JPH06228713A - Austenitic heat resistant cast steel excellent in strength at high temperature and machinability and exhaust system parts using same - Google Patents

Abstract

PURPOSE:To obtain an austenitic heat resistant cast steel, excellent in machinability as well as in strength at high temp., and automibile exhaust system parts made thereof, such as exhaust manifold and turbine housing. CONSTITUTION:The austenitic heat resistant cast steel has a composition consisting of, by weight ratio, 0.1-0.5% C, <1.5% Si, <=1.0% Mn, 8-20% Ni, 15-30% Cr, 0.2-1.0% Nb, 2-6% W, 0.01-0.3% N, 0.001-0.01% B, and the balance Fe with inevitable impurities or further containing, besides the above, 0.2-1.0% Mo, 0.02-0.3% S, and 0.001-0.1% of one or >=2 elements among REM (Ce, La, Nd, Pr), Mg, and Ca. This austenitic heat resistant cast steel can be used for automobile exhaust parts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant cast steel suitable for an exhaust system component of an automobile engine, etc., and relates to an austenitic heat-resistant cast steel excellent in strength at high temperature and excellent in machinability, and an exhaust system component comprising the same.

[0002]

2. Description of the Related Art Conventional heat-resistant cast iron and heat-resistant cast steel include, for example, those having the compositions shown in Table 1 as comparative materials.
For exhaust system parts such as exhaust manifolds and turbine housings of automobiles, the operating conditions become severe at high temperatures. Therefore, high Si spheroidal graphite cast iron, ferritic heat-resistant cast steel, and Niresist cast iron (Ni-Cr-
Heat-resistant cast iron such as Cu-based austenitic cast iron) has been adopted.

As heat-resistant austenitic cast steel, Japanese Patent Laid-Open No. 61-87852 discloses C, Si, Mn, N, N.
There is a disclosure in which a composition consisting of i, Cr, V, Nb, Ti, B, W and Fe is specified to improve creep strength and proof stress. Further, Japanese Patent Laid-Open No. 61-177352 discloses C,
It is disclosed that the composition of Si, Mn, Cr, Ni, Al, Ti, B, Nb and Fe is limited, the oxygen content and cleanliness are specified, and the room temperature characteristics as well as the high temperature characteristics are improved. Further, Japanese Patent Publication No. 57-8183 discloses that Fe
There is a disclosure that the carbon content of a —Ni—Cr austenitic heat-resistant cast steel is increased and Nb and Co are added to improve the high temperature strength without lowering the high temperature oxidation resistance.

[0004]

Among the conventional heat-resistant cast iron and heat-resistant cast steel described above, high Si spheroidal graphite cast iron has relatively good room temperature strength but poor high temperature strength and oxidation resistance. Further, the ferritic heat-resistant cast steel has a problem that the temperature lowering strength at 900 ° C. or higher is absolutely inferior. Further, Ni-resist cast iron has relatively good high-temperature strength up to 900 ° C, but is inferior in durability at temperatures higher than that. Further, this Ni-resist cast iron has a problem that it has a high Ni content and is expensive.

Further, in the above-mentioned Japanese Patent Laid-Open No. 61-87852, since the C content is as low as 0.15% by weight or less, the high temperature strength at 900 ° C. or higher is insufficient, and the Ti content is 0.002 to 0.002. Since it is contained in an amount of 0.5% by weight, there is a possibility that harmful non-metallic inclusions may be produced by melting in air.

Further, since the above-mentioned Japanese Patent Laid-Open No. 61-177352 contains a large amount of Ni, it may be damaged in the presence of a sulfur (S) atmosphere at a high temperature.

[0007] Further, Japanese Patent Publication No. 57-8183 has a high carbon content (C), which may cause embrittlement during long-term use at high temperature.

Therefore, the present invention provides the above-mentioned conventional heat-resistant cast iron,
It is an object of the present invention to solve the problems of heat-resistant cast steel, to provide heat-resistant cast steel that is superior in high-temperature strength, machinability, and can be manufactured at low cost.

Another object of the present invention is to provide an exhaust system component made of such heat-resistant cast steel.

[0010]

As a result of earnest research in view of the above objects, the present inventors have added Nb, W, N, B or Mo to Nb, W, N, B or those to Fe-Ni-Cr base austenitic heat-resistant cast steel. It was found that the high temperature strength can be improved by the above, and further, the machinability and the room temperature ductility can be improved by adding S, REM, Mg and Ca, and the present invention was conceived.

That is, the austenitic heat-resistant cast steel excellent in high temperature strength and machinability of the first aspect of the present invention has a weight ratio of C: 0.1 to 0.5%, Si: less than 1.5%, Mn. : 1.0% or less, Ni: 8 to 20%, Cr: 15 to 30%, Nb: 0.2 to 1.0%, W: 2 to 6%, N: 0.01 to 0.3%, B: 0.001 to 0.01%, S: 0.02 to 0.3%, balance: Fe and inevitable impurities.

The desirable range of the first invention is, in terms of weight ratio, C: 0.15 to 0.45%, Ni: 8 to 15%, Cr: 17 to 25%, Nb: 0.2 to 0. 7%, W: 2 to 5%, N: 0.05 to 0.2%, B: 0.001 to 0.008%, S: 0.03 to 0.25%.

Next, the austenitic heat-resistant cast steel excellent in high temperature strength and machinability of the second aspect of the present invention has a weight ratio of C: 0.1 to 0.5%, Si: less than 1.5%, Mn: 1.0% or less, Ni: 8 to 20%, Cr: 15 to 30%, Nb: 0.2 to 1.0%, W: 2 to 6%, N: 0.01 to 0.3% , B: 0.001 to 0.01%, one or more of REM (Ce, La, Nd, Pr), Mg and Ca: 0.001 to 0.1%, balance: Fe and unavoidable impurities It is characterized by

The desirable range of the second invention is, in terms of weight ratio, C: 0.15 to 0.45%, Ni: 8 to 15%, Cr: 17 to 25%, Nb: 0.2 to 0. 7%, W: 2-5%, N: 0.05-0.2%, B: 0.001-0.008%, REM: 0.01-0.1%.

Next, the austenitic heat-resistant cast steel excellent in high temperature strength and machinability of the third aspect of the present invention has a weight ratio of C: 0.1 to 0.5%, Si: less than 1.5%, Mn: 1.0% or less, Ni: 8 to 20%, Cr: 15 to 30%, Nb: 0.2 to 1.0%, W: 2 to 6%, Mo: 0.2 to 1.0% , N: 0.01 to 0.3%, B: 0.001 to 0.01%, S: 0.02 to 0.3%, and the balance: Fe and inevitable impurities.

A desirable range of the third aspect of the present invention is a weight ratio of C: 0.15 to 0.45%, Ni: 8 to 15%, Cr: 17 to 25%, Nb: 0.2 to 0. 7%, W: 2 to 5%, Mo: 0.3 to 1.0%, N: 0.05 to 0.2%, B: 0.001 to 0.008%, S: 0.03 to 0. 0.25%.

Next, the austenitic heat-resistant cast steel excellent in high temperature strength and machinability of the fourth aspect of the present invention has a weight ratio of C: 0.15 to 0.5%, Si: less than 1.5%, Mn: 1.0% or less, Ni: 8 to 20%, Cr: 15 to 30%, Nb: 0.2 to 1.0%, W: 2 to 6%, Mo: 0.2 to 1.0% , N: 0.01 to 0.3%, B: 0.001 to 0.01%, one or more of REM (Ce, La, Nd, Pr), Mg and Ca: 0.001 to 0 0.1%, balance: Fe and unavoidable impurities.

A desirable range of the fourth invention is, by weight ratio, C: 0.15 to 0.45%, Ni: 8 to 15%, Cr: 17 to 25%, Nb: 0.2 to 0. 7%, W: 2 to 5%, Mo: 0.3 to 1.0%, N: 0.05 to 0.2%, B: 0.001 to 0.008%, REM: 0.01 to 0. It is 1%.

Next, the austenitic heat-resistant cast steel excellent in high temperature strength and machinability of the fifth aspect of the present invention has a weight ratio of C: 0.1 to 0.5%, Si: less than 1.5%, Mn: 1.0% or less, Ni: 8 to 20%, Cr: 15 to 30%, Nb: 0.2 to 1.0%, W: 2 to 6%, N: 0.01 to 0.3% , B: 0.001 to 0.01%, S: 0.02 to 0.3%, one or more of REM (Ce, La, Nd, Pr), Mg and Ca: 0.001 to 0 0.1%, balance: Fe and unavoidable impurities.

A desirable range of the fifth invention is, in terms of weight ratio, C: 0.15 to 0.45%, Ni: 8 to 15%, Cr: 17 to 25%, Nb: 0.2 to 0. 7%, W: 2-5%, N: 0.05-0.2%, B: 0.001-0.008%, S: 0.03-0.25% REM: 0.01-0. It is 1%.

Next, the austenitic heat-resistant cast steel excellent in high temperature strength and machinability of the sixth aspect of the present invention has a weight ratio of C: 0.1 to 0.5%, Si: less than 1.5%, Mn: 1.0% or less, Ni: 8 to 20%, Cr: 15 to 30%, Nb: 0.2 to 1.0%, W: 2 to 6%, Mo: 0.2 to 1.0% , N: 0.01 to 0.3%, B: 0.001 to 0.01%, S: 0.02 to 0.3%, REM (Ce, La, Nd, Pr), 1 of Mg and Ca. One or more kinds: 0.001-0.1%, balance: Fe and unavoidable impurities.

The desirable range of the sixth aspect of the present invention is, by weight ratio, C: 0.15 to 0.45%, Ni: 8 to 15%, Cr: 17 to 25%, Nb: 0.2 to 0. 7%, W: 2 to 5%, Mo: 0.3 to 1.0%, N: 0.05 to 0.2%, B: 0.001 to 0.008%, S: 0.03 to 0 0.25% REM: 0.01 to 0.1%.

[0023]

The reason for limiting the composition range of each alloy element of the austenitic heat-resistant cast steel excellent in high temperature strength and machinability of the present invention will be described in detail below.

(1) C (carbon): 0.1 to 0.5% C has the effect of improving the fluidity of the molten metal, that is, the castability, and also forms a solid solution in a part of the matrix to strengthen the solid solution. It has an effect. Further, it is necessary to form primary carbides and enhance high temperature strength. In order to effectively exhibit such an effect, C is required to be at least 0.1% or more.

On the other hand, when the content of C exceeds 0.5%, secondary carbides are excessively precipitated and the toughness is significantly deteriorated. Therefore, C is 0.1 to 0.5%. Desirably 0.1
It is 5 to 0.45%.

(2) Si (silicon): less than 1.5% Si serves as a deoxidizer for the molten metal and is an element effective for improving the oxidation resistance. However, if added excessively, the austenite structure becomes unstable and the high temperature strength deteriorates, so the Si content is made less than 1.5%.

(3) Mn (manganese): 1.0% or less Like Mn, Mn is effective as a deoxidizer for the molten metal, but if too much is added, the oxidation resistance deteriorates.
It is 0% or less.

(4) Ni (nickel): 8 to 20% Ni is an element which is effective for stabilizing the structure of the heat-resistant cast steel of the present invention and austenite structure and enhancing high temperature strength together with Cr. In particular, in order to have good high-temperature strength in a high temperature range of 900 ° C. or higher, 8% or more must be added. The above characteristics improve with an increase in Ni, but even if it exceeds 20%, the effect is saturated, which is economically disadvantageous. Therefore, the Ni content is 8 to 20%. It is preferably 8 to 15%.

(5) Cr (Chromium): 15 to 30% Cr coexists with Ni to austenite the cast steel structure to enhance high temperature strength and oxidation resistance, and also to form carbides to enhance high temperature strength. Is an effective element. Especially, 9
In order to make these effects effective in a high temperature range of 00 ° C. or higher, addition of 15% or more is necessary. However, if the amount added exceeds 30%, secondary carbides are excessively precipitated, and brittle precipitates such as σ phase are precipitated, resulting in significant embrittlement. Therefore, the Cr content is set to 15 to 30%. It is preferably 17 to 25%.

(6) W (tungsten): 2 to 6% W improves high temperature strength. 2% to get this effect
The above additions are necessary. However, if added in a large amount, the oxidation resistance deteriorates, so 6% is the upper limit. Therefore, the W content is set to 2 to 6%. It is preferably 2 to 5%.

(7) Mo (molybdenum): 0.2-1.
0% Mo is an element having the same action as W. But,
Addition of Mo alone is less effective than W. The content of Mo is 0.2-
It is 1.0%. Desirably, it is 0.3 to 1.0%.

(8) Nb (niobium): 0.2 to 1.0% Nb combines with C to form fine carbides and improves high temperature strength. Further, the oxidation resistance is improved by suppressing the generation of Cr carbide. In order to exert these effects effectively, it is necessary to add 0.2% or more.
However, addition of a large amount deteriorates toughness, so the upper limit is 1.
0% Therefore, the Nb content is 0.2 to 1.0.
%. It is preferably 0.2 to 0.7%.

(9) N (nitrogen): 0.01 to 0.3% N is a strong austenite forming element and stabilizes the austenite matrix. Further, it is an element effective for refining crystal grains, and is extremely effective for a cast member such as the present invention in which refining of crystal grains by processing such as forging and rolling is impossible. Further, N delays the diffusion rate of C and delays the agglomeration of precipitated carbides, and is therefore effective against embrittlement. To obtain this effect, addition of 0.01% or more is necessary.
However, addition of a large amount causes precipitation of Cr ₂ N—Cr ₂₃ C ₆ at grain boundaries to promote embrittlement, while reducing the amount of effective Cr, so the upper limit is 0.3%. Therefore, the content of N is set to 0.01 to 0.3%. Desirably 0.05 to 0.
2%. For heat resistant cast steel, W
And Mo and Nb are added, but these elements are ferrite-forming elements and the austenite matrix becomes unstable. Therefore, the combination of W, Mo, Nb and N is particularly effective in the case of heat-resistant cast steel. .

(10) B (boron): 0.001 to 0.
01% B not only strengthens the crystal grain boundaries of cast steel, but also makes the grain boundary carbides finer and delays the agglomeration and coarsening of them to improve high temperature strength and toughness. To obtain this result, 0.001
% Or more is desirable. On the other hand, addition of a large amount of B causes boride to precipitate and deteriorates high temperature strength.
Is the upper limit. Therefore, the content of B is 0.001 to 0.
It is set to 01%. It is preferably 0.001 to 0.008%.

(11) S (sulfur): 0.02 to 0.3% S produces spheroidized or lumpy sulfide in cast steel and accelerates cutting of chips during machining, so that it is cut. The property is improved. To obtain this effect, addition of 0.02% or more is necessary. However, if added in a large amount, a large amount of sulfide will be precipitated at the grain boundaries, deteriorating the high temperature strength.
% Is the upper limit. Therefore, the S content is 0.02 to 0.
3%. It is preferably 0.03 to 0.25%.

(12) REM (rare earth metal) [C
e (cerium), La (lanthanum), Nb (neodymium), Pr (plutonium)], Mg (magnesium), Ca (calcium): 0.001 to 0.1% REM, Mg, Ca forms non-metallic inclusions and is dispersed in the matrix to promote cutting of chips during machining and improve machinability. On the other hand, its shape is spherical or lumpy to improve room temperature ductility. To obtain that effect, addition of 0.001% or more is necessary. However, if added in a large amount, the total amount of non-metallic inclusions increases, rather reducing ductility, so 0.1% is made the upper limit. Therefore, their contents are 0.
It is 001% to 0.1%. Desirably 0.01 to 0.
1%.

The austenitic heat-resistant cast steel excellent in high-temperature strength and machinability of the present invention is used as an exhaust system part for automobiles, especially as an exhaust manifold or a turbine housing attached to an engine, after being thinly cast and used for heating. Even if it undergoes a cooling cycle, it is slightly deformed and has excellent durability.

[0038]

EXAMPLES The present invention will be described below with reference to examples.

Examples 1 to 10 and Comparative Examples 11 to 13 JIS standard Y type B test materials were prepared for heat resistant materials having the compositions shown in Table 1. When casting,
Immediately dissolve in air using a 100 kg high-frequency furnace and immediately
Hot water was poured out at 50 ° C or higher and poured at 1500 ° C or higher.

Regarding the austenitic heat-resistant cast steels of the materials of the present invention (Examples 1 to 10), the molten metal flow during casting was good and no casting defects were found. Next, the cast material of the present invention ((Examples 1 to 10)) and the test materials of Comparative Examples 11 to 13 (Y block) were subjected to a heat treatment of heating at 800 ° C for 2 hours and then air cooling.

In Table 1, the comparative material (Comparative Example 11
13 to 13) are used for heat-resistant parts such as automobile turbocharger housings and exhaust manifolds, and the test materials of Comparative Examples 11 and 12 are Niresist cast irons D2 and D5S, respectively.

Comparative Example 13 is a general-purpose austenitic heat-resistant cast steel, JIS standard SCH-12.

[0043]

[Table 1] Chemical composition (wt%) Example C Si Mn Ni Cr Mo W No.1 0.12 1.01 0.52 8.30 15.80-2.50 2 0.25 0.91 0.48 10.56 20.05-3.55 3 0.48 0.95 0.58 19.82 29.50-5.91 4 0.35 0.86 0.45 13.50 25.10-4.20 5 0.32 0.89 0.50 9.95 22.05-3.01 6 0.13 1.12 0.54 8.15 15.65 0.25 2.44 7 0.22 0.95 0.51 11.25 21.08 0.58 2.05 8 0.47 0.88 0.44 19.72 29.13 0.88 1.52 9 0.31 0.92 0.53 12.95 24.95 0.49 2.35 10 0.28 0.97 0.53 10.08 20.15 2.41 Comparative example C Si Mn Ni Cr Mo 11 2.77 2.12 0.88 21.10 2.44-12 1.89 5.32 0.41 34.50 2.35-13 0.21 1.24 0.50 9.10 18.80-

(Continued Table 1) Chemical composition (% by weight) Example Nb N B S REM Mg Ca No.1 0.25 0.25 0.002 0.034---2 0.48 0.08 0.008 0.09 0.06--3 0.96 0.02 0.009 0.28-0.005-4 0.51 0.09 0.004 0.15--0.005 5 0.45 0.12 0.004 0.08 0.06 0.008 0.005 6 0.23 0.26 0.003 0.22---7 0.44 0.15 0.004 0.04 0.08--8 0.48 0.03 0.005 0.07-0.005-9 0.51 0.11 0.004 0.09--0.005 10 0.55 0.09 0.004 0.10 0.06 0.008 0.005 Comparative Example 11----0.05-12----0.07-13------

Next, various evaluation tests described below were carried out using each test material. (1) Room Temperature Tensile Test A round bar test piece (JIS No. 4 test piece) having a gauge length of 50 mm and a gauge diameter of 14 mm was used.

(2) High Temperature Tensile Test A brittle test piece having a gauge length of 50 mm and a gauge diameter of 10 mm was used at 1000 ° C.

(3) Thermal Fatigue Test Using a round bar test piece having a gauge length of 20 mm and a gauge diameter of 10 mm, the following test was carried out in a state in which the expansion and contraction due to heating and cooling were mechanically completely restrained. The heating and cooling cycle was repeated under the conditions of 1 to cause thermal fatigue failure. Lower limit temperature: 150 ° C. Upper limit temperature: 1000 ° C. 1 cycle for each: 7 minutes In addition, an electro-hydraulic servo type thermal fatigue tester was used as a tester.

(4) Oxidation test A round bar test piece having a diameter of 10 mm and a length of 20 mm was prepared and
After keeping in the air at 000 ° C. for 200 hours, after taking out, shot blasting treatment is applied to remove the oxide scale, and the weight change per unit area before and after the oxidation test (oxidation weight loss: mg / mm ² ) is determined to obtain the acid resistance. The chemical conversion was evaluated.

(5) Machinability test The machinability test was conducted by a drill test in which the machinability is the most problematic in this type of material. The test was conducted under the conditions shown in Table 2, and after drilling 10 times, the flank wear width of the drill was measured, and the wear width per hole was compared.

[0050]

[Table 2] Cutting conditions Machine tool: Vertical machining center (5.5 kW) Drill: Solid carbide drill (φ6.8) Cutting speed: 40 m / min Feed: 0.2 mm / rev, step feed Hole depth: 20mm Projection length: 42mm Cutting oil: Oily

The above room temperature tensile test results are shown in Table 3, the high temperature tensile test results are shown in Table 4, and the thermal fatigue test results and oxidation test results are shown in Table 5.

[0052]

[Table 3]

[0053]

TABLE 4 Tensile test at a high temperature (1000 ° C.) result of 0.2% proof stress Tensile strength elongation (MPa) (MPa) (% ) Example No.1 42 73 62 2 50 84 35 3 72 115 40 4 65 98 52 5 56 84 40 6 52 88 48 7 55 98 35 8 65 90 30 9 77 118 52 10 68 110 42 Comparative example No. 11 30 41 33 12 33 44 29 13 35 55 49

[0054]

[Table 5] Thermal fatigue test results and oxidation resistance test results Thermal fatigue life Oxidation weight loss (cycle) (mg / mm ² ) Example No. 1 109 52 2 120 46 3 170 20 4 225 35 5 265 38 6 190 50 7 205 35 8 184 30 9 230 15 10 220 30 Comparative example No. 11 56 765 12 85 55 13 80 85

[0055]

[Table 6]

As is clear from Tables 2, 3, and 4, Examples 1 to 10 according to the present invention are particularly high in strength at high temperature as compared with the conventional Niresist cast irons D2 and D5S of Comparative Examples 11 to 12. Is significantly improved and the room temperature properties are equal or higher. Furthermore, SCH1 of Comparative Example 13
It can be seen that the high temperature strength at 1000 ° C. is improved as compared with 2. Further, as shown in Table 5, the materials of the present invention (Examples 1 to 10) are ordinary austenitic heat-resistant cast steel SCH.
It can be seen that the wear amount of the drill is smaller than that of No. 12 and the machinability is excellent.

Next, using the austenitic heat-resistant cast steels of Examples 5 and 15, exhaust manifolds (wall thickness: 2.5 to 3.4 mm) and turbine housings (wall thickness: 2.7) of automobile exhaust system parts were used. .About.4.1 mm) was cast. The heat-resistant cast steel parts obtained were all sound.

Further, these cast steel parts were subjected to machining to evaluate their machinability, but no problems occurred in any of them.

Next, an in-line 4-cylinder in which an exhaust manifold and a turbine housing are assembled has a displacement of 2000
An endurance test was conducted using an exhaust simulator that emits exhaust gas equivalent to a high-performance gasoline engine of cc. As test conditions, full load operation (continuous 14
Min) -idling (1 min) -complete stop (14 min) -idling (1 min) 1 cycle thermal cooling (GO-S
The TOP) cycle was performed up to 500 cycles. The exhaust gas temperature at full load was 1050 ° C. at the inlet temperature of the turbine housing. Under this condition, the surface temperature of the exhaust manifold was about 980 ° C. at the gathering portion of the exhaust manifold, and the surface temperature of the turbine housing was about 1020 ° C. at the waste gate part. As a result of the evaluation test, it was confirmed that gas leakage and thermal cracking due to thermal deformation did not occur, and that it had excellent durability and reliability.

[0060]

As described above, the austenitic heat-resistant cast steel of the present invention is excellent in strength especially in a high temperature region of over 900 ° C., does not impair room temperature ductility, and is excellent in castability and workability. , Can be manufactured at low cost. Such austenitic heat-resistant cast steel of the present invention,
It is suitable for automobile exhaust system parts such as exhaust manifolds and turbine housings. The exhaust system component made of the austenitic heat-resistant cast steel of the present invention has excellent high-temperature strength,
Shows extremely excellent durability.

Claims (9)

[Claims] 1. By weight ratio, C: 0.1 to 0.5%, Si: less than 1.5%, Mn: 1.0% or less, Ni: 8 to 20%, Cr: 15 to 30%, Nb: 0.2 to 1.0%, W: 2 to 6%, N: 0.01 to 0.3%, B: 0.001 to 0.01%, S: 0.02 to 0.3% , Balance: Fe and inevitable impurities, austenitic heat-resistant cast steel with excellent high-temperature strength and machinability. 2. By weight ratio, C: 0.1 to 0.5%, Si: less than 1.5%, Mn: 1.0% or less, Ni: 8 to 20%, Cr: 15 to 30%, Nb: 0.2 to 1.0%, W: 2 to 6%, N: 0.01 to 0.3%, B: 0.001 to 0.01%, REM (Ce, La, Nd, Pr). , Mg, Ca one or more kinds: 0.001 to 0.1%, balance: Fe and inevitable impurities, an austenitic heat-resistant cast steel excellent in high-temperature strength and machinability. 3. By weight ratio, C: 0.1 to 0.5%, Si: less than 1.5%, Mn: 1.0% or less, Ni: 8 to 20%, Cr: 15 to 30%, Nb: 0.2 to 1.0%, W: 2 to 6%, Mo: 0.2 to 1.0%, N: 0.01 to 0.3%, B: 0.001 to 0.01%. , S: 0.02 to 0.3%, balance: Fe and inevitable impurities, an austenitic heat-resistant cast steel excellent in high-temperature strength and machinability. 4. By weight ratio, C: 0.1 to 0.5%, Si: less than 1.5%, Mn: 1.0% or less, Ni: 8 to 20%, Cr: 15 to 30%, Nb: 0.2 to 1.0%, W: 2 to 6%, Mo: 0.2 to 1.0%, N: 0.01 to 0.3%, B: 0.001 to 0.01%. , REM (Ce, La, Nd, Pr), Mg, Ca one or more kinds: 0.001 to 0.1%, balance: Fe and inevitable impurities, characterized by high temperature strength and cutting Austenitic heat-resistant cast steel with excellent properties. 5. By weight ratio, C: 0.1 to 0.5%, Si: less than 1.5%, Mn: 1.0% or less, Ni: 8 to 20%, Cr: 15 to 30%, Nb: 0.2 to 1.0%, W: 2 to 6%, N: 0.01 to 0.3%, B: 0.001 to 0.01%, S: 0.02 to 0.3% , REM (Ce, La, Nd, Pr), Mg, Ca one or more kinds: 0.001 to 0.1%, balance: Fe and inevitable impurities, characterized by high temperature strength and cutting Austenitic heat-resistant cast steel with excellent properties. 6. By weight ratio, C: 0.1 to 0.5%, Si: less than 1.5%, Mn: 1.0% or less, Ni: 8 to 20%, Cr: 15 to 30%, Nb: 0.2 to 1.0%, W: 2 to 6%, Mo: 0.2 to 1.0%, N: 0.01 to 0.3%, B: 0.001 to 0.01%. , S: 0.02 to 0.3%, one or more of REM (Ce, La, Nd, Pr), Mg and Ca: 0.001 to 0.1%, balance: Fe and unavoidable impurities Austenitic heat-resistant cast steel with excellent high-temperature strength and machinability. 7. An exhaust system component made of an austenitic heat-resistant cast steel excellent in high-temperature strength and machinability according to any one of claims 1 to 6. 8. The exhaust system component according to claim 7,
Exhaust system parts characterized by being an exhaust manifold. 9. The exhaust system component according to claim 7,
An exhaust system component characterized by a turbine housing.