JP2015151555A - Ferritic stainless steel for turbo housing and turbo housing - Google Patents
Ferritic stainless steel for turbo housing and turbo housing Download PDFInfo
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- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 45
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 21
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 18
- 239000012535 impurity Substances 0.000 claims abstract description 4
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 9
- 238000000465 moulding Methods 0.000 claims description 8
- 239000000463 material Substances 0.000 claims description 7
- 229910052719 titanium Inorganic materials 0.000 claims description 7
- 229910052720 vanadium Inorganic materials 0.000 claims description 7
- 229910052726 zirconium Inorganic materials 0.000 claims description 7
- 229910052748 manganese Inorganic materials 0.000 claims description 6
- 229910052804 chromium Inorganic materials 0.000 claims description 3
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 229910052710 silicon Inorganic materials 0.000 claims description 3
- 229910052721 tungsten Inorganic materials 0.000 claims description 3
- 230000008021 deposition Effects 0.000 abstract 1
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- 238000000137 annealing Methods 0.000 description 17
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- 229910000831 Steel Inorganic materials 0.000 description 6
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- 229910001566 austenite Inorganic materials 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
- 238000005097 cold rolling Methods 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
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- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
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- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
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- 239000010941 cobalt Substances 0.000 description 1
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- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
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- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
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Abstract
Description
本発明は、ターボチャージャーのハウジングであるターボハウジングに用いられる加工性および耐熱性に優れたターボハウジング用フェライト系ステンレス鋼およびターボハウジングに関する。 The present invention relates to a ferritic stainless steel for turbo housing and a turbo housing which are excellent in workability and heat resistance used for a turbo housing which is a housing of a turbocharger.
従来、排気ガスのエネルギーを利用して内燃機関の熱効率を高めるターボチャージャーは、鋳物にて形成されることが多い。 Conventionally, a turbocharger that increases the thermal efficiency of an internal combustion engine using the energy of exhaust gas is often formed of a casting.
この種のターボチャージャーのハウジングであるターボハウジング用耐熱鋼としては、オーステナイト系鋳物（例えば、特許文献１参照。）や、比較的に安価なフェライト系鋳物（例えば、特許文献２参照。）等が知られている。 As a heat-resisting steel for a turbo housing which is a housing of this type of turbocharger, an austenitic cast (for example, see Patent Document 1), a relatively inexpensive ferritic cast (for example, see Patent Document 2), and the like. Are known.
また、比較的に安価なフェライト系鋳物をより高温環境での使用に適した構成とするため、合金成分や組織を制御することにより高強度化や熱疲労特性の向上を図ったフェライト系鋳物（例えば、特許文献３参照。）が知られている。 In addition, in order to make a relatively inexpensive ferritic casting suitable for use in a higher temperature environment, a ferritic casting that has improved strength and improved thermal fatigue properties by controlling the alloy composition and structure ( For example, see Patent Document 3).
ここで、上述のターボハウジングについて、軽量化および低熱容量化を図るため、フェライト系ステンレス鋼板を用いてプレス成形することも検討されている。 Here, in order to reduce the weight and reduce the heat capacity of the above-described turbo housing, it has been studied to press-form using a ferritic stainless steel plate.
しかしながら、設計自由度や剛性設計のし易さ等の観点から、ターボハウジングの製造には、プレス成形を適用しにくく、鋳物が多く使用されているのが現状である。 However, from the viewpoints of design flexibility and ease of rigidity design, it is difficult to apply press molding to the manufacture of turbo housings, and castings are often used at present.
そして、フェライト系ステンレス鋼板を用いてターボハウジングをプレス成形するには、用いられるフェライト系ステンレス鋼に関して、鋼板からハウジングへ加工するための二次加工性を含めた成形性等の加工性と、高温の排気ガス環境下における優れた耐熱性の確保が重要である。 In order to press-mold a turbo housing using a ferritic stainless steel sheet, the ferritic stainless steel used has a workability such as formability including secondary workability for processing from the steel sheet to the housing, and a high temperature. It is important to ensure excellent heat resistance in the exhaust gas environment.
具体的に耐熱性とは、ターボハウジングと、このターボハウジング内で回転する回転体であるターボとのクリアランスを、使用状態で所定の範囲以内に維持できるように、加熱によって変形しにくいことが重要である。 Specifically, heat resistance means that the clearance between the turbo housing and the turbo, which is a rotating body that rotates in the turbo housing, is difficult to be deformed by heating so that it can be maintained within a predetermined range in use. It is.
また、ターボチャージャーの駆動中は、加熱と冷却とが繰り返されるため、加熱および冷却の繰り返しによる熱疲労特性が良好であることも重要である。 Further, since heating and cooling are repeated while the turbocharger is driven, it is also important that the thermal fatigue characteristics by repeated heating and cooling are good.
さらに、高温の排気ガス環境を考慮し、耐加速酸化性および耐スケール剥離性等の高温酸化特性が良好であることが重要である。 Furthermore, considering the high temperature exhaust gas environment, it is important that the high temperature oxidation characteristics such as accelerated oxidation resistance and scale peeling resistance are good.
また、ターボチャージャーの動作を考慮し、高温高サイクル疲労特性が良好であることが重要である。 Also, considering the operation of the turbocharger, it is important that the high temperature and high cycle fatigue characteristics are good.
したがって、ターボハウジングの製造にてプレス成形を適用にするために、加工性が良好で、かつ、高温の排気ガス環境下における耐熱性に優れたフェライト系ステンレス鋼が求められていた。 Therefore, in order to apply press molding in the manufacture of a turbo housing, a ferritic stainless steel having good workability and excellent heat resistance in a high-temperature exhaust gas environment has been demanded.
本発明はこのような点に鑑みなされたもので、加工性が良好で、かつ、高温の排気ガス環境下における耐熱性に優れたターボハウジング用フェライト系ステンレス鋼およびターボハウジングを提供することを目的とする。 The present invention has been made in view of these points, and it is an object of the present invention to provide a ferritic stainless steel for turbo housing and a turbo housing that have good workability and excellent heat resistance in a high-temperature exhaust gas environment. And
請求項１に記載されたターボハウジング用フェライト系ステンレス鋼は、Ｃ：０．０２質量％以下、Ｓｉ：０．５質量％以下、Ｍｎ：０．６質量％以上１．５質量％以下、Ｎｉ：３質量％以下、Ｃｒ：１６質量％以上２５質量％以下、Ｎｂ：０．４質量％以上０．７質量％以下、Ｍｏ：１質量％以上２．５質量％以下、Ａｌ：０．１５質量％以下およびＮ：０．０２質量％以下を含有し、残部がＦｅおよび不可避的不純物からなり、かつ、１５Ｎｂ＋２Ｍｏ≧１０．５を満たす成分で構成され、析出相として存在するＮｂおよびＭｏの総量が０．２質量％以下であるものである。 The ferritic stainless steel for turbo housing according to claim 1 is C: 0.02 mass% or less, Si: 0.5 mass% or less, Mn: 0.6 mass% or more and 1.5 mass% or less, Ni : 3 mass% or less, Cr: 16 mass% or more and 25 mass% or less, Nb: 0.4 mass% or more and 0.7 mass% or less, Mo: 1 mass% or more and 2.5 mass% or less, Al: 0.15 The total amount of Nb and Mo that is contained as a precipitated phase, containing less than mass% and N: 0.02 mass% or less, the balance being composed of Fe and inevitable impurities and satisfying 15Nb + 2Mo ≧ 10.5 Is 0.2 mass% or less.
請求項２に記載されたターボハウジング用フェライト系ステンレス鋼は、請求項１記載のターボハウジング用フェライト系ステンレス鋼において、Ｃｕ：１質量％以上２質量％以下およびＷ：１質量％以上２．５質量％以下のうちの少なくとも１種を含有するものである。 The ferritic stainless steel for turbo housing according to claim 2 is the ferritic stainless steel for turbo housing according to claim 1, wherein Cu: 1% by mass to 2% by mass and W: 1% by mass to 2.5%. It contains at least one of mass% or less.
請求項３に記載されたターボハウジング用フェライト系ステンレス鋼は、請求項１または２記載のターボハウジング用フェライト系ステンレス鋼において、Ｖ、ＴｉおよびＺｒのうちの少なくとも１種を合計１質量％未満で含有するものである。 The ferritic stainless steel for turbo housing according to claim 3 is the ferritic stainless steel for turbo housing according to claim 1 or 2, wherein at least one of V, Ti and Zr is less than 1% by mass in total. It contains.
請求項４に記載されたターボハウジング用フェライト系ステンレス鋼は、請求項１ないし３いずれか一記載のターボハウジング用フェライト系ステンレス鋼において、Ｂ：０．０２質量％以下およびＣｏ：２質量％以下のうちの少なくとも１種を含有するものである。 The ferritic stainless steel for turbo housing described in claim 4 is the ferritic stainless steel for turbo housing according to any one of claims 1 to 3, wherein B: 0.02 mass% or less and Co: 2 mass% or less. It contains at least one of them.
請求項５に記載されたターボハウジング用フェライト系ステンレス鋼は、請求項１ないし４いずれか一記載のターボハウジング用フェライト系ステンレス鋼において、希土類元素およびＣａのうちの少なくとも１種を合計０．１質量％以下で含有するものである。 The ferritic stainless steel for turbo housing according to claim 5 is the ferritic stainless steel for turbo housing according to any one of claims 1 to 4, wherein at least one of rare earth elements and Ca is 0.1 in total. It is contained at a mass% or less.
請求項６に記載されたターボハウジングは、請求項１ないし５いずれか一記載のターボハウジング用フェライト系ステンレス鋼を用いてプレス成形にて形成され、使用状態にて少なくとも一部の材料温度が９００℃を超える温度環境下に曝されるものである。 The turbo housing according to claim 6 is formed by press molding using the ferritic stainless steel for turbo housing according to any one of claims 1 to 5, and at least a part of the material temperature is 900 in use. It is exposed to a temperature environment exceeding ℃.
請求項７に記載されたターボハウジングは、請求項６に記載されたターボハウジングにおいて、表面硬さが２２０ＨＶ以下であるものである。 A turbo housing according to a seventh aspect is the turbo housing according to the sixth aspect, wherein the surface hardness is 220 HV or less.
本発明によれば、成分の各元素の含有量が所定の範囲で制御されているため、加工性が良好である。また、成分が１５Ｎｂ＋２Ｍｏ≧１０．５を満たすとともに、析出相として存在するＮｂおよびＭｏの総量が０．２質量％以下であるため、高温強度および熱疲労特性を向上でき、高温の排気ガス環境下における耐熱性を向上できる。 According to the present invention, since the content of each element of the component is controlled within a predetermined range, the workability is good. In addition, since the component satisfies 15Nb + 2Mo ≧ 10.5 and the total amount of Nb and Mo present as a precipitated phase is 0.2% by mass or less, the high temperature strength and thermal fatigue characteristics can be improved, and in a high temperature exhaust gas environment The heat resistance in can be improved.
以下、本発明の一実施の形態の構成について詳細に説明する。 Hereinafter, the configuration of an embodiment of the present invention will be described in detail.
ターボハウジング用フェライト系ステンレス鋼は、排気ガスのエネルギーを利用して内燃機関の熱効率を高めるターボチャージャーのハウジングであるターボハウジングの製造に用いられるものである。 The ferritic stainless steel for turbo housing is used for manufacturing a turbo housing that is a turbo charger housing that uses the energy of exhaust gas to increase the thermal efficiency of an internal combustion engine.
このターボハウジング用フェライト系ステンレス鋼は、０．０２質量％以下のＣ（炭素）、０．５質量％以下のＳｉ（ケイ素）、０．６質量％以上１．５質量％以下のＭｎ（マンガン）、３質量％以下のＮｉ（ニッケル）、１６質量％以上２５質量％以下のＣｒ（クロム）、０．４質量％以上０．７質量％以下のＮｂ（ニオブ）、１質量％以上２．５質量％以下のＭｏ（モリブデン）、０．１５質量％以下のＡｌ（アルミニウム）、および、０．０２質量％以下のＮ（窒素）を含有し、残部がＦｅ（鉄）および不可避的不純物からなる。 This ferritic stainless steel for turbo housing is composed of 0.02 mass% or less C (carbon), 0.5 mass% or less Si (silicon), 0.6 mass% or more and 1.5 mass% or less Mn (manganese) 3% by mass or less of Ni (nickel), 16% by mass or more and 25% by mass or less of Cr (chromium), 0.4% by mass or more and 0.7% by mass or less of Nb (niobium), 1% by mass or more. 5% by mass or less of Mo (molybdenum), 0.15% by mass or less of Al (aluminum), and 0.02% by mass or less of N (nitrogen), with the balance being Fe (iron) and inevitable impurities Become.
Ｃは、クリープ特性等の高温強度を向上させる合金成分であるが、０．０２質量％を超えて過剰に含有させると、加工性や低温靭性が低下する可能性がある。したがって、Ｃの含有量は０．０２質量％以下（無添加を含まず。）とする。 C is an alloy component that improves high-temperature strength such as creep characteristics. However, if it exceeds 0.02% by mass, workability and low-temperature toughness may be reduced. Therefore, the C content is 0.02% by mass or less (excluding no addition).
Ｓｉは、耐スケール剥離性等の耐高温酸化性を向上させる合金成分であるが、０．５質量％を超えて過剰に含有させると、延性が低下し加工性が低下する可能性や、低温靭性が低下する可能性がある。したがって、Ｓｉの含有量は０．５質量％以下（無添加を含まず。）とする。 Si is an alloy component that improves high-temperature oxidation resistance such as scale peel resistance, but if it exceeds 0.5% by mass, ductility may decrease and workability may decrease. Toughness may be reduced. Therefore, the Si content is 0.5% by mass or less (excluding no addition).
Ｍｎは、耐スケール剥離性等の耐高温酸化性を向上させる合金成分であり、このような効果を奏するには０．６質量％以上含有させる必要がある。一方、１．５質量％を超えて過剰に含有させると、加工性および溶接性が低下する可能性がある。したがって、Ｍｎの含有量は０．６質量％以上１．５質量％以下とする。なお、Ｍｎはオーステナイト相安定化元素であるため、Ｃｒの含有量が少ない場合にＭｎの添加によりマルテンサイト相の形成が促進され、熱疲労特性および加工性が低下する可能性がある。このような熱疲労特性および加工性の低下を効果的に防止する観点からも、Ｍｎの含有量は上記範囲内にすることが好ましい。 Mn is an alloy component that improves high-temperature oxidation resistance such as scale peel resistance, and it is necessary to contain 0.6% by mass or more in order to achieve such an effect. On the other hand, if the content exceeds 1.5% by mass, workability and weldability may be deteriorated. Therefore, the Mn content is set to 0.6% by mass or more and 1.5% by mass or less. In addition, since Mn is an austenite phase stabilizing element, when the content of Cr is small, formation of a martensite phase is promoted by addition of Mn, and thermal fatigue characteristics and workability may be reduced. Also from the viewpoint of effectively preventing such deterioration in thermal fatigue characteristics and workability, the Mn content is preferably within the above range.
Ｎｉは、熱疲労特性および加工性の低下を防止する合金成分であるが、３質量％を超えて過剰に含有させると、オーステナイト相の析出によって熱疲労特性が低下する可能性がある。したがって、Ｎｉの含有量は、３質量％以下（無添加を含まず。）とする。 Ni is an alloy component that prevents deterioration of thermal fatigue characteristics and workability. However, if Ni is contained in excess of 3% by mass, thermal fatigue characteristics may be deteriorated due to precipitation of the austenite phase. Therefore, the Ni content is 3% by mass or less (excluding no addition).
Ｃｒは、熱膨張係数の低下や、フェライト相を安定化させ耐酸化性を向上させて耐高温酸化性を向上させる合金成分であり、このような効果を奏するには１６質量％以上含有させる必要がある。一方、２５質量％を超えて過剰に含有させると、脆化するとともに、硬質化して加工性が低下する可能性がある。したがって、Ｃｒの含有量は１６質量％以上２５質量％以下とする。 Cr is an alloy component that lowers the thermal expansion coefficient and stabilizes the ferrite phase to improve oxidation resistance and improve high-temperature oxidation resistance. To achieve such effects, it is necessary to contain 16% by mass or more. There is. On the other hand, when it contains excessively exceeding 25 mass%, while embrittlement, it hardens | cures and workability may fall. Therefore, the Cr content is 16% by mass or more and 25% by mass or less.
Ｎｂは、高温域での機械的強度を向上させるとともに、固溶強化により高温強度を向上させて熱疲労特性を向上させる合金成分であり、このような効果を奏するには、０．４質量％以上含有させる必要がある。一方、０．７質量％を超えて過剰に含有させると、溶接高温割れに対する感受性、加工性および低温靭性が低下する可能性がある。したがって、Ｎｂの含有量は０．４質量％以上０．７質量％以下とする。 Nb is an alloy component that improves the mechanical fatigue in the high temperature range and improves the thermal fatigue characteristics by improving the high temperature strength by solid solution strengthening. To exhibit such an effect, 0.4 mass% It is necessary to contain above. On the other hand, if the content exceeds 0.7% by mass, the sensitivity to weld hot cracking, workability, and low temperature toughness may be reduced. Therefore, the Nb content is set to 0.4% by mass or more and 0.7% by mass or less.
Ｍｏは、固溶強化により高温強度を向上させ熱疲労特性を向上させて、耐高温酸化性を向上させる合金成分であり、このような効果を奏するには１質量％以上含有させる必要がある。一方、２．５質量％を超えて過剰に含有させると、脆化するとともに、硬質化して加工性が低下する可能性がある。したがって、Ｍｏの含有量は１質量％以上２．５質量％以下とする。 Mo is an alloy component that improves high-temperature strength by solid solution strengthening and improves thermal fatigue properties, thereby improving high-temperature oxidation resistance. In order to achieve such effects, it is necessary to contain 1% by mass or more. On the other hand, when it contains excessively exceeding 2.5 mass%, it embrittles and hardens | cures and workability may fall. Therefore, the Mo content is 1% by mass or more and 2.5% by mass or less.
Ａｌは、フェライト系ステンレス鋼表面に緻密な保護性の酸化被膜を形成して耐酸化性を向上させる合金成分であるが、０．１５質量％を超えて過剰に含有させると、低温靭性が低下する可能性がある。そこで、Ａｌの含有量は、０．１５質量％以下（無添加を含まず。）とする。 Al is an alloy component that improves the oxidation resistance by forming a dense protective oxide film on the surface of ferritic stainless steel, but if it exceeds 0.15% by mass, the low temperature toughness decreases. there's a possibility that. Therefore, the content of Al is set to 0.15% by mass or less (excluding no addition).
Ｎは、クリープ特性等の高温強度を向上させる合金成分であるが、０．０２質量％を超えて過剰に含有させると、加工性や低温靭性が低下する可能性がある。したがって、Ｃの含有量は０．０２質量％以下（無添加を含まず。）とする。 N is an alloy component that improves high-temperature strength such as creep characteristics. However, if it exceeds 0.02% by mass, workability and low-temperature toughness may be reduced. Therefore, the C content is 0.02% by mass or less (excluding no addition).
そして、ターボハウジング用フェライト系ステンレス鋼では、添加した合金元素を固溶状態とすることで加工性を確保する。 And in the ferritic stainless steel for turbo housing, workability is ensured by making the added alloy element into a solid solution state.
また、ターボハウジング用フェライト系ステンレス鋼は、ＮｂおよびＭｏの含有量が上記範囲内において１５Ｎｂ＋２Ｍｏ≧１０．５で示す関係を満たすことにより、高温強度が向上し、高温高サイクル疲労特性を向上する。なお、式中のＮｂはＮｂの含有量（質量％）を示し、式中のＭｏはＭｏの含有量（質量％）を示す。 Further, the ferritic stainless steel for turbo housing satisfies the relationship expressed by 15Nb + 2Mo ≧ 10.5 in the Nb and Mo contents within the above range, thereby improving the high temperature strength and improving the high temperature / high cycle fatigue characteristics. In addition, Nb in a formula shows content (mass%) of Nb, and Mo in a formula shows content (mass%) of Mo.
さらに、ターボハウジング用フェライト系ステンレス鋼は、ＮｂおよびＭｏの固溶強化により高温強度を向上することで、熱疲労特性を確保する。そのためには、冷延焼鈍板に存在する析出物中のＮｂおよびＭｏの総量、すなわち析出相として存在するＮｂおよびＭｏの総量を０．２質量％以下にすることが重要である。 Furthermore, the ferritic stainless steel for turbo housing secures thermal fatigue characteristics by improving high temperature strength by solid solution strengthening of Nb and Mo. For that purpose, it is important that the total amount of Nb and Mo in the precipitates existing in the cold-rolled annealed plate, that is, the total amount of Nb and Mo existing as a precipitation phase is 0.2% by mass or less.
ターボハウジング用フェライト系ステンレス鋼は、必要に応じて、１質量％以上２質量％以下のＣｕ（銅）、および、１質量％以上２．５質量％以下のＷ（タングステン）うちの少なくとも１種を含有させることが好ましい。 The ferritic stainless steel for turbo housing is, if necessary, at least one of Cu (copper) of 1% by mass to 2% by mass and W (tungsten) of 1% by mass to 2.5% by mass It is preferable to contain.
Ｃｕは、８００℃以下での微細析出により高温強度を向上させ、熱疲労特性を向上させる合金成分であり、このような効果を奏するには、１質量％以上含有させる必要がある。一方、２質量％を超えて過剰に含有させると、硬質化して加工性が低下する可能性がある。したがって、Ｃｕを含有させる場合の含有量は、１質量％以上２質量％以下とする。 Cu is an alloy component that improves the high temperature strength by fine precipitation at 800 ° C. or less and improves the thermal fatigue characteristics. In order to exhibit such an effect, it is necessary to contain 1% by mass or more. On the other hand, if it is contained in excess of 2% by mass, it may be hardened and the workability may be lowered. Therefore, the content when Cu is contained is 1% by mass or more and 2% by mass or less.
Ｗは、固溶強化により高温強度を向上させ、熱疲労特性を向上させる合金成分であり、このような効果を奏するには、１質量％以上含有させる必要がある。一方、２．５質量％を超えて過剰に含有させると、硬質化して加工性が低下する可能性がある。したがって、Ｗを含有させる場合の含有量は、１質量％以上２．５質量％以下とする。 W is an alloy component that improves high-temperature strength by solid solution strengthening and improves thermal fatigue characteristics. In order to achieve such an effect, it is necessary to contain 1% by mass or more. On the other hand, when it contains excessively exceeding 2.5 mass%, it may harden and workability may fall. Therefore, the content when W is contained is 1% by mass or more and 2.5% by mass or less.
また、ターボハウジング用フェライト系ステンレス鋼は、必要に応じて、Ｖ（バナジウム）、Ｔｉ（チタン）およびＺｒ（ジルコニウム）のうちの少なくとも１種を合計１質量％未満で含有させることが好ましい。 Moreover, it is preferable that the ferritic stainless steel for turbo housing contains at least one of V (vanadium), Ti (titanium), and Zr (zirconium) in a total amount of less than 1% by mass as necessary.
Ｖは、靭性を損なわずに高温強度を向上させる合金成分である。また、Ｔｉは、析出強化により高温強度を向上させる合金成分である。さらに、Ｚｒは、フェライト系ステンレス鋼表面の酸化被膜に固溶し被膜強度を向上させて、高温強度を高める合金成分である。これらＶ、ＴｉおよびＺｒは、過剰に含有させると硬質化して加工性が低下する可能性がある。したがって、Ｖ、ＴｉおよびＺｒを含有させる場合は、Ｖ、ＴｉおよびＺｒのうちの少なくとも１種を合計１質量％未満で含有させることが好ましい。 V is an alloy component that improves high-temperature strength without impairing toughness. Ti is an alloy component that improves high-temperature strength by precipitation strengthening. Further, Zr is an alloy component that is dissolved in the oxide film on the surface of the ferritic stainless steel to improve the film strength and increase the high temperature strength. If these V, Ti, and Zr are contained excessively, they may become hard and workability may be reduced. Therefore, when V, Ti and Zr are contained, it is preferable to contain at least one of V, Ti and Zr in a total of less than 1% by mass.
また、ターボハウジング用フェライト系ステンレス鋼は、必要に応じて、０．０２質量％以下のＢ（ホウ素）、および、２質量％以下のＣｏ（コバルト）のうちの少なくとも１種を含有させることが好ましい。 Moreover, the ferritic stainless steel for turbo housing may contain at least one of 0.02% by mass or less of B (boron) and 2% by mass or less of Co (cobalt) as necessary. preferable.
Ｂは、低温靭性を向上させる合金成分であるが、０．０２質量％を超えて過剰に含有させると、延性が低下し加工性が低下する可能性がある。したがって、Ｂを含有させる場合の含有量は０．０２質量％以下が好ましい。 B is an alloy component that improves low-temperature toughness. However, if it exceeds 0.02% by mass, ductility may be reduced and workability may be reduced. Therefore, the content when B is contained is preferably 0.02% by mass or less.
Ｃｏは、固溶強化により高温強度を向上させて熱疲労特性を向上させる合金成分であるが、２．０質量％を超えて過剰に含有させると、加工性や低温靭性を低下させる可能性がある。したがって、Ｃｏを含有させる場合の含有量は、２．０質量％以下とする。 Co is an alloy component that improves high temperature strength by solid solution strengthening and improves thermal fatigue properties. However, if it is excessively contained in excess of 2.0% by mass, there is a possibility that workability and low temperature toughness may be reduced. is there. Therefore, the content when Co is contained is 2.0% by mass or less.
また、ターボハウジング用フェライト系ステンレス鋼は、ＲＥＭ（希土類元素）、および、Ｃａ（カルシウム）のうちの少なくとも１種を合計０．１質量％以下で含有させることが好ましい。 Moreover, it is preferable that the ferritic stainless steel for turbo housing contains at least one of REM (rare earth element) and Ca (calcium) in a total amount of 0.1% by mass or less.
ＲＥＭおよびＣａは、フェライト系ステンレス鋼表面の酸化被膜に固溶し被膜強度を向上させて、高温強度を高める合金成分であるが、過剰に含有させると、硬質化して加工性が低下する可能性や、製造時に表面疵が生じやすくなり製造性が低下する可能性がある。したがって、ＲＥＭおよびＣａを含有させる場合には、ＲＥＭおよびＣａのうちの少なくとも１種を合計０．１質量％以下で含有させることが好ましい。 REM and Ca are alloy components that dissolve in the oxide film on the surface of ferritic stainless steel to improve the film strength and increase the high-temperature strength. However, if excessively contained, REM and Ca may be hardened and workability may be reduced. In addition, surface flaws are likely to occur at the time of manufacture, and the productivity may be reduced. Therefore, when REM and Ca are contained, it is preferable to contain at least one of REM and Ca in a total amount of 0.1% by mass or less.
上記範囲内で所定の成分組成にて溶製されたターボハウジング用フェライト系ステンレス鋼は、熱間圧延、冷間圧延および焼鈍が施されて冷延焼鈍板とされる。また、この冷延焼鈍板を用いてターボハウジングがプレス成形される。 The ferritic stainless steel for turbohousing melted with a predetermined component composition within the above range is subjected to hot rolling, cold rolling and annealing to form a cold rolled annealed plate. Moreover, a turbo housing is press-molded using this cold-rolled annealing plate.
なお、ターボハウジングは、高温の排気ガス環境下において使用されるため、使用状態においては、少なくとも一部の材料温度が９００℃を超える温度環境下に曝されて加熱されることになる。 Since the turbo housing is used in a high-temperature exhaust gas environment, at the time of use, at least a part of the material temperature is exposed to a temperature environment exceeding 900 ° C. and heated.
そのため、ターボハウジング用フェライト系ステンレス鋼を溶製しプレス成形した後に焼鈍を行うことにより、加工（プレス成形）の際に導入されたひずみを除去するとともに、ステンレス鋼の表面のビッカース硬さを２２０ＨＶ以下に調整すると、使用状態に加熱による変形を抑制できるので好ましい。 Therefore, by melting and press-molding ferritic stainless steel for turbo housing and performing annealing, the strain introduced during processing (press molding) is removed, and the Vickers hardness of the stainless steel surface is set to 220 HV. Adjustment to the following is preferable because deformation due to heating can be suppressed in the use state.
そして、上記ターボハウジング用フェライト系ステンレス鋼によれば、構成する成分の各元素の含有量が上述のように所定の範囲で制御されているため、冷延焼鈍板にて各元素が固溶状態となり、加工性を向上できる。その結果、プレス成形に適用可能である。 And according to the ferritic stainless steel for turbo housing, since the content of each element of the constituent components is controlled within a predetermined range as described above, each element is in a solid solution state in the cold-rolled annealing plate. Thus, workability can be improved. As a result, it can be applied to press molding.
また、ＮｂおよびＭｏの含有量が、上記範囲内において１５Ｎｂ＋２Ｍｏ≧１０．５の式で示す関係を満たすとともに、析出相として存在するＮｂおよびＭｏの総量を０．２質量％以下とすることにより、ＮｂおよびＭｏによる固溶強化作用を確保できるため、ＮｂおよびＭｏの固溶強化により高温強度を向上でき、熱疲労特性を向上できる。したがって、高温の排気ガス環境下における耐熱性を向上できる。 In addition, the Nb and Mo contents satisfy the relationship represented by the formula of 15Nb + 2Mo ≧ 10.5 within the above range, and the total amount of Nb and Mo existing as a precipitated phase is 0.2% by mass or less. Since the solid solution strengthening action by Nb and Mo can be secured, the high temperature strength can be improved by the solid solution strengthening of Nb and Mo, and the thermal fatigue characteristics can be improved. Therefore, heat resistance in a high temperature exhaust gas environment can be improved.
その結果、上記ターボハウジング用フェライト系ステンレス鋼を用いてプレス成形されたターボハウジングは、使用状態において、少なくとも一部の材料温度が９００℃を超える高温の排気ガス環境下においても変形や酸化が生じにくい。 As a result, the turbo housing press-molded using the ferritic stainless steel for turbo housing is deformed and oxidized even in a high temperature exhaust gas environment in which at least a part of the material temperature exceeds 900 ° C. in use. Hateful.
すなわち、高温の排気ガス環境下で使用しても、ターボハウジングと、このターボハウジング内で回転する回転体であるターボとのクリアランスを所定の範囲以内に維持できる。 That is, even when used in a high-temperature exhaust gas environment, the clearance between the turbo housing and the turbo which is a rotating body rotating in the turbo housing can be maintained within a predetermined range.
また、ターボチャージャーの駆動時に加熱と冷却とが繰り返されても、加熱および冷却の繰り返しによる熱疲労特性が良好である。 Moreover, even if heating and cooling are repeated when the turbocharger is driven, thermal fatigue characteristics due to repeated heating and cooling are good.
さらに、耐加速酸化性および耐スケール剥離性等の高温酸化特性が良好であり、高温の排気ガス環境下での使用に適用しやすい。 Furthermore, it has good high-temperature oxidation characteristics such as accelerated oxidation resistance and scale peel resistance, and is easily applied to use in a high-temperature exhaust gas environment.
また、高温高サイクル疲労特性が良好であり、高温の排気ガス環境下におけるターボチャージャーの動作に適用しやすい。 Moreover, it has good high-temperature and high-cycle fatigue characteristics and is easy to apply to the operation of a turbocharger in a high-temperature exhaust gas environment.
上記ターボハウジング用フェライト系ステンレス鋼は、必要に応じてＣｕおよびＷのうちの少なくとも１種を上記範囲で含有させることにより、析出強化や固溶強化により高温強度を向上でき、熱疲労特性を向上できる。 The ferritic stainless steel for turbo housing can improve the high temperature strength by precipitation strengthening or solid solution strengthening and improve thermal fatigue characteristics by containing at least one of Cu and W within the above range as necessary. it can.
また、必要に応じてＶ、ＴｉおよびＺｒのうちの少なくとも１種を上記範囲で含有させることのより、析出強化や固溶強化により高温強度を向上でき、熱疲労特性を向上できる。 Moreover, by containing at least one of V, Ti and Zr in the above range as required, the high temperature strength can be improved by precipitation strengthening or solid solution strengthening, and the thermal fatigue characteristics can be improved.
さらに、ＢおよびＣｏのうちの少なくとも１種を上記範囲で含有させることにより、低温靭性や高音強度を向上できる。 Furthermore, low temperature toughness and high sound intensity can be improved by containing at least one of B and Co in the above range.
また、ＲＥＭおよびＣａのうちの少なくとも１種を上記範囲で含有させることにより、被膜強度を向上できるため、高温強度を向上できる。 Moreover, since film | membrane intensity | strength can be improved by containing at least 1 sort (s) of REM and Ca in the said range, high temperature intensity | strength can be improved.
ターボハウジングは、プレス成形後に焼鈍を施して鋼板表面のビッカース硬さを２２０ＨＶ以下にすることにより、高温の排気ガス環境下における使用での加熱による変形を抑制できる。 The turbo housing can suppress deformation due to heating in use in a high-temperature exhaust gas environment by annealing after press forming so that the Vickers hardness of the steel sheet surface is 220 HV or less.
以下、本実施例および比較例について説明する。 Hereinafter, this example and a comparative example will be described.
まず、表１に示す成分のフェライト系ステンレス鋼を溶製した。なお、表１における各元素の含有量は質量％で示す。また、表１では、ＮｂおよびＭｏの含有量に基づく１５Ｎｂ＋２Ｍｏの値を、式（１）の値として示す。 First, ferritic stainless steel having the components shown in Table 1 was melted. In addition, content of each element in Table 1 is shown by the mass%. Moreover, in Table 1, the value of 15Nb + 2Mo based on content of Nb and Mo is shown as a value of Formula (1).
表１に示す各成分で溶製したフェライト系ステンレス鋼を熱間圧延、冷間圧延および焼鈍を順次施して冷延焼鈍板の供試材とした。 Ferritic stainless steel melted with each component shown in Table 1 was subjected to hot rolling, cold rolling and annealing in order to obtain a cold rolled annealed specimen material.
各供試材を用いて、加工性に関する引張試験と、耐熱性に関する熱疲労試験、高温強度試験および高温酸化試験とをそれぞれ行った。 Using each test material, a tensile test for workability, a thermal fatigue test for heat resistance, a high temperature strength test, and a high temperature oxidation test were performed.
引張試験では、常温での引張試験による伸びで加工性を評価した。すなわち、破断伸びが３０％以上だったのもの加工性が良好であると判断して○と評価し、破断伸びが３０％未満だったものを×と評価した。 In the tensile test, workability was evaluated by the elongation by a tensile test at room temperature. That is, when the elongation at break was 30% or more, it was judged that the processability was good and evaluated as good, and when the elongation at break was less than 30%, it was evaluated as x.
高温強度試験は、９００℃での０．２％耐力を測定した。そして、０．２％耐力が２５ＭＰａ以上のものを高温強度が良好であると判断して○と評価し、２５ＭＰａ未満のものを×と評価した。 The high temperature strength test measured 0.2% proof stress at 900 ° C. Then, those having a 0.2% proof stress of 25 MPa or more were evaluated as “good” by judging that the high temperature strength was good, and those having less than 25 MPa were evaluated as “x”.
熱疲労試験では、冷延焼鈍板である上記各供試材をパイプ状に造管して試験片とし、拘束率２０％にて、２００℃から９００℃で加熱と冷却とを繰り返した。そして、熱疲労寿命が１０００サイクル以上のものを熱疲労特性が良好であると判断して○と評価し、熱疲労寿命が１０００サイクル未満だったものを×と評価した。 In the thermal fatigue test, each of the above-mentioned test materials, which are cold-rolled annealed plates, was formed into a pipe shape to form a test piece, and heating and cooling were repeated at 200 to 900 ° C. at a constraint rate of 20%. Then, those having a thermal fatigue life of 1000 cycles or more were evaluated as “good” by judging that the thermal fatigue characteristics were good, and those having a thermal fatigue life of less than 1000 cycles were evaluated as “x”.
高温酸化試験は、１０％水蒸気中にて室温から９００℃までの加熱と９００℃から室温までの冷却とを繰り返す断続酸化試験を行った。そして、スケール剥離による酸化減量がないものを高温酸化特性が良好であると判断して○と評価し、スケール剥離による酸化減量があったものを×と評価した。 The high temperature oxidation test was an intermittent oxidation test in which heating from room temperature to 900 ° C. and cooling from 900 ° C. to room temperature were repeated in 10% steam. And the thing without the oxidation weight loss by scale peeling judged that the high temperature oxidation characteristic was favorable, and evaluated it as (circle), and the thing with the oxidation weight loss by scale peeling was evaluated as x.
これら引張試験、熱疲労試験、高温強度試験および高温酸化試験の結果を表２に示す。 Table 2 shows the results of the tensile test, thermal fatigue test, high temperature strength test, and high temperature oxidation test.
表２に示すように、本実施例のいずれも加工性および耐熱性が良好であった。 As shown in Table 2, all of the examples had good workability and heat resistance.
一方、式（１）の値が１０．５未満であるか、または、析出物中のＮｂおよびＭｏの総量が０．２質量％より多い比較例である鋼種番号１０、鋼種番号１１、鋼種番号１２、鋼種番号１４および鋼種番号１５は、熱疲労特性および高温強度が低かった。 On the other hand, the value of Formula (1) is less than 10.5, or the steel type number 10, steel type number 11, and steel type number which are comparative examples in which the total amount of Nb and Mo in the precipitate is greater than 0.2% by mass. No. 12, Steel No. 14 and Steel No. 15 had low thermal fatigue properties and high temperature strength.
ＭｏやＭｎの含有量が上記範囲より少ない比較例である鋼種番号１２、鋼種番号１３および鋼種番号１４は、高温酸化特性が低かった。 Steel type No. 12, steel type No. 13 and steel type No. 14 which are comparative examples in which the content of Mo or Mn is less than the above range had low high temperature oxidation characteristics.
次に、各供試材に関して、図１（ａ）に示す形状に加工する際の成形性試験、および、最高排気ガス温度９５０℃での冷熱サイクル繰り返しによる耐熱性試験を行った。 Next, each sample material was subjected to a formability test when processing into the shape shown in FIG. 1A and a heat resistance test by repeated cooling and heating cycles at a maximum exhaust gas temperature of 950 ° C.
成形性試験は、各供試材を図１（ａ）に示す形状にプレス成形した後に割れの観察を行った。そして、割れが未発生のものを加工性が良好であると判断して○と評価し、割れが発生したものを×と評価した。 In the moldability test, each specimen was press-molded into the shape shown in FIG. And the thing in which the crack did not generate | occur | produce was evaluated as (circle) judging that workability was favorable, and the thing in which the crack generate | occur | produced was evaluated as x.
耐熱性試験は、成形試験にて加工性が良好であったものの一部に関して、焼鈍にて硬さを調整した場合と焼鈍を行わず硬さを調整しなかった場合とで、図１（ａ）に示すように固定した状態で冷熱サイクルを繰り返した。そして、図１（ｂ）に示すように冷熱サイクルを繰り返した後の状態にて、変形量と、亀裂の発生と、加速酸化の発生とを評価した。 The heat resistance test is shown in FIG. 1 (a) in the case where the hardness was adjusted by annealing and the hardness was not adjusted without annealing, with respect to a part of which the workability was good in the molding test. The cooling and heating cycle was repeated in a fixed state as shown in FIG. Then, as shown in FIG. 1B, the deformation amount, the occurrence of cracks, and the occurrence of accelerated oxidation were evaluated in a state after the cooling and heating cycle was repeated.
なお、耐熱性試験前に焼鈍を行ってビッカース硬さを２２０ＨＶ以下に調整したものを○で示し、耐熱性試験前に焼鈍を行わずにビッカース硬さを調整しなかったものを×で示した。 In addition, what performed annealing before a heat resistance test and adjusted Vickers hardness to 220HV or less was shown by (circle), and what did not adjust Vickers hardness without performing annealing before heat resistance test was shown by x. .
変形量の評価は、冷熱サイクルの繰り返し前の外形の寸法をＷ０とし、冷熱サイクルの繰り返し後の外形寸法をＷとし、冷熱サイクルの繰り返し前後での外形寸法の変形量の絶対値をΔＷとすると、ΔＷ＝Ｗ−Ｗ０となる。そして、ΔＷが５００μｍ以下のものを変形量が良好と判断して○と評価し、ΔＷが５００μｍを超えたものを×と評価した。 The deformation amount is evaluated by setting the outer dimension before repeating the cooling cycle as W 0 , the outer dimension after repeating the cooling cycle as W, and the absolute value of the deformation amount before and after the cooling cycle as ΔW. Then, the ΔW = W-W 0. And the thing with (DELTA) W of 500 micrometers or less was judged that the deformation | transformation amount was favorable, and evaluated as (circle), and the thing (DELTA) W exceeded 500 micrometers was evaluated as x.
亀裂および加速酸化の評価は、冷熱サイクルを繰り返し後に亀裂および加速酸化をそれぞれ別個に観察した。そして、未発生のものを良好と判断して○と評価し、それ以外を×と評価した。 For evaluation of cracks and accelerated oxidation, cracks and accelerated oxidation were observed separately after repeated cooling cycles. And the thing which did not generate | occur | produce was judged favorable and was evaluated as (circle), and the others were evaluated as x.
これら成形性試験および耐熱性試験の結果を表３に示す。 Table 3 shows the results of the moldability test and the heat resistance test.
表３に示すように、上記引張試験において伸びが３０％未満であった比較例である鋼種番号１１や鋼種番号１４は、加工後に割れが発生したのに対し、伸びが３０％以上だったものはいずれも割れが確認されず、加工性が良好であった。 As shown in Table 3, steel type No. 11 and steel type No. 14, which were comparative examples whose elongation was less than 30% in the tensile test, had cracks after processing, but had an elongation of 30% or more. In any case, no cracks were observed, and the workability was good.
耐熱性試験では、成形性試験にて割れが確認されなかった本実施例である鋼種番号１および鋼種番号３と、同様に割れが確認されなかった比較例である鋼種番号１０および鋼種番号１３とを用いて評価に供した。 In the heat resistance test, steel type number 1 and steel type number 3 which are the present examples in which cracks were not confirmed in the formability test, and steel type number 10 and steel type number 13 which were comparative examples in which no cracks were similarly confirmed, We used for evaluation.
変形量の評価では、本実施例である鋼種番号１および鋼種番号３と比較例である鋼種番号１０とは、焼鈍による硬さ調整を行わなかった場合は、上記基準より変形量が大きかったが、焼鈍による硬さ調整を行った場合は上記基準より変形量が少なく良好だった。 In the evaluation of the deformation amount, the steel type number 1 and steel type number 3 as the present example and the steel type number 10 as the comparative example had a deformation amount larger than the above standard when the hardness adjustment by annealing was not performed. When the hardness was adjusted by annealing, the amount of deformation was smaller than the above standard, which was good.
一方、ＭｎやＭｏの含有量が上記範囲より少ない比較例である鋼種番号１３は、焼鈍による硬さ調整の有無に関わらず、上記基準より変形量が大きかった。 On the other hand, Steel Type No. 13, which is a comparative example in which the content of Mn or Mo is less than the above range, had a larger deformation than the above reference regardless of whether or not the hardness was adjusted by annealing.
亀裂の発生の評価では、本実施例である鋼種番号１および鋼種番号３と比較例である鋼種番号１３とは、焼鈍による硬さの調整の有無に関わらず、熱疲労による亀裂の発生は確認されなかった。 In the evaluation of the occurrence of cracks, the occurrence of cracks due to thermal fatigue was confirmed in steel type Nos. 1 and 3 as a working example and steel type No. 13 as a comparative example regardless of whether or not the hardness was adjusted by annealing. Was not.
一方、析出物中のＮｂおよびＭｏの総量が０．２質量％より多い比較例である鋼種番号１０は、焼鈍による硬さ調整の有無に関わらず、熱疲労による亀裂が発生していた。 On the other hand, in Steel No. 10, which is a comparative example in which the total amount of Nb and Mo in the precipitate is more than 0.2% by mass, cracks due to thermal fatigue occurred regardless of whether or not the hardness was adjusted by annealing.
加速酸化の発生の評価では、本実施例である鋼種番号１および鋼種番号３と、比較例である鋼種番号１０とは、焼鈍による硬さ調整の有無に関わらず、加速酸化が確認されなかった。 In the evaluation of the occurrence of accelerated oxidation, the steel type No. 1 and steel type No. 3 which are the present examples and the steel type No. 10 which is the comparative example were not confirmed to be accelerated regardless of whether or not the hardness was adjusted by annealing. .
一方、ＭｎやＭｏの含有量が上記範囲より少ない比較例である鋼種番号１３は、焼鈍による硬さ調整の有無に関わらず、加速酸化が発生していた。 On the other hand, in steel type No. 13, which is a comparative example in which the content of Mn or Mo is less than the above range, accelerated oxidation occurred regardless of whether or not the hardness was adjusted by annealing.
これら結果から、本実施例である鋼種番号１および鋼種番号３は、ターボハウジングへの二次加工性を含む加工性が良好であるだけでなく、変形量も小さく、熱疲労による亀裂の発生や加速酸化の発生もないため、耐熱性が良好であることが示される。 From these results, steel type No. 1 and steel type No. 3 which are the present examples not only have good workability including secondary workability to the turbo housing, but also have a small deformation amount, occurrence of cracks due to thermal fatigue, Since there is no generation of accelerated oxidation, it indicates that the heat resistance is good.
Claims (7)
析出相として存在するＮｂおよびＭｏの総量が０．２質量％以下である
ことを特徴とするターボハウジング用フェライト系ステンレス鋼。 C: 0.02 mass% or less, Si: 0.5 mass% or less, Mn: 0.6 mass% or more and 1.5 mass% or less, Ni: 3 mass% or less, Cr: 16 mass% or more and 25 mass% or less Nb: 0.4% by mass or more and 0.7% by mass or less, Mo: 1% by mass or more and 2.5% by mass or less, Al: 0.15% by mass or less and N: 0.02% by mass or less, The balance is composed of Fe and inevitable impurities, and is composed of a component that satisfies 15Nb + 2Mo ≧ 10.5,
A ferritic stainless steel for turbo housing, wherein the total amount of Nb and Mo present as a precipitated phase is 0.2% by mass or less.
ことを特徴とする請求項１記載のターボハウジング用フェライト系ステンレス鋼。 The ferritic stainless steel for turbo housing according to claim 1, comprising at least one of Cu: 1 mass% to 2 mass% and W: 1 mass% to 2.5 mass%.
ことを特徴とする請求項１または２記載のターボハウジング用フェライト系ステンレス鋼。 3. The ferritic stainless steel for turbo housing according to claim 1, wherein at least one of V, Ti, and Zr is contained in a total of less than 1% by mass.
ことを特徴とする請求項１ないし３いずれか一記載のターボハウジング用フェライト系ステンレス鋼。 The ferritic stainless steel for turbo housing according to any one of claims 1 to 3, characterized by containing at least one of B: 0.02 mass% or less and Co: 2 mass% or less.
ことを特徴とする請求項１ないし４いずれか一記載のターボハウジング用フェライト系ステンレス鋼。 The ferritic stainless steel for turbo housing according to any one of claims 1 to 4, characterized in that it contains at least one of rare earth elements and Ca in a total amount of 0.1% by mass or less.
使用状態にて少なくとも一部の材料温度が９００℃を超える温度環境下に曝される
ことを特徴とするターボハウジング。 It is formed by press molding using the ferritic stainless steel for turbo housing according to any one of claims 1 to 5.
A turbo housing characterized by being exposed to a temperature environment in which at least a part of the material temperature exceeds 900 ° C. in use.
ことを特徴とする請求項６記載のターボハウジング。 The surface hardness is 220 HV or less. The turbo housing according to claim 6.
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