JP5893659B2 - Low thermal expansion cast alloy and manufacturing method thereof - Google Patents

Description

  The present invention relates to a low thermal expansion cast alloy having a very low thermal expansion suitable for an ultra-precision equipment member such as a semiconductor manufacturing apparatus and a method for manufacturing the same.

Conventionally, low thermal expansion alloys have been used for the purpose of maintaining and improving the precision of ultra-precise equipment. Among them, the alloy of 32% Ni-5% Co-remaining Fe (hereinafter referred to as Super Invar) has a heat around room temperature. The expansion coefficient is 1 × 10 ⁻⁶ / ° C. or less, and rolled materials and forged materials (hereinafter referred to as steel materials) are commercialized and commercially available (for example, Non-Patent Document 1).

  Patent Document 1 includes an iron-based alloy containing, by weight, C: 0.1% or less, Ni: 30 to 34%, Co: 4 to 6%, and Mn: 0.1 to 1.0. % And S: 0.02 to 0.15%, and a free-cutting low thermal expansion casting alloy with Mn / 54.94> S / 32.06 has been proposed.

On the other hand, in Patent Document 2 and Patent Document 3, a super invar having a thermal expansion coefficient of 0.5 × 10 ⁻⁶ / ° C. is used for a resonator of a microwave waveguide and a wafer stage of a semiconductor immersion exposure apparatus. It is described.

JP 2002-206142 A JP 2010-206615 A JP 2005-183416 A

Fujikoshi Co., Ltd., Technical data, [Search on March 7, 2014], Internet <URL: HTTP://www.nachi-fujikoshi.co.jp/kou/fm_alloy/fm_alloy_exeo.pdf>

By the way, the above-mentioned Super Invar steel material has been required to suppress C to an impurity level of 0.02% or less in order to reliably obtain a thermal expansion coefficient of 1 × 10 ⁻⁶ / ° C. or less. According to the inventor's knowledge, when such a low C super invar is melted and cast in the atmosphere, gas defects frequently occur and industrial production is very difficult, so it is necessary to perform vacuum melting. is there. It is impractical to perform complex operations using expensive equipment for ordinary casters, and it is virtually impossible to produce a low-C super invar casting.

On the other hand, in the alloy for low thermal expansion casting of Patent Document 1, the Ni content and the Co content are equivalent to those of Super Invar, and the C content is allowed to be within 0.1% or less to an air casting range. In the examples, only an alloy having a very low C content of 0.008 to 0.011% is disclosed, and the coefficient of thermal expansion is 0.773 × 10 ⁻⁶ / ° C. or less at such a very low C content. It is only shown that. That is, Patent Document 1 also suggests that in order to obtain a thermal expansion coefficient of 1 × 10 ⁻⁶ / ° C. or less, C needs to be an extremely low value of about 0.01%. For this reason, although it is described in Patent Document 1 that an alloy suitable for the production of a thin-walled large casting can be provided, since it is actually necessary to reduce the C content, it is still necessary to melt and cast in the atmosphere. It is very difficult, and it is considered difficult for an ordinary caster to industrially use a cast alloy using the technique of Patent Document 1.

  In addition, Super Invar steel shown in Non-Patent Document 1 can be applied only to simple shapes such as plates and rods, and complicated shapes and large parts used for precision devices are manufactured by cutting or welding assembly. Although it is necessary, there is also a problem that a great number of man-hours and costs are required due to the low machinability and weldability of Super Invar.

In Patent Document 1, such a problem is solved by adding a predetermined amount of S and Mn and improving machinability by MnS in the matrix. However, as described above, the alloy of Patent Document 1 is used. However, in order to obtain a low coefficient of thermal expansion of 1 × 10 ⁻⁶ / ° C. or less, it is necessary to set C to an extremely low value of about 0.01%, and air casting is difficult. It cannot be applied to large parts, and such problems cannot be solved essentially.

  The present invention has been made in view of such circumstances, and has a low thermal expansion cast alloy having an extremely small thermal expansion coefficient equivalent to that of Super Invar, while containing C at a level capable of ordinary atmospheric dissolution and casting. It is another object of the present invention to provide a manufacturing method thereof.

  Further, a low thermal expansion cast alloy having a very low thermal expansion coefficient equivalent to that of Super Invar and containing a machinability superior to Super Invar, while containing C at a level capable of normal atmospheric dissolution, and its production It is an object to provide a method.

As a result of repeated investigations to solve the above problems, the present inventors have made the C content in the alloy a level that enables atmospheric dissolution and atmospheric casting,
i) adjusting the Co content according to the C content;
ii) It was found that by defining the Ni content according to the Co content, an extremely small thermal expansion coefficient equivalent to that of Super Invar can be obtained.

Conventionally, the effects of C, Ni, and Co on the thermal expansion coefficient have not been studied in detail. For example, although Patent Document 1 describes the reasons for limiting the ranges of C, Ni, and Co, the composition of the example is a super invar composition (32% Ni-5% Co—Fe with C of about 0.01%). ) it is only thereby 1 although × 10 ^{-6 /} ° C. or less of the thermal expansion coefficient is obtained, it is shown that the thermal expansion coefficient of 1 × 10 ^{-6 /} ° C. or less in the composition of claims is obtained It has not been.

Summarizing the conventional knowledge, the range of C content and Co content of Super Invar is the range indicated by region A in FIG. That is, conventionally, if C is suppressed to an impurity level, the coefficient of thermal expansion can be surely reduced to 1 × 10 ⁻⁶ / ° C. or less in the range of 4 to 6% Co, but the range becomes narrower as C increases. If C exceeds 0.05%, it has been considered impossible to obtain a thermal expansion coefficient of 1 × 10 ⁻⁶ / ° C. or less even if the amount of Co is adjusted.

In the conventional super invar composition (region A in FIG. 1), in which C capable of obtaining an air-dissolved casting is more than 0.02% to 0.05% or less (region B in FIG. 1), Although a thermal expansion coefficient of 1 × 10 ⁻⁶ / ° C. or less can be obtained, when producing a cast product by melting in the atmosphere, in addition to C, Si and Mn that increase the thermal expansion coefficient are deoxidized and castability Since it is added for the purpose of improvement, a region where the thermal expansion coefficient actually exceeds 1 × 10 ⁻⁶ / ° C. is generated. Therefore, in order to obtain a thermal expansion coefficient of 1 × 10 ⁻⁶ / ° C. or lower, it is necessary to limit C lower as seen in Patent Document 1. As a result, in the casting material, the region B in FIG. 1 is translated to the low C side, the components must be adjusted to a limited range, and it is difficult to reliably produce an appropriate cast product. It was thought.

On the other hand, in the present invention, a composition that can obtain a thermal expansion coefficient of 1 × 10 ⁻⁶ / ° C. or less is premised on the assumption that the C content exceeds 0.02%, which allows atmospheric melting and casting. As a result, the range of C content and Co content satisfies the range of region C in FIG. 1, and by defining the Ni content according to the Co content, thermal expansion of 1 × 10 ⁻⁶ / ° C. or less It was newly found that the coefficient can be obtained.

Further, after defining the C content, the Co content, and the Ni content as described above, and further defining the S content, the Mn content, and their ratio within a predetermined range, Tool lubrication can be promoted by appropriately distributing sulfides, and a cast alloy having a low machinability of 1 × 10 ⁻⁶ / ° C. or less and good machinability without causing solidification cracks can be obtained. I found out.

It has also been found that it is effective to appropriately control the heat treatment in order to make the alloy having the above composition a low expansion coefficient of 1 × 10 ⁻⁶ / ° C. or less.

  This invention is completed based on the said knowledge, and provides the following (1)-(7).

(1) In mass%,
C: more than 0.02%, 0.15% or less,
Si: 0.3% or less,
Mn: 0.25 to 0.6%,
Ni: 29-32.5%,
Co: 5 to 9.5%
Containing
When the C content (mass%) is expressed as [C] and the Co content (mass%) is expressed as [Co], these are (a) [Co] ≧ 40 × [C] +3, (b) [ C] ≦ 0.15, (c) [Co] ≦ (70/3) × [C] +6, (d) [C]> 0.02, (e) [Co] ≧ −20 × [C] +6 Is a range that satisfies
When the Ni content (mass%) is represented by [Ni] and the Co content (mass%) is represented by [Co], the Ni equivalent represented by [Ni] + 0.8 × [Co] is 35. 5 to 36.5%, the balance being Fe and inevitable impurities (however, C: 0.052%, Si: 0.19%, Mn: 0.61%, Ni: 32.21%) , Co: 5.07%, except for the composition composed of Fe and unavoidable impurities in the balance) .

(2) In mass%,
C: more than 0.02%, 0.15% or less,
Si: 0.3% or less,
Mn: 0.25 to 0.6%,
S: 0.015-0.035%
Ni: 29-32.5%,
Co: 5 to 9.5%
Containing
When the C content (mass%) is expressed as [C] and the Co content (mass%) is expressed as [Co], these are (a) [Co] ≧ 40 × [C] +3, (b) [ C] ≦ 0.15, (c) [Co] ≦ (70/3) × [C] +6, (d) [C]> 0.02, (e) [Co] ≧ −20 × [C] +6 Is a range that satisfies
And when the Ni content (mass%) is represented by [Ni] and the Co content (mass%) is represented by [Co],
The Ni equivalent expressed as [Ni] + 0.8 × [Co] is in the range of 35.5 to 36.5%,
Furthermore, when Mn content (% by mass) is represented by [Mn], S content (% by mass) is represented by [S], and the maximum thickness (mm) of the cast product is represented by t, [Mn] / [S] A low thermal expansion cast alloy characterized by satisfying ≧ 46−1335 / t + 1430 / t ² , the balance being Fe and inevitable impurities.

(3) A low thermal expansion cast alloy having the composition as described in (1) or (2) above, having an average coefficient of thermal expansion of 20 to 25 ° C. of 1 × 10 ⁻⁶ / ° C. or less.

(4) A low thermal expansion cast alloy having the composition described in the above (1) or (2) and having an average thermal expansion coefficient of 20 to 25 ° C. of 0.5 × 10 ⁻⁶ / ° C. or less. .

  (5) After heating the alloy having the composition described in (1) or (2) above in a temperature range of 700 to 950 ° C., 5 ° C./sec. The manufacturing method of the low thermal expansion cast alloy characterized by cooling to 450 degrees C or less with the above cooling rate.

  According to the present invention, there is provided a low thermal expansion cast alloy having a very low thermal expansion coefficient equivalent to that of Super Invar and a method for producing the same, while containing C at a level that allows normal atmospheric dissolution and atmospheric casting.

  In addition, according to the present invention, low heat having a very low thermal expansion coefficient equivalent to that of Super Invar and having a machinability superior to that of Super Invar while containing C at a level capable of normal atmospheric dissolution. Expanded cast alloys and methods for making the same are provided.

It is a figure which shows the range of C content and Co content in the alloy of this invention, and the alloy of a prior art. It is a figure which shows the influence of C content which acts on the thermal expansion coefficient in the alloy of this invention, and the conventional super invar. It is a figure which shows a solidification cracking evaluation test piece. It is a figure which shows the relationship between the maximum thickness of the casting and solid Mn / S which influences a solidification crack.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

<First Embodiment>
The first embodiment is to obtain a cast alloy having a low thermal expansion coefficient equivalent to that of Super Invar while containing C at a level that allows normal atmospheric dissolution and atmospheric casting.

  Hereinafter, the reason for limitation in the present embodiment will be described in detail. In addition, unless otherwise indicated, the% display in a component is a mass%, and a thermal expansion coefficient is an average thermal expansion coefficient of 20-25 degreeC.

[Chemical composition]
C: more than 0.02% and not more than 0.15% C is an element that remarkably increases the coefficient of thermal expansion. In the conventional super invar composition (32% Ni-5% Co-residual Fe), C is 0 If the content exceeds 0.02%, it has been difficult to obtain a low thermal expansion coefficient of 1 × 10 ⁻⁶ / ° C. or less. However, C has an effect of improving the castability and soundness of a low thermal expansion alloy cast product having a super invar composition, and in the present invention, an appropriate casting design is performed so that a sound cast product can be obtained even in air melting. The C content is more than 0.02%. Specifically, as shown in FIG. 1 (details will be described later), by adjusting the Co content according to the C content, even if the C content exceeds 0.02%, it is 1 × 10 ⁻⁶ / ° C. or less. It was possible to obtain a low coefficient of thermal expansion. However, if its content exceeds 0.15%, graphite starts to precipitate in a part of the structure, and the amount of solute C changes. Therefore, even by adjusting the Co amount, 1 × 10 ⁻⁶ / A coefficient of thermal expansion of less than 0 ° C cannot be obtained. Therefore, the C content is set to a range of more than 0.02% and 0.15% or less.

  FIG. 2 shows the relationship between the C content and the coefficient of thermal expansion in the conventional alloy (Super Invar) and the alloy of the present invention. As shown in this figure, it can be seen that in the present invention, low thermal expansion is obtained even if the C content is large.

-Si: 0.3% or less Si is an element added for the purpose of deoxidation and improvement of hot water flow. However, if its content exceeds 0.3%, an increase in the coefficient of thermal expansion cannot be ignored like C. Therefore, the Si content is set to 0.3% or less.

・ Mn: 0.25 to 0.6%
Mn is an element effective for deoxidation. However, if the content is less than 0.25%, the effect is small, and if it exceeds 0.6%, the thermal expansion coefficient increases greatly. Therefore, the Mn content is in the range of 0.25 to 0.6%.

・ Co: 5 to 9.5%
Co is an important element that determines the thermal expansion coefficient together with Ni, which will be described later, and is an indispensable element for obtaining a smaller thermal expansion coefficient than when Ni alone is added.
If it is less than 5%, the coefficient of thermal expansion exceeds 1 × 10 ⁻⁶ / ° C., and if it exceeds 9.5%, the coefficient of thermal expansion is still 1 × 10 ⁻⁶ / ° C. even if the amount of Co is adjusted with respect to the amount of C described later. Over. Therefore, the Co content is in the range of 5 to 9.5%.

Ni: 29-32.5%
Ni is an important element that determines the thermal expansion coefficient together with Co, and the thermal expansion coefficient can be reduced to 1 × 10 ⁻⁶ / ° C. or less by adjusting it to the range described later according to the amount of Co. However, if Ni is less than 29% or more than 32.5%, the thermal expansion coefficient exceeds 1 × 10 ⁻⁶ / ° C. even by the above adjustment. Therefore, Ni is made 29 to 32.5% of range.

Co and C are (a) [Co] ≧ 40 × [C] +3,
(B) [C] ≦ 0.15,
(C) [Co] ≦ (70/3) × [C] +6,
(D) [C]> 0.02.
(E) [Co] ≧ −20 × [C] +6
[Ni] + 0.8 × [Co] is in a range of 35.5 to 36.5% As a result of detailed examinations of the C content and Co content in the alloy, (A) [Co] ≧ 40 × [C] +3, (b) [C] ≦ 0.15, (c) [Co] ≦ (70/3) shown in the region C of FIG. X [C] +6, (d) [C]> 0.02, (e) If [Co] ≧ −20 × [C] +6 is satisfied, [Ni] + 0.8 × [Co] It was newly found that a thermal expansion coefficient of 1 × 10 ⁻⁶ / ° C. or less can be obtained when the Ni equivalent is in the range of 35.5 to 36.5%. However, [C], [Co], and [Ni] are contents (mass%) of each element.

When the area C is out of FIG. 1, the following inconvenience occurs. That is, in [Co] <40 × [C] +3 (below the region C), the thermal expansion coefficient exceeds 1 × 10 ⁻⁶ / ° C., and the region of [Co] <− 20 × [C] +6 (region C In the lower side), it is difficult to reliably obtain a thermal expansion coefficient of 1 × 10 ⁻⁶ / ° C. or lower in the cast alloy, and the region [Co]> (70/3) × [C] +6 (the upper side of the region C) ), Expansion occurs due to martensitic transformation in a part of the structure, and in the region of [C]> 0.15 (on the right side of region C), C exceeds the solid solubility limit and is dissolved in supersaturation or precipitated as graphite. As a result, the coefficient of thermal expansion becomes unstable, and in the region [C] ≦ 0.02 (left side of region C), defects frequently occur in the cast product.

  Further, the low thermal expansion of the Fe—Ni—Co alloy is remarkably obtained when the Ni equivalent represented by [Ni] + 0.8 × [Co] is in the range of 35.5 to 36.5%. Even if it is less than 5% or more than 36.6%, it is difficult to obtain a desired low thermal expansion property. Therefore, the Ni equivalent is set in the range of 35.5 to 36.5%.

  The balance is Fe and inevitable impurities. In this embodiment, S is contained as an impurity.

[Production conditions]
When an alloy having these composition ranges is rapidly cooled after high-temperature heating, the thermal expansion coefficient can be reduced. The reason for this is considered to be that the magnetization state changes due to the action of internal stress generated during rapid cooling, which affects the spontaneous magnetization strain. If the heating temperature is less than 700 ° C., the low thermal expansion effect is insufficient, and if it exceeds 950 ° C., the effect is not improved and there is a risk of causing deformation or cracking. After heating, the average cooling rate up to 450 ° C. is 5 ° C./sec. If the ratio is less than 1, the generation of internal stress is small, and the effect of reducing the thermal expansion coefficient is small. Therefore, after heating in the temperature range of 700 to 950 ° C., 5 ° C./sec. It cools to 450 degrees C or less with the above cooling rate.

The cast alloy of the present embodiment as described above can obtain a low coefficient of thermal expansion of 1 × 10 ⁻⁶ / ° C. or less, and is 0.5 × 10 ⁻⁶ / ° C. or less by optimizing the composition. An extremely low coefficient of thermal expansion can be obtained.

  In the first embodiment, since it has a low thermal expansion coefficient equivalent to that of Super Invar and contains C at a level that allows normal atmospheric melting and atmospheric casting, a low thermal expansion cast alloy can be obtained. For this reason, it can obtain without welding the complicated shape goods and large sized parts of low thermal expansion.

<Second Embodiment>
The second embodiment can obtain a thermal expansion coefficient equivalent to that of Super Invar while containing C at a level that allows normal atmospheric dissolution and atmospheric casting, and has excellent machinability.

Hereinafter, the reason for limitation in the present embodiment will be described in detail.
In the present embodiment, the contents of C, Si, Co, and Ni, the relationship between the C content and the Co content, the Ni equivalent range, and the manufacturing conditions are the same as in the first embodiment. Hereinafter, conditions unique to the second embodiment will be described.

・ Mn: 0.25 to 0.6%
Mn is an element effective for deoxidation, and also plays an important role in improving machinability by forming sulfides with S as described later. If the content is less than 0.25%, the effect is small, and if it exceeds 0.6%, the thermal expansion coefficient increases greatly. Therefore, the Mn content is in the range of 0.25 to 0.6%.

・ S: 0.015-0.035%
Since S forms sulfides with Mn and contributes to improvement of machinability, it is positively added in this embodiment. However, if it is contained in a large amount in the alloy, low melting point FeS is formed at the grain boundary and becomes brittle, causing ductility and cracking. If it exceeds 0.035%, it becomes a complicated shape or a large casting. Prone to solidification cracking. On the other hand, if the content is less than 0.015%, the machinability improving effect is small. Therefore, the S content is in the range of 0.015 to 0.035%.

[Mn] / [S] ≧ 46-1335 / t + 1430 / t ²
(However, [Mn] and [S] are their contents, and t is the maximum thickness (mm) of the cast product)
[Mn] / [S] influences the amount and composition of sulfides and is an important parameter for determining the tendency of solidification cracking. The tendency of solidification cracking is influenced not only by the ratio of Mn and S but also by t. In the range of Mn and S described above, when [Mn] / [S] is less than 46-1335 / t + 1430 / t ² , Mn is insufficient with respect to S, and excessive S forms the above-described FeS, which causes solidification cracking, etc. Cause. On the other hand, when [Mn] / [S] is 46-1335 / t + 1430 / t ² or more, since S exists as MnS having a high melting point, it is difficult to cause solidification cracking.

  Since the influence of the maximum thickness t (mm) of the cast product on solidification cracking is related to R (mm) of the solidification cracking specimen shown in FIG. 3, the relation between t and solidification cracking is grasped using the cracking specimen. can do. According to the knowledge of the present inventor, the relationship between R and t is approximately expressed by t = 500 / R. That is, as R is smaller, a thick cast product is simulated.

Actually, the size of R of the solidification cracking test piece shown in FIG. The results obtained using 21 to 24 are shown in FIG. FIG. 4 also shows the maximum thickness t (mm) corresponding to the size of R.

As shown in FIG. 4, the smaller the R, that is, the greater the corresponding wall thickness, the larger the value of [Mn] / [S] that is less likely to cause solidification cracks, and the boundary line that is less likely to cause solidification cracks is 46. It is represented by −1335 / t + 1430 / t ² . Therefore, it is defined as [Mn] / [S] ≧ 46−1335 / t + 1430 / t ² . For example, solidification cracking can be effectively prevented by setting Mn / S to about 34 for a casting having a maximum thickness of 100 mm.

  In the present embodiment, the balance of C, Si, Mn, S, Co, and Ni is Fe and inevitable impurities.

In the present embodiment, the alloy of the first embodiment further contains S. However, if the S content is within the range of the present embodiment, thermal expansion is not affected. That is, the cast alloy of the present embodiment can obtain a low coefficient of thermal expansion of 1 × 10 ⁻⁶ / ° C. or less, as well as the cast alloy of the first embodiment. A very low coefficient of thermal expansion of × 10 ⁻⁶ / ° C. or less can be obtained.

  In the second embodiment, while having a low thermal expansion coefficient equivalent to that of Super Invar, it contains C at a level that allows normal atmospheric dissolution and casting, and improves machinability without causing solidification cracking. Thus, a free-cutting low thermal expansion cast alloy can be obtained. For this reason, it is possible to manufacture a complex shape product or a large component with low thermal expansion without welding and with good machinability.

  Examples of the present invention will be described below.

<First embodiment>
The first example corresponds to the first embodiment.
Here, alloys having chemical compositions shown in Table 1 are melted in the atmosphere in a high frequency induction furnace, and JIS
A specimen according to FIG. 1b) of G0307 was cast. In either case, a CO ₂ silica sand mold was used as a mold.

After subjecting each test material to heat treatment under Condition 8 in Table 3, a φ6 × 12 mm thermal expansion test piece was sampled, and an average thermal expansion coefficient between 20 and 25 ° C. was measured with a laser interference thermal dilatometer.

The results are shown in Table 1. As shown in Table 1, no. Nos. 1 to 7 all have an average coefficient of thermal expansion between 20 and 25 ° C. of 1 × 10 ⁻⁶ / ° C. or less. 1 and No. 2 and no. No. 7 is 0.5 × 10 ⁻⁶ / ° C. or less . 1 is less than 0.2 × 10 ⁻⁶ / ° C., which is equivalent to a conventional super invar, and has been confirmed to have characteristics that can meet recent severe demands. Moreover, all of these had no casting defects and good castability was obtained.

  On the other hand, in the comparative example, no. Since C was less than the lower limit of No. 8, gas defects occurred and the castability was poor. No. For Nos. 9-15, no. No. 9 has Si and Ni exceeding the upper limit, Co being less than the lower limit, No. 10 has Ni below the lower limit, Co exceeds the upper limit, and the relationship between the C content and the Co content is outside the scope of the invention of FIG. 11 and no. No. 12 is within the range of each element, but the relationship between the C content and the Co content is out of the scope of the invention of FIG. 13 and no. 14 is within the range of the individual elements, but the Ni equivalent is No. 14. 13 is less than the lower limit. 14 exceeds the upper limit. In No. 15, C exceeded the upper limit, graphite was formed in the structure, the structure became unstable, and none of the desired thermal expansion coefficients could be obtained.

<Second embodiment>
The second example corresponds to the second embodiment.
Here, alloys of chemical compositions shown in Table 2 are melted in the atmosphere in a high frequency induction furnace, and JIS
G0307 according to FIG. 1b) and a test piece of 60 mm × 250 mm × 25 mm machinability test piece, 21-No. 24 and no. For the alloy No. 37, a solidified cracking test piece shown in FIG. 3 was cast. In either case, a CO ₂ silica sand mold was used as a mold.

  After performing the same heat treatment as in the first example, a φ6 × 12 mm thermal expansion test piece was taken from the test material, and the average thermal expansion coefficient between 20 and 25 ° C. was measured with a laser interference thermal dilatometer.

  The crack test piece confirmed the presence or absence of the crack of four types of R parts in FIG. 3 with the dyeing | penetration penetrant inspection method.

  In the machinability test, surface grinding was performed so that two surfaces of 60 mm x 250 mm were parallel, and then a drill equipped with a high-speed steel tool of φ5 mm was used. A hole having a thickness of 10 mm was drilled, and a case where 25 holes or more could be drilled was determined to have good machinability.

These results are shown in Table 2. As shown in Table 2, the alloy of the present invention is No. Nos. 21 to 28 all have an average coefficient of thermal expansion of 1 × 10 ⁻⁶ / ° C. or less between 20 to 25 ° C. 21 and no. 27 and no. 28 is 0.5 × 10 ⁻⁶ / ° C. or less . ^No. 28 is 0.2 × 10 ⁻⁶ / ° C., which is equivalent to the conventional super invar, and it has been confirmed that it has characteristics that can meet recent severe demands. In addition, no gas defects were produced during casting, and no cracks could be confirmed in any R part of the solidification cracking test piece, indicating good solidification cracking resistance. Furthermore, machinability was also good.

  On the other hand, in the comparative example, no. Since C was less than the lower limit of No. 29, the coefficient of thermal expansion was low, but gas defects occurred and the castability was poor. No. For Nos. 30 to 35, no. In No. 30, Si exceeded the upper limit, and the relationship between the C content and the Co content deviated from the scope of the invention of FIG. No. 31 is within the range of the individual elements, but the relationship between the C content and the Co content is out of the invention range of FIG. In No. 32, Ni is less than the lower limit, C exceeds the upper limit, graphite is formed in the structure, and the structure becomes unstable. No. 33 causes martensitic transformation when Ni is less than the lower limit. No. 34 has Ni equivalent below the lower limit. No. 35 has a Ni equivalent exceeding the upper limit. In No. 36, Co was less than the lower limit, and any desired thermal expansion coefficient could not be obtained. Furthermore, No. of the comparative example. In No. 37, the value of Mn / S was smaller than 15 at which cracks did not occur at R20. Therefore, cracks were observed in all R parts of the cracked test pieces. Furthermore, the comparative example No. In No. 38, machinability was not good because S was less than the lower limit.

<Third embodiment>
The third embodiment relates to manufacturing conditions.
Here, first, in Table 1, No. A plurality of test bodies having a composition of 5 and heat-treated under the respective heat treatment conditions 1 to 13 shown in Table 3 were prepared, and the thermal expansion coefficient was obtained. The results are shown in Table 4. As shown in Table 4, after heating in the temperature range of 700 to 950 ° C., 5 ° C./sec. If conditions 5, 6, 8, 9, and 11 satisfying the conditions for cooling to 450 ° C. or lower at the above cooling rate, the thermal expansion coefficient is 1 × 10 ⁻⁶ / ° C. or lower and cracks are not generated. It was done. On the other hand, in conditions 1, 2, 3, 4, 7, 10, and 12 that deviate from this, the thermal expansion coefficient exceeds 1 × 10 ⁻⁶ / ° C., and in condition 13 the thermal expansion coefficient is 1 × 10 ⁻⁶ / ° C. Although it is as follows, fine cracks were observed in the specimen.

Next, no. Similarly, a plurality of test bodies were prepared by heat-treating 25 composition alloys under the respective heat treatment conditions 1 to 13 shown in Table 3, and the thermal expansion coefficient was obtained. The results are shown in Table 5. As shown in Table 5, no. Similarly to the composition of No. 5, after heating in a temperature range of 700 to 950 ° C., 5 ° C./sec. If conditions 5, 6, 8, 9, and 11 satisfying the conditions for cooling to 450 ° C. or lower at the above cooling rate, the thermal expansion coefficient is 1 × 10 ⁻⁶ / ° C. or lower and cracks are not generated. It was done. On the other hand, in conditions 1, 2, 3, 4, 7, 10, and 12 that deviate from this, the thermal expansion coefficient exceeds 1 × 10 ⁻⁶ / ° C., and in condition 13 the thermal expansion coefficient is 1 × 10 ⁻⁶ / ° C. Although it is as follows, fine cracks were observed in the specimen.

Claims (5)

% By mass
C: more than 0.02%, 0.15% or less,
Si: 0.3% or less,
Mn: 0.25 to 0.6%,
Ni: 29-32.5%,
Co: 5 to 9.5%
Containing
When the C content (mass%) is expressed as [C] and the Co content (mass%) is expressed as [Co], these are (a) [Co] ≧ 40 × [C] +3, (b) [ C] ≦ 0.15, (c) [Co] ≦ (70/3) × [C] +6, (d) [C]> 0.02, (e) [Co] ≧ −20 × [C] +6 Is a range that satisfies
When the Ni content (mass%) is represented by [Ni] and the Co content (mass%) is represented by [Co], the Ni equivalent represented by [Ni] + 0.8 × [Co] is 35.5. ˜36.5%, the balance being Fe and inevitable impurities (provided that C: 0.052%, Si: 0.19%, Mn: 0.61%, Ni: 32.21%, Co: 5.07% is contained, and the balance is excluding the composition consisting of Fe and inevitable impurities). % By mass
C: more than 0.02%, 0.15% or less,
Si: 0.3% or less,
Mn: 0.25 to 0.6%,
S: 0.015-0.035%
Ni: 29-32.5%,
Co: 5 to 9.5%
Containing
When the C content (mass%) is expressed as [C] and the Co content (mass%) is expressed as [Co], these are (a) [Co] ≧ 40 × [C] +3, (b) [ C] ≦ 0.15, (c) [Co] ≦ (70/3) × [C] +6, (d) [C]> 0.02, (e) [Co] ≧ −20 × [C] +6 Is a range that satisfies
And when Ni content (mass%) is represented by [Ni] and Co content (mass%) is represented by [Co], the Ni equivalent represented by [Ni] + 0.8 × [Co] is 35. 5 to 36.5% of range,
Furthermore, when Mn content (% by mass) is represented by [Mn], S content (% by mass) is represented by [S], and the maximum thickness (mm) of the cast product is represented by t, [Mn] / [S] A low thermal expansion cast alloy characterized by satisfying ≧ 46−1335 / t + 1430 / t ² , the balance being Fe and inevitable impurities. A low thermal expansion cast alloy having the composition according to claim 1 or 2 and having an average thermal expansion coefficient of 20 to 25 ° C of 1 x 10 ^-6 / ° C or less. A low thermal expansion cast alloy having the composition according to claim 1 or 2 and having an average coefficient of thermal expansion of 20 to 25 ° C of 0.5 × 10 ^-6 / ° C or less.   The alloy having the composition according to claim 1 or 2 is heated in a temperature range of 700 to 950 ° C, and then 5 ° C / sec. The manufacturing method of the low thermal expansion cast alloy characterized by cooling to 450 degrees C or less with the above cooling rate.

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