JP3946071B2

JP3946071B2 - Tough ductile cast iron material and method for producing the same

Info

Publication number: JP3946071B2
Application number: JP2002091839A
Authority: JP
Inventors: 恵一前川; 吉貞道浦; 渉高原; 眞好喜多川; 皓堀江
Original assignee: Kurimoto Ltd
Current assignee: Kurimoto Ltd
Priority date: 2002-03-28
Filing date: 2002-03-28
Publication date: 2007-07-18
Anticipated expiration: 2022-03-28
Also published as: JP2003286538A

Description

【０００１】
【発明の属する技術分野】
本発明はダクタイル鋳鉄材、およびその製造方法に係り、生型、乾燥型、時硬性鋳型の他、たとえば消失模型鋳型など特殊な鋳造法によって製造されるダクタイル鋳鉄製の鋳造品において焼鈍特性に優れ、組織が緻密で強度と靭性を兼ね具えた材料の製造に関する。
【０００２】
【従来の技術】
ダクタイルとは靭性を意味し、従来の鋳鉄の常識を破った材料として広く多用され今日に至っている。球状黒鉛鋳鉄とも呼ばれ、従来のネズミ鋳鉄では異方性の強い薄片状の黒鉛が析出するのに対し、ダクタイル鋳鉄の黒鉛は小結晶が共通の核から放射状に発達した集合体として球状を呈しており、材料強度と伸びを具えた特性の原因となっている。現在は自動車産業をはじめ産業用機器、装置の部材として多方面で利用され、さらに材質の向上を目指して多くの開発、研究が続けられている。
【０００３】
特開平１−３０９９３９号公報による従来技術では、自動車などのフェライト地の球状黒鉛鋳鉄において、伸び、特に低温衝撃値を向上し熱処理を省略、または容易にすることを課題とし、通常の球状黒鉛鋳鉄成分の他に、Ｃｒ：０．１％未満、Ｂｉ：０．００１５〜０．００８％を含み、Ｃ．Ｅ値を３．９〜４．６にすることで黒鉛粒数を３００個／ｍｍ²以上の組織としたとしている。
【０００４】
本来、球状黒鉛鋳鉄では、Ｓを筆頭にＳｂ、Ａｓ、Ｂｉ、Ｐｂなどが微量含まれると、球状の黒鉛が晶出し難いというのが定説である。しかし、この従来技術では適量のＢｉを添加して黒鉛粒数を３００個／ｍｍ²以上とすることでパーライトを減少させ、低温熱処理、または熱処理なしで十分な伸びと衝撃値を得たと謳っている。しかし、Ｂｉは溶湯に対する溶込み歩留りが悪く、歩留り率の変動も大きいから、残留含有量を維持するためには添加量を０．００５〜０．０２５％の範囲に設定する必要があるが、残留Ｂｉ量が０．００８％を超えてしまうと黒鉛の球状化が阻害され、球状化率が８０％以下となるので注意が必要であるとしている。同じ出願人による特開平２−７００１５号の従来技術もほぼ同じ要旨からなっている。Ｂｉの添加について、この従来技術では円錐形の塊状Ｂｉを添加し、または粒状として紙などに包んで添加してＢｉ歩留まりを向上させたとあり、同時にＦｅ−Ｓｉの接種剤を使用した実施例を報告している。
【０００５】
特開平６−９３３６９号公報に係る別の従来技術では、従来の球状黒鉛鋳鉄よりも微細な球状黒鉛、および快削元素としてＣａ化合物を鋳鉄中に均一に分布させることによって被削性の向上を図るため、溶湯にＭｇの存在下でＣａを添加し、その後、Ｂｉを添加することによってＣａ化合物を微細化して多数晶出させることができ、鋳放しのままで被削性と機械的性質の改善ができると謳っている。
【０００６】
【発明が解決しようとする課題】
実際にＢｉの添加は明らかに黒鉛の微細化に有効であるとはいえ、その使用方法を誤ると黒鉛の球状化を阻害して機械的強度と伸びを失い、ダクタイル鋳鉄としての折角の特徴が薄れてくる危惧がある。そのため添加量に厳しい上限を設けているが、本来、Ｂｉ自体の蒸気圧が低く、歩留まりの悪いことではトップクラスの成分であるから、如何に毎チャージの溶湯条件を均一に保つように努めたとしても、溶湯中に溶存する酸素量やＳ分を厳密にコントロールすることはかなり難しく、実用上、その厳しい上限が足かせとなる恐れは十分にある。
【０００７】
後に引用した最後の従来技術は、この点、Ｍｇの存在下でＣａを添加し、その後、Ｂｉを添加するというようにＣａの添加を要件としたことで前記引用例の危惧を解消する一つの答になっている。この従来技術の特徴は添加の順序によって快削性向上に差の出ることに着目し、添加剤の順序を変えてテストを重ねた末、このような結論に達したのではないかと推定されるが、実施例としてサポートされたのは、切削工具（ドリル）の磨耗量と切削長の関係グラフだけで、成分と組織や機械的性質との因果関係について具体的に何の例証もされていないので、詳細は分からない。
【０００８】
とくに該引用例は鋳放しのままで快削性と機械的性質の向上を図ることを課題とし、Ｃａを鋳鉄の基地組織内へ快削物質（ＣａＯ）として晶出させることに焦点を絞って説明されているが、普通、ＣａＯのような溶湯と反応した酸化生成物はノロとして浮上分離させて排除するものであり、それを鉄基地内に留めて分散させるためには何か開示されないノウハウがあるのかも知れない。しかし、鉄基地に微細に封じ込んで分散晶出しているとすれば、無数のミクロ的な欠陥が均等に分散しているのに等しく、確かに切削時に工具に掛かる負担は軽減され、快削性の向上に繋がるであろうことは理解できる。
【０００９】
しかし、ＣａＯという通常は非金属介在物（微滓とも呼ぶ）として取り扱われるミクロ的な不純物が全体に分散しているのであれば、なぜ機械的性質、具体的には引張強度や伸びが向上するのか、具体的な実施例の記載がないだけに理解し難い。たとえＢｉの添加によって黒鉛が微細化しても、無数の介在物の存在は基地の清浄度を著しく汚損し、構造材としての価値を問われる懸念があるのではないか。
【００１０】
また、鋳型との関係からいえば、従来から生型、乾燥型、有機、無機の自硬性型、シェル型、など多様な種類が実用化され、Ｖプロや消失模型鋳型などもかなり普及しつつある。Ｖプロは鋳型内が減圧されているから、溶湯の流動性にはプラスに働くが、消失模型（フルモールド）は砂中に埋め込んだ発砲ポリスチレン模型が溶湯の熱で直ちに燃焼し、ガス化してわずかの燃え滓が残る現象を原理とするので、原料である発砲ポリスレンの熱分解による吸熱反応によって湯流れにはマイナスに働き、製品の一部に前記の燃え滓を巻き込んだり、一部がチル化したり、複雑な形状の場合には湯回り不良による形状・寸法上の不良原因となる。そのため出湯温度を他の鋳型より高める必要があり、エネルギーコストの点で不利な条件は否めないという課題もある。
【００１１】
本発明は以上の公知事実をベースとした上で、全面清浄度の高いフェライト基地として高い靭性を与えた上、組織の微細化とほぼ完全な黒鉛の球状化によって強度も兼ね合わせた強靭なダクタイル鋳鉄材の提供を目的とする。
【００１２】
【課題を解決するめの手段】
本発明に係る強靭なダクタイル鋳鉄材は、Ｃ：３．０〜４．０％，Ｓｉ：１．５〜３．０％、Ｍｎ：０．１〜０．４％、Ｐ：０．０５％以下、Ｓ：０．０１％以下、残りＦｅの成分よりなるダクタイル鋳鉄材であって、特にＢｉ：０．０００５〜０．０５％、Ｃａ：０．０００１〜０．０５％を含み、多数の球状黒鉛が球状化率９０％以上を維持したままフェライトベースの基地に晶出し、引張強度４５０ＭＰａ以上、かつ伸び２０％以上を維持することによって前記の課題を解決した。
【００１３】
また、該ダクタイル鋳鉄材を製造する方法としては、溶湯成分がＣ：３．０〜４．０％，Ｓｉ：１．５〜３．０％、Ｍｎ：０．１〜０．４％、Ｐ：０．０５％以下、Ｓ：０．０１％以下、残りＦｅとなるように溶解、精練した後、該溶湯にＭｇを主体とした球状化処理剤を加えて黒鉛の球状化処理を行なうと同時にまたはその後に、接種剤を溶湯に接種して最終的にＢｉ：０．０００５〜０．０５％、Ｃａ：０．０００１〜０．０５％の範囲で明確に検出できるように歩留まりを計算に入れて添加して鋳造を行なう手順を要件とする。なお接種のタイミングは球状化処理後の方がより好ましい。
【００１４】
この場合、具体的には、Ｂｉ、Ｃａの添加は化学成分がＳｉ：２０〜８０％、Ｂｉ：０．１〜２５．０％、Ｃａ：１〜４０．０％、残りＦｅよりなる合金粉末または混合粉末を接種剤として使用することが望ましい。
【００１５】
接種材の粒径は細かいほど接種の歩留まりは向上し効果が上がるが、細かすぎると接種時に粉末が飛散し逆に効果が低減する。よって下限を０．０５ｍｍとする。また、上限は６ｍｍを超えると接種剤が均一に溶湯中に拡散できず効果が出ない。よって、粒径範囲を０．０５ｍｍ〜６ｍｍとする。最適範囲は、下限が粉末管理面からまた経済性から０．１ｍｍ以上とする。
【００１６】
このダクタイル鋳鉄材の成分限定は通常のＪＩＳＧ５５２６・５５２７、または日本水道協会の規定（ＪＷＷＡＧ１１３・１１４）をほぼ踏襲し、ただ、鋳造直前にＢｉを最終的に０．０００５〜０．０５％、またＣａを０．０００１〜０．０５％が明確に検出できるように歩留まりを考慮した添加量を接種して、黒鉛を微細に晶出して球状黒鉛数を大量に増発させ、マトリックスをフェライト組織とし緻密で強靱な組織に調質することを特徴とする。
【００１７】
球状黒鉛鋳鉄の溶湯へＢｉを添加して黒鉛を微細化し均一に基地中へ分配する作用自体は公知であり、同じような働きをする元素としてＳｂ、Ｔｅ、Ｓｎなども知られている。Ｂｉは０．０００５％を超えてから優れた黒鉛晶出能を示し、０．０５％以上では黒鉛晶出能が低下したり、球状化阻害などの悪影響が出てくる。しかし本発明ではＢｉの添加は粉粒体状による接種で、Ｂｉの添加と共にＣａ添加をＦｅ−Ｓｉ−Ｂｉ−Ｃａの混合粉末または合金粉末を使用することによって発明の目的を効果的に達成できることを特に挙げておきたい。Ｃａは接種することによってＢｉの歩留まりを向上する安定化作用が顕れる。すなわち黒鉛核発生の凝固初期の段階でＣａが液化し、液相ＣａとＢｉが接触するとＢｉ−Ｃａの金属間化合物を形成して、蒸気圧が低いＢｉの気化損耗を抑止する作用があるのではないかと推定される。いうまでもなくＣａには溶湯に対する脱酸、脱硫の作用があって黒鉛球状化の大敵であるＳを取り除く作用が具わっているから、Ｂｉと共存することによってＢｉの球状化阻害要因を補って正常な球状化の進行に貢献する相乗作用があると考えられる。Ｃａは０．０００１％を超えてから明確にＢｉとの相乗効果が確認され、０．０５％を超えると不経済な上、相乗効果は減少し、外観不良等も増加する。なお、このような働きはＣａ以外の元素としてＭｇ、Ｓｒ、Ｂａなど周期律表ＩＩA族の金属や、希土類元素をブレンドした接種剤でも期待される。
【００１８】
また、Ｃａによる有効な脱硫、脱酸作用は溶湯の流動性改善にも有効である。溶湯の湯流れを決める要素の第一は当然、その保有する熱エネルギーであるが、溶湯内に残るＯ₂，Ｈ₂，Ｎ₂などの溶存ガスの存在も無視できず、また消失模型では鋳型内を先行する湯先部の酸化、鋳型との反応で発生する燃焼ガスの侵入などの影響も考えられ、Ｃａの存在はこれら負の条件を退ける阻止要因として期待され、事実、消失模型（フルモールド）に鋳造した場合の不良率の発生に如実に反映している。
【００１９】
【発明の実施の形態】
表１は本発明の実施例および比較例の成分一覧表であり、各成分ともに通常のダクタイル鋳鉄材として適用される標準成分であるが、Ｂｉ、Ｃａ添加の有無だけが両者を分ける相違点である。比較例１はＢｉ、Ｃａ共に０％であり、比較例２はＢｉのみの添加でＣａを欠き、実施例１〜３は明確にＢｉ、Ｃａが検出された例である。
【００２０】
【表１】

【００２１】
溶解はキュポラ炉によって行ない、成分調整、脱酸、脱硫など基準通りの溶製を行なった後、１４５０℃にてＭｇの圧力添加、取鍋に出湯後、口径１００ｍｍの異形管用消失模型鋳型に注湯する。管厚は８．５ｍｍである。この注湯に際して、化学成分がＳｉ：２０〜８０％、Ｂｉ：０．１〜２５．０、Ｃａ：１〜４０％、残りＦｅよりなる合金粉末または混合粉末を流下しつつある溶湯へ散布して万遍なくＢｉ、Ｃａの添加を行なう。なお、Ｂｉ、Ｃａの添加については、該注湯流接種のみではなく、取鍋中添加してもよく、また、両者を併用してもよい。鋳型への注湯温度は約１３００℃で、凝固後、鋳型から製品を取り出す。この実施例１〜２に使用した接種剤は、Ｂｉ：１０％、Ｃａ：１８％、Ｓｉ：４７％、残りＦｅからなり、実施例３に使用した接種剤は、Ｂｉ：１８％、Ｃａ：２７％、Ｓｉ：５０％、残りＦｅで、すべて粒径は０．１〜０．５ｍｍの混合粉末を選んだ。接種量については経験的に目標残留％に対する歩留まりを勘案しつつ溶湯量、製品サイズなどの要素に基づいて区分けして決定している。
【００２２】
図１は本発明の比較例１〜２と実施例１の顕微鏡組織の写真（倍率１００倍）であり、図１（Ａ）（Ｂ）が比較例１、比較例２でパーライトの面積率がそれぞれ約２４％と９％と残存し、球状黒鉛数が３８６、７４８個／ｍｍ²の数値が計測され、通常のダクタイル鋳鉄の標準品では、パーライトの残留が多く完全フェライト化に達していないことを立証している。また、薄肉部においてはチル化しているものもあった。これに対し図１（Ｃ）の実施例１では、パーライト面積率０％で完全にフェライト化し、球状黒鉛数も２０００個／ｍｍ²を超え、きわめて微細で清浄な単一基地に完全球状化した黒鉛が均等に分散している。もちろんＣａＯのような非金属介在物の析出もなく、高い靭性と強度を同時に具えている特性を示唆している。なお、本発明の実施例における球状黒鉛数とは、倍率１００倍の視野で測定し粒径１μｍ以下の粒数を除いた値である。
【００２３】
このことからも例証されるように、Ｂｉ単独の残留によっても鋳放し状態における黒鉛粒数は公知の通り確かに増加するが、Ｃａが検知できる程度まで共存すれば、相乗作用によって黒鉛粒数の増加は一層昂進し、組織緻密化という改善効果はさらに高まることが判る。また、非常に冷却速度の早い薄肉部や、金型の場合などにおいても、チル化を防止する効果が期待できる。
【００２４】
【表２】

【００２５】
表２は前記比較例１〜２と実施例１〜３の機械的性質をまとめたもので、実施例は４５０ＭＰａ以上というＦＣＤ４５０の引張強さをクリアした上、２０％以上というＦＣＤ４００の伸びも満足することができ、強度と伸びとは逆行するという金属一般の原則を超えるきわめて異例の強靭性を具える万能振りを示す。基地のフェライト相を晶出する前組織であるオーステナイト一次結晶粒が微細化され、黒鉛の粒数増加と微細化と高い球状化率の維持が、これをバックアップした結果と推定できる。
【００２６】
【発明の効果】
鉄系材料の溶湯から凝固初期にかけてのＣａの挙動にはまだ判らない一面もあるが、本発明の顕微鏡組織を見る限り、ＣａＯのような非金属介在物の晶出は認められない。発明者らの別のラボテストでは、球状黒鉛粒子を分析すると粒子中心はきわめてＣａリッチであることが確認され、黒鉛核発生の凝固初期の段階でＣａがその起点となる可能性が捉えられた。少なくともＣａの存在がＢｉの特殊な作用と共働きして、上手に利用すれば理想に近い強靭材料を構成するという効果は大きく、多数の球状黒鉛数と細かい二次晶出のフェライト結晶の基地によって強度、靭性、耐食性、耐摩耗性、疲労強度など、すべての面で従来技術を凌駕する組織を構築する効果がある。これは製造したダクタイル鋳鉄材自体の品質を理想的な状態に向上させる等、画期的な影響を産業界にもたらす効果も図り知れない。
【図面の簡単な説明】
【図１（Ａ）】本発明の比較例１の顕微鏡組織の写真である。
【図１（Ｂ）】本発明の比較例２の顕微鏡組織の写真である。
【図１（Ｃ）】本発明の実施例１の顕微鏡組織の写真である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ductile cast iron material and a method for producing the same. In addition to a green mold, a dry mold, and a time-hard mold, the present invention is excellent in annealing characteristics in a cast product made of a ductile cast iron manufactured by a special casting method such as a vanishing model mold. , And relates to the production of a material having a dense structure and having both strength and toughness.
[0002]
[Prior art]
Ductile means toughness and has been widely used today as a material that breaks the common sense of conventional cast iron. Also called spheroidal graphite cast iron, conventional gray cast iron deposits flaky graphite with strong anisotropy, whereas ductile cast iron graphite has a spherical shape as a collection of small crystals that radiate from a common nucleus. It is the cause of the properties with material strength and elongation. Currently, it is used in various fields as a member of industrial equipment and devices including the automobile industry, and many developments and researches are being continued with the aim of further improving the materials.
[0003]
In the prior art disclosed in Japanese Patent Application Laid-Open No. 1-309939, in the spheroidal graphite cast iron of a ferrite ground such as an automobile, it is an object to improve the elongation, particularly the low temperature impact value and to omit or facilitate the heat treatment. In addition to the components, Cr: less than 0.1%, Bi: 0.0015-0.008%, C.I. The E value is set to the number of graphite grains was 300 pieces / mm ² or more tissue by the 3.9 to 4.6.
[0004]
Originally, in the case of spheroidal graphite cast iron, it is the established theory that when a small amount of Sb, As, Bi, Pb, etc. is contained with S at the top, spherical graphite is difficult to crystallize. However, in this prior art, pearlite was reduced by adding an appropriate amount of Bi to increase the number of graphite particles to 300 particles / mm ² or more, and sufficient elongation and impact values were obtained without low-temperature heat treatment or heat treatment. Yes. However, since Bi has a poor penetration yield with respect to the molten metal and a large fluctuation in the yield rate, it is necessary to set the addition amount in the range of 0.005 to 0.025% in order to maintain the residual content. If the amount of residual Bi exceeds 0.008%, spheroidization of graphite is hindered, and the spheroidization rate becomes 80% or less. The prior art disclosed in Japanese Patent Laid-Open No. 2-70015 by the same applicant has almost the same gist. Regarding the addition of Bi, in this prior art, it is said that the Bi yield was improved by adding a conical block-like Bi or wrapping it in paper as a granule, and at the same time an example using an Fe-Si inoculum. Reporting.
[0005]
In another prior art related to Japanese Patent Laid-Open No. 6-93369, machinability is improved by evenly distributing spherical graphite finer than conventional spheroidal graphite cast iron and a Ca compound as a free-cutting element in cast iron. Therefore, by adding Ca to the molten metal in the presence of Mg and then adding Bi, a large number of Ca compounds can be refined and crystallized, and machinability and mechanical properties can be maintained as cast. He says he can improve.
[0006]
[Problems to be solved by the invention]
In fact, the addition of Bi is obviously effective in making graphite finer, but if it is used incorrectly, it will hinder the spheroidization of graphite and lose its mechanical strength and elongation. There is a risk of fading. For this reason, there is a strict upper limit on the amount added, but since the vapor pressure of Bi itself is low and the yield is poor, it is a top-class component, so we tried to keep the molten metal conditions uniform for each charge. Even so, it is quite difficult to strictly control the amount of oxygen and S content dissolved in the molten metal, and there is a sufficient possibility that the strict upper limit will be hampered in practice.
[0007]
The last prior art cited later is one of the points to eliminate the concern of the above cited example by adding Ca in the presence of Mg in the presence of Mg and then adding Bi. It is the answer. Focusing on the difference in the free-cutting property improvement depending on the order of addition, the feature of this prior art is presumed that such a conclusion was reached after repeated tests with changing the order of additives. However, only the graph of the relationship between the amount of wear of the cutting tool (drill) and the cutting length is supported as an example, and no specific example is given of the causal relationship between the component and the structure or mechanical properties. So I don't know the details.
[0008]
In particular, the cited example is aimed at improving free machinability and mechanical properties as it is, and focusing on crystallizing Ca as a free-cutting material (CaO) into the base structure of cast iron. Although it is explained, oxidation products that react with molten metal such as CaO are usually levitated and separated as noro and eliminated, and know-how that is not disclosed in order to keep it in the iron base and disperse it There may be. However, if it is finely confined in the iron base and dispersed crystals appear, it is equivalent to countless microscopic defects being evenly distributed, and the burden on the tool during cutting is certainly reduced, and free cutting It can be understood that it will lead to improvement of sex.
[0009]
However, if micro impurities such as CaO, which are usually treated as non-metallic inclusions (also called fine wrinkles), are dispersed throughout, why the mechanical properties, specifically, tensile strength and elongation are improved. However, it is difficult to understand because there is no description of specific examples. Even if the graphite is refined by the addition of Bi, the presence of countless inclusions may seriously detract from the cleanliness of the base, and there is a concern that the value as a structural material may be questioned.
[0010]
In terms of the relationship with molds, various types such as green molds, dry molds, organic and inorganic self-hardening molds, shell molds, etc. have been put into practical use, and V pros and vanishing model molds are becoming quite popular. is there. V Pro has a reduced pressure inside the mold, so it works positively on the fluidity of the molten metal. However, the disappeared model (full mold) immediately burns the foamed polystyrene model embedded in the sand with the heat of the molten metal and gasifies it. Since the principle is that a small amount of flaming residue remains, the endothermic reaction due to thermal decomposition of the foamed polyslene, which is the raw material, works negatively on the hot water flow. In the case of a complicated shape, it may cause a defect in shape and size due to a lack of hot water. Therefore, it is necessary to raise the temperature of the hot water from other molds, and there is also a problem that a disadvantageous condition in terms of energy cost cannot be denied.
[0011]
The present invention is based on the above-mentioned known facts, and provides high toughness as a ferrite base with high cleanliness over the entire surface. In addition, the tough ductile combines strength with finer structure and almost perfect spheroidization of graphite. The purpose is to provide cast iron materials.
[0012]
[Means for solving the problems]
The tough ductile cast iron material according to the present invention is C: 3.0-4.0%, Si: 1.5-3.0%, Mn: 0.1-0.4%, P: 0.05% Hereinafter, S: 0.01% or less, ductile cast iron material composed of the remaining Fe component, including Bi: 0.0005-0.05%, Ca: 0.0001-0.05%, Spherical graphite crystallized on a ferrite-based matrix while maintaining a spheroidization rate of 90% or more, and the above problems were solved by maintaining a tensile strength of 450 MPa or more and an elongation of 20% or more.
[0013]
Moreover, as a method of manufacturing the ductile cast iron material, the molten metal components are C: 3.0 to 4.0%, Si: 1.5 to 3.0%, Mn: 0.1 to 0.4%, P : 0.05% or less, S: 0.01% or less, and after melting and refining so that the remaining Fe is obtained, a spheroidizing agent mainly composed of Mg is added to the molten metal to perform spheroidizing treatment of graphite. At the same time or afterwards, the yield is calculated so that the inoculant is inoculated into the molten metal and finally Bi: 0.0005-0.05% and Ca: 0.0001-0.05% can be clearly detected. The requirement is to add, add, and cast. The inoculation timing is more preferably after the spheroidization treatment.
[0014]
In this case, specifically, addition of Bi and Ca is an alloy powder composed of Si: 20 to 80%, Bi: 0.1 to 25.0%, Ca: 1 to 40.0%, and the remaining Fe. Alternatively, it is desirable to use a mixed powder as an inoculum.
[0015]
As the particle size of the inoculum becomes finer, the yield of the inoculation improves and the effect increases. However, if it is too fine, the powder is scattered at the time of inoculation and the effect is reduced. Therefore, the lower limit is set to 0.05 mm. On the other hand, if the upper limit exceeds 6 mm, the inoculum cannot be uniformly diffused into the molten metal, and the effect is not achieved. Therefore, the particle size range is 0.05 mm to 6 mm. The lower limit of the optimum range is 0.1 mm or more from the viewpoint of powder management and economy.
[0016]
The component limitation of this ductile cast iron material almost follows JIS G 5526/5527 or Japan Water Works Association regulations (JWWA G 113.114), but Bi is finally 0.0005-0. 05% and Ca were added in consideration of the yield so that 0.0001 to 0.05% could be clearly detected, the graphite was finely crystallized to increase the number of spheroidal graphite in large quantities, It is characterized by tempering into a fine and tough structure with a ferrite structure.
[0017]
The action itself of adding Bi to the melt of spheroidal graphite cast iron to refine the graphite and distributing it uniformly throughout the matrix is well known, and Sb, Te, Sn, etc. are also known as elements having the same function. Bi exhibits an excellent graphite crystallization ability after exceeding 0.0005%, and if it exceeds 0.05%, the graphite crystallization ability is reduced, and adverse effects such as inhibition of spheroidization occur. However, in the present invention, Bi is added by inoculation in the form of a granular material, and the object of the invention can be effectively achieved by using mixed powder or alloy powder of Fe-Si-Bi-Ca as well as adding Bi. I want to mention in particular. When Ca is inoculated, a stabilizing effect that improves the yield of Bi appears. That is, when Ca is liquefied at the initial stage of solidification of graphite nucleation and liquid phase Ca and Bi come into contact with each other, Bi—Ca intermetallic compound is formed, and there is an action to suppress vaporization wear of Bi having a low vapor pressure. It is estimated that. Needless to say, Ca has a deoxidizing and desulfurizing action on the molten metal and an action to remove S, which is a major enemy of graphite spheroidization. Therefore, coexisting with Bi compensates for the spheroidizing inhibition factor of Bi. It is thought that there is a synergistic effect that contributes to the progress of normal spheroidization. When Ca exceeds 0.0001%, a synergistic effect with Bi is clearly confirmed, and when it exceeds 0.05%, the synergistic effect decreases and appearance defects increase. Such a function is also expected in an inoculant blended with a Group IIA metal such as Mg, Sr, Ba, or a rare earth element as an element other than Ca.
[0018]
Moreover, the effective desulfurization and deoxidation action by Ca is also effective for improving the fluidity of the molten metal. The first factor that determines the flow of molten metal is, of course, the thermal energy that it holds, but the presence of dissolved gases such as O ₂ , H ₂ , and N ₂ that remain in the molten metal cannot be ignored. The influence of the oxidation of the hot water leading portion in the interior and the invasion of combustion gas generated by the reaction with the mold is also considered, and the presence of Ca is expected as a blocking factor to reject these negative conditions. In fact, the disappearance model (full This is clearly reflected in the occurrence of a defective rate when cast into a mold.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Table 1 is a list of components of Examples and Comparative Examples of the present invention, and each component is a standard component applied as a normal ductile cast iron material. is there. Comparative Example 1 is 0% for both Bi and Ca, Comparative Example 2 is a case where only Bi is added and lacks Ca, and Examples 1 to 3 are examples in which Bi and Ca are clearly detected.
[0020]
[Table 1]

[0021]
Melting is performed in a cupola furnace, and after melting according to the standard such as component adjustment, deoxidation, and desulfurization, pressure is added to Mg at 1450 ° C. I boil water. The tube thickness is 8.5 mm. In this pouring, chemical components are Si: 20 to 80%, Bi: 0.1 to 25.0, Ca: 1 to 40%, and an alloy powder or mixed powder composed of the remaining Fe is sprayed on the flowing molten metal. Add Bi and Ca evenly. In addition, about addition of Bi and Ca, you may add not only in this pouring inoculation but in a ladle, and you may use both together. The temperature of pouring into the mold is about 1300 ° C. After solidification, the product is taken out from the mold. The inoculum used in Examples 1-2 was composed of Bi: 10%, Ca: 18%, Si: 47%, and the remaining Fe. The inoculum used in Example 3 was Bi: 18%, Ca: A mixed powder having a particle size of 0.1 to 0.5 mm was selected with 27%, Si: 50%, and the remaining Fe. The inoculation amount is empirically determined based on factors such as the amount of molten metal and product size, taking into account the yield relative to the target residual%.
[0022]
FIG. 1 is a photograph of the microstructures of Comparative Examples 1 and 2 of the present invention and Example 1 (magnification 100 times). FIGS. 1A and 1B are Comparative Examples 1 and 2, and the area ratio of pearlite is Remaining about 24% and 9% respectively, the number of spheroidal graphite was measured as 386, 748 pieces / mm ² , and normal ductile iron standard products had a lot of residual pearlite and did not reach full ferrite Is proved. Some thin portions were chilled. On the other hand, in Example 1 of FIG. 1 (C), it was fully ferritized at a pearlite area ratio of 0%, and the number of spheroidal graphite exceeded 2000 pieces / mm ² , and it was completely spheroidized into a very fine and clean single base. Graphite is evenly dispersed. Of course, there is no precipitation of non-metallic inclusions such as CaO, suggesting the characteristic of having high toughness and strength at the same time. In addition, the number of spheroidal graphite in the Example of this invention is a value which remove | excluded the number of particle | grains with a particle size of 1 micrometer or less measured in a 100-times magnification visual field.
[0023]
As can be seen from this fact, the number of graphite grains in the as-cast state is certainly increased as is known even if Bi remains alone. However, if Ca is present to the extent that it can be detected, the number of graphite grains can be increased by synergistic action. It can be seen that the increase has further progressed, and that the improvement effect of organization densification has further increased. In addition, the effect of preventing chilling can be expected even in a thin portion with a very fast cooling rate or in the case of a mold.
[0024]
[Table 2]

[0025]
Table 2 summarizes the mechanical properties of Comparative Examples 1 and 2 and Examples 1 to 3, and the Examples cleared the tensile strength of FCD450 of 450 MPa or more and satisfied the elongation of FCD400 of 20% or more. It is a versatile tool with extremely unusual toughness that goes beyond the general principle of metals, where strength and elongation go backwards. The austenite primary crystal grains, which are the microstructure before the base ferrite phase is crystallized, are refined, and the increase in the number of graphite grains and the maintenance of a high spheroidization rate can be presumed to be the backup results.
[0026]
【The invention's effect】
Although there is still one aspect of the behavior of Ca from the molten iron-based material to the initial solidification, crystallization of non-metallic inclusions such as CaO is not observed as far as the microscopic structure of the present invention is seen. In another laboratory test conducted by the inventors, the spherical graphite particles were analyzed and the center of the particles was confirmed to be extremely Ca-rich, and the possibility of Ca as the starting point was captured at the early stage of solidification of graphite nucleation. At least the presence of Ca works together with the special action of Bi, and if used well, it has a great effect of constructing a tough material that is close to the ideal. It depends on the base of a large number of spherical graphite and fine secondary crystallization ferrite crystals. It has the effect of constructing a structure that surpasses the prior art in all aspects such as strength, toughness, corrosion resistance, wear resistance, and fatigue strength. This has the potential to bring epoch-making effects to the industry, such as improving the quality of the manufactured ductile iron material itself to an ideal state.
[Brief description of the drawings]
FIG. 1 (A) is a photograph of a microstructure of Comparative Example 1 of the present invention.
FIG. 1 (B) is a photograph of the microstructure of Comparative Example 2 of the present invention.
FIG. 1 (C) is a photograph of the microstructure of Example 1 of the present invention.

Claims

C: 3.0-4.0%, Si: 1.5-3.0%, Mn: 0.1-0.4%, P: 0.05% or less, S: 0.01% or less, Bi : 0.0005~0.05%, Ca: 0.0001~0.05% , and includes Mg contained in performing the spheroidizing treatment of graphite in ductile cast iron consisting of components of the remaining Fe, spherical graphite crystallized ferrite based base while maintaining a 90% degree of spheroidization, tensile strength 450MPa or more, and maintained at least elongation of 20%, the ferrite-based spheroidal graphite crystallize out and the base is at least 2, A tough ductile cast iron material characterized by being measured at least 000 pieces / mm ² .

Molten metal components are C: 3.0-4.0%, Si: 1.5-3.0%, Mn: 0.1-0.4%, P: 0.05% or less, S: 0.01% Hereinafter, after melting and scouring to become the remaining Fe, the spheroidizing treatment agent mainly composed of Mg is added to the molten metal, and simultaneously or after performing the spheroidizing treatment of graphite, the inoculum is inoculated into the molten metal. Finally, Bi is added so that it can be clearly detected in the range of 0.0005 to 0.05% and Ca in the range of 0.0001 to 0.05%, and cast so that the pearlite area ratio is 0% and CaO does not precipitate. A method for producing a tough ductile cast iron material.

In Claim 2 , addition of Bi and Ca inoculates the alloy powder or mixed powder which a chemical component consists of Si: 20-80%, Bi: 0.1-25.0%, Ca: 1-40%, and remaining Fe. A method for producing a tough ductile cast iron material, characterized by being used as an agent.

The method for producing a tough ductile cast iron material according to claim 2 or 3, wherein the particle size of the inoculum when adding Bi and Ca is 0.05 mm to 6 mm.