JP2015196894A - Two-phase stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welded joint having high pitting corrosion resistance.SOLUTION: There is provided a two-phase stainless steel welded joint in which each of a base metal and a weld metal has a chemical composition containing, by mass%, C:0.03% or less, Si:0.5% or less, Mn:2% or less, P:0.04% or less, S:0.003% or less, Cr:21 to 29%, Ni:4.0 to 10.5%, Mo:0.8 to 4.0%, N:0.1 to 0.4%, sol.Al:0.040% or less, W:0 to 4.0%, Cu:0 to 4.0%, B:0 to 0.005%, REM:0 to 0.2% and the balance Fe with inevitable impurities and in which an austenite index a represented by the formula (1) is 0.1 to 0.4, Mn/N≥2, a PF index represented by the formula (2) is 1.0 or less, and thickness of an oxidized scale of the surfaces of the base metal and the weld metal upon welding is 500 nm or less. a={Ni+30(C+N)-0.6(Cr+1.5Si+Mo)+5.6}/{Cr+1.5Si+Mo-6}(1) PF=Mn×(100 Pb+50Sb+30Zn+40As)(2)

Description

  The present invention relates to a duplex stainless steel, and more particularly to a duplex stainless steel having excellent weldability and pitting corrosion resistance.

  Since the duplex stainless steel is excellent in strength and corrosion resistance, in particular, seawater corrosion resistance, it has long been used in a wide range of technical fields as a heat exchanger steel pipe and the like. Conventionally, many composition examples have already been proposed for duplex stainless steel with improved corrosion resistance, strength, workability, and the like.

  For example, Patent Document 1 discloses a high-strength duplex stainless steel containing 1.5% by mass to 5% by mass of W and PREW [PREW = Cr + 3.3 (Mo + 0.5W) + 16N] of 40 or more. Yes. In this duplex stainless steel, corrosion resistance is drastically improved by adding a large amount of W, and mechanical properties and corrosion resistance deterioration due to precipitation of intermetallic compounds (such as sigma phase) are said to be small.

  In Patent Document 2, duplex stainless steel having excellent pitting corrosion resistance and weldability, in particular, excellent pitting corrosion resistance and weldability in which an intermetallic compound such as a fine sigma phase is not generated even in a welding heat affected zone. A duplex stainless steel is disclosed. Regarding the improvement of pitting corrosion resistance, Patent Document 3 contains Sn with N / Sn in a specific range, which makes it easier to form a passive film, and further increases its stability, thereby significantly increasing local corrosion. It is disclosed that it can be suppressed.

  Further, as a welding material for high corrosion resistance and high toughness duplex stainless steel welding, Patent Document 4 restricts the contents of Cr and Mo, contains W, sets the pitting corrosion resistance index PREW to 42.0 or more, and By setting the ferrite capacity index Ph to 0.25 to 0.35%, a welding material excellent in hot workability, weld metal toughness and pitting corrosion resistance is disclosed.

JP-A-5-132741 International Publication No. 2005/001151 JP 2013-253315 A JP-A-8-260101

  As of today, various welded structures are widely used. For example, when duplex stainless steel is used as a welded structure such as a pipe, heat exchanger, pump or the like used in a high temperature seawater environment, the corrosion resistance of the welded portion, particularly pitting corrosion resistance has been a problem. In Patent Document 2, by controlling the amount of N and Mo in the steel and the density of the alumina-based coarse inclusions, it is possible to suppress the fine sigma phase and nitride generated in the weld heat affected zone that becomes the starting point of pitting corrosion. It is shown that it is effective for improving the pitting corrosion resistance of the weld.

  However, these do not suppress the deterioration of pitting corrosion resistance when the oxide scale generated during welding remains. If polishing is possible after welding, there is no problem, but when welding is performed from one side, the scale is completely removed on the pipe inner surface side of the peripheral welded part of the pipe and the inner surface side of the welded part of the box-shaped structure. It is difficult to do.

  The present invention has been made to solve such problems of the prior art, and an object of the present invention is to provide a welded joint having high pitting corrosion resistance even at a site where an oxide scale is generated during welding.

  The pitting corrosion resistance of the duplex stainless steel is manifested by a passive film made of Cr. And it becomes possible to endure even a severe corrosive environment, if Mo, W, and N are contained together with increasing Cr and reinforcing the passive film. As a result of intensive studies on a mechanism and a solution to the problem that the scale generated on the surface of the weld heat-affected zone and the weld metal during welding reduces pitting corrosion resistance, the present inventors have found the following.

  On the surface of the region heated to 1000 ° C. or higher during welding, an alloy element in the steel reacts with O in the welding atmosphere to generate a new oxide scale. Since it is a reaction at a high temperature, O reacts not only with Cr having a strong affinity but also with Mn having a low vapor pressure, and further with Fe existing in a large amount in steel. As a result, the scale mainly composed of Cr formed by the reaction at room temperature becomes a scale in which Fe and Mn are enriched and the Cr concentration is lowered. Since this scale has low resistance to corrosion, the pitting corrosion resistance deteriorates.

  This deterioration of the film can be suppressed by setting the amount of Mn in the steel and the oxide scale thickness formed by welding to 500 nm or less.

  Inhibiting the amount of Mn in the steel is effective in that the amount of Mn that reacts with O and enters the oxide scale can be directly suppressed. However, since Mn in steel increases the solid solubility of N, it also plays a role of preventing the deterioration of pitting corrosion resistance by suppressing the precipitation of nitride in the weld heat affected zone. It is necessary to contain 2 times or more.

  On the other hand, if an appropriate amount of N is added to the steel, the formation of the austenite phase can be promoted from a state in which the ferrite phase that is temporarily generated is enriched at a high temperature during welding, which is effective in suppressing nitrides. It is. This is because N has a higher diffusion rate than substitutional alloy elements such as Ni and Cr, and therefore sufficiently contributes to diffusion transformation even under conditions of a relatively high cooling rate such as welding. Assuming that such control is performed, Mn can be reduced to the minimum necessary.

  However, as long as Mn is present in the steel, the deterioration of the passive film is inevitable. However, if the thickness of the oxide scale formed during welding is sufficiently reduced, the reaction between O and the metal in the steel at 1000 ° C. or higher. As a result, a stable film having a high Cr concentration can be obtained.

  Furthermore, when Pb, Sb, Zn and As are mixed from the steel into the oxide scale produced during welding, fine cracks are likely to occur in the oxide film of Cr having a high Mn and Fe concentration, and depending on the corrosive environment, Damage to the film is likely to occur. Therefore, it is necessary to regulate the amount of these impurities according to the amount of Mn.

  In addition, said technical matter is the same not only in a welding heat affected zone but in a weld metal, and is applicable also to a welding material.

  This invention is made | formed based on said knowledge, and makes a summary the following duplex stainless steel welded joint and duplex stainless steel welding material.

(1) The chemical composition of the base metal and the weld metal is mass%,
C: 0.03% or less,
Si: 0.5% or less,
Mn: 2% or less,
P: 0.04% or less,
S: 0.003% or less,
Cr: 21% or more and less than 29%,
Ni: 4.0 to 10.5%,
Mo: 0.8 to 4.0%,
N: more than 0.1% and 0.4% or less,
sol. Al: 0.040% or less,
W: 0 to 4.0%,
Cu: 0 to 4.0%,
B: 0 to 0.005%,
REM: 0-0.2%
Balance: Fe and impurities,
The austenite index a calculated | required from the following (1) Formula is 0.1-0.4,
Mn / N ≧ 2 is satisfied, and
The PF index obtained from the following formula (2) is 1.0 or less,
The oxide scale thickness at the time of welding formed on the surface of the base metal and the weld metal is 500 nm or less,
Duplex stainless steel welded joint.
a = {Ni + 30 (C + N) −0.6 (Cr + 1.5Si + Mo) +5.6} / {Cr + 1.5Si + Mo−6} (1)
PF = Mn × (100Pb + 50Sb + 30Zn + 40As) (2)
However, each element symbol in the above formula means the content (% by mass) of each element.

(2) The chemical composition is
Cu: including 0.2 to 2.0%,
The duplex stainless steel welded joint of (1) above.

(3) The chemical composition is
One or more selected from B: 0.0005-0.005% and REM: 0.0005-0.2%,
The duplex stainless steel welded joint according to (1) or (2) above.

(4) The chemical composition is mass%,
C: 0.03% or less,
Si: 0.5% or less,
Mn: 2% or less,
P: 0.04% or less,
S: 0.003% or less,
Cr: 21% or more and less than 29%,
Ni: 4.0 to 10.5%,
Mo: 0.8 to 4.0%,
N: more than 0.1% and 0.4% or less,
sol. Al: 0.040% or less,
W: 0 to 4.0%,
Cu: 0 to 4.0%,
B: 0 to 0.005%,
REM: 0-0.2%
Balance: Fe and impurities,
The austenite index a calculated | required from the following (1) Formula is 0.1-0.4,
Mn / N ≧ 2 is satisfied, and
The PF index calculated from the following formula (2) is 1.0 or less,
Duplex stainless steel welding material.
a = {Ni + 30 (C + N) −0.6 (Cr + 1.5Si + Mo) +5.6} / {Cr + 1.5Si + Mo−6} (1)
PF = Mn × (100Pb + 50Sb + 30Zn + 40As) (2)
However, each element symbol in the above formula means the content (% by mass) of each element.

(5) The chemical composition is
Cu: including 0.2 to 2.0%,
The duplex stainless steel welding material according to (4) above.

(6) The chemical composition is
One or more selected from B: 0.0005-0.005% and REM: 0.0005-0.2%,
The duplex stainless steel welding material according to (4) or (5) above.

  According to the present invention, deterioration of pitting corrosion resistance of a welded joint can be prevented without removing the oxide scale generated during welding. Therefore, it is possible to provide a welded structure having high pitting corrosion resistance even at a site where an oxide scale is generated during welding.

Diagram showing gas shielding method during welding Figure showing the sampling position of the corrosion test piece

  First, the duplex stainless steel constituting the base metal and weld metal of the welded joint, and the duplex stainless steel constituting the weld material (hereinafter referred to as the duplex stainless steel constituting the base metal, weld metal and weld material of the weld joint) Will be simply referred to as “duplex stainless steel” or “steel”). In the following description, “%” for the content of each element means “mass%”.

C: 0.03% or less C is an element effective for stabilizing the austenite phase. However, when the content exceeds 0.03%, carbides are likely to precipitate, and the corrosion resistance is deteriorated. Therefore, the C content is 0.03% or less. Preferably it is 0.02% or less. The above effect is exhibited even when the content is at the impurity level, but it is particularly preferably 0.005% or more.

Si: 0.5% or less Si is effective for deoxidation of steel, but when its content is excessive, it promotes the formation of intermetallic compounds (such as sigma phase). Therefore, the content is 0.5% or less. The above effect is exhibited even when the content is an impurity level, but it is particularly preferably 0.05% or more.

Mn: 2% or less Mn improves hot workability by desulfurization and deoxidation effects during the melting of duplex stainless steel. Further, the solid solubility of N is increased to suppress nitride precipitation at the weld. However, if the content is excessive, the corrosion resistance is deteriorated, so the content is made 2% or less. Preferably it is 1.0% or less. The above effect is exhibited even at the impurity level, but it is necessary to satisfy Mn / N ≧ 2 particularly in relation to N. In particular, it is preferably 0.2% or more.

P: 0.04% or less P is an impurity element inevitably mixed in steel, and when its content exceeds 0.04%, deterioration of corrosion resistance and toughness becomes remarkable. Therefore, the upper limit of P is 0.04%.

S: 0.003% or less S is an impurity element inevitably mixed in steel, and deteriorates the hot workability of steel. In addition, the sulfide becomes a starting point of pitting corrosion and impairs pitting corrosion resistance. In order to avoid these adverse effects, the content is limited to 0.003% or less.

Cr: 21% or more and less than 29% Cr is a basic component effective for maintaining corrosion resistance. When the content is less than 21.0%, pitting corrosion resistance is insufficient. On the other hand, when the Cr content is 29.0% or more, the precipitation of intermetallic compounds (such as sigma phase) becomes remarkable, leading to a decrease in hot workability and a deterioration in weldability. Therefore, the Cr content is 21% or more and less than 29%. A preferred lower limit is 23% and a preferred upper limit is 27%.

Ni: 4.0 to 10.5%,
Ni is an essential component for stabilizing austenite, but if its content exceeds 10.5%, it becomes difficult to secure the basic properties of duplex stainless steel due to the decrease in ferrite content, and sigma Precipitation of phases and the like becomes easy. On the other hand, if the Ni content is less than 4.0%, the amount of ferrite becomes too large and the characteristics of the duplex stainless steel are lost. In addition, since the solid solubility of N in ferrite is small, nitride precipitates and the corrosion resistance deteriorates. Therefore, the Ni content is 4.0 to 10.5%. A preferred lower limit is 5.0% and a preferred upper limit is 9.5%.

Mo: 0.8-4.0%
Mo, like Cr, is a very effective component for improving corrosion resistance. In particular, in order to improve the pitting corrosion resistance and crevice corrosion resistance, the content needs to be 0.8% or more. It is preferably 1.5% or more, and more preferably 2% or more. On the other hand, if Mo is excessively contained, it causes embrittlement of the raw material during production, and has a strong effect of facilitating the precipitation of intermetallic compounds like Cr. Therefore, the upper limit of the Mo content is 4.0%. A preferable upper limit is 3.5%.

N: More than 0.1% and 0.4% or less N is a strong austenite-forming element and is effective in improving the thermal stability and corrosion resistance of the duplex stainless steel. In the present invention that contains a large amount of ferrite-forming elements such as Cr and Mo, it is necessary to contain more than 0.1% N in order to achieve an appropriate balance between the two phases of ferrite and austenite.

  Further, N contributes to the improvement of PREW and improves the corrosion resistance of the alloy in the same manner as Cr, Mo and W. However, if the duplex stainless steel according to the present invention contains more than 0.4% N, the toughness and corrosion resistance of the steel deteriorate due to defects caused by blowholes or the formation of nitrides due to the thermal effect during welding. Let Therefore, the N content is more than 0.1% and 0.4% or less. A preferable upper limit is 0.35%.

  In addition, in order to reduce the activity of N in steel and to make it fully solid-solution by containing Mn, it is indispensable to contain Mn more than twice N. Therefore, in the present invention, it is essential that the ratio of Mn / N in the steel is 2.0 or more.

sol. Al: 0.040% or less Al is effective as a deoxidizer for steel, but when the amount of N in the steel is high, it precipitates as AlN (aluminum nitride) and deteriorates toughness and corrosion resistance. Furthermore, an oxide is formed and becomes a nucleation site of a sigma phase. Therefore, Al is suppressed to 0.040% or less as the content of acid-soluble Al (sol. Al). In the present invention, since a large amount of Si is avoided, Al is often used as a deoxidizing agent. However, when vacuum melting is performed, it is not always necessary to include Al. A preferable upper limit is 0.03%. Although the Al content is preferably as small as possible, reducing it too much increases the manufacturing cost. For this reason, it is preferable that the lower limit of Al is 0.001%.

W: 0 to 4.0%
W, like Mo, is an element that improves corrosion resistance, in particular resistance to pitting corrosion and crevice corrosion, and is particularly effective in forming stable oxides and improving corrosion resistance in low pH environments. Element. Therefore, W may be contained. However, if the W content exceeds 4.0%, there is no increase in the effect commensurate with it, and the cost only increases. Therefore, when it contains W, the content shall be 4.0% or less. A preferred lower limit is 0.5% and a preferred upper limit is 3.5%.

Cu: 0 to 4.0%
Cu is an element particularly effective for improving acid resistance in a reducing low pH environment, for example, H ₂ SO ₄ or hydrogen sulfide environment. Therefore, Cu may be contained. However, when Cu is contained excessively, hot workability is deteriorated. Therefore, when it contains Cu, the content shall be 4.0% or less. In order to sufficiently obtain the above effect, it is preferable to contain 0.2% or more. A preferable upper limit is 3.0%.

B: 0 to 0.005%
REM: 0 to 0.2%
The duplex stainless steel of the present invention keeps the S content low, and even if it contains a large amount of W, it does not promote the formation of a sigma phase or the like, so that the hot workability is originally good. . Further, the duplex stainless steel of the present invention can be used as a casting, and can be made into a product such as a tube by powder metallurgy such as pressing and sintering. In the case of such a manufacturing method, hot workability is not a problem. However, when it is made into a product through processes such as forging, rolling, and extrusion, it is required that the hot workability is excellent.

  Since B and REM are both effective elements for improving hot workability, they may be contained. However, when the respective contents are excessive, the non-metallic inclusions of those oxides and sulfides increase, becoming a nucleation site of sigma phase precipitation, or starting point of pitting corrosion, It causes deterioration of corrosion resistance. Therefore, when these elements are contained, the B content is 0.005% or less, and the REM content is 0.2% or less. In order to sufficiently obtain the above effects, it is preferable to contain B in an amount of 0.0005% or more and REM in an amount of 0.0005% or more. The minimum with preferable B content is 0.0010%, and a preferable upper limit is 0.0040%. The preferable lower limit of the REM content is 0.01%, and the preferable upper limit is 0.1%.

  B and REM may contain either one or both. REM is a general term for a total of 17 elements of Sc, Y and lanthanoid, and the content of REM means the total amount of the above elements.

  The duplex stainless steel of the present invention contains each of the above elements, with the balance being Fe and impurities. And an impurity means the component mixed by raw materials and other factors, such as an ore and a scrap, when manufacturing steel materials industrially.

Austenite index a: 0.1 to 0.4
In the duplex stainless steel, since the ratio of the ferrite phase and the austenite phase varies sensitively depending on the amount of alloy elements in the weld zone, it is not sufficient to specify the content range of each element. ) The austenite index a determined from the formula needs to be in the range of 0.1 to 0.4.
a = {Ni + 30 (C + N) −0.6 (Cr + 1.5Si + Mo) +5.6} / {Cr + 1.5Si + Mo−6} (1)
However, each element symbol in the above formula means the content (% by mass) of each element.

  When the austenite index a exceeds 0.4, a small amount of sigma phase precipitation occurs at a low temperature HAZ, and when it is less than 0.1, nitride precipitation occurs at a high temperature HAZ. Therefore, the austenite index a is set to a range of 0.1 to 0.4. A preferable lower limit of the austenite index a is 0.12%, and a preferable upper limit is 0.35%.

PF index: 1.0 or less When Pb, Sb, Zn, and As are mixed from the steel into the oxide scale generated during welding, fine cracks are likely to occur in the Cr oxide film having a high Mn and Fe concentration. When such a crack occurs, the coating tends to be damaged depending on the corrosive environment, and the pitting corrosion resistance is deteriorated. However, even if there is a scale at the time of welding, the amount of Pb, Sb, Zn, As is restricted to an appropriate range according to the amount of Mn, that is, the PF index obtained from the following equation (2) is 1.0 or less. If so, damage to the coating can be prevented, and deterioration of pitting corrosion resistance can be prevented.
PF = Mn × (100Pb + 50Sb + 30Zn + 40As) (2)
However, each element symbol in the above formula means the content (% by mass) of each element.

  About the base material and weld metal of a welded joint, the oxide scale thickness at the time of the welding formed in the surface needs to be 500 nm or less.

  On the surface of the region heated to 1000 ° C. or higher during welding, an alloy element in the steel reacts with O in the welding atmosphere to generate a new oxide scale. Since it is a reaction at a high temperature, O reacts not only with Cr having a strong affinity but also with Mn having a low vapor pressure, and further with Fe existing in a large amount in steel. As a result, the scale mainly composed of Cr formed by the reaction at room temperature becomes a scale in which Fe and Mn are enriched and the Cr concentration is lowered. Since this scale has low resistance to corrosion, the pitting corrosion resistance deteriorates. By setting the scale thickness to 500 nm or less, the reaction amount of O with 1000 Mn or more and Mn and Fe in the steel can be reduced, and as a result, a stable film having a high Cr concentration can be obtained. The scale thickness is preferably 400 nm or less. On the other hand, the lower limit of the scale thickness is preferably 10 nm or more.

  Base metal duplex stainless steel having the chemical composition shown in Table 1 and welding material duplex stainless steel having the chemical composition shown in Table 2 were melted in a laboratory-scale electric furnace.

  The duplex stainless steel for base metal was heated to 1200 ° C. after casting and formed into a plate material having a thickness of 40 mm by forging. The obtained plate was heated to 1250 ° C. and rolled to obtain a test steel plate having a thickness of 10 mm. This steel plate was made into a test material by machining it with a V groove of 8 mm thickness x width 100 mm x length 200 mm and a groove angle of 30 degrees at the end of the long side.

  About the duplex stainless steel for welding materials, after casting, it heated at 1200 degreeC and made it the rod material of the outer diameter of 30 mm by forging. The obtained bar was formed into a wire having an outer diameter of 1.6 mm by hot rolling and cold rolling at 1250 ° C.

Two kinds of welded joints were prepared by matching test materials having the same chemical composition and performing multilayer welding by TIG welding from one side under the condition of a heat input of 13 kJ / cm used in general stainless steel. As the welding material, the above wire was appropriately selected and used. As shown in FIG. 1, on the back side of the groove, a gas shield box made of a copper plate bent into a U-shape with two short sides of 10 mm and the other side of 30 mm is placed. By changing the shielding gas composition in the box supplied in minutes in the range of pure Ar and Ar + 100 to 1000 ppm O ₂ , oxide scales at the time of welding with various thicknesses were generated on the back surface welded part. Table 3 shows the chemical composition of the weld metal.

  The oxide scale thickness at the time of welding of each obtained welded joint was measured. Further, from each of the obtained welded joints, as shown in FIG. 2, the weld bead and the welded portion on the back side with the oxide scale at the time of welding remain, the side perpendicular to the weld line is 40 mm, the rolling surface A corrosion test piece having a thickness of 3 mm, a width of 10 mm, and a length of 40 mm was taken with a surface parallel to the surface of 3 × 10 mm. Further, a corrosion test piece having a thickness of 3 mm, a width of 10 mm, and a length of 40 mm was taken from the specimen of the duplex stainless steel for base material. These corrosion test pieces were immersed in a 10% ferric chloride aqueous solution maintained at a constant temperature for 24 hours, and the surface on the first layer welding side was examined. The temperature was raised and further immersed for 24 hours. This immersion-microscope-temperature increase was repeated until pitting corrosion occurred, and the critical pitting corrosion temperature CPT was determined. However, for the test material having a PREW value of less than 34, a 4% ferric chloride aqueous solution was used as the test solution. These results are shown in Table 4.

As shown in Tables 3 and 4, the examples (AW1 to AW9) satisfying all the requirements of the present invention were evaluated without polishing the scales generated during welding, but the CPT with the base material was evaluated. The difference was at most 12.5 ° C., indicating excellent pitting corrosion resistance.
On the other hand, examples where the oxide scale thickness at the time of welding is excessive (BW1, BW2), and the range of the content of each element are in the range defined by the present invention, but PF, austenite index a, PF index and In the example (BW3 to BW9) in which any of Mn / N is out of the range defined in the present invention (BW3 to BW9), pitting corrosion occurs in the weld heat affected zone, and the CPT is 30 ° C. or higher compared to the base material. The pitting corrosion resistance deteriorated due to the oxide scale during welding. Further, in the examples (BW10 to BW12) using the welding material that does not satisfy the requirements defined in the present invention even if the base material satisfies all the requirements defined in the present invention, the chemical composition of the weld metal is the present invention. Therefore, the pitting corrosion resistance deteriorated due to the oxide scale during welding in the weld metal.

  According to the present invention, deterioration of pitting corrosion resistance of a welded joint can be prevented without removing the oxide scale generated during welding. Therefore, it is possible to provide a welded structure having high pitting corrosion resistance even at a site where an oxide scale is generated during welding.

Claims (6)

The chemical composition of the base metal and the weld metal is mass%,
C: 0.03% or less,
Si: 0.5% or less,
Mn: 2% or less,
P: 0.04% or less,
S: 0.003% or less,
Cr: 21% or more and less than 29%,
Ni: 4.0 to 10.5%,
Mo: 0.8 to 4.0%,
N: more than 0.1% and 0.4% or less,
sol. Al: 0.040% or less,
W: 0 to 4.0%,
Cu: 0 to 4.0%,
B: 0 to 0.005%,
REM: 0-0.2%
Balance: Fe and impurities,
The austenite index a calculated | required from the following (1) Formula is 0.1-0.4,
Mn / N ≧ 2 is satisfied, and
The PF index obtained from the following formula (2) is 1.0 or less,
The oxide scale thickness at the time of welding formed on the surface of the base metal and the weld metal is 500 nm or less,
Duplex stainless steel welded joint.
a = {Ni + 30 (C + N) −0.6 (Cr + 1.5Si + Mo) +5.6} / {Cr + 1.5Si + Mo−6} (1)
PF = Mn × (100Pb + 50Sb + 30Zn + 40As) (2)
However, each element symbol in the above formula means the content (% by mass) of each element. The chemical composition is
Cu: including 0.2 to 2.0%,
The duplex stainless steel welded joint according to claim 1. The chemical composition is
One or more selected from B: 0.0005-0.005% and REM: 0.0005-0.2%,
The duplex stainless steel welded joint according to claim 1 or 2. Chemical composition is mass%,
C: 0.03% or less,
Si: 0.5% or less,
Mn: 2% or less,
P: 0.04% or less,
S: 0.003% or less,
Cr: 21% or more and less than 29%,
Ni: 4.0 to 10.5%,
Mo: 0.8 to 4.0%,
N: more than 0.1% and 0.4% or less,
sol. Al: 0.040% or less,
W: 0 to 4.0%,
Cu: 0 to 4.0%,
B: 0 to 0.005%,
REM: 0-0.2%
Balance: Fe and impurities,
The austenite index a calculated | required from the following (1) Formula is 0.1-0.4,
Mn / N ≧ 2 is satisfied, and
The PF index calculated from the following formula (2) is 1.0 or less,
Duplex stainless steel welding material.
a = {Ni + 30 (C + N) −0.6 (Cr + 1.5Si + Mo) +5.6} / {Cr + 1.5Si + Mo−6} (1)
PF = Mn × (100Pb + 50Sb + 30Zn + 40As) (2)
However, each element symbol in the above formula means the content (% by mass) of each element. The chemical composition is
Cu: including 0.2 to 2.0%,
The duplex stainless steel welding material according to claim 4. The chemical composition is
One or more selected from B: 0.0005-0.005% and REM: 0.0005-0.2%,
The duplex stainless steel welding material according to claim 4 or 5.

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