KR101822201B1 - High strength flake graphite iron using rare earth element and preparation method thereof - Google Patents

Abstract

More particularly, the present invention relates to a cast iron graphite cast iron having high strength and excellent fluidity and a method of producing the same. More particularly, the present invention relates to a cast iron cast iron having high strength and excellent fluidity, (RE / S) of the rare earth element (Rare Earth Element, RE) and controlling the content thereof and the content ratio of sulfur and rare earth element (RE / S) And a method of manufacturing the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high strength graphite cast iron and a method of manufacturing the same. 2. Description of the Related Art HIGH STRENGTH FLAKE GRAPHITE IRON USING RARE EARTH ELEMENT AND PREPARATION METHOD THEREOF

TECHNICAL FIELD The present invention relates to a method for producing high-strength graphite cast iron and a graphite cast iron produced by the method. More particularly, the present invention relates to a graphite cast iron which is uniform in graphite shape, Flat graphite cast iron exhibiting excellent fluidity and castability, and a method of manufacturing the same.

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

Commonly used materials for conventional cylinder blocks are cast iron, common cast iron is generally gray cast iron. Gray cast iron is sometimes referred to as gray cast iron because it is separated and formed into graphite when it is cast and grayish in surface, or it is also called flake graphite cast iron because it is flake graphite structure.

Generally, cast iron has many differences depending on the shape, size and distribution of graphite contained in the matrix. In general, the graphite cast iron has a tensile strength of about 15 to 20 kg / mm ² . These flake graphite cast iron has excellent castability, vibration damping ability, and thermal conductivity, but since the developed materials have low strength, they can not be used as cylinder block materials for engines with high explosion pressure.

As the cast iron which improves physical properties of the cast cast iron, there is a cast iron of spheroidal graphite. Spherical graphite cast iron is a cast iron that has improved toughness by changing the leaf-piece structure of graphite, which appears in ordinary cast iron (gray cast iron) structure, into a spherical structure. These ductile iron castings are also called nodular cast iron or ductile cast iron. The spheroidal graphite cast iron is excellent in abrasion resistance, heat resistance and corrosion resistance, and has a modulus of elasticity larger than general graphite cast iron, brinell hardness of about 220, and machinability better than ordinary cast iron having the same hardness. The above-described spheroidal graphite cast iron has a high strength enough to be applied to a cylinder block, but has insufficient fluidity, castability, and low thermal conductivity, and thus has a limit to be applied to a cylinder block of a complicated shape.

Disclosure of the Invention The present invention has been conceived to solve the above-mentioned problems. It is an object of the present invention to provide a method of manufacturing a carbon steel sheet, which comprises the steps of mixing a rare earth element (Rare Earth) with carbon (C), silicon (Si), manganese (RE / S) in a specific range by controlling the content thereof and the content ratio of sulfur and rare earth element (RE / S) to a specific range, and a process for producing the same. .

The present invention also aims at providing cast iron having a stable structure, excellent fluidity, high tensile strength and hardness by precisely controlling the ratio of use of sulfur (S) and rare earth element (RE) It is an object of the present invention to provide a flat plate cast iron applicable to an engine cylinder block and / or an engine cylinder head of this complicated diesel engine.

The present invention provides a method for producing a steel sheet, comprising (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) And a remaining amount of iron (Fe) in a furnace to produce a cast iron cast iron; (Ii) adding 0.15 to 0.2% by weight of sulfur (S) and 0.01 to 0.03% by weight of a rare earth element (RE) to the melted cast iron master batch; (Iii) inoculating an iron-based inoculant into the molten iron casting tank; And (iv) injecting the inoculated cast iron melt into a casting mold.

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

According to an embodiment of the present invention, the cast iron raw material of step (ii) is obtained by adding 0.15 to 0.2% by weight of sulfur (S) to the molten cast iron molten metal (i) % By weight based on the total weight of the composition.

At this time, it is preferable that the rare earth element (RE) is introduced into the cast iron cast iron without directly contacting the cast iron cast iron. For example, the rare earth element RE may be provided in a contact preventive member for preventing direct contact with the cast iron cast iron, and may be introduced into the cast iron cast iron.

According to an embodiment of the present invention, the carbon equivalent (CE) in the cast iron recirculating bath is adjusted to be in the range of 3.97 to 4.13.

According to an embodiment of the present invention, the hot water temperature is adjusted to be in the range of 1520 占 10 占 폚.

The present invention also provides a cast iron cast iron produced by the above-described production method.

The graphite cast iron is composed of 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), 0.15 to 0.2% by weight of sulfur (RE) content of the rare earth element (RE), 0.01 to 0.03 wt% of rare earth element (RE), 0.04 wt% or less of phosphorus (P), and 100 wt% S) content (RE / S) in the range of 0.05 to 0.2.

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

Also, according to an embodiment of the present invention, the flatness of the graphite cast iron is in the range of 300 to 350 MPa, and the Brinell hardness value (BHW) is in the range of 200 to 230.

According to an embodiment of the present invention, the speckle length of the fluidity test piece may be 800 to 850 mm.

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

According to the present invention, tensile strength, fluidity, and Brinell hardness can be changed according to the content ratio (RE / S) of sulfur (S) and rare earth element (RE). In order to be applied to a cylinder block of a diesel engine having a complicated shape The RE / S content ratio (RE / S) should be between 0.05 and 0.2.

As described above, in the present invention, by precisely controlling the ratio (RE / S) of the amount of the rare earth element RE added to the cast iron and the content of the rare earth element RE to the sulfur content S, It is possible to provide a flat graphite cast iron having a high tensile strength of 300 to 350 MPa, an excellent flowability of 800 mm or more, and a Brinell hardness of 200 to 230 without using the steel sheet.

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

1 schematically shows an example of a manufacturing process of a piecemeal graphite cast iron according to the present invention.
Fig. 2 shows a mold for producing a spiral test piece for measuring the flow of a piece-shaped graphite cast iron according to the present invention.
<Brief Description of Symbols>
100: melting furnace 110: cast iron melt
200: sulfur (S) 210: rare earth element (Rare Earth Element)
220: Sr-based inoculant 300: metal rod
400: ladle 500:

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

Conventionally, rare earth elements have been added to the molten metal in order to prevent chill formation due to the added alloying iron in order to increase the strength of cast iron graphite cast iron. However, in this case, it has been difficult to obtain an input effect due to the strong oxidizing property of rare earth elements, The flowability of the molten metal is lowered and chilling is promoted by the added rare earth element, so that there is a limit to the application as an engine cylinder block material having a complicated shape.

However, in the present invention, only rare earth elements are added to cast iron without use of ferroalloys, and the content of the five elements (e.g., C, Si, Mn, S, P) and rare earth elements (RE) Precisely controlling the content ratio (RE / S) of the rare earth element to a specific range, respectively, assists in the growth and crystallization of the sound type A flake graphite without deteriorating the flowability of the molten metal by the added rare earth element, , Flowability and hardness can be provided.

The RE content and the RE / S ratio (RE / S) between the rare-earth element RE and S in the cast iron are made to be in the range of 300 MPa or more and flowability of 800 mm or more Is the most important factor. Therefore, the cast graphite cast iron of the present invention is required to be limited to the production method and the chemical composition shown below.

Hereinafter, the method for producing cast iron graphite cast iron according to the present invention and the chemical composition of the cast graphite cast iron 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% by weight.

(Si), 0.6 to 0.8% by weight of manganese (Mn) and 0.04% by weight of phosphorus (P), based on the total weight% % Or less, and the remaining amount of iron (Fe).

The method for producing the cast iron melt bath 110 according to the present invention is not particularly limited, and examples of the cast iron melt may include carbon (C), silicon (Si), manganese (Mn), sulfur (S) P) contained in the above-mentioned content range is melted in the blast furnace 100 to prepare the cast iron melt bath 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 cast iron is the same as that described in the case of the chemical composition of the cast iron graphite cast iron to be described later, and a description thereof will be omitted.

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

At this time, since the rare earth element (RE) is a highly oxidative substance, it is essential that an appropriate dosing period and dosing method are required. In the present invention, when sulfur (S) and rare earth element (RE) are added to the cast iron melt bath 110, 0.15 to 0.2% by weight of sulfur (S) is first added and melted, 0.03% is preferably added.

Further, when the rare-earth element RE having a strong oxidizing property is put in a state of being in direct contact with the cast iron melt bath 110, the effect of charging the rare-earth element hardly appears, so that it is necessary to put the rare- . Accordingly, in the present invention, the rare earth element RE is placed in the cast iron cast iron in the contact preventive member for preventing direct contact with the cast iron cast iron 110.

The contact preventive member prevents the direct contact between the cast iron quick-drying bath 110 and the rare earth element RE, and there is no particular limitation on the composition, shape and content of the contact preventive member as long as it does not affect the composition of the cast iron cast iron after the casting. Non-limiting examples of contact preventive members that can be used include aluminum foil and the like.

As an example of the adding step (ii) of sulfur (S) and rare earth element (RE) according to the present invention, the sulfur 200 is firstly charged and then the melting is completed, Oxidizing rare earth element 210 is introduced to minimize the reaction of the cast iron melt with the molten steel bath 110. The stirring is performed using the metal rod 300 so that the charged rare earth element 210 can be uniformly contained in the raw water 110.

At this time, in the present invention, the chemical composition of the cast iron graphite cast iron is limited as described above, and the ratio RE / S of the added rare earth element RE to the sulfur content is limited to 0.05 to 0.2 There is a need. If the ratio of RE / S is less than 0.05, the strength is lowered, and if the ratio of RE / S is more than 0.2, the workability may be deteriorated. By limiting the RE / S ratio in this way, a stable type A flake graphite can be obtained and chillability can be reduced, so that a high strength flake graphite cast iron for an engine cylinder block having a tensile strength of 300 MPa or more and excellent workability can be obtained.

The thus prepared cast iron melt liquid bath 110 is analyzed by using a carbon equivalent meter, a carbon / sulfur analyzer, and a spectrometer.

Thereafter, the ladle (ladle) 400 serving as a container for tapping the cast iron fresh water 110 is prepared and spouted. In order to stabilize the material of the high strength cast graphite cast iron, The Sr-based inoculant 220 is spouted while being inoculated with a stream. When the cast iron raw material is spouted in the ladle as described above, the Sr-based inoculation treatment results in the formation of a stable type A flake graphite to obtain a piece-shaped graphite cast iron having stable mechanical properties and fluidity.

In this case, the size of the injecting agent to be injected may be in the range of 1 to 3 mm in diameter, and the amount of the inoculant injected to achieve the material stabilizing effect of the high strength graphite cast iron is preferably limited to 0.3 ± 0.05% by weight (%).

Then, the temperature of the molten metal of the reed 400 having been spouted is measured using a thermometer of the immersion type, and the temperature is measured. Then, the cast iron melt 110 is injected into the prepared mold 500 to produce a high strength flattened graphite cast iron It completes.

The high strength graphite cast iron of the present invention produced as described above has a strength of 300 to 350 MPa higher than that of graphite cast iron having a tensile strength of 250 MPa which is currently used for an engine cylinder block and a head, and exhibits excellent fluidity and proper hardness of 800 mm or more. Therefore, the cast graphite cast iron according to the present invention has a complicated shape and a hypoeutectic gray cast iron (GC) applicable to a cylinder block and / or a head of a diesel engine in which a higher level of rigidity is required as the explosion pressure is increased. It corresponds to cast iron.

The graphite cast iron of the present invention has high tensile strength, hardness and fluidity. Therefore, it is useful for an engine cylinder block and a head of complex shape in which a thick portion having a thickness of 10 mm or more and a thin portion having a thickness of 5 mm or less exist simultaneously Lt; / RTI &gt;

The present invention provides a high strength piecemeal graphite cast iron produced by the above-described method. More specifically, the graphite cast iron has a composition containing 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) (RE) in an amount of 0.1 to 0.2% by weight, a rare earth element (RE) in an amount of 0.01 to 0.03% by weight, a phosphorus (P) in an amount of 0.04% And the ratio (RE / S) to the sulfur (S) content is in the range of 0.05 to 0.2.

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

1) carbon (C) 3.3 to 3.4 weight%

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

2) silicon (Si) 2.0-2.2 wt%

When added in an optimal ratio with carbon, silicon maximizes graphite crystallization and increases the strength of cast iron. If the content of silicon (Si) is less than 2.0% by weight in the cast iron graphite cast iron according to the present invention, the amount of graphite crystallization decreases. When the content of silicon exceeds 2.2% by weight, the ductility is lowered. Degradation occurs. Therefore, in the present invention, the content of silicon (Si) is preferably limited to 2.0 to 2.2% by weight.

3) 0.6 to 0.8% by weight of manganese (Mn)

Manganese is an element added for improving the strength of cast iron graphite cast iron by refinement of pearlite. If the content of manganese (Mn) is less than 0.6% by weight in the cast iron graphite cast iron according to the present invention, the strength is lowered. If the content is more than 0.8% by weight, the brittleness is increased and the workability is lowered. Therefore, in the present invention, the content of manganese (Mn) is preferably limited to 0.6 to 0.8 wt%.

4) Sulfur (S) 0.15-0.2 wt%

Hwang reacts with trace elements (eg, rare earth elements) contained in the cast iron castle to form sulfides. These sulfides serve as nucleation sites for graphite and assist in the growth of graphite. If the content of sulfur (S) is less than 0.15% by weight in the cast iron graphite cast iron according to the present invention, the graphite nuclei are not generated due to reaction with the rare earth element, so that the strength is lowered. There arises a problem that the brittleness is increased. Therefore, in the present invention, the content of sulfur (S) is preferably limited to 0.15 to 0.2% by weight.

5) 0.04% by weight or less of phosphorus (P)

Phosphorus is also a kind of impurities added naturally in the air during cast iron manufacturing process. Such phosphorus also plays a role of stabilizing pearlite. When the content exceeds 0.04% by weight, brittleness is rapidly increased, which is also related to shrinkage defect due to segregation. Therefore, in the cast graphite cast iron according to the present invention, it is preferable to limit the content of phosphorus (P) to 0.04 wt% or less.

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

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

The rare earth element acts as a nucleus generating source of strong graphite and is added for fine crystallization of fine graphite. If the content of the rare earth element (RE) is less than 0.01% by weight in the cast graphite cast iron according to the present invention, the crystallization amount of the graphite is small and the fluidity is lowered and the chill is generated. When the content is more than 0.03% And a sudden drop in the fluidity. Therefore, in the present invention, it is preferable that the content of the rare earth element is controlled 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 graphite cast iron of the present invention is not only limited to the above chemical composition but also has a stable A-type flake (RE) content by limiting the ratio (RE / S) of the rare earth element (RE) Graphite can be obtained, and a high strength flat piece graphite cast iron applicable to an engine cylinder block and a head can be obtained while having a tensile strength of 300 MPa or more and excellent workability.

According to one example of the present invention, the carbon equivalent (CE) is 3.97 to 4.13. In the cast iron according to the present invention, when the carbon equivalent (CE) is less than 3.97, chill occurs in a thin-walled part having a thickness of 5 mm or less, resulting in poor casting and fluidity, CE) exceeds 4.13, the strength of the graphite is lowered due to excessive formation of primary graphite. Therefore, in the present invention, it is preferable to limit the range of carbon equivalent (CE) to 3.97 to 4.13. At this time, the carbon equivalent (CE) is defined as carbon + (silicon + phosphorus) x 1/3, and the value can be appropriately adjusted for controlling the mechanical properties of the engine cylinder block and head, .

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

According to an embodiment of the present invention, the length of the spiral of the fluidity test piece to which the cast graphite iron having the chemical composition is applied ranges from 800 to 850 mm. At this time, the fluidity test piece can be shown as shown in FIG.

Since the cast iron graphite cast iron of the present invention is a high strength material having a tensile strength of 300 MPa or more, it is suitable for use in diesel engine parts, particularly in engine cylinder blocks, engine cylinder heads, brake discs or both 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.

&Lt; Examples 1 to 5 and Comparative Examples 1 to 5 >

Flat graphite cast iron according to Examples 1 to 5 and Comparative Examples 1 to 5 was produced according to the composition shown in Table 1 below.

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. In this case, the unit of each component constituting the gyogen is weight%. Phosphorus (P) was less than 0.04 wt% due to brittle problems and shrinkage problems.

The cast iron melt liquid thus prepared was analyzed for components of the raw pot by using a carbon equivalent meter and a spectrometer. 0.15 to 0.2% by weight of sulfur (S) and 0.01 to 0.03% by weight of a rare earth element (RE) were added to the molten cast iron melt bath in such a manner. In the case of Comparative Examples 4 and 5 in which the rare earth element (RE) was not contained, chromium (Cr), tin (Sn) and copper (Cu) were added to the molten metal bath immediately before the tapping.

Thereafter, ladle vessels for tapping the cast-iron raw tanks were prepared and tap water was added while introducing a Sr-based inoculant. The temperature of the molten metal was measured after completion of tapping on the reed and the molten metal was injected into the prepared mold to prepare an engine cylinder block and a head piece graphite cast iron product.

The carbon equivalent, tensile strength, hardness, and fluidity of cast iron of Examples 1 to 5 and Comparative Examples 1 to 5 prepared according to the composition of Table 1 were measured and are 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 was adjusted in the range of 0.05 to 0.2, was in the range of 300 to 350 MPa, the Brinell hardness value was in the range of 200 to 230 HB, It was found that the angle was 800 mm or more.

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

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

Comparative Example 4 is an example of a material having a tensile strength of 250 MPa which is used as a conventional engine cylinder block and head piece graphite cast iron.

Comparative Example 5 is a 300 MPa grade material used as a conventional engine cylinder block and head high-strength graphite cast iron, and is an example showing low fluidity.

Claims (14)

(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) Melting a cast iron material containing iron (Fe) in a furnace to produce a cast iron cast iron;
(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 melted cast iron master batch;
(Iii) inoculating an iron-based inoculant into the molten iron casting tank; And
(Iv) injecting the inoculated cast iron melt into a sand mold
Wherein the cast iron is cast iron. 2. The method according to claim 1, wherein the RE / S ratio of the rare earth element (RE) content to the sulfur (S) content is controlled in the range of 0.05 to 0.2. The method according to claim 1, wherein the cast iron raw material of step (ii) is obtained by adding 0.15 to 0.2% by weight of sulfur (S) to the molten cast iron molten salt (i) Wherein the cast iron is produced by casting the cast iron. The method according to claim 1, wherein the rare earth element (RE) is introduced into a cast iron cast iron without directly contacting the cast iron cast iron. The method according to claim 1, wherein the rare earth element (RE) is provided in a contact preventive member for preventing direct contact with the cast iron cast iron, and is introduced into the cast iron cast iron. The method according to claim 1, wherein the carbon equivalent (CE) in the cast iron bath is in the range of 3.97 to 4.13. The method according to claim 1, wherein the tapping temperature is controlled within a range of 1520 占 폚 to 10 占 폚. A flaked graphite cast iron produced by the method according to any one of claims 1 to 7. The cast iron according to claim 8, wherein the cast iron contains 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) (Fe) satisfying 0.2 wt% of rare earth element (RE), 0.01-0.03 wt% of rare earth element (RE), 0.04 wt% or less of phosphorus (P), and 100 wt%
(RE / S) of the rare earth element (RE) content to the sulfur (S) content is 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 flaky graphite cast iron according to claim 8, wherein the carbon equivalent (CE) is 3.97 to 4.13. The flaky graphite cast iron according to claim 8, wherein the Brinell hardness value (BHW) is in the range of 200 to 230. The flat cast iron according to claim 8, wherein the cast iron is a cylinder head, a cylinder block, or a brake disk cast iron.

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