JP3937128B2

JP3937128B2 - Spheroidal carbide alloy white cast iron

Info

Publication number: JP3937128B2
Application number: JP2001074906A
Authority: JP
Inventors: 恒夫高田; 忠橘堂; 守武村; 光昭松室
Original assignee: OSAKAPREFECTURAL GOVERNMENT
Current assignee: OSAKAPREFECTURAL GOVERNMENT
Priority date: 2001-03-15
Filing date: 2001-03-15
Publication date: 2007-06-27
Anticipated expiration: 2021-03-15
Also published as: JP2002275573A

Description

【０００１】
【発明の属する技術分野】
本発明は耐摩耗性の優れた高硬度材でありながら、さらに靭性も兼ね具えた合金白鋳鉄に係る。
【０００２】
【従来の技術】
多岐に亘る産業用機器、装置において摩耗作用に直面する部材は、自らの摩耗の進行によって装置毎に設定された所期の機能を失うに至るので部材の耐摩耗性は装置の運転効率を左右する重要な要因となる。摩耗作用は種々の形態に大別されるが、最も一般的には流動する処理材料との間に発生する擦過摩耗（アブレージョン）に対抗するため部材表面の硬度を高めることがまず有効とされ、硬度にほぼ比例的に耐摩耗性の向上が連動する。その意味で従来からＦｅ−Ｃ系では白鋳鉄、とくにＣｒなどを相当量配合して高い硬度の複合炭化物（ダブルカーバイド、たとえばＦｅ−Ｃｒ−Ｃ炭化物）を初晶、または共晶の形で晶出させて所期の耐摩耗性を満足させる合金白鋳鉄が多用されている。
【０００３】
一方、適用される装置の種類によっては単純な耐摩耗性だけでは十分な機能を果たし得ず、さらに別の要件を満たすことが求められる場合も少なくない。とくに問題となることは、耐摩耗性を向上する要件である炭化物そのものが硬い反面、脆いというマイナスの要素を本質的に具え、基地に晶出した形態も板状や網目状となって現れるため、白鋳鉄は本質的に脆性材料であって衝撃に対しては弱いという欠点から逃れ難い。このため高耐摩耗性に加え、如何に靭性を兼ね具えるかということが材料の適用範囲の広がりを決定する大きな条件となる。
【０００４】
特公昭３７−７６０２号公報の従来技術では、耐摩耗性に優れた白鋳鉄が衝撃や打撃に脆弱なのは炭化物の形状が片状、板状、または網目状であるからからであることに着目し、Ｃ：１．５〜４．８％、Ｓｉ：０．２〜３．０％、Ｖ：２．０〜１５．０％、残部Ｆｅの合金鋳鉄を提案し、Ｖの添加によって炭化物の形状を均一微細な球状、または擬球状の析出に変えて耐衝撃性を向上させたと謳っている。
【０００５】
一方、特開平１１−１２４６５１号の従来技術では、Ｃ：０．６〜６．５、Ｓｉ：０．２〜３．０、Ｍｎ：０．２〜１．０、Ｃｒ：１３．０〜３０．０、Ｎｉ：４．０〜１５．０、Ｖ：４．０〜１５．０％、残りＦｅの成分で、組織中に主として共有結合性の粒状、または球状Ｖ−Ｃ系炭化物、およびＦｅ−Ｃｒ系炭化物を晶出させた強靱高炭素バナジウムセメンタイト系合金鋳鉄を提起している。この材料は耐食性、耐摩耗性、耐熱性の全ての特性を十分に兼ね具え、とくに球状のＶ炭化物晶出による耐衝撃性を向上させる点に特徴があり、公報によれば従来、腐食や高温における酸化作用に比較的耐え得る材料として各種化学プラント、ボイラなどの部材に多用されてきたステンレス鋼も硬度が低く耐摩耗性の劣る点が否定できず、この課題を解決するために強靱高炭素系の合金鋳鉄を開発（特開平６−２４０４０４号）したが、しかし、この新材料においても、たとえば灰流し管、水中ポンプの汚泥用プロペラなど衝撃の加わる危険度の高い用途では破壊される可能性があるなど万全とは言えないので、形状が平面で脆弱なＦｅ−Ｃｒ炭化物であった組織をＶ添加によって粒状、球状のＶ炭化物を晶出させて耐衝撃性を大幅に向上させたと謳っている。
【０００６】
【発明が解決しようとする課題】
引用した中で第一の従来技術は、特に高価な合金成分を大量に添加することなく、単にＶを適量添加しただけでＣとの親和力が非常に高く、そのため形成された炭化物の形状も球状、または擬球状となって板状、片状、網目状の形状に起因する脆性を大幅に改善し、かつ、その炭化物の硬度も極めて高い（マイクロビッカース硬度、約２７００）ために耐摩耗性も一層強化された点は評価できる。しかし、この場合、炭化物の最終的な形状は人為的に制御して得られたものではないから、その形状を完結する割合のバラツキも否定し難く、信頼できるレベルの靭性が常に確実に具えられるか否かは必ずしも保証の限りに非ず、鋳造条件の変動によってかなりのバラツキの生じる懸念は疑えないし、自然発生的に自由に晶出するままの炭化物の形状は当然、球状化の割合にある限界があると言わざるを得ない。
【０００７】
一方、第二の従来技術はステンレス鋼を出発材とし、高硬度のセメンタイト系の高炭素合金鋳鉄に進み、さらにＶ添加によって球状または粒状の炭化物の晶出によって耐摩耗性と靭性を具えるという経緯を経たものであるが、大量のＣｒ添加が必須の要件で、少なくとも１３％は含まないと強固なＦｅ−Ｃｒ系の炭化物が晶出しないことや、Ｎｉについても４．０％以上含まないとマルテンサイト化が起こりやすくなるため必須の要件としているから、大量の合金成分の添加は製造コストを著しく高騰させる欠点がある。さらにＶ炭化物の粒状、球状化は前の従来技術と同様、とくに人為的な制御、操作によるものではなく自然発生的な金属間の反応に依存するだけであるから、多くの鋳造条件の相違によってその作用のバラツキも避け難く、必ずしも確実な球状化、粒状化を保証するものではない。このことは添付された顕微鏡組織写真にも明らかに認められ、菊花弁状の不安定、不規則な塊状の炭化物と、ヒゲ状または網目状に混在する多数のＦｅ−Ｃｒ系炭化物が晶出している状態からも明確に確認できる。
【０００８】
さらに基地についていえば、鋳放しの場合でも、焼鈍、焼準の熱処理を施した場合でも、何れも組織としてはオーステナイト（γ）＋セメンタイト（Ｆｅ−Ｃｒ−Ｃ）＋ＶＣ複合体であってほぼ変らないと記載があり、添付された顕微鏡写真においてもこのことが裏付けられている。結局、問題は用途との適合性であって、耐熱、耐食性を重視する化学プラント、ボイラ部材などでは好適であっても、衝撃を伴う摩耗がより過酷な分野、たとえば廃棄物や車両用のシュレッダーミルのハンマー、打撃子などに対しては、基地の硬度が低きに失し、たとえ炭化物を球状、粒状にさせただけでは、なお、不十分な結果しか期待できないのではないかという疑問が残る。
【０００９】
本発明は以上の課題を解決するため、確実にＶとＣとの化合物である炭化物を球状の形態で晶出させることにより、従来通りの耐摩耗性のレベルを維持しつつ耐衝撃性を著しく向上させ、少なくとも同一成分の耐衝撃性に比べてほぼ１．４倍を超える靭性を兼ね具えた合金白鋳鉄を広く産業機械、土木機械など広範囲の用途に供することを目的とする。
【００１０】
【課題を解決するための手段】
本発明に係る合金白鋳鉄は、重量％にしてＣ：２．０〜４．０、Ｓｉ：０．５〜３．０、Ｍｎ：０．０６〜１．５、Ｖ：６．０〜１６．０、Ｍｇ：０．０１〜０．１、Ｎｉ：０〜１．０、残り実質的に不純物を含むＦｅよりなり、顕微鏡組織においてほぼパーライトの母相へＭｇの溶湯添加処理によって球状化したＶ炭化物が晶出することにより無処理のほぼ同一成分の材料よりほぼ１．４倍以上の衝撃値を具えたことによって前記の課題を解決した。
【００１１】
また、この基本構成のうち、Ｎｉ：１．０．〜５．０と増量し、Ｍｏ：０．０１〜０．８％をさらに添加して顕微鏡組織がほぼ下部ベイナイトまたはマルテンサイトの母相として耐摩耗性をさらに向上することにより一層目的を有効に達成する場合もある。Ｎｉ、Ｍｏ添加の有無やその添加量は、基地をパーライト相にするか、下部ベイナイトまたはマルテンサイト相にするか、製品の使用条件によって求められる耐摩耗性と耐衝撃性のバランスの取り方によって異なる。
【００１２】
【発明の実施の形態】
本発明の合金白鋳鉄の成分限定理由を以下に説明する。
▲１▼Ｃ：鋳鉄という限りＦｅ−Ｃ状態図上から２．０〜６．６７％ＣのＦｅ−Ｃ合金とされるが、Ｓｉとの関係によってその組織には決定的な差が顕れ、マウラー（Ｍａｕｒｅｒ）の組織図からは、白鋳鉄の領域はＡ点（Ｃ：４．３％、Ｓｉ：０％、共晶点）とＢ点（Ｃ：１．０％、Ｓｉ：２．０％）を結んだ直線ＡＢと横軸、縦軸で囲む直角三角形の範囲とされる。本発明ではＣ：２．０〜４．０％としてこの領域をカバーしたが、実用的に好ましいのは２．５〜３．５％の範囲が推奨される。
▲２▼Ｓｉ：前記の組織図に従えばＳｉ：０〜２．０％の範囲になるが、Ｓｉは溶解時の脱酸や鋳造時の湯流れの点から不可欠の成分であり、少なくとも０．５％含まれないと健全な鋳造が難しい。また、他成分の添加の影響によって白鋳鉄の範囲は拡張するが、３．０％を超えると靭性を劣化させ、また黒鉛晶出を許容する範囲に入って来るので０．５〜３．０％に限定したが、好ましくは１．０〜２．５％が推奨される。
【００１３】
▲３▼Ｖ：含有するＣと結合して硬度の高い炭化物を晶出するには少なくとも６．０％を要する。しかし１６．０％を超えると、最早結合すべきＣとのバランスが崩れて加えただけの炭化物を晶出することができなくなり効果が伴わないばかりか、却って耐衝撃性が低下する原因となるので６．０〜１６．０％に限定した。しかし、実用的には後述の実施例の結果からみても８．０〜１３．０％の範囲が好ましい。
▲４▼Ｍｇ：自然凝固過程で晶出するＶ炭化物の形状を、そのままでは不安定な菊弁状ともなり得るのを確実に球状、粒状に変化させる作用として不可欠の要素である。球状黒鉛鋳鉄で提唱されている球状黒鉛化理論の一つである気泡説に従えば、鋳鉄溶湯中に添加されたＭｇは気泡となり、その気泡外周から黒鉛が求心的に球状に成長するとされている。本発明の鋳鉄のように母成分が白鋳鉄の場合にもこのようなＭｇの気泡が炭化物を球状化する要素であるか否かは定かには不明であり、Ｍｇの脱酸効果そのものが本来、球状であるバナジウム炭化物を球状の形態に還元するとも考えられる。何れにしてもＭｇ添加が球状化を促進する一因であるとは推察される。Ｍｇの添加は瞬間的な爆発的燃焼による酸化消耗を見越した上で十分な球状化反応を保証するために、球状黒鉛化の場合と同じ添加技術を転用し、凝固後の分析においてなお、０．０１〜０．１％の残留成分が確認できる程度の添加量と添加方法が必要である。
【００１４】
▲５▼Ｎｉ：添加の有無は基地の組織を変え、組織によって硬度や耐摩耗性が大きな影響を受ける。特に耐摩耗性を重視する製品の場合には０．０４％以上添加すれば熱処理によってマルテンサイト化する可能性も確かめられている。鋳放しで基地をマルテンサイト化するには１％以上の添加が必要であり、好ましくは１〜３％の添加が推奨できる。製品（鋳造品）の肉厚や、耐摩耗性と靭性の何れに重点をおくかによって添加の有無や添加量は定められるが、耐摩耗性と耐衝撃性の両立という原点に立てば、上限としては５．０％に留めるべきであり、結局、添加量は０〜５．０％に限定される。
▲６▼その他、Ｍｎは溶解時の脱酸調整作用、脱硫作用に有効で最低限は欠かせないが、一方では白銑化が助長する顕著な働きもすることや偏析を促進する作用が無視できないことなどから、０．０６〜１．５％に限定する。また、ＰやＳについても通常の鋳鉄とほぼ同等の範疇であれば特に問題はないが、Ｓは黒鉛の場合と同様に球状化を阻害する因子であるから、Ｍｎとの関係によってできるだけ排除することが必要である。
【００１５】
【実施例】
本発明の作用と効果を確認するためには、所望％のＶを添加した白鋳鉄を無処理で鋳造した比較例と、ほぼ同一成分の溶湯にＭｇを添加して球状化処理をした実施例の試験片をそれぞれ作成し、衝撃値、硬さの測定、衝撃摩耗試験の結果得られた摩耗係数、さらにそれぞれの顕微鏡組織写真を画像処理して計測される炭化物の球状化率を対比することによって純粋にＭｇ添加の有無による両者の差違を知る事ができる。
【００１６】
試験片の作成はすべて同一条件で統一した。すなわち黒鉛坩堝内へ成分調整した材料を挿入し高周波炉で溶解し、昇温後、比較例はそのままクロマイトサンドで造形した鋳型に鋳造する。実施例は溶湯中へＭｇ添加処理後、直ちにクロマイトサンドの鋳型に鋳造、何れも断面が１０×１０ｍｍのテストブロックを作成し、ＪＩＳ規定のシャルピー衝撃試験片を削り出した。試験後の試料はロックウェルＣ硬度（ＨＲＣ）を測定し、ショア硬度（ＨＳ）にも換算して表示した。表１は実施例および比較例の化学成分とＭｇ処理の有無、基地の種類を一括して示したものであるが、純粋にＭｇ添加処理の作用、効果だけを比較するため基地毎にグループ分けして、基地がパーライトのグループ１（請求項１）と、基地が下部ベイナイトまたはマルテンサイトのグループ２（請求項２）の二群に分けて表示し、それぞれのグループの中に実施例と比較例とを含めた。各グループに含まれる比較例はそれぞれ同群の実施例に準じた成分、基地よりなる。表２はこれら実施例、比較例の衝撃値、硬さ、摩耗係数の試験結果を一括示したものである。
【００１７】
【表１】

【００１８】
【表２】

【００１９】
衝撃摩耗係数を計測するには乾式摩耗試験機を使用した。試験機の概略は図４に示す通り、回転軸１から出た４本のアーム２に試験片ＴＰを取り付け、所定時間、回転軸１を電動機３によって回転して試験片を石英斑岩Ｒに衝突させ、その間に生じた各試験片ＴＰの重量減を計測して標準材（ＳＳ４００）の重量減と比較して耐摩耗性の優劣の指標とした。
【００２０】
炭化物の球状化率は顕微鏡組織においてＪＩＳＧ５５０２（球状黒鉛鋳鉄品）の規定に準じて表すことにした。該規定によれば、顕微鏡倍率は８００倍、５視野に亘って行ない平均値を求める。図５（Ａ）（Ｂ）に示す標準の球状化に達した視野中の炭化物の個数を数え、全視野の炭化物の総数に対する割合を％で示して球状化率とするとあり、コンピュータによる画像処理を行なって算出する場合もこれに準ずるとある。画像処理の一例を図２に示す。
【００２１】
図１（Ａ）は画像処理の対象となる実施例２および同図（Ｂ）は比較例１の顕微鏡組織写真をそれぞれ示し、ナイタール腐食によって組織を現出させ倍率は８００倍である。図２（Ａ）（Ｂ）は実施例２と比較例１の試験片の組織写真を画像処理、二値化した炭化物の形状を示したもので、各炭化物粒子毎に形状係数Ｋを画像解析により求めた。各炭化物粒子の面積Ｍ、周囲Ｓを測定し、これから形状係数Ｋ＝４πＭ／Ｓ2を算出し、この値が０．５２３を超えた粒子を前記の図５（Ａ）（Ｂ）に示す球状化に達した合格粒子として計数した。なお、誤差を避けるために直径２μｍ以下の円相当面積を有する微細な粒子は形状係数を求める粒子から除外した。
表３は実施例２、比較例１の各試料の１視野について、炭化物粒子毎の形状係数を計算し、球状化率を算出した一例を示したもので、Ｍｇ添加による球状化処理の有無による球状化の差違が如実に顕示されている。
【００２２】
【表３】

【００２３】
図３（Ａ）（Ｂ）は別の実施形態であるＮｉ：２．７４％、Ｍｏ：０．４５％配合のグループ２（請求項２）に係る実施例４と、これとほぼ同成分で無処理の比較例３の顕微鏡組織写真であって、組織はナイタール腐食により基地を現出させたものである。写真中白色に観察されるＶ炭化物は比較例３では球状化の崩れたものや棒状の形態であるのに対し、実施例４のＶ炭化物は明らかに球状化が達成されている。また、基地組織は、Ｎｉ、Ｍｏを配合しない図１（Ａ）の実施例２のパーライトに対し、硬度が大きく耐摩耗性に優れたマルテンサイトと下部ベイナイト組織の混合組織が鋳放しで得られている。このことから実施例４では鋳造後の熱処理により耐摩耗性に優れた特性を具えたマルテンサイト、ベイナイト組織とすることが容易であると考えられる。先に説明した炭化物の球状化率を表１に掲げたすべての試験片について計測した結果（各試験片につき、５視野の球状化率の平均値を最終球状化率とした）を纏めたものが表４である。
【００２４】
【表４】

【００２５】
実施例、比較例の成分、衝撃値、硬度、衝撃摩耗係数および球状率を総括して判断すれば、無処理の比較例もＭｇ処理の実施例も基地の組織自体には大差は見られないにも拘わらず、衝撃値に顕著な差違が顕れることが第一に挙げられる。衝撃値はＮｉ、またはＭｏを全く、または低くしか含まないグループ１の場合、基地は何れもパーライトと変りはないが、実施例の平均衝撃値９．２Ｊ／ｃｍ2は比較例の平均衝撃値６．０Ｊ／ｃｍ2の１．５３倍に相当し、Ｎｉ：３％、Ｍｏ：０．５％前後のグループ２では、基地は何れも下部ベイナイトまたはマルテンサイトと変りはないが、比較例３に対して実施例４、５は何れも衝撃値において１．６６〜１．６４倍を示し、何れの実施形態でも確実に大幅な衝撃値の向上、少なくともほぼ１．４倍以上の向上を示している。
【００２６】
硬度については基地自体が前記のように実施例、比較例、共に大きな差違がなく、結果的に衝撃摩耗係数はこの硬度差に応じてほぼ同じレベルの範囲に収っている。このように衝撃値に関しては顕著な大差があり、硬度と耐摩耗性については明瞭な差違が認め難いことからも、これらの物理的数値の変化の傾向は、晶出した炭化物の球状率の多寡とよく整合すると認められ、成分上、唯一の差であるＭｇ添加による球状化処理の有無のみに基づく成果であることと断定される。
【００２７】
【発明の効果】
以上述べた通り本発明に係る合金白鋳鉄は、耐摩耗性をほぼ同じレベルに持続したまま、耐衝撃性を大幅に向上する効果がある。しかもそのためにＮｉ、Ｃｒなどの高価な合金元素を大量に配合する必要がなく、溶湯処理だけで確実に実施できることから経済的にも従来技術に比べると遥かに有利である。この結果、とくに衝撃摩耗が装置の機能を決定的に支配する破砕機、粉砕機、その他のハンマーや打撃子類をはじめ全ての摩耗部材に好適な靭性と耐摩耗性とを同時に満足する理想的な材質として産業上に貢献するところ極めて大である。
【図面の簡単な説明】
【図１】本発明の実施形態である実施例２（Ａ）と、ほぼ同一成分からなる比較例１（Ｂ）の腐食により現出させた顕微鏡組織の写真（倍率８００）をそれぞれ示す。
【図２】同じ実施例、比較例の球状化率計測対象である炭化物を画像処理により二値化した画像を（Ａ）（Ｂ）でそれぞれ示す。
【図３】本発明の別の実施形態における実施例４（Ａ）と、比較例３（Ｂ）の腐食により現出させた顕微鏡組織の写真（倍率８００）をそれぞれ示す。
【図４】摩耗試験に使用した摩耗試験機の概要を示す一部断面正面図である。
【図５】ＪＩＳ規定において組織上、球状と認められる標準の二形態を（Ａ）（Ｂ）で示す。
【符号の説明】
１回転軸
２アーム
３電動機
ＴＰ試験片
Ｒ石英斑岩[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an alloy white cast iron that is a high-hardness material having excellent wear resistance and also has toughness.
[0002]
[Prior art]
In a wide range of industrial equipment and devices, members facing wear action lose their intended functions set for each device as their wear progresses, so the wear resistance of the members affects the operating efficiency of the device. Will be an important factor. Although the wear action is roughly classified into various forms, it is first effective to increase the hardness of the member surface in order to counter the abrasion (abrasion) that occurs most commonly with the flowing processing material, The improvement in wear resistance is linked in proportion to the hardness. In that sense, conventionally, in a Fe-C system, a high amount of complex carbide (double carbide, for example, Fe-Cr-C carbide) is crystallized in the form of primary crystal or eutectic by mixing a considerable amount of white cast iron, particularly Cr. Alloy white cast iron, which can be made to satisfy the desired wear resistance, is often used.
[0003]
On the other hand, depending on the type of equipment applied, simple wear resistance alone cannot perform a sufficient function, and there are many cases where further requirements are required to be satisfied. What is particularly problematic is that the carbide itself, which is a requirement for improving wear resistance, is hard, but essentially has the negative element of being brittle, and the crystallized form at the base also appears as a plate or network. White cast iron is essentially a brittle material and is difficult to escape from the disadvantage of being weak against impact. For this reason, in addition to high wear resistance, how to have toughness is a major condition for determining the expansion of the application range of materials.
[0004]
In the prior art disclosed in Japanese Patent Publication No. 37-7602, attention is paid to the fact that white cast iron, which has excellent wear resistance, is vulnerable to impacts and blows because the shape of the carbide is flake, plate, or mesh. , C: 1.5 to 4.8%, Si: 0.2 to 3.0%, V: 2.0 to 15.0%, Fe alloy cast iron is proposed, the shape of carbide by adding V It is said that the impact resistance is improved by changing to a uniform fine spherical or pseudo-spherical precipitate.
[0005]
On the other hand, in the prior art disclosed in JP-A-11-124651, C: 0.6 to 6.5, Si: 0.2 to 3.0, Mn: 0.2 to 1.0, Cr: 13.0 to 30 0.0, Ni: 4.0 to 15.0, V: 4.0 to 15.0%, remaining Fe component, mainly covalently-bonded granular or spherical V-C based carbide in the structure, and Fe -Proposes tough, high-carbon vanadium cementite-based alloy cast iron crystallized from Cr-based carbides. This material has all the characteristics of corrosion resistance, wear resistance, and heat resistance, and is particularly characterized in that it has improved impact resistance due to spherical V carbide crystallization. Stainless steel, which has been widely used in various chemical plants, boilers and other materials as a material that can withstand the oxidative action in steel, cannot be denied due to its low hardness and inferior wear resistance. -Based alloy cast iron was developed (Japanese Patent Laid-Open No. 6-240404). However, this new material can also be destroyed in high-risk applications such as ash-flow pipes and sludge propellers for submersible pumps. Since it is not perfect, for example, the structure of a flat and brittle Fe-Cr carbide is crystallized into granular and spherical V carbide by adding V, and the impact resistance is greatly improved. It was that the singing.
[0006]
[Problems to be solved by the invention]
Among the cited prior arts, the first prior art has a very high affinity with C simply by adding an appropriate amount of V without adding a large amount of expensive alloy components, and the shape of the formed carbide is also spherical. In addition, the brittleness caused by the plate-like, piece-like, and mesh-like shapes is greatly improved by becoming pseudo-spherical, and the hardness of the carbide is extremely high (micro Vickers hardness, about 2700), so that the wear resistance is also high. The further strengthened points can be evaluated. However, in this case, since the final shape of the carbide is not obtained by artificial control, it is difficult to deny the variation in the ratio of completing the shape, and a reliable level of toughness is always provided. This is not necessarily guaranteed, and there is no doubt that there will be considerable variation due to fluctuations in casting conditions, and the shape of carbides that spontaneously crystallize freely is naturally in the proportion of spheroidization. I have to say that there is a limit.
[0007]
On the other hand, the second conventional technology starts from stainless steel, proceeds to high-hardness cementite-type high-carbon alloy cast iron, and further has wear resistance and toughness by crystallization of spherical or granular carbides by addition of V. Although it has gone through the history, it is an essential requirement to add a large amount of Cr, and if it does not contain at least 13%, strong Fe—Cr-based carbides will not crystallize, and Ni will not contain 4.0% or more. Therefore, the addition of a large amount of alloy components has a drawback of significantly increasing the production cost. Furthermore, the V carbide grain and spheroidization, like the previous prior art, are not dependent on artificial control and operation, but only depend on reactions between naturally occurring metals. Variations in the action are unavoidable, and reliable spheroidization and granulation are not necessarily guaranteed. This is clearly seen in the attached micrograph, and chrysanthemum petal-like unstable, irregular lumps of carbides and many Fe-Cr carbides mixed in a beard-like or network-like shape crystallize. It can be clearly confirmed from the state of being.
[0008]
Furthermore, as for the base, both in the case of as-cast, annealing, and normalizing heat treatment, the structure is austenite (γ) + cementite (Fe—Cr—C) + VC composite, which is almost unchanged. This is supported by the attached photomicrograph. In the end, the problem is compatibility with the application, which is suitable for chemical plants and boiler parts that emphasize heat resistance and corrosion resistance, but where wear with impact is more severe, such as shredders for waste and vehicles. For mill hammers, hammers, etc., there is a question that the hardness of the base will be lost and even if the carbide is made spherical or granular, only insufficient results can be expected. Remain.
[0009]
In order to solve the above problems, the present invention reliably recrystallizes the carbide, which is a compound of V and C, in a spherical form, thereby significantly improving the impact resistance while maintaining the conventional wear resistance level. The purpose of the invention is to provide an alloy white cast iron having at least 1.4 times the toughness that is at least 1.4 times the impact resistance of the same component and widely used in a wide range of applications such as industrial machinery and civil engineering machinery.
[0010]
[Means for Solving the Problems]
The alloy white cast iron according to the present invention is C: 2.0 to 4.0, Si: 0.5 to 3.0, Mn: 0.06 to 1.5, V: 6.0 to 16 in terms of% by weight. 0.0, Mg: 0.01 to 0.1, Ni: 0 to 1.0, and remaining Fe containing substantially impurities, and spheroidized by adding molten Mg to the pearlite matrix in the microstructure. The above problem has been solved by providing an impact value of about 1.4 times or more than that of an untreated material of substantially the same component by crystallization of V carbide.
[0011]
Of these basic configurations, Ni: 1.0. The amount is increased to ˜5.0, and Mo: 0.01 to 0.8% is further added to make the microstructure more effective as a parent phase of the lower bainite or martensite. Sometimes achieved. The presence or absence of Ni and Mo and the amount of addition depends on how to balance the wear resistance and impact resistance required by the usage conditions of the product, whether the base is a pearlite phase, the lower bainite or martensite phase. Different.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The reasons for limiting the components of the alloy white cast iron of the present invention will be described below.
(1) C: As long as it is cast iron, it is considered to be an Fe-C alloy of 2.0 to 6.67% C from the Fe-C phase diagram. From the structure diagram of Maurer, the area of white cast iron is point A (C: 4.3%, Si: 0%, eutectic point) and point B (C: 1.0%, Si: 2.0). %) And a range of right triangles surrounded by a horizontal axis and a vertical axis. In the present invention, this region is covered with C: 2.0 to 4.0%, but a range of 2.5 to 3.5% is recommended for practical use.
(2) Si: According to the above structure diagram, Si is in the range of 0 to 2.0%, but Si is an indispensable component in terms of deoxidation during melting and hot water flow during casting. If 5% is not included, sound casting is difficult. Moreover, the range of white cast iron is expanded by the influence of the addition of other components, but if it exceeds 3.0%, the toughness is deteriorated, and the graphite crystallization is allowed. %, But preferably 1.0 to 2.5% is recommended.
[0013]
{Circle around (3)} V: At least 6.0% is required to crystallize a high-hardness carbide by combining with the contained C. However, if it exceeds 16.0%, the balance with C that should be bonded is lost, and the carbide just added cannot be crystallized, and this is not accompanied by an effect. Therefore, it was limited to 6.0 to 16.0%. However, practically, the range of 8.0 to 13.0% is preferable from the results of Examples described later.
(4) Mg: It is an indispensable element for reliably changing the shape of the V carbide crystallized in the process of spontaneous solidification into a spherical shape or a granular shape, which can be an unstable chrysanthemum shape as it is. According to the bubble theory, which is one of the spheroidal graphitization theories proposed for spheroidal graphite cast iron, Mg added to the cast iron melt becomes bubbles, and it is said that graphite grows centripetally from the periphery of the bubbles. Yes. Even when the base component is white cast iron as in the cast iron of the present invention, it is unclear whether such Mg bubbles are elements that spheroidize the carbide, and the deoxidation effect itself of Mg itself is inherent. It is also considered that spherical vanadium carbide is reduced to a spherical form. In any case, it is presumed that Mg addition is one factor that promotes spheroidization. In order to guarantee sufficient spheroidization reaction in anticipation of oxidative consumption due to instantaneous explosive combustion, the addition of Mg is diverted to the same addition technique as in the case of spherical graphitization. An addition amount and an addition method so that a residual component of 0.01 to 0.1% can be confirmed are necessary.
[0014]
(5) Ni: The presence or absence of addition changes the structure of the base, and the hardness and wear resistance are greatly affected by the structure. In particular, in the case of products that place importance on wear resistance, the possibility of martensite formation by heat treatment has been confirmed if 0.04% or more is added. In order to make the base martensite by as-casting, addition of 1% or more is necessary, and addition of 1 to 3% can be recommended. The presence or absence and the amount of addition are determined depending on the thickness of the product (cast product) and whether the wear resistance or toughness is emphasized, but if the origin is to achieve both wear resistance and impact resistance, the upper limit Should be limited to 5.0%. After all, the addition amount is limited to 0 to 5.0%.
(6) In addition, Mn is effective for deoxidation adjustment and desulfurization at the time of dissolution, and is indispensable as a minimum. On the other hand, it has a remarkable function to promote whitening and promotes segregation. Since it cannot be done, it is limited to 0.06 to 1.5%. Also, there is no particular problem with P and S as long as they are in the same range as ordinary cast iron, but since S is a factor that inhibits spheroidization as in the case of graphite, it is eliminated as much as possible by the relationship with Mn. It is necessary.
[0015]
【Example】
In order to confirm the operation and effect of the present invention, a comparative example in which white cast iron added with desired% V was cast without treatment, and an example in which Mg was added to molten metal having almost the same components and spheroidized. Each test specimen is made and the impact value, hardness measurement, wear coefficient obtained as a result of impact wear test, and comparison of the spheroidization rate of carbide measured by image processing each micrograph. Thus, the difference between the two depending on whether or not Mg is added can be known.
[0016]
All specimens were created under the same conditions. That is, a component-adjusted material is inserted into a graphite crucible and melted in a high-frequency furnace. After the temperature rises, the comparative example is cast as it is into a mold formed with chromite sand. In Examples, after adding Mg into the molten metal, immediately cast into a chromite sand mold, and in each case, a test block having a cross section of 10 × 10 mm was prepared, and a Charpy impact test piece defined by JIS was cut out. Samples after the test were measured by Rockwell C hardness (HRC) and converted to Shore hardness (HS). Table 1 shows the chemical components of Examples and Comparative Examples, the presence or absence of Mg treatment, and the types of bases, but it is grouped for each base to compare purely the effects and effects of Mg addition treatment. The base is divided into two groups: perlite group 1 (Claim 1), and the base is lower bainite or martensite group 2 (Claim 2). Examples were included. The comparative examples included in each group consist of components and bases according to the examples of the same group. Table 2 collectively shows the test results of impact value, hardness, and wear coefficient of these examples and comparative examples.
[0017]
[Table 1]

[0018]
[Table 2]

[0019]
A dry wear tester was used to measure the impact wear coefficient. The outline of the testing machine is as shown in FIG. 4. The test piece TP is attached to the four arms 2 coming out from the rotating shaft 1, and the rotating shaft 1 is rotated by the electric motor 3 for a predetermined time to turn the test piece into the quartz porphyry R. The weight loss of each test piece TP produced during the collision was measured and used as an index of superiority or inferiority in wear resistance compared to the weight loss of the standard material (SS400).
[0020]
The spheroidization rate of the carbide was determined in accordance with JIS G5502 (spheroid graphite cast iron product) in the microstructure. According to this rule, the microscope magnification is 800 times, and the average value is obtained over 5 fields of view. The number of carbides in the field of view that has reached the standard spheroidization shown in FIGS. 5 (A) and 5 (B) is counted, and the ratio to the total number of carbides in the entire field of view is expressed in%, which is the spheroidization rate. The same applies to the case where the calculation is performed by performing the above. An example of image processing is shown in FIG.
[0021]
FIG. 1 (A) shows a microscopic structure photograph of Example 2 to be subjected to image processing and FIG. 1 (B), respectively, showing the structure by nital corrosion, and the magnification is 800 times. 2 (A) and 2 (B) show the shape of carbide obtained by image processing and binarizing the structure photographs of the test pieces of Example 2 and Comparative Example 1, and analyzing the shape factor K for each carbide particle. Determined by The area M and the circumference S of each carbide particle are measured, and from this, the shape factor K = 4πM / S 2 is calculated, and particles whose value exceeds 0.523 are spheroidized as shown in FIGS. 5 (A) and 5 (B). Were counted as acceptable particles. In order to avoid errors, fine particles having a circle-equivalent area with a diameter of 2 μm or less were excluded from particles for which a shape factor was obtained.
Table 3 shows an example of calculating the shape factor for each carbide particle and calculating the spheroidization rate for one field of view of each sample of Example 2 and Comparative Example 1, and depending on the presence or absence of spheroidizing treatment by adding Mg The difference in spheroidization is clearly demonstrated.
[0022]
[Table 3]

[0023]
3 (A) and 3 (B) show another embodiment of Ni: 2.74% and Mo: 0.45%, which is Group 4 (Claim 2), and substantially the same component as Example 4. It is a microscope structure photograph of the non-processed comparative example 3, Comprising: A structure | tissue showed the base | substrate by the nital corrosion. The V carbide observed in white in the photograph is in the form of a broken spheroid or a rod-like shape in Comparative Example 3, whereas the V carbide of Example 4 clearly achieves spheroidization. Further, the base structure is obtained by as-casting a mixed structure of martensite and lower bainite structure having high hardness and excellent wear resistance with respect to the pearlite of Example 2 in FIG. 1 (A) not containing Ni or Mo. ing. From this, in Example 4, it is considered that it is easy to obtain a martensite and bainite structure having excellent wear resistance by heat treatment after casting. Summarizing the results of measuring the spheroidization rate of the carbide described above for all the test pieces listed in Table 1 (the average value of the spheroidization rate of 5 fields of view was the final spheroidization rate for each test piece) Is Table 4.
[0024]
[Table 4]

[0025]
If the components of Examples and Comparative Examples, impact values, hardness, impact wear coefficient, and spherical ratio are collectively judged, neither the untreated Comparative Example nor the Mg-treated Example shows a great difference in the base structure itself. Nevertheless, a significant difference in the impact value appears first. In the case of group 1 which contains Ni or Mo at all or only low in impact value, the bases are not different from pearlite, but the average impact value of 9.2 J / cm @ 2 of the example is an average impact value of 6 of the comparative example. It is equivalent to 1.53 times of 0.0 J / cm2, and in Group 2 where Ni is 3% and Mo is around 0.5%, the base is not changed from lower bainite or martensite, but with respect to Comparative Example 3 In Examples 4 and 5, the impact value is 1.66 to 1.64 times, and in any embodiment, the impact value is surely greatly improved, and at least approximately 1.4 times or more is shown. .
[0026]
As for the hardness, the base itself does not have a large difference between the examples and the comparative examples as described above, and as a result, the impact wear coefficient is within the same level range according to the hardness difference. In this way, there is a remarkable difference in impact value, and it is difficult to recognize a clear difference in hardness and wear resistance. It is confirmed that the result is based on the presence or absence of spheroidizing treatment with Mg addition, which is the only difference in terms of composition.
[0027]
【The invention's effect】
As described above, the alloy white cast iron according to the present invention has an effect of greatly improving the impact resistance while maintaining the wear resistance at substantially the same level. Moreover, it is not necessary to mix a large amount of expensive alloy elements such as Ni and Cr, and it can be carried out reliably only by the molten metal treatment, so that it is economically much more advantageous than the prior art. As a result, it is ideal to satisfy both toughness and wear resistance suitable for all wear parts, especially crushers, crushers, other hammers and hammers whose impact wear dominates the function of the device. As a new material, it contributes to the industry.
[Brief description of the drawings]
FIG. 1 shows photographs (magnification 800) of microstructures developed by corrosion in Example 2 (A), which is an embodiment of the present invention, and Comparative Example 1 (B) comprising substantially the same components.
FIGS. 2A and 2B show images obtained by binarizing carbides, which are objects for measuring the spheroidization rate of the same example and comparative example, by image processing, respectively.
FIG. 3 shows photographs (magnification 800) of microscopic structures revealed by corrosion in Example 4 (A) and Comparative Example 3 (B) in another embodiment of the present invention.
FIG. 4 is a partially sectional front view showing an outline of an abrasion tester used for an abrasion test.
FIGS. 5A and 5B show two standard forms recognized as spherical in terms of tissue according to JIS regulations.
[Explanation of symbols]
1 Rotating shaft 2 Arm 3 Electric motor TP Test piece R Quartz porphyry

Claims

C: 2.0 to 4.0 % by weight , Si: 0.5 to 3.0 % by weight , Mn: 0.06 to 1.5 % by weight , V: 6.0 to 16.0 % by weight , Mg: 0.01 to 0.1%, Ni: 0 to 1.0 wt%, and the balance being Fe and inevitable components, and, by the molten metal addition treatment of Mg, and spheres Joka in the parent phase of pearlite V carbides are caused to crystallize, 1 Ri by material of the same components of the untreated not subjected to melt addition treatment of the Mg. Globular carbide white cast iron, characterized in that it comprises more than four times the impact value.

C: 2.0 to 4.0 wt%, Si: 0.5 to 3.0 wt%, Mn: 0.06 to 1.5 wt%, V: 6.0 to 16.0 wt%, Mg: 0.01 to 0.1% by weight, Ni: 1.0 to 5.0 % by weight , Mo: 0.01 to 0.8% by weight, and the balance consists of Fe and inevitable components, and the molten Mg By the addition treatment, a spheroidized V carbide is crystallized in the parent phase of lower bainite or martensite , and the impact value is 1.4 times or more than the untreated material of the same component not subjected to the molten metal addition treatment. with spherical carbide white cast iron, characterized in that it comprises an excellent wear resistance.