KR20140061165A - Nodular graphite cast iron with high strength and high toughness and parts of an automobile manufactured from the same - Google Patents

Abstract

The present invention relates to nodular graphite cast iron comprising 3.2-3.8 wt% of carbon (C), 2.6-3.3wt% of silicon (Si), 0.1-0.5 wt% of manganese (Mn), 0.4-0.8 wt% of copper (Cu), 0.001-0.03 of wt% tin (Sn), 0.001-0.03 wt% of bismuth (Bi), unavoidable impurities, and remaining amount of iron (Fe) and to parts of automobile manufactured from the same.

Description

TECHNICAL FIELD [0001] The present invention relates to a high-strength and high-strength spheroidal graphite cast iron, and an automobile part manufactured from the same. BACKGROUND ART < RTI ID = 0.0 >

The present invention relates to spheroidal graphite cast iron and automobile parts made therefrom. More specifically, the present invention relates to a non-heat-treated spheroidal graphite cast iron, which can control the element content of an alloy component to ensure high strength and toughness, and an automobile component made therefrom.

Car knuckles / carriers are usually made of cast iron or aluminum. In particular, small and medium-sized vehicles use low-cost spheroidal graphite cast iron.

For this purpose, high strength ductile iron (eg, Austenitic spheroidal graphite cast iron, ADI) through heat treatment and high strength normal spheroidal graphite cast iron with GCD 700-800 grade through control of components and process conditions in non-heat treated state are used. However, high-strength spheroidal graphite cast iron through heat treatment may be accompanied by an increase in cost due to heat treatment and poor workability due to high hardness. In addition, GCD 700-800 non-heat treated high-strength cast iron may have poor elongation at 2% elongation.

In this connection, Korean Patent No. 10-0325125 (filed on Mar. 02, 2002, entitled Heat-resistant spheroidal graphite cast iron and its heat treatment method) has a heat resistance, abrasion resistance and oxidation resistance, C: 2.2-3.8 weight % Of Si, 3.0-5.5% of Si, 1.0% or less of Mn, 0.5% or less of Ni, 0.5% or less of Cr, 0.01-6.0% or less of W and 3.0% or less of Mo, Discloses a spheroidal graphite cast iron in which Fe, inevitable impurities, or a composite of Mg, Zr, Bi and rare earth elements added for spheroidization of graphite are each added or added in a total amount of 0.001-0.6 wt%.

An object of the present invention is to provide a spheroidal graphite cast iron having high tensile strength and yield strength and high elongation.

Another object of the present invention is to provide a spheroidal graphite cast iron which is high in light weight effect and stability and can secure toughness.

It is still another object of the present invention to provide an automobile part made of the above-described spheroidal graphite cast iron.

In order to solve the above problems, the spheroidal graphite cast iron according to one aspect of the present invention is a spheroidal graphite cast iron containing 3.2-3.8 wt% of carbon (C), 2.6-3.3 wt% of silicon (Si) (Cu), 0.4-0.8 wt.% Of tin (Sn), 0.001-0.03 wt.% Of bismuth (Bi), 0.001-0.03 wt.% Of bismuth and unavoidable impurities and balance iron (Fe).

The bismuth (Bi) may be contained in an amount of 0.01-0.02 wt%.

The spheroidal graphite cast iron may further contain 0.015-0.04% by weight of magnesium (Mg), 0.004-0.01% by weight of phosphorus (P), and 0.001-0.004% by weight of sulfur (S).

The spheroidal graphite cast iron may have a tensile strength of 700 MPa or more, a yield strength of 420 MPa or more, and an elongation of 7% or more.

Another aspect of the present invention is a method for producing ductile iron which comprises the steps of: 3.2-3.8% by weight of carbon (C), 2.6-3.3% by weight of silicon (Si), 0.1-0.5% by weight of manganese (Mn) (Fe) in an amount of 0.001-0.03 wt.%, Tin (Sn) 0.001-0.03 wt.%, Bismuth (Bi) 0.001-0.03 wt.% And unavoidable impurities and the balance of iron RTI ID = 0.0 > 90 minutes < / RTI > in a mold.

An automotive part, which is another aspect of the present invention, can be made of the spheroidal graphite cast iron.

According to the embodiment of the present invention, a spheroidal graphite cast iron having high tensile strength and yield strength and high elongation is provided. In addition, it provides a ductile graphite cast iron which is high in light weight effect and stability, can secure robustness, and can secure the robustness of noise, vibration, and hardness (NVH) of automobile.

The spheroidal graphite cast iron, which is one aspect of the present invention, is spherical graphite cast iron which is composed of 3.2-3.8 wt% of carbon (C), 2.6-3.3 wt% of silicon (Si), 0.1-0.5 wt% of manganese (Fe) of 0.4-0.8 wt% of copper (Cu), 0.001-0.03 wt% of tin (Sn), 0.001-0.03 wt% of bismuth (Bi) and unavoidable impurities and balance.

Hereinafter, each element in the spheroidal graphite cast iron of the present invention will be described in detail.

Carbon (C) exists mainly as spherical graphite particles in spheroidal graphite cast iron and can improve mechanical properties such as strength, elongation and impact properties as compared with long ribbon-shaped cast graphite existing in gray cast iron.

The carbon (C) may be included in the spheroidal graphite cast iron in an amount of 3.2-3.8 wt%, preferably 3.3-3.6 wt%, more preferably 3.48-3.50 wt%. If the carbon (C) content is less than 3.2% by weight, the elongation of the cast iron is less than 7%, and desired properties can not be obtained. When the carbon (C) content exceeds 3.8% by weight, the steel has low tensile strength and yield strength and can not be used as cast iron.

In the spheroidal graphite cast iron, graphite may have an average particle size of 10 탆 or less, preferably 7-9 탆.

Silicon (Si) is a basic alloy element that forms a matrix structure in spheroidal graphite cast iron.

Silicon (Si) may be included in 2.6-3.3 wt%, preferably 2.7-2.9 wt%, and more preferably 2.74-2.9 wt% of the spheroidal graphite cast iron. When the silicon (Si) content is less than 2.6% by weight, the elongation is less than 7% and desired physical properties can not be obtained. When the silicon (Si) content exceeds 3.3% by weight, the oxidation resistance is poor and the fracture toughness and impact properties may be deteriorated.

Manganese (Mn) is added as a pearlite promoting element for strength improvement in spheroidal graphite cast iron. The manganese (Mn) may be contained in an amount of 0.1-0.5 wt%, preferably 0.3-0.4 wt%, more preferably 0.3-0.33 wt%. If the manganese (Mn) content is less than 0.1% by weight, impurities due to sulfur (S) may cause deterioration of properties and tissue instability. If the manganese (Mn) content is more than 0.5% by weight, there is no strength / texture effect, and an increase in cost occurs.

Copper (Cu) has an aging property and can increase strength and hardness.

Copper (Cu) may be included in an amount of 0.4-0.8 wt%, preferably 0.4-0.5 wt%, more preferably 0.45-0.50 wt%, and most preferably 0.45-0.47 wt%. When copper (Cu) is less than 0.4% by weight, tensile strength, yield strength, and elongation may be poor. When the content of copper (Cu) exceeds 0.8% by weight, tensile strength and yield strength may be poor.

Tin (Sn) may be included in the spheroidal graphite cast iron at 0.001-0.03 wt%, preferably 0.005-0.015 wt%, more preferably 0.005-0.011 wt%, and most preferably 0.008-0.011 wt%. When the amount of tin (Sn) is less than 0.001% by weight, it is not easy to manage due to the characteristics of the extruded material using scrap, and the instability of the material due to carelessness may result. When tin (Sn) is contained in an amount exceeding 0.03% by weight, the tensile and yield strength may be increased, but there may be a problem of causing a decrease in elongation.

Bismuth (Bi) plays a role in improving the shape of graphite and improving the elongation in spherical graphite cast iron containing carbon (C), silicon (Si), copper (Cu), manganese (Mn) and tin do. Bismuth (Bi) may be contained in 0.001-0.03% by weight, preferably 0.005-0.02% by weight, more preferably 0.01-0.02% by weight of the spheroidal graphite cast iron. When the bismuth (Bi) content is less than 0.001% by weight, tensile strength, yield strength, or elongation may be poor. When bismuth (Bi) is contained in an amount of more than 0.03% by weight, it is possible to promote the formation of carbides and undesirable graphite structures which degrade tensile properties.

The spherical cast iron alloy of the present invention may further contain magnesium (Mg), phosphorus (P) and sulfur (S) in addition to the above-described components. These elements can promote graphitic spheroidization in a core alloy composed of carbon (C), sulfur (Si), manganese (Mn), copper (Cu), tin (Sn) and bismuth (Bi). Magnesium (Mg) may be contained in an amount of 0.015% by weight or more, preferably 0.015-0.05% by weight. The phosphorus (P) may be contained in an amount of 0.05% by weight or less, preferably 0.001-0.01% by weight. Sulfur (S) may be included in an amount of 0.05% by weight or less, preferably 0.001-0.01% by weight.

The spheroidal graphite cast iron of the present invention can attain a tensile strength of 700 MPa or more, a yield strength of 420 MPa or more, and an elongation of 7% or more. Preferably, the tensile strength is 700-850 MPa, the yield strength is 450-490 MPa, and the elongation is 9.0-10.5%.

The spheroidal graphite cast iron of the present invention can be used as a chassis component material for automobile knuckles / carriers and the like, but is not limited thereto.

Another aspect of the present invention is a method for producing ductile graphite cast iron which comprises, by weight, spherical graphite cast iron containing 3.2-3.8 wt% of carbon (C), 2.6-3.3 wt% of silicon (Si) (Fe) in an amount of 0.001-0.03% by weight, copper (Cu) in an amount of 0.4-0.8% by weight, tin (Sn) in an amount of 0.001-0.03% by weight, bismuth (Bi) in an amount of 0.001-0.03% by weight and unavoidable impurities and balance And the like.

Methods of making spheroidal graphite cast iron by specific heat treatment are known to those skilled in the art. For example, injecting the melt of the composition at 1350-1500 C and cooling in a mold for 45-90 minutes may be included.

An automotive part, which is another aspect of the present invention, can be made of the above-mentioned spheroidal graphite cast iron. The automotive part is not limited, but may be, for example, an automobile knuckle / carrier, but is not limited thereto.

Hereinafter, the structure and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

Example  1-2 and Comparative Example  1-4

The composition and the remaining amount of Fe shown in the following Table 1 were mixed and the melt was injected at 1350-1500 占 폚 using an electric furnace (silicon and bismuth-based inoculation), and the casting was performed in a mold for 45-90 minutes to prepare cast iron .

C Si Mn Cu Sn Bi Mg P S Example 1 3.48 2.90 0.33 0.46 0.011 0.01 0.04 0.010 0.004 Example 2 3.50 2.74 0.30 0.46 0.008 0.02 0.04 0.004 0.001 Comparative Example 1 3.86 2.80 0.30 0.08 0.010 - 0.04 0.004 0.001 Comparative Example 2 2.82 2.36 0.27 0.54 0.008 0.01 0.04 0.020 0.003 Comparative Example 3 3.55 2.60 0.45 0.33 0.007 0.01 0.05 0.030 0.010 Comparative Example 4 3.79 2.75 0.32 0.12 0.042 - 0.04 0.030 0.001

Tensile strength, yield strength and elongation were measured for the alloy thus prepared by a conventional method, and the results are shown in Table 2 below.

Tensile Strength (MPa) Yield strength (MPa) Elongation (%) Example 1 781 485 10.4 Example 2 806 454 9.0 Comparative Example 1 580 372 14.0 Comparative Example 2 865 489 6.2 Comparative Example 3 650 470 9.0 Comparative Example 4 728 492 3.0

As shown in Table 2, the spheroidal graphite cast iron of the present invention may have a tensile strength of 700 MPa or more, a yield strength of 420 MPa or more, and a elongation of 7% or more.

On the other hand, in Comparative Example 1-4 in which the content of carbon (C), silicon (Si), copper (Cu), tin (Sn) and bismuth (Bi) in the spheroidal graphite cast iron of the present invention deviates, Tensile strength or elongation was not good.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (6)

The spheroidal graphite cast iron is characterized in that it contains 3.2-3.8 wt% of carbon (C), 2.6-3.3 wt% of silicon (Si), 0.1-0.5 wt% of manganese (Mn), 0.4-0.8 wt% of copper (Cu) 0.001-0.03% by weight of bismuth (Bi), 0.001-0.03% by weight of bismuth, and iron (Fe) of unavoidable impurities and balance.
The spheroidal graphite cast iron according to claim 1, wherein the bismuth (Bi) is contained in an amount of 0.01-0.02 wt%.
The spheroidal graphite cast iron according to claim 1, wherein the spheroidal graphite cast iron further contains 0.015-0.04% by weight of magnesium (Mg), 0.004-0.01% by weight of phosphorus (P), and 0.001-0.004% by weight of sulfur (S).
The spheroidal graphite cast iron according to claim 1, wherein the spheroidal graphite cast iron has a tensile strength of 700 Mpa or more, a yield strength of 420 MPa or more, and an elongation of 7% or more.
(Si) 2.6-3.3 wt.%, Manganese (Mn) 0.1-0.5 wt.%, Copper (Cu) 0.4-0.8 wt.%, Tin (Sn) 0.001-0.03 wt.%, (Ii) 0.001-0.03 wt.% Of bismuth (Bi) and iron (Fe) of unavoidable impurities and the balance iron is injected at 1350-1500 ° C and cooled in a mold for 45-90 minutes Wherein the graphite cast iron is produced by a method comprising the steps of:
An automotive part made of the spheroidal graphite cast iron according to any one of claims 1 to 4.