JP2021123736A - Low thermal expansion casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low thermal expansion casting having a small change over time and excellent machinability.
SOLUTION: The chemical composition of a low thermal expansion casting is C: 1.00 to 2.50%, Si: 2.50% or less, Mn: 1.00% or less, Ni: 28.0 to 40 in mass%. It contains 0.00%, Co: 0 to 10.00%, Mg: 0 to 0.090%, the balance is Fe and unavoidable impurities, and the amount of solid solution C is 0.08% by mass or less.
[Selection diagram] None

Description

The present invention relates to a low thermal expansion alloy casting, and more particularly to a low thermal expansion casting having a small change over time (hereinafter referred to as "aging") and excellent machinability.

Thermally stable Invar alloys are widely used as component materials for electronics, semiconductor-related equipment, laser processing machines, and ultra-precision processing equipment. On the other hand, it has been pointed out that low thermal expansion alloys used for components of precision equipment have a problem of aging over a long period of time.

In Patent Document 1, as a means for solving this problem, the secular change obtained by setting the contents of B and N in an appropriate range in addition to C, which is considered to be the cause of γ expansion, is ± 0.5 ppm. / Years of low thermal expansion cast steel and forged steel products are disclosed.

On the other hand, since the conventional Invar alloy has low machinability, there is a problem that practical use is limited to a fairly narrow field.

Patent Document 2 discloses low thermal expansion cast iron having a component in which graphite can crystallize in an alloy structure during a casting process as a means for solving this problem.

Japanese Unexamined Patent Publication No. 2018-178151 Japanese Unexamined Patent Publication No. 6-172919

Alloys used for components of precision equipment are required to have excellent machinability from the viewpoint of ease of processing.

In order to improve the machinability of the low thermal expansion cast steel having a small secular change as in Patent Document 1, it is conceivable to increase the C content and crystallize graphite as in Patent Document 2. However, if the amount of solid solution C increases with the increase in the amount of C, the secular change becomes large. It is considered that this is because C dissolved in the steel diffuses or precipitates with the passage of time, so that the structure of the steel changes slightly.

In view of the above circumstances, it is an object of the present invention to provide a low thermal expansion casting having a small change over time and excellent machinability.

The present inventors have diligently studied a method for obtaining a low-thermal expansion casting having a small change over time and excellent machinability. As a result, even when the C content is increased and graphite is crystallized to improve the machinability, the solid solution C content can be reduced by performing an appropriate heat treatment, the γ aging change is small, and It was found that a low thermal expansion casting with excellent machinability can be obtained.

The present invention has been made based on the above findings, and the gist thereof is as follows.

(1) In terms of mass%, C: 1.00 to 2.50%, Si: 2.50% or less, Mn: 1.00% or less, Ni: 28.0 to 40.00%, Co: 0 to 10 A low thermal expansion casting containing .00%, Mg: 0 to 0.090%, the balance being Fe and unavoidable impurities, and the amount of solid solution C being 0.08% by mass or less.

(2) The low thermal expansion casting according to (1) above, which contains Mg: 0.040 to 0.090% in mass%.

(3) The low thermal expansion casting according to (1) or (2) above, wherein the average coefficient of thermal expansion at 25 to 100 ° C. is 5.0 × 10 ^{-6 / ° C. or less.}

(4) A method for producing a low thermal expansion casting according to any one of (1) to (3) above, wherein in terms of mass%, C: 1.00 to 2.50%, Si: 2.50% or less, Mn. : 1.00% or less, Ni: 28.0 to 40.00%, Co: 0 to 10.00%, Mg: 0 to 0.090%, and the balance is Fe and unavoidable impurities after solidification. A method for producing a low thermal expansion casting, which comprises a step of subjecting the slab to a heat treatment of holding the slab at 500 to 700 ° C. for 30 to 60 hours.

According to the present invention, since a low thermal expansion casting having a small aging change and excellent machinability can be obtained, it can be applied to a component part of a precision instrument or the like in which a slight dimensional change over a long period of time becomes a problem. It will be possible to easily process the components of precision equipment.

Hereinafter, the present invention will be described in detail. Hereinafter, "%" regarding the component composition shall represent "mass%" unless otherwise specified. First, the component composition of the casting of the present invention will be described.

[C: 1.00 to 2.50%]
C is an element that crystallizes as graphite in castings and enhances machinability. In order to obtain this effect, the amount of C is set to 1.00 or more, preferably 1.50% or more. If the amount of C is too large, the mechanical strength may decrease and the castability may decrease. Therefore, the amount of C is 2.50% or less, preferably 2.40% or less. C is divided into C that crystallizes as graphite and C that dissolves in the casting. The amount of C defined here is the total amount of C including C that crystallizes as graphite and C that dissolves in the casting. The amount of solid solution C will be described later.

[Si: 2.50% or less]
Si is added as a deoxidizing material. It is also an element that promotes the crystallization of graphite. Since the low thermal expansion casting of the present invention contains about 30% of Ni, which is a graphitization promoting element, Si is not essential and the content may be 0, but it may be contained in the range of 2.50% or less. If the amount of Si is too large, the coefficient of thermal expansion increases, so the amount of Si is 2.50% or less, preferably 2.10% or less.

[Mn: 1.00% or less]
Mn is added as a deoxidizing material. It also contributes to the improvement of strength by strengthening the solid solution. In order to obtain this effect, the amount of Mn is preferably 0.10% or more. Since the coefficient of thermal expansion increases when the Mn content exceeds 1.00%, the Mn amount is set to 1.00% or less, preferably 0.50% or less. Mn is not an essential element and its content may be zero.

[Ni: 28.0 to 40.00]
Ni is an essential element that lowers the coefficient of thermal expansion. The low thermal expansion casting of the present invention has an average coefficient of thermal expansion of 5.0 × 10 ^-6 / ° C or less at 25 to 100 ° C. This coefficient of thermal expansion is mainly obtained by setting the contents of Ni and Co in an appropriate range. If the amount of Ni is too large or too small, the coefficient of thermal expansion will not be sufficiently small. In order to sufficiently reduce the coefficient of thermal expansion, the amount of Ni is set in the range of 28.0 to 40.00%, preferably 30.00 to 37.00%.

[Co: 0 to 10.00%]
Co contributes to a decrease in the coefficient of thermal expansion in combination with Ni. The Co content may be zero. In order to obtain a desired coefficient of thermal expansion, the range of Co is 0 to 10.00%, preferably 0 to 9.00%.

[Mg: 0 to 0.090%]
Mg is an element that spheroidizes and crystallizes graphite, and can be contained as needed. In order to obtain this effect, the Mg content is preferably 0.040% or more. Mg is not an essential element and its content may be zero.

[Solid solution C: 0.08% or less]
The solid solution C dissolves in the grain boundaries or in the grains, and diffuses or precipitates as carbides with the passage of time. As a result, the dimensions of the casting are slightly changed. In the low thermal expansion casting of the present invention, the amount of solid solution C is 0.08% or less in order to minimize the change over time. The method for reducing the amount of solid solution C to 0.08% or less will be described later. Here, the amount of solid solution C is determined as a value obtained by subtracting the amounts of graphite and carbides in the casting from the C content of the chemical composition of the casting. The amount of graphite and carbides in the casting can be obtained from a known method of performing extraction residue analysis on the casting.

The rest of the composition is Fe and unavoidable impurities. The unavoidable impurities refer to those that are unavoidably mixed from the raw materials, the manufacturing environment, etc. when the casting having the component composition specified in the present invention is industrially manufactured.

Next, a manufacturing method for obtaining the low thermal expansion casting of the present invention will be described.

First, a slab having the above chemical components is produced. The mold used for producing the slab, the apparatus for injecting molten steel into the mold, and the injection method are not particularly limited, and a known apparatus and method may be used.

Subsequently, a heat treatment is performed in which the solidified slab is held at 500 to 700 ° C. for 30 to 60 hours. By this treatment, the precipitation of C dissolved in the casting as graphite is further promoted, and the amount of solid C dissolved in the casting is reduced. As a result, it is possible to obtain a low thermal expansion casting having a small change over time and excellent machinability.

Further, if necessary, the cooled casting may be heated to 300 to 350 ° C. and subjected to a stress-relieving annealing treatment that holds it for 1 to 5 hours. Thereby, the residual stress generated in the process of solidification and cooling can be removed.

[Example 1]
A molten metal adjusted to have the composition shown in Table 1 was poured into a mold to produce a slab. Then, the heat treatment shown in Table 1 was performed to obtain a casting.

A test piece having a diameter of 5 × 20 L was processed from each of the obtained castings, and an average coefficient of thermal expansion from 25 ° C. to 100 ° C. was obtained by a thermal expansion measuring device.

In addition, No. For 2, 3, 7, 8, 12, and 13, 9 mm × 35 mm × 200 mm rectangular parallelepiped samples were prepared, and the length between the 9 × 35 end faces was measured to investigate the secular change for 24 months. The parallelism in the length direction of the sample was 0.01, and the squareness of the 9 × 200 plane and the 200 × 35 plane was 0.1. The measurement surface flatness intersection was set to K class of JIS B7506.

The results are shown in Table 1.

It was confirmed that the low thermal expansion casting of the present invention has a small amount of solid solution C and a small change over time. On the other hand, in the comparative example, the amount of solid solution C was large and the change over time was large. In addition, No. Reference numeral 13 denotes a reference example in which a conventional low thermal expansion cast steel having a small change over time is used. It was confirmed that the low thermal expansion casting of the present invention has the same secular change as the conventionally known low thermal expansion cast steel having a small secular change.

[Example 2]
No. 1 shown in Table 1. For castings having a composition of 2, 3, 7, 12, and 13, using a drill (cobalt heiss, drill diameter 2.6 mm) and cutting oil, cutting speed: 45 m / min, feed per rotation. The machinability was evaluated by the cutting resistance when drilling with a depth of 13 mm at a quantity of 0.013 mm / rev. The evaluation was performed by the average value of thrust and torque measured at the time of cutting.

No. with a large amount of C Nos. 2, 3, 7, and 12 are No. It was confirmed that both the thrust and the torque were lower than those of No. 13, the cutting resistance was small, and the machinability was high. In addition to Example 1, No. 1 of the present invention example. Regarding 2, 3 and 7, it was confirmed that low thermal expansion castings with little change over time and excellent machinability were obtained.

Claims (4)

By mass%
C: 1.00 to 2.50%,
Si: 2.50% or less,
Mn: 1.00% or less,
Ni: 28.0 to 40.00%,
Co: 0 to 10.00%,
Mg: 0 to 0.090%
The balance is Fe and unavoidable impurities.
A low thermal expansion casting characterized in that the amount of solid solution C is 0.08% by mass or less. The low thermal expansion casting according to claim 1, wherein the low thermal expansion casting contains Mg: 0.040 to 0.090% in mass%. The low thermal expansion casting according to claim 1 or 2, wherein the average coefficient of thermal expansion at 25 to 100 ° C. is 5.0 × 10 ^{-6 / ° C. or less.} The method for producing a low thermal expansion casting according to any one of claims 1 to 3.
By mass%
C: 1.00 to 2.50%,
Si: 2.50% or less,
Mn: 1.00% or less,
Ni: 28.0 to 40.00%,
Co: 0 to 10.00%,
Mg: 0 to 0.090%
A method for producing a low thermal expansion casting, which comprises a step of subjecting a solidified slab containing Fe and an unavoidable impurity to a heat treatment for holding the slab at 500 to 700 ° C. for 30 to 60 hours.