JP4465066B2 - Welding materials for ferrite and austenitic duplex stainless steels - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a welding material used for welding ferritic / austenitic duplex stainless steel used as a material for water tanks, water heaters and other water environments, or oil wells and seawater structures, and the welding material. The present invention relates to an apparatus or a structure excellent in corrosion resistance that has been welded.
[0002]
[Prior art]
Ferritic / austenitic duplex stainless steels are widely put into practical use as SUS329 series because they complement the respective defects of the ferrite phase and austenitic phase and are particularly excellent in corrosion resistance. For example, according to Japanese Patent Laid-Open No. 56-142855, a duplex stainless steel excellent in hot workability and local corrosion resistance has been proposed, and many other duplex stainless steels excellent in various properties have been proposed. Proposals have been made.
[0003]
The characteristics of duplex stainless steels are as follows: (1) Resistance to stress corrosion cracking (2) High strength (3) Excellent corrosion resistance with a large amount of Cr and Mo (4) Low Ni but resource saving etc. The duplex stainless steel has a drawback that hot workability and weldability are inferior to those of ferritic stainless steel and austenitic stainless steel. As a welding material when welding duplex stainless steel, it is common to use a co-metal material of the same component as the base material, but in this case the amount of precipitation of the austenite phase in the weld becomes insufficient. In addition, since the phase balance is lost, the corrosion resistance of the welded portion is deteriorated as compared with the base material.
[0004]
As a measure for preventing the corrosion resistance deterioration in the welded portion, improvement is made by improvement and development of the welding material. For example, in Japanese Patent Laid-Open No. 3-204196, duplex stainless steel welding having excellent resistance to concentrated sulfuric acid corrosion is performed. Wires have been proposed. However, there is no mention of corrosion resistance in an environment containing Cl ions, such as a water receiving tank, a water heater and a seawater structure in which duplex stainless steel is widely used. JP-A-8-260101 proposes to improve toughness and corrosion resistance during multilayer welding in duplex stainless steel for thick plates.
[0005]
According to Japanese Patent Laid-Open No. 8-260101, the toughness and corrosion resistance in the weld zone are certainly improved, but the N content is as high as 0.24 to 0.35%, so that it is extremely difficult to process the wire. There's a problem. Moreover, since it is intended for super duplex stainless steel, it contains W and is expensive. It is not necessary to contain expensive W in the welding of thin plate products such as a water receiving tank and a hot water tank which are the subject of the present invention.
[0006]
Improving the corrosion resistance of welds, particularly pitting corrosion resistance, which is a local corrosion form in an environment containing Cl ions, improves the structural stability and reliability of the structure, and can be used in more severe conditions. There is the strongest demand to endure. A measure to solve the defect of deterioration of pitting corrosion resistance of welds is to optimize the ratio of ferrite phase to austenite phase, and this proposal has solved this problem by carrying out precise component design. It is.
[0007]
[Problems to be solved by the invention]
The object of the present invention is to optimize the alloy elements in the welding material so that the ratio of ferrite phase to austenite phase in the weld metal is approximately 1: 1, and the component composition distribution during solidification is uniform. An object of the present invention is to provide a welded material for ferrite / austenite duplex stainless steel having excellent corrosion resistance even in the welded portion, and to provide a welded structure device and structure having excellent corrosion resistance.
[0008]
A first aspect of the invention is a welding material for ferrite-austenite duplex stainless steel having the following component composition (wt%).
C: 0.05% or less, Si: 0.05-2.0%,
Mn: 2.0% or less, P: 0.03% or less,
S: 0.03% or less, Ni: 5-12%,
Cr: 22-28%, Mo: 3.0-5.0%,
Cu: 0.2% or less, N: 0.10 to 0.22%,
Co: 0 to 3% or less, B: 0.0005 to 0.01%,
Al: 0.07% or less, O: 0.01% or less,
And the balance consists of Fe and inevitable impurities.
[0009]
A second aspect of the invention is (a) a welding material for ferrite-austenite duplex stainless steel having the following component composition (wt%) , wherein C: 0.05% or less, Si: 0.05 to 2.0%, Mn: 2.0% or less, P: 0.03% or less, S: 0.03% or less, Ni: 5-12%, Cr: 22-28%, Mo: 3.0-5 0.0%, Cu: 0.01 to 0.2 %, N: 0.10 to 0.22%, Co: 0.1 to 3 %, B: 0.0005 to 0.01%, Al: 0.0. 07% or less, O: 0.01% or less, and the balance Fe and unavoidable impurities was the Ph value shown in (b) below SL (1) from 0.25 to 0.60 are shown in the following equation (2) γcal is 80 or less, the PRE value shown in the following formula (3) satisfies 35 or more, and is a wire used for TIG method or MIG method . Ph = {Ni + 0.5Mn + 0.1Co + 30 (C + N) -0.4 (Cr + 1.5Si + Mo) +5.6} / {Cr + 1.5Si + Mo-6} (1) γcal = 151.9 × C-6.15 × Si− 2.8 × Mn + 6.5 × (Ni + Co) −5.7 × Cr−3.8 × Mo + 209.3 × N + 129.8 (2) PRE = Cr + 3.3Mo + 20N (3)
[0010]
A third aspect of the invention is an apparatus or a structure in which ferrite-austenitic duplex stainless steel is welded by the TIG method or the MIG method using the welding material.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Below, the effect of each component of the welding material of this invention and the reason for limitation of content are demonstrated. The component composition is wt%.
C: An austenite-forming element that contributes to the strengthening and pitting corrosion resistance of welding materials. However, if it exceeds 0.05%, the hot workability and toughness deteriorate, so the upper limit is 0.05%. Stipulate.
[0012]
Si: Used as a deoxidizer during refining. However, when it exceeds 2.0%, the hot workability deteriorates, and further, the upper limit is set to 2.0% in order to reduce the toughness of the weld metal. Moreover, since the surface tension of a molten metal falls that it is less than 0.05% and a favorable bead shape cannot be obtained, a minimum is made into 0.05%.
[0013]
Like Mn: Si, it is used as a deoxidizer during refining. The addition of Mn is effective for improving the hot workability by forming sulfides, but if it exceeds 2.0%, the oxidation resistance is deteriorated, so the upper limit is defined as 2.0%.
[0014]
P: It is desirable to have less than the aspects of weldability and hot workability, but it is an element inevitably mixed in, and the upper limit is set to 0.03% from the viewpoint of manufacturing technology and economy.
S: An element that is inevitably mixed, and if it exceeds 0.03%, it segregates at the grain boundary and decreases hot workability, so the upper limit is made 0.03%.
[0015]
Ni: an austenite generating element and a basic element for adjusting the phase ratio of the weld metal. Furthermore, it is also an extremely effective element for improving toughness and corrosion resistance. In order to acquire the said effect, content of 5% or more is required. On the other hand, if the content exceeds 12%, the balance between the ferrite phase and the austenite phase is lost, and this is disadvantageous economically, so the upper limit needs to be 12%.
[0016]
Cr: A ferrite-forming element and an element effective for improving pitting corrosion resistance. When the content is 22.0% or less, the above effects cannot be sufficiently obtained. When the content exceeds 28.0%, a ferrite single phase is likely to be formed at a high temperature range, and further, the precipitation of σ phase is promoted, and toughness and In order to deteriorate the corrosion resistance, the upper limit needs to be 28.0%.
[0017]
Mo: Like Cr, it is an effective element for improving pitting corrosion resistance. In order to improve the pitting corrosion resistance of the weld metal, it is necessary to contain at least 3.0%. However, if it exceeds 5.0%, precipitation of the σ phase is promoted and toughness and corrosion resistance are deteriorated, so the upper limit needs to be 5.0%.
[0018]
Cu: An austenite-forming element and an element effective for improving corrosion resistance and weather resistance. However, since a large amount of addition deteriorates hot workability, the upper limit was made 0.2%.
[0019]
N: It is a strong austenite forming element and is also an extremely effective element for improving toughness and pitting corrosion resistance. In order to precipitate an appropriate amount of austenite on the weld metal, it is necessary to contain at least 0.10%. However, if the content exceeds 0.22%, hot workability is hindered and blowholes are likely to be generated in the weld metal, so the upper limit is made 0.22%.
[0020]
Co: An element that promotes precipitation of austenite in a high temperature range, and is desirably contained in order to precipitate an appropriate amount of austenite in the weld metal. However, if it exceeds 3%, nitride is liable to precipitate, and the corrosion resistance and toughness are deteriorated.
[0021]
B: It is an extremely effective element for suppressing grain boundary segregation of S and improving hot workability. When the content is 0.0005% or less, the above effect is small. When the content exceeds 0.01%, a large amount of brittle compounds are formed and embrittlement occurs. Therefore, the content is limited to 0.0005 to 0.01%.
[0022]
Al: Al is a powerful deoxidizing element at the time of refining, and is an effective element for increasing the cleanliness of steel. However, if it exceeds 0.07%, the penetration property at the time of welding deteriorates, so the upper limit is 0. .07% is specified.
O: O is an element that hinders hot workability. If it exceeds 0.01% (100 ppm), wire processing becomes difficult, but it is inevitably an incorporated element and is acceptable up to 0.01%.
[0023]
The above component composition is already a component composition of ferrite-austenite duplex stainless steel and can be used as a welding material. However, it is more desirable that the above component composition satisfies the following parameters. That is, the reason why the Ph value (value indicating phase balance), γcal value (workability index) and PRE value (pitting corrosion resistance index) are specified will be described.
[0024]
Here, the Ph value, the γcal value, and the PRE value are calculated by the following equations, respectively.
Ph = {Ni + 0.5Mn + 0.1Co + 30 (C + N) −0.4 (Cr + 1.5Si + Mo) +5.6} / {Cr + 1.5Si + Mo−6} (1)
γcal = 151.9 × C−6.15 × Si−2.8 × Mn + 6.5 × (Ni + Co) −5.7 × Cr−3.8 × Mo + 209.3 × N + 129.8 (2)
PRE = Cr + 3.3Mo + 20N (3)
[0025]
In order to ensure the corrosion resistance and strength characteristics of the weld metal, it is necessary to optimize the phase ratio of the ferrite phase and the austenite phase. That is, in a weld metal part, since there exists a tendency for a ferrite phase to increase from a base material, you have to add an austenite production | generation element positively.
[0026]
If the Ph value is less than 0.25, an austenite phase sufficient to ensure corrosion resistance and strength characteristics is not generated. On the other hand, if it exceeds 0.60, the ferrite phase in the weld metal part is conversely reduced. Cr and Mo are excessively dissolved in the phase and the precipitation of the σ phase is promoted, and the corrosion resistance and toughness are extremely deteriorated. Therefore, it is desirable to adjust the Ph value to 0.25 to 0.60.
[0027]
On the other hand, it is necessary to consider the workability to the wire for manufacturing the welding rod. If the γcal value exceeds 80, the hot workability is remarkably deteriorated, the wire processing becomes difficult, and the production yield is also remarkably deteriorated. Therefore, the γcal value is desirably 80 or less.
Furthermore, a pitting corrosion resistance index PRE, which is an index for judging whether or not pitting corrosion resistance is good, is generally proposed, and it is desirable to set PRE to 35 or more in order to show sufficient pitting corrosion resistance in the environment.
[0028]
In order to ensure only the corrosion resistance and strength characteristics of the welded portion, it is desirable to adjust the Ph value to 0.25 to 0.60. In addition, when the welding rod is processed into a wire, γcal is desirably 80 or less. Furthermore, in order to indicate that sufficient pitting corrosion resistance is required in the use environment, it is desirable to set PRE to 35 or more.
[0029]
When welding a ferrite-austenite duplex stainless steel with the welding material of the present invention, it is necessary to avoid fluctuations in components of the welding material, such as Al, Si, Cr, and the like, which are easily oxidized. Therefore, the TIG method or the MIG method is desirable. This is because all of these welding methods are gas shield welding methods, and fluctuations in the components that are easily oxidized can be avoided. Then, the apparatus or structure welded with the said welding method is excellent in corrosion resistance. In some cases, a plasma welding method or an electron beam welding method having a sealing property against atmospheric gas can be applied.
[0030]
【Example】
Test steels having various chemical components shown in Table 1 in FIG. 1 were melted and then ingot-formed, and a plate having a thickness of 12 mm was prepared by forging. At this time, the presence or absence of forging cracks was visually examined to evaluate hot workability. Thereafter, solution heat treatment at 1050 ° C. and cold rolling were repeated to form a wire having a diameter of 2 mm, which was used as a welding material.
[0031]
As the base material, SUS329J4L equivalent duplex stainless steel (plate thickness 1.5mm) according to JIS standard is used, and the welded joint shown in Fig. 2 is created by butt TIG welding while adding welding material as appropriate. Corrosion resistance was evaluated by tissue and pitting corrosion tests. A photomicrograph of the weld is shown in FIG. This photograph is an observation of the structure of the weld after etching with a solution of oxalic acid and KOH. Further, the ratio of the ferrite phase was quantified by a point calculation method using a 20 × 20 lattice with a 400 × microscope. The pitting corrosion test was performed according to JIS G 0577. However, the test temperature was 70 ° C. The results are shown in Table 4 as Table 2.
[0032]
Welding material Nos. Satisfying all the component ranges defined in the present invention. Nos. 1 to 5 are excellent in hot workability and easy to be processed into a wire, and the phase ratio of the welded portion is approximately ferrite phase: austenite phase = 1: 1, and is excellent in pitting corrosion resistance. On the other hand, No. which is a comparative example. Since 6 to 10 have items that do not satisfy the scope of the present invention (indicated by the underline in the table), hot workability or corrosion resistance deteriorates. No. In No. 6, since the Ph value is smaller than the range of the present invention, the austenite phase precipitation in the weld metal is not sufficient, and the corrosion resistance deteriorates.
[0033]
No. In No. 7, cracks occurred during hot forging because the γcal value was larger than the range of the present invention. No. No. 8 has a PRE of less than 35, so it is clearly inferior in corrosion resistance compared to the base material. No. In No. 9, since the amount of Mo was high and the σ phase was generated, In No. 10, cracking during hot forging occurred because the amount of B effective for improving hot workability was small.
2 is an optical microscope structure of the welded portion. Three materials, ferrite phase: austenite phase is approximately 1: 1, while (b) is No. It is not desirable because it is a six material and the ferrite phase is excessively distributed and the precipitation of the austenite phase is extremely small.
[0034]
【The invention's effect】
The welding material of the present invention is a duplex stainless steel having excellent corrosion resistance, and is desirable as a welding material for the duplex stainless steel. Further, by setting the Ph value and the PRE value within a predetermined range, the structure and element distribution of the weld metal portion can be optimized, and particularly the pitting corrosion resistance can be enhanced. Moreover, it is excellent also in the hot workability to a wire by making (gamma) cal into a predetermined range. Therefore, when this welding material is used for welding ferritic / austenitic duplex stainless steels for water tanks, water heaters and oil wells, pitting corrosion resistance equivalent to that of the base metal can be imparted, and the equipment or structure The safety and economy associated with the improvement of the corrosion resistance of objects can be made extremely high.
[Brief description of the drawings]
FIG. 1 is a table showing component compositions of a welding material of the present invention and a comparative material.
FIG. 2 is a view showing a joint cross section in a bead shape when a duplex stainless steel sheet is TIG welded.
FIG. 3 is a diagram showing an optical microstructure of a welded part of the steel of the present invention and a comparative steel.
(A) Steel of the present invention (b) is a comparative steel. FIG. 4 is a table showing the characteristics of a weld metal as a table in comparison with a comparative material.

Claims (2)

(A) a welding material for ferrite-austenite duplex stainless steel having the following component composition (wt%) ,
C: 0.05% or less, Si: 0.05-2.0%, Mn: 2.0% or less, P: 0.03% or less, S: 0.03% or less, Ni: 5-12%, cr: 22~28%, Mo: 3.0~5.0 %, Cu: 0.01~ 0.2%, N: 0.10~0.22%, Co: 0.1 ~3%, B : 0.0005~0.01%, Al: 0.07% or less, O: 0.01% or less, and the balance Fe and unavoidable impurities was,
(B) is Ph value shown below SL of (1) from 0.25 to 0.60, the following (2) Ganmacal shown in equation 80 below, PRE value shown in the following equation (3) is satisfied more than 35 A welding material for ferritic-austenitic duplex stainless steel, characterized by being a wire used in the TIG method or MIG method .
Ph = {Ni + 0.5Mn + 0.1Co + 30 (C + N) −0.4 (Cr + 1.5Si + Mo) +5.6} / {Cr + 1.5Si + Mo-6} (1)
γcal = 151.9 × C-6.15 × Si−2.8 × Mn + 6.5 × (Ni + Co) −5.7 × Cr−3.8 × Mo + 209.3 × N + 129.8 (2)
PRE = Cr + 3.3Mo + 20N (3) An apparatus or a structure in which ferrite-austenite duplex stainless steel is welded by the TIG method or the MIG method using the welding material according to claim 1 .

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