JP2001113388A - Welding material for ferritic-austenitic two phase stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding material used for the welding of ferritic- austenitic two phase stainless steel to be form/into the stock of apparatus used in the water environment such as a water receiving tank and a water heater or structures for oil wells and seawater. SOLUTION: This welding material for ferritic-austenitic two phase stainless steel has the following componential composition (wt.%): <=0.05% C, 0.05 to 2.0% Si, <=2.0% Mn, <=0.03% P, <=0.03% S, 5 to 12% Ni, 22 to 28% Cr, 3.0 to 5.0% Mo, <=0.2% Cu, 0.10 to 0.22% N, 0 to 3% Co, 0.0005 to 0.01% B, <=0.07% Al and <=0.01% O, and the balance Fe with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for welding equipment used in a water environment such as a water receiving tank and a water heater, or for welding a ferritic austenitic duplex stainless steel used as a material for an oil well or seawater structure. The present invention relates to a welding material and a device or structure excellent in corrosion resistance welded by using the welding material.

[0002]

2. Description of the Related Art A ferritic / austenite duplex stainless steel complements the disadvantages of a ferrite phase and an austenitic phase and is particularly excellent in corrosion resistance.
It is widely used as Ninth Series. For example, JP-A-56
According to -142855, a duplex stainless steel excellent in hot workability and local corrosion resistance has been proposed, and many other proposals have been made regarding a duplex stainless steel excellent in various properties.

The characteristics of duplex stainless steels are stress corrosion cracking resistance, high strength, high Cr and Mo content, excellent corrosion resistance, low Ni content, and resource saving. Generally, duplex stainless steels are hot-worked. There is a drawback that the properties 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 common metal material of the same component as the base metal, but in this case, the amount of austenite phase deposited in the weld becomes insufficient. In addition, there is a disadvantage that the corrosion resistance of the welded portion is deteriorated as compared with the base material because the phase balance is lost.

[0004] In order to prevent the corrosion resistance from being deteriorated in the welded portion, improvements and developments have been made to the welding materials. For example, Japanese Patent Application Laid-Open No. 3-204196 discloses a two-phase system excellent in concentrated sulfuric acid corrosion resistance. Stainless steel welding 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 structure for seawater, in which duplex stainless steel is widely used. Japanese Patent Application Laid-Open No. 8-260101 proposes improvement of toughness and corrosion resistance of a duplex stainless steel for a thick plate during multi-layer welding.

According to Japanese Patent Application Laid-Open No. Hei 8-260101, the toughness and corrosion resistance in the welded portion are certainly improved, but the N content is as high as 0.24 to 0.35%, which makes it extremely difficult to process into a wire. There is a problem that is. Also, since it is intended for super duplex stainless steel, it contains W and is expensive. Water receiving tank targeted by the present invention,
In welding thin sheet products such as hot water tanks, it is not necessary to contain expensive W.

[0006] Improving the corrosion resistance of a weld, particularly the pitting corrosion resistance, which is a localized form of corrosion in an environment containing Cl ions, improves the quality stability and reliability of the structure and under severer conditions. There is the strongest demand to be able to withstand the use. The solution to the problem of the deterioration of the pitting corrosion resistance of the weld is to optimize the ratio between the ferrite phase and the austenite phase.This proposal solves this problem by performing a precise component design. It is.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to optimize the alloying elements in a welding material so that the ratio of a ferrite phase to an austenite phase is approximately 1: 1 in a weld metal, and the The composition distribution of the ferrite and the ferrite
An object of the present invention is to provide a welding material for austenitic duplex stainless steel and a welded structural device and structure having excellent corrosion resistance.

The first aspect of the present invention provides the following component composition (w
(% by weight) for ferrite-austenite duplex stainless steel. C: 0.05% or less, Si: 0.05-2.0%, M
n: 2.0% or less, P: 0.03% or less, S: 0.0
3% or less, Ni: 5 to 12%, Cr: 22 to 28%,
Mo: 3.0 to 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, with the balance being Fe and unavoidable impurities.

In a second aspect of the present invention, the following component composition (w
(% by weight) for ferrite-austenite duplex stainless steel. (A) 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 to 12%, Cr: 22 to
28%, Mo: 3.0 to 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 consisting of Fe and inevitable impurities, (b) and the Ph value shown in the following formula (1) is 0.25 to 0.60, Γca shown
1 satisfies 80 or less, and the PRE value shown in the following equation (3) satisfies 35 or more. 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)

In a third aspect of the present invention, a ferritic-austenite duplex stainless steel is formed by using the welding material,
Equipment or structure welded by the TIG method or the MIG method.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the effects of each component of the welding material of the present invention and the reasons for limiting the content will be described. The component composition is wt%. C: an austenite-forming element that contributes to the strengthening of the welding material and the pitting resistance, but 0.05%
If it exceeds, the hot workability and toughness deteriorate, so the upper limit is specified at 0.05%.

Si: Used as a deoxidizer during refining. However, if it exceeds 2.0%, the hot workability deteriorates, and furthermore, the toughness of the weld metal is reduced, so the upper limit is set to 2.0%. If the content is less than 0.05%, the surface tension of the molten metal is lowered and a good bead shape cannot be obtained, so the lower limit is made 0.05%.

Mn: Like Si, it is used as a deoxidizing material during refining. The addition of Mn is effective for improving hot workability by generating sulfide,
%, The upper limit is 2.0% because the oxidation resistance is deteriorated.
Stipulated.

P: It is preferable that the content is smaller than the weldability and hot workability, but it is an element that is inevitably mixed.
The upper limit is made 0.03% in terms of manufacturing technology and economy. S: Element inevitably mixed. If the content exceeds 0.03%, segregation at grain boundaries lowers hot workability, so the upper limit is made 0.03%.

Ni: an austenite-forming element and a basic element for adjusting the phase ratio of the weld metal. Further, it is an element extremely effective in improving toughness and corrosion resistance. To obtain the above effects, a content of 5% or more is required. On the other hand, when the content exceeds 12%, the ferrite phase,
Since the balance of the austenite phase is lost and the economy is disadvantageous, the upper limit must be set to 12%.

Cr: a ferrite forming element, an element effective for improving pitting resistance. This content is 2
If it is less than 2.0%, the above effect cannot be obtained sufficiently,
If it exceeds 28.0%, a single phase of ferrite is apt to be formed in a high temperature range. Further, the upper limit needs to be 28.0% in order to promote precipitation of the σ phase and deteriorate toughness and corrosion resistance.

Mo: Like Cr, it is an element effective for improving pitting corrosion resistance. To improve the pitting corrosion resistance in the weld metal, it is necessary to contain at least 3.0%. However, 5.
If it exceeds 0%, the precipitation of the σ phase is promoted, and the toughness and corrosion resistance are deteriorated.

Cu: an austenite forming element, an element effective for improving corrosion resistance and weather resistance. However, the addition of a large amount deteriorates the hot workability, so the upper limit was made 0.2%.

N: A strong austenite-forming element, and also an extremely effective element for improving toughness and pitting resistance. To precipitate an appropriate amount of austenite in the weld metal, it is necessary to contain at least 0.10%. However, when the content exceeds 0.22%, the hot workability is impaired, and further, blow holes are easily generated in the weld metal. Therefore, the upper limit is set to 0.22%.

Co: an element that promotes the precipitation of austenite in a high temperature range, and is desirably contained in the weld metal to precipitate an appropriate amount of austenite. However, if it exceeds 3%, nitrides are likely to precipitate and the corrosion resistance and toughness are deteriorated.

B: S is an extremely effective element for suppressing the segregation of grain boundaries of S and improving the hot workability. The content is 0.
If the content is less than 0005%, the above effect is small, and if it exceeds 0.01%, a large amount of brittle compound is generated and embrittlement occurs, so the content is limited to 0.0005 to 0.01%.

Al: Al is a powerful deoxidizing element at the time of refining and is an element effective for improving the cleanliness of steel.
If it exceeds 7%, the penetration at the time of welding deteriorates, so the upper limit is set to 0.07%. O: O is an element that inhibits hot workability, and if it exceeds 0.01% (100 ppm), it becomes difficult to process a wire rod. However, it is inevitably a mixed element, and up to 0.01% is allowable.

The above component composition is a component composition of a ferritic / austenite duplex stainless steel and can be used as a welding material. However, it is more desirable that the above-mentioned component composition satisfy the following parameters.
That is, the reason for defining the Ph value (a value indicating the phase balance), the γcal value (the workability index), and the PRE value (the pitting corrosion resistance index) will be described.

Here, the Ph value, γcal value, and PR
The E value is calculated by the following equation. 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)

In order to ensure the corrosion resistance and strength characteristics of the weld metal, it is necessary to optimize the phase ratio between the ferrite phase and the austenite phase. That is, since the ferrite phase tends to be larger in the weld metal than in the base metal, the austenite forming element must be positively added.

If the Ph value is less than 0.25, an austenite phase sufficient to ensure corrosion resistance and strength properties is not generated, while if it exceeds 0.60, the ferrite phase in the weld metal part is reduced, As a result, Cr in the ferrite phase
And Mo are excessively dissolved to promote the precipitation of the σ phase, which extremely deteriorates corrosion resistance and toughness. Therefore, it is desirable to adjust the Ph value to 0.25 to 0.60.

On the other hand, in the production of a welding rod, it is necessary to consider the workability of the wire. When the γcal value exceeds 80, the hot workability is significantly deteriorated, the wire rod processing becomes difficult, and the production yield is remarkably deteriorated. Therefore, the γcal value is desirably 80 or less. Further, a pitting corrosion resistance index PRE, which is an index for judging the quality of pitting corrosion resistance, is generally proposed, and it is desirable that the PRE be 35 or more in order to show sufficient pitting corrosion resistance in the environment.

In order to secure only the corrosion resistance and strength characteristics of the weld, it is desirable to adjust the Ph value to 0.25 to 0.60. When the welding rod is formed into a wire, the γcal is desirably 80 or less. Furthermore,
In order to show that sufficient pitting corrosion resistance is required in the use environment, it is desirable that PRE is 35 or more.

When welding a ferritic-austenite duplex stainless steel with the welding material of the present invention, it is necessary to avoid fluctuations in components of the welding material, for example, easily oxidizable components such as Al, Si, and Cr. Therefore TIG method or M
The IG method is desirable. Each of these welding methods is a gas shield welding method, so that the fluctuation of the easily oxidizable component can be avoided. Therefore, the equipment or structure welded by the above welding method has excellent corrosion resistance. In some cases, a plasma welding method or an electron beam welding method having a sealing property with respect to atmospheric gas can be applied.

[0030]

EXAMPLES Test steels of various chemical components shown in Table 1 in FIG. 1 were melted, ingoted, and forged to form a 12 mm thick plate. At this time, the presence or absence of forging cracks was visually inspected, and hot workability was evaluated. 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.

The base material is SUS329 according to JIS standard.
Using a duplex stainless steel equivalent to J4L (thickness: 1.5 mm), butt TIG welding was used to create the welded joint shown in Fig. 2 while appropriately adding welding materials, and the welded structure and corrosion resistance were determined by a pitting corrosion test. Was evaluated. A micrograph of the weld is shown in FIG. This photograph is a microscopic observation of the weld after etching with a solution comprising oxalic acid and KOH. The ratio of the ferrite phase was 20 × 2 with a 400 × microscope.
Quantification was performed by the point calculation method using a grid of zero. Pitting test is J
Performed according to IS G0577. However, the test temperature was 70 ° C. The results are shown in Table 2 in FIG.

The welding material No. satisfying any of the component ranges defined in the present invention. Nos. 1 to 5 have excellent hot workability and are easy to be processed into a wire rod, and the phase ratio of a welded portion is almost 1: 1 ferrite phase: austenitic phase = 1, and also excellent in pitting corrosion resistance. On the other hand, in Comparative Example No. Since items 6 to 10 do not satisfy the range of the present invention (indicated by underlines 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, austenite phase precipitation in the weld metal is not sufficient, and the corrosion resistance is deteriorated.

In addition, No. In No. 7, cracks occurred during hot forging because the γcal value was larger than the range of the present invention.
No. Sample No. 8 had a PRE of less than 35, and thus had a significantly lower corrosion resistance than the base metal. No. In No. 9, the Mo content was high and the σ phase was generated. In No. 10, cracks occurred during hot forging because the amount of B effective for improving hot workability was small. FIG. 2 shows the optical microscopic structure of the welded portion.
o. The ferrite phase and the austenite phase were approximately 1: 1 in the three materials. This is an undesirable material because the ferrite phase is excessively distributed and the precipitation of the austenite phase is extremely small.

[0034]

The welding material of the present invention is a duplex stainless steel having excellent corrosion resistance, and is desirable as a welding material for a 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 improved.
In addition, by setting γcal within a predetermined range, the wire can be excellent in hot workability. Therefore, when this welding material is used for welding of ferritic / austenitic duplex stainless steel for water receiving tanks, water heaters and oil wells, it can provide the same pitting corrosion resistance as the base metal, and The safety and economic efficiency accompanying the improvement of the corrosion resistance of the product can be made extremely high.

[Brief description of the drawings]

FIG. 1 is a table showing the component compositions of a welding material of the present invention and a comparative material.

FIG. 2 is a diagram showing a cross section of a joint in a bead shape when a duplex stainless steel plate is TIG-welded.

FIG. 3 is a view showing the optical microstructures of a welded steel of the present invention steel and a comparative steel. (A) is the inventive steel (b) is the comparative steel

FIG. 4 is a table showing characteristics of a weld metal in comparison with a comparative material.

Claims (3)

[Claims] 1. A welding material for a ferritic / austenite duplex stainless steel having the following composition (wt%): 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 to 12%, Cr: 22 to 28%, Mo: 3.0 to 5.0%, Cu: 0.2% or less, N: 0.10 to 0.22%, Co: 0 to 3% or less, B: 0.0005 ~ 0.01
%, Al: 0.07% or less, O: 0.01% or less, the balance being F
e and unavoidable impurities. 2. A welding material for a ferritic / austenite duplex stainless steel having the following composition. (A) 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 to 12%, Cr: 22 to 28%, Mo: 3.0 to 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, the balance consisting of Fe and unavoidable impurities, (b) and the Ph value shown in the following formula (1) is 0.25 to 0.60, following
Γcal shown in equation (2) is 80 or less, and P shown in equation (3) below
A welding material for a ferritic-austenite duplex stainless steel, wherein the RE value satisfies 35 or more. 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) 3. An apparatus or structure obtained by welding a ferritic austenitic duplex stainless steel using the welding material according to claim 1 or 2 by a TIG method or a MIG method.