KR20230025184A - Cgi cast iron having enhanced manufacturability and manufacturing method thereof - Google Patents

Abstract

The present invention provides CGI cast iron having a chemical composition in which carbon (C), silicon (Si), manganese (Mn), copper (Cu), tin (Sn), and magnesium (Mg) are controlled to specific content ranges, respectively, and a copper equivalent (Cu_eq) is controlled to be within a specific range and a manufacturing method thereof. In the present invention, provided is CGI cast iron which exhibits high stiffness and toughness and at the same time ensures excellent castability and workability, thereby being applicable to engine parts such as engine cylinder blocks and cylinder heads. To this end, the CGI cast iron comprises, based on the total weight, 3.4 to 3.8 wt% of carbon (C), 2.1 to 2.4 wt% of silicon (Si), 0.2 to 0.4 wt% of manganese (Mn), 0.4 to 0.8 wt% of copper (Cu), 0.02 to 0.06 wt% of tin (Sn), 0.009 to 0.02 wt% of magnesium (Mg), and the remaining amount of iron (Fe) satisfying 100 wt%, and the copper equivalent (Cu_eq) according to equation 1 is 1.1 to 1.6.

Description

CGI cast iron with excellent manufacturability and its manufacturing method {CGI CAST IRON HAVING ENHANCED MANUFACTURABILITY AND MANUFACTURING METHOD THEREOF}

The present invention relates to CGI (Compacted Graphite Iron) cast iron with excellent manufacturability and a method for manufacturing the same, and more particularly, to CGI cast iron that exhibits high stiffness and toughness and at the same time secures excellent castability and workability, which can be applied to high-output engine parts. and a manufacturing method thereof.

Due to recent environmental regulations and the demand for high-output engines in the market, it is inevitable to increase the explosion pressure of the engine. As the explosion pressure of the engine increases, it is inevitable to improve the rigidity of the cylinder block and head to cope with it.

Cast iron used for cylinder blocks and heads has a tensile strength of 200 to 300 MPa. A material commonly used in conventional cylinder blocks is gray cast iron. This gray cast iron has excellent vibration damping ability, thermal conductivity, castability and workability, but due to its relatively low tensile strength, an engine explosion pressure of 230 bar or more, that is, 23 MPa or more. has a problem that is difficult to deal with.

There is nodular cast iron as cast iron having improved physical properties of the aforementioned gray cast iron. Spheroidal graphite cast iron is cast iron in which rigidity and toughness are improved by changing the shape of graphite appearing in the microstructure of gray cast iron from a flake structure to a spherical structure. Such ductile graphite cast iron has high strength required by engines requiring high explosion pressure, but has poor vibration damping ability, thermal conductivity, castability and workability compared to gray cast iron, limiting its application to engine cylinder blocks and heads with complex shapes. there is

On the other hand, CGI (Compacted Graphite Iron) cast iron has the advantages of gray cast iron such as vibration damping ability, thermal conductivity, castability, and processability, and simultaneously possesses the high stiffness and toughness of nodular cast iron, so it is applied as a material for next-generation engine parts. . However, in the case of CGI cast iron material having a tensile strength of more than 460 MPa, compared to gray cast iron, molten metal fluidity and processability were significantly poor, so there was a limit to its application to commercial diesel engines.

The present invention has been made to solve the above problems, the content of carbon (C), silicon (Si), manganese (Mn), copper (Cu), tin (Sn) and magnesium (Mg) contained in cast iron To provide CGI cast iron and its manufacturing method having stable physical properties, microstructure, castability and workability by precisely controlling the amounts of copper (Cu), tin (Sn), and magnesium (Mg) while adjusting to a specific range. as a technical challenge.

In addition, another technical problem of the present invention is to provide engine parts such as a cylinder block and a head, which are provided in a high-output diesel engine, including the aforementioned CGI cast iron.

Other objects and advantages of the present invention can be more clearly described by the following detailed description and claims.

In order to achieve the above technical problem, the present invention is carbon (C) 3.4 ~ 3.8% by weight, silicon (Si) 2.1 ~ 2.4% by weight, manganese (Mn) 0.2 ~ 0.4% by weight, copper (Cu) 0.4 to 0.8 wt%, tin (Sn) 0.02 to 0.06 wt%, magnesium (Mg) 0.009 to 0.02 wt%, and the remaining amount of iron (Fe) to satisfy 100 wt%, and copper equivalent (Copper Equivalent, Cu _eq ) is 1.1 to 1.6 to provide CGI cast iron.

In one embodiment according to the present invention, the CGI cast iron includes a ferrite-pearlite two-phase mixed matrix structure, and may be composed of 17 to 39% ferrite and 61 to 83% pearlite in area fraction. there is.

For one embodiment according to the present invention, the nodularity of the graphite distributed in the base tissue may be 5 to 30%.

For one embodiment according to the present invention, the carbon equivalent (C.E.) of the CGI cast iron may be 4.1 to 4.6.

For one embodiment according to the present invention, the CGI cast iron has a tensile strength of (i) 400 to 460 MPa at 20 ± 5 ° C; (ii) Yield Strength of 300 to 335 MPa; (iii) Elongation of 1 to 3%; and (iv) a Brinell hardness of 185 to 230 HBW.

For one embodiment according to the present invention, the CGI cast iron may have a fluidity length of 700 to 850 mm at a molten metal injection temperature of 1360 ± 40 °C.

For one embodiment according to the present invention, the thermal conductivity of the CGI cast iron may be 34.5 to 45 W / m K.

In addition, the present invention provides an engine part that includes the aforementioned CGI cast iron and is applied to at least one of an engine cylinder block and an engine cylinder head.

Furthermore, the present invention is a method for producing the above-described CGI graphite cast iron, (i) 3.4 to 3.8% by weight of carbon (C), 2.1 to 2.4% by weight of silicon (Si), 0.2 to 0.4% by weight of manganese (Mn), and 100 Manufacturing a cast iron wontang by melting a CGI cast iron material including a residual amount of iron (Fe) that satisfies the weight percent in a furnace; (ii) preparing a ladle in which 0.4 to 0.8% by weight of copper (Cu), 0.02 to 0.06% by weight of tin (Sn), and 0.009 to 0.02% by weight of magnesium (Mg) are disposed; (iii) preparing a cast iron melt by tapping the cast iron wontang on the ladle, adjusting the copper equivalent (Cu _eq ) of the cast iron melt to 1.1 to 1.6; (iv) secondarily adding magnesium (Mg) to the molten cast iron after determining the magnesium content contained in the molten cast iron; and (v) injecting the molten cast iron of step (iv) into a mold.

For one embodiment according to the present invention, the cast iron wontang of step (i) may have a carbon equivalent (C.E.) adjusted to 4.1 to 4.6.

For one embodiment according to the present invention, the tapping temperature in step (iii) may be adjusted to 1510 ± 20 ° C.

For one embodiment according to the present invention, the magnesium added secondarily in step (iv) may be magnesium (Mg) in a wire form.

According to one embodiment of the present invention, the content of carbon (C), silicon (Si), manganese (Mn), copper (Cu), tin (Sn), and magnesium (Mg) constituting cast iron is adjusted to a specific range. At the same time, by precisely controlling the amount of copper (Cu), tin (Sn), and magnesium (Mg), the tensile strength of 400 ~ 460 MPa, the yield strength of 300 ~ 335 MPa, and the Brinell hardness (HBW) of 185 ~ 230 CGI cast iron with high mechanical properties can be provided.

In addition, the CGI cast iron according to the present invention secures the same level of molten metal fluidity as compared to conventional gray cast iron and excellent workability compared to conventionally commercialized CGI cast iron, making it useful for manufacturing cylinder blocks and heads provided in high-power and high-horsepower diesel engines. can be applied

In particular, in the present invention, CGI cast iron having high strength and a homogeneous microstructure that can be applied for cylinder blocks and heads for high-horsepower diesel engines can be manufactured through precise control of magnesium (Mg) content. Hardness and tensile strength can be adjusted in various ways by controlling the amount of alloying elements copper (Cu), manganese (Mn), and tin (Sn).

Effects according to the present invention are not limited by the contents exemplified above, and more diverse effects are included in the present specification.

1 is a graph showing the tensile strength of CGI cast iron prepared in Examples 1 to 7 and Comparative Examples 1 to 8.
Figure 2 is a graph showing the yield strength (Yield Strength) of CGI cast iron prepared in Examples 1 to 7 and Comparative Examples 1 to 8.
3 is a graph showing the elongation of CGI cast iron prepared in Examples 1 to 7 and Comparative Examples 1 to 8.
4 is a graph showing the hardness of CGI cast iron prepared in Examples 1 to 7 and Comparative Examples 1 to 8.
5 and 6 are a plan view and a cross-sectional view showing a mold for manufacturing a spiral test piece used for fluidity measurement in Experimental Example 2, respectively.
7 is a graph showing the fluidity of molten metals prepared in Examples 1 to 7 and Comparative Examples 1 to 8.
8 is a photograph of tool wear amount showing the machinability of CGI cast irons prepared in Example 1, Comparative Example 3, and Comparative Examples 7 and 8.
9 is a microstructure photograph of gray cast iron of Comparative Example 6, CGI cast iron of Example 1, and spheroidal graphite cast iron of Comparative Example 8.

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

All terms (including technical and scientific terms) used in this specification, unless otherwise defined, may be used in a meaning commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, terms defined in commonly used dictionaries are not interpreted ideally or excessively unless explicitly specifically defined.

In addition, throughout this specification, when a certain component is said to "include", this is an open term that implies the possibility of further including other components, not excluding other components, unless otherwise stated. (open-ended terms). In addition, throughout the specification, "above" or "on" means not only the case of being located above or below the target part, but also the case of another part in the middle thereof, necessarily based on the direction of gravity. does not mean that it is located at the top. Also, terms such as "first" and "second" in the present specification do not indicate any order or importance, but are used to distinguish components from each other.

Also used herein, “preferred” and “preferably” refer to embodiments of the invention that can provide certain advantages under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Additionally, the recitation of one or more preferred embodiments does not imply that the other embodiments are not useful, nor is it intended to exclude the other embodiments from the scope of the present invention.

<CGI Cast Iron>

One embodiment according to the present invention is CGI cast iron (Compacted Graphite Iron) having the thermal conductivity, castability and workability of gray cast iron and high stiffness and toughness of spheroidal graphite cast iron at the same time, which is superior to conventional CGI cast iron of 450 MPa or more commercially available. It is differentiated in that it has fluidity and processability.

For example, the CGI cast iron contains 3.4 to 3.8 wt% of carbon (C), 2.1 to 2.4 wt% of silicon (Si), 0.2 to 0.4 wt% of manganese (Mn), and 0.4 wt% of copper (Cu), based on the total weight. ~0.8% by weight, tin (Sn) 0.02~0.06% by weight, magnesium (Mg) 0.009~0.02% by weight, the remaining amount of iron (Fe) satisfying 100% by weight and unavoidable impurities, and at the same time copper (Cu) It has a chemical composition that satisfies the Copper Equivalent (Cu _eq ) of 1.1 to 1.6 by precisely controlling the amounts of Sn and Mg.

Here, each content of carbon (C), silicon (Si), manganese (Mn), copper (Cu), tin (Sn) and magnesium (Mg) constituting CGI cast iron; The copper equivalent weight (Cu _eq ) according to the control of the copper, manganese, and magnesium content ratio is 700 to 850 mm of fluidity and workability as well as 400 to 460 MPa of tensile strength, 300 to 335 MPa of yield strength, It is an important factor in producing CGI cast iron having a Brinell hardness (HBW) of 185 to 230. Accordingly, the CGI cast iron of the present invention needs to be limited to the following chemical composition.

Hereinafter, each component and content of the CGI cast iron according to the present invention will be described. Here, the addition amount of each element is % by weight, and may be simply expressed as % in the following content.

1) 3.4 to 3.8% by weight of carbon (C)

Carbon is an element added for the crystallization of compacted graphite. If the carbon content in the CGI cast iron according to the present invention is less than 3.4% by weight, chilling behavior is observed in the thin-walled part, and if it exceeds 3.8% by weight, graphite spheroidization shrinkage and poor flow occur . In order to prevent defects in high-strength cylinder blocks having various thicknesses, the carbon content is set to 3.4 to 3.8% by weight in the present invention.

2) 2.1 to 2.4% by weight of silicon (Si)

When silicon is added in an optimal ratio with carbon, it maximizes the crystallization amount of compacted graphite and increases the strength of cast iron. In the CGI cast iron according to the present invention, when the silicon content is less than 2.1% by weight, the crystallization amount of reinforced graphite is lowered, and when it exceeds 2.4% by weight, ductility is lowered. Accordingly, in the present invention, the content of silicon is set to 2.1 to 2.4% by weight.

3) 0.2 to 0.4% by weight of manganese (Mn)

Manganese is added for refinement of graphite and stabilization of pearlite. If the content of manganese in the CGI cast iron according to the present invention is less than 0.2% by weight, the hardness is lowered, and if it exceeds 0.4% by weight, brittleness is increased. Accordingly, in the present invention, the content of manganese is set to 0.2 to 0.4% by weight.

4) 0.4 to 0.8% by weight of copper (Cu)

Copper is a necessary element to secure strength because it promotes the creation of pearlite and acts to refine it. In the cast iron according to the present invention, when the copper content is less than 0.4% by weight, strength is insufficient, and when the content exceeds 0.8% by weight, castability is deteriorated. Accordingly, in the present invention, the copper content is set to 0.4 to 0.8% by weight.

5) Tin (Sn) 0.02 ~ 0.06% by weight

Tin is a very strong pearlite formation promoting element, and is added for the purpose of improving strength, like copper. When the content of tin in the cast iron according to the present invention is less than 0.02% by weight, the strength is lowered, and when it exceeds 0.06% by weight, brittleness is rapidly increased and castability is also lowered. Accordingly, in the present invention, the content of tin is set to 0.02 to 0.06% by weight.

6) Magnesium (Mg) 0.009 to 0.02% by weight

Magnesium functions as nodularity of graphite and at the same time promotes nucleation and growth of compacted graphite. In the cast iron according to the present invention, when the magnesium content is less than 0.009% by weight, graphite is flattened, and when it exceeds 0.02% by weight, the spheroidization rate of graphite increases and causes poor shrinkage. Limited to % range.

7) Iron (Fe): balance

Iron is the main constituent of the cast iron according to the present invention. The content of this iron may be a residual amount that satisfies the total amount of the CGI cast iron to be 100% by weight.

8) Inevitable Impurities

CGI cast iron according to the present invention may contain some unavoidable impurities. These unavoidable impurities include phosphorus (P) and sulfur (S).

Phosphorus (P) is an impurity naturally added during the manufacturing process of CGI cast iron, and is dissolved in the matrix structure, but most of it exists as a phase called Steadite, which is a phosphide. Steadite strengthens the base structure and lowers the melting point of cast iron, thereby improving the fluidity and castability of the molten metal. The phosphorus content is not particularly limited, but when the phosphorus content exceeds about 0.06% by weight, brittleness is rapidly increased due to the formation of excessive phosphides, and processability may be deteriorated. Accordingly, the phosphorus content is preferably adjusted to about 0.06% by weight or less, specifically more than 0% by weight and 0.03% by weight or less based on the total amount of the CGI cast iron.

In addition, sulfur (S) is an element that inhibits spheroidization of graphite, and its content is not particularly limited. However, when the sulfur content in the CGI cast iron according to the present invention exceeds about 0.01% by weight, the production of compacted graphite may be inhibited and flake graphite may be formed. Accordingly, the sulfur content is preferably adjusted to about 0.01% by weight or less, specifically more than 0% by weight and less than 0.01% by weight based on the total amount of the CGI cast iron.

9) Copper Equivalent (Cu) _eq )

In the present invention, the chemical composition constituting the CGI cast iron is limited as described above, and the copper equivalent (Cu _eq ) described later is adjusted to be in the range of 1.1 to 1.6. Here, the copper equivalent can be calculated according to Equation 1 below. For reference, the unit of copper equivalent is weight%, but the unit is usually omitted in the art.

[Equation 1]

In the above formula,

Cu is the content (wt%) of copper relative to the total amount of the CGI cast iron,

Mn is the content (wt%) of manganese relative to the total amount of the CGI cast iron,

Sn is the content (wt%) of tin relative to the total amount of the CGI cast iron.

In the CGI cast iron according to the present invention, when the copper equivalent weight (Cu _eq ) is less than about 1.1, a sufficient amount of pearlite may not be produced, and the tensile strength may be lowered. On the other hand, when the copper equivalent weight (Cu _eq ) exceeds about 1.6, castability and workability may be deteriorated. Accordingly, in the present invention, by adjusting the copper equivalent (Cu _eq ) to 1.1 to 1.6, mechanical properties such as tensile strength, yield strength, elongation, and hardness are stabilized, and CGI having excellent castability and processability and high thermal conductivity Cast iron can be made.

10) Carbon Equivalent (C.E.)

The CGI cast iron of the present invention has a carbon equivalent (C.E.) in the range of 4.1 to 4.6. Here, the carbon equivalent (C.E.) can be calculated according to Equation 2 below. For reference, the unit of Carbon Equivalent (C.E.) is weight%, but the unit is usually omitted in the art.

[Equation 2]

In the above formula,

C is the carbon content (wt%) relative to the total amount of the CGI cast iron,

Si is the content (wt%) of silicon relative to the total amount of the CGI cast iron.

In the CG cast iron according to the present invention, when the carbon equivalent is less than 4.1, the thin-walled part tends to be chilled, and when it exceeds 4.6, primary graphite is excessively produced. Shrinkage and poor flow occur. Accordingly, in the present invention, the carbon equivalent (C.E.) is limited to 4.1 to 4.6.

According to one example, the CGI cast iron of the present invention includes a ferrite-pearlite two-phase mixed matrix structure, and consists of 17 to 39% ferrite and 61 to 83% pearlite in area fraction It can be.

According to another example, the CGI cast iron of the present invention includes graphite distributed in the matrix structure, but the nodularity of graphite formed by carbon may be 5 to 30%.

According to another example, the CGI graphite cast iron of the present invention has (i) tensile strength of 400 to 460 MPa, (ii) yield strength of 300 to 335 MPa at room temperature of about 20 ± 5 ° C. ; (iii) an elongation of 1 to 3%, and (iv) a Brinell hardness of 185 to 230 HBW.

According to another example, the CGI graphite cast iron of the present invention may have a thermal conductivity of about 34.5 to 45 W/m·K.

According to another example, the CGI graphite cast iron of the present invention may have a fluidity length of about 700 to 850 mm at a molten metal injection temperature of 1360 ± 40 °C.

The CGI cast iron of the present invention having the above-described chemical composition has remarkably excellent molten metal fluidity and workability compared to commercially available CGI cast iron with a grade of 450 MPa or higher, as well as exhibiting mechanical properties equal to or better than these. By securing stable mechanical properties, excellent molten metal fluidity, and processability at the same time, it can be usefully applied to the cylinder block and/or head of a high-output diesel engine.

Hereinafter, a method for manufacturing CGI cast iron according to the present invention will be described. However, it is not limited only by the following manufacturing method, and each process step may be modified or selectively used in combination as needed.

For one embodiment of the manufacturing method, (i) satisfies 3.4 to 3.8% by weight of carbon (C), 2.1 to 2.4% by weight of silicon (Si), 0.2 to 0.4% by weight of manganese (Mn), and 100% by weight Melting the CGI cast iron material containing the remaining amount of iron (Fe) in a furnace to produce a cast iron wontang; (ii) preparing a ladle in which 0.4 to 0.8% by weight of copper (Cu), 0.02 to 0.06% by weight of tin (Sn), and 0.009 to 0.02% by weight of magnesium (Mg) are disposed; (iii) preparing a cast iron melt by tapping the cast iron wontang on the ladle, adjusting the copper equivalent (Cu _eq ) of the cast iron melt to 1.1 to 1.6; (iv) secondarily adding magnesium (Mg) to the molten cast iron after determining the magnesium content contained in the molten cast iron; and (v) injecting the molten cast iron of step (iv) into a mold.

(i) Manufacture of cast iron wontang

The method for producing cast iron wontang according to the present invention is not particularly limited, and for example, cast iron raw materials containing carbon (C), silicon (Si), manganese (Mn), etc., which are representative elements of cast iron, are weighed to have a target chemical composition After that, it is melted in a blast furnace to produce cast iron wontang. At this time, based on the total weight of the raw material molten metal, carbon (C) 3.4 ~ 3.8% by weight, silicon (Si) 2.1 ~ 2.4% by weight, manganese (Mn) 0.2 ~ 0.4% by weight, and the remaining amount satisfying 100% by weight Adjust the content of each raw material to include iron (Fe). In particular, the carbon equivalent (C.E.) of the cast iron wontang is adjusted to be 4.1 to 4.6.

Before tapping the raw molten metal prepared as described above, component analysis of the raw metal is completed using an emission spectrometer, a carbon/sulfur determinator, a carbon equivalent meter, and the like.

(ii) Ladle Preparation

In a ladle, which is a container for tapping molten cast iron wontang in a blast furnace, 0.4 to 0.8 wt% of copper (Cu), 0.02 to 0.06 wt% of tin (Sn), and 0.009 to 0.009 wt% of magnesium (Mg), which are the remaining components of cast iron. Prepare the ladle by placing 0.02% by weight. In particular, copper (Cu), manganese (Mn), and tin (Sn) are adjusted to the above-mentioned content range, but the amount of each component is adjusted so that the copper equivalent (Cu _eq ) is in the range of 1.1 to 1.6 and placed in the ladle .

(iii) Preparation of cast iron melt

The prepared cast iron wontang is tapped with a ladle in which predetermined amounts of copper (Cu), tin (Sn), and magnesium (Mg) are disposed to prepare a cast iron molten solution.

At this time, the tapping temperature can be adjusted to be 1510 ± 20 ° C, and can be measured using an immersion type thermometer. In addition, component analysis of the cast iron molten solution prepared as described above is completed using an emission spectrometer, a carbon/sulfur determinator, a copper equivalence meter, and the like.

(iv) Magnesium secondary addition and/or inoculation

The amount of magnesium (Mg) to be added is determined by determining the magnesium (Mg) content contained in the tapped cast iron melt. At this time, a thermal analyzer may be used to determine the magnesium (Mg) content.

Upon completion of the thermal analysis, the thermal analyzer determines the amount of magnesium to be added. At this time, if the amount of magnesium to be added is 0, magnesium is not added separately, and if the amount of magnesium to be added exceeds 0, the amount of magnesium determined in the thermal analyzer is added to the cast iron solution tapped secondarily. For the formation of CGI cast iron, it is preferable to use wire-type magnesium as the secondary added magnesium (Mg). However, it is not limited thereto. If the amount of magnesium determined in the thermal analyzer is not added secondaryly, the mechanical properties of the CGI cast iron to be manufactured are significantly deteriorated, so magnesium (Mg) must be added secondaryly by the determined amount.

In addition to the magnesium addition described above, a conventional inoculant commonly used in the cast iron manufacturing process may be added. The inoculant is not particularly limited, and a silicone-based inoculant may be used as an example. Silicone-based inoculants may be purchased and used commercially. In addition, the type and content of the inoculum can be easily selected and determined by those skilled in the art as needed, and is not particularly limited. The aforementioned inoculants may also be used in wire form.

(v) mold injection

The cast iron molten liquid to which magnesium (Mg) is added is injected into a mold of a certain shape. Subsequently, a cast product is obtained by desanding from the mold, and then, if necessary, a CGI cast iron product having a final shape and a required surface quality may be obtained through mechanical processing such as grinding.

The CGI cast iron of the present invention manufactured as described above has stable physical properties such as tensile strength of 400 ~ 460 MPa and fluidity length of 700 ~ 850 mm, microstructure, castability and workability, so that the shape It can be usefully applied to engine parts such as complex engine cylinder blocks, engine cylinder heads, pistons, and piston rings. In addition to the aforementioned uses, exhaust system components such as exhaust manifolds, turbocharger housings, turbocharger housing-integrated exhaust manifolds, catalyst cases, catalyst case-integrated exhaust manifolds, and exhaust outlets; It can be used for the furnace floor of an incinerator or heat treatment furnace, or parts for combustion furnaces such as carts, etc., and can also be used without limitation for sliding parts such as disc brake rotors.

Hereinafter, the present invention will be described in more detail by way of Examples and Comparative Examples. However, the present invention is not limited thereto.

[Examples 1 to 7]

CGI cast irons of Examples 1 to 7 were prepared according to the chemical compositions shown in Table 1 below.

As an example, CGI containing 3.4 to 3.8% by weight of carbon (C), 2.1 to 2.4% by weight of silicon (Si), 0.2 to 0.4% by weight of manganese (Mn), and the balance iron (Fe) according to the composition of Table 1, first. The cast iron material was melted in a blast furnace to produce a cast iron wontang. Before tapping, the carbon equivalent (CE) was adjusted to be in the range of 4.1 to 4.6 using a carbon equivalent meter.

0.4 to 0.8 wt% of copper (Cu), 0.02 to 0.06 wt% of tin (Sn), and 0.009 to 0.02 wt% of magnesium (Mg) are placed in a ladle, which is a container for tapping the cast iron wontang, respectively. The amounts of copper (Cu), tin (Sn), and magnesium (Mg) were adjusted so that the equivalent (Copper Equivalent, Cu _eq ) was in the range of 1.1 to 1.6.

A cast iron melt was prepared by tapping the cast iron wontang on the ladle, and at this time, the tapping temperature was adjusted to 1510 ± 20 ° C. Subsequently, after determining the content of magnesium (Mg) contained in the molten cast iron, the amount of magnesium to be added was determined. In order to add the amount of magnesium to be added, magnesium in the form of a wire was added to the cast iron melt, and then the cast iron melt was injected into a mold to manufacture a CGI cast iron product.

Chemical composition (% by weight) C.E. Cu _eq C Si Mn P S Mg Cu Sn Fe Example 1 4.2 1.49 3.5 2.2 0.3 0.017 0.008 0.012 0.66 0.07 balance Example 2 4.2 1.45 3.5 2.3 0.3 0.018 0.007 0.014 0.64 0.07 balance Example 3 4.2 1.47 3.5 2.3 0.3 0.018 0.006 0.009 0.64 0.07 balance Example 4 4.3 1.41 3.5 2.5 0.3 0.02 0.008 0.013 0.60 0.07 balance Example 5 4.3 1.46 3.5 2.3 0.3 0.019 0.007 0.013 0.65 0.06 balance Example 6 4.3 1.45 3.5 2.3 0.3 0.019 0.008 0.015 0.65 0.06 balance Example 7 4.5 1.12 3.8 2.1 0.3 0.017 0.006 0.016 0.75 0.02 balance Comparative Example 1 4.2 1.79 3.42 2.42 0.30 0.028 0.005 0.01 0.822 0.082 balance Comparative Example 2 4.3 0.78 3.4 2.6 0.3 0.026 0.006 0.011 0.20 0.04 balance Comparative Example 3 4.3 2.30 3.5 2.3 0.3 0.019 0.01 0.012 1.25 0.09 balance Comparative Example 4 4.5 2.35 3.74 2.2 0.3 0.02 0.01 0.011 1.3 0.09 balance Comparative Example 5 4.4 2.48 3.65 2.24 0.44 0.019 0.01 0.017 1.36 0.09 balance Comparative Example 6 4.0 1.43 3.3 2.2 0.7 0.027 0.074 0 0.58 0.05 balance Comparative Example 7 3.9 0.81 3.19 2.21 0.6 0.035 0.07 0 0.51 0 balance Comparative Example 8 4.4 1.18 3.66 2.11 0.23 0.047 0.007 0.041 0.771 0.03 balance

[Comparative Examples 1 to 8]

Cast iron according to Comparative Examples 1 to 8 was prepared according to the chemical composition of Table 1 below. Specifically, Comparative Examples 1 to 5 are CGI cast iron with a tensile strength of 450 MPa or higher that is commercially used, and Comparative Examples 6 to 7 are 300 MPa gray cast iron (GC300), which is currently commonly used in diesel engine cylinder blocks and heads. . In addition, in the case of Comparative Example 8, it is nodular graphite cast iron (GCD600) used for casings for hydraulic equipment.

As shown in FIG. 9, in the case of the gray cast iron of Comparative Example 6, the flake graphite structure can be confirmed, and in the case of the nodular graphite cast iron of Comparative Example 8 having a high magnesium (Mg) content, the graphite (black part) shape is on the microstructure It was confirmed that it was formed in a perfect spherical shape.

[Experimental Example 1: Evaluation of mechanical properties of CGI cast iron]

Mechanical properties of the CGI cast iron according to the present invention were evaluated as follows.

Specifically, using the cast iron melts of Examples 1 to 7 and Comparative Examples 1 to 8, a test piece of the standard of 'metallic material tensile test piece' of KS B 0801 was manufactured, and then a universal testing machine was prepared in accordance with the KS B 0802 standard. Tensile strength, yield strength and elongation were respectively measured at room temperature (20±5° C.) using The results are shown in Table 2 and FIGS. 1 to 4 below, respectively.

At this time, in the case of Comparative Examples 6 and 7, which are gray cast iron materials (GC300), yield strength and elongation cannot be measured due to the characteristics of gray cast iron, so they are marked with '-'.

carbon
equivalent weight
(CE) copper
equivalent weight
(Cu _eq ) tensile strength
(MPa) yield strength
(MPa) elongation rate
(%) Hardness
(HBW) nodularization rate
(%) perlite
fraction
(%) Example 1 4.2 1.49 456 326 2 223 6 76 Example 2 4.2 1.45 460 331 2 219 5 78 Example 3 4.2 1.47 442 325 2 224 17 75 Example 4 4.3 1.41 432 317 2 217 10 80 Example 5 4.3 1.46 417 315 3 208 8 83 Example 6 4.3 1.45 403 305 2 186 24 61 Example 7 4.5 1.12 411 314 One 199 23 74 Comparative Example 1 4.2 1.79 501 367 2 231 2 94 Comparative Example 2 4.3 0.78 340 210 3 170 5 21 Comparative Example 3 4.3 2.30 485 375 One 252 3 100 Comparative Example 4 4.5 2.35 490 384 One 253 3 99 Comparative Example 5 4.4 2.48 514 422 One 267 17.8 100 Comparative Example 6 4.0 1.43 330 - - 235 0 100 Comparative Example 7 3.9 0.81 325 - - 231 0 100 Comparative Example 8 4.4 1.18 679 390 4 236 87 91

[Experimental Example 2: Castability evaluation of CGI cast iron]

The castability of the CGI cast iron according to the present invention was evaluated as follows.

Specifically, as shown in FIGS. 5 and 6, a mold for a standard fluidity spiral test piece designated by the American Foundry Society (AFS) was manufactured, and then manufactured in Examples 1 to 7 and Comparative Examples 1 to 8 Each cast iron melt was injected into the mold to prepare a test piece. Castability was evaluated by measuring the fluidity length (Fluidity Length) of each cast iron melt using points regularly marked at 50 mm intervals on the manufactured test piece, and the results are shown in Table 3 and FIG. 7, respectively.

Injection temperature (℃) Fluidity (mm) Example 1 1327 720 Example 2 1322 700 Example 3 1330 730 Example 4 1342 750 Example 5 1368 850 Example 6 1384 850 Example 7 1388 760 Comparative Example 1 1331 600 Comparative Example 2 1360 720 Comparative Example 3 1369 650 Comparative Example 4 1362 640 Comparative Example 5 1380 580 Comparative Example 6 1350 770 Comparative Example 7 1327 750 Comparative Example 8 1417 650

According to Table 3, in the case of the commercialized CGI cast iron of Comparative Examples 1 and 3 to 5 and the spheroidal graphite cast iron of Comparative Example 8, the fluidity length was about 580 to 650 mm, indicating that the castability was poor. At this time, in the case of the CGI cast iron of Comparative Example 2, since the injection temperature was high and the content of the added chemical component was small, excellent fluidity results were shown compared to the poor mechanical properties described above.

In contrast, the fluidity length of the CGI cast iron solutions prepared in Examples 1 to 7 was 700 to 850 mm, indicating that the fluidity length (750 to 770 mm) of Comparative Examples 6 to 7, which is gray cast iron, was equivalent to or better than that. I was able to confirm.

Through the above results, since the CGI cast iron satisfying the specific chemical composition according to the present invention has excellent fluidity, when producing castings of complex shapes such as engine cylinder blocks and heads using the CGI cast iron of the present invention, -rum), it was confirmed that castings with perfect shapes could be produced without occurrence of casting defects such as surface defects.

[Experimental Example 3: Machinability of CGI Cast Iron]

The workability of the CGI cast iron according to the present invention was evaluated as follows.

Specifically, after making a test piece of 230 × × 70 × 125 mm in size using each cast iron material prepared in Example 1 and Comparative Example 3 and 7, face milling was performed under the processing conditions shown in Table 4 below. Processability was evaluated by measuring the wear amount (mm) of the tool used when processing up to 47 rows was measured through an optical microscope, and the results are shown in Table 5 and FIG. 8, respectively.

item unit Evaluation of face milling machinability Spindle speed rpm 1000 Feed rate mm/min. 300 cutting depth mm 3 tool material - Carbide cooling condition - deflation note - Tool wear evaluation after 5 layer machining

carbon equivalent
(CE) copper equivalent
(Cu _eq ) tool wear
(mm) Example 1 4.2 1.49 0.1 Comparative Example 3 4.3 2.30 0.3 Comparative Example 7 3.9 0.81 0.1 Comparative Example 8 4.4 1.18 0.6

According to Table 5, the tool wear amount of Comparative Example 3, which is a commercial CGI material, was 0.3 mm. In addition, it can be seen that the tool wear amount of Comparative Example 8, which is a commercial spheroidal graphite cast iron material, is 0.6 mm. In contrast, the CGI material prepared in Example 1 showed a tool wear amount of 0.1 mm during machining, indicating that it had excellent workability equivalent to that of Comparative Example 7, which was gray cast iron.

Accordingly, it was confirmed that the CGI cast iron having a specific chemical composition according to the present invention can produce a complete cast product without deformation in the machining process when manufacturing castings such as engine cylinder blocks and heads through excellent workability.

[Experimental Example 4: Evaluation of Thermal Conductivity of CGI Cast Iron]

The thermal conductivity of the CGI cast iron according to the present invention was evaluated as follows.

Specifically, after fabricating a test piece with a size of Φ 12.5 × 4 mm using each cast iron material prepared in Example 1 and Comparative Examples 3 and 7-8, thermal conductivity was evaluated using LFA (Laser Flash Apparatus), , The measurement results are shown in Table 6 below.

carbon equivalent
(CE) copper equivalent
(Cu _eq ) thermal conductivity
(W/m K) Example 1 4.2 1.49 39.89 Comparative Example 3 4.3 2.30 34.22 Comparative Example 7 3.9 0.81 44.98 Comparative Example 8 4.4 1.18 32.5

According to Table 6, the thermal conductivity of Example 1 was lower than that of Comparative Example 7, which was gray cast iron, but was about 5 W/m K higher than that of CGI cast iron of Comparative Example 3, which is currently commercialized for cylinder blocks. It was found that it was significantly superior to Comparative Example 8, which was spheroidal graphite cast iron.

As described above, since the CGI cast iron having a specific chemical composition according to the present invention exhibits excellent thermal conductivity compared to the general-purpose CGI material that is generally used, castings such as engine cylinder blocks and heads are manufactured using the CGI cast iron of the present invention. It was confirmed that it can be operated safely even at high explosion pressure.

Claims (12)

Based on the total weight, 3.4 to 3.8 wt% of carbon (C), 2.1 to 2.4 wt% of silicon (Si), 0.2 to 0.4 wt% of manganese (Mn), 0.4 to 0.8 wt% of copper (Cu), and 0.02 to 0.02 wt% of tin (Sn) 0.06% by weight, 0.009 to 0.02% by weight of magnesium (Mg), and the remaining amount of iron (Fe) satisfying 100% by weight,
CGI cast iron having a copper equivalent (Cu _eq ) of 1.1 to 1.6 according to Formula 1 below:
[Equation 1]

In the above formula,
Cu is the weight percent of copper relative to the total weight of the CGI cast iron,
Mn is the weight percent of manganese relative to the total weight of the CGI cast iron,
Sn is the weight percent of tin relative to the total weight of the CGI cast iron. According to claim 1,
The CGI cast iron includes a ferrite-pearlite two-phase mixed matrix structure, and is composed of 17 to 39% ferrite and 61 to 83% pearlite in area fraction, CGI cast iron. According to claim 2,
The nodularity of the graphite distributed in the base structure is 5 to 30%, CGI cast iron. According to claim 1,
CGI cast iron with a Carbon Equivalent (CE) of 4.1 to 4.6. According to claim 1,
CGI cast iron, which satisfies the following conditions (i) to (iv) at 20 ± 5 ° C:
(i) Tensile strength of 400 to 460 MPa;
(ii) Yield Strength of 300 to 335 MPa;
(iii) Elongation of 1 to 3%; and
(iv) a Brinell hardness of 185 to 230 HBW. According to claim 1,
CGI cast iron having a fluidity length of 700 to 850 mm at a molten metal injection temperature of 1360 ± 40 ° C. According to claim 1,
CGI cast iron with a thermal conductivity of 34.5 to 45 W/m K. Including the CGI cast iron according to any one of claims 1 to 7,
An engine part applied to at least one of an engine cylinder block and an engine cylinder head. (i) CGI containing 3.4 to 3.8 wt% of carbon (C), 2.1 to 2.4 wt% of silicon (Si), 0.2 to 0.4 wt% of manganese (Mn), and a balance of iron (Fe) satisfying 100 wt% Melting the cast iron material in a furnace to produce a cast iron wontang;
(ii) preparing a ladle in which 0.4 to 0.8% by weight of copper (Cu), 0.02 to 0.06% by weight of tin (Sn), and 0.009 to 0.02% by weight of magnesium (Mg) are disposed;
(iii) preparing a cast iron melt by tapping the cast iron wontang on the ladle, adjusting the copper equivalent (Cu _eq ) of the cast iron melt to 1.1 to 1.6;
(iv) secondarily adding magnesium (Mg) to the molten cast iron after determining the magnesium content contained in the molten cast iron; and
(v) injecting the molten cast iron of step (iv) into a mold;
Method for producing CGI cast iron comprising a. According to claim 9,
The cast iron wontang of step (i) is a manufacturing method in which the carbon equivalent (CE) is adjusted to 4.1 to 4.6. According to claim 9,
The method of manufacturing CGI cast iron, wherein the tapping temperature of step (iii) is adjusted to 1510 ± 20 ° C. According to claim 9,
Magnesium added secondarily in step (iv) is magnesium (Mg) in the form of a wire, a method for producing CGI cast iron.

Images