JPS6372850A - Spheroidal graphite cast iron excellent in wear resistance and oxidation resistance - Google Patents

Abstract

PURPOSE:To improve the wear resistance and oxidation resistance, in a high temp. region, of the titled cast iron to be obtained, by incorporating C, Si, Cr, Nb, etc., in a specified blending proportion and also by constituting the structure of ferrite, a lumpy carbonitride of Nb, Cr, etc., dispersed in the ferrite, and spheroidal graphite. CONSTITUTION:The cast iron has a composition consisting of, by weight, 3.0-4.0% C, 3.5-5.0% Si, 0.02-0.06% Mg, 0.1-0.5% Nb, 0.05-0.2% Cr, <=0.5% Mn, <=0.1% P, <=0.05% S, and the balance Fe with inevitable impurities and also has a structure constituted of ferrite, a lumpy carbonitride composed principally of Nb and Cr and dispersed into the above ferrite, and spheroidal graphite. Moreover, it is desirable that average grain size of the above lumpy carbonitride is regulated to about 1-20mum. Owing to this composition, the cast iron excellent in resistance to wear and oxidation in a high temp. region can be obtained without sacrificing workability. Accordingly, this cast iron is suitably used for exhaust parts for engine, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the improvement of spheroidal graphite cast iron which has excellent wear resistance and oxidation resistance in high temperature ranges. INDUSTRIAL APPLICATION This invention can be utilized for the turbo housing of the turbocharger, exhaust manifold, etc. which are engine parts of an automobile, for example. Here, the exhaust manifold is for sending high-temperature exhaust gas discharged from the cylinder of one engine to the exhaust pipe. The turbo housing is a housing for a turbocharger that uses the energy of exhaust gas to rotate an exhaust turbine to drive a compressor and supply high-density air at or above atmospheric pressure to the engine.

[Prior Art 1] For example, self-developed products include a turbo housing for a turbocharger and an exhaust manifold.

These materials are required to have wear resistance and oxidation resistance in high temperature ranges. Therefore, turbo housings and exhaust manifolds have traditionally been made of high-silicon spheroidal graphite cast iron, which contains around 4% silicon, which is a high-grade material.

By the way, as the performance of engines has improved in recent years, the temperature of exhaust gas has increased, and therefore, the above-mentioned turbo housings and exhaust manifolds are required to have even higher wear resistance and oxidation resistance in high-temperature regions.

For example, in the turbo housing of a turbo charger, the shaft for operating the wastegate valve comes into contact with the turbo housing, so the temperature of exhaust gas is rising, so abnormal wear is likely to occur during use. When abnormal wear occurs in this way, exhaust gas leaks from the turbo housing, malfunction of the wastegate valve, etc. are likely to occur. Conventionally, a sleeve has been inserted into the shaft in order to prevent malfunctions of the wastegate valve, but the sleeve sometimes comes off due to the difference in thermal expansion between the sleeve and the turbo housing.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a high-silicon based spheroidal graphite cast iron that has excellent wear resistance and oxidation resistance in high temperature ranges. There is something to do.

[Means for Solving the Problems] The high-silicon spheroidal graphite cast iron according to the present invention is completed by adding carbon, silicon, niobium, chromium, etc. in a well-balanced manner. That is, the high silicon-based spheroidal graphite cast iron according to the present invention has a carbon content of 3.0 to 4.0 in terms of demolding percentage.
%, silicon 3.5% to 5.0%, manganese 0.5% or less, phosphorus 0.1% or less, sulfur 0.05% or less, magnesium 0.02 to 0.06%, niobium 70.1 to 0 .5%
, 0.05 to 0.2% chromium, balance iron and unavoidable impurities, and its structure is composed of ferrite, massive carbonitride mainly composed of niobium and chromium dispersed in ferrite, and spheroidal graphite. It is characterized by being configured. Here, the average particle size of the massive carbonitride is preferably about 1 to 20 μm.

Here, the reasons for limiting the composition will be explained. 3.0 carbon
The reason for setting it to ~4.0% is that when the carbon content is less than 360%,
This is because the castability of the molten metal deteriorates, and on the other hand, if it exceeds 4.0%, dross in the molten metal increases and dross defects increase.

The reason why the silicon content is limited to 3.5 to 5.0% is that if the silicon content is less than 3.5%, the heat resistance necessary for exhaust system parts cannot be obtained. On the other hand, if the silicon content exceeds 5.0%, the castability of the molten metal deteriorates and the ferrite 11 weave becomes extremely brittle.

The reason why manganese is set to 0.5% or less is because manganese deteriorates heat resistance, so it is better to have as little as possible.
less than This amount is necessarily mixed in from the dissolved raw materials.

The reason why the phosphorus content is 0.1% or less is because phosphorus embrittles the tissue, so it is preferable to keep it as low as possible.
% or less.

The sulfur content is 0.05% or less4. Sulfur inhibits the spheroidization of graphite, so it is preferable to have as little sulfur as possible.
Therefore, the content was set at 0.05% or less.

The reason for setting the magnesium content to 0.02 to 0.06% is that if the magnesium content is less than 0.02%, the degree of spheroidization of graphite will be insufficient and it will not be possible to produce good spheroidal graphite cast iron.
．． If the content exceeds 0.06%, cementite becomes stabilized or dross defects occur, so the upper limit was set at 0.06%.

The reason why chromium is set at 0.05 to 0.2% is because chromium is an element that is effective in improving oxidation resistance when dissolved in solid solution, and also because it coexists with niobium to form lumpy carbonitrides and improves wear resistance. Improve. Therefore, 0.05% or more is necessary. In addition, if chromium exceeds 0.2%, coarse cementite tends to form and deteriorates mechanical properties and workability, so the upper limit should be set to 0.
．． It was set at 2%. The reason why niobium was set at 0.1% to 0.5% was because
Niobium is an element that generates fine carbonitrides and improves the wear resistance of the structure. Therefore, it is preferable to contain 0.1% or more, and on the other hand, if the content exceeds 0.5%, no improvement in the effect can be expected, and on the contrary, the processability deteriorates, so the upper limit was set at 0.5%.

[Test Examples] Each test example of the spheroidal graphite cast iron according to the present invention will be explained below together with comparative materials. First, using a 2Oka high frequency induction furnace, melt at a melting temperature of 1500℃, and after melting, iron -50%
A silicone-10% magnesium alloy was added to perform spheroidization treatment. For the spheroidization process, the temperature of the spheroidization process was 1450℃.
The test was carried out using a phosphorizer. The invasion, Fe-7
It was inoculated with 5% Si and poured into Y block. As a result, specimens A and B of the present invention material having the composition shown in Table 1
and specimens CSD and E1F as comparison materials.

G was also melted.

(The following is a blank space) Table 1 Specimen A1 as the material of the present invention and Specimen B as the material of the present invention shown in Table 1 are materials in which chromium and niobium, which are the elements of the present invention, are added to the specimen C as the comparative material. The specimen used as a comparison material is a material in which chromium and 2A of the present invention material are added to specimen C in an amount exceeding the upper limit. Specimens E and G as comparative materials are materials in which chromium and niobium are added to specimen C as a comparative material, respectively. In addition, specimen F as a comparative material is J[5F
This material is made by adding chromium and niobium, which are the elements of the present invention, to a material equivalent to CD40.

An oxidation test was conducted on specimens A to G formed as described above. In the oxidation test, the sample was kept in the air at 700°C for 200 hours, and then the maximum oxide scale thickness was determined, and this was taken as the amount of oxidation. Furthermore, even at 800℃, 200%
The maximum oxide scale thickness was determined by holding the sample for a certain period of time. The results are shown in FIG. In the bar graph in Figure 1, the white area is 700℃, and the hatched area is 800℃.
oxide scale thickness.

The wear resistance test was carried out using the test 1) apparatus schematically shown in FIG. That is, the mating material 1 was made of 4% JIS-8UH (length: 40 mm, width: 2 Q mm).

This mating material 1 and specimen 2 (length 5
Qmm, outer diameter 10mm) and the load 11 from the direction of the arrow.
Press with KO and in that state slide speed iooorpm
After the test was completed, the difference in level between the friction surface and the reference surface was measured using a surface roughness meter, and the difference was taken as the wear depth. The results of the wear resistance test are shown in Figure 3.

In this case, the temperature was 700° C. and the test was carried out in an air atmosphere.

As shown in FIG. 1, improvements in oxidation resistance at 700° C. and 800° C. were observed in specimen A1 and specimen B as materials of the present invention. Furthermore, as shown in Fig. 3, the wear depth of specimens A and B, which are the materials of the present invention, is approximately 2μ, which is significantly greater than that of specimen C, which is the comparison material (wear depth is 7μ). It's improving.

As shown in FIG. 1, the oxidation resistance of the comparative specimens was improved, and the abrasion resistance was almost the same as that of specimens A and [3, which were the materials of the present invention.

However, the hardness of specimens A and B as materials of the present invention is HV.
192 to 215, whereas the hardness of the sample as a comparative material is considerably higher, HV262, which causes a problem of poor workability.

In the case of specimen E as a comparative material, as shown in Fig. 3, specimen E
The wear depth was about 5.5μ, and the improvement in wear resistance was small. Specimen G as a comparison material had slightly improved oxidation resistance as shown in FIG. 1, but the wear depth was as large as 7μ as shown in FIG. 3, and the wear resistance was not improved.

In specimen F as a comparison material, as shown in Fig. 1, 800
The oxide scale thickness at ℃ is as thick as 500μ or more, and therefore the oxidation resistance is extremely poor. Not only this, but as shown in FIG. 3, the wear depth is about 6.5μ, and the wear resistance is not improved. The reason for this is that in Specimen F, although carbonitrides precipitate due to the addition of chromium and niobium, the oxidation resistance of the base ferrite is poor, so consolidation progresses during the wear test, and the oxide film is I! jll! This is presumed to be due to deterioration of wear resistance due to peeling.

(Margins below) Table 2 Next, in order to evaluate the actual durability, a turbo housing for a turbocharger was manufactured using the inventive material with the chemical composition shown in Table 2, and a turbo housing was installed at the wastegate valve operating shaft. We have manufactured a turbocharger with a structure that eliminates the sintered gold 11E% sleeve that is normally inserted. And the maximum rotation speed is 550 with an actual 2000cc gasoline engine.
A repeated durability test was conducted for 300 hours at 0 rpm, repeating full load and idle. This test is 1M! The results showed that there was no damage to the shaft and good results were obtained. This is presumed to be due to improved wear resistance and oxidation resistance of the turbo housing.

[Effects of the Invention] As explained above, in the high silicon-based spheroidal graphite cast iron according to the present invention, carbon, silicon, chromium, and niobium are added in a well-balanced manner, thereby changing the structure to ferrite, niobium and niobium dispersed in the ferrite. It is composed of massive carbonitride mainly composed of chromium and spheroidal graphite. Therefore,
It has excellent wear resistance and oxidation resistance in high temperature ranges without decreasing processability.

Therefore, the high-silicon spheroidal graphite cast iron according to the present invention can be applied to engine exhaust parts that require both oxidation resistance and wear resistance at high temperatures, such as parts such as turbo housings of turbochargers and exhaust manifolds. can.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the test results of the oxidation resistance test, and FIG. 2 is a perspective view schematically showing the abrasion resistance testing apparatus. FIG. 3 is a bar graph showing the results of the abrasion test. In the figure, 1 indicates the mating material and 2 indicates the specimen.

Claims (3)

[Claims] (1) Carbon 3.0-4.0%, silicon 3.5% by weight
%~5.0%, manganese 0.5% or less, phosphorus 0.1% or less, sulfur 0.05% or less, magnesium 0.02~0
．． 06%, niobium 0.1~0.5%, chromium 0.05~
0.2%, the balance being iron and unavoidable impurities, and its structure is composed of ferrite, massive carbonitride mainly composed of niobium and chromium dispersed in the ferrite, and spheroidal graphite. Spheroidal graphite cast iron with excellent wear resistance and oxidation resistance in high temperature ranges. (2) The spheroidal graphite cast iron having excellent wear resistance and oxidation resistance in a high temperature range according to claim 1, wherein the massive carbonitride has an average particle size of about 1 to 20 μm. (3) Spheroidal graphite cast iron having excellent wear resistance and oxidation resistance in a high temperature region as described in claim 1, which is used for a turbocharger housing and an exhaust manifold.