JP2014189863A - Thermostable austenite stainless steel for metallic gasket - Google Patents
Thermostable austenite stainless steel for metallic gasket Download PDFInfo
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- 229910001566 austenite Inorganic materials 0.000 title abstract description 8
- 229910001220 stainless steel Inorganic materials 0.000 title abstract description 8
- 239000010935 stainless steel Substances 0.000 title abstract description 8
- 238000010438 heat treatment Methods 0.000 claims abstract description 12
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 3
- 239000012535 impurity Substances 0.000 claims abstract description 3
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 3
- 229910052748 manganese Inorganic materials 0.000 claims abstract 2
- 229910052759 nickel Inorganic materials 0.000 claims abstract 2
- 239000002244 precipitate Substances 0.000 claims description 29
- 229910052751 metal Inorganic materials 0.000 claims description 22
- 239000002184 metal Substances 0.000 claims description 22
- 229910000963 austenitic stainless steel Inorganic materials 0.000 claims description 17
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 7
- 229910052758 niobium Inorganic materials 0.000 claims description 2
- 229910052802 copper Inorganic materials 0.000 claims 1
- 229910052720 vanadium Inorganic materials 0.000 claims 1
- 229910000831 Steel Inorganic materials 0.000 description 15
- 239000011324 bead Substances 0.000 description 15
- 239000010959 steel Substances 0.000 description 15
- 229910045601 alloy Inorganic materials 0.000 description 12
- 239000000956 alloy Substances 0.000 description 12
- 239000000463 material Substances 0.000 description 12
- 230000007797 corrosion Effects 0.000 description 10
- 238000005260 corrosion Methods 0.000 description 10
- 238000005728 strengthening Methods 0.000 description 10
- 238000001556 precipitation Methods 0.000 description 8
- 230000000052 comparative effect Effects 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 229910000734 martensite Inorganic materials 0.000 description 5
- 238000012545 processing Methods 0.000 description 5
- 239000006104 solid solution Substances 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- 206010070834 Sensitisation Diseases 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 239000002436 steel type Substances 0.000 description 4
- 239000010949 copper Substances 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 230000008313 sensitization Effects 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 229910000859 α-Fe Inorganic materials 0.000 description 3
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 238000003483 aging Methods 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 238000002955 isolation Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 238000000465 moulding Methods 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 230000002093 peripheral effect Effects 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 238000002791 soaking Methods 0.000 description 2
- 230000035882 stress Effects 0.000 description 2
- 229910019590 Cr-N Inorganic materials 0.000 description 1
- 229910019588 Cr—N Inorganic materials 0.000 description 1
- 229910017060 Fe Cr Inorganic materials 0.000 description 1
- 229910002544 Fe-Cr Inorganic materials 0.000 description 1
- 229910018651 Mn—Ni Inorganic materials 0.000 description 1
- 238000003917 TEM image Methods 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- UPHIPHFJVNKLMR-UHFFFAOYSA-N chromium iron Chemical compound [Cr].[Fe] UPHIPHFJVNKLMR-UHFFFAOYSA-N 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 229910000365 copper sulfate Inorganic materials 0.000 description 1
- ARUVKPQLZAKDPS-UHFFFAOYSA-L copper(II) sulfate Chemical compound [Cu+2].[O-][S+2]([O-])([O-])[O-] ARUVKPQLZAKDPS-UHFFFAOYSA-L 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000007710 freezing Methods 0.000 description 1
- 230000008014 freezing Effects 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 238000007665 sagging Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 229910000601 superalloy Inorganic materials 0.000 description 1
- 238000005496 tempering Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Abstract
Description
本発明は、内燃機関のエンジン、排気ガス経路部材（エキゾーストマニホールド、触媒コンバータ）、ＥＧＲクーラーならびにターボチャージャー等の高温雰囲気に曝されても、優れた耐へたり性を維持するメタルガスケットとして使用されるオーステナイト系ステンレス鋼に関する。 INDUSTRIAL APPLICABILITY The present invention is used as a metal gasket that maintains excellent sag resistance even when exposed to a high temperature atmosphere such as an engine of an internal combustion engine, an exhaust gas passage member (exhaust manifold, catalytic converter), an EGR cooler, and a turbocharger. Relates to austenitic stainless steel.
加熱・冷却が頻繁に繰り返される雰囲気に曝されるエンジン等には、従来からメタルガスケットが使用されてきたが、エンジンの高性能化や環境規制に伴い排気ガス温度が上昇し、６００〜８００℃の温度に曝されるガスケットが増加している。材料温度の上昇にともない、従来のガスケット材では以下の課題を生じている。 Conventionally, metal gaskets have been used for engines that are exposed to an atmosphere in which heating and cooling are frequently repeated, but the exhaust gas temperature rises due to engine performance and environmental regulations, and 600 to 800 ° C. More gaskets are exposed to temperatures. With the increase in material temperature, the conventional gasket material has the following problems.
特許文献１、２に代表されるＳＵＳ３０１系の加工誘起マルテンサイト相に強化された材料や、特許文献３に代表されるＳＵＳ４３１系の焼入−焼戻しマルテンサイト相に強化された材料は、加熱される温度がマルテンサイト相の分解温度に相当するため軟化が著しく耐へたり性に劣る。 The material reinforced by the SUS301-based work-induced martensite phase represented by Patent Literatures 1 and 2 and the material reinforced by the SUS431-based quenching-tempering martensite phase represented by Patent Literature 3 are heated. The temperature corresponding to the decomposition temperature of the martensite phase is remarkably soft and inferior to sag resistance.
ＪＩＳＧ４９０２（耐食耐熱超合金板）に規定されるＮＣＦ６２５、ＮＣＦ７１８やＪＩＳＧ４３１２（耐熱鋼板）に規定されるＳＵＨ６６０等の析出強化系の材料は使用中に微細析出物を生成するため、６００〜８００℃の析出強化には有効であるが、高価なＮｉが多量に含まれるためコスト高となる。 Precipitation strengthening materials such as NCF625, NCF718 and SUH660 specified in JISG4312 (heat-resistant steel plate) defined in JIS G4902 (corrosion-resistant heat-resistant superalloy plate) generate fine precipitates during use. Although effective for precipitation strengthening, it is expensive because it contains a large amount of expensive Ni.
これらの課題を解決させるために、特許文献４ではＮとＮｂにより強化されたＦｅ−Ｃｒ−Ｎオーステナイト系ステンレス鋼が、また、特許文献５、６、７では、Ｎにより強化されたＦｅ−Ｃｒ−Ｍｎ−Ｎｉオーステナイト系ステンレス鋼が開示されており、一部の耐熱用ガスケットに適用されつつある。 In order to solve these problems, in Patent Document 4, Fe—Cr—N austenitic stainless steel reinforced with N and Nb is used. In Patent Documents 5, 6, and 7, Fe—Cr reinforced with N is used. -Mn-Ni austenitic stainless steel is disclosed and is being applied to some heat resistant gaskets.
しかし、これらの鋼はＮを多く含むために降伏応力（０．２％耐力）が非常に高くなるという課題を有する。すなわち、ガスケットに必要な平坦度を矯正加工にて確保するには焼なまし材で比較的軟質であることが望ましく、使用中の耐熱性を確保するには高温でのへたり性に優れることが望ましいが、多量にＮを添加する鋼では前者の特性を満足するとは必ずしも言い難い。また、一部のエンジンでは、排気ガスの凝縮水がメタルガスケット部に結露し腐食するという事例も認められており、耐粒界腐食感受性に対しても、従来以上に留意した成分設計とすることが好ましい。しかし、上述した開示例では、耐食性まで加味した成分設計が必ずしもされていないのが定常である。 However, since these steels contain a large amount of N, they have a problem that the yield stress (0.2% proof stress) becomes very high. In other words, it is desirable that the annealed material should be relatively soft to ensure the flatness required for the gasket by straightening, and that it has excellent sagability at high temperatures to ensure heat resistance during use. However, it is not always possible to say that the steel added with a large amount of N satisfies the former characteristics. In some engines, it has been recognized that the condensed water of the exhaust gas can condense and corrode on the metal gasket, and the component design should be designed with greater attention to intergranular corrosion resistance. Is preferred. However, in the above-described disclosure example, it is a steady state that the component design considering the corrosion resistance is not necessarily performed.
以上述ベたように、Ｎｉを多量に含まないオーステナイト系ステンレス鋼において初期の耐力が比較的低く、高温での耐熱性（へたり性）に優れ、耐食性にも優れた鋼、すなわち過剰なＣやＮを含有しない耐熱用ステンレス鋼が必要となってきているが、その成分系は必ずしも明確化されていないのが現状であった。 As described above, an austenitic stainless steel that does not contain a large amount of Ni has a relatively low initial yield strength, excellent heat resistance (sagging) at high temperatures, and excellent corrosion resistance, that is, excess C However, the heat resistant stainless steel containing no N is required, but the component system is not necessarily clarified.
本発明は、比較的安価で常温での加工性と高温での耐へたり性を同時に向上させた耐熱用メタルガスケットに適したオーステナイト系ステンレス鋼を提供することを目的とする。 An object of the present invention is to provide an austenitic stainless steel suitable for a heat-resistant metal gasket that is relatively inexpensive and has improved workability at room temperature and sag resistance at high temperature at the same time.
本発明のメタルガスケット用耐熱オーステナイト系ステンレス鋼は、その目的を達成するため、Ｃ：０．０３質量％以下、Ｓｉ：１．５〜５．０質量％、Ｍｎ：２．５質量％以下、Ｎｉ：７．０〜１７．０質量％、Ｃｒ：１３．０〜２３．０質量％、Ｎ：０．２０質量％以下を含み、残部がＦｅおよび不可避的不純物からなり、７００℃、１００ｈ加熱後に１００ｎｍ以下のＭＸ系およびＭ２Ｘ析出物が１００μｍ２に２００個以上存在することを特徴とする。 In order to achieve the object, the heat-resistant austenitic stainless steel for metal gaskets of the present invention is C: 0.03% by mass or less, Si: 1.5-5.0% by mass, Mn: 2.5% by mass or less, Ni: 7.0 to 17.0% by mass, Cr: 13.0 to 23.0% by mass, N: 0.20% by mass or less, with the balance being Fe and inevitable impurities, heating at 700 ° C. for 100 hours Later, 200 or more MX systems and M 2 X precipitates of 100 nm or less exist in 100 μm 2 .
本発明においては、さらにＭｏ：３．０質量％以下．Ｃｕ：１．５質量％未満、Ｎｂ：０．８０質量％以下Ｔｉ：０．５質量％以下、V：１．０質量％以下、Ｂ：０．０２０質量％以下の１種以上を含み、さらにＡｌ：０．２質量％以下、ＲＥＭ（希土類元素）：０．２質量％以下、Ｙ：０．２質量％以下、Ｃａ：０．１質量％以下、Ｍｇ：０．１質量％以下の１種又は２種以上を含むことができる。 In the present invention, Mo: 3.0% by mass or less. Cu: Less than 1.5% by mass, Nb: 0.80% by mass or less, Ti: 0.5% by mass or less, V: 1.0% by mass or less, B: 0.020% by mass or less, Furthermore, Al: 0.2% by mass or less, REM (rare earth element): 0.2% by mass or less, Y: 0.2% by mass or less, Ca: 0.1% by mass or less, Mg: 0.1% by mass or less 1 type (s) or 2 or more types can be included.
本発明のオーステナイト系ステンレス鋼は、メタルガスケットに要求される５００〜８００℃の高温環境での耐へたり性に優れている。また、このオーステナイト系ステンレス鋼をエギゾーストマニホールド、インテークマニホールド等の低温用メタルガスケットとして自動車用エンジンに組み込むと、周辺機器の寿命やエンジン自体の性能が向上する。また、エンジン用ガスケットの他に、自動車排ガス部品、自動車捷気管の振動遮断用継手に使用されるボールジョイント部に組み込まれる弾性ガスケットにも使用できる。 The austenitic stainless steel of the present invention is excellent in sag resistance in a high temperature environment of 500 to 800 ° C. required for a metal gasket. In addition, when this austenitic stainless steel is incorporated in an automobile engine as a low-temperature metal gasket such as an exhaust manifold or an intake manifold, the life of peripheral devices and the performance of the engine itself are improved. In addition to engine gaskets, the present invention can also be used for elastic gaskets incorporated in ball joint parts used in automobile exhaust parts and vibration isolation joints for automobile air pipes.
本発明者らは、上記課題を解決するために種々検討を行い、以下の知見を得て本発明に至った。 The inventors of the present invention have made various studies in order to solve the above-described problems, and have obtained the following knowledge to arrive at the present invention.
（１）初期の軟質化はＣを０．０３％以下かつＮを０．２０％以下とすることにより達成される。
（２）高温でのへたり性はビード部（加工部）を長時間の加熱によっても軟化させにくい因子で強化しておくこと、すなわち本発明ではＣの添加を極力抑制し、長時間加熱に対して安定なＭＸおよびＭ２Ｘ系微細析出物の粒子分散強化を利用することにより達成される。
（３）Ｃ添加量の減少は、Ｃｒ２３Ｃ６を経由したσ相生成を抑制することからガスケットの脆化に対しても非常に有効である。
〈４）また、Ｃ添加量を減らすことによって株ガスの凝縮水に対する耐食性（耐鋭敏化感受性）に対しても有効に作用する。
（５）さらに、固溶強化元素や析出強化元素を添加して所望の強度−延性バランスを調整することが可能である。
(1) The initial softening is achieved by setting C to 0.03% or less and N to 0.20% or less.
(2) The sagability at high temperature is strengthened by a factor that makes it difficult to soften the bead part (processed part) even by heating for a long time. In other words, in the present invention, the addition of C is suppressed as much as possible and the heating is performed for a long time. On the other hand, it is achieved by utilizing the particle dispersion strengthening of stable MX and M 2 X-based fine precipitates.
(3) The decrease in the amount of C added is very effective for embrittlement of the gasket because it suppresses the formation of the σ phase via Cr 23 C 6 .
<4) Moreover, it acts effectively also on the corrosion resistance (sensitivity-sensitization sensitivity) with respect to the condensed water of stock gas by reducing C addition amount.
(5) Furthermore, it is possible to adjust a desired strength-ductility balance by adding a solid solution strengthening element or a precipitation strengthening element.
以上のように本発明は、これまでクリープ強度や耐へたり性の向上に有効とされてきたＣ（例えば、特開平７−３４０５、特開平９−２７９３１５、特開平１１−２４１１４５など数多く、Ｃの効果が示されている）を極力低減することによって達成される。Ｃ低減によって、Ｃｒ２３Ｃ６型炭化物の総量は減る反面、７００℃、１００ｈおよび１０００ｈ程度の加熱でも、非常に安定した１００μｍ程度の微細なＭＸおよびＭ２Ｘ系析出物が生成することを明らかにした。さらに、低Ｃ材に固溶強化元素および析出強化元素を添加してもこの効果が失われないことを新たに知見し、本発明に至ったのである。 As described above, the present invention has been effective for improving the creep strength and sag resistance so far (for example, C7, JP9-279315, JP11-241145, C This is achieved by reducing as much as possible). Although the total amount of Cr 23 C 6 type carbide is reduced by reducing C, it is clear that very stable fine MX and M 2 X-based precipitates of about 100 μm are formed even when heated at about 700 ° C., 100 hours and 1000 hours. I made it. Furthermore, the inventors have newly found that this effect is not lost even when a solid solution strengthening element and a precipitation strengthening element are added to the low C material, and the present invention has been achieved.
以下、本発明が対象とするオーステナイト系ステンレス鋼に含まれる合金成分、含有量等を説明する。
Ｃ：０．０３質量％以下
長時間の加熱保持によっても微細で安定なＭＸ系およびＭ２Ｘ系析出物を生成させるため、Ｃは極力低減することが好ましい。Ｃ含有量がこれを上回る場合、Ｍ２３Ｘ６系析出物、とくに粗大化しやすいＣｒ２３Ｃ６が生成しやすくなり、軟化を促進する。また、Ｃｒ２３Ｃ６を経由したσ相への生成にともなう脆化も懸念される。よって、本発明では０．０３質量％以下に制限する。より安定してＭＸ系およびＭ２Ｘ系析出物を微細に生成させるためには、Ｃの範囲は０．０２質量％未満とすることが好ましい。
Hereinafter, alloy components, contents, and the like included in the austenitic stainless steel targeted by the present invention will be described.
C: 0.03 mass% or less C is preferably reduced as much as possible in order to produce fine and stable MX-based and M 2 X-based precipitates even by heating and holding for a long time. If the C content exceeds this, M 23 X 6 based precipitates becomes particularly easy easy Cr 23 C 6 is produced coarse, it promotes softening. There is also concern about embrittlement that accompanies the formation of σ phase via Cr 23 C6. Therefore, in this invention, it restrict | limits to 0.03 mass% or less. In order to more stably produce MX-based and M 2 X-based precipitates more stably, the range of C is preferably less than 0.02% by mass.
Ｓｉ：１．５〜５．０質量％
フェライト形成元素であり、オーステナイト相中で大きな固溶強化能を呈し、高温保持中に歪み時効によって時効硬化を促進させる。このような効果は、１．５質量％以上のＳｉ含有量で顕著になる。しかし、５．０質量％を超える過剰量のＳｉを添加すると、高温割れが誘発され、製造上で種々のトラブルを引き起こす。Ｓｉ含有量は３．０超〜５．０質量％以下の範囲とすることが一層好ましい。
Si: 1.5-5.0 mass%
It is a ferrite forming element, exhibits a large solid solution strengthening ability in the austenite phase, and promotes age hardening by strain aging while maintaining a high temperature. Such an effect becomes remarkable when the Si content is 1.5% by mass or more. However, when an excessive amount of Si exceeding 5.0% by mass is added, hot cracking is induced, causing various troubles in production. The Si content is more preferably in the range of more than 3.0 to 5.0% by mass or less.
Ｍｎ：２．５質量％以下
オーステナイト形成元素であり、高価なＮｉの代替成分として使用され、Ｎｉの必要量を低減できる。また、Ｓを固定することによって熟間加工性を改善することにも有効である。しかし、２．５質量％を超える過剰量のＭｎ添加は、高温強度や機械的性質を低下させる。
Mn: 2.5% by mass or less An austenite-forming element that is used as an alternative component of expensive Ni and can reduce the required amount of Ni. It is also effective to improve the maturing workability by fixing S. However, addition of an excessive amount of Mn exceeding 2.5% by mass lowers the high-temperature strength and mechanical properties.
Ｎｉ：７．０〜１７．０質量％
安定なオーステナイト組織を確保するために必須の合金成分であり、Ｎｉの最適含有量は鋼材に含まれるＣｒ、Ｓｉ、Ｍｏ等のフェライト形成元素量に依存する。しかし、７．０質量％未満のＮｉ含有量ではオーステナイト相の安定化が困難になる。他方、１７．０質量％を越えるＮｉ含有量では、鋼材コストが上昇して経済的に不利となる。Ｎｉ含有量は１１．０〜１５．０質量％の範囲とすることが一層好ましい。
Ni: 7.0 to 17.0% by mass
It is an essential alloy component for ensuring a stable austenite structure, and the optimum content of Ni depends on the amount of ferrite-forming elements such as Cr, Si, and Mo contained in the steel material. However, when the Ni content is less than 7.0% by mass, it becomes difficult to stabilize the austenite phase. On the other hand, if the Ni content exceeds 17.0% by mass, the steel material cost increases, which is economically disadvantageous. The Ni content is more preferably in the range of 11.0 to 15.0 mass%.
Ｃｒ：１３．０〜２３．０質量％
耐食性・耐酸化性に必要な合金成分であり、過酷な高温腐食雰囲気に曝されるメタルガスケット用途を考慮すると少なくとも１３．０質量％のＣｒ量が必要である。しかし、２３．０質量％を超える過剰量のＣｒが含まれると、δフェライトが形成され、安定したオーステナイト相が維持できなくなる。
Cr: 13.0-23.0 mass%
It is an alloy component necessary for corrosion resistance and oxidation resistance, and when considering a metal gasket application exposed to a severe high temperature corrosion atmosphere, an amount of Cr of at least 13.0% by mass is necessary. However, if an excessive amount of Cr exceeding 23.0% by mass is contained, δ ferrite is formed and a stable austenite phase cannot be maintained.
Ｎ：０．２０質量％以下
オーステナイト系ステンレス鋼の高温強度の上昇に有効な合金成分であるが、過剰量のＮが含まれると、Ｍ２３Ｘ６中のＸにおけるＮの割合が増加する。析出強化に寄与しない粗大なＭ２３Ｘ６系析出物が生成する結果、固溶強化に有効な固溶Ｎ量が減少し、高温強度を低下させる。よって、本発明では０．２０質量％以下に制限する。
N: 0.20% by mass or less Although it is an alloy component effective for increasing the high temperature strength of austenitic stainless steel, when an excessive amount of N is included, the ratio of N in X in M 23 X 6 increases. As a result of the formation of coarse M 23 X 6- based precipitates that do not contribute to precipitation strengthening, the amount of solid solution N effective for solid solution strengthening is reduced, and the high-temperature strength is lowered. Therefore, in this invention, it limits to 0.20 mass% or less.
Ｍｏ：３．０質量％以下
必要に応じて添加される合金成分であり、耐食性の向上に有効であると共に、高温保持中に炭窒化物となって微細に分散し高温強度を上昇させる。そのため、メタルガスケットが過酷な高温雰囲気に曝されても、Ｍｏ添加により強度の低下が防止される。しかし、３．０質量％を超えるＭｏの過剰添加は、高温域でのδフェライト生成を促進させる。
Mo: 3.0% by mass or less Mo is an alloy component that is added as necessary, and is effective in improving corrosion resistance, and becomes carbonitride during high temperature holding to finely disperse and increase high temperature strength. Therefore, even if the metal gasket is exposed to a severe high temperature atmosphere, the strength is prevented from being reduced by the addition of Mo. However, excessive addition of Mo exceeding 3.0% by mass promotes the formation of δ ferrite at high temperatures.
Ｃｕ：１．５質量％未満
必要に応じて添加される合金成分であり、メタルガスケットが使用される雰囲気の温度上昇に伴ってＭＸ系析出物やＭ２Ｘ系析出物とは異なるＣｕ系析出物を生成させ、高温強度、耐軟化性を改善する。しかし、過剰添加は、熱間加工性を低下させ、割れ発生の原因となる。
Cu: Less than 1.5% by mass An alloy component added as necessary, and Cu-based precipitation different from MX-based precipitates and M 2 X-based precipitates as the temperature of the atmosphere in which the metal gasket is used is increased. To produce high-temperature strength and softening resistance. However, excessive addition reduces hot workability and causes cracking.
Ｎｂ：０．８０質量％以下
メタルガスケットが曝される高温雰囲気下で析出物を形成し、或いはオーステナイトマトリックスに固溶することにより、硬度を上昇させ、耐軟化性を改善する。しかし、０．８０質量％を超える過剰量のＮｂ含有は、高温延性低下に起因して熱間加工性を低下させる。
Nb: 0.80% by mass or less By forming a precipitate in a high temperature atmosphere to which the metal gasket is exposed or by dissolving in austenite matrix, the hardness is increased and the softening resistance is improved. However, containing an excessive amount of Nb exceeding 0.80% by mass reduces hot workability due to a decrease in high-temperature ductility.
Ｔｉ：０．５質量％以下
必要に応じて添加される合金成分であり、硬度上昇・耐ヘタリ性の改善に有効な析出物を高温雰囲気で形成する。しかし、０．５質量％を超えるＴｉの過剰添加は、表面疵を発生させる原因となる。
Ti: 0.5% by mass or less Ti is an alloy component added as necessary, and forms a precipitate effective in increasing the hardness and improving the anti-sag property in a high-temperature atmosphere. However, excessive addition of Ti exceeding 0.5% by mass causes surface defects.
Ｖ：１．００質量％以下
必要に応じて添加される合金成分であり、硬度上昇、耐ヘタリ性の改善に有効な析出物を高温雰囲気で形成する。しかし、１．０質量％を超えるＶの過剰添加は、表加工性、靭性を低下させる原因となる。
V: 1.00% by mass or less An alloy component that is added as necessary, and forms precipitates that are effective in increasing hardness and improving resistance to settling in a high-temperature atmosphere. However, excessive addition of V exceeding 1.0% by mass causes a reduction in surface workability and toughness.
Ｂ：０．０２０質量％以下
必要に応じて添加される合金成分であり、高温強度上昇に有効な炭窒化物の微細析出を促進させ、熱間圧延温度域においてはＳ等の粒界偏析を抑制しエッジクラックの発生を防止する作用を呈する。しかし、０．０２０質量％を超える過剰量のＢを添加すると、低融点ホウ化物が生成しやすく、かえって熱間加工性が劣化する。
B: 0.020% by mass or less An alloy component added as necessary, promotes fine precipitation of carbonitrides effective for increasing high-temperature strength, and causes grain boundary segregation such as S in the hot rolling temperature range. Suppresses and prevents the occurrence of edge cracks. However, when an excessive amount of B exceeding 0.020% by mass is added, a low-melting boride tends to be generated, and hot workability is deteriorated.
Ａｌ：０．２質量％以下
必要に応じて添加される合金成分であり、製鋼時に脱酸剤として添加されると共に、鋼板をガスケット形状に打抜く際に打抜き性に悪影響を及ぼすＡ２系介在物を激減させる効果を奏する。
このような効果は０．２質量％のＡｌ含有量で飽和し、それ以上Ａｌを増量しても却って表面欠陥の増加を招くため、上限を０．２％とする。
Al: 0.2% by mass or less An alloy component that is added as necessary. It is added as a deoxidizer during steelmaking, and has an adverse effect on punchability when a steel plate is punched into a gasket shape. Has the effect of drastically reducing.
Such an effect is saturated at an Al content of 0.2% by mass, and even if the Al content is increased further, surface defects are increased. Therefore, the upper limit is set to 0.2%.
ＲＥＭ（希土類元素）：０．２質量％以下
Ｙ：０．２質量％以下
Ｃａ：０．１質量％以下
Ｍｇ：０．１質量％以下
必要に応じて添加される合金成分であり、何れも熱間加工性を改善し、耐酸化性の向上にも有効である。熱間加工性、耐酸化性に及ぼす効果は何れも添加量の増加に応じて顕著になるが、ＲＥＭ、Ｙでは０．２０質量％、Ｃａ、Ｍｇでは０．１０質量％で飽和するため、これらの値を上限とする。
REM (rare earth element): 0.2% by mass or less Y: 0.2% by mass or less Ca: 0.1% by mass or less Mg: 0.1% by mass or less It is effective in improving hot workability and improving oxidation resistance. The effects on hot workability and oxidation resistance are all marked with an increase in the amount added, but because REM and Y are saturated at 0.20% by mass, Ca and Mg at 0.10% by mass, These values are the upper limit.
従来からＭＸ系析出物やＭ２Ｘ系析出物の生成を利用して、クリープ強度の改善を図った例はある。しかし、これらを排気ガスに曝される耐熱用メタルガスケットに使用した場合、耐へたり性は必ずしも改善されるとは限らず、信頼性の面では満足できなかった。この面を改善すべ<検討を行った結果、ガスケットのへたり量は１００ｈ以内の加熱で大幅に進行することを明らかにした。この結果、７００℃，１００ｈ加熱において微細な析出物を生成するような調整を行えば、優れた耐へたり性を有することを明らかにした。７００℃，１００ｈの加熱において１００μｍ２に２００個以上の析出物が存在しないと十分な耐へたり性を維持できない。また、１００ｎｍを超える粗大な析出物を生成する場合は、析出物の間隔が一般に広<なってしまい、１００μｍ２に２００個以上生成させようとすると、合金元素の添加量が過剰となり、ガスケットへの成形性が不十分となる。なお、上述した析出物の大きさと個数は、鋼鈑素材における合金元素の含有量と製造条件を種々変動させて決定されるものである。本発明で規定した成分量において、鋼板素材における析出物の存在状態は特に規定しないが、１００ｎｍ超えの粗大析出物、１００ｎｍ以下の微細析出物ともに、１００μｍ２に２０個以下と少ないことが好ましい。発明者らの実験では、後述の成分組織を有するオーステナイト系ステンレス鋼鈑の製造工程において連続ラインに１０５０℃〜１２００℃×均熱０秒〜均熱６０秒の仕上焼鈍を施す場合の例では、１０００℃から５００℃までの平均冷却速度を１０℃／秒以上にコントロールすることで望ましい金属組織が得られた。 Conventionally, there is an example in which the creep strength is improved by using generation of MX-based precipitates and M 2 X-based precipitates. However, when these are used for heat-resistant metal gaskets exposed to exhaust gas, the sag resistance is not always improved, and the reliability cannot be satisfied. As a result of investigations to improve this aspect, it was clarified that the amount of gasket sag progressed greatly with heating within 100 hours. As a result, it has been clarified that if adjustment is made so as to produce fine precipitates when heated at 700 ° C. for 100 hours, it has excellent sag resistance. Sufficient sag resistance cannot be maintained unless there are 200 or more precipitates in 100 μm 2 when heated at 700 ° C. for 100 hours. When coarse precipitates exceeding 100 nm are produced, the interval between the precipitates is generally widened, and if 200 or more particles are to be produced in 100 μm 2 , the amount of alloy elements added becomes excessive, resulting in the gasket. The moldability of is insufficient. The size and number of precipitates described above are determined by variously changing the alloy element content and the manufacturing conditions in the steel sheet material. In the component amounts defined in the present invention, the state of precipitates in the steel sheet material is not particularly defined, but both coarse precipitates exceeding 100 nm and fine precipitates of 100 nm or less are preferably as small as 20 or less in 100 μm 2 . In the experiment of the inventors, in the case of performing a finish annealing of 1050 ° C. to 1200 ° C. × soaking 0 seconds to soaking 60 seconds in a continuous line in the manufacturing process of an austenitic stainless steel plate having a component structure described later, A desirable metal structure was obtained by controlling the average cooling rate from 1000 ° C. to 500 ° C. to 10 ° C./second or more.
表１に示す組成のステンレス鋼を３００ｋｇ真空溶解炉で溶製し、その後スラブを熱間鍛造、切り出し、熱間圧延、煉鈍、酸洗、冷間圧延、焼鈍、酸洗工程または最終の酸洗後に３０〜６０％冷間圧延工程を経て板厚０．５〜０．２ｍｍのステンレス鋼帯を製造した。 Stainless steel having the composition shown in Table 1 is melted in a 300 kg vacuum melting furnace, and then the slab is hot forged, cut, hot rolled, blunted, pickled, cold rolled, annealed, pickled, or final acid picked. After washing, a stainless steel strip having a thickness of 0.5 to 0.2 mm was produced through a 30 to 60% cold rolling process.
各ステンレス鋼帯からφ５０ｍｍの円形試験片を切り出し、試験片の中央に内径３２ｍｍの円形開口を形成し、開口周辺に幅３ｍｍ、高さ０．５ｍｍのビードをプレス成形することによりメタルガスケット（図１）を作製した。常温での加工性はビード成形時の割れの有無で評価した。加工割れ無のものを良好（○）とし、加工割れ有のものを×とした。なお、ビード成形時に加工割れが生じた鋼については成形高さを０．４５ｍｍとした。ついで、ビード高さが０．４ｍｍになるように治具で押え、７００℃に１００時間保持した後、室温まで徐冷した。徐冷後の試験片について、室温での残存ビード高さを測定した。なお、残存ビード高さの測定には焦点顕微鏡を使用し、８点の平均値として算出した。 仕上焼鈍材の鋼板について、圧延方向における金属組織観察を行った。透過型電子顕微鏡を用いて、ＭＸ系析出物およびＭ２Ｘ系析出物のサイズを調べ、観察される１０ｎｍ以上、１００ｎｍ以下の析出物の数を求めた。1つの試料につき少なくとも２０視野の観察を行い、１００μｍ２あたりの析出物の数に換算した。 A circular test piece having a diameter of 50 mm is cut out from each stainless steel strip, a circular opening having an inner diameter of 32 mm is formed in the center of the test piece, and a bead having a width of 3 mm and a height of 0.5 mm is formed around the opening by pressing a metal gasket (see FIG. 1) was produced. The processability at room temperature was evaluated by the presence or absence of cracks during bead molding. Those with no processing cracks were evaluated as good (O), and those with processing cracks were evaluated as x. In addition, about the steel in which the work crack generate | occur | produced at the time of bead forming, the forming height was 0.45 mm. Subsequently, the bead height was pressed with a jig so as to be 0.4 mm, held at 700 ° C. for 100 hours, and then gradually cooled to room temperature. About the test piece after slow cooling, the residual bead height at room temperature was measured. In addition, the focus bead microscope was used for the measurement of residual bead height, and it computed as an average value of 8 points | pieces. The steel structure of the finish annealed material was observed for the metal structure in the rolling direction. Using a transmission electron microscope, the sizes of the MX-based precipitates and the M 2 X-based precipitates were examined, and the number of observed precipitates of 10 nm or more and 100 nm or less was determined. At least 20 fields of view were observed for one sample, and converted into the number of precipitates per 100 μm 2 .
表２の測定結果にみられるように、鋼種Ｎｏ．１〜１１（本発明例）では０．５ｍｍのビード加工が可能であるとともに７００℃×１００時間加熱後に室温での残存ビード高さが０．１５０ｍｍ以上であり、メタルガスケットに要求される残存ビード高さを備えていた。他方、比較鋼Ｎｏ．１２〜１６（比較例）では、何れも残存ビード高さが０．１５０ｍｍ未満であり、メタルガスケットとしての性能上に問題があった。残存ビード高さが低い理由には、次のような原因が考えられる。
比較鋼Ｎｏ．１２は、図２の透過型電子顕微鏡による観察結果に見られるように、加熱保持中に巨大な粒界炭化物が析出したため時効硬化能が低下し、残存ビード高さが十分でない。比較鋼Ｎｏ．１３．１４は、加熱される温度がマルテンサイト相の分解温度に相当するため著しく軟化し、残存ビード高さが低くなった。比較鋼Ｎｏ．１５、１６は過剰量のＮを含有していることから、ビード成形時に加工割れが生じるとともに、７００℃の加熱評価においても加工誘起マルテンサイトが高温保持中に焼戻しされたため、残存ビード高さが低くなった。
As seen in the measurement results in Table 2, the steel type No. 1 to 11 (examples of the present invention), 0.5 mm bead processing is possible, and the residual bead height at room temperature after heating at 700 ° C. for 100 hours is 0.150 mm or more. Had a height. On the other hand, Comparative Steel No. In Nos. 12 to 16 (comparative examples), the remaining bead height was less than 0.150 mm, and there was a problem in performance as a metal gasket. The reason why the remaining bead height is low can be considered as follows.
Comparative steel No. As can be seen from the observation result of the transmission electron microscope of FIG. 2, the age-hardening ability is lowered due to the precipitation of huge grain boundary carbides during heating and holding, and the residual bead height is not sufficient. Comparative steel No. In 13.14, the heating temperature was equivalent to the decomposition temperature of the martensite phase, so that it was remarkably softened and the residual bead height was lowered. Comparative steel No. 15 and 16 contain an excessive amount of N, so that processing cracks occur during bead molding, and the processing-induced martensite was tempered while being held at a high temperature even in a 700 ° C. heating evaluation. It became low.
表２の試験結果にみられるように、鋭敏化特性改善を目的にＣ量を低減させた鋼種Ｎｏ．１〜１１（本発明例）および鋼種Ｎｏ．１４，１５（比較例）では鋭敏化特性は壊れるが、鋼種Ｎｏ．１２，１３および鋼種Ｎｏ．１６は本発明範囲を超えるＣ量を有し、Ｃ固定元素がＣ量に見合う量だけ十分に添加されていないために鋭敏化特性が著しく劣った。 As can be seen from the test results in Table 2, the steel type No. with the C content reduced for the purpose of improving the sensitization characteristics. 1 to 11 (examples of the present invention) and steel types No. 14 and 15 (comparative example), the sensitization characteristics are broken, but the steel grade no. 12, 13 and steel type no. No. 16 has a C amount exceeding the range of the present invention, and the C-fixing element was not sufficiently added in an amount commensurate with the C amount.
この対比から明らかなように、Ｃ量を低減したオーステナイト系ステンレス鋼であっても、非常に安定した微細な析出物の生成により、形状凍結性に優れ、長期間にわたって気密性を維持するメタルガスケットが得られることが確認された。 As is clear from this comparison, even with austenitic stainless steel with a reduced amount of C, a metal gasket that has excellent shape freezing properties and maintains hermeticity over a long period of time by generating very stable fine precipitates. It was confirmed that
以上説明したように、本発明のオーステナイト系ステンレス鋼は、メタルガスケットに要求される５００〜８００℃の高温環境での耐へたり性に優れている。また、このオーステナイト系ステンレス鋼をエギゾーストマニホールド、インテークマニホールド等の低温用メタルガスケットとして自動車用エンジンに組み込むと、周辺機器の寿命やエンジン自体の性能が向上する。また、エンジン用ガスケットの他に、自動車排ガス部品、自動車排気管の振動遮断用継手に使用されるボールジョイント部に組み込まれる弾性ガスケットにも使用できる。
As described above, the austenitic stainless steel of the present invention is excellent in sag resistance in a high temperature environment of 500 to 800 ° C. required for a metal gasket. In addition, when this austenitic stainless steel is incorporated in an automobile engine as a low-temperature metal gasket such as an exhaust manifold or an intake manifold, the life of peripheral devices and the performance of the engine itself are improved. In addition to engine gaskets, the present invention can also be used for elastic gaskets incorporated in ball joint parts used in automobile exhaust parts and vibration isolation joints for automobile exhaust pipes.
Claims (3)
Further, Al: 0.2% by mass or less, REM (rare earth element): 0.2% by mass or less Y: 0.2% by mass or less, Ca: 0.1% by mass or less, Mg: 0.1% by mass or less 1 The heat-resistant austenitic stainless steel for metal gaskets according to claim 1 or 2, comprising seeds or two or more kinds.
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| JP2015014242A (en) * | 2013-07-04 | 2015-01-22 | 本田技研工業株式会社 | Gasket |
| WO2015151771A1 (en) * | 2014-04-02 | 2015-10-08 | 日新製鋼株式会社 | Austenitic stainless-steel sheet for gasket, and gasket |
| JP2016204714A (en) * | 2015-04-24 | 2016-12-08 | 新日鐵住金ステンレス株式会社 | Stainless steel for automobile exhaust system component fastening component |
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| JP2010202936A (en) * | 2009-03-04 | 2010-09-16 | Nisshin Steel Co Ltd | Austenitic stainless steel for heat-resistant member |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2015014242A (en) * | 2013-07-04 | 2015-01-22 | 本田技研工業株式会社 | Gasket |
| WO2015151771A1 (en) * | 2014-04-02 | 2015-10-08 | 日新製鋼株式会社 | Austenitic stainless-steel sheet for gasket, and gasket |
| JP2015196889A (en) * | 2014-04-02 | 2015-11-09 | 日新製鋼株式会社 | Austenitic stainless steel sheet for gasket and the gasket |
| US10161524B2 (en) | 2014-04-02 | 2018-12-25 | Nisshin Steel Co., Ltd. | Austenitic stainless steel sheet for gasket, and gasket |
| JP2016204714A (en) * | 2015-04-24 | 2016-12-08 | 新日鐵住金ステンレス株式会社 | Stainless steel for automobile exhaust system component fastening component |
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| JP6296435B2 (en) | 2018-03-20 |
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