JP2010261074A - Ferritic stainless steel wire for boss-material excellent in high temperature durability - Google Patents
Ferritic stainless steel wire for boss-material excellent in high temperature durability Download PDFInfo
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- 239000000463 material Substances 0.000 title claims abstract description 39
- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 32
- 229910000831 Steel Inorganic materials 0.000 claims description 15
- 239000010959 steel Substances 0.000 claims description 15
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 5
- 239000002244 precipitate Substances 0.000 claims description 5
- 239000012535 impurity Substances 0.000 claims description 3
- 229910052742 iron Inorganic materials 0.000 claims description 2
- 230000007797 corrosion Effects 0.000 abstract description 46
- 238000005260 corrosion Methods 0.000 abstract description 46
- 238000001556 precipitation Methods 0.000 abstract description 15
- 238000003466 welding Methods 0.000 abstract description 10
- 229910052804 chromium Inorganic materials 0.000 abstract description 6
- 229910052758 niobium Inorganic materials 0.000 abstract description 6
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 abstract description 3
- 229910052750 molybdenum Inorganic materials 0.000 abstract description 2
- 230000001276 controlling effect Effects 0.000 abstract 1
- 230000001105 regulatory effect Effects 0.000 abstract 1
- 239000011651 chromium Substances 0.000 description 36
- 230000000694 effects Effects 0.000 description 11
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- 239000010410 layer Substances 0.000 description 10
- 238000007254 oxidation reaction Methods 0.000 description 10
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- 238000012360 testing method Methods 0.000 description 9
- 230000002950 deficient Effects 0.000 description 8
- 230000015572 biosynthetic process Effects 0.000 description 7
- 238000010273 cold forging Methods 0.000 description 7
- 229910045601 alloy Inorganic materials 0.000 description 5
- 239000000956 alloy Substances 0.000 description 5
- 229910001566 austenite Inorganic materials 0.000 description 5
- 239000010949 copper Substances 0.000 description 5
- 230000000573 anti-seizure effect Effects 0.000 description 4
- 229910000365 copper sulfate Inorganic materials 0.000 description 4
- ARUVKPQLZAKDPS-UHFFFAOYSA-L copper(II) sulfate Chemical compound [Cu+2].[O-][S+2]([O-])([O-])[O-] ARUVKPQLZAKDPS-UHFFFAOYSA-L 0.000 description 4
- 239000011159 matrix material Substances 0.000 description 4
- 150000001247 metal acetylides Chemical class 0.000 description 4
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- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 238000000137 annealing Methods 0.000 description 3
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 150000004767 nitrides Chemical class 0.000 description 3
- 239000006104 solid solution Substances 0.000 description 3
- 239000010935 stainless steel Substances 0.000 description 3
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 2
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- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- OFOBLEOULBTSOW-UHFFFAOYSA-N Propanedioic acid Natural products OC(=O)CC(O)=O OFOBLEOULBTSOW-UHFFFAOYSA-N 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 1
- CKUAXEQHGKSLHN-UHFFFAOYSA-N [C].[N] Chemical compound [C].[N] CKUAXEQHGKSLHN-UHFFFAOYSA-N 0.000 description 1
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- 238000009529 body temperature measurement Methods 0.000 description 1
- GVEHJMMRQRRJPM-UHFFFAOYSA-N chromium(2+);methanidylidynechromium Chemical compound [Cr+2].[Cr]#[C-].[Cr]#[C-] GVEHJMMRQRRJPM-UHFFFAOYSA-N 0.000 description 1
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- VZCYOOQTPOCHFL-UPHRSURJSA-N maleic acid Chemical compound OC(=O)\C=C/C(O)=O VZCYOOQTPOCHFL-UPHRSURJSA-N 0.000 description 1
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- 229910000734 martensite Inorganic materials 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 229910017464 nitrogen compound Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
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- 239000013535 sea water Substances 0.000 description 1
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- 238000010998 test method Methods 0.000 description 1
- QEMXHQIAXOOASZ-UHFFFAOYSA-N tetramethylammonium Chemical compound C[N+](C)(C)C QEMXHQIAXOOASZ-UHFFFAOYSA-N 0.000 description 1
- 229910003470 tongbaite Inorganic materials 0.000 description 1
- VZCYOOQTPOCHFL-UHFFFAOYSA-N trans-butenedioic acid Natural products OC(=O)C=CC(O)=O VZCYOOQTPOCHFL-UHFFFAOYSA-N 0.000 description 1
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Abstract
Description
本発明は、高温における耐久性に優れた円筒形部材（ボス材）用ステンレス鋼線に関するものである。ここで耐久性とは、焼付き防止性能、軟化抵抗、耐高温酸化性、耐食性（特に耐粒界腐食性）を意味するものである。 The present invention relates to a stainless steel wire for a cylindrical member (boss material) having excellent durability at high temperatures. Here, durability means anti-seizure performance, softening resistance, high-temperature oxidation resistance, and corrosion resistance (particularly intergranular corrosion resistance).
自動車の排ガス規制や熱効率向上のため、排気系部品にガス測定や温度測定用のセンサー取付け用の円筒形部材（以下、ボス材という）が多く使用される。ボス材の代表的な形状を図１に示す。 In order to control automobile exhaust gas and improve thermal efficiency, cylindrical members (hereinafter referred to as boss materials) for mounting sensors for gas measurement and temperature measurement are often used for exhaust system parts. A typical shape of the boss material is shown in FIG.
このボス材には耐熱性や耐食性が要求されることからステンレス鋼が使用される。 Since this boss material requires heat resistance and corrosion resistance, stainless steel is used.
ボス材は、鋼線を冷間鍛造にて成形し、更に各種センサー取付け用に冷間にて雌ねじ加工して製造された後、プロジェクション溶接、隅肉溶接等によりエギゾーストパイプなどの本体に取り付けられる。 The boss material is manufactured by forming a steel wire by cold forging and processing it with a female thread in the cold for mounting various sensors. Then, the boss material is attached to the body such as an exhaust pipe by projection welding, fillet welding, etc. .
従来 ボス材として十分な特性を有する材料として、Ｎｉを多く含有するオーステナイト系ステンレス鋼が耐熱性、耐食性の観点から選択されていた。 Conventionally, austenitic stainless steel containing a large amount of Ni has been selected as a material having sufficient characteristics as a boss material from the viewpoints of heat resistance and corrosion resistance.
しかしながら、オーステナイト系ステンレス鋼は熱膨張率が大きく高温での伸びが大きいことや自動車部品に対するさらなる経済性追及のため、Ｎｉを低減したフェライト系ステンレス鋼のボス材への適用が求められた。ステンレス鋼のボス材としては焼付きが起きないこと、使用環境にて十分な耐食性を有すること、冷間鍛造性に優れること、等が必要であり、そのためには、以下の課題を解決する必要があった。 However, since austenitic stainless steel has a high coefficient of thermal expansion and high elongation at high temperatures, and to pursue further economic efficiency for automobile parts, application to ferritic stainless steel with reduced Ni has been required. Stainless steel boss materials need to have no seizure, have sufficient corrosion resistance in the usage environment, and have excellent cold forgeability. To that end, it is necessary to solve the following problems: was there.
焼付きとは、「それまで安定した状態にあった摩擦面で潤滑膜の破れなどにより摩擦が大きくなり、面間に巨視的な凝着を生じ、すべらなくなる現象」（金属材料技術研究所編、図解 金属材料技術用語辞典−第２版−２０００年１月３０日、日刊工業新聞社発行、ｐ．４５３）のことであるが、ボス材は、その使用環境が高温であることから、長時間使用後にボスのねじ部に取り付けたセンサー部品とボスの焼付きが生じ、かじりついて取れなくなる不具合があった。 Seizure is a phenomenon in which friction is increased on a friction surface that has been stable until then due to the tearing of the lubricating film, causing macroscopic adhesion between the surfaces, and slipping. , Illustrated Metal Material Technical Glossary-Second Edition-January 30, 2000, published by Nikkan Kogyo Shimbun, p. 453). There was a problem that the sensor part attached to the screw part of the boss and the boss were seized after use for a long time and could not be removed due to galling.
また、フェライト系ステンレス鋼の溶接部には、粒界にクロム炭化物が生成しその近傍にクロム欠乏層が生成しやすく、海塩粒子や凍結防止剤等の塩分が付着する環境に晒された場合では、溶接部にクロム欠乏層を起点とした粒界腐食が発生しボス材が脱落する虞があった。 In addition, when chromium carbide is formed at the grain boundary in the ferritic stainless steel weld zone and a chromium-deficient layer is likely to be formed in the vicinity, it is exposed to an environment in which salt such as sea salt particles or antifreezing agents adheres. Then, there is a possibility that the boss material may fall off due to the occurrence of intergranular corrosion starting from the chromium-deficient layer in the weld.
本発明は、経済性を重視したボス材用として優れた特性を有するフェライト系ステンレス鋼線を提案するものである。 The present invention proposes a ferritic stainless steel wire having excellent characteristics as a boss material with an emphasis on economy.
従来技術として特許文献１には、Ｃｒ１８.０-２０%、Ｎｉ１０.０-１１.５%含有の酸素センサーボスが記載されている。しかしながら、特許文献１にはオーステナイト系ステンレス鋼が開示されているのみであり、フェライト系ステンレス鋼については開示されていない。
As a prior art,
自動車部品製造のさらなる経済性を追及するためにはＮｉを低減したフェライト系ステンレス鋼のボス材への適用が求められていた。そのためには、以下の３つの課題を解決する必要があった。 In order to pursue further economic efficiency in the production of automobile parts, application to a boss material of ferritic stainless steel with reduced Ni has been required. For that purpose, it was necessary to solve the following three problems.
ボス部品に加工するための冷間鍛造性を確保すること。 Ensure cold forgeability for processing into boss parts.
ボス材の使用環境は高温であり、ボス材のねじ部に取り付けた部品が長時間使用後にねじ部で焼付き、かじりついて取れなくなる不具合があり、それを防止するために焼付き防止性能を確保すること。 The use environment of the boss material is high temperature, and the parts attached to the screw part of the boss material are seized by the screw part after a long period of use, and there is a problem that it can not be picked up. To prevent it, secure anti-seizure performance. To do.
また、海水や凍結防止剤などが付着する塩化物イオンによる腐食性環境では、ボス材基底部と本体との溶接部に粒界腐食が発生しボス材が脱落する虞があり、それを防止するために溶接部の耐粒界腐食性を確保すること。 Also, in a corrosive environment due to chloride ions to which seawater or antifreezing agents adhere, there is a possibility that the boss material may fall off due to the occurrence of intergranular corrosion at the welded portion between the boss material base and the main body. Therefore, ensure the intergranular corrosion resistance of the weld.
そこで、従来フェライト系ステンレス鋼線において達成困難であった冷間鍛造加工性、焼付き防止性能、塩化物イオンに対する耐食性、特に溶接部の耐粒界腐食性を有するフェライト系ステンレス鋼線を提示することを課題とする。 Therefore, a ferritic stainless steel wire having cold forging workability, seizure prevention performance, corrosion resistance to chloride ions, especially intergranular corrosion resistance of welds, which has been difficult to achieve with conventional ferritic stainless steel wires, is presented. This is the issue.
発明者等は、上記のそれぞれの特性に対し、合金成分の役割や合金指標を見出し、これらを満足する合金成分にて製造すればボス材として好適なフェライト系ステンレス鋼線を得ることができることを見出した。 The inventors have found that the role of the alloy component and the alloy index for each of the above characteristics, and that it is possible to obtain a ferritic stainless steel wire suitable as a boss material if manufactured with an alloy component that satisfies these characteristics. I found it.
冷間鍛造加工性については、合金成分を規定することにより、焼付き防止性能や耐粒界腐食性にも関連して、十分な特性が得られることを見出した。 Regarding cold forging workability, it was found that sufficient characteristics can be obtained in relation to anti-seizure performance and intergranular corrosion resistance by defining the alloy components.
焼付き防止性能に関しては、種々の実験を重ねた結果、使用中にねじ部の軟化により焼付きが生じることから、ねじ部を軟化させないことが必要であり、そのためには、鋼材（ねじ部）の軟化抵抗や高温酸化性を確保する必要があることを知見し、そのためにＣｒ、Ｎｂ及びＭｏの含有量とＮｂ析出量を特定量確保することを規定した。 Regarding anti-seizure performance, as a result of various experiments, seizure occurs due to softening of the screw part during use. Therefore, it is necessary not to soften the screw part. To that end, steel (screw part) is required. It was found that it was necessary to ensure the softening resistance and high-temperature oxidization property, and for that purpose, it was stipulated that the Cr, Nb and Mo contents and the Nb precipitation amount should be secured.
また、溶接部の耐粒界腐食性に関しては、溶接時にＣｒ炭化物が粒界に析出して粒界に沿ったＣｒ欠乏層が形成されないように、Ｔｉ、Ｎｂを適量添加するが、更に鋼線の成分において（Ｔｉ＋Ｎｂ）／（Ｃ＋Ｎ）≧１０ を満足する範囲とすることによって、溶接部における粒界腐食の発生を抑制できることを見出した。具体的な解決手段は、下記のとおりである。
（１）質量％で、
Ｃ ：０.００１％以上０.０２％以下、
Ｓｉ：０.１％以上１.０％以下、
Ｍｎ：１.０％以下、
Ｐ：０.０４％以下、
Ｓ：０.０３％以下、
Ｃｒ：１５.０%以上２１.０％以下、
Ｎ：０.０２５％以下、を含有し、更に、
Ｎｂ：０.３０以上０.８０％以下、
Ｔｉ：０.５％以下、の１種以上を含有し、
残部は鉄および不可避的不純物からなり、
Ｃｒ+３Ｎｂ≧１７、および、（Ｎｂ＋Ｔｉ）／(Ｃ+Ｎ)≧１０を満足し、
鋼中の全Ｎｂ含有量の５０％〜８０％が析出物として存在していることを特徴とするボス材用フェライト系ステンレス鋼線。
（２）質量％で、更に、
Ｃｕ：０.２０%以上１.０%以下、
Ｎｉ：０.２０%以上１.０%以下、の１種以上を含有することを特徴とする（１）に記載のボス用フェライト系ステンレス鋼線。
（３）質量％で、更に
Ｍｏ：０．３％以上２．５％以下を含有し、
Ｃｒ+３（Ｍｏ+Ｎｂ）≧１７を満足することを特徴とする（１）または（２）に記載のボス材用フェライト系ステンレス鋼線。
（４）ビッカース硬さ（Ｈｖ１）が１４０以上２８０以下であることを特徴とする（１）乃至（３）のいずれか１項に記載のボス材用フェライト系ステンレス鋼線。
In addition, regarding the intergranular corrosion resistance of the welded portion, an appropriate amount of Ti and Nb is added so that Cr carbide precipitates at the grain boundary during welding and a Cr-deficient layer is not formed along the grain boundary. It was found that the occurrence of intergranular corrosion in the welded portion can be suppressed by making the component satisfying (Ti + Nb) / (C + N) ≧ 10. The specific solution is as follows.
(1) In mass%,
C: 0.001% or more and 0.02% or less,
Si: 0.1% or more and 1.0% or less,
Mn: 1.0% or less,
P: 0.04% or less,
S: 0.03% or less,
Cr: 15.0% to 21.0%,
N: 0.025% or less, and
Nb: 0.30 to 0.80%,
Containing one or more of Ti: 0.5% or less,
The balance consists of iron and inevitable impurities,
Cr + 3Nb ≧ 17 and (Nb + Ti) / (C + N) ≧ 10 are satisfied,
A ferritic stainless steel wire for a boss material, wherein 50% to 80% of the total Nb content in the steel is present as a precipitate.
(2) In mass%,
Cu: 0.20% to 1.0%,
Ni: The ferritic stainless steel wire for boss | hub as described in (1) characterized by including 1 or more types of 0.20% or more and 1.0% or less.
(3) By mass%, further containing Mo: 0.3% or more and 2.5% or less,
The ferritic stainless steel wire for a boss material according to (1) or (2), wherein Cr + 3 (Mo + Nb) ≧ 17 is satisfied.
(4) The ferritic stainless steel wire for a boss material according to any one of (1) to (3), wherein the Vickers hardness (Hv1) is 140 or more and 280 or less.
本発明によれば、高温耐久性に優れたボス材用ステンレス鋼線を得ることができる。この鋼線を用いたボス材は、ねじ部に取り付けた部品が焼付くことがなく、また粒界腐食に起因する脱落なども防止できるなど、産業上有用な著しい効果を奏する。 ADVANTAGE OF THE INVENTION According to this invention, the stainless steel wire for boss | hub materials excellent in high temperature durability can be obtained. The boss material using this steel wire has significant industrially useful effects such as the parts attached to the threaded portion are not seized and can be prevented from falling off due to intergranular corrosion.
以下、本発明について具体的に説明する。まず、本発明において、ステンレス鋼線の成分組成を上記の範囲に限定した理由について説明する。
＜Ｃ：０．００１％以上０．０２％以下＞
Ｃは、マトリックスのフェライト組織の強度を高め、更に、オーステナイト相および炭化物の生成元素である。オーステナイト相は、溶接後においてマルテンサイト組織を生じて強度を向上させ、また微細炭化物も強度の向上に寄与し、鋼線としての高温強度を確保する。しかしながら、 ０．０２％超ではＣｒ炭化物の粒界への析出によりその回りにＣｒ欠乏層が生成するようになる。腐食環境では、粒界に沿ったＣｒ欠乏層が溶解するので、いわゆる粒界腐食が発生する。従って、Ｃ量を ０．０２％以下の範囲に限定した。さらに粒界腐食を防止するには、Ｃ量は０．０１５％以下の範囲にすることが望ましい。
Hereinafter, the present invention will be specifically described. First, the reason why the component composition of the stainless steel wire is limited to the above range in the present invention will be described.
<C: 0.001% or more and 0.02% or less>
C increases the strength of the ferrite structure of the matrix, and is an austenite phase and carbide forming element. The austenite phase generates a martensite structure after welding to improve the strength, and fine carbides also contribute to the improvement of strength, ensuring high-temperature strength as a steel wire. However, if it exceeds 0.02%, a Cr-depleted layer will be formed around it due to the precipitation of Cr carbide at the grain boundaries. In a corrosive environment, so-called intergranular corrosion occurs because the Cr-depleted layer along the grain boundary dissolves. Therefore, the C content is limited to a range of 0.02% or less. Furthermore, in order to prevent intergranular corrosion, it is desirable that the C content be in the range of 0.015% or less.
また、０．００１％未満では鋼線のオーステナイト相や微細炭化物の生成量が少なすぎて強度が不足するため、０．００１％以上含有させる。
＜Ｓｉ：０．１％以上１．０％以下＞
Ｓｉは、脱酸剤として、またＳｉＯ２の酸化皮膜を形成して酸化の進行を抑制するので耐高温酸化性に有用な元素であるが、含有量が １．０％超になると硬くなり機械的性質が劣化する。従って、Ｓｉ量は １．０％以下とした。
Further, if it is less than 0.001%, the austenite phase of the steel wire and the amount of fine carbide produced are too small and the strength is insufficient, so 0.001% or more is contained.
<Si: 0.1% to 1.0%>
Si is a useful element for high-temperature oxidation resistance because it suppresses the progress of oxidation by forming an oxide film of SiO 2 as a deoxidizer, but it becomes hard when the content exceeds 1.0%. The physical properties deteriorate. Therefore, the Si content is set to 1.0% or less.
また、０．１％未満では脱酸効果が得られないため０．１%以上含有させる。
＜Ｍｎ:１．０％以下＞
ＭｎもＣと同様マトリックスのフェライト組織の強度を高め、更に、オーステナイト相生成元素であるが、オーステナイトＭｎ含有量が １．０％を超えると鋼中に残存する介在物が多くなり耐食性が劣化する。従って、Ｍｎ量は１．０％以下の範囲とした。
Further, if it is less than 0.1%, the deoxidation effect cannot be obtained, so 0.1% or more is contained.
<Mn: 1.0% or less>
Mn also increases the strength of the ferrite structure of the matrix like C, and is an austenite-forming element. However, if the austenite Mn content exceeds 1.0%, more inclusions remain in the steel and the corrosion resistance deteriorates. . Therefore, the amount of Mn was made into the range of 1.0% or less.
また、含有量が０．１％より少ないと鋼線の強度が低く、また、溶接後も強度不足となる。したがって０．１％以上含有することが望ましい。
＜Ｐ：０．０４％以下＞
Ｐは、靱性等の機械的性質を劣化させるのみならず、耐食性に対しても有害な元素であり、特にＰ含有量が０．０４％超になるとその悪影響が顕著になるので、Ｐ量は０．０４％以下とした。
＜Ｓ：０．０３％以下＞
Ｓは、Ｍｎと結合してＭｎＳを形成し、初期発銹の起点となる。またＳは、結晶粒界に偏析して粒界脆化を促進する有害元素でもあるので、極力低減することが好ましい。特にＳ含有量が０．０３％を超えるとその悪影響が顕著になるので、Ｓ量は０．０３％以下とした。
＜Ｃｒ：１５．０％以上２１．０％以下＞
Ｃｒは、本発明における耐食性発現成分として重要な元素である。本発明で対象にするボス材用鋼線は、高温耐久性及び耐食性に必要なＣｒ量として、少なくとも１５．０％が必要である。これは、１５．０％未満になると強固な不動態皮膜や高温酸化皮膜が生成され難くなるためである。一方、Ｃｒ濃度が２１．０％超になると、耐食性は良くなるものの、フェライト相の生成量が多くなって溶接部の靱性不足となることやコストアップに繋がる。従って、固溶Ｃｒ濃度は１５．０％以上２１．０％以下とした。
＜Ｎｂ:０．３０％以上０．８０％以下＞
Ｎｂは、本発明における高温強度、耐高温酸化性、耐粒界腐食性発現成分として重要な元素である。固溶したＮｂは強度を高め、高温強度の劣化を防止する。また、炭窒化物として析出したＮｂは再結晶の抑制に寄与し再結晶温度を高くするため軟化抵抗を増加させる。
On the other hand, if the content is less than 0.1%, the strength of the steel wire is low, and the strength is insufficient after welding. Therefore, it is desirable to contain 0.1% or more.
<P: 0.04% or less>
P is an element harmful not only to mechanical properties such as toughness but also to corrosion resistance. Particularly, when the P content exceeds 0.04%, its adverse effect becomes significant. It was set to 0.04% or less.
<S: 0.03% or less>
S combines with Mn to form MnS, which is the starting point for initial firing. S is also a harmful element that segregates at the grain boundaries and promotes embrittlement of the grain boundaries, so it is preferably reduced as much as possible. In particular, when the S content exceeds 0.03%, the adverse effect becomes remarkable, so the S content is set to 0.03% or less.
<Cr: 15.0% to 21.0%>
Cr is an important element as a corrosion resistance developing component in the present invention. The steel wire for a boss material to be used in the present invention requires at least 15.0% as the Cr amount necessary for high temperature durability and corrosion resistance. This is because when the content is less than 15.0%, it is difficult to form a strong passive film or a high-temperature oxide film. On the other hand, if the Cr concentration exceeds 21.0%, the corrosion resistance is improved, but the amount of ferrite phase generated is increased, leading to insufficient toughness of the welded part and an increase in cost. Therefore, the solid solution Cr concentration is set to 15.0% or more and 21.0% or less.
<Nb: 0.30% or more and 0.80% or less>
Nb is an important element as a component exhibiting high-temperature strength, high-temperature oxidation resistance, and intergranular corrosion resistance in the present invention. The solid solution Nb increases the strength and prevents the deterioration of the high temperature strength. Further, Nb precipitated as carbonitride contributes to suppression of recrystallization and increases the recrystallization temperature, thereby increasing the softening resistance.
Ｎｂは、炭窒化物を形成するので、Ｃｒ炭化物の生成を抑制し、その結果Ｃｒ欠乏層の生成を抑制するので粒界腐食を防止することができる。 Since Nb forms carbonitrides, it suppresses the formation of Cr carbides and consequently suppresses the formation of Cr-deficient layers, thereby preventing intergranular corrosion.
Ｎｂは、耐食性を向上させる有用な元素であるが、含有量が ０．８０％超になると冷間鍛造性や耐高温酸化性が劣化する。従って、０．８０％以下とした。
また、０．３０％未満では耐食性向上効果が得られ難いため下限を０．３０％とした。
＜Ｔｉ：０．５０％以下＞
Ｔｉは、Ｎｂと同様、炭化物や窒化物を形成するので、Ｃｒ炭化物の生成を抑制し、その結果Ｃｒ欠乏層の生成を抑制するので粒界腐食を防止することができる。
Nb is a useful element that improves corrosion resistance, but when the content exceeds 0.80%, cold forgeability and high-temperature oxidation resistance deteriorate. Therefore, it was set to 0.80% or less.
Further, if it is less than 0.30%, it is difficult to obtain the effect of improving the corrosion resistance, so the lower limit was made 0.30%.
<Ti: 0.50% or less>
Ti forms carbides and nitrides similarly to Nb, and thus suppresses the formation of Cr carbides, and consequently suppresses the formation of Cr-deficient layers, thereby preventing intergranular corrosion.
Ｔｉは、耐食性を向上させる有用な元素であるが、含有量が ０．５０％超になると冷間鍛造性や耐高温酸化性が劣化する。とくにTiは多く含むと酸化皮膜が緻密でなくなるため高温酸化が進行しやすくなる。従って、０．５０％以下とした。酸化皮膜の緻密さを増すためにはＮｂも添加する。 Ti is a useful element that improves corrosion resistance, but when the content exceeds 0.50%, cold forgeability and high-temperature oxidation resistance deteriorate. In particular, if a large amount of Ti is contained, the oxide film becomes less dense and high-temperature oxidation tends to proceed. Therefore, it was made 0.50% or less. Nb is also added to increase the density of the oxide film.
また、Ｔｉ含有量の下限は特に定めないが、Tiの効果を発現させるためには、０．１０％以上添加することが望ましい。
＜Ｃｕ：０．２０％以上１．０％以下＞
Ｃｕは、耐食性および強度を向上させる有用な元素であるが、含有量が １．０％超になると靭性が劣化するばかりか冷間鍛造性が劣化する。従って、１．０％以下とした。
Moreover, although the minimum of Ti content is not specifically defined, in order to express the effect of Ti, adding 0.10% or more is desirable.
<Cu: 0.20% to 1.0%>
Cu is a useful element for improving the corrosion resistance and strength. However, when the content exceeds 1.0%, not only the toughness is deteriorated but also the cold forgeability is deteriorated. Therefore, it was set to 1.0% or less.
また、０．２％未満では耐食性向上効果が得られ難いため好ましくは下限を０．２％とした。
＜Ｎｉ：０．２０％以上１．０％以下＞
Ｎｉは、Ｃｕと同様に耐食性および強度を向上させる有効な元素であるが、含有量が１．０％超になると冷間鍛造性が劣化する。従って、１．０％以下とした。
また、０．２％未満では耐食性および強度向上効果が得られ難いため下限を０．２％とした。
＜Ｎ：０．０２５％以下＞
Ｎは、マトリックスのフェライト組織の強度を高め、更に、オーステナイト相および窒化物の生成元素であり強度を高めるが、耐食性、冷間鍛造性を劣化させるため上限を０．０２５％とした。また、０．００１％未満では鋼線の窒化物の生成が少なく強度向上の効果が得られないため０．００１％以上が望ましい範囲である。
Further, if it is less than 0.2%, it is difficult to obtain an effect of improving the corrosion resistance, so the lower limit is preferably set to 0.2%.
<Ni: 0.20% or more and 1.0% or less>
Ni is an effective element that improves the corrosion resistance and strength in the same way as Cu, but when the content exceeds 1.0%, the cold forgeability deteriorates. Therefore, it was set to 1.0% or less.
Further, if it is less than 0.2%, it is difficult to obtain an effect of improving corrosion resistance and strength, so the lower limit was made 0.2%.
<N: 0.025% or less>
N increases the strength of the ferrite structure of the matrix and further increases the strength because it is an element forming the austenite phase and nitride, but the upper limit was made 0.025% in order to deteriorate the corrosion resistance and cold forgeability. Further, if it is less than 0.001%, the formation of steel wire nitride is small and the effect of improving the strength cannot be obtained, so 0.001% or more is a desirable range.
＜Ｍｏ：０．３％以上２．５％以下＞
Ｍｏは、高温強度を高め、フェライト生成元素であり、０．３％より少ないと耐食性および高温強度向上（焼き付き防止）効果が発現されない。一方２．５％を超えるとσ相が析出しやすく脆化し、冷間鍛造性が劣化するので０．３〜２．５％とする。
なお、上記成分以外の残部は、Ｆｅおよび不可避的不純物からなる。
Ａｌについては特に規定しないが、Ａｌは脱酸剤として有用な元素である。含有量が０．０５mass％超になると靭性が劣化するため、０．０５mass％以下が好ましい。また、０．００１％未満では脱酸効果が得られ難いため下限を０．００１％とすることが好ましい。
<Mo: 0.3% to 2.5%>
Mo increases the high-temperature strength and is a ferrite-forming element. If it is less than 0.3%, the corrosion resistance and the high-temperature strength improvement (prevention of seizing) effects are not exhibited. On the other hand, if it exceeds 2.5%, the σ phase tends to precipitate and becomes brittle, and the cold forgeability deteriorates, so the content is made 0.3 to 2.5%.
The balance other than the above components is composed of Fe and inevitable impurities.
Al is not particularly defined, but Al is an element useful as a deoxidizer. When the content exceeds 0.05 mass%, toughness deteriorates, so 0.05 mass% or less is preferable. Further, if it is less than 0.001%, it is difficult to obtain a deoxidation effect, so the lower limit is preferably made 0.001%.
次に、Ｃｒ+３Ｎｂ≧１７、Ｃｒ+３（Ｍｏ+Ｎｂ）≧１７とした理由について説明する。
成分を変えたφ８mmのフェライト系ステンレス鋼円柱試料を８０%圧縮加工し（ねじ山加工量に相当）その後７００℃に保持して硬さ（Ｈｖ１）の時間変化を測定した。その結果、Ｃｒ＋３Ｎｂ≧１７を満足すれば硬さＨｖ＝２５０以上確保でき、軟化が十分に抑制できることが判明した。以上より、Ｃｒ＋３Ｎｂ≧１７ とした。
Next, the reason why Cr + 3Nb ≧ 17 and Cr + 3 (Mo + Nb) ≧ 17 will be described.
A φ8 mm ferritic stainless steel cylindrical sample with different components was subjected to 80% compression processing (corresponding to the thread processing amount), and then held at 700 ° C. to measure the time change in hardness (Hv1). As a result, it was found that if Cr + 3Nb ≧ 17 is satisfied, the hardness Hv = 250 or more can be secured, and the softening can be sufficiently suppressed. From the above, Cr + 3Nb ≧ 17.
Ｍｏが添加された場合においても同様の試験結果にもとづき、Ｃｒ＋３（Ｍｏ＋Ｎｂ）≧１７とした。 Even when Mo was added, Cr + 3 (Mo + Nb) ≧ 17 based on the same test results.
また、(Ｎｂ＋Ｔｉ)／(Ｃ＋Ｎ)≧１０ とした理由について説明する。 The reason why (Nb + Ti) / (C + N) ≧ 10 will be described.
フェライト系ステンレス鋼は溶接時にＣｒ炭窒化物が粒界に沿って形成され、その回りには耐食性が劣化したＣｒ欠乏層が存在し、急冷を行ってもＣｒ欠乏層の形成を抑制することは難しい。そのためＴｉ、Ｎｂを添加し、Ｔｉ、Ｎｂ炭窒化物を優先的に析出させることでＣｒ炭化物析出を抑制しＣｒ欠乏層の形成を抑制する。溶接部の粒界腐食感受性を検出する試験方法として、ＪＩＳ G ０５７５の硫酸濃度を変えた硫酸・硫酸銅腐食試験を実施した。試験条件は、沸騰させた溶液中（硫酸濃度：０．５％、硫酸銅：５％）に試験片を銅片に接触させながら１６ｈ連続浸漬した。 In ferritic stainless steel, Cr carbonitride is formed along the grain boundary during welding, and there is a Cr-deficient layer with deteriorated corrosion resistance around it. Even if rapid cooling is performed, the formation of Cr-deficient layer is suppressed. difficult. Therefore, by adding Ti and Nb and preferentially precipitating Ti and Nb carbonitride, Cr carbide precipitation is suppressed and formation of a Cr-deficient layer is suppressed. As a test method for detecting the intergranular corrosion sensitivity of the welded portion, a sulfuric acid / copper sulfate corrosion test in which the sulfuric acid concentration of JIS G 0575 was changed was performed. The test condition was that the test piece was immersed continuously for 16 hours in a boiled solution (sulfuric acid concentration: 0.5%, copper sulfate: 5%) while contacting the test piece with the copper piece.
試験後、試験片の断面を切出し、光学顕微鏡で溶着金属部の粒界腐食状況を観察した。 After the test, a cross section of the test piece was cut out and the intergranular corrosion state of the weld metal part was observed with an optical microscope.
硫酸・硫酸銅腐食試験における粒界腐食発生有無と溶着金属成分の関係を調査した結果、(Ｎｂ＋Ｔｉ)/(Ｃ＋Ｎ)≧１０であれば粒界腐食の発生が抑制されることが判明した。 As a result of investigating the relationship between the presence or absence of intergranular corrosion and the deposited metal component in the sulfuric acid / copper sulfate corrosion test, it was found that the occurrence of intergranular corrosion is suppressed if (Nb + Ti) / (C + N) ≧ 10.
以上より(Ｔｉ＋Ｎｂ)／(Ｃ＋Ｎ)≧１０ とした。 From the above, (Ti + Nb) / (C + N) ≧ 10.
また、 鋼中の全Ｎｂ含有量の ５０％〜８０％が析出物として存在していることと規定した理由について説明する。Ｎｂは、（a）加工性向上のための組織の微細化（b）軟化抵抗(c)耐高温酸化性を確保するための重要な元素である。ボス材は、その材料としての線材から逐次加工されて製造されるが、その代表的な製造プロセスは以下の通りである。 In addition, the reason why 50% to 80% of the total Nb content in the steel exists as precipitates will be described. Nb is an important element for ensuring (a) structure refinement for improving workability, (b) softening resistance, and (c) high-temperature oxidation resistance. The boss material is manufactured by being sequentially processed from a wire material as the material, and a typical manufacturing process is as follows.
１）ビレット−２）線材圧延−３）焼鈍−４）伸線−５）焼鈍−６）スキンパス伸線−７）冷間鍛造−８）転造（ねじ）−９）溶接−１０）部品として使用。 1) Billet-2) Wire rolling-3) Annealing-4) Wire drawing-5) Annealing-6) Skin pass wire drawing-7) Cold forging-8) Rolling (screw)-9) Welding-10) As parts use.
このプロセスの中でそれぞれ高温となる工程の温度と時間の条件において、Ｎｂは炭窒素化合物としての析出と合金中への固溶を繰返すが、６）スキンパス伸線後におけるＮｂ析出量を全Ｎｂ含有量の５０〜８０％とすれば、組織微細化により冷間鍛造加工性が向上し、さらに９）の溶接後の組織の微細化が達成され、ボス材として使用した場合の軟化抵抗、耐高温酸化性を確保できることが判明した。５０％未満では冷間鍛造中に割れが発生しやすくなり，また、溶接後の組織の微細化が達成されない。８０％超では固溶Ｎｂ量が少なくなり使用中の高温強度が低下し軟化抵抗が小さくなって焼付きが発生する。したがってＮｂの析出量を上記のごとく規定した。 In this process, Nb repeats precipitation as a carbon-nitrogen compound and solid solution in the alloy under the conditions of the temperature and time of the high temperature process, respectively. If the content is 50 to 80%, cold forging processability is improved by refinement of the structure, and further refinement of the structure after welding in 9) is achieved, and softening resistance and resistance when used as a boss material are achieved. It has been found that high temperature oxidation can be secured. If it is less than 50%, cracks are likely to occur during cold forging, and the microstructure after welding cannot be refined. If it exceeds 80%, the amount of dissolved Nb decreases, the high-temperature strength during use decreases, the softening resistance decreases, and seizure occurs. Therefore, the precipitation amount of Nb was defined as described above.
ここで、Ｎｂ析出量の測定方法(ｍａｓｓ％)について示す。表層を＃５００番研磨紙にて研磨した３ｇの伸線材を非水溶液中（３ｍａｓｓ％マレイン酸＋１ｍａｓｓ％テトラメチルアンモニウムクロイド＋残部メタノール）で電解（１００ｍＶ定電圧）してマトリックスを溶解し、０．２μｍ穴径のフィルターでろ過して、炭窒化物を抽出した。その後、析出物を酸中にて完全に溶解してイオン化し、高周波誘導結合プラズマ発光分光分析装置（ＩＣＰ）にてＮｂの抽出残渣量を測定した（その量をＡ％とする）。鋼中の全Ｎｂ含有量は、スパーク放電発光分光分析装置（Ｑｕａｎｔｖａｃ）により測定した（その量をＢ％とする）。以上より Ａ／Ｂ×１００（％）をＮｂの析出割合とした。 Here, it shows about the measuring method (mass%) of Nb precipitation amount. 3 g of wire drawing material whose surface layer was polished with # 500 polishing paper was electrolyzed (100 mV constant voltage) in a non-aqueous solution (3 mass% maleic acid + 1 mass% tetramethylammonium croid + remaining methanol) to dissolve the matrix. The carbonitride was extracted by filtering with a 2 μm hole diameter filter. Thereafter, the precipitate was completely dissolved and ionized in an acid, and the amount of Nb extraction residue was measured with a high frequency inductively coupled plasma optical emission spectrometer (ICP) (the amount is defined as A%). The total Nb content in the steel was measured with a spark discharge optical emission spectrometer (Quantvac) (the amount is B%). From the above, A / B × 100 (%) was defined as the Nb precipitation ratio.
Ｎｂ析出量は以下のように制御する。ビレット加熱時にＮｂ量の９０％以上を固溶させ、４）伸線後に試料を切出しＮｂ析出量を調査する。そのＮｂ析出量に応じて５）焼鈍における加熱温度と保持時間を制御し、６）スキンパス伸線後におけるＮｂ析出量を全Ｎｂ含有量の５０〜８０％に制御する。 The amount of Nb precipitation is controlled as follows. 90% or more of the amount of Nb is dissolved at the time of heating the billet. 4) A sample is cut out after wire drawing and the amount of Nb deposited is investigated. According to the Nb precipitation amount, 5) the heating temperature and holding time in annealing are controlled, and 6) the Nb precipitation amount after skin pass drawing is controlled to 50 to 80% of the total Nb content.
また、ボス材用ステンレス鋼線を、ビッカース硬さ（Ｈｖ１）が１４０以上２８０以下であることに限定した理由について説明する。ビッカース硬さ（Ｈｖ１）は以下のように測定した。スキンパス伸線後の鋼線の１断面において、その円形断面の中心から表面まで引いた線の中間点において硬さを測定し、その線を９０°回転させた位置で計４個所測定し、その平均値を断面のビッカース硬さとした。硬さと焼付きの関係を調べた結果、硬さが１４０以上あれば軟化が抑制され焼付きが防止できることが判明した。また、硬さが２８０を超えると冷間鍛造性が低下する。以上より、ボス材用ステンレス鋼線を、ビッカース硬さ（Ｈｖ１）が１４０以上２８０以下であることに限定した。 The reason why the stainless steel wire for the boss material is limited to the Vickers hardness (Hv1) of 140 or more and 280 or less will be described. Vickers hardness (Hv1) was measured as follows. In one cross section of the steel wire after drawing the skin pass, the hardness is measured at the midpoint of the line drawn from the center of the circular cross section to the surface, and a total of four points are measured at the position where the line is rotated 90 °. The average value was taken as the Vickers hardness of the cross section. As a result of examining the relationship between hardness and seizure, it was found that if the hardness is 140 or more, softening is suppressed and seizure can be prevented. Moreover, when hardness exceeds 280, cold forgeability will fall. As mentioned above, the stainless steel wire for boss | hub materials was limited to Vickers hardness (Hv1) being 140-280.
１）ビレット−２）線材圧延−３）焼鈍−４）伸線−５）焼鈍−６）酸洗−７）スキンパス伸線の工程で線材コイルを製造した。４）伸線後にＮｂ析出量を調査し５）焼鈍(Ｎｂ析出量に応じ９００〜９５０℃×１〜３ｈ、水冷等)を実施した。７）スキンパス伸線後にＮｂ析出量を測定した（表１に記載）。また，スキンパス伸線後サンプルを切出し、冷間鍛造後に雌ねじ加工を施してボス形状とし、ステンレス鋼板にプロジェクション溶接を施した。サンプル雌ねじ部に雄ねじを取付け、大気中で７００℃において６時間保持した。 1) Billet-2) Wire rod rolling-3) Annealing-4) Wire drawing-5) Annealing-6) Pickling-7) A wire coil was manufactured in the skin pass wire drawing process. 4) After wire drawing, the amount of Nb precipitation was investigated, and 5) annealing (900-950 ° C. × 1-3 h, water cooling, etc. depending on the amount of Nb precipitation) was performed. 7) The amount of Nb precipitation was measured after skin pass drawing (described in Table 1). In addition, a sample was cut out after drawing the skin pass, and after cold forging, a female thread was formed into a boss shape, and projection welding was performed on the stainless steel plate. A male screw was attached to the sample female screw portion, and the sample was held in the atmosphere at 700 ° C. for 6 hours.
その後、雄ねじを取外し焼付きの有無を調査した。さらに、そのサンプルについて硫酸・硫酸銅腐食試験を施し、溶接部に垂直な断面を光学顕微鏡にて１００〜５００倍にて観察し、プロジェクション溶接部における粒界腐食の有無を調査した。 Then, the male screw was removed and the presence or absence of seizure was investigated. Furthermore, the sample was subjected to a sulfuric acid / copper sulfate corrosion test, and a cross section perpendicular to the welded portion was observed with an optical microscope at a magnification of 100 to 500 times to investigate the presence or absence of intergranular corrosion in the projection welded portion.
表１に本発明のボス材用ステンレス鋼線の化学成分とボス材の評価結果を示す。
No.１〜No.２０は、いずれも焼付きは無く粒界腐食も検出されなかった。 No. 1 to No. 20 were not seized and no intergranular corrosion was detected.
一方、Ｎｏ．２１は、Ｃｒ量が１５．０％を下回っており、さらにＣｒ＋３Ｎｂが１７を下回っておりかつＣｒ＋３（Ｍｏ＋Ｎｂ）も１７を下回っており、焼付きが生じた。 On the other hand, no. In No. 21, the Cr amount was less than 15.0%, Cr + 3Nb was less than 17, and Cr + 3 (Mo + Nb) was also less than 17, and seizure occurred.
Ｎｏ．２２は、Ｃｒ量が２１．０％を超えており、溶接部の靭性が不足したため評価を行わなかった。 No. No. 22 was not evaluated because the Cr content exceeded 21.0% and the toughness of the welded portion was insufficient.
Ｎｏ．２３は、Ｎｂ量が０．３０％を下回っており、耐食性が劣化した。 No. In No. 23, the Nb content was less than 0.30%, and the corrosion resistance deteriorated.
Ｎｏ．２４は、Ｃ量が０．０２％を超えており、耐食性が劣化した。 No. In No. 24, the C content exceeded 0.02%, and the corrosion resistance deteriorated.
Ｎｏ．２５は、最終焼鈍条件が適切でなくＮｂ析出量が全Ｎｂ量の５０％を下回っており、冷間鍛造中に割れが生じたため評価を行わなかった。 No. No. 25 was not evaluated because the final annealing conditions were not appropriate and the Nb precipitation amount was less than 50% of the total Nb amount, and cracking occurred during cold forging.
以上の実施例から明らかなように、本発明により高温における耐久性に優れた円筒形部材（ボス材）用フェライト系ステンレス鋼線の提供が可能であり、経済性の点で極めて有用である。 As is clear from the above examples, the present invention can provide a ferritic stainless steel wire for a cylindrical member (boss material) having excellent durability at high temperatures, which is extremely useful in terms of economy.
１ ボス主体
２ 本体（エキゾーストパイプ等）への溶接部分
３ センサー取付け用の雌ねじ加工部位
1 Boss
Claims (4)
Ｃ ：０.００１％以上０.０２％以下、
Ｓｉ：０.１％以上１.０％以下、
Ｍｎ：１.０％以下、
Ｐ：０.０４％以下、
Ｓ：０.０３％以下、
Ｃｒ：１５.０%以上２１.０％以下、
Ｎ：０.０２５％以下、を含有し、更に、
Ｎｂ：０.３０以上０.８０％以下、
Ｔｉ：０.５％以下、の１種以上を含有し、
残部は鉄および不可避的不純物からなり、
Ｃｒ+３Ｎｂ≧１７、および、（Ｎｂ＋Ｔｉ）／(Ｃ+Ｎ)≧１０を満足し、
鋼中の全Ｎｂ含有量の５０％〜８０％が析出物として存在していることを特徴とするボス材用フェライト系ステンレス鋼線。 % By mass
C: 0.001% or more and 0.02% or less,
Si: 0.1% or more and 1.0% or less,
Mn: 1.0% or less,
P: 0.04% or less,
S: 0.03% or less,
Cr: 15.0% to 21.0%,
N: 0.025% or less, and
Nb: 0.30 to 0.80%,
Containing one or more of Ti: 0.5% or less,
The balance consists of iron and inevitable impurities,
Cr + 3Nb ≧ 17 and (Nb + Ti) / (C + N) ≧ 10 are satisfied,
A ferritic stainless steel wire for a boss material, wherein 50% to 80% of the total Nb content in the steel is present as a precipitate.
Ｃｕ：０.２０%以上１.０%以下、
Ｎｉ：０.２０%以上１.０%以下、の１種以上を含有することを特徴とする請求項１に記載のボス用フェライト系ステンレス鋼線。 In mass%,
Cu: 0.20% to 1.0%,
2. The ferritic stainless steel wire for a boss according to claim 1, comprising at least one of Ni: 0.20% to 1.0%.
Ｍｏ：０．３％以上２．５％以下を含有し、
Ｃｒ+３（Ｍｏ+Ｎｂ）≧１７を満足することを特徴とする請求項１または請求項２に記載のボス材用フェライト系ステンレス鋼線。 % By mass, and further Mo: 0.3% or more and 2.5% or less,
3. The ferritic stainless steel wire for a boss material according to claim 1, wherein Cr + 3 (Mo + Nb) ≧ 17 is satisfied.
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