Low thermal expansion alloy

Abstract

To provide a low thermal expansion alloy having a low thermal expansion coefficient in a wide range from the cryogenic temperature to the room temperature without using Co.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: 35.0-37.0%, Al: 0.10% or less with the balance being Fe and impurities. The index numbers of cleanliness defined by JIS G 0555 are: A and B series of 1.5 or less; and C, D and DS series of 1.0 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 discloses a CFRP alloy for use as a member of an ultra-precision device, including a CFRP mold, which contains 0.1 wt.% or less of C, 0.1 to 0.4 wt.% of Si, 0.15 to 0.4 wt.% of Mn, more than 2 to 4 wt.% of Ti, 1 wt.% or less of Al, 30.7 to 43.0 wt.% of Ni, and 14 wt.% or less of Co, and the contents of the Ni and Co satisfy the following formula (1), with the balance being Fe and unavoidable impurities, and which has a thermal expansion coefficient of 4×10 -6 / ℃ or less, and Young's modulus is 16100kgf / mm 2 As described above, the use of alloy steel having excellent thermal shape stability and rigidity is disclosed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-293413 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional low thermal expansion alloys, which have a small thermal expansion coefficient over a wide temperature range, contain Ni and Co. Co and its inorganic compounds are designated as specific chemical substances, and therefore require special care in handling at sites where steel containing Co is manufactured.

[0006] In view of the above circumstances, an object of the present invention is to provide a low thermal expansion alloy that does not use Co and has thermal expansion characteristics equivalent to those of an Fe-Ni-Co alloy. [Means for solving the problem]

[0007] The present inventors have conducted extensive research into a method for obtaining a low thermal expansion alloy having thermal expansion properties equivalent to those of an Fe-Ni-Co alloy without using Co. As a result, it has been found that low thermal expansion properties can be obtained by increasing the purity of an Fe-Ni alloy to obtain a highly clean alloy with few nonmetallic inclusions.

[0008] The present invention has been made based on the above findings, and the gist of the present invention is as follows.

[0009] (1) A low thermal expansion alloy containing, by mass%, C: 0.010% or less, Si: 0.100% or less, Mn: 0.15% or less, Ni: 35.00 to 37.00%, Al: 0.100% or less, with the balance being Fe and impurities, and characterized in that the cleanliness index number defined in JIS G 0555 is 1.5 or less for A and B types, and 1.0 or less for C, D and DS types.

[0010] (2) The low thermal expansion alloy according to (1) above, characterized in that it contains, in place of a portion of the Fe, one or more of the following, by mass%, Cu: 0.030% or less, Cr: 0.010% or less, Mo: 0.010% or less, W: 0.010% or less, Ti: 0.0100% or less, and Nb: 0.010% or less.

[0011] (3) The average thermal expansion coefficient from -100 to 50°C is 0.5 × 10 -6 / °C or less. Effect of the Invention

[0012] According to the present invention, it is possible to obtain a low thermal expansion alloy having thermal expansion characteristics equivalent to those of an Fe-Ni-Co alloy without using Co. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] 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.

[0014] 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 35.00 to 37.00% in order to sufficiently reduce the thermal expansion coefficient over a wide temperature range.

[0015] The low thermal expansion alloy of the present invention may contain C, Si, Mn, and Al in addition to Ni.

[0016] C dissolves in austenite and contributes to increasing strength, so it may be added 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 casting of the present invention, C is not an essential element, and the C content may be 0.

[0017] Silicon may be added as a deoxidizer. It can also improve the fluidity of the molten metal. If the amount of silicon exceeds 0.100%, the thermal expansion coefficient increases, so the amount of silicon is set to 0.100% or less, preferably 0.010% or less, and more preferably 0.005% or less. In the low thermal expansion casting of the present invention, silicon is not an essential element, and the content may be 0.

[0018] 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 casting of the present invention, Mn is not an essential element, and the content may be 0.

[0019] 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.

[0020] 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.

[0021] The low thermal expansion alloy of the present invention has a cleanliness index defined in JIS G 0555 of 1.5 or less for A and B types, and 1.0 or less for C, D and DS types. A, B, C, D and DS types respectively refer to the following particles defined in JIS G 0555.

[0022] Series A are sulfide-based inclusions, typically grey discrete grains with rounded edges, high ductility, and a wide range of aspect ratios (length / thickness).

[0023] The B series are alumina-based inclusions, which are numerous non-deformed, angular, deformation-aligned particles that are black or bluish in color and have a low aspect ratio (typically less than 3).

[0024] C type is a silicate-based inclusion that is generally a black or dark gray discrete particle with sharp edges, high ductility, and a wide range of aspect ratios (generally greater than 3).

[0025] The D series are granular oxide inclusions, which are non-deformed, angular or circular, black or bluish randomly distributed particles with a low aspect ratio (typically less than 3).

[0026] The DS system is a system of discrete particulate inclusions, consisting of single particles that are round or nearly round and have a diameter of 13 μm or more.

[0027] By setting the cleanliness index of each system within the above range, it is possible to obtain a low thermal expansion alloy having a low thermal expansion coefficient over a wide range, even without the inclusion of Co.

[0028] Furthermore, taking into consideration the effect on the thermal expansion coefficient of each system, it is preferable that ((cleanliness index of A system)+(cleanliness index of B system)×0.5+(cleanliness index of C system)+(cleanliness index of D system)+(cleanliness index of DS system)×0.5) / 5 is 1.0 or less.

[0029] 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: 0.030% or less, Cr: 0.010% or less, Mo: 0.010% or less, W: 0.010% or less, Ti: 0.0100% or less, and Nb: 0.010% or less, in order not to increase the thermal expansion coefficient.

[0030] Cu is an element that improves strength, and may be contained in the range of 0.030% or less.

[0031] 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 0.010% or less.

[0032] Mo dissolves in austenite and has the effect of increasing the yield strength at high temperatures due to its solution strengthening action, and may be contained in the range of 0.010% or less.

[0033] Ti has an effect as an inoculant for generating solidification nuclei. Ti is also an element that improves hardness and tensile strength. Ti may be contained in a range of 0.0100% or less.

[0034] Like Mo, W dissolves in austenite and has the effect of increasing the yield strength at high temperatures due to its solution strengthening effect, and may be contained in the range of 0.010% or less.

[0035] Nb dissolves in austenite and has the effect of increasing the yield strength at high temperatures due to its solution strengthening action, and may be contained in the range of 0.010% or less.

[0036] Next, a method for producing the low thermal expansion alloy of the present invention will be described.

[0037] 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.

[0038] As the raw material for the low thermal expansion alloy of the present invention, it is preferable to use high purity pure iron, electrolytic iron, electrolytic nickel, and high purity aluminum.

[0039] 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.

[0040] The obtained ingot is subjected to a diffusion treatment by heating to 1000-1300°C and holding for 10-50 hours before or during the hot forging process, and is then subjected to a solution treatment process by heating to 700-1050°C and holding for 1.5-5.0 hours. This treatment makes it possible to lower the thermal expansion coefficient in a wide range from cryogenic temperature to room temperature. This reduces the microsegregation of Ni, making it possible to further lower the thermal expansion coefficient in a wide range from cryogenic temperature to room temperature. Preferably, the average thermal expansion coefficient at -100-50°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

[0041] 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.

[0042] 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.

[0043] [Table 1]

[0044] After melting the ingots, they were subjected to diffusion treatment, hot forging, and solution heat treatment. The resulting alloys were subjected to "Test Method A" specified in JIS G 0555:2020 to determine the cleanliness index for each inclusion type.

[0045] The thermal expansion coefficient was determined as the average thermal expansion coefficient from -100 to 50°C using a thermal expansion measuring device.

[0046] The results are shown in Table 2.

[0047] [Table 2]

[0048] According to the present invention, it was confirmed that a low thermal expansion alloy having a low average thermal expansion coefficient in a wide range of -100 to 50°C can be obtained in an alloy not containing Co.

Claims

1. In mass percent, C: 0.010% or less, Si: 0.10% or less, Mn: 0.15% or less, Ni: 35.0 to 37.0%, Al: 0.10% or less with the balance being Fe and impurities; The cleanliness index number defined in JIS G 0555 is: A and B series: 1.5 or less, C series, D series and DS series: 1.0 or less and Average thermal expansion coefficient between -100 and 50°C is 0.5 x 10 -6 / °C or less A low thermal expansion alloy.

2. Instead of a part of the Fe, Cu: 0.03% or less, Cr: 0.01% or less, Mo: 0.01% or less, W: 0.01% or less, Ti: 0.01% or less, and Nb: 0.01% or less 2. The low thermal expansion alloy according to claim 1, further comprising at least one of the following:

Images