KR20150108129A - Ductile cast iron for hydraulic device, method of preparing the same - Google Patents

Abstract

A spherical graphite cast iron composed of: 3.5-3.8 wt% of C; 2.0-2.4 wt% of Si; 0.2-0.5 wt% of Mn; greater than at least 0 and not more than 0.05 wt% of P; greater than at least 0 and not more than 0.01 wt% of S; 0.01-0.06 wt% of Mg, Cu, Ni; and the balance of Fe. Moreover, a sum of contents of the Cu and the Ni is within a range of 0.5-1.1 wt%, and a content ratio (Ni/Cu) of the Cu and the Nickel is within the range of 0.15-0.8.

Description

TECHNICAL FIELD [0001] The present invention relates to a spherical graphite cast iron for a hydraulic machine, and a manufacturing method thereof. BACKGROUND OF THE INVENTION [0002]

 The present invention relates to spheroidal graphite cast iron for a hydraulic machine and a method of manufacturing the same. More particularly, to a spheroidal graphite cast iron for a hydraulic machine having improved tensile strength and elongation, and a method of manufacturing the same.

Spheroidal graphite cast iron is widely used for casing or housing of hydraulic equipment. In this field, nodular graphite cast iron is required to have excellent tensile strength and elongation. Currently used ductile iron has a tensile strength in the range of about 400 to 800 MPa, but the elongation is inversely proportional to 2 to 20%. That is, the ductility graphite cast iron currently used has a tendency that the tensile strength and the elongation are inversely proportional to each other, and the spheroid graphite cast iron having an excellent tensile strength can cause cracks in use due to low elongation.

In the prior art, an Austempered Ductile Iron (ADI) was formed through an austempering process. The ADI has a microstructure different from conventional pearlite or ferrite, and can have both an improved tensile strength and an elongation at the same time. For example, the ADI can secure physical properties having a tensile strength of 850 MPa or more and an elongation of 8% or more. However, the ADI is not widely used because of the problems that the manufacturing cost increases due to the addition of the above-mentioned tempering process, the workability decreases, and the tensile strength becomes uneven when the thickness of the casting is more than a certain thickness.

Therefore, there is a demand for ductile iron having high tensile strength and high elongation in a state of not undergoing a heat treatment process such as an ashing process (that is, in a state of as-casting).

SUMMARY OF THE INVENTION It is an object of the present invention to provide a spheroidal graphite cast iron having improved tensile strength and elongation, and a method of manufacturing the same, without increasing costs due to an additional heat treatment process such as an Aust tempering process.

To achieve the above object, the spheroidal graphite cast iron for a hydraulic machine according to the present invention is characterized in that an alloy element is added to carbon (C), silicon (Si), manganese (Mn), phosphorus (P) and sulfur (S) (Ni / Cu) at the same time, by controlling the sum of the content of copper (Cu) and the content of nickel (Ni) and the content ratio of copper and nickel (Ni / Cu) to a specific range at the same time to provide a cast iron having high tensile strength and high elongation do. It is possible to satisfy the physical properties required in an as-casting process not subjected to an additional heat treatment process.

The high tensile strength and high elongation ductility graphite cast iron according to the present invention comprises about 3.5 to 3.8 wt% carbon (C), about 2.0 to 2.4 wt% silicon (Si), about 0.2 to 0.5 wt% (Mn), greater than 0 and less than about 0.05 wt% phosphorous (P), greater than 0 and less than about 0.01 wt% sulfur, about 0.01 to 0.06 wt% magnesium (Mg) (Cu), nickel (Ni), and the balance iron (Fe). In addition, the total content of copper (Cu) and nickel (Ni) ranges from 0.5 to 1.1 wt%, and the content ratio of copper to nickel (Ni / Cu) ranges from about 0.15 to 0.8.

According to a preferred embodiment of the present invention, the tensile strength of the spheroidal graphite cast iron is about 682 MPa or more.

According to a preferred embodiment of the present invention, the elongation of the spheroidal graphite cast iron may be about 11% or more.

According to a preferred embodiment of the present invention, the microstructure of the spheroidal graphite cast iron may be composed of about 70 to 90 wt% of pearlite and about 10 to 30 wt% of ferrite.

As described above, the nodular graphite cast iron according to the present invention can have an improved tensile strength and elongation in an as-cast state without undergoing an additional heat treatment such as an os tempering process. Specifically, the spheroidal graphite cast iron may have a high tensile strength of about 682 MPa or more and an elongation of about 11% or more.

FIG. 1 schematically shows an example of a process for producing spheroidal graphite cast iron for a hydraulic machine according to the present invention.
Fig. 2 is a view showing the application position of the as-cast spheroidal graphite cast iron for a hydraulic machine according to the present invention and the sampling position of a test piece for measuring mechanical properties.
Fig. 3 shows the tensile strength and elongation test results of the as-cast spheroidal graphite cast iron for a hydraulic machine according to the present invention.
4 is a sectional view showing an exemplary hydraulic cylinder according to the present invention.

For the embodiments of the invention disclosed herein, specific structural and functional descriptions are set forth for the purpose of describing an embodiment of the invention only, and it is to be understood that the embodiments of the invention may be practiced in various forms, The present invention should not be construed as limited to the embodiments described in Figs.

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

In the present invention, copper and nickel are used as additional components of cast iron, and the content ratio (Cu + Ni) of copper and nickel in the cast iron and the content ratio (Ni / Cu) of copper and nickel are controlled to respective specific ranges .

At this time, the sum of the contents of copper and nickel (Cu + Ni) and the content ratio of copper and nickel (Ni / Cu) are the most important factors for producing the spheroidal graphite cast iron having a tensile strength of 682 MPa or more and elongation of 11% or more. Therefore, the spheroidal graphite cast iron of the present invention is required to be limited to the chemical composition exemplified below.

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

≪ Process for producing spheroidal graphite cast iron &

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a process schematic diagram for explaining a method for producing eutectic graphite cast iron according to exemplary embodiments. Fig. FIG. 2 is a perspective view and a plan view for explaining a position of sampling a test piece of the nodular graphite cast iron according to the exemplary embodiments. FIG.

Referring to FIG. 1, a cast iron material is melted in a melting furnace 100 to produce a first molten metal 110 (step S10).

According to exemplary embodiments, the first molten metal 110 may comprise a cast iron component comprising carbon (C), silicon (Si), manganese (Mn), phosphorus (P), and sulfur (S). Wherein the cast iron component comprises a first molten metal at a weight ratio of about 3.5 to 3.8 wt% carbon (C), about 2.0 to 2.4 wt% silicon (Si), and about 0.2 to 0.5 wt% manganese (Mn) S and P may be inevitably contained in the raw material of the first molten metal 110 and the content of phosphorus P is not more than about 0.05 wt% ) Can be controlled to about 0.01 wt% or less.

According to exemplary embodiments, the first molten metal 110 may further include copper (Cu) and nickel (Ni) as additional components. In one embodiment, the additional component has a composition ratio of copper to nickel (Ni / Ni) of 0.5 to 1.1 wt%, the sum of the contents of copper (Cu) and nickel (Ni) Cu) can have a chemical composition ranging from about 0.15 to about 0.8.

According to one embodiment, the cast iron components and the additional components may be made into a first melt 110. According to another embodiment, the raw molten metal may be prepared as the cast iron component, and the additional molten metal may be separately added to the raw molten metal to produce the first molten metal 110.

According to one embodiment, after preparing a preliminary molten metal and analyzing the composition of the preliminary molten metal through a thermal analyzer or a spectrometer component meter, if there is an insufficient component, the first molten metal 110 ) Can be obtained.

Then, the first molten metal 110 is drained into the ladle 200 (step S20). At the same time as the tapping, the seeding process by the seeding agent 210 and the spheroidizing process by the spheroidizing agent (for example, magnesium) can be performed.

According to exemplary embodiments, the spheronizing agent may include magnesium (Mg), which reacts with sulfur (S) and oxygen (O), which are spheroidizing inhibiting elements, to form molten salt in the form of MgS and MgO The sulfur (S) and oxygen (O) in the graphite can be removed to promote the crystallization of spheroidal graphite.

Accordingly, the second molten metal 120 can be obtained by performing the inoculating step and the spheroidizing step on the first molten metal 110 in the ladle 200 (step S30).

In one embodiment, the second molten metal 120 in the ladle 200 may be subjected to component analysis using a thermal analyzer or a spectrometer component meter to further add the insufficient components. Accordingly, replenishment of the lost ingredient in the tapping process can be performed. In particular, copper (Cu) and nickel (Ni) contents can be precisely controlled. That is, the content of copper (Cu) and nickel (Ni) in the second molten metal 120 is about 0.5-1.1 wt% in the sum of the contents of copper (Cu) and nickel (Ni) And nickel (Ni / Cu) in the range of about 0.15 to 0.8.

Then, the second molten metal 120 inside the ladle 200 is injected into the mold 300 (step S40).

The mold 300 may include an injection part 310 into which the second molten metal 120 is injected and a mold body 320. The injection part 310 and the mold body 320 may be integrally formed.

In one embodiment, an additional inoculation process may be performed in the process of injecting the second molten metal 120 into the mold 300. Accordingly, the second molten metal 120 can be converted into a cast iron melt. The cast iron melt may be introduced into the mold body 320 through the injection path 330.

Thereafter, the cast iron melt is cast in the casting mold body 330 for a predetermined time, and then the final casted graphite cast iron is manufactured through a cooling process. The spheroidal graphite cast iron may have a high tensile strength of at least about 682 MPa and an elongation of at least about 11% without undergoing an additional heat treatment such as an as-casting process, such as an as-casting process.

<Spheroidal graphite cast iron>

The spheroidal graphite cast iron according to the present invention contains about 3.5 to 3.8 wt% of carbon (C), about 2.0 to 2.4 wt% of silicon (Si), about 0.2 to 0.5 wt% of manganese (Mn) (P) greater than 0 and less than about 0.05 wt%, at least greater than 0 and less than about 0.01 wt% sulfur (S), between about 0.01 and 0.06 wt% magnesium (Mg), copper (Cu) Ni) and the balance iron (Fe). It is preferable that the content ratio of copper (Cu) and nickel (Ni) is in the range of about 0.5-1.1 wt% and the content ratio of copper (Cu) and nickel (Ni) Chemical composition.

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

1) carbon (C) 3.5 to 3.8 wt%

Carbon (C) is an element for purifying spherical graphite. When the content of carbon in the spheroidal graphite cast iron according to the present invention is as low as less than about 3.5 wt%, the possibility of shrinkage defect increases and the content of carbon is about 3.8 wt% If it is excessively added in excess, the elongation rate is lowered, so that a spheroidal graphite cast iron having a high elongation can not be obtained. Therefore, in the present invention, the content of carbon (C) is preferably limited to about 3.5 to 3.8 wt%.

2) 2.0 to 2.4 wt% of silicon (Si)

Silicon (Si) increases tensile strength and hardness when added in an optimum ratio with carbon (C). In the spheroidal graphite cast iron according to the present invention, when the content of silicon (Si) is as low as less than about 2.0 wt%, it is impossible to obtain a spheroidal graphite cast iron having a high tensile strength due to a decrease in tensile strength. %, It is impossible to obtain spheroidal graphite cast iron having a high tensile strength by promoting segregation of carbide. Therefore, in the present invention, it is preferable to limit the content of silicon (Si) to about 2.0 to 2.4 wt%.

3) Manganese (Mn) 0.2 to 0.5 wt%

Manganese (Mn) is an element that strengthens the matrix of spheroidal graphite cast iron by densely interlayer spacing in pearlite. However, when the content of manganese (Mn) is over 0.5 wt%, the effect of stabilizing the carbide is greater than that of the base strengthening effect, so that the elongation rate is lowered. When the content is less than about 0.2 wt% It is hard to get. Therefore, in the present invention, the content of manganese (Mn) is preferably limited to about 0.2 to 0.5 wt%.

4) phosphorus (P) not more than 0.05wt%, sulfur (S) not more than 0.01wt%

Phosphorus (P) and sulfur (S) may be included in the raw material of the nodular graphite cast iron or may be added naturally in the cast iron manufacturing process. When the content of the graphite exceeds a certain level, the spheroidization of the graphite may be hindered or the elongation of the spheroidal graphite cast iron may be lowered. Therefore, in the present invention, it is preferable to control the content of phosphorus (P) to about 0.05 wt% or less and limit the content of sulfur (S) to about 0.01 wt% or less. At this time, the lower limit of the content of phosphorus (P) and sulfur (S) may exceed 0 wt%.

5) 0.01 to 0.06 wt% of magnesium (Mg)

Magnesium (Mg) plays a role in neutralizing the graphite shape. When the magnesium (Mg) content exceeds about 0.06 wt%, excessive addition increases the tensile strength by promoting dross defects. On the other hand, when the content of magnesium is less than about 0.01 wt%, it is difficult to obtain a spheroidizing effect of graphite. Therefore, in the present invention, the content of magnesium (Mg) is preferably limited to about 0.01 to 0.06 wt%.

6) Copper (Cu) and nickel (Ni)

Copper (Cu) is a base strengthening element of ductile iron. It accelerates the pearlite formation and makes it fine and improves the hardenability. Therefore, it is an element necessary for securing strength. On the other hand, nickel (Ni) is also an element for reinforcing pearlite as a matrix strengthening element of ductile graphite cast iron to improve the base of spheroidal graphite cast iron. That is, when the sum of the contents of copper (Cu) and nickel (Ni) is lower than a specific value, the effect of strengthening the tensile strength can not be obtained and the sum of the contents of copper (Cu) and nickel (Ni) If it exceeds, elongation becomes low. Therefore, the total content of copper (Cu) and nickel (Ni) ranges from about 0.5 to 1.1 wt%, and the content ratio of copper (Cu) to nickel (Ni) .

7) Iron (Fe)

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

Below, a comparison is made between Examples 1 to 5 and Comparative Examples 1 to 5, and the conditions for the spheroidal graphite cast iron according to the present invention to simultaneously satisfy the improved tensile strength and elongation are described.

&Lt; Example 1-5 and Comparative Example 1-5 >

Spheroidal 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. Thereafter, as shown in FIG. 2, test pieces were taken from the upper part of the product of the spheroidal graphite cast iron for hydraulic machine to measure tensile strength and elongation.

[Table 1]

First, a raw tea containing carbon (C), silicon (Si), manganese (Mn), phosphorus (P) and sulfur (S) was prepared according to the composition shown in Table 1. The content of phosphorus (P) is controlled to be about 0.05 wt% or less and sulfur (S) is not added separately in the case of phosphorus (P) and sulfur (S) but used as impurities contained in raw materials for casting, ) Was adjusted to about 0.01 wt% or less.

Copper (Cu), nickel (Ni), manganese (Mn), and the like were added and adjusted to the composition shown in Table 1 above.

Examples 1 to 5 and Comparative Examples 1 to 5 prepared according to the composition of Table 1 were measured for tensile strength and elongation, respectively, and are shown in Table 2 and FIG. 3, respectively.

 [Table 2]

As shown in Table 2 and FIG. 3, the content ratio (Ni / Cu) of nickel to copper is in the range of 0.15 to 0.8, and the content of copper (Cu) and the content of nickel It was confirmed that the spheroidal graphite cast iron according to Examples 1 to 5, in which the sum (Cu + Ni) was adjusted in the range of 0.5 to 1.1 wt%, had a tensile strength of about 682 MPa or more and an elongation of about 11% or more.

In Comparative Examples 2 and 4, the content and manufacturing process of the composition of Example are the same, but the content ratio (Ni / Cu) of Ni to Cu is less than 0.15 or more than 0.8, Is out of the range of the composition.

In Comparative Example 3, the content ratio (Ni / Cu) of the sum (Cu + Ni) and the content of nickel (Ni) to copper (Cu) , Which is an example deviating from the composition range of the present invention.

In Comparative Examples 1 and 5, the content ratio of nickel (Ni) to copper (Ni / Cu) corresponds to the composition of the present invention, but the sum of the content of copper (Cu) and the content of nickel (Ni) + Ni) is outside the composition range of the present invention.

The spheroidal graphite cast iron according to Comparative Examples 1 to 5 had a tensile strength of less than about 682 MPa or an elongation of less than about 11%.

As a result, since the spheroidal graphite cast iron for a hydraulic machine according to the present invention has both stable tensile strength and elongation, it can be applied to parts for hydraulic machines which require a high tensile strength of 682 MPa or more and an elongation of 11% or more have.

<Hydraulic Cylinder>

4 is a sectional view showing an exemplary hydraulic cylinder according to the present invention.

Referring to FIG. 4, the hydraulic cylinder may include a cylinder housing 10, a front cover 14, a piston 20, and a cylinder rod 30.

In the exemplary embodiments, the front cover 14 may seal the inner diameter 12 of the cylinder housing 10. [ The piston 20 is movably disposed in the inner diameter 12 of the cylinder housing 10 and the inner diameter 12 can be divided into a first chamber 12a and a second chamber 12b. The cylinder rod 30 is connected to the piston 20 and can extend to the outside of the cylinder housing 10 through the front cover 14. [

The hydraulic cylinder can work mechanically while stretching and contracting by the operating fluid that goes in and out. At this time, the cylinder housing 10 may be made of a metal material having high strength. Since the piston 20 is in frictional contact with the inner wall of the cylinder housing 10, the piston 20 is made of a material that is softer than the cylinder housing 10 so as not to generate scratches on the wall of the inner diameter 12 of the cylinder housing 10 . On the other hand, since the cylinder rod 30 receives many impact loads and banding loads in the course of mechanical work, it has a high-strength material so as not to be bent or damaged by the impact load and the banding load. Particularly, It can have high resistance and high toughness.

In the exemplary embodiments, the cylinder housing 10 may be composed of a spherical graphite cast iron in a state of being formed by the above-mentioned manufacturing method. The spheroidal graphite cast iron may have excellent elongation and tensile strength without an additional heat treatment process. Therefore, the hydraulic cylinder can have excellent reliability and mechanical stability.

In the exemplary embodiments, the spheroidal graphite cast iron may be used not only in hydraulic cylinders but also in other hydraulic devices such as hydraulic pumps, hydraulic motors, hydraulic valves, oil tanks, and the like.

Claims (7)

(C), 2.0 to 2.4 wt% of silicon (Si), 0.2 to 0.5 wt% of manganese (Mn), at least 0 and 0.05 wt% or less of phosphorus P), a total of at least 0 and 0.01 wt% or less of sulfur (S), 0.01 to 0.06 wt% of magnesium (Mg), and a content of copper (Cu) and nickel (Ni) A spheroidal graphite cast iron for a hydraulic machine, comprising copper (Cu), nickel (Ni), and balance iron (Fe) having a content ratio (Ni / Cu) of copper (Cu) to nickel (Ni / Cu) of 0.15 to 0.8.  The spheroidal graphite cast iron for a hydraulic machine according to claim 1, which has a tensile strength of 682 MPa or more.  The spheroidal graphite cast iron for a hydraulic machine according to claim 1, wherein the elongation is at least 11%  The spheroidal graphite cast iron for a hydraulic machine according to claim 1, wherein the microstructure of the spheroidal graphite cast iron is composed of 70 to 90 wt% of pearlite and 10 to 30 wt% of ferrite.  A component material for a hydraulic machine comprising the spheroidal graphite cast iron of any one of claims 1 to 4. (C), 2.0 to 2.4 wt% of silicon (Si), 0.2 to 0.5 wt% of manganese (Mn), at least 0 and 0.05 wt% or less of phosphorus P), a total of at least 0 and 0.01 wt% or less of sulfur (S), 0.01 to 0.06 wt% of magnesium (Mg), and a content of copper (Cu) and nickel (Ni) A method for manufacturing a cast iron casting machine, comprising the steps of: preparing a cast iron melt containing copper (Cu), nickel (Ni) and a residual amount of iron (Fe) having a content ratio (Ni / Cu) of copper (Cu) to nickel (Ni / Cu)
Tapping the cast iron melt onto a ladle; And
And injecting the molten cast iron into the prepared mold. &Lt; RTI ID = 0.0 &gt; 8. &lt; / RTI &gt; 7. The method of claim 6, further comprising the step of casting the molten cast iron into a prepared mold, and then cooling the molten cast iron to produce as-cast spheroidal graphite cast iron,
Wherein the as-cast spheroidal graphite cast iron satisfies a tensile strength of 682 MPa or more and an elongation of 11% or more.

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