JP2000119793A - Low expansion cast iron with low temperature stability, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low expansion cast iron having low temperature stability, which is free from martensitic transformation even if cooled to about -100 deg.C and has such a low expansion property as to have <=2×10/K coefficient of thermal expansion in the vicinity of room temperature, and its manufacturing method. SOLUTION: This cast iron is an austenitic cast iron having graphite structure and has a composition containing, by weight, 0.6-1.5% carbon(C), 32-37% nickel(Ni), 0-1.0% silicon(Si), and 0-1.0% manganese(Mn) and having 0.2-0.4% solid- solution carbon(C) content. This cast iron can be manufactured by subjecting a cast iron, which has a composition containing, at least, 0.6-1.5%, by weight, carbon(C), 32-37% nickel(Ni), 0-1.0% silicon(Si), 0-1.0% manganese(Mn), and 0-3% cobalt(Co) and having the balance iron(Fe), to heating and holding at 900-1200 deg.C and subjecting this heated and held cast iron to furnace cooling down to 600-850 deg.C and then to rapid cooling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-expansion cast iron and a method for producing the same, and more particularly, to a low-temperature-stable low-expansion cast iron having a low coefficient of thermal expansion at 300 ° C. or lower and not causing tissue transformation. It relates to a manufacturing method.

[0002]

2. Description of the Related Art In recent years, demands for dimensional accuracy have been increasing in semiconductor manufacturing equipment, precision processing equipment, analysis evaluation equipment, and the like, and the thermal expansion of parts or members constituting those equipment has been minimized. As a result, the number of cases that meet the demand for dimensional accuracy is increasing. In recent years, as a material for parts or members having such a small thermal expansion,
Low expansion cast iron containing 4040% nickel (Ni) has been attracting attention.

[0003] That is, 36% Ni-
Invar alloy cast iron with improved machinability and castability by precipitating (or crystallizing) graphite in its metal structure based on low expansion alloy composition such as Fe alloy and 30-6% Co-Fe alloy And Super Invar alloy cast iron are attracting attention.

[0004]

However, a precision device incorporating parts or members made of the low expansion cast iron as described above, for example, when used in rolling or cold regions passing through a cold region, is not suitable for use in a low expansion cast iron. The problem of organizational transformation and dimensional variation still occurs. That is, the base composition of the above-mentioned invar alloy cast iron or super invar alloy cast iron has a crystal structure transformed from austenite to martensite at a temperature below the freezing point, and a portion transformed into martensite expands and leaves strain, thereby causing dimensional fluctuation. . In addition, since the portion where the martensitic transformation occurs is non-uniform, the dimensional change and the distribution of residual strain are also non-uniform, and the accuracy of the parts or members is likely to be greatly impaired. In this type of low-expansion cast iron, when the matrix has an invar composition or a super invar composition, the same transformation takes place.

By the way, the martensitic transformation is 5
It is a reversible transformation in a temperature range of 00 ° C. or less. Once transformed, it remains a martensite structure even if its temperature rises to room temperature, and its thermal expansion coefficient also increases.

Further, low-expansion cast iron is used as a casting material because it contains graphite. However, segregation of the alloy composition in the casting structure is remarkable. Therefore, a composition that easily causes martensitic transformation is easily formed in the dendrite phase gap, and the stability at low temperatures is further deteriorated.
For this reason, there is a problem that the apparatus cannot be used as a part if the apparatus is assembled into parts or members and the apparatus is likely to be exposed to low temperatures.

As low-temperature-stable low-expansion cast iron, for example, Japanese Patent Application Laid-Open Nos. 1-111842 and 62-284039,
Austenitic cast iron containing a graphite structure is also known from Japanese Patent Application Laid-Open No. 3-90541, but is not sufficiently satisfactory in terms of the balance of various properties, such as securing low expansion properties and preventing martensitic transformation. .

The inventors of the present invention have examined the problem of martensitic transformation in the dendrite phase in the microstructure of the low-expansion cast iron system, and have confirmed the following. That is, the problematic martensite structure is involved not in the transformation of the entire cast iron but in the transformation of the dendrite phase gap. In a normal production process, segregation which is a cause is inevitably formed. In addition, it has been found that by controlling the amount of solute carbon within a certain limited range, it is possible to simultaneously achieve low expansion and prevent martensitic transformation.

The present invention has been made based on the above findings, and does not cause martensitic transformation even when cooled to about -100 ° C., and has a thermal expansion coefficient near room temperature of 2 × 10 ⁻⁶ / K or less. It is an object of the present invention to provide a low-temperature stable low-expansion cast iron having a low expansion property and a method for producing the same.

[0010]

According to the first aspect of the present invention, there is provided an austenitic cast iron having a graphite structure.
0.6-1.5% carbon (C), 32-37% nickel (Ni), 0
~ 1.0% silicon (Si) and 0 ~ 1.0% manganese (Mn)
And low-temperature-stable low-expansion cast iron characterized by containing 0.2% to 0.4% of solute carbon (C).

According to a second aspect of the present invention, there is provided the low-temperature-stable low-expansion cast iron according to the first aspect, wherein the weight ratio of cobalt is 0 to 3%.
(Co), and the total amount of nickel (Ni) and cobalt (Co) is 33 to 37%.

According to a third aspect of the present invention, in the low-temperature-stable low-expansion cast iron according to the first or second aspect, at least one of magnesium (Mg) and calcium (Ca) is contained in a weight ratio of 0.02 to 0.1%. It is characterized by containing.

According to a fourth aspect of the present invention, there is provided a low-temperature-stable low-expansion cast iron according to the second or third aspect, wherein
The amount of C), the amount of nickel (Ni) and the amount of cobalt (Co) are calculated by the following formula: [340 x solid solution carbon (C)% + 17.5 x nickel (Ni)%-
19.0 ×% of nickel (Co)%] ≧ 570.

According to a fifth aspect of the present invention, there is provided a low-temperature stable low-expansion cast iron according to any one of the first to fourth aspects, wherein niobium (Nb), titanium (Ti), tantalum (Ta), zirconium (Z
r), at least one of hafnium (Hf), vanadium (V), chromium (Cr), tungsten (W) and molybdenum (Mo)
It is characterized by containing 0.2-2.0% by weight of seed elements.

The invention according to claim 6 is characterized in that the weight ratio is 0.6 to 1.5%.
At least carbon (C), 32-37% nickel (Ni), 0-1.0% silicon (Si), 0-1.0% manganese (Mn) and 0-3% cobalt (Co). Is a step of heating and holding the cast iron, which is iron (Fe), at a temperature of 900 to 1200 ° C., and after cooling the heated and held cast iron to a temperature of 600 to 850 ° C.,
This is a method for producing a low-temperature-stable low-expansion cast iron characterized by quenching.

The invention according to claim 7 is characterized in that the weight ratio is 0.6 to 1.5%.
At least carbon (C), 32-37% nickel (Ni), 0-1.0% silicon (Si), 0-1.0% manganese (Mn) and 0-3% cobalt (Co). Is a step of heating and holding the cast iron, which is iron (Fe), at a temperature of 900 to 1200 ° C., and after cooling the heated and held cast iron to a temperature near room temperature,
This is a method for producing a low-temperature-stable low-expansion cast iron, which is characterized by heating and holding at a temperature of 00 to 850 ° C. and then quenching.

According to an eighth aspect of the present invention, there is provided a method for producing a low-temperature stable low-expansion cast iron according to the sixth or seventh aspect,
Cast iron is niobium (Nb), titanium (Ti), tantalum (Ta), zirconium (Zr), hafnium (Hf), vanadium (V), chromium
(Cr), tungsten (W) and molybdenum (Mo) are characterized by containing at least one element in a weight ratio of 0.2 to 2.0%.

In the low expansion cast iron according to the present invention, Ni, Ni
+ Co is a basic constituent element as an invar phenomenon,
Carbon (C) is an essential element for obtaining a graphite dispersed structure. The selection of these constituent elements and composition ratios is determined based on experiments as follows.

That is, component samples of low-expansion cast iron obtained by many melting experiments are prepared, and the temperatures at which the martensitic transformation points of these component samples are generated are measured. Here, the measurement of the martensitic transformation start temperature utilizes the fact that the temperature below the freezing point is obtained with a stable gradient inside the dewar containing liquid nitrogen according to the distance from the liquid nitrogen liquid level. That is, after holding the low-expansion cast iron sample together with the thermocouple at a predetermined distance (each freezing point temperature) from the liquid nitrogen liquid level inside the dewar, observe the micro-structure and check whether martensite deformation occurs in the dendrite gap. Was done in a way to confirm. The measurement of the martensitic transformation onset temperature is, for example, about −20 ° C. for a typical low expansion tension iron of 30% Ni-5% Co system.

In the low expansion cast iron containing Si, Mn, Mg, Ti, Cr, etc., the martensitic transformation start temperature is measured by the above-mentioned method of measuring the martensite transformation start temperature. It is clear that the relationship is expressed by the following equation.

Martensitic transformation onset temperature = 470-340 x solute carbon content% -17.5 x Ni% + 19 x Co% (1) In other words, as the Ni content increases, the martensitic transformation onset temperature decreases, and Co The higher the amount, the higher the onset temperature of martensitic transformation. The martensitic transformation start temperature in (1) above does not indicate the tissue transformation of the entire alloy, but indicates the transformation start temperature occurring in some dendrite phase gaps.

In the low expansion cast iron according to the present invention, Co
Exhibits low expansion due to Invar effect when contained below
The total amount of Ni + Co is about 33 to 37%, and if the condition is out of this range, the low expansion property is greatly impaired.
~ 37%. In other words, even if the amount of Co exceeds 3%,
Even when Ni is less than 32%, the martensitic transformation start temperature increases.

In the low expansion cast iron according to the present invention, the amount of solute carbon is measured by a method of directly analyzing the amount of solute carbon in a matrix region where there is no graphite from the metal cross section by an EPMA (Electron Prove Micro Analysis) method, or by atomic absorption analysis. From the measured value of the total carbon amount by the method, there is a method of calculating from the amount of residual graphite after dissolving the metal part with an acid, but here,
It was measured by the former method.

The content of solute carbon is determined as follows:
% Of iron-nickel (Fe-Ni) alloy solidified in a normal sand mold, most of the total carbon becomes graphite, and the amount of solid solution in the metal matrix is about 1.0-1.6% It is. On the other hand, when the total C content is 0.8% or less, if the carbide element is not contained, the carbon is substantially in a solid solution, and the total carbon amount and the solute carbon amount are almost the same value.

Here, the martensitic transformation onset temperature is-
The appropriate range for the amount of solute carbon to be reduced to 100 ° C or less is 0.2
~ 0.4%. That is, when it is less than 0.2%, the thermal expansion coefficient at around room temperature can be as low as 1.5 × 10 ⁻⁶ / K or less, but the martensitic transformation onset temperature is -100 ° C. or more. On the other hand, if it exceeds 0.4, the coefficient of thermal expansion becomes 3
× 10 ⁻⁶ / K or more.

In the low-expansion cast iron according to the present invention, Si may be contained as a graphitization promoting element and an oxidation-reducing element in dissolution in the atmosphere. Mn is an element that contributes to the effect of reducing oxidation and strengthening solid solution.
% Is the limit.

Further, Mg and Ca are elements that are pooled to increase the strength of the low-expansion cast iron by spheroidizing graphite, and are added if necessary. The amounts thereof are 0.02 to 0.1%. That is, if the content exceeds 0.1%, workability may be impaired due to precipitation of intermetallic compounds. Low expansion cast iron according to the present invention, the basic components Fe, Ni and C, other Co, Si,
In addition to the elements of Mn and Mg (Ca), at least one element such as Nb, Ti, Ta, Zr, Hf and V can be contained in order to improve strength, Young's modulus, corrosion resistance and the like. These elements have a large tendency to form carbides, disperse and precipitate the carbides in the matrix, and have the effect of increasing the strength and hardness of the low expansion cast iron. And this carbide is more stable than graphite, and as an as cast material, it further reduces the solute carbon as compared to the case of only graphite tissue, thus improving the low expansion property of the cast material. However, the martensitic transformation temperature tends to increase.

Therefore, by performing the decomposition of graphite in the solution treatment at 900 to 1200 ° C. and the heat treatment for controlling the solute carbon at 600 to 850 ° C., the strength improvement of the low temperature stable low expansion cast iron is achieved. . If the content of these elements is large, coarse carbides are formed at the crystal grain boundaries and the strength is lowered, so that the content is at most 2.0%.

Further, at least one element such as Cr, W, and Mo may be added or contained because it has an effect of increasing the Young's modulus of the low expansion cast iron, but if it is too much, the low expansion property is greatly impaired. So at most 2% is the limit. The above Cr is effective not only in improving Young's modulus but also in improving corrosion resistance. Low-expansion cast iron has high corrosion resistance to alkaline aqueous solution and nitric acid due to high Ni content, and exhibits excellent corrosion resistance to hydrochloric acid and seawater when it contains Cr.

In the low expansion cast iron according to the present invention, the predetermined amount of solid solution graphite is controlled, for example, as follows.
That is, the total C content of this low expansion cast iron is 0.6 to 1.5%, and a cast iron containing C is prepared within this range.
Heat and hold at a high temperature of 900-1200 ° C. By this heat holding, the amount of solid solution carbon increases to reach the equilibrium carbon concentration at the heating temperature, compared with the cast material. In other words, 900-12
During heating and holding at a temperature of 00 ° C (solution heat treatment), the solid solution amount becomes about 2 to 6.5% due to re-solution from graphite,
The entire solid solution carbon concentration distribution becomes almost uniform.

Next, from the heating and holding state, 600 to 850
After slowly cooling by furnace cooling to a temperature of ° C. and holding for a predetermined time according to the thickness of the workpiece, cooling to a room temperature is performed at a relatively high speed by air cooling, oil cooling, or water cooling. By this quenching treatment, the cast iron is graphitized again, and the amount of solute carbon is reduced.
It is easily controlled to 0.2-0.4%. In other words, the following formula [340 x solid solution carbon (C) content% + 17.5 x nickel (Ni) content%-
19.0 × amount of nickel (Co)%] ≧ 570.

The heat treatment according to the sixth aspect of the present invention not only controls the amount of solute carbon, but also has the effect of reducing Ni segregation in the dendrite phase gap. In other words, after Ni is homogenized by heating and holding at 900-1200 ° C (solution heat treatment), Ni is segregated again when it is generally cooled down to 500 ° C or less in the furnace cooling process. However, the above-mentioned Ni segregation does not occur between the furnace cooling to a temperature of 600 to 850 ° C. and the temperature maintenance.

In this heat treatment process, Ni segregation is reduced while controlling the amount of dissolved carbon. Since the reduction of the Ni segregation increases the Ni concentration in the dendrite phase gap, it lowers the martensitic transformation temperature and reduces the deviation from the invar composition to improve the low expansion property.

In the heat treatment according to the seventh aspect of the present invention, the heat treatment is performed after the solution is solidified at a temperature of 900 to 1200 ° C., rapidly cooled to room temperature, further heated and maintained at a temperature of 600 to 850 ° C., and then rapidly cooled. This is because, while controlling the decomposition of Ni misfolding due to solution treatment and the amount of solute carbon, the re-generation of Ni segregation due to cooling in a temperature range of 500 ° C. or lower is prevented. In addition, in the case of any heat treatment, a mold, a graphite mold,
Alternatively, in the case of a product that has been rapidly solidified by a water-cooling type, low-temperature stability and low expansibility can be obtained by applying only heat treatment (quick cooling after holding at 600 to 850 ° C) to control solid solution carbon. .

[0035]

Embodiments of the present invention will be described below.

Example 1 First, each cast iron material having the component composition (% by weight) shown in Table 1 was
Melt using a high-frequency electric furnace with a capacity of 25 kg each, 1 inch Y
A cast iron sample was manufactured by pouring into a block sand mold. Next, each of the cast iron samples was subjected to 900-1200 ° C. as shown in Table 2.
After holding for 2 hours in a heat treatment furnace (in the air) set at a temperature of 5 ° C., water-cooling was carried out, followed by holding at a temperature of 600 to 850 ° C. for 4 hours, followed by rapid cooling by water cooling to produce a low-expansion cast iron.

[0037]

[Table 1]

[Table 2] For each of the low-expansion cast irons produced above, the amount of dissolved carbon (% by weight) measured and the coefficient of thermal expansion up to 100 ° C. (× 10
⁻⁶ / K) and the martensitic transformation onset temperature (° C.) are shown in Table 3.

[0038]

[Table 3] As can be seen from Table 3, each low expansion cast iron according to the present invention is:
In each case, the solute carbon content is in the range of about 0.2 to 0.4%, the coefficient of thermal expansion from room temperature to 100 ° C is 3.0% or less, and the onset temperature of martensitic transformation of dendrite phase gap is -100 ° C or less. Was.

Comparative Example 1 For comparison, each cast iron material having the component composition (% by weight) shown in Table 4 was melted using a high-frequency electric furnace having a capacity of 25 kg, and poured into a 1-inch Y block sand mold. A cast iron sample was made.
Next, the above-mentioned cast iron samples were sequentially subjected to a solution heat treatment and a solute carbon control heat treatment under the conditions shown in Table 4 to produce a low expansion cast iron.

[0040]

[Table 4] For each of the low-expansion cast irons produced above, the amount of dissolved carbon (% by weight) measured and the coefficient of thermal expansion up to 100 ° C. (× 10
^-6 / K) and the martensitic transformation onset temperature (° C.) are shown in Table 5.

[0041]

[Table 5] Comparative Example 2 C was 1.0%, Ni was 32%, Si was 0.1%, and Mn was 0.1% by weight.
%, Co 3.0%, Ni + Co 35%, Mg 0.06% Cast iron material is melted using a 25kg capacity high frequency electric furnace and 1 inch
Cast iron samples were prepared by pouring into a Y block sand mold. Next, the cast iron samples were prepared under the conditions shown in Table 6 together.
Solution heat treatment and solid solution carbon amount control heat treatment are sequentially performed,
A low expansion cast iron was manufactured.

[0042]

[Table 6] With respect to the low expansion cast iron produced above, the measured solid solution carbon amount (% by weight), the coefficient of thermal expansion up to 100 ° C. (× 10 ⁻⁶ / K), and the martensite transformation start temperature (° C.) are shown in Table 5 above. Show.

As can be seen from Table 5, the content of Ni is 30%,
For Sample B ₁ which is outside the composition range of Co low expansion cast iron according to the present invention in a content of 5%, the thermal expansion coefficient is low, high martensitic transformation temperature, also the composition ratio of Ni is larger sample Sample B ₃ , in which the composition ratio of B ₂ , Si and Mni is large,
And the case of C-intensive Sample B _4, respectively low expansion is significantly impaired.

On the other hand, in the case of Comparative Example 2 relating to the heat treatment conditions,
For Sample C ₁ is the solution temperature is low, to dendrite phase
Ni segregation cannot be avoided and cast iron with a high martensitic transformation temperature has not been formed. In Sample C _2, since the specific carbon content control heat treatment 500 ° C. and lower, and recurrence segregation of Ni, which is assumed martensitic transformation temperature is high.

Further, in each of the samples C ₃ and C ₄ , if the cooling rates of the solution heat treatment and the solute carbon amount control heat treatment are slow, re-segregation of Ni occurs as in the case of the low temperature heating of the sample C ₂ . Conversely, Sample C ₅ is dissolved carbon amount limiting temperature 900 ° C.
The result is that the thermal expansion coefficient increases because of the high solubility of carbon in the alloy matrix.

Example 2 Each of the cast iron materials having the component compositions (% by weight) shown in Table 7 was weighed in an amount of 25 kg.
It was melted using a high-frequency electric furnace having a capacity and poured into a 1-inch Y block sand mold to produce a cast iron sample. Next, the above-mentioned cast iron samples were subjected to a solution heat treatment and a solid solution carbon amount control heat treatment sequentially under the conditions shown in Table 7 to produce low expansion cast iron.

[0047]

[Table 7] Samples A ₁ of each low-expansion cast iron and Example 1 prepared above, dissolved carbon amount measured respectively (wt%), 100
Table 8 shows the coefficient of thermal expansion up to ° C. (× 10 ⁻⁶ / K), the martensite transformation start temperature (° C.), and the Young's modulus (GPa).

[0048]

[Table 8] As can be seen from Table 8, each low expansion cast iron according to the present invention is:
All have a solute carbon content in the range of about 0.2 to 0.4%, a coefficient of thermal expansion from room temperature to 100 ° C of 3.0% or less, a low expansion property with a martensitic transformation initiation temperature of dendrite phase gap of -100 ° C or less, and Young. The rate was around 110-160.

Comparative Example 3 Each of the cast iron materials having the component compositions (% by weight) shown in Table 9 was weighed in an amount of 25 kg.
It was melted using a high-frequency electric furnace having a capacity and poured into a 1-inch Y block sand mold to produce a cast iron sample. Next, the above-mentioned cast iron samples were sequentially subjected to a solution heat treatment and a solid solution carbon amount control heat treatment under the conditions shown in Table 9 to produce low expansion cast iron.

[0050]

[Table 9] Samples A ₁ of each low-expansion cast iron and Example 1 prepared above, dissolved carbon amount measured respectively (wt%), 100
Table 10 shows the coefficient of thermal expansion up to ° C. (× 10 ⁻⁶ / K), the martensite transformation start temperature (° C.), and the Young's modulus (GPa).

[0051]

[Table 10] In Example 2 and Comparative Example 3, Ti, Ta, Nb, Hf, V,
It shows the effect when Zr, Cr, Mo and W are added and contained.If it is an appropriate amount as in each low expansion cast iron according to the present invention, it is partially dispersed as a carbide and simultaneously partially dispersed. Is dissolved to improve strength, Young's modulus and hardness. However, if the amount exceeds the appropriate range,
Excessive solid solution increases the coefficient of thermal expansion, and coarse carbides precipitate at the crystal grain boundaries, reducing the contribution to the improvement of Young's modulus and hardness.

[0052]

According to the first to fifth aspects of the present invention, there is provided a low-temperature-stable low-expansion cast iron having a low coefficient of thermal expansion at a low temperature of 300 ° C. or lower and causing no structural transformation.
That is, a low expansion cast iron suitable for a component or a component of a semiconductor manufacturing apparatus, a precision processing apparatus, or an analysis and evaluation apparatus that requires dimensional accuracy is provided.

According to the invention of claims 6 to 8,
A low-temperature-stable low-expansion cast iron that has a low coefficient of thermal expansion at a low temperature of 300 ° C. or less and does not cause structural transformation can be mass-produced with good yield.

[0054]

Claims (8)

[Claims] An austenitic cast iron having a graphite structure, comprising 0.6 to 1.5% by weight of carbon (C) and 32 to 37% of nickel.
(Ni), 0-1.0% silicon (Si) and 0-1.0% manganese (Mn), and the amount of solute carbon (C) is 0.2-0.4%
Low temperature stable low expansion cast iron characterized by the following. 2. The composition contains 0 to 3% by weight of cobalt (Co) and has a total amount of nickel (Ni) and cobalt (Co) of 33%.
The low-temperature-stable low-expansion cast iron according to claim 1, wherein the low-temperature-stable low-expansion cast iron is at most 37%. 3. Magnesium (Mg) and calcium (Ca)
The low-temperature-stable low-expansion cast iron according to claim 1 or 2, wherein at least one of the following is contained in a weight ratio of 0.02 to 0.1%. 4. The amount of solid solution carbon (C), the amount of nickel (Ni) and the amount of cobalt (Co) are expressed by the following formula: [340 × solid solution carbon (C)% + 17.5 × nickel (Ni)% −
The low-temperature-stable low-expansion cast iron according to claim 2 or 3, wherein 19.0 x amount of nickel (Co)%] ≥ 570. 5. Niobium (Nb), titanium (Ti), tantalum (T
a), zirconium (Zr), hafnium (Hf), vanadium (
V), chromium (Cr), tungsten (W) and molybdenum (M
The low-temperature-stable low-expansion cast iron according to any one of claims 1 to 4, wherein at least one element in o) is contained in a weight ratio of 0.2 to 2.0%. 6. Carbon (C) of 0.6-1.5% by weight,
37% nickel (Ni), 0-1.0% silicon (Si), 0-
900-1200 cast iron containing at least 1.0% manganese (Mn) and 0-3% cobalt (Co) with the balance being iron (Fe)
A method for producing low-temperature stable low-expansion cast iron, comprising: a step of heating and holding at a temperature of 600 ° C .; 7. Carbon (C) of 0.6-1.5% by weight,
37% nickel (Ni), 0-1.0% silicon (Si), 0-
Cast iron containing at least 1.0% manganese (Mn) and 0-3% cobalt (Co), with the balance being iron (Fe),
A step of heating and holding at a temperature of 00 ° C .; a step of cooling the heated and held cast iron to a temperature close to room temperature, heating and holding it again at a temperature of 600 to 850 ° C., and then quenching. A method for producing expanded cast iron. 8. The cast iron is composed of niobium (Nb), titanium (Ti), tantalum (Ta), zirconium (Zr), hafnium (Hf), vanadium (V), chromium (Cr), tungsten (W) and molybdenum (Mo). )) At least one element in a weight ratio of 0.2 to 2.0
The method for producing low-temperature-stable low-expansion cast iron according to claim 6 or 7, wherein