KR20130087213A - High strength flake graphite iron using rare earth element and preparation method thereof - Google Patents

Abstract

PURPOSE: High-strength flake graphite iron using rare-earth elements and a manufacturing method thereof are provided to obtain stable structure, excellent fluidity, high tensile strength, and high hardness by precisely controlling a ratio of sulfur and the rare-earth elements. CONSTITUTION: A manufacturing method of high-strength flake graphite iron using rare-earth elements is as follows: a step of melting iron materials containing 3.3-3.4 wt.% of C, 2.0-2.2 wt.% of Si, 0.6-0.8 wt.% of Mn, 0.04 wt.% or less of P, and the rest of Fe in a furnace to manufacture molten iron; a step of adding 0.15-0.2 wt.% of S and 0.01-0.03 wt.% of the rare-earth elements to the molten iron; a step of adding Sr-based inoculants to the molten iron tapped to a ladle; and a step of injecting the molten iron to a mold (500).

Description

High-strength flake graphite cast iron using rare earth element and its manufacturing method {HIGH STRENGTH FLAKE GRAPHITE IRON USING RARE EARTH ELEMENT AND PREPARATION METHOD THEREOF}

The present invention relates to a method for producing high strength flaky graphite cast iron and flaky graphite cast iron produced by the method, and more particularly, by controlling the contents of the main component and the additive component constituting the cast iron, the graphite shape is uniform and high strength and The present invention relates to a flake graphite cast iron exhibiting excellent fluidity and castability, and a method of manufacturing the same.

Due to the recent tightening of environmental regulations, it is inevitable to reduce the amount of environmental pollutants such as COx and NOx emitted from engines. In the case of diesel engines, it is necessary to increase the explosion pressure of the engine in order to reduce the emission of environmental pollutants such as COx and NOx. Thus, in order to increase the explosion pressure of the engine, the strength of the cylinder block or head of the engine constituting the engine must be increased.

The material commonly used in conventional cylinder blocks is cast iron, common grade cast iron is usually gray cast iron. Gray cast iron is called gray cast iron because carbon is separated and produced by graphite when cast, and the surface is gray, or gray graphite cast iron is also called flake graphite structure.

In general, cast iron has a lot of difference depending on the shape, size, and distribution of graphite contained in the matrix. Generally, the tensile strength of flake graphite cast iron called cast iron is about 15 to 20 kg / mm ² . These flaky graphite cast irons have excellent castability, vibration damping ability, and thermal conductivity, but the materials developed to date have low strength and are limited to being used as cylinder block materials of high explosion pressure engines.

As cast iron which improved the physical property of the said flake graphite cast iron, spherical graphite cast iron is mentioned. Spherical graphite cast iron is a cast iron that improves toughness by converting the flake-like structure of graphite that appears in a normal cast iron (gray cast iron) structure into a spherical structure. Such nodular cast iron is also called nodular cast iron or ductile cast iron. The spheroidal graphite cast iron has excellent abrasion resistance, heat resistance, corrosion resistance, and the like, and has a large elastic modulus, brinell hardness of about 220, and better machinability than ordinary cast iron having the same hardness. While the above-described spherical graphite cast iron has a high strength enough to be applied to a cylinder block, there is a limitation in that it is insufficient to be applied to a cylinder block having a complex shape due to a lack of fluidity and castability and low thermal conductivity.

The present invention has been made in order to solve the above problems, and the rare earth elements (Rare Earth) in the five major elements of cast iron, carbon (C), silicon (Si), manganese (Mn), sulfur (S), phosphorus (P) Element, RE), but by controlling their content, the content ratio of sulfur and rare earth elements (RE / S) to a specific range, to provide a flat graphite cast iron having a high strength and excellent workability and fluidity at the same time and a method for producing the same For the purpose of

In addition, an object of the present invention is to provide a cast iron having a stable structure and excellent fluidity, high tensile strength and hardness by precisely controlling the use ratio of sulfur (S) and rare earth elements (RE), in particular the shape It is an object to provide flat graphite cast iron applicable to the engine cylinder block and / or engine cylinder head of this complex diesel engine.

The present invention (i) 3.3 to 3.4% by weight of carbon (C), 2.0 to 2.2% by weight of silicon (Si), 0.6 to 0.8% by weight of manganese (Mn), 0.04% by weight or less of phosphorus (P), And melting the cast iron material including the remaining amount of iron (Fe) in a blast furnace to produce a cast iron wontang; (Ii) adding 0.15 to 0.2% by weight of sulfur (S) and 0.01 to 0.03% by weight of rare earth element (RE) to the molten cast iron wontang; (Iii) inoculating the Sr-based inoculant on the cast iron wontang which is tapping into the ladle; And (iii) injecting the inoculated cast iron melt into a sand mold.

Here, the ratio (RE / S) of the rare earth element (RE) content to the sulfur (S) content is preferably adjusted in the range of 0.05 to 0.2.

According to one embodiment of the present invention, the cast iron wontang of the step (ii) is melted by adding 0.15 to 0.2% by weight of sulfur (S) to the molten cast iron won (i) in the furnace, and then rare earth element (RE) 0.01 ~ 0.03 It is possible to manufacture by adding%.

At this time, the rare earth element (RE) is preferably added to the cast iron wontang state in direct contact with the cast iron wontang. For example, the rare earth element RE may be provided inside the contact preventing member that prevents direct contact with the cast iron wontang.

According to an example of the present invention, the carbon equivalent (CE: Carbon Equivalent) in the cast iron wontang is adjusted to be in the range of 3.97 ~ 4.13.

In addition, according to an example of the present invention, the tapping temperature is adjusted to 1520 ± 10 ℃ range.

In addition, the present invention provides a flake graphite cast iron produced by the above-described manufacturing method.

Here, the flaky graphite cast iron is 3.3 to 3.4% by weight of carbon (C), 2.0 to 2.2% by weight of silicon (Si), 0.6 to 0.8% by weight of manganese (Mn), and 0.15 to 0.2% by weight of sulfur (S). %, 0.01 to 0.03 wt% of rare earth elements (RE), 0.04 wt% or less of phosphorus (P), and remaining amount of iron (Fe) satisfying 100 wt%, wherein the sulfur content of the rare earth element (RE) content S) The ratio to content (RE / S) has a composition in the range from 0.05 to 0.2.

According to one embodiment of the present invention, the carbon equivalent (CE: Carbon Equivalent) of the flake graphite cast iron is in the range of 3.97 to 4.13 when calculated by the method of CE = carbon + (silicon +) x 1/3.

In addition, according to one embodiment of the present invention, the tensile strength of the flake graphite cast iron (Tensile Strength) is in the range of 300 ~ 350 MPa, Brinell hardness value (BHW) may be in the range of 200 ~ 230.

Meanwhile, according to one example of the present invention, the flaky graphite cast iron may have a length of 800 to 850 mm of the spiral of the fluidity test piece.

In addition, according to an example of the present invention, the flake graphite cast iron can be used as a cast iron for a cylinder head, a cylinder block, or a brake disk.

According to the present invention, tensile strength, flow rate and brinell hardness may vary according to the content ratio (RE / S) of sulfur (S) and rare earth element (RE). RE / S content ratio (RE / S) should be 0.05 ~ 0.2.

As described above, in the present invention, by controlling the amount of rare earth element (RE) added to the cast iron, and the ratio (RE / S) to the sulfur (S) content of the rare earth element (RE) content, the ferroalloy It is possible to provide flake graphite cast iron with high tensile strength of 300 to 350 MPa, excellent flowability of more than 800 mm, and Brinell hardness in the range of 200 to 230 without using.

Accordingly, the flaky graphite cast iron of the present invention has high tensile strength, excellent flowability and appropriate hardness at the same time, and thus can be usefully applied to engine parts such as cylinder blocks and cylinder heads of diesel engines having complicated shapes.

1 briefly illustrates an example of the manufacturing process of flaky graphite cast iron according to the present invention.
Figure 2 shows a mold for producing a spiral test piece for measuring the flow of flake graphite cast iron according to the present invention.
<Short description of symbols>
100: melting furnace 110: cast iron melt
200: sulfur (S) 210: rare earth element
220: Sr-based inoculant 300: metal rod
400 ladle 500 death penalty

Hereinafter, the present invention will be described in more detail with specific examples.

Conventionally, rare earth elements were added to the molten metal to prevent chilling by ferroalloy added to increase the strength of the flake graphite cast iron, but in this case, it was not only difficult to obtain a charging effect due to the strong oxidizing property of the rare earth elements. The added rare earth element promotes the decrease in fluidity and chilling of the molten metal, and thus has a limitation in being applied to an engine cylinder block material having a complicated shape.

In the present invention, however, only the rare earth elements are added to cast iron without the use of ferroalloy, and the five major elements constituting the cast iron (for example, C, Si, Mn, S, P) and the content of rare earth elements (RE), and sulfur and By precisely controlling the content ratio (RE / S) of the rare earth elements in a specific range, the fluidity of the molten metal due to the added rare earth elements is not reduced, and the growth and crystallization of the healthy type A flake graphite is assisted, thereby achieving high strength and excellent processability. It is possible to provide a flake graphite cast iron having fluidity and hardness.

At this time, the content of the rare earth element (RE) added, and the content ratio (RE / S) of the rare earth element (RE) and sulfur (S) in the cast iron to produce flake graphite cast iron having a tensile strength of 300 MPa or more and fluidity of 800 mm or more. Is the most important factor. Therefore, it is necessary to limit the flaky graphite cast iron of the present invention to the production method and chemical composition exemplified below.

Hereinafter, a method of manufacturing flake graphite cast iron and a chemical composition of the flake graphite cast iron produced according to the present invention will be described. However, the present invention is not limited to the following production methods, and the steps of each process may be modified or selectively mixed if necessary.

Here, the addition amount of each element is weight%.

Referring to FIG. 1, first, 3.3 to 3.4 wt% of carbon (C), 2.0 to 2.2 wt% of silicon (Si), 0.6 to 0.8 wt% of manganese (Mn), and 0.04 wt% of phosphorus (P) based on the total wt% A cast iron melt raw water 110 containing% or less, and a residual amount of iron (Fe) is manufactured.

The method for producing the cast iron melt bath 110 according to the present invention is not particularly limited. For example, the five major elements of cast iron are carbon (C), silicon (Si), manganese (Mn), sulfur (S), and phosphorus ( The cast iron material containing P) in the above-described content range is melted in the furnace 100 to prepare the cast iron melt raw water 110.

At this time, the phosphorus (P) may be contained in the raw material for casting as an impurity, or may be added separately. In the present invention, the reason for limiting the chemical composition in the cast iron wontang is the same as the reason described in the case of the chemical composition of the flaky graphite cast iron described later, the description thereof will be omitted.

Sulfur (S) 0.15 to 0.2% by weight and rare earth element (RE) 0.01 to 0.03% by weight are added to the molten cast iron melt bath 110 as described above.

At this time, since the rare earth element (RE) is a highly oxidizable material, appropriate timing and input method are essential. In the present invention, when sulfur (S) and rare earth element (RE) are added to the molten iron casting 110, 0.15 to 0.2% by weight of sulfur (S) is added and melted, followed by 0.01 to rare earth element (RE). It is preferable to add 0.03%.

In addition, the rare earth element (RE) having high oxidizing property is added to the molten metal round bath 110 in direct contact with the rare earth element so that the effect of the rare earth element is hardly exhibited. . Thus, in the present invention, the rare iron element (RE) is provided inside the contact preventing member for preventing direct contact with the cast iron wontang 110 is cast into the cast iron wontang.

The contact preventing member is a material that does not affect the composition of the cast iron wontang, while preventing direct contact between the cast iron wontang 110 and the rare earth element (RE), there is no particular limitation on the component, form, content thereof. Non-limiting examples of contact preventing members that can be used include aluminum foil and the like.

For example of the sulfur (S) and rare earth element (RE) addition step (ii) according to the present invention, sulfur (200) is preferentially added, complete dissolution, and then individually packaged with aluminum (Al) foil. A strong oxidizing rare earth element 210 is added to minimize the reaction when the cast iron melt is injected with the raw water 110. Agitation is performed using the metal rod 300 so that the introduced rare earth element 210 can be uniformly included in the round bath 110.

In this invention, the chemical composition of flake graphite cast iron is limited as described above, and the ratio (RE / S) to the sulfur (S) content of the added rare earth element (RE) content is limited to the range of 0.05 to 0.2. There is a need. When the ratio of RE / S is less than 0.05, a decrease in strength is caused, and when the ratio of RE / S exceeds 0.2, workability may decrease. By limiting the RE / S ratio in this manner, stable A-shaped graphite graphite can be obtained, and since the Chilling is reduced, a high-strength graphite graphite cast iron for an engine cylinder block having a tensile strength of 300 MPa or more and excellent workability can be obtained.

The cast iron melt bath 110 prepared as described above completes the component analysis of the bath using a carbon equivalent meter, a carbon / sulfur analyzer, and a spectrometer.

After preparing and tapping the ladle (400, ladle), which is a container for tapping the cast iron wontang 110, the cast iron melt bath is tapping into the ladle 400 in terms of stabilization of the material of high-strength graphite cast iron. The Sr-based inoculum 220 is tapping while stream inoculation. In this way, when the Sr-based inoculation treatment is carried out when tapping the cast iron wontang into the ladle, stable graphite A-type graphite is crystallized, thereby obtaining graphite graphite cast iron having stable mechanical properties and fluidity.

At this time, the size of the inoculant may be in the range of 1 to 3mm in diameter, and the amount of the inoculant to obtain a material stabilization effect of the high strength flaky graphite cast iron is preferably limited to 0.3 ± 0.05% by weight ratio (%).

Subsequently, the molten metal temperature of the ladle 400 which is completed tapping is measured by using an immersion type thermometer, and after the temperature is measured, the cast iron melt 110 is injected into the prepared sand mold 500 to prepare high-strength flake graphite cast iron. Complete

The high-strength flake graphite cast iron of the present invention prepared as described above exhibits excellent fluidity and appropriate hardness of 800 mm or more while having a strength of 300 to 350 MPa higher than that of 250 MPa grade graphite cast iron, which is currently used in engine cylinder blocks and heads. Therefore, the flaky graphite cast iron according to the present invention is a hypoeutectic gray cast iron (GC) applicable to a cylinder block and / or a head of a diesel engine having a complicated shape and requiring a higher level of rigidity as the explosion pressure increases. Corresponds to cast iron.

In addition, since the flaky graphite cast iron of the present invention has both high tensile strength, hardness, and fluidity, it is useful for complex cylinder cylinder blocks and heads in which thick portions having a cross section thickness of 10 mm or more and thin portions having a cross section thickness of 5 mm or less exist simultaneously. Can be applied.

The present invention provides a high strength flaky graphite cast iron produced by the method described above. More specifically, the flaky graphite cast iron is 3.3 to 3.4 wt% of carbon (C), 2.0 to 2.2 wt% of silicon (Si), 0.6 to 0.8 wt% of manganese (Mn), and 0.15 to sulfur (S). 0.2 wt%, 0.01 to 0.03 wt% of rare earth elements (RE), 0.04 wt% or less of phosphorus (P), and a residual amount of iron (Fe) satisfying 100 wt%, wherein the rare earth element (RE) content The ratio (RE / S) to sulfur (S) content has a composition in the range from 0.05 to 0.2.

Hereinafter, the reason for adding each component contained in the flaky graphite cast iron in the present invention and the reason for limiting the range of the added content are as follows.

1) Carbon (C) 3.3 ~ 3.4 wt%

Carbon is added for graphite crystallization. In the flaky graphite cast iron according to the present invention, when the carbon content is less than 3.3 wt%, the chilling behavior is observed in the thin-walled part having a cross-sectional thickness of 5 mm or less, and when the content exceeds 3.4 wt%, the strength decreases. Occurs. Therefore, in order to secure stable strength and stable graphite structure in the high strength cylinder block having various thicknesses, in the present invention, it is preferable to limit the content of carbon to 3.3 to 3.4% by weight.

2) Silicon (Si) 2.0 ~ 2.2 wt%

Silicon, when added in the optimum ratio with carbon, maximizes graphite crystallization and increases the strength of cast iron. When the content of silicon (Si) in the flaky graphite cast iron according to the present invention is less than 2.0% by weight, a problem of lowering the crystallization amount of graphite occurs. When the content of the flaky graphite cast iron exceeds 2.2% by weight, the ductility is lowered. Deterioration occurs. Therefore, in the present invention, it is preferable to limit the content of silicon (Si) to 2.0 to 2.2% by weight.

3) Manganese (Mn) 0.6 ~ 0.8 wt%

Manganese is an element added for improving the strength of flake graphite cast iron by miniaturization of pearlite. When the content of manganese (Mn) in the flaky graphite cast iron according to the present invention is less than 0.6% by weight, the strength is lowered. If the content of the manganese (Mn) is more than 0.8% by weight, brittleness increases and workability decreases with carbide production. Therefore, in the present invention, it is preferable to limit the content of manganese (Mn) to 0.6 to 0.8% by weight.

4) Sulfur (S) 0.15 ~ 0.2 wt%

Sulfur reacts with trace elements (e.g., rare earth elements) contained in the cast iron mound to form sulfides, which act as nucleation sources for the graphite and assist in the growth of the graphite. When the content of sulfur (S) in the flaky graphite cast iron according to the present invention is less than 0.15% by weight, it does not react with rare earth elements to produce many graphite nucleation sites, resulting in a decrease in strength, and when exceeding 0.2% by weight. There is a problem of increased brittleness. Therefore, in the present invention, it is preferable to limit the content of sulfur (S) to 0.15 to 0.2% by weight.

5) Phosphorus (P) 0.04 wt% or less

Phosphorus is also a kind of impurities that are naturally added in the air during the cast iron manufacturing process. Such phosphorus also stabilizes perlite, but when the content exceeds 0.04% by weight, brittleness is rapidly increased, which is also associated with shrinkage defects due to segregation. Therefore, in the flaky graphite cast iron according to the present invention, the content of phosphorus (P) is preferably limited to 0.04% by weight or less.

On the other hand, it is practically difficult to make the content of phosphorus (P) in the cast iron raw material to 0, even if the content of phosphorus in the cast iron raw material may be contained in the manufacturing process of cast iron. Therefore, in the present invention, it is important to adjust the content of phosphorus not to exceed 0.04% by weight.

6) Rare Earth Element (RE) 0.01 ~ 0.03 wt%

Rare earth elements act as a nucleation source for strong graphite and are added for many crystallization of fine graphite. When the content of rare earth element (RE) in the flaky graphite cast iron according to the present invention is less than 0.01% by weight, the amount of crystallization of graphite is small, which causes a decrease in fluidity and generation of chills, and when it exceeds 0.03% by weight, the strength due to excessive crystallization of graphite. The decrease of and the rapid decrease of fluidity will occur. Therefore, in the present invention, the content of the rare earth element is preferably adjusted to 0.01 to 0.03% by weight.

7) Iron (Fe)

Iron is the mainstay of cast iron according to the present invention. Residual components other than the above components are iron (Fe), and some other unavoidable impurities may be contained.

The flaky graphite cast iron of the present invention is not only limited to the chemical composition, but also stable A-type flaky by limiting the ratio (RE / S) to the sulfur (S) content of the rare earth element (RE) in the range of 0.05 to 0.2. Graphite can be obtained, and the high strength flaky graphite cast iron which can be applied to an engine cylinder block and a head is excellent in workability, while tensile strength is 300 Mpa or more.

According to one embodiment of the invention, the carbon equivalent (CE) is to be 3.97 ~ 4.13. In the cast iron according to the present invention, when the carbon equivalent (CE) is less than 3.97, a chill occurs in a thin-walled part having a thickness of 5 mm or less in cross section, resulting in poor casting and fluidity, and a carbon equivalent ( When CE) exceeds 4.13, the strength decreases due to excessive generation of primary graphite. Therefore, in this invention, it is preferable to limit the range of carbon equivalent (CE) to 3.97-4.13. At this time, the carbon equivalent (CE) is defined as carbon + (silicon +) × 1/3, the value can be appropriately adjusted to control the mechanical properties of the engine cylinder block and head, the physical properties and quality of the product. .

According to an example of the present invention, the tensile strength of the flaky graphite cast iron having the above-described chemical composition is in the range of 300 to 350 MPa, and the Brinell hardness value (BHW) is about 200 to 230.

According to an example of the present invention, the length of the spiral of the fluidity test piece to which the flake graphite cast iron having the chemical composition is applied is in the range of 800 to 850 mm. In this case, the fluidity test specimen may be shown as shown in FIG. 2.

In addition, the flaky graphite cast iron of the present invention is a high-strength material having a tensile strength of 300 MPa or more. It is possible to apply.

Hereinafter, embodiments of the present invention will be described in more detail. It should be understood, however, that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. It is possible.

<Examples 1-5 and Comparative Examples 1-5>

According to the composition of Table 1, flake graphite cast iron according to Examples 1 to 5 and Comparative Examples 1 to 5 were prepared.

division C Si Mn S P Cr Sn Cu RE RE / S Fe Example 1 3.31 2.15 0.68 0.157 0.026 - - - 0.02 0.127 Balance Example 2 3.34 2.10 0.63 0.20 0.028 - - - 0.02 0.096 Balance Example 3 3.34 2.0 0.58 0.180 0.028 - - - 0.02 0.11 Balance Example 4 3.31 2.0 0.65 0.20 0.027 - - - 0.01 0.05 Balance Example 5 3.39 2.21 0.66 0.151 0.028 - - - 0.03 0.2 Balance Comparative Example 1 3.33 2.05 0.61 0.081 0.027 - - - 0.04 0.49 Balance Comparative Example 2 3.33 2.13 0.63 0.104 0.028 - - - 0.005 0.05 Balance Comparative Example 3 3.42 1.95 0.67 0.18 0.024 - - - 0.008 0.04 Balance Comparative Example 4 3.38 2.1 0.67 0.08 0.032 0.18 0.06 - - - Balance Comparative Example 5 3.31 1.95 0.67 0.053 0.03 0.2 0.07 0.40 - - Balance

First, a raw tea containing carbon (C), silicon (Si), manganese (Mn), sulfur (S) and phosphorus (P) was prepared according to the composition shown in Table 1. At this time, the unit of each component constituting the wontang is weight%. Phosphorus (P) is less than 0.04% by weight due to brittleness and shrinkage problems.

The cast iron melt bath prepared as described above completed a component analysis of the bath using a carbon equivalent meter and a spectrometer. Thus, the molten cast iron melt was added by adjusting the sulfur (S) 0.15 ~ 0.2% by weight and the rare earth element (RE) 0.01 ~ 0.03% by weight. In this case, in the case of Comparative Examples 4 to 5 that do not contain the rare earth element (RE), chromium (Cr), tin (Sn), and copper (Cu) were added to the molten liquid bath just by adjusting the appropriate weight.

Then, to prepare and tap the ladle, which is a container for tapping the cast iron wontang, tapping while adding a Sr-based inoculant. After completion of the tapping on the ladle, the temperature of the molten metal was measured, and the molten metal was injected into the prepared mold to prepare flake graphite cast iron products for the engine cylinder block and the head.

Carbon equivalents, tensile strength, hardness, and flow rate of the cast iron of Examples 1 to 5 and Comparative Examples 1 to 5 prepared according to the composition of Table 1 were measured and shown in Table 2 below.

division Carbon equivalent
(CE) The tensile strength
(N / mm ² ) Hardness
(HBW) Flow rate
(mm) Example 1 4.03 308 227 845 Example 2 4.04 302.5 217.7 832 Example 3 4.01 315.7 209.3 815 Example 4 3.98 349 229.7 801 Example 5 4.13 306.2 207.5 849 Comparative Example 1 4.01 271 197.3 795 Comparative Example 2 4.04 284 217.3 625 Comparative Example 3 4.07 253.7 211 680 Comparative Example 4 4.08 273.5 191.7 808.5 Comparative Example 5 3.96 305.7 208 642.5

As shown in Table 2, the tensile strength of the cast iron according to Examples 1 to 5 in which the RE / S ratio is adjusted to 0.05 ~ 0.2 range is 300 ~ 350 MPa range, Brinell hardness value is 200 ~ 230 HB range, flow The figure was found to be 800 mm or more.

For reference, Comparative Examples 1 and 3 are the same as the wontang of Examples 1 to 5, except that the RE content and the RE / S ratio are outside the composition range of the present invention.

Comparative Example 2 is the same as the wontang of Examples 1 to 5, except that the RE content is outside the composition range of the present invention.

Comparative Example 4 is an example of a tensile strength 250 MPa class material conventionally used for flake graphite cast iron for engine cylinder blocks and heads.

Comparative Example 5 is a 300 MPa class material conventionally used for high strength single-strand graphite cast iron for engine cylinder blocks and heads, and is an example showing low fluidity.

Claims (14)

(i) 3.3 to 3.4 wt% of carbon (C), 2.0 to 2.2 wt% of silicon (Si), 0.6 to 0.8 wt% of manganese (Mn), 0.04 wt% or less of phosphorus (P), and the balance of Melting the cast iron material including iron (Fe) in a blast furnace to produce a cast iron wontang;
(Ii) adding 0.15 to 0.2% by weight of sulfur (S) and 0.01 to 0.03% by weight of rare earth element (RE) to the molten cast iron wontang;
(Iii) inoculating the Sr-based inoculant on the cast iron wontang which is tapping into the ladle; And
(Iii) injecting the inoculated cast iron melt into a mold;
Method for producing flake graphite cast iron comprising a. The method of claim 1, wherein the ratio (RE / S) of the rare earth element (RE) to the sulfur (S) content is controlled in a range of 0.05 to 0.2. The method of claim 1, wherein the cast iron wontang of the step (ii) is melted by adding 0.15 to 0.2% by weight of sulfur (S) to the molten cast iron won (i) in the furnace, 0.01 to 0.03% rare earth element (RE) Method for producing flake graphite cast iron, characterized in that it is prepared by adding a. The method of claim 1, wherein the rare earth element (RE) is introduced into the cast iron wontang without being in direct contact with the cast iron wontang. The method of claim 1, wherein the rare earth element (RE) is provided inside a contact preventing member that prevents direct contact with the cast iron wontang and is introduced into the cast iron wontang. The method of claim 1, wherein the carbon equivalent (CE: Carbon Equivalent) in the cast iron wontang is characterized in that the range of 3.97 ~ 4.13. The method of claim 1, wherein the tapping temperature is controlled to be in the range of 1520 ± 10 ℃. The flaky graphite cast iron produced by the method according to any one of claims 1 to 7. According to claim 8, wherein the cast iron is carbon (C) 3.3 to 3.4% by weight, silicon (Si) 2.0 to 2.2% by weight, manganese (Mn) 0.6 to 0.8% by weight, sulfur (S) 0.15 ~ 0.2% by weight, 0.01 to 0.03% by weight of rare earth elements (RE), 0.04% by weight or less of phosphorus (P), and a residual amount of iron (Fe) that satisfies 100% by weight,
Particle graphite cast iron, characterized in that the ratio of the rare earth element (RE) to the sulfur (S) content (RE / S) has a composition in the range of 0.05 to 0.2. The flaky graphite cast iron according to claim 8, wherein the tensile strength is 300 to 350 MPa. The flaky graphite cast iron according to claim 8, wherein the length of the spiral of the fluidity test piece is 800 to 850 mm. The planar graphite cast iron according to claim 8, wherein the carbon equivalent (CE) is 3.97 to 4.13. The planar graphite cast iron according to claim 8, wherein the Brinell hardness value (BHW) is in the range of 200 to 230. The flaky graphite cast iron according to claim 8, which is a cast head for a cylinder head, a cylinder block, or a brake disc.

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