferred lower limit for inclusion is 0.010%. A more preferable lower limit is 0.020%.
[0048]
"REM" is a general term for a total of 17 elements of Sc, Y and lanthanoids, and the content of REM refers to the total content of one or more elements of REM. REM is generally contained in mischmetal. Therefore, for example, it may be added in the form of misch metal so that the amount of REM is within the above range.
[0049]
The chemical composition of the welding material for Ni-based heat-resistant alloys used in the present disclosure is not particularly limited, but is preferably the composition shown below. In the following description, the "%" indication of the content of each element means "mass%".
[0050]
C: 0.005% to 0.180%
C is an austenite-forming element and is an effective element 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 contained in an amount of 0.005% or more. However, if it is contained in an excessive amount, it precipitates in a large amount as a carbide and reduces creep ductility or corrosion resistance at high temperature. Therefore, the content of C is set to 0.180% or less. The preferred lower limit is 0.008% and the preferred upper limit is 0.150%. A more preferable lower limit is 0.010%, and a further preferable upper limit is 0.120%.
[0051]
Si: 0.02% -1.20%
Si is added as a deoxidizing agent, but is an element effective for the steam oxidation resistance of weld metals. In order to obtain the effect, it is contained in an amount of 0.02% or more. However, if it is excessively contained, the Si content is limited to 1.20% because the susceptibility to solidification and cracking of the weld metal is increased. The preferred lower limit is 0.05% and the preferred upper limit is 1.00%. A more preferable lower limit is 0.1%, and a further preferable upper limit is 0.80%.
[0052]
Mn: 0.02% to 4.00%
Mn, like Si, is added as a deoxidizing agent, 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 contained in an amount of 0.02% or more. However, if it is contained in an excessive amount, it causes embrittlement, so the content of Mn is set to 4.00% or less. The preferred lower limit is 0.05% and the preferred upper limit is 3.50%. A more preferable lower limit is 0.08%, and a further preferable upper limit is 3.00%.
[0053]
P: 0% to 0.020%
P is contained as an impurity, which increases the susceptibility to solidification cracking during solidification of the weld metal and causes a decrease in creep ductility. Therefore, the content of P is 0.020% or less. The content of P is preferably 0.018% or less, and more preferably 0.016% or less. The lower the content of P, the better, that is, the content may be 0%, but the extreme reduction significantly increases the material cost. Therefore, the preferable lower limit of the P content is 0.0005%, and the more preferable lower limit is 0.001%.
[0054]
S: 0% to 0.010%
Like P, S 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 content of S is 0.010% or less. The S content is preferably 0.008% or less, and more preferably 0.005% or less. The lower the content of S, the better, that is, the content may be 0%, but the extreme reduction significantly increases the manufacturing cost. Therefore, the preferable lower limit of the S content is 0.0001%, and the more preferable lower limit is 0.0002%.
[0055]
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 effective element for stabilizing the structure of the weld metal at high temperature and improving the creep strength. However, if added in excess, creep strength and creep ductility will rather decrease. In addition, since it is a very expensive element, it increases the material cost. Therefore, the upper limit is set to 15.0%. The preferred upper limit is 14.5%, and the more preferred upper limit is 14.0%. The content may be 0%, but may be more than 0%, and the preferable lower limit for the content is 0.02%, and the more preferable lower limit is 0.05%.
[0056]
Cu: 0% to 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 effective element for stabilizing the structure of the weld metal at high temperature and improving the creep strength. However, if it is added in excess, the creep ductility is rather lowered. Therefore, the upper limit is set to 0.80%. The preferred upper limit is 0.60%, and the more preferred upper limit is 0.50%. The content may be 0%, but may be more than 0%, and the preferable lower limit for the content is 0.02%, and the more preferable lower limit is 0.05%.
[0057]
Cr: 16.0% to 25.0%
Cr is an element effective for steam oxidation resistance and corrosion resistance of weld metal at high temperature. 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, the content is 16.0% or more. However, if it is excessively contained, the tissue stability at high temperature is lowered and the creep strength is lowered. Therefore, the Cr content is set to 25.0% or less. The preferred lower limit of the Cr content is 16.5%, and the preferred upper limit is 24.5%. A more preferable lower limit is 17.0%, and a further preferable upper limit is 24.0%.
[0058]
Mo: 0% -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 high temperatures. However, excessive content reduces tissue stability at high temperatures and rather reduces creep strength. Therefore, it should be 12.0% or less. The preferred upper limit is 11.5%, and the more preferred upper limit is 11.0%. The content may be 0%, but may be more than 0%, and the preferable lower limit for the content is 0.02%, and the more preferable lower limit is 0.05%.
[0059]
Total of at least one of Nb and Ta: 0% to 4.50%
Nb and Ta may be contained because they precipitate 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, it precipitates in a large amount and coarsely, which in turn causes a decrease in creep strength and creep ductility. Therefore, the upper limit is 4.50%. The preferred upper limit is 4.20%, and the more preferred upper limit is 4.00%. The content may be 0%, but may be more than 0%, and the preferable lower limit for the content is 0.02%, and the more preferable lower limit is 0.05%.
[0060]
Ti: 0% to 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 and contributes to the improvement of the creep strength of the weld metal. It may be contained. However, if the content is excessive, it precipitates in a large amount and coarsely, which in turn causes a decrease in creep strength and creep ductility. Therefore, the upper limit is 1.00%. The preferred upper limit is 0.90%, and the more preferable upper limit is 0.80%. The content may be 0%, but may be more than 0%, and the preferable lower limit for the content is 0.02%, and the more preferable lower limit is 0.05%.
[0061]
Fe: 0% to 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 an excessive amount, the coefficient of thermal expansion of the alloy becomes large and the steam oxidation resistance deteriorates. Its content is limited to 6.00%. It is preferably 5.50% or less, more preferably 5.00% or less. The content may be 0%, but may be more than 0%, and the preferable lower limit for the content is 0.01%, and the more preferable lower limit is 0.02%.
[0062]
N: 0% to 0.050%
N is an element effective for enhancing the weld metal structure stability at high temperatures, but if it is contained in an excessive amount, it causes precipitation of a large amount of nitride during use at high temperatures and reduces toughness and ductility. , 0.050% or less. The content of N is preferably 0.030% or less, and more preferably 0.010% or less. The lower limit of the N content is not particularly provided, that is, the content may be 0%, but may be more than 0%, the preferable lower limit is 0.0005%, and the more preferable lower limit is 0.001%.
[0063]
Al: 0.002% to 1.800%
Al binds to Ni and finely precipitates in the grain as an intermetallic compound, which contributes to improving the creep strength of the weld metal. In order to obtain this effect, it is contained in an amount of 0.002% or more. On the other hand, if it is contained in an excessive amount, it causes an excessive precipitation of the intermetallic compound phase and lowers the toughness. Therefore, the Al content is 1.800% or less. The preferred lower limit of Al content is It is 0.005% and the desired upper limit is 1.600%. A more preferable lower limit is 0.010%, and a further preferable upper limit is 1.500%.
[0064]
O: 0% to 0.020%
O is contained as an impurity, but if it is contained in a large amount, it reduces the ductility of the weld metal. Therefore, the upper limit is 0.020%. The content of O is preferably 0.015% or less, and more preferably 0.010% or less. The content of O is preferably reduced as much as possible, that is, the content may be 0%, but since an extreme reduction leads to an increase in material cost, it may be more than 0%, and the preferable lower limit is 0. It is 0005%. A more preferable lower limit is 0.001%.
[0065]
When the method for manufacturing a ferritic heat-resistant steel welded joint according to the present disclosure is carried out, for example, a ferrite-based heat-resistant steel base material having the above-mentioned chemical composition and a welding material for a Ni-based heat-resistant alloy are used, and the groove shape of the base material is used. Welding conditions such as gap, welding method, supply speed of welding material, welding heat input, shield gas type, etc. are adjusted to perform first layer welding. Next, the area [SBM] of the molten base metal and the area [SWM] of the weld metal in the cross section of the welded portion after the first layer welding are measured by image processing, and the ratio [SBM] / [SWM]. To find the welding conditions satisfying the equation (1).
Perform the first layer welding under the welding conditions satisfying the formula (1), and then perform the welding of the second and subsequent layers to perform multi-layer welding.
[0066]
・ Usage
The welded structure having the ferritic heat-resistant steel welded joint manufactured by the method for manufacturing the ferritic heat-resistant steel welded joint according to the present disclosure is used for equipment used at high temperature 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 in petrochemical plants; etc.
Here, the "use at high temperature" in the present disclosure includes, for example, an embodiment of use in an environment of 350 ° C. or higher and 700 ° C. or lower (further, 400 ° C. or higher and 650 ° C. or lower).
Example
[0067]
Hereinafter, the method for manufacturing the ferritic heat-resistant steel welded joint according to the present disclosure will be described more specifically by way of examples, but the method for manufacturing the ferritic heat-resistant steel welded joint according to the present disclosure is limited to these examples. is not it.
[0068]
The ingots in which the materials A to H having the chemical compositions shown in Table 1 are melted and cast in a laboratory are heat-treated by hot forging, hot rolling, molding, quenching, and tempering, and then the plate. It was processed into a plate material having a thickness of 12 mm, a width of 50 mm, and a length of 200 mm, and manufactured for a welding base material.
[0069]
[table 1]

[0070]
After processing the U groove in FIG. 2 in the longitudinal direction of the above welding base plate, butt welding is performed for a Ni-based heat-resistant alloy having an outer diameter of 1.2 mm and having the chemical composition shown in Table 2. The first layer was welded using the material by automatic gas tungsten arc welding with Ar as the shield gas. During welding, the heat input was varied from 6 to 10 kJ / cm and the supply rate of the welding material was varied from 2.5 to 7.5 mm / s.
After performing a penetrant inspection test on the weld metal surface of the obtained welded joint and confirming the presence or absence of cracks, the cross section of the weld was revealed by the above method, and melted in the cross section of the weld after the first layer weld. The area of ​​the base metal [SBM] and the area of ​​the weld metal [SWM] were measured by image processing, the ratio [SBM] / [SWM] was obtained, and the relationship with the crack of the first layer weld metal was evaluated. .. Furthermore, the presence or absence of back wave formation was visually observed. Then, the welded joint in which there was no instruction pattern of cracking and the back wave was formed in the penetrant inspection test was regarded as "pass".
[0071]
[Table 2]

[0072]
In addition, some of the accepted welded joint codes were laminated and welded by automatic gas tungsten arc welding with a heat input of 12 kJ / cm and a welding material supply speed of 5.5 mm / s.
From the obtained welded joint, a round bar creep test piece having a weld metal in the center of the parallel portion was collected. 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". The results are shown in Table 3, Table 4, and Table 5. A "-" in the creep rupture test of a welded joint means that the creep rupture test was not performed.
[0073]
[Table 3]

[0074]
[Table 4]

[0075]
[Table 5]

[0076]
Table 3, Table 4, and Table 5 also show the results of each of the above tests.
From Tables 3, 4, and 5, welded joint codes that satisfy the conditions specified in the present disclosure do not cause weld metal cracks or back wave formation during initial layer welding, and the welded joint also has high creep strength. It turns out that it can be obtained.
On the other hand, welded joint substitutes A-1, A-11, A-16, A-21, D-1 to D-4, D-6 to D-7, D-11 to D-15, and Since G-1 to G-3 exceed the upper limit determined by the relational expression (formula (1)) of the ratio between the area of ​​the molten base metal [SBM] and the area of ​​the weld metal [SWM], they are used as the weld metal. A crack has occurred. In A-10, D-10, and G-5, the ratio of the area of ​​the molten base metal [SBM] to the area of ​​the weld metal [SWM] was less than 0.1, so that back wave non-formation occurred. bottom.
Further, since the B content of the base metal of the welded joints E-1 to E-10 exceeds the range of the present disclosure, it is not possible to suppress the cracking of the weld metal and form the back wave at the same time.
Although the weld metal cracks can be stably suppressed in the welded joint substitutes F-1 to F-5, the B content of the base metal is below the range of the present disclosure, so that high creep strength of the welded joint cannot be obtained. ..
[0077]
It can be seen that a sound welded joint can be obtained only when the requirements of the present disclosure are satisfied.
Industrial applicability
[0078]
According to the present disclosure, it is possible to provide a manufacturing method that stably suppresses solidification cracking when a ferrite heat-resistant steel base material containing a large amount of B is multi-layer welded using a welding material for a Ni-based heat-resistant alloy. can.
Code description
[0079]
2A, 2B base material
4 Weld metal (first layer weld metal)
The scope of the claims
[Claim 1]
It has a multi-layer welding process in which a ferritic heat-resistant steel base material containing 0.006% by mass to 0.023% by mass of B is multi-layer welded with a welding material for Ni-based heat-resistant alloys.
The area [SBM] of the molten ferrite heat-resistant steel base material and the area [SWM] of the weld metal in the cross section of the welded portion after the first layer welding and before the second layer welding in the multilayer welding step. A method for manufacturing a ferrite heat-resistant steel welded joint in which the first layer is welded under the welding conditions satisfying the following formula (1) with respect to the mass% [% B BM] of B contained in the ferrite heat-resistant steel base material. ..
0.1 ≤ [S BM] / [S WM] ≤ -50 x [% B BM] +1.3 ... (1)
[Claim 2]
The ferrite-based heat-resistant steel base material is by mass%,
C: 0.04% to 0.15%,
Si: 0.05% to 0.80%,
Mn: 0.10% to 1.00%,
P: 0% to 0.020%,
S: 0% to 0.010%,
Cr: 8.0% to 10.0%,
Total of at least one of Mo and W: 0.5% -4.0%,
Total of at least one of Nb and Ta: 0.02% to 0.30%,
V: 0.05% to 0.40%,
B: 0.006% -0.023%
N: 0.002% to 0.025%,
Al: 0% to 0.030%, and
The method for producing a ferritic heat-resistant steel welded joint according to claim 1, wherein O: contains 0% to 0.020% and the balance is Fe and impurities.
[Claim 3]
The method for manufacturing a ferrite heat-resistant steel welded joint according to claim 2, wherein the ferrite-based heat-resistant steel base material contains at least one element selected from the following group in mass% instead of a part of the Fe. ..
Group Co: 4.0% or less,
Ni: 1.00% or less,
Cu: 1.0% or less,
Ti: 0.30% or less,
Ca: 0.050% or less,
Mg: 0.050% or less,
REM: 0.100% or less
[Claim 4]
The welding material for Ni-based heat-resistant alloy is by mass%,
C: 0.005% to 0.180%,
Si: 0.02% to 1.20%,
Mn: 0.02% to 4.00%,
P: 0% to 0.020%,
S: 0% to 0.010%,
Co: 0% to 15.0%,
Cu: 0% to 0.80%,
Cr: 16.0% to 25.0%,
Mo: 0% -12.0%,
Total of at least one of Nb and Ta: 0% to 4.50%,
Ti: 0% to 1.00%,
Fe: 0% to 6.00%,
N: 0% to 0.050%,
Al: 0.002% to 1.800%, and
The method for producing a ferritic heat-resistant steel welded joint according to any one of claims 1 to 3, wherein O: contains 0% to 0.020% and the balance is Ni and impurities.