JP3550132B2

JP3550132B2 - Precipitation hardening type soft magnetic ferritic stainless steel

Info

Publication number: JP3550132B2
Application number: JP2002111568A
Authority: JP
Inventors: 常美滝口; 貴司江幡
Original assignee: Tohoku Steel Co Ltd
Current assignee: Tohoku Steel Co Ltd
Priority date: 2002-04-15
Filing date: 2002-04-15
Publication date: 2004-08-04
Anticipated expiration: 2022-04-15
Also published as: DE60207983D1; JP2003301245A; EP1357199A1; EP1357199B1; DE60207983T2; US20030192626A1

Description

【０００１】
【発明の属する技術分野】
この発明は、析出硬化型軟磁性フェライト系ステンレス鋼に関し、より詳細には、磁気特性及び耐食性に優れるだけでなく、可動部を含む磁気回路装置の耐摩耗性、耐座屈性等の耐久性の向上に寄与する高い硬さと良好な冷間加工性をも兼ね備えた析出硬化型軟磁性フェライト系ステンレス鋼に関するものであり、特に各種電磁弁、電子制御燃料噴射装置、その他の磁芯用材料などの用途に用いて好適なものである。
【０００２】
【従来の技術】
各種電磁弁、電子制御燃料噴射装置等の磁芯材料としては、磁気特性や耐食性に対する要求から、軟磁性フェライト系ステンレス鋼が実用材として多用されている。ところで、軟磁性フェライト系ステンレス鋼製の部品が装置の動作時の摺動部や衝突部に用いられる場合には、摩耗や座屈による変形が寸法変化のみならず磁気回路特性や気密性の低下による制御精度の低下がしばしば問題とされてきた。このような問題に対し、摺動部や衝突部にＣｒメッキや窒化処理等の表面硬化処理を施して強度アップと磨耗低減を図ることで対策が講じられてきた。
【０００３】
しかしながら、これらの対策は、軟磁性材料にとって重要な特性である磁気特性の低下と、装置の製造コストの上昇を招くため好ましくない。
【０００４】
更に近年においては環境上の問題から、メッキ処理工程のようにクロム等の有害物質を取り扱う工程を廃止したいという要望も多いため、かかる工程を経ることなく、優れた磁気特性を確保しつつ良好な機械的耐久性、特に高い硬さ（２７０ＨＶ以上）を有する軟磁性材料の開発が望まれている。
【０００５】
しかしながら、磁気特性を劣化させずにフェライト系ステンレス鋼自体の硬さを高める試みは、合金元素の固溶強化によって多少の硬さの増加（１７０〜２２０ＨＶ程度）が図られている事例は数多く見られるものの、２７０ＨＶ以上といった格段に高い硬さを有する高軟磁性材料の開発は他に例を見ない。
【０００６】
【発明が解決しようとする課題】
この発明の目的は、例えば各種電磁弁、電子制御燃料噴射装置、その他の磁芯用材料に要求される磁気特性及び耐食性に優れているのは言うまでもなく、耐摩耗性や耐座屈性等の耐久性向上に寄与する高い硬さと良好な冷間加工性をも兼ね備えた析出硬化型軟磁性フェライト系ステンレス鋼を提案するところにある。
【０００７】
【課題を解決するための手段】
従来より、１７−４ＰＨ鋼に代表される析出硬化型ステンレス鋼は種々あるが、それらの殆どは鋼組織のベースがマルテンサイト単相又はオーステナイト単相からなる単一系、或いはフェライト相も含めた２相系であり、フェライト単相からなる単一系の析出硬化型軟磁性フェライト系ステンレス鋼の研究・開発事例は極めて少なく、特に優れた軟磁性を有するフェライト系ステンレス鋼の開発事例としては、出願人が出願して特許された特許第１１９４８９２号公報及び同第１８３２１９１号公報に記載がある以外は見当たらない。
【０００８】
特許第１１９４８９２号公報に記載された発明は、析出硬化型軟磁性フェライト系ステンレス鋼の先鞭をつけた画期的な発明であり、フェライト相を安定化させる条件が詳細に示されており、また、特許第１８３２１９１号公報に記載された発明は、さらに材料の外観光沢の改善を図ったものである。
上掲特許公報に記載された発明はいずれも、溶体化処理と時効処理を行った後の硬さが４００ＨＶ以上と軟磁性フェライト単相材料としては非常に高い硬さを有しているものの、磁気特性が、近年の電子制御機器に用いる場合に必要とされる磁気特性レベルにまでは達してなく、加えて、硬さが高すぎることに起因して冷間加工性が劣るため量産性等にも難点があるという問題があった。
【０００９】
このため、発明者らは、上記の問題点を解決すべく、鋼中の成分組成につき検討を行った。その結果、鋼中に共添加したＮｉ及びＡｌの金属間化合物（Ｔｉ及びＺｒも添加時は一部が化合物中に含まれると考えられる。）の時効析出を主要な硬化因子とする析出硬化型軟磁性フェライト系ステンレス鋼において、時効処理前の冷間加工性を悪化させずに、時効処理後の硬さを十分実用的価値のある３００〜４００ＨＶ程度にすることができ、しかも、上記特許公報に記載された発明が提供するよりも優れた軟磁気特性を有し、所期した目的の達成に関し極めて有効な知見を得た。
【００１０】
この発明は、上記の知見に立脚するものであって、その要旨は以下に示す通りである。
（１）質量％で、
Ｃ：0.2％以下、
Si：0.01〜3.0％、
Mn：0.5％以下、
Ｓ：0.3％以下、
Cr：12.0〜19.0％、
Ni：1.0〜4.0％及び
Al：0.2〜4.0％を含有するとともに、Ti：0.5％未満及びZr：0.3％未満のうち少なくとも一種を含有し、残部は不可避的不純物及び実質的にFeの組成になり、かつ、溶体化処理と時効処理を行った後の組織が実質的にフェライト相であって、時効処理後の硬さが 300HV 以上であることを特徴とする析出硬化型軟磁性フェライト系ステンレス鋼（第１発明）。
【００１１】
（２）質量％で、
Ｃ：0.2％以下、
Si：0.01〜3.0％、
Mn：0.5％以下、
Ｓ：0.3％以下、
Cr：12.0〜19.0％、
Ni：1.0〜4.0％及び
Al：0.2〜4.0％を含有するとともに、Ti：0.5％未満及びZr：0.3％未満のうち少なくとも一種を含有し、さらに、Nb：1.0％以下、Mo：4.0％以下、Cu：2.0％以下、B：0.01％以下及びREM：0.1％以下のうち少なくとも一種を含有し、残部は不可避的不純物及び実質的にFeの組成になり、かつ、溶体化処理と時効処理を行った後の組織が実質的にフェライト相であって、時効処理後の硬さが 300HV 以上であることを特徴とする析出硬化型軟磁性フェライト系ステンレス鋼（第２発明）。
【００１２】
【発明の実施の形態】
この発明において、鋼中の成分組成を上記の範囲に限定した理由を以下で説明する。なお、鋼中の成分組成における質量％は単に％と記す。
【００１３】
・Ｃ：０．２％以下
Ｃは、フェライト相をベースとする鋼組織を生成するのを阻害するオーステナイト安定化元素であり、また、磁気特性に悪影響を及ぼす元素であることから、Ｃ含有量はできるだけ少なくする方が望ましく、Ｃは、Ｔｉ、Ｚｒ、Ｎｂにより炭化物や炭硫化物として固定されること、及び製造性を考慮して、Ｃ含有量を０．２％以下とした。
【００１４】
・Ｓｉ：０．０１〜３．０％
Ｓｉは、ステンレス鋼中にあって脱酸剤として有用な元素であるだけではなく、フェライト安定化元素であり、磁気特性のうち、最大透磁率の上昇と保磁力の低下にも有効に寄与し、また、比抵抗を増加させ高周波領域の応答性の改善にも有用な元素であり、フェライト相の硬さを上昇させる効果も大きく、かかる効果を発揮させるため、Ｓｉを０．０１％以上含有させる必要がある。しかしながら、Ｓｉ含有量が３．０％を超えると、冷間加工性を阻害し製造性の低下を招くことから、Ｓｉ含有量を０．０１〜３．０％とした。
【００１５】
・Ｍｎ：０．５％以下
Ｍｎは、ステンレス鋼中にあって脱酸剤として有用な元素であり、Ｓを硫化物として固定し更に被削性を向上させる効果もある。しかしながら、Ｍｎは、オーステナイト安定化元素なので０．５％を超える過剰な添加はフェライト相を不安定化し、更に磁気特性や耐食性を阻害するため、Ｍｎ含有量を０．５％以下とした。なお、Ｍｎ含有量の下限は、特に制限しないが、上記効果を顕著に発揮させるため、０．０５％とすることが好ましい。
【００１６】
・Ｓ：０．３％以下
Ｓも、Ｃと同様、磁気特性を悪化させる傾向があることから、Ｓ含有量をできるだけ少なくする方が望ましく、Ｓは、Ｍｎ、Ｔｉ、Ｚｒによる固定効果によりある程度の磁気特性の劣化は防ぐことができる点を考慮して、Ｓ含有量は０．３％以下とした。尚、Ｓは被削性を向上させる元素でもあることから、被削性が要求されるステンレス鋼の場合には、Ｓ含有量を０．０２％以上とすることが好ましい。
【００１７】
・Ｃｒ：１２．０〜１９．０％
Ｃｒは、この発明のフェライト系ステンレス鋼中における主要成分の一つであり、フェライト相を安定化するとともに、耐食性の向上及び比抵抗の増加にも効果的な元素であるが、Ｃｒ含有量が１２．０％に満たないとそれらの効果に乏しく、一方、１９．０％を超える過剰な添加は磁気特性に悪影響を及ぼすことから、Ｃｒ含有量を１２．０〜１９．０％とした。
【００１８】
・Ｎｉ：１．０〜４．０％
Ｎｉは、Ａｌとともに溶体化処理と時効処理を行った後において、金属間化合物として鋼中に析出することによって硬さを上昇させる効果を有する元素であり、かかる効果を発揮させるには、Ｎｉ含有量を１．Ｏ％以上にする必要がある。しかしながら、過度のＮｉの添加は、溶体化処理時にマルテンサイト相やオーステナイト相の生成を誘発し易くなるため、Ｎｉ含有量の上限は、他の添加元素のフェライト安定化効果も考慮し、実質的にフェライト単相となる限界として４．０％とした。
【００１９】
・Ａｌ：０．２〜４．０％
Ａｌは、Ｎｉとともに金属間化合物として鋼中に析出することによって、硬さを上昇させるだけでなく、脱酸剤としても有用な元素であり、加えて、フェライト安定化作用もある。また、溶体化処理と時効処理を行った後は、Ｎｉとともに金属間化合物を形成する量よりも多く添加したＡｌは、Ｓｉと同様、最大透磁率の上昇及び保磁力の低下、更に比抵抗の増加に寄与して高周波領域での応答性を改善する作用があることから、Ｎｉ含有量との兼ね合いで、Ａｌを少なくとも０．２％以上含有させることとした。しかしながら、４．０％を超えるＡｌの過剰な添加は、特殊な精錬方法が必要になるだけでなく、冷間加工性を阻害するので、Ａｌ含有量の上限を４．０％とした。
【００２０】
・Ｔｉ：０．５％未満以下及びＺｒ：０．３％未満のうち少なくとも一種を含有すること
Ｔｉ及びＺｒは、Ｃ及びＳを固定することによって磁気特性や耐食性を高めるのに有効に作用する元素であり、この発明では、Ｔｉ及びＺｒのうち少なくとも一種を含有させる必要がある。また、Ｔｉ及びＺｒの一部は、溶体化処理と時効処理を行った後にＮｉ及びＡｌの金属間化合物中に固溶して硬さ上昇に寄与すると考えられるが、Ｔｉ含有量が０．５％以上、Ｚｒ含有量が０．３％以上では、硬さ上昇には寄与しても、冷間加工性を阻害し製造性を低下させるので、Ｔｉ含有量を０．５％未満、Ｚｒ含有量を０．３％未満とした。なお、磁気特性及び耐食性を高める効果を発揮させるため、Ｔｉ含有量を０．１％以上とし、Ｚｒの含有量を０．０１％以上とするのが好ましい。
【００２１】
また、本発明では、上記した組成成分に加えて、さらにＮｂ：１．０％以下、Ｍｏ：４．０％以下、Ｃｕ：２．０％以下、Ｂ：０．０１％以下及びＲＥＭ：０．１％以下のうち少なくとも一種を必要に応じて含有させることができる。
【００２２】
・Ｎｂ：１．０％以下
Ｎｂは、Ｃを固定して磁気特性と耐食性を高めるのに有効な元素であるが、１．０％を超える過剰なＮｂの添加は、却って磁気特性を阻害し冷間加工性も阻害するので、Ｎｂ含有量は１．０％以下とする。
【００２３】
・Ｍｏ：４．０％以下
Ｍｏは、フェライト安定化元素であるとともに、耐食性の改善に有効な元素であるが、４．０％を超える過剰なＭｏの添加は、冷間加工性を阻害し製造性を低下させるので、Ｍｏ含有量は４．０％以下とする。
【００２４】
・Ｃｕ：２．０％以下
Ｃｕは、耐食性の改善に有効な元素であるとともに、時効硬化にも寄与するが、２．０％を超える過剰な添加は、脆化を招き、冷間引抜きや曲り矯正等の冷間加工を困難にし製造性を低下させるので、Ｃｕ含有量は２．０％以下とする。
【００２５】
・Ｂ：０．０１％以下、ＲＥＭ：０．１％以下
Ｂ及びＲＥＭは、いずれも冷間加工性の向上に寄与するが、それぞれ０．０１％及び０．１％を超えると、却って冷間加工性を阻害する要因となるため、Ｂ及びＲＥＭの含有量はそれぞれ０．０１％以下及びＲＥＭ：０．１％以下とする。
【００２６】
次に、この発明に従う析出硬化型軟磁性フェライト系ステンレス鋼の製造方法の一例を以下で説明する。
【００２７】
まず、上記成分組成の鋼素材を、例えば真空誘導炉にて、溶解、精錬したのち、造塊し、次いで１０００〜１１００℃で分塊し、１０００〜１１００℃に加熱した後、熱間圧延して線、棒、または板形状の素材とする。
次に、７５０〜１１００℃で焼鈍後、線材素材の場合には、５〜２５％の減面率で冷間引抜きと曲り矯正を行う。棒、板材素材の場合には冷間で曲り矯正を行う。
その後、１０００〜１１００℃に加熱し、この温度に１〜２時間保持してから、強制空冷ファンまたは水スプレイ等を用いて急冷することによって溶体化処理した後、曲り矯正し、５００〜６００℃の温度で２〜３時間保持してから空冷または窒素ガス等による徐冷をする時効処理を施して析出硬化させることによって、この発明の析出硬化型軟磁性フェライト系ステンレス鋼を製造することができる。尚、溶体化−曲り矯正状態で部品加工を行った後、時効硬化処理を行ってもよい。或いは、冷間曲り矯正後に部品加工を行った後、真空または雰囲気炉内での加熱と窒素ガス等による急冷による溶体化処理及び時効硬化処理を行ってもよい
【００２８】
【実施例】
表１に示す種々の成分組成になる鋼素材を、Ａｒ気流中で７ｋｇ溶製し、金型に鋳込むことによって８０ｍｍφのインゴットを作製した。次に、各インゴットを１０００〜１０５０℃で熱間鍛造して２４ｍｍφの丸棒とし、更に１０００〜１０５０℃で熱間スウェージングにより１８ｍｍφの丸棒とし、更に９００℃で焼鈍した後、１７ｍｍφまで冷間引抜きを行って種々の試験に供した。かくして得られた試料の、硬さ、磁気特性、耐食性及び冷間加工性について調べた結果を表２に示す。尚、磁気特性は、外径１０ｍｍ、内径４．５ｍｍ、厚み５ｍｍのリング試料を作製し、真空炉にて１０５０℃で１時間加熱した後、室素ガス急冷による溶体化処理を行い、引き続き５５０℃で２時間の時効処理を行った後、Ｂ−Ｈループトレーサーを用いて測定した。更に同試料を用いて硬さも測定した。耐食性は、１５ｍｍφ、長さ１００ｍｍの丸棒を磁気特性評価試料と同様の熱処理を行い、８００番のエメリー紙で研磨した試料に対して、５％ＮａＣｌ水溶液を３５℃で４８時間噴霧した後の試料表面の発銹の程度により耐食性を評価した。尚、耐食性の評価は、錆発生が無いかあっても丸棒端部の角部等に局所的に薄く発錆している場合を「○」、それ以外で錆発生が明らかな場合を「×」とする２段階で行った。また、冷間加工性は、上記試料作製時の冷間引抜時における引割れや折損等の欠陥の発生の有無や程度により評価し、より具体的には、前記欠陥が発生することなく容易に冷間加工できる場合を「○」、それ以外で前記欠陥が発生し冷間加工を含む量産工程が困難である場合を「×」として２段階で評価した。表２に、これらの評価結果を示す。
【００２９】
【表１】

【００３０】
【表２】

【００３１】
表２に示す結果から、実施例の試料Ｎｏ．１〜７はいずれも、耐食性と冷間加工性に優れ、時効処理後の硬さが３４０ＨＶ５以上であり、磁気特性も時効処理前後で殆ど差がなく、軟磁性材料として優れた値を示している。
一方、比較例の試料Ｎｏ．８はＣｒ含有量が低く、また、比較例の試料Ｎｏ．９はＮｉ含有量が多過ぎるため、いずれもオーステナイト安定化元素の影響が大きく磁束密度がＢ_２５で１テスラよりも小さく保持力も高いため、磁性材料としての磁気特性に劣る。比較例１０は、磁気特性については優れているものの、ＮｉとＡｌの添加量が少なすぎるために、時効処理後でも硬さは３００ＨＶ５を大きく下回っている。比較例１１は、ＴｉやＺｒなどのＣやＳを強力に固定元素が添加されていないために、磁気特性に劣る。比較例１２は、硬さや磁気特性については優れているものの、Ｃｕ添加量が高すぎるために、冷間加工性に劣り、供試鋼製作中でも冷間引抜きにおいて折れや引き割れが多発し試験片作製までの歩留りも極めて低かった。
【００３２】
【発明の効果】
かくしてこの発明によれば、磁気特性及び耐食性に優れているのは言うまでもなく、耐摩耗性や耐座屈性等の耐久性向上に寄与する高い硬さと良好な冷間加工性をも兼ね備えた析出硬化型軟磁性フェライト系ステンレス鋼の提供を可能にし、このステンレス鋼を、例えば各種電磁弁、電子制御燃料噴射装置等の磁芯材料に適用すれば、耐久性の向上や製造コストの低減が図れるとともに、環境保護の観点からも好ましく、産業界に貢献するところ大である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a precipitation hardening type soft magnetic ferritic stainless steel, and more particularly, to not only excellent magnetic properties and corrosion resistance, but also durability such as wear resistance and buckling resistance of a magnetic circuit device including a movable part. The present invention relates to precipitation hardening type soft magnetic ferritic stainless steel that combines high hardness and good cold workability that contribute to the improvement of steel, especially various solenoid valves, electronically controlled fuel injection devices, and other materials for magnetic cores. It is suitable for use in applications.
[0002]
[Prior art]
As magnetic core materials for various solenoid valves, electronically controlled fuel injection devices, and the like, soft magnetic ferritic stainless steels are widely used as practical materials due to requirements for magnetic properties and corrosion resistance. By the way, when parts made of soft magnetic ferritic stainless steel are used for sliding parts and collision parts during operation of the device, deformation due to wear and buckling not only reduces dimensional changes but also decreases magnetic circuit characteristics and airtightness. It has often been a problem that the control accuracy is reduced due to this. To cope with such a problem, measures have been taken to increase the strength and reduce wear by applying a surface hardening treatment such as Cr plating or nitriding treatment to the sliding portion or the collision portion.
[0003]
However, these countermeasures are not preferable because they lower the magnetic characteristics, which are important characteristics for the soft magnetic material, and increase the manufacturing cost of the device.
[0004]
Further, in recent years, due to environmental problems, there are many requests to abolish a process for handling harmful substances such as chromium, such as a plating process. Development of a soft magnetic material having mechanical durability, particularly high hardness (270 HV or more) is desired.
[0005]
However, attempts to increase the hardness of ferritic stainless steel itself without deteriorating its magnetic properties have seen many cases of some increase in hardness (about 170 to 220 HV) by solid solution strengthening of alloying elements. However, there is no other example of the development of a high soft magnetic material having a remarkably high hardness of 270 HV or more.
[0006]
[Problems to be solved by the invention]
The object of the present invention is, of course, to be excellent in magnetic properties and corrosion resistance required for various solenoid valves, electronically controlled fuel injection devices, and other magnetic core materials, as well as wear resistance and buckling resistance. An object of the present invention is to propose a precipitation hardening type soft magnetic ferritic stainless steel having both high hardness and good cold workability contributing to improvement of durability.
[0007]
[Means for Solving the Problems]
Conventionally, there are various precipitation hardening stainless steels represented by 17-4PH steel, and most of them include a single system in which the base of the steel structure is a martensite single phase or an austenite single phase, or a ferrite phase. There are very few R & D examples of single-phase precipitation hardening soft magnetic ferritic stainless steels that are two-phase and consist of a single ferrite phase. Nothing is found other than those described in Japanese Patent Nos. 1194892 and 1832191 filed and filed by the applicant.
[0008]
The invention described in Japanese Patent No. 1194892 is an epoch-making invention in which a precipitation hardening type soft magnetic ferritic stainless steel was pioneered, and conditions for stabilizing a ferrite phase are shown in detail. The invention described in Japanese Patent No. 1832191 further improves the appearance gloss of the material.
Although any of the inventions described in the above-mentioned patent publications have a hardness of 400 HV or more after the solution treatment and the aging treatment and a very high hardness as a soft magnetic ferrite single phase material, The magnetic properties have not reached the level of magnetic properties required for use in recent electronic control devices, and in addition, the cold workability is inferior due to the hardness being too high, so that mass productivity etc. There was a problem that there are also difficulties.
[0009]
For this reason, the inventors have studied the composition of components in steel in order to solve the above problems. As a result, a precipitation hardening type in which aging precipitation of the intermetallic compound of Ni and Al co-added to the steel (it is considered that Ti and Zr are partially contained in the compound when added) is a main hardening factor. In a soft magnetic ferritic stainless steel, the hardness after aging treatment can be set to a sufficiently practical value of about 300 to 400 HV without deteriorating the cold workability before aging treatment. The present invention has a soft magnetic property superior to that provided by the invention described in (1), and has obtained extremely effective knowledge on achieving the intended purpose.
[0010]
The present invention is based on the above findings, and the gist is as follows.
(1) In mass%,
C: 0.2% or less,
Si: 0.01-3.0%,
Mn: 0.5% or less,
S: 0.3% or less,
Cr: 12.0-19.0%,
Ni: 1.0-4.0% and
Al: 0.2 to 4.0%, at least one of Ti: less than 0.5% and Zr: less than 0.3%, the balance being unavoidable impurities and substantially Fe composition, and solution treatment A precipitation hardening type soft magnetic ferritic stainless steel (first invention), wherein the structure after the aging treatment is substantially a ferrite phase and the hardness after the aging treatment is 300 HV or more .
[0011]
(2) In mass%,
C: 0.2% or less,
Si: 0.01-3.0%,
Mn: 0.5% or less,
S: 0.3% or less,
Cr: 12.0-19.0%,
Ni: 1.0-4.0% and
Al: 0.2 to 4.0%, Ti: less than 0.5% and Zr: at least one of less than 0.3%, Nb: 1.0% or less, Mo: 4.0% or less, Cu: 2.0% or less, B: Contains at least one of 0.01% or less and REM: 0.1% or less, with the balance being unavoidable impurities and substantially Fe composition, and the structure after the solution treatment and the aging treatment being substantially A precipitation hardening type soft magnetic ferritic stainless steel characterized by being a ferrite phase and having a hardness after aging treatment of 300 HV or more (second invention).
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, the reason why the component composition in steel is limited to the above range will be described below. In addition, the mass% in the component composition in steel is simply described as%.
[0013]
C: 0.2% or less C is an austenite stabilizing element that inhibits the formation of a steel structure based on a ferrite phase, and also has an adverse effect on magnetic properties. Is desirably as small as possible, and the C content is set to 0.2% or less in consideration of the fact that C is fixed as a carbide or carbosulfide by Ti, Zr, and Nb, and in consideration of manufacturability.
[0014]
-Si: 0.01 to 3.0%
Si is not only a useful element as a deoxidizing agent in stainless steel, but also a ferrite stabilizing element, which effectively contributes to the increase in the maximum magnetic permeability and the decrease in the coercive force among the magnetic properties. Also, it is an element useful for increasing the specific resistance and improving the responsiveness in the high frequency region, and has a great effect of increasing the hardness of the ferrite phase. To exhibit such an effect, it contains Si in an amount of 0.01% or more. Need to be done. However, when the Si content exceeds 3.0%, the cold workability is impaired and the productivity is lowered, so the Si content was set to 0.01 to 3.0%.
[0015]
Mn: 0.5% or less Mn is a useful element as a deoxidizing agent in stainless steel, and has an effect of fixing S as a sulfide and further improving machinability. However, since Mn is an austenite stabilizing element, an excessive addition exceeding 0.5% destabilizes the ferrite phase and further impairs magnetic properties and corrosion resistance. Therefore, the Mn content is set to 0.5% or less. Note that the lower limit of the Mn content is not particularly limited, but is preferably set to 0.05% in order to remarkably exert the above effect.
[0016]
S: 0.3% or less Since S also tends to deteriorate magnetic properties like C, it is desirable to reduce the S content as much as possible, and S is somewhat controlled by the fixing effect of Mn, Ti, and Zr. In consideration of the fact that the deterioration of the magnetic characteristics of the above can be prevented, the S content is set to 0.3% or less. Since S is also an element that improves machinability, in the case of stainless steel requiring machinability, the S content is preferably set to 0.02% or more.
[0017]
Cr: 12.0 to 19.0%
Cr is one of the main components in the ferritic stainless steel of the present invention, and is an element that stabilizes the ferrite phase and is also effective in improving corrosion resistance and increasing specific resistance. If the content is less than 12.0%, these effects are poor. On the other hand, an excessive addition exceeding 19.0% adversely affects magnetic properties. Therefore, the Cr content is set to 12.0 to 19.0%.
[0018]
-Ni: 1.0 to 4.0%
Ni is an element having an effect of increasing hardness by precipitating in steel as an intermetallic compound after performing a solution treatment and an aging treatment together with Al. In order to exert such an effect, Ni is contained. The amount is 1. It must be O% or more. However, excessive addition of Ni tends to induce the formation of a martensite phase or an austenite phase during the solution treatment. Therefore, the upper limit of the Ni content is substantially determined in consideration of the ferrite stabilizing effect of other added elements. Was 4.0% as a limit to become a ferrite single phase.
[0019]
-Al: 0.2 to 4.0%
Al is an element that not only increases hardness but also is useful as a deoxidizing agent by precipitating in steel as an intermetallic compound together with Ni, and also has an effect of stabilizing ferrite. After the solution treatment and the aging treatment, Al added in an amount larger than that forming an intermetallic compound together with Ni increases the maximum magnetic permeability and the coercive force as well as Si, and further decreases the specific resistance. Since it has the effect of improving the response in the high frequency region by contributing to the increase, it was decided to contain Al at least 0.2% or more in view of the Ni content. However, excessive addition of Al exceeding 4.0% not only requires a special refining method but also impairs cold workability. Therefore, the upper limit of the Al content was set to 4.0%.
[0020]
-Contains at least one of Ti: less than 0.5% or less and Zr: less than 0.3% Ti and Zr work effectively to enhance magnetic properties and corrosion resistance by fixing C and S. In the present invention, it is necessary to contain at least one of Ti and Zr. Further, it is considered that a part of Ti and Zr is dissolved in the intermetallic compound of Ni and Al after the solution treatment and the aging treatment and contributes to the increase in hardness. % Or more and a Zr content of 0.3% or more, even if contributing to an increase in hardness, inhibits cold workability and lowers manufacturability. The amount was less than 0.3%. In order to exert the effect of enhancing the magnetic properties and corrosion resistance, it is preferable that the Ti content is 0.1% or more and the Zr content is 0.01% or more.
[0021]
In the present invention, in addition to the above-mentioned composition components, Nb: 1.0% or less, Mo: 4.0% or less, Cu: 2.0% or less, B: 0.01% or less, and REM: 0 At least one of 0.1% or less can be contained as necessary.
[0022]
Nb: 1.0% or less Nb is an element effective for fixing C to enhance magnetic properties and corrosion resistance, but excessive addition of Nb exceeding 1.0% rather impairs magnetic properties. Since the cold workability is also impaired, the Nb content is set to 1.0% or less.
[0023]
Mo: 4.0% or less Mo is a ferrite stabilizing element and an element effective for improving corrosion resistance. However, the addition of excess Mo exceeding 4.0% impairs cold workability. To reduce the productivity, the Mo content is set to 4.0% or less.
[0024]
Cu: 2.0% or less Cu is an element effective for improving corrosion resistance and also contributes to age hardening. However, excessive addition exceeding 2.0% causes embrittlement and causes cold drawing or cold drawing. The Cu content is set to 2.0% or less because cold work such as straightening becomes difficult and productivity is reduced.
[0025]
B: 0.01% or less, REM: 0.1% or less Both B and REM contribute to the improvement of the cold workability. The contents of B and REM are set to 0.01% or less and REM: 0.1% or less, respectively, because they may be factors that impair workability.
[0026]
Next, an example of a method for producing a precipitation hardening type soft magnetic ferritic stainless steel according to the present invention will be described below.
[0027]
First, after melting and refining a steel material having the above component composition, for example, in a vacuum induction furnace, ingot, then slab at 1000 to 1100 ° C, and after heating to 1000 to 1100 ° C, hot rolling is performed. Wire, rod, or plate-shaped material.
Next, after annealing at 750 to 1100 ° C., in the case of a wire material, cold drawing and straightening are performed at a reduction in area of 5 to 25%. In the case of bar and plate materials, bend straightly in the cold.
Then, it heats to 1000-1100 degreeC, and after holding at this temperature for 1-2 hours, after performing a solution treatment by quenching using a forced air cooling fan or a water spray, etc., it bends and corrects, 500-600 degreeC Temperature for 2 to 3 hours and then subjected to aging treatment of air cooling or slow cooling with nitrogen gas or the like to precipitate and harden, whereby the precipitation hardening type soft magnetic ferritic stainless steel of the present invention can be manufactured. . It is to be noted that the age hardening treatment may be performed after the parts are processed in a solution-curved state. Alternatively, after the parts are processed after straightening in a cold state, a solution treatment and an age hardening treatment by heating in a vacuum or atmosphere furnace and quenching by nitrogen gas or the like may be performed.
【Example】
7 kg of steel materials having various component compositions shown in Table 1 were melted in an Ar gas flow, and cast into a mold to produce an ingot of 80 mmφ. Next, each ingot was hot forged at 1000 to 1050 ° C. to form a 24 mmφ round bar, further hot-swaging at 1000 to 1050 ° C. to form an 18 mmφ round bar, further annealed at 900 ° C., and cooled to 17 mmφ. Thinning was performed and subjected to various tests. Table 2 shows the results obtained by examining the hardness, magnetic properties, corrosion resistance, and cold workability of the samples thus obtained. The magnetic properties were as follows: a ring sample having an outer diameter of 10 mm, an inner diameter of 4.5 mm, and a thickness of 5 mm was prepared, heated at 1050 ° C. for 1 hour in a vacuum furnace, and then subjected to a solution treatment by quenching of the chamber gas. After aging treatment at 2 ° C. for 2 hours, measurement was performed using a BH loop tracer. Furthermore, the hardness was measured using the same sample. Corrosion resistance was determined by subjecting a round bar having a diameter of 15 mm and a length of 100 mm to the same heat treatment as a magnetic property evaluation sample, and spraying a 5% NaCl aqueous solution at 35 ° C. for 48 hours on a sample polished with No. 800 emery paper. The corrosion resistance was evaluated based on the degree of rust on the sample surface. The corrosion resistance was evaluated as "O" when rusting occurred locally or thinly at the corners of the end of the round bar even if there was no rusting, and "Rusting" when rusting was apparent otherwise. X "in two stages. In addition, the cold workability is evaluated by the presence or absence and the degree of occurrence of defects such as cracking and breakage during cold drawing during sample preparation, and more specifically, easily without the occurrence of the defects. The case where cold working was possible was evaluated as “○”, and the case where the defect occurred and the mass production process including cold working was difficult in other cases was evaluated as “X” in two stages. Table 2 shows the evaluation results.
[0029]
[Table 1]

[0030]
[Table 2]

[0031]
From the results shown in Table 2, the sample Nos. 1 to 7 are excellent in corrosion resistance and cold workability, have a hardness of 340 HV5 or more after aging treatment, and have almost no difference in magnetic properties before and after aging treatment, showing excellent values as a soft magnetic material. I have.
On the other hand, the sample No. Sample No. 8 has a low Cr content, and sample No. 8 of the comparative example. 9 because the Ni content is too large, a large magnetic flux density effects of both austenite stabilizing elements for small holding power even greater than 1 tesla B _25, poor magnetic properties as a magnetic material. In Comparative Example 10, although the magnetic properties were excellent, the hardness was significantly lower than 300 HV5 even after the aging treatment because the added amounts of Ni and Al were too small. Comparative Example 11 is inferior in magnetic properties because C and S, such as Ti and Zr, are not strongly added with a fixing element. Comparative Example 12 is excellent in hardness and magnetic properties, but is inferior in cold workability due to too high an addition amount of Cu, and frequently generates breaks and tears during cold drawing during production of a test steel. The yield before fabrication was also very low.
[0032]
【The invention's effect】
Thus, according to the present invention, it is needless to say that not only the magnetic properties and the corrosion resistance are excellent, but also the precipitation having both high hardness and good cold workability contributing to the improvement of durability such as wear resistance and buckling resistance. It is possible to provide hardened soft magnetic ferritic stainless steel, and if this stainless steel is applied to magnetic core materials such as various solenoid valves and electronically controlled fuel injection devices, durability can be improved and manufacturing costs can be reduced. In addition, it is preferable from the viewpoint of environmental protection and greatly contributes to the industry.

Claims

In mass%,
C: 0.2% or less,
Si: 0.01-3.0%,
Mn: 0.5% or less,
S: 0.3% or less,
Cr: 12.0-19.0%,
Ni: 1.0-4.0% and
Al: 0.2 to 4.0%, at least one of Ti: less than 0.5% and Zr: less than 0.3%, the balance being unavoidable impurities and substantially Fe composition, and solution treatment A precipitation hardening type soft magnetic ferritic stainless steel, wherein the structure after the aging treatment is substantially a ferrite phase, and the hardness after the aging treatment is 300 HV or more .

In mass%,
C: 0.2% or less,
Si: 0.01-3.0%,
Mn: 0.5% or less,
S: 0.3% or less,
Cr: 12.0-19.0%,
Ni: 1.0-4.0% and
Al: 0.2 to 4.0%, Ti: less than 0.5% and Zr: at least one of less than 0.3%, Nb: 1.0% or less, Mo: 4.0% or less, Cu: 2.0% or less, B: Contains at least one of 0.01% or less and REM: 0.1% or less, with the balance being unavoidable impurities and substantially Fe, and the structure after the solution treatment and the aging treatment is substantially Precipitation hardening type soft magnetic ferritic stainless steel characterized by a ferrite phase and a hardness after aging treatment of 300 HV or more .