JP2017179561A - Austenitic stainless steel excellent in high temperature slidability and turbocharger component manufactured by using the same - Google Patents
Austenitic stainless steel excellent in high temperature slidability and turbocharger component manufactured by using the same Download PDFInfo
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- 239000012535 impurity Substances 0.000 claims abstract description 6
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- 229910052802 copper Inorganic materials 0.000 claims abstract description 4
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 3
- 229910052758 niobium Inorganic materials 0.000 claims description 6
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 5
- 229910052735 hafnium Inorganic materials 0.000 claims description 3
- 229910052715 tantalum Inorganic materials 0.000 claims description 3
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- 229910052721 tungsten Inorganic materials 0.000 claims description 3
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- 229910052727 yttrium Inorganic materials 0.000 claims description 3
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Landscapes
- Heat Treatment Of Sheet Steel (AREA)
Abstract
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 part having a sliding mechanism in an exhaust system part of an internal combustion engine such as an automobile such as a turbocharger and a turbocharger manufactured from the steel. It relates to exhaust system parts.
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 widely used especially in Europe as fuel-saving and environmental regulations for automobiles, and are expected to increase globally in the future. In this turbocharger, a variable displacement type in which the supercharging pressure is controlled by a variable nozzle vane is the mainstream, and is called a VG (Variable Geometry) method or a VGS (Variable Geometry System). However, since the variable nozzle mechanism is used in a high-temperature and 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 technology that meets this requirement, Patent Document 1 discloses an austenitic stainless steel having Si: 2.0 to 4.0%, Ni: 8.0 to 16.0%, and Cr: 18.0 to 20.0%. An exhaust guide part of a nozzle vane turbocharger to be manufactured is shown. Addition of Si improves the elongation and hole expansion rate of the material, making it suitable for the production of exhaust guide parts, and producing less scale of oxide scale. It is said that there is little scale peeling or 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 exhaust manifold and turbocharger housing are made thinner in order to exhaust the exhaust gas at a higher temperature, and the temperature of the material to be used rises. Therefore, Si: 1.0 to 3.0%, Ni: 8.0 to 15%, Cr: more than 22 to 26%, N: more than 0.15 to 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 peel resistance, the addition of Nb can suppress a decrease in high temperature strength after aging, and the increase in N can increase 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, it is reported that high-Si stainless steel is excellent in high-temperature slidability. However, the evaluation of high temperature slidability is a comparison between high Si stainless steel and conventional steel, and the controlling factor of 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。 Examination of the technology described in the background art revealed the following issues. It has been found that the improvement in high-temperature strength by adding Si in Patent Document 1 is small and the improvement in high-temperature slidability is small. The invention steel of Patent Document 2 is one in which oxidation resistance is enhanced with Si and high-temperature strength is enhanced with Nb and N, but it has been found that the effect of improving the high-temperature slidability necessary for the turbocharger is insufficient. . According to Non-Patent Documents 1 and 2, in order to improve the durability and performance of turbochargers, the governing factor of high-temperature slidability is clarified, and high-temperature slidability superior to existing steel, that is, wear resistance at high temperatures. 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 technology, to provide an austenitic stainless steel excellent in high-temperature slidability, and to provide a turbocharger part 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 affecting the high temperature slidability of austenitic stainless steel. Oxidation resistance, high temperature strength, and seizure resistance can be considered as the controlling factors for high temperature slidability. From these viewpoints, the requirements for improving the high temperature slidability of austenitic stainless steel without degrading manufacturability are studied. 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)
High oxidation resistance is desirable for oxidation resistance, and SUS310S steel of 25% Cr-20% Ni is used as a heat resistant material. A material such as SUS302B to which Si is added instead of reducing Cr has also been developed. Since Si forms an internal oxide layer at the austenite grain boundary directly under the scale, it has been known to have an effect of suppressing the peeling of the scale. However, in an environment where heating and cooling are repeated, scale peeling 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. Austenitic stainless steel having a large coefficient of thermal expansion has a more pronounced effect, and conventionally, high-Si stainless steel has been used in environments where oxidation resistance is required. However, the exhaust gas temperature introduced into the turbocharger tends to increase year by year, and oxidation resistance superior to that of high Si steel is required.
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 is found that Al addition is effective for further improving the oxidation resistance in this environment, and in particular, the addition of 1% or more of Al greatly improves the oxidation resistance in an automobile exhaust gas environment. It was. Oxidation is suppressed by high Al, and scale peeling 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 nitrogenation and precipitation strengthening by intermetallic compounds are effective in improving the high temperature strength of the stainless steel constituting the internal combustion engine. If the heat-resistant temperature is 400 to 500 ° C., a material whose high-temperature strength is increased by adding 0.2 to 0.3% N is practical, but it is effective to improve the wear resistance in the environment where the turbocharger is used. I can't get. SUH660 and Inconel 718 are known as materials for strengthening by precipitating 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 or precipitation strengthened alloy of Ni 3 Nb, Fe 2 Nb, or the like. These steels and alloys have insufficient oxidation resistance and are not suitable for use in an environment exposed to automobile exhaust gas. There is Ni 3 Al as an intermetallic compound, but Ni 3 Al is easily coarsened during use in a high temperature environment as compared with Ni 3 Ti or Ni 3 Nb, and therefore, when it is evaluated by creep life, an effect is not recognized, 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 temperatures by the present inventors, it has been found that high Al stainless steel exhibits high wear resistance due to precipitation of Ni 3 Al. This is considered to have the effect of reducing the seizure by 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 (steel of the present invention). In this test, a sample was pre-oxidized in an air atmosphere for 1 hour, and then the ball-on-disk method was used to change the sliding speed to 3.3 mm / s and the load to two levels of 0.5 and 2.0 N. It was carried out at 850 ° C. with a dynamic length of 20 m. The conventional evaluation of the sliding member of the turbocharger has been performed at 800 ° C., but the inventors conducted the high temperature sliding test at 850 ° C. because of 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 wear surface of the appearance after the test is shown in FIG. 1A is a wear surface photograph of SUS310S (25Cr-20Ni), FIG. 1B is a wear surface photograph of high Si stainless steel (20Cr-14Ni-3Si), and FIG. 1C is high Al stainless steel (present invention). It is a wear surface photograph of steel. Moreover, the symbol “Pt” in FIGS. 1A to 1C indicates the measured value of the surface roughness of the portion of the photograph that has been cut into a circumferential shape. It can be seen from FIG. 1 that the oxidation state differs depending on the steel component. However, the oxidation of the high Si stainless steel and the high Al stainless steel (the steel of the present invention) is small, and is not an area where scale peeling occurs.
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。 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. 2 and 3, it can be seen that the oxidation resistance is already at a sufficient level due to the high Si and high Al, but the wear resistance is greatly improved by the high Al. In addition, the effect of increasing the Al is also remarkable in the friction coefficient, and it can be seen that the friction coefficient is greatly 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)
Moreover, there is a possibility of adversely affecting manufacturability such as casting, hot rolling, welding, etc. due to the high Al of stainless steel. That is, it is necessary to consider the control of a solidified structure that is greatly different from that of conventional steel, as well as the reduction of embrittlement due to precipitation of Ni 3 Al, which is an intermetallic compound. 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 much 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 a decrease in 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。 In addition, the present inventors have found that wear resistance is clearly improved by setting the hardness measured at room temperature after aging at 850 ° C. for 2 hours as 180 HV or higher as an evaluation of wear resistance.
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: 0.0001-0.0030%, Cr: 15-20%, Ni: 10-27%, Mo: 0.01-2.0%, Cu: 0.01-2.0, Co: 0.00. DB containing 01 to 2.0%, Al: 1.0 to 6.0%, N: 0.001 to 0.02%, the balance being Fe and inevitable impurities, and defined by the following formula An austenitic stainless steel excellent in high-temperature slidability, characterized in that the value is -10 to 0 and the hardness after aging at 850 ° C. for 2 hours is 180 HV or more.
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], characterized by containing one or more of the above.
[3] The austenitic stainless steel for turbocharger parts having excellent high-temperature slidability according to [1] or [2].
[4] A turbocharger part manufactured using the austenitic stainless steel excellent in high-temperature slidability described in [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 slidability, in particular, oxidation resistance, wear resistance, and seizure resistance, without sacrificing productivity. Another object of the present invention is to provide a turbocharger part having excellent durability by using the austenitic stainless steel of the present invention for the turbocharger part.
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 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 enhancing the stability of the austenite structure and the high temperature slidability. Since the effect is manifested 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 to make it 0.04% or more. On the other hand, when used in a high temperature environment such as turbocharger parts, M 23 C 6 type carbides are formed and the oxidation resistance of the material is lowered, so the upper limit is made 0.10% or less. From the viewpoint of corrosion resistance, it is desirable to make it 0.08% or less.
（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 oxidation resistance, but its effect is hardly recognized in high Al-added steel. However, in the steelmaking process, since it is effective as a deoxidizing element before Al addition, 0.10% or more 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 it is made 1.0% or less. In order to avoid embrittlement due to the sigma phase in which δ ferrite is transformed during use in a high temperature environment, the content 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 deoxidizer, and contributes to the stabilization of the structure by expanding the austenite single phase region. The effect appears clearly at 0.2% or more, so 0.2% or more. Moreover, since there exists an effect which improves hot workability by forming sulfide and reducing the amount of solid solution S in steel, it is desirable to set it as 0.5% or more. On the other hand, excessive addition reduces the corrosion resistance, so it is 4.5% or less. Further, from the viewpoint of oxidation resistance, an oxide mainly composed of Cr 2 O 3 is desirable, and an oxide of Mn is not preferable.
（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 to 0.040%)
P is an element contained as an impurity in the main raw material such as hot metal or ferrochrome. Since it is an element harmful to hot workability, it is set to 0.040% or less. In addition, Preferably it is 0.030% or less. Excessive reduction leads to an increase in cost, such as making it necessary to use a high-purity raw material, so 0.010% or more. Economically preferably 0.020% or more is desirable.
（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%)
S forms sulfide inclusions and degrades the general corrosion resistance (entire corrosion and pitting corrosion) of steel materials. Therefore, the upper limit of the content is preferably as small as 0.0030%. Further, the smaller the S content, the better the corrosion resistance. However, since the desulfurization load increases and the production cost increases for lowering the S content, the lower limit is preferably made 0.0001%. In addition, Preferably it is 0.0001-0.0010.
（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. On the other hand, if it exceeds 20%, the austenite single phase region is reduced and the hot workability at the time of production is impaired, so the content is made 15 to 20%. From the viewpoint of oxidation resistance, 17% or more is desirable. Further, if the amount of Cr is increased, embrittlement occurs due to the formation of a sigma phase.
（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 Ni 3 Al precipitates that exhibit excellent wear resistance in the present invention. Further, Ni is an element that stabilizes the austenite phase like Mn, and has an effect superior to that of Mn in terms of oxidation resistance. Since these effects are obtained at 10% or more, the lower limit is made 10% or more. Further, since it has an effect of suppressing the generation of the sigma phase, it is desirable to make it 20% or more. On the other hand, excessive addition of Ni increases the susceptibility to solidification cracking and also decreases hot workability, so the content is made 27% or less. Furthermore, in order to suppress scale peeling in intermittent oxidation, it is desirable to make it 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 for 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 corrosion resistance, it is desirable to add 0.3% or more. On the other hand, it is also a ferrite stabilizing element, and as the amount of Mo added increases, it is necessary to increase the amount of Ni added. Further, since the formation of the sigma phase is promoted to cause embrittlement, the content is made 2.0% or less. Since the effect of improving the corrosion resistance and oxidation resistance is almost saturated at 0.8% or more, it is desirable to make it 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 substitutes for Ni as a Cu austenite stabilizing element. Furthermore, it is effective in suppressing the progress of crevice corrosion and pitting corrosion. 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 about 0.2% as an additional impurity. However, if it exceeds 2.0%, the hot workability is lowered, 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%)
Since Co is extremely effective in improving heat resistance even when added in a trace amount, 0.01% or more is added. However, excessive addition is made 2.0% or less in order to impair hot workability. Since it is an element effective for corrosion resistance, it is desirable to make it 0.10% or more. Moreover, in order to suppress formation of a sigma phase, it is desirable to make it 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 element that is extremely effective for improving 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 the wear resistance by precipitation strengthening, it is desirable to make it 2.0% or more. On the other hand, Al is a ferrite phase stabilizing element, and it is necessary to add an austenite stabilizing element that balances with Al, and excessive addition of Ni, Mn, and C increases the raw material cost and decreases the corrosion resistance. In order to become a problem, the upper limit is set to 6.0%. It is desirable to make it 5.0% or less because hot rolling is likely to occur due to improved oxidation resistance.
（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 to 0.02%)
N, like C, increases the high temperature slidability, and Ni can also be reduced by increasing the austenite stability. Further, since the effect of reducing corrosion resistance due to sensitization is smaller than that of C, it can be added in a larger amount than C. However, when N is added to stainless steel that increases oxidation resistance by increasing the Al content as in the steel of the present invention, N nitrides are formed, so that N does not contribute to high temperature slidability. Manufacturability such as nozzle clogging is greatly impaired. For this reason, the upper limit was made 0.02%. Considering stable production, it is desirable to make it 0.01% or less. 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 when combined with stirring and refining with an inert gas in a vacuum. 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)
Phase balance control is important for manufacturability and quality stability of austenitic stainless steel. If it is the most general-purpose SUS304, it solidifies in the two-phase region of δ ferrite and austenite at the time of solidification, and austenite single phase structure is formed in the hot rolling process. For this reason, solidification cracking hardly occurs, and the final product has an austenite single phase structure. However, δ ferrite may remain slightly in the solidified segregation part. 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 a decrease in product productivity and quality stability.
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. In order to use it in a high-temperature environment like a turbocharger part, it is necessary to reduce the residual δ ferrite as much as possible, so the upper limit was set to zero. When the DB value exceeds 0, the remaining δ ferrite deteriorates the high-temperature slidability (friction coefficient or wear scar roughness), and cracks at the edge of the steel sheet during hot rolling, so-called ear cracks, occur, resulting in manufacturability. Is significantly inhibited. In order to stably reduce δ ferrite in the solidified segregation part, it is desirable to set it to −2 or less. On the other hand, lowering the DB value more than necessary requires an increase in Ni, Mn, Cu, C, and N, which are austenite stabilizing elements, and tends to increase costs and decrease corrosion resistance and oxidation resistance. In order to reduce these adverse effects, the DB value is limited to −10 or more. In order to reduce wrinkles 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)
In order to improve the high temperature slidability, the wear resistance as well as the oxidation resistance of the material is important. For this purpose, it is necessary that the hardness is high even after aging. The aging hardness was set to 180 HV or more in order to ensure the effect of improving the wear resistance. On the other hand, since excessive hardening leads to a decrease in toughness as a part, the upper limit is desirably set to 350 HV. What is hardened by aging is also desirably restricted to 300 HV or less in the manufacturing process because it hardens and tends to break the plate when held at a similar temperature.
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。 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 One or two or more of 0.05% may be added.
（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 suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride. Moreover, since it has the effect of suppressing the grain growth in a high temperature environment and improving a high temperature slidability, it is desirable to add 0.01% or more. However, the formation of large steelmaking inclusions causes a reduction in fatigue life, so the upper limit is made 0.3%. Considering improvement in high-temperature slidability by securing the amount of dissolved C and N, 0.05% or less is desirable. 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 to 0.6%)
Nb is an element that suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride. Moreover, since it has the effect of suppressing the grain growth in a high temperature environment and improving a high temperature slidability, it is desirable to add 0.01% or more. However, forming a large steel-making inclusion tends to cause surface flaws and also causes a reduction in fatigue life, so the upper limit is made 0.6%. Considering improvement in high-temperature slidability by securing the amount of dissolved C and N, 0.05% or less is desirable. 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 as an inevitable impurity in the alloy raw material of stainless steel, and is difficult to remove in the refining process. Therefore, V is generally contained in the range of 0.02 to 0.15%. Moreover, since it forms fine carbonitride and has the effect of suppressing grain growth, it is an element that is intentionally added as necessary. Since the effect is stably manifested by addition of 0.01% or more, it is desirable to add 0.01% or more. On the other hand, if added excessively, the precipitates may be coarsened. As a result, the toughness after quenching is lowered, so that the content is preferably made 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 to 0.1%)
Zr is an element that suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride. Moreover, since it has the effect of suppressing the grain growth in a high temperature environment and improving a high temperature slidability, it is desirable to add 0.01% or more. However, the formation of large steelmaking inclusions causes a decrease in fatigue life, so the upper limit is made 0.1%. Considering improvement in high-temperature slidability by securing the amount of dissolved C and N, 0.05% or less is desirable. 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 suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride. Moreover, since it has the effect of suppressing the grain growth in a high temperature environment and improving a high temperature slidability, it is desirable to add 0.01% or more. However, the formation of large steelmaking inclusions causes a decrease in fatigue life, so the upper limit is made 0.1%. Considering improvement in high-temperature slidability by securing the amount of dissolved C and N, 0.05% or less is desirable. 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 to 0.1%)
Hf is an element that suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride. Moreover, since it has the effect of suppressing the grain growth in a high temperature environment and improving a high temperature slidability, it is desirable to add 0.01% or more. However, the formation of large steelmaking inclusions causes a decrease in fatigue life, so the upper limit is made 0.1%. Considering improvement in high-temperature slidability by securing the amount of dissolved C and N, 0.05% or less is desirable. 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 suppresses deterioration of sensitization and corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride. Moreover, since it has the effect of suppressing the grain growth in a high temperature environment and improving a high temperature slidability, it is desirable to add 0.01% or more. However, the formation of large steelmaking inclusions causes a decrease in fatigue life, so the upper limit is made 0.1%. Considering improvement in high-temperature slidability by securing the amount of dissolved C and N, 0.05% or less is desirable. 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 to 0.1%)
Sn is an element that improves corrosion resistance, and has an effect of suppressing progress after pitting corrosion occurs. 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 may not 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%)
Mg is added as a desulfurization element in the same manner as Ca, and in general, a parallel amount is dissolved in the molten steel from the slag and may be contained as MgO in the composite oxide. In addition, MgO in the refractory may be dissolved into the molten steel. Since the desulfurization effect is 0.0002% or more, it is desirable to set the lower limit to 0.0002%. On the other hand, excessive addition causes the water-soluble inclusion MgS to coarsely precipitate and lower the corrosion resistance, so it is desirable to make it 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 for improving the hot workability, and since the effect is manifested at 0.0002% or more, 0.0002% or more is added. In order to improve the hot workability in a wider temperature range, the content is preferably 0.0005% or more. On the other hand, excessive addition causes surface flaws due to a decrease in hot workability, so 0.0050% is made the upper limit. In consideration of 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 desulfurization element, and has the effect of reducing S in steel and improving hot workability. Generally, it is added as CaO in the slag at the time of melting and refining, and a part of this is dissolved as Ca in the 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 can be obtained from 0.0001%, it is desirable to make it 0.0001% or more. On the other hand, when it is contained in a large amount, a relatively coarse water-soluble inclusion CaS precipitates and lowers the corrosion resistance.
（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 a desulfurization element as well as an effect of improving 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 it is desirable to make it 0.05% or less in order to impair the fatigue life of the gasket due to the formation of large oxide inclusions.
（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 desulfurization element as well as an effect of improving 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 it is desirable to make it 0.05% or less in order to impair the fatigue life of the gasket due to the formation of large oxide inclusions.
（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 plate to be subjected to finish rolling is not particularly limited. The steel melted by a known means (for example, an electric furnace) is cast into a slab having a thickness of 150 to 250 mm by a continuous casting machine, the surface is ground as required, and then heated to 1200 ° C. or higher to perform hot rolling. Hot rolling is performed by a machine to obtain a hot-rolled steel strip having a 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 annealed pickling finish (2B finish) or a BA (Bright Annealing) finish that is annealed in a non-oxidizing atmosphere. In addition, the process after finish rolling is not particularly limited, and a shape forcing or 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, in the high temperature sliding test under the same conditions as the high temperature sliding test results shown in FIGS. 2 and 3, the austenitic stainless steel has a wear coefficient of 0.4 or less when the load is 0.5 N. Steel can be obtained. Further, according to the present invention, in the high temperature sliding test, it is possible to obtain an austenitic stainless steel having a Pt of 40 μm or less when the load is 2.0 N. Thus, according to the present invention, an austenitic stainless steel excellent in high-temperature slidability can be provided.
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 200 mm-thick slabs. The slab was heated to 1250 ° C., followed by rough hot rolling and finish hot rolling to obtain a hot rolled steel plate having a thickness of 20 mm. Subsequently, the hot-rolled steel sheet was annealed at 1050 ° C. for 20 seconds and then water-cooled. As for the inspection of hot-rolled steel sheets, the edge cracks at the end of the steel sheet are visually inspected, the defects appearing due to the solidification cracks at the time of casting are visually inspected, and a commercially available ultrasonic flaw detection test apparatus. It was done with the examination by. In this example, if the ear cracks or wrinkles were minor or could not be confirmed, the test was accepted, 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。 Thereafter, the high temperature slidability was evaluated by a ball-on-disk method. The test temperature was 850 ° C. and the test was performed in the air. Until the start of the test, the test piece was held at 850 ° C. for 1 hour to oxidize the surface. The test load was two levels of 0.5 and 2.0N. The sliding speed was 3.3 mm / s and the sliding length was 20 m. Changes in the coefficient of friction over the entire test time were continuously measured, and the coefficient of friction was evaluated as an average value. Moreover, about the abrasion trace after a test, the roughness measurement was performed with the two-dimensional roughness meter. The hardness of the test piece after the test was measured. The roughness was measured in a direction perpendicular to the line of wear marks cut into a 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 at a load of 0.5 N, and the wear amount was evaluated by a test value at a load of 2.0 N. The acceptance criteria for 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. The hardness was converted to Vickers hardness by measuring the surface hardness of a sample cooled to room temperature after a high temperature sliding test with a Rockwell hardness meter.
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 showed a good value of 40 μm or less. On the other hand, as shown in Table 2, the comparative steels are out of the scope of the present invention as shown in Table 2. The high temperature wear resistance decreases, δ ferrite remains, and Cr carbide formation and hot rolling The amount of wear increased due to generation and the like, and the wear scar roughness Pt exceeded 40 μm. In addition, the friction coefficient of 0.4 or less was obtained in the method of the present invention, but the comparison steel produced a value of 0.6 or more exceeding 0.4. Or both failed.
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 slidability, in particular, oxidation resistance, wear resistance, and seizure resistance, without sacrificing productivity. By using the material to which the present invention is applied, particularly as a material for a turbocharger of an automobile, the durability can be greatly improved as compared with a conventional casting. It should be noted that the present invention can be applied to any of the parts used for turbochargers. Specifically, the housing that forms the outer frame of the turbocharger, the precision components inside the nozzle vane turbocharger (for example, the so-called 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, and 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
In 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 0.0001-0.0030%, Cr: 15-20%, Ni: 10-27%, Mo: 0.01-2.0%, Cu: 0.01-2.0, Co: 0.01-2 0.0%, Al: 1.0 to 6.0%, N: 0.001 to 0.02%, the balance is Fe and inevitable impurities, and the DB value defined by the following formula is − An austenitic stainless steel excellent in high-temperature slidability, characterized by being 10 to 0 and having a hardness after aging at 850 ° C. for 2 hours of 180 HV or higher.
DB = 3 (Cr + 1.5Si + Mo + 2.7Al) -2.8 (Ni + 0.5Mn + 0.5Cu) -84 (C + N) -19.8
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 : 0.01-0.1%, Hf: 0.01-0.1%, W: 0.01-0.1%, Sn: 0.01-0.1%, Mg: 0.0002-0 .0030%, B: 0.0002 to 0.0050%, Ca: 0.0001 to 0.0030%, REM: 0.01 to 0.05%, Y: 0.01 to 0.05% Or it contains 2 or more types, The austenitic stainless steel excellent in high temperature slidability of Claim 1 characterized by the above-mentioned.
The austenitic stainless steel for turbocharger parts excellent in high temperature slidability according to claim 1 or 2.
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| CN110484836B (en) * | 2019-09-24 | 2021-01-05 | 南京佑天金属科技有限公司 | Hafnium zirconium titanium molybdenum reinforced austenitic stainless steel and preparation method thereof |
| CN114574757A (en) * | 2022-02-17 | 2022-06-03 | 天津水泥工业设计研究院有限公司 | High-temperature roll ring material for roll pair machine and preparation method thereof |
| WO2022123812A1 (en) * | 2020-12-10 | 2022-06-16 | 日立金属株式会社 | Method for manufacturing austenitic stainless steel strip |
| WO2022144995A1 (en) * | 2020-12-28 | 2022-07-07 | 三菱重工エンジン＆ターボチャージャ株式会社 | Nozzle component, variable nozzle mechanism for variable-capacity turbocharger, variable-capacity turbocharger, and method for manufacturing nozzle component |
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| CN110484836B (en) * | 2019-09-24 | 2021-01-05 | 南京佑天金属科技有限公司 | Hafnium zirconium titanium molybdenum reinforced austenitic stainless steel and preparation method thereof |
| WO2022123812A1 (en) * | 2020-12-10 | 2022-06-16 | 日立金属株式会社 | Method for manufacturing austenitic stainless steel strip |
| WO2022144995A1 (en) * | 2020-12-28 | 2022-07-07 | 三菱重工エンジン＆ターボチャージャ株式会社 | Nozzle component, variable nozzle mechanism for variable-capacity turbocharger, variable-capacity turbocharger, and method for manufacturing nozzle component |
| JPWO2022144995A1 (en) * | 2020-12-28 | 2022-07-07 | ||
| JP7348415B2 (en) | 2020-12-28 | 2023-09-20 | 三菱重工エンジン＆ターボチャージャ株式会社 | Nozzle parts, variable nozzle mechanism of variable displacement turbocharger, variable displacement turbocharger and method for manufacturing nozzle parts |
| CN114574757A (en) * | 2022-02-17 | 2022-06-03 | 天津水泥工业设计研究院有限公司 | High-temperature roll ring material for roll pair machine and preparation method thereof |
| CN114574757B (en) * | 2022-02-17 | 2022-08-09 | 天津水泥工业设计研究院有限公司 | High-temperature roll ring material for roll pair machine and preparation method thereof |
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