Low thermal expansion alloy with excellent mechanical properties and method for producing same

Abstract

To provide a low thermal expansion alloy having excellent mechanical properties which can obtain a product with a complex shape having a strength of 1000 MPa or more and an elongation of 5% or more without applying plastic working such as wire drawing and to provide a method for producing the same.SOLUTION: There is provided a low thermal expansion alloy which comprises, by mass%, 0.05% or less of C, 0.4% or less of Si, 0.5% or less of Mn, more than 2.0 to 3.0% of Ti, 0.1 to 0.4% of Al, 30.0 to 37.0% of Ni, 20.0% or less of Co and the balance Fe with inevitable impurities, wherein the average crystal particle diameter is 80 μm or less, the tensile strength at room temperature is 1000 MPa or more, the elongation is 5% or more, the average coefficient of thermal expansion between 10 and 40°C is 5.0 ppm / °C or less, the average coefficient of thermal expansion between 10 and 200°C is 6.0 ppm / °C or less and the average coefficient of thermal expansion between 10 and 350°C is 7.0 ppm / °C or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a low thermal expansion alloy having excellent mechanical properties suitable for use as a precision equipment member, and a method for producing the same. [Background technology]

[0002] Conventionally, alloys such as Invar (36% Ni-Fe alloy) and Super Invar (32% Ni-5% Co-Fe alloy) have been known as practical low-thermal expansion alloys, and are used in applications requiring dimensional accuracy, such as precision instrument parts.

[0003] Although the thermal deformation of precision equipment components made from these low-thermal expansion alloys is significantly smaller than that of general-purpose steel, the tensile strength (hereinafter referred to as "strength") of these low-thermal expansion alloys at room temperature is around 400 MPa, which is smaller than that of general-purpose structural materials. For this reason, these low-thermal expansion alloys are often not applicable to components that are subject to high loads, and various high-strength, low-thermal expansion alloys are being investigated.

[0004] As a technique for increasing the strength of low-thermal expansion alloys, for example, Patent Document 1 proposes a low-thermal expansion, high-strength alloy in which specific amounts of fluorine compounds of group IIa elements and other elements are added to an Fe-Ni-Co alloy, and these intermetallic compounds and the α' phase formed by deformation-induced transformation are utilized.

[0005] Furthermore, Patent Document 2 proposes high-strength, low-thermal expansion alloy wires in which Fe—Ni and Fe—Ni—Co alloys are strengthened by aging precipitation of (Mo, V)C-based composite carbides.

[0006] Furthermore, Patent Document 3 proposes a high-strength, low-thermal expansion casting alloy that is strengthened by adding Ti to an Fe-Ni-Co-based low-thermal expansion alloy and precipitating fine Ni3Ti-based intermetallic compounds through aging treatment. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-162820 [Patent Document 2] International Publication No. 2018 / 193810 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-286546 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the high-strength, low-thermal-expansion alloy disclosed in Patent Document 1 achieves low thermal expansion and high strength by utilizing the strain-induced transformation phase and work-hardening strain obtained through wiredrawing. Therefore, it is expected that dimensional changes over a long period of time due to the reverse transformation of the α' phase and the release of strain, i.e., aging, will occur, and there is a possibility of a decrease in accuracy when used in ultra-precision devices. In addition, it contains fluorine compounds, the use of which is increasingly restricted, raising concerns about future supply. Furthermore, since wiredrawing is required, there are significant restrictions on the shape of the components to which it can be applied, among other issues.

[0009] Furthermore, the technology disclosed in Patent Document 2 is an alloy wire manufactured by wire drawing, and similarly to Patent Document 1, there are significant restrictions on the shapes of components to which it can be applied. In addition, the alloys of the present invention in the examples have a maximum breaking elongation in a tensile test (hereinafter referred to as "elongation") of 3.1%, which means low ductility and limited applications.

[0010] Furthermore, the technology disclosed in Patent Document 3 is a cast alloy, so it can accommodate complex product shapes, but it has low strength and limited applications because it does not undergo wiredrawing or wiredrawing processes as in Patent Documents 1 and 2. Specifically, the examples in Patent Documents 1 and 2 have strengths of over 1000 MPa due to wiredrawing or wiredrawing processes, whereas the examples of the present invention in Patent Document 3 have a maximum strength of 884 MPa.

[0011] Therefore, an object of the present invention is to provide a low thermal expansion alloy with excellent mechanical properties that has a strength of 1000 MPa or more, an elongation of 5% or more, and can be used to produce products with complex shapes without the need for plastic processing such as wire drawing, and a method for producing the alloy. [Means for solving the problem]

[0012] Conventional techniques for improving the strength of Fe-Ni or Fe-Ni-Co (hereinafter referred to as "Fe-Ni(-Co)") low thermal expansion alloys can be summarized as follows: (1) adding elements that produce carbides or intermetallic compounds by aging treatment to the base Fe-Ni(-Co) alloy, and utilizing the resulting precipitation hardening; (2) cold working the Fe-Ni(-Co) alloy to generate strain-induced transformation and hardening strain, and utilizing the work hardening that occurs during this process; and a combination of (1) and (2).

[0013] According to confirmation tests conducted by the present inventors, it is not impossible to obtain a strength of 1000 MPa or more by using the above (1) alone, but the elongation is small, and it has been found that in order to obtain an elongation of 5% or more at the same time, plastic processing such as forging or hot rolling is required. Ultimately, in the past, in order to obtain a low thermal expansion alloy that simultaneously has a strength of 1000 MPa or more and an elongation of 5% or more, the application of plastic processing was essential, which significantly restricted the shape of the applicable component and limited the applications.

[0014] Therefore, the present inventors investigated the possibility of obtaining an Fe-Ni(-Co)-based low thermal expansion alloy that can simultaneously achieve a strength of 1000 MPa or more and an elongation of 5% or more without plastic processing such as wire drawing. As a result, they found that by adding Ti or Al to an Fe-Ni(-Co) low thermal expansion alloy and aging it, the alloy's grain size can be refined, thereby simultaneously increasing strength and elongation while maintaining low thermal expansion without undergoing plastic processing. Specifically, they found that by setting the average grain size to 80 μm or less, a low thermal expansion alloy can be obtained that has excellent mechanical properties, such as a strength of 1000 MPa or more and an elongation of 5% or more, and also has a desired thermal expansion coefficient.

[0015] The present invention was completed based on these findings, and provides the following (1) to (4).

[0016] (1) In mass%, C: 0.05% or less, Si: 0.4% or less, Mn: 0.5% or less, Ti: over 2.0~3.0%, Al: 0.1 to 0.4%, Ni: 30.0-37.0%, Co:20.0% or less, The balance consists of Fe and unavoidable impurities, the average crystal grain size is 80 μm or less, the tensile strength at room temperature is 1000 MPa or more, and the elongation is 5% or more, A low thermal expansion alloy with excellent mechanical properties, characterized in that the average thermal expansion coefficient between 10 and 40°C is 5.0 ppm / °C or less, the average thermal expansion coefficient between 10 and 200°C is 6.0 ppm / °C or less, or the average thermal expansion coefficient between 10 and 350°C is 7.0 ppm / °C or less.

[0017] (2) In mass%, C: 0.05% or less, Si: 0.4% or less, Mn: 0.5% or less, Ti: over 2.0~3.0%, Al: 0.1 to 0.4%, Ni: 30.0-37.0%, Co:20.0% or less, Furthermore, when the Ni content (mass%) is expressed as [Ni], the Co content (mass%) as [Co], the Ti content (mass%) as [Ti], and the Al content (mass%) as [Al], the Ni equivalent, expressed as [Ni] + 0.8 × [Co] - 2.75 × [Ti] - 4.89 × [Al], is 35.9 - 0.00025 × [T] + 0.0000375 × [T] 2.026 -0.5~35.9-0.00025×[T]+0.0000375×[T] 2.026 +0.5% (However, [T] is The temperature range for measuring thermal expansion when calculating the average thermal expansion coefficient upper limit temperature T (°C), The balance consists of Fe and unavoidable impurities, the average crystal grain size is 80 μm or less, the tensile strength at room temperature is 1000 MPa or more, and the elongation is 5% or more, and, The upper limit temperature T (°C) is 40°C Average thermal expansion coefficient between 10 and 40°C is 2.0 ppm / °C or less. The upper limit temperature T (°C) is 200°C The average coefficient of thermal expansion between 10 and 200°C is 4.0 ppm / °C or less, or The upper limit temperature T (°C) is 350°C A low thermal expansion alloy with excellent mechanical properties, characterized by an average thermal expansion coefficient of 6.0 ppm / °C or less between 10 and 350°C.

[0018] (3) A method for producing a low thermal expansion alloy with excellent mechanical properties, characterized by melting a low thermal expansion alloy material having the composition described in (1) or (2) above and rapidly solidifying it at a cooling rate of 100°C / sec or more.

[0019] (4) A method for producing a low thermal expansion alloy with excellent mechanical properties as described in (3), characterized in that a low thermal expansion alloy powder is used as the low thermal expansion alloy material, and the low thermal expansion alloy powder is melted and rapidly solidified using a laser or electron beam, followed by layer-by-layer manufacturing. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a low thermal expansion alloy with excellent mechanical properties, which has a strength of 1000 MPa or more, an elongation of 5% or more, and can be used to produce products with complex shapes without the need for plastic processing such as wire drawing, and a method for producing the alloy.

[0021] This allows the alloy to be used in various precision equipment components that operate under high loads, a field for which conventional low-expansion alloys have been limited. Furthermore, it is possible to achieve the desired low thermal expansion coefficient for each applicable temperature range, significantly contributing to the improvement of precision in these fields. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing the appearance of powder for additive manufacturing. [Figure 2] FIG. 1 shows a pure copper mold. [Figure 3] FIG. 1 is a diagram showing optical micrographs of an example alloy and a comparative alloy. [Figure 4] FIG. 1 is a diagram showing the relationship between average crystal grain size and tensile strength. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described. In the following description, unless otherwise specified, % for components means mass %. Furthermore, the thermal expansion coefficient is represented as α.

[0024] First Embodiment First, the reasons for limitations of the first embodiment, which is a basic embodiment, will be explained item by item.

[0025] [Chemical composition] C: 0.05% or less C is an element that significantly increases the α of the Fe-Ni(-Co) alloy that forms the base of the low thermal expansion alloy of the present invention, and its content is desirably low. If the C content exceeds 0.05%, α will exceed the desired range even if the contents of other elements described below are adjusted. Therefore, the C content is set to 0.05% or less.

[0026] Si: 0.4% or less Si is an element added to reduce oxygen in the alloy. However, Si significantly increases the α of the Fe-Ni(-Co) alloy that forms the base of the low thermal expansion alloy of the present invention, so a low Si content is desirable. If the Si content exceeds 0.4%, the increase in α becomes significant, as with C. Therefore, the Si content is set to 0.4% or less.

[0027] Mn: 0.5% or less Mn, like Si, is an effective deoxidizing element. However, Mn significantly increases the α of the Fe-Ni(-Co) alloy that forms the base of the low thermal expansion alloy of the present invention, so a low Mn content is desirable. If the Mn content exceeds 0.5%, the increase in α becomes significant, as with C. Therefore, the Mn content is set to 0.5% or less.

[0028] Ti: over 2.0~3.0% Ti is a particularly important alloying element in the present invention, as it forms fine Ni-Ti intermetallic compounds in Ni-containing alloys during aging treatment, contributing to increased strength. When the Ti content exceeds 2.0%, the strength increases significantly, achieving a tensile strength of 1000 MPa or more. On the other hand, when the Ti content exceeds 3.0%, the decrease in ductility becomes significant, the elongation becomes less than 5%, and the increase in α becomes significant. Therefore, the Ti content is set to be more than 2.0% but not more than 3.0%.

[0029] Al: 0.1 to 0.4% Like Ti, Al is an alloying element that forms fine Ni-Al intermetallic compounds in Ni-containing alloys during aging treatment, contributing to increased strength. This effect is enhanced when it coexists with Ti. However, if the Al content is less than 0.1%, this effect is small, and if it exceeds 0.4%, the decrease in ductility and the increase in α cannot be ignored. Therefore, the Al content is set to 0.1 to 0.4%.

[0030] Ni: 30.0 to 37.0% Ni is the element that determines the basic α of the alloy and is an important element for achieving the desired low α. To achieve a lower α, it is preferable to adjust the Ni content to the range described below depending on the Co content. If the Ni content is less than 30.0%, austenite becomes unstable, and the temperature at which martensitic transformation accompanied by abnormal expansion occurs rises to above 0°C. Furthermore, if the Ni content exceeds 37.0%, it is difficult to achieve α within the desired range. Therefore, the Ni content is set to the range of 30.0 to 37.0%.

[0031] Co:20.0% or less Co, together with Ni, is an important element that determines α. It is added to obtain a smaller α than when Ni is added alone, and is particularly effective in reducing the increase in α at high temperatures. However, if Co exceeds 20.0%, it is difficult to achieve α within the desired range when Ni is contained within the above range. Furthermore, if Co exceeds 20.0%, the amount of Ni obtained based on the relationship between the Ni content and the Co content (described below) decreases, destabilizing austenite and raising the temperature at which martensitic transformation accompanied by abnormal expansion occurs to above 0°C. Therefore, the Co content is set to 20.0% or less. Furthermore, from the viewpoint of further reducing α, a Co content of 3.0% or more is preferred.

[0032] In the present invention, the balance other than C, Si, Mn, Ni, Co, Ti, and Al is Fe and unavoidable impurities.

[0033] [Crystal grain size] In the present invention, the average crystal grain size of the alloy is set to 80 μm or less. Conventionally, in order to achieve both high strength and high elongation in Fe-Ni(-Co) based low thermal expansion alloys, the application of plastic processing was essential. However, in the present invention, by reducing the average crystal grain size to 80 μm or less, it is possible to achieve both high strength and high elongation while maintaining the desired low α.

[0034] In the present invention, the addition of strengthening elements such as Ti and Al increases α, but this increase can be suppressed by refining the alloy structure, i.e., by reducing the crystal grain size. In other words, the increase in α due to the addition of strengthening elements such as Ti and Al to obtain high strength can be offset by refining the metal structure. The reason why the increase in α is suppressed by refining the alloy structure is that the microsegregation of Ni and Co is reduced by refining the alloy structure. Furthermore, refining the alloy structure can increase strength and elongation without undergoing plastic working. Specifically, by setting the average crystal grain size to 80 μm or less, it is possible to simultaneously achieve a strength of 1000 MPa or more and an elongation of 5% or less while maintaining the desired low α described below.

[0035] In the present invention, the reason why the mechanical properties targeted are strength of 1000 MPa or more and elongation of 5% or more is that, as a standard for casting, which is a processing method that does not involve plastic processing, JIS G 5503-1995 specifies a high-strength, high-ductility austempered spheroidal graphite cast iron having a strength of 1000 MPa or more and an elongation of 5% or more, although it is not a low-thermal expansion material.

[0036] [Coefficient of thermal expansion] In the present invention, by satisfying the component composition, in mass%, of C: 0.05% or less, Si: 0.4% or less, Mn: 0.5% or less, Ti: over 2.0 to 3.0%, Al: 0.1 to 0.4%, Ni: 30.0 to 37.0%, and Co: 20.0% or less, and by satisfying an average crystal grain size of 80 μm or less, it is possible to satisfy an average α of 5.0 ppm / °C or less between 10 and 40°C, an average α of 6.0 ppm / °C or less between 10 and 200°C, and an average α of 7.0 ppm / °C or less between 10 and 350°C. In this way, it is possible to achieve the desired low α for each applicable temperature range, making it applicable to various precision device components operating under high loads and greatly contributing to higher precision in these fields.

[0037] [Manufacturing conditions] A low-thermal-expansion alloy material having the above-mentioned composition is melted and rapidly solidified at a cooling rate of 100°C / sec or more. This results in a fine microstructure with an average crystal grain size of 80 μm or less without undergoing plastic processing. As a method for performing this melting and rapid solidification, an additive manufacturing method is used, in which an alloy material having the above-mentioned composition, such as an alloy powder, is melted and rapidly solidified using a laser or electron beam to form an additive manufacturing process, since this method has a cooling rate of 3000°C / sec or more during solidification. However, other methods may be used as long as they can rapidly solidify at the above-mentioned cooling rate. For example, die casting can achieve a cooling rate of up to 800°C / sec.

[0038] By using this method to refine the alloy microstructure to an average crystal grain size of 80 μm or less, the increase in the thermal expansion coefficient due to the addition of the strengthening elements Ti and Al can be offset, resulting in an alloy with the desired strength and the desired low α. Furthermore, by setting the average crystal grain size to 80 μm or less, it is possible to simultaneously satisfy strength of 1000 MPa or more and elongation of 5% or less.

[0039] <Second embodiment> Next, a second embodiment will be described. The second embodiment is the same as the first embodiment, but with the following limitation on the Ni equivalent:

[0040] Ni equivalent: 35.9-0.00025×[T]+0.0000375×[T] 2.026 -0.5~35.9-0.00025×[T]+0.0000375×[T] 2.026 +0.5% If the Ni content (mass%) is expressed as [Ni], the Co content (mass%) is expressed as [Co], the Ti content (mass%) is expressed as [Ti], and the Al content (mass%) is expressed as [Al], the α of the alloy can be made extremely small by adjusting the Ni equivalent, which is expressed as [Ni] + 0.8 × [Co] - 2.75 × [Ti] - 4.89 × [Al], within a certain range depending on the application temperature. The Ni equivalent is 35.9 - 0.00025 × [T] + 0.0000375 × [T]. 2.026 -0.5~35.9-0.00025×[T]+0.0000375×[T] 2.026 By setting the range to +0.5% (where [T] is the upper limit temperature T°C for α measurement), the average α between 10 and T°C can be significantly reduced, resulting in a lower α range, as described below. Therefore, the Ni equivalent is 35.9 - 0.00025 × [T] + 0.0000375 × [T] 2.026 -0.5~35.9-0.00025×[T]+0.0000375×[T] 2.026 A range of +0.5% is preferable.

[0041] In this way, by adjusting the Ni equivalent expressed by [Ni] + 0.8 × [Co] - 2.75 × [Ti] - 4.89 × [Al] within a certain range depending on the application temperature in addition to the component composition of the first embodiment, it is possible to achieve even lower α, with an average α of 2.0 ppm / °C or less between 10 and 40°C, an average α of 4.0 ppm / °C or less between 10 and 200°C, and an average α of 6.0 ppm / °C or less between 10 and 350°C.

[0042] In the second embodiment, the other component compositions are the same as those in the first embodiment, and the remainder other than C, Si, Mn, Ni, Co, Ti, and Al is Fe and unavoidable impurities. The grain size is also 80 μm or less, as in the first embodiment, and the strength is 1000 MPa or more and the elongation is 5% or more. Furthermore, the manufacturing conditions are also the same as those in the first embodiment. [Example]

[0043] Examples of the present invention will be described below. Samples were prepared for alloys with the chemical components and compositions shown in Table 1. In Table 1, Nos. 1 to 9 are invention examples within the scope of the present invention, while Nos. 21 to 28 are comparative examples outside the scope of the present invention. Of the above samples, test specimens Nos. 1 to 9 and 21 to 24 are additively manufactured samples produced by additive manufacturing, while Nos. 25 to 28 are cast samples produced by casting using a CO2 silica sand mold or a pure copper mold, as described below. Note that, for reference, No. 31 is Invar, and No. 32 is Super Invar, both of which were produced by casting using a CO2 silica sand mold.

[0044] The additive manufacturing samples were manufactured as follows. Each alloy was melted in a high-frequency induction furnace under an argon atmosphere using an atomizer. The molten metal was then broken into droplets by spraying an inert gas (nitrogen gas in this example) from a nozzle while dripping. This resulted in spherical powder. The spherical powder was then sieved to obtain the additive manufacturing powder with a particle size of 10 to 63 μm, as shown in Figure 1. This additive manufacturing powder was then additive manufactured using a laser additive manufacturing device under the following conditions: power output 200 W, laser movement speed 1050 mm / s, laser scanning pitch 0.11 mm, and powder layer thickness 0.04 mm. A 22 mm × 130 mm tensile test specimen blank, a 12 mm × 120 mm room-temperature thermal expansion measurement specimen blank, a 12 mm × 70 mm high-temperature thermal expansion measurement specimen blank, and a 20 mm × 10 mm grain size measurement specimen were manufactured. The cooling rate when the powder for shaping is melted with a laser and then cooled is 3000°C / sec or more.

[0045] The cast samples were prepared by air-melting alloys of each composition in a high-frequency induction furnace and casting them into CO2 silica sand molds or the pure copper mold shown in Figure 2, each with a cavity of 130 mm x 100 mm x 25 mm, 130 mm x 100 mm x 50 mm, or 130 mm x 100 mm x 100 mm. Samples No. 25 to 27 were produced using the CO2 silica sand mold, and No. 28 was produced using the pure copper mold. The cooling rate when using the CO2 silica sand mold was 10°C / sec or less, and the cooling rate when using the pure copper mold was 20°C / sec or less.

[0046] All of the samples prepared as described above were subjected to solution treatment by heating to 1050°C, holding for 1 hour, and then water cooling, and aging treatment by heating to 700°C, holding for 1 hour, and then air cooling.

[0047] Each sample was machined to prepare room-temperature tensile test specimens with a parallel section of φ10 mm, a gauge length of 50 mm, a grip section of φ16 mm, and a length of 120 mm, as well as room-temperature thermal expansion measurement specimens with a diameter of φ8 mm × 100 mm and a diameter of φ8 mm × 50 mm for high-temperature thermal expansion measurement.

[0048] Each property was evaluated as follows. Tensile tests were performed at room temperature using a method in accordance with JIS Z 2241 to determine tensile strength and elongation. Thermal expansion tests were performed using a differential transformer push-rod type dilatometer, measuring thermal expansion while raising the temperature between 10°C and T°C at a rate of 2°C / min. The average α was calculated from the resulting thermal expansion curve. The average crystal grain size was determined by mirror-polishing the final molded surface of the additively molded sample and by measuring the central portion of the wall thickness of the cast sample using an optical microscope, followed by etching with nitric acid alcohol. The equivalent circle diameter of the crystal grains was measured at 20 locations and then averaging these values.

[0049] Inventive Examples Nos. 1 to 9 had a composition within the range of the present invention, and the crystal grain size was reduced to 80 μm or less by additive manufacturing. All of them had a strength of 1000 MPa or more and an elongation of 5% or more. They also satisfied the following conditions: average α between 10 and 40°C: 5.0 ppm / °C or less, average α between 10 and 200°C: 6.0 ppm / °C or less, and average α between 10 and 350°C: 7.0 ppm / °C or less. In addition, the Ni equivalent was 35.9 - 0.00025 × [T] + 0.0000375 × [T] 2.026 -0.5~35.9-0.00025×[T]+0.0000375×[T] 2.026 Nos. 7 to 9, which fulfill the second embodiment adjusted to a range of +0.5%, had even lower α, with an average α of 2.0 ppm / °C or less between 10 and 40°C, an average α of 4.0 ppm / °C or less between 10 and 200°C, and an average α of 6.0 ppm / °C or less between 10 and 350°C.

[0050] On the other hand, comparative examples Nos. 21 to 24 were manufactured by additive manufacturing, but their component compositions were outside the range of the present invention, and the values ​​of strength, elongation, or α were outside the specified ranges.

[0051] Furthermore, comparative alloys Nos. 25 to 28, although their chemical compositions were within the range of the present invention, were cast using a CO₂ silica sand mold or a pure copper mold. As a result, the cooling rate was less than 100°C / sec and the average grain size exceeded 80 μm. Consequently, all of these alloys had strengths less than 1000 MPa, and Nos. 26 and 27 had elongations less than 5%. Figure 3 shows optical microscope photographs of alloy No. 1, an example of the present invention, and alloy No. 28, a comparative alloy. These photographs confirm that alloy No. 1, an example of the present invention, has finer grains than comparative alloy No. 28, which was cast in a pure copper mold. Figure 4 plots the relationship between average grain size and strength for alloys Nos. 1 to 9, an example of the present invention, and alloys Nos. 25 to 28, a comparative alloy. Figure 4 shows that strengths of 1000 MPa or greater can be achieved when the average grain size is 80 μm or less. The strength variations in Figure 4 reflect the influence of the amount of strengthening elements.

[0052] From the above results, it was confirmed that the present invention can produce a low thermal expansion alloy with a strength of 1000 MPa or more, an elongation of 5% or more, and a desired α without undergoing plastic processing, and that it can be used to produce products with complex shapes.

[0053] [Table 1]

Claims

1. In mass%, C: 0.05% or less, Si: 0.4% or less, Mn: 0.5% or less, Ti: more than 2.0 to 3.0%, Al: 0.1-0.4%, Ni: 30.0-37.0%, Co: 20.0% or less, the balance being Fe and unavoidable impurities, the average crystal grain size being 80 μm or less, the tensile strength at room temperature being 1000 MPa or more, and the elongation being 5% or more; and a low thermal expansion alloy with excellent mechanical properties, characterized in that the average thermal expansion coefficient between 10 and 40°C is 5.0 ppm / °C or less, the average thermal expansion coefficient between 10 and 200°C is 6.0 ppm / °C or less, or the average thermal expansion coefficient between 10 and 350°C is 7.0 ppm / °C or less.

2. In mass%, C: 0.05% or less, Si: 0.4% or less, Mn: 0.5% or less, Ti: more than 2.0 to 3.0%, Al: 0.1-0.4%, Ni: 30.0-37.0%, Co: 20.0% or less, Furthermore, when the Ni content (mass%) is represented as [Ni], the Co content (mass%) is represented as [Co], the Ti content (mass%) is represented as [Ti], and the Al content (mass%) is represented as [Al], the Ni equivalent expressed as [Ni] + 0.8 × [Co] - 2.75 × [Ti] - 4.89 × [Al] is 35.9 - 0.00025 × [T] + 0.0000375 × [T] ２．０２６ -0.5~35.9-0.00025×[T]+0.0000375×[T] ２．０２６ +0.5% (where [T] is the upper limit temperature T (°C) of the thermal expansion measurement temperature range when determining the average thermal expansion coefficient), the balance being Fe and unavoidable impurities, the average crystal grain size being 80 μm or less, the tensile strength at room temperature being 1000 MPa or more, and the elongation being 5% or more; and wherein the average thermal expansion coefficient between 10 and 40°C is 2.0 ppm / °C or less when the upper limit temperature T (°C) is 40°C, the average thermal expansion coefficient between 10 and 200°C is 4.0 ppm / °C or less when the upper limit temperature T (°C) is 200°C, or the average thermal expansion coefficient between 10 and 350°C is 6.0 ppm / °C or less when the upper limit temperature T (°C) is 350°C.

3. A method for producing a low thermal expansion alloy having excellent mechanical properties, comprising melting a low thermal expansion alloy material having the composition according to claim 1 or 2 and rapidly solidifying it at a cooling rate of 100°C / sec or more.

4. 4. A method for producing a low thermal expansion alloy with excellent mechanical properties as described in claim 3, characterized in that a low thermal expansion alloy powder is used as the low thermal expansion alloy material, and the low thermal expansion alloy powder is melted and rapidly solidified by a laser or an electron beam, and then layer-by-layer manufacturing is performed.

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