JP6492811B2 - Welding material and weld metal and welded joint formed using the same - Google Patents

Description

  The present invention relates to a welding material and a weld metal and weld joint formed using the same, and more particularly to a stainless steel weld material and a weld metal and weld joint formed using the same.

  High strength and high toughness are required for steel pipes used for line pipes and oil well pipes. As a material having high strength and high toughness, high nitrogen duplex stainless steel and martensitic stainless steel are used. When manufacturing a welded joint using these high-strength stainless steels as a base material, the weld metal is also required to have high strength and high toughness. A welding material having high strength is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2014-39953 (Patent Document 1) and International Publication No. WO2012 / 111535 (Patent Document 2).

  A gas shielded arc welding method is used for welding steel materials. The gas shielded arc welding method is roughly classified into a non-consumable electrode type and a consumable electrode type. For the welding of austenitic steel, a gas tungsten arc (Gas Tungsten Arc, abbreviated as GTA) welding method which is a non-consumable electrode type welding method is usually used. The GTA welding method is a method in which tungsten is used as an electrode and a base material is melted and welded. The GTA welding method is easy to form a good quality weld metal, but the welding speed is slow.

  On the other hand, the gas shielded arc method includes a gas metal arc (Gas Metal Arc, abbreviated as GMA) welding method, which is a consumable electrode type welding method. The GMA welding method is a method of welding by using a welding wire as an electrode and forming a weld metal with a molten wire and a molten base material. In the GMA welding method, a wire having a small diameter is used as an electrode, so that the welding speed is high. Therefore, it is preferable to use the GMA welding method instead of the GTA welding method.

  However, since the GMA welding method has a faster solidification rate of the weld metal than the GTA welding method, the weld metal tends to solidify while the gas generated in the molten metal remains. Therefore, blow holes are likely to occur.

  Duplex stainless steel is used as a welding material for GMA welding. Since the duplex stainless steel has high strength and high toughness, it is suitable for manufacturing a welded joint using the above-described high strength stainless steel as a base material. However, duplex stainless steel contains a large amount of nitrogen for strength improvement. In this case, a large amount of nitrogen gas is generated in the molten metal, and blow holes are easily generated. For this reason, the welding material and welded joint which can suppress generation | occurrence | production of a blowhole are calculated | required.

A method for manufacturing a welded joint by the GMA welding method that suppresses blowholes is disclosed in Japanese Unexamined Patent Application Publication No. 2014-607 (Patent Document 3). The manufacturing method described in Patent Document 3 includes a step of preparing a base material containing 10.5% or more of Cr by mass%, and 1 to 2% by volume or 35 to 50% by volume of CO with respect to the base material. ₂ and the balance is made of an inert gas, and GMA welding is performed. By mass%, C: 0.080% or less, Si: 0.20 to 1.00%, Mn: 8. 00% or less, P: 0.040% or less, S: 0.0100% or less, Cu: 2.0% or less, Cr: 20.0-30.0%, Ni: 7.00-12.00%, N: 0.100 to 0.350%, O: 0.02 to 0.14%, Al: 0.040% or less, and Mo: 1.00 to 4.00% and W: 1.00 to 4 And a step of forming a weld metal composed of Fe and impurities. Thus, Patent Document 3 describes that a welded joint having a weld metal having high strength and high toughness and having few blow holes can be manufactured.

JP 2014-39953 A International Publication WO2012 / 111535 JP 2014-607 A

  However, blow holes may occur even with the manufacturing method disclosed in Patent Document 3 described above.

  An object of the present invention is to provide a welding material having high strength and high toughness and capable of producing a welded joint with few blow holes, and a weld metal and a welded joint using the same.

The welding material according to the present embodiment is mass%, C: 0.02% or less, Si: 0.25 to 1.00%, Mn: 0.30 to 3.00%, P: 0.020% or less, S: 0.01% or less, Cu: 2.00% or less, Cr: 20.0-30.0%, Ni: 7.00 to 12.00%, N: 0.10 to 0.350%, Al : 0.001 to 0.040%, V: 0.010 to 1.50%, and Mo: 1.00 to 4.00%, and W: 1.00 to 4.00% It contains one or more selected, the balance is made of Fe and impurities, and has a chemical composition that satisfies the formula (1).
0.13C + 0.05Si−0.02Mn + 0.1P + 0.01Cu−0.0555Cr + 0.007Ni−0.013Mo−0.002W−0.12V ≦ −1.04N−1.116 (1)
Here, the content (mass%) of each element is substituted for each element symbol.

  The weld metal according to the present embodiment is formed by gas metal arc welding using the above welding material. The weld metal according to the present embodiment is mass%, C: 0.03% or less, Si: 0.25 to 1.00%, Mn: 0.30 to 3.00%, P: 0.020% or less, S: 0.005% or less, Cu: 2.00% or less, Cr: 20.0 to 30.0%, Ni: 7.00 to 12.00%, N: 0.10 to 0.350%, Al : 0.005 to 0.040%, V: 0.010 to 1.50%, O: 0.010% to 0.030%, Mo: 1.00 to 4.00%, and W: It contains one or more selected from the group consisting of 1.00 to 4.00%, and the balance consists of Fe and impurities.

  The weld joint according to the present embodiment includes the weld metal and a stainless steel base material.

  By producing a welded joint using the welding material according to the present embodiment, it is possible to obtain a weld metal and a welded joint having high strength and high toughness and few blow holes.

FIG. 1 is a perspective view of a welded joint for illustrating a blow hole confirmation method. FIG. 2 is a diagram showing a sampling position of a test piece for the Charpy impact test. FIG. 3 is a schematic diagram of a test piece used in the tensile test. FIG. 4 is a diagram showing the relationship between the N content of the welding material, the solubility of N defined in F1, and the presence or absence of blowholes.

  Hereinafter, this embodiment will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  The inventors have made various studies on the welding material. As a result, the following knowledge was obtained.

  (A) During welding, gas is generated due to a decrease in solubility in the molten metal due to a decrease in temperature and a rapid decrease in solubility due to crystallization of the solid phase. When bubbles due to the generated gas remain until after the end of welding, a defect called blowhole occurs.

  (B) In order to obtain high strength and high toughness required for a welded joint, high strength stainless steel is used as a welding material. High strength stainless steel represented by high nitrogen duplex stainless steel contains a large amount of nitrogen for strength improvement. In this case, a large amount of nitrogen gas is generated in the molten metal, and blow holes are easily generated.

  (C) During welding, nitrogen that cannot be dissolved in the molten metal may become nitrogen gas as described above. Therefore, generation | occurrence | production of nitrogen gas can be suppressed by raising the solubility of nitrogen with respect to a molten metal. Nitrogen dissolved in the molten metal dissolves in the weld metal when the weld metal solidifies. In this case, nitrogen in the molten metal dissolves in the weld metal without becoming a gas. Therefore, the occurrence of blow holes can be suppressed.

  (D) When manganese (Mn), chromium (Cr), molybdenum (Mo) and tungsten (W) are contained in the molten metal, these elements increase the solubility of nitrogen in the molten metal. On the other hand, when carbon (C), silicon (Si), phosphorus (P), copper (Cu) and nickel (Ni) are contained in the molten metal, these elements lower the solubility of nitrogen in the molten metal.

  (E) When vanadium (V) is contained in the molten metal, V forms a nitride. Therefore, generation | occurrence | production of nitrogen gas is suppressed.

  (F) When the content of the element in the molten metal is appropriate, the generation of blowholes is suppressed, and a weld metal having high strength and high toughness is obtained.

The welding material according to the present embodiment completed based on the above knowledge is mass%, C: 0.02% or less, Si: 0.25 to 1.00%, Mn: 0.30 to 3.00%. , P: 0.020% or less, S: 0.010% or less, Cu: 2.00% or less, Cr: 20.0-30.0%, Ni: 7.00-12.00%, N: 0 100 to 0.350%, Al: 0.001 to 0.040%, V: 0.010 to 1.50%, Mo: 1.00 to 4.00%, and W: 1.00 One or more selected from the group consisting of ˜4.00% is contained, the balance is made of Fe and impurities, and has a chemical composition satisfying the formula (1).
0.13C + 0.05Si−0.02Mn + 0.1P + 0.01Cu−0.0555Cr + 0.007Ni−0.013Mo−0.002W−0.12V ≦ −1.04N−1.116 (1)
Here, the content (mass%) of each element is substituted for each element symbol.

  By producing a welded joint using a welding material having the above chemical composition, it is possible to obtain a weld metal and a welded joint having high strength and high toughness and few blow holes.

  The weld metal according to the present embodiment is formed by gas metal arc welding using the above welding material. The weld metal according to the present embodiment is mass%, C: 0.03% or less, Si: 0.25 to 1.00%, Mn: 0.30 to 3.00%, P: 0.020% or less, S: 0.005% or less, Cu: 2.00% or less, Cr: 20.0 to 30.0%, Ni: 7.00 to 12.00%, N: 0.10 to 0.350%, Al : 0.005 to 0.040%, V: 0.010 to 1.50%, O: 0.010% to 0.030%, Mo: 1.00 to 4.00%, and W: It contains one or more selected from the group consisting of 1.00 to 4.00%, and the balance consists of Fe and impurities.

  The weld joint according to the present embodiment includes the weld metal and a stainless steel base material.

  The base material of the stainless steel of the welded joint is mass%, C: 0.001 to 0.100%, Si: 0.050 to 1.00%, Mn: 0.10 to 1.50%, P: 0.040% or less, S: 0.010% or less, Cu: 0.010 to 2.00%, Cr: 10.50 to 14.00%, Ni: 0.50 to 10.00%, N: 0 .10% or less, Al: 0.040% or less, and Mo: 0.10 to 4.00%, and W: one or more selected from the group consisting of 0.20 to 6.00% The balance is preferably martensitic stainless steel made of Fe and impurities.

  The base material of the stainless steel of the welded joint is mass%, C: 0.03% or less, Si: 0.20 to 1.00%, Mn: 8.00% or less, P: 0.040% or less, S: 0.010% or less, Cu: 0.20 to 4.00%, Cr: 20.00 to 30.00%, Ni: 4.00 to 8.00%, N: 0.100 to 0.350 %, Al: 0.040% or less, and Mo: 0.50 to 4.00%, and W: 0.01 to 4.00%. Is preferably a duplex stainless steel comprising Fe and impurities.

  The base material of the duplex stainless steel of the welded joint is further replaced by a part of the Fe in mass%, Ca: 0.020% or less, Mg: 0.020% or less, and B: 0.020. % Or less, or a rare earth element: 0.20% or less.

  Hereinafter, preferable conditions for obtaining the welding material, the weld metal, and the weld joint according to the present embodiment will be described. With respect to chemical composition, “%” means mass%.

[Welded joint]
The welded joint according to the present embodiment includes a base material and a weld metal. For example, the welded joint is obtained by welding steel pipes or steel plates to each other at their ends. The steel pipe may be a seamless steel pipe or a welded steel pipe. The weld metal is formed by melting and solidifying a part of the base material and the welding material by GMA welding during welding.

[Chemical composition of welding material]
The welding material according to the present embodiment has the following chemical composition.

C: 0.02% or less Carbon (C) stabilizes the austenite phase in the weld metal. C further increases the strength of the weld metal by solid solution strengthening. However, if the C content is too high, the hardness of the weld metal becomes too high and the toughness is reduced. C further reduces the solubility of nitrogen (N) in the molten metal. Therefore, the C content is 0.02% or less. The upper limit with preferable C content is 0.015%. Although a lower limit is not particularly provided, when the austenite phase is stabilized, a preferable lower limit of the C content is 0.01%.

Si: 0.25 to 1.00%
Silicon (Si) deoxidizes the weld metal during welding. Si further increases the strength of the weld metal. However, Si lowers the solubility of N in the molten metal. Furthermore, when Si content is too high, the toughness of a weld metal will fall. Therefore, the Si content is 0.25 to 1.00%. The upper limit with preferable Si content is 0.50%.

Mn: 0.30 to 3.00%
Manganese (Mn) desulfurizes and deoxidizes the weld metal during welding. Mn further increases the strength of the weld metal. Mn further increases the solubility of N in the molten metal. Therefore, generation | occurrence | production of a blowhole is suppressed. However, if the Mn content is too high, the corrosion resistance of the weld metal decreases. Therefore, the Mn content is 0.30 to 3.00%. The upper limit with preferable Mn content is 2.00%. A preferable lower limit of the Mn content is 0.50%.

P: 0.020% or less Phosphorus (P) is an impurity. P lowers the solubility of N in the molten metal. P further segregates at the grain boundaries and lowers the toughness of the weld metal. By reducing the P content, P can be dissolved in the ferrite phase, and a decrease in toughness can be suppressed. When welding by high heat input welding is performed to improve welding efficiency, the heat-affected zone (HAZ) of the welded portion tends to become brittle. Even in this case, excellent toughness can be obtained by reducing the P content. Therefore, it is preferable that the P content is small. The upper limit of the P content is 0.020%, preferably 0.010%.

S: 0.010% or less Sulfur (S) is an impurity. S decreases the ductility and corrosion resistance of the weld metal, and further increases the cracking susceptibility of the weld metal at high temperatures. Therefore, it is preferable that the S content is small. The upper limit of the S content is 0.010%, preferably 0.002%.

Cu: 2.00% or less Copper (Cu) is an essential element. Cu strengthens the passive film of the weld metal and enhances corrosion resistance including SCC resistance. However, Cu lowers the solubility of N in the molten metal. Furthermore, when Cu content is too high, the toughness of a weld metal will fall. Therefore, the Cu content is 2.00% or less. The upper limit with preferable Cu content is 0.60%.

Cr: 20.0-30.0%
Chromium (Cr) increases the corrosion resistance and strength of the weld metal. Cr further increases the solubility of N in the molten metal. However, when the Cr content is too high, the corrosion resistance of the weld metal decreases. Therefore, the Cr content is 20.0-30.0%. The upper limit with preferable Cr content is 27.0%. A preferable lower limit of the Cr content is 22.0%.

Ni: 7.00 to 12.00%
Nickel (Ni) stabilizes the austenite phase in the weld metal and reduces the amount of ferrite. Ni further increases the toughness of the weld metal. When the Ni content is 7.00% or more, the amount of ferrite in the weld metal is appropriate. In this case, the weld metal has characteristics as a duplex stainless steel. Furthermore, the solid solubility of N in ferrite is small. Therefore, blowholes can be suppressed by reducing the ferrite content. However, Ni lowers the solubility of N in the molten metal. Furthermore, when the Ni content is too high, the amount of ferrite in the weld metal decreases excessively. In this case, the mechanical properties of the duplex stainless steel cannot be obtained. If the Ni content is too high, the strength of the weld metal further decreases. Therefore, the Ni content is 7.00 to 12.00%. The upper limit with preferable Ni content is 10.00%. A preferable lower limit of the Ni content is 8.40%.

N: 0.100 to 0.350%
Nitrogen (N) is a strong austenite-forming element and enhances the thermal stability and corrosion resistance of the weld metal. N further increases the strength of the weld metal by solid solution strengthening. In order to maintain an appropriate ratio of the ferrite phase to the austenite phase, it is preferable to determine the content of N in consideration of the content of Cr and Mo that are ferrite forming elements. However, if the N content is too high, blow holes are likely to occur. Further, when the N content is too high, excessive nitride is generated due to heat generated during welding. Excessive nitrides reduce the toughness and corrosion resistance of the weld metal. Therefore, the N content is 0.100 to 0.350%.

Al: 0.001 to 0.040%
Aluminum (Al) deoxidizes the weld metal during welding. Al further produces N and nitrides that cause blowholes. Therefore, blow holes are suppressed. However, when the Al content is too high, the aluminum nitride is excessively precipitated. The excessively precipitated aluminum nitride precipitates an embrittled layer and lowers the ductility and toughness of the weld metal. Therefore, the Al content is 0.001 to 0.040%. The upper limit with preferable Al content is 0.030%, More preferably, it is 0.020%.

V: 0.010-1.50%
Vanadium (V) improves the corrosion resistance of the weld metal. V further suppresses blowholes by generating N and nitrides, and contributes to Equation (1) described below. However, when the V content is too high, nitrides are excessively precipitated, and the ductility and toughness of the weld metal are lowered. Therefore, the V content is 0.010 to 1.50%. The upper limit with preferable V content is 0.10%. The minimum with preferable V content is 0.020%, More preferably, it is 0.030%.

Mo: 1.00 to 4.00%, and
W: One or more selected from 1.00 to 4.00% Molybdenum (Mo) and tungsten (W) increase the corrosion resistance and strength of the weld metal. Mo and W further increase the solubility of N in the molten metal. However, when the Mo content is too high, the toughness of the weld metal decreases. When the W content is too high, the effect of adding W is saturated and an unnecessary cost increase is caused. Therefore, the Mo content is 1.00 to 4.00%, and the W content is 1.00 to 4.00%. It only needs to contain one type selected from Mo and W, and may contain two types.

  The balance of the welding material according to the present embodiment is composed of Fe and impurities. Here, the impurities are mixed from ore as a raw material, scrap, or a manufacturing environment when industrially manufacturing steel materials, and in a range that does not adversely affect the welding material according to the present embodiment. It means what is allowed. The impurity is, for example, oxygen (O).

[Formula (1) showing solubility of nitrogen]
The chemical composition further satisfies the following formula (1).
0.13C + 0.05Si−0.02Mn + 0.1P + 0.01Cu−0.0555Cr + 0.007Ni−0.013Mo−0.002W−0.12V ≦ −1.04N−1.116 (1)
Here, the content (mass%) of each element is substituted for each element symbol.

  The left side of Equation (1) is defined as F1. The right side of equation (1) is defined as F2. F1 indicates the solubility of N in the molten metal. The smaller F1, the higher the solubility of N in the molten metal. If the solubility of N in molten metal is large, nitrogen gas is difficult to be generated during welding. N dissolved in the molten metal dissolves in the weld metal when the weld metal is solidified. Therefore, blow holes are suppressed. As described above, when Mn, Cr, Mo, and W are contained in the molten metal, these elements increase the solubility of nitrogen in the molten metal. On the other hand, when C, Si, P, Cu and Ni are contained in the molten metal, these elements lower the solubility of nitrogen in the molten metal. Vanadium (V) suppresses generation | occurrence | production of nitrogen gas by the production | generation of nitride. Therefore, blow holes are suppressed as F1 is smaller.

  F2 indicates the lower limit of the solubility of N that can suppress blowholes. When the solubility of N in the molten metal indicated by F1 is larger than the lower limit of the solubility of N indicated by F2, generation of nitrogen gas during welding is suppressed. Therefore, blow holes are suppressed. That is, blow holes are suppressed when F1 is smaller than F2.

[Chemical composition of weld metal]
The weld metal of this embodiment is formed by GMA welding using the above-described welding material. The weld metal is in mass%, C: 0.03% or less, Si: 0.25 to 1.00%, Mn: 0.30 to 3.00%, P: 0.020% or less, S: 0.00. 005% or less, Cu: 2.00% or less, Cr: 20.0 to 30.0%, Ni: 7.00 to 12.00%, N: 0.10 to 0.350%, Al: 0.005 -0.040%, V: 0.010-1.50%, O: 0.010% -0.030%, and Mo: 1.00-4.00%, and W: 1.00 It contains one or more selected from the group consisting of 4.00%, and the balance consists of Fe and impurities.

  Among the elements in the weld metal, the effects of the elements overlapping with the welding material are the same as in the case of the welding material. Among the elements in the weld metal, when the numerical range is the same as the corresponding element of the welding material, the preferable upper limit and the preferable lower limit are the same as the corresponding element of the welding material. For example, the numerical range of Si in the weld metal (0.25 to 1.00%) is the same as the numerical range of Si in the welding material (0.25 to 1.00%). Therefore, the preferable upper limit of the Si content in the weld metal is 0.80%, which is the same as the preferable upper limit of the Si content in the welding material. Similarly, the preferable lower limit of the Si content in the weld metal is 0.10%, which is the same as the preferable lower limit of the Si content in the welding material.

  The numerical range of the C content (0.03% or less), S content (0.005% or less) and Al content (0.005 to 0.040%) in the weld metal is the C content in the welding material. The effect of these elements in the weld metal, although different from the numerical ranges of the amount (0.02% or less), S content (0.010% or less) and Al content (0.001 to 0.040%) Is the same as the welding material. The upper limit with preferable C content in a weld metal is 0.020%, and a preferable minimum is 0.01%. The upper limit with preferable Al content in a weld metal is 0.02%.

The weld metal further contains oxygen (O) as described above.
O: 0.010 to 0.030%
Oxygen (O) is an impurity. O forms oxidative inclusions and lowers the toughness of the weld metal. Therefore, it is preferable that the O content is small. However, in GMA welding used at the time of manufacturing the welded joint according to the present embodiment, an oxygen component is contained in the shield gas in order to stabilize the arc. Therefore, the oxygen component in the shielding gas is taken into the weld metal during welding. Therefore, the weld metal contains 0.010% or more of O. By adjusting the component of the shielding gas, the O content of the weld metal can be made 0.030% or less. Therefore, the O content is 0.010 to 0.030%. The upper limit with preferable O content is 0.020%.

  The weld metal of this embodiment is manufactured with the above-mentioned welding material. Therefore, the occurrence of blow holes in the weld metal is suppressed.

[Base material for welded joints]
The base material for forming the welded joint according to the present embodiment is preferably stainless steel having a Cr content of 10.5% or more. Preferably, it is martensitic stainless steel or duplex stainless steel. Thereby, excellent corrosion resistance can be obtained.

[Chemical composition of martensitic stainless steel]
When the base material is martensitic stainless steel, the base material preferably has the following chemical composition.

C: 0.001 to 0.100%
Carbon (C) increases the strength of the steel. However, when the C content is too high, the toughness and stress corrosion cracking resistance of the steel are reduced. Therefore, the C content is 0.001 to 0.100%. The upper limit with preferable C content is 0.07%, More preferably, it is 0.05%. The minimum with preferable C content is 0.002%, More preferably, it is 0.003%.

Si: 0.050 to 1.00%
Silicon (Si) deoxidizes steel. However, if the Si content is too high, the toughness of the steel decreases. Therefore, the Si content is 0.050 to 1.00%. The upper limit with preferable Si content is 0.80%, More preferably, it is 0.60%. The minimum with preferable Si content is 0.10%, More preferably, it is 0.15%.

Mn: 0.10 to 1.50%
Manganese (Mn) deoxidizes steel. Mn further increases the toughness of the steel. However, if the Mn content is too high, the corrosion resistance decreases. Therefore, the Mn content is 0.10 to 1.50%. The upper limit with preferable Mn content is 1.40%, More preferably, it is 1.30%. The minimum with preferable Mn content is 0.13%, More preferably, it is 0.15%.

P: 0.040% or less Phosphorus (P) is an impurity. P decreases the hot workability of steel. P further increases cracking susceptibility due to high temperatures during welding. Therefore, it is preferable that the P content is small. The P content is 0.040% or less. The upper limit with preferable P content is 0.030%, More preferably, it is 0.025%.

S: 0.01% or less Sulfur (S) is an impurity. S decreases the hot workability of steel. Furthermore, S forms sulfides and increases cracking susceptibility due to high temperatures during welding. Therefore, it is preferable that the S content is small. The S content is 0.01% or less. The upper limit with preferable S content is 0.0050%, More preferably, it is 0.0020%.

Cu: 0.010 to 2.00%
Copper (Cu) enhances the corrosion resistance of steel by strengthening the passive film of steel. However, if the Cu content is too high, the effect of Cu addition is saturated, causing an unnecessary cost increase. Therefore, the Cu content is 0.010 to 2.00%. The upper limit with preferable Cu content is 1.95%, More preferably, it is 1.90%. The minimum with preferable Cu content is 0.013%, More preferably, it is 0.015%.

Cr: 10.5-14.00%
Chromium (Cr) enhances the corrosion resistance of the steel by strengthening the passive film of the steel. However, when the Cr content is too high, the weldability is lowered and weld cracks are likely to occur. Therefore, the Cr content is 10.5 to 14.00%. The upper limit with preferable Cr content is 13.80%, More preferably, it is 13.50%. The minimum with preferable Cr content is 11.00%, More preferably, it is 11.50%.

Ni: 0.50 to 10.00%
Nickel (Ni) improves the corrosion resistance of steel. However, when the Ni content is too high, the effect of adding Ni is saturated, resulting in unnecessary cost increase. Therefore, the Ni content is 0.50 to 10.00%. The upper limit with preferable Ni content is 9.50%, More preferably, it is 9.00%. The minimum with preferable Ni content is 1.00%, More preferably, it is 2.00%.

N: 0.1% or less When the base material is martensitic stainless steel, nitrogen (N) is an impurity. N decreases the toughness of the steel and further causes blowholes. Therefore, it is preferable that the N content is low. N content is 0.1% or less.

Al: 0.040% or less Aluminum (Al) deoxidizes steel. However, when the Al content is too high, aluminum nitride is excessively generated. Therefore, the toughness and corrosion resistance of the steel are reduced. Therefore, the Al content is 0.040% or less. The upper limit with preferable Al content is 0.035%, More preferably, it is 0.030%. The minimum with preferable AL content is 0.003%, More preferably, it is 0.005%.

Mo: 0.10 to 4.00%, and
W: One or more selected from 0.20 to 6.00% Molybdenum (Mo) and tungsten (W) enhance the corrosion resistance and stress corrosion cracking resistance of the weld metal. However, when the Mo content is too high, the toughness of the weld metal decreases. When the W content is too high, the effect of adding W is saturated and an unnecessary cost increase is caused. Therefore, the Mo content is 0.10 to 4.00%, and the W content is 0.20 to 6.00%. It only needs to contain one type selected from Mo and W, and may contain two types.

  The balance of the martensitic stainless steel according to the present embodiment is composed of Fe and impurities. Here, the impurities are mixed from ore as a raw material, scrap, or production environment when industrially producing steel, and have an adverse effect on the martensitic stainless steel according to the present embodiment. It means what is allowed in the range.

[Chemical composition of duplex stainless steel]
When the base material is duplex stainless steel, preferably the base material has the following chemical composition.

C: 0.03% or less Carbon (C) stabilizes the austenite phase. However, when the C content is too high, the carbide is excessively precipitated, and the corrosion resistance is lowered. Therefore, the C content is 0.03% or less. The upper limit with preferable C content is 0.025%, More preferably, it is 0.020%.

Si: 0.20 to 1.00%
Silicon (Si) maintains the fluidity of the molten metal during welding and reduces welding defects. However, when the Si content is too high, an intermetallic compound is generated, and hot workability is reduced. Therefore, the Si content is 0.20 to 1.00%. The upper limit with preferable Si content is 0.80%, More preferably, it is 0.60%. The minimum with preferable Si content is 0.25%, More preferably, it is 0.30%.

Mn: 8.00% or less Manganese (Mn) deoxidizes steel. Mn further forms sulfides to desulfurize the steel and enhances the hot workability of the steel. However, if the Mn content is too high, the corrosion resistance decreases. Therefore, the Mn content is 8.00% or less. The upper limit with preferable Mn content is 7.50%, More preferably, it is 5.00%. The minimum with preferable Mn content is 0.03%, More preferably, it is 0.05%.

P: 0.040% or less Phosphorus (P) is an impurity. P reduces the corrosion resistance and toughness of the steel. P further increases cracking susceptibility due to high temperatures during welding. Therefore, it is preferable that the P content is small. The P content is 0.040% or less. The upper limit with preferable P content is 0.030%, More preferably, it is 0.025%.

S: 0.010% or less Sulfur (S) is an impurity. S decreases the hot workability of steel. Furthermore, S forms sulfides and increases cracking susceptibility due to high temperatures during welding. Therefore, it is preferable that the S content is small. S content is 0.010% or less. The upper limit with preferable S content is 0.0050%, More preferably, it is 0.0020%.

Cu: 0.20 to 4.00%
Copper (Cu) enhances the corrosion resistance of steel by strengthening the passive film of steel. However, when the Cu content is too high, the hot workability of the steel decreases. Therefore, the Cu content is 0.20 to 4.00%. The upper limit with preferable Cu content is 3.50%, More preferably, it is 3.00%. The minimum with preferable Cu content is 0.23%, More preferably, it is 0.25%.

Cr: 20.00-30.00%
Chromium (Cr) increases the corrosion resistance of steel. However, when the Cr content is too high, an intermetallic compound is generated, and the hot workability is lowered. Therefore, the Cr content is 20.00 to 30.00%. The upper limit with preferable Cr content is 29.00%, More preferably, it is 28.00%. The minimum with preferable Cr content is 21.00%, More preferably, it is 22.00%.

Ni: 4.00 to 8.00%
Nickel (Ni) stabilizes the austenite phase. Ni further increases the toughness and corrosion resistance of the steel. However, when the Ni content is too high, the effect of adding Ni is saturated, resulting in unnecessary cost increase. Therefore, the Ni content is 4.00 to 8.00%. The upper limit with preferable Ni content is 7.80%, More preferably, it is 7.50%. The minimum with preferable Ni content is 4.50%, More preferably, it is 5.00%.

N: 0.100 to 0.350%
Nitrogen (N) is a strong austenite forming element and enhances the thermal stability and corrosion resistance of the steel. N further increases the strength of the steel by solid solution strengthening. In order to maintain an appropriate ratio of the ferrite phase to the austenite phase, it is preferable to determine the content of N in consideration of the content of Cr and Mo that are ferrite forming elements. However, if the N content is too high, blow holes are likely to occur. Therefore, the N content is 0.100 to 0.350%. The upper limit with preferable N content is 0.330%, More preferably, it is 0.320%.

Al: 0.040% or less Aluminum (Al) deoxidizes steel. However, when the Al content is too high, aluminum nitride is excessively generated. Therefore, the toughness and corrosion resistance of the steel are reduced. Therefore, the Al content is 0.040% or less. The upper limit with preferable Al content is 0.035%, More preferably, it is 0.030%. The minimum with preferable AL content is 0.003%, More preferably, it is 0.005%.

Mo: 0.50 to 4.00%, and
W: One or more selected from 0.01 to 4.00% Molybdenum (Mo) and tungsten (W) increase the corrosion resistance and the corresponding corrosion cracking resistance of the steel. However, when the Mo content is too high, the hot workability of the steel decreases. When the W content is too high, the effect of adding W is saturated and an unnecessary cost increase is caused. Therefore, the Mo content is 0.50 to 4.00%, and the W content is 0.01 to 4.00%. It only needs to contain one type selected from Mo and W, and may contain two types.

  The balance of the duplex stainless steel according to the present embodiment is composed of Fe and impurities. Here, the impurities are mixed from ore as a raw material, scrap, or production environment when industrially producing steel materials, and do not adversely affect the duplex stainless steel according to the present embodiment. It means what is allowed in the range.

[Selective elements for duplex stainless steel]
When the base material is the above-mentioned duplex stainless steel, it contains one or more selected from at least one of the following first group and second group instead of part of Fe: Also good.

Group 1: Ca: 0.020% or less, Mg: 0.020% or less, and B: 0.020% or less Group 2: Rare earth elements (REM): 0.20% or less

[First group]
Ca: 0.020% or less Mg: 0.020% or less B: 0.020% or less Calcium (Ca), magnesium (Mg), and boron (B) are contained as necessary. Ca, Mg and B form a compound with S and O in the steel. For this reason, the hot workability of steel is improved. When high hot workability is required for the base material, high hot workability can be obtained by adding these elements. However, when the content of these elements is too high, sulfides and oxides of these elements are excessively precipitated. For this reason, the corrosion resistance of steel falls. Therefore, the Ca content is 0.020% or less, the Mg content is 0.020% or less, and the B content is 0.020% or less.

[Second group]
Rare earth element (REM): 0.20% or less Rare earth element (REM) means 15 elements from lanthanum (La) of atomic number 57 to lutetium (Lu) of atomic number 71, yttrium (Y) and scandium (Sc) ) Is a general term for 17 elements. The REM content means the total content of these elements. REM is contained as necessary. REM forms compounds with S and O in steel. For this reason, the hot workability of steel is improved. However, when the REM content is too high, REM sulfides and oxides are excessively precipitated. For this reason, the corrosion resistance of steel falls. Therefore, the REM content is 0.20% or less.

[Production method]
The weld joint according to the present embodiment is manufactured by GMA welding using the above-described welding material and the above-described stainless steel base material.

  First, stainless steel as a base material is prepared. Stainless steel as a base material has the above-described chemical composition and is manufactured by a normal manufacturing method. For example, the raw material may be melted to form a billet, and then rolled to form a seamless steel pipe. The base material may be a steel plate. Preferably, the thickness of the base material is 10 to 30 mm.

  Next, duplex stainless steel as a welding material is prepared. The welding material has the chemical composition described above and is formed into a shape suitable for GMA welding. The shape of the welding material is, for example, a solid wire. The wire diameter is appropriately selected according to the base material and the welding speed. In general, the thicker the base material, the thicker the wire diameter and the higher current welding is applied. The wire diameter is, for example, 0.8 to 3.5 mm.

  GMA welding is performed using the prepared welding material and base material. First, a welding apparatus is prepared. The welding device may be a semi-automatic welding device or an automatic welding device. The welding apparatus includes a welding power source, a welding material supply device, a gas supply device, and a welding torch. As the output of the welding power source, a direct current is generally used, but an alternating current may be used. The welding power source preferably has a stable output even when external conditions such as input voltage fluctuate. The welding material supply device supplies welding material to the welding torch. The piping of the gas supply device is connected to the welding torch, and the gas supply device supplies shield gas to the welding torch. The welding torch generates an arc between the supplied welding material and the base material, and forms a weld metal by forming a weld pool and a weld bead. The welded portion is covered with the supplied shielding gas so that it is cut off from the atmosphere, and the arc is stabilized.

The shield gas used is, for example, a mixed gas of an inert gas such as argon (Ar) or helium (He) and carbon dioxide (CO ₂ ) gas. As described above, the oxygen (O) content in the weld metal can be adjusted to 0.030% or less by adjusting the components of the shield gas. Therefore, the gas mixing ratio and flow rate may be adjusted so that the O content in the weld metal is 0.030% or less. For example, by setting the mixing ratio of the shielding gas to the range of CO ₂ : Ar = 1.0: 99.0 to 5.0: 95.0 and the flow rate of the shielding gas to the range of 20 to 30 L / min, the weld metal The O content is 0.030% or less.

[Strength, toughness and blowhole of welded joints]
Through the above steps, a welded joint including a base material and a weld metal is manufactured. The welded joint according to the present embodiment has a tensile strength of 700 MPa or more, and the absorbed energy of the Charpy impact test at −30 ° C. is 150 J or more. Furthermore, the occurrence of blow holes is suppressed.

  The blowhole can be confirmed by the following method. Referring to FIG. 1, a region 3 of 100 mm in the longitudinal direction of weld metal 2 and 30 mm in the width direction of weld metal 2 is selected in weld metal 2 of weld joint 1. Based on JIS Z3104 (1995), a radiation transmission test method for a steel welded joint is performed on the selected region 3, and a transmission image is taken. In the obtained image, the presence or absence of blowholes is confirmed.

[Preparation of base material]
Stainless steel having the chemical composition shown in Table 1 was prepared. Each stainless steel was a steel plate having a thickness of 10 mm.

  Base material number X and base material number Y were duplex stainless steels. Base material number X was 22% Cr and base material number Y was a duplex stainless steel containing 25% Cr. Base material number Z was a martensitic stainless steel containing 13% Cr.

[Preparation of welding materials]
Wires having chemical compositions shown in Table 2 were prepared. Welding material numbers A, C, G, K, and O have chemical compositions set based on so-called 22Cr steel. Welding material numbers B, D to F, H to J, and L to N have chemical compositions set based on so-called 25Cr steel. The wire was a solid wire with a diameter of 1.2 mm.

  In Table 2, “◯” described in the determination column of the formula (1) indicates that the chemical composition satisfies the formula (1). “X” indicates that the chemical composition did not satisfy the formula (1).

[Manufacture of welded joints by GMA welding]
GMA welding was performed using the prepared base material and welding material to produce a welded joint. The shielding gas used was a mixed gas of CO ₂ : Ar = 1.0: 99.0 to 6.0: 94.0, the gas flow rate was 25 L / min, and the nozzle inner diameter was 15.0 to 20.0 mm. The amount of heat input was changed as shown in Table 4, and welding was performed.

  The chemical composition of the obtained weld metal was as shown in Table 3.

  The following tests were performed on the obtained weld metal and weld joint.

[Blowhole presence check test]
The above-mentioned measurement method was implemented with respect to the obtained weld metal of each weld joint, and the presence or absence of the blowhole in a weld metal was confirmed. The results are shown in Table 4. “◯” described in the column of presence / absence of blow holes in Table 4 indicates that no blow holes were confirmed in the weld metal. “X” indicates that a blowhole was confirmed in the weld metal.

[Charpy impact test]
The toughness of each weld metal obtained was evaluated by a Charpy impact test. A Charpy impact test piece (V-notch test piece) was collected from each obtained weld metal. FIG. 2 is a schematic view of a cross section perpendicular to the steel plate surface of the steel plate used in the test as seen from the front. With reference to FIG. 2, the V notch of the test piece 4 was located at the center of the weld metal 2 of the weld joint 1. The V-notch test piece 4 had a width of 10 mm, a thickness of 10 mm, a length of 55 mm, and a notch depth of 2 mm. Using the collected V-notch test piece, a Charpy impact test was performed based on JIS Z2242 (2005), and the absorbed energy at −30 ° C. was obtained. The results are shown in Table 4. “◯” described in the column of the impact test in Table 4 indicates that the absorbed energy of the weld metal at −30 ° C. was 150 J or more as a result of the Charpy impact test. “X” indicates that the absorbed energy of the weld metal at −30 ° C. was less than 150 J as a result of the Charpy impact test.

[Tensile test]
The strength of each welded joint obtained was evaluated by a tensile test. From each of the obtained welded joints, a 4A arc-shaped test piece was sampled based on JIS Z3121 (2004). With reference to FIG. 3, the weld metal 2 was located in the center part of the test piece, and the welding heat affected zone 5 and the base material 6 were sequentially located on both sides thereof. A tensile test was performed using the collected test pieces, and the tensile strength (MPa) at room temperature (25 ° C.) was measured. The results are shown in Table 4. “◯” described in the column of the tensile test in Table 4 indicates that the tensile strength of the welded joint at room temperature (25 ° C.) was 700 MPa or more as a result of the tensile test. “X” indicates that the tensile strength of the welded joint at room temperature (25 ° C.) was less than 700 MPa.

  In Table 4, “◯” described in the determination column of the formula (1) indicates that the chemical composition satisfies the formula (1). “X” indicates that the chemical composition did not satisfy the formula (1).

[Evaluation results]
Referring to Tables 1 to 4, the chemical compositions of welding material numbers A to F were appropriate and satisfied the formula (1) (see Table 1). Furthermore, the chemical composition of the obtained weld metal was appropriate (refer to weld metal numbers 1 to 7 in Table 3). Therefore, no blowhole was confirmed in the weld metal of the obtained welded joint, and the absorbed energy in the Charpy impact test was 150 J or more, indicating excellent toughness (refer to welded joint numbers 1 to 7 in Table 4). Furthermore, the tensile strength of the obtained welded joint was 700 MPa or more, indicating an excellent strength (see welded joint numbers 1 to 7 in Table 4).

  Welded joint number 1 is an example (welding material number A) in which the base metal is duplex stainless steel and the chemical composition of the welding material is set based on 22Cr steel. The weld metal of welded joint number 1 was suppressed in blowholes, and the absorbed energy in the Charpy impact test was 150 J or more, indicating excellent toughness. Furthermore, the welded joint with welded joint number 1 had a tensile strength of 700 MPa or more and exhibited excellent strength.

  Welded joint numbers 2 and 5 are examples (welding material numbers B and E) in which the base metal is duplex stainless steel and the chemical composition of the welding material is set based on 25Cr steel. In any weld metal, blowholes were suppressed, and the absorbed energy in the Charpy impact test was 150 J or more, indicating excellent toughness. Furthermore, all the welded joints had a tensile strength of 700 MPa or more, indicating excellent strength.

  The weld joint number 3 is an example in which a weld material (weld material number C) having a higher N content than the weld joint number 1 is used. Even when the N content is high, it was possible to suppress weld metal blowholes by increasing the Cr, Mo, and Mn contents of the welding material to increase the solubility of N.

  Welded joint numbers 4 and 7 are examples in which the heat input is increased using welding materials (welding material numbers D and B) in which the base material is martensitic stainless steel and the chemical composition is set based on 25Cr steel. . Even with a large heat input, the absorbed energy of the obtained weld metal in the Charpy impact test was 150 J or more, indicating excellent toughness.

  The weld joint number 6 is an example in which a weld material (weld material number F) having a higher N content than the weld joint numbers 4 and 7 is used. Even when the N content is high, it was possible to suppress weld metal blowholes by increasing the Cr, Mo, and Mn contents of the welding material to increase the solubility of N.

  On the other hand, although the chemical composition of the welding material (welding material number G, K, L, and M) used for the welding joint numbers 8 and 12-14 was appropriate, it did not satisfy | fill Formula (1). Therefore, blow holes were generated.

  The P content of the welding materials (welding material numbers H, I and J) used for the welded joint numbers 9 to 11 was too high. Therefore, the toughness was lowered and the absorbed energy in the Charpy impact test was less than 150 J.

The chemical composition of the welding material (welding material number N) used for welded joint number 15 was appropriate and satisfied the formula (1). However, since the CO ₂ content in the shielding gas is as high as 6%, the O content of the weld metal was too high. Therefore, the toughness was lowered and the absorbed energy in the Charpy impact test was less than 150 J.

  The Ni content of the welding material (welding material number O) used for the welded joint number 16 was too high, and the N content was too low. For this reason, toughness fell and the absorbed energy of the Charpy impact test was less than 150J. Furthermore, the strength decreased and the tensile strength became less than 700 MPa.

  FIG. 4 is a diagram showing the relationship between the N content of the welding material, the solubility of N defined in F1 and the presence or absence of blowholes, and the results of the examples are plotted. “◯” described in FIG. 4 indicates that no blowhole was observed in the weld metal. “X” indicates that a blowhole was confirmed in the weld metal. Referring to FIG. 4, it can be seen that blowholes are generated when the solubility of N defined in F1 is greater than the lower limit of the solubility of N defined in F2.

  The embodiment of the present invention has been described above. However, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately changing the above-described embodiment without departing from the spirit thereof.

1 Welded joint 2 Weld metal 6 Base material

Claims (7)

Welding material in mass%
C: 0.02% or less,
Si: 0.25 to 1.00%,
Mn: 0.30 to 3.00%,
P: 0.020% or less,
S: 0.010% or less,
Cu: 2.00% or less,
Cr: 20.0-30.0%,
Ni: 7.00 to 12.00%,
N: 0.100 to 0.350%,
Al: 0.001 to 0.040%,
V: 0.010 to 1.50%, and
Mo: 3.27 to 4.00% and
W: containing one or more selected from the group consisting of 1.00 to 4.00%,
The balance consists of Fe and impurities, and has a chemical composition satisfying the formula (1).
0.13C + 0.05Si−0.02Mn + 0.1P + 0.01Cu−0.0555Cr + 0.007Ni−0.013Mo−0.002W−0.12V ≦ −1.04N−1.116 (1)
Here, the content (mass%) of each element is substituted for each element symbol. Using the welding material according to claim 1, formed by gas metal arc welding,
% By mass
C: 0.03% or less,
Si: 0.25 to 1.00%,
Mn: 0.30 to 3.00%,
P: 0.020% or less,
S: 0.005% or less,
Cu: 2.00% or less,
Cr: 20.0-30.0%,
Ni: 7.00 to 12.00%,
N: 0.100 to 0.350%,
Al: 0.005 to 0.040%,
V: 0.010 to 1.50%,
O: 0.010% to 0.030%, and
Mo: 1.00 to 4.00%, and
W: A weld metal containing one or more selected from the group consisting of 1.00 to 4.00%, with the balance being Fe and impurities. A weld metal according to claim 2;
A welded joint comprising a stainless steel base material. The weld joint according to claim 3,
The stainless steel base material is mass%,
C: 0.001 to 0.100%,
Si: 0.050 to 1.00%,
Mn: 0.10 to 1.50%,
P: 0.040% or less,
S: 0.010% or less,
Cu: 0.010 to 2.00%,
Cr: 10.50-14.00%,
Ni: 0.50 to 10.00%,
N: 0.10% or less,
Al: 0.040% or less, and
Mo: 0.10 to 4.00%, and
W: A welded joint containing one or more selected from the group consisting of 0.20 to 6.00% and the balance being martensitic stainless steel made of Fe and impurities. The weld joint according to claim 3,
The stainless steel base material is mass%,
C: 0.03% or less,
Si: 0.20 to 1.00%,
Mn: 8.00% or less,
P: 0.040% or less,
S: 0.010% or less,
Cu: 0.20 to 4.00%,
Cr: 20.00-30.00%,
Ni: 4.00 to 8.00%,
N: 0.100 to 0.350%,
Al: 0.040% or less, and
Mo: 0.50 to 4.00%, and
W: A welded joint containing one or more selected from the group consisting of 0.01 to 4.00%, the balance being duplex stainless steel made of Fe and impurities. The weld joint according to claim 5,
The base material of the duplex stainless steel is further
Instead of a part of the Fe, in mass%,
Ca: 0.020% or less,
Mg: 0.020% or less, and
B: A welded joint containing one or more selected from the group consisting of 0.020% or less. The weld joint according to claim 5 or 6,
The base material of the duplex stainless steel is further
Instead of a part of the Fe, in mass%,
Rare earth element: A welded joint containing 0.20% or less.