JP2004115888A

JP2004115888A - Tire rim material and frame material for stainless steel-made two-wheeled vehicle excellent in deflecting resistance

Info

Publication number: JP2004115888A
Application number: JP2002283413A
Authority: JP
Inventors: Hiroki Tomimura; 冨村　宏紀; Hiroshi Fujimoto; 藤本　廣; Kenichi Morimoto; 森本　憲一; Naoto Hiramatsu; 平松　直人
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 2002-09-27
Filing date: 2002-09-27
Publication date: 2004-04-15
Anticipated expiration: 2022-09-27
Also published as: JP3920185B2; TWI275649B; TW200406494A; EP1403394A1; CN1490184A

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire rim material and a frame material for using stainless steel-made two-wheeled vehcle, such as a bicycle, a motorcycle, excellent in deflecting resistance without damaging corrosion resistance in welded point and this heat-affected part caused by welding. <P>SOLUTION: This tire material has the steel composition composed by mass% of ≤0.04% C, ≤2.0% Si, ≤2.0% Mn, 10.0-20.0% Cr, ≤4.0% Ni, ≤3.0% Cu, ≤0.12% N and the balance substantially Fe. Further, this tire rim material has ferrite + martensite double phase structure having the martensite amount adjusted so that value of a sensitizing index St shown in the following formula (1) becomes in the range of -31 to <-7, and also, the steel plate having ≥270 HV surface hardness, is formed as the blank. Then, the above formula is shown as the following. St=100C+30N-0.32γ. Wherein, γ is the martensite amount (%) at room temperature after annealing into the double phases. Further, this tire rim material can be contained of one or more elements among ≤0.015% B, ≤3.0% Mo, ≤0.10% Ti, ≤0.40% Nb and ≤0.30% V. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【産業上の利用分野】
本発明は、溶接熱影響部の耐食性ならびに耐たわみ性に優れた自転車，オートバイ，車いす等の二輪車用のタイヤリム材またはフレーム材に関する。
【０００２】
【従来の技術】
自転車，オートバイ，車いす等の二輪車に使用されるタイヤリム材またはフレーム材としては、使用環境によっては耐食性が要求されるため、従来のめっき品に代わってＳＵＳ４３０系のフェライト系ステンレス鋼が使用されている。
また上記部材は溶接接合されて使用されるので、優れた溶接性も要求される。このため、例えば特開昭６１−７３８６６号公報では、１０〜２０％のＣｒを含有するフェライト系ステンレス鋼に、０．１〜０．３％のＴｉと０．１５〜０．３％のＮｂを添加して、溶接部の靭性，延性及び耐食性を確保しつつ溶接時の座屈を防止することが提案されている。また、特開昭６２−１６４８５７号公報では、１２．５〜１７％のＣｒを含有するフェライト系ステンレス鋼において、Ｃ，Ｎを適度に低減した上で、Ｎｉ，Ｍｎ，Ｃｕ等のオーステナイト形成元素を適量添加し、溶接部にマルテンサイトを形成させることにより、Ｔｉ，Ｎｂの安定化元素を用いなくても、溶接部靭性及び加工性に問題を生じさせることなく、溶接の耐粒界腐食性を向上させた高強度のリム用ステンレス鋼材が得られることが報告されている。そして当該公報においては、マルテンサイト相を形成しやすくするために、その指標であるＣＥ値を所定に範囲にすることが示されている。
【０００３】
しかながら、特開昭６１−７３８６６号公報に記載されたような、Ｔｉを多量に含むフェライト系ステンレス鋼は、Ｔｉ介在物に起因したＴｉストリークが生成するといった問題点がある。
また、特開昭６２−１６４８５７号公報に記載されたステンレス鋼では、Ｃ＋Ｎを０．０４％以下に規定しているために、マルテンサイトを形成しても充分な強度がでない。強度向上のためには、合金元素の添加量を多くする必要が有り、結果的にコストが高くなっている。
本発明は、このような問題を解消すべく案出されたものであり、溶接性に優れ、溶接熱影響部及び母材の耐食性に優れ、且つ強度が高く、耐たわみ性も良好な自転車，オートバイ，車いす等の二輪車用のタイヤリム材またはフレーム材を低コストで提供することを目的とする。
【０００４】
【課題を解決するための手段】
本発明の耐たわみ性に優れたステンレス鋼製の二輪車用タイヤリム材は、その目的を達成するため、質量％で、Ｃ：０．０４％以下，Ｓｉ：２．０％以下，Ｍｎ：２．０％以下，Ｃｒ：１０．０〜２０．０％，Ｎｉ：４．０％以下，Ｃｕ：３．０％以下，Ｎ：０．１２％以下を含み、残部が実質的にＦｅからなる鋼組成を有し、５〜７５体積％のフェライトと２５〜９５体積％のマルテンサイトからなる複相組織であって、しかも下記（１）式で表される鋭敏化指数Ｓｔの値が−３１以上−７未満の範囲となるように調整されたマルテンサイト量の組織を有するとともに、表面硬度がＨＶ２７０以上の鋼板からなることを特徴とする。
Ｓｔ＝１００Ｃ＋３０Ｎ−０．３２γ　　・・・・（１）
ただし、γは複相化焼鈍後の室温でのマルテンサイト量（％）である。
【０００５】
また、本発明の耐たわみ性に優れたステンレス鋼製の二輪車用フレーム材は、質量％で、Ｃ：０．０４％以下，Ｓｉ：２．０％以下，Ｍｎ：２．０％以下，Ｃｒ：１０．０〜２０．０％，Ｎｉ：４．０％以下，Ｃｕ：３．０％以下，Ｎ：０．１２％以下を含み、残部が実質的にＦｅからなる鋼組成を有し、５〜７５体積％のフェライトと２５〜９５体積％のマルテンサイトからなる複相組織であって、しかも下記（１）式で表される鋭敏化指数Ｓｔの値が−３１以上−７未満の範囲となるマルテンサイト量の組織を有する鋼板を素材として造管され、母材部の表面硬度がＨＶ２７０以上の鋼管からなることを特徴とする。
Ｓｔ＝１００Ｃ＋３０Ｎ−０．３２γ　　・・・・（１）
ただし、γは複相化焼鈍後の室温でのマルテンサイト量（％）である。
【０００６】
このステンレス鋼製の二輪車用タイヤリム材及び二輪車用フレーム材は、さらに０．０１５％以下のＢ，３．０％以下のＭｏ，０．１０％以下のＴｉ，０．４０％以下のＮｂ，０．３０％以下のＶを１種または２種以上含有するものでもよい。
そして、このような溶接熱影響部の耐食性に優れる高強度複相ステンレス鋼帯，鋼板は、所定組成の冷延鋼帯を連続焼鈍炉に導入し、フェライト＋オーステナイトの二相域となる温度８５０〜１１００℃に加熱した後冷却する仕上げ複相化焼鈍を施すことにより、５体積％以上のフェライトを含むフェライト＋マルテンサイトの二相組織に調整することにより製造される。
【０００７】
【作用】
本発明者等は、溶接熱影響部の耐食性ならびに耐たわみ性に優れた自転車，オートバイ，車いす等の二輪車用のタイヤリム材或いはフレーム材に使用されるステンレス鋼板を得る手段について、種々検討した。なお、以下の説明では、自転車部品に限って説明する。オートバイ，車いす等でも同様であることは言うまでもない。
自転車の車体を構成する主要材料としては、タイヤリム材や各種パイプ材が挙げられる。これらの材料には、走行中の自転車に対してその安定性を維持するために、剛性、すなわちたわみ難いことが必要である。また、路面に近いタイヤリム材については、走行環境での腐食環境の影響を受けやすく、耐食性も必要である。さらに、タイヤリム材については、ブレーキ部品であるゴムに対する耐摩耗性も必要である。さらにまた、タイヤリム材或いはフレーム材では、走行中の小石等の飛散による凹凸の発生を抑制する耐デント性の改善も必要である。
【０００８】
その結果、加工誘起マルテンサイトとオーステナイトからなる準安定オーステナイト系ステンレス鋼ではなく、Ｃ含有量０．０４％以下，Ｎ含有量０．１２％以下，Ｃｒ含有量１０．０〜２０．０％のフェライトとマルテンサイトの複相組織のステンレス鋼において、複相化処理後の室温でのマルテンサイト量と、含有Ｃ量及び含有Ｎ量が関係する鋭敏化指数Ｓｔを所定の範囲内に設定することにより、目標とする耐たわみ性と耐食性を有する二輪車用タイヤリム材及び二輪車用フレーム材を得ることができたものである。
耐たわみ性は、硬度ＨＶを２７０以上に硬くすること、およびフェライト＋マルテンサイトの微細複合組織にすることでヤング率を大きくすることにより改善することができる。また、マルテンサイト相の生成により強度が上昇するため、耐デント性や耐摩耗性も向上されることになる。
【０００９】
ところで、フェライト＋マルテンサイトの複相組織を呈する母材に溶接を施すと、その入熱で温度が６００〜９００℃の温度域に達する。このような高温に達すると、Ｃｒ系炭窒化物が析出して母相にＣｒ欠乏層が生じ、鋭敏化現象が起きて耐食性が低下することになる。
フェライト，マルテンサイトともに結晶構造がｂｃｃ系で、Ｃ及びＮの固溶限がほとんどない。さらにｆｃｃ系のオーステナイトに比べ拡散が速いために炭窒化物系析出物が形成されやすい。そして、マルテンサイトは温度が上昇するとオーステナイトに逆変態する。このオーステナイトでは、フェライトやマルテンサイトに比べてはるかに多くのＣやＮを固溶する。特にＮは多く固溶する。逆変態に伴い、フェライトやマルテンサイト中に一度析出した炭窒化物は、逆変態で生成したオーステナイト中に再度固溶していく。もしくは、炭化物の生成には時間がかかるので、フェライトやマルテンサイト中に炭窒化物が析出する前に、オーステナイト域まで素早く昇温して逆変態すれば、炭窒化物生成によるＣｒ欠乏層に起因した鋭敏化は回避できると考えられる。速度論的にも、昇温過程でまずフェライトやマルテンサイトでの析出物形成領域を通過するが、析出現象にある程度潜伏期があることを考えると、析出前に逆変態が生じることは十分予想される。
そして、Ｃを含有したオーステナイトを冷却すると、Ｃ固溶オーステナイト相はマルテンサイト相に変態し、炭化物を析出させることなく強度も向上することができる。
【００１０】
本発明者等は、このようなメカニズムから、鋭敏化現象を促進する要素がＣ量とＮ量（特にＣはＮよりその作用が大きい）で、逆に鋭敏化を抑制する要素が複相化加熱状態での逆変態オーステナイト量（言い換えれば、逆変態し得る室温でのマルテンサイト量）であることを見出したものである。そして、室温でのマルテンサイト量を、高温で逆変態させたオーステナイト相に含有Ｃ，Ｎを固溶させるように、室温でのマルテンサイト量と含有Ｃ，Ｎ量を所定の関係にすれば、Ｃｒ炭化物の析出に起因する鋭敏化を防止でき、耐食性が良くなることを見出したものである。この３者の関係については、後に詳述する。
以下に、本発明タイヤリム材或いはフレーム材に含まれる合金成分，含有量等について詳しく説明する。なお、各元素の含有量を示す「％」は、本明細書中では、特に示さない限り「質量％」を意味する。
【００１１】
Ｃ：０．０４％以下
Ｃはオーステナイト形成元素で、マルテンサイト相の強化に極めて有効であり、高温でのオーステナイト化温度Ａｃ１点以上の温度に加熱熱処理を行った後のマルテンサイト量を調整でき、強度の制御及び高強度化に有効に作用する。これらの作用は、０．１％以上のＣ含有量で顕著になる。しかし、多量のＣ含有は複相化処理後の冷却中や時効処理で粒界にＣｒ炭化物が析出し、耐粒界腐食性低下の原因となるので、Ｃは０．０４％以下とした。
Ｓｉ：２．０％以下
Ｓｉは通常脱酸の目的で添加される。また、Ｓｉはマルテンサイト相を硬くするとともに、オーステナイト相にも固溶しこれを硬化させ、冷間加工後の強度を大きくする。さらに時効処理においては歪み時効により時効硬化能を促進する。このようにＳｉには種々の効果があるが、過度の添加は高温割れを誘発しやすくし、製造上種々の問題が生じる。このため、Ｓｉ添加量は２．０％以下とした。
【００１２】
Ｃｒ：１０．０〜２０．０質量％
Ｃｒは耐食性上、必須の成分である。意図する耐食性を賦与するためには、少なくとも１０．０％のＣｒを必要とする。しかし、２０．０％を超える過剰のＣｒは、靭性を低下する。またマルテンサイトを生成させて高強度を得るために必要なオーステナイト形成元素（Ｃ，Ｎ，Ｎｉ，Ｍｎ，Ｃｕ等）を添加しなければならなくなって、鋼帯，鋼板のコスト上昇を招くばかりでなく、室温でのオーステナイトの安定化をもたらして高強度を得ることが不可能になる。したがって、Ｃｒ含有量の上限は２０．０％とする。
【００１３】
Ｍｎ：２．０％以下
Ｎｉ：４．０％以下
Ｃｕ：３．０％以下
Ｎｉ，Ｍｎ及びＣｕはオーステナイト形成元素で、高温でフェライト＋オーステナイトの組織（室温でフェライト＋マルテンサイトの組織）を得るために必要である。これらの元素の含有量が増加するにしたがってマルテンサイト量が増加し、高強度化をもたらすことができる。しかし、過剰の添加は、高温で生成したオーステナイト相が室温までの冷却中にマルテンサイトに変態せず、オーステナイトのまま残留し、強度低下を招くことになる。したがって、Ｍｎ量は２．０％以下、Ｎｉ量は４．０％以下、さらにＣｕ量は３．０％以下とした。
【００１４】
Ｎ：０．１２％以下
ＮもＣと同様にオーステナイト形成元素で、Ｃほどではないがマルテンサイト相の強化に極めて有効であり、高温でのオーステナイト化温度Ａｃ１点以上の温度に加熱熱処理を行った後のマルテンサイト量を調整でき、強度の制御及び高強度化に有効に作用する。また、Ｃに比較して鋭敏化が起こり難いので、複相化処理後の冷却中や時効処理で粒界に窒化物として析出して耐食性を低下させる窒素量は、Ｃに比べて高い。ただし、過度の含有はブローホール等の内部欠陥をもたらすので、Ｎ含有量の上限は０．１２％とした。
【００１５】
Ｂ：０．０１５％以下
Ｂは、熱間圧延温度域でのフェライト相とオーステナイト相の変形抵抗の差異により生じる熱延鋼帯でのエッジクラックの発生防止に有効な元素であるが、過度の添加は低融点硼化物を形成しやすくし、逆に熱間加工性や溶接高温割れをもたらすので、添加する場合も、上限は０．０１５％とする。
Ｍｏ：１．０％以下
Ｍｏは、耐食性向上に寄与するので、必要に応じて添加される。しかし、過剰のＭｏ添加は、熱間加工性の低下や鋼材コスト上昇の原因となるので、添加する場合、その上限は１．０％とする。
【００１６】
Ｔｉ：０．１０％以下
Ｎｂ：０．４０％以下
Ｖ：０．３０％以下
Ｔｉ，ＮｂならびにＶは、ＣやＮを炭窒化物として固定することにより、溶接熱影響部の耐食性を改善する元素である。さらに、結晶粒を微細にする作用があり、強度上昇面でも有効な元素である。しかし、ＴｉはＴｉクラスター起因の表面欠陥をもたらすので、添加する場合、その上限は０．１０％とする。Ｎｂは低融点合金層もしくは酸化に起因した溶接高温割れをもたらすので、添加する場合、その上限は０．４０％とする。また、Ｖは過剰添加で極端に高温強度が上昇して製造面で障害となるので、添加する場合、その上限は０．３０％とする。
【００１７】
なお、本発明が対象とする溶接熱影響部の耐食性ならびに耐たわみ性に優れた自転車，オートバイ，車いす等の二輪車用のタイヤリム材或いはフレーム材に適した高強度複相組織のステンレス鋼では、各合金成分の個々の含有量を以上のように規制するとともに、フェライト形成元素であるＡｌ等を添加し、常温でフェライト＋マルテンサイトの複合組織が得られるように各合金成分を調整してもよい。また、必要とする強度を低下させない限り、耐酸化性や熱間加工性を向上させる目的で、Ｙ，ＣａやＲＥＭ（希土類元素）を添加することもできる。
【００１８】
鋭敏化指数Ｓｔ：−３１以上−７未満
先に説明したように、溶接時に高温下に曝されると、Ｃｒ系炭窒化物が析出して母相にＣｒ欠乏層が生じ鋭敏化現象が起きて耐食性が低下することになる。そして、鋭敏化現象を促進する要素がＣ量とＮ量で、逆に鋭敏化を抑制する要素が複相化加熱状態での逆変態オーステナイト量（言い換えれば、逆変態し得る室温でのマルテンサイト量）である。そして、鋭敏化指数値Ｓｔとして、含有Ｃ量，含有Ｎ量及び室温でのマルテンサイト量を所定の関係にすれば、鋭敏化し難く、耐食性が良くなることを見出した。その鋭敏化指数値Ｓｔは後述する種々の予備実験を繰り返すことにより、下記（１）式なる関係式で表され、この値が−７未満であれば鋭敏化が起こらなくなることを見出した。しかし、−３１より小さくなると、強化元素であるＣやＮが不足してＨＶ２７０以上の高強度が得られなくなる。
Ｓｔ＝１００Ｃ＋３０Ｎ−０．３２γ　　・・・・（１）
ただし、γは複相化焼鈍後の室温でのマルテンサイト量（％）である。
このようなマルテンサイト量の鋼板は、例えば、７８０℃×１２時間均熱・炉冷の熱延板焼鈍を施した後、８０％の冷間圧延を行い、その後９５０℃×１分均熱・空冷の焼鈍を施すような熱処理法で得られる。
【００１９】
母材表面硬度：ＨＶ２７０以上
ＣやＮ、Ｎｉ含有量の選定及びマルテンサイト量の調整により、本発明鋼の溶接熱影響部の耐食性ならびに耐たわみ性に優れた自転車，オートバイ，車いす等の二輪車に使用されるタイヤリム材やフレーム材の硬度は調整されるが、軽量化やばね性も加味すると、溶接の熱影響のない母材での表面硬度はＨＶ２７０以上が必要である。この値に満たないと、二輪車に使用する際、所望の強度を持たせるためには肉厚を厚くせざるを得ず、結果的に重くなる。
このような強度を発現させ、二輪車に使用するのに充分な耐デント性や耐摩耗性を持たせるためには、室温で２５体積％以上のマルテンサイト相を形成させる必要がある。
【００２０】
【予備実験】
表１に示す成分の鋼材を真空溶解炉にて溶製し、鋳造，熱延にて板厚４．５ｍｍとし、７８０℃×１２時間均熱・炉冷の熱延板焼鈍を施した。さらに酸洗後、冷間圧延をして板厚１．５ｍｍとし、８００℃×１分均熱・空冷の中間焼鈍を施した後、再度、冷間圧延後、９５０℃×１分加熱での連続複相化熱処理を施し、最終板厚０．５ｍｍとした。
上記方法で製造した板厚０．５ｍｍｍのステンレス鋼板を素材にし、タイヤリム材を模擬した図１に示す形状の枠を作製した。溶接はＴＩＧ溶接で実施した。複相化処理後のマルテンサイト量は、板厚断面の２００μｍ×２００μｍ１０視野で算出した。溶接は溶接芯線を使用しないなめづけ溶接であり、溶接条件は以下の通りである
ＴＩＧ溶接条件；
電極：Ｗ（直径１．６ｍｍ），溶接電流：７０Ａ，トーチ移動速度：３００ｍｍ／ｍｉｎ，シールガス：アルゴン，流量：１０Ｌ／ｍｉｎ
溶接ビード部凸部をグラインダーで平滑化し、最終的に母材部と併せて＃４００研磨で仕上げた。試験片サイズは１００ｍｍ×１５０ｍｍとした。
耐食性試験はＪＩＳ　Ｈ８５０２に基づいたキャス試験で、２００時間実施した。キャス試験の条件は、ｐＨ３．０〜３．１の（５％ＮａＣｌ＋０．２６ｇ／ｌＣｕＣｌ_２＋酢酸）で、温度３５±２℃で行った。
そして溶接熱影響部の発銹の有無を調べて耐食性評価を評価した。その結果を図２に示す。なお、図中、発銹が認められなかったものを○で、発銹があったものを×で示している。
この結果から、１００Ｃ＋３０Ｎ−０．３２γ＝−７を境に溶接部発銹の有無が整理でき、溶接部の耐食性を維持するためには、Ｓｔ＝１００Ｃ＋３０Ｎ−０．３２γのＳｔを−７未満にする必要がある。なお、Ｓｔが−３１より小さくなると、強化元素であるＣやＮが不足してＨＶ２７０以上の高強度が得られなくなることは前記した通りである。
【００２１】

【００２２】
【実施例】
表２に示す成分の鋼材を真空溶解炉にて溶製し、鋳造，熱延にて板厚４．５ｍｍとし、７８０℃×１２時間均熱・炉冷の熱延板焼鈍を施した。さらに酸洗後、冷間圧延をして板厚１．５ｍｍとし、８００℃×１分均熱・空冷の中間焼鈍を施した後、再度、冷間圧延後、１０３０℃で均熱１分の焼鈍を施し、最終板厚０．５ｍｍとした。なお、表２中、鋼Ｎｏ．ＫはＳＵＳ４３０ＬＸであり、この鋼については、熱延板焼鈍ならびに冷延板の中間焼鈍条件は１０００℃×１分均熱とした。
【００２３】
表２の成分組成をもつ板厚０．５ｍｍのステンレス鋼板を素材にし、タイヤリム材を模擬した図１に示す形状の枠、及び直径３０ｍｍのステンレス鋼管を作製した。いずれもＴＩＧ溶接を行った。ＴＩＧ溶接は、溶接電流密度１５０Ａ，移動速度５００ｍｍ／ｍｉｎで実施した。溶接ビード部凸部をグラインダーで平滑化し、最終的に母材部と併せて、＃４００研磨で仕上げた。
耐たわみ試験は、図３に示したようなタイヤリム材を模擬した形状のハーフサイズ形状枠試験片Ｒに荷重５０ｋｇの重りＷをのせる試験の、試験前のＬ方向の高さと荷重を除去した後の高さの差を永久歪みとして評価した。５０ｋｇ荷重の重りを１時間のせて、荷重除去後の永久歪みが１ｍｍ以下であったものを合格（表３中では○）とした。
【００２４】

【００２５】
以上のようにして作製した各鋼板について、複相化処理後の室温でマルテンサイト量を測定して前記（１）式でＳｔ値を算出するとともに、表面ビッカース硬度（荷重１ｋｇ）、リム材たわみ試験前後のたわみ量ならびにリム材・フレーム材の耐食性試験を行った。
複相化処理後のマルテンサイト量は、板厚断面の２００μｍ×２００μｍ１０視野で算出した。耐食性試験はＪＩＳ　Ｈ８５０２に基づいたキャス試験で、２００時間実施した。キャス試験の条件は、ｐＨ３．０〜３．１の（５％ＮａＣｌ＋０．２６ｇ／ｌＣｕＣｌ_２＋酢酸）で、温度３５±２℃で行った。そして溶接熱影響部ならびに母材部の発銹の有無を調べて耐食性評価を評価した。
その結果を、耐たわみ試験の結果と併せて表３に示す。なお、表中、２００時間のキャス試験後、発銹が認められなかったものを○で、発銹があったものを×で示している。
【００２６】
表３の結果に見られるように、本発明鋼では、母材硬度ＨＶ２７０以上を維持しつつ、リム材ならびにステンレス鋼管はいずれもキャス試験で溶接部熱影響部・母材とも発銹していなかった。溶接熱影響部の耐食性も優れていることがわかった。また、耐たわみ試験でも、永久歪み量は１ｍｍ以下であった。
これに対して、比較鋼Ｎｏ．Ｉ、ならびにＮｏ．Ｊは、マルテンサイトとフェライトの複相組織が得られず、硬度ＨＶ２７０以上の高強度材が得られなかった。このため、耐たわみ試験でも永久歪み量は１ｍｍを大きく超えていた。
比較鋼Ｎｏ．Ｇ〜Ｊは、本発明鋼から成分もしくは鋭敏化指数Ｓｔ値が請求項に規定した範囲を外れるものである。比較鋼Ｎｏ．Ｇは含有Ｃが高く、比較鋼Ｎｏ．Ｈは含有Ｃ，Ｎ量が高いものである。このため溶接熱影響部の耐食性が十分でなかった。また比較鋼Ｎｏ．ＩはＣｒ含有量が低いために十分な耐食性を得ることができず、耐たわみ性も十分でなかった。比較鋼Ｎｏ．Ｊは成分含有量は規定の範囲内であるが、鋭敏化指数Ｓｔ値が請求項に規定した範囲を外れるために、溶接熱影響部の耐食性が劣っていた。溶接時の熱で鋭敏化が進み耐食性が低下したものである。
なお、比較鋼Ｎｏ．ＫはＳＵＳ４３０ＬＸであり、耐たわみ性が十分でなかった。
【００２７】

【００２８】
【発明の効果】
以上に説明したように、本発明では、フェライトとマルテンサイトの複相組織からなるステンレス鋼において、Ｃ及びＮの含有量をさほど低減させることなく、含有Ｃ量及び含有Ｎ量と、複相化処理でオーステナイトに逆変態するマルテンサイト量との関係を、所定の関係にすることにより、溶接後の溶接熱影響部等で鋭敏化することなく、目標とする耐たわみ性と耐食性を併せ持つ二輪車用タイヤリム材及び二輪車用フレーム材を得ることができたものである。
【図面の簡単な説明】
【図１】タイヤリム模擬成形品形状を説明する断面図
【図２】Ｃ，Ｎ含有量及びγ量と溶接部耐食性の関係を示す図
【図３】耐たわみ試験方法の概略を説明する図[0001]
[Industrial applications]
The present invention relates to a tire rim material or a frame material for motorcycles such as bicycles, motorcycles, wheelchairs and the like, which has excellent corrosion resistance and bending resistance of a weld heat affected zone.
[0002]
[Prior art]
As a tire rim material or a frame material used for motorcycles such as bicycles, motorcycles, wheelchairs, etc., corrosion resistance is required depending on the use environment, so SUS430-based ferritic stainless steel is used instead of conventional plated products. .
Further, since the above members are used by being welded and joined, excellent weldability is also required. Therefore, for example, in Japanese Patent Application Laid-Open No. 61-73866, a ferritic stainless steel containing 10 to 20% of Cr is added with 0.1 to 0.3% of Ti and 0.15 to 0.3% of Nb. Has been proposed to prevent buckling during welding while ensuring the toughness, ductility and corrosion resistance of the weld. Japanese Patent Application Laid-Open No. Sho 62-164857 discloses an austenite-forming element such as Ni, Mn, and Cu, in a ferritic stainless steel containing 12.5 to 17% of Cr, after appropriately reducing C and N. By adding an appropriate amount of to form martensite in the welded portion, without using a stabilizing element for Ti and Nb, without causing problems in weld toughness and workability, and at the intergranular corrosion resistance of the weld. It has been reported that a high-strength stainless steel material for rims having improved properties can be obtained. In this publication, in order to facilitate the formation of a martensite phase, it is disclosed that the CE value, which is an index thereof, is set within a predetermined range.
[0003]
However, a ferritic stainless steel containing a large amount of Ti as described in JP-A-61-73866 has a problem that Ti streaks are generated due to Ti inclusions.
Further, in the stainless steel described in Japanese Patent Application Laid-Open No. 62-164857, since C + N is regulated to 0.04% or less, sufficient strength is not obtained even when martensite is formed. In order to improve the strength, it is necessary to increase the addition amount of the alloy element, and as a result, the cost is increased.
The present invention has been devised to solve such a problem, and has excellent weldability, excellent corrosion resistance of a weld heat affected zone and a base material, high strength, and good bending resistance. It is an object to provide a low cost tire rim material or frame material for motorcycles such as motorcycles and wheelchairs.
[0004]
[Means for Solving the Problems]
In order to achieve the object, the stainless steel tire rim material of the present invention, which is excellent in deflection resistance and is made of stainless steel, has C: 0.04% or less, Si: 2.0% or less, Mn: 2. 0% or less, Cr: 10.0 to 20.0%, Ni: 4.0% or less, Cu: 3.0% or less, N: 0.12% or less, the balance being substantially Fe It has a composition, has a dual phase structure of 5 to 75% by volume of ferrite and 25 to 95% by volume of martensite, and has a value of a sensitization index St represented by the following formula (1) of -31 or more. It has a structure of a martensite amount adjusted to be less than −7 and is made of a steel plate having a surface hardness of HV270 or more.
St = 100C + 30N−0.32γ (1)
Here, γ is the amount of martensite (%) at room temperature after the dual phase annealing.
[0005]
Further, the frame material for a motorcycle made of stainless steel having excellent flex resistance according to the present invention is, in mass%, C: 0.04% or less, Si: 2.0% or less, Mn: 2.0% or less, Cr: Having a steel composition containing 10.0 to 20.0%, Ni: 4.0% or less, Cu: 3.0% or less, N: 0.12% or less, and the balance substantially consisting of Fe; It has a dual phase structure composed of 5 to 75% by volume of ferrite and 25 to 95% by volume of martensite, and has a value of a sensitization index St represented by the following formula (1) of -31 or more and less than -7. The steel pipe is made from a steel sheet having a structure of the amount of martensite, and has a surface hardness of HV270 or more in a base material portion.
St = 100C + 30N−0.32γ (1)
Here, γ is the amount of martensite (%) at room temperature after the dual phase annealing.
[0006]
The tire rim material and the frame material for motorcycle made of stainless steel further include B at 0.015% or less, Mo at 3.0% or less, Ti at 0.10% or less, and Nb, 0 at 0.40% or less. It may contain one or more kinds of V of .30% or less.
The high-strength duplex stainless steel strip and steel sheet having excellent corrosion resistance in the weld heat affected zone are introduced into a continuous annealing furnace by introducing a cold-rolled steel strip having a predetermined composition into a continuous annealing furnace at a temperature of 850 in a two-phase region of ferrite + austenite. It is manufactured by adjusting to a two-phase structure of ferrite + martensite containing 5% by volume or more of ferrite by performing finish dual-phase annealing in which the steel is heated to １1100 ° C. and then cooled.
[0007]
[Action]
The present inventors have studied various means for obtaining a stainless steel plate used for a tire rim material or a frame material for motorcycles such as bicycles, motorcycles and wheelchairs, which has excellent corrosion resistance and bending resistance of the weld heat affected zone. In the following description, only the bicycle parts will be described. It goes without saying that the same applies to motorcycles and wheelchairs.
The main materials constituting the bicycle body include tire rim materials and various pipe materials. These materials need to be rigid, i.e., non-flexible, in order to maintain their stability against the running bicycle. Further, tire rim materials close to the road surface are susceptible to a corrosive environment in a running environment and need to have corrosion resistance. Further, the tire rim material needs to have abrasion resistance to rubber as a brake component. Further, in the case of a tire rim material or a frame material, it is necessary to improve dent resistance for suppressing the occurrence of unevenness due to scattering of pebbles or the like during running.
[0008]
As a result, it is not a metastable austenitic stainless steel composed of work-induced martensite and austenite, but a C content of 0.04% or less, an N content of 0.12% or less, and a Cr content of 10.0 to 20.0%. In a stainless steel having a dual phase structure of ferrite and martensite, the martensite amount at room temperature after the dual phase treatment and the sensitization index St related to the content of C and the content of N are set within a predetermined range. As a result, a tire rim material for a motorcycle and a frame material for a motorcycle having target deflection resistance and corrosion resistance can be obtained.
The bending resistance can be improved by increasing the hardness HV to 270 or more and increasing the Young's modulus by forming a fine composite structure of ferrite and martensite. Further, since the strength is increased by the formation of the martensite phase, the dent resistance and the wear resistance are also improved.
[0009]
By the way, when welding is performed on a base material exhibiting a dual phase structure of ferrite and martensite, the temperature reaches a temperature range of 600 to 900 ° C. due to the heat input. When the temperature reaches such a high temperature, Cr-based carbonitride precipitates to form a Cr-deficient layer in the parent phase, causing a sensitization phenomenon and a reduction in corrosion resistance.
Both ferrite and martensite have a bcc-based crystal structure, and have almost no solid solubility limit of C and N. In addition, carbon nitride-based precipitates are easily formed due to faster diffusion than fcc-based austenite. Then, martensite reversely transforms to austenite when the temperature rises. In this austenite, much more C and N form a solid solution than ferrite and martensite. In particular, N forms a large solid solution. Along with the reverse transformation, the carbonitride once precipitated in ferrite or martensite forms a solid solution again in the austenite formed by the reverse transformation. Alternatively, since the formation of carbides takes time, if the temperature is quickly raised to the austenite region and reverse transformation occurs before the carbonitrides are precipitated in ferrite or martensite, the carbon-nitride formation causes a Cr-deficient layer. It is thought that the sensitization can be avoided. Kinetics also pass through the precipitate formation region of ferrite or martensite during the temperature rise process, but considering that the precipitation phenomenon has a certain incubation period, it is well anticipated that reverse transformation will occur before precipitation. You.
Then, when the C-containing austenite is cooled, the C-dissolved austenite phase is transformed into a martensite phase, and the strength can be improved without depositing carbides.
[0010]
According to the present inventors, from such a mechanism, the elements that promote the sensitization phenomenon are the C amount and the N amount (particularly, C has a larger effect than N), and the element that suppresses the sensitization is a polyphase. It has been found that the amount of reverse transformed austenite in the heated state (in other words, the amount of martensite at room temperature at which reverse transformation is possible). If the amount of martensite at room temperature and the amount of contained C and N are set so as to form a solid solution of the contained C and N in the austenite phase reverse-transformed at high temperature, It has been found that sensitization caused by the precipitation of Cr carbide can be prevented and the corrosion resistance is improved. The relationship between the three will be described later.
Hereinafter, alloy components, contents, and the like contained in the tire rim material or the frame material of the present invention will be described in detail. In addition, “%” indicating the content of each element means “% by mass” in this specification unless otherwise specified.
[0011]
C: 0 . C of less than 04% is an austenite-forming element and is extremely effective in strengthening the martensite phase. The amount of martensite after heat treatment at a temperature equal to or higher than the austenitizing temperature Ac1 at a high temperature can be adjusted to control the strength. And effectively acts to increase the strength. These effects become remarkable at a C content of 0.1% or more. However, a large amount of C causes precipitation of Cr carbide at the grain boundaries during cooling after aging treatment or aging treatment, which causes a decrease in intergranular corrosion resistance. Therefore, C was set to 0.04% or less.
Si: 2.0% or less Si is usually added for the purpose of deoxidation. In addition, Si hardens the martensite phase and also forms a solid solution in the austenite phase to harden it, thereby increasing the strength after cold working. Further, in the aging treatment, age hardening ability is promoted by strain aging. As described above, Si has various effects, but excessive addition easily causes hot cracking, and causes various problems in production. For this reason, the addition amount of Si is set to 2.0% or less.
[0012]
Cr: 10.0 to 20.0 mass%
Cr is an essential component in terms of corrosion resistance. At least 10.0% Cr is required to provide the intended corrosion resistance. However, an excessive amount of Cr exceeding 20.0% lowers toughness. In addition, an austenite forming element (C, N, Ni, Mn, Cu, etc.) necessary for forming martensite and obtaining high strength must be added, which only increases costs of steel strips and steel sheets. In addition, it becomes impossible to obtain high strength by stabilizing austenite at room temperature. Therefore, the upper limit of the Cr content is 20.0%.
[0013]
Mn: 2.0% or less
Ni: 4.0% or less
Cu: 3.0% or less Ni, Mn and Cu are austenite forming elements and are necessary to obtain a ferrite + austenite structure at high temperature (a ferrite + martensite structure at room temperature). As the content of these elements increases, the amount of martensite increases, and higher strength can be achieved. However, excessive addition does not transform the austenite phase formed at a high temperature into martensite during cooling to room temperature, but remains as austenite, resulting in a decrease in strength. Therefore, the Mn content was 2.0% or less, the Ni content was 4.0% or less, and the Cu content was 3.0% or less.
[0014]
N: 0.12% or less N is also an austenite-forming element like C, and although not as effective as C, is extremely effective in strengthening the martensitic phase, and is subjected to heat treatment at a temperature higher than the austenitizing temperature Ac1 point at a high temperature. The amount of martensite after the heat treatment can be adjusted, which effectively controls the strength and increases the strength. In addition, since sensitization is less likely to occur as compared with C, the amount of nitrogen that precipitates as nitrides at grain boundaries during cooling after aging treatment and aging treatment and lowers corrosion resistance is higher than that of C. However, since excessive content causes internal defects such as blowholes, the upper limit of the N content is set to 0.12%.
[0015]
B: 0.015% or less B is an element effective in preventing the occurrence of edge cracks in a hot-rolled steel strip caused by a difference in deformation resistance between a ferrite phase and an austenite phase in a hot rolling temperature range. The addition facilitates the formation of low-melting-point borides and, on the contrary, causes hot workability and hot cracking of the weld. Therefore, the upper limit of the addition is also 0.015%.
Mo: 1.0% or less Mo contributes to the improvement of corrosion resistance, and is added as necessary. However, excessive Mo addition causes a reduction in hot workability and an increase in steel material cost. Therefore, when adding Mo, the upper limit is made 1.0%.
[0016]
Ti: 0.10% or less
Nb: 0.40% or less
V: 0.30% or less Ti, Nb and V are elements that improve the corrosion resistance of the heat affected zone by fixing C and N as carbonitrides. Further, it has an effect of making crystal grains fine, and is also an effective element in terms of increasing strength. However, since Ti causes a surface defect caused by Ti clusters, the upper limit when added is 0.10%. Since Nb causes a high-temperature welding crack due to a low-melting alloy layer or oxidation, the upper limit of Nb is set to 0.40%. Further, when V is added excessively, the high-temperature strength is extremely increased and hinders production, so when V is added, the upper limit is set to 0.30%.
[0017]
In addition, in the stainless steel having a high-strength duplex structure suitable for a tire rim material or a frame material for motorcycles such as bicycles, motorcycles and wheelchairs, which is excellent in corrosion resistance and bending resistance of the weld heat affected zone targeted by the present invention, The individual contents of the alloy components may be regulated as described above, and a ferrite-forming element such as Al may be added, and the alloy components may be adjusted so that a composite structure of ferrite and martensite is obtained at room temperature. . Further, as long as the required strength is not reduced, Y, Ca or REM (rare earth element) can be added for the purpose of improving oxidation resistance and hot workability.
[0018]
Sensitization index St: -31 or more and less than -7 As described above, when exposed to a high temperature during welding, a Cr-based carbonitride precipitates and a Cr-deficient layer is formed in the matrix, resulting in a sharpness. A corrosion phenomenon occurs and the corrosion resistance decreases. The elements that promote the sensitization phenomenon are the amounts of C and N, while the elements that suppress the sensitization are the amounts of the reverse-transformed austenite in the multi-phase heating state (in other words, martensite at room temperature at which the reverse transformation can be performed). Amount). Then, it was found that when the content C content, the content N content, and the amount of martensite at room temperature were in a predetermined relationship as the sensitization index value St, sensitization was difficult, and the corrosion resistance was improved. The sensitization index value St is represented by the following equation (1) by repeating various preliminary experiments described later, and it has been found that sensitization does not occur if this value is less than -7. However, if it is smaller than -31, the strengthening elements C and N are insufficient, so that a high strength of HV270 or more cannot be obtained.
St = 100C + 30N−0.32γ (1)
Here, γ is the amount of martensite (%) at room temperature after the dual phase annealing.
The steel sheet having such a martensite amount is, for example, subjected to hot rolling of 780 ° C. × 12 hours for soaking and furnace cooling, then to cold rolling of 80%, and then to 950 ° C. × 1 minute soaking. It can be obtained by a heat treatment such as air-cooled annealing.
[0019]
Base material surface hardness: HV270 or more By selecting the content of C, N, and Ni and adjusting the amount of martensite, the steel of the present invention can be applied to motorcycles such as bicycles, motorcycles, wheelchairs, etc., which are excellent in the corrosion resistance and bending resistance of the weld heat affected zone. The hardness of the tire rim material and frame material used is adjusted, but in consideration of weight reduction and resilience, the surface hardness of the base material having no heat effect of welding must be HV270 or more. If the value is less than this value, when used for a motorcycle, the thickness must be increased in order to have a desired strength, resulting in a heavy weight.
In order to develop such strength and provide sufficient dent resistance and wear resistance for use in a motorcycle, it is necessary to form a martensite phase of 25% by volume or more at room temperature.
[0020]
【Preliminary experiment】
A steel material having the components shown in Table 1 was melted in a vacuum melting furnace, cast and hot-rolled to a sheet thickness of 4.5 mm, and annealed at 780 ° C. × 12 hours for soaking and furnace cooling. Further, after pickling, cold rolling was performed to a sheet thickness of 1.5 mm, intermediate annealing at 800 ° C. × 1 minute for soaking and air cooling was performed, and after cold rolling again, heating was performed at 950 ° C. × 1 minute. Continuous heat treatment for two-phase was performed to a final thickness of 0.5 mm.
A stainless steel sheet having a thickness of 0.5 mm manufactured by the above method was used as a material, and a frame having a shape shown in FIG. 1 simulating a tire rim material was produced. The welding was performed by TIG welding. The amount of martensite after the biphasic treatment was calculated in 10 visual fields of 200 μm × 200 μm in the plate thickness cross section. The welding is tanning welding without using a welding core wire, and welding conditions are as follows: TIG welding conditions;
Electrode: W (diameter 1.6 mm), welding current: 70 A, torch moving speed: 300 mm / min, seal gas: argon, flow rate: 10 L / min
The convex portion of the weld bead portion was smoothed with a grinder, and finally finished with # 400 polishing together with the base material portion. The test piece size was 100 mm x 150 mm.
The corrosion resistance test was a Cas test based on JIS H8502 and was performed for 200 hours. The conditions of the Cass test were (pH 5 to 3.1) (5% NaCl + 0.26 g / l CuCl ₂ + acetic acid) at a temperature of 35 ± 2 ° C.
Then, the presence or absence of rust in the weld heat affected zone was examined to evaluate the corrosion resistance. The result is shown in FIG. In the figure, the symbol 銹 indicates that no rust was observed, and the symbol X indicates that rust occurred.
From this result, the presence or absence of rust on the weld can be arranged at the boundary of 100C + 30N−0.32γ = −7, and in order to maintain the corrosion resistance of the weld, the St of St = 100C + 30N−0.32γ should be less than −7. There is a need to. Note that, as described above, when St becomes smaller than -31, C and N as the strengthening elements become insufficient and high strength of HV270 or more cannot be obtained.
[0021]

[0022]
【Example】
Steel materials having the components shown in Table 2 were melted in a vacuum melting furnace, cast and hot-rolled to a sheet thickness of 4.5 mm, and subjected to 780 ° C. × 12 hours soaking and furnace-cooled hot rolled sheet annealing. Further, after pickling, cold rolling was performed to a sheet thickness of 1.5 mm, an intermediate annealing at 800 ° C. × 1 minute for soaking and air cooling was performed, and after cold rolling again, soaking at 1030 ° C. for 1 minute Annealing was performed to a final thickness of 0.5 mm. In Table 2, steel No. K is SUS430LX. For this steel, the conditions for hot-rolled sheet annealing and cold-rolled sheet intermediate annealing were 1000 ° C. × 1 minute soaking.
[0023]
Using a stainless steel plate having a component composition of Table 2 and a thickness of 0.5 mm as a material, a frame having a shape shown in FIG. 1 simulating a tire rim material and a stainless steel tube having a diameter of 30 mm were produced. In each case, TIG welding was performed. TIG welding was performed at a welding current density of 150 A and a moving speed of 500 mm / min. The convex portion of the weld bead portion was smoothed with a grinder, and finally finished together with the base material portion by # 400 polishing.
In the deflection test, the height and the load in the L direction before the test were removed in a test in which a weight W having a load of 50 kg was placed on a half-size frame test piece R having a shape simulating a tire rim material as shown in FIG. The later difference in height was evaluated as permanent strain. A weight with a 50 kg load was applied for 1 hour, and a specimen having a permanent set of 1 mm or less after the load was removed was evaluated as acceptable (in Table 3).
[0024]

[0025]
For each of the steel sheets prepared as described above, the amount of martensite was measured at room temperature after the dual phase treatment, the St value was calculated by the above equation (1), the surface Vickers hardness (load 1 kg), the rim material deflection The deflection amount before and after the test and the corrosion resistance test of the rim material and frame material were performed.
The amount of martensite after the biphasic treatment was calculated in 10 visual fields of 200 μm × 200 μm in the plate thickness cross section. The corrosion resistance test was a Cas test based on JIS H8502 and was performed for 200 hours. The conditions of the Cass test were (pH 5 to 3.1) (5% NaCl + 0.26 g / l CuCl ₂ + acetic acid) at a temperature of 35 ± 2 ° C. Then, the presence or absence of rust in the weld heat affected zone and the base metal was examined to evaluate the corrosion resistance.
Table 3 shows the results together with the results of the deflection test. In the table, ○ indicates that no rust was observed after the 200-hour cast test, and X indicates that rust occurred.
[0026]
As can be seen from the results in Table 3, in the steel of the present invention, while maintaining the base metal hardness of HV 270 or more, neither the rim material nor the stainless steel tube rusted in the weld heat-affected zone / base metal in the cast test. Was. It was also found that the corrosion resistance of the heat affected zone was excellent. Also, in the deflection resistance test, the amount of permanent distortion was 1 mm or less.
On the other hand, the comparative steel No. I, and No. As for J, a double phase structure of martensite and ferrite was not obtained, and a high-strength material having a hardness of HV270 or more was not obtained. For this reason, even in the deflection resistance test, the amount of permanent strain was much more than 1 mm.
Comparative steel No. G to J are those in which the component or sensitization index St value of the steel of the present invention is out of the range defined in the claims. Comparative steel No. G has a high content C, and comparative steel No. H has a high C and N content. Therefore, the corrosion resistance of the heat affected zone was not sufficient. In addition, the comparative steel No. I was not able to obtain sufficient corrosion resistance due to the low Cr content, and was not sufficiently flexible. Comparative steel No. J had a component content within the specified range, but the sensitization index St value was out of the range specified in the claims, so that the corrosion resistance of the weld heat affected zone was poor. The sensitization was advanced by the heat during welding, and the corrosion resistance was reduced.
In addition, comparative steel No. K was SUS430LX, and the deflection resistance was not sufficient.
[0027]

[0028]
【The invention's effect】
As described above, in the present invention, in a stainless steel having a dual phase structure of ferrite and martensite, the content of C and N is reduced without significantly reducing the content of C and N. By setting the relationship between the amount of martensite which reversely transforms to austenite during processing to a predetermined relationship, it does not sensitize the weld heat affected zone after welding, etc. A tire rim material and a frame material for a motorcycle can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating the shape of a simulated tire rim. FIG. 2 is a diagram illustrating the relationship between the C and N contents and the γ content and the corrosion resistance of a welded part. FIG.

Claims

In mass%, C: 0.04% or less, Si: 2.0% or less, Mn: 2.0% or less, Cr: 10.0 to 20.0%, Ni: 4.0% or less, Cu: 3 0.02% or less, N: 0.12% or less, the balance having a steel composition substantially consisting of Fe, and a multi-phase structure composed of 5 to 75% by volume of ferrite and 25 to 95% by volume of martensite. And a structure having a martensite amount adjusted so that the value of the sensitization index St represented by the following formula (1) falls within a range of −31 or more and less than −7, and a surface hardness of HV 270 or more A tire rim material for motorcycles made of stainless steel, which is made of stainless steel and has excellent resistance to bending.
St = 100C + 30N−0.32γ (1)
Here, γ is the amount of martensite (%) at room temperature after the dual phase annealing.

The steel composition further contains one or two types of B of 0.015% or less, Mo of 3.0% or less, Ti of 0.10% or less, Nb of 0.40% or less, and V of 0.30% or less. The tire rim material for motorcycles made of stainless steel having excellent flex resistance according to claim 1, which contains the above.

In mass%, C: 0.04% or less, Si: 2.0% or less, Mn: 2.0% or less, Cr: 10.0 to 20.0%, Ni: 4.0% or less, Cu: 3 0.02% or less, N: 0.12% or less, the balance having a steel composition substantially consisting of Fe, and a multi-phase structure composed of 5 to 75% by volume of ferrite and 25 to 95% by volume of martensite. The steel pipe having a structure of the martensite amount adjusted so that the value of the sensitization index St represented by the following formula (1) is in a range of −31 or more and less than −7 is formed into a pipe. A stainless steel frame material having excellent bending resistance, comprising a steel pipe having a base material having a surface hardness of HV270 or more.
St = 100C + 30N−0.32γ (1)
Here, γ is the amount of martensite (%) at room temperature after the dual phase annealing.

The steel composition further contains one or two types of B of 0.015% or less, Mo of 3.0% or less, Ti of 0.10% or less, Nb of 0.40% or less, and V of 0.30% or less. The frame material for a motorcycle made of stainless steel having excellent bending resistance according to claim 3, which contains the above.