JP4732280B2 - Cast iron with excellent heat and corrosion resistance - Google Patents
Cast iron with excellent heat and corrosion resistance Download PDFInfo
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- JP4732280B2 JP4732280B2 JP2006238960A JP2006238960A JP4732280B2 JP 4732280 B2 JP4732280 B2 JP 4732280B2 JP 2006238960 A JP2006238960 A JP 2006238960A JP 2006238960 A JP2006238960 A JP 2006238960A JP 4732280 B2 JP4732280 B2 JP 4732280B2
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- 229910001018 Cast iron Inorganic materials 0.000 title claims description 82
- 230000007797 corrosion Effects 0.000 title description 24
- 238000005260 corrosion Methods 0.000 title description 24
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 64
- 229910002804 graphite Inorganic materials 0.000 claims description 64
- 239000010439 graphite Substances 0.000 claims description 64
- 239000002245 particle Substances 0.000 claims description 9
- 239000011159 matrix material Substances 0.000 claims description 7
- 239000012535 impurity Substances 0.000 claims description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 6
- 229910052804 chromium Inorganic materials 0.000 claims description 3
- 229910052748 manganese Inorganic materials 0.000 claims description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims description 3
- 239000013078 crystal Substances 0.000 description 24
- 238000000034 method Methods 0.000 description 16
- 239000000463 material Substances 0.000 description 15
- 229910052725 zinc Inorganic materials 0.000 description 14
- 239000011701 zinc Substances 0.000 description 14
- 230000000694 effects Effects 0.000 description 13
- 238000005266 casting Methods 0.000 description 12
- 239000002184 metal Substances 0.000 description 11
- 229910052751 metal Inorganic materials 0.000 description 11
- 150000001247 metal acetylides Chemical class 0.000 description 11
- 239000002244 precipitate Substances 0.000 description 10
- 229910000831 Steel Inorganic materials 0.000 description 9
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 9
- 238000005087 graphitization Methods 0.000 description 9
- 239000010959 steel Substances 0.000 description 9
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 8
- 230000007423 decrease Effects 0.000 description 7
- 229910000805 Pig iron Inorganic materials 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 238000007654 immersion Methods 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 238000001556 precipitation Methods 0.000 description 5
- 239000002994 raw material Substances 0.000 description 5
- 229910000851 Alloy steel Inorganic materials 0.000 description 4
- 230000002411 adverse Effects 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000005520 cutting process Methods 0.000 description 4
- 238000007711 solidification Methods 0.000 description 4
- 230000008023 solidification Effects 0.000 description 4
- 238000001816 cooling Methods 0.000 description 3
- 230000005496 eutectics Effects 0.000 description 3
- 238000013467 fragmentation Methods 0.000 description 3
- 238000006062 fragmentation reaction Methods 0.000 description 3
- 230000008018 melting Effects 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 229910001141 Ductile iron Inorganic materials 0.000 description 2
- 229910001035 Soft ferrite Inorganic materials 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000001376 precipitating effect Effects 0.000 description 2
- 238000007670 refining Methods 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 238000009750 centrifugal casting Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 230000003628 erosive effect Effects 0.000 description 1
- -1 ferrous metals Chemical class 0.000 description 1
- 238000005246 galvanizing Methods 0.000 description 1
- 238000011081 inoculation Methods 0.000 description 1
- 235000000396 iron Nutrition 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Landscapes
- Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
Description
本発明は、優れた耐熱性および耐食性を有する鋳鉄に関するものである。なお、ここで耐熱性，耐食性とは、溶融状態の非鉄金属（たとえばAl，Zn）に対する耐熱性，耐食性を指す。 The present invention relates to cast iron having excellent heat resistance and corrosion resistance. Here, the heat resistance and corrosion resistance refer to heat resistance and corrosion resistance against a molten non-ferrous metal (for example, Al, Zn).
従来から複雑な形状の機械部品を製造する方法として、
(a)機械部品を構成する部材を個別に製作して組立てる方法、
(b)機械部品を一体的に鋳造し、さらに切削加工して所定の寸法精度に仕上げる方法
がある。上記の(a)の方法では、鋼板を加工して製作した各部材の強度は高いが、部材の接合部（たとえば溶接，ボルト等）の強度が低下するのは避けられない。一方、(b)の方法では接合部が存在しないので均質な機械部品を製造できるという利点はある。しかし(b)の方法で鋳鉄を鋳込んで製作した機械部品の特性は、(a)の方法で鋼板を加工して製作した部材に比べて劣るという欠点がある。
As a method of manufacturing machine parts with complicated shapes from the past,
(a) A method of individually producing and assembling the members constituting the machine part,
(b) There is a method in which mechanical parts are integrally cast and further cut to finish to a predetermined dimensional accuracy. In the method (a), the strength of each member manufactured by processing a steel plate is high, but it is inevitable that the strength of the joint portion (for example, welding, bolt, etc.) of the member is lowered. On the other hand, the method (b) has an advantage that a homogeneous machine part can be manufactured because there is no joint. However, the characteristic of the machine part produced by casting cast iron by the method (b) is inferior to that of a member produced by processing a steel plate by the method (a).
そこで(b)の方法で製作した機械部品の特性を改善するために、材料となる鋳鉄の特性を向上する技術が種々検討されている。
たとえば特許文献１には、成分を規定することによって耐溶湯溶損性を高めた鋳鉄が開示されている。この鋳鉄は、溶湯に接触するルツボ等を鋳造にて製作するために用いられる。ルツボは単純な形状であり、厳しい寸法精度は要求されない。したがって鋳込んだ後で切削加工を行なう必要はなく、Crを10〜30質量％含む硬い鋳鉄であっても使用できる。つまり特許文献１に開示された鋳鉄は、脆弱で切削加工が困難であるから、限られた用途にしか使用できない。
Therefore, various techniques for improving the properties of cast iron as a material have been studied in order to improve the properties of machine parts manufactured by the method (b).
For example, Patent Document 1 discloses a cast iron whose molten metal resistance to melting is improved by defining components. This cast iron is used to manufacture a crucible or the like that contacts the molten metal by casting. The crucible has a simple shape and does not require strict dimensional accuracy. Therefore, it is not necessary to perform cutting after casting, and even hard cast iron containing 10 to 30% by mass of Cr can be used. That is, the cast iron disclosed in Patent Document 1 is fragile and difficult to cut, and therefore can only be used for limited applications.
また特許文献２には、成分を規定することによって耐食性を高めた合金鋼が開示されている。この合金鋼は、溶融亜鉛めっきを行なうシンクロールやコーティングロールを遠心鋳造にて製作するために用いられる。これらのロールは厳しい寸法精度と優れた表面性状が要求されるので、鋳込んだ後で切削加工を行ない、所定の寸法精度と表面性状を確保しなければならない。ところがCrを20〜35質量％かつNiを10〜20質量％含む合金鋼は、オーステナイト組織を有し極めて軟らかく、切削抵抗が高いので、鋳込んだ後で切削加工するのは困難である。しかも合金鋼は多大な加工コストを費やしてロール等を製作しても、オーステナイト組織を有する故に割れが発生し易いので、ロール等を使用するにあたって十分な耐用性は得られない。
本発明は、従来の鋳鉄が備えている延性，靭性，切削性を維持しつつ、溶融状態の非鉄金属に対する耐熱性および耐食性に優れた鋳鉄を提供することを目的とする。 An object of the present invention is to provide a cast iron excellent in heat resistance and corrosion resistance to a molten non-ferrous metal while maintaining the ductility, toughness, and machinability of conventional cast iron.
発明者は、溶融状態の非鉄金属（たとえばAl，Zn）に対する鋳鉄の耐熱性，耐食性を改善する技術について鋭意検討した。その結果、Moを結晶粒内に固溶させることによって、鋳鉄の耐熱性および耐食性を改善することが可能であることを見出した。ところがMoは鋳鉄の延性や切削性に悪影響を及ぼすばかりでなく、結晶粒界に炭化物を析出し易いので靭性を低下させる原因になる。一方で、鋳鉄の結晶粒を細かくすれば、Moが結晶粒内に固溶し易く、有害な炭化物が析出しないので、靭性の低下を防止できることが判明した。しかも結晶粒を細かくすることによって鋳鉄の延性が向上し、Mo添加に起因する延性低下を防止できることが明らかになった。 The inventor has intensively studied a technique for improving the heat resistance and corrosion resistance of cast iron against molten non-ferrous metals (eg, Al, Zn). As a result, it was found that the heat resistance and corrosion resistance of cast iron can be improved by dissolving Mo in the crystal grains. However, Mo not only has an adverse effect on the ductility and machinability of cast iron, but also causes a reduction in toughness because carbide tends to precipitate at the grain boundaries. On the other hand, it has been found that if cast iron crystal grains are made fine, Mo easily dissolves in the crystal grains, and harmful carbides do not precipitate, so that a reduction in toughness can be prevented. Moreover, it has been clarified that by reducing the crystal grains, the ductility of the cast iron is improved, and the ductility decrease due to the Mo addition can be prevented.
そこで発明者は、溶解した鋳鉄を鋳込んで凝固させる過程で結晶粒を細分化する技術を研究した。発明者の研究によれば、鋳鉄の成分を規定するとともに、凝固過程における冷却速度を制御することによって、凝固の過程で黒鉛を基地に細かく分散して析出せることができ、その多数の黒鉛が結晶の生成核となって鋳鉄の結晶粒を細分化できることが明らかになった。しかも、黒鉛が析出することによって切削性を維持することができる。 Therefore, the inventor studied a technique for subdividing crystal grains in the process of casting and solidifying molten cast iron. According to the inventor's research, by defining the components of cast iron and controlling the cooling rate in the solidification process, the graphite can be finely dispersed and precipitated in the base during the solidification process. It became clear that the crystal grains of cast iron can be subdivided as crystal nuclei. Moreover, the machinability can be maintained by the precipitation of graphite.
本発明はこれらの知見に基づいてなされたものである。
すなわち本発明は、Ｃ：3.2〜3.8質量％，Si：2.0〜2.8質量％，Mn：0.4質量％以下，Al：0.05質量％以下，Cr：0.2質量％以下，Mo：1.0〜3.0質量％，Ｐ：0.05質量％以下およびＳ：0.02質量％以下を含有し、残部Feおよび不可避的不純物からなる組成を有し、基地に粒径20〜50μｍの範囲内の球状黒鉛が分散して析出した組織を有する鋳鉄である。
The present invention has been made based on these findings.
That is, the present invention includes C: 3.2 to 3.8% by mass, Si: 2.0 to 2.8% by mass, Mn: 0.4% by mass or less, Al: 0.05% by mass or less, Cr: 0.2% by mass or less, Mo: 1.0 to 3.0% by mass, A structure containing P: 0.05% by mass or less and S: 0.02% by mass or less, having a composition consisting of the balance Fe and inevitable impurities, and in which spherical graphite having a particle diameter of 20 to 50 μm is dispersed and precipitated in the matrix Cast iron having
また本発明は、Ｃ：2.6〜3.2質量％，Si：1.6〜2.2質量％，Mn：0.4質量％以下，Al：0.05質量％以下，Cr：0.6質量％以下，Mo：1.0〜3.0質量％，Ｐ：0.05質量％以下およびＳ：0.05質量％以下を含有し、残部Feおよび不可避的不純物からなる組成を有し、基地に片状のＡ型黒鉛が大きさ４で析出した組織を有する鋳鉄である。 Or The present invention, C: from 2.6 to 3.2 wt%, Si: 1.6-2.2 mass%, Mn: 0.4 wt% or less, Al: 0.05 wt% or less, Cr: 0.6 wt% or less, Mo: 1.0 to 3.0 mass% , P: 0.05% by mass or less and S: 0.05% by mass or less, having a composition composed of the balance Fe and inevitable impurities, and having a structure in which flake A-type graphite is precipitated with a size of 4 on the base It is.
なお、ここでＡ型黒鉛とは、片状に析出する黒鉛（平成５年１月18日発行「鋳鉄の生産技術」p21参照）を指し、その大きさはISO945-1975（平成５年１月18日発行「鋳鉄の生産技術」p20参照）に規定される分類に準拠する。 Here, A-type graphite refers to graphite that precipitates in the form of flakes (see “Cast Iron Production Technology” p21 issued on January 18, 1993), and its size is ISO945-1975 (January 1993). It conforms to the classification stipulated in “Cast iron production technology” p.
本発明によれば、延性，靭性，切削性を維持しつつ、優れた耐熱性および耐食性を有する鋳鉄を得ることができる。したがって本発明の鋳鉄を鋳込んで製作した機械部品は、形状や用途の制約を受けず、様々な分野で使用できる。 According to the present invention, cast iron having excellent heat resistance and corrosion resistance can be obtained while maintaining ductility, toughness, and machinability. Therefore, the machine parts manufactured by casting the cast iron of the present invention can be used in various fields without being restricted by shape and application.
まず本発明の球状黒鉛が分散した鋳鉄の組成について説明する。
Ｃ：3.2〜3.8質量％
Ｃは、鋳鉄の強度を確保するとともに、基地に球状黒鉛を分散して析出させるために必要な元素である。Ｃが3.2質量％未満では、十分な強度の鋳鉄が得られず、しかも十分な黒鉛化が得られない。一方、3.8質量％を超えると、基地に析出する球状黒鉛が大粒になり、結晶粒を細分化できない。したがって、Ｃは3.2〜3.8質量％の範囲内とする。
First, the composition of cast iron in which the spheroidal graphite of the present invention is dispersed will be described.
C: 3.2 to 3.8% by mass
C is an element necessary for ensuring the strength of cast iron and dispersing and precipitating spherical graphite on the base. If C is less than 3.2% by mass, cast iron with sufficient strength cannot be obtained, and sufficient graphitization cannot be obtained. On the other hand, if it exceeds 3.8% by mass, the spherical graphite precipitated on the matrix becomes large and the crystal grains cannot be subdivided. Therefore, C is in the range of 3.2 to 3.8% by mass.
Si：2.0〜2.8質量％
Siは、Mnと同様に、酸素を除去する作用（以下、脱酸作用という）と基地に析出する黒鉛を細粒化する作用（以下、黒鉛細粒化作用という）とを有する元素であり、鋳込みに先立って溶解した鋳鉄の酸化を防止するとともに、鋳込んで凝固させる過程にて細かい球状黒鉛を基地に分散して析出させる効果がある。Siが2.0質量％未満では、有害な炭化物が析出することがあり、十分な黒鉛化が得られない。また、溶解した鋳鉄に種々の酸化物が形成されて鋳鉄の特性に悪影響を及ぼすばかりでなく、基地に析出する球状黒鉛が大粒になり、結晶粒を細分化できない。一方、2.8質量％を超えると、鋳鉄基地の靭性が著しく低下する。したがって、Siは2.0〜2.8質量％の範囲内とする。
Si: 2.0 to 2.8% by mass
Si, like Mn, is an element having an action of removing oxygen (hereinafter referred to as deoxidation action) and an action of finely pulverizing graphite deposited on the matrix (hereinafter referred to as graphite refinement action). In addition to preventing the cast iron melted prior to casting from being oxidized, fine spherical graphite is dispersed and precipitated in the base during the casting and solidifying process. If Si is less than 2.0% by mass, harmful carbides may precipitate, and sufficient graphitization cannot be obtained. In addition, various oxides are formed in the molten cast iron to adversely affect the properties of the cast iron, and the spherical graphite deposited on the matrix becomes large and the crystal grains cannot be subdivided. On the other hand, if it exceeds 2.8% by mass, the toughness of the cast iron base is remarkably lowered. Therefore, Si is in the range of 2.0 to 2.8% by mass.
Mn：0.4質量％以下
Mnは、著しく偏析し易く、黒鉛化を阻害する元素である。ただし黒鉛化を阻害するMnの影響は、球状黒鉛の粒径が後述する範囲内では、Mn含有量0.4質量％以下で抑えられる。その理由は、Mn含有量が0.4質量％を超えると炭化物の析出を促進するからである。したがって、Mnは0.4質量％以下とする。
Mn: 0.4% by mass or less
Mn is an element that remarkably easily segregates and inhibits graphitization. However, the influence of Mn that inhibits graphitization can be suppressed at an Mn content of 0.4% by mass or less within the range in which the particle size of the spherical graphite is described later. The reason is that if the Mn content exceeds 0.4% by mass, the precipitation of carbides is promoted. Therefore, Mn is 0.4% by mass or less.
Al：0.05質量％以下
Alは、Crと同様に、鋳鉄の原材料となる鋼材スクラップや銑鉄から混入する元素である。Alが0.05質量％を超えると、軟弱なフェライト組織が生成し、溶融状態の非鉄金属（たとえばAl，Zn）に対する鋳鉄の耐熱性，耐食性が低下する。したがって、Alは0.05質量％以下とする。
Al: 0.05% by mass or less
Al, like Cr, is an element mixed from steel scrap and pig iron as raw materials for cast iron. When Al exceeds 0.05% by mass, a soft ferrite structure is formed, and the heat resistance and corrosion resistance of cast iron against a molten non-ferrous metal (eg, Al, Zn) are lowered. Therefore, Al is made 0.05 mass% or less.
Cr：0.2質量％以下
Crは、Alと同様に、鋳鉄の原材料となる鋼材スクラップや銑鉄から混入する元素である。Crが0.2質量％を超えると、鋳鉄の強度が上昇して延性が低下し、かつ黒鉛化を阻害して有害な炭化物が析出して切削性が低下する。したがって、Crは可能な限り低減する必要があり、0.2質量％以下とする。
Cr: 0.2% by mass or less
Cr, like Al, is an element mixed from steel scrap and pig iron as raw materials for cast iron. When Cr exceeds 0.2% by mass, the strength of cast iron increases, ductility decreases, and graphitization is inhibited, harmful carbides precipitate, and machinability decreases. Therefore, Cr needs to be reduced as much as possible, and is 0.2% by mass or less.
Mo：1.0〜3.0質量％
Moは、鋳鉄の結晶粒内に固溶することによって、溶融状態の非鉄金属に対する鋳鉄の耐熱性，耐食性を高める作用を有する元素である。ところがMoは結晶粒界に析出し易い元素であり、Moが結晶粒界に析出した鋳鉄は炭化物の析出によって靭性が低下する。これに対して結晶粒を細分化すれば、Moは結晶粒内に均一に固溶する。本発明では、鋳鉄の成分を規定することによって黒鉛細粒化作用が発揮され、細かい黒鉛が基地に分散して析出する。その黒鉛が結晶の生成核となり、結晶の細分化が達成される。つまり本発明では、Moが鋳鉄の結晶粒内に固溶し、耐熱性および耐食性が向上する。Moが1.0質量％未満では、耐熱性，耐食性が十分に向上しない。一方、3.0質量％を超えると、Moは炭化物として析出し易くなり、鋳鉄の強度が上昇して延性，切削性が低下する。したがって、Moは1.0〜3.0質量％の範囲内とする。
Mo: 1.0-3.0 mass%
Mo is an element that has the effect of improving the heat resistance and corrosion resistance of cast iron against molten non-ferrous metal by being dissolved in crystal grains of cast iron. However, Mo is an element that easily precipitates at the grain boundaries, and cast iron in which Mo precipitates at the grain boundaries has a reduced toughness due to the precipitation of carbides. On the other hand, if the crystal grains are subdivided, Mo is uniformly dissolved in the crystal grains. In the present invention, the effect of refining graphite is exhibited by defining the components of cast iron, and fine graphite is dispersed and precipitated in the matrix. The graphite serves as a nucleus for crystal formation, and crystal fragmentation is achieved. That is, in the present invention, Mo is dissolved in the crystal grains of cast iron, and heat resistance and corrosion resistance are improved. If Mo is less than 1.0% by mass, heat resistance and corrosion resistance are not sufficiently improved. On the other hand, if it exceeds 3.0% by mass, Mo tends to precipitate as carbide, and the strength of cast iron increases and ductility and machinability decrease. Therefore, Mo is in the range of 1.0 to 3.0 mass%.
Ｐ：0.05質量％以下
Ｐは、不可避的に混入する元素である。Ｐが0.05質量％を超えると、高温で鋳鉄に割れが発生し易くなる。したがって、Ｐは0.05質量％以下として可能な限り低減する必要がある。
Ｓ：0.02質量％以下
Ｓは、不可避的に混入する元素である。Ｓが0.02質量％を超えると、黒鉛の球状化を阻害し、鋳鉄の靭性が低下する。したがって、Ｓは0.02質量％以下として可能な限り低減する必要がある。
P: 0.05 mass% or less P is an element inevitably mixed. If P exceeds 0.05% by mass, cracks are likely to occur in cast iron at high temperatures. Therefore, P needs to be reduced as much as possible as 0.05% by mass or less.
S: 0.02 mass% or less S is an element inevitably mixed. When S exceeds 0.02 mass%, the spheroidization of graphite is inhibited and the toughness of cast iron is lowered. Therefore, S needs to be reduced as much as possible as 0.02% by mass or less.
残部はFeおよび不可避的不純物である。
次に、本発明のＡ型黒鉛が分散した鋳鉄の組成について説明する。
Ｃ：2.6〜3.2質量％
Ｃは、鋳鉄の強度を確保するとともに、基地に片状のＡ型黒鉛を分散して析出させるために必要な元素である。Ｃが2.6質量％未満では、十分な強度の鋳鉄が得られず、しかも十分な黒鉛化が得られない。一方、3.2質量％を超えると、基地に析出する片状のＡ型黒鉛が著しく成長した大きさ１となり、材料強度を劣化させる。したがって、Ｃは2.6〜3.2質量％の範囲内とする。
The balance is Fe and inevitable impurities.
Next, the composition of cast iron in which the A-type graphite of the present invention is dispersed will be described.
C: 2.6-3.2 mass%
C is an element necessary for ensuring the strength of cast iron and for dispersing and precipitating flake A-type graphite on the base. When C is less than 2.6% by mass, cast iron with sufficient strength cannot be obtained, and sufficient graphitization cannot be obtained. On the other hand, if it exceeds 3.2% by mass, the flake A-type graphite deposited on the matrix will have a significantly grown size 1 and the material strength will be deteriorated. Therefore, C is in the range of 2.6 to 3.2 mass%.
Si：1.6〜2.2質量％
Siは、Mnと同様に、脱酸作用と黒鉛細粒化作用とを有する元素であり、鋳込みに先立って溶解した鋳鉄の酸化を防止するとともに、鋳込んで凝固させる過程にて片状の細かいＡ型黒鉛を分布させる効果がある。Siが1.6質量％未満では、有害な炭化物が析出することがあり、十分な黒鉛化が得られない。また、溶解した鋳鉄に種々の酸化物が形成されて鋳鉄の特性に悪影響を及ぼすばかりでなく、基地に析出する黒鉛がＡ型黒鉛とならない。一方、2.2質量％を超えると、黒鉛が著しく成長した大きさ１および２となり、鋳鉄基地の靭性が著しく低下する。したがって、Siは1.6〜2.2質量％の範囲内とする。
Si: 1.6-2.2% by mass
Si, like Mn, is an element that has a deoxidizing effect and a graphite refining effect. It prevents oxidation of cast iron that has been melted prior to casting, and in the process of casting and solidifying, flakes are fine. There is an effect of distributing A-type graphite. If Si is less than 1.6% by mass, harmful carbides may precipitate, and sufficient graphitization cannot be obtained. In addition, various oxides are formed on the molten cast iron to adversely affect the properties of the cast iron, and the graphite deposited on the base does not become A-type graphite. On the other hand, if it exceeds 2.2% by mass, the graphite grows in size 1 and 2, and the toughness of the cast iron base is significantly reduced. Therefore, Si is in the range of 1.6 to 2.2 mass%.
Mn：0.4質量％以下
Mnは、著しく偏析し易く、黒鉛化を阻害する元素である。ただし黒鉛化を阻害するMnの影響は、Ａ型黒鉛の粒径が後述する範囲内では、Mn含有量0.4質量％以下で抑えられる。その理由は、Mn含有量が0.4質量％を超えると共晶セル粒界への炭化物の析出を促進するからである。したがって、Mnは0.4質量％以下とする。
Mn: 0.4% by mass or less
Mn is an element that remarkably easily segregates and inhibits graphitization. However, the influence of Mn that inhibits graphitization can be suppressed at an Mn content of 0.4% by mass or less within the range in which the particle size of A-type graphite is described later. The reason is that if the Mn content exceeds 0.4% by mass, the precipitation of carbides on the eutectic cell grain boundaries is promoted. Therefore, Mn is 0.4% by mass or less.
Al：0.05質量％以下
Alは、Crと同様に、鋳鉄の原材料となる鋼材スクラップや銑鉄から混入する元素である。Alが0.05質量％を超えると、軟弱なフェライト組織が生成し、溶融状態の非鉄金属に対する鋳鉄の耐熱性，耐食性が低下する。したがって、Alは0.05質量％以下とする。
Cr：0.6質量％以下
Crは、Alと同様に、鋳鉄の原材料となる鋼材スクラップや銑鉄から混入する元素である。Crが0.6質量％を超えると、鋳鉄の強度が上昇して延性が低下し、かつ有害な炭化物が析出して切削性が低下する。しかしながら片状黒鉛鋳鉄においては、Cr添加による劣化の作用は緩やかであり、耐食性を向上する効果があるので、Crは0.05〜0.6質量％の範囲内が好ましい。
Al: 0.05% by mass or less
Al, like Cr, is an element mixed from steel scrap and pig iron as raw materials for cast iron. When Al exceeds 0.05% by mass, a soft ferrite structure is formed, and the heat resistance and corrosion resistance of cast iron against molten non-ferrous metal are lowered. Therefore, Al is made 0.05 mass% or less.
Cr: 0.6% by mass or less
Cr, like Al, is an element mixed from steel scrap and pig iron as raw materials for cast iron. If Cr exceeds 0.6% by mass, the strength of cast iron increases and ductility decreases, and harmful carbides precipitate to reduce machinability. However, in flake graphite cast iron, the effect of deterioration due to the addition of Cr is gradual and has the effect of improving corrosion resistance, so Cr is preferably in the range of 0.05 to 0.6 mass%.
Mo：1.0〜3.0質量％
Moは、鋳鉄の結晶粒内に固溶することによって、溶融状態の非鉄金属に対する鋳鉄の耐熱性，耐食性を高める作用を有する元素である。Moは結晶粒界（共晶セル粒界）に析出し易い元素であり、Moが共晶セル粒界に析出した鋳鉄は炭化物の析出によって靭性が低下する。片状のＡ型黒鉛を大きさ４にして分布させることによって、このMoの悪影響を排除できる。MoはＡ型黒鉛の成長を抑制する効果があり、Moの添加によって片状のＡ型黒鉛が適度に成長した大きさ４の組織を得ることができる。溶融状態の非鉄金属は、片状黒鉛に沿って鋳鉄内部に拡散進入し、材料を劣化するので、黒鉛の粗大化を回避しなければならない。つまり本発明では、Moが鋳鉄の結晶粒内に固溶し、耐熱性および耐食性が向上する。Moが1.0質量％未満では、耐熱性，耐食性が十分に向上しない。一方、3.0質量％を超えると、Moは炭化物として析出し易くなり、鋳鉄の強度が上昇して延性，切削性が低下する。したがって、Moは1.0〜3.0質量％の範囲内とする。
Mo: 1.0-3.0 mass%
Mo is an element that has the effect of improving the heat resistance and corrosion resistance of cast iron against molten non-ferrous metal by being dissolved in crystal grains of cast iron. Mo is an element that easily precipitates at a crystal grain boundary (eutectic cell grain boundary), and cast iron in which Mo precipitates at the eutectic cell grain boundary has reduced toughness due to precipitation of carbides. By distributing the flake-shaped A-type graphite to a size of 4, this adverse effect of Mo can be eliminated. Mo has an effect of suppressing the growth of A-type graphite, and by adding Mo, it is possible to obtain a size 4 structure in which flake-shaped A-type graphite is appropriately grown. Since the molten non-ferrous metal diffuses and enters the cast iron along the flake graphite and deteriorates the material, the coarsening of the graphite must be avoided. That is, in the present invention, Mo is dissolved in the crystal grains of cast iron, and heat resistance and corrosion resistance are improved. If Mo is less than 1.0% by mass, heat resistance and corrosion resistance are not sufficiently improved. On the other hand, if it exceeds 3.0% by mass, Mo tends to precipitate as carbide, and the strength of cast iron increases and ductility and machinability decrease. Therefore, Mo is in the range of 1.0 to 3.0 mass%.
Ｐ：0.05質量％以下
Ｐは、不可避的に混入する元素である。Ｐが0.05質量％を超えると、高温で鋳鉄に割れが発生し易くなる。したがって、Ｐは0.05質量％以下として可能な限り低減する必要がある。
Ｓ：0.05質量％以下
Ｓは、不可避的に混入する元素である。Ｓが0.05質量％を超えると、鋳鉄の靭性が低下する。したがって、Ｓは0.05質量％以下として可能な限り低減する必要がある。
P: 0.05 mass% or less P is an element inevitably mixed. If P exceeds 0.05% by mass, cracks are likely to occur in cast iron at high temperatures. Therefore, P needs to be reduced as much as possible as 0.05% by mass or less.
S: 0.05 mass% or less S is an element inevitably mixed. When S exceeds 0.05 mass%, the toughness of cast iron decreases. Therefore, S needs to be reduced as much as possible as 0.05% by mass or less.
残部はFeおよび不可避的不純物である。
次に本発明の鋳鉄の組織（すなわち基地に球状黒鉛または片状Ａ型黒鉛が分散して析出した組織）について説明する。
球状黒鉛が分散して析出した鋳鉄（いわゆる球状黒鉛鋳鉄）では、その多数の細かい黒鉛が生成核となるので結晶の細分化が達成される。結晶が細分化されることによって、鋳鉄の延性，靭性が向上するばかりでなく、Moが結晶粒内に固溶して耐熱性，耐食性が向上する。また、その黒鉛は鋳鉄の切削性を高める効果も有する。球状黒鉛鋳鉄では、球状黒鉛の粒径が20〜50μｍの範囲内である。球状黒鉛の粒径が20μｍ未満では、鋳鉄の切削性を向上する効果が得られず、かつ結晶の生成核として機能しないので結晶の細分化が達成されない。一方、50μｍを超えると、鋳鉄の靭性が低下し、かつ粗大な結晶が成長する。なお、ここで球状黒鉛の粒径とは、鋳鉄の任意の断面における球状黒鉛の最大径を指す。
The balance is Fe and inevitable impurities.
Next, the structure of the cast iron of the present invention (that is, the structure in which spherical graphite or flake A-type graphite is dispersed and precipitated on the base) will be described.
In cast iron in which spheroidal graphite is dispersed and precipitated (so-called spheroidal graphite cast iron), a large number of fine graphite serves as nuclei of formation, so that crystal fragmentation is achieved. By subdividing the crystal, not only the ductility and toughness of cast iron are improved, but Mo is dissolved in the crystal grains to improve heat resistance and corrosion resistance. The graphite also has the effect of improving the machinability of cast iron. The spheroidal graphite cast iron, the particle size of the spherical graphite Ru der range of 20 to 50 m. If the particle diameter of the spherical graphite is less than 20 μm, the effect of improving the machinability of cast iron cannot be obtained, and it does not function as a crystal formation nucleus, so that the crystal fragmentation cannot be achieved. On the other hand, if it exceeds 50 μm, the toughness of cast iron is lowered and coarse crystals grow. Here, the particle diameter of the spheroidal graphite refers to the maximum diameter of the spheroidal graphite in an arbitrary cross section of the cast iron.
片状のＡ型黒鉛が分散して析出した鋳鉄では、Ａ型黒鉛を大きさ４に成長させる。Ｃ型黒鉛はＣ，Si含有量が大き過ぎるために生じる大粒の黒鉛であり、材料の強度，延性が著しく低下する。一方、Ｂ，Ｄ，Ｅ型黒鉛はＣ，Si含有量が少な過ぎる場合、あるいは接種が不十分な場合に生じ、Mo炭化物の生成を促進する傾向がある。本発明では、成分を上記のように規定することによってＡ型黒鉛を析出させる。Ａ型黒鉛の大きさ１〜３は、凝固速度が極めて遅い場合に大きく成長した黒鉛の大きさを指す。この大きさ１〜３の黒鉛では、Moが偏析しMo炭化物を析出し易くなり、材料の強度，延性を低下させる。一方、大きさ５以上は、凝固速度が著しく速い場合に黒鉛が細分化した大きさを指す。この大きさ５以上では、材料の強度，延性が著しく低下する。本発明では、大きさ４のＡ型黒鉛を析出させる。 In cast iron in which flake A-type graphite is dispersed and precipitated, A-type graphite is grown to a size of 4. C-type graphite is large-sized graphite produced because the C and Si contents are too large, and the strength and ductility of the material are significantly reduced. On the other hand, B, D and E type graphites are produced when the C and Si contents are too low or when inoculation is insufficient, and tend to promote the formation of Mo carbides. In the present invention, A-type graphite is precipitated by defining the components as described above. The size 1 to 3 of A-type graphite refers to the size of graphite that has grown greatly when the solidification rate is extremely slow. In the graphite of this size 1 to 3, Mo is segregated and Mo carbides are easily precipitated, and the strength and ductility of the material are lowered. On the other hand, the size of 5 or more refers to the size of the graphite that is subdivided when the solidification rate is remarkably high. If the size is 5 or more, the strength and ductility of the material are significantly reduced. In the present invention, size 4 A-type graphite is deposited.
以上に説明した鋳鉄を鋳込んで機械部品を製造する際には、
(1)原材料となる鋼材スクラップや銑鉄を溶解する、
(2)溶融状態の鋳鉄の成分を上記した範囲内に調整する、
(3)溶融状態の鋳鉄を所定の形状の鋳型に流し込む、
(4)鋳型内の鋳鉄を凝固させるにあたって950〜1150℃の温度範囲を50〜300℃／分の冷却速度で冷却する
という手順を採用することによって、鋳鉄の基地に細かい球状黒鉛またはＡ型黒鉛が分散して析出した機械部品が得られる。
When manufacturing machine parts by casting the cast iron described above,
(1) Melting steel scrap and pig iron as raw materials,
(2) adjusting the components of the molten cast iron within the above range;
(3) Pour molten cast iron into a mold of a predetermined shape,
(4) In order to solidify the cast iron in the mold, by adopting the procedure of cooling the temperature range of 950 to 1150 ° C. at a cooling rate of 50 to 300 ° C./min, fine spherical graphite or A-type graphite A mechanical part in which is dispersed and precipitated is obtained.
このようにして製造した機械部品は、溶融状態の非鉄金属（たとえばAl，Zn）に接触しても、AlやZnの拡散浸透を防止でき、機械部品の表面劣化を防止できる。 The machine part manufactured in this way can prevent diffusion and penetration of Al and Zn even if it contacts with a molten non-ferrous metal (for example, Al, Zn), and can prevent surface deterioration of the machine part.
鋼材スクラップと銑鉄を溶解炉に装入して溶解し、さらに成分を調整して、表１に示す成分の鋳鉄を溶製した。表１中の発明例１〜３は、本発明の球状黒鉛が分散した鋳鉄の成分を満足する例であり、発明例４，５は、本発明の片状Ａ型黒鉛が分散した鋳鉄の成分を満足する例である。比較例１〜４はMoを含有しない例である。 Steel scrap and pig iron were charged into a melting furnace and melted, and the components were adjusted to produce cast iron having the components shown in Table 1. Inventive Examples 1 to 3 in Table 1 are examples satisfying the components of cast iron in which the spherical graphite of the present invention is dispersed. Inventive Examples 4 and 5 are components of cast iron in which the flake A-type graphite of the present invention is dispersed. It is an example that satisfies Comparative Examples 1-4 are examples which do not contain Mo.
これらの鋳鉄を鋳型に流し込み、900〜1150℃の温度範囲を110℃／分で冷却して直径30mm，長さ500mmの丸棒とし、さらに切削加工を施して直径25mm，長さ400mmの試験材を作製した。得られた試験材を用いて溶融亜鉛浸漬試験を行ない、各試験材の耐熱性，耐食性を調査した。溶融亜鉛浸漬試験は、純亜鉛を溶解した亜鉛浴を440〜450℃に保持しつつ、試験材を18日間連続して浸漬した後、亜鉛浴から試験材を引き上げて浸漬部位の直径を測定することによって、溶融亜鉛による浸食の進行を評価する試験である。溶融亜鉛浸漬試験の結果を表２に示す。表２に示した試験後の試験材の直径は、亜鉛浴に浸漬した部位の測定値である。 These cast irons are poured into a mold, cooled at a temperature range of 900 to 1150 ° C at 110 ° C / min to form a round bar with a diameter of 30 mm and a length of 500 mm, and further subjected to cutting to give a test material with a diameter of 25 mm and a length of 400 mm Was made. A molten zinc immersion test was conducted using the obtained test materials, and the heat resistance and corrosion resistance of each test material were investigated. In the molten zinc immersion test, the test material is immersed for 18 days continuously while maintaining a zinc bath in which pure zinc is dissolved at 440 to 450 ° C., and then the diameter of the immersion part is measured by pulling up the test material from the zinc bath. This is a test for evaluating the progress of erosion by molten zinc. The results of the molten zinc immersion test are shown in Table 2. The diameter of the test material after the test shown in Table 2 is a measured value of the portion immersed in the zinc bath.
表２から明らかなように溶融亜鉛浸漬試験を終了した後の試験材の直径は、発明例が20.5〜22.6mmであったのに対して、比較例は0.0〜16.0mmであった。したがって、本発明の鋳鉄は耐熱性，耐食性に優れていることが確かめられた。
なお、発明例１〜３の試験材の任意の断面を顕微鏡で観察したところ、いずれも鋳鉄の基地に球状黒鉛が析出しており、球状黒鉛の粒径は20〜50μｍの範囲内であった。発明例４，５の試験材の任意の断面を顕微鏡で観察したところ、いずれも鋳鉄の基地にＡ型黒鉛が析出していた。一方、比較例１は、球状黒鉛の粒径が83μｍであり、耐食性が阻害された。。比較例２，４は、片状のＡ型黒鉛であるが、その大きさは大き過ぎる（大きさ２）ので、耐食性が阻害された。比較例３は、Ｅ型黒鉛が析出したので、耐食性が阻害された。
As is apparent from Table 2, the diameter of the test material after completion of the hot dip zinc immersion test was 20.5 to 22.6 mm in the inventive example, whereas it was 0.0 to 16.0 mm in the comparative example. Therefore, it was confirmed that the cast iron of the present invention is excellent in heat resistance and corrosion resistance.
In addition, when arbitrary cross sections of the test materials of Invention Examples 1 to 3 were observed with a microscope, spherical graphite was precipitated on the cast iron base, and the particle size of the spherical graphite was in the range of 20 to 50 μm. . When arbitrary cross sections of the test materials of Invention Examples 4 and 5 were observed with a microscope, A-type graphite was deposited on the cast iron base. On the other hand, in Comparative Example 1, the particle size of the spherical graphite was 83 μm, and the corrosion resistance was inhibited. . Comparative Examples 2 and 4 are flake-shaped A-type graphite, but its size is too large (size 2), and thus corrosion resistance is inhibited. In Comparative Example 3, since E-type graphite was precipitated, the corrosion resistance was inhibited.
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| JP2000104139A (en) * | 1998-09-29 | 2000-04-11 | Kawasaki Steel Corp | Cast iron casting for hot dip aluminum-zinc plated bathtub excellent in erosion resistance |
| JP2001520313A (en) * | 1997-10-14 | 2001-10-30 | カムキャスト・インダストリーズ・ピーティーワイ・リミテッド | Molybdenum-containing iron alloy |
| JP2002194477A (en) * | 2000-12-26 | 2002-07-10 | Wakamatsu Seisakusho:Kk | Member for molten nonferrous metal |
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| JP2001520313A (en) * | 1997-10-14 | 2001-10-30 | カムキャスト・インダストリーズ・ピーティーワイ・リミテッド | Molybdenum-containing iron alloy |
| JP2000104139A (en) * | 1998-09-29 | 2000-04-11 | Kawasaki Steel Corp | Cast iron casting for hot dip aluminum-zinc plated bathtub excellent in erosion resistance |
| JP2002194477A (en) * | 2000-12-26 | 2002-07-10 | Wakamatsu Seisakusho:Kk | Member for molten nonferrous metal |
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