JP6684629B2 - Austenitic stainless steel with excellent high-temperature slidability, and turbocharger parts manufactured using it - Google Patents
Austenitic stainless steel with excellent high-temperature slidability, and turbocharger parts manufactured using it Download PDFInfo
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- 229910000963 austenitic stainless steel Inorganic materials 0.000 title claims description 25
- 229910052757 nitrogen Inorganic materials 0.000 claims description 14
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- 229910052748 manganese Inorganic materials 0.000 claims description 4
- 229910052802 copper Inorganic materials 0.000 claims description 3
- 229910052735 hafnium Inorganic materials 0.000 claims description 3
- 229910052742 iron Inorganic materials 0.000 claims description 3
- 229910052715 tantalum Inorganic materials 0.000 claims description 3
- 229910052718 tin Inorganic materials 0.000 claims description 3
- 229910052721 tungsten Inorganic materials 0.000 claims description 3
- 229910052720 vanadium Inorganic materials 0.000 claims description 3
- 229910052727 yttrium Inorganic materials 0.000 claims description 3
- 229910052726 zirconium Inorganic materials 0.000 claims description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims description 2
- 229910052698 phosphorus Inorganic materials 0.000 claims description 2
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Description
本発明は、ターボチャージャ等の自動車などの内燃機関の排気系部品において、摺動機構を有する部品に適した高温摺動性に優れたオーステナイト系ステンレス鋼と当該鋼で製造されたターボチャージャに代表される排気系部品に関するものである。 The present invention is representative of an austenitic stainless steel excellent in high-temperature slidability suitable for a component having a sliding mechanism in an exhaust system component of an internal combustion engine such as an automobile such as a turbocharger, and a turbocharger manufactured from the steel. Exhaust system parts to be used.
自動車の省燃費・環境規制対応技術として、タ−ボチャージャを組み合わせたディーゼルエンジンが特に欧州で普及しており、今後グローバルに増加することが予想されている。このターボチャージャでは過給圧を可変ノズルベーンで制御する可変容量型が主流であり、ＶＧ(Variable Geometry)方式、或いはＶＧＳ(Variable Geometry System)と呼称されている。しかし可変ノズル機構は高温無潤滑環境で使用されることから、高温摺動性(高温摩擦摩耗特性)に優れる材料が求められている。 Diesel engines combined with turbochargers are particularly popular in Europe as a technology for complying with fuel efficiency and environmental regulations for automobiles, and are expected to increase globally in the future. The mainstream of this turbocharger is a variable capacity type in which supercharging pressure is controlled by a variable nozzle vane, which is called a VG (Variable Geometry) system or a VGS (Variable Geometry System). However, since the variable nozzle mechanism is used in a high temperature non-lubricated environment, a material excellent in high temperature slidability (high temperature friction and wear characteristics) is required.
この要求に応える技術として、特許文献１ではＳｉ：２．０〜４．０％、Ｎｉ：８．０〜１６．０％、Ｃｒ：１８．０〜２０．０％を有するオーステナイト系ステンレス鋼で製作されるノズルベーン式ターボチャージャの排気ガイド部品が示されている。Ｓｉを添加することで、素材の伸び、穴広げ率が向上し排気ガイド部品の製作に適すると共に、酸化スケールの生成が少なく、生成した場合にも耐剥離性に優れたスケールを形成することから、摺動によるスケール剥離や摩耗が少なく、優れた高温摺動性を維持できるとされている。 As a technique to meet this requirement, in Patent Document 1, an austenitic stainless steel having Si: 2.0 to 4.0%, Ni: 8.0 to 16.0%, and Cr: 18.0 to 20.0% is used. Exhaust guide components for the nozzle vane turbocharger being manufactured are shown. By adding Si, the elongation of the material and the hole expansion rate are improved, which is suitable for the production of exhaust guide parts, and the formation of oxide scale is small, and even if it is produced, a scale excellent in peeling resistance is formed. It is said that there is little scale peeling and wear due to sliding, and excellent high temperature slidability can be maintained.
また、特許文献２ではエキゾーストマニホールドやターボチャージャのハウジングにおいて、より高温で排ガスを排出させるべく材料の薄肉化が図られており、使用される材料の温度が上がるために、高温での強度と共に高温での強度の長時間安定性が必要とされるため、Ｓｉ：１．０〜３．０％、Ｎｉ：８．０〜１５％、Ｃｒ：２２超〜２６％、Ｎ：０．１５超〜０．３％、Ｎｂ：０．０５〜０．３％以下を含む耐熱部材用オーステナイト系ステンレス鋼が示されている。Ｓｉ添加により耐スケール剥離性を向上できること、Ｎｂ添加により時効後の高温強度の低下を抑制できること、Ｎを高めることで固溶強化により高温強度を高められることを特徴としている。 Further, in Patent Document 2, the material of the exhaust manifold or the housing of the turbocharger is thinned in order to discharge the exhaust gas at a higher temperature, and since the temperature of the material used is increased, the strength at a high temperature and the high temperature are increased. Since long-term stability of strength in Si is required, Si: 1.0 to 3.0%, Ni: 8.0 to 15%, Cr: more than 22% to 26%, N: more than 0.15% Austenitic stainless steel for heat resistant members containing 0.3% and Nb: 0.05 to 0.3% or less is shown. It is characterized in that the addition of Si can improve the scale peeling resistance, the addition of Nb can suppress the decrease in high temperature strength after aging, and the increase in N can enhance the high temperature strength by solid solution strengthening.
非特許文献１、２によると、高Siステンレス鋼が高温摺動性に優れると報告されている。 しかしながら、高温摺動性の評価は高Ｓｉステンレス鋼と従来鋼との比較であり、高温摺動性の支配因子は明確でなかった。 According to Non-Patent Documents 1 and 2, high Si stainless steel is reported to have excellent high temperature slidability. However, the evaluation of the high temperature slidability was a comparison between the high Si stainless steel and the conventional steel, and the controlling factor of the high temperature slidability was not clear.
背景技術に記載の技術を検討したところ以下の課題が明らかになった。特許文献１の、Ｓｉ添加による高温強度の向上は小さく、高温摺動性の向上は少ないことが分かった。特許文献２の発明鋼は、Ｓｉで耐酸化性を、ＮｂとＮで高温強度を高めたものであるが、ターボチャージャに必要な高温摺動性の向上効果は不十分であることが分かった。非特許文献１、２によれば、ターボチャージャの耐久性や性能向上のためには、高温摺動性の支配因子を明らかにし、既存鋼に勝る高温摺動性、すなわち高温での耐摩耗性と低摩擦係数を有する材料を開発することが求められている。 When the technology described in the background art was examined, the following problems became clear. It was found that in Patent Document 1, the improvement in high temperature strength due to the addition of Si was small and the improvement in high temperature slidability was small. The invention steel of Patent Document 2 is one in which the oxidation resistance is enhanced by Si and the high temperature strength is enhanced by Nb and N, but it was found that the effect of improving the high temperature slidability required for the turbocharger is insufficient. . According to Non-Patent Documents 1 and 2, in order to improve the durability and performance of a turbocharger, the controlling factors of high temperature slidability are clarified, and high temperature slidability superior to existing steel, that is, wear resistance at high temperature Therefore, it is required to develop a material having a low coefficient of friction.
本発明の目的は、上記の既知技術の問題点を解決し、高温摺動性に優れたオーステナイト系ステンレス鋼を提供すること、また当該鋼を用いた耐久性に優れるターボチャージャ部品を提供することにある。 An object of the present invention is to solve the above-mentioned problems of the known art, to provide an austenitic stainless steel excellent in high-temperature slidability, and to provide a turbocharger component excellent in durability using the steel. It is in.
上記課題を解決するために、本発明者らはオーステナイト系ステンレス鋼の高温摺動性に及ぼす各種要因を調べた。高温摺動性の支配因子として、耐酸化性、高温強度、耐焼付き性が考えられるので、これらの観点から、製造性を損なうこと無くオーステナイト系ステンレス鋼の高温摺動性を向上する要件について検討した。 In order to solve the above problems, the present inventors investigated various factors that affect the high temperature slidability of austenitic stainless steel. Oxidation resistance, high temperature strength, and seizure resistance can be considered as the main factors of high temperature slidability. From these viewpoints, the requirements for improving the high temperature slidability of austenitic stainless steel without impairing manufacturability are examined. did.
（耐酸化性の向上）
耐酸化性には高Ｃｒ化が望ましく、２５％Ｃｒ-２０％ＮｉのＳＵＳ３１０Ｓ鋼が耐熱材料として用いられている。また、Ｃｒを低減する代わりにＳｉを添加したＳＵＳ３０２Ｂ等の材料も開発されている。Ｓｉはスケール直下オーステナイト粒界などに内部酸化層を形成するためにスケールの剥離を抑制する作用が知られている。しかし、加熱-冷却を繰り返す環境においては、スケールと金属材料との熱膨張差によってスケール剥離が生じやすく、スケールの剥離性が耐酸化性に大きく影響する。熱膨張率の大きいオーステナイト系ステンレス鋼ではその影響が更に顕著であるため、従来から、耐酸化性の求められる環境では高Ｓｉステンレス鋼が用いられている。しかしながら、ターボチャージャに導入される排ガス温度は年々高温化する傾向にあり、高Ｓｉ鋼に勝る耐酸化性が求められている。
(Improved oxidation resistance)
Higher Cr is desirable for oxidation resistance, and SUS310S steel of 25% Cr-20% Ni is used as a heat resistant material. Also, materials such as SUS302B in which Si is added instead of reducing Cr have been developed. It is known that Si forms an internal oxide layer at an austenite grain boundary directly below the scale and thus suppresses scale peeling. However, in an environment where heating and cooling are repeated, peeling of scale is likely to occur due to the difference in thermal expansion between the scale and the metal material, and the peelability of the scale greatly affects the oxidation resistance. Since the effect is more remarkable in austenitic stainless steel having a large coefficient of thermal expansion, high Si stainless steel has been conventionally used in an environment where oxidation resistance is required. However, the temperature of the exhaust gas introduced into the turbocharger tends to increase year by year, and it is required to have oxidation resistance superior to that of high Si steel.
本発明者らの調査の結果、この環境で更に耐酸化性を高めるためにはＡｌ添加が有効であり、特に１％以上のＡｌ添加によって自動車排ガス環境における耐酸化性が大きく向上することが分かった。高Ａｌ化により酸化が抑制されると共に、スケールの剥離も抑制される。 As a result of the investigation by the present inventors, it was found that the addition of Al is effective for further increasing the oxidation resistance in this environment, and particularly, the addition of 1% or more of Al significantly improves the oxidation resistance in the exhaust gas environment of the automobile. It was Owing to the high Al content, oxidation is suppressed and peeling of the scale is also suppressed.
（高温での耐摩耗性と耐焼付き性の向上）
ターボチャージャ等の自動車などの内燃機関の部品には、高温強度が要求される。前述の内燃機関を構成するステンレス鋼の高温強度の向上には高窒素化や金属間化合物による析出強化が有効であることが知られている。耐熱温度が４００〜５００℃であれば、０．２〜０．３％Ｎ添加により高温強度を高めた材料が実用的であるが、ターボチャージャの使用環境で耐摩耗性を向上するほどの効果は得られないことが分かった。高温強度を向上させるために金属間化合物を微細析出させて強化する材料としてはＳＵＨ６６０やＩｎｃｏｎｅｌ７１８が知られている。ＳＵＨ６６０はＮｉ３Ｔｉの析出による強化、Ｉｎｃｏｎｅｌ７１８はＮｉ３Ｎｂ、Ｆｅ２Ｎｂなどによる析出強化鋼、析出強化合金である。これらの鋼、合金では耐酸化性が不十分であり、自動車の排ガスに曝される環境で使用するには適さなかった。金属間化合物としてはＮｉ３Ａｌがあるが、Ｎｉ３ＡｌはＮｉ３ＴｉやＮｉ３Ｎｂに比べて高温環境で使用中に容易に粗大化するためクリープ寿命などで評価すると効果が認められず、耐熱材料において一般的にＡｌの添加は避けるべきと考えられてきた。
(Improved wear resistance and seizure resistance at high temperatures)
High temperature strength is required for parts of internal combustion engines such as automobiles such as turbochargers. It is known that high nitrogen and precipitation strengthening by an intermetallic compound are effective for improving the high temperature strength of the stainless steel forming the internal combustion engine. If the heat resistance temperature is 400 to 500 ° C., a material with high temperature strength increased by adding 0.2 to 0.3% N is practical, but it is effective enough to improve wear resistance in the usage environment of the turbocharger. I found that I could not get. SUH660 and Inconel 718 are known as materials for finely precipitating and strengthening intermetallic compounds in order to improve high temperature strength. SUH660 is strengthened by precipitation of Ni 3 Ti, and Inconel 718 is precipitation strengthened steel and precipitation strengthened alloy such as Ni 3 Nb and Fe 2 Nb. These steels and alloys had insufficient oxidation resistance and were not suitable for use in environments exposed to automobile exhaust gas. As an intermetallic compound, there is Ni 3 Al. However, Ni 3 Al easily coarsens during use in a high temperature environment as compared with Ni 3 Ti and Ni 3 Nb, and therefore the effect is not recognized when evaluated by creep life, etc. It has been generally considered that addition of Al should be avoided in heat-resistant materials.
しかしながら、本発明者らが高温での耐摩耗性を評価した結果、高Ａｌステンレス鋼はＮｉ３Ａｌの析出により高い耐摩耗性を発揮することが分かった。これはＮｉ３Ａｌ自体の硬度と共に、Ｎｉ３Ａｌによる焼付き性の低減効果もあると考えられた。 However, as a result of evaluating the wear resistance at high temperature by the present inventors, it was found that high Al stainless steel exhibits high wear resistance due to precipitation of Ni 3 Al. This was considered to have the effect of reducing the seizure property due to Ni 3 Al, as well as the hardness of Ni 3 Al itself.
そこで、ＳＵＳ３１０Ｓ（２５Ｃｒ−２０Ｎｉ）と高Ｓｉステンレス鋼（２０Ｃｒ−１４Ｎｉ−３Ｓｉ）、高Ａｌステンレス鋼（本発明鋼）について８５０℃で高温摺動試験を実施した。この試験は、大気雰囲気中で試料を１時間予備酸化させた後に、ボールオンディスク法を用いて、摺動速度３．３ｍｍ／ｓ、荷重を０．５、２．０Ｎの２水準とし、摺動長を２０ｍとして、８５０℃にて実施した。尚、ターボチャージャの摺動部材の従来の評価は８００℃にて行われてきたのに対して、本発明者らが８５０℃にて高温摺動試験を実施したのは、加速試験のためである。 Therefore, a high temperature sliding test was performed at 850 ° C. for SUS310S (25Cr-20Ni), high Si stainless steel (20Cr-14Ni-3Si), and high Al stainless steel (inventive steel). In this test, after pre-oxidizing the sample for 1 hour in the air atmosphere, using the ball-on-disk method, the sliding speed was 3.3 mm / s and the load was 0.5 and 2.0 N. It was carried out at 850 ° C. with a moving length of 20 m. The conventional evaluation of the sliding member of the turbocharger has been performed at 800 ° C., whereas the present inventors conducted the high temperature sliding test at 850 ° C. for the acceleration test. is there.
当該試験後の外観の摩耗表面写真を図１に示す。尚、図１（ａ）はＳＵＳ３１０Ｓ（２５Ｃｒ−２０Ｎｉ）の摩耗表面写真、（ｂ）は高Ｓｉステンレス鋼（２０Ｃｒ−１４Ｎｉ−３Ｓｉ）の摩耗表面写真、（ｃ）は高Ａｌステンレス鋼（本発明鋼）の摩耗表面写真である。また、図１（ａ）〜（ｃ）の符号「Ｐｔ」は、写真の内側の円周状に削られた部分の表面粗さの測定値を示す。図１から、鋼成分の違いにより酸化状態が異なることが分かる。但し、高Ｓｉステンレス鋼と高Ａｌステンレス鋼（本発明鋼）の酸化は小さく、スケールの剥離が生じる領域ではない。 A photograph of the worn surface of the appearance after the test is shown in FIG. 1 (a) is a photograph of a worn surface of SUS310S (25Cr-20Ni), (b) is a photograph of a worn surface of high Si stainless steel (20Cr-14Ni-3Si), and (c) is a high Al stainless steel (the present invention). It is a photograph of a worn surface of (steel). In addition, the symbol "Pt" in FIGS. 1A to 1C indicates the measured value of the surface roughness of the circumferentially cut portion inside the photograph. From FIG. 1, it can be seen that the oxidation state differs depending on the steel composition. However, the oxidation of the high Si stainless steel and the high Al stainless steel (the steel of the present invention) is small, and the scale does not peel off.
また、図２に高温摺動試験後の摩耗痕の粗さ、図３に高温摺動試験後における摩擦係数を示す。図２及び図３から、高Ｓｉ化、高Ａｌ化により耐酸化性は既に十分なレベルであるが、耐摩耗性は高Ａｌ化で大きく向上することが分かる。また摩擦係数についても高Ａｌ化の効果は顕著であり、ＳＵＳ３１０Ｓ、高Ｓｉ鋼に比べて大きく低減することが分かる。 Further, FIG. 2 shows the roughness of wear marks after the high temperature sliding test, and FIG. 3 shows the friction coefficient after the high temperature sliding test. From FIGS. 2 and 3, it can be seen that the oxidation resistance is already at a sufficient level by increasing the Si and the Al, but the wear resistance is significantly improved by increasing the Al. Further, it can be seen that the effect of increasing Al is remarkable also in the friction coefficient, and is significantly reduced as compared with SUS310S and high Si steel.
（製造性に及ぼす影響）
また、ステンレス鋼の高Ａｌ化により鋳造、熱間圧延、溶接等の製造性に悪影響を及ぼすおそれがある。すなわち、金属間化合物であるＮｉ３Ａｌ析出による脆化の軽減化と共に、従来鋼とは大きく異なる凝固組織の制御も考慮する必要がある。凝固偏析を低減し、鋳造性、熱間加工性、溶接性等の製造性を改善するために、Ａｌの影響を正確に把握して相バランスを調整することが必要である。しかし、Ａｌが相バランスにどのように作用するかはこれまで殆ど明らかにされていなかった。そこで、本発明者は、下式で表されるＤＢ値（Delta-ferrite Brittle Index）を用いてＡｌの影響を調査した結果、ＤＢ値が−１０以上０以下になるように調整することによって、製造性の低下を防ぎつつ、高温摺動性を十分に維持できることを見出した。
ＤＢ=3(Cr+1.5Si+Mo+2.7Al)-2.8(Ni+0.5Mn+0.5Cu)-84(C+N)-19.8
(Influence on manufacturability)
Further, the high Al content of stainless steel may adversely affect the productivity such as casting, hot rolling, and welding. That is, it is necessary to reduce the embrittlement caused by precipitation of Ni 3 Al, which is an intermetallic compound, and control the solidification structure, which is significantly different from that of conventional steel. In order to reduce solidification segregation and improve manufacturability such as castability, hot workability and weldability, it is necessary to accurately grasp the influence of Al and adjust the phase balance. However, how Al acts on the phase balance has not been clarified so far. Therefore, as a result of investigating the influence of Al using the DB value (Delta-ferrite Brittle Index) represented by the following formula, the present inventor adjusted the DB value to be -10 or more and 0 or less. It has been found that high temperature slidability can be sufficiently maintained while preventing deterioration of manufacturability.
DB = 3 (Cr + 1.5Si + Mo + 2.7Al) -2.8 (Ni + 0.5Mn + 0.5Cu) -84 (C + N) -19.8
また、本発明者らは、耐摩耗性の評価として８５０℃で２時間時効後の室温で測定した硬度を１８０ＨＶ以上にすることで耐摩耗性が明らかに向上することを見出した。 Further, the present inventors have found that, as an evaluation of wear resistance, the wear resistance is obviously improved by setting the hardness measured at room temperature after aging at 850 ° C. for 2 hours to 180 HV or more.
上記課題を解決する本発明の要旨は次のとおりである。
[１] 質量％で、Ｃ：０．０２〜０．１０、Ｓｉ：０．１０〜１．０％、Ｍｎ：０．２〜４．５％、Ｐ：０．０１０〜０．０４０％、Ｓ：０．０００１〜０．００３０％、Ｃｒ：１５〜２０％、Ｎｉ：１０〜２７％、Ｍｏ：０．０１〜２．０％、Ｃｕ：０．０１〜２．０、Ｃｏ：０．０１〜２．０％、Ａｌ：１．０〜６．０％、Ｎ：０．００１〜０．０２％含有し、残部がＦｅおよび不可避的不純物からなり、かつ下式で規定される、ＤＢ値が−１０〜０であり、８５０℃で２時間時効後の硬さが１８０ＨＶ以上であることを特徴とする高温摺動性に優れたオーステナイト系ステンレス鋼。
ＤＢ=3(Cr+1.5Si+Mo+2.7Al)-2.8(Ni+0.5Mn+0.5Cu)-84(C+N)-19.8
[２] 質量％にて、Ｔｉ：０．０１〜０．３％、Ｎｂ：０．０１〜０．６％、Ｖ：０．０１〜０．３％、Ｚｒ：０．０１〜０．１％、Ｔａ：０．０１〜０．１％、Ｈｆ：０．０１〜０．１％、Ｗ：０．０１〜０．１％、Ｓｎ：０．０１〜０．１％、Ｍｇ：０．０００２〜０．００３０％、Ｂ：０．０００２〜０．００５０％、Ｃａ：０．０００１〜０．００３０％、ＲＥＭ：０．０１〜０．０５％、Ｙ：０．０１〜０．０５％の１種または２種以上を含有することを特徴とする[１]に記載の高温摺動性に優れたオーステナイト系ステンレス鋼。
[３] [１]または[２]に記載の高温摺動性に優れたターボチャージャ部品用オーステナイト系ステンレス鋼。
[４] [１]または[２]に記載の高温摺動性に優れたオーステナイト系ステンレス鋼を用いて製造されたターボチャージャ部品。
The gist of the present invention for solving the above problems is as follows.
[1]% by mass, C: 0.02 to 0.10, Si: 0.10 to 1.0%, Mn: 0.2 to 4.5%, P: 0.010 to 0.040%, S: 0.0001 to 0.0030%, Cr: 15 to 20%, Ni: 10 to 27%, Mo: 0.01 to 2.0%, Cu: 0.01 to 2.0, Co: 0. 01-2.0%, Al: 1.0-6.0%, N: 0.001-0.02%, the balance consisting of Fe and inevitable impurities, and defined by the following formula: DB An austenitic stainless steel excellent in high-temperature slidability, which has a value of -10 to 0 and a hardness of 180 HV or more after aging at 850 ° C for 2 hours.
DB = 3 (Cr + 1.5Si + Mo + 2.7Al) -2.8 (Ni + 0.5Mn + 0.5Cu) -84 (C + N) -19.8
[2] In mass%, Ti: 0.01 to 0.3%, Nb: 0.01 to 0.6%, V: 0.01 to 0.3%, Zr: 0.01 to 0.1 %, Ta: 0.01 to 0.1%, Hf: 0.01 to 0.1%, W: 0.01 to 0.1%, Sn: 0.01 to 0.1%, Mg: 0. 0002 to 0.0030%, B: 0.0002 to 0.0050%, Ca: 0.0001 to 0.0030%, REM: 0.01 to 0.05%, Y: 0.01 to 0.05% The austenitic stainless steel excellent in high-temperature slidability according to [1], which contains one or more of the above.
[3] The austenitic stainless steel for turbocharger parts according to [1] or [2], which has excellent high-temperature slidability.
[4] A turbocharger part manufactured by using the austenitic stainless steel excellent in high temperature slidability according to [1] or [2].
本発明によれば、生産性を犠牲にすること無く、高温摺動性、特に、耐酸化性、耐摩耗性、耐焼付き性に優れたオーステナイト系ステンレス鋼を提供することができる。また、本発明のオーステナイト系ステンレス鋼をターボチャージャ部品に用いることにより、耐久性に優れるターボチャージャ部品を提供することにある。 According to the present invention, it is possible to provide an austenitic stainless steel excellent in high-temperature sliding property, particularly in oxidation resistance, wear resistance and seizure resistance, without sacrificing productivity. Another object of the present invention is to provide a turbocharger component having excellent durability by using the austenitic stainless steel of the present invention for the turbocharger component.
以下に本発明における鋼の組成範囲について説明する。
以下の説明において、各元素の含有量を表す「％」は特に断りがない限り質量％を意味する。
The composition range of the steel in the present invention will be described below.
In the following description, “%” representing the content of each element means mass% unless otherwise specified.
（Ｃ：０．０２〜０．１０％）
Ｃは、オーステナイト組織の安定と高温摺動性を高めるために有効である。その効果は０．０２％Ｃ以上で発現するので、下限を０．０２％とする。オーステナイト相を安定化して製品にδフェライトが残ることを避けるためには０．０４％以上にすることが望ましい。一方、ターボチャージャ部品のように高温環境で使用する場合、Ｍ２３Ｃ６型の炭化物が形成し、素材の耐酸化性を低下させるため、上限を０．１０％以下とする。耐食性の観点からは０．０８％以下にすることが望ましい。
(C: 0.02-0.10%)
C is effective for improving the stability of the austenite structure and the high temperature slidability. Since the effect is exhibited at 0.02% C or more, the lower limit is made 0.02%. In order to stabilize the austenite phase and avoid leaving δ-ferrite in the product, it is desirable that the content be 0.04% or more. On the other hand, when used in a high temperature environment such as a turbocharger component, M 23 C 6 type carbides are formed and the oxidation resistance of the material is reduced, so the upper limit is made 0.10% or less. From the viewpoint of corrosion resistance, 0.08% or less is desirable.
（Ｓｉ：０．１０〜１．０％）
Ｓｉは耐酸化性を改善する元素であるが、高Ａｌ添加鋼においてはその効果がほとんど認められなくなる。但し、製鋼工程においては、Ａｌ投入前の脱酸元素として有効であるため、０．１０％以上の添加を行う。脱酸効率を考えると０．２０％以上が望ましい。一方、Ｓｉはフェライト相を安定化する元素であるため、過度な添加は製品にδフェライトが残りやすくなるため、１．０％以下にする。高温環境で使用中にδフェライトが変態したシグマ相に起因する脆化を避けるためには０．８％以下にすることが望ましい。
(Si: 0.10 to 1.0%)
Si is an element that improves the oxidation resistance, but its effect is hardly recognized in high Al-added steel. However, in the steelmaking process, 0.10% or more is added because it is effective as a deoxidizing element before Al is added. Considering deoxidation efficiency, 0.20% or more is desirable. On the other hand, since Si is an element that stabilizes the ferrite phase, excessive addition tends to leave δ ferrite in the product, so the content is made 1.0% or less. In order to avoid embrittlement due to the sigma phase, which is the transformation of δ-ferrite during use in a high temperature environment, it is preferably 0.8% or less.
（Ｍｎ：０．２〜４．５％）
Ｍｎは、脱酸剤として添加される元素であるとともに、オーステナイト単相域を拡大し組織の安定化に寄与する。その効果は０．２％以上で明確に現れるため０．２％以上とする。また硫化物を形成し鋼中の固溶Ｓ量を低減する事で熱間加工性を向上させる効果もあることから、０．５％以上とすることが望ましい。一方、過度の添加は耐食性を低下させることから４．５％以下とする。また耐酸化性の点ではＣｒ２Ｏ３主体の酸化物が望ましく、Ｍｎの酸化物は好ましくないため、２．０％以下にすることが望ましい。
(Mn: 0.2-4.5%)
Mn is an element added as a deoxidizing agent, and contributes to the stabilization of the structure by expanding the austenite single phase region. The effect clearly appears at 0.2% or more, so 0.2% or more is set. Further, since it has an effect of improving hot workability by forming a sulfide and reducing the amount of solid solution S in the steel, it is preferably set to 0.5% or more. On the other hand, excessive addition lowers the corrosion resistance, so the content is made 4.5% or less. Further, in terms of oxidation resistance, an oxide mainly composed of Cr 2 O 3 is desirable, and an oxide of Mn is not desirable, so it is desirable to set it to 2.0% or less.
（Ｐ：０．０１０〜０．０４０％）
Ｐは原料である溶銑やフェロクロム等の主原料中に不純物として含まれる元素である。熱間加工性に対しては有害な元素であるため、０．０４０％以下とする。なお、好ましくは０．０３０％以下である。過度な低減は高純度原料の使用を必須にするなど、コストの増加に繋がるため０．０１０％以上とする。経済的に好ましくは、０．０２０％以上にすることが望ましい。
(P: 0.010-0.040%)
P is an element contained as an impurity in the main raw materials such as hot metal and ferrochrome as raw materials. Since it is an element harmful to hot workability, it is set to 0.040% or less. The content is preferably 0.030% or less. Since excessive reduction leads to an increase in cost, such as the use of high-purity raw materials is essential, the amount is made 0.010% or more. It is economically preferable that the content be 0.020% or more.
（Ｓ：０．０００１〜０．００３０％）
Ｓは、硫化物系介在物を形成し、鋼材の一般的な耐食性（全面腐食や孔食）を劣化させるため、その含有量の上限は少ないほうが好ましく、０．００３０％とする。また、Ｓの含有量は少ないほど耐食性は良好となるが、低Ｓ化には脱硫負荷が増大し、製造コストが増大するので、その下限を０．０００１％とするのが好ましい。なお、好ましくは０．０００１〜０．００１０である。
(S: 0.0001 to 0.0030%)
Since S forms a sulfide-based inclusion and deteriorates the general corrosion resistance (general corrosion or pitting corrosion) of the steel material, the upper limit of its content is preferably as small as possible, and is set to 0.0030%. Further, the smaller the S content, the better the corrosion resistance, but the desulfurization load increases and the manufacturing cost increases for lowering S, so the lower limit is preferably 0.0001%. In addition, it is preferably 0.0001 to 0.0010.
（Ｃｒ：１５〜２０％）
Ｃｒは、本発明において、耐酸化性や耐食性確保のために必須な元素である。１５％未満では、これらの効果は発現せず、一方で、２０％超ではオーステナイト単相域が縮小し、製造時の熱間加工性を損ねるため、１５〜２０％とする。なお、耐酸化性の観点からは１７％以上にすることが望ましい。また、Ｃｒ量を高くするとシグマ相の形成により脆化するため、１９％以下にすることが望ましい。
(Cr: 15-20%)
In the present invention, Cr is an essential element for ensuring oxidation resistance and corrosion resistance. If it is less than 15%, these effects are not exhibited, while if it exceeds 20%, the austenite single-phase region is reduced and the hot workability during production is impaired, so the content is made 15 to 20%. From the viewpoint of oxidation resistance, it is desirable that the content be 17% or more. Further, if the amount of Cr is increased, embrittlement occurs due to the formation of a sigma phase, so it is desirable to set it to 19% or less.
（Ｎｉ：１０〜２７％）
Ｎｉは、本発明において優れた耐摩耗性を発揮するＮｉ３Ａｌ析出物を構成する元素である。更にＮｉは、Ｍｎと同様にオーステナイト相を安定化させる元素であって、耐酸化性の面では、Ｍｎよりも優れた効力を有する。これらの効果は１０％以上で得られるため、下限を１０％以上とする。また、シグマ相の生成を抑制する効果もあるので２０％以上にすることが望ましい。一方、過度なＮｉの添加は凝固割れ感受性を高めると共に、熱間加工性も低下させるために、２７％以下とする。更に、断続酸化におけるスケール剥離を抑制するためには、２５％以下にすることが望ましい。
(Ni: 10-27%)
Ni is an element constituting the Ni 3 Al precipitate exhibiting excellent wear resistance in the present invention. Further, Ni is an element that stabilizes the austenite phase similarly to Mn, and has a higher effect than Mn in terms of oxidation resistance. These effects are obtained at 10% or more, so the lower limit is made 10% or more. Further, since it also has an effect of suppressing the generation of sigma phase, it is desirable to set it to 20% or more. On the other hand, excessive addition of Ni raises the solidification cracking susceptibility and also lowers the hot workability. Further, in order to suppress scale peeling in intermittent oxidation, it is desirable to be 25% or less.
（Ｍｏ：０．０１〜２．０％）
ＭｏもＳｉやＣｒと共には、表面の保護性スケール形成に有効であり、その効果は０．０１％で得られることから、その下限を０．０１％以上とする。また耐食性の向上にも有効な元素であることから０．３％以上添加することが望ましい。一方、フェライト安定化元素でもあり、Ｍｏ添加量が増えるとＮｉの添加も増やす必要が生じるため、過度な添加は好ましくない。また、シグマ相の形成を促進して脆化を生じることがあるため、２．０％以下とする。耐食性や耐酸化性の向上効果は0.8％以上でほぼ飽和するために、０．８％以下にすることが望ましい。
(Mo: 0.01-2.0%)
Mo, together with Si and Cr, is effective in forming a protective scale on the surface, and the effect is obtained at 0.01%, so the lower limit is made 0.01% or more. Further, since it is an element effective for improving the corrosion resistance, it is desirable to add 0.3% or more. On the other hand, since it is also a ferrite stabilizing element, it is necessary to increase the addition of Ni as the amount of Mo added increases, so excessive addition is not preferable. Further, the formation of the sigma phase may be promoted and embrittlement may occur, so the content is made 2.0% or less. Since the effect of improving the corrosion resistance and the oxidation resistance is almost saturated at 0.8% or more, it is preferably 0.8% or less.
（Ｃｕ：０．０１〜２．０％）
Ｃｕオーステナイト安定化元素としてＮｉを代替する相対的に安価な元素である。更に隙間腐食や孔食の進展抑制に効果があり、そのためには０．０１％以上添加することが望ましい。但し、オーステナイト系ステンレス鋼の製造においてＣｕは、スクラップ等の原料から混入することが多く、付加的な不純物として０．２％程度含まれることが多い。但し、２．０％を超えると熱間加工性を低下させるため２．０％以下とする。
(Cu: 0.01-2.0%)
It is a relatively inexpensive element that replaces Ni as a Cu austenite stabilizing element. Further, it is effective in suppressing the progress of crevice corrosion and pitting corrosion, and for that purpose, it is desirable to add 0.01% or more. However, in the production of austenitic stainless steel, Cu is often mixed from raw materials such as scrap, and is often contained as an additional impurity in an amount of about 0.2%. However, if it exceeds 2.0%, the hot workability deteriorates, so the content is made 2.0% or less.
（Ｃｏ：０．０１〜２．０％）
Ｃｏは微量の添加でも耐熱性の向上にきわめて有効であるため、０．０１％以上添加する。但し、過度な添加は熱間加工性を損ねるために２．０％以下にする。耐食性にも有効な元素であるため、０．１０％以上にすることが望ましい。また、シグマ相の形成を抑制するためには０．５％以下にすることが望ましい。
(Co: 0.01-2.0%)
Even if a small amount of Co is added, it is extremely effective in improving the heat resistance, so 0.01% or more is added. However, excessive addition impairs hot workability, so the content is made 2.0% or less. Since it is an element effective also in corrosion resistance, it is desirable to set it to 0.10% or more. Further, in order to suppress the formation of a sigma phase, it is desirable that the content be 0.5% or less.
（Ａｌ：１．０〜６．０％）
Ａｌは、高温摺動性の向上にきわめて有効な元素である。その効果は１．０％以上で得られるため、下限を１．０％以上にする。析出強化による耐摩耗性向上効果を確実に得るためには２．０％以上にすることが望ましい。一方、Ａｌはフェライト相の安定化元素であり、Ａｌとバランスさせるだけのオーステナイト安定化元素の添加が必要になり、Ｎｉ、Ｍｎ、Ｃの過度な添加による原料コストの増加、耐食性の低下などが問題になるために、その上限は６．０％とする。耐酸化性が向上することで、熱延疵が出やすくなるために、５．０％以下にすることが望ましい。
(Al: 1.0-6.0%)
Al is an extremely effective element for improving the high temperature slidability. Since the effect is obtained at 1.0% or more, the lower limit is made 1.0% or more. In order to surely obtain the effect of improving wear resistance by precipitation strengthening, it is desirable to set it to 2.0% or more. On the other hand, Al is a stabilizing element of the ferrite phase, and it is necessary to add an austenite stabilizing element to balance it with Al. Therefore, excessive addition of Ni, Mn, and C causes an increase in raw material cost and a decrease in corrosion resistance. Since it becomes a problem, the upper limit is made 6.0%. The improvement of the oxidation resistance facilitates the appearance of hot-rolled defects, and therefore it is preferably 5.0% or less.
（Ｎ：０．００１〜０．０２％）
ＮはＣと同様に高温摺動性を高めるほか、オーステナイト安定度を高めることでＮｉの低減も可能になる。またＣよりも鋭敏化による耐食性低下影響が小さいためＣよりも多量の添加が可能である。しかしながら、本発明鋼のような高Ａｌ化により耐酸化性を高めるステンレス鋼においてＮを添加すると、Ａｌの窒化物が形成するために、Ｎが高温摺動性に寄与しないだけでなく、鋳造時のノズル詰まりなど製造性を大きく損ねることになる。このためにその上限を０．０２％とした。安定製造を考えると０．０１％以下にすることが望ましい。一方、ステンレス鋼の精錬においてＮを低減する事は技術的に難しく、真空中での不活性ガスによる攪拌精錬を併用してもＮを０．００１％以下に下げることは難しいため、下限を０．００１％とした。脱ガスによる精錬時間を考慮すると０．００５％以上が望ましい。
(N: 0.001-0.02%)
Similar to C, N enhances high-temperature slidability, and also enhances austenite stability, so that Ni can be reduced. Further, since the effect of reducing corrosion resistance due to sensitization is smaller than that of C, a larger amount of C can be added. However, when N is added to stainless steel such as the steel of the present invention that has high oxidation resistance due to high Al content, N does not contribute to high temperature slidability because Nitride of Al is formed. Therefore, the nozzle clogging and the productivity will be greatly impaired. Therefore, the upper limit is set to 0.02%. Considering stable production, 0.01% or less is desirable. On the other hand, it is technically difficult to reduce N in the refining of stainless steel, and it is difficult to reduce N to 0.001% or less even if agitation refining with an inert gas in a vacuum is used together, so the lower limit is 0. It was set to 0.001%. Considering the refining time by degassing, 0.005% or more is desirable.
（ＤＢ値：−１０〜０）
オーステナイト系ステンレス鋼の製造性や品質安定性には相バランスの制御が重要である。最も汎用的なＳＵＳ３０４であれば、凝固時はδフェライトとオーステナイトの二相域で凝固し、熱延工程でオーステナイト単相組織化する。このため凝固割れも生じにくく、最終製品はオーステナイト単相組織となる。但し、凝固偏析部などに僅かにδフェライトが残る場合がある。本発明鋼は高Ａｌ鋼であるが、下記式で定義されるＤＢ値を−１０以上０以下に調整することによって、製品の製造性及び品質安定性の低下を防ぐことができる。
ＤＢ=3(Cr+1.5Si+Mo+2.7Al)-2.8(Ni+0.5Mn+0.5Cu)-84(C+N)-19.8
(DB value: -10 to 0)
Control of phase balance is important for manufacturability and quality stability of austenitic stainless steel. With the most general-purpose SUS304, solidification occurs in the two-phase region of δ ferrite and austenite during solidification, and austenite single-phase structure is formed in the hot rolling process. For this reason, solidification cracking does not easily occur, and the final product has an austenite single-phase structure. However, a small amount of δ-ferrite may remain in the solidified segregated portion. The steel of the present invention is a high Al steel, but by adjusting the DB value defined by the following formula to -10 or more and 0 or less, it is possible to prevent the deterioration of the manufacturability and quality stability of the product.
DB = 3 (Cr + 1.5Si + Mo + 2.7Al) -2.8 (Ni + 0.5Mn + 0.5Cu) -84 (C + N) -19.8
Ａｌの寄与を考慮したＤＢ値において、ＤＢ値を−１０以上０以下にすることによってオーステナイト安定側に相バランスを調整でき、δフェライトの残存を低減することができる。ターボチャージャ部品のように高温環境で使用するために、δフェライトの残存を極力低減することが必要になるため、上限を０とした。ＤＢ値が０を超えると、残存したδフェライトが、高温摺動性（摩擦係数または摩耗痕粗さ）を劣化させるうえ、熱間圧延時に鋼板端部の亀裂、いわゆる耳割れが発生し製造性を著しく阻害する。凝固偏析部のδフェライトも安定して低減するためには−２以下にすることが望ましい。一方、ＤＢ値を必要以上に下げることは、オーステナイト安定化元素であるＮｉ、Ｍｎ、ＣｕやＣ，Ｎの増加が必要になり、コスト増や、耐食性、耐酸化性の低下も生じやすくなる。これらの弊害を軽減するために、ＤＢ値を−１０以上に制限する。また、鋳造時の凝固割れ起因の疵を低減するためには、ＤＢ値を−７以上とすることが望ましい。 In the DB value considering the contribution of Al, by setting the DB value to -10 or more and 0 or less, the phase balance can be adjusted to the austenite stable side, and the residual δ ferrite can be reduced. The upper limit was set to 0 because it is necessary to reduce the residual δ ferrite as much as possible for use in a high temperature environment such as a turbocharger part. When the DB value exceeds 0, the residual δ ferrite deteriorates the high-temperature slidability (friction coefficient or wear scar roughness), and cracks at the steel sheet edges, so-called edge cracks, occur during hot rolling, and manufacturability is improved. Significantly inhibits. In order to stably reduce the δ ferrite in the solidified segregated portion, it is desirable to set it to −2 or less. On the other hand, if the DB value is lowered more than necessary, it is necessary to increase the austenite stabilizing elements Ni, Mn, Cu, C, and N, and the cost is increased, and the corrosion resistance and the oxidation resistance are easily deteriorated. In order to reduce these adverse effects, the DB value is limited to -10 or more. Further, in order to reduce defects due to solidification cracking during casting, it is desirable that the DB value is -7 or more.
（８５０℃で２時間時効後の硬度：１８０〜３５０ＨＶ）
高温摺動性の向上には材料の耐酸化性と共に耐摩耗性が重要であり、そのためには時効後も硬度が高いことが必要である。耐摩耗性の向上効果を確実に発揮させるため時効硬度は１８０ＨＶ以上とした。一方、過度な硬化は部品としての靭性低下に繋がるため、上限を３５０ＨＶとすることが望ましい。時効して硬化するものは製造工程においても、似た温度で保持されると硬化して板破断を生じやすくなるために、更に３００ＨＶ以下に制限することが望ましい。
(Hardness after aging at 850 ° C. for 2 hours: 180 to 350 HV)
Abrasion resistance as well as oxidation resistance of the material is important for improving high temperature slidability, and for that purpose, it is necessary to have high hardness even after aging. The aging hardness was set to 180 HV or more in order to surely exhibit the effect of improving wear resistance. On the other hand, excessive hardening leads to a decrease in toughness as a part, so it is desirable to set the upper limit to 350 HV. In the manufacturing process, the material that ages and hardens easily hardens if it is held at a similar temperature, and plate breakage easily occurs. Therefore, it is desirable to further limit it to 300 HV or less.
また、本発明では、上記元素に加えて、Ｔｉ：０．０１〜０．３％、Ｎｂ：０．０１〜０．６％、Ｖ：０．０１〜０．３％、Ｚｒ：０．０１〜０．１％、Ｔａ：０．０１〜０．１％、Ｈｆ：０．０１〜０．１％、Ｗ：０．０１〜０．１％、Ｓｎ：０．０１〜０．１％、Ｍｇ：０．０００２〜０．００３０％、Ｂ：０．０００２〜０．００５０％、Ｃａ：０．０００１〜０．００３０％、ＲＥＭ：０．０１〜０．０５％、Ｙ：０．０１〜０．０５％の１種又は２種以上を添加しても良い。 Further, in the present invention, in addition to the above elements, Ti: 0.01 to 0.3%, Nb: 0.01 to 0.6%, V: 0.01 to 0.3%, Zr: 0.01 ~ 0.1%, Ta: 0.01-0.1%, Hf: 0.01-0.1%, W: 0.01-0.1%, Sn: 0.01-0.1%, Mg: 0.0002 to 0.0030%, B: 0.0002 to 0.0050%, Ca: 0.0001 to 0.0030%, REM: 0.01 to 0.05%, Y: 0.01 to. You may add 0.05% of 1 type (s) or 2 or more types.
（Ｔｉ：０．０１〜０．３％）
Ｔｉは炭窒化物を形成することで、ステンレス鋼におけるクロム炭窒化物の析出による鋭敏化や耐食性の低下を抑制する元素である。また高温環境での粒成長を抑制し高温摺動性を高める効果があるため０．０１％以上添加することが望ましい。但し、大型の製鋼介在物を形成することで、疲労寿命を下げる原因になるため、その上限は０．３％とする。固溶Ｃ，Ｎ量の確保による高温摺動性向上を考慮すると０．０５％以下にすることが望ましい。Ｔｉは含有していなくても良い。
(Ti: 0.01-0.3%)
Ti is an element that forms carbonitrides and thereby suppresses sensitization and deterioration of corrosion resistance due to precipitation of chromium carbonitrides in stainless steel. Further, 0.01% or more is desirable because it has the effect of suppressing grain growth in a high temperature environment and enhancing high temperature slidability. However, the formation of large steel inclusions causes the fatigue life to be shortened, so the upper limit is made 0.3%. Considering improvement of high temperature slidability by securing the amount of solid solution C and N, it is desirable to set the content to 0.05% or less. Ti may not be contained.
（Ｎｂ：０．０１〜０．６％）
Ｎｂは、炭窒化物を形成することでステンレス鋼におけるクロム炭窒化物の析出による鋭敏化や耐食性の低下を抑制する元素である。また高温環境での粒成長を抑制し高温摺動性を高める効果があるため０．０１％以上添加することが望ましい。しかしながら、大型の製鋼介在物を形成することで、表面疵の原因になり易く、疲労寿命低下の原因にもなるため、その上限は０．６％とする。固溶Ｃ，Ｎ量の確保による高温摺動性向上を考慮すると０．０５％以下にすることが望ましい。Ｎｂは含有していなくても良い。
(Nb: 0.01-0.6%)
Nb is an element that suppresses sensitization and deterioration of corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride. Further, 0.01% or more is desirable because it has the effect of suppressing grain growth in a high temperature environment and enhancing high temperature slidability. However, the formation of large steel-making inclusions easily causes surface defects and shortens the fatigue life, so the upper limit is made 0.6%. Considering improvement of high temperature slidability by securing the amount of solid solution C and N, it is desirable to set the content to 0.05% or less. Nb may not be contained.
（Ｖ：０．０１〜０．３％）
Ｖは、ステンレス鋼の合金原料に不可避的不純物として混入し、精錬工程における除去が困難であるため、一般的に０．０２〜０．１５％の範囲で含有される。また、微細な炭窒化物を形成し、粒成長抑制効果を有するため、必要に応じて、意図的な添加も行われる元素である。その効果は０．０１％以上の添加で安定して発現するため、０．０１％以上添加することが望ましい。一方、過剰に添加すると、析出物の粗大化を招くおそれがあり、その結果、焼入れ後の靭性が低下してしまうため、０．３％以下にとすることが望ましい。Ｖは含有していなくても良い。
(V: 0.01-0.3%)
V is mixed in the alloy raw material of stainless steel as an unavoidable impurity and is difficult to remove in the refining process, so V is generally contained in the range of 0.02 to 0.15%. Further, since it forms a fine carbonitride and has a grain growth suppressing effect, it is an element that is intentionally added as necessary. Since the effect is stably exhibited by adding 0.01% or more, it is desirable to add 0.01% or more. On the other hand, if added excessively, coarsening of precipitates may be caused, and as a result, the toughness after quenching will decrease, so it is desirable to make it 0.3% or less. V may not be contained.
（Ｚｒ：０．０１〜０．１％）
Ｚｒは炭窒化物を形成することで、ステンレス鋼におけるクロム炭窒化物の析出による鋭敏化や耐食性の低下を抑制する元素である。また高温環境での粒成長を抑制し高温摺動性を高める効果があるため０．０１％以上添加することが望ましい。しかしながら、大型の製鋼介在物を形成することで、疲労寿命を下げる原因になるため、その上限は０．１％とする。固溶Ｃ，Ｎ量の確保による高温摺動性向上を考慮すると０．０５％以下にすることが望ましい。Ｚｒは含有していなくても良い。
(Zr: 0.01-0.1%)
Zr is an element that forms carbonitrides and suppresses sensitization and deterioration of corrosion resistance due to the precipitation of chromium carbonitrides in stainless steel. Further, 0.01% or more is desirable because it has the effect of suppressing grain growth in a high temperature environment and enhancing high temperature slidability. However, the formation of large steel inclusions causes the fatigue life to be shortened, so the upper limit is made 0.1%. Considering improvement of high temperature slidability by securing the amount of solid solution C and N, it is desirable to set the content to 0.05% or less. Zr may not be contained.
（Ｔａ：０．０１〜０．１％）
Ｔａは炭窒化物を形成することで、ステンレス鋼におけるクロム炭窒化物の析出による鋭敏化や耐食性の低下を抑制する元素である。また高温環境での粒成長を抑制し高温摺動性を高める効果があるため０．０１％以上添加することが望ましい。しかしながら、大型の製鋼介在物を形成することで、疲労寿命を下げる原因になるため、その上限は０．１％とする。固溶Ｃ，Ｎ量の確保による高温摺動性向上を考慮すると０．０５％以下にすることが望ましい。Ｔａは含有していなくても良い。
(Ta: 0.01 to 0.1%)
Ta is an element that forms carbonitrides and suppresses sensitization and deterioration of corrosion resistance due to precipitation of chromium carbonitrides in stainless steel. Further, 0.01% or more is desirable because it has the effect of suppressing grain growth in a high temperature environment and enhancing high temperature slidability. However, the formation of large steel inclusions causes the fatigue life to be shortened, so the upper limit is made 0.1%. Considering improvement of high temperature slidability by securing the amount of solid solution C and N, it is desirable to set the content to 0.05% or less. Ta may not be contained.
（Ｈｆ：０．０１〜０．１％）
Ｈｆは炭窒化物を形成することで、ステンレス鋼におけるクロム炭窒化物の析出による鋭敏化や耐食性の低下を抑制する元素である。また高温環境での粒成長を抑制し高温摺動性を高める効果があるため０．０１％以上添加することが望ましい。しかしながら、大型の製鋼介在物を形成することで、疲労寿命を下げる原因になるため、その上限は０．１％とする。固溶Ｃ，Ｎ量の確保による高温摺動性向上を考慮すると０．０５％以下にすることが望ましい。Ｈｆは含有していなくても良い。
(Hf: 0.01-0.1%)
Hf is an element that forms carbonitrides and suppresses sensitization and deterioration of corrosion resistance due to precipitation of chromium carbonitrides in stainless steel. Further, 0.01% or more is desirable because it has the effect of suppressing grain growth in a high temperature environment and enhancing high temperature slidability. However, the formation of large steel inclusions causes the fatigue life to be shortened, so the upper limit is made 0.1%. Considering improvement of high temperature slidability by securing the amount of solid solution C and N, it is desirable to set the content to 0.05% or less. Hf may not be contained.
（Ｗ：０．０１〜０．１％）
Ｗは炭窒化物を形成することで、ステンレス鋼におけるクロム炭窒化物の析出による鋭敏化や耐食性の低下を抑制する元素である。また高温環境での粒成長を抑制し高温摺動性を高める効果があるため０．０１％以上添加することが望ましい。しかしながら、大型の製鋼介在物を形成することで、疲労寿命を下げる原因になるため、その上限は０．１％とする。固溶Ｃ，Ｎ量の確保による高温摺動性向上を考慮すると０．０５％以下にすることが望ましい。Ｗは含有していなくても良い。
(W: 0.01-0.1%)
W is an element that forms carbonitrides and suppresses sensitization and deterioration of corrosion resistance due to precipitation of chromium carbonitrides in stainless steel. Further, 0.01% or more is desirable because it has the effect of suppressing grain growth in a high temperature environment and enhancing high temperature slidability. However, the formation of large steel inclusions causes the fatigue life to be shortened, so the upper limit is made 0.1%. Considering improvement of high temperature slidability by securing the amount of solid solution C and N, it is desirable to set the content to 0.05% or less. W may not be contained.
（Ｓｎ：０．０１〜０．１％）
Ｓｎは耐食性を向上させる元素であり、孔食発生後の進展を抑制する効果がある。その効果は０．０１％以上で得られるため、０．０１％以上添加することが望ましい。また、偏析なども考慮すると０．０２％以上が好ましい。一方、Ｓｎはフェライト安定化元素であり、相安定性の点からは過度な添加が好ましくないため、その上限を０．１％とする。熱間加工性への悪影響も考慮すると０．０６％以下にすることが好ましい。Ｓｎは含有していなくても良い。
(Sn: 0.01-0.1%)
Sn is an element that improves the corrosion resistance and has an effect of suppressing the progress after the occurrence of pitting corrosion. Since the effect is obtained at 0.01% or more, it is desirable to add 0.01% or more. Further, considering segregation and the like, 0.02% or more is preferable. On the other hand, Sn is a ferrite stabilizing element, and excessive addition is not preferable from the viewpoint of phase stability, so the upper limit is made 0.1%. Considering the adverse effect on hot workability, it is preferably 0.06% or less. Sn does not have to be contained.
（Ｍｇ：０．０００２〜０．００３０％）
ＭｇはＣａと同様に脱硫元素として添加され、一般にはスラグ中から溶鋼中に平行量が固溶するほか、複合酸化物中にＭｇＯとして含有される場合もある。また耐火物中のＭｇＯが溶鋼中に溶け出す場合もある。脱硫効果は０．０００２％以上であられるため、下限を０．０００２％とすることが望ましい。一方、過度な添加は水溶性介在物ＭｇＳが粗大析出し耐食性を低下させるため、０．００３０％以下にすることが望ましい。
(Mg: 0.0002 to 0.0030%)
Similar to Ca, Mg is added as a desulfurizing element, and generally, a parallel amount of slag forms a solid solution in molten steel, and Mg may be contained in the complex oxide as MgO. In addition, MgO in the refractory may be dissolved in the molten steel. Since the desulfurization effect is 0.0002% or more, the lower limit is preferably 0.0002%. On the other hand, excessive addition causes coarse precipitation of water-soluble inclusions MgS and reduces corrosion resistance. Therefore, it is desirable to add 0.0030% or less.
（Ｂ：０．０００２〜０．００５０％）
Ｂは、熱間加工性の向上に有効な元素であり、その効果は０．０００２％以上で発現するため、０．０００２％以上添加する。より広い温度域における熱間加工性を向上させるためには０．０００５％以上とすることが望ましい。一方、過度な添加は熱間加工性の低下により表面疵の原因となるため、０．００５０％を上限とする。耐食性も考慮すると０．００２５％以下が望ましい。Ｂは含有していなくても良い。
(B: 0.0002 to 0.0050%)
B is an element effective in improving the hot workability, and its effect is exhibited at 0.0002% or more, so 0.0002% or more is added. In order to improve hot workability in a wider temperature range, 0.0005% or more is desirable. On the other hand, excessive addition causes deterioration of the hot workability and causes surface defects, so the upper limit is 0.0050%. Considering corrosion resistance, 0.0025% or less is desirable. B may not be contained.
（Ｃａ：０．０００１〜０．００３０％）
Ｃａは脱硫元素として添加され、鋼中のＳを低減して熱間加工性を向上させる効果がある。一般には、溶解精錬時のスラグ中にＣａＯとして添加させ、この一部が鋼中にＣａとして溶解しているものである。また、ＣａＯ-ＳｉＯ２-Ａｌ２Ｏ３-ＭｇＯなどの複合酸化物としても鋼中に含有する。熱間加工性の改善効果は０．０００１％から得られるために、０．０００１％以上にすることが望ましい。一方、多量に含有すると比較的粗大な水溶性介在物ＣａＳが析出し耐食性を低下させるために０．００３０％以下にすることが望ましい。
(Ca: 0.0001 to 0.0030%)
Ca is added as a desulfurizing element and has the effect of reducing S in steel and improving hot workability. Generally, CaO is added to slag during melting and refining, and a part of this is dissolved as Ca in steel. Also included in steel as a composite oxide such as CaO-SiO 2 -Al 2 O 3 -MgO. Since the effect of improving hot workability is obtained from 0.0001%, it is desirable to set it to 0.0001% or more. On the other hand, if it is contained in a large amount, a relatively coarse water-soluble inclusion CaS precipitates and the corrosion resistance is lowered, so it is desirable that the content be 0.0030% or less.
（ＲＥＭ：０．０１〜０．０５０％）
ＲＥＭは耐酸化性を高める効果と共に、脱硫元素でもある。その効果は０．０１％以上で得られるので０．０１％以上添加することが望ましい。しかしながら過度な添加は連続鋳造時にノズル閉塞の問題を生じるほか、大型の酸化物系介在物の形成により、ガスケットの疲労寿命を損ねるため０．０５％以下にすることが望ましい。
(REM: 0.01 to 0.050%)
REM is also a desulfurizing element together with the effect of increasing the oxidation resistance. Since the effect is obtained at 0.01% or more, it is desirable to add 0.01% or more. However, excessive addition causes the problem of nozzle clogging during continuous casting, and the formation of large oxide inclusions impairs the fatigue life of the gasket, so it is desirable that the content be 0.05% or less.
（Ｙ：０．０１〜０．０５％）
Ｙは耐酸化性を高める効果と共に、脱硫元素でもある。その効果は０．０１％以上で得られるので０．０１％以上添加することが望ましい。しかしながら過度な添加は連続鋳造時にノズル閉塞の問題を生じるほか、大型の酸化物系介在物の形成により、ガスケットの疲労寿命を損ねるため０．０５％以下にすることが望ましい。
(Y: 0.01-0.05%)
Y is a desulfurizing element as well as having an effect of enhancing oxidation resistance. Since the effect is obtained at 0.01% or more, it is desirable to add 0.01% or more. However, excessive addition causes the problem of nozzle clogging during continuous casting, and the formation of large oxide inclusions impairs the fatigue life of the gasket, so it is desirable that the content be 0.05% or less.
（製造工程）
本発明におけるオーステナイト系ステンレス鋼の製造方法において、仕上げ圧延に供される鋼板を製造する工程は、特に限定されない。公知の手段（例えば電気炉）により溶製された鋼を連続鋳造機で１５０〜２５０ｍｍ厚のスラブに鋳造し、必要に応じて表面を研削した後、１２００℃以上に加熱して、熱間圧延機で熱間圧延を行って板厚３〜６ｍｍ程度の熱延鋼帯とする。熱延鋼帯を１１００℃程度の温度で焼鈍し、酸洗する。引き続き冷間圧延と焼鈍を繰り返して、所望厚みの薄板とする。仕上げ焼鈍は焼鈍酸洗仕上げ（２Ｂ仕上げ）でも、無酸化雰囲気で焼鈍するＢＡ（Ｂｒｉｇｈｔ Ａｎｎｅａｌｉｎｇ）仕上げでも構わない。尚、仕上げ圧延後の工程も特に限定されない、形状強制や脱脂洗浄工程を付与する場合もある。
(Manufacturing process)
In the method for producing austenitic stainless steel according to the present invention, the step of producing a steel sheet to be subjected to finish rolling is not particularly limited. Steel that has been melted by known means (for example, an electric furnace) is cast into a slab with a thickness of 150 to 250 mm by a continuous casting machine, the surface is ground as necessary, and then heated to 1200 ° C or higher, and hot rolled. Hot rolling is performed by a machine to obtain a hot rolled steel strip having a plate thickness of about 3 to 6 mm. The hot rolled steel strip is annealed at a temperature of about 1100 ° C. and pickled. Subsequently, cold rolling and annealing are repeated to obtain a thin plate having a desired thickness. The finish annealing may be an annealing pickling finish (2B finish) or a BA (Bright Annealing) finish that is annealed in a non-oxidizing atmosphere. The process after finish rolling is not particularly limited, and a process for forcing a shape or a degreasing / cleaning process may be applied.
本発明によれば、図２及び図３に示される高温摺動試験結果と同一条件下で高温摺動試験において、荷重が０．５Ｎの場合に摩耗係数が０．４以下となるオーステナイト系ステンレス鋼を得ることができる。また、本発明によれば、前記高温摺動試験において、荷重が２．０Ｎの場合にＰｔが４０μｍ以下となるオーステナイト系ステンレス鋼を得ることができる。このように、本発明によれば、高温摺動性に優れたオーステナイト系ステンレス鋼を提供することができる。 According to the present invention, the austenitic stainless steel having a wear coefficient of 0.4 or less when the load is 0.5 N in the high temperature sliding test under the same conditions as the high temperature sliding test results shown in FIGS. 2 and 3. You can get steel. Further, according to the present invention, it is possible to obtain austenitic stainless steel having Pt of 40 μm or less when the load is 2.0 N in the high temperature sliding test. As described above, according to the present invention, it is possible to provide an austenitic stainless steel excellent in high temperature slidability.
以下、実施例により本発明の効果を説明するが、本発明は、以下の実施例で用いた条件に限定されるものではない。 Hereinafter, the effects of the present invention will be described with reference to examples, but the present invention is not limited to the conditions used in the following examples.
本実施例では、まず、表１及び表２に示す成分組成の鋼を溶製して２００ｍｍ厚のスラブに鋳造した。このスラブを１２５０℃に加熱後、粗熱延、仕上熱延を経て板厚２０ｍｍの熱延鋼板とした。引き続き熱延鋼板の焼鈍を、１０５０℃で２０秒行った後水冷した。なお、熱延鋼板の検査については、鋼板端部の耳割れを目視検査で行うと共に、鋳造時の凝固割れに起因して現れる疵を目視検査、および、一般に市販されている超音波探傷試験装置による検査を併用して行った。本実施例では、耳割れまたは疵が軽微または確認できない場合は合格とし、それ以外を不合格とした。 In this example, first, steels having the component compositions shown in Tables 1 and 2 were melted and cast into a slab having a thickness of 200 mm. After heating this slab to 1250 ° C., it was subjected to rough hot rolling and finish hot rolling to obtain a hot rolled steel sheet having a plate thickness of 20 mm. Subsequently, the hot-rolled steel sheet was annealed at 1050 ° C. for 20 seconds and then water-cooled. Regarding the inspection of the hot rolled steel sheet, the edge crack of the steel sheet is visually inspected, and the flaws appearing due to the solidification crack at the time of casting are visually inspected, and the ultrasonic flaw detector is generally available on the market. It was also performed by the inspection by. In the present example, when the ear crack or the flaw was slight or could not be confirmed, the result was passed, and the others were rejected.
その後、ボールオンディスク法で高温摺動性の評価を行った。試験温度は８５０℃とし、大気中で行った。試験開始迄、試験片を８５０℃で１時間保持し表面を酸化させた。試験荷重は０．５，２．０Ｎの二水準とした。摺動速度は３．３ｍｍ／ｓで摺動長は２０ｍとした。全試験時間に渡る摩擦係数の変化を連続測定し、平均値で摩擦係数を評価した。また、試験後の摩耗痕について、二次元粗さ計で粗さ測定を行った。試験後の試験片の硬度を測定した。なお、粗さは円周状に削られた摩耗痕の線と直交する方向で測定した。 After that, high temperature slidability was evaluated by the ball-on-disk method. The test temperature was 850 ° C., and the test was performed in the atmosphere. Until the start of the test, the test piece was kept at 850 ° C. for 1 hour to oxidize the surface. The test load was set to two levels of 0.5 and 2.0N. The sliding speed was 3.3 mm / s and the sliding length was 20 m. The change in friction coefficient over the entire test time was continuously measured, and the average value was used to evaluate the friction coefficient. Further, with respect to the abrasion mark after the test, the roughness was measured with a two-dimensional roughness meter. The hardness of the test piece after the test was measured. The roughness was measured in the direction orthogonal to the line of the wear mark cut in the circumferential shape.
摩擦係数は、荷重０．５Ｎの試験値、摩耗量は荷重２．０Ｎの試験値で評価した。高温摺動性の合格基準を、摩擦係数が０．４以下、Ｐｔが４０μｍ以下であり、且つ試験後の試験片の硬度が１８０ＨＶ以上であることとした。硬度は高温摺動試験後に室温まで冷却したサンプルの表面硬度をロックウエル硬度計で測定しビッカース硬度に換算した。 The friction coefficient was evaluated by a test value under a load of 0.5 N, and the wear amount was evaluated by a test value under a load of 2.0 N. The acceptance criteria for the high temperature slidability were that the friction coefficient was 0.4 or less, Pt was 40 μm or less, and the hardness of the test piece after the test was 180 HV or more. For the hardness, the surface hardness of the sample cooled to room temperature after the high temperature sliding test was measured with a Rockwell hardness meter and converted into Vickers hardness.
表１における本発明例は摩擦係数が０．４以下であり、試験後の摩耗痕粗さＰｔが４０μm以下と良好な値を示した。一方比較鋼は、表２に示すように、各組成が本発明範囲を外れることで、高温耐摩耗性が低下する、δフェライトが残存したことで、また、Ｃｒ炭化物の形成や熱延疵の発生等により摩耗量が多くなり、摩耗痕粗さＰｔが４０μmを超える結果となった。また、摩擦係数も本発明法では０．４以下の値が得られたが、比較鋼では０．４を上回る０．６以上の値が生じるなど、摩耗痕の粗度、摩擦係数の何れかまたは両方で不良となった。 In the examples of the present invention in Table 1, the friction coefficient was 0.4 or less, and the wear scar roughness Pt after the test was 40 μm or less, which is a good value. On the other hand, in the comparative steels, as shown in Table 2, when each composition deviates from the range of the present invention, the high temperature wear resistance decreases, δ ferrite remains, and the formation of Cr carbides and the hot rolling defects occur. As a result, the amount of wear increased, and the wear scar roughness Pt exceeded 40 μm. In addition, the friction coefficient of the present invention was 0.4 or less, but the comparative steel had a value of 0.6 or more exceeding 0.4. Or both were bad.
本発明によれば、生産性を犠牲にすること無く、高温摺動性、特に、耐酸化性、耐摩耗性、耐焼付き性に優れたオーステナイト系ステンレス鋼を提供することができる。本発明を適用した材料を、特に自動車のターボチャージャ用材料として使用することによって、従来の鋳物よりも大幅に耐久性を向上することができる。なお、本発明は、ターボチャージャ用として使用する各部品のいずれに対しても適用対象にすることができる。具体的にはターボチャージャの外枠を構成するハウジング、ノズルベーン式ターボチャージャ内部の精密部品（例えば、バックプレート、オイルディフレクター、コンプレッサーホイール、ノズルマウント、ノズルプレート、ノズルベーン、ドライブリング、ドライブレバーと呼ばれるものなど）である。更に、自動車、二輪に限らず、各種ボイラー、燃料電池システム等の高温環境に使用される排気部品に適用することも可能であり、本発明は産業上極めて有益である。 According to the present invention, it is possible to provide an austenitic stainless steel excellent in high-temperature sliding property, particularly in oxidation resistance, wear resistance and seizure resistance, without sacrificing productivity. By using the material to which the present invention is applied, especially as a material for automobile turbochargers, it is possible to significantly improve durability as compared with conventional castings. The present invention can be applied to any of the components used for the turbocharger. Specifically, a housing that constitutes the outer frame of the turbocharger, precision parts inside the nozzle vane type turbocharger (for example, back plate, oil deflector, compressor wheel, nozzle mount, nozzle plate, nozzle vane, drive ring, drive lever) Etc.). Furthermore, the present invention is not limited to automobiles and motorcycles, but can be applied to exhaust parts used in high temperature environments such as various boilers and fuel cell systems, and the present invention is extremely useful industrially.
Claims (4)
ＤＢ=3(Cr+1.5Si+Mo+2.7Al)-2.8(Ni+0.5Mn+0.5Cu)-84(C+N)-19.8 % By mass, C: 0.02 to 0.10, Si: 0.10 to 1.0%, Mn: 0.2 to 4.5%, P: 0.010 to 0.040%, S: 0. 0.0001 to 0.0030%, Cr: 15 to 20%, Ni: 10 to 27%, Mo: 0.01 to 2.0%, Cu: 0.01 to 2.0, Co: 0.01 to 2 0.0%, Al: 1.0 to 6.0%, N: 0.001 to 0.02%, the balance consisting of Fe and inevitable impurities, and the DB value defined by the following formula: Austenitic stainless steel excellent in high-temperature slidability, which is 10 to 0 and has a hardness of 180 HV or more and 350 HV or less after aging at 850 ° C. for 2.68 hours.
DB = 3 (Cr + 1.5Si + Mo + 2.7Al) -2.8 (Ni + 0.5Mn + 0.5Cu) -84 (C + N) -19.8
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