JPH10195587A - Spheroidal graphite cast iron and exhaust manifold excellent in intermediate temperature ductility, and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce spheroidal graphite cast iron and exhaust manifold excellent in ductility in an intermediate temp. brittle region of about 400 deg.C. SOLUTION: This cast iron has a compsn. contg., by weight, 2.7 to 4.2% C, 3.5 to 5.2% Si, <=1.0% Mn, <=0.03% S, 0.02 to 0.15% Mg (or contg. at least 0.02% Mg and at least one or more kinds among Mg, Ca and rare earth elements by 0.02 to 0.15%), 0.03 to 0.20% As, and the balance Fe with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spheroidal graphite cast iron excellent in medium-temperature ductility, an exhaust manifold, and a method for producing the same.

[0002]

2. Description of the Related Art Since materials for exhaust system parts of automobiles are used in an environment where heating and cooling are repeatedly performed at high temperatures, they are required to have oxidation resistance and thermal fatigue resistance, are inexpensive and have excellent shape easiness. Spheroidal graphite cast iron is used. In recent years, due to higher engine output and lower fuel consumption, the exhaust gas temperature has become higher and the operating environment has become more severe.
Improvements such as strengthening the base by adding Mo or the like have been studied. However, these conventional high Si spheroidal graphite cast irons have a phenomenon that ductility decreases at around 400 ° C.
This phenomenon is called a medium-temperature embrittlement phenomenon (medium-temperature embrittlement) and is a peculiar phenomenon observed in spheroidal graphite cast iron. It occurs at around 400 ° C. and decreases ductility due to grain boundary fracture. This is a cause of characteristic deterioration.

[0003] In order to solve these problems, a "high toughness oxidation-resistant ferritic spheroidal graphite cast iron" in which the content of P or P + Ti is controlled (Japanese Patent Application Laid-Open No. 61-73859).
Has been proposed. This spheroidal graphite cast iron has excellent oxidation resistance despite the fact that the Si content is higher than the JIS spheroidal graphite cast iron but less than the so-called high Si spheroidal graphite cast iron, and the toughness can be increased by making the crystal grains finer. , And In addition, not only the content of Mg and P
"Spheroidal graphite cast iron and a method for producing the same" in which g / P (weight ratio) is controlled (Japanese Patent Application Laid-Open No. H7-18367) has been proposed. Even if the spheroidal graphite cast iron has the chemical composition of conventional JIS standard spheroidal graphite cast iron, high silicon-containing spheroidal graphite cast iron, and other general spheroidal graphite cast irons, the composition range of Mg and P and their ratios are particularly high. By specifying and casting, it is possible to obtain a material having remarkably excellent resistance to blue heat brittleness.

[0004]

However, Japanese Unexamined Patent Publication No.
Both "high toughness oxidation resistant ferrite spheroidal graphite cast iron" described in 1-73859 and "spheroidal graphite cast iron and its production method" described in Japanese Patent Application Laid-Open No. 7-18367 are disclosed in M.
There is a problem that it is difficult to control the composition of g and P. That is, the Mg content varies depending on the temperature of the molten metal, the holding time, the method of the spheroidizing treatment, and the like during the spheroidizing treatment. Further, P is an unavoidable impurity element mixed from pig iron and steel scrap used as a raw material for melting, and has a large variation depending on the raw material. For this reason, it is difficult to control the content of these elements in the final casting product. The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems of the prior art, and have conducted various systematic experiments. As a result, the present invention has been accomplished.

(Object of the invention)
An object of the present invention is to provide a spheroidal graphite cast iron excellent in ductility in a medium temperature embrittlement region in the vicinity. An object of the present invention is to provide an exhaust manifold having excellent ductility in a medium temperature embrittlement region at around 400 ° C. Another object of the present invention is to use Mg or P
It is an object of the present invention to provide a method capable of easily producing a spheroidal graphite cast iron having excellent ductility in a medium-temperature embrittlement region at around 400 ° C., regardless of the content of iron, without requiring complicated and complicated management.

[0006]

[Means for Solving the Problems]

[First Invention] The spheroidal graphite cast iron of the present invention, which is excellent in medium-temperature ductility, contains C, Si, and Mn as main components, at least Mg as a graphite spheroidizing component, and the balance of Fe and unavoidable impurities. Spheroidal graphite cast iron comprising 0.03 to 0.20% by weight of As.

[0008]

【The invention's effect】

[Effect of the First Invention] The spheroidal graphite cast iron of the present invention is excellent in ductility in a moderate temperature embrittlement region at around 400 ° C.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in further detail, inventions other than the above-mentioned invention, and embodiments of these inventions.

(Points of Interest) The present inventors have focused on the following points in relation to the above-mentioned problems of the prior art. That is, the above-mentioned conventional spheroidal graphite cast iron has a problem that the medium temperature ductility is not sufficient and it is difficult to control the composition of Mg and P. Therefore, the present inventors obtain a spheroidal graphite cast iron excellent in ductility in a moderate temperature embrittlement region at around 400 ° C., regardless of the content of Mg and P, without requiring difficult and complicated management. For this purpose, the inventors focused on adding a special element other than the impurity element usually mixed in the spheroidal graphite cast iron. Then, it was thought that by including this special element in the final casting product, the intermediate temperature embrittlement was suppressed, and a spheroidal graphite cast iron excellent in medium temperature ductility could be obtained.

[First Embodiment] The spheroidal graphite cast iron of the present invention having excellent medium temperature ductility contains C, Si, and Mn as main components, and at least Mg as a graphite spheroidizing component.
The balance is spheroidal graphite cast iron composed of Fe and unavoidable impurities, characterized in that it contains 0.03 to 0.20% by weight of As.

The mechanism by which the spheroidal graphite cast iron of the present invention exerts an excellent effect is not necessarily clear yet, but is considered as follows. That is, the spheroidal graphite cast iron of the present invention contains C, Si, and Mn as main components,
Since at least Mg is contained as a graphite spheroidizing component, a spheroidal graphite cast iron can be obtained. The spheroidal graphite cast iron of the present invention contains As in an amount of 0.03 to 0.20% by weight. As is an element that moderates and suppresses medium-temperature embrittlement. This moderate embrittlement is caused by excess M other than that which contributed to the spheroidization of graphite.
g is considered to be present at the grain boundaries and to be expressed. A
s is an element that easily segregates in the final solidified portion or the ferrite grain boundary, and combines with Mg in the grain boundary to prevent embrittlement behavior of Mg, or surplus As after binding with Mg.
Is considered to improve the bonding state between the crystal grains and exert the effect of alleviating and / or suppressing the intermediate temperature brittleness.
When the content of As is less than 0.03% by weight, the effect of alleviating embrittlement at an intermediate temperature cannot be sufficiently obtained. Further, the content of As is 0.2.
When the content exceeds 0% by weight, the impact characteristics at low temperatures are deteriorated and the spheroidization of graphite is inhibited.

As described above, the spheroidal graphite cast iron of the present invention
It is considered that the ductility is excellent in the middle temperature embrittlement region around 00 ° C.

[Preferred Embodiment of the First Embodiment] The spheroidal graphite cast iron of the present invention having excellent medium-temperature ductility can employ the following preferred embodiments (inventions) in the first embodiment.

(Content of C) The content of C is from 2.7 to
4.2% by weight is preferred. C has a hypoeutectic composition of 2.6.
If it is less than% by weight, the number of spheroidal graphite is small, the solidification starting temperature is high, and the castability is poor. If the C content is high, the graphite tends to coarsen and dross increases.
% By weight or less is preferred.

(Content of Si) The content of Si is 3.5
~ 5.2% by weight is preferred. Si is an element that improves the oxidation resistance, and if it is less than 3.5% by weight, the oxidation resistance at 700 ° C. or more is insufficient, which is not preferable. Also, 5.
If it exceeds 2% by weight, a problem may occur in ductility, which is not preferable. When oxidation resistance is required, the content of Si is more preferably set to 4% by weight to 5.2% by weight. Further, for the purpose of ensuring good melting and castability, it is preferable that carbon equivalent, that is, C amount + Si amount / 3 be 4.0 to 5.5.

(Content of Mn) The content of Mn is 1.0
If the content is more than 1.0% by weight, the ductility is reduced. Further, for the purpose of ensuring sufficient ductility at low temperatures, 0.5 wt% or less is more preferable.

(S content) S is an unavoidable element, and its content is preferably 0.03% by weight or less. If the content of S exceeds 0.03% by weight, S may bind to Mg or Ca and inhibit graphite spheroidization.

(Mg content) Mg is a graphite spheroidizing component. The content of Mg is preferably 0.02 to 0.15% by weight. If the amount of Mg is less than 0.02% by weight, spheroidization of graphite may not be sufficient. If the Mg content exceeds 0.15% by weight, the graphite spheroidizing effect is saturated,
Furthermore, there is a possibility that excessive Mg is crystallized in the final solidified portion and causes intermediate temperature embrittlement. The content of Mg is 0.0
3 to 0.08% by weight is more preferred. Mg content is 0.0
If it exceeds 5% by weight, Mg may become an oxide and impair ductility at low temperatures. The graphite spheroidizing component is Mg
At least 0.02% by weight, and at least one of Mg, Ca, and rare earth elements in an amount of 0.02 to 0.15% by weight.
It may be configured to contain.

(Content of As) The preferred content of As is
0.03 to 0.15% by weight. This ensures sufficient ductility at low temperatures.

[Second Embodiment] A spheroidal graphite cast iron having excellent medium temperature ductility according to the second embodiment is a preferred embodiment of the first embodiment. That is, the spheroidal graphite cast iron excellent in the medium temperature ductility of the present invention has C: 2.7 to 4.2% by weight, Si:
3.5 to 5.2% by weight, Mn: 1.0% by weight or less, S:
0.03% by weight or less, Mg: 0.02 to 0.15% by weight
(Or at least 0.02% by weight of Mg,
At least one of Ca and rare earth elements: 0.02 to
0.15% by weight), As: 0.03 to 0.20% by weight,
The balance: Fe and Fe are inevitable.

That is, the spheroidal graphite cast iron of the present invention is the same as the first embodiment of the present invention, except that C: 2.7 to
4.2% by weight, Si: 3.5 to 5.2% by weight, Mn:
1.0% by weight or less, S: 0.03% by weight or less, Mg:
0.02 to 0.15% by weight (or at least 0.02% by weight of Mg and at least one of Mg, Ca and rare earth elements: 0.02 to 0.15% by weight). And Accordingly, it is considered that the spheroidal graphite cast iron of the present invention has excellent ductility in a medium temperature embrittlement region at around 400 ° C. When at least one of Ca and rare earth elements is contained in addition to Mg, spheroidization of graphite can be performed more stably.

[Third Embodiment] The spheroidal graphite cast iron of the present invention having excellent medium-temperature ductility contains C, Si, and Mn as main components, and at least Mg as a graphite spheroidizing component.
Cr, Mo, W, Ti, V, Ni,
A spheroidal graphite cast iron containing at least one or more types of Cu, the balance being Fe and unavoidable impurities, and having an As content of 0.1.
It is characterized by comprising from 0.3 to 0.20% by weight.

The mechanism by which the spheroidal graphite cast iron of the present invention exhibits an excellent effect is not necessarily clear yet, but is considered as follows. That is, the spheroidal graphite cast iron according to the first embodiment of the present invention further includes Cr, Mo, W, Ti, V, and N as matrix strengthening components.
It contains at least one of i and Cu. As a result, the matrix structure is strengthened and improved, for example, a solid solution substituted with or partially formed of Fe in the matrix forms a carbide or promotes graphitization. In addition, As and the base strengthening component do not interfere with each other, and therefore, As can improve the high-temperature strength while maintaining ductility at medium temperatures.

As described above, the spheroidal graphite cast iron of the present invention
It is considered that the ductility is excellent in the middle temperature embrittlement region around 00 ° C. In addition, since the high-temperature strength is improved, the heating between the low-temperature and high-temperature regions sandwiching the intermediate-temperature embrittlement region is repeatedly performed.
This is considered to be excellent in thermal fatigue life when cooled.

[Preferred Embodiment of Third Embodiment] The spheroidal graphite cast iron of the present invention having excellent medium-temperature ductility can adopt the following preferred embodiment (invention) in the third embodiment.

(Cr, Mo, W, Ti, V) The spheroidal graphite cast iron of the present invention may contain at least one of Cr, Mo, W, Ti, and V in an amount of 1.0% by weight or less. preferable. These Cr, Mo, W, Ti, and V are elements that improve high-temperature strength. In particular, when it is desired to improve the creep strength at high temperatures, the addition of Mo is effective. Note that these elements may be compounded. If the content of the above element is too large, ductility may be impaired.
The following is preferred. The above elements [Cr, Mo, W, T
at least one of i and V] is preferably 0.1
1 to 0.8% by weight. Thereby, high-temperature strength can be increased without impairing ductility.

(Ni, Cu) The spheroidal graphite cast iron of the present invention comprises:
It is preferable that at least one of Ni and Cu is contained in an amount of 3% by weight or less. Ni and Cu are graphitization promoting elements. Even if the content of Ni is large, there is little adverse effect, but if the content of Cu is large, the spheroidization of graphite is hindered. Therefore, the element and the content are selected according to the purpose or the desired composition. Among the above, Cr, Mo, W, and V are elements for promoting white iron, and therefore it is desirable to use Ni and Cu as graphitization promoting elements in combination. In that case, it is preferable to add an amount equal to or more than the above-mentioned white pig iron promoting element. The preferred content of the above element [at least one of Ni and Cu] is 0.2 to 1.0% by weight. Thereby, carbide formation is suppressed and cast iron excellent in ductility is obtained.

[Fourth Embodiment] A spheroidal graphite cast iron having excellent medium-temperature ductility according to the fourth embodiment is a preferred embodiment of the third embodiment. That is, the spheroidal graphite cast iron excellent in the medium temperature ductility of the present invention has C: 2.7 to 4.2% by weight, Si:
3.5 to 5.2% by weight, Mn: 1.0% by weight or less, S:
0.03% by weight or less, Mg: 0.02 to 0.15% by weight
(Or at least 0.02% by weight of Mg,
At least one of Ca and rare earth elements: 0.02 to
0.15% by weight), at least one kind of Cr, Mo, W, Ti, V: 1% by weight or less, at least one kind of Ni, Cu: 3% by weight or less, As: 0.03 to 0.20 % By weight, balance: Fe and unavoidable impurities.

That is, the spheroidal graphite cast iron according to the third embodiment of the present invention further comprises Cr, Mo,
At least one of W, Ti, and V: 1% by weight or less;
At least one kind of i and Cu: 3% by weight or less. Thereby, the spheroidal graphite cast iron of the present invention is 400
It is considered that the ductility is excellent in the middle temperature embrittlement region around ℃. In addition, since the high-temperature strength is improved, it is considered that the material has excellent thermal fatigue life when heating and cooling are repeatedly performed between a low temperature and a high temperature region sandwiching the intermediate temperature embrittlement region.

[Fifth Embodiment] The exhaust manifold of the present invention is characterized by being made of any of the spheroidal graphite cast irons described in the first to fourth embodiments and the preferred embodiments. .

The mechanism by which the spheroidal graphite cast iron of the present invention exhibits an excellent effect is not yet clear, but is considered as follows. That is, the exhaust manifold is repeatedly heated and cooled between the low temperature region and the high temperature region sandwiching the medium temperature embrittlement region. Therefore, when medium-temperature embrittlement occurs, thermal fatigue cracks are likely to occur and the growth thereof is fast. Since the exhaust manifold of the present invention is made of any of the spheroidal graphite cast irons described in the first to fourth embodiments and the preferred embodiments, the exhaust manifold has excellent ductility at a medium temperature, and has a thermal fatigue crack. Has excellent durability against

From the above, it is considered that the exhaust manifold of the present invention has excellent ductility in the middle temperature embrittlement region at around 400 ° C. and has excellent durability. .

[Sixth Embodiment] The method for producing spheroidal graphite cast iron of the present invention is to provide any of the spheroidal graphite cast irons described in the first to fourth embodiments and the preferred embodiments thereof. The raw material is prepared and cast into 4
It is characterized by being formed as spheroidal graphite cast iron having excellent ductility in a medium temperature embrittlement region at around 00 ° C.

The mechanism by which the spheroidal graphite cast iron of the present invention exhibits an excellent effect is not necessarily clear yet, but is considered as follows. That is, in spheroidal graphite cast iron containing Mg added for graphite spheroidization, medium temperature embrittlement is considered to cause medium temperature embrittlement due to grain boundary segregation of Mg. In the method for producing a spheroidal graphite cast iron of the present invention, a raw material is prepared and cast so as to have any composition of the spheroidal graphite cast iron described in the first to fourth embodiments and each preferred embodiment. By:
By adding As, Mg is bonded to Mg in the crystal grain boundary to prevent the embrittlement behavior of Mg, or excess As after bonding with Mg improves the bonding state between the crystal grains, and the medium temperature brittleness is improved. It is considered that the effect of reducing and / or suppressing is exhibited.

As described above, according to the method for producing spheroidal graphite cast iron of the present invention, spheroidal graphite cast iron excellent in medium temperature ductility can be easily produced regardless of the content of Mg or P, without requiring complicated and complicated management. It is thought that it can be manufactured. Further, the spheroidal graphite cast iron obtained by the present production method has excellent ductility in a moderate temperature embrittlement region at around 400 ° C.

[Examples of Preferred Fields of Application of the Invention] The spheroidal graphite cast iron obtained in the present invention and the above-mentioned embodiment is made of As
By adding an appropriate amount, moderate embrittlement is suppressed and
Necessary ductility near 00 ° C. can be ensured. A
Since s is also an element that turns the base structure of cast iron into pearlite, when the amount of As added is large, there is a method of performing ferritizing annealing before practical use. In addition, this spheroidal graphite cast iron has better ductility when the cast iron base is ferrite than when it is pearlite, but also has excellent ductility in the medium temperature embrittlement region at around 400 ° C. even when it is pearlite. It has the effect. The dissolution is not different from a general dissolution method, and a normal dissolution method can be adopted, and a cast iron which is inexpensive and excellent in medium temperature ductility can be easily obtained. The graphite spheroidal cast iron of the present invention (including the embodiments) is preferably applied to parts used in locations where high-temperature heating and cooling are repeated, in addition to automobile exhaust system parts such as exhaust manifolds.

[0039]

Embodiments of the present invention will be described below.

(First Example) In this example, the medium temperature embrittlement phenomenon of spheroidal graphite cast iron and the effect of As on the medium temperature embrittlement were examined. First, a sample made of spheroidal graphite cast iron was prepared. Ductile iron, graphite, and metal Si are prepared as melting raw materials, and 25 kg of this raw material is melted in a high frequency induction melting furnace. Then, Fe-Si-Mg is added to perform spheroidizing treatment, and Fe-Si is added to inoculate. And cast into a Y block sand mold. A necessary portion was cut out and subjected to ferrite annealing in a furnace at 920 ° C. × 3 h + 730 ° C. × 3 h in a nitrogen atmosphere electric furnace. Thereafter, a test sample was obtained by cutting. The chemical components of the obtained sample are shown in Table 1 (sample numbers: 1 to 6). In addition, about the sample of the sample number 3, the sample was cut out from the as-cast material.

[0041]

[Table 1]

Comparative Example 1 For comparison, As was not added (sample number: C
1) or a comparative sample having the same composition as in the first embodiment except that the content of As is out of the range of the present invention (sample number: C2: C3), in the same manner as in the first embodiment. It was produced (sample numbers: C1 to C3).

(Performance Evaluation Test) Performance evaluation tests of the obtained sample according to the first example and the comparative sample of Comparative Example 1 were performed by a tensile test and a bending test at 400 ° C. The results obtained are shown in FIG. The tensile test piece had a parallel portion having a shape of φ8 × 40 mm, and a 2.5 × 1
The test was performed at a strain rate of 0 ^-4 / sec. 400 ° C bending test
The purpose of this test was to evaluate the ductility of the test piece more easily than the tensile test. A three-point bending test as shown in FIG.
^{Performed at} a displacement speed of ^-3 mm / sec. Next, for the comparative sample (sample number C1), the change in tensile elongation at break due to the test temperature was examined. The result is shown in FIG. The tensile test piece had a parallel portion having a shape of φ8 × 40 mm.
The test was performed at a strain rate of × 10 ^-4 / sec.

(Results of Performance Evaluation Test) As is apparent from FIG. 1, the elongation at break at 400 ° C. and the flexure at bending at 400 ° C. change in the same manner as the As amount increases. In other words, in any case, the content is extremely low when the As content is 0.02% or less, but increases rapidly when the As content exceeds 0.03%, and tends to become maximum when the content is about 0.1%. Can be seen. Thus, according to the present example, it is found that the medium temperature embrittlement is suppressed by the addition of As. Also,
As for the effect of suppressing the medium temperature embrittlement by the addition of As, the amount thereof is about 0.5%.
When the content is saturated at 1% and exceeds 0.2%, the effect is reduced.
It turns out that 2% is desirable. On the other hand, as is clear from FIG. 3, in the comparative sample of Sample No. C1 to which As was not added, the elongation at break was remarkably reduced at a temperature around 400 ° C., indicating that the medium-temperature embrittlement occurred. . In sample No. 3, in the as-cast material, about 60% of the matrix had a pearlite structure. As a result of bending at 400 ° C. using the as-cast material, a deflection amount of 1.02 mm was obtained. I knew it was there.

(Second Embodiment) In the same manner as in the first embodiment, spheroidal graphite cast iron with different amounts of C and Si (sample number:
7-9), spheroidal graphite cast iron to which Ca or a rare earth is added together with Mg as a spheroidizing agent (sample numbers 10-1)
2), spheroidal graphite cast iron (Sample Nos. 13 to 17) to which Cr, Ti, V, Mo, and W are added, which are known as elements that strengthen the matrix to increase the high-temperature strength, and Ni and Cu, which are known as graphitization promoting elements. Spheroidal graphite cast iron (sample No. 18 ~
20) were manufactured and cut into desired sizes to prepare samples (sample numbers: 7 to 20). The medium-temperature embrittlement phenomenon of spheroidal graphite cast iron and the effect of As on the medium-temperature embrittlement were examined. Table 2 shows the chemical components of the obtained sample. In addition,
The performance evaluation test was performed by a bending test at 400 ° C. The obtained results are also shown in Table 2.

[0046]

[Table 2]

Comparative Example 2 For comparison, a comparative sample having the same composition as that of the second embodiment except that the As content was outside the range of the present invention was prepared in the same manner as in the second embodiment ( Sample number: C4 to C17),
Similarly, a performance evaluation test was performed by a bending test at 400 ° C. The results obtained are shown in Table 3. Table 3 shows the chemical components of the obtained comparative sample.

[0048]

[Table 3]

As is clear from Tables 2 and 3, in all cases, the amount of deflection of the sample according to the present example was larger than that of the comparative sample of Comparative Example 2, and the medium temperature embrittlement was caused by the addition of As. Is suppressed.

As is clear from the above examples, the spheroidal graphite cast iron of the present invention can suppress the medium temperature embrittlement and secure the ductility at around 400 ° C. by adding an appropriate amount of As. Further, it is apparent that the ferrite is more excellent in the case where the cast iron base is made of pearlite than in the case where it is made of pearlite, but the effect is exhibited even when the amount of pearlite is large. The melting is not different from the ordinary melting method, and a cast iron which is inexpensive and excellent in medium-temperature ductility can be easily obtained. Therefore, the spheroidal graphite cast iron of the present invention is more suitable for exhaust system parts for automobiles such as exhaust manifolds. That is, since it is excellent in medium-temperature ductility, even when it is applied to a use environment in which high-temperature heating and cooling are repeated, the life is long, and an extremely large practical effect can be expected.

[Brief description of the drawings]

FIG. 1 is a diagram showing performance evaluation test results of a spheroidal graphite cast iron obtained in a first example of the present invention and a spheroidal graphite cast iron for comparison of Comparative Example 1.

FIG. 2 is an explanatory diagram illustrating a bending test performed for evaluating the performance of the spheroidal graphite cast iron obtained in the first example of the present invention and the spheroidal graphite cast iron for comparison of Comparative Example 1.

FIG. 3 is a diagram showing performance evaluation test results of a comparative spheroidal graphite cast iron of Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Test piece 2 ... Thermocouple 3 ... Support base 4 ... Jig for reduction

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shogo Iwanaga 41-Cho Chu-Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Institute, Inc. 41, Yokomichi, Toyota Central Research Laboratory, Inc. (72) Inventor Yoshihiro Hibino 1, Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Harumi Ueno 1, Toyota Town, Toyota City, Aichi Prefecture Toyota Automobile Co., Ltd.

Claims (6)

[Claims] 1. A spheroidal graphite cast iron containing C, Si, and Mn as main components, at least Mg as a graphite spheroidizing component, and the balance being Fe and unavoidable impurities. A spheroidal graphite cast iron having excellent medium temperature ductility, characterized by comprising .20% by weight. 2. C: 2.7 to 4.2% by weight, Si: 3.5 to 5.2% by weight, Mn: 1.0% by weight or less, S: 0.03% by weight or less, Mg: 0 0.02 to 0.15% by weight, or at least 0.02% by weight of Mg, at least one or more of Mg, Ca and rare earth elements: 0.02 to 0.15% by weight, As: 0.03 to 0% .20% by weight, balance: Spheroidal graphite cast iron excellent in medium temperature ductility, characterized by being composed of Fe and unavoidable impurities. 3. C, Si, Mn as main components, at least Mg as a graphite spheroidizing component, and Cr, Mo, W, Ti, V, Ni, C as a matrix strengthening component.
u is a spheroidal graphite cast iron containing at least one element of u and the balance of Fe and unavoidable impurities.
A spheroidal graphite cast iron excellent in medium temperature ductility, characterized in that it contains 3 to 0.20% by weight. 4. C: 2.7 to 4.2% by weight, Si: 3.5 to 5.2% by weight, Mn: 1.0% by weight or less, S: 0.03% by weight or less, Mg: 0 0.02 to 0.15% by weight or at least 0.02% by weight of Mg, at least one of Mg, Ca and rare earth elements: 0.02 to 0.15% by weight, Cr, Mo, W, Ti , V: at least 1% by weight, Ni, Cu at least one: 3% by weight, As: 0.03 to 0.20% by weight, balance: Fe and unavoidable impurities Spheroidal graphite cast iron with excellent medium temperature ductility. 5. An exhaust manifold comprising any of the spheroidal graphite cast irons according to claim 1. 6. A ductile material in a medium temperature embrittlement region at around 400 ° C. by preparing and casting a raw material so as to have any composition of the spheroidal graphite cast iron according to any one of claims 1 to 4. A method for producing spheroidal graphite cast iron, characterized by being obtained as excellent spheroidal graphite cast iron.