JP2017095786A - Al-CONTAINING FERRITIC STAINLESS STEEL WELD JOINT EXCELLENT IN 475°C BRITTLE EMBRITTLEMENT RESISTANCE - Google Patents
Al-CONTAINING FERRITIC STAINLESS STEEL WELD JOINT EXCELLENT IN 475°C BRITTLE EMBRITTLEMENT RESISTANCE Download PDFInfo
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- 229910052733 gallium Inorganic materials 0.000 claims description 6
- 229910052750 molybdenum Inorganic materials 0.000 claims description 6
- 229910052721 tungsten Inorganic materials 0.000 claims description 6
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- 238000010248 power generation Methods 0.000 claims description 4
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- 229910052739 hydrogen Inorganic materials 0.000 abstract description 7
- 239000001257 hydrogen Substances 0.000 abstract description 7
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 abstract description 6
- 239000004215 Carbon black (E152) Substances 0.000 abstract description 4
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Abstract
Description
本発明は、都市ガス、メタン、天然ガス、プロパン、灯油、ガソリン等の炭化水素系燃料を水素に改質する際に使用される改質器、熱交換器などの燃料電池高温部材に好適な耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手およびその製造方法に関する。 The present invention is suitable for high-temperature members of fuel cells such as reformers and heat exchangers used when reforming hydrocarbon fuels such as city gas, methane, natural gas, propane, kerosene, and gasoline into hydrogen. The present invention relates to an Al-containing ferritic stainless steel welded joint excellent in resistance to brittleness at 475 ° C. and a method for producing the same.
最近、石油を代表とする化石燃料の枯渇化、ＣＯ2排出による地球温暖化現象等の問題から、従来の発電システムに替わる新しいシステムの普及が加速している。その１つとして、分散電源，自動車の動力源としても実用的価値が高い「燃料電池」が注目されている。燃料電池にはいくつかの種類があるが、その中でも固体高分子型燃料電池（ＰＥＦＣ）や固体酸化物型燃料電池（ＳＯＦＣ）はエネルギー効率が高く、将来の普及拡大が有望視されている。 Recently, the spread of new systems replacing conventional power generation systems is accelerating due to problems such as depletion of fossil fuels such as petroleum and global warming due to CO 2 emissions. As one of them, “fuel cell”, which has high practical value as a distributed power source and a power source for automobiles, is attracting attention. There are several types of fuel cells. Among them, polymer electrolyte fuel cells (PEFC) and solid oxide fuel cells (SOFC) have high energy efficiency, and are expected to expand in the future.
燃料電池は、水の電気分解と逆の反応過程を経て電力を発生する装置であり、水素を必要とする。水素は、都市ガス（ＬＮＧ）、メタン、天然ガス、プロパン、灯油、ガソリン等の炭化水素系燃料を触媒の存在下で改質反応させることにより製造される。中でも都市ガスを原燃料とする燃料電池は、都市ガス配管が整備された地区において水素を製造できる利点がある。 A fuel cell is a device that generates electric power through a reaction process opposite to that of water electrolysis, and requires hydrogen. Hydrogen is produced by a reforming reaction of hydrocarbon fuels such as city gas (LNG), methane, natural gas, propane, kerosene, and gasoline in the presence of a catalyst. Above all, a fuel cell using city gas as a raw fuel has an advantage that hydrogen can be produced in an area where city gas piping is provided.
燃料改質器は、水素の改質反応に必要な熱量を確保するため、通常、２００〜９００℃までの高温で運転される。このような高温運転下において、多量の水蒸気、二酸化炭素、一酸化炭素等を含む酸化性の雰囲気に曝され、水素の需要に応じて起動・停止による加熱・冷却サイクルが繰り返される。また、ＳＯＦＣシステムでは、高Ｃｒ含有ステンレス鋼を適用した場合、ＳＯＦＣ動作温度においてＣｒの蒸発によるセラミックス電極の被毒を防止する課題がある。 The fuel reformer is usually operated at a high temperature of 200 to 900 ° C. in order to ensure the amount of heat necessary for the hydrogen reforming reaction. Under such a high temperature operation, it is exposed to an oxidizing atmosphere containing a large amount of water vapor, carbon dioxide, carbon monoxide and the like, and the heating / cooling cycle by starting and stopping is repeated according to the demand for hydrogen. Further, in the SOFC system, when high Cr content stainless steel is applied, there is a problem of preventing poisoning of the ceramic electrode due to Cr evaporation at the SOFC operating temperature.
また、Ｃｒを１５％以上含有するフェライト系ステンレス鋼では、４００〜５００℃程度の温度域に長時間曝されると、高Ｃｒ濃度相と低Ｃｒ濃度相のスピノーダル分解に起因した硬質化が生じる可能性が考えられる。いわゆる４７５℃脆性である。したがって、ＳＯＦＣシステムにおける高温使用環境においては、４７５℃脆性に起因した材料劣化が生じる可能性が考えられる。 Further, in a ferritic stainless steel containing 15% or more of Cr, when it is exposed to a temperature range of about 400 to 500 ° C. for a long time, hardening due to spinodal decomposition of a high Cr concentration phase and a low Cr concentration phase occurs. There is a possibility. It is so-called 475 ° C brittle. Therefore, there is a possibility that material deterioration due to brittleness at 475 ° C. occurs in a high temperature use environment in the SOFC system.
ＳＯＦＣ用途では、良好な耐酸化性・耐Ｃｒ蒸発性を有するＡｌ含有フェライト系ステンレス鋼の適用が推奨されている。しかしながら、Ａｌ含有フェライト系ステンレス鋼は他のフェライト系ステンレス鋼と比べ強度が高いため低靭性であり、例えば非特許文献１で開示されている通り、鉄鋼材料の延性脆性遷移温度はＡｌ添加により増大することが知られている。 For SOFC applications, application of Al-containing ferritic stainless steel having good oxidation resistance and Cr evaporation resistance is recommended. However, since Al-containing ferritic stainless steel has higher strength than other ferritic stainless steels, it has low toughness. For example, as disclosed in Non-Patent Document 1, the ductile brittle transition temperature of steel materials increases with Al addition. It is known to do.
特許文献１には、高温水蒸気含有雰囲気での耐酸化性とクリープ破断寿命を兼備する燃料電池用フェライト系ステンレス鋼が開示されている。本ステンレス鋼のＣｒ量は１３〜２０％であるが、Ｃｒ量が４７５℃脆性を示さない１５％以下の場合、耐酸化性確保のために４％以上のＡｌ添加が必要となるが、このように多量のＡｌを含む鋼板の靭性は著しく低下するため、実製造が困難となる。 Patent Document 1 discloses a ferritic stainless steel for fuel cells that has both oxidation resistance in a high-temperature steam-containing atmosphere and a creep rupture life. The amount of Cr in this stainless steel is 13 to 20%. If the amount of Cr is 15% or less that does not show brittleness at 475 ° C., 4% or more of Al should be added to ensure oxidation resistance. Thus, since the toughness of a steel sheet containing a large amount of Al is significantly reduced, actual production becomes difficult.
特許文献２には、耐酸化性、二次加工性に優れ、自動車排ガス経路に設置されるセンサの素子カバーなどの耐酸化性と高成形加工性が要求される用途に好適なフェライト系ステンレス鋼が開示されている。本ステンレス鋼の場合、実質１８％程度のＣｒを含有するため、４７５℃脆性が発現する可能性が考えられる。 Patent Document 2 discloses a ferritic stainless steel that is excellent in oxidation resistance and secondary workability, and suitable for applications requiring oxidation resistance and high formability such as a sensor element cover installed in an automobile exhaust gas path. Is disclosed. In the case of this stainless steel, it contains about 18% of Cr, so that it is possible that brittleness at 475 ° C. will develop.
特許文献３には、表面性状に優れた高Ａｌ含有フェライト系ステンレス鋼板、その製造方法、ステンレス箔が開示されている。本ステンレス鋼の場合、実質１８％程度のＣｒおよび３％以上のＡｌを含有するため、４７５℃脆性の発現および高Ａｌ含有による靭性低下が生じると考えられる。 Patent Document 3 discloses a high Al-containing ferritic stainless steel sheet having excellent surface properties, a method for producing the same, and a stainless steel foil. In the case of the present stainless steel, it contains substantially 18% Cr and 3% or more Al, so that it is considered that the 475 ° C. brittleness expression and the toughness reduction due to the high Al content occur.
特許文献４には、溶接性と加工性に優れた触媒担持用耐熱フェライト系ステンレス鋼が開示されている。本ステンレス鋼はＡｌを１〜２．５％程度含有し、溶接後も優れた成形加工性を有している点に特徴がある。 Patent Document 4 discloses a heat-resistant ferritic stainless steel for supporting a catalyst excellent in weldability and workability. This stainless steel is characterized in that it contains about 1 to 2.5% of Al and has excellent formability after welding.
本発明では、ＳＯＦＣシステムにおいて溶接構造を採用する場合に、４７５℃脆性に起因した溶接部の脆性破壊を回避することが特に重要な解決課題であると知見した。
特許文献１〜４においては、４７５℃脆性起因の硬化後の溶接部における課題は認識されていない。すなわち、溶接部における耐４７５℃脆性を確保する観点から開発されたフェライト系ステンレス鋼は現状存在しない。
本発明は、上述した課題を解消すべく開発されたものであり、耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手を提供するものである。
In the present invention, when adopting a welded structure in the SOFC system, it has been found that avoiding brittle fracture of the weld due to brittleness at 475 ° C. is a particularly important solution.
In patent documents 1-4, the problem in the welded part after hardening resulting from 475 degreeC brittleness is not recognized. That is, there is currently no ferritic stainless steel developed from the viewpoint of ensuring 475 ° C. brittleness resistance at the weld.
The present invention has been developed to solve the above-described problems, and provides an Al-containing ferritic stainless steel welded joint excellent in 475 ° C. brittleness resistance.
（１）溶接金属部の化学成分が、質量％にて、Ｃ：０．０３％以下、Ｎ：０．０３％以下、Ｓｉ：２．０％以下、Ｍｎ：２．０％以下、Ｐ：０．０４０％以下、Ｓ：０．０１％以下、Ｃｒ：１５．０〜２５．０％、Ａｌ：１．０〜４．０％を含み、更にＴｉ：１．０％以下、Ｎｂ：１．０％以下、Ｖ：１．０％以下の１種類または２種以上からなり且つ式（１）を満たす第１群、およびＭｇ：０．０１０％以下、Ｃａ：０．００５％以下の１種または２種以上からなる第２群のうち少なくともいずれかの群を含有し、残部がＦｅおよび不可避的不純物であることを特徴とする耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手。
（［Ｔｉ］＋［Ｎｂ］＋［Ｖ］）／（２×［Ｃ］＋［Ｎ］）≧４．０・・・・式（１）
ここで、［Ｔｉ］、［Ｎｂ］、［Ｖ］、［Ｃ］、［Ｎ］は、それぞれの元素の含有量（質量％）を示す。
（２）溶接金属部の化学成分が、更に、質量％にて、
Ｎｉ：１．０％以下、Ｃｕ：１．０％以下、Ｍｏ：１．０％以下、Ｗ：１．０％以下の１種または２種以上からなる第３群、および、Ｃｏ：０．１０％以下、Ｓｎ０．１０％以下、Ａｓ：０．０５％以下、Ｂ：０．００５％以下、Ｐｂ：０．００５％以下、Ｚｒ：０．１％以下、Ｚｎ：０．０３％以下、Ｙ：０．１０％以下、Ｇａ：０．１０％以下、Ｌａ：０．１０％以下、Ｈｆ：０．１０％以下、Ｓｂ：０．１０％以下、ＲＥＭ：０．１０％以下、Ｔａ：０．５％以下の１種または２種以上からなる第４群のうち、少なくともいずれかの群を含有することを特徴とする（１）に記載の耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手。
（３）式（２）が質量％にて、０．２０％以下であることを特徴とする請求項２に記載の耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手。
［Ｃｏ］＋［Ｓｎ］＋［Ａｓ］＋［Ｂ］＋［Ｐｂ］＋［Ｚｒ］＋［Ｚｎ］＋［Ｙ］＋［Ｇａ］＋［Ｌａ］＋［Ｈｆ］＋［Ｓｂ］＋［ＲＥＭ］＋［Ｔａ］・・・式（２）
ここで、［Ｃｏ］、［Ｓｎ］、［Ａｓ］、［Ｂ］、［Ｐｂ］、［Ｚｒ］、［Ｚｎ］、［Ｙ］、［Ｇａ］、［Ｌａ］、［Ｈｆ］、［Ｓｂ］、［ＲＥＭ］、［Ｔａ］は、それぞれの元素の含有量（質量％）を示す。
（４）溶接金属部における結晶粒径の大きさが３５０μｍ以下であることを特徴とする（１）〜（３）に記載の耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手。
（５）燃料改質器、熱交換器あるいは燃料電池高温部材に適用されることを特徴とする（１）〜（４）に記載の耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手。
（６）ガスタービン及び発電システムの少なくともいずれかに用いられる高温部材に適用されることを特徴とする（１）〜（４）のいずれかに記載の耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手。
（７）エキゾーストマニホールド、コンバータ、マフラー、ターボチャージャー、ＥＧＲクーラー、フロントパイプ及びセンターパイプの少なくともいずれかの自動車用部材に適用されることを特徴とする（１）〜（４）のいずれかに記載の耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手。
（８）ストーブ及びファンヒータの少なくともいずれかの燃焼機器に用いられる高温部材に適用されることを特徴とする（１）〜（４）のいずれかに記載の耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手。
以下、上記（１）〜（８）に係るＡｌ含有フェライト系ステンレス鋼溶接継手をそれぞれ本発明という。
(1) The chemical composition of the weld metal part is, in mass%, C: 0.03% or less, N: 0.03% or less, Si: 2.0% or less, Mn: 2.0% or less, P: 0.040% or less, S: 0.01% or less, Cr: 15.0-25.0%, Al: 1.0-4.0%, Ti: 1.0% or less, Nb: 1 0.0% or less, V: 1.0% or less, the first group consisting of one or more and satisfying the formula (1), and Mg: 0.010% or less, Ca: 0.005% or less Al-containing ferritic stainless steel welded joint with excellent resistance to brittleness at 475 ° C., characterized in that it contains at least one of the seeds or the second group consisting of two or more kinds, the balance being Fe and inevitable impurities .
([Ti] + [Nb] + [V]) / (2 × [C] + [N]) ≧ 4.0 (1)
Here, [Ti], [Nb], [V], [C], and [N] indicate the content (% by mass) of each element.
(2) The chemical composition of the weld metal part is further in mass%,
A third group consisting of one or more of Ni: 1.0% or less, Cu: 1.0% or less, Mo: 1.0% or less, W: 1.0% or less, and Co: 0. 10% or less, Sn 0.10% or less, As: 0.05% or less, B: 0.005% or less, Pb: 0.005% or less, Zr: 0.1% or less, Zn: 0.03% or less, Y: 0.10% or less, Ga: 0.10% or less, La: 0.10% or less, Hf: 0.10% or less, Sb: 0.10% or less, REM: 0.10% or less, Ta: The Al-containing ferrite system having excellent resistance to brittleness at 475 ° C. according to (1), characterized in that it contains at least one of the fourth group consisting of one or more of 0.5% or less Stainless steel welded joint.
(3) The Al-containing ferritic stainless steel welded joint having excellent 475 ° C brittleness resistance according to claim 2, wherein the formula (2) is 0.20% or less in terms of mass%.
[Co] + [Sn] + [As] + [B] + [Pb] + [Zr] + [Zn] + [Y] + [Ga] + [La] + [Hf] + [Sb] + [REM ] + [Ta] Formula (2)
Here, [Co], [Sn], [As], [B], [Pb], [Zr], [Zn], [Y], [Ga], [La], [Hf], [Sb] , [REM], and [Ta] indicate the content (% by mass) of each element.
(4) The Al-containing ferritic stainless steel welded joint having excellent brittleness resistance at 475 ° C. according to (1) to (3), wherein the crystal grain size in the weld metal part is 350 μm or less.
(5) The Al-containing ferritic stainless steel welded joint having excellent brittle resistance at 475 ° C. according to (1) to (4), which is applied to a fuel reformer, a heat exchanger, or a fuel cell high-temperature member .
(6) The Al-containing ferrite system having excellent resistance to brittleness at 475 ° C. according to any one of (1) to (4), which is applied to a high-temperature member used in at least one of a gas turbine and a power generation system. Stainless steel welded joint.
(7) It is applied to at least one of automotive components such as an exhaust manifold, a converter, a muffler, a turbocharger, an EGR cooler, a front pipe, and a center pipe. 475 ° C Al-containing ferritic stainless steel welded joint with excellent brittleness.
(8) Al content having excellent resistance to brittleness at 475 ° C. according to any one of (1) to (4), which is applied to a high temperature member used in at least one of combustion equipment of a stove and a fan heater Ferritic stainless steel welded joint.
Hereinafter, each of the Al-containing ferritic stainless steel welded joints according to the above (1) to (8) is referred to as the present invention.
本発明により、耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手を提供することができる。 According to the present invention, it is possible to provide an Al-containing ferritic stainless steel welded joint excellent in resistance to brittleness at 475 ° C.
本発明者らは、前記した課題を解決するため、フェライト系ステンレス鋼における４７５℃脆性に起因した脆性破壊機構の解明および脆性破壊挙動におよぼす各種合金元素の影響について実験と検討を重ね、本発明を完成させた。以下に本発明で得られた知見について説明する。 In order to solve the above-mentioned problems, the present inventors have conducted experiments and studies on the elucidation of the brittle fracture mechanism due to brittleness at 475 ° C. in ferritic stainless steel and the effects of various alloy elements on the brittle fracture behavior. Was completed. The knowledge obtained by the present invention will be described below.
（ａ）母材部に対し、溶接部では結晶粒径が大きくなるため、４７５℃脆性起因の破壊が生じやすくなる。この破壊の場合、へき開破面を呈する。Ａｌ含有フェライト系ステンレス鋼では、Ａｌを含有していないフェライト系ステンレス鋼と比較し溶接時の結晶粒径が粗大化しやすい傾向にある。溶接継手における溶金部（溶接金属部、本発明では溶接施工時に溶融して凝固した領域のことを意味する）の結晶粒径は３５０μｍ以下であることが好ましい。また、４７５℃脆性起因の硬化挙動は例えばビッカース硬さ試験により評価できる。耐４７５℃脆性確保のためには、５００℃時効後のビッカース硬さが３００以下であることが好ましい。 (A) Since the crystal grain size is larger in the welded portion than in the base metal portion, fracture due to 475 ° C. brittleness is likely to occur. In the case of this destruction, it exhibits a cleavage plane. Al-containing ferritic stainless steel tends to be coarser in crystal grain size during welding than ferritic stainless steel not containing Al. It is preferable that the crystal grain size of the molten metal part (welded metal part, which means a region melted and solidified at the time of welding in the present invention) in the welded joint is 350 μm or less. Further, the curing behavior due to brittleness at 475 ° C. can be evaluated by, for example, a Vickers hardness test. In order to ensure 475 ° C. brittleness resistance, it is preferable that the Vickers hardness after aging at 500 ° C. is 300 or less.
（ｂ）詳細な組織観察を行った結果、４７５℃脆性起因の破壊には双晶変形が関与しており、変形双晶導入によりせん断歪が発生する。このせん断歪を解放するため、へき開き裂が生成し、伝播することで破壊に至る。また、上述のせん断歪の解放時、粒界き裂が生じる場合もあることが分かった。この場合、ＰやＳ，Ｓｎ等の粒界偏析による粒界強度低下にともなう粒界破壊がき裂生成の起点となる。 (B) As a result of detailed structure observation, twin deformation is involved in the fracture due to brittleness at 475 ° C., and shear strain is generated by introducing the deformation twin. In order to release this shear strain, a cleaved crack is generated and propagates to break. It was also found that a grain boundary crack may occur when the above-described shear strain is released. In this case, intergranular fracture resulting from a decrease in grain boundary strength due to segregation of grain boundaries such as P, S, and Sn is the starting point for crack generation.
（ｃ）溶接部における４７５℃脆性起因の破壊を抑制するためには、(i)双晶変形を発現しにくくすること、(ii)溶接時の結晶粒の粗大化を抑制すること、(iii)不純物元素の過剰な粒界偏析による粒界強度の低下を抑制することが重要となる。 (C) In order to suppress breakage due to brittleness at 475 ° C. in the welded part, (i) making it difficult to develop twin deformation, (ii) suppressing coarsening of crystal grains during welding, (iii) It is important to suppress a decrease in grain boundary strength due to excessive grain boundary segregation of impurity elements.
（ｄ）Ａｌは従来、フェライト鋼の強度を増加させ、延性脆性遷移温度を増加させる、すなわち脆性破壊を助長させる元素であることが知られていた。しかしながら、溶接部のような結晶粒が粗大で、かつ４７５℃脆性起因の硬化によりすべり変形が非常に困難な状況において、適量のＡｌ添加は双晶変形応力を高め、相対的にすべり変形を容易にすることが新たに分かった。 (D) Al is conventionally known to be an element that increases the strength of ferritic steel and increases the ductile brittle transition temperature, that is, promotes brittle fracture. However, in a situation where crystal grains are coarse like welds and slip deformation is very difficult due to brittleness due to 475 ° C brittleness, an appropriate amount of Al increases twin deformation stress and makes slip deformation relatively easy. I have newly found out.
（ｅ）通常、Ａｌ含有フェライト系ステンレス鋼の溶接組織は柱状晶の成長により構成されるため、Ａｌを含有していないフェライト系ステンレス鋼に対して粗大となる傾向にある。しかしながら、溶接金属中の化学成分の制御により（Ｔｉ，Ｎｂ，Ｖ）（Ｃ，Ｎ）から成る炭窒化物、あるいはＭｇＯ、ＣａＯなどから成る介在物を生成させることで等軸晶の形成が助長され、溶接組織が微細化することがわかった。 (E) Usually, since the weld structure of Al-containing ferritic stainless steel is constituted by the growth of columnar crystals, it tends to be coarser than ferritic stainless steel not containing Al. However, formation of equiaxed crystals is promoted by generating carbonitrides composed of (Ti, Nb, V) (C, N) or inclusions composed of MgO, CaO, etc. by controlling chemical components in the weld metal. It was found that the weld structure was refined.
（ｆ）フェライト系ステンレス鋼において、炭窒化物Ｔｉ（Ｃ，Ｎ）の生成挙動は［Ｔｉ］／（［Ｃ］＋［Ｎ］）で整理させる。しかしながら、Ａｌ含有フェライト系ステンレス鋼においては、ＡｌがＣの活量を増加させるため、Ｃｒ炭化物の析出挙動は、通常のフェライト系ステンレス鋼に対してＣ量の影響をより強く受けることが新たに分かった。（ｅ）で述べた炭窒化物（Ｔｉ，Ｎｂ，Ｖ）（Ｃ，Ｎ）による等軸晶の形成促進効果を得るためには、（［Ｔｉ］＋［Ｎｂ］＋［Ｖ］）／（２×［Ｃ］＋［Ｎ］）の値を４．０以上とすることが好ましい。或いは、同様の効果を得るためにＭｇを０．０００５％以上、Ｃａを０．０００１％以上添加することが好ましいことが分かった。 (F) In ferritic stainless steel, the formation behavior of carbonitride Ti (C, N) is arranged by [Ti] / ([C] + [N]). However, in Al-containing ferritic stainless steel, since Al increases the activity of C, the precipitation behavior of Cr carbide is newly affected by the amount of C more strongly than ordinary ferritic stainless steel. I understood. In order to obtain the effect of promoting the formation of equiaxed crystals by the carbonitrides (Ti, Nb, V) (C, N) described in (e), ([Ti] + [Nb] + [V]) / ( 2 × [C] + [N]) is preferably 4.0 or more. Or in order to acquire the same effect, it turned out that it is preferable to add Mg 0.0005% or more and Ca 0.0001% or more.
（ｇ）粒界偏析による粒界移動を抑制する元素はＣｏ、Ｓｎ、Ａｓ、Ｂ、Ｐｂ、Ｚｒ、Ｚｎ、Ｙ、Ｇａ、Ｌａ、Ｈｆ、Ｓｂ、ＲＥＭ、Ｔａである。これら元素を１種類または２種類以上含有し、その合計量が０．０１０％以上であることが好ましい。一方、これら元素の過剰な含有は粒界強度の低下による粒界破壊を助長するため、合計量を０．１０％以下とすることが好ましい。 (G) Elements that suppress grain boundary migration due to grain boundary segregation are Co, Sn, As, B, Pb, Zr, Zn, Y, Ga, La, Hf, Sb, REM, and Ta. It is preferable that one or more of these elements are contained and the total amount thereof is 0.010% or more. On the other hand, since excessive inclusion of these elements promotes grain boundary fracture due to a decrease in grain boundary strength, the total amount is preferably made 0.10% or less.
以下、本発明の各要件について詳しく説明する。なお、各元素の含有量の「％」表示は「質量％」を意味する。 Hereinafter, each requirement of the present invention will be described in detail. In addition, "%" display of the content of each element means "mass%".
溶接金属部の化学成分の限定理由を以下に説明する。 The reason for limiting the chemical composition of the weld metal part will be described below.
＜Ｃ：０．０３％以下＞
Ｃは、フェライト相に固溶あるいはＣｒ炭化物を形成して耐酸化性を阻害する。また、溶接時の粒界におけるＣｒ炭化物形成を促進させる。このため、Ｃ量は少ないほど良く、上限を０．０３％とする。但し、過度な低減は精錬コストの上昇に繋がるため、下限は０．００１％とすることが好ましい。より好ましい範囲は０．００２〜０．０２０％である。
<C: 0.03% or less>
C inhibits oxidation resistance by forming a solid solution or Cr carbide in the ferrite phase. Moreover, Cr carbide formation at the grain boundary during welding is promoted. For this reason, the smaller the amount of C, the better. The upper limit is made 0.03%. However, excessive reduction leads to an increase in refining costs, so the lower limit is preferably 0.001%. A more preferable range is 0.002 to 0.020%.
＜Ｎ：０．０３０％以下＞
Ｎは、Ｃと同様に本発明の目標とする耐酸化性を阻害する。このため、Ｎ量は少ないほど良く、上限を０．０３０％とする。但し、過度な低減は精錬コストの上昇に繋がるため、下限は０．００１％とする。好ましい範囲は０．００２〜０．０２０％である。
<N: 0.030% or less>
N, like C, inhibits the target oxidation resistance of the present invention. For this reason, the smaller the amount of N, the better. The upper limit is made 0.030%. However, excessive reduction leads to an increase in refining costs, so the lower limit is made 0.001%. A preferred range is 0.002 to 0.020%.
＜Ｓｉ：２．０％以下＞
Ｓｉは、耐酸化性を確保する上で重要な元素である。Ｓｉは、Ａｌ系酸化皮膜中へ僅かに固溶するとともに、酸化皮膜直下／鋼界面にも濃化し、改質ガス環境下の耐酸化性を向上させる。これら効果を得るために下限は０．２％とすることが好ましい。一方、過度な添加は、Ｃｒのスピノーダル分解を助長させ、耐４７５℃脆性を低下させる。また、鋼の靭性や加工性の低下ならびにＡｌ系酸化皮膜の形成を阻害する場合もあるため、上限は２．０％とする。好ましい上限は１．２％である。
<Si: 2.0% or less>
Si is an important element in securing oxidation resistance. Si slightly dissolves in the Al-based oxide film and also concentrates directly under the oxide film / steel interface to improve the oxidation resistance under the reformed gas environment. In order to obtain these effects, the lower limit is preferably 0.2%. On the other hand, excessive addition promotes the spinodal decomposition of Cr and reduces the 475 ° C. brittleness resistance. In addition, the upper limit is set to 2.0% because it may hinder the toughness and workability of steel and the formation of an Al-based oxide film. A preferable upper limit is 1.2%.
＜Ｍｎ：２．０％以下＞
Ｍｎは、改質ガス環境下でＳｉとともに酸化皮膜中に固溶して保護性を高める。これら効果を得るために下限は０．１％とすることが好ましい。一方、過度な添加は、鋼の耐食性やＡｌ系酸化皮膜の形成を阻害するため、上限は２．０％以下とする。耐酸化性と基本特性の点から、１．２％以下が好ましい。
<Mn: 2.0% or less>
Mn is dissolved in the oxide film together with Si in the reformed gas environment to enhance the protection. In order to obtain these effects, the lower limit is preferably 0.1%. On the other hand, excessive addition inhibits the corrosion resistance of steel and the formation of an Al-based oxide film, so the upper limit is made 2.0% or less. From the viewpoint of oxidation resistance and basic characteristics, 1.2% or less is preferable.
＜Ｐ：０．０４０％以下＞
Ｐは、製造性や溶接性を阻害し、溶接部における粒界強度を低下させる元素である。その含有量は少ないほど良いため、上限は０．０４０％とする。但し、過度な低減は精錬コストの上昇に繋がるため、下限は０．００３％とすることが好ましい。製造性と溶接性の点から、好ましい範囲は０．００４〜０．０２８％である。
<P: 0.040% or less>
P is an element that impedes manufacturability and weldability and lowers the grain boundary strength at the weld. The lower the content, the better, so the upper limit is made 0.040%. However, excessive reduction leads to an increase in refining costs, so the lower limit is preferably 0.003%. From the viewpoint of manufacturability and weldability, the preferred range is 0.004 to 0.028%.
＜Ｓ：０．０１０％以下＞
Ｓは、鋼中に含まれる不可避的不純物元素であり、Ａｌ系皮膜の保護性を低下させる。特に、Ｍｎ系介在物や固溶Ｓの存在は、高温・長時間使用におけるＡｌ系酸化皮膜の破壊起点としても作用する。また、溶接部における粒界強度を低下させる元素である。従って、Ｓ量は低いほど良いため、上限は０．０１０％とする。但し、過度の低減は原料や精錬コストの上昇に繋がるため、下限は０．０００１％とする。製造性と耐酸化性、耐４７５℃脆性の観点から、好ましい範囲は０．０００１〜０．００１０％である。
<S: 0.010% or less>
S is an inevitable impurity element contained in the steel, and lowers the protective properties of the Al-based film. In particular, the presence of Mn-based inclusions and solute S also acts as a fracture starting point for Al-based oxide films when used at high temperatures for long periods of time. Further, it is an element that lowers the grain boundary strength in the weld zone. Therefore, the lower the amount of S, the better. Therefore, the upper limit is made 0.010%. However, excessive reduction leads to an increase in raw materials and refining costs, so the lower limit is made 0.0001%. From the viewpoint of manufacturability, oxidation resistance, and 475 ° C. brittleness, the preferred range is 0.0001 to 0.0010%.
＜Ｃｒ：１５．０〜２５．０％＞
Ｃｒは、耐食性に加えて、表面酸化皮膜の保護性を確保する上で基本となる構成元素であり、これら効果を得るためには１５．０％以上のＣｒ量が必要である。一方、過度なＣｒの添加は、４７５℃脆性起因の著しい材料硬化に加え、高温雰囲気に曝された際、脆化相であるσ相の生成を助長する。また、合金コストの上昇とＣｒ蒸発を助長する場合があるため上限は２５．０％とする。好ましい範囲は１５．５〜２０．０％である。より好ましい範囲は、１６．０〜２０．０％である。
<Cr: 15.0 to 25.0%>
In addition to corrosion resistance, Cr is a basic constituent element for securing the protective property of the surface oxide film. In order to obtain these effects, a Cr amount of 15.0% or more is required. On the other hand, excessive addition of Cr promotes the formation of a σ phase which is an embrittled phase when exposed to a high temperature atmosphere in addition to significant material hardening due to brittleness at 475 ° C. Moreover, since an increase in alloy cost and Cr evaporation may be promoted, the upper limit is made 25.0%. A preferable range is 15.5 to 20.0%. A more preferable range is 16.0 to 20.0%.
＜Ａｌ：１．０〜４．０％＞
Ａｌは、脱酸元素に加えて、Ａｌ系酸化皮膜を形成してＣｒ蒸発を抑止するために必須の添加元素である。また、溶接部における双晶変形発現を抑制する元素である。本発明においては、１．０％未満ではこれら効果が得られないため、下限は１．０％とする。しかし、過度なＡｌの添加は、鋼の靭性や溶接部における脆性破壊を助長するため、上限は、４．０％とする。好ましい範囲は１．２〜３．５％である。
<Al: 1.0-4.0%>
In addition to the deoxidizing element, Al is an additional element essential for forming an Al-based oxide film and suppressing Cr evaporation. In addition, it is an element that suppresses twin deformation in the weld. In the present invention, since these effects cannot be obtained at less than 1.0%, the lower limit is made 1.0%. However, excessive addition of Al promotes the toughness of steel and brittle fracture in welds, so the upper limit is made 4.0%. A preferable range is 1.2 to 3.5%.
＜Ｔｉ、Ｎｂ、Ｖ：１．０％以下＞
Ｔｉは、Ｃ，Ｎを固定する安定化元素の作用により、溶接時のＣｒ炭化物生成抑制に寄与する元素である。また、Ａｌ系酸化皮膜の外層側へＴｉ系酸化物を形成してＣｒの蒸発を抑止する有効な元素である。これら効果を得るために下限は０．０１％とすることが好ましい。一方、過度な添加は合金コストの上昇や再結晶温度上昇に伴う製造性の低下や耐酸化性の低下にも繋がるため、上限は１．０％とする。好ましい範囲は０．１０〜０．５０％である。
ＮｂおよびＶは固溶強化により材料強度を高め、過剰な添加は脆性破壊を助長するため、上限をそれぞれ１．０％とする必要がある。好ましい成分範囲は０．００８〜０．７％である。
<Ti, Nb, V: 1.0% or less>
Ti is an element that contributes to suppression of Cr carbide generation during welding by the action of a stabilizing element that fixes C and N. In addition, it is an effective element that suppresses evaporation of Cr by forming a Ti-based oxide on the outer layer side of the Al-based oxide film. In order to obtain these effects, the lower limit is preferably 0.01%. On the other hand, excessive addition leads to a decrease in manufacturability and a decrease in oxidation resistance accompanying an increase in alloy costs and a recrystallization temperature, so the upper limit is made 1.0%. A preferable range is 0.10 to 0.50%.
Nb and V increase material strength by solid solution strengthening, and excessive addition promotes brittle fracture, so the upper limit must be 1.0%. A preferable component range is 0.008 to 0.7%.
＜（［Ｔｉ］＋［Ｎｂ］＋［Ｖ］）／（２×［Ｃ］＋［Ｎ］）＞（第１群）
また、本発明に係る溶接継手では、Ｔｉ、Ｎｂ、Ｖからなる元素群が上記で限定した溶接金属の化学組成を満たしつつ、溶接金属部のＴｉ、Ｎｂ、Ｖ、Ｃ、Ｎの含有量（質量％）が以下の式（１）を満たすことが好ましい。
（［Ｔｉ］＋［Ｎｂ］＋［Ｖ］）／（２×［Ｃ］＋［Ｎ］）≧４．０・・・・式（１）
ここで、［Ｔｉ］、［Ｎｂ］、［Ｖ］、［Ｃ］、［Ｎ］は、溶接金属部におけるそれぞれの元素の含有量（質量％）を示す。
<([Ti] + [Nb] + [V]) / (2 × [C] + [N])> (first group)
In the welded joint according to the present invention, the element group consisting of Ti, Nb, and V satisfies the chemical composition of the weld metal defined above, while the content of Ti, Nb, V, C, and N in the weld metal part ( % By mass) preferably satisfies the following formula (1).
([Ti] + [Nb] + [V]) / (2 × [C] + [N]) ≧ 4.0 (1)
Here, [Ti], [Nb], [V], [C], and [N] indicate the content (mass%) of each element in the weld metal part.
＜Ｍｇ、Ｃａ＞（第２群）
Ｍｇ、Ｃａは鋼の清浄度や熱間加工性を高めるのに有効な元素である。また、溶接時にＭｇＯ、ＣａＯなどから成る介在物を生成させることで等軸晶の形成が助長され、溶接組織の微細化に寄与する元素でもある。これら効果を得るため、Ｍｇは０．０００５％以上、Ｃａは０．０００５％以上含むことが好ましい。一方、過度な添加は製造性の低下を招くため、Ｍｇは０．０１０％以下、Ｃａは０．００５％以下であることが好ましい。尚、Ｍｇ：０．０００５％以上０．０１０％以下、Ｃａ：０．０００５％以上０．００５％以下の１種または２種以上からなる第２群を溶接金属部に含有させることによって、溶接金属部のＴｉ、Ｎｂ及びＶの少なくとも１種以上からなり且つ前記式（１）を満たす第２群を含有する場合と同様の効果を得ることができる。また、溶接金属部の組成は、第１群又は第２群のうち少なくともいずれかの群を含有すれば良く、溶接金属部がＭｇ及び／又はＣａを前記範囲未満（例えば、不純物レベルの濃度）で含有している場合であっても、前記式（１）を満たせば良い。
<Mg, Ca> (second group)
Mg and Ca are effective elements for enhancing the cleanliness and hot workability of steel. In addition, by forming inclusions made of MgO, CaO or the like during welding, formation of equiaxed crystals is promoted, and it is also an element contributing to refinement of the weld structure. In order to acquire these effects, it is preferable to contain 0.0005% or more of Mg and 0.0005% or more of Ca. On the other hand, excessive addition causes a decrease in manufacturability, so Mg is preferably 0.010% or less and Ca is preferably 0.005% or less. In addition, welding is carried out by including a second group consisting of one or more of Mg: 0.0005% to 0.010% and Ca: 0.0005% to 0.005% in the weld metal part. The same effect can be obtained as in the case of containing the second group consisting of at least one of Ti, Nb and V in the metal part and satisfying the above formula (1). Further, the composition of the weld metal portion may include at least one of the first group and the second group, and the weld metal portion contains Mg and / or Ca less than the above range (for example, impurity level concentration). Even if it is contained, the above formula (1) may be satisfied.
＜Ｎｉ、Ｃｕ、Ｍｏ、Ｗ：１．０％以下＞（第３群）
Ｎｉ、Ｃｕ、Ｍｏ、Ｗは高温強度と耐食性を高めるのに有効な元素であり、必要に応じて少なくとも１種（以下、「第３群」ともいう。）を添加しても良い。但し、過度な添加は合金コストの上昇や製造性を阻害することに繋がるため、Ｎｉ、Ｃｕ、Ｍｏ、Ｗの上限は１．０％とする。前記効果を発現させるためには、Ｎｉ，Ｃｏ，Ｍｏ，Ｗは０．０２％以上が好ましい。更に好ましくは０．０８％以上である。
<Ni, Cu, Mo, W: 1.0% or less> (third group)
Ni, Cu, Mo, and W are effective elements for increasing high-temperature strength and corrosion resistance, and at least one (hereinafter also referred to as “third group”) may be added as necessary. However, excessive addition leads to an increase in alloy cost and obstructs manufacturability, so the upper limit of Ni, Cu, Mo, W is 1.0%. In order to exhibit the effect, Ni, Co, Mo, and W are preferably 0.02% or more. More preferably, it is 0.08% or more.
＜Ｃｏ、Ｓｎ、Ａｓ、Ｂ、Ｐｂ、Ｚｒ、Ｚｎ、Ｙ、Ｇａ、Ｌａ、Ｈｆ、Ｓｂ、ＲＥＭ、Ｔａ＞（第４群）
これらの元素は粒界に偏析して溶接時の結晶粒の粗大化を抑制する。また、Ｚｒ、Ｌａ、Ｙ、Ｈｆ、ＲＥＭ、Ｔａは、熱間加工性や鋼の清浄度を向上ならびに耐酸化性改善に対しても、従来から有効な元素である。Ｇａ、Ｚｎ、Ｓｎ、Ｓｂは表面近傍に濃化してＣｒの酸化を抑制する。
<Co, Sn, As, B, Pb, Zr, Zn, Y, Ga, La, Hf, Sb, REM, Ta> (fourth group)
These elements segregate at the grain boundaries and suppress the coarsening of crystal grains during welding. Zr, La, Y, Hf, REM, and Ta are elements that have been conventionally effective for improving hot workability, cleanliness of steel, and improving oxidation resistance. Ga, Zn, Sn, and Sb are concentrated near the surface to suppress oxidation of Cr.
これらの効果を得るため、Ｃｏ：０．００５％以上、Ｓｎ０．００３％以上、Ａｓ：０．００１％以上、Ｂ：０．０００１％以上、Ｐｂ：０．０００１％以上、Ｚｒ：０．０００１％以上、Ｚｎ：０．０１％以上、Ｙ：０．０００１％以上、Ｇａ：０．００１％以上、Ｌａ：０．０００１％以上、Ｈｆ：０．０００１％以上、Ｓｂ：０．００３％以上、ＲＥＭ：０．００１％以上、Ｔａ：０．００２％以上でこれらの元素を１種類または２種類以上含有し、合計量が０．０１０％以上であることが好ましい。本発明のＡｌ含有フェライト系ステンレス鋼溶接継手は、その溶接金属部が、前記第３群とともに、或いは、Ｎｉ、Ｃｕ、Ｍｏ、Ｗの元素群の代わりに、Ｃｏ、Ｓｎ、Ａｓ、Ｂ、Ｐｂ、Ｚｒ、Ｚｎ、Ｙ、Ｇａ、Ｌａ、Ｈｆ、Ｓｂ、ＲＥＭ、Ｔａの元素群のうちの少なくとも１種の元素からなる第４群を前述の含有量の範囲で含有しても良い。 In order to obtain these effects, Co: 0.005% or more, Sn 0.003% or more, As: 0.001% or more, B: 0.0001% or more, Pb: 0.0001% or more, Zr: 0.0001 %: Zn: 0.01% or more, Y: 0.0001% or more, Ga: 0.001% or more, La: 0.0001% or more, Hf: 0.0001% or more, Sb: 0.003% or more REM: 0.001% or more, Ta: 0.002% or more, one or more of these elements are contained, and the total amount is preferably 0.010% or more. In the Al-containing ferritic stainless steel welded joint according to the present invention, the weld metal part thereof has Co, Sn, As, B, Pb together with the third group or instead of the element group of Ni, Cu, Mo, W. , Zr, Zn, Y, Ga, La, Hf, Sb, REM, and Ta, the fourth group consisting of at least one element may be contained within the above-described content range.
一方、これらの元素の過度な添加は粒界強度低下による粒界破壊を助長するため、前記第４群は、Ｃｏ：０．１０％以下、Ｓｎ０．１０％以下、Ａｓ：０．０５％以下、Ｂ：０．００５％以下、Ｐｂ：０．００５％以下、Ｚｒ：０．１％以下、Ｚｎ：０．０３％以下、Ｙ：０．１０％以下、Ｇａ：０．１０％以下、Ｌａ：０．１０％以下、Ｈｆ：０．１０％以下、Ｓｂ：０．１０％以下、ＲＥＭ：０．１０％以下、Ｔａ：０．５％以下の１種類または２種類以上からなる元素群であって、合計量（以下の式（２））を０．２０％以下とする必要がある。
［Ｃｏ］＋［Ｓｎ］＋［Ａｓ］＋［Ｂ］＋［Ｐｂ］＋［Ｚｒ］＋［Ｚｎ］＋［Ｙ］＋［Ｇａ］＋［Ｌａ］＋［Ｈｆ］＋［Ｓｂ］＋［ＲＥＭ］・・・式（２）
ここで、［Ｃｏ］、［Ｓｎ］、［Ａｓ］、［Ｂ］、［Ｐｂ］、［Ｚｒ］、［Ｚｎ］、［Ｙ］、［Ｇａ］、［Ｌａ］、［Ｈｆ］、［Ｓｂ］、［ＲＥＭ］、［Ｔａ］は、それぞれの元素の含有量（質量％）を示す。
On the other hand, excessive addition of these elements promotes grain boundary destruction due to a decrease in grain boundary strength. Therefore, the fourth group contains Co: 0.10% or less, Sn 0.10% or less, As: 0.05% or less. B: 0.005% or less, Pb: 0.005% or less, Zr: 0.1% or less, Zn: 0.03% or less, Y: 0.10% or less, Ga: 0.10% or less, La : 0.10% or less, Hf: 0.10% or less, Sb: 0.10% or less, REM: 0.10% or less, Ta: 0.5% or less. Therefore, the total amount (the following formula (2)) needs to be 0.20% or less.
[Co] + [Sn] + [As] + [B] + [Pb] + [Zr] + [Zn] + [Y] + [Ga] + [La] + [Hf] + [Sb] + [REM ] Formula (2)
Here, [Co], [Sn], [As], [B], [Pb], [Zr], [Zn], [Y], [Ga], [La], [Hf], [Sb] , [REM], and [Ta] indicate the content (% by mass) of each element.
製造方法について以下に説明する。
本発明の耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手は、Ａｌ含有フェライト系ステンレス鋼をなめ付けあるいは溶接棒を使用した溶接により作製される。本発明の溶接継手は、後述する本発明の溶接材料を用いて製造することで、実現が容易になるが、本発明の溶接継手は、当該製造条件に限定されるものでないことは言うまでもない。つまり、溶接する母鋼材、用いる溶接材料、溶接手法、さらに溶接条件を適切に選択することで、最終的な溶接継手における溶接金属の化学組成を本発明の範囲内に制御することができる。溶接材料を使用する場合、ＳＯＦＣ用途では良好な耐酸化性・耐Ｃｒ蒸発性が求められるため、これら特性を兼ね備えたＡｌ含有フェライト系ステンレス鋼を母材として溶接継手を製造することは、本発明の好ましい例である。また、溶接継手の成分制御を容易にする意味では、母材あるいは溶接材料が本発明の溶接継手に近い成分系であることはさらに好ましい。
The manufacturing method will be described below.
The Al-containing ferritic stainless steel welded joint having excellent 475 ° C brittleness resistance according to the present invention is produced by tanning an Al-containing ferritic stainless steel or welding using a welding rod. The welded joint of the present invention can be easily realized by using the welding material of the present invention described later, but it goes without saying that the welded joint of the present invention is not limited to the manufacturing conditions. That is, the chemical composition of the weld metal in the final welded joint can be controlled within the scope of the present invention by appropriately selecting the base steel material to be welded, the welding material to be used, the welding technique, and the welding conditions. When using welding materials, good oxidation resistance and Cr evaporation resistance are required for SOFC applications. Therefore, manufacturing a welded joint using an Al-containing ferritic stainless steel having these properties as a base material is the present invention. Is a preferred example. Further, in terms of facilitating component control of the welded joint, it is further preferable that the base material or the welding material is a component system close to the welded joint of the present invention.
本発明の好適な母材の化学組成は、質量％で、Ｃ：０．０２％以下、Ｓｉ：０．１５〜０．７０％、Ｍｎ：０．３％以下、Ｃｒ：１３〜２０％、Ａｌ：１．５〜６％、Ｎ：０．０２％以下、Ｔｉ：０．０３〜０．５％を含有し、残部がＦｅおよび不可避的不純物である。また、本発明の好適な溶接材料の化学組成は、質量％で、Ｃ：０．０２％以下、Ｓｉ：０．１〜０．６％、Ｍｎ：０．０５〜０．４％、Ｃｒ：１３〜２０％、Ｔｉ：０．０５〜０．４％、Ｐ：０．０２０％以下、Ｓ：０．０１５％以下、Ｎ：０．０４０％以下を含有し、残部がＦｅおよび不可避的不純物である。 The chemical composition of a suitable base material of the present invention is, in mass%, C: 0.02% or less, Si: 0.15 to 0.70%, Mn: 0.3% or less, Cr: 13 to 20%, Al: 1.5 to 6%, N: 0.02% or less, Ti: 0.03 to 0.5% is contained, and the balance is Fe and inevitable impurities. Moreover, the chemical composition of the suitable welding material of this invention is the mass%, C: 0.02% or less, Si: 0.1-0.6%, Mn: 0.05-0.4%, Cr: 13-20%, Ti: 0.05-0.4%, P: 0.020% or less, S: 0.015% or less, N: 0.040% or less, the balance being Fe and inevitable impurities It is.
なお、ＳＯＦＣ用途以外の用途であって、耐４７５℃脆性を要求される用途において、本発明の溶接継手を構成する母材は、Ａｌ含有フェライト系ステンレス鋼に限定されない。また、例えば、ガスタービン、発電システムなどに用いられる高温部材、エキゾーストマニホールド、コンバータ、マフラー、ターボチャージャー、ＥＧＲクーラー、フロントパイプ、センターパイプなどの自動車部材、ストーブ・ファンヒータなどの燃焼機器といった高温環境下で使用される部材全般に好適である。 In addition, in applications other than SOFC applications that require brittle resistance at 475 ° C., the base material constituting the welded joint of the present invention is not limited to Al-containing ferritic stainless steel. Also, for example, in high-temperature environments such as high-temperature components used in gas turbines, power generation systems, exhaust manifolds, converters, mufflers, turbochargers, EGR coolers, front pipes, center pipes, and other combustion components such as stove / fan heaters Suitable for all members used.
以下に、本発明の実施例について述べる。
表１−１及び表１−２に成分を示す鋼種１〜３５のフェライト系ステンレス鋼を溶製し、熱間圧延、焼鈍酸洗、冷間圧延後、仕上げ焼鈍・酸洗により厚さ１．０ｍｍの冷延焼鈍鋼板を製造した。尚、表１−１の「発明例の組成」とは、鋼の組成が本発明のＡｌ含有フェライト系ステンレス鋼溶接継手の溶接金属部の組成を満たすことを意味する。また、表１−２の「比較例の組成」とは、鋼の組成が本発明のＡｌ含有フェライト系ステンレス鋼溶接継手の溶接金属部の組成を満たしていないことを意味する。尚、表１−１、表１−２、表２及び表３の空欄は、該当する成分を添加していないことを意味する。
Examples of the present invention will be described below.
Ferritic stainless steels of steel types 1-35 whose components are shown in Table 1-1 and Table 1-2 are melted, and after hot rolling, annealing pickling, cold rolling, finish annealing and pickling to obtain a thickness of 1. A 0 mm cold-rolled annealed steel sheet was produced. The “composition of the inventive example” in Table 1-1 means that the steel composition satisfies the composition of the weld metal part of the Al-containing ferritic stainless steel welded joint of the present invention. Further, “composition of comparative example” in Table 1-2 means that the composition of steel does not satisfy the composition of the weld metal part of the Al-containing ferritic stainless steel welded joint of the present invention. In addition, the blank of Table 1-1, Table 1-2, Table 2, and Table 3 means that the applicable component is not added.
各鋼種のフェライト系ステンレス鋼板から幅１２０ｍｍ、長さ２５０ｍｍの試験片を切り出した。次いで、同じ鋼種のフェライト系ステンレス鋼板同士を母材として、電流８０〜１００Ａ、溶接速度５０ｃｍ／ｍｉｎにて、Ａｒシールドガスを用いてＴＩＧなめ付け溶接して、鋼種１〜３１のフェライト系ステンレス鋼板毎にフェライト系ステンレス鋼溶接継手を製造した。溶接位置は板幅中央で、溶接方向は板長手方向とした。 A test piece having a width of 120 mm and a length of 250 mm was cut out from a ferritic stainless steel plate of each steel type. Next, using ferritic stainless steel sheets of the same steel type as base materials, TIG tanning welding is performed using an Ar shield gas at a current of 80 to 100 A and a welding speed of 50 cm / min. A ferritic stainless steel welded joint was produced every time. The welding position was the center of the plate width, and the welding direction was the plate longitudinal direction.
また、表２に成分を示す記号Ａ〜ＣのＡｌ含有フェライト系ステンレス鋼溶接材料を溶製した。表１−１及び表１−２の鋼種４，５，１４，２２，２９を母材とし、前記記号Ａ〜Ｃの溶接材料を用いて溶接継手を作製した。溶接条件は電流２００Ａ、溶接速度５０ｃｍ／ｍｉｎ、溶接材料供給量８ｇ／ｍｉｎであり、Ａｒガスシールドを実施した。得られた溶接継手の溶接金属部から化学分析用試料を採取し、成分分析を行った。表３に各溶接継手の溶接金属部の化学成分を示す。ここで、表３の記号は、例えば４Ａの場合、母材は４、溶接材料はＣを使用して製造した溶接継手であることを意味する。 Moreover, the Al containing ferritic stainless steel welding material of the symbol AC which shows a component in Table 2 was melted. Using steel types 4, 5, 14, 22, and 29 in Table 1-1 and Table 1-2 as base materials, weld joints were prepared using the welding materials of the symbols A to C. The welding conditions were an electric current of 200 A, a welding speed of 50 cm / min, a welding material supply amount of 8 g / min, and an Ar gas shield was implemented. A sample for chemical analysis was collected from the weld metal part of the obtained welded joint, and component analysis was performed. Table 3 shows the chemical composition of the weld metal part of each weld joint. Here, for example, in the case of 4A, the symbols in Table 3 indicate that the base material is 4 and the welding material is a welded joint manufactured using C.
各溶接継手の溶接部より試料を切り出し、樹脂埋めを行った後、王水によるエッチングを行った。エッチング後の試料に対し、光学顕微鏡により撮影した溶金部において、溶金部中心の厚さ８００μｍ×幅１６００μｍの領域内の結晶粒の数をカウントした。測定領域の１辺をまたいだ結晶粒は０．５個、２辺をまたいだ場合は０．２５個とした。（測定領域の面積）／（測定領域内の結晶粒の数）の平方根をその溶接継手の結晶粒径と定義した。 A sample was cut out from the welded portion of each welded joint, filled with resin, and then etched with aqua regia. With respect to the sample after etching, the number of crystal grains in the region of thickness 800 μm × width 1600 μm at the center of the molten metal was counted in the molten metal photographed by an optical microscope. The number of crystal grains straddling one side of the measurement region was 0.5, and the number of crystal grains straddling two sides was 0.25. The square root of (area of measurement region) / (number of crystal grains in measurement region) was defined as the crystal grain size of the weld joint.
各溶接継手に対し大気中で５００℃、３０００時間の時効処理を行った。耐４７５℃脆性は、これら５００℃時効処理材に対し、Ｖ曲げ試験により評価した。曲げ半径２．０ｍｍ、曲げ角度９０度とし、試料の裏ビードに押金具が接触するようにしてＶ曲げを行った。目視にて割れが生成することなくＶ曲げ成型が完了した場合、耐４７５℃脆性は極めて良好（◎）、Ｖ曲げ成型が完了するが目視にて割れが確認できた場合は良好（○）、Ｖ曲げ成型中に割れが貫通した場合、耐４７５℃脆性は不良（×）とした。 Each welded joint was subjected to aging treatment at 500 ° C. for 3000 hours in the atmosphere. The resistance to brittleness at 475 ° C. was evaluated by a V-bending test on these 500 ° C. aging-treated materials. V-bending was performed with a bending radius of 2.0 mm and a bending angle of 90 degrees so that the pressing metal was in contact with the back bead of the sample. When V-bending molding is completed without visual cracking, 475 ° C. brittleness resistance is very good (◎), and when V-bending molding is completed, but cracking can be confirmed by visual inspection (◯), When cracks penetrated during V-bending molding, the 475 ° C. brittleness resistance was judged as poor (x).
表４に試験結果を示す。記号１〜３２の試験片は、各記号に対応する鋼種のフェライト系ステンレス鋼板をなめ付け溶接して得られた溶接継手の溶接金属部なので、各記号に対応する鋼種のフェライト系ステンレス鋼板と同一の組成を有している。従って、記号１〜２２の試験片は本発明の規定する成分範囲を満たしている。その結果、５００℃、３０００時間の時効処理後も溶接部にてＶ曲げによる割れの生成は確認されず、優れた耐４７５℃脆性を示した。 Table 4 shows the test results. Since the test pieces of symbols 1 to 32 are welded metal parts of welded joints obtained by tanning the ferritic stainless steel plates corresponding to the respective symbols, they are the same as the ferritic stainless steel plates of the steel types corresponding to the respective symbols. It has the composition of. Therefore, the test pieces of symbols 1 to 22 satisfy the component range defined by the present invention. As a result, even after aging treatment at 500 ° C. for 3000 hours, generation of cracks due to V-bending was not confirmed in the welded portion, and excellent 475 ° C. brittleness resistance was exhibited.
記号８ａは、記号Ｈの溶接継手よりも高い入熱量で作製した試験片である。溶接部の結晶粒径は３６０μｍで本発明の好ましい範囲よりも大きいが、本発明の規定する成分範囲を満たしているため、良好な耐４７５℃脆性を示した。
記号２３の試験片はＰ量が本発明の規定範囲よりも多い。その結果、溶接金属部の粒界強度が低下し、粒界破壊が生じた。
記号２４の試験片はＣｒ量が本発明の規定範囲よりも多い。その結果、Ｃｒのスピノーダル分解による素材の著しい硬化が生じ、へき開破壊が生じた。
記号２５の試験片はＡｌ量が本発明の規定範囲よりも多い。その結果、Ａｌ添加による双晶変形の抑制効果を、Ａｌの固溶強化による著しい硬化が上回り、へき開破壊が生じた。
記号２６および３０の試験片はＡｌ量が本発明の規定範囲よりも少ない。その結果、Ａｌ添加による双晶変形の抑制効果を十分に得ることができず、へき開破壊が生じた。
記号２７の試験片は、Ｓｎの含有量が０．１０％を超過しており、Ｓｎ、Ｓｂ及びＧａの含有量の合計も本発明の規定範囲より多い。また、記号２８の試験片は、Ｚｎ、Ｂ及びＰｂのそれぞれの含有量が本発明の規定範囲よりも多く、Ｚｎ、Ｂ、Ａｓ及びＰｂの含有量の合計も本発明の規定範囲より多い。その結果、記号２７及び２８の試験片の溶接部の粒界強度は著しく低下し、粒界破壊が生じた。
記号２９の試験片は、溶接金属部Ａｓ、Ｚｒ、Ｙ、Ｇａ及びＴａの含有量が本発明の規定範囲内であるにも関わらず、前記式（２）で表される合計量が本発明の規定範囲よりも多い。その結果、溶接部の結晶粒径が大きくなり、へき開破壊が生じた。
記号３１の試験片は、前記式（１）の値が本発明の規定範囲よりも少ない。また、記号３２の試験片は、Ｃ含有量が本発明の規定範囲より多い。その結果、いずれの試験片も溶接部の結晶粒径が大きくなり、へき開破壊が生じた。
記号３３の試験片は、Ｓｂ含有量が０．１０％を超過している。また、記号３４の試験片は、Ａｓ含有量が０．０５％、Ｐｂ含有量が０．００５％を超過している。その結果記号３３および３４の試験片の溶接部の粒界強度は著しく低下し、粒界破壊が生じた。
記号３５の試験片はＣａ含有量が０．００５％を超過している。その結果記号３５の試験片の溶接部で過剰に生成した介在物が破壊の起点となり、へき開破壊が生じた。
Symbol 8a is a test piece produced with a higher heat input than the welded joint of symbol H. Although the crystal grain size of the welded portion was 360 μm, which was larger than the preferred range of the present invention, it exhibited satisfactory 475 ° C. brittleness resistance because it satisfied the component range defined by the present invention.
The test piece of the symbol 23 has a P amount larger than the specified range of the present invention. As a result, the grain boundary strength of the weld metal part was lowered, and grain boundary fracture occurred.
The test piece of the symbol 24 has a Cr amount larger than the specified range of the present invention. As a result, the material was markedly hardened due to the spinodal decomposition of Cr, and cleavage fracture occurred.
The test piece of the symbol 25 has an Al amount larger than the specified range of the present invention. As a result, the effect of suppressing twin deformation due to the addition of Al exceeded the remarkable hardening due to the solid solution strengthening of Al, resulting in cleavage fracture.
The specimens of symbols 26 and 30 have an Al content less than the specified range of the present invention. As a result, the effect of suppressing twin deformation due to the addition of Al could not be sufficiently obtained, and cleavage fracture occurred.
In the test piece of symbol 27, the Sn content exceeds 0.10%, and the total content of Sn, Sb and Ga is larger than the specified range of the present invention. Moreover, the test piece of the code | symbol 28 has each content of Zn, B, and Pb more than the prescription | regulation range of this invention, and the sum total of content of Zn, B, As, and Pb is also larger than the prescription | regulation range of this invention. As a result, the grain boundary strength of the welded portions of the test pieces of symbols 27 and 28 was remarkably lowered, and grain boundary fracture occurred.
The test piece of symbol 29 has a total amount represented by the above formula (2) in spite of the fact that the contents of the weld metal parts As, Zr, Y, Ga and Ta are within the specified range of the present invention. More than the specified range. As a result, the crystal grain size of the welded portion increased and cleavage fracture occurred.
The test piece of the symbol 31 has a value of the formula (1) smaller than the specified range of the present invention. Moreover, the test piece of the symbol 32 has more C content than the specified range of the present invention. As a result, in all the test pieces, the crystal grain size of the welded portion was increased, and cleavage fracture occurred.
The test piece of symbol 33 has an Sb content exceeding 0.10%. Moreover, the test piece of the symbol 34 has As content exceeding 0.05% and Pb content exceeding 0.005%. As a result, the grain boundary strength of the welded portion of the test pieces of symbols 33 and 34 was remarkably reduced, and grain boundary fracture occurred.
The specimen of symbol 35 has a Ca content exceeding 0.005%. As a result, inclusions generated excessively in the welded portion of the test piece of symbol 35 became the starting point of the fracture, and cleavage fracture occurred.
記号４Ａ、５Ｃ、１４Ａ、２２Ｃ、２９Ｂの試験片はいずれも本発明の規定する成分範囲を満たしている。その結果、５００℃、３０００時間の時効処理後も溶接部にてＶ曲げによる割れの生成は確認されず、優れた耐４７５℃脆性を示した。特に２９Ｂの試験片については、母材ＸのＴＩＧなめ付け溶接継手では脆性破壊が生じていることから、本発明において、母材の成分は限定されるものではなく、溶接金属の化学組成が重要であると示唆する結果である。 All the test pieces of symbols 4A, 5C, 14A, 22C, and 29B satisfy the component ranges defined by the present invention. As a result, even after aging treatment at 500 ° C. for 3000 hours, generation of cracks due to V-bending was not confirmed in the welded portion, and excellent 475 ° C. brittleness resistance was exhibited. Especially for the specimen of 29B, since brittle fracture occurs in the TIG tanned welded joint of the base material X, the composition of the base material is not limited in the present invention, and the chemical composition of the weld metal is important. This result suggests that
本発明によれば、都市ガス、メタン、天然ガス、プロパン、灯油、ガソリン等の炭化水素系燃料を水素に改質する際に使用される改質器、熱交換器などの燃料電池高温部材、エキゾーストマニホールド、コンバータ、マフラー、ターボチャージャー、ＥＧＲクーラー、フロントパイプ、センターパイプなどの自動車用部材、ストーブ・ファンヒータなどの燃焼機器など、高温環境下で使用される部材全般に好適な耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手を提供することができる。 According to the present invention, fuel cell high-temperature members such as reformers and heat exchangers used when reforming hydrocarbon-based fuels such as city gas, methane, natural gas, propane, kerosene, and gasoline into hydrogen, Excellent 475 ° C brittleness resistance suitable for all parts used in high-temperature environments such as exhaust manifolds, converters, mufflers, turbochargers, EGR coolers, front pipes, center pipes and other automotive parts, and stove / fan heaters and other combustion equipment An Al-containing ferritic stainless steel welded joint can be provided.
Claims (8)
更にＴｉ：１．０％以下、Ｎｂ：１．０％以下、Ｖ：１．０％以下の１種類または２種以上からなり且つ式（１）を満たす第１群、および、
Ｍｇ：０．０１０％以下、Ｃａ：０．００５％以下の１種または２種以上からなる第２群のうち少なくともいずれかの群を含有し、
残部がＦｅおよび不可避的不純物であることを特徴とする耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手。
（［Ｔｉ］＋［Ｎｂ］＋［Ｖ］）／（２×［Ｃ］＋［Ｎ］）≧４．０・・・・式（１）
ここで、［Ｔｉ］、［Ｎｂ］、［Ｖ］、［Ｃ］、［Ｎ］は、それぞれの元素の含有量（質量％）を示す。 The chemical composition of the weld metal part is, in mass%, C: 0.03% or less, N: 0.03% or less, Si: 2.0% or less, Mn: 2.0% or less, P: 0.040. %: S: 0.01% or less, Cr: 15-25%, Al: 1.0-4.0%,
Furthermore, the first group consisting of one or more of Ti: 1.0% or less, Nb: 1.0% or less, V: 1.0% or less and satisfying the formula (1), and
Mg: 0.010% or less, Ca: 0.005% or less, containing at least one of the second group consisting of one or more,
An Al-containing ferritic stainless steel welded joint excellent in brittleness resistance at 475 ° C, wherein the balance is Fe and inevitable impurities.
([Ti] + [Nb] + [V]) / (2 × [C] + [N]) ≧ 4.0 (1)
Here, [Ti], [Nb], [V], [C], and [N] indicate the content (% by mass) of each element.
Ｎｉ：１．０％以下、Ｃｕ：１．０％以下、Ｍｏ：１．０％以下、Ｗ：１．０％以下の１種または２種以上からなる第３群、および、
Ｃｏ：０．１０％以下、Ｓｎ０．１０％以下、Ａｓ：０．０５％以下、Ｂ：０．００５％以下、Ｐｂ：０．００５％以下、Ｚｒ：０．１％以下、Ｚｎ：０．０３％以下、Ｙ：０．１０％以下、Ｇａ：０．１０％以下、Ｌａ：０．１０％以下、Ｈｆ：０．１０％以下、Ｓｂ：０．１０％以下、ＲＥＭ：０．１０％以下、Ｔａ：０．５％以下の１種または２種以上からなる第４群のうち、
少なくともいずれかの群を含有することを特徴とする請求項１に記載の耐４７５℃脆性に優れたＡｌ含有フェライト系ステンレス鋼溶接継手。 The chemical composition of the weld metal part is further mass%,
A third group consisting of one or more of Ni: 1.0% or less, Cu: 1.0% or less, Mo: 1.0% or less, W: 1.0% or less, and
Co: 0.10% or less, Sn: 0.10% or less, As: 0.05% or less, B: 0.005% or less, Pb: 0.005% or less, Zr: 0.1% or less, Zn: 0. 03% or less, Y: 0.10% or less, Ga: 0.10% or less, La: 0.10% or less, Hf: 0.10% or less, Sb: 0.10% or less, REM: 0.10% Hereinafter, among the fourth group consisting of one or more of Ta: 0.5% or less,
2. The Al-containing ferritic stainless steel welded joint having excellent 475 ° C. brittleness resistance according to claim 1, comprising at least one group.
［Ｃｏ］＋［Ｓｎ］＋［Ａｓ］＋［Ｂ］＋［Ｐｂ］＋［Ｚｒ］＋［Ｚｎ］＋［Ｙ］＋［Ｇａ］＋［Ｌａ］＋［Ｈｆ］＋［Ｓｂ］＋［ＲＥＭ］＋［Ｔａ］・・・式（２）
ここで、［Ｃｏ］、［Ｓｎ］、［Ａｓ］、［Ｂ］、［Ｐｂ］、［Ｚｒ］、［Ｚｎ］、［Ｙ］、［Ｇａ］、［Ｌａ］、［Ｈｆ］、［Ｓｂ］、［ＲＥＭ］、［Ｔａ］は、それぞれの元素の含有量（質量％）を示す。 The Al-containing ferritic stainless steel welded joint having excellent 475 ° C brittleness resistance according to claim 2, wherein the formula (2) is 0.20% or less in terms of mass%.
[Co] + [Sn] + [As] + [B] + [Pb] + [Zr] + [Zn] + [Y] + [Ga] + [La] + [Hf] + [Sb] + [REM ] + [Ta] Formula (2)
Here, [Co], [Sn], [As], [B], [Pb], [Zr], [Zn], [Y], [Ga], [La], [Hf], [Sb] , [REM], and [Ta] indicate the content (% by mass) of each element.
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