Low thermal expansion alloy

Abstract

To provide a low thermal expansion alloy stably exhibiting low thermal expansibility in a wide temperature range.SOLUTION: The low thermal expansion alloy contains prescribed amounts of C, Si, Mn, P, S, Cu, Ni, V, Cr, Mo, Co, Al, Ti, Nb, W, Zr, Hf, Ta, B, Mg, Ca and REM, and the balance Fe with inevitable impurities, and satisfies A ≥ 38.0 and 40.6 <B ≤ 44.5. A = [Ni] + [Co] + 0.7 * [Cu] - [Si] - [Mn] - [Cr] - 0.5 * [Mo] - 0.5 * [V], B = [Ni] + 0.8 * [Co] + [Cu] + 6 * [C] + 1.1 * [Si] + [Mn] + 1.2 * [Cr] + 0.2 * [Mo] - 0.5 * [V].SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a low thermal expansion alloy, and more particularly to a low thermal expansion alloy that is substantially free of Co and has a small thermal expansion coefficient over a wide temperature range. [Background technology]

[0002] The semiconductor and semiconductor manufacturing equipment markets continue to grow alongside advances in IT technology. To meet the diverse requirements of end products, high precision is also required for various sensor components used to control semiconductor manufacturing equipment. For example, the pressure sensor's pressure-sensitive element comprises a diaphragm and a semiconductor formed on the diaphragm. When pressure acts on the diaphragm, distortion occurs in the semiconductor, and the pressure can be measured from the magnitude of this distortion. To measure pressure with high precision using such a pressure sensor, it is necessary to suppress distortion caused by differences in the thermal expansion coefficients between the diaphragm and the semiconductor when the temperature changes.

[0003] Kovar (Fe-29Ni-17Co alloy) has a low thermal expansion coefficient close to that of semiconductors, and has been used as a material for the diaphragms of pressure sensors. In addition, Kovar has a high magnetic transformation point, which allows it to maintain a thermal expansion coefficient equivalent to that of semiconductors over a wide temperature range. However, Kovar has a high content of expensive Co and low strength, which hinders the miniaturization of products, and as a result, resource risks and material costs are considered problems.

[0004] Therefore, various proposals have been made in the past to solve this problem. For example, Patent Document 1 discloses a low thermal expansion alloy consisting of 36 to 40 mass % Ni, 1 to 5 mass % Co, 39 to 42 mass % Ni+Co, the balance being Fe and unavoidable impurities. The document states that an alloy having such a composition has a thermal expansion coefficient close to that of Si, and a magnetic transformation point of 300° C. or higher.

[0005] Patent Document 2 discloses a high-strength, high-hardness, low-thermal expansion alloy containing 1.00 mass% C, 1.20 mass% Si, 28.97 mass% Ni, 5.29 mass% Co, 0.21 mass% Mn, and 0.02 mass% Mg, with the remainder being Fe and unavoidable impurities, in which a part of the austenite is transformed into martensite. The document states that when a part of the austenite is transformed into martensite, the thermal expansion coefficient increases slightly, but the strength, hardness, and thermal conductivity are improved.

[0006] Patent Document 1 discloses a low thermal expansion alloy that has a reduced Co content while maintaining a high magnetic transformation point and low thermal expansion. However, Patent Document 1 does not mention strength. In addition, since the alloy contains approximately 5 mass% Co, there is a resource risk issue.

[0007] Patent Document 2 discloses a high-strength, high-hardness, low-thermal expansion alloy. However, the alloy described in Patent Document 2 also contains approximately 5 mass% Co, which poses a high resource risk. Furthermore, martensitic transformation may occur in low-temperature environments, potentially impairing the low thermal expansion properties. In addition, Patent Document 2 does not mention the magnetic transformation point, raising concerns about instability of thermal expansion properties in high-temperature environments. Furthermore, there has never been a proposal for an alloy that has high tensile strength and exhibits stable low thermal expansion over a wide temperature range. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 09-324243 [Patent Document 2] Japanese Patent Application Publication No. 04-354848 Summary of the Invention [Problem to be solved by the invention]

[0009] The problem to be solved by the present invention is to provide a low thermal expansion alloy that exhibits stable low thermal expansion over a wide temperature range. Another problem to be solved by the present invention is to provide a low thermal expansion alloy that exhibits high tensile strength in addition to low thermal expansion. [Means for solving the problem]

[0010] The low thermal expansion alloy according to the present invention for solving the above problems comprises: 0.10≦C≦0.40mass%, Si≦1.00mass%, 0.10≦Mn≦2.00mass%, P≦0.050mass%, S≦0.015mass%, 0.10≦Cu≦4.00mass%, 35.0≦Ni≦45.0mass%, 0.10≦V≦1.00mass%, 0≦Cr≦0.50mass%, 0≦Mo≦4.00mass%, 0≦Co≦0.50mass%, 0≦Al≦0.50mass%, 0≦Ti≦0.50mass%, 0≦Nb≦0.50mass%, 0≦W≦0.50mass%, 0≦Zr≦0.50mass%, 0≦Hf≦0.50mass%, 0≦Ta≦0.50mass%, 0≦B≦0.050mass%, 0≦Mg≦0.050mass%, 0≦Ca≦0.050mass%, and 0≦REM≦0.050mass% and the balance being Fe and unavoidable impurities, The following formulas (1) and (2) are satisfied.

[0011] A≧38.0 …(1) 40.6 <B≦44.5 …(2) however, A=[Ni]+[Co]+0.7*[Cu]-[Si]-[Mn]-[Cr]-0.5*[Mo]-0.5*[V], B=[Ni]+0.8*[Co]+[Cu]+6*[C]+1.1*[Si]+[Mn]+1.2*[Cr]+0.2*[Mo]-0.5*[V]. [Effects of the Invention]

[0012] Adding appropriate amounts of C and V to the alloy and adjusting the balance of V and C components causes the precipitation of fine carbides in the matrix, which makes it possible to achieve high strength while suppressing the deterioration of the thermal expansion coefficient due to the solid solution of elements (especially C).

[0013] Furthermore, by optimizing the A value (particularly the Ni and Cu components) and optimizing the manufacturing conditions, it is possible to achieve a magnetic transformation point of 280°C or higher, which allows low thermal expansion to be maintained in high-temperature environments. Furthermore, by optimizing the B value (especially the Ni and Cu components) and optimizing the manufacturing conditions, the thermal expansion coefficient can be reduced to 3.5 to 6.0 × 10 over a wide temperature range. -6 / °C range. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of the present invention will be described in detail below. [1. Low thermal expansion alloy] [1.1. Main constituent elements] The low thermal expansion alloy according to the present invention contains the following elements, with the balance being Fe and unavoidable impurities. The types of added elements, their component ranges, and the reasons for their limitations are as follows:

[0015] (1) 0.10≦C≦0.40mass%: C has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening due to carbide precipitation. To obtain such effects, the C content must be 0.10 mass% or more. The C content is preferably 0.20 mass% or more. On the other hand, if the C content is excessive, the toughness, ductility, and hot workability may decrease, or the thermal expansion coefficient may increase. Therefore, the C content must be 0.40 mass% or less. The C content is preferably 0.36 mass% or less.

[0016] (2) Si≦1.00mass%: If the Si content is excessive, the thermal expansion coefficient increases and the magnetic transformation point may decrease. Therefore, the Si content must be 1.00 mass% or less. The Si content is preferably 0.40 mass% or less, or 0.30 mass% or less. The lower the Si content, the better. However, excessive reduction in the Si content may result in increased manufacturing costs. Si also has the effect of improving tensile strength through solid solution strengthening. Therefore, the Si content may be 0.01 mass% or more.

[0017] (3) 0.10≦Mn≦2.00mass% Mn forms inclusions such as MnS and has the effect of improving the manufacturability (machinability) of the alloy. To obtain this effect, the Mn content must be 0.10 mass% or more. On the other hand, if the Mn content is excessive, the thermal expansion coefficient increases and the magnetic transformation point may decrease. Therefore, the Mn content must be 2.00 mass% or less. The Mn content is preferably 0.50 mass% or less.

[0018] (4) P≦0.050 mass%: If the P content is excessive, the hot workability may be reduced, so the P content must be 0.050 mass% or less. The lower the P content, the better. However, an extreme reduction in the P content may lead to an increase in production costs. Therefore, the P content may be 0.001 mass% or more.

[0019] (5) S≦0.015 mass%: If the S content is excessive, the hot workability may be reduced, so the S content must be 0.015 mass% or less. The lower the S content, the better. However, an extreme reduction in the S content may lead to an increase in production costs. Therefore, the S content may be 0.001 mass% or more.

[0020] (6) 0.10≦Cu≦4.00mass% In Fe-Ni alloys (especially Fe-Ni alloys containing 30 mass% or more of Ni), Cu, like Ni, has the effect of reducing the thermal expansion coefficient and increasing the magnetic transformation point. To achieve these effects, the Cu content must be 0.10 mass% or more. The Cu content is preferably 1.60 mass% or more, or 1.80 mass% or more. On the other hand, an excessive Cu content may increase the thermal expansion coefficient. Also, an excessive Cu content may promote element segregation, which may cause a decrease in hot workability. Therefore, the Cu content must be 4.00 mass% or less.

[0021] (7) 35.0≦Ni≦45.0mass% In Fe-Ni alloys, the thermal expansion coefficient is smallest when the Ni content is around 36 mass%. When the Ni content exceeds 36 mass%, the thermal expansion coefficient increases. On the other hand, the magnetic transformation point, which is the transition temperature between ferromagnetic and paramagnetic materials, tends to increase as the Ni content increases. At temperatures above the magnetic transformation point, the thermal expansion coefficient increases significantly. To maintain a low thermal expansion coefficient even at high temperatures above 280°C, the Ni content must be 35.0 mass% or more.

[0022] Ni is an expensive element. Therefore, if the Ni content is excessive, the raw material cost will increase. In addition, if the Ni content is excessive, the thermal expansion coefficient at temperatures below the magnetic transformation point may increase. Therefore, the Ni content must be 45.0 mass% or less. The Ni content is more preferably 40.0 mass% or less.

[0023] (8) 0.10≦V≦1.00mass%: V has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening due to precipitation of carbides. To obtain these effects, the V content must be 0.10 mass% or more. On the other hand, if V is added in excess of the amount necessary to precipitate carbides, the thermal expansion coefficient increases and the magnetic transformation point may decrease. Therefore, the V content must be 1.00 mass% or less. The V content is preferably 0.50 mass% or less.

[0024] (9) Inevitable impurities: The low thermal expansion alloy according to the present invention may contain unavoidable impurities. Here, "unavoidable impurities" refer to components that are mixed in during industrial production of the low thermal expansion alloy due to various factors such as raw materials and production processes, and the content of these impurities is within a range that does not adversely affect the properties of the low thermal expansion alloy according to the present invention.

[0025] Inevitable impurities include the following elements in addition to the above-mentioned Si, P, and S. When the content of the following elements is equal to or less than the upper limit value shown below, such elements are treated as "inevitable impurities" in the low thermal expansion alloy according to the present invention. The low thermal expansion alloy according to the present invention may contain one or more of the following unavoidable impurities, however, in order to maintain the high properties of the low thermal expansion alloy, the total content of the unavoidable impurities is preferably 0.5 mass% or less.

[0026] (9.1) Sn≦0.010mass%: If the Sn content is excessive, the hot workability may be reduced, so the Sn content is preferably 0.010 mass% or less. The smaller the Sn content, the better. However, an extreme reduction in the Sn content increases the manufacturing cost. Therefore, the Sn content may be more than 0 mass%.

[0027] (9.2) Zn≦0.010 mass%: If the Zn content is excessive, the hot workability may be reduced, so the Zn content is preferably 0.010 mass% or less. The smaller the Zn content, the better. However, an extreme reduction in the Zn content leads to an increase in production costs. Therefore, the Zn content may be more than 0 mass%.

[0028] (9.3)As≦0.010mass%: If the As content is excessive, the hot workability may be reduced, so the As content is preferably 0.010 mass% or less. The smaller the As content, the better. However, the coexistence of As and Cu may improve the corrosion resistance of the alloy. Therefore, the As content may be more than 0 mass%.

[0029] (9.4) Se≦0.010 mass%: If the amount of Se is excessive, the hot workability may be reduced, so the amount of Se is preferably 0.010 mass% or less. The smaller the Se content, the better. However, an appropriate amount of Se has the effect of improving the machinability of the alloy. Therefore, the Se content may be more than 0 mass%.

[0030] (9.5) Sb≦0.010mass%: If the Sb content is excessive, the thermal expansion coefficient may become large, so the Sb content is preferably 0.010 mass% or less. The smaller the Sb content, the better. However, the coexistence of Sb and Cu may improve the corrosion resistance of the alloy. Therefore, the Sb content may be more than 0 mass%.

[0031] (9.6)Ag≦0.010mass%: If the Ag content is excessive, the hot workability may be reduced, so the Ag content is preferably 0.010 mass% or less. The smaller the Ag content, the better. However, an extreme reduction in the Ag content increases the production cost. Therefore, the Ag content may be more than 0 mass%.

[0032] (9.7) Bi≦0.0010 mass%: If the Bi content is excessive, the hot workability may be reduced, so the Bi content is preferably 0.0010 mass% or less. The smaller the Bi content, the better. However, an extreme reduction in the Bi content increases the production cost. Therefore, the Bi content may be more than 0 mass%.

[0033] (9.8)O≦0.050mass%: If the O content is excessive, the thermal expansion coefficient may increase, so the O content is preferably 0.050 mass% or less. The smaller the O content, the better. However, an extreme reduction in the O content leads to an increase in production costs. Therefore, the O content may be more than 0 mass%.

[0034] (9.9)N≦0.050mass%: If the amount of N is excessive, the thermal expansion coefficient may become large, so the amount of N is preferably 0.050 mass% or less. The smaller the N content, the better. However, an extreme reduction in the N content leads to an increase in production costs. Therefore, the N content may be more than 0 mass%.

[0035] [1.2. Sub-constituent elements] The low thermal expansion alloy according to the present invention may further contain one or more of the following elements in addition to the above-mentioned main constituent elements and unavoidable impurities. The types of added elements, their component ranges, and the reasons for their limitations are as follows:

[0036] (1) 0≦Cr≦0.50mass%: The Cr content may be 0 mass%. However, an extreme reduction in the Cr content may result in an increase in manufacturing costs. Cr also has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening due to carbide precipitation. Therefore, the Cr content is preferably 0.01 mass% or more. On the other hand, if the Cr content is excessive, the thermal expansion coefficient increases and the magnetic transformation point may decrease, so the Cr content is preferably 0.50 mass% or less.

[0037] (2) 0≦Mo≦4.00mass% The Mo content may be 0 mass%. However, an extreme reduction in the Mo content may result in an increase in manufacturing costs. Mo also has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening due to carbide precipitation. Therefore, the Mo content is preferably 0.01 mass% or more. On the other hand, if the amount of Mo is excessive, the thermal expansion coefficient increases and the magnetic transformation point may decrease, so the amount of Mo is preferably 4.00 mass% or less.

[0038] (3) 0≦Co≦0.50mass% The Co content may be 0 mass %. However, an extreme reduction in the Co content may result in an increase in production costs. Therefore, the Co content is preferably 0.01 mass % or more. On the other hand, since Co is an expensive element, an excessive amount of Co may lead to an increase in production costs, and therefore the Co amount is preferably 0.50 mass% or less.

[0039] (4) 0≦Al≦0.50mass% The Al content may be 0 mass%. In addition to being a deoxidizing element, Al also has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening due to carbide precipitation. Therefore, the Al content is preferably more than 0 mass%. On the other hand, if the Al content is excessive, the ductility may decrease and the thermal expansion coefficient may increase, so the Al content is preferably 0.50 mass% or less.

[0040] (5) 0≦Ti≦0.50mass% The Ti content may be 0 mass%. Ti has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening due to carbide precipitation. Therefore, the Ti content is preferably more than 0 mass%. On the other hand, if the Ti content is excessive, the ductility may decrease and the thermal expansion coefficient may increase, so the Ti content is preferably 0.50 mass% or less.

[0041] (6) 0≦Nb≦0.50mass% The Nb content may be 0 mass%. Nb has the effect of refining crystal grains and improving tensile strength. Therefore, the Nb content is preferably more than 0 mass%. On the other hand, if the Nb content is excessive, the hot workability may be reduced, so the Nb content is preferably 0.50 mass% or less.

[0042] (7) 0≦W≦0.50mass%: The W content may be 0 mass%. W has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening due to carbide precipitation. Therefore, the W content is preferably more than 0 mass%. On the other hand, if the W content is excessive, the ductility may decrease and the thermal expansion coefficient may increase, so the W content is preferably 0.50 mass% or less.

[0043] (8) 0≦Zr≦0.50mass% The Zr content may be 0 mass%. Zr is a deoxidizing element and also has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening due to carbide precipitation. Therefore, the Zr content is preferably more than 0 mass%. On the other hand, if the Zr content is excessive, the ductility may decrease and the thermal expansion coefficient may increase, so the Zr content is preferably 0.50 mass% or less.

[0044] (9) 0≦Hf≦0.50mass% The Hf content may be 0 mass%. Hf has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening due to precipitation of carbides. Therefore, the Hf content is preferably more than 0 mass%. On the other hand, if the Hf content is excessive, the ductility may decrease and the thermal expansion coefficient may increase, so the Hf content is preferably 0.50 mass% or less.

[0045] (10) 0≦Ta≦0.50mass%: The Ta content may be 0 mass%. Ta has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening due to carbide precipitation. Therefore, the Ta content is preferably more than 0 mass%. On the other hand, if the Ta content is excessive, the ductility may decrease and the thermal expansion coefficient may increase, so the Ta content is preferably 0.50 mass% or less.

[0046] (11) 0≦B≦0.050mass%: The B content may be 0 mass%. B has the effect of improving hot workability by strengthening grain boundaries and the effect of improving grain boundary oxidation resistance. Therefore, the B content is preferably more than 0 mass%. On the other hand, if the B content is excessive, the hot workability may be deteriorated. Therefore, the B content is preferably 0.050 mass% or less.

[0047] (12) 0≦Mg≦0.050mass% The Mg content may be 0 mass%. Mn has the effect of immobilizing S, improving hot workability, and reducing the thermal expansion coefficient. Therefore, the Mg content is preferably more than 0 mass%. On the other hand, if the Mg content is excessive, the hot workability may be reduced, so the Mg content is preferably 0.050 mass% or less.

[0048] (13) 0≦Ca≦0.050mass% The Ca content may be 0 mass%. Ca has the effect of immobilizing S, improving hot workability, and reducing the thermal expansion coefficient. Therefore, the Ca content is preferably more than 0 mass%. On the other hand, an excessive Ca content may actually deteriorate the hot workability, so the Ca content is preferably 0.050 mass% or less.

[0049] (14) 0≦REM≦0.050mass%: The REM content may be 0 mass%. REM has the effect of improving oxidation resistance in high-temperature environments and expanding the usable temperature range. Therefore, the REM content is preferably greater than 0 mass%. Examples of REM include Nd, Pr, La, Ce, and Y. On the other hand, an excessive REM content may result in a significant increase in production costs, so the REM content is preferably 0.050 mass% or less.

[0050] [1.3. Ingredient Balance] The low thermal expansion alloy according to the present invention must satisfy the following formulas (1) and (2).

[0051] A≧38.0 …(1) 40.6 <B≦44.5 …(2) however, A=[Ni]+[Co]+0.7*[Cu]-[Si]-[Mn]-[Cr]-0.5*[Mo]-0.5*[V], B=[Ni]+0.8*[Co]+[Cu]+6*[C]+1.1*[Si]+[Mn]+1.2*[Cr]+0.2*[Mo]-0.5*[V].

[0052] [1.3.1. Formula (1)] The A value in formula (1) is an index correlated with the magnetic transformation point of a low-thermal expansion alloy. Optimizing the alloy's components and manufacturing conditions to satisfy formula (1) can increase the magnetic transformation point. In general, the larger the A value, the higher the magnetic transformation point.

[0053] Specifically, if the alloy components are optimized so that the A value is 38.0 or higher, and the manufacturing conditions are also optimized, the magnetic transformation point will be 280°C or higher. Similarly, if the alloy components are optimized so that the A value is 38.5 or higher, and the manufacturing conditions are also optimized, the magnetic transformation point will be 290°C or higher. Furthermore, if the alloy components are optimized so that the A value is 39.0 or higher, and the manufacturing conditions are optimized, the magnetic transformation point will be 300°C or higher.

[0054] [1.3.2. Formula (2)] The B value in formula (2) represents an index correlated with the thermal expansion coefficient of a low-thermal expansion alloy. By optimizing the alloy components and manufacturing conditions to satisfy formula (2), it is possible to maintain a thermal expansion coefficient close to that of a semiconductor. In general, the larger the B value, the larger the thermal expansion coefficient.

[0055] Specifically, when the alloy composition is optimized so that the B value is greater than 40.6 and less than 44.5, and the manufacturing conditions are also optimized, the thermal expansion coefficient is 3.5 to 6.0 × 10 -6 / ℃.

[0056] [1.4. Characteristics] 1.4.1 Tensile strength "Tensile strength" refers to the value obtained by conducting a tensile test in accordance with ASTM A730 using a No. 3 round bar test piece with a parallel section diameter of 6 mm at room temperature (25°C) in the air.

[0057] High tensile strength can be achieved by adding appropriate amounts of C and V to the alloy and precipitating fine carbides in the matrix. Optimizing the manufacturing conditions can increase the tensile strength of the alloy to 500 MPa or more. Further optimization of the manufacturing conditions can increase the tensile strength to 550 MPa or more, or even 600 MPa or more.

[0058] 1.4.2. Coefficient of thermal expansion In the present invention, the "coefficient of thermal expansion" refers to the average coefficient of linear thermal expansion from 30°C to 100°C.

[0059] By reducing the amount of Co and optimizing the alloy components so as to satisfy the above-mentioned formula (2), the thermal expansion coefficient of the alloy can be maintained at a value close to that of a semiconductor over a wide temperature range. By optimizing the manufacturing conditions, the thermal expansion coefficient of the alloy can be maintained at 3.5 to 6.0 × 10 -6 / ℃.

[0060] [1.4.3. Magnetic transformation point] When a low-thermal expansion alloy is heated to a temperature above its magnetic transformation point, the thermal expansion coefficient increases. To achieve low thermal expansion in high-temperature environments, the higher the magnetic transformation point of the alloy, the better. Optimizing the alloy's components to satisfy the above-mentioned formula (1) can increase the magnetic transformation point. Optimizing the manufacturing conditions can raise the alloy's magnetic transformation point to 280°C or higher. Further optimizing the manufacturing conditions can raise the magnetic transformation point to 290°C or higher, or even 300°C or higher.

[0061] [1.5. Organization] As will be described later, the low thermal expansion alloy according to the present invention is processed into various shapes through melting and casting, primary hot working, secondary hot working, annealing, and post-processing. The low thermal expansion alloy according to the present invention may be in an as-hot-worked state, an as-annealed state, or a state in which necessary post-processing has been performed after annealing. In order to dissolve coarse carbonitrides and reduce production costs, it is preferable that the low thermal expansion alloy include a portion in an as-annealed state.

[0062] Here, "including a portion in an as-annealed state" means (a) The entire low thermal expansion alloy is in the as-annealed state, or (b) A part of the low thermal expansion alloy has undergone necessary processing (for example, cutting), but the other part is in the as-annealed state. This refers to...

[0063] [1.6. Shape] In the present invention, the shape of the low thermal expansion alloy is not particularly limited, and an optimum shape can be selected depending on the purpose. Examples of the shape of the low thermal expansion alloy include a tube, a rod, a wire, and a plate.

[0064] [2. Manufacturing method of low thermal expansion alloy] The method for producing a low thermal expansion alloy according to the present invention comprises the steps of: A melting and casting process in which raw materials blended to form a predetermined composition are melted and cast; a primary hot working step of performing primary hot working on the obtained ingot; A secondary hot processing step in which secondary hot processing is performed on the material that has been subjected to the primary hot processing; an annealing process in which the secondary hot-processed material is annealed as necessary; If necessary, a post-processing process is performed on the secondary hot-processed or annealed material. It is equipped with:

[0065] [2.1. Melting and Casting Process] First, raw materials blended to obtain a predetermined composition are melted and cast. The melting and casting methods and conditions are not particularly limited, and the most suitable method and conditions can be selected depending on the purpose. For example, an electric furnace, an AOD (Argon Oxygen Decarburization) furnace, or a VOD (Vacuum Oxygen Decarburization) furnace can be used to produce the molten metal. The obtained ingot may be subjected to a homogenization heat treatment to remove segregation, if necessary.

[0066] [2.2. Primary hot working process] Next, the obtained ingot is subjected to a primary hot working. The primary hot working is performed to destroy the coarse cast structure, refine the structure, and at the same time, to convert the ingot into a material for slabs, blooms, billets, etc. The primary hot working method is not particularly limited, and an optimum method can be selected depending on the purpose. Examples of the primary hot working method include hot forging and hot rolling. The molten metal produced in the melting and casting process may be used to directly produce materials such as slabs, blooms, and billets by continuous casting. In this case, the primary hot working process can be omitted.

[0067] [2.3. Secondary hot working process] Next, the material that has been subjected to the primary hot processing is subjected to secondary hot processing. The secondary hot processing is performed to finish the material that has been subjected to the primary hot processing into the final product shape (e.g., plate, bar, wire rod, pipe, etc.) or a shape close to the final product shape. The secondary hot processing method is not particularly limited, and an optimum method can be selected depending on the purpose. Examples of secondary hot processing methods include hot rolling, hot extrusion, and hot piercing rolling.

[0068] The conditions for the secondary hot working are not particularly limited, and optimal conditions can be selected depending on the purpose. Furthermore, the secondary hot working may be performed multiple times depending on the purpose. The heating temperature of the material before the secondary hot working is preferably 900°C or higher and 1300°C or lower. Furthermore, when the secondary hot working is performed multiple times, the material temperature at the end of the final secondary hot working is preferably 800° C. or higher and 1200° C. or lower, in order to optimize the crystal grains.

[0069] [2.4. Annealing process] Next, if necessary, the material that has been subjected to the second hot working is annealed. Annealing may be performed only once or may be performed multiple times.

[0070] The annealing temperature affects the characteristics of the material. If annealing is not performed or if the annealing temperature is too low, a large amount of coarse carbonitrides may precipitate. As a result, the mechanical properties may deteriorate or the thermal expansion coefficient may increase. Furthermore, the crystal grains may become excessively fine, which may reduce machinability. Therefore, the annealing temperature is preferably 800°C or higher. The annealing temperature is more preferably 900°C or higher. On the other hand, if the annealing temperature is too high, the material may melt locally. Also, the complete solid solution of fine carbonitrides such as VC may cause abnormal grain growth, which may result in deterioration of mechanical properties. Therefore, the annealing temperature is preferably 1300°C or less.

[0071] The optimum holding time at the annealing temperature can be selected depending on the purpose. Generally, the longer the annealing holding time, the fewer fine crystal grains there will be. On the other hand, if the holding time is longer than necessary, the crystal grains may become excessively coarse. The optimum holding time varies depending on the annealing temperature, but is usually 1 minute to 3 hours. After the holding time is over, the material is cooled by water cooling, oil cooling, air cooling, or at a cooling rate equivalent to these. Although the size of the crystal grains does not have a significant effect on the thermal expansion coefficient, if the crystal grains become too large, it may have a negative effect on the mechanical properties. The optimum grain size varies depending on the application, but is preferably #0 to #10. The grain size is more preferably #3 to #7.

[0072] [2.5. Post-processing process] Next, if necessary, the secondary hot-worked or annealed material is subjected to post-processing, such as cutting, welding, cold working, etc. The low thermal expansion alloy obtained in this manner is used for various purposes.

[0073] [3. Effect] Adding appropriate amounts of C and V to the alloy and adjusting the balance of V and C components causes the precipitation of fine carbides in the matrix, which makes it possible to achieve high strength while suppressing the deterioration of the thermal expansion coefficient due to the solid solution of elements (especially C).

[0074] Furthermore, by optimizing the A value (particularly the Ni and Cu components) and optimizing the manufacturing conditions, it is possible to achieve a magnetic transformation point of 280°C or higher, which allows low thermal expansion to be maintained in high-temperature environments. Furthermore, by optimizing the B value (especially the Ni and Cu components) and optimizing the manufacturing conditions, the thermal expansion coefficient can be reduced to 3.5 to 6.0 × 10 over a wide temperature range. -6 / °C range. [Example]

[0075] (Examples 1 to 16, Comparative Examples 1 to 20) 1. Sample Preparation Five kg of alloys having the compositions shown in Tables 1 and 2 were melted in a vacuum induction furnace and cast into ingots, which were then hot forged and annealed to produce rods with a diameter of 15 mm.

[0076] [Table 1]

[0077] [Table 2]

[0078] 2. Test Method 2.1. Evaluation of tensile strength A round bar tensile test specimen was taken from the center of each bar. The parallel part of the round bar tensile test specimen was parallel to the longitudinal direction of the bar. The diameter of the parallel part was 6 mm. A tensile test was carried out using the round bar tensile test specimen at room temperature (25°C) in air to determine the tensile strength TS (MPa). A sample having a tensile strength TS (MPa) of 500 MPa or more was evaluated as "◯ (high strength)", and a sample having a tensile strength of less than 500 MPa was evaluated as "× (not high strength)".

[0079] 2.2. Evaluation of the mean coefficient of linear thermal expansion A round bar test piece was taken from the center of each bar. The longitudinal direction of the round bar test piece was parallel to the longitudinal direction of the bar. The thermal expansion coefficient was measured using the obtained round bar test piece. The thermal expansion coefficient was measured in the temperature range of 20°C to 800°C. The average coefficient of linear thermal expansion from 30°C to 100°C is 3.5 x 10 -6 / ℃ or more 6.0×10 -6 / ℃ or less was evaluated as "○ (good)" and 3.5 × 10 -6 / ℃ or less than 6.0×10 -6 / °C was evaluated as "× (bad)".

[0080] [2.3. Evaluation of magnetic transformation point] The magnetic transformation point was determined from a chart of the displacement versus test temperature obtained during the measurement of the thermal expansion coefficient. The bending point that appeared on the chart was taken as the magnetic transformation point. If the magnetic transformation point was 280°C or higher, it was rated as "○ (good)", if it was 290°C or higher, it was rated as "◎ (better)", if it was 300°C or higher, it was rated as "● (best)", and if it was less than 280°C, it was rated as "× (bad)".

[0081] [3. Results] The results are shown in Table 3. From Table 2, the following can be seen.

[0082] (1) The tensile strength was reduced in Comparative Examples 1 and 2. This is thought to be due to the low C content and / or V content. (2) In Comparative Example 3, the magnetic transformation point was less than 280° C. This is thought to be because the A value was less than 38. (3) Comparative Example 4 had a magnetic transformation point of less than 280°C. This is thought to be due to the small amount of Cu and the A value being less than 38. In addition, Comparative Example 4 had a thermal expansion coefficient of 3.5 × 10 -6 / °C. This is thought to be because the B value was 40.6 or less.

[0083] (4) Comparative Examples 5 and 6 have a thermal expansion coefficient of 6.0 × 10 -6 / °C. This is thought to be due to the excessive Cu content and the B value exceeding 44.5. (5) Comparative Example 7 had a magnetic transformation point of less than 280°C. This is thought to be due to the excessive Cr content and the A value being less than 38. In addition, Comparative Example 7 had a thermal expansion coefficient of 3.5 × 10-6 / °C. This is thought to be due to the excessive amount of Cr and the B value being 40.6 or less.

[0084] (6) In Comparative Example 8, the magnetic transformation point was less than 280°C. This is thought to be due to the excessive amount of Si and the A value being less than 38. In addition, in Comparative Example 8, the thermal expansion coefficient was 6.0 × 10 -6 / °C. This is thought to be due to the excessive amount of Si and the B value exceeding 44.5. (7) In Comparative Example 9, the magnetic transformation point was less than 280° C. This is thought to be because the A value was less than 38.

[0085] (8) Comparative Example 10 had a magnetic transformation point of less than 280°C. This is thought to be because the A value was less than 38. In addition, Comparative Example 10 had a thermal expansion coefficient of 3.5 × 10 -6 / °C. This is thought to be because the B value was 40.6 or less. (9) In Comparative Examples 11 to 13, the magnetic transformation point was less than 280° C. This is thought to be because the A value was less than 38. (10) Comparative Example 14 had a magnetic transformation point of less than 280°C. This is thought to be because the A value was less than 38. In addition, Comparative Example 14 had a thermal expansion coefficient of 3.5 × 10 -6 / °C. This is thought to be because the B value was 40.6 or less.

[0086] (11) In Comparative Example 15, the magnetic transformation point was less than 280° C. This is thought to be because the A value was less than 38. (12) In Comparative Example 16, the magnetic transformation point was less than 280°C. This is thought to be due to the small amount of Cu and the A value being less than 38. In Comparative Example 17, the thermal expansion coefficient was 3.5 × 10 -6 / °C. This is thought to be because the B value was 40.6 or less. (13) Comparative Example 17 has a thermal expansion coefficient of 6.0 × 10 -6 / °C. This is thought to be due to the excessive amount of Ni and the B value exceeding 44.6.

[0087] (14) In Comparative Example 18, the magnetic transformation point was less than 280° C. This is thought to be because the A value was less than 38. (15) In Comparative Example 19, the magnetic transformation point was lower than 280° C. This is thought to be due to the excessive Cr content and the A value being lower than 38. (16) Comparative Example 20 had a magnetic transformation point of less than 280°C. This is thought to be because the A value was less than 38. In addition, Comparative Example 20 had a thermal expansion coefficient of 3.5 × 10 -6 / °C. This is thought to be because the B value was 40.6 or less.

[0088] (17) In Examples 1 to 16, the tensile strength exceeded 600 MPa. In addition, in Examples 1 to 16, the magnetic transformation point was 280°C or higher. Furthermore, in Examples 1 to 16, the thermal expansion coefficient was 3.5 to 6.0 × 10 -6 / ℃. (18) In Examples 3 to 6, the magnetic transformation point was 300° C. or higher. This is thought to be because the A value was 39.0 or higher.

[0089] [Table 3]

[0090] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the gist of the present invention. [Industrial Applicability]

[0091] The low thermal expansion alloy according to the present invention can be used for the diaphragm of a pressure sensor, the lead of a hermetic seal, and the like.

Claims

1. 0.10≦C≦0.40mass%, Si≦1.00mass%, 0.10≦Mn≦2.00 mass%, P≦0.050mass%, S≦0.015mass%, 0.10≦Cu≦4.00mass%, 35.0≦Ni≦45.0mass%, 0.10≦V≦1.00mass%, 0≦Cr≦0.50mass%, 0≦Mo≦4.00mass%, 0≦Co≦0.50 mass%, 0≦Al≦0.50 mass%, 0≦Ti≦0.50mass%, 0≦Nb≦0.50mass%, 0≦W≦0.50mass%, 0≦Zr≦0.50mass%, 0≦Hf≦0.50mass%, 0≦Ta≦0.50 mass%, 0≦B≦0.050mass%, 0≦Mg≦0.050 mass%, 0≦Ca≦0.050 mass%, and 0≦REM≦0.050mass% and the balance being Fe and unavoidable impurities, A low thermal expansion alloy that satisfies the following formulas (1) and (2). A ≧ 38.0 ... (1) 40.6<B≦44.5 ... (2) however, A=[Ni]+[Co]+0.7*[Cu]-[Si]-[Mn]-[Cr]-0.5*[Mo]-0.5*[V], B=[Ni]+0.8*[Co]+[Cu]+6*[C]+1.1*[Si]+[Mn]+1.2*[Cr]+0.2*[Mo]-0.5*[V].

2. 2. The low thermal expansion alloy according to claim 1, having a tensile strength of 500 MPa or more. The "tensile strength" refers to a value obtained by conducting a tensile test in accordance with ASTM A370 using a No. 3 round bar test piece having a parallel portion diameter of 6 mm at room temperature (25°C) in the air.

3. Thermal expansion coefficient is 3.5 x 10 -6 / ℃ or more 6.0 x 10 -6 2. The low thermal expansion alloy according to claim 1, wherein the thermal expansion coefficient is 0.1 / °C or less. The "thermal expansion coefficient" refers to the average linear thermal expansion coefficient from 30°C to 100°C.

4. 2. The low thermal expansion alloy according to claim 1, wherein the magnetic transformation point is 280° C. or higher.

5. The inevitable impurities include: Sn≦0.010mass%, Zn≦0.010mass%, As≦0.010mass%, Se≦0.010 mass%, Sb≦0.010mass%, Ag≦0.010mass%, Bi≦0.0010mass%, O≦0.050 mass%, and N≦0.050mass% 2. The low thermal expansion alloy according to claim 1, comprising at least one selected from the group consisting of:

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