JP2005256088A - Spheroidal graphite cast-iron member - Google Patents
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本発明は、球状黒鉛鋳鉄部材に関し、特に、鋳放し状態において表面層がフェライト主体の組織であり、内部が表面層よりもパーライト面積率の高い組織とし、別途熱処理を行うことなく、切り欠き効果に対して強く、かつ伸びや衝撃値が高く、引張強さが高い球状黒鉛鋳鉄部材に関する。 The present invention relates to a spheroidal graphite cast iron member, and in particular, the surface layer is a structure mainly composed of ferrite in the as-cast state, and the inside is a structure having a higher pearlite area ratio than the surface layer, and a notch effect is performed without performing a separate heat treatment. The present invention relates to a spheroidal graphite cast iron member having a high tensile strength and a high tensile strength.
従来のフェライト基地を有する球状黒鉛鋳鉄部材FCD370〜450は、切り欠き効果に対して強くかつ伸びや衝撃値が高いが、引張強さが低いという問題がある。また、パーライト基地を主体とする球状黒鉛鋳鉄部材FCD500〜800は、引張り強さは高いが、切り欠き効果に対して弱くかつ伸びや衝撃値が低いという球状黒鉛鋳鉄部材FCD370〜450とは相反した問題がある。 The conventional spheroidal graphite cast iron members FCD370 to 450 having a ferrite base have a problem that they are strong against a notch effect and have high elongation and impact values, but low tensile strength. Further, spheroidal graphite cast iron members FCD500 to 800 mainly composed of pearlite bases are contrary to spheroidal graphite cast iron members FCD370 to 450 which are high in tensile strength but weak against notch effect and low in elongation and impact value. There's a problem.
この問題を解決するために、表面層をフェライトにし、内部をパーライトにした球状黒鉛鋳鉄部材がある(例えば、特許文献1参照)。この球状黒鉛鋳鉄部材は、Mn、Cu、Sn、Pb、CrおよびSbなどのパーライト元素を添加し、後に熱処理を行って表面層をフェライト化し、表面層を軟らかく伸びのある材料とすることにより、曲げ応力や衝撃がかかった際に表面層にクラックが入りづらくなり壊れ難くなるという現象を利用したものであるが、後に別途熱処理を行う必要があるという問題がある。 In order to solve this problem, there is a spheroidal graphite cast iron member in which the surface layer is made of ferrite and the inside is made of pearlite (see, for example, Patent Document 1). This spheroidal graphite cast iron member is made by adding a pearlite element such as Mn, Cu, Sn, Pb, Cr and Sb, and then performing a heat treatment to make the surface layer ferritic, making the surface layer a soft and stretchable material, This method utilizes the phenomenon that when the bending stress or impact is applied, the surface layer becomes difficult to crack and is difficult to break, but there is a problem that a separate heat treatment is required later.
本発明は、上記の問題に鑑みてなされたものであって、鋳放し状態において表面層がフェライト主体の組織であり、内部が表面層よりもパーライト面積率の高い組織とし、別途熱処理を行うことなく、切り欠き効果に対して強く、かつ伸びや衝撃値が高く、引張強さが高い球状黒鉛鋳鉄部材を提供することを目的とする。 The present invention has been made in view of the above problems, and in the as-cast state, the surface layer has a structure mainly composed of ferrite, and the inside has a structure having a higher pearlite area ratio than the surface layer, and is subjected to a separate heat treatment. The object of the present invention is to provide a spheroidal graphite cast iron member that is strong against the notch effect, has high elongation and impact value, and high tensile strength.
本発明の球状黒鉛鋳鉄部材は、1.0〜2.5重量%のNiを少なくとも含み、鋳放し状態に置いて表面層がフェライト主体の基地組織で内部の基地が前記表面層よりもパーライト面積率が高いこととした。 The spheroidal graphite cast iron member of the present invention contains at least 1.0 to 2.5% by weight of Ni, is placed in an as-cast state, and the surface layer is a ferrite-based matrix structure, and the inner matrix is a pearlite area than the surface layer. The rate was high.
また、前記Niに加え、3.0〜4.0重量%のC、1.7〜3.5重量%Si、0.7重量%未満のMn、0.02重量%未満のS、0.05重量%未満のP、0.02〜0.1重量%のMgの元素を含むこととした。 Further, in addition to Ni, 3.0 to 4.0% by weight of C, 1.7 to 3.5% by weight of Si, less than 0.7% by weight of Mn, less than 0.02% by weight of S, 0.0. The element of less than 05% by weight of P and 0.02 to 0.1% by weight of Mg was included.
また、前記元素を含み、残部が鉄および不可避的不純物から成り、かつ前記Cと前記SiにつきC重量%+0.23Si重量%の値が3.8〜4.4であることとした。 Further, the element is contained, the balance is made of iron and inevitable impurities, and the value of C weight% + 0.23 Si weight% for the C and Si is 3.8 to 4.4.
また、前記内部の基地の伸びが8%以上であることとした。 In addition, the elongation of the internal base is 8% or more.
また、前記Niおよび前記Siのうちいずれか1つまたは両方の元素の含有量を調整することにより前記表面層の深さおよび前記内部の基地の伸びを調整し、前記表面層の深さおよび前記内部の基地の伸びとをそれぞれ所定の値とすることとした。 Further, the depth of the surface layer and the elongation of the inner base are adjusted by adjusting the content of one or both of the elements of Ni and Si, and the depth of the surface layer and the The internal base growth was set to a predetermined value.
また、0.7未満のMnの重量%、0.5未満のCuの重量%、0.35未満のCrの重量%、0.02未満のSnの重量%および、0.02未満のSbの重量%を満たす範囲で、これらの前記元素のうち少なくとも1種類以上の元素の含有量を調整することにより前記表面層の深さおよび前記内部の伸びを調整し、前記表面層の深さおよび前記内部の基地の伸びとをそれぞれ所定の値とすることとした。 Less than 0.7% by weight of Mn, less than 0.5% by weight of Cu, less than 0.35% by weight of Cr, less than 0.02% by weight of Sn and less than 0.02 by weight of Sb. The depth of the surface layer and the internal elongation are adjusted by adjusting the content of at least one element among these elements within a range satisfying weight%, and the depth of the surface layer and the The internal base growth was set to a predetermined value.
また、前記球状黒鉛鋳鉄部材の鋳物の冷却過程における共析変態温度通過時の冷却速度を調整することにより前記表面層の深さおよび前記内部の伸びを調整し、前記表面層の深さおよび前記内部の基地の伸びとをそれぞれ所定の値とすることとした。 Further, by adjusting the cooling rate at the eutectoid transformation temperature passage in the cooling process of the casting of the spheroidal graphite cast iron member, the depth of the surface layer and the internal elongation are adjusted, the depth of the surface layer and the The internal base growth was set to a predetermined value.
また、前記球状黒鉛鋳鉄部材の鋳物の溶湯中のレアアース含有量に対するアンチモン量の比率が0.4を超え、かつ含有するSbが0.02重量%未満とすることとした。 Further, the ratio of the antimony amount to the rare earth content in the melt of the spheroidal graphite cast iron member exceeds 0.4, and the contained Sb is less than 0.02% by weight.
また、前記球状黒鉛鋳鉄部材は、ダイキャスト用金型の可動主型、固定主型、ホルダーおよびまたはダイベースに用いることとした。 The spheroidal graphite cast iron member is used for a movable main mold, a fixed main mold, a holder, and / or a die base of a die casting mold.
さらに、前記球状黒鉛鋳鉄部材は、自動車の足回り部品、プレス機械または工作機械に用いることとした。 Further, the spheroidal graphite cast iron member is used for automobile undercarriage parts, press machines or machine tools.
本発明の球状黒鉛鋳鉄部材は、1.0〜2.5重量%のNiを少なくとも含み、鋳放し状態に置いて表面層がフェライト主体の基地組織で内部の基地が前記表面層よりもパーライト面積率が高いこととしたため、別途熱処理を行うことなく、切り欠き効果に対して強く、かつ伸びや衝撃値が高く、引張強さも高くすることができる。 The spheroidal graphite cast iron member of the present invention contains at least 1.0 to 2.5% by weight of Ni, is placed in an as-cast state, and the surface layer is a ferrite-based matrix structure, and the inner matrix is a pearlite area than the surface layer. Since the ratio is high, it is strong against the notch effect, has a high elongation and impact value, and can have high tensile strength without performing a separate heat treatment.
また、前記Niに加え、3.0〜4.0重量%のC、1.7〜3.5重量%Si、0.7重量%未満のMn、0.02重量%未満のS、0.05重量%未満のP、0.02〜0.1重量%のMgの元素を含むこととしたため、より確実に所定の高性能とすることができる。 Further, in addition to Ni, 3.0 to 4.0% by weight of C, 1.7 to 3.5% by weight of Si, less than 0.7% by weight of Mn, less than 0.02% by weight of S, 0.0. Since the element of less than 05% by weight of P and 0.02 to 0.1% by weight of Mg is included, the predetermined high performance can be achieved more reliably.
また、前記元素を含み、残部が鉄および不可避的不純物から成り、かつ前記Cと前記SiにつきC重量%+0.23Si重量%の値が3.8〜4.4であることとしたため、さらに確実に所定の高性能とすることができる。 Further, since the element is contained, the balance is made of iron and inevitable impurities, and the value of C weight% + 0.23 Si weight% for the C and the Si is 3.8 to 4.4. It is possible to achieve a predetermined high performance.
また、前記内部の基地の伸びが8%以上であることとしたため、破壊を確実に防ぐことができる。 Further, since the elongation of the internal base is 8% or more, destruction can be reliably prevented.
また、前記Niおよび前記Siのうちいずれか1つまたは両方の元素の含有量を調整することにより前記表面層の深さおよび前記内部の基地の伸びを調整し、前記表面層の深さおよび前記内部の基地の伸びとをそれぞれ所定の値とすることとしたため、所望の高性能に容易にすることができる。 Further, the depth of the surface layer and the elongation of the inner base are adjusted by adjusting the content of one or both of the elements of Ni and Si, and the depth of the surface layer and the Since the elongation of the internal base is set to a predetermined value, the desired high performance can be easily achieved.
また、0.7未満のMnの重量%、0.5未満のCuの重量%、0.35未満のCrの重量%、0.02未満のSnの重量%および、0.02未満のSbの重量%を満たす範囲で、これらの前記元素のうち少なくとも1種類以上の元素の含有量を調整することにより前記表面層の深さおよび前記内部の伸びを調整し、前記表面層の深さおよび前記内部の基地の伸びとをそれぞれ所定の値とすることとしたため、所望の高性能に容易にすることができる。 Less than 0.7% by weight of Mn, less than 0.5% by weight of Cu, less than 0.35% by weight of Cr, less than 0.02% by weight of Sn and less than 0.02 by weight of Sb. The depth of the surface layer and the internal elongation are adjusted by adjusting the content of at least one element among these elements within a range satisfying weight%, and the depth of the surface layer and the Since the elongation of the internal base is set to a predetermined value, the desired high performance can be easily achieved.
また、前記球状黒鉛鋳鉄部材の鋳物の冷却過程における共析変態温度通過時の冷却速度を調整することにより前記表面層の深さおよび前記内部の伸びを調整し、前記表面層の深さおよび前記内部の基地の伸びとをそれぞれ所定の値とすることとしたため、所望の高性能に容易にすることができる。 Further, by adjusting the cooling rate at the eutectoid transformation temperature passage in the cooling process of the casting of the spheroidal graphite cast iron member, the depth of the surface layer and the internal elongation are adjusted, the depth of the surface layer and the Since the elongation of the internal base is set to a predetermined value, the desired high performance can be easily achieved.
また、前記球状黒鉛鋳鉄部材の鋳物の溶湯中のレアアース含有量に対するアンチモン量の比率が0.4を超え、かつ含有するSbが0.02重量%未満とすることとしたため、チャンキー黒鉛の発生を防止し、特に大物鋳物に有効のものとすることができる。 Further, since the ratio of the antimony amount to the rare earth content in the molten metal of the spheroidal graphite cast iron member exceeds 0.4 and the contained Sb is less than 0.02% by weight, generation of chunky graphite And can be effective particularly for large castings.
また、前記球状黒鉛鋳鉄部材は、ダイキャスト用金型の可動主型、固定主型、ホルダーおよびまたはダイベースに用いることとしたため、高強度で高靭性を発揮でき有効に用いることができる。 Further, since the spheroidal graphite cast iron member is used for a movable main mold, a fixed main mold, a holder and / or a die base of a die casting mold, it can exhibit high strength and high toughness and can be used effectively.
さらに、前記球状黒鉛鋳鉄部材は、自動車の足回り部品、プレス機械または工作機械に用いることとしたため、衝撃が断続的に繰り返されても壊れ難く、高寿命とすることができる。 Further, since the spheroidal graphite cast iron member is used for undercarriage parts of automobiles, press machines or machine tools, even if the impact is intermittently repeated, the spheroidal graphite cast iron member is hardly broken and can have a long life.
以下、本発明の実施の形態の球状黒鉛鋳鉄部材につき説明する。 The spheroidal graphite cast iron member according to the embodiment of the present invention will be described below.
本発明の第1の実施の形態の球状黒鉛鋳鉄部材につき説明する。本発明の第1の実施の形態の球状黒鉛鋳鉄部材は、Niの含有効果により、所定の高性能とするものである。 The spheroidal graphite cast iron member according to the first embodiment of the present invention will be described. The spheroidal graphite cast iron member according to the first embodiment of the present invention has a predetermined high performance due to the Ni containing effect.
表1は、本発明の第1の実施の形態の球状黒鉛鋳鉄部材と比較部材の試料の化学成分を示す。 Table 1 shows chemical components of the samples of the spheroidal graphite cast iron member and the comparative member according to the first embodiment of the present invention.
試料1〜8は、C、Si、Mn、P、S、Ni、Cu、Mg、Sb、Cr、Snの化学成分の元素と、残部が鉄および不可避的不純物からなり、この組成を有する球状黒鉛鋳鉄を高周波誘導炉にて溶製し、酸硬化フェノールの自硬性鋳型で作製した径200mm×高さ200mmの鋳物重量45Kgの円筒形試験型および、厚さ25mm×長さ200mm×高さ150mmの鋳物重量7KgのYブロックに注湯して鋳造し、鋳造後、鋳型内で鋳放しの自然冷却をして、円筒形試験型においては底面より30mmの位置にて、YブロックにおいてはJISに規定された位置にて機械的性質試験用の試験片を切り出したもので、JISに規定された方法により硬度、引張強さ、0.2%耐力および伸びを測定した。また、円筒形試験型およびYブロックより鋳肌付きの小片を切り出し、鏡面研磨後、基地中のフェライトとパーライトが区別できるように腐食を施して基地組織を観察した。観察試料において基地が完全にフェライトである表面層の厚さ(表面フェライト層厚さ)およびフェライトとパーライトの比率が一定となるまでの鋳肌からの距離(内部均一組織までの距離)を測定した。さらに、内部の組織については光学顕微鏡により組織観察し、基地に占めるパーライト面積率を求めた。 Samples 1 to 8 are spheroidal graphite having chemical composition elements of C, Si, Mn, P, S, Ni, Cu, Mg, Sb, Cr, and Sn, the balance being iron and unavoidable impurities. Cast iron was melted in a high-frequency induction furnace, and a cylindrical test die with a casting weight of 45 kg having a diameter of 200 mm × height of 200 mm and made of an acid-cured phenol self-hardening mold, and a thickness of 25 mm × length of 200 mm × height of 150 mm Cast into a Y block with a casting weight of 7Kg, cast, cast, and then naturally cool in the mold, cast at a position 30mm from the bottom for cylindrical test dies, and JIS for Y block A specimen for a mechanical property test was cut out at the position, and the hardness, tensile strength, 0.2% proof stress and elongation were measured by the method specified in JIS. Further, a small piece with a cast surface was cut out from the cylindrical test die and the Y block, and after mirror polishing, corrosion was applied so that ferrite and pearlite in the matrix could be distinguished, and the matrix was observed. In the observation sample, the thickness of the surface layer whose surface is completely ferrite (surface ferrite layer thickness) and the distance from the casting surface until the ratio of ferrite and pearlite becomes constant (distance to the internal uniform structure) were measured. . Further, the internal structure was observed with an optical microscope, and the pearlite area ratio in the base was determined.
鋳鉄の光学顕微鏡組織は、腐食前の状態であれば、黒鉛のみが黒色に現われ、基地のフェライトとパーライトは白色になり、その区別ができない。一方、フェライトとパーライトが区別できるように腐食を施すと、黒鉛とパーライトが黒色に現われ、フェライトのみが白色になる。この現象を利用すると、基地中に占めるパーライト面積率を画像処理装置により求めることができる。即ち、腐食前の観察視野中の黒鉛の面積率と腐食後の観察視野中の黒鉛とパーライトを合わせた面積率を求め、(1)式を用いて基地に占めるパーライト面積率を求めた。 In the optical microstructure of cast iron, if it is in a state before corrosion, only graphite appears black, and the base ferrite and pearlite become white, and cannot be distinguished. On the other hand, when corrosion is performed so that ferrite and pearlite can be distinguished, graphite and pearlite appear black, and only ferrite becomes white. By utilizing this phenomenon, the pearlite area ratio in the base can be obtained by the image processing apparatus. That is, the area ratio of graphite in the observation visual field before corrosion and the area ratio of graphite and pearlite in the observation visual field after corrosion were determined, and the pearlite area ratio occupying the base was calculated using equation (1).
図1は、本発明の第1の実施の形態の球状黒鉛鋳鉄部材の鋳肌付近の基地組織の写真図を示す。 FIG. 1 shows a photograph of a base structure near the casting surface of a spheroidal graphite cast iron member according to the first embodiment of the present invention.
図1は、本発明の球状黒鉛鋳鉄部材の試料3〜6の代表的な写真図を示すもので、図1に示すように、本発明の球状黒鉛鋳鉄部材は、黒く示した部分が基地中のパーライトであり、白く示した部分が基地中のフェライトであり、本発明の特徴である鋳放しのままでも、すなわち特別の熱処理を行うことなく鋳物表面に表面フェライト層11が形成されていることが分かる。従来の球状黒鉛鋳鉄部材では、本発明の球状黒鉛鋳鉄部材のような表面がフェライトで内部がパーライトという2層構造は鋳放しのままでは形成されず、このような2層構造を得るためには特別な熱処理が必要であったが、本発明の球状黒鉛鋳鉄部材は、鋳放しのままでも2層構造を持つことが可能となり、中間層12では表面フェライト層11の終端からは鋳物の内部に向かってパーライトが徐々に増加し、ある所定の位置から内部はパーライトとフェライトが一定の比率となった均一な基地組織の内部均一組織13となる。内部均一組織13の部分は後述するように高強度と高靭性を合わせ持つ機械的性質を有している。 FIG. 1 shows a representative photograph of samples 3 to 6 of the spheroidal graphite cast iron member of the present invention. As shown in FIG. 1, the spheroidal graphite cast iron member of the present invention has a black portion in the base. The white ferrite part is the ferrite in the base, and the surface ferrite layer 11 is formed on the casting surface without performing any special heat treatment, which is a feature of the present invention. I understand. In a conventional spheroidal graphite cast iron member, a two-layer structure in which the surface of the spheroidal graphite cast iron member of the present invention is ferrite and the inside is pearlite is not formed as it is, and in order to obtain such a two-layer structure Although a special heat treatment was required, the spheroidal graphite cast iron member of the present invention can have a two-layer structure even in an as-cast state, and in the intermediate layer 12 from the end of the surface ferrite layer 11 to the inside of the casting. The pearlite gradually increases, and from the predetermined position, the inside becomes an internal uniform structure 13 of a uniform base structure in which the ratio of pearlite and ferrite is a constant ratio. The portion of the internal uniform structure 13 has mechanical properties having both high strength and high toughness as described later.
図2は、円筒形試験型による試料ついて、Ni含有量に対する表面フェライト層厚さと内部均一組織までの距離との関係図を示し、図3は、Yブロックによる試料ついて、Ni含有量に対する表面フェライト層厚さと内部均一組織までの距離との関係図を示す。 FIG. 2 is a graph showing the relationship between the thickness of the surface ferrite layer with respect to the Ni content and the distance to the internal uniform structure, and FIG. 3 is the surface ferrite with respect to the Ni content of the sample using the Y block. The relationship figure of layer thickness and the distance to an internal uniform structure | tissue is shown.
図2、3に示すように、円筒形試験型に比べ冷却速度が小さいYブロックにおいても、鋳物の表面にはフェライト層が形成されていることが分かる。さらに、円筒形試験型、Yブロックいずれの場合にも、表面フェライト層の厚さ、内部均一組織までの距離はNi量に応じて変化し、両者ともNiが1.5重量%のときが最大であることも分かる。この結果は、鋳物の大きさにかかわらず表面にフェライト層が形成されること、および本発明の球状黒鉛鋳鉄部材を構成する成分元素をある範囲内で調整することにより、表面フェライト層の厚さを意図的に調整できることを示す。 As shown in FIGS. 2 and 3, it can be seen that a ferrite layer is formed on the surface of the casting even in the Y block having a cooling rate lower than that of the cylindrical test die. Furthermore, in both the cylindrical test type and the Y block, the thickness of the surface ferrite layer and the distance to the internal uniform structure change according to the amount of Ni, and both are maximum when Ni is 1.5% by weight. You can also see that. This result shows that the ferrite layer is formed on the surface regardless of the size of the casting, and the thickness of the surface ferrite layer is adjusted by adjusting the constituent elements constituting the spheroidal graphite cast iron member of the present invention within a certain range. This indicates that can be adjusted intentionally.
本発明の球状黒鉛鋳鉄部材は、表面層がフェライトで内部がパーライトの2層の球状黒鉛鋳鉄部材にするだけでも切り欠き効果に対して強くなるが、さらに伸びや衝撃値が高く引張り強さの高い材料にするためには、内部を伸びのある材料にしている。 The spheroidal graphite cast iron member of the present invention is strong against the notch effect just by making the surface layer ferrite and the inside of the pearlite two-layer spheroidal graphite cast iron member, but the elongation and impact value are high and the tensile strength is high. In order to make it a high material, the inside is made of a stretchable material.
表2は、本発明の球状黒鉛鋳鉄部材と比較部材の試料の内部の機械的性質および内部のパーライト面積率を示す。 Table 2 shows the internal mechanical properties and internal pearlite area ratio of the spheroidal graphite cast iron member and the comparative member sample of the present invention.
一般に球状黒鉛鋳鉄部材は、引張強さと伸びの関係において、伸びが高いと引張強さが低く、逆に引張強さが高いと伸びが低いという、相反した関係がある。 In general, the spheroidal graphite cast iron member has a contradictory relationship in that the tensile strength and the elongation are low when the elongation is high and the tensile strength is low when the tensile strength is high.
表2と、図4、5に示すように、比較部材も含めた本発明部材の場合も、Ni含有量が増えるに従って引張強さは高くなるが、一方で伸びは低くなる関係があることが分かるが、本発明の球状黒鉛鋳鉄部材は、引張り強さと伸びの両者がともに高い値であるNi含有量を決定し、2層にして切り欠き効果に対し強くするとともに、引張り強さと伸びを高くすることを実現する。 As shown in Table 2 and FIGS. 4 and 5, in the case of the member of the present invention including the comparative member, the tensile strength increases as the Ni content increases, but the elongation decreases on the other hand. As can be seen, the spheroidal graphite cast iron member of the present invention determines the Ni content in which both the tensile strength and the elongation are high values, and makes the two layers stronger against the notch effect, while increasing the tensile strength and elongation. Realize that.
構造物の伸びは高いほど好ましいが、一般的には8%以上の伸びがあれば急激な脆性破壊が起こる前に変形が起こり破壊することはない。円筒形試験型において、伸びが8%以上の値を得るためには、表2および図4よりNi含有量が2.5重量%以下でなければならないことが分かる。また、構造物材料としてよく用いられる炭素鋼鋳鋼SC480の引張強さは480N/mm2以上、FCD500の引張強さは500N/mm2以上なので、強度の下限を500N/mm2とすると、円筒形試験型において、500N/mm2以上の値を得るためには、表2および図4よりNi含有量が1.0重量%以上でなければならないことが分かる。即ち、伸び8%以上かつ引張強さ500N/mm2以上を満足するNi含有量の範囲は、1.0〜2.5重量%であり、この範囲を本発明における球状黒鉛鋳鉄部材のNi含有量の範囲と決定した。さらに、伸びを10%以上確保するためには、Ni含有量の範囲が1.0〜2.5重量%とする必要があることも分かる。 The higher the elongation of the structure, the better. However, generally, if there is an elongation of 8% or more, deformation occurs before a sudden brittle fracture occurs, and the structure does not break. In the cylindrical test mold, it is understood from Table 2 and FIG. 4 that the Ni content must be 2.5% by weight or less in order to obtain a value of 8% or more in elongation. Moreover, since the tensile strength of carbon steel cast steel SC480 often used as a structural material is 480 N / mm 2 or more and the tensile strength of FCD500 is 500 N / mm 2 or more, if the lower limit of strength is 500 N / mm 2 , the cylindrical shape In order to obtain a value of 500 N / mm 2 or more in the test mold, it can be seen from Table 2 and FIG. 4 that the Ni content must be 1.0 wt% or more. That is, the range of Ni content satisfying the elongation of 8% or more and the tensile strength of 500 N / mm 2 or more is 1.0 to 2.5% by weight, and this range is the Ni content of the spheroidal graphite cast iron member in the present invention. The amount range was determined. Furthermore, it can also be seen that the Ni content range needs to be 1.0 to 2.5% by weight in order to ensure elongation of 10% or more.
YブロックではNi含有量の範囲が1.0〜2.5重量%の場合において、伸び9%以上、引張強さ640N/mm2以上であり、円筒形試験型をさらに上回る伸びと引張強さの値を得ている。円筒形試験型に比べ、冷却速度が速いYブロックでは、伸びおよび引張強さを低減させる要因である組織の粗大化や粒界間への不純物元素の偏析が起こらないためである。冷却速度の遅い大物鋳物においてはNi1.0〜2.5重量%が必要条件となるが、冷却速度の速い小物鋳物においてはNi0.5〜2.5重量%でも問題はない。また、本発明の球状黒鉛鋳鉄部材におけるNi含有量の範囲において、内部の基地組織に占めるパーライト面積率は、円筒形試験型で24〜78%であるが、Yブロックで48〜84%であり、この差は冷却速度に起因している。 In the Y block, when the Ni content is 1.0 to 2.5% by weight, the elongation is 9% or more and the tensile strength is 640 N / mm 2 or more. The value is obtained. This is because the Y block, which has a faster cooling rate than the cylindrical test die, does not cause coarsening of the structure and segregation of impurity elements between grain boundaries, which are factors that reduce elongation and tensile strength. For large castings with a slow cooling rate, Ni 1.0 to 2.5% by weight is a necessary condition, but for small castings with a fast cooling rate, Ni 0.5 to 2.5% by weight has no problem. Moreover, in the range of Ni content in the spheroidal graphite cast iron member of the present invention, the pearlite area ratio occupying the inner base structure is 24 to 78% in the cylindrical test mold, but 48 to 84% in the Y block. This difference is due to the cooling rate.
次に、本発明の球状黒鉛鋳鉄部材に含有する他の元素について説明する。 Next, other elements contained in the spheroidal graphite cast iron member of the present invention will be described.
Cは、3.0重量%未満では、炭化物が発生し伸びが低下すると共に引け巣を生じやすく、一方、4.0重量%以上になると爆発状黒鉛や黒鉛が浮上するカーボンフローテーションを起こすため機械的性質の低下を招くため、3.0〜4.0重量%の含有にする必要がある。 If C is less than 3.0% by weight, carbides are generated and elongation is reduced, and shrinkage cavities are likely to occur. On the other hand, if it exceeds 4.0% by weight, carbon flotation in which explosive graphite or graphite floats occurs. In order to reduce the mechanical properties, it is necessary to contain 3.0 to 4.0% by weight.
Siは、1.7重量%未満では、炭化物が発生し伸びが低下すると共に引け巣を生じやすく、一方、3.5重量%以上になるとフェライト基地中に固溶したSiがフェライト基地組織を脆化させるため伸びや衝撃値等の機械的性質の低下を招くため、1.7〜3.5重量%の含有にする必要がある。 When Si is less than 1.7% by weight, carbides are generated and elongation is reduced and shrinkage cavities are easily formed. On the other hand, when it is 3.5% by weight or more, Si dissolved in the ferrite matrix weakens the ferrite matrix. In order to reduce the mechanical properties such as elongation and impact value, it is necessary to contain 1.7 to 3.5% by weight.
C重量%+0.23Si重量%は、球状黒鉛鋳鉄部材の亜共晶側での炭素当量を示すものであり、上記に示したCとSiの組成範囲で、かつC重量%+0.23Si重量%が3.8〜4.4を満たし球状黒鉛鋳鉄部材を鋳造する必要がある。C重量%+0.23Si重量%が3.8未満では、炭化物が発生し伸びが低下すると共に引け巣を生じやすく、一方、4.4以上になると過共晶成分となるため初晶黒鉛が晶出し、晶出した初晶黒鉛が浮上して介在するカーボンフローテーションを起こすため伸びや衝撃値等の機械的性質の低下を招く。 C wt% + 0.23 Si wt% indicates the carbon equivalent on the hypoeutectic side of the spheroidal graphite cast iron member, and is within the composition range of C and Si described above, and C wt% + 0.23 Si wt% However, it is necessary to cast a spheroidal graphite cast iron member satisfying 3.8 to 4.4. When C weight% + 0.23 Si weight% is less than 3.8, carbides are generated and elongation tends to be reduced and shrinkage cavities are easily formed. On the other hand, when it is 4.4 or more, primary eutectic graphite is crystallized. Since the primary graphite that has come out and crystallized floats and causes intervening carbon flotation, mechanical properties such as elongation and impact value are lowered.
Mnは、0.7重量%以上では炭化物が発生しやすく、伸びや衝撃値等の機械的性質の低下を招き、また引け巣も生じやすくなるため、Mn<0.7重量%の含有にする必要がある。 When Mn is 0.7% by weight or more, carbide is likely to be generated, and mechanical properties such as elongation and impact value are deteriorated, and shrinkage cavities are likely to be generated. There is a need.
Pは、0.05重量%以上では硬いステダイト相が生成し伸びや衝撃値を著しく低下させ、また引け巣も生じやすくなるため、P<0.05 重量%の含有にする必要がある。 When P is 0.05% by weight or more, a hard steadite phase is generated, the elongation and impact value are remarkably lowered, and shrinkage cavities are liable to occur. Therefore, it is necessary to contain P <0.05% by weight.
Sは、黒鉛球状化元素であるMgと反応してMgSを生成し、0.02重量%以上では黒鉛球状化に作用するMg量が減少し球状化不良を起こすため、S<0.02 重量%の含有にする必要がある。 S reacts with Mg, which is a graphite spheroidizing element, to produce MgS. If it is 0.02% by weight or more, the amount of Mg acting on the graphite spheroidization decreases and spheroidization failure occurs, so S <0.02 wt. % Content must be included.
Niは、前記したように、含有量の範囲を1.0〜2.5重量%とすることにより、2層にして切り欠き効果に対し強くするとともに、引張り強さと伸びを高くすることができる。 As described above, Ni can increase the tensile strength and elongation as well as strengthen the notch effect by forming two layers by setting the content range to 1.0 to 2.5% by weight. .
Cuは、パーライト化促進元素であるため添加量が増すに従い強度も増すが、Cu0.5重量%以上ではパーライト化促進効果が強くなりすぎて黒皮付近のフェライト層が生成しなくなるため、Cu<0.5重量%の含有にする必要がある。 Since Cu is a pearlite-promoting element, the strength increases as the amount added increases. However, when Cu is 0.5% by weight or more, the effect of promoting pearlite becomes too strong and a ferrite layer near the black skin is not generated, so Cu < It is necessary to contain 0.5% by weight.
Mgは、黒鉛を球状化させる元素である。そのためMg0.02重量%未満では黒鉛の球状化率が低下し、一方、0.1重量%以上では遊離Mgにより引け巣が発生しやすくなり、伸びや衝撃値が低下するため、Mg0.02重量%〜0.1重量%の含有にする必要がある。 Mg is an element that spheroidizes graphite. Therefore, if the Mg content is less than 0.02% by weight, the spheroidization rate of the graphite is reduced. On the other hand, if it is 0.1% by weight or more, shrinkage cavities are likely to occur due to free Mg, and the elongation and impact value decrease. It is necessary to make it contain from 0.1% to 0.1% by weight.
Crは、0.35重量%以上では炭化物が発生しやすく伸びや衝撃値等の機械的性質の低下を招き、また、パーライト化促進元素であるため0.35重量%以上では黒皮付近のフェライト層が生成しなくなるため、Cr<0.35重量%の含有にする必要がある。 When Cr is 0.35% by weight or more, carbide is likely to be generated, and mechanical properties such as elongation and impact value are deteriorated. In addition, since Cr is an element that promotes pearlization, if 0.35% by weight or more, ferrite near the black skin is formed. Since no layer is formed, it is necessary to contain Cr <0.35% by weight.
Snは、強力なパーライト化促進元素でるため、Sn0.02重量%以上ではパーライト化促進効果が強くなりすぎて黒皮付近のフェライト層が生成しなくなり、また伸びや衝撃値も低下するため、Sn<0.02重量%の含有にする必要がある。 Sn is a strong pearlite-promoting element. Therefore, if Sn is 0.02% by weight or more, the effect of promoting pearlite becomes too strong to prevent the formation of a ferrite layer near the black skin, and the elongation and impact value also decrease. It is necessary to contain <0.02% by weight.
本発明の球状黒鉛鋳鉄部材は、Niを含むために冷却速度の遅い鋳物においてはチャンキー黒鉛と呼ばれる異常黒鉛が発生する。この問題を解決するために、材料に添加するアンチモン(Sb)とレア・アース(RE)の量比Sb/REについて検討した結果、Sb/RE>0.4以上においてチャンキー黒鉛の発生を防止できることが分かった。小物鋳物では冷却速度が速いためにチャンキー黒鉛が発生することは少なく、Sb/RE>0.4は冷却速度の遅い大物鋳物に有効である。ただし、Sbは強力なパーライト化促進元素であるため、含有量が多くなると伸びや衝撃値が低下する。したがって、Sb<0.02重量%の含有にする必要がある。 Since the spheroidal graphite cast iron member of the present invention contains Ni, abnormal graphite called chunky graphite is generated in a casting with a slow cooling rate. In order to solve this problem, the amount ratio Sb / RE of antimony (Sb) and rare earth (RE) added to the material was examined. As a result, generation of chunky graphite was prevented when Sb / RE> 0.4 or more. I understood that I could do it. Chunky graphite is rarely generated in a small casting because the cooling rate is high, and Sb / RE> 0.4 is effective for a large casting with a slow cooling rate. However, since Sb is a strong pearlite-promoting element, the elongation and impact value decrease as the content increases. Therefore, it is necessary to contain Sb <0.02% by weight.
以上述べたように、本発明の球状黒鉛鋳鉄部材は、鋳放し状態において表面層がフェライト主体の組織であり、内部が表面層よりもパーライト面積率の高い組織とし、別途熱処理を行うことなく、切り欠き効果に対して強く、かつ伸びや衝撃値が高く、引張強さが高いものとすることができる。 As described above, the spheroidal graphite cast iron member of the present invention has a structure in which the surface layer is mainly ferrite in the as-cast state, and the inside has a structure having a higher pearlite area ratio than the surface layer, without performing a separate heat treatment, It is strong against the notch effect, has high elongation and impact value, and high tensile strength.
なお、本発明の球状黒鉛鋳鉄部材は、内部の機械的特性だけでも高強度でかつ8%以上の高い伸びを出すことができるので、たとえばダイキャスト主型のように高強度で高靭性が要求される部材に好適である。さらに、本発明の球状黒鉛鋳鉄部材は、表面に高い伸びがあり衝撃吸収能に優れたフェライト層が形成されるため、部材に負荷される衝撃が断続的に繰り返されてもクラックのような微小欠陥が入りにくく、なおかつ、たとえ微小欠陥が入ったとしても壊れにくいため、断続的衝撃が負荷される機械部品に対し高寿命にすることができる。 Note that the spheroidal graphite cast iron member of the present invention requires high strength and high toughness, such as a die-cast main mold, because it has high strength and high elongation of 8% or more only with internal mechanical characteristics. It is suitable for the member made. Furthermore, the spheroidal graphite cast iron member of the present invention has a ferrite layer that has a high elongation on the surface and excellent shock absorption capability. Therefore, even if the impact applied to the member is repeated intermittently, it is very small like a crack. Since it is difficult for a defect to enter, and even if a micro defect is entered, it is difficult to break, so that a long service life can be achieved for a machine part subjected to intermittent impact.
本発明の第2の実施の形態の球状黒鉛鋳鉄部材の大物鋳物への適用につき説明する。 The application of the spheroidal graphite cast iron member of the second embodiment of the present invention to a large casting will be described.
表3は、本発明の第2の実施の形態の球状黒鉛鋳鉄部材と比較部材の試料の化学成分を示す。 Table 3 shows chemical components of the samples of the spheroidal graphite cast iron member and the comparative member according to the second embodiment of the present invention.
表4は、本発明の球状黒鉛鋳鉄部材と比較部材の試料9〜11の内部の機械的性質を示す。 Table 4 shows the mechanical properties inside the samples 9 to 11 of the spheroidal graphite cast iron member and the comparative member of the present invention.
図6は、本発明の球状黒鉛鋳鉄部材の試料の鋳肌付近の基地組織の写真図を示し、図7は、比較材の試料の鋳肌付近の基地組織の写真図を示す。 FIG. 6 shows a photograph of the base structure near the casting surface of the sample of the spheroidal graphite cast iron member of the present invention, and FIG. 7 shows a photograph of the base structure near the casting surface of the sample of the comparative material.
図6に示すように、本発明の球状黒鉛鋳鉄部材の試料9は、実施例1で観察した表面フェライト層が500角ブロックの場合にも現われていることが分かる。一方、図7に示すように、比較部材の試料10は、本発明の球状黒鉛鋳鉄部材の試料9のような表面フェライト層は観察されず、鋳肌直下よりパーライトとフェライトの混合組織となっている。従って、本発明の球状黒鉛鋳鉄部材は、冷却速度の遅い大物鋳物に適用した場合でも、一般の球状黒鉛鋳鉄部材では得ることができない表面フェライト層が存在し得ることが分がる。
As shown in FIG. 6, it can be seen that Sample 9 of the spheroidal graphite cast iron member of the present invention appears even when the surface ferrite layer observed in Example 1 is a 500 square block. On the other hand, as shown in FIG. 7, in the
図8は、本発明の球状黒鉛鋳鉄部材の試料に対し鋳肌から5mm間隔で基地中に占めるパーライト面積率を測定したグラフを示し、図9は、本発明の球状黒鉛鋳鉄部材の試料に対し鋳肌から5mm間隔で基地中に占める硬度を測定したグラフを示す。 FIG. 8 shows a graph in which the pearlite area ratio occupying the base at an interval of 5 mm from the casting surface is measured for the sample of the spheroidal graphite cast iron member of the present invention, and FIG. 9 shows the sample of the spheroidal graphite cast iron member of the present invention. The graph which measured the hardness which occupies in a base at intervals of 5 mm from a casting surface is shown.
本発明の球状黒鉛鋳鉄部材の試料9は、大物鋳物であり、基地中のパーライトは鋳肌より15mmの位置から現われ、内部に行くにしたがってパーライト面積率が増加し、鋳肌より30mmの位置から内部はパーライト面積率が一定の均一な組織となった。また、硬度もパーライト面積率の増加に伴って増加し、鋳肌より30mmの位置から内部はHB185前後で安定した硬度となった。また、鋳造品全体にわたってミクロ組織を観察したが、チャンキー黒鉛と呼ばれる異常形態黒鉛の発生も見られず、きわめて望ましい組織である。
Sample 9 of the spheroidal graphite cast iron member of the present invention is a large casting, and the pearlite in the base appears from a
本発明の球状黒鉛鋳鉄部材の表面フェライト層の厚さは15mmであり、表面フェライト層の厚さは実施例1、2で示した結果から製品肉厚によって変化することが分かる。実際の鋳鉄系構造部材を考えた場合、製品の肉厚は製品毎に異なり、同じ製品でも肉厚は各部によって異なるため、フェライト層の厚さが製品各部において異なることが考え得る。また、所定の寸法を出すために鋳肌を削る加工が施される場合もあるので、ある箇所ではフェライト層がなくなってしまう恐れもある。しかし、本発明の球状黒鉛鋳鉄部材はフェライト固溶化元素であるNi、Siやパーライト化元素であるMn、Cu、Sbなどの添加量を調整しても、また共析変態温度通過時の冷却速度を調整しても、フェライト層の厚さを調整することができる。ここで、共析変態温度通過時の冷却速度は注湯後の鋳型内での冷却過程、熱処理時の冷却過程を問わない。したがって、本発明の球状黒鉛鋳鉄部材の鋳造品に加工工程が加わる場合でも、フェライト層が残るように材質を調整することが可能である。 It can be seen that the thickness of the surface ferrite layer of the spheroidal graphite cast iron member of the present invention is 15 mm, and the thickness of the surface ferrite layer varies depending on the product thickness from the results shown in Examples 1 and 2. When considering an actual cast iron-based structural member, the thickness of the product varies from product to product, and even in the same product, the thickness varies from part to part. Therefore, the thickness of the ferrite layer may be different from part to part. In addition, there is a possibility that the ferrite layer is lost at a certain portion because a process of cutting the casting surface may be performed in order to obtain a predetermined dimension. However, the spheroidal graphite cast iron member of the present invention has a cooling rate when passing through the eutectoid transformation temperature even if the addition amount of Ni, Si, which is a ferrite solidifying element, Mn, Cu, Sb, which is a pearlite element, is adjusted. Even if is adjusted, the thickness of the ferrite layer can be adjusted. Here, the cooling rate when passing through the eutectoid transformation temperature may be the cooling process in the mold after pouring or the cooling process during heat treatment. Therefore, even when a processing step is added to the cast product of the spheroidal graphite cast iron member of the present invention, it is possible to adjust the material so that the ferrite layer remains.
以上述べたように、本発明の球状黒鉛鋳鉄部材は、表面の基地組織がフェライトで、内部の基地組織がパーライトとフェライトが一定の比率を持った均一組織の2層構造を有し、内部の機械的性質だけを見ても、高強度かつ高靭性であり、ダイキャスト主型など、繰り返し衝撃負荷がかかる大物鋳物の大物高強度部材への適用が可能である。さらに、表面に高い伸びを持つフェライト層を有することで、切り欠き強度に優れ、耐衝撃性が増すため、部材に断続的に衝撃が負荷されても疲労劣化が少なく、従来品に比べて耐用期間が延長し高寿命化(耐用期間の延長)が図られる。 As described above, the spheroidal graphite cast iron member of the present invention has a two-layer structure having a uniform structure in which the matrix structure on the surface is ferrite and the inner matrix structure has a certain ratio of pearlite and ferrite. Even if only the mechanical properties are seen, it has high strength and high toughness, and can be applied to large-sized, high-strength members such as die-cast main molds, which are subjected to repeated impact loads. In addition, by having a ferrite layer with high elongation on the surface, it has excellent notch strength and increased impact resistance, so there is less fatigue degradation even when impact is intermittently applied to the member, and it is more durable than conventional products The period is extended to extend the service life (extension of the service life).
また、本発明の球状黒鉛鋳鉄部材は、大物高強度部材に用いられている鋳鋼品に比べ同等の機械的性質を持ちながらも、溶解温度が低いため溶解エネルギーが少なく、溶解炉に使用される耐火物の消耗も少なく、さらに熱処理などの余分な工程を必要とせず、鋳放しのままで2層構造が得られるので、短い製造期間で製造でき、製造コストも安価にすることができる。 In addition, the spheroidal graphite cast iron member of the present invention has the same mechanical properties as cast steel products used for large, high-strength members, but has a low melting temperature and is used for melting furnaces because of its low melting temperature. Since the refractory is less consumed, an extra process such as heat treatment is not required, and a two-layer structure can be obtained as it is, so that it can be manufactured in a short manufacturing period and the manufacturing cost can be reduced.
11 表面フェライト層
12 中間層
13 内部均一組織
11 Surface ferrite layer 12 Intermediate layer 13 Internal uniform structure
Claims (10)
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JP2007245217A (en) * | 2006-03-17 | 2007-09-27 | Kubota Corp | Composite rolling mill roll |
KR20150108129A (en) * | 2014-03-17 | 2015-09-25 | 두산인프라코어 주식회사 | Ductile cast iron for hydraulic device, method of preparing the same |
KR20200005821A (en) * | 2018-07-09 | 2020-01-17 | 한국기계연구원 | Spheroidal graphite cast iron with excellent tensile property and preparation method thereof |
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JP2007245217A (en) * | 2006-03-17 | 2007-09-27 | Kubota Corp | Composite rolling mill roll |
KR20150108129A (en) * | 2014-03-17 | 2015-09-25 | 두산인프라코어 주식회사 | Ductile cast iron for hydraulic device, method of preparing the same |
KR102264261B1 (en) | 2014-03-17 | 2021-06-14 | 두산인프라코어 주식회사 | Ductile cast iron for hydraulic device, method of preparing the same |
KR20200005821A (en) * | 2018-07-09 | 2020-01-17 | 한국기계연구원 | Spheroidal graphite cast iron with excellent tensile property and preparation method thereof |
KR102174021B1 (en) | 2018-07-09 | 2020-11-04 | 한국기계연구원 | Spheroidal graphite cast iron with excellent tensile property and preparation method thereof |
JP2020023747A (en) * | 2018-07-25 | 2020-02-13 | 旭メタルズ株式会社 | Spheroidal graphite cast iron and heat treatment method for spheroidal graphite cast iron |
JP7316606B2 (en) | 2018-07-25 | 2023-07-28 | 旭メタルズ株式会社 | Spheroidal graphite cast iron and heat treatment method for spheroidal graphite cast iron |
CN112226670A (en) * | 2020-12-14 | 2021-01-15 | 日月重工股份有限公司 | QT700-8 special nodular cast iron for diesel engine parts and preparation method thereof |
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