JP2002371335A - Heat-resistant spherical cast graphite iron for exhaust part superior in oxidation resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-resistant spherical cast graphite iron for exhaust parts superior in oxidation resistance, which can prevent oxidation under a high-temperature condition and control increase of wall thickness caused by the oxidation. SOLUTION: The heat-resistant spherical cast graphite iron for exhaust parts superior in oxidation resistance, includes 2.5-41 wt.% C, 3.4-5.0 wt.% Si, 1.0 wt.% or less Mn, 0.1 wt.% or less P, 0.01 wt.% or less S, 0.02-0.10 wt.% Mg, 0.1-1.5 wt.% Mo, 0.5-2.0 wt.% Ni, and the balance Fe with unavoidable impurities, and has a matrix including mainly ferrite phase. The method for manufacturing the heat-resistant spherical cast graphite iron is characterized by adding a very small quantity of nickel to a high-silicon spherical cast graphite iron. Then, the addition prevents the iron from being oxidized under a high- temperature condition, and greatly reduces increment of wall thickness caused by the oxidation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant spheroidal graphite cast iron for exhaust system components having excellent oxidation resistance under high-temperature operating conditions, and for example, for a turbine housing or an exhaust manifold which is an exhaust system component of an automobile. It can be suitably used.

[0002]

2. Description of the Related Art As is well known, austenitic high nickel spheroidal graphite cast iron (Niresist) containing a large amount of nickel (Ni) is generally widely used as heat-resistant spheroidal graphite cast iron having excellent oxidation resistance for exhaust system components. Have been. But,
Such a high nickel spheroidal graphite cast iron contains expensive nickel in an amount of about 20 to 35% by weight, and thus has a problem in cost.

[0003] Conventionally, high silicon spheroidal graphite cast iron having a base structure mainly composed of a ferrite phase has attracted attention as a heat-resistant spheroidal graphite cast iron having excellent oxidation resistance for inexpensive exhaust system components. This high silicon spheroidal graphite cast iron is obtained by increasing the silicon content (for example, about 2.5% by weight) of general spheroidal graphite cast iron to about 3.5 to 5.5% by weight.

[0004] By the way, the above-mentioned heat-resistant spheroidal graphite cast iron having excellent oxidation resistance for exhaust system components has a high temperature (for example, 8%).
(00 ° C.) may be employed as a material for a turbocharger turbine housing, an exhaust manifold, or the like of an automobile exhaust system component used under severe conditions of (00 ° C.). Here, the turbocharger rotates the turbine by applying exhaust gas flowing through the turbine housing to the turbine blades, and compresses intake air (intake air) by driving an air compressor through the turbine.
By supplying the compressed high-density intake air to the engine, the output of the engine is increased.
In this turbocharger, a minute clearance (for example, 0.5 mm) is set between the inner peripheral surface of the turbine housing and the turbine blade, and the function of the turbine is sufficiently exhibited by the clearance. ing.

[0005]

However, the heat-resistant spheroidal graphite cast iron (high silicon spheroidal graphite cast iron) for exhaust system components according to the prior art described above does not sufficiently suppress the oxidation under high-temperature use conditions. Therefore, there is a possibility that the amount of increase in wall thickness due to the above will be excessive. In particular, in the case where the turbine housing is formed of heat-resistant spheroidal graphite cast iron for exhaust system components according to the prior art, if the increase in the thickness of the turbine housing due to oxidation becomes excessive (for example, 0.5 mm or more). In addition, there is a possibility that the inner peripheral surface of the turbine housing and the turbine blades interfere with each other to make the turbine unrotatable, so that the function of the turbine and eventually the turbocharger cannot be exhibited. In addition, due to the excessive increase in wall thickness due to oxidation of the turbine housing and exhaust manifold made of heat-resistant spheroidal graphite cast iron for exhaust system components according to the prior art, the flow state of exhaust gas flowing inside the turbine housing and the exhaust manifold, etc. There was also a risk of adversely affecting

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to suppress oxidation under a use condition at a high temperature and to suppress an increase in wall thickness due to the oxidation. It is an object of the present invention to provide a heat-resistant spheroidal graphite cast iron for an exhaust system component having excellent oxidation resistance.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above-mentioned circumstances, and as a result, by adding a small amount of nickel to high silicon spheroidal graphite cast iron, the use conditions at high temperatures It has been found that the oxidation suppression effect underneath is significantly improved over that of the high silicon spheroidal graphite cast iron according to the prior art. Reached.

That is, the heat-resistant spheroidal graphite cast iron having excellent oxidation resistance for exhaust system components according to the first aspect of the present invention has a hardness of 2.5%.
~ 4.1 wt% C, 3.4-5.0 wt% Si,
1.0% by weight or less of Mn, 0.1% by weight or less of P,
01% by weight or less of S, 0.02 to 0.10% by weight of M
g, containing 0.1 to 1.5% by weight of Mo and 0.5 to 2.0% by weight of Ni, with the balance being Fe and unavoidable impurities, and the base structure being mainly composed of a ferrite phase. And

Here, the reason why C is set to be 2.5 to 4.1% by weight is that when C is less than 2.5% by weight, it becomes difficult for C to be graphitized, (Fluidity of molten metal) may be deteriorated, and C is 4.1.
If the amount exceeds 10% by weight, the CE value (C + ／ Si) becomes high, and dross may be easily generated.

The reason for setting the Si content to be 3.4 to 5.0% by weight is that when the Si content is less than 3.4% by weight, the heat resistance of the heat-resistant spheroidal graphite cast iron for exhaust system components is reduced. If the content of Si exceeds 5.0% by weight, the ferrite phase of the base structure becomes brittle, and cracks or the like may occur in the heat-resistant spheroidal graphite cast iron for exhaust system components. Because.

Further, the reason why Mn is set to 1.0% by weight or less is that if Mn exceeds 1.0% by weight, a large amount of pearlite phase is formed in heat-resistant spheroidal graphite cast iron for exhaust system parts. This is because there is a danger.

The reason why P is set to 0.1% by weight or less is that if P is more than 0.1% by weight, there is a possibility that sturdite is formed and becomes brittle, and S is 0.01% by weight. The reason for setting below is that if S is more than 0.01% by weight, the spheroidization rate of graphite is deteriorated, and the toughness may be deteriorated.

In addition, 0.02 to 0.10% by weight of Mg
The reason is that if Mg is less than 0.02% by weight, the spheroidization rate of graphite may be deteriorated and toughness may be deteriorated. If Mg exceeds 0.10% by weight, This is because a casting defect such as a pinhole may easily occur.

The reason for setting Mo to be 0.1 to 1.5% by weight is that when Mo is less than 0.1% by weight,
The heat resistance of the heat-resistant spheroidal graphite cast iron for exhaust system parts may be insufficient, and if Mo exceeds 1.5% by weight, Mo carbides may be generated and the toughness may be deteriorated. It is.

Furthermore, the reason why Ni is set to be 0.5 to 2.0% by weight is that when Ni is less than 0.5% by weight, the heat-resistant spheroidal graphite cast iron for exhaust system parts at high temperatures is used. There is a possibility that the effect of suppressing oxidation under use conditions may be reduced, and if Ni exceeds 2.0% by weight, a structure other than the ferrite phase may be easily generated and the cost may be increased. It is.

According to the first aspect of the present invention, the steel contains the predetermined amounts of C, Si, Mn, P, S, Mg, Mo, and Ni, and the balance is made of Fe and unavoidable impurities. Since it is a heat-resistant spheroidal graphite cast iron for exhaust system components mainly composed of a ferrite phase, the oxidation of the heat-resistant spheroidal graphite cast iron under high-temperature use conditions is suppressed, and the heat-resistant spheroidal graphite cast iron is caused by the oxidation. The amount of increase in thickness is suppressed.

When the turbine housing of the turbocharger is formed of the heat-resistant spheroidal graphite cast iron for exhaust system components having excellent oxidation resistance according to the first aspect, the wall thickness of the turbine housing increases due to oxidation. Since the amount is suppressed, the inner peripheral surface of the turbine housing and the turbine blade do not interfere with each other during rotation of the turbine, and the function of the turbine, and eventually the turbocharger, can be sufficiently exhibited.

Further, when the heat-resistant spheroidal graphite cast iron for exhaust system parts is improved in oxidation resistance, when the heat-resistant spheroidal graphite cast iron is used as a material for a turbine housing or an exhaust manifold, unlike the conventional technology, the turbine housing And the exhaust gas flowing through the inside of the exhaust manifold and the like may be adversely affected.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The components of the heat-resistant spheroidal graphite cast iron having excellent oxidation resistance according to the present invention for exhaust system components include iron (Fe) as a main component and carbon of 2.5 to 4.1% by weight. (C),
3.4-5.0% by weight of silicon (Si), 1.0% by weight
Manganese (Mn) below, phosphorus (P) not more than 0.1% by weight, sulfur (S) not more than 0.01% by weight,
0.10% by weight of magnesium (Mg), 0.1-1.
5% by weight molybdenum (Mo), 0.5-2.0% by weight
Nickel (Ni), and a very small amount of unavoidable impurities. Mg in the heat-resistant spheroidal graphite cast iron is used as a spheroidizing agent (an additive for crystallizing graphite in cast iron into spheres).

In heat-resistant spheroidal graphite cast iron,
0-3.6 wt% C, 4.0-4.6 wt% Si,
It is preferable to contain 0.1 to 1.0% by weight of Mo and 0.6 to 1.8% by weight of Ni. In particular, the content of nickel in the heat-resistant spheroidal graphite cast iron is more preferably 0.7 to 1.5% by weight, and more preferably 0.8 to 1.3% by weight, and 0.9 to 1.5% by weight.
1.2% by weight, more preferably 1.0 to 1.1% by weight.

In the heat-resistant spheroidal graphite cast iron according to the present invention, the matrix structure is mainly composed of a ferrite phase, and the high silicon spheroidal graphite cast iron according to the prior art contains a trace amount (predetermined amount) of nickel. A heat-resistant spheroidal graphite cast iron having excellent oxidation resistance for exhaust system components can be obtained. This heat-resistant spheroidal graphite cast iron has heat resistance enough to withstand high-temperature use conditions of 800 ° C., and can be used as a material for a turbine housing or an exhaust manifold of a turbocharger, which is an exhaust system part of an automobile.

[0022]

Examples Examples of the present invention and Comparative Examples 1 and 2 according to the prior art will be described below.

First, three types of heat-resistant spheroidal graphite cast irons for exhaust system components containing predetermined amounts of chemical components shown in Table 1 were obtained by casting. Although not explicitly shown in Table 1 as a chemical component, it goes without saying that heat-resistant spheroidal graphite cast iron contains Fe as its main component. The obtained heat-resistant spheroidal graphite cast iron is length 50 mm × width 50 mm × wall thickness 5 mm.
To form test pieces of Example, Comparative Example 1 and Comparative Example 2. The test piece of the example is the heat-resistant spheroidal graphite cast iron according to the present invention, and the test pieces of the comparative examples 1 and 2 are the heat-resistant spheroidal graphite cast iron (high silicon spheroidal graphite cast iron) according to the prior art.

Then, the graphite spheroidization rate and the pearlite rate of each test piece were investigated, and the results are shown in Table 1. The “spheroidization ratio” in Table 1 is a graphite spheroidization ratio, and is a numerical value that quantitatively indicates the spheroidization of graphite in heat-resistant spheroidal graphite cast iron. That is, the higher the numerical value of the spheroidization ratio, the greater the degree of spheroidization of graphite in the heat-resistant spheroidal graphite cast iron. The “pearlite ratio” in Table 1 indicates the ratio of the pearlite phase to the structure when the area of the entire base structure excluding graphite is 100%, and the remainder of the structure is the ferrite phase. Therefore, the smaller the pearlite ratio, the more ferrite phase is present in the matrix structure.

As shown in Table 1, in the examples, the spheroidization ratio of graphite was 82%, and the pearlite ratio was 14%. In Comparative Example 1, the spheroidization ratio of graphite was 82%, and the pearlite ratio was 7%. Further, in Comparative Example 2, the graphite spheroidization ratio was 84%, and the pearlite ratio was 6%. From the above, it can be seen that the heat-resistant spheroidal graphite cast iron of the present example has a slightly higher pearlite rate and a substantially equal graphite spheroidization rate as compared with the comparative example.
There is no difference in that the base structure is mainly composed of the ferrite phase and the graphite is spherical.

Micrographs (magnification: 100 times) of each test piece were taken to observe the structure of each test piece, and the micrographs are shown in FIGS. 2 shows a micrograph of the example, FIG. 3 shows a micrograph of Comparative Example 1, and FIG. 4 shows a micrograph of Comparative Example 2. Figure 2
In the micrograph shown in FIG. 4, the black spherical portion represents graphite, the gray portion represents a ferrite phase, and the striped black portion represents a pearlite phase. From FIG. 2 to FIG. 4 and Table 1, it was confirmed that in the three types of heat-resistant spheroidal graphite cast irons of the present example, comparative example 1, and comparative example 2, the base structure was mainly composed of a ferrite phase, and the graphite was spheroidized. did it.

[0027]

【table 1】

The test pieces of Example, Comparative Example 1, and Comparative Example 2 were heated in air at a temperature of 800 ° C. and kept at that temperature for 100 hours to perform an oxidation test. Then, let each test piece cool down to room temperature,
The thickness increase of each test piece was investigated. The result is shown in FIG.

As shown in FIG. 1, the thickness increase of the test piece of this embodiment is 0.09 mm, and the thickness increase of the test piece of Comparative Example 1 is 0.52 mm. The thickness increase of the test piece No. 2 was 0.43 mm. From the comparison between the example and Comparative Examples 1 and 2, it was confirmed that the increase in the thickness of the test piece of the present example was significantly reduced. That is, it can be said that the oxidation suppressing effect of the present embodiment under the high temperature use condition is significantly improved compared with the oxidation suppression effect of the comparative examples 1 and 2 under the high temperature use condition.

In addition, when the embodiment and the comparative example 2 were compared, a great difference between the chemical components of the two was due to the difference in whether or not nickel was contained.
Of high silicon spheroidal graphite cast iron (0.99 in this example)
(% By weight) of nickel, the effect of suppressing oxidation under high-temperature use conditions was significantly improved.

[0031]

According to the first aspect of the present invention, the oxidation of heat-resistant spheroidal graphite cast iron for exhaust system components under high-temperature operating conditions can be suppressed, and the thickness of the heat-resistant spheroidal graphite cast iron caused by the oxidation can be suppressed. The amount of increase in thickness can be suppressed. In addition, when the turbine housing of the turbocharger is formed of the heat-resistant spheroidal graphite cast iron having excellent oxidation resistance of the present invention, an increase in the thickness of the turbine housing caused by oxidation can be suppressed, so that the rotation of the turbine during rotation of the turbine can be suppressed. Interference between the inner peripheral surface of the turbine housing and the turbine blades can be prevented,
The function of the turbine, and eventually the turbocharger, can be fully exhibited. Further, by improving the oxidation resistance of the heat-resistant spheroidal graphite cast iron of the present invention, when the heat-resistant spheroidal graphite cast iron is used as a material for a turbine housing or an exhaust manifold, unlike the case of the prior art, the inside of the turbine housing or the exhaust manifold is different. Can be less likely to have an adverse effect on the state of flow of the exhaust gas flowing through the fuel cell.

[Brief description of the drawings]

FIG. 1 is a graph showing the thickness increase (mm) of each test piece after heating and holding in Examples according to the present invention and Comparative Examples 1 and 2 according to the prior art.

FIG. 2 is a micrograph (100 times magnification) showing a heat-resistant spheroidal graphite cast iron of an example according to the present invention.

FIG. 3 is a micrograph (100 times magnification) showing a heat-resistant spheroidal graphite cast iron of Comparative Example 1 according to the prior art.

FIG. 4 is a micrograph (magnification: 100 times) showing a heat-resistant spheroidal graphite cast iron of Comparative Example 2 according to the prior art.

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[Procedure amendment]

[Submission date] June 20, 2001 (2001.6.2)
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Claims (1)

[Claims] 1. The composition according to claim 1, wherein the content of C is from 2.5 to 4.1% by weight.
5.0% by weight of Si, 1.0% by weight or less of Mn, 0.1%
Wt% or less of P, 0.01 wt% or less of S, 0.02 to
0.10 wt% Mg, 0.1-1.5 wt% Mo,
A heat-resistant sphere for exhaust system parts having excellent oxidation resistance, characterized by containing 0.5 to 2.0% by weight of Ni, the balance being Fe and unavoidable impurities, and having a base structure mainly composed of a ferrite phase. Graphite cast iron.