JPH01283342A - Cobalt-containing austenitic low thermal expansion cast iron - Google Patents

Abstract

PURPOSE:To provide the title cast iron in which reduction in thermal expansion coefficient is attained to a greater extent while maintaining castability, workability, mechanical strength, etc., by limiting the compositional limit values of a Co-containing austenitic cast iron. CONSTITUTION:The above cast iron having a composition consisting of, by weight, <=3.0% C, <=3.0% Si, <=2.0% Mn, 25.0-40.0% Ni, 6.0-12.0% Co, and the balance Fe besides impurities is prepared. If necessary, Co content in the above composition is regulated to 12.0-25.0%. By the above constitution, reduction in the coefficient of thermal expansion can be attained to a greater extent in a low temp. region of <=about 200 deg.C and also in a high temp. region higher than the above while maintaining various properties, such as castability, workability, and mechanical strength, generally required of precision structural parts to the values equal to those of Ni-resist cast iron, respectively. Accordingly, this cast iron is suitable for use in precision mechanical equipment parts, dies, etc.

Description

[Detailed Description of the Invention] [Industrial Application Fields] The present invention is used for precision equipment parts, jigs, molds, etc.
The present invention relates to an austenitic low thermal expansion cast iron having a low coefficient of thermal expansion at low and/or high temperatures.

[Prior Art] Conventionally, high nickel austenitic cast iron (resist cast iron) containing 34 to 36 wt% Ni (similar to invar alloy) has been mainly used as a cast iron material with low thermal expansion. However, the coefficient of thermal expansion of this cast iron from room temperature (RT) to 100°C is 4 to 5 x 10-67°C, and even lower expansion is being sought for precision structural parts.

In order to meet such demands, the special public
Publication No. 547 states that N15C)~34wt%, Co4~
6 wt% and its thermal expansion coefficient is 3 to 4 x 10-6
Low thermal expansion cast iron has been proposed with a thermal expansion as low as /℃. That is, the low thermal expansion cast iron shown in this prior art is super invar (32Ni-5Co-BolFe) in which Ni in known austenitic cast iron is replaced with an appropriate amount of Co.
It consists of a material with a composition corresponding to .

[Problems to be solved by the invention] However, with these existing low thermal expansion cast iron materials,
When the temperature of any of them reaches high temperatures, that is, 200°C or higher, the coefficient of thermal expansion increases rapidly, and at 700°C, it becomes no different from that of ordinary cast iron or steel (14 x 10-6/°C), and it is no longer the same. It has the disadvantage that it cannot be called a low thermal expansion material.

Furthermore, according to the results of the test and research conducted by the present inventor regarding the above-mentioned low thermal expansion cast iron, in the specification of the publication, the Co4-6
There is little concrete basis for the range of %, and it has been confirmed that even if Co is contained beyond this range (substituted with Ni), low expansion properties equivalent to or higher than that can be achieved.

Based on such considerations and findings, the present invention has been developed to provide cast iron with low thermal expansion in a low temperature range of 200°C or less while ensuring castability, workability, mechanical strength, etc. generally required for structural parts. The object of the present invention is to provide a new cobalt-containing austenitic low thermal expansion cast iron that exhibits a low thermal expansion property equivalent to or higher than that of the present invention, and a new cobalt-containing austenitic low thermal expansion cast iron that exhibits a small increase in the coefficient of thermal expansion, particularly in a high temperature range of 200°C or higher.

[Means for Solving the Problems] The austenitic low thermal expansion cast iron according to the first aspect of the present invention has C: 3.0 or less, Si ;3.0 or less, Mn;
2.0 or less, Ni; 25.0 to 40.0 SCo; 6
．． Contains 0 to 12.0 in each wt%, excluding remaining impurities
Consists of e.

Further, the austenitic low thermal expansion cast iron according to the second invention has good low thermal expansion properties particularly in a high temperature range (200° C. or higher), and has C: 3.0 or less, Si: 3.0 or less, Mn: 2 .0 or less, Ni; 25.0 to 40.0, Co
;12. O~25. 0 in each wt%, and is made of Fe except for the remaining impurities.

The cast iron according to the first invention is disclosed in Japanese Patent Publication No. 60-51547.
The range presented by the low thermal expansion cast iron of the publication (Co; 4°0~
6. 0wt%), and the Ni amount from the known austenitic cast iron (resist cast iron) is 6.0 to 12.
This corresponds to the chemical component replaced with 0wt% of Co. In other words, even if the amount of C'o exceeds 6%, the coefficient of thermal expansion does not increase, but rather exhibits an equivalent or lower thermal expansion near room temperature, and when the amount of Co exceeds 10%, the thermal expansion coefficient at high temperatures decreases. This will have an improvement effect on the decrease in the coefficient.

In addition, the cast iron according to the second invention is made by further increasing the CO content of the cast iron according to the first invention, and is made of Kovar (trade name, L), which is known as a high temperature and low thermal expansion glass sealing alloy.
OW C, Si 29Ni-17Co alloy), which has a composition similar to that of
There is little increase in the coefficient of thermal expansion in the high temperature range of 00°C or higher, and even at high temperatures of 700°C or higher, it is similar to that of Kovar (
It is said that it can maintain a low coefficient of thermal expansion comparable to about 10XIO'/'C).

Both the low-4 thermal expansion cast irons according to the first invention and the second invention described above have different contents of Ni and Co, and other basic cast iron components (C, Si, M n ). The range and reason for its limitation are similar to those for Niresist cast iron. Note that the cast iron according to the first invention has a Ni equivalent (Ni%+0.
75Co%) -35 to 36 is desirable. Further, in order to ensure mechanical properties, particularly elongation, the C◯ content is preferably 6.0 to 8.0 wt%.

On the other hand, in the low thermal expansion cast iron according to the second invention, the composition of Kovar (29% Ni-17% Co) is aimed as the optimum component in order to maintain low thermal expansion in a high temperature range. The preferred content range for Co is 14 to 17 wt%.

[Functions and Effects] Cobalt-containing austenitic low thermal expansion cast iron with the above-mentioned composition has properties such as castability, workability, and mechanical strength, which are generally required for precision structural parts, on the same level as Niresist cast iron. As confirmed from the examples below, it is possible to further reduce the coefficient of thermal expansion in the low temperature and high temperature ranges while ensuring the following.

That is, the cast iron according to the first invention has a low temperature range (0 to 100°
C), conventional low thermal expansion cast iron has a diameter of 4 to 5 x 10'/
The coefficient of thermal expansion, which was 0.degree. C., can be lowered to 3 to 4.times.10@-6/'C. In addition, the cast iron according to the second invention is also effective in reducing the coefficient of thermal expansion in the low temperature range,
Especially in the high temperature range (0 to 500°C), conventional cast iron has 12 to 1
The coefficient of thermal expansion which was 3X10'/°C was changed to 8~9X
The temperature can be reduced to 10-6/'C.

[Example] Example 1 Tables 1 and 2 show examples (No.
The chemical composition, thermal expansion coefficient and mechanical property test results in each temperature range of various high nickel austenitic ductile cast irons corresponding to F-J) and comparative examples (No., A-E) are shown. From this result, looking at the influence of Co content on the coefficient of thermal expansion, it can be seen that the example product with a Co content exceeding 6°0wt% has a Co content of 6.
．． It can be seen that the coefficient of thermal expansion tends to be lower than that of the comparative examples below 0 wt%.

Example 2 Tables 3 and 4 show examples (No.
The chemical composition of various high nickel-high cobalt cast irons corresponding to K-J), and the test results of the thermal expansion coefficient and mechanical properties in each high temperature range are shown below. From this result, it is confirmed that the example products with a high Co content exhibit good low thermal expansion in the high temperature range of 200°C or higher, and that the increase in the coefficient of thermal expansion is small even at temperatures exceeding 700°C.

Claims (2)

[Claims] (1) A cobalt-containing product characterized by containing C3.0 or less, Si3.0 or less, Mn2.0 or less, Ni25.0-40.0, Co6.0-12.0 in each wt%, and consisting of Fe excluding the remaining impurities. Austenitic low thermal expansion cast iron. (2) A cobalt-containing material characterized by containing C3.0 or less, Si3.0 or less, Mn2.0 or less, Ni25.0 to 40.0, Co12.0 to 25.0 in each wt%, and consisting of Fe excluding the remaining impurities. Austenitic low thermal expansion cast iron.