JP2003138346A - Low thermal expansion cast alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low thermal expansion cast alloy in which the defects of the conventional low thermal expansion material are solved, and which has a sufficiently low thermal expansion coefficient and satisfactory castability, and whose thermal expansion is extremely reduced by the application of suitable heat treatment after casting. SOLUTION: The low thermal expansion cast alloy has a componential composition containing, by weight, 25.0 to 32.0% Ni, 7.0 to 14.0% Co, 0.3 to <1.0% C, <0.5% Si and <0.3% Mn, and containing 0.01 to 0.06% rare earth elements as well, and the balance substantially Fe. In the cast alloy, on casting, spheroidization treatment of graphite and deoxidation/degassing treatment are performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low thermal expansion casting alloy, and more particularly to a low thermal expansion casting alloy used for equipment, parts and the like that require dimensional stability accuracy against temperature.

[0002]

2. Description of the Related Art Conventionally, as an iron-based low thermal expansion material, an Invar alloy having a thermal expansion coefficient of about 1/10 that of a steel material or a cast iron material at room temperature has been used, and further, a Super Invar having a thermal expansion coefficient of about 0 at room temperature is close to 0. It has been known. However, since the above-mentioned Invar and Super Invar do not contain C or Si, they are extremely poor in castability and have a problem that they cannot be used as a casting alloy. Further, since the solidified structure is austenite containing no graphite, there is a problem that its machinability is poor. In addition, JP-A-4-28914
As shown in No. 9, there is a problem that special processing must be performed to manufacture the above-mentioned Invar or Super Invar. Further, JP-A-58-210149,
JP-A-3-90541, JP-A-4-136136,
JP-A-8-269613, JP-A-11-158542
In No. 6, a low thermal expansion material having improved castability by adding C and Si is provided. However, in such a composition, a microstructure change from austenite to martensite is likely to occur, while avoiding it. In that case, the low thermal expansion property is compositionally impaired. In addition, Niresist cast iron and the like are known as materials having good castability and small thermal expansion, but regarding the thermal expansion coefficient, it is about 1 / third that of steel materials and cast iron materials.
It is about 2.

[0003]

Therefore, the present invention solves the above-mentioned drawbacks of the conventional low thermal expansion materials, has a sufficiently small thermal expansion coefficient, and has good castability. An object of the present invention is to provide a low thermal expansion cast alloy having an extremely small expansion.

[0004]

In order to achieve the above object, the low thermal expansion cast alloy of the present invention has a composition of wt%.
And Ni: 25.0 to 32.0%, Co: 7.0 to 1
4.0%, C: 0.3 to less than 1.0%, Si: 0.5%
%, Mn: less than 0.3%, 0.01 to 0.06% of a rare earth element, the balance being substantially Fe, and spheroidizing and deoxidizing graphite during casting. The first feature is that degassing is performed. Further, the low thermal expansion cast alloy of the present invention has, in addition to the above-mentioned first characteristic, 0.20 to 1.50 one or more elements selected from Mo, V, W and Nb as a component composition. The second feature is that the content is wt% and the balance is substantially Fe. Further, the low thermal expansion casting alloy of the present invention has, in addition to the above-mentioned first or second characteristics, 1000 to 11 after casting.
The third characteristic is that the solid solution C in the matrix is precipitated as graphite or carbide by performing a rapid cooling treatment after heating and holding at 50 ° C.

According to the low thermal expansion cast alloy according to the first aspect of the present invention, the alloy composition having the composition shown therein can provide an alloy having good low thermal expansion characteristics and good castability and workability. Can be provided. The present inventors have found that the coefficient of thermal expansion can be made extremely small by containing a rare earth element in a predetermined range,
The alloy of the present invention was obtained. Hereinafter, all component compositions are shown by weight%.

The rare earth element content is 0.01 to 0.06%. By adding a rare earth element, the coefficient of thermal expansion can be greatly reduced. Because it also has a degassing effect,
Improving castability can also be expected. The addition of the rare earth element is to function as a nucleus for forming graphite, which allows the graphite to be present in a finer amount than usual in the matrix, and at the same time, the C concentration in the matrix can be reduced, resulting in heat generation. The expansion coefficient can be lowered. Further, by making graphite exist minutely, segregation of Ni and Co can be reduced. The rare earth element to be added is, for example, Ce.
A misch metal in which a, Nd, and Pr are mixed (it is difficult to separate each component) can be used. The content of the rare earth element is preferably 0.02 to 0.05%.

Regarding the spheroidizing treatment and deoxidizing / degassing treatment of graphite, for example, Mg is used for the spheroidizing treatment, and
The degassing process can be performed by adding Al and Ca. By making the graphite spherical, the workability can be improved and the toughness can be increased. By performing deoxidation and degassing, casting defects can be reduced and castability can be improved.

In the first feature, Ni is 25.0-3.
2.0%. Ni transforms the base into austenite and significantly reduces the coefficient of thermal expansion. Although related to the amount of Co added, it is set to 25.0 to 30.0. Preferably 26.0
30.0%. Co is set to 7.0 to 14.0%.
By using Co together with Ni, the coefficient of thermal expansion of the material can be further reduced significantly, and therefore Co is positively added. Preferably, Ni + Co = 36.0 to 37.0%. C is 0.3 to less than 1.0%. This alloy has a cast steel structure. The larger the content of C, the larger the coefficient of thermal expansion. Therefore, it is preferable that the C content be as low as possible. However, in consideration of castability, and in order to improve workability by crystallizing graphite in the structure, the above range is included. Preferably it is 0.5 to 0.9%. Si is 0.5
% Is included. Si is preferably made as low as possible in order to reduce the coefficient of thermal expansion, but is contained in a small amount in order to improve castability. The Si content is preferably 0.30 to 0.45%. Mn contains less than 0.3%. Since the thermal expansion coefficient increases as the content of Mn increases, it is better to reduce the content of Mn as much as possible, but MnS is formed to prevent the damage of S. It also has a deoxidizing effect, so it is preferable to add a small amount. Therefore, it was decided to contain less than 0.3%. Preferably it is 0.15 to 0.28%. In addition, P, S, Cr, etc. may be mixed as unavoidable impurities, but the amount should be reduced as much as possible. P is preferably 0.02% or less, S is 0.02% or less, and Cr is 0.1% or less. S is a graphite spheroidization inhibiting element, and Cr increases the thermal expansion coefficient and inhibits graphitization.

According to the second feature of the present invention, in addition to the action and effect of the first feature, the component composition further comprises one or more elements selected from Mo, V, W and Nb. By including 0.20 to 1.50% of C, the thermal expansion coefficient can be further reduced. Mo, V, W, N
b preferentially bonds with C to form a carbide. Since the coefficient of thermal expansion becomes smaller as the amount of solute C in the matrix decreases, the inclusion of these elements within the above range results in binding with the solute C in the matrix during casting and heat treatment, resulting in the solid solution in the matrix. The molten C is reduced and the coefficient of thermal expansion is lowered. If less than the above range, no effect can be expected. On the other hand, if it exceeds the above range, coarse carbides are crystallized during casting and the coefficient of thermal expansion is increased. Preferably it is 0.25 to 0.50%.

According to a third aspect of the present invention, in addition to the function and effect obtained by the first or second aspect, the first aspect after casting is
After being once heated to 000 to 1150 ° C., it is subjected to a rapid cooling treatment, so that the present alloy has a lower thermal expansion coefficient than the Invar alloy and a thermal expansion coefficient close to that of the Super Invar alloy
Moreover, it can have much better castability and workability than those alloys. 1000-
The holding time at 1150 ° C is adjusted by the wall thickness of the product. For example, it can be about 1 hour for a wall thickness of 25 mm. Further, when the wall thickness is 50 mm, it takes about 2 hours or more. The rapid cooling is preferably water cooling, but may be a combination of mist and forced air cooling depending on the shape, size, and other factors of the product. By heating and holding at a high temperature and then rapidly cooling, solid solution C in the matrix is precipitated as graphite or carbide, and as a result, the amount of solid solution C in the matrix is reduced and the coefficient of thermal expansion is reduced. At the same time, the workability is improved because the graphite in the structure is increased.

[0011]

EXAMPLE An example of the present invention was melted so as to have the composition shown in Table 1, and a Y block and a diameter of 100 mm and a length of 300 were used.
mm round bar was cast. During casting, graphite is spheroidized and deoxidized and degassed. Also in the comparative example, the composition was as shown in Table 1 and the casting was performed in the same manner.

[0012]

[Table 1]

The round bar was subjected to cutting after casting, and the castability was evaluated by observing the state of the cut surface. Also, for the Y block, 2 at 1100 ° C after casting.
The coefficient of thermal expansion at room temperature (RT) to 100 ° C. was measured for those that were subjected to rapid cooling in water after being held for a time and those that were not subjected to heat treatment. The results are shown in Table 2.

[0014]

[Table 2]

As can be seen from Table 2, in Examples 1 to 4, the gas defect evaluation as the castability evaluation was good, and the shrinkage cavity defect evaluation was also reasonable. The coefficient of thermal expansion at room temperature to 100 ° C. is 1.01 to 2.29 × 10 in Examples 1 to 4 without heat treatment.
^The temperature was ⁻⁶ / ° C., indicating a very good low thermal expansion. In the case of heat treatment, 0.38 to 0.78 × 10 ⁻⁶
/ ° C, and the thermal expansion coefficient is 1 /
It can be seen that the value is reduced to about 3. The content of C has a great influence on the castability and the coefficient of thermal expansion. The lower the C content, the lower the coefficient of thermal expansion, but the worse the castability. In Examples 1 to 4, the content of C was mainly changed to clarify the effect. In Example 1, the C content was the lowest at 0.38%, and the coefficient of thermal expansion was low, but the castability was not very good. In Example 4, C
Content exceeds 0.9% and the coefficient of thermal expansion is 2.2.
It is as large as 9. In the data for this example, the preferred range of C content is 0.5-0.9.
%It turns out that.

Comparative Example 3 differs from the alloy of the present invention only in that the rare earth element is not added. And this comparative example 3
The coefficient of thermal expansion is 2.02 × 10 ⁻⁶ / ° C., which is considerably larger than the coefficient of thermal expansion of Example 3 in which the content of each component is close. That is, conversely, it can be seen that the coefficient of thermal expansion can be greatly reduced by adding the rare earth element. In Comparative Example 1, the content of C is within the range of the present invention (0.3 to
(Less than 1.0%). Although the coefficient of thermal expansion is a very low value, the castability is very poor and casting is practically impossible. In Comparative Example 2, the content of C and the content of Si are outside the range of the present invention. Good castability, but high thermal expansion coefficient. Comparative Example 4 is a Super Invar alloy component, and Comparative Example 5 is an Invar alloy component. All of them have a low coefficient of thermal expansion and are good, but the castability is poor, and casting of Comparative Examples 4 and 5 is substantially impossible. In addition, Example 1
In each of the alloys Nos. 4 to 4, a large number of fine spherical graphite crystallizes in the structure, and the workability is extremely good as compared with the Super Invar alloy, Invar alloy and the like that do not contain graphite.

[0017]

EFFECTS OF THE INVENTION The present invention has the above-mentioned constitution and action. According to the low thermal expansion casting alloy of claim 1, the composition of components is% by weight, Ni: 25.0 to 32.0%, Co: 7.0
˜14.0%, C: 0.3 to less than 1.0%, Si: 0.
In addition to containing less than 5% and Mn: less than 0.3%, 0.01 to 0.06% of a rare earth element is contained, and the balance is substantially F.
It is made of e and is subjected to spheroidizing treatment and deoxidizing / degassing treatment of graphite during casting, so by adopting the component composition shown therein, it is possible to maintain castability and processing while maintaining low thermal expansion characteristics. It is possible to provide an alloy having good properties. As a result, it can be greatly expected to be used for equipments, machine parts, etc. that require dimensional accuracy against temperature. In particular, the coefficient of thermal expansion can be made extremely small by including a rare earth element in a predetermined range. Further, since the rare earth element also has a degassing effect, improvement in castability can be expected. Graphite can be made to exist finely in the matrix by adding a rare earth element, and N
Segregation of i and Co can also be reduced. Further, by crystallizing a large number of fine spherical graphite, the workability can be improved and the toughness can be increased. Further, by performing deoxidation / degas treatment, casting defects can be reduced and castability can be improved. Further, according to the low thermal expansion casting alloy of claim 2, in addition to the effect of the configuration of claim 1, Mo, V,
0.2 of one or more elements selected from W and Nb
Since the content is 0 to 1.50% by weight and the balance is substantially Fe, the thermal expansion coefficient can be further reduced. According to the low thermal expansion casting alloy of claim 3, in addition to the effect of the configuration of claim 1 or 2, by heating and holding at 1000 to 1150 ° C. after casting, and then performing a quenching treatment, Since the solid solution C in the matrix is precipitated as graphite or carbide, this alloy has a lower coefficient of thermal expansion than Invar alloy, has a coefficient of thermal expansion close to that of Super Invar alloy, and is much higher than those alloys. It can have excellent castability and workability. Further, by heating and holding at a high temperature and then rapidly cooling, solid solution C in the matrix can be precipitated as graphite or carbide, and the workability can be improved by increasing the amount of graphite in the structure.

Continued front page    (72) Inventor Toru Kuroda             Rainbow, 3-12 Kanbei-cho, Otsu-ku, Himeji-shi, Hyogo             Himeji East factory

Claims (3)

[Claims] 1. The composition of the composition is% by weight, Ni: 25.0 to 32.0% Co: 7.0 to 14.0% C: 0.3 to less than 1.0% Si: less than 0.5%. Mn: In addition to containing less than 0.3%, it contains 0.01 to 0.06% of a rare earth element, and the balance consists essentially of Fe. During casting, the graphite is spheroidized and deoxidized / deoxidized. A low thermal expansion casting alloy characterized by being gas-treated. 2. The component composition further comprises Mo, V, W and N.
0.20 to one or more elements selected from b
The low thermal expansion casting alloy according to claim 1, characterized in that the content is 1.50% by weight and the balance is substantially Fe. 3. The solid solution C in the matrix is precipitated as graphite or carbide by heating and holding at 1000 to 1150 ° C. after casting and then performing a quenching treatment. The low thermal expansion casting alloy according to.