Low thermal expansion alloy

Abstract

The present invention relates to a low thermal expansion alloy consisting of the following components: 0.10 to 0.40 mass% of C; si up to 1.00 mass%; 0.10 to 2.00 mass% of Mn; up to 0.050 mass% P; up to 0.015 mass% S; 0.10 to 4.00 mass% of Cu; ni in an amount of 35.0 to 45.0 mass%; 0.10 to 1.00 mass% of V; up to 4.00 mass% Mo; up to 0.50 mass% of each of Cr, Co, Al, Ti, Nb, W, Zr, Hf and Ta; and a maximum of 0.050 mass% of B, Mg, Ca, and REM, the remainder being Fe and unavoidable impurities. The low thermal expansion alloy satisfies A > = 38.0 and 40.6 < B < = 44.5. A and B are defined in the specification.

Description

Technical Field

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

[0002] With the advancement of IT technology, the semiconductor market and the semiconductor manufacturing equipment market continue to grow. To meet the diverse requirements of end products, the various sensor components used to control semiconductor manufacturing equipment also need to possess high accuracy. For example, the pressure sensor's pressure-sensitive element includes a diaphragm and a semiconductor formed on the diaphragm. When pressure is applied to the diaphragm, the semiconductor experiences strain, and the pressure can be measured based on the magnitude of this strain. To measure pressure with high accuracy using such a pressure sensor, it is necessary to reduce the strain caused by the difference in thermal expansion coefficients between the diaphragm and the semiconductor due to temperature changes.

[0003] Kovar alloy (Fe-29Ni-17Co alloy) has a low coefficient of thermal expansion, close to that of semiconductors, and is therefore commonly used as a diaphragm material in pressure sensors. Furthermore, Kovar has a high magnetic transition point, allowing it to maintain a coefficient of thermal expansion similar to that of semiconductors over a wide temperature range.

[0004] However, Kovar has a high content of expensive Co and low strength, which hinders the miniaturization of the product. Therefore, the resource risks and material costs of Kovar are considered problematic.

[0005] Various proposals have been put forward in the past to address this problem.

[0006] For example, Patent Document 1 discloses a low thermal expansion alloy in which the content of Ni is 36% to 40% by mass, the content of Co is 1% to 5% by mass, the content of Ni + Co is 39% to 42% by mass, and the balance is Fe and unavoidable impurities.

[0007] Patent document 1 discloses an alloy with a thermal expansion coefficient close to that of Si and a magnetic transition point of 300 °C or higher.

[0008] Patent document 2 discloses a high-strength, high-hardness, low-thermal-expansion alloy, wherein the content of C is 1.00 wt%, the content of Si is 1.20 wt%, the content of Ni is 28.97 wt%, the content of Co is 5.29 wt%, the content of Mn is 0.21 wt%, the content of Mg is 0.02 wt%, and the balance is Fe and unavoidable impurities. In this alloy, a portion of austenite is transformed into martensite.

[0009] Patent document 2 discloses that when a portion of austenite is transformed into martensite, the coefficient of thermal expansion increases slightly, but the strength, hardness, and thermal conductivity are improved.

[0010] Patent Document 1 discloses a low thermal expansion alloy that reduces the Co content while maintaining a high magnetic transition point and low thermal expansion characteristics. However, Patent Document 1 does not mention strength. Furthermore, it contains approximately 5% by mass of Co, thus posing a resource risk issue.

[0011] Patent Document 2 discloses a low-thermal-expansion alloy with high strength and hardness. However, the alloy described in Patent Document 2 also contains approximately 5% by mass of Co, thus posing a significant resource risk. Furthermore, martensitic transformation may occur at low temperatures, potentially impairing the low-thermal-expansion properties. Additionally, Patent Document 2 does not mention the magnetic transition point, raising concerns about the instability of its thermal expansion properties at high temperatures.

[0012] Furthermore, no examples of alloys exhibiting high tensile strength and consistently low thermal expansion characteristics over a wide temperature range have been proposed in the relevant technologies.

[0013] Reference List

[0014] Patent documents

[0015] Patent Document 1: JPH09-324243A

[0016] Patent Document 2: JPH04-354848A Summary of the Invention

[0017] One object of the present invention is to provide a low thermal expansion alloy that stably exhibits low thermal expansion characteristics over a wide temperature range.

[0018] Another object of the present invention is to provide a low thermal expansion alloy that, in addition to having low thermal expansion characteristics, also has high tensile strength.

[0019] To address the above problems, the present invention provides a low thermal expansion alloy composed of the following components:

[0020] 0.10% by mass ≤ C ≤ 0.40% by mass;

[0021] Si ≤ 1.00% by mass;

[0022] 0.10% by mass ≤ Mn ≤ 2.00% by mass;

[0023] P ≤ 0.050% by mass;

[0024] S ≤ 0.015% by mass;

[0025] 0.10% by mass ≤ Cu ≤ 4.00% by mass;

[0026] 35.0% by mass ≤ Ni ≤ 45.0% by mass;

[0027] 0.10% mass ≤ V ≤ 1.00% mass;

[0028] 0% by mass ≤ Cr ≤ 0.50% by mass;

[0029] 0% by mass ≤ Mo ≤ 4.00% by mass;

[0030] 0% by mass ≤ Co ≤ 0.50% by mass;

[0031] 0% by mass ≤ Al ≤ 0.50% by mass;

[0032] 0% by mass ≤ Ti ≤ 0.50% by mass;

[0033] 0% by mass ≤ Nb ≤ 0.50% by mass;

[0034] 0% by mass ≤ W ≤ 0.50% by mass;

[0035] 0% by mass ≤ Zr ≤ 0.50% by mass;

[0036] 0% by mass ≤ Hf ≤ 0.50% by mass;

[0037] 0% by mass ≤ Ta ≤ 0.50% by mass;

[0038] 0% by mass ≤ B ≤ 0.050% by mass;

[0039] 0% by mass ≤ Mg ≤ 0.050% by mass;

[0040] 0% by mass ≤ Ca ≤ 0.050% by mass; and

[0041] 0% by mass ≤ REM ≤ 0.050% by mass

[0042] The balance is Fe and unavoidable impurities.

[0043] Low thermal expansion alloys satisfy the following formulas (1) and (2).

[0044] A ≥ 38.0 (1)

[0045] 40.6 < B ≤ 44.5 (2)

[0046] Here,

[0047] A = [Ni] + [Co] + 0.7 [Cu] - [Si] - [Mn] - [Cr] - 0.5 [Mo] - 0.5 [V], and

[0048] B = [Ni] + 0.8 [Co] + [Cu] + 6 [C] + 1.1 [Si] + [Mn] + 1.2 [Cr] + 0.2 [Mo] - 0.5 [V].

[0049] By adding appropriate amounts of carbon (C) and v (V) to the alloy and adjusting the compositional balance between V and C, fine carbides will precipitate in the matrix. Therefore, while achieving high strength, it also prevents the decrease in the coefficient of thermal expansion caused by the solid solution of elements (especially C).

[0050] Furthermore, by optimizing the A value (especially the composition of Ni and Cu) and optimizing manufacturing conditions, a magnetic transition point of 280 °C or higher can be achieved. Therefore, low thermal expansion characteristics can be maintained at high temperatures.

[0051] Furthermore, when the B value (especially the composition of Ni and Cu) and manufacturing conditions are optimized, the coefficient of thermal expansion can be maintained at 3.5 × 10⁻⁶ over a wide temperature range. -6 / ℃ to 6.0×10 -6 Within the range of / ℃. Detailed Implementation

[0052] An embodiment of the present invention will now be described in detail.

[0053] [1. Low thermal expansion alloy]

[0054] [1.1. Main Constituent Elements]

[0055] The low thermal expansion alloy according to the present invention comprises the following elements, with the remainder being Fe and unavoidable impurities. The types of added elements, the composition range, and the reasons for their limitations are as follows.

[0056] (1) 0.10% mass ≤ C ≤ 0.40% mass:

[0057] C has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening caused by carbide precipitation. To achieve this effect, the C content needs to be 0.10% by mass or more. The C content is preferably 0.20% by mass or more.

[0058] On the other hand, excessively high C content may reduce toughness, ductility, and hot workability, or increase the coefficient of thermal expansion. Therefore, the C content needs to be 0.40% by mass or less. Preferably, the C content is 0.36% by mass or less.

[0059] (2) Si ≤ 1.00 wt%

[0060] If the Si content is too high, the coefficient of thermal expansion may increase and the magnetic transition point may decrease. Therefore, the Si content needs to be 1.00% by mass or less. The Si content is preferably 0.70% by mass or less, more preferably 0.40% by mass or less, and even more preferably 0.30% by mass or less.

[0061] The lower the Si content, the better. However, excessively reducing the Si content may increase manufacturing costs. Si also has the effect of improving tensile strength through solid solution strengthening. Therefore, the Si content needs to be 0.01% by mass or more.

[0062] (3) 0.10% by mass ≤ Mn ≤ 2.00% by mass:

[0063] Mn has the effect of forming inclusions such as MnS and improving the manufacturability (machinability) of alloys. To achieve these effects, the Mn content needs to be 0.10% by mass or more.

[0064] On the other hand, if the Mn content is too high, the coefficient of thermal expansion may increase and the magnetic transition point may decrease. Therefore, the Mn content needs to be 2.00% by mass or less. Preferably, the Mn content is 0.50% by mass or less.

[0065] (4) P ≤ 0.050 wt%

[0066] Excessive phosphorus (P) content may reduce hot working properties. Therefore, the P content needs to be 0.050% by mass or less.

[0067] The lower the phosphorus (P) content, the better. However, excessively reducing the P content may increase manufacturing costs. Therefore, the P content can be 0.001% by mass or more.

[0068] (5) S ≤ 0.015% by mass:

[0069] Excessive sulfur content may reduce hot working properties. Therefore, the sulfur content needs to be 0.015% by mass or less.

[0070] The lower the sulfur content, the better. However, excessively reducing the sulfur content may increase manufacturing costs. Therefore, the sulfur content can be 0.001% by mass or more.

[0071] (6) 0.10 wt% ≤ Cu ≤ 4.00 wt%:

[0072] In Fe-Ni based alloys (especially Fe-Ni based alloys containing 30% by mass or more of Ni), Cu has a similar effect to Ni in reducing the coefficient of thermal expansion and increasing the magnetic transition point. To achieve this effect, the Cu content needs to be 0.10% by mass or more. The Cu content is preferably 1.60% by mass or more, and more preferably 1.80% by mass or more.

[0073] Conversely, excessive Cu content may increase the coefficient of thermal expansion. Furthermore, excessive Cu content may promote component segregation, potentially reducing hot workability. Therefore, the Cu content should be 4.00% by mass or less.

[0074] (7) 35.0% by mass ≤ Ni ≤ 45.0% by mass:

[0075] In Fe-Ni based alloys, the coefficient of thermal expansion is minimal when the Ni content is around 36% by mass. The coefficient of thermal expansion increases when the Ni content exceeds 36% by mass.

[0076] On the other hand, the magnetic transition point, i.e., the transition temperature between ferromagnetic and paramagnetic materials, increases with increasing Ni content. Above the magnetic transition point, the coefficient of thermal expansion increases significantly. To maintain a low coefficient of thermal expansion even at temperatures of 280 °C or higher, the Ni content needs to be 35.0% by mass or more.

[0077] Ni is an expensive element. Therefore, if the Ni content is too high, the cost of raw materials will increase.

[0078] Furthermore, if the Ni content is too high, the coefficient of thermal expansion at temperatures equal to or below the magnetic transition point may increase. Therefore, the Ni content needs to be 45.0% by mass or less. More preferably, the Ni content is 40.0% by mass or less.

[0079] (8) 0.10% mass ≤ V ≤ 1.00% mass:

[0080] V has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening caused by carbide precipitation. To achieve this effect, the V content needs to be 0.10% by mass or more.

[0081] On the other hand, if the V content is too high, exceeding the amount required for carbide precipitation, the coefficient of thermal expansion may increase, and the magnetic transition point may decrease. Therefore, the V content needs to be 1.00% by mass or less. Preferably, the V content is 0.50% by mass or less.

[0082] (9) Unavoidable impurities:

[0083] The low thermal expansion alloy according to the present invention may contain unavoidable impurities. Here, "unavoidable impurities" refers to components that are mixed in during the industrial production of the low thermal expansion alloy due to various factors such as raw materials and production processes, and their content is within a range that will not adversely affect the performance of the low thermal expansion alloy of the present invention.

[0084] In addition to Si, P, and S mentioned above, unavoidable impurities also include the following elements. These elements are considered "unavoidable impurities" in the low thermal expansion alloy according to the present invention when their contents are equal to or less than the following upper limits.

[0085] The low thermal expansion alloy according to the present invention may contain any one of the following unavoidable impurities, or two or more of the following unavoidable impurities. However, in order to maintain the high performance of the low thermal expansion alloy, the total content of unavoidable impurities is preferably 1.1% by mass or less, more preferably 0.5% by mass or less.

[0086] (9.1) Sn ≤ 0.010 wt%

[0087] Excessive Sn content may reduce hot working properties. Therefore, the Sn content is preferably 0.010% by mass or less.

[0088] The lower the Sn content, the better. However, excessively reducing the Sn content will increase manufacturing costs. Therefore, the Sn content can be greater than 0% by mass.

[0089] (9.2) Zn ≤ 0.010 wt%

[0090] Excessive Zn content may reduce hot working properties. Therefore, the Zn content is preferably 0.010% by mass or less.

[0091] The lower the Zn content, the better. However, excessively reducing the Zn content will increase manufacturing costs. Therefore, the Zn content can be greater than 0% by mass.

[0092] (9.3) As ≤ 0.010 wt%

[0093] Excessive As content may reduce hot working properties. Therefore, the As content is preferably 0.010% by mass or less.

[0094] The lower the As content, the better. However, the corrosion resistance of the alloy may be improved when As and Cu coexist. Therefore, the As content can be greater than 0% by mass.

[0095] (9.4) Se ≤ 0.010 wt%

[0096] Excessive Se content may reduce hot working properties. Therefore, the Se content is preferably 0.010% by mass or less.

[0097] The lower the selenium (Se) content, the better. However, an appropriate amount of Se can improve the machinability of the alloy. Therefore, the Se content can be greater than 0% by mass.

[0098] (9.5)Sb ≤ 0.010 wt%

[0099] If the Sb content is too high, the coefficient of thermal expansion may increase. Therefore, the Sb content is preferably 0.010% by mass or less.

[0100] The lower the Sb content, the better. However, the corrosion resistance of the alloy may be improved when Sb and Cu coexist. Therefore, the Sb content can be greater than 0% by mass.

[0101] (9.6)Ag ≤ 0.010 wt%

[0102] Excessive Ag content may reduce hot working properties. Therefore, the Ag content is preferably 0.010% by mass or less.

[0103] The lower the Ag content, the better. However, excessively reducing the Ag content will increase manufacturing costs. Therefore, the Ag content can be greater than 0% by mass.

[0104] (9.7)Bi ≤ 0.0010 wt%

[0105] Excessive Bi content may reduce hot working properties. Therefore, the Bi content is preferably 0.0010% by mass or less.

[0106] The lower the Bi content, the better. However, excessively reducing the Bi content will increase manufacturing costs. Therefore, the Bi content can be greater than 0% by mass.

[0107] (9.8)O ≤ 0.050 wt%

[0108] Excessive oxygen content may increase the coefficient of thermal expansion of steel. Therefore, the oxygen content is preferably 0.050% by mass or less.

[0109] The lower the oxygen content, the better. However, excessively reducing the oxygen content will increase manufacturing costs. Therefore, the oxygen content can be greater than 0% by mass.

[0110] (9.9)N ≤ 0.050 wt%

[0111] Excessive nitrogen (N) content can increase the coefficient of thermal expansion of steel. Therefore, the N content is preferably 0.050% by mass or less.

[0112] The lower the nitrogen content, the better. However, excessively reducing the nitrogen content will increase manufacturing costs. Therefore, the nitrogen content can be greater than 0% by mass.

[0113] [1.2. Secondary Constituent Elements]

[0114] The low thermal expansion alloy according to the present invention, in addition to the aforementioned main constituent elements and unavoidable impurities, may further include one, two, or more of the following elements. The types of added elements, the range of compositions, and the reasons for their limitations are as follows.

[0115] (1) 0% by mass ≤ Cr ≤ 0.50% by mass:

[0116] The Cr content can be 0% by mass. However, excessively reducing the Cr content may lead to increased manufacturing costs. Furthermore, Cr also has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening caused by carbide precipitation. Therefore, the Cr content is preferably 0.01% by mass or more.

[0117] On the other hand, if the Cr content is too high, the coefficient of thermal expansion may increase and the magnetic transition point may decrease. Therefore, the Cr content is preferably 0.50% by mass or less.

[0118] (2) 0% by mass ≤ Mo ≤ 4.00% by mass:

[0119] The Mo content can be 0% by mass. However, excessively reducing the Mo content may increase manufacturing costs. Furthermore, Mo also has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening caused by carbide precipitation. Therefore, the Mo content is preferably 0.01% by mass or more.

[0120] On the other hand, if the Mo content is too high, the coefficient of thermal expansion may increase and the magnetic transition point may decrease. Therefore, the Mo content is preferably 4.00% by mass or less.

[0121] (3) 0 ≤ Co ≤ 0.50 wt%

[0122] The Co content can be 0% by mass. However, excessively reducing the Co content may lead to increased manufacturing costs. Therefore, the Co content is preferably 0.01% by mass or more.

[0123] On the other hand, Co is an expensive element, so excessive Co content may lead to increased manufacturing costs. Therefore, the Co content is preferably 0.50% by mass or less.

[0124] (4) 0% by mass ≤ Al ≤ 0.50% by mass:

[0125] The Al content can be 0% by mass. Besides being a deoxidizing element, Al also enhances tensile strength through solid solution strengthening and precipitation strengthening caused by carbide precipitation. Therefore, the Al content is preferably above 0% by mass.

[0126] On the other hand, if the Al content is too high, the ductility may decrease and the coefficient of thermal expansion may increase. Therefore, the Al content is preferably 0.50% by mass or less.

[0127] (5) 0% by mass ≤ Ti ≤ 0.50% by mass:

[0128] The Ti content can be 0% by mass. Ti has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening caused by carbide precipitation. Therefore, the Ti content is preferably 0% by mass or more.

[0129] On the other hand, if the Ti content is too high, the ductility may decrease and the coefficient of thermal expansion may increase. Therefore, the Ti content is preferably 0.50% by mass or less.

[0130] (6) 0% by mass ≤ Nb ≤ 0.50% by mass:

[0131] The Nb content can be 0% by mass. Nb has the effect of refining grains and improving tensile strength. Therefore, the Nb content is preferably above 0% by mass.

[0132] On the other hand, excessively high Nb content may reduce hot working properties. Therefore, the Nb content is preferably 0.50% by mass or less.

[0133] (7) 0% mass ≤ W ≤ 0.50% mass:

[0134] The content of W can be 0% by mass. W has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening caused by carbide precipitation. Therefore, the content of W is preferably 0% by mass or more.

[0135] On the other hand, if the W content is too high, the ductility may decrease and the coefficient of thermal expansion may increase. Therefore, the W content is preferably 0.50% by mass or less.

[0136] (8) 0% by mass ≤ Zr ≤ 0.50% by mass:

[0137] The Zr content can be 0% by mass. Besides being a deoxidizing element, Zr also enhances tensile strength through solid solution strengthening and precipitation strengthening caused by carbide precipitation. Therefore, the Zr content is preferably above 0% by mass.

[0138] On the other hand, if the Zr content is too high, the ductility may decrease and the coefficient of thermal expansion may increase. Therefore, the Zr content is preferably 0.50% by mass or less.

[0139] (9) 0 ≤ Hf ≤ 0.50 % by mass:

[0140] The Hf content can be 0% by mass. Hf has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening caused by carbide precipitation. Therefore, the Hf content is preferably 0% by mass or more.

[0141] On the other hand, if the Hf content is too high, the ductility may decrease and the coefficient of thermal expansion may increase. Therefore, the Hf content is preferably 0.50% by mass or less.

[0142] (10) 0% mass ≤ Ta ≤ 0.50% mass:

[0143] The Ta content can be 0% by mass. Ta has the effect of improving tensile strength through solid solution strengthening and precipitation strengthening caused by carbide precipitation. Therefore, the Ta content is preferably 0% by mass or more.

[0144] On the other hand, if the Ta content is too high, the ductility may decrease and the coefficient of thermal expansion may increase. Therefore, the Ta content is preferably 0.50% by mass or less.

[0145] (11) 0% mass ≤ B ≤ 0.050% mass:

[0146] The content of boron (B) can be 0% by mass. B has the effect of improving hot working properties through grain boundary strengthening, as well as improving the oxidation resistance of grain boundaries. Therefore, the content of B is preferably 0% by mass or more.

[0147] On the other hand, if the B content is too high, the hot working performance may decrease. Therefore, the B content is preferably 0.050% by mass or less.

[0148] (12) 0% by mass ≤ Mg ≤ 0.050% by mass:

[0149] The Mg content can be 0% by mass. Mg has the effect of fixing S to improve hot working properties, and also has the effect of reducing the coefficient of thermal expansion. Therefore, the Mg content is preferably 0% by mass or more.

[0150] On the other hand, if the Mg content is too high, the hot working properties may decrease. Therefore, the Mg content is preferably 0.050% by mass or less.

[0151] (13) 0 ≤ Ca ≤ 0.050 wt%

[0152] The Ca content can be 0% by mass. Ca has the effect of fixing S to improve hot working performance, and also reduces the coefficient of thermal expansion. Therefore, the Ca content is preferably 0% by mass or higher.

[0153] On the other hand, if the Ca content is too high, the hot working performance may decrease. Therefore, the Ca content is preferably 0.050% by mass or less.

[0154] (14) 0% mass ≤ REM ≤ 0.050% mass:

[0155] The content of REM can be 0% by mass. REM has the effect of improving antioxidant properties at high temperatures and expanding the operating temperature range. Therefore, the content of REM is preferably 0% by mass or higher. Examples of REM include Nd, Pr, La, Ce, and Y.

[0156] On the other hand, excessive REM can lead to a significant increase in manufacturing costs. Therefore, the REM content is preferably 0.050% by mass or less.

[0157] [1.3 Composition Balance]

[0158] The low thermal expansion alloy according to the present invention needs to satisfy the following formulas (1) and (2).

[0159] A ≥ 38.0 (1)

[0160] 40.6 < B ≤ 44.5 (2)

[0161] Here,

[0162] A = [Ni] + [Co] + 0.7 [Cu] - [Si] - [Mn] - [Cr] - 0.5 [Mo] - 0.5 [V],

[0163] B = [Ni] + 0.8 [Co] + [Cu] + 6 [C] + 1.1 [Si] + [Mn] + 1.2 [Cr] + 0.2 [Mo] - 0.5 [V].

[0164] [1.3.1. Formula (1)]

[0165] The A value in formula (1) is an indicator related to the magnetic transition point of low thermal expansion alloys. Optimizing the alloy composition to satisfy formula (1) and optimizing manufacturing conditions can increase the magnetic transition point. Generally, the magnetic transition point increases with increasing A value.

[0166] Specifically, when the alloy composition is optimized to achieve an A value of 38.0 or more, and the manufacturing conditions are optimized, the magnetic transition point can reach 280 °C or higher.

[0167] Similarly, when the composition of the alloy is optimized to achieve an A value of 38.5 or more, and the manufacturing conditions are optimized, the magnetic transition point can reach 290 °C or higher.

[0168] Furthermore, when the alloy composition is optimized to achieve an A value of 39.0 or more, and the manufacturing conditions are optimized, the magnetic transition point can reach 300 °C or higher.

[0169] [1.3.2. Formula (2)]

[0170] The B value in formula (2) is an indicator related to the coefficient of thermal expansion of low thermal expansion alloys. When the alloy composition is optimized to satisfy formula (2) and the manufacturing conditions are optimized, the coefficient of thermal expansion can be maintained at a value close to that of semiconductors. Generally speaking, the coefficient of thermal expansion increases with the increase of the B value.

[0171] Specifically, when the alloy composition is optimized to achieve a B value greater than 40.6 and less than 44.5, and the manufacturing conditions are optimized, the coefficient of thermal expansion can reach 3.5 × 10⁻⁶. -6 / ℃ to 6.0×10-6 / ℃.

[0172] [1.4. Performance]

[0173] [1.4.1 Tensile Strength]

[0174] "Tensive strength" refers to the value obtained by tensile testing of a No. 3 round bar specimen with a parallel section of 6 mm in diameter at atmospheric pressure at room temperature (25 °C) according to ASTM A370-17 standard.

[0175] High tensile strength can be obtained by adding appropriate amounts of carbon and v to the alloy and precipitating fine carbides in the matrix. With optimized manufacturing conditions, the tensile strength of the alloy can reach 500 MPa or more. With further optimization of manufacturing conditions, the tensile strength can reach 550 MPa or more, or 600 MPa or more.

[0176] [1.4.2. Coefficient of thermal expansion]

[0177] In this invention, "coefficient of thermal expansion" refers to the average linear coefficient of thermal expansion from 30 °C to 100 °C, measured using a measuring device (TMA8310, manufactured by Rigaku) ​​according to ASTM E228-17 standard.

[0178] When the Co content is reduced and the composition of the alloy is optimized to meet the above formula (2), the coefficient of thermal expansion of the alloy can be maintained at a value close to that of the semiconductor over a wide temperature range.

[0179] When manufacturing conditions are optimized, the coefficient of thermal expansion of the alloy can reach 3.5 × 10⁻⁶. -6 / ℃ to 6.0×10 -6 / ℃.

[0180] [1.4.3. Magnetic Transition Point]

[0181] When a low thermal expansion alloy is heated to a temperature above its magnetic transition point, its coefficient of thermal expansion increases. To achieve low thermal expansion characteristics at high temperatures, a higher magnetic transition point is preferable. Optimizing the alloy composition to satisfy the above formula (1) can increase the magnetic transition point. With optimized manufacturing conditions, the magnetic transition point of the alloy can reach 280 °C or higher. With further optimization of manufacturing conditions, the magnetic transition point can reach 290 °C or higher, or 300 °C or higher.

[0182] [1.5 Structure]

[0183] As described below, the low thermal expansion alloy according to the present invention can be processed into various shapes by melting and casting, primary hot working, secondary hot working, annealing and post-treatment.

[0184] The low thermal expansion alloy of the present invention can be in any state, including a hot-worked state, an annealed state, and a state after necessary post-treatment following annealing. To dissolve crude carbonitrides and reduce manufacturing costs, the low thermal expansion alloy preferably includes a portion in the annealed state.

[0185] The phrase “including a portion in the annealed state” here means: (a) the entire low thermal expansion alloy is in the annealed state, or (b) a portion of the low thermal expansion alloy has undergone necessary processing (e.g., cutting), but other portions are in the annealed state.

[0186] [1.6. Shape]

[0187] The shape of the low thermal expansion alloy in this invention is not particularly limited, and the optimal shape can be selected according to its purpose. Examples of shapes for the low thermal expansion alloy include tubes, bars, wires, and plates.

[0188] [2. Manufacturing method of low thermal expansion alloy]

[0189] The method for manufacturing the low thermal expansion alloy according to the present invention includes: a smelting and casting process, wherein smelting and casting are mixed to form raw materials having a predetermined composition to obtain an ingot; a primary heat treatment process, wherein the obtained ingot is subjected to primary heat treatment; a secondary heat treatment process, wherein the material subjected to primary heat treatment is subjected to secondary heat treatment; if necessary, an annealing process, wherein the material subjected to secondary heat treatment is annealed; and if necessary, a post-treatment process, wherein the material subjected to secondary heat treatment or the annealed material is subjected to post-treatment.

[0190] [2.1. Smelting and Casting Processes]

[0191] First, raw materials mixed with a predetermined composition are melted and cast to obtain ingots. There are no particular restrictions on the methods and conditions for melting and casting the raw materials; the optimal methods and conditions can be selected according to the purpose. For example, when manufacturing molten metal, electric furnaces, argon-oxygen decarburization (AOD) furnaces, vacuum oxygen decarburization (VOD) furnaces, etc., can be used.

[0192] It should be noted that, if necessary, the obtained steel ingots can be subjected to homogenization heat treatment to eliminate segregation.

[0193] [2.2. One-time hot working process]

[0194] Next, the obtained ingot undergoes a primary hot working process. This process aims to break down the coarse casting structure and refine it, while simultaneously transforming the ingot into materials such as slabs, blooms, and billets. There are no particular limitations on the primary hot working method; the optimal method can be selected based on the objective. Examples of primary hot working methods include hot forging and hot rolling.

[0195] Materials such as slabs, rough-rolled billets, or small square billets can be manufactured directly by continuous casting from molten metal produced in melting and casting processes. In this case, a single hot working process can be omitted.

[0196] [2.3. Secondary heat treatment process]

[0197] Next, the material that has undergone primary heat treatment is subjected to secondary heat treatment. The purpose of secondary heat treatment is to shape the material into a final product shape (e.g., sheet, bar, wire, or tube) or a shape close to the final product shape. There are no particular limitations on the secondary heat treatment method; the optimal method can be selected based on the objective. Examples of secondary heat treatment methods include hot rolling, hot extrusion, and hot piercing rolling.

[0198] There are no particular restrictions on the conditions for secondary heat treatment; the optimal conditions can be selected based on the purpose. Furthermore, secondary heat treatment can be performed multiple times depending on the purpose. Preferably, the material is heated to 900 °C or higher, or 1300 °C or lower, before secondary heat treatment.

[0199] Furthermore, in cases involving multiple secondary heat treatments, the material temperature at the end of the final secondary heat treatment is preferably 800 °C or higher, or 1200 °C or lower. This is to optimize the grain size.

[0200] [2.4 Annealing Process]

[0201] Next, the material that has undergone secondary heat treatment is annealed as needed. Annealing can be performed once or multiple times.

[0202] Annealing temperature can affect the properties of a material. Without annealing or at too low an annealing temperature, a large amount of coarse nitrides may precipitate. Therefore, mechanical properties may decrease or the coefficient of thermal expansion may increase. Furthermore, the grain size may become excessively refined, and machinability may decrease. Therefore, an annealing temperature of 800 °C or higher is preferred. An annealing temperature of 900 °C or higher is more preferred.

[0203] On the other hand, if the annealing temperature is too high, the material may melt locally. Furthermore, due to the complete dissolution of fine carbonitrides (such as VC), abnormal grain growth may occur, potentially leading to a decrease in mechanical properties. Therefore, the annealing temperature is preferably 1300 °C or lower.

[0204] The optimal holding time at the annealing temperature can be selected based on the intended purpose. Generally, as the annealing holding time increases, the number of fine grains decreases. On the other hand, if the holding time is extended beyond what is necessary, the grains may become excessively coarsened. The optimal holding time varies depending on the annealing temperature, but is typically from 1 minute to 3 hours. After the holding time is completed, the material is cooled by water cooling, oil cooling, or air cooling, or at a comparable cooling rate.

[0205] Grain size does not significantly affect the coefficient of thermal expansion, but excessively large grains may adversely affect mechanical properties. The optimal grain size varies depending on the application, but is preferably between #0 and #10. A grain size between #3 and #7 is more preferred.

[0206] [2.5. Post-processing]

[0207] Next, the material that has undergone secondary hot working or annealing is post-treated as needed. Examples of post-treatment include machining, welding, and cold working. The resulting low-thermal-expansion alloy can be used for a variety of applications.

[0208] [3. Effect]

[0209] By adding appropriate amounts of carbon (C) and v (V) to the alloy and adjusting the compositional balance between V and C, fine carbides will precipitate in the matrix. Therefore, while achieving high strength, it also prevents the decrease in the coefficient of thermal expansion caused by the solid solution of elements (especially C).

[0210] Furthermore, by optimizing the A value (especially the composition of Ni and Cu) and optimizing manufacturing conditions, a magnetic transition point of 280 °C or higher can be achieved. Therefore, low thermal expansion characteristics can be maintained at high temperatures.

[0211] Furthermore, when the B value (especially the composition of Ni and Cu) and manufacturing conditions are optimized, the coefficient of thermal expansion can be maintained at 3.5 × 10⁻⁶ over a wide temperature range. -6 / ℃ to 6.0×10 -6 Within the range of / ℃.

[0212] Example

[0213] (Examples 1 to 16 and Comparative Examples 1 to 20)

[0214] [1. Sample preparation]

[0215] In a vacuum induction furnace, 5 kg of an alloy with the compositions shown in Tables 1 and 2 was melted and cast into an ingot. The ingot was then hot-forged and annealed to produce bars with a diameter of 15 mm.

[0216] [Table 1]

[0217]

[0218] [Table 1 (continued)]

[0219]

[0220] [Table 2]

[0221]

[0222] [Table 2 (continued)]

[0223]

[0224] [2. Experimental Methods]

[0225] [2.1 Assessment of tensile strength]

[0226] Round bar tensile specimens are taken from the center of each type of bar. The parallel section of the round bar tensile specimen is parallel to the longitudinal direction of the bar. The diameter of the parallel section is 6 mm. The tensile strength TS (MPa) is obtained by performing a tensile test on the round bar tensile specimen at atmospheric pressure at room temperature (25 °C) according to ASTM A370-17 standard.

[0227] A tensile strength TS (MPa) of 500 MPa or more is rated as "A (high strength)" and a tensile strength TS (MPa) of less than 500 MPa is rated as "B (non-high strength)".

[0228] [2.2 Evaluation of the average linear thermal expansion coefficient]

[0229] Round bar specimens were taken from the center of each type of bar. The longitudinal direction of the round bar specimens was parallel to the longitudinal direction of the bar. The obtained round bar specimens were used to measure the coefficient of thermal expansion. The coefficient of thermal expansion was measured according to ASTM E228-17 using a measuring device (TMA8310, manufactured by Rigaku) ​​over a temperature range of 20 °C to 800 °C.

[0230] The average linear coefficient of thermal expansion from 30 ℃ to 100 ℃ is 3.5 × 10⁻⁶. -6 / ℃ or more, 6.0×10 -6 A temperature of / ℃ or less is rated "A (Good)", and the average linear coefficient of thermal expansion is less than 3.5 × 10. -6 / ℃ or greater than 6.0×10 -6 The condition of / ℃ is rated as "B (poor)".

[0231] [2.3. Evaluation of Magnetic Transition Point]

[0232] The magnetic transition point is determined based on a displacement graph relative to the test temperature obtained when measuring the coefficient of thermal expansion. The bends that appear in the graph are defined as the magnetic transition points.

[0233] A magnetic transition point of 280 ℃ or more but below 290 ℃ is rated as "C (good)", a magnetic transition point of 290 ℃ or more but below 300 ℃ is rated as "B (good)", a magnetic transition point of 300 ℃ or more is rated as "A (best)" and a magnetic transition point below 280 ℃ is rated as "D (poor)".

[0234] [3. Results]

[0235] The results are shown in Table 3. The following information can be gleaned from Tables 1-3.

[0236] (1) In Comparative Examples 1 and 2, the tensile strength decreased. This was thought to be due to the lower content of C and / or V.

[0237] (2) In Comparative Example 3, the magnetic transition point was below 280 °C. This was thought to be because the A value was less than 38.

[0238] (3) In Comparative Example 4, the magnetic transition point was below 280 °C. This is believed to be due to the low Cu content and an A value less than 38. In Comparative Example 4, the coefficient of thermal expansion was less than 3.5 × 10⁻⁶. -6 / ℃. The reason is believed to be that the B value is 40.6 or less.

[0239] (4) In Comparative Examples 5 and 6, the coefficient of thermal expansion is greater than 6.0 × 10⁻⁶. -6 / ℃. The reason is believed to be excessive Cu content, with a B value greater than 44.5.

[0240] (5) In Comparative Example 7, the magnetic transition point was below 280 °C. This was attributed to the excessively high Cr content, resulting in an A value less than 38. In Comparative Example 7, the coefficient of thermal expansion was less than 3.5 × 10⁻⁶. -6 / ℃. The reason is believed to be excessive Cr content, with a B value of 40.6 or less.

[0241] (6) In Comparative Example 8, the magnetic transition point was below 280 °C, which was attributed to excessive Si content and an A value less than 38. In Comparative Example 8, the coefficient of thermal expansion was greater than 6.0 × 10⁻⁶. -6 / ℃. The reason is believed to be the excessive Si content, with a B value greater than 44.5.

[0242] (7) In Comparative Example 9, the magnetic transition point was below 280 °C. This was thought to be because the A value was less than 38.

[0243] (8) In Comparative Example 10, the magnetic transition point was below 280 °C. This was attributed to an A value less than 38. In Comparative Example 10, the coefficient of thermal expansion was less than 3.5 × 10⁻⁶. -6 / ℃. The reason is believed to be that the B value is 40.6 or less.

[0244] (9) In Comparative Examples 11 to 13, the magnetic transition point was below 280 °C. This is believed to be because the A value was less than 38.

[0245] (10) In Comparative Example 14, the magnetic transition point was below 280 °C. This was attributed to an A value less than 38. In Comparative Example 14, the coefficient of thermal expansion was less than 3.5 × 10⁻⁶. -6 / ℃. The reason is believed to be that the B value is 40.6 or less.

[0246] (11) In Comparative Example 15, the magnetic transition point was below 280 °C. This was thought to be because the A value was less than 38.

[0247] (12) In Comparative Example 16, the magnetic transition point was below 280 °C. This was attributed to the low Cu content and an A value less than 38. In Comparative Example 17, the coefficient of thermal expansion was less than 3.5 × 10⁻⁶. -6 / ℃. The reason is believed to be that the B value is 40.6 or less.

[0248] (13) In Comparative Example 17, the coefficient of thermal expansion is greater than 6.0 × 10⁻⁶. -6 / ℃. The reason is believed to be the excessive Ni content, with a B value greater than 44.6.

[0249] (14) In Comparative Example 18, the magnetic transition point was below 280 °C. This was thought to be because the A value was less than 38.

[0250] (15) In Comparative Example 19, the magnetic transition point was below 280 °C. This was thought to be due to excessive Cr content and an A value of less than 38.

[0251] (16) In Comparative Example 20, the magnetic transition point was below 280 °C. This was attributed to an A value less than 38. In Comparative Example 20, the coefficient of thermal expansion was less than 3.5 × 10⁻⁶. -6 / ℃. The reason is believed to be that the B value is 40.6 or less.

[0252] (17) In Examples 1 to 16, the tensile strength is greater than 600 MPa. Furthermore, in Examples 1 to 16, the magnetic transition point is 280 °C or higher. Furthermore, in Examples 1 to 16, the coefficient of thermal expansion is 3.5 × 10⁻⁶. -6 / ℃ to 6.0×10 -6 / ℃.

[0253] (18) In Examples 3 to 6, the magnetic transition point is 300 °C or higher. The reason is believed to be that the A value is 39.0 or higher.

[0254] [Table 3]

[0255]

[0256] [Table 3 (continued)]

[0257]

[0258] 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 can be made without departing from the spirit of the present invention.

[0259] This application is based on Japanese Patent Application No. 2024-135356, filed on August 14, 2024, the contents of which are incorporated herein by reference.

[0260] Industrial applicability

[0261] The low thermal expansion alloy according to the present invention can be used for diaphragms of pressure sensors, hermetically sealed leads, etc.

Claims

1. A low thermal expansion alloy, comprising the following components 0.10% by mass ≤ C ≤ 0.40% by mass; Si ≤ 1.00% by mass; 0.10% by mass ≤ Mn ≤ 2.00% by mass; P ≤ 0.050% by mass; S ≤ 0.015% by mass; 0.10% by mass ≤ Cu ≤ 4.00% by mass; 35.0% by mass ≤ Ni ≤ 45.0% by mass; 0.10% mass ≤ V ≤ 1.00% mass; 0% by mass ≤ Cr ≤ 0.50% by mass; 0% by mass ≤ Mo ≤ 4.00% by mass; 0% by mass ≤ Co ≤ 0.50% by mass; 0% by mass ≤ Al ≤ 0.50% by mass; 0% by mass ≤ Ti ≤ 0.50% by mass; 0% by mass ≤ Nb ≤ 0.50% by mass; 0% by mass ≤ W ≤ 0.50% by mass; 0% by mass ≤ Zr ≤ 0.50% by mass; 0% by mass ≤ Hf ≤ 0.50% by mass; 0% by mass ≤ Ta ≤ 0.50% by mass; 0% by mass ≤ B ≤ 0.050% by mass; 0% by mass ≤ Mg ≤ 0.050% by mass; 0% by mass ≤ Ca ≤ 0.050% by mass; as well as 0% by mass ≤ REM ≤ 0.050% by mass The balance consists of Fe and unavoidable impurities. The low thermal expansion alloy satisfies the following formulas (1) and (2): A ≥ 38.0 (1), and 40.6 ＜ B ≤ 44.5 (2), Where A = [Ni] + [Co] + 0.7 [Cu] - [Si] - [Mn] - [Cr] - 0.5 [Mo] – 0.5 [V], and B = [Ni] + 0.8 [Co] + [Cu] + 6 [C] + 1.1 [Si] + [Mn] + 1.2 [Cr]+ 0.2 [For] - 0.5 [V]。 2. The low thermal expansion alloy according to claim 1, wherein its tensile strength is 500 MPa or more, wherein, The "tensile strength" refers to the value obtained by tensile testing of a No. 3 round bar specimen with a parallel section of 6 mm in diameter, at room temperature (25 °C) and atmospheric pressure, according to ASTM A370-17 standard.

3. The low thermal expansion alloy according to claim 1, wherein the coefficient of thermal expansion is 3.5 × 10⁻⁶. -6 / ℃ or more, 6.0×10 -6 / ℃ or less, The "coefficient of thermal expansion" refers to the average linear coefficient of thermal expansion from 30 °C to 100 °C as measured according to ASTM E228-17 standard.

4. The low thermal expansion alloy according to claim 1 has a magnetic transition point of 280 °C or higher.

5. The low thermal expansion alloy according to any one of claims 1 to 4, wherein, The unavoidable impurities include at least one selected from the group consisting of: Sn ≤ 0.010% by mass; Zn ≤ 0.010 wt%; As ≤ 0.010% by mass; Se ≤ 0.010% by mass; Sb ≤ 0.010% by mass; Ag ≤ 0.010% by mass; Bi ≤ 0.0010 wt%; O ≤ 0.050% by mass, and N ≤ 0.050% by mass

Images