JPS61139649A - Heat resistant cast steel - Google Patents

Abstract

PURPOSE:To obtain a cast steel having superior heat and oxidation resistances as well as the superior castability without adding expensive alloying elements in large quantities by reducing the amounts of impurities such as P and S and adding C, Si and Cr in a well-balanced state. CONSTITUTION:This annealed heat resistant cast steel consists of, by weight, 0.3-2.0% C, 2.5-3.5% Si, <=0.7% Mn, <=0.01% P, <=0.1% S. 5.0-10.0% Cr and the balance Fe. The cast steel has the heat and resistant cast steel as well as castability comparable to that of a conventional heat resistant cast iron. The cast steel is suitable for use as a material for the parts of an exhaust system for an engine for a vehicle from the viewpoint of cost and performance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heat-resistant cast steel suitable for exhaust system parts of vehicle engines.

(Prior art) In recent years, efforts have been made to improve the combustion efficiency of vehicle engines, especially automobile engines, in order to achieve high output and high fuel efficiency, regardless of whether they are gasoline engines or diesel engines.As a result, the exhaust gas temperature increases. There is a tendency. Especially the exhaust manifold.

Exhaust system parts such as turbochargers, turbine wheels, and TASEL engine chambers are used under increasingly harsh operating conditions, and the importance of material selection is once again being questioned.

Conventionally, heat-resistant cast irons such as high-silicon cast iron, Niresist cast iron, and aluminum cast iron have been generally used as exhaust system parts, and high-Cr type and high-Cr-high-Ni type heat-resistant cast steels have been specially used.

(Problems to be solved by the present invention) However, although heat-resistant cast iron has excellent productivity due to its good castability, it has poor heat resistance and oxidation resistance when used at temperatures above 800°C, and has a short lifespan. On the other hand, heat-resistant cast steel has excellent heat resistance and oxidation resistance even at temperatures above 800℃, but has poor castability and machinability, resulting in poor productivity, and requires the use of expensive alloying elements. Since it is added to a polyacid, it has the disadvantage that it has to become lighter overall.

(Means for solving the problems) In order to solve the above-mentioned problems, the present invention aims to solve the problems described above.
(C) 0.3~zO%, Silicon (Si)? , 5-3
．． 5%, manga (Mn) 0.7% or less, phosphorus (P) 0.01% or less, sulfur (S) 0.1% or less,
It is characterized by being made of heat-resistant cast steel so that the remaining portion is iron (Fe).

The heat-resistant 1114 steel is preferably annealed to 900~
Heating layer at 950℃ for 0.5Hr (hour) or more, 680~
It is used after being annealed at 750°C for 0.5 hours or more.

Therefore, the microscopic structure of the material obtained in the above case disperses dendrite-like primary carbide (eutectic carbide) and granular secondary carbide in the ferrite base, and it becomes one that does not penetrate graphite ( Effect) In the heat-resistant cast steel having the above structure, C is effective in improving strength and castability, but if it is less than 0.3%, the effect is small, and if it exceeds 2.0%, it will graphitize and reduce the strength. , this was set as 0.3 to 20*. 8i is effective in improving oxidation resistance and castability, but if it is less than 15%, the effect is small, and if it exceeds &5%, primary carbides tend to become coarse and machinability deteriorates, so it is reduced to 25%. ~3.5 inches. Mn is effective as a deoxidizing agent along with 8i, but since it is an element unfavorable for ferrite formation, it was set to 0.796 or less. If P exceeds 0.011, there is a risk of crystallizing steadite, so set it to 0.0.
It was set to 1 m or less. Since S may cause the material to become brittle, it was set to as low as possible, 0.1 inch or less. Or, like Si, is effective in improving oxidation resistance, but its effect decreases when the ratio is less than 5.0%. If it exceeds o*, high hardness carbides will be generated and the workability will be deteriorated, so it should be set at 5.0 to 10. It was Ochi.

The present heat-resistant cast steel whose components are limited in this way has heat resistance and oxidation resistance equivalent to conventional heat-resistant cast steel while ensuring castability equivalent to that of conventional heat-resistant cast iron.

(Example) An example of the present invention will be explained below by comparing it with a comparative example.

The following table summarizes the chemical components of the example materials of the present invention and the comparative materials prepared on a laboratory scale.

Surface casting was performed by atmospheric melting using a 20KP high frequency melting furnace, deoxidized with 1% Fe-8i (75'fi), and 1550
The hot water was tapped at a temperature of 1450°C or higher, and the hot water was poured at a temperature of 1450°C or higher. The type is J
For Examples 1 to 3 and Comparative Examples 1 to 2, using the IBA, the cast specimens were heated at 930°C x 005 hours, then placed in a furnace at 720°C for 3 hours, and then air cooled to the inner shrine FFA. did. After that, various test pieces were manufactured from the casting test, and these were subjected to oxidation, dimensional change, and thermal fatigue tests.

Figures 1 and 2 show the results of the oxidation test. The test was conducted by maintaining the temperature at 800° C. and 900° C. for 100 hours each, and determining the post-oxidation weight loss.

According to the results shown in Figures 1 and 2, Samples A, B, and C, which are examples of the present invention, are JIS SC8 high Cr cast steels.
1(H) showed an oxidation loss equivalent to y, and it became clear that it had excellent oxidation resistance. On the other hand, it is similar to the present invention.

Samples with some Cr content as low as 2.0 and sample E with some St content as low as 1 have poor oxidation resistance), cast iron (F, G) fi or better. The result is inferior.

FIG. 3 shows the results of the dimensional change test. The test was conducted by reciprocating the temperature between 900° C. and 500° C. up to 300 times, and the dimensional change of the needle during that time was determined. Incidentally, the amount of change in dimension 111)ll was based on equation (1).

From this, sample A, which is an example of the present invention, shows almost no dimensional change even after 300 repetitions, and the heat
It was confirmed that the stability is high. In contrast, sample F, which is made of high-quality cast iron, shows an extremely large dimensional change. The dimensional change of FUTANIREGIS (I) is small compared to the above-mentioned high 81 cast iron, but the product of the present invention shows a large dimensional change.

Figure 4 is a book showing the results of thermal fatigue tests. The test was conducted by restraining the test piece and moving it back and forth between 900°C and 400°C, and the number of repetitions until breakage was determined. The restraint rate is expressed by formula (2).1 Sample A, which is an example of the present invention, can withstand a much higher number of repetitions than Sample F, which is made of high 8i cast iron, and Sample ■, which is made of Ni-resist, and its thermal fatigue resistance is It was confirmed that it was excellent. Especially the restraint rate 30
%, even after 6 x 103 repetitions, the result is still broken cast iron (F
, G), and the same heat resistance as 5C8I(H), and both have hardness of Hv3.
00 or less, it was confirmed that there was no problem in machinability.

In addition, a turbine housing having the same components as in Example 1(A) was melted and subjected to a bench durability test. The test was conducted by incorporating the housing into a 20,000C% 6-cylinder gasoline engine under the conditions of a cooling pattern with a maximum exhaust temperature of 950°C. As a result, compared to the conventional material (high Sf cast iron), the oxide scale thickness was V5 or less, and the warping time was L6 times longer.

In addition, FIG. 5 shows a microstructure 100 times that of Example 1 (A), and FIG. 6 shows a microstructure that is 400 times that of Example 1 (A). Primary carbide 2 and granular secondary carbide 3 are dispersed.

(Effects of the Invention) As explained above in detail, the heat-resistant cast steel according to the present invention suppresses impurities such as P and S to a low level, while *C* "*"
This makes it possible to maintain the same castability as conventional heat-resistant cast iron, while also ensuring heat resistance and oxidation resistance equivalent to conventional high-Cr heat-resistant cast steel. This has the effect of making it suitable for exhaust system parts of vehicle engines in terms of cost and performance.

[Brief explanation of the drawing]

Figures 1 and 2 are characteristic diagrams showing the oxidation resistance test results of the heat-resistant cast steel of the present invention in comparison with a comparative example, and Figure 3 shows the dimensional change test results of the heat-resistant cast steel of the present invention in comparison with a comparative example. Figure 4 is a characteristic diagram showing the results of a thermal fatigue test of this heat-resistant cast steel in comparison with a comparative example, and Figures 5 and 6 are micrographs showing the microstructure of this heat-resistant cast steel. . (1 other person) Fig. 1 Fig. 2 A bU DEFGH Fig. 3 Fig. 4 Repetition ff (Nf) Fig. 5 Fig. 6 Procedure amendment 1, case indication 1982 Patent Application No. 260419 2
・Name of the invention Heat-resistant cast steel 3, Relationship with the amended person's case Name of patent applicant (320) Toyota Motor Corporation 4, representative
Administrator □ 5. Date of amendment order “voluntary” 6. Column for detailed explanation of the invention of the specification/book to be amended/゛;7λL\ 7. Contents of amendment (1) “Table” on page 5 of the specification Correct as shown in the attached sheet. 12) "Casting test" on page 5, line 3 of the specification is corrected to "casting specimen." (Separate sheet) Table

Claims (1)

[Claims] (1) Weight ratio: C0.3-2.0%, Si2.5-3
．． 5%, Mn 0.7% or less, P 0.01% or less, S0.
1% or less, Cr5.0-10.0%, Fe balance included,
Heat-resistant cast steel that has been annealed.