JP3577100B2

JP3577100B2 - Pig iron for castings with excellent melting efficiency

Info

Publication number: JP3577100B2
Application number: JP01275894A
Authority: JP
Inventors: 勝福田; 章福島; 良二伊藤
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 1994-02-04
Filing date: 1994-02-04
Publication date: 2004-10-13
Anticipated expiration: 2019-10-13
Also published as: JPH07216494A

Description

【０００１】
【産業上の利用分野】
本発明は、銑鉄鋳物の原料に使用される鋳物用銑鉄に関し、さらに詳しくは、溶解効率の優れた鋳物用銑鉄に関するものである。
【０００２】
【従来の技術】
従来の鋳物用銑鉄（ＪＩＳ１〜３種）は主に溶鉱炉で製造される。溶鉱炉炉内は強還元性雰囲気であるため、製造された鋳物用銑鉄中には過飽和状態まで炭素が吸収され、その後Ｓｉ調整によって炭素は若干低下するが、それでも共晶飽和度（ＳＣ値）は１．２０以上の超過共晶組成となっており、このため融点も高いところにある。
【０００３】
一方、高純度銑鉄は溶鉱炉から出銑した銑鉄を、溶銑予備処理装置を用い酸素吹精によって脱燐処理し型銑として鋳銑して製造される。このように、酸素吹精されることにより溶銑中の珪素は酸化除去され、また、炭素も酸化低減する。したがって、共晶飽和度としては亜共晶組成となり融点も高くなる。
【０００４】
さらに高純度銑鉄の場合は、酸素吹きのため溶銑中に多量（１００ｐｐｍ以上）の酸素が含有され、これが鋳銑時の冷却時にＯ_２またはＣＯ_２ガスとなって放出されるため、型銑の表面がクレーター状となり、内部には気泡巣が生じた型銑となる。このような型銑が雨濡れした場合、気泡巣等に侵入した水分はなかなか抜けないため、鋳物工場での溶解時に水蒸気爆発等の事故原因となって銑鉄多量配合の阻害要因となっている。
【０００５】
これらの改善のため、脱燐処理した後、軽脱酸する方法、あるいは特公昭５７−６４８９号公報では、Ｆｅ−Ｓｉ合金を添加して溶銑中の酸素含有量を４０ｐｐｍ以下にする方法等が提案されている。しかし、特公昭５７−６４８９号公報においても、珪素がほとんど含有されていないため、型銑の組織は黒鉛化せずセメンタイト組織（白銑）となるため凝固時の収縮が大きく、型銑の内部には収縮巣が生じやすい。また、セメンタイト組織の銑鉄は硬くて脆いため折損しやすく内部の収縮巣が露出して、前記と同様に溶解時の水蒸気爆発等の事故原因となって銑鉄多量配合の阻害要因となっている。
【０００６】
【発明が解決しようとする課題】
銑鉄鋳物製品は、鋼屑を主原料とし、これに上記の鋳物用銑鉄、自家発生の戻り屑、故銑、さらに合金鉄、加炭剤等の種々雑多な原料を配合し溶解して鋳物製品を製造している。このように成分元素も溶融点も異なる原料を配合するため、溶解燃料（電気、コークス）費の上昇、さらに溶解能力の低下となり銑鉄鋳物製品の製造コストを押し上げている。
【０００７】
上述のように、従来の溶鉱炉から直接製造される鋳物用銑鉄は過共晶組成であるため融点が高く、溶解燃料費の低減、溶解能力の向上効果は少ない。また、球状黒鉛鋳鉄製造時の黒鉛球状化阻害元素であるＴｉ等の含有量も高い。また、従来の高純度銑鉄は逆に亜共晶組成であるため融点が高く、溶解燃料費の低減、溶解能力の向上効果は少ない。また、気泡巣、収縮巣等の存在により溶解時の水蒸気爆発等を考慮して、安全上多量配合はできない。
【０００８】
本発明は、上記の問題点を解決するためになされたもので、溶銑中のＣ量に応じて共晶組成値になるようにＳｉ量を調整し、最も融点の低い組成とするとともに、型銑組織を規制して気泡巣、収縮巣をなくし、さらに黒鉛球状化阻害元素であるＴｉ、Ｓ含有量を規制し球状黒鉛鋳鉄の製造を容易にすることにより、鋳物用銑鉄の多量配合が可能で、溶解時の溶解燃料費の低減、さらに溶解能力の向上が可能である溶解効率の優れた鋳物用銑鉄を提供することを目的とする。
【０００９】
【課題を解決するための手段】
Ｓｉ：０．５％以上、Ｐ：０．０４０％以下、Ｓ：０．０２０％以下、Ｔｉ：０．０２０％以下を含有し、共晶飽和度＝〔Ｃ〕／（４．２３−〔Ｓｉ〕／３．２）
ただし、〔Ｃ〕は銑鉄中の炭素成分（重量％）、〔Ｓｉ〕は銑鉄中の珪素成分（重量％）である共晶飽和度が０．９〜１．１の範囲で、かつ型銑断面の５０％以上が黒鉛の生成した組織である溶解効率の優れた鋳物用銑鉄である。
【００１０】
【作用】
本発明では、鋳物用銑鉄の共晶飽和度を０．９〜１．１の範囲に限定する。その理由は、共晶飽和度を０．９〜１．１の範囲に限定することにより鋳物用銑鉄の融点が共晶温度近傍になり、溶解し易くなるからである。すなわち、鋳物用銑鉄は、共晶飽和度が１．０の時、融点が共晶点に相当し、最も融点が低い。このように、鋳物用銑鉄の融点を低融点にすることで、誘導電気炉溶解の場合は、早期に溶け落ちするため電気効率が向上し、電力原単位の低減、溶解能力の向上効果が得られる。また、キュポラ溶解でも低温域から溶解開始するため同様の効果が得られる。
【００１１】
共晶飽和度は、共晶飽和度＝〔Ｃ〕／（４．２３−〔Ｓｉ〕／３．２）で表され、鋳銑前の溶銑のＣ量に応じて、Ｓｉを添加して共晶飽和度を０．９〜１．１の範囲に調整した後、鋳銑して融点の低い鋳物用銑鉄とする。ただし、〔Ｃ〕は銑鉄中の炭素成分（重量％）、〔Ｓｉ〕は銑鉄中の珪素成分（重量％）を示す。なを、共晶飽和度は周知である。
【００１２】
Ｓｉ含有量を０．５％以上に、かつ型銑断面の５０％以上をグラファイト系組織に限定する理由は、次のとおりである。鋳物用銑鉄を多量配合するには、溶解時の安全確保が重要な課題であり、このためには型銑から気泡巣や収縮巣等をなくし、かつ型銑が折損して内部の巣が露出しないようにする必要がある。折損がなく巣が発生しない条件は、型銑断面の組織の５０％以上をセメンタイト系から黒鉛の生成したグラファイト系にする必要がある。
【００１３】
このため本発明者らは、収縮巣およびセメンタイト系組織に及ぼすＳｉ含有量の影響について調査した。その結果を図３に示す。図３に示すように銑鉄中のＳｉ含有量が増加するとともに、収縮巣発生率は低下し、セメンタイト面積率も減少する。収縮巣発生率はＳｉ含有量が０．５％のとき０％となり、収縮巣は発生しなくなる。また、セメンタイト面積率はＳｉ含有量が０．５％のとき５０％となり、黒鉛の生成した組織であるグラファイト系組織が５０％発生していることになる。したがって、Ｓｉ含有量を０．５％以上、かつ型銑断面の５０％以上を黒鉛の生成した組織であるグラファイト系組織に限定する。
【００１４】
Ｐは３元共晶の燐化鉄を生成させ鋳鉄（鋳物）の靱性を劣化させる要因となる。したがって、銑鉄を多量配合した場合でも、燐化鉄が生成しないように、Ｐ含有量は０．０４０％以下に限定する。
【００１５】
Ｔｉ、Ｓは強力な黒鉛球状化阻害元素であることが知られており、銑鉄を多量配合した場合でも、このような阻害作用がないように、Ｔｉ、Ｓ含有量はそれぞれ０．０２０％以下に限定する。
【００１６】
【実施例】
以下に、本発明の実施例について説明する。
実施例１
溶解量５ｔの低周波炉を用いダクタイル鋳鉄の溶解を行った。使用した鋳物用銑鉄の化学成分、共晶飽和度、原料配合率を表１に、溶解結果を表２に示す。
【００１７】
【表１】

【００１８】
【表２】

【００１９】
表１に示すように、本発明に係わる鋳物用銑鉄を使用した実施例では、銑鉄が主原料で鋼屑の配合率は２０％と低くなっている。このため早期に溶融状態となり、表２に示すように、溶解能力が２０％向上している。これにともない電力原単位は約１５％低減している。また、鋼屑の配合率が低いため、溶解歩留も０．６％向上している。このような効果については、溶解状況を観察すると従来配合に比較して装入原料が早期に溶融状態になっており、このため電気効率が向上することにある。
【００２０】
実施例２
溶解能力２ｔ／ｈの冷風キュポラを用いダクタイル鋳鉄の溶解を行った。使用した鋳物用銑鉄の化学成分、共晶飽和度、原料配合率を表３に、溶解結果の例を表４に示す。また、このときのコークス比と溶解能力（出湯速度）との関係を図１に示す。
【００２１】
【表３】

【００２２】
【表４】

【００２３】
表３に示すように、本発明に係わる鋳物用銑鉄を使用した実施例では、銑鉄が主原料で鋼屑の配合率は０％まで低くすることができる。このため図１に示すように、コークス比を低減することが可能で、このため、出湯温度は若干低くなるものの、表４に示すように、溶解能力は約２５％向上している。また、成分が均一な銑鉄を主原料とできるため、溶解目標成分に対する出湯成分のばらつきも小さくなっている。
【００２４】
実施例３
本発明に係わる三種類の鋳物用銑鉄を使用した、冷風キュポラを用いたダクタイル鋳鉄の溶解時の出湯Ｓ量の実績を図２に示す。なお、使用した鋳物用銑鉄の化学成分、共晶飽和度、原料配合率を表５に示す。図２は溶解毎に、出湯温度と出湯Ｓ量をプロットしたもので、銑鉄配合量が１００％でない通常の配合では、高融点の鋼屑が溶解するまでコークスと長時間接触するためコークスからのＳの吸収が多く溶湯のＳ量が大となり、さらに、融点の異なる材料を配合しているため、出湯毎のＳ量のばらつきが大きい。一方、本発明に係わる鋳物用銑鉄を１００％配合した場合は、低温度域から溶解しコークスの間隙を速やかに通過しコークスとの接触時間が短く、また、実施例２で示したようにコークス比を低減可能なためＳ吸収量、ばらつきともに少なくなり、出湯Ｓ量は通常の配合の５０％程度まで低下することを確認している。このように、本発明に係わる鋳物用銑鉄を使用することにより、出湯Ｓ量が大幅に低下するため、特に球状黒鉛鋳鉄製造時には脱硫コストの低減と黒鉛球状化が促進され、高品質の球状黒鉛鋳鉄が得られる。
【００２５】
【表５】

【００２６】
実施例では比較的高Ｃ、低Ｓｉの鋳物用銑鉄を使用しているが、共晶飽和度が０．９〜１．１の範囲であれば、低Ｃ、高Ｓｉあるいは中Ｃ、中Ｓｉの鋳物用銑鉄を製品の目標成分に合わせて使用することができる。以上、説明したように、本発明に係わる鋳物用銑鉄を使用することによって、溶解温度の低下にともなう溶解燃料費の低減、溶解能力の向上による生産性の向上、成分の調整が容易となり成分のばらつきが小さくなることによる品質の向上、黒鉛球状化が促進されることによる高品質の球状黒鉛鋳鉄を得ることが可能となる。
【００２７】
【発明の効果】
以上、述べたところから明らかなように、本発明に係わる鋳物用銑鉄によれば、特に球状黒鉛鋳鉄の製造を容易にし、多量配合が可能で、溶解時の溶解燃料費の低減、さらに溶解能力の向上が可能である。
【図面の簡単な説明】
【図１】冷風キュポラを用いたときのコークス比と溶解能力（出湯速度）との関係を示す図である。
【図２】本発明に係わる三種類の鋳物用銑鉄を使用した、冷風キュポラを用いたダクタイル鋳鉄の溶解時の出湯Ｓ量の実績を示す図である。
【図３】収縮巣およびセメンタイト系組織に及ぼすＳｉ含有量の影響を示す図である。[0001]
[Industrial applications]
The present invention relates to pig iron for casting used as a raw material for pig iron castings, and more particularly, to pig iron for casting having excellent melting efficiency.
[0002]
[Prior art]
Conventional pig iron for casting (JIS 1-3) is mainly produced in blast furnaces. Since the blast furnace furnace is in a strongly reducing atmosphere, carbon is absorbed into the manufactured pig iron to a supersaturated state, and then carbon is slightly reduced by Si adjustment, but the eutectic saturation (SC value) is still low. It has an excess eutectic composition of 1.20 or more, and therefore has a high melting point.
[0003]
On the other hand, high-purity pig iron is produced by subjecting pig iron from a blast furnace to dephosphorization by oxygen blowing using a hot metal pretreatment device and casting it as shaped pig iron. As described above, the oxygen in the hot metal is oxidized and removed by the oxygen blowing, and the carbon is also oxidized and reduced. Therefore, the eutectic saturation becomes a hypoeutectic composition and the melting point becomes high.
[0004]
Further, in the case of high-purity pig iron, a large amount (100 ppm or more) of oxygen is contained in the hot metal due to oxygen blowing, and this is released as O ₂ or CO ₂ gas at the time of cooling at the time of casting iron. The surface becomes a crater-like shape, and inside becomes a pig iron with bubble cavities. When such a pig iron gets wet, the moisture that has invaded the bubble cavities and the like does not easily escape, and this causes an accident such as a steam explosion when dissolving in a foundry, which is a hindrance factor for the mixing of a large amount of pig iron.
[0005]
In order to improve these, a method of dephosphorizing and then lightly deoxidizing, or a method of adding an Fe-Si alloy to reduce the oxygen content in the hot metal to 40 ppm or less is disclosed in Japanese Patent Publication No. 57-6489. Proposed. However, even in Japanese Patent Publication No. 57-6489, since the silicon hardly contains silicon, the structure of the pig iron is not graphitized but becomes a cementite structure (white iron). Tend to have shrinkage nests. Further, pig iron having a cementite structure is hard and brittle, so that it is easily broken and the internal shrinkage cavities are exposed, which causes an accident such as a steam explosion at the time of dissolution as described above, which is a hindrance factor for the large amount of pig iron.
[0006]
[Problems to be solved by the invention]
Pig iron casting products are mainly made of steel scrap, and mixed with various raw materials such as the above-mentioned pig iron for casting, self-generated return scrap, waste iron, ferroalloys, and carburizing agents, and then melted into a cast product. Has been manufactured. As described above, since raw materials having different component elements and different melting points are blended, the cost of molten fuel (electricity, coke) is increased, and the melting capacity is lowered, thereby increasing the production cost of pig iron casting products.
[0007]
As described above, pig iron for castings directly produced from a conventional blast furnace has a high melting point due to its hypereutectic composition, and thus has little effect on reducing the cost of melting fuel and improving melting capacity. In addition, the content of Ti or the like, which is a graphite spheroidization inhibiting element during the production of spheroidal graphite cast iron, is high. On the other hand, conventional high-purity pig iron has a low melting point due to its hypoeutectic composition, and has little effect on reducing the cost of melting fuel and improving the melting capacity. In addition, in view of the steam explosion at the time of dissolution due to the presence of bubble cavities, shrinkage cavities, etc., a large amount cannot be blended for safety.
[0008]
The present invention has been made in order to solve the above-mentioned problems, and adjusts the amount of Si so as to have a eutectic composition value in accordance with the amount of C in the hot metal to obtain a composition having the lowest melting point and a mold. A large amount of pig iron for casting is possible by regulating the pig structure to eliminate bubble cavities and shrinkage cavities, and also to regulate the contents of Ti and S, which are graphite spheroidizing inhibitors, to facilitate the production of spheroidal graphite cast iron. Accordingly, it is an object of the present invention to provide a pig iron for casting with excellent melting efficiency, which can reduce the cost of melting fuel at the time of melting and further improve the melting capacity.
[0009]
[Means for Solving the Problems]
Si: 0.5% or more, P: 0.040% or less, S: 0.020% or less, Ti: 0.020% or less, eutectic saturation = [C 2] / (4.23- [ Si] /3.2)
However, [C] is the carbon component (wt%) in pig iron, [Si] is the silicon component (wt%) in pig iron, and the eutectic saturation is in the range of 0.9 to 1.1, and This is pig iron for castings having an excellent dissolution efficiency in which 50% or more of the cross section has a structure in which graphite is generated .
[0010]
[Action]
In the present invention, the eutectic saturation of pig iron for casting is limited to the range of 0.9 to 1.1. The reason for this is that by limiting the eutectic saturation to the range of 0.9 to 1.1, the melting point of the pig iron for casting becomes close to the eutectic temperature, and it becomes easy to dissolve. That is, when pig iron for casting has a eutectic saturation of 1.0, the melting point corresponds to the eutectic point and has the lowest melting point. In this way, by lowering the melting point of pig iron for casting, in the case of melting in an induction electric furnace, it melts out early, improving the electrical efficiency, reducing the power consumption and improving the melting capacity. Can be Also, the same effect can be obtained in cupola dissolution since the dissolution starts from a low temperature range.
[0011]
The eutectic saturation is expressed as eutectic saturation = [C] / (4.23- [Si] /3.2), and Si is added according to the C content of the hot metal before the cast iron. After adjusting the crystal saturation to the range of 0.9 to 1.1, cast iron is used to make casting iron having a low melting point. Here, [C] indicates the carbon component (wt%) in pig iron, and [Si] indicates the silicon component (wt%) in pig iron. Note that the eutectic saturation is well known.
[0012]
The reason why the Si content is limited to 0.5% or more and 50% or more of the cross section of the pig iron is limited to the graphite structure is as follows. In order to mix a large amount of pig iron for castings, it is important to ensure safety during melting.To this end, bubble porosity and shrinkage cavities are eliminated from the pig iron, and the fin is exposed due to breakage of the pig iron. You need to avoid it. The condition that there is no breakage and no burrs is generated is that it is necessary that at least 50% of the structure of the cross section of the pig iron is made of a cementite-based graphite-based graphite.
[0013]
Therefore, the present inventors investigated the effect of Si content on shrinkage cavities and cementite-based structures. The result is shown in FIG. As shown in FIG. 3, as the Si content in pig iron increases, the shrinkage porosity decreases, and the cementite area ratio also decreases. The shrinkage porosity is 0% when the Si content is 0.5%, and no shrinkage porosity occurs. Further, the area ratio of cementite is 50% when the Si content is 0.5%, which means that 50% of the graphite-based structure, which is the structure in which graphite is generated, is generated. Therefore, the Si content is limited to 0.5% or more and 50% or more of the cross section of the pig iron is limited to a graphite-based structure in which graphite is generated .
[0014]
P forms ternary eutectic iron phosphide and becomes a factor of deteriorating the toughness of cast iron (casting). Therefore, even if a large amount of pig iron is blended, the P content is limited to 0.040% or less so that iron phosphide is not generated.
[0015]
Ti and S are known to be strong graphite spheroidizing elements, so that even when a large amount of pig iron is blended, the contents of Ti and S are each 0.020% or less so as not to have such an inhibitory effect. Limited to.
[0016]
【Example】
Hereinafter, examples of the present invention will be described.
Example 1
The ductile cast iron was melted using a low-frequency furnace having a melting amount of 5 t. Table 1 shows the chemical composition, eutectic saturation, and raw material mixing ratio of the used pig iron for casting, and Table 2 shows the results of dissolution.
[0017]
[Table 1]

[0018]
[Table 2]

[0019]
As shown in Table 1, in the example using pig iron for casting according to the present invention, pig iron is a main raw material and the mixing ratio of steel chips is as low as 20%. For this reason, the molten state was obtained early, and as shown in Table 2, the melting ability was improved by 20%. As a result, the power consumption rate has been reduced by about 15%. In addition, the melting ratio is improved by 0.6% due to the low mixing ratio of steel scrap. Regarding such an effect, when observing the dissolution state, the charged raw material is in a molten state earlier than in the case of the conventional compounding, so that the electric efficiency is improved.
[0020]
Example 2
The ductile cast iron was melted using cold air cupola having a melting capacity of 2 t / h. Table 3 shows the chemical components, eutectic saturation, and raw material mixing ratio of the used pig iron for casting, and Table 4 shows examples of the melting results. FIG. 1 shows the relationship between the coke ratio and the dissolving capacity (the tapping speed) at this time.
[0021]
[Table 3]

[0022]
[Table 4]

[0023]
As shown in Table 3, in the example using the pig iron for casting according to the present invention, pig iron is the main raw material, and the mixing ratio of steel scrap can be reduced to 0%. For this reason, as shown in FIG. 1, the coke ratio can be reduced. As a result, although the tapping temperature is slightly lowered, as shown in Table 4, the melting capacity is improved by about 25%. In addition, since pig iron having a uniform component can be used as a main raw material, variation of a tapping component with respect to a target component for dissolution is small.
[0024]
Example 3
FIG. 2 shows the results of the tapping S amount at the time of melting of ductile cast iron using cold air cupolas using three types of pig iron for casting according to the present invention. Table 5 shows the chemical composition, eutectic saturation, and raw material mixing ratio of the used pig iron for casting. Fig. 2 plots the tapping temperature and tapping S amount for each melting. In the normal mixing of the pig iron compounding amount which is not 100%, since the high melting point steel scrap is in contact with the coke for a long time until it melts, the coke Since the molten metal absorbs a large amount of S 2, the amount of S 2 in the molten metal is large, and the materials having different melting points are blended, the variation in the amount of S 2 in each molten metal is large. On the other hand, when 100% of the pig iron for casting according to the present invention is blended, it melts from a low temperature range, quickly passes through the gap of the coke, and has a short contact time with the coke. It has been confirmed that since the ratio can be reduced, both the amount of S absorbed and the amount of dispersion are reduced, and the amount of discharged S is reduced to about 50% of that of a normal mixture. As described above, by using the pig iron for casting according to the present invention, the amount of tapping S is greatly reduced. Therefore, particularly in the production of spheroidal graphite cast iron, reduction of desulfurization cost and spheroidization of graphite are promoted, and high quality spheroidal graphite is promoted. Cast iron is obtained.
[0025]
[Table 5]

[0026]
In the embodiment, pig iron for castings having relatively high C and low Si is used, but if the eutectic saturation is in the range of 0.9 to 1.1, low C and high Si or medium C and medium Si Can be used according to the target components of the product. As described above, by using the pig iron for casting according to the present invention, the melting fuel cost is reduced due to the lowering of the melting temperature, the productivity is improved by improving the melting ability, and the adjustment of the components is facilitated. It is possible to obtain high quality spheroidal graphite cast iron by improving the quality by reducing the variation and promoting the spheroidization of graphite.
[0027]
【The invention's effect】
As is clear from the above description, according to the pig iron for casting according to the present invention, the production of spheroidal graphite cast iron is particularly easy, a large amount can be blended, the melting fuel cost during melting is reduced, and the melting capacity is further improved. Can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between a coke ratio and a dissolving ability (a tapping speed) when using a cold air cupola.
FIG. 2 is a graph showing the results of tapping S when melting ductile cast iron using cold air cupolas using three types of pig iron for casting according to the present invention.
FIG. 3 is a diagram showing the effect of Si content on shrinkage cavities and cementite-based structures.

Claims

Si: 0.5% or more, P: 0.040% or less, S: 0.020% or less, Ti: 0.020
% Or less,
Eutectic saturation = [C] / (4.23- [Si] /3.2)
However, [C] is the carbon component (wt%) in pig iron, [Si] is the silicon component (wt%) in pig iron, and the eutectic saturation is in the range of 0.9 to 1.1, and Pig iron for castings having excellent melting efficiency, characterized in that at least 50% of the cross section has a structure in which graphite is formed .