Low thermal expansion alloy

Abstract

To provide a low thermal expansion alloy that has a small amount of Co and has a low thermal expansion coefficient in a wide range from the cryogenic temperature to the room temperature, and further has a low 0.2% proof stress.SOLUTION: The inventive low thermal expansion alloy contains, in mass%, C: 0.010% or less, Si: 0.10% or less, Mn: 0.15% or less, Ni: 34.0-37.0%, Co: 0.2-1.0%, Al: 0.10% or less with the balance being Fe and impurities and has a 0.2% proof stress of 200 MPa or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to low thermal expansion alloys. [Background technology]

[0002] Thermally stable Invar alloys are widely used as materials for parts in electronics and semiconductor-related equipment, laser processing machines, and ultra-precision processing equipment. In recent years, materials with a small thermal expansion coefficient in the temperature range from cryogenic to room temperature are also required for components in the aviation and space fields that are used at extremely low temperatures.

[0003] Patent Document 1 describes a ceramic material with improved press formability, resonance resistance, and buckling resistance, which is composed of, by weight, 0.10% or less C, 0.30% or less Si, 0.30% or less Al, 0.1 to 1.0% Mn, 30 to 34% Ni, 1.0 to 4.0% Cr, 2.0 to 5.0% Co, the balance being Fe and unavoidable impurities, and has a thermal expansion coefficient of 2.5 × 10 -6 A shadow mask of about 1 / °C has been disclosed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 112759 / 1983 Summary of the Invention [Problem to be solved by the invention]

[0005] In the fields mentioned above, it is conceivable to use low thermal expansion alloys in vibration-damping materials that suppress vibration. Vibration-damping materials are required to have a low yield point. This is because when the yield point is low, the alloy deforms with a small force, so its deformation capacity is large, it is less likely to break, and it is easier to absorb the energy of vibration.

[0006] Furthermore, conventional low thermal expansion alloys that have a small thermal expansion coefficient over a wide temperature range contain Ni and a few percent of Co. Co and its inorganic compounds are designated as specific chemical substances, and therefore require special care in their handling at manufacturing sites of steels that contain Co.

[0007] In view of the above circumstances, an object of the present invention is to provide a low thermal expansion alloy that uses a reduced amount of Co, has thermal expansion characteristics equivalent to those of alloys containing a few percent of Co, such as conventional Fe-32Ni-5Co alloys, and further has low 0.2% yield strength. [Means for solving the problem]

[0008] The present inventors have conducted extensive research into a method for obtaining a low thermal expansion alloy that uses less Co and has thermal expansion properties equivalent to those of an Fe-32Ni-5Co alloy, etc. As a result, it has been found that low thermal expansion properties can be obtained by increasing the purity of the alloy and making it into a clean alloy with few nonmetallic inclusions.

[0009] In addition, it was found that by hot forging the obtained high-purity alloy and then subjecting it to heat treatment, the crystal grains become coarse and the 0.2% yield strength is reduced, thereby obtaining properties suitable for use in vibration-damping components.

[0010] The present invention has been made based on the above findings, and the gist of the present invention is as follows.

[0011] (1) A low thermal expansion alloy comprising, by mass%, C: 0.010% or less, Si: 0.10% or less, Mn: 0.15% or less, Ni: 34.0 to 37.0%, Co: 0.2 to 1.0%, Al: 0.10% or less, the balance being Fe and impurities, and having a 0.2% yield strength of 200 MPa or less.

[0012] (2) The low thermal expansion alloy according to (1) above, characterized in that the crystal grain size is 200 μm or more.

[0013] (3) The average thermal expansion coefficient from -100 to 50°C is 0.5 × 10-6 / °C or less.

[0014] (4) A low thermal expansion alloy according to any one of (1) to (3), characterized in that it contains, in place of a portion of the Fe, one or more of the following, by mass%, Cu: 0.30% or less, Cr: 0.10% or less, Mo: 0.10% or less, W: 0.10% or less, Ti: 0.10% or less, and Nb: 0.10% or less. Effect of the Invention

[0015] According to the present invention, it is possible to obtain a low thermal expansion alloy that has thermal expansion characteristics equivalent to those of an Fe-32Ni-5Co alloy and the like while reducing the amount of Co used, and further has a low 0.2% proof stress. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention will be described in detail below. In the following, "%" regarding the composition of a component means "mass %" unless otherwise specified. First, the composition of the low thermal expansion alloy of the present invention will be described.

[0017] In the present invention, Ni is an essential element that contributes to lowering the thermal expansion coefficient by its addition. In the present invention, the Ni content is set to 34.0 to 37.0% in order to sufficiently reduce the thermal expansion coefficient over a wide temperature range.

[0018] Co is an element that contributes to lowering the thermal expansion coefficient when added together with Ni. In the present invention, for the reasons mentioned above, the amount of Co is small, ie, 0.2 to 1.0%.

[0019] The low thermal expansion alloy of the present invention may contain C, Si, Mn, and Al in addition to Ni and Co.

[0020] C dissolves in austenite and contributes to increasing strength, so it may be included as necessary. If the C content is high, the thermal expansion coefficient increases and the dimensional change over time increases, so the C content is set to 0.010% or less, preferably 0.005% or less, and more preferably 0.003% or less. In the low thermal expansion alloy of the present invention, C is not an essential element and the content may be 0.

[0021] Si may be added as a deoxidizer. It can also improve the fluidity of the molten metal. If the Si content exceeds 0.100%, the thermal expansion coefficient increases, so the Si content is set to 0.100% or less, preferably 0.050% or less, and more preferably 0.010% or less. In the low thermal expansion alloy of the present invention, Si is not an essential element, and the content may be 0.

[0022] Mn may be added as a deoxidizer. It also contributes to improving strength through solid solution strengthening. If the Mn content exceeds 0.15%, the thermal expansion coefficient increases, so the Mn content is set to 0.15% or less, preferably 0.10% or less, and more preferably 0.05% or less. In the low thermal expansion alloy of the present invention, Mn is not an essential element, and the content may be 0.

[0023] Al may be added for the purpose of deoxidization. In order to suppress the formation of inclusions, reduce casting defects, and obtain a low thermal expansion coefficient, the content is set to 0.100% or less, preferably 0.050% or less, and more preferably 0.010% or less.

[0024] The balance of the composition is Fe and impurities. The impurities refer to substances that are inevitably mixed in from raw materials, the manufacturing environment, and the like when industrially manufacturing steel having the composition specified in the present invention, and specifically include P, S, O, N, and the like.

[0025] The low thermal expansion alloy of the present invention has a 0.2% yield strength of 200 MPa or less. If the yield strength is too high, springback occurs during forming, causing deformation of the shape and leaving localized distortion. Furthermore, in order to be used as a vibration-damping member that suppresses vibration, the 0.2% yield strength is set to 200 MPa or less.

[0026] The low thermal expansion alloy of the present invention preferably has a crystal grain size of 200 μm or more. As the crystal grain size increases, the 0.2% proof stress decreases.

[0027] The low thermal expansion alloy of the present invention preferably has an average thermal expansion coefficient of 0.5×10 -6 / °C or less, and more preferably 0.3 × 10 -6 / °C or less, more preferably 0.2×10 -6 / ℃ or less.

[0028] The low thermal expansion alloy of the present invention may contain one or more of Cu, Cr, Mo, W, Ti, and Nb in place of a portion of the Fe described above, provided that the respective contents are within the ranges of Cu: 0.30% or less, Cr: 0.10% or less, Mo: 0.10% or less, W: 0.10% or less, Ti: 0.10% or less, and Nb: 0.10% or less, in order not to increase the thermal expansion coefficient.

[0029] Cu is an element that improves strength, and may be contained in the range of 0.30% or less.

[0030] Cr is effective in forming a solid solution in the alloy and increasing the Young's modulus, and may be contained in the range of 0.10% or less.

[0031] Mo dissolves in austenite and has the effect of increasing the yield strength at high temperatures due to its solution strengthening action, but may be contained in the range of 0.10% or less.

[0032] Ti has an effect as an inoculant that generates solidification nuclei. Ti is also an element that improves hardness and tensile strength. Ti may be contained in a range of 0.10% or less.

[0033] Like Mo, W dissolves in austenite and has the effect of increasing the yield strength at high temperatures due to its solution strengthening effect, but may be contained in the range of 0.10% or less.

[0034] Nb dissolves in austenite and has the effect of increasing the yield strength at high temperatures due to its solution strengthening action, but may be contained in the range of 0.10% or less.

[0035] Next, a method for producing the low thermal expansion alloy of the present invention will be described.

[0036] The high purity of the low thermal expansion alloy of the present invention can be achieved by appropriately selecting raw materials and using a manufacturing method that employs vacuum melting or further remelting.

[0037] As raw materials for the low thermal expansion alloy of the present invention, it is preferable to use highly pure iron, electrolytic nickel, metallic cobalt, and pure aluminum.

[0038] The melting method used is vacuum induction melting (VIM), electric furnace melting (EF)-VAR (vacuum arc remelting), electroslag remelting (EF-ESR), VIM-VAR, or VIM-ESR. This allows the production of high-purity, low-thermal expansion alloys with few impurities.

[0039] After the ingot is melted, it is subjected to hot forging, and then to grain coarsening heat treatment.

[0040] Specifically, the grain-enlarging heat treatment is a process in which the alloy after hot forging is heated to 900 to 1200°C, held at that temperature for 2 to 50 hours, and then cooled. This process can coarsen the grain size and reduce the 0.2% yield strength.

[0041] The obtained alloy is subjected to solution treatment by heating to 700 to 1050°C and holding for 1.5 to 5.0 hours. This treatment makes it possible to reduce the thermal expansion coefficient over a wide range from cryogenic temperatures to room temperature. Preferably, the average thermal expansion coefficient at -100 to 50°C is less than 0.5×10 -6 / °C or less, more preferably 0.3×10 -6 / °C or less, more preferably 0.2×10 -6 / ℃ or less. EXAMPLES

[0042] The effects of the present invention will be described below using examples. Note that the following examples are merely one embodiment for illustrating the effects of the present invention, and the present invention is not limited to only the examples shown below.

[0043] As raw materials, pure iron, electrolytic iron, or Armco iron, electrolytic nickel, or high purity aluminum as comparative examples were used, and VIM-VAR or VIM-ESR, or EF or VIM as comparative examples, were used to produce 50 kg ingots having the chemical compositions shown in Table 1. The balance of the chemical composition was Fe.

[0044] [Table 1]

[0045] After the ingot was melted, it was subjected to hot forging, and then the alloy after hot forging was subjected to a grain coarsening heat treatment by heating to 900 to 1200°C, holding for 2 to 50 hours, and then cooling.

[0046] After the grain-coarsening heat treatment, the alloy was heated to 700 to 1050°C and held at that temperature for 1.5 to 5.0 hours to carry out a solution treatment process. The average thermal expansion coefficient of the alloy obtained after the solution heat treatment was measured at -100 to 50°C using a thermal expansion coefficient measuring device.

[0047] In addition, the 0.2% yield strength was measured in accordance with JIS Z2241:2011.

[0048] The results are shown in Table 2.

[0049] [Table 2]

[0050] It was confirmed that the present invention provides a low thermal expansion alloy having a low average thermal expansion coefficient in a wide range of -100 to 50°C and a low 0.2% proof stress.

[0051] Furthermore, even if the chemical components are within the range of the present invention, if the raw materials or manufacturing method are not appropriate, the crystal grain size does not become large and the desired 0.2% proof stress cannot be obtained.

Claims

1. In mass percent, C: 0.010% or less, Si: 0.10% or less, Mn: 0.15% or less, Ni: 34.0-37.0%, Co: 0.2 to 1.0%, and Al: 0.10% or less with the balance being Fe and impurities; The 0.2% yield strength is 200 MPa or less, Average thermal expansion coefficient between -100 and 50°C is 0.5 x 10 -6 / °C or less A low thermal expansion alloy.

2. 2. The low thermal expansion alloy according to claim 1, characterized in that the crystal grain size is 200 μm or more.

3. Instead of a part of the Fe, Cu: 0.30% or less, Cr: 0.10% or less, Mo: 0.10% or less, W: 0.10% or less, Ti: 0.10% or less, and Nb: 0.10% or less 3. The low thermal expansion alloy according to claim 1, further comprising at least one of the following:

Images