JP6820757B2 - Ferritic stainless steel sheets for fastening parts with excellent heat resistance, fastening parts, and circular clamps for heat-resistant tubular members - Google Patents
Ferritic stainless steel sheets for fastening parts with excellent heat resistance, fastening parts, and circular clamps for heat-resistant tubular members Download PDFInfo
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Description
本発明は、特に高温で使用される排気部品同士を締結する締結部品に最適な耐熱性に優れた締結部品用フェライト系ステンレス鋼板および締結部品並びに耐熱管状部材用円状クランプに関するものである。 The present invention relates to a ferritic stainless steel plate for fasteners having excellent heat resistance, which is most suitable for fasteners for fastening exhaust parts used at high temperatures, fasteners, and circular clamps for heat-resistant tubular members.
自動車の排気マニホールド、フロントパイプおよびセンターパイプなどの排気系部材は、エンジンから排出される高温の排気ガスを通すため、排気部材を構成する材料には耐酸化性、高温強度、熱疲労特性など多様な特性が要求され、主としてステンレス鋼が使用されている。 Exhaust system members such as automobile exhaust manifolds, front pipes and center pipes allow high-temperature exhaust gas discharged from the engine to pass through, so the materials that make up the exhaust members have various characteristics such as oxidation resistance, high-temperature strength, and thermal fatigue characteristics. Is required, and stainless steel is mainly used.
従来、自動車排気部材には鋳鉄が使用されるのが一般的であったが、排ガス規制の強化、エンジン性能の向上、車体軽量化などの観点から、ステンレス鋼製の排気マニホールドが使用されるようになった。排ガス温度は、車種によって異なるが、近年では７００〜９００℃程度が多く、このような温度域で長時間使用される環境において高い高温強度、耐酸化性を有する材料が要望されている。これに対して、ＳＵＳ４２９系やＳＵＳ４４４系等のフェライト系ステンレス鋼板が開発および実用化されている。また、近年では、排気ガス規制の強化が更に強まる他、燃費性能の向上、ダウンサイジング等の動きから、特にエンジン直下のエキゾーストマニホールドを通気する排気ガス温度は上昇傾向にある。加えて、ターボチャージャーのような過給機を搭載するケースも多くなっており、エキゾーストマニホールドやターボチャージャーに使用されるステンレス鋼には耐熱性の一層の向上が求められる。排気ガス温度の上昇に関しては、従来９００℃程度であった排気ガス温度が１０００℃程度まで上昇することも見込まれている。一方、ターボチャージャーの内部構造は複雑で、過給効率を高めるとともに、耐熱信頼性の確保が重要であり、主として耐熱オーステナイト系ステンレス鋼の使用が開示されている。 Conventionally, cast iron was generally used for automobile exhaust members, but from the viewpoint of tightening exhaust gas regulations, improving engine performance, reducing the weight of the vehicle body, etc., stainless steel exhaust manifolds will be used. Became. The exhaust gas temperature varies depending on the vehicle type, but in recent years, it is often about 700 to 900 ° C., and a material having high high temperature strength and oxidation resistance is required in an environment where it is used for a long time in such a temperature range. On the other hand, ferrite stainless steel sheets such as SUS429 series and SUS444 series have been developed and put into practical use. Further, in recent years, exhaust gas regulations have been further tightened, fuel efficiency has been improved, downsizing and other movements have led to an increase in the temperature of exhaust gas that ventilates the exhaust manifold directly under the engine. In addition, there are many cases where a supercharger such as a turbocharger is installed, and the stainless steel used for the exhaust manifold and the turbocharger is required to have further improved heat resistance. Regarding the rise in the exhaust gas temperature, it is expected that the exhaust gas temperature, which was about 900 ° C. in the past, will rise to about 1000 ° C. On the other hand, the internal structure of the turbocharger is complicated, and it is important to improve supercharging efficiency and ensure heat resistance, and the use of heat resistant austenitic stainless steel is mainly disclosed.
上記のエキゾーストマニホールドやターボチャージャーは、部品間の結合に溶接および機械的締結が用いられる。後者の機械的締結に際して、クランプあるいは排気Ｖバンド等と呼ばれる締結部品で部品間を結合される。このクランプは排気ガスが流れる排気部品間を締結することから、締結性や気密性が重要となる。また、高温の排気ガスに直接曝されることは無いものの、排気部品からの伝熱により７００℃近くまでは高温化するため、耐熱性が重要となる。エキゾーストマニホールドでは高温強度や熱疲労特性が重要となるが、クランプ部品では、常温で締結する際の強度とともに、高温環境で長時間使用された際の気密性が要求される。使用中にクランプの緩みが生じると気密性が悪くなり排気ガスの漏れが生じるが、気密性を支配する材料要因は十分に知られていなかった。 The exhaust manifolds and turbochargers described above use welding and mechanical fastening to connect the parts. When the latter is mechanically fastened, the parts are joined by fastening parts called clamps or exhaust V-bands. Since this clamp fastens between exhaust parts through which exhaust gas flows, fastness and airtightness are important. Further, although it is not directly exposed to high-temperature exhaust gas, heat resistance is important because the temperature rises to nearly 700 ° C. due to heat transfer from the exhaust parts. High-temperature strength and thermal fatigue characteristics are important for exhaust manifolds, but clamp parts are required to have strength when fastened at room temperature and airtightness when used for a long time in a high-temperature environment. If the clamp becomes loose during use, the airtightness deteriorates and exhaust gas leaks, but the material factors that govern the airtightness are not fully known.
排気部品に使用される締結用クランプは、特許文献１に示されているようにＶバンドクランプとも呼ばれており、一般的にはオーステナイト系ステンレス鋼（ＳＵＳ３０４やＳＵＳ３０１等）が使用される。これらは常温強度や高温強度が高いものの、フェライト系ステンレス鋼に比べて熱膨張係数が大きい、高コストになるという課題があった。 The fastening clamp used for the exhaust component is also called a V-band clamp as shown in Patent Document 1, and generally austenitic stainless steel (SUS304, SUS301, etc.) is used. Although these have high normal temperature strength and high temperature strength, they have a problem that they have a large coefficient of thermal expansion and high cost as compared with ferritic stainless steel.
本発明は、特に高温で使用される排気部品同士、具体的にはエキゾーストマニホールドやターボチャージャーを構成する部品間を締結するために最適な耐熱性に優れた締結部品用フェライト系ステンレス鋼板の高耐熱化、および締結部品並びに耐熱管状部材用円状クランプに関するものである。 INDUSTRIAL APPLICABILITY The present invention has high heat resistance of a ferritic stainless steel plate for fastening parts, which has excellent heat resistance and is optimal for fastening exhaust parts used at particularly high temperatures, specifically, parts constituting an exhaust manifold or turbocharger. It relates to ferritic stainless steel, fastening parts, and circular clamps for heat-resistant tubular members.
上記課題を解決するために、排気部品間を締結するクランプの重要特性である気密性と材料因子について詳細に検討した。そして、本発明者らは７００℃におけるクリープ特性が使用中の緩みおよび気密性と密接に関係することを見出し、フェライト系ステンレス鋼板を耐熱締結部品として使用する上で、最小クリープ歪速度を０．０１％／ｈｒ以下にすることが有効であることを知見した。フェライト系ステンレス鋼板のクリープ挙動は、１次クリープ、２次クリープ、３次クリープの段階に分けられるが、２次クリープにおいては時間とともに安定的にクリープ歪みが増加する。この際クリープ歪速度が最少となる領域が存在し、この歪速度を最小クリープ歪速度という。常温で部品間を締結したクランプは高温に曝されるとクリープ歪による変形が生じ、歪量が大きいとクランプの緩みが生じて排気ガスの漏れに繋がる恐れがある。クリープ歪を小さくするためには、高温での変形抵抗を大きくするため、転位の移動度を小さくするとともに、転位の再配列を伴う動的な回復および再結晶を抑制する必要がある。そこで、フェライト系ステンレス鋼板から構成されるクランプが長時間７００℃近傍の高温環境下で動的回復および再結晶を抑制し、最小クリープ歪速度を０．０１％／ｈｒ以下にする方法を種々検討した。なお、本発明の検討に際し、最小クリープ歪速度を０．０１％／ｈｒ以下にすることで、実際の自動車排気部品に使用されるクランプが高温で緩みが生じず、ガス漏れ発生等の不具合が無いことを確認した。７００℃でのクリープ試験を種々の合金成分で行った中で、本発明において、合金元素の効果として以下の知見を得た。この特徴として、７００℃程度の温度域でのクリープ変形において、動的な回復が生じると最小クリープ歪速度は増加する。動的な回復が生じると結晶方位差が１５°未満の小角粒界が増加し、小角粒界での転位の合体・消滅によって動的再結晶が生じてしまう。クリープ変形過程の動的回復・再結晶を抑制するためには、初期組織として小角粒界の存在比率を抑制することを見出し、この存在頻度が１５％以下であれば７００℃での最小クリープ歪速度を０．０１％／ｈｒ以下に抑えることを知見した。図１に種々の小角粒界比率を有するフェライト系ステンレス鋼板を７００℃で３５ＭＰａの負荷を作用させて最小クリープ歪速度を求めた結果を示す。ここで、結晶粒界の方位はＥＢＳＰ（Electron Back-Scattering pattern）を用い、板厚中心近傍について結晶粒毎の方位を測定し、各結晶粒界の方位差を求め１５°未満を小角粒界と定義し、比率を算出した。これより、製品板の小角粒界が１５％以下の場合、最小クリープ歪速度が０．０１％／ｈとなり、クランプの締結性能として満足することがわかる。小角粒界比率が１５％超の場合、クリープ変形初期に該粒界移動が容易であるとともに、大角粒界とは異なりクリープ試験中に発生する転位のパイルアップ効果が生じないため、回復・再結晶が加速すると推定される。また、後述するクリープ変形過程に析出する析出物が小角粒界に粗大に析出し易くなる要素もある。一方、小角粒界比率が１５％以下の場合、新たな転位の発生源が少ないとともに、大角粒界による転位運動の抑制、粒内への均一析出によって転位の運動が抑制され、クリープ抵抗が増加すると考えられる。以上、金属組織の精緻な制御によって締結部品に要求されるクリープ変形抑制を効率的に可能とする金属組織を見出し、本発明とした。なお、小角粒界比率を０％にするには鋼成分の高純化や製造工程において工程増加などのコスト増が必要なことから、下限は３％が望ましい。 In order to solve the above problems, the airtightness and material factors, which are important characteristics of the clamp that fastens the exhaust parts, were examined in detail. Then, the present inventors have found that the creep property at 700 ° C. is closely related to the looseness and airtightness during use, and when using a ferritic stainless steel sheet as a heat-resistant fastening part, the minimum creep strain rate is set to 0. It was found that it is effective to make it 01% / hr or less. The creep behavior of ferritic stainless steel sheets is divided into the stages of primary creep, secondary creep, and tertiary creep. In the secondary creep, creep strain increases stably with time. At this time, there is a region where the creep strain rate is the minimum, and this strain rate is called the minimum creep strain rate. When the clamp that fastens the parts at room temperature is exposed to high temperature, it may be deformed due to creep strain, and if the amount of strain is large, the clamp may loosen, leading to exhaust gas leakage. In order to reduce the creep strain, it is necessary to reduce the mobility of dislocations and suppress dynamic recovery and recrystallization accompanied by dislocation rearrangement in order to increase the deformation resistance at high temperature. Therefore, various methods have been studied in which a clamp made of a ferritic stainless steel plate suppresses dynamic recovery and recrystallization in a high temperature environment of around 700 ° C. for a long time, and the minimum creep strain rate is 0.01% / hr or less. did. In the study of the present invention, by setting the minimum creep strain rate to 0.01% / hr or less, the clamp used for the actual automobile exhaust parts does not loosen at high temperature, and problems such as gas leakage occur. I confirmed that there was no such thing. While the creep test at 700 ° C. was carried out with various alloy components, the following findings were obtained as the effects of the alloying elements in the present invention. As a feature of this, in creep deformation in a temperature range of about 700 ° C., the minimum creep strain rate increases when dynamic recovery occurs. When dynamic recovery occurs, small-angle grain boundaries with a crystal orientation difference of less than 15 ° increase, and dynamic recrystallization occurs due to the coalescence and disappearance of dislocations at the small-angle grain boundaries. In order to suppress the dynamic recovery and recrystallization of the creep deformation process, we found that the abundance ratio of small-angle grain boundaries was suppressed as the initial structure, and if this abundance frequency was 15% or less, the minimum creep strain at 700 ° C. It was found that the speed was suppressed to 0.01% / hr or less. FIG. 1 shows the results of obtaining the minimum creep strain rate by applying a load of 35 MPa at 700 ° C. to a ferritic stainless steel sheet having various small grain boundary ratios. Here, the orientation of the crystal grain boundaries is EBSP (Electron Back-Scattering pattern), the orientation of each crystal grain is measured near the center of the plate thickness, the orientation difference of each crystal grain boundary is obtained, and less than 15 ° is the small angle grain boundary. The ratio was calculated. From this, it can be seen that when the small grain boundaries of the product plate are 15% or less, the minimum creep strain rate is 0.01% / h, which is satisfactory for the clamping performance of the clamp. When the small-angle grain boundary ratio is more than 15%, the grain boundary movement is easy at the initial stage of creep deformation, and unlike the large-angle grain boundary, the pile-up effect of dislocations generated during the creep test does not occur, so recovery / recrystallization is performed. It is estimated that the crystals accelerate. In addition, there is also an element in which the precipitates deposited during the creep deformation process, which will be described later, are likely to be coarsely precipitated at the small grain boundaries. On the other hand, when the small-angle grain boundary ratio is 15% or less, there are few sources of new dislocations, the dislocation movement is suppressed by the large-angle grain boundaries, and the dislocation movement is suppressed by uniform precipitation into the grains, and creep resistance increases. It is thought that. As described above, the present invention has been made by finding a metal structure that efficiently suppresses creep deformation required for a fastening part by finely controlling the metal structure. The lower limit is preferably 3% because it is necessary to increase the purity of the steel component and increase the cost in the manufacturing process in order to reduce the small grain boundary ratio to 0%.
上記課題を解決する本発明の要旨は、以下のとおりである。
（１）質量％にて、Ｃ：０．０２％以下、Ｎ：０．０２％以下、Ｓｉ：４％以下、Ｐ：０．０２〜０．１％、Ｓ：０．０１％以下、Ｍｎ：３％以下、Ｃｒ：１０〜２５％、Ｃｕ：０．０１〜３％、Ｍｏ：０．０１〜３％、Ａｌ：０．０１〜５％、Ｂ：０．０００２〜０．００５０％、Ｖ：０．０１〜１％、ＴｉおよびＮｂを１種または２種以上をそれぞれ０．０１〜０．８％を含有し、残部がＦｅおよび不可避的不純物であり、結晶方位差１５°未満の小角粒界の比率が１５％以下であることを特徴とする耐熱性に優れた耐熱部材締結部品用フェライト系ステンレス鋼板。
（２）質量％にて、Ｎｉ：０．０１〜１％、Ｗ：０．１〜３％、Ｍｇ：０．０００２〜０．０１％、Ｓｎ：０．０１〜０．５％、Ｓｂ：０．０１〜０．５％、Ｚｒ：０．０１〜０．３％、Ｔａ：０．０１〜０．３％、Ｈｆ：０．０１〜０．３％、Ｃｏ：０．０１〜０．３％、Ｃａ：０．０００１〜０．０１％、ＲＥＭ：０．００１〜０．２％、Ｇａ：０．０００２〜０．３％の１種または２種以上を含有することを特徴とする（１）に記載の耐熱性に優れた耐熱部材締結部品用フェライト系ステンレス鋼板。
（３）（１）または（２）の耐熱性に優れたフェライト系ステンレス鋼板を使用した耐熱部材締結部品。
（４）（１）または（２）の耐熱性に優れたフェライト系ステンレス鋼板を使用した耐熱管状部材用円状クランプ。
The gist of the present invention for solving the above problems is as follows.
(1) In terms of mass%, C: 0.02% or less, N: 0.02% or less, Si: 4% or less, P: 0.02-0.1%, S: 0.01% or less, Mn : 3% or less, Cr: 10 to 25%, Cu: 0.01 to 3%, Mo: 0.01 to 3%, Al: 0.01 to 5%, B: 0.0002 to 0.0050%, V: 0.01 to 1%, Ti and Nb containing 1 or 2 or more, respectively 0.01 to 0.8%, the balance being Fe and unavoidable impurities, and a crystal orientation difference of less than 15 °. A ferrite-based stainless steel plate for fastening parts for heat-resistant members, which has excellent heat resistance and is characterized in that the ratio of small square grain boundaries is 15% or less.
(2) In terms of mass%, Ni: 0.01 to 1%, W: 0.1 to 3%, Mg: 0.0002 to 0.01%, Sn: 0.01 to 0.5%, Sb: 0.01 to 0.5%, Zr: 0.01 to 0.3%, Ta: 0.01 to 0.3%, Hf: 0.01 to 0.3%, Co: 0.01 to 0. It is characterized by containing one or more of 3%, Ca: 0.0001 to 0.01%, REM: 0.001 to 0.2%, and Ga: 0.0002 to 0.3%. The ferrite-based stainless steel plate for fastening parts for heat-resistant members according to (1), which has excellent heat resistance.
(3) Heat-resistant member fastening parts using the ferrite-based stainless steel plate having excellent heat resistance of (1) or (2).
(4) A circular clamp for heat-resistant tubular members using the ferrite-based stainless steel plate having excellent heat resistance according to (1) or (2).
以上の説明から明らかなように、本発明によれば従来オーステナイト系ステンレス鋼が使用されていた排気部品の締結用途に対して安価なフェライト系ステンレス鋼板を提供でき、優れた耐熱性から、特に自動車部品の環境対策や部品の低コスト化などに大きな効果が得られる。また、本発明鋼は必要特性に応じて締結用のみならず排気部品全般に対しても適用可能である。 As is clear from the above description, according to the present invention, it is possible to provide an inexpensive ferritic stainless steel sheet for fastening applications of exhaust parts in which austenitic stainless steel has been conventionally used, and because of its excellent heat resistance, particularly an automobile. Great effects can be obtained on environmental measures for parts and cost reduction of parts. Further, the steel of the present invention can be applied not only to fastening but also to exhaust parts in general according to the required characteristics.
以下、本発明について詳細に説明する。 Hereinafter, the present invention will be described in detail.
最初に鋼の成分範囲の限定理由について説明する。成分含有量の％は質量％を意味する。 First, the reason for limiting the composition range of steel will be explained. The% of the component content means the mass%.
Ｃは、成形性と耐食性を劣化させるとともに、再結晶を遅延させるために小角粒界が残存し易く高温強度の低下をもたらしクリープ歪速度を増加させるため、その含有量は少ないほど良いため、０．０２％以下とした。但し、過度の低減は精錬コストの増加に繋がるため、０．００１〜０．００５％が望ましい。 C deteriorates moldability and corrosion resistance, and delays recrystallization, so that small-angle grain boundaries tend to remain, resulting in a decrease in high-temperature strength and an increase in creep strain rate. Therefore, the smaller the content, the better. It was set to 0.02% or less. However, since excessive reduction leads to an increase in refining cost, 0.001 to 0.005% is desirable.
ＮはＣと同様、成形性と耐食性を劣化させるとともに、再結晶を遅延させるために小角粒界が残存し易く、高温強度の低下をもたらしクリープ歪速度の増加させるため、その含有量は少ないほど良いため、０．０２％以下とした。但し、過度の低減は精錬コストの増加に繋がるため、０．００３〜０．０１５％が望ましい。 Similar to C, N deteriorates moldability and corrosion resistance, and small angle grain boundaries tend to remain due to delaying recrystallization, which lowers high-temperature strength and increases creep strain rate. Therefore, the smaller the content, the more. Since it is good, it was set to 0.02% or less. However, since excessive reduction leads to an increase in refining cost, 0.003 to 0.015% is desirable.
Ｓｉは、脱酸剤としても有用な元素であるが、高温強度、クリープ特性と耐酸化性を改善するために非常に重要な元素である。特に７００℃程度の温度域で高温強度および耐酸化性は、Ｓｉ量の増加とともに向上するが、４％超になると再結晶を遅延させるために小角粒界が残存し易い。また、延性が不足しクランプ形状への加工が困難になるとともに、靭性が著しく劣化するため鋼板製造性が困難となる。したがって、Ｓｉは４％以下とした。Ｓｉは含有しなくてもよいが、過度な低減は精錬コストの増加に繋がるため、０．１〜４％が望ましい。 Si is an element that is also useful as a deoxidizer, but is a very important element for improving high temperature strength, creep properties and oxidation resistance. Especially in the temperature range of about 700 ° C., the high temperature strength and oxidation resistance improve as the amount of Si increases, but when it exceeds 4%, recrystallization is delayed and small grain boundaries tend to remain. In addition, ductility is insufficient, making it difficult to process into a clamp shape, and the toughness is significantly deteriorated, which makes steel sheet manufacturability difficult. Therefore, Si was set to 4% or less. Si may not be contained, but excessive reduction leads to an increase in refining cost, so 0.1 to 4% is desirable.
Ｐは、加工性を劣化させるために低減する方が望ましいが、本発明ではクリープ変形抵抗を増加させるために０．０２％以上添加する。これは、ＦｅあるいはＴｉ、Ｎｂと結合してＦｅＰあるいはＦｅＴｉＰ、ＦｅＮｂＰの析出物が高温変形中に粒界析出し、転位の運動を抑制し、動的回復の抑制ならびに最小クリープ歪速度の低減に寄与することを見出したためである。特に、ＣｕやＮｂとの複合添加においては、他析出物との微細析出強化が効果的に作用するため、より効果的である。一方、０．１％超添加すると常温加工性が劣化する他、上記析出が粗大化してクリープ抵抗が小さくなるため、０．０２〜０．１％とした。この他、クランプ加工性を考慮すると０．０２〜０．０６％が望ましい。更に、安定的なクリープ変形抑制のためには、０．０３〜０．０６％が望ましい。 It is desirable to reduce P in order to deteriorate workability, but in the present invention, 0.02% or more is added in order to increase creep deformation resistance. This is because the precipitates of FeP, FeTiP, and FeNbP combine with Fe, Ti, and Nb to precipitate at the grain boundaries during high-temperature deformation, suppress the movement of dislocations, suppress dynamic recovery, and reduce the minimum creep strain rate. This is because they found that they would contribute. In particular, in the case of composite addition with Cu or Nb, the strengthening of fine precipitation with other precipitates works effectively, which is more effective. On the other hand, if more than 0.1% is added, the workability at room temperature deteriorates, and the precipitation becomes coarse and the creep resistance becomes small. Therefore, it was set to 0.02 to 0.1%. In addition, 0.02 to 0.06% is desirable in consideration of clamp workability. Further, 0.03 to 0.06% is desirable for stable suppression of creep deformation.
Ｓは、耐食性を劣化させる元素であるため、その含有量は少ないほど良く、０．０１％超の場合、ＭｎＳ、Ｔｉ４Ｃ２Ｓ２等の析出物生成に起因して靭性が劣化するため、上限を０．０１％とした。精錬コストや排ガスによる隙間腐食抑制を考慮すると、０．００１０〜０．００６０％が望ましい。 Since S is an element that deteriorates corrosion resistance, the smaller the content, the better. If it exceeds 0.01%, the toughness deteriorates due to the formation of precipitates such as MnS and Ti 4 C 2 S 2. , The upper limit was set to 0.01%. Considering the refining cost and the suppression of crevice corrosion due to exhaust gas, 0.0010 to 0.0060% is desirable.
Ｍｎは、脱酸剤として添加される元素で、７００℃程度の中温域での強度上昇に寄与する。また、長時間使用中にＭｎ系酸化物が表層に形成し、スケール密着性や異常酸化抑制効果に寄与する。一方、３％超の過度な添加は、再結晶を遅延させるために小角粒界が残存し易いとともに、常温の均一伸びを低下させる他、ＭｎＳを形成して耐食性を低下させたり、耐酸化性の劣化をもたらす。これらの観点から、上限を３％とした。Ｍｎは含有しなくてもよい。更に、高温延性やスケール密着性を考慮すると、０．３〜１．５％が望ましい。 Mn is an element added as an antacid and contributes to an increase in strength in a medium temperature range of about 700 ° C. In addition, Mn-based oxides are formed on the surface layer during long-term use, contributing to scale adhesion and the effect of suppressing abnormal oxidation. On the other hand, excessive addition of more than 3% delays recrystallization, so that small grain boundaries tend to remain, and in addition to lowering uniform elongation at room temperature, MnS is formed to lower corrosion resistance and oxidation resistance. Causes deterioration. From these viewpoints, the upper limit is set to 3%. Mn may not be contained. Further, considering high temperature ductility and scale adhesion, 0.3 to 1.5% is desirable.
Ｃｒは、本発明において、耐酸化性確保のために必須な元素である。１０％未満では、その効果は発現せず、２５％超では加工性を低下させたり、靭性の劣化をもたらしクランプ形状への加工が困難となるため、１０〜２５％とした。更に、１３％未満では製造過程でオーステナイト相が析出して再結晶を遅延させるために小角粒界が残存し易くなるため、１３％以上が望ましい。また高温延性、製造コストを考慮すると２３％以下が望ましい。 Cr is an essential element for ensuring oxidation resistance in the present invention. If it is less than 10%, the effect is not exhibited, and if it exceeds 25%, the workability is lowered and the toughness is deteriorated, which makes it difficult to process into a clamp shape. Therefore, the ratio was set to 10 to 25%. Further, if it is less than 13%, the austenite phase is precipitated in the production process and recrystallization is delayed, so that small grain boundaries are likely to remain. Therefore, 13% or more is desirable. Further, considering high temperature ductility and manufacturing cost, 23% or less is desirable.
Ａｌは、脱酸元素として添加される他、耐酸化性を向上させる元素である。また、固溶強化元素として７００℃程度の温度域におけるクリープ変形抵抗を向上させる。そのため、０．０１％以上添加する。一方、５％超の添加により著しく加工性や靭性が劣化する他、再結晶遅延により小角粒界が残存し易いため、上限を５％とした。加工性や製造性を考慮すると、０．０１〜２％が望ましい。更に、溶接性を考慮すると０．０１〜１．５％が望ましい。 Al is an element that is added as a deoxidizing element and also improves oxidation resistance. Further, as a solid solution strengthening element, the creep deformation resistance in a temperature range of about 700 ° C. is improved. Therefore, 0.01% or more is added. On the other hand, the upper limit was set to 5% because the processability and toughness were significantly deteriorated by the addition of more than 5% and the small grain boundaries were likely to remain due to the delay in recrystallization. Considering workability and manufacturability, 0.01 to 2% is desirable. Further, considering weldability, 0.01 to 1.5% is desirable.
Ｂは、製品のプレス加工時の２次加工性を向上させる元素であるが、高温域ではＢの粒界偏析によってクリープ変形抵抗を向上させる元素でもある。また、ＴｉやＮｂ、Ｃｕ等との複合添加の場合、Ｌａｖｅｓ相やＣｕ析出物、ＦｅＴｉＰ等を微細析出させる効果がある。また、クリープ過程における析出粗大化抑制効果も作用する。これらの微細析出によって最小クリープ歪速度は低減することを本発明では見出した。これらの効果は粒界や析出物界面でのＢの偏析によって界面エネルギーが変化する作用と考えられる。そのため、０．０００２％以上添加する。一方、０．００５０％超の添加によってボライドと呼ばれるほう化物が生成し、粒界腐食感受性が著しく低下する他、再結晶遅延により小角粒界が残存し易いため上限を０．００５０％とした。製造性や溶接性、加工性等を考慮すると、０．０００４〜０．００１０％が望ましい。 B is an element that improves the secondary workability during press working of the product, but is also an element that improves creep deformation resistance by segregation of B grain boundaries in the high temperature range. Further, in the case of composite addition with Ti, Nb, Cu and the like, there is an effect of finely precipitating the Laves phase, Cu precipitate, FeTiP and the like. In addition, the effect of suppressing precipitation coarsening in the creep process also acts. It has been found in the present invention that the minimum creep strain rate is reduced by these fine precipitations. These effects are considered to be the action of changing the interface energy due to the segregation of B at the grain boundaries and the interface of the precipitate. Therefore, 0.0002% or more is added. On the other hand, if more than 0.0050% is added, a boride called boride is formed, the intergranular corrosion sensitivity is remarkably lowered, and small angle grain boundaries are likely to remain due to the delay in recrystallization, so the upper limit is set to 0.0050%. Considering manufacturability, weldability, workability, etc., 0.0004 to 0.0010% is desirable.
Ｖは、微細な炭窒化物を形成し、析出強化作用が生じて高温強度、クリープ変形抵抗の向上に寄与する。また、本発明ではリン化物（ＦｅＴｉＰ）との複合析出によってクリープ歪が付与されている環境下で極めて微細なＶ析出物が生成し最小クリープ歪速度の低減に寄与することを見出した。そのため、０．０１％以上添加する。一方、１％超の添加によって加工性が低下する他、再結晶遅延により小角粒界が残存し易いため上限を１％とした。また、製造コストや製造性を考慮すると、０．１〜０．５％が望ましい。 V forms fine carbonitrides and has a precipitation strengthening action, which contributes to improvement of high temperature strength and creep deformation resistance. Further, in the present invention, it has been found that extremely fine V precipitates are generated in an environment where creep strain is applied by composite precipitation with a phosphide (FeTiP), which contributes to reduction of the minimum creep strain rate. Therefore, 0.01% or more is added. On the other hand, the upper limit was set to 1% because the processability was lowered by adding more than 1% and the small grain boundaries were likely to remain due to the delay in recrystallization. Further, considering the manufacturing cost and manufacturability, 0.1 to 0.5% is desirable.
ＴｉまたはＮｂは、Ｃ、Ｎ、Ｓと結合して耐食性、耐粒界腐食性、深絞り性の指標となるｒ値を向上させる元素である。Ｔｉ、Ｎｂは、固溶強化および析出物微細化強化による高温強度、クリープ特性向上に大きく寄与する。特に、本発明ではＢ添加されているため、Ｎｂ系析出物が微細に析出するため、クリープ速度の低減に極めて効果的である。また、ＴｉとＮｂを複合添加する場合、高温強度の向上、高温延性の向上が大きく、単独あるいは複合にてそれぞれ、０．０１〜０．８％添加する。０．８％超の添加によりクランプ製造時の割れが生じ易くなる他、伸び低下など低靭化する他、再結晶遅延により小角粒界が残存し、耐クリープ性が低下するため、上限を０．８％とした。粗大なＴｉ系析出物、Ｎｂ系析出物の抑制や耐酸化性を考慮すると、０．０５〜０．６％が望ましい。 Ti or Nb is an element that binds to C, N, and S to improve the r value, which is an index of corrosion resistance, intergranular corrosion resistance, and deep drawing property. Ti and Nb greatly contribute to the improvement of high temperature strength and creep characteristics by strengthening solid solution and strengthening precipitation miniaturization. In particular, since B is added in the present invention, Nb-based precipitates are finely precipitated, which is extremely effective in reducing the creep rate. Further, when Ti and Nb are added in combination, the improvement in high temperature strength and the improvement in high temperature ductility are large, and 0.01 to 0.8% of each is added alone or in combination. Addition of more than 0.8% makes it easier for cracks to occur during clamp manufacturing, lowers the toughness such as elongation reduction, and small angle grain boundaries remain due to recrystallization delay, reducing creep resistance, so the upper limit is 0. It was set to 8.8%. Considering the suppression of coarse Ti-based precipitates and Nb-based precipitates and oxidation resistance, 0.05 to 0.6% is desirable.
Ｃｕは、７００℃程度の温度域においてε−Ｃｕとして析出し、高温強化によってクリープ歪速度の低減に寄与する。また、本発明では、ＢやＶと複合添加されることでε−Ｃｕが結晶粒内に均一析出し、クリープ歪速度低減に有効に作用することを見出し、０．０１％以上添加する。通常のＣｕ添加では結晶粒界に析出し、早期に粗大化するため強化能はクリープ初期に限定されるが、粒内均一析出させることで、粗大化も抑えられ、転位の移動を効果的に抑制する作用が得られる。Ｂとの複合添加ではＢの粒界偏析によって粒界へのＣｕ析出が抑制されると考えられる。また、Ｖとの複合添加では粒内に析出した微細なＶＣやＶＮがε−Ｃｕの析出核になるとともに、Ｃｕの拡散を抑制し、ε−Ｃｕの成長を阻害すると考えられる。この効果は０．０１％以上で発現するが、３％超の添加により著しく硬質化し、製品板の常温延性や製造時の靭性が得られない他、再結晶遅延により小角粒界が残存し易いため、０．０１〜３％を添加範囲とする。また、耐食性や成形性を考慮すると、０．３〜１．５％が望ましい。 Cu precipitates as ε-Cu in a temperature range of about 700 ° C., and contributes to a reduction in creep strain rate by strengthening at a high temperature. Further, in the present invention, it has been found that ε-Cu is uniformly precipitated in the crystal grains when combined with B and V, and effectively acts to reduce the creep strain rate, and 0.01% or more is added. With normal Cu addition, it precipitates at the grain boundaries and coarsens at an early stage, so the strengthening ability is limited to the initial stage of creep. However, by uniformly precipitating within the grains, coarsening is suppressed and dislocation movement is effective. An inhibitory effect can be obtained. It is considered that the composite addition with B suppresses Cu precipitation at the grain boundaries due to the segregation of B at the grain boundaries. Further, it is considered that in the combined addition with V, fine VCs and VNs precipitated in the grains become precipitation nuclei of ε-Cu, suppress the diffusion of Cu, and inhibit the growth of ε-Cu. This effect is exhibited at 0.01% or more, but it is remarkably hardened by addition of more than 3%, and the ductility at room temperature and toughness during manufacturing cannot be obtained, and small grain boundaries are likely to remain due to the delay in recrystallization. Therefore, the addition range is 0.01 to 3%. Further, considering corrosion resistance and moldability, 0.3 to 1.5% is desirable.
Ｍｏは、耐食性を向上させるとともに、高温酸化を抑制したり、固溶強化による高温強度向上に対して有効である。しかしながら、高価であるとともに、常温における均一伸びを低下させる。また、過度な添加はＬａｖｅｓ相の粗大析出を促進し、中温域における析出強化能を低下させる。特にＮｂ−Ｃｕ−Ｂ複合添加鋼においては、Ｃｕ添加およびＬａｖｅｓ相の微細析出強化が効果的に得られ、クリープ歪速度の低減に大きく寄与するため、０．０１％以上の添加とする。３％超の過度な添加はＬａｖｅｓ相の粗大化を促進して高温強度には寄与せず、かつコスト増になる他、再結晶遅延により小角粒界が残存し易いことから、上限を３％とした。更に、製造性、コストおよび９００℃のような高温域での強度安定性を考慮すると、０．２〜２％が望ましい。 Mo is effective for improving corrosion resistance, suppressing high-temperature oxidation, and improving high-temperature strength by strengthening solid solution. However, it is expensive and reduces uniform elongation at room temperature. In addition, excessive addition promotes coarse precipitation of the Laves phase and reduces the ability to enhance precipitation in the medium temperature range. In particular, in the Nb-Cu-B composite-added steel, Cu addition and fine precipitation strengthening of the Laves phase can be effectively obtained, which greatly contributes to the reduction of creep strain rate. Therefore, the addition is 0.01% or more. Excessive addition of more than 3% promotes coarsening of the Laves phase, does not contribute to high temperature strength, increases cost, and small grain boundaries tend to remain due to recrystallization delay, so the upper limit is 3%. And said. Further, considering the manufacturability, cost and strength stability in a high temperature region such as 900 ° C., 0.2 to 2% is desirable.
Ｎｉは、高価な元素であるため、添加しない方が望ましいが、０．０１％以上の添加によってクリープ変形抵抗や耐食性を向上させるため添加しても構わない。１％超の添加は極度に硬質化する他コスト高になる他、再結晶遅延により小角粒界が残存し易いため、上限を１％とする。更に、精錬コストや製造性を考慮すると、０．０５〜０．５％が望ましい。 Since Ni is an expensive element, it is desirable not to add it, but it may be added in order to improve creep deformation resistance and corrosion resistance by adding 0.01% or more. If the addition exceeds 1%, the upper limit is set to 1% because the addition is extremely hard and the cost is high, and small grain boundaries are likely to remain due to the delay in recrystallization. Further, considering the refining cost and manufacturability, 0.05 to 0.5% is desirable.
Ｗは、Ｍｏと同様な効果を有し、高温特性を向上させる元素であるため、必要に応じて０．１％以上添加しても良いが、３％超では再結晶遅延により小角粒界が残存し易くなるため、上限を３％とする。しかしながら、コストや耐酸化性等を考慮すると、０．５〜２．８％が望ましい。 Since W is an element that has the same effect as Mo and improves high temperature characteristics, 0.1% or more may be added if necessary, but if it exceeds 3%, small grain boundaries may occur due to recrystallization delay. The upper limit is set to 3% because it is easy to remain. However, considering cost, oxidation resistance, etc., 0.5 to 2.8% is desirable.
Ｍｇは、脱酸元素として必要に応じて添加させる場合がある他、スラブの組織を微細化させ、成形性向上に寄与する元素である。また、Ｍｇ酸化物はＴｉ（Ｃ、Ｎ）やＮｂ（Ｃ、Ｎ）等の炭窒化物の析出サイトになり、これらを微細分散析出させる効果がある。この作用は０．０００２％以上で発現し、靭性向上に寄与するため下限を０．０００２％とした。但し、過度な添加は、耐クリープ性、溶接性や耐食性の劣化につながるため、上限を０．０１％とした。精錬コストを考慮すると、０．０００３〜０．００１０％が望ましい。 Mg may be added as a deoxidizing element as needed, and is an element that refines the structure of the slab and contributes to the improvement of moldability. Further, the Mg oxide becomes a precipitation site of carbonitrides such as Ti (C, N) and Nb (C, N), and has an effect of finely dispersing and precipitating these. This action is expressed at 0.0002% or more, and the lower limit is set to 0.0002% because it contributes to the improvement of toughness. However, since excessive addition leads to deterioration of creep resistance, weldability and corrosion resistance, the upper limit is set to 0.01%. Considering the refining cost, 0.0003 to 0.0010% is desirable.
ＳｎやＳｂは、耐食性と高温強度の向上に寄与するため、必要に応じてそれぞれ０．０１％以上添加する。０．５％超の添加により鋼板製造時のスラブ割れや延性低下が過度に生じる場合がある他、再結晶遅延により小角粒界が残存し易いためそれぞれ上限を０．５％とする。更に、精錬コストや製造性を考慮すると、０．０１〜０．１５％が望ましい。 Sn and Sb are added in an amount of 0.01% or more as necessary in order to contribute to the improvement of corrosion resistance and high temperature strength. Addition of more than 0.5% may cause excessive slab cracking and ductility reduction during steel sheet production, and small angle grain boundaries are likely to remain due to recrystallization delay, so the upper limit is set to 0.5% for each. Further, considering the refining cost and manufacturability, 0.01 to 0.15% is desirable.
Ｚｒ、ＴａおよびＨｆは、ＣやＮと結合して靭性の向上に寄与するため必要に応じてそれぞれ０．０１％以上添加する。但し、０．３％超の添加によりコスト増になる他、製造性を著しく劣化させる他、再結晶遅延により小角粒界が残存し易いため、上限をそれぞれ０．３％とする。更に、精錬コストや製造性を考慮すると、０．０１〜０．０８％が望ましい。 Zr, Ta and Hf are added in an amount of 0.01% or more as necessary because they bind to C and N and contribute to the improvement of toughness. However, since the addition of more than 0.3% increases the cost, significantly deteriorates the manufacturability, and the small grain boundaries tend to remain due to the delay in recrystallization, the upper limit is set to 0.3% for each. Further, considering the refining cost and manufacturability, 0.01 to 0.08% is desirable.
Ｃｏは、高温強度の向上に寄与するため、必要に応じて０．０１％以上添加する。０．３％超の添加により靭性劣化につながる他、再結晶遅延により小角粒界が残存し易いため、上限を０．３％とする。更に、精錬コストや製造性を考慮すると、０．０１〜０．１％が望ましい。 Co is added in an amount of 0.01% or more as necessary in order to contribute to the improvement of high temperature strength. The upper limit is set to 0.3% because addition of more than 0.3% leads to deterioration of toughness and small angle grain boundaries are likely to remain due to delayed recrystallization. Further, considering the refining cost and manufacturability, 0.01 to 0.1% is desirable.
Ｃａは、脱硫のために添加される場合があり、この効果は０．０００１％以上で発現することから下限を０．０００１％とした。しかしながら、０．０１％超の添加により粗大なＣａＳが生成し、靭性や耐食性を劣化させるため、上限を０．０１％とした。更に、精錬コストや製造性を考慮すると、０．０００３〜０．００２０％が望ましい。 Ca may be added for desulfurization, and since this effect is exhibited at 0.0001% or more, the lower limit is set to 0.0001%. However, since coarse CaS is generated by addition of more than 0.01% and the toughness and corrosion resistance are deteriorated, the upper limit is set to 0.01%. Further, considering the refining cost and manufacturability, 0.0003 to 0.0020% is desirable.
ＲＥＭは、種々の析出物の微細化による靭性向上や耐酸化性の向上の観点から必要に応じて添加される場合があり、この効果は０．００１％以上で発現することから下限を０．００１％とした。しかしながら、０．２％超の添加により鋳造性が著しく悪くなる他、延性の低下をもたらすことから上限を０．２％とした。更に、精錬コストや製造性を考慮すると、０．００１〜０．０５％が望ましい。ＲＥＭ（希土類元素）は、一般的な定義に従い、スカンジウム（Ｓｃ）、イットリウム（Ｙ）の２元素と、ランタン（Ｌａ）からルテチウム（Ｌｕ）までの１５元素（ランタノイド）の総称を指す。単独で添加してもよいし、混合物であってもよい。 REM may be added as needed from the viewpoint of improving toughness and oxidation resistance by refining various precipitates, and since this effect is exhibited at 0.001% or more, the lower limit is set to 0. It was set to 001%. However, the upper limit is set to 0.2% because the addition of more than 0.2% significantly deteriorates the castability and lowers the ductility. Further, considering the refining cost and manufacturability, 0.001 to 0.05% is desirable. REM (rare earth element) is a general term for two elements, scandium (Sc) and yttrium (Y), and 15 elements (lanthanoids) from lanthanum (La) to lutetium (Lu), according to a general definition. It may be added alone or as a mixture.
Ｇａは、耐食性向上や水素脆化抑制のため、０．３％以下で添加してもよい。硫化物や水素化物形成の観点から下限は０．０００２％とする。更に、製造性やコストの観点ならびに、延性や靭性の観点から０．００２０％以下が好ましい。 Ga may be added in an amount of 0.3% or less in order to improve corrosion resistance and suppress hydrogen embrittlement. From the viewpoint of sulfide and hydride formation, the lower limit is 0.0002%. Further, 0.0020% or less is preferable from the viewpoint of manufacturability and cost, as well as ductility and toughness.
その他の成分について本発明では特に規定するものではないが、本発明においては、Ｂｉ等を必要に応じて、０．００１〜０．１％添加してもよい。なお、Ａｓ、Ｐｂ等の一般的な有害な元素や不純物元素はできるだけ低減することが好ましい。 Other components are not particularly specified in the present invention, but in the present invention, 0.001 to 0.1% of Bi or the like may be added as needed. It is preferable to reduce general harmful elements such as As and Pb and impurity elements as much as possible.
次に本発明の合金組織について述べる。 Next, the alloy structure of the present invention will be described.
合金組織は、結晶方位が２°以上異なる境界を粒界として定義した際に、前記全粒界長さに対する、結晶方位差１５°未満の小角粒界長さの比率を、結晶方位差１５°未満の小角粒界の比率と定義する。この結晶方位差１５°未満の小角粒界の比率が１５％以下である必要がある。１５％を超えると、７００℃で３５ＭＰａ負荷した際の最小クリープ歪速度が増大する。 In the alloy structure, when boundaries with different crystal orientations of 2 ° or more are defined as grain boundaries, the ratio of the small angle grain boundary lengths with a crystal orientation difference of less than 15 ° to the total grain boundary length is defined as the crystal orientation difference of 15 °. Defined as the ratio of small grain boundaries less than. The ratio of small grain boundaries with a crystal orientation difference of less than 15 ° needs to be 15% or less. If it exceeds 15%, the minimum creep strain rate when a load of 35 MPa is applied at 700 ° C. increases.
本発明は、耐熱部材締結部品に用いることに限定されたフェライト系ステンレス鋼板である。本発明にいう、耐熱部材とは、少なくとも７００℃以上、１ｈｒ以上はさらされても必要な強度を維持する部材であり、典型的には、熱機関、燃焼排気部材等として用いられる部材をいう。また、本発明にいう、締結部品とは、締結する対象である耐熱部材同士を複数、挟み込むか、締め付けることにより接続する部材である。すなわち、締結部品と耐熱部材を溶接接合するものや、締結部品と耐熱部材にネジ穴をあけて、双方をネジ止めするものは対象外である。一方で、締結部品側のみに締め上げ用の溝やネジ穴を形成し、締結部品の各部同士をネジ止め、ネジ締めする部材は本発明の対象である。締結部品として、典型的には、クランプが挙げられ、その中でも円形クランプに用いるのが最も好ましい。円形クランプは、管同士を接続、締めつけるものであり、ここでいう円形には、側面の断面形状が、略コの字型、略Ｃの字型も含まれる。 The present invention is a ferritic stainless steel sheet limited to use for heat-resistant member fastening parts. The heat-resistant member referred to in the present invention is a member that maintains the required strength even when exposed to at least 700 ° C. or higher and 1 hr or higher, and typically refers to a member used as a heat engine, a combustion exhaust member, or the like. .. Further, the fastening component referred to in the present invention is a member that connects a plurality of heat-resistant members to be fastened by sandwiching or tightening them. That is, the ones in which the fastening parts and the heat-resistant member are welded together and the ones in which the fastening parts and the heat-resistant member are screwed together are not covered. On the other hand, a member in which a groove or a screw hole for tightening is formed only on the fastening part side, and each part of the fastening part is screwed and screwed is an object of the present invention. Clamps are typically used as fastening parts, and most preferably, they are used for circular clamps. The circular clamp connects and tightens pipes to each other, and the circular shape here includes a substantially U-shaped cross section and a substantially C-shaped cross section.
本発明のフェライト系ステンレス鋼板は、延性に優れていることから、これら複雑形状の耐熱部材締結部品を形成することが容易である。また、本発明のフェライト系ステンレス鋼板により、耐熱部材締結部品を形成し、この耐熱部材締結部品により、耐熱部材を締め付けた際にも、７００℃で３５ＭＰａ負荷した際の最小クリープ歪速度が低いため、高温環境下で使用中にもゆるみが生じることがない。
なお、本発明において、耐熱部材締結部品を形成するとは、本発明のフェライト系ステンレス鋼板の合金組織を維持したまま塑性加工、あるいは部分的に切削等を施して目的の耐熱部材締結部品の形状とすることである。
本発明の耐熱部材締結部品用フェライト系ステンレス鋼板を使用することにより耐熱部材締結部品とすることができる。上記「耐熱部材締結部品用フェライト系ステンレス鋼板を使用する」耐熱部材締結部品とは、耐熱部材締結部品用フェライト系ステンレス鋼板を材質とする耐熱部材締結部品を意味する。そしてこの耐熱部材締結部品は、成形や切削等により所定の締結部品形状とされたものであり、高温におけるクリープ速度が低いため、耐熱性部品同士を締結して接続した際に、高温となっても接続部の隙間を生じない。
特に、耐熱部材締結部品を円状クランプとして、管状部材同士を締結して接続した際に、管状部材のガス漏れを防止あるいは低減できる。
Since the ferrite-based stainless steel sheet of the present invention has excellent ductility, it is easy to form these heat-resistant member fastening parts having complicated shapes. Further, since the heat-resistant member fastening component is formed from the ferritic stainless steel plate of the present invention and the heat-resistant member fastening component is used to tighten the heat-resistant member, the minimum creep strain rate is low when a load of 35 MPa is applied at 700 ° C. , No looseness occurs even during use in a high temperature environment.
In the present invention, forming a heat-resistant member fastening part means that the shape of the heat-resistant member fastening part is defined by plastic working or partial cutting while maintaining the alloy structure of the ferritic stainless steel plate of the present invention. It is to be.
By using the ferritic stainless steel plate for the heat-resistant member fastening part of the present invention, the heat-resistant member fastening part can be obtained. The above-mentioned "using a ferritic stainless steel plate for a heat-resistant member fastening part" means a heat-resistant member fastening part made of a ferritic stainless steel plate for a heat-resistant member fastening part. The heat-resistant member fastening parts have a predetermined fastening part shape by molding, cutting, etc., and have a low creep speed at high temperatures. Therefore, when the heat-resistant parts are fastened and connected to each other, the temperature becomes high. Does not create a gap at the connection part.
In particular, when the heat-resistant member fastening parts are used as circular clamps and the tubular members are fastened and connected to each other, gas leakage of the tubular members can be prevented or reduced.
耐熱部材締結部品の素材となる本発明のフェライト系ステンレス鋼板の製造方法については、上記に規定した鋼成分を有する冷延板に対して９００〜１０７０℃で焼鈍することによって本発明に規定する再結晶組織が得られる。焼鈍時の小角粒界の消失に対しては、熱処理時間は長い方が有効であるため、保持時間を３秒以上にすることが望ましい。クランプ部品への成形性には鋼板素材の伸びが影響するので、鋼板の破断伸びが３０％以上とすることが望ましく、本発明の成分を有する素材を用い、鋳造、熱延、焼鈍、冷延等の一般的な製造工程における最適条件を選択すれば良い。製品板厚についても、要求部材厚に応じて選択すれば良い。 The method for producing a ferritic stainless steel sheet of the present invention, which is a material for fastening parts for heat-resistant members, is recrystallized according to the present invention by annealing a cold-rolled sheet having the steel component specified above at 900 to 1070 ° C. A crystal structure is obtained. A longer heat treatment time is more effective for the disappearance of small grain boundaries during annealing, so it is desirable to set the holding time to 3 seconds or longer. Since the elongation of the steel sheet material affects the formability to the clamp parts, it is desirable that the elongation at break of the steel sheet is 30% or more, and the material having the component of the present invention is used for casting, hot rolling, annealing, and cold rolling. The optimum conditions in a general manufacturing process such as, etc. may be selected. The product plate thickness may also be selected according to the required member thickness.
表１、２に示した成分組成（数値は質量％）の鋼を溶製してスラブに鋳造し、スラブを熱間圧延して５ｍｍ厚の熱延コイルとした。その後、熱延コイルを焼鈍・酸洗を施し、２ｍｍ厚まで冷間圧延し、焼鈍・酸洗を施して製品板とした。冷延板の焼鈍温度は、結晶方位差１５°未満の小角粒界の比率を１５％以下にするために、本発明では、９００〜１０７０℃とした。 The steels having the component compositions (numerical value: mass%) shown in Tables 1 and 2 were melted and cast into a slab, and the slab was hot-rolled to obtain a hot-rolled coil having a thickness of 5 mm. Then, the hot-rolled coil was annealed and pickled, cold-rolled to a thickness of 2 mm, and annealed and pickled to obtain a product plate. The annealing temperature of the cold rolled plate was set to 900 to 1070 ° C. in the present invention in order to reduce the ratio of small angle grain boundaries having a crystal orientation difference of less than 15 ° to 15% or less.
このようにして得られた製品板から、高温クリープ試験片を採取し、７００℃で３５ＭＰａを負荷するクリープ試験を行い、最小クリープ歪速度を求めた。また、クランプの形状に成形するためには、伸びが３０％以上必要なため、常温での引張試験（ＪＩＳ１３号Ｂ試験片）を行い、破断伸びを調べた。 A high-temperature creep test piece was collected from the product plate thus obtained, and a creep test in which 35 MPa was applied at 700 ° C. was performed to determine the minimum creep strain rate. In addition, since elongation of 30% or more is required to form the shape of the clamp, a tensile test (JIS No. 13B test piece) at room temperature was performed to examine the elongation at break.
合金組織の解析については、日本電子製、走査型電子顕微鏡を用い、ＥＢＳＤにより行った。測定は、上記冷延板の３００×３００μｍの領域に対して、１μｍのピッチで方位を測定し、隣接点と２°以上の方位差が生じた場合を粒界と定義した。更に、１５°以上方位差がある場合を大角粒界、１５°未満を小角粒界と定義した。結晶方位解析ソフト、ＴＳＬ製ＯＩＭ（Ｖｅｒ．７）により、測定領域において全粒界長さが算出し、小角粒界の比率を求めた。
また、測定部位は板厚の１／４〜１／２部位で行った。
The alloy structure was analyzed by EBSD using a scanning electron microscope manufactured by JEOL Ltd. In the measurement, the orientation was measured at a pitch of 1 μm with respect to the region of 300 × 300 μm of the cold-rolled plate, and the case where an orientation difference of 2 ° or more from the adjacent point occurred was defined as a grain boundary. Further, a case where there is an orientation difference of 15 ° or more is defined as a large angle grain boundary, and a case where there is an orientation difference of less than 15 ° is defined as a small angle grain boundary. The total grain boundary length was calculated in the measurement region by the crystal orientation analysis software, OIM (Ver.7) manufactured by TSL, and the ratio of the small angle grain boundaries was obtained.
The measurement site was 1/4 to 1/2 of the plate thickness.
更に、上記の冷延板から、絞りおよび曲げ成形により、直径１００ｍｍの円状クランプを製造し、クランプ作製後にターボチャージャーに取り付け、７００℃で、１００ｈｒの耐久試験を実施し、クランプの不具合を調べ合否判定した。この際のクランプの材料温度は、最高温度７００℃であった。７００℃、３５ＭＰａで最小クリープ歪速度が０．０１％／ｈｒであり、単純には１ｈｒで０．０１％変形する、φ１００ｍｍ（外周３１４ｍｍ）の円状クランプの場合、７００℃、３５ＭＰａの負荷により、１ｈｒで外周約０．０３ｍｍ広がるが、クランプの不具合とは、緩みによる排気ガスの漏れや酸化による損傷である。なお、クランプを取り付けた際、締め付け応力は特に付与していない。 Furthermore, a circular clamp with a diameter of 100 mm is manufactured from the above cold-rolled plate by drawing and bending, attached to a turbocharger after the clamp is manufactured, and a durability test of 100 hr is carried out at 700 ° C. to investigate the defect of the clamp. A pass / fail judgment was made. The material temperature of the clamp at this time was a maximum temperature of 700 ° C. In the case of a circular clamp with a diameter of 100 mm (outer circumference 314 mm), which has a minimum creep strain rate of 0.01% / hr at 700 ° C and 35 MPa and is simply deformed by 0.01% at 1 hr, a load of 700 ° C and 35 MPa causes it to deform. The outer circumference spreads by about 0.03 mm in 1 hr, but the malfunction of the clamp is the leakage of exhaust gas due to loosening and the damage due to oxidation. When the clamp is attached, no tightening stress is particularly applied.
各々の実施例の製造のための焼鈍条件と測定結果について、表３、４に示した。比較例１〜４、６〜１５、１７〜２３、２５、２６は、本発明の成分範囲を外れているため、本発明の小角粒界の比率を満たしていない。その結果、最小クリープ歪速度が０．０１％／ｈｒを超え耐熱性が不十分であった。比較例５、１６、２４、２７は、本発明の成分範囲を外れているため、最小クリープ歪速度が０．０１％／ｈｒを超え耐熱性が不十分であった。比較例２８は焼鈍温度が低すぎ、比較例２９は焼鈍時間が短すぎるため、本発明の小角粒界の比率を満たしていない。その結果、７００℃で３５ＭＰａ負荷した際の最小クリープ歪速度が０．０１％／ｈｒ超と耐熱性が不十分であった。また、比較例２、８、９、１１、１２、１４、１５、１７〜２２、２５、２６、２８では伸び不足によりクランプ形状への形成不可であった。比較例１、３〜７、１０、１３、１５、１６、２３、２４、２７〜２９は、クランプを製造して取り付けた際にも、ガス漏れ等の不具合を生じた。よって、排気部品の締結部品としては不適であることがわかる。 The annealing conditions and measurement results for the production of each example are shown in Tables 3 and 4. Comparative Examples 1 to 4, 6 to 15, 17 to 23, 25, and 26 do not satisfy the ratio of the small grain boundaries of the present invention because they are outside the component range of the present invention. As a result, the minimum creep strain rate exceeded 0.01% / hr and the heat resistance was insufficient. Since Comparative Examples 5, 16, 24, and 27 were out of the component range of the present invention, the minimum creep strain rate exceeded 0.01% / hr and the heat resistance was insufficient. In Comparative Example 28, the annealing temperature is too low, and in Comparative Example 29, the annealing time is too short, so that the ratio of the small grain boundaries of the present invention is not satisfied. As a result, the minimum creep strain rate when a load of 35 MPa was applied at 700 ° C. was more than 0.01% / hr, and the heat resistance was insufficient. Further, in Comparative Examples 2, 8, 9, 11, 12, 14, 15, 17 to 22, 25, 26, and 28, the clamp shape could not be formed due to insufficient elongation. In Comparative Examples 1, 3 to 7, 10, 13, 15, 16, 23, 24, and 27 to 29, problems such as gas leakage occurred even when the clamps were manufactured and attached. Therefore, it can be seen that it is not suitable as a fastening part for exhaust parts.
一方、本発明１〜３２は、適切な成分組成を満たし、適切な小角粒界の比率を満たした。その結果、３０％以上の十分な常温延性を有し、７００℃で３５ＭＰａ負荷した際の最小クリープ歪速度が０．０１％／ｈｒ以下と耐熱性が良好であった。また、本発明１〜３２は、クランプを製造して取り付けた際にも、ガス漏れ等の不具合は発生しなかった。この結果より、本発明例は、排気部品の締結部品としては好適であることがわかる。 On the other hand, the present inventions 1 to 32 satisfied an appropriate component composition and an appropriate ratio of small grain boundaries. As a result, it had sufficient room temperature ductility of 30% or more, and had good heat resistance with a minimum creep strain rate of 0.01% / hr or less when a load of 35 MPa was applied at 700 ° C. Further, in the present inventions 1 to 32, problems such as gas leakage did not occur even when the clamp was manufactured and attached. From this result, it can be seen that the example of the present invention is suitable as a fastening component for an exhaust component.
以上の説明から明らかなように、本発明のステンレス鋼板を用いた締結部品によりターボチャージャー等の排気部品を締結することにより、信頼性の確保と低コスト化に寄与するため、社会的貢献度を高めることが可能となり、産業上極めて有益である。 As is clear from the above explanation, by fastening the exhaust parts such as the turbocharger with the fastening parts using the stainless steel plate of the present invention, the reliability is ensured and the cost is reduced. It is possible to increase it, which is extremely beneficial in industry.
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