JP2004099973A

JP2004099973A - Martensitic and ferritic stainless steel superior in hot workability and machinability

Info

Publication number: JP2004099973A
Application number: JP2002263610A
Authority: JP
Inventors: Satoshi Suzuki; 鈴木　聡; Hideki Tanaka; 田中　秀記; Naoto Hiramatsu; 平松　直人
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 2002-09-10
Filing date: 2002-09-10
Publication date: 2004-04-02
Anticipated expiration: 2022-09-10
Also published as: JP4272397B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a martensitic or ferritic stainless steel which controls reduction of the hot workability originating in a Cu-rich phase precipitated in grain boundaries, along with improving the machinability by dispersing the precipitations of the Cu-rich phase. <P>SOLUTION: This stainless steel has the Cu-rich phase containing Sn and/or In of 20 mass% or more dispersively precipitated in a martensitic or ferritic matrix at a rate of 0.2 vol.% or more, and contains B and/or Ti added so as to inhibit the Cu-rich phase from precipitating in the grain boundaries. The martensitic steel has an adjusted composition including 0.01-0.5% C, 1.0% or less Si, 1.0% or less Mn, 10-15% Cr, 0.60% or less Ni, 0.5-6.0% Cu, 0.5-3.0% Sn and/or In, 0.0005-0.2% B and/or 0.01-0.5% Ti. The ferritic steel has an adjusted composition including 0.001-0.5% C, 1.0% or less Si, 1.0% or less Mn, 15-30% Cr, 0.60% or less Ni, 0.5-6.0% Cu, 0.5-3.0% Sn and/or In, 0.0005-0.2% B and/or 0.01-0.5% Ti. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【産業上の利用分野】
本発明は、毒性のないＣｕの添加によって被削性を改善し、熱間加工性も良好なフェライト系又はマルテンサイト系ステンレス鋼及びその製造方法に関する。
【０００２】
【従来の技術】
精密機械工業の発達や家庭電気器具，家具調度品等の需要増加に応じ、従来ステンレス鋼が使用されていなかった部分にもステンレス鋼が使用されるようになってきた。また、工作機械の自動化・省力化に伴って被削性に優れたステンレス鋼に対するニーズが急増している。フェライト系では、快削性元素としてＳを添加したＪＩＳ　Ｇ４３０３規定のＳＵＳ４３０Ｆ，Ｓｅを添加したＳＡＥ規定の５１４３０（ＡＩＳＩ規格でＴｙｐｅ４３０Ｓｅ相当）等の鋼種がある。マルテンサイト系では、Ｐｂを添加したＪＩＳＧ４３０３規定のＳＵＳ４１０Ｆ，Ｓを添加したＳＵＳ４１６，ＳＵＳ４２０Ｆ等の鋼種がある。
【０００３】
快削性元素として有効なＳは、熱間加工性，延性及び耐食性を著しく低下させ、機械的性質に異方性を生じさせる原因にもなる。Ｐｂ添加で被削性を改善したフェライト系又はマルテンサイト系ステンレス鋼は、使用中に有害なＰｂが溶出し、リサイクル利用しにくい材料でもある。Ｓｅ添加で被削性を改善した鋼種では、有毒なＳｅが環境に悪影響を及ぼす。
【０００４】
【発明が解決しようとする課題】
快削性元素の添加に起因した材質の劣化や環境問題を考慮すると、快削性元素に代わる手段で被削性を改善する必要がある。このような観点から、本発明者等は、Ｃ含有量が一定量以上のマルテンサイト系又はフェライト系ステンレス鋼にＣｕを主体とする第二相（以下、Ｃｕリッチ相という）を所定量析出させると、材質や環境に有害な快削性元素の添加が必要なく被削性が著しく改善されることを見出した（特願２０００−１７７７８６号）。Ｃｕリッチ相にＳｎ又はＩｎを含ませるとＣｕリッチ相が低融点化し、被削性が更に改善される（特願２００１−２０５３４９号）。
【０００５】
ところが、低融点化したＣｕリッチ相を析出分散させたステンレス鋼を熱間加工すると、溶融状態又は半溶融状態になったＣｕリッチ相に応力が集中し、Ｃｕリッチ相を起点にする割れが散見される。割れ抑制の面からＣｕリッチ相の低融点化、換言すればＣｕリッチ相のＳｎ及び／又はＩｎ濃度に制約が加わり，被削性の向上に限界が生じる。他方、高形状精度の高い部品，部材への用途展開に伴ってステンレス鋼に対する被削性の要求が格段に過酷になっており、被削性の更なる改善が望まれる。
【０００６】
【課題を解決するための手段】
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、Ｃｕリッチ相の低融点化に伴う熱間加工性の劣化をＢ，Ｔｉを含む合金設計により抑え、Ｃｕリッチ相を一層低融点化させて被削性を更に改善したマルテンサイト系及びフェライト系ステンレス鋼を提供することを目的とする。
本発明に従ったマルテンサイト系及びフェライト系ステンレス鋼は、その目的を達成するため、Ｓｎ及び／又はＩｎ濃度２０質量％以上のＣｕリッチ相が０．２体積％以上の割合でマトリックスに分散析出し、Ｂ及び／又はＴｉ添加によってＣｕリッチ相の粒界析出を抑制している。
【０００７】
マルテンサイト系ステンレス鋼は、Ｃ：０．０１〜０．５質量％，Ｓｉ：１．０質量％以下，Ｍｎ：１．０質量％以下，Ｃｒ：１０〜１５質量％，Ｎｉ：０．６０質量％以下，Ｃｕ：０．５〜６．０質量％，Ｓｎ及び／又はＩｎ：０．５〜３．０質量％，Ｂ：０．０００５〜０．２質量％及び／又はＴｉ：０．０１〜０．５質量％を含んでいる。
フェライト系では，Ｃ：０．００１〜０．５質量％，Ｓｉ：１．０質量％以下，Ｍｎ：１．０質量％以下，Ｃｒ：１５〜３０質量％，Ｎｉ：０．６０質量％以下，Ｃｕ：０．５〜６．０質量％，Ｓｎ及び／又はＩｎ：０．５〜３．０質量％，Ｂ：０．０００５〜０．２質量％及び／又はＴｉ：０．０１〜０．５質量％，残部実質的にＦｅの合金設計が採用される。
Ｓｎ及び／又はＩｎが濃化されたＣｕリッチ相は、所定組成に調整されたマルテンサイト系又はフェライト系ステンレス鋼を熱間圧延した後、最終製品になるまでの過程で５００〜９００℃の温度域に１時間以上加熱する時効処理を施すことにより、マトリックスに分散析出する。
【０００８】
【作用】
先願・特願２００１−２０５３４９号で提案したように、ステンレス鋼に添加したＣｕの一部を微細なＣｕリッチ相として均一に分散析出させると被削性が改善される。Ｃｕリッチ相による被削性の改善は、切削時において工具掬い面上でのＣｕリッチ相による潤滑，熱伝導作用に基づく減摩により、切削抵抗の減少に併せて工具寿命が延びることによるものと考えられる。フェライト系ステンレス鋼や焼き鈍し状態のマルテンサイト系ステンレス鋼にＣｕリッチ相を分散析出させると、体心立方晶ｂ．ｃ．ｃ．のマトリックスに面心立方晶ｆ．ｃ．ｃ．のＣｕリッチ相が分散するため、Ｃｕリッチ相によって結晶整合性が低下し、大きな転位の集積が可能になる。その結果、Ｃｕリッチ相と同じ結晶構造のオーステナイト系ステンレス鋼に比較して格段に大きな被削性改善効果が得られる。
【０００９】
Ｃｕリッチ相が被削性に及ぼす影響は、Ｓｎ及び／又はＩｎの濃化によりＣｕリッチ相を低融点化すると格段に大きくなる。低融点化したＣｕリッチ相が分散したマトリックスは破壊現象である切削作用を受けやすく、しかも低融点のＣｕリッチ相（異物）が切削工具に対する潤滑剤として働き、ステンレス鋼板の被削性を向上させると共に切削工具を長寿命化する。低融点化による被削性改善効果は、Ｃｕリッチ相にＳｎ及び／又はＩｎを濃度２０質量％以上で濃化させるとき顕著になる。
しかし、Ｃｕリッチ相の低融点化は、被削性の向上には有効であるが熱間加工性に悪影響を及ぼす。熱間加工性の低下は、低融点化したＣｕリッチ相の粒界析出に起因した液膜脆化に原因がある。熱間加工性が低下すると、熱間圧延中のステンレス鋼板に割れが発生しやすくなり、工業的レベルでの安定製造が困難になる。このようなことから、先願（特願２００１−２０５３４９号）では、ステンレス鋼に添加するＳｎ及び／又はＩｎの上限を０．５質量％に規制している。
【００１０】
熱間加工性の低下がステンレス鋼の材質改善により防止可能になると、被削性の改善に有効なＣｕリッチ相の低融点化を一層進めることができる。そこで、本発明では、低融点化したＣｕリッチ相が熱間加工性を低下させるメカニズムを前提として、Ｃｕリッチ相の粒界析出をＢ及び／又はＴｉの添加によって抑制している。Ｂは結晶粒界に優先的に偏析する作用があり、Ｂの粒界偏析によってＣｕリッチ相の粒界析出が抑制される。Ｔｉは、Ｃｕリッチ相の析出核として働く炭化物，窒化物，硫化物等としてマトリックスに分散析出し、粒界に析出するＣｕリッチ相の絶対量を軽減する。Ｃｕリッチ相の粒界析出抑制に及ぼすＢ及び／又はＴｉの効果は、０．０００５質量％以上のＢ及び／又は０．０１質量％以上のＴｉで顕著になる。Ｂ及び／又はＴｉの添加によってＣｕリッチ相の粒界析出が抑えられるので、Ｃｕリッチ相を低融点化しても液膜脆化が発生しがたく、良好な熱間加工性が確保される。
【００１１】
被削性改善効果のあるＣｕリッチ相は、Ｃｕリッチ相が析出し易い温度域における時効等の等温加熱，加熱後の降温過程で析出温度域の通過時間を可能な限り長くする条件下での徐冷等によって析出する。具体的には、最終焼鈍後に５００〜９００℃の温度域で時効処理するとＳｎ又はＩｎを２０質量％以上含む低融点のＣｕリッチ相の析出が促進され、優れた被削性がマルテンサイト系及びフェライト系ステンレス鋼に付与される。
Ｔｉは、液膜脆化に起因した熱間加工性の低下防止に有効であると共に、Ｃｕリッチ相の析出を促進させる作用も呈する。Ｎｂ，Ｍｏ等もＴｉと同様に炭化物、窒化物となってＣｕリッチ相の析出を促進させる。炭化物，窒化物等は、Ｃｕリッチ相の析出核として働き、マトリックスにＣｕリッチ相を均一分散させ、結果としてＣｕリッチ相の粒界析出が抑制される。Ｃｕリッチ相の析出は、Ｓ含有量を増やして硫化物を形成することによっても促進される。
【００１２】
以下、本発明のマルテンサイト系及びフェライト系ステンレス鋼に含まれる合金成分，含有量等を説明する。
Ｃ：０．００１〜０．１質量％（フェライト系）
Ｃ：０．０１〜０．５質量％（マルテンサイト系）
Ｃｕリッチ相の析出核として有効なＣｒ炭化物を生成し、微細なＣｕリッチ相をマトリックス全体に渡って均一分散させる作用を呈する。このような作用を呈するためには、マルテンサイト系では０．０１質量％以上，フェライト系では０．００１質量％以上のＣ含有量が必要である。しかし、過剰なＣ含有は製造性や耐食性を低下させる原因となるので、マルテンサイト系では０．５質量％，フェライト系では０．１質量％にＣ含有量の上限を設定した。
【００１３】
Ｓｉ：１．０質量％以下
耐食性の改善に有効な合金成分であるが、１．０質量％を超える過剰量のＳｉ含有は製造性を劣化させる。
Ｍｎ：１．０質量％以下
製造性を改善すると共に、鋼中の有害なＳをＭｎＳとして固定する作用を呈する。ＭｎＳは、被削性の向上にも有効に働くと共に、Ｃｕリッチ相生成の核として作用するため、微細なＣｕリッチ相の生成に有効である。しかし、１．０質量％を超える過剰量のＭｎが含まれると、耐食性が劣化する傾向を示す。
Ｓ：０．１５質量％以下
被削性の改善に有効なＭｎＳを形成する元素であるが、０．１５重量％を超える過剰量のＳが含まれると熱間加工性及び延性が著しく低下する。
【００１４】
Ｃｒ：１０〜１５質量％（マルテンサイト系）
Ｃｒ：１０〜３０質量％（フェライト系）
ステンレス鋼本来の耐食性を維持するために必要な合金成分であり、要求される耐食性を確保するために１０質量％以上のＣｒを添加する。しかし、フェライト系では３０質量％を超える過剰量のＣｒが含まれると、製造性，加工性に悪影響を及ぼす。マルテンサイト系では１５質量％を超える過剰量のＣｒが含まれると、フェライト相が安定化し、焼入れ時にマルテンサイト組織が得られがたくなる。
Ｎｉ：０．６０質量％以下
フェライト系及びマルテンサイト系ステンレス鋼の工業的な製造工程では、原料から不可避的に混入する成分である。本発明では、通常の生産ラインで混入するレベルの上限値０．６０質量％にＮｉ含有量の上限を設定した。
【００１５】
Ｃｕ：０．５〜６．０質量％
被削性改善効果のあるＣｕリッチ相の析出に必要な合金成分であり、０．２体積％以上の割合でＣｕリッチ相をマトリックスに析出させるため、Ｃｕ含有量を０．５質量％以上に設定している。しかし、６．０質量％を超える過剰量のＣｕ添加は、製造性，加工性，耐食性等に悪影響を及ぼす。マトリックスに析出するＣｕリッチ相は、析出物のサイズに特別な制約を受けるものではないが、被削性を安定して改善する上で表面及び内部に均一分散していることが好ましい。
Ｓｎ及び／又はＩｎ：０．５〜３．０質量％
Ｃｕリッチ相の低融点化に有効な合金成分であり、Ｃｕリッチ相に２０質量％以上の濃度でＳｎ及び／又はＩｎを濃化させるためにＳｎ及び／又はＩｎを０．５質量％以上を添加する。しかし、Ｓｎ及び／又はＩｎの過剰添加はＣｕリッチ相の低融点化を必要以上に進め、熱間加工性に及ぼすＣｕリッチ相の悪影響をＢ及び／又はＴｉで抑制できなくなるので、Ｓｎ及び／又はＩｎ含有量の上限を３．０質量％に設定した。
【００１６】
Ｂ：０．０００５〜０．２質量％以下
熱間加工時に粒界に偏析し、熱間加工性に悪影響を及ぼすＣｕリッチ相の粒界析出を抑制する作用を呈する。マトリックスに分散したＢの析出物は析出核としても働き、Ｃｕリッチ相の均一分散に有効である。このような効果は、０．０００５質量％以上のＢ添加で顕著になる。しかし、Ｂの過剰添加は熱間加工性を低下させるので、Ｂ含有量の上限を０．２質量％に規制した。
【００１７】
Ｔｉ：０．０２〜０．５質量％
Ｃｕリッチ相の析出核となる炭化物，窒化物，炭窒化物，硫化物等の介在物として分散し、微細なＣｕリッチ相をマトリックスに均一分散させる。その結果、Ｃｕリッチ相の粒界析出が防止され、ひいては熱間加工性が向上する。しかし、０．５質量％を超える過剰量のＴｉを添加すると、鋼材の清浄度が低下し、耐食性，プレス加工性等が損なわれる。
以上に掲げた成分のほかに、必要に応じてＮｂ，Ｍｏ，Ｚｒ，Ａｌ，Ｖ，希土類元素（ＲＥＭ）等を添加することもできる。これらの任意成分は、以下の作用を呈する。
【００１８】
Ｎｂ：０．０１〜１質量％
Ｔｉと同様にＣｕリッチ相の析出核として有効な炭化物，窒化物，炭窒化物等を形成し、微細なＣｕリッチ相をマトリックスに均一分散させる。Ｎｂの添加効果は０．０１質量％以上でみられる。しかし、１質量％を超える過剰量のＮｂ添加は、製造性や加工性に悪影響を及ぼす。
Ｍｏ：３質量％以下
耐食性を向上させると共に、微細なＣｕリッチ相の核サイトとして有効なＦｅ_２Ｍｏ等の金属間化合物として析出する。しかし、３質量％を超える過剰なＭｏ含有は、製造性及び加工性に悪影響を及ぼす。
【００１９】
Ｚｒ：１質量％以下
微細なＣｕリッチ相の核サイトとして有効な炭窒化物となって析出する。しかし、Ｚｒの過剰添加は製造性や加工性に悪影響を及ぼすので、Ｚｒを添加する場合には含有量の上限を１質量％に規制する。
【００２０】
Ａｌ：１質量％以下
Ｍｏと同様に耐食性を改善すると共に、微細なＣｕリッチ相の核サイトとして有効な化合物として析出する。しかし、過剰なＡｌ添加は製造性及び加工性を劣化させるので、Ａｌを添加する場合には含有量の上限を１質量％に規制する。
【００２１】
Ｖ：１質量％以下
Ｚｒと同様に微細なＣｕリッチ相の核サイトとして有効な炭窒化物となって析出する。しかし、Ｖの過剰添加は製造性や加工性に悪影響を及ぼすので、Ｖを添加する場合には含有量の上限を１質量％に規制する。
【００２２】
希土類元素（ＲＥＭ）：０．０５質量％以下
必要に応じて添加される合金成分であり、適量の添加によってＢと同様に熱間加工性を改善する。また、Ｃｕリッチ相の析出に有効な析出物となってマトリックスに分散する。しかし、過剰に添加すると熱間加工性が劣化するので、希土類元素を添加する場合には含有量の上限を０．０５質量％に規制する。
【００２３】
熱処理温度：５００〜９００℃
Ｃｕリッチ相の析出により優れた被削性を得るためには、５００〜９００℃の時効処理が有効である。時効処理温度が低くなるほど、マトリックス中の固溶Ｃｕ量が少なくなり、Ｃｕリッチ相の析出量が増加する。しかし、低すぎる時効処理温度では、拡散速度が遅くなるため、析出量が却って減少する傾向がみられる。被削性に有効なＣｕリッチ相の析出に及ぼす時効処理温度の影響を種々の実験から調査したところ、５００〜９００℃の温度域で時効処理するとき、被削性に最も有効なＣｕリッチ相が０．２体積％以上の割合で析出することを見出した。析出したＣｕリッチ相は、抗菌性の向上にも有効である。時効処理は、好ましくは１時間以上で施され、熱間圧延終了後から製品となるまでの何れの段階で実施しても良い。
【００２４】
【実施例】
表１に示した組成をもつ各種マルテンサイト系ステンレス鋼を３００ｋｇ真空溶解炉で溶製し、鋳造後に１２３０℃で１時間加熱し、熱延工程を経て種々の温度で時効処理した。時効処理後のステンレス鋼帯を酸洗し、板厚４ｍｍ，板幅５００ｍｍ，長さ１２００ｍｍの供試材を得た。
【００２５】

【００２６】
横型フライス盤を用いた切削性評価試験で各鋼帯の切削性を評価した。切削性評価試験（図１）では、ＪＩＳ　Ｂ４１０７に規定される外径１２５ｍｍ，幅１０ｍｍの超硬バイト１を円周方向に等間隔で１６個装着させたフライス２を用い、圧延方向に直交する方向に送り方向Ｄを設定し、回転速度２０００ｒｐｍ，送り速度０．６ｍ／分，送り速度０．６ｍ／分，切込み深さ０．５ｍｍ，無潤滑の条件下で沿って被切削片３（鋼帯）をダウンカット方式で切削した。被切削片３の長手方向１２００ｍｍを切削した後、被切削片３の幅方向にフライス２を１０ｍｍ送って隣接する長手方向の切削を繰り返した。被切削片３の表面全域を０．５ｍｍ切り込んだ後、起点に戻り、新たに０．５ｍｍの切込みを繰り返した。この条件下で切削を継続し、超硬バイト１の刃先が０．１ｍｍ減少するまでの切削時間を寿命判定基準としてバイト摩耗を評価した。
【００２７】
同じ鋼帯から切り出された試験片を透過型電子顕微鏡で組織観察し、画像処理によってマトリックスに分散析出しているＣｕリッチ相を定量し、Ｃｕリッチ相の体積分率（体積％）を求めた。
更に、ＥＤＸ分析によりＣｕリッチ相のＳｎ，Ｉｎ濃度を測定した。
８１０℃×９時間で時効処理した試験番号ＭＡ−１〜ＭＯ−１の各鋼材について、熱間圧延された鋼帯のエッジ部を観察し、平滑な形状のエッジ部を○，圧延方向に直交する方向に沿って１ｍｍ以上の切込み（耳切れ）が検出されたエッジ部を×としてエッジ部の外観から熱間加工性を評価した。
【００２８】
更に、先願・特願２０００−１７７７８６号で紹介した被削性の良好な材料ＭＯ−１を基準とし、ＭＯ−１よりも優れた被削性を示す試験片を○，ＭＯ−１より被削性が劣る試験片を×として被削性を評価した。
表２の調査結果にみられるように、本発明で規定した成分・組成，Ｃｕリッチ相に関する条件を満足するＭＡ−１，ＭＢ−１，ＭＣ−１，ＭＤ−１，ＭＥ−１，ＭＪ−１，ＭＫ−１，ＭＬ−１，ＭＭ−１，ＭＮ−１は、何れも良好な被削性を示し、熱間加工性も優れていた。
【００２９】
他方、ＭＦ−１はＣｕが過剰，ＭＨ−１はＳｎが過剰，ＭＧ−１はＣｕ含有量が０．５質量％以上で０．５質量％以上のＳｎが添加されているもののＢ及び／又はＴｉが不足しているため、熱間加工性に劣っていた。成分・組成条件を満足するものの未時効のＭＡ−２，ＭＢ−２，ＭＣ−２，ＭＤ−２，ＭＥ−２では、Ｃｕリッチ相の体積分率が０．２体積％を下回っていることから被削性に劣っていた。時効処理材であってもＣｕ含有量が０．５質量％のＭＩ−１，ＭＩ−２では、Ｃｕリッチ相の析出量が０．２体積％に達せず、被削性に劣っていた。
【００３０】

【００３１】
【実施例２】
表１の鋼材ＭＣを用いて、実施例１と同じ条件で供試材を作製し、４５０〜９５０℃及び０．５〜１６時間の範囲で条件を種々変更した時効処理を施した。時効処理材の被削性を実施例１と同様に調査した。
表３の調査結果から、５００〜９００℃で１時間以上時効処理された試験番号ＭＣ−４，ＭＣ−６〜ＭＣ−１０は、Ｓｎ濃度２０質量％以上のＣｕリッチ相が０．２体積％以上の体積分率で析出しており、優れた被削性を示すことが判る。
【００３２】
時効処理温度が５００〜９００℃の範囲にあっても、時効処理時間が１時間に満たない試験番号ＭＣ−５では、Ｃｕリッチ相が０．２体積％に達せず、被削性に劣っていた。時効処理温度が５００℃未満のＭＣ−３や９００℃を超えるＭＣ−１１は、Ｃｕリッチ相の析出量が０．２体積％未満で、被削性に劣っていた。
以上の結果から、被削性の改善には０．５質量％以上のＣｕ含有量でＳｎ及び／又はＩｎの濃度が２０質量％以上のＣｕリッチ相が０．２体積％以上の体積分率で析出している必要があり、Ｃｕリッチ相を０．２体積％以上で析出させるために５００〜９００℃×１時間以上の時効処理が必要であることが確認された。
【００３３】

【００３４】
【実施例３】
表４に示した組成をもつ各種フェライト系ステンレス鋼を３００ｋｇ真空溶解炉で溶製し、鋳造後に１２３０℃で１時間加熱し、熱延工程を経て種々の温度で時効処理した。時効処理後のステンレス鋼帯を酸洗し、板厚４ｍｍ，板幅５００ｍｍ，長さ１２００ｍｍの供試材を得た。
【００３５】

【００３６】
実施例１と同じ被削性評価試験で各供試材の被削性を評価すると共に、Ｃｕリッチ相の体積分率，Ｓｎ濃度，Ｉｎ濃度を求めた。各供試材の被削性は、８２０℃×９時間の時効処理を施した後、先願・特願２０００−１７７７８６号で紹介した被削性の良好な材料ＦＭ−１を基準とし、ＦＭ−１より良好な被削性を示す供試材を○，ＦＭ−１より被削性が劣る供試材を×として評価した。
【００３７】
表５の調査結果にみられるように、本発明で規定した成分・組成及びＣｕリッチ相に関する条件を満足するＦＡ−１，ＦＢ−１，ＦＣ−１，ＦＧ−１，ＦＨ−１，ＦＩ−１，ＦＪ−１，ＦＫ−１は、何れも被削性に優れ、熱間加工性も良好であった。
他方、Ｃｕ含有量が０．５質量％以上であっても未時効のＦＡ−２，ＦＢ−２，ＦＣ−２では、Ｃｕリッチ相の体積分率が０．２体積％を下回っていることから被削性に劣っていた。時効処理材であってもＣｕ含有量が０．５質量％のＦＬ−１，ＦＬ−２では、Ｃｕリッチ相の析出量が０．２体積％に達せず被削性に劣っていた。
【００３８】

【００３９】
【実施例４】
表４に示した鋼材ＦＣを用い、実施例３と同じ条件で作製した供試材に４５０〜９５０℃及び０．５〜１６時間の範囲で条件を種々変更した時効処理を施した。時効処理材の被削性を実施例１と同様に調査した。
表６の調査結果にみられるように、５００〜９００℃で１時間以上時効処理された試験番号ＦＣ−４，ＦＣ−６〜ＦＣ−１０は、Ｓｎ濃度２０質量％以上のＣｕリッチ相が０．２体積％以上の体積分率で析出しており、優れた被削性を示した。
【００４０】
時効処理温度が５００〜９００℃の範囲にあっても、時効処理時間が１時間に満たない試験番号ＦＣ−５では、Ｃｕリッチ相が０．２体積％に達せず、被削性に劣っていた。時効処理温度が５００℃未満のＦＣ−３や９００℃を超えるＦＣ−１１では、Ｃｕリッチ相の析出量が０．２体積％未満で被削性に劣っていた。
以上の結果から、被削性の改善には０．５質量％以上のＣｕ含有量でＳｎ及び／又はＩｎの濃度が２０質量％以上のＣｕリッチ相が０．２体積％以上の体積分率で析出している必要があり、Ｃｕリッチ相を０．２体積％以上で析出させるために５００〜９００℃×１時間以上の時効処理が必要であることが確認された。
【００４１】

【００４２】
【発明の効果】
以上に説明したように、Ｓｎ及び／又はＩｎ濃度が２０質量％以上のＣｕリッチ相を０．２体積％以上の体積分率でマトリックスに分散析出させると共に、Ｂ及び／又はＴｉの添加によってＣｕリッチ相の粒界析出を抑制することにより、Ｃｕリッチ相により被削性を改善し、且つＣｕリッチ相の粒界析出に起因する液膜脆化を抑えて良好な熱間加工性を確保している。しかも、被削性改善のためにＳ，Ｐｂ，Ｂｉ，Ｓｅ等の有害元素を含んでいないため、材質の劣化がなく環境対策にかかる負担も軽減される。このようにして、本発明に従ったマルテンサイト系又はフェライト系ステンレス鋼は、優れた被削性を活かして必要形状に精度良く切削加工され、加工後の表面も良好なため、家庭電気器具，家具調度品，厨房機器，各種機械・器具，機器等の材料として広範な分野で使用される。
【図面の簡単な説明】
【図１】切削性評価試験の説明図
【符号の説明】
１：超硬バイト　　２：フライス　　３：被切削片　　Ｄ：送り方向[0001]
[Industrial application fields]
The present invention relates to a ferritic or martensitic stainless steel having improved machinability by addition of non-toxic Cu and good hot workability, and a method for producing the same.
[0002]
[Prior art]
With the development of the precision machine industry and the increasing demand for household appliances and furniture, stainless steel has come to be used in areas where stainless steel has not been used. In addition, with the automation and labor saving of machine tools, the need for stainless steel with excellent machinability is rapidly increasing. In the ferrite series, there are steel types such as SUS430F defined by JIS G4303 with S added as a free-cutting element, 51430 defined by SAE with Se added (equivalent to Type 430Se in AISI standard), and the like. In the martensite system, there are steel types such as SUS410F defined by JISG4303 with Pb added, SUS416F with S added, and SUS420F.
[0003]
S effective as a free-cutting element significantly reduces hot workability, ductility, and corrosion resistance, and causes anisotropy in mechanical properties. Ferritic or martensitic stainless steel with improved machinability by addition of Pb is also a material that is difficult to recycle due to the release of harmful Pb during use. In steel types that have improved machinability by adding Se, toxic Se has an adverse effect on the environment.
[0004]
[Problems to be solved by the invention]
Considering material deterioration and environmental problems caused by the addition of free-cutting elements, it is necessary to improve machinability by means in place of free-cutting elements. From such a viewpoint, the present inventors deposit a predetermined amount of a second phase (hereinafter referred to as Cu-rich phase) mainly composed of Cu in martensitic or ferritic stainless steel having a C content of a certain amount or more. It was found that the machinability was remarkably improved without the addition of a free-cutting element harmful to the material and the environment (Japanese Patent Application No. 2000-177786). When Sn or In is contained in the Cu rich phase, the Cu rich phase has a low melting point, and the machinability is further improved (Japanese Patent Application No. 2001-205349).
[0005]
However, when hot-working stainless steel in which a Cu-rich phase with a low melting point is precipitated and dispersed, stress concentrates on the Cu-rich phase that is in a molten or semi-molten state, and cracks that originate from the Cu-rich phase are scattered. Is done. In terms of suppressing cracking, lowering of the melting point of the Cu-rich phase, in other words, limiting the Sn and / or In concentration of the Cu-rich phase, limits the improvement of machinability. On the other hand, the demand for machinability for stainless steel has become extremely severe with the development of applications to parts and members with high shape accuracy, and further improvement of machinability is desired.
[0006]
[Means for Solving the Problems]
The present invention has been devised to solve such a problem, and the deterioration of hot workability due to the lowering of the melting point of the Cu-rich phase is suppressed by the alloy design containing B and Ti, and the Cu-rich phase is suppressed. An object of the present invention is to provide martensitic and ferritic stainless steels having a further lowered melting point and further improved machinability.
In order to achieve the object, the martensitic and ferritic stainless steels according to the present invention have a Cu-rich phase with Sn and / or In concentration of 20% by mass or more dispersed and precipitated in the matrix at a rate of 0.2% by volume or more. In addition, the addition of B and / or Ti suppresses the grain boundary precipitation of the Cu rich phase.
[0007]
Martensitic stainless steel has C: 0.01 to 0.5 mass%, Si: 1.0 mass% or less, Mn: 1.0 mass% or less, Cr: 10 to 15 mass%, Ni: 0.60 % By mass or less, Cu: 0.5 to 6.0% by mass, Sn and / or In: 0.5 to 3.0% by mass, B: 0.0005 to 0.2% by mass and / or Ti: 0.00%. 01-0.5 mass% is included.
In the ferrite system, C: 0.001 to 0.5 mass%, Si: 1.0 mass% or less, Mn: 1.0 mass% or less, Cr: 15 to 30 mass%, Ni: 0.60 mass% or less , Cu: 0.5 to 6.0 mass%, Sn and / or In: 0.5 to 3.0 mass%, B: 0.0005 to 0.2 mass%, and / or Ti: 0.01 to 0 .5% by weight, the balance being substantially Fe alloy design is adopted.
A Cu-rich phase enriched with Sn and / or In is a temperature of 500 to 900 ° C. in the process of hot rolling a martensitic or ferritic stainless steel adjusted to a predetermined composition until it becomes a final product. By subjecting the region to an aging treatment for heating for 1 hour or more, it is dispersed and precipitated in the matrix.
[0008]
[Action]
As proposed in Japanese Patent Application No. 2001-205349, machinability is improved when a part of Cu added to stainless steel is uniformly dispersed and precipitated as a fine Cu-rich phase. The improvement of the machinability due to the Cu-rich phase is due to the fact that the tool life is extended along with the reduction of the cutting resistance due to the lubrication due to the Cu-rich phase on the tool scooping surface at the time of cutting, and the anti-friction based on the heat conduction action. Conceivable. When the Cu-rich phase is dispersed and precipitated in ferritic stainless steel or annealed martensitic stainless steel, body-centered cubic b. c. c. Face-centered cubic f. c. c. Since the Cu-rich phase is dispersed, the crystal consistency is lowered by the Cu-rich phase, and a large amount of dislocations can be accumulated. As a result, a significantly greater machinability improving effect can be obtained as compared with austenitic stainless steel having the same crystal structure as the Cu-rich phase.
[0009]
The influence of the Cu-rich phase on the machinability is markedly increased when the melting point of the Cu-rich phase is lowered by Sn and / or In concentration. The matrix in which the low melting point Cu-rich phase is dispersed is susceptible to the cutting action that is a destructive phenomenon, and the low melting point Cu-rich phase (foreign matter) acts as a lubricant for the cutting tool to improve the machinability of the stainless steel plate. At the same time, the tool life is extended. The effect of improving the machinability by lowering the melting point becomes prominent when Sn and / or In is concentrated in the Cu-rich phase at a concentration of 20% by mass or more.
However, lowering the melting point of the Cu-rich phase is effective for improving machinability but adversely affects hot workability. The decrease in hot workability is caused by liquid film embrittlement due to grain boundary precipitation of the Cu-rich phase having a low melting point. When the hot workability is lowered, cracks are likely to occur in the stainless steel plate during hot rolling, and stable production at an industrial level becomes difficult. For this reason, in the prior application (Japanese Patent Application No. 2001-205349), the upper limit of Sn and / or In added to the stainless steel is regulated to 0.5 mass%.
[0010]
If the deterioration of hot workability can be prevented by improving the quality of stainless steel, it is possible to further reduce the melting point of the Cu-rich phase, which is effective for improving the machinability. Therefore, in the present invention, the grain boundary precipitation of the Cu-rich phase is suppressed by the addition of B and / or Ti on the premise of the mechanism by which the Cu-rich phase having a lowered melting point decreases the hot workability. B has an effect of preferentially segregating at the crystal grain boundaries, and the grain boundary segregation of the Cu-rich phase is suppressed by the grain boundary segregation of B. Ti disperses and precipitates in the matrix as carbides, nitrides, sulfides, etc. that act as precipitation nuclei for the Cu-rich phase, and reduces the absolute amount of the Cu-rich phase that precipitates at the grain boundaries. The effect of B and / or Ti on the grain boundary precipitation suppression of the Cu-rich phase becomes significant with 0.0005 mass% or more of B and / or 0.01 mass% or more of Ti. Since the addition of B and / or Ti suppresses grain boundary precipitation of the Cu-rich phase, even if the melting point of the Cu-rich phase is lowered, liquid film embrittlement hardly occurs and good hot workability is ensured.
[0011]
The Cu-rich phase, which has a machinability improving effect, is obtained under the condition that the passage time of the precipitation temperature range is made as long as possible during the isothermal heating such as aging in the temperature range where the Cu-rich phase is likely to precipitate and the temperature lowering process after the heating. Precipitated by slow cooling or the like. Specifically, when an aging treatment is performed in a temperature range of 500 to 900 ° C. after the final annealing, precipitation of a low melting point Cu-rich phase containing Sn or In at 20% by mass or more is promoted, and excellent machinability and It is given to ferritic stainless steel.
Ti is effective for preventing a decrease in hot workability due to liquid film embrittlement, and also has an effect of promoting precipitation of a Cu-rich phase. Nb, Mo, etc. also become carbides and nitrides like Ti, and promote the precipitation of the Cu rich phase. Carbides, nitrides, and the like act as precipitation nuclei for the Cu-rich phase and uniformly disperse the Cu-rich phase in the matrix, and as a result, grain boundary precipitation of the Cu-rich phase is suppressed. Precipitation of the Cu rich phase is also promoted by increasing the S content to form sulfides.
[0012]
Hereinafter, alloy components, contents, and the like included in the martensitic and ferritic stainless steels of the present invention will be described.
C: 0 . 001 to 0 . 1% by mass (ferrite type)
C: 0 . 01-0 . 5% by mass (Martensite)
Cr carbide effective as precipitation nuclei for the Cu-rich phase is generated, and the fine Cu-rich phase is uniformly dispersed throughout the matrix. In order to exhibit such an action, a C content of 0.01% by mass or more is required for the martensite system and 0.001% by mass or more for the ferrite system. However, since excessive C content causes a decrease in manufacturability and corrosion resistance, the upper limit of the C content is set to 0.5% by mass in the martensite system and 0.1% by mass in the ferrite system.
[0013]
Si: 1 . 0% by mass or less Although it is an effective alloy component for improving corrosion resistance, an excessive Si content exceeding 1.0% by mass deteriorates manufacturability.
Mn: 1 . 0% by mass or less Improves manufacturability and fixes harmful S in steel as MnS. MnS works effectively for improving machinability and also acts as a nucleus for the formation of a Cu-rich phase, so it is effective for producing a fine Cu-rich phase. However, when an excessive amount of Mn exceeding 1.0% by mass is contained, the corrosion resistance tends to deteriorate.
S: 0 . 15% by mass or less An element that forms MnS effective in improving machinability, but if excessive amount of S exceeding 0.15% by weight is contained, hot workability and ductility are remarkably reduced. .
[0014]
Cr: 10 to 15% by mass (Martensite series)
Cr: 10 to 30% by mass (ferrite type)
It is an alloy component necessary for maintaining the original corrosion resistance of stainless steel, and 10% by mass or more of Cr is added to ensure the required corrosion resistance. However, if the ferrite system contains an excessive amount of Cr exceeding 30% by mass, the manufacturability and workability are adversely affected. In the martensite system, if an excessive amount of Cr exceeding 15% by mass is contained, the ferrite phase is stabilized, and it is difficult to obtain a martensite structure during quenching.
Ni: 0 . 60% by mass or less In the industrial production process of ferritic and martensitic stainless steels, it is a component inevitably mixed from raw materials. In this invention, the upper limit of Ni content was set to the upper limit of 0.60 mass% of the level mixed in a normal production line.
[0015]
Cu: 0 . 5-6 . 0% by mass
It is an alloy component necessary for the precipitation of a Cu-rich phase having an effect of improving machinability, and the Cu-rich phase is precipitated in the matrix at a ratio of 0.2% by volume or more, so the Cu content is set to 0.5% by mass or more. It is set. However, addition of an excessive amount of Cu exceeding 6.0% by mass adversely affects manufacturability, workability, corrosion resistance, and the like. The Cu-rich phase precipitated in the matrix is not particularly restricted by the size of the precipitate, but is preferably uniformly dispersed on the surface and inside in order to stably improve the machinability.
Sn and / or In: 0.5-3 . 0% by mass
It is an alloy component effective for lowering the melting point of the Cu-rich phase, and in order to concentrate Sn and / or In at a concentration of 20% by mass or more in the Cu-rich phase, 0.5% by mass or more of Sn and / or In Added. However, excessive addition of Sn and / or In further advances the lowering of the melting point of the Cu-rich phase, and the adverse effect of the Cu-rich phase on hot workability cannot be suppressed by B and / or Ti. Or the upper limit of In content was set to 3.0 mass%.
[0016]
B: 0 . 0005-0 . 2% by mass or less It exhibits segregation at grain boundaries during hot working and suppresses grain boundary precipitation of a Cu-rich phase that adversely affects hot workability. B precipitates dispersed in the matrix also act as precipitation nuclei, and are effective for uniform dispersion of the Cu-rich phase. Such an effect becomes remarkable when B is added in an amount of 0.0005 mass% or more. However, excessive addition of B reduces hot workability, so the upper limit of B content was regulated to 0.2% by mass.
[0017]
Ti: 0.02-0 . 5% by mass
Disperse as inclusions such as carbides, nitrides, carbonitrides, sulfides, etc., which are Cu-rich phase precipitation nuclei, and fine Cu-rich phases are uniformly dispersed in the matrix. As a result, grain boundary precipitation of the Cu-rich phase is prevented, and consequently hot workability is improved. However, when an excessive amount of Ti exceeding 0.5% by mass is added, the cleanliness of the steel material is lowered, and the corrosion resistance, press workability and the like are impaired.
In addition to the components listed above, Nb, Mo, Zr, Al, V, rare earth elements (REM), and the like can be added as necessary. These optional components exhibit the following actions.
[0018]
Nb: 0 . 01-1% by mass
Like Ti, carbides, nitrides, carbonitrides and the like effective as precipitation nuclei for the Cu-rich phase are formed, and the fine Cu-rich phase is uniformly dispersed in the matrix. The effect of adding Nb is seen at 0.01% by mass or more. However, addition of an excessive amount of Nb exceeding 1% by mass adversely affects manufacturability and workability.
Mo: improves the 3 wt% or less <br/> corrosion resistance, precipitated as an intermetallic compound effective Fe 2 _Mo, etc. as nuclei sites fine Cu-rich phase. However, excessive Mo content exceeding 3% by mass adversely affects manufacturability and workability.
[0019]
Zr: 1% by mass or less Precipitated as a carbonitride effective as a nucleus site of a fine Cu-rich phase. However, excessive addition of Zr adversely affects manufacturability and processability, so when adding Zr, the upper limit of the content is restricted to 1% by mass.
[0020]
Al: 1% by mass or less In the same manner as Mo, the corrosion resistance is improved and the compound is precipitated as an effective compound as a core site of a fine Cu-rich phase. However, excessive addition of Al deteriorates manufacturability and workability, so when adding Al, the upper limit of the content is restricted to 1% by mass.
[0021]
V: 1% by mass or less As with Zr, it precipitates as a carbonitride effective as a nucleus site of a fine Cu-rich phase. However, excessive addition of V adversely affects manufacturability and workability. Therefore, when V is added, the upper limit of the content is restricted to 1% by mass.
[0022]
Rare earth elements (REM): 0 . 05% by mass or less An alloy component added as necessary, and by adding an appropriate amount, hot workability is improved in the same manner as B. Moreover, it becomes a precipitate effective for precipitation of the Cu-rich phase and is dispersed in the matrix. However, since hot workability deteriorates when excessively added, the upper limit of the content is restricted to 0.05 mass% when rare earth elements are added.
[0023]
Heat treatment temperature: 500-900 ° C
An aging treatment at 500 to 900 ° C. is effective for obtaining excellent machinability by precipitation of the Cu-rich phase. As the aging treatment temperature decreases, the amount of solid solution Cu in the matrix decreases and the precipitation amount of the Cu-rich phase increases. However, when the aging treatment temperature is too low, the diffusion rate becomes slow, so that the precipitation amount tends to decrease. The effect of aging temperature on the precipitation of Cu-rich phase effective for machinability was investigated from various experiments. When aging was performed in the temperature range of 500 to 900 ° C, Cu-rich phase most effective for machinability. Was found to precipitate at a rate of 0.2% by volume or more. The precipitated Cu rich phase is also effective in improving antibacterial properties. The aging treatment is preferably performed for 1 hour or longer, and may be performed at any stage from the end of hot rolling to the product.
[0024]
【Example】
Various martensitic stainless steels having the compositions shown in Table 1 were melted in a 300 kg vacuum melting furnace, heated at 1230 ° C. for 1 hour after casting, and subjected to aging treatment at various temperatures through a hot rolling process. The stainless steel strip after the aging treatment was pickled to obtain a test material having a plate thickness of 4 mm, a plate width of 500 mm, and a length of 1200 mm.
[0025]

[0026]
The machinability of each steel strip was evaluated by a machinability evaluation test using a horizontal milling machine. In the machinability evaluation test (FIG. 1), a milling machine 2 in which 16 carbide tools 1 having an outer diameter of 125 mm and a width of 10 mm defined by JIS B4107 are mounted at equal intervals in the circumferential direction is used, and is orthogonal to the rolling direction. The feed direction D is set in the direction, and the work piece 3 (steel) along the conditions of a rotational speed of 2000 rpm, a feed speed of 0.6 m / min, a feed speed of 0.6 m / min, a cutting depth of 0.5 mm, and no lubrication. Band) was cut by the down cut method. After cutting the longitudinal direction 1200 mm of the workpiece 3, the milling cutter 2 was fed 10 mm in the width direction of the workpiece 3 and the adjacent longitudinal cutting was repeated. After cutting the entire surface of the work piece 3 by 0.5 mm, it returned to the starting point and repeated 0.5 mm cutting. Cutting was continued under these conditions, and cutting tool wear was evaluated using the cutting time until the cutting edge of the carbide cutting tool 1 was reduced by 0.1 mm as a life criterion.
[0027]
The specimens cut from the same steel strip were observed with a transmission electron microscope, the Cu-rich phase dispersed and precipitated in the matrix was quantified by image processing, and the volume fraction (% by volume) of the Cu-rich phase was determined. .
Further, the Sn and In concentrations of the Cu rich phase were measured by EDX analysis.
For each steel material of test numbers MA-1 to MO-1 subjected to aging treatment at 810 ° C. for 9 hours, the edge portion of the hot-rolled steel strip was observed, the smooth edge portion was ○, and perpendicular to the rolling direction The hot workability was evaluated from the appearance of the edge portion, where x was an edge portion where a cut (ear breakage) of 1 mm or more was detected along the direction of cutting.
[0028]
Furthermore, on the basis of the material ma-1 with good machinability introduced in the prior application / Japanese Patent Application No. 2000-177786, a test piece exhibiting machinability superior to MO-1 was taken from ○ and MO-1. The machinability was evaluated with a test piece having inferior machinability as x.
As can be seen from the investigation results in Table 2, MA-1, MB-1, MC-1, MD-1, ME-1, MJ- satisfying the conditions related to the components / compositions and Cu rich phase defined in the present invention. 1, MK-1, ML-1, MM-1, and MN-1 all showed good machinability and excellent hot workability.
[0029]
On the other hand, MF-1 has an excess of Cu, MH-1 has an excess of Sn, MG-1 has a Cu content of 0.5 mass% or more and 0.5 mass% or more of Sn is added. Or since Ti was insufficient, it was inferior to hot workability. In the unaged MA-2, MB-2, MC-2, MD-2, and ME-2 that satisfy the component / composition conditions, the volume fraction of the Cu-rich phase is less than 0.2% by volume. It was inferior to machinability. Even in the case of aging treatment materials, in MI-1 and MI-2 having a Cu content of 0.5% by mass, the precipitation amount of the Cu-rich phase did not reach 0.2% by volume, and the machinability was poor.
[0030]

[0031]
[Example 2]
Using steel material MC of Table 1, the test material was produced on the same conditions as Example 1, and the aging treatment which changed various conditions in the range of 450-950 degreeC and 0.5 to 16 hours was performed. The machinability of the aging treatment material was investigated in the same manner as in Example 1.
From the investigation results shown in Table 3, test numbers MC-4 and MC-6 to MC-10 that were aged at 500 to 900 ° C. for 1 hour or more had 0.2% by volume of Cu-rich phase with Sn concentration of 20% by mass or more. It is found that the material is precipitated at the above volume fraction and exhibits excellent machinability.
[0032]
Even when the aging treatment temperature is in the range of 500 to 900 ° C., in the test number MC-5 in which the aging treatment time is less than 1 hour, the Cu-rich phase does not reach 0.2% by volume, and the machinability is inferior. It was. MC-3 having an aging treatment temperature of less than 500 ° C. or MC-11 exceeding 900 ° C. had a Cu-rich phase deposition amount of less than 0.2% by volume and was inferior in machinability.
From the above results, the volume fraction in which the Cu-rich phase having a Cu content of 0.5% by mass or more and the Sn and / or In concentration of 20% by mass or more is 0.2% by volume or more is used for improving machinability. It was confirmed that an aging treatment of 500 to 900 ° C. × 1 hour or more was necessary in order to precipitate the Cu-rich phase at 0.2% by volume or more.
[0033]

[0034]
[Example 3]
Various ferritic stainless steels having the compositions shown in Table 4 were melted in a 300 kg vacuum melting furnace, heated at 1230 ° C. for 1 hour after casting, and subjected to aging treatment at various temperatures through a hot rolling process. The stainless steel strip after the aging treatment was pickled to obtain a test material having a plate thickness of 4 mm, a plate width of 500 mm, and a length of 1200 mm.
[0035]

[0036]
The machinability of each test material was evaluated in the same machinability evaluation test as in Example 1, and the volume fraction, Sn concentration, and In concentration of the Cu-rich phase were determined. The machinability of each test material is FM based on the material FM-1 with good machinability introduced in the prior application / Japanese Patent Application No. 2000-177786 after aging treatment at 820 ° C. for 9 hours. The test material exhibiting better machinability than -1 was evaluated as ◯, and the test material inferior in machinability from FM-1 was evaluated as x.
[0037]
As can be seen from the investigation results of Table 5, FA-1, FB-1, FC-1, FG-1, FH-1, and FI- satisfying the conditions relating to the components and composition and Cu rich phase defined in the present invention. 1, FJ-1 and FK-1 were all excellent in machinability and good in hot workability.
On the other hand, the volume fraction of the Cu-rich phase is less than 0.2% by volume in unaged FA-2, FB-2, FC-2 even if the Cu content is 0.5 mass% or more. It was inferior to machinability. Even with an aging treatment material, in FL-1 and FL-2 having a Cu content of 0.5% by mass, the precipitation amount of the Cu-rich phase did not reach 0.2% by volume and the machinability was poor.
[0038]

[0039]
[Example 4]
Using the steel material FC shown in Table 4, the specimens produced under the same conditions as in Example 3 were subjected to an aging treatment in which the conditions were variously changed in the range of 450 to 950 ° C. and 0.5 to 16 hours. The machinability of the aging treatment material was investigated in the same manner as in Example 1.
As can be seen from the investigation results in Table 6, the test numbers FC-4 and FC-6 to FC-10 that were aged at 500 to 900 ° C. for 1 hour or more had 0 Cu-rich phase with an Sn concentration of 20 mass% or more. Precipitation was performed at a volume fraction of 2% by volume or more, and excellent machinability was exhibited.
[0040]
Even when the aging treatment temperature is in the range of 500 to 900 ° C., in the test number FC-5 in which the aging treatment time is less than 1 hour, the Cu rich phase does not reach 0.2% by volume and the machinability is inferior. It was. In FC-3 having an aging treatment temperature of less than 500 ° C. or FC-11 exceeding 900 ° C., the amount of Cu-rich phase deposited was less than 0.2% by volume, and the machinability was poor.
From the above results, the volume fraction in which the Cu-rich phase having a Cu content of 0.5% by mass or more and the Sn and / or In concentration of 20% by mass or more is 0.2% by volume or more is required for improving machinability It was confirmed that an aging treatment of 500 to 900 ° C. × 1 hour or more was necessary in order to precipitate the Cu-rich phase at 0.2% by volume or more.
[0041]

[0042]
【The invention's effect】
As explained above, a Cu-rich phase having a Sn and / or In concentration of 20% by mass or more is dispersed and precipitated in a matrix at a volume fraction of 0.2% by volume or more, and Cu and / or Ti are added to add Cu. By suppressing the grain boundary precipitation of the rich phase, the machinability is improved by the Cu rich phase, and the liquid film embrittlement due to the grain boundary precipitation of the Cu rich phase is suppressed to ensure good hot workability. ing. In addition, since no harmful elements such as S, Pb, Bi, and Se are included for improving machinability, the material is not deteriorated and the burden on environmental measures is reduced. In this way, the martensitic or ferritic stainless steel according to the present invention is precisely machined into the required shape by taking advantage of excellent machinability, and the surface after processing is also good. Used in a wide range of fields as materials for furniture furniture, kitchen equipment, various machines / appliances and equipment.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a machinability evaluation test.
1: Carbide bit 2: Milling 3: Piece to be cut D: Feed direction

Claims

C: 0.01 to 0.5 mass%, Si: 1.0 mass% or less, Mn: 1.0 mass% or less, Cr: 10 to 15 mass%, Ni: 0.60 mass% or less, Cu: 0 0.5-6.0 mass%, Sn and / or In: 0.5-3.0 mass%, B: 0.0005-0.2 mass% and / or Ti: 0.01-0.5 mass% The second phase mainly composed of Cu having the composition of Fe and the Sn and / or In concentration of 20% by mass or more is dispersed in the matrix at a ratio of 0.2% by volume or more. Martensitic stainless steel with excellent hot workability and machinability.

C: 0.001 to 0.5 mass%, Si: 1.0 mass% or less, Mn: 1.0 mass% or less, Cr: 15 to 30 mass%, Ni: 0.60 mass% or less, Cu: 0 0.5-6.0 mass%, Sn and / or In: 0.5-3.0 mass%, B: 0.0005-0.2 mass% and / or Ti: 0.01-0.5 mass% The second phase mainly composed of Cu having the composition of Fe and the Sn and / or In concentration of 20% by mass or more is dispersed in the matrix at a ratio of 0.2% by volume or more. Ferritic stainless steel with excellent hot workability and machinability.

After hot rolling the martensitic or ferritic stainless steel according to claim 1 or 2, an aging treatment is performed by heating in a temperature range of 500 to 900 ° C. for 1 hour or longer in the process until becoming a final product, Sn and A method for producing martensitic or ferritic stainless steel excellent in hot workability and machinability, characterized by promoting precipitation of a second phase mainly composed of Cu having an In concentration of 20% by mass or more.