JP2001262277A - Low thermal expansion alloy excellent in machinability and its producing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an invar series low thermal expansion material whose thermal expansion coefficient at ordinary temperatures is made minimum by making the chemical composition a ppropviate in accordance with the content of expensive Co. SOLUTION: This low thermal expansion alloy excellent in machinability has a composition comprising, by weight, <=0.05% C, <=0.3% Si, 0.45 to 1.2% Mn, <=0.5% P, 0.015 to 0.035% S, 33.0 to 34.5% Ni and 3.0 to 4.0% Co, and the balance substantially iron. In the case [Mn] is defined as the weight % of Mn, and [S] is defined as the weight % of S, [Mn]/[S] is made to satisfy >=15, so that the average thermal expansion coefficient at ordinary temperatures falls in a range of <=1.0×10-6/ deg.C.

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 alloy excellent in machinability and suitable for use in precision machine parts and the like that require low thermal expansion and a method for producing the same.

[0002]

2. Description of the Related Art Among practical metal materials currently used for the purpose of low thermal expansion, Super Invar and Invar have a thermal expansion coefficient α in a temperature range of 20 to 100 ° C., and the former has a thermal expansion coefficient α of 0 to 1 × 10 ^{−. 6} / ° C., 1-2 × 10 ^{−6 for the} latter
/ ° C, and has a characteristic that thermal expansion is very small. These are formed mainly by plastic working,
It is supplied in materials such as wires, plates, bars, etc. Therefore, a lot of machining is required to make a finished part, but the machinability is low and the cost is high, so the range of use is limited.

The low machinability of Super Invar and Invar is due to (1) heat generation due to high cutting resistance.
(2) short tool life, (3) low chip controllability,
(4) It is considered to be due to easy work hardening.

As means for solving this problem, S, C
Although materials having free cutting properties are provided by adding a, Pb, Zr, Se, etc., there are disadvantages associated with a decrease in mechanical properties, an increase in thermal expansion coefficient, and a complicated manufacturing method. .

On the other hand, a material disclosed in Japanese Patent Publication No. 60-51547, in which castability is imparted to Super Invar, and ASTM. A-436, T
Type 5 and Type A-439 and Type D-5 have improved machinability compared to Super Invar and Invar because graphite is generated in the tissue during the coagulation process, but are 3.0 × 10 ⁻⁶ respectively. It is insufficient for applications requiring even higher precision, with an increase in the coefficient of thermal expansion of around / ° C, and has a thermal expansion coefficient similar to that of Super Invar and Invar. A low thermal expansion alloy excellent in machinability is desired.

[0006] There is a low thermal expansion alloy described in JP-A-3-90541 invented in order to solve these problems, but the cost is high because it contains a large amount of expensive Co. There is a disadvantage that it will.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems such as Super Invar, Invar and low thermal expansion alloy,
That is, (1) the problems of low machinability and limited material shape in Super Invar and Invar, (2) high thermal expansion coefficient of low thermal expansion cast iron, and (3) high material cost It is intended to solve the problems and the like, and to provide a low-cost low-thermal-expansion alloy excellent in machinability, thermal expansion, and castability, and particularly suitable for a cast alloy, and a method for producing the same. I do.

[0008]

SUMMARY OF THE INVENTION The present invention has a low thermal expansion property equivalent to that of Super Invar and Invar, has excellent machinability, has excellent castability like low thermal expansion cast iron, and is manufactured at low cost. The present invention provides a low thermal expansion alloy that can be used.
That is, in the first invention, C: 0.05% or less, Si: 0.3% or less, Mn: 0.45 to 1.2% by weight,
P: 0.5% or less, S: 0.015 to 0.035%, N
i: 33.0 to 34.5%, Co: 3.0 to 4.0%, the balance is substantially composed of iron, and [Mn] is Mn.
%, And [M]] / [M]
[S]: Provided is a low-thermal-expansion alloy excellent in machinability, having an average thermal expansion coefficient at room temperature of 1.0 × 10 ⁻⁶ / ° C. or less, characterized by being 15 or more.

In the second invention, C: 0.
05% or less, Si: 0.3% or less, Mn: 0.45-
1.2%, P: 0.5% or less, S: 0.015 to 0.0
35%, Ni: 33.5 to 35.5%, Co: 2.0 to
3.0% with the balance substantially consisting of iron and [M
[Mn] / [S]: 15 or more when [n] is% by weight of Mn and [S] is% by weight of S, and the average coefficient of thermal expansion at room temperature is 1.5 × 10 A low thermal expansion alloy having a thermal expansion coefficient of ⁻⁶ / ° C. or less and excellent in machinability.

[0010] Further, a third aspect of the present invention relates to a method for preparing C:
0.05% or less, Si: 0.3% or less, Mn: 0.45
１．２1.2%, P: 0.5% or less, S: 0.015-0.
035%, Ni: 34.0-36.5%, Co: 1.0
[Mn] / [S]: 15 or more where [Mn] is the weight% of Mn and [S] is the weight% of S. An object of the present invention is to provide a low-thermal-expansion alloy excellent in machinability, having an average thermal expansion coefficient at room temperature of 2.0 × 10 ⁻⁶ / ° C. or less.

Furthermore, a fourth invention provides an alloy having any one of the first to third inventions having a composition of 700 to 950.
A method for producing a low-thermal-expansion alloy excellent in machinability, characterized in that the alloy is cooled to 450 ° C. or less at a cooling rate of 5 ° C./sec or more after heating in a temperature range of ° C.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention defines an optimum composition range for achieving both free-cutting properties (that is, excellent machinability) and low thermal expansion properties. This specifies the optimum heat treatment conditions.

The composition of the alloy according to the present invention is expressed in terms of% by weight:
C: 0.05% or less, Si: 0.3% or less, Mn: 0.
45 to 1.2%, P: 0.5% or less, S: 0.015 to
0.035%, with the balance substantially consisting of iron and [M
[Mn] / [S]: 15 or more when [n] is the weight% of Mn and [S] is the weight% of S, and Ni and Co
With Ni: 33.0 to 34.5% and Co: 3.0
-4.0%, Ni: 33.5-35.5% and C
o: 2.0 to 3.0%, Ni: 34.0 to 36.5%
And Co: any one of three levels of 1.0 to 2.0%.

C: 0.05% or less C has a significant effect on the coefficient of thermal expansion when it is dissolved in a matrix, and when it exceeds 0.05%, the coefficient of thermal expansion becomes large, and a desired low thermal expansion is obtained. The property cannot be obtained. Therefore, the C content is set to 0.05% or less.

Si: 0.3% or less Si is added to steel as a deoxidizing element. However, as in the case of C, if the amount of solid solution in the matrix increases, the coefficient of thermal expansion increases. % Or less.

Mn: 0.45 to 1.2% Mn forms a compound with S as described later and plays an important role in improving machinability. If it is less than 0.45%, it is difficult to form a compound of Mn and S, the machinability is inferior, and casting cracks are liable to occur. On the other hand, if it exceeds 1.2%, C,
Since the coefficient of thermal expansion increases like Si, the Mn content is set to 0.45 to 1.2%.

P: 0.5% or less P is contained as an impurity in steel. However, if P is contained in a large amount, it will be present at the grain boundary and cause a reduction in the strength of the material. Therefore, the content of P is preferably small. Such a decrease in strength is caused by P
When the content exceeds 0.5%, the content becomes remarkable, so the upper limit of the P content is set to 0.5%.

S: 0.015 to 0.035% S is an element that forms a compound with Mn and contributes to the improvement of machinability. However, when contained in a large amount in steel, the strength is reduced. If the S content is less than 0.015%, the amount of the compound with Mn effective for improving machinability is not sufficient, and the effect of improving machinability cannot be obtained. If the S content exceeds 0.035%, the strength decreases. Bring. Therefore, the S content is set to 0.015 to 0.03.
5%.

[Mn] / [S]: 15 or more [Mn] / [S] is an important parameter that affects the amount of the compound formed between Mn and S. Although the contents of Mn and S are as described above, if the value of [Mn] / [S] is less than 15, excess S forms a compound with Fe which is a main element in the matrix, Since FeS having a melting point is generated and cracks are easily generated during solidification, it is inconvenient especially when a casting is manufactured. When the value of [Mn] / [S] is 15 or more, S is mainly a compound with Mn, and harmful FeS hardly occurs, and solidification cracking hardly occurs. For this reason, the value of [Mn] / [S] is set to 15 or more. However, depending on the product shape and size, [Mn] / [S] is preferably set to 30 or more.

Ni: 33.0-34.5% and C
o: 3.0 to 4.0% Ni: 33.5 to 35.5% and Co: 2.0 to
3.0% Ni: 34.0-36.5% and Co: 1.0-
2.0% Ni, Co is an important element that most affects the coefficient of thermal expansion. In the present invention, an alloy having excellent low thermal expansion is achieved by setting the Ni amount and the Co amount to the optimum combination obtained through various experiments. Co
Is from 1.0 to 4. depending on required thermal expansion properties, cost, and the like.
0%, but depending on the level of Co, N
By limiting the amount of i, the coefficient of thermal expansion can be minimized. That is, when the amount of Co is 3.0 to 4.0%,
By setting the Ni content to 33.0% to 34.5%, the thermal expansion property is minimized, and the average thermal expansion coefficient at room temperature is 1.0 ×
It can be 10 ⁻⁶ / ° C. or less. When the Co amount is 2.0 to 3.0%, the Ni amount is 33.5 to 3%.
By setting it to 5.5%, the thermal expansion property is minimized, and the average thermal expansion coefficient at room temperature can be 1.5 × 10 ⁻⁶ / ° C. or less. When the amount of Co is 1.0 to 2.0%, the thermal expansion is minimized by setting the amount of Ni to 34.0 to 36.5%, and the average thermal expansion coefficient at normal temperature is 2.
It can be 0 × 10 ⁻⁶ / ° C. or less. Any C
Even at the level of the amount of o, if the amount of Ni is out of these ranges, the desired low thermal expansion property cannot be obtained. As described above, the optimum amount of Ni is added in accordance with the level of the expensive Co amount, so that the effect of reducing the coefficient of thermal expansion due to Co can be maximized, and excellent characteristics can be obtained at a minimum cost. Alloy can be obtained.

The balance of the alloy of the present invention having the above composition substantially consists of iron. That is, unavoidable impurities and trace addition elements within the range not impairing the effects of the present invention are allowed.

The alloy of the present invention as described above is suitable for a cast alloy produced by casting a molten metal having the above-mentioned composition into a casting mold. An alloy used after being subjected to plastic working may be used.
The manufacturing conditions are not particularly limited. However, in the present invention, a material manufactured in a predetermined shape is
After heating to 00 to 950 ° C, it is preferable to perform a heat treatment of cooling to 450 ° C or less at a cooling rate of 5 ° C / sec or more. Such heat treatment can further reduce the coefficient of thermal expansion at room temperature. In particular, when producing a casting, the heat treatment is effective for homogenizing the alloy elements.

In this case, if the heating temperature is lower than 700 ° C., the time required for homogenization by diffusion of alloy elements becomes long, which is uneconomical. If the heating temperature exceeds 950 ° C., the mechanical properties are deteriorated due to the coarsening of the crystal grains. At the same time, the scale generation becomes intense and the process for removing the scale becomes complicated. From the viewpoint of economy, the heating temperature was set to 700 to 950 ° C.

Further, the cooling rate after heating has a great influence on the coefficient of thermal expansion at room temperature. If the cooling rate is less than 5 ° C./sec after heating to 700 to 950 ° C., the desired coefficient of thermal expansion cannot be obtained. Therefore, the cooling rate after heating was set to 5 ° C./sec or more.

[0025]

[Embodiment 1] An embodiment of the present invention will be described below. Using a 30 kVA high-frequency electric furnace, a test material having the components shown in Table 1 and the balance consisting of iron was dissolved,
_A JIS G 5122B test piece (hereinafter referred to as No. B test piece) and a machinability test piece of 25 × 60 × 250 mm were cast using a _2- silica sand mold. From the No. B test piece, after performing the heat treatment shown in Table 1, a φ8 × 100 mm thermal expansion coefficient measurement test piece (hereinafter referred to as a thermal expansion test piece) was collected by machining.
The average coefficient of thermal expansion at 20 to 25 ° C (hereinafter referred to as the average coefficient of thermal expansion near room temperature) was measured using a push-rod type horizontal thermal dilatometer. The machinability test piece was subjected to a drilling test after two surfaces of 60 × 250 mm were smoothed with a grinder. The drilling test was performed using a high-speed steel drill having a diameter of 5 mm and rotating at 1274 RPM at a feed rate of 0.2 mm /
Times, without lubrication, under the test conditions of hole depth 10mm, 5
When 0 or more holes could be drilled, the machinability was determined to be good. In addition, in the column of "alloy level" in Table 1, Ni: 33.0 to 34.5% and Co:
1 that satisfies 3.0 to 4.0%, Ni: 33.5
2 that satisfy 〜35.5% and Co: 2.0-3.0%, Ni: 34.0-36.5% and Co:
The one satisfying 1.0 to 2.0% is designated as 3.

[0026]

[Table 1]

As shown in Table 1, the alloy 1 of the present invention was
To 11, the desired value of the thermal expansion coefficient corresponding to the alloy level (hereinafter 1.0 × ^{10 -6} / ° C. If the alloy level is 1, 1.5 × when the alloy level is 2 10 ^{- 6} / ° C or lower, and 2.0 × 10 ⁻⁶ / ° C or lower when the alloy level is 3), and the machinability was good in each case.

On the other hand, alloys 12 to 1 as comparative examples
No. 9 was inferior in either property. Specifically, the alloy 12 has a C content larger than the range of the present invention, so that the coefficient of thermal expansion is larger than a desired value. Further, since the S content is smaller than the range of the present invention, the machinability is low. Not good. Alloy 1
Nos. 3 and 14 have poor machinability because the S content is less than the range of the present invention. Although the alloy 15 contains 4.0% by weight of Co, the coefficient of thermal expansion is larger than a desired value because the content of Ni is larger than the range of the present invention. Although the alloy 16 contains 2.5% by weight of Co, the content of Ni is smaller than the range of the present invention, so that the coefficient of thermal expansion is larger than a desired value. Alloy 17
Has a thermal expansion coefficient larger than a desired value because the content of Ni is smaller than the range of the present invention, although 1.6% by weight of Co is contained. The alloy 18 has a larger coefficient of thermal expansion than the desired value because the Si content is larger than the range of the present invention. Although the alloy 19 contains 1.8% by weight of Co, the thermal expansion coefficient is larger than a desired value because the content of Ni is larger than the range of the present invention.

Embodiment 2 Next, another embodiment of the present invention will be described. A 30 kVA high-frequency electric furnace was used to melt a test material having the components shown in Table 2 and the balance being iron, and cast a No. B test piece and a crack test piece having the shape shown in FIG. 2 using a CO ₂ silica sand mold. . After performing a predetermined heat treatment from the No. B test piece, a thermal expansion test piece of φ8 × 100 mm was sampled by machining, and the average thermal expansion coefficient near room temperature was measured using a push-rod type horizontal thermal dilatometer. . In the crack specimen,
Cracks at point A (R = 2 mm and R = 4 mm) in FIG. 2 were visually inspected and the presence or absence of cracks was confirmed by dye penetrant inspection. The “alloy level” shown in Table 2 is the same as that in Table 1.

[0030]

[Table 2]

As shown in Table 2, the alloy 2 of the present invention was
0-alloy 28 has a desired value of thermal expansion coefficient according to the level of Co (Co: 3.0% to 4.0% in the case of 3.0% to 4.0%).
× 10 ⁻⁶ / ° C. or less, Co: 2.0% to 3.0%, 1.5 × 10 ⁻⁶ / ° C. or less, Co: 1.0% to 2.0%.
0% at 2.0% × 10 ⁻⁶ / ° C. or less), and has excellent low thermal expansion properties. Was not confirmed, and the occurrence of solidification cracking was suppressed. Furthermore, alloys 20 to 30 of which [Mn] / [S] is 30 or more in the examples of the present invention.
In No. 24, no crack was confirmed even at the point A of R = 2 mm of the crack test piece, and the occurrence of solidification crack was suppressed to an extremely low level.

On the other hand, alloys 29 to 35 as comparative examples were inferior in any of the characteristics. Specifically, alloy 29 has the same chemical composition as alloy 20, alloy 30 has alloy 22, and alloy 31 has the same chemical composition as alloy 23.
Because the cooling rate is less than the scope of the present invention, the coefficient of thermal expansion is greater than desired. Although the alloy 32 has the same chemical composition as the alloy 20, the heating temperature is lower than the range of the present invention, so that the coefficient of thermal expansion near normal temperature is larger than a desired value. Alloy 33 has a Mn content lower than the range of the present invention, and [M
n] / [S] was smaller than the range of the present invention, and solidification cracking occurred. Alloy 34 had solidification cracking because [Mn] / [S] was within the range of the present invention, but the Mn content was lower than the range of the present invention. On the other hand, the alloy 35 has [Mn]
Only the value of / [S] was smaller than the range of the present invention, and solidification cracking occurred.

FIG. 1 shows the occurrence of solidification cracks in the alloy according to the present embodiment, organized based on the contents of S and Mn. The shaded portion in FIG. 1 is the range of the present invention relating to Mn and S. From Table 2 and FIG. 1, it can be seen that according to the present invention, a desired low thermal expansion alloy having a small thermal expansion coefficient at room temperature can be produced according to the Co content without causing cracks.

[0034]

As described above, according to the present invention, it is possible to provide a low-thermal-expansion alloy excellent in machinability at low cost as compared with the prior art.

[Brief description of the drawings]

FIG. 1 is a graph showing the occurrence of solidification cracking in the alloy of Example 2 arranged on a coordinate plane with the S content on the horizontal axis and the Mn content on the vertical axis.

FIG. 2 is a drawing showing the shape of a crack test piece in Example 2.

Claims (4)

[Claims] C .: 0.05% or less by weight, Si:
0.3% or less, Mn: 0.45 to 1.2%, P: 0.5
%, S: 0.015 to 0.035%, Ni: 33.%.
0 to 34.5%, Co: 3.0 to 4.0%, the balance substantially consisting of iron, and [Mn] is the weight% of Mn,
[Mn] / [S]: 1 when [S] is expressed as% by weight of S
A low-thermal-expansion alloy excellent in machinability, having an average coefficient of thermal expansion at room temperature of 1.0 × 10 ⁻⁶ / ° C. or less, characterized by being 5 or more. 2. In% by weight, C: 0.05% or less, Si:
0.3% or less, Mn: 0.45 to 1.2%, P: 0.5
%, S: 0.015 to 0.035%, Ni: 33.%.
5 to 35.5%, Co: 2.0 to 3.0%, the balance substantially consisting of iron, and [Mn] is the weight% of Mn,
[Mn] / [S]: 1 when [S] is expressed as% by weight of S
A low thermal expansion alloy excellent in machinability, having an average coefficient of thermal expansion at room temperature of 1.5 × 10 ⁻⁶ / ° C. or less, characterized by being 5 or more. 3. The method according to claim 1, wherein C: 0.05% or less, Si:
0.3% or less, Mn: 0.45 to 1.2%, P: 0.5
% Or less, S: 0.015 to 0.035%, Ni: 34.
0 to 36.5%, Co: 1.0 to 2.0%, the balance substantially consisting of iron, and [Mn] is the weight% of Mn,
[Mn] / [S]: 1 when [S] is expressed as% by weight of S
A low-thermal-expansion alloy excellent in machinability, having an average coefficient of thermal expansion at room temperature of 2.0 × 10 ⁻⁶ / ° C. or less, characterized by being 5 or more. 4. An alloy having a composition according to any one of claims 1 to 3 is heated in a temperature range of 700 to 950 ° C., and then cooled to 450 ° C. or less at a cooling rate of 5 ° C./sec or more. A method for producing a low thermal expansion alloy having excellent machinability.