JP3658488B2 - Method for producing eutectic graphite cast iron - Google Patents

Description

【００１２】
表１から明らかなように、１５φ丸棒及び３０φ丸棒にはＤ形黒鉛（共晶黒鉛）が晶出した。図１は、１５φ丸棒の表面近傍部の破面の光学顕微鏡写真（３％ナイタール腐食、１００倍）であり、微細なＤ型黒鉛（共晶黒鉛）を有する共晶黒鉛鋳鉄を示す。
１５φ丸棒の表面近傍部の網目数は２１２個／ｃｍ^２であり、丸棒中心部の網目数は１８８個／ｃｍ^２であり、３０φ丸棒の表面近傍部の網目数は２０８個／ｃｍ^２であり、丸棒中心部の網目数は１６８個／ｃｍ^２であった。
【００１３】
（比較例１）
実施例に対してＳ量が多い鋳鉄溶湯から鋳込んだ場合を比較するために、重量％でＣ：３．１４％、Ｓｉ：２．０８％、Ｍｎ：０．５９％、Ｐ：０．０３％、Ｓ：０．０４８％、Ｔｉ：０．１８％残部がＦｅおよび不可避的不純物よりなる溶湯を低周波炉で溶製し、１４５０℃以上で２０分以上保持した後、Ｆｅ−Ｓｉ（５０％）合金を該溶湯に対して０．４重量％接種し、次いで１４２０℃の注湯温度で生砂鋳型に注湯して１５φ丸棒及び３０φ丸棒を鋳込んだ。
（比較例２）
実施例に対してＴｉ量が少ない鋳鉄溶湯から鋳込んだ場合を比較するために、重量％でＣ：３．２４％、Ｓｉ：２．１２％、Ｍｎ：０．５８％、Ｐ：０．０４％、Ｓ：０．０１２％、Ｔｉ：０．１３％残部がＦｅおよび不可避的不純物よりなる溶湯を低周波炉で溶製し、１４５０℃以上で２０分以上保持した後、Ｆｅ−Ｓｉ（５０％）合金を該溶湯に対して０．４重量％接種し、次いで１４２０℃の注湯温度で生砂鋳型に注湯して１５φ丸棒及び３０φ丸棒を鋳込んだ。
（比較例３）
実施例に対して接種処理を施さない場合を比較するために、重量％でＣ：３．１９％、Ｓｉ：２．０４％、Ｍｎ：０．５９％、Ｐ：０．０３％、Ｓ：０．０１２％、Ｔｉ：０．１８％残部がＦｅおよび不可避的不純物よりなる鋳鉄溶湯を低周波炉で溶製し、１４８０℃で３０分保持した後、接種処理を施すことなく、１４２０℃の注湯温度で生砂鋳型に注湯し、次いで１５φ丸棒と３０φ丸棒とを鋳込んだ。
【００１４】
比較例１〜３の鋳造条件及び各比較例で鋳造した１５φ丸棒及び３０φ丸棒の黒鉛形状、比較例３で鋳造した丸棒の表面近傍部の破面での網目数（個／ｃｍ^２）及び丸棒中心部の破面での網目数（個／ｃｍ^２）を表１に併記する。
表１より、比較例１及び比較例２は、１５φ丸棒ではいずれもＤ形黒鉛（共晶黒鉛）が晶出したが、３０φ丸棒ではいずれもＤ形黒鉛（共晶黒鉛）の他、Ｂ形黒鉛及びＥ形黒鉛が晶出した。
比較例３で鋳造した１５φ丸棒及び３０φ丸棒には共晶黒鉛（Ｄ型黒鉛）が晶出したが、１５φ丸棒の表面近傍部の網目数は２０４個／ｃｍ^２であり、丸棒中心部の網目数は１５６個／ｃｍ^２であり、３０φ丸棒の表面近傍部の網目数は１９６個／ｃｍ^２であり、丸棒中心部の網目数は９２個／ｃｍ^２であった。比較例１〜３は、実施例１に比べ、丸棒表面近傍部の網目数と丸棒中心部の網目数との差が大きく、組織が不均一であった。
【００１５】
【発明の効果】
本発明の共晶黒鉛鋳鉄の製造方法によれば、重量％でＣ：２．６〜３．６％、Ｓｉ：１．８〜２．４％、Ｍｎ：１．０％以下、Ｐ：０．２％以下、Ｓ：０．００６〜０．０２％、Ｔｉ：０．１５〜０．３０％、残部がＦｅ及び不可避不純物からなる鋳鉄溶湯中に、重量％でＳｉ：５０％残部ＦｅからなるＦｅ−Ｓｉ（５０％）合金を０．２〜０．６重量％接種した後、砂型に注湯するので、鋳物の表面近傍部の網目数と鋳物中心部の網目数との差が小さくなり、均一な組織の共晶黒鉛鋳鉄が得られ、鋳物品質が安定化する。
【図面の簡単な説明】
【図１】本発明の製造方法によって製造した共晶黒鉛鋳鉄の金属組織を示す顕微鏡写真である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing eutectic graphite cast iron, and more particularly to a method for producing eutectic graphite cast iron by a sand mold casting method.
[0002]
[Prior art]
As a conventional method for producing eutectic graphite cast iron, a cast iron melt having the composition of ordinary cast iron is strongly desulfurized and strongly deoxidized to a sulfur content of 0.005 to 0.001%, and then poured into a sand mold. There is a method (described in Japanese Patent Publication No. 5-14005).
[0003]
[Problems to be solved by the invention]
Generally, the amount of molten iron in ordinary cast iron is 0.03 to 0.1%. When this is poured into a sand mold, the graphite crystallizes into flakes and turns into flake graphite cast iron. After deoxidizing to a sulfur content of 0.005 to 0.001%, pouring into a sand mold, there is a problem that uniform eutectic graphite cast iron cannot be obtained.
Therefore, the present invention has been made to solve the above problems, and an object thereof is to provide a method for producing eutectic graphite cast iron having a uniform structure.
[0004]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventor adjusts the amount of S in the cast iron melt, contains Ti in the cast iron melt, and further inoculates an Fe—Si (50%) alloy. As a result, it has been found that eutectic graphite cast iron having a uniform structure can be obtained, and the present invention has been completed.
[0005]
The method for producing eutectic graphite cast iron of the present invention is as follows: C: 2.6-3.6% by weight, Si: 1.8-2.4%, Mn: 1.0% or less, P: 0.2 %: S: 0.006 to 0.02%, Ti: 0.15 to 0.30%, Fe is composed of Fe: Fe: 50% by weight in a cast iron melt composed of Fe and inevitable impurities. It is characterized by pouring into a sand mold after inoculating 0.2-0.6% of -Si (50%) alloy.
[0006]
According to the method for producing eutectic graphite cast iron of the present invention, the network structure of the fracture surface at the center of the casting is formed substantially the same as the network structure of the fracture surface near the surface.
[0007]
If the amount of C is less than 2.6%, the chilling tendency of the casting increases. Therefore, the lower limit is set to 2.6%, and if the amount of C is more than 3.6%, coarse graphite is crystallized during solidification and has a uniform structure. The eutectic graphite cast iron cannot be obtained, so the upper limit was made 3.6%.
When the Si content is less than 1.8%, the tendency to chill increases. Therefore, the lower limit is set to 1.8%, and when the Si content is greater than 2.4%, coarse graphite crystallizes during solidification and the uniform structure is shared. Since no crystal graphite cast iron can be obtained, the upper limit was made 2.4%.
If the amount of Mn is greater than 1.0%, the tendency to chill increases, so the upper limit of the amount of Mn is set to 1.0%.
If the amount of P is more than 0.2%, steadite is generated and machinability is lowered, so the upper limit of the amount of P is set to 0.2%.
If the amount of S is less than 0.006%, the tendency to chill is increased and the structure of eutectic graphite cast iron becomes non-uniform, so the lower limit of the amount of S is set to 0.006% and the amount of S is greater than 0.02%. The upper limit of the amount of S was set to 0.02% because eutectic graphite was unable to crystallize.
If the Ti content is less than 0.15%, eutectic graphite is difficult to crystallize, so the lower limit is set to 0.15%. If the Ti content is greater than 0.30%, the machinability and the molten metal flowability decrease, so the upper limit is set to 0. 30%.
If the Fe-Si (50%) alloy inoculation amount is less than 0.2% by weight, the structure of eutectic graphite cast iron becomes non-uniform, so the lower limit is 0.2% by weight, and if it is more than 0.6% by weight Since the flake graphite crystallizes, the upper limit was set to 0.6% by weight.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Melting of the cast iron melt is performed at 1450 ° C. or more for 20 minutes or more, and pouring of the cast iron melt into the sand mold is performed at 1350 to 1450 ° C.
The type of the sand mold is not particularly limited, and a CO ₂ mold, a fresh sand mold, a dical mold, a furan mold, and the like can be used.
[0009]
【Example】
Examples of the present invention will be described below.
(Example 1)
C: 3.17% by weight, Si: 2.05%, Mn: 0.59%, P: 0.03%, S: 0.013%, Ti: 0.17% The balance is Fe and inevitable A molten cast iron made of impurities is melted in a low-frequency furnace and held at 1480 ° C. for 30 minutes, then in a ladle, 0.4% by weight of Fe—Si (50%) alloy is inoculated at 1460 ° C., and then 1420 ° C. Was poured into a green sand mold at a casting temperature of 15 mm and cast 15φ round bar and 30φ round bar.
[0010]
Graphite shape in 15φ round bar and 30φ round bar, number of meshes at the fracture surface in the vicinity of the surface of both round bars (number / cm ² ), and number of meshes at the fracture surface at the center of round bar (numbers / cm ² ) Is shown in Table 1. B, D, and E in the column of graphite shape in Table 1 respectively indicate B type, D type, and E type in “graphite shape and distribution classification (AFS-ASTM)”.
[0011]
[Table 1]

[0012]
As apparent from Table 1, D-type graphite (eutectic graphite) was crystallized on the 15φ round bar and the 30φ round bar. FIG. 1 is an optical micrograph (3% nital corrosion, 100 times) of a fracture surface near the surface of a 15φ round bar, showing eutectic graphite cast iron having fine D-type graphite (eutectic graphite).
The number of meshes near the surface of the 15φ round bar is 212 / cm ² , the number of meshes at the center of the round bar is 188 / cm ² , and the number of meshes near the surface of the 30φ round bar is 208 / cm 2. ² and the number of meshes at the center of the round bar was 168 / cm ² .
[0013]
(Comparative Example 1)
In order to compare the case of casting from a cast iron melt with a large amount of S relative to the examples, C: 3.14%, Si: 2.08%, Mn: 0.59%, P: 0.00% by weight. 03%, S: 0.048%, Ti: 0.18% A molten metal consisting of Fe and inevitable impurities is melted in a low frequency furnace and held at 1450 ° C. or higher for 20 minutes or longer. 50%) alloy was inoculated into the molten metal in an amount of 0.4% by weight, and then poured into a fresh sand mold at a pouring temperature of 1420 ° C. to cast 15φ round bars and 30φ round bars.
(Comparative Example 2)
In order to compare the case of casting from a cast iron melt with a small amount of Ti compared to the examples, C: 3.24%, Si: 2.12%, Mn: 0.58%, P: 0.00% by weight. 04%, S: 0.012%, Ti: 0.13% A molten metal comprising Fe and unavoidable impurities is melted in a low-frequency furnace, held at 1450 ° C. or higher for 20 minutes or longer, and then Fe—Si ( 50%) alloy was inoculated into the molten metal in an amount of 0.4% by weight, and then poured into a fresh sand mold at a pouring temperature of 1420 ° C. to cast 15φ round bars and 30φ round bars.
(Comparative Example 3)
In order to compare the case where the inoculation treatment is not performed on the examples, C: 3.19%, Si: 2.04%, Mn: 0.59%, P: 0.03%, S: Cast iron melt consisting of 0.012%, Ti: 0.18% balance Fe and inevitable impurities in a low frequency furnace, held at 1480 ° C. for 30 minutes, and then subjected to inoculation treatment at 1420 ° C. The green sand mold was poured at the pouring temperature, and then 15φ round bar and 30φ round bar were cast.
[0014]
The casting conditions of Comparative Examples 1 to 3, the graphite shape of the 15φ round bar and 30φ round bar cast in each comparative example, the number of meshes at the fracture surface near the surface of the round bar cast in Comparative Example 3 (pieces / cm ² ) And the number of meshes (pieces / cm ² ) at the fracture surface at the center of the round bar are also shown in Table 1.
From Table 1, in Comparative Example 1 and Comparative Example 2, D-type graphite (eutectic graphite) was crystallized in the 15φ round bar, but in addition to D-type graphite (eutectic graphite) in the 30φ round bar, B-type graphite and E-type graphite were crystallized.
Eutectic graphite (D-type graphite) was crystallized on the 15φ round bar and 30φ round bar cast in Comparative Example 3, but the number of meshes in the vicinity of the surface of the 15φ round bar was 204 pieces / cm ^2. The number of meshes at the center was 156 / cm ² , the number of meshes near the surface of the 30φ round bar was 196 / cm ² , and the number of meshes at the center of the round bar was 92 / cm ² . In Comparative Examples 1 to 3, the difference between the number of meshes in the vicinity of the round bar surface and the number of meshes in the central part of the round bar was larger than that in Example 1, and the structure was not uniform.
[0015]
【The invention's effect】
According to the method for producing eutectic graphite cast iron of the present invention, C: 2.6 to 3.6%, Si: 1.8 to 2.4%, Mn: 1.0% or less, P: 0% by weight. .2% or less, S: 0.006 to 0.02%, Ti: 0.15 to 0.30%, in the cast iron melt consisting of Fe and inevitable impurities, and by weight% Si: 50% balance Fe After inoculating 0.2 to 0.6% by weight of Fe-Si (50%) alloy, the sand mold is poured, so the difference between the number of meshes near the surface of the casting and the number of meshes at the center of the casting is small. Thus, eutectic graphite cast iron having a uniform structure is obtained, and the casting quality is stabilized.
[Brief description of the drawings]
FIG. 1 is a photomicrograph showing the metal structure of eutectic graphite cast iron produced by the production method of the present invention.

Claims (1)

C: 2.6-3.6% by weight, Si: 1.8-2.4%, Mn: 1.0% or less, P: 0.2% or less, S: 0.006-0.02 %, Ti: 0.15 to 0.30%, and the balance is Fe-Si (50%) alloy consisting of Fe: 50% balance Fe: 0.2% by weight in a cast iron melt composed of Fe and inevitable impurities. A method for producing eutectic graphite cast iron, characterized in that after 0.6% inoculation, a sand mold is poured.

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