Low thermal expansion alloy

Abstract

The present invention addresses the problem of obtaining a low thermal expansion alloy having improved machinability. A low thermal expansion alloy according to the present invention contains, in terms of mass%, at most 0.050% of C, 0.30-1.00% of Si, 0.50-2.00% of Mn, 0.030-0.150% of S, 27.00-38.00% of Ni, 0-12.00% of Co, 0.003-0.100% of sol. Al, and at most 0.010% of O, with the remainder consisting of Fe and impurities, wherein [Mn], [S], [Ni], [Co], and [Si], which are the contents of Mn, S, Ni, Co, and Si expressed as mass%, satisfy [Mn] / [S]≥10.0, 32.0%≤[Ni]+0.4[Co]≤38.0%, and [Si]+[Mn]≤2.50%, and the average thermal expansion coefficient at 25-100ºC is at most 3.0×10-6 / ºC.

Description

[Technical Field]

[0001] The present invention relates to a low thermal expansion alloy, and more particularly to a low thermal expansion alloy with excellent machinability. [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. However, conventional Invar alloys have a problem in that their practical use has been limited to a very narrow range of fields due to their poor machinability.

[0003] Patent Document 1 discloses, as a means for solving this problem, a steel sheet containing S as a free-cutting element, and characterized in that the steel sheet is composed of, by weight %, 0.05% or less of C, 0.3% or less of Si, 0.45 to 1.2% of Mn, 0.5% or less of P, 0.015 to 0.035% of S, 33.0 to 34.5% of Ni, 3.0 to 4.0% of Co, and the balance is essentially iron, and that when [Mn] is the weight % of Mn and [S] is the weight % of S, the ratio [Mn] / [S] is 15 or more, and has an average thermal expansion coefficient at room temperature of 1.0 × 10 -6 The present invention discloses a low thermal expansion alloy with excellent machinability, having a thermal expansion coefficient of 1 / °C or less.

[0004] Patent Document 2 describes a cast iron that uses C as a free-cutting element and has a graphite structure in an austenite matrix iron, and that contains, by weight, 0.09% to 0.43% of solute carbon, less than 1.0% of silicon, 29% to 34% of nickel, and 4% to 8% of cobalt, with the balance being iron, and has a thermal expansion coefficient of 4×10 in the temperature range of 0 to 200°C. -6 / °C or less.

[0005] Patent Document 3 discloses a cast iron that uses C as a free-cutting element and is characterized by containing 0.8 to 3.0% carbon, 1.0 to 3.0% silicon, 0.4 to 2.0% manganese, 30.0 to 33.0% nickel, and 4.0 to 6.0% cobalt. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-262277 [Patent Document 2] Japanese Patent Application Publication No. 6-172919 [Patent Document 3] Japanese Patent Application Publication No. 58-210149 Summary of the Invention [Problem to be solved by the invention]

[0007] Alloys used for components of precision instruments are required to have excellent machinability in terms of ease of processing. There is room for further improvement in the machinability of alloys with low thermal expansion coefficients. In view of the above circumstances, an object of the present invention is to provide a low thermal expansion alloy with excellent machinability. [Means for solving the problem]

[0008] The present inventors have conducted extensive research into methods for obtaining low thermal expansion alloys with improved machinability, and have found that by appropriately controlling the contents of Si, Mn, S, Ni, and Co, in particular, it is possible to obtain low thermal expansion alloys with a small thermal expansion coefficient and excellent machinability.

[0009] The present invention has been made based on the above findings, and the gist of the present invention is as follows.

[0010] The alloy contains, by mass%, C: 0.050% or less, Si: 0.30 to 1.00%, Mn: 0.50 to 2.00%, S: 0.030 to 0.150%, Ni: 27.00 to 38.00%, Co: 0 to 12.00%, sol.Al: 0.003 to 0.100%, and O: 0.010% or less, with the balance being Fe and impurities. The contents of Mn, S, Ni, Co, and Si, expressed by mass%, [Mn], [S], [Ni], [Co], and [Si] satisfy the following: [Mn] / [S] ≥ 10.0, 32.0% ≤ [Ni] + 0.4[Co] ≤ 38.0%, and [Si] + [Mn] ≤ 2.50%. The alloy has an average thermal expansion coefficient of 3.0 × 10 at 25 to 100°C. -6 / °C or less. [Effects of the Invention]

[0011] According to the present invention, a low thermal expansion alloy with excellent machinability can be obtained, which makes it possible to easily process the alloy into components for precision equipment, for example. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram for explaining the evaluation of tool wear amount in the examples. [Figure 2] FIG. 2 is a diagram illustrating the evaluation of chip crushability in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below. Hereinafter, "%" regarding the composition of a component represents "% by mass" unless otherwise specified. First, the composition of the low thermal expansion alloy of the present invention will be described.

[0014] (C: 0.050% or less) C is an element that crystallizes as graphite in castings to improve machinability, but also increases the thermal expansion coefficient. In the low thermal expansion alloy of the present invention, the C content is set to 0.050% or less to prevent an increase in the thermal expansion coefficient. It is preferably 0.040% or less, more preferably 0.030% or less, and even more preferably 0.020% or less.

[0015] (Si: 0.30 to 1.00%) Si is an element that improves machinability when combined with S. As the Si content increases, the thermal expansion coefficient increases, so the Si content is set to 0.30 to 1.00%, taking into consideration the balance between machinability and the thermal expansion coefficient. The lower limit of the Si content may be 0.40% or 0.50%, and the upper limit of the Si content may be 0.90% or 0.80%.

[0016] (Mn: 0.50 to 2.00%) Mn is an element that forms a compound with S and improves machinability. It is also an element that suppresses cracking during casting and forging. Since an increase in the Mn content increases the thermal expansion coefficient, the Mn content is set to 0.50 to 2.00%, taking into consideration the balance between machinability and the thermal expansion coefficient. The lower limit of the Mn content may be 0.60%, 0.70%, or 0.80%. The upper limit of the Mn content may be 1.90%, 1.80%, or 1.70%.

[0017] (S:0.030~0.150%) S is an element that forms a compound with Mn and improves machinability. If the S content is too high, S segregates at grain boundaries, embrittling the alloy and making it more susceptible to cracking during casting and forging. Therefore, taking into consideration the balance between machinability and embrittlement of the alloy, the S content is set to 0.030 to 0.150%. The lower limit of the S content may be 0.040%, 0.050%, or 0.060%. The upper limit of the S content may be 0.140%, 0.130%, or 0.120%.

[0018] (Ni: 27.00-38.00%) Ni is an element that reduces the thermal expansion coefficient. The low thermal expansion alloy of the present invention has an average thermal expansion coefficient of 3.0×10 between 25 and 100°C. -6 / °C or less. This thermal expansion coefficient is mainly obtained by setting the Ni and Co contents within appropriate ranges. If the Ni content is too high or too low, the thermal expansion coefficient will not be sufficiently small. In order to sufficiently reduce the thermal expansion coefficient, the Ni content is set to 27.00 to 38.00%. The lower limit of the Ni content may be 28.00%, 29.00%, or 30.00%. The upper limit of the Ni content may be 37.00%, 36.00%, or 35.00%.

[0019] (Co: 0-12.00%) Co contributes to a decrease in the thermal expansion coefficient when combined with Ni. The Co content may be 0. To obtain a desired thermal expansion coefficient, the Co content is set to 0 to 12.00%. The upper limit of the Co content may be set to 11.00%, 10.00%, or 8.00%.

[0020] (sol.Al:0.003~0.100%) Sol. Al is an element that improves machinability. Because it also increases the thermal expansion coefficient, the sol. Al content is set to 0.003 to 0.100% to balance machinability and the thermal expansion coefficient. Here, sol. Al refers to acid-soluble Al that is soluble in acid and does not form oxides such as Al2O3. The sol. Al content is determined by subtracting the insoluble residue on the filter paper generated during the Al analysis process. The lower limit of the sol. Al content may be 0.010%, 0.020%, or 0.030%. The upper limit of the sol. Al content may be 0.090%, 0.080%, or 0.070%.

[0021] (O: 0.010% or less) O is an element contained as an impurity, not an essential element, and the lower limit is 0. When O combines with Al, it forms alumina. Alumina is hard and promotes tool wear. Furthermore, the formation of alumina reduces the amount of sol. Al, which reduces machinability. Therefore, the O content is set to 0.010% or less. Preferably, it is 0.008% or less, more preferably 0.007% or less, and even more preferably 0.006% or less.

[0022] The remainder of the composition is Fe and impurities. The term "impurities" as used herein refers to elements that are inevitably mixed in from raw materials or the manufacturing environment during the industrial production of castings having the composition specified in the present invention, and are elements other than those mentioned above that, even if mixed in, do not impair the machinability or thermal expansion coefficient of the low thermal expansion alloy of the present invention. For example, 0.050% or less of P is an example.

[0023] In the low thermal expansion alloy of the present invention, the contents of Mn, S, Ni, Co, and Si, expressed as mass%, [Mn], [S], [Ni], [Co], and [Si] further satisfy the following formula:

[0024] ([Mn] / [S]≧10.0) The ratio [Mn] / [S] is set to 10.0 or more so that S can sufficiently form compounds with Mn and improve machinability. It is preferably 15.0 or more, more preferably 20.0 or more, and even more preferably 30.0 or more. A small ratio [Mn] / [S] means that the amount of S is relatively large compared to the amount of Mn, and the amount of S segregating to grain boundaries increases, which may make cracks more likely to occur during casting and forging.

[0025] (32.0%≦[Ni]+0.4[Co]≦38.0%) Both Ni and Co are elements that reduce the thermal expansion coefficient, and by optimizing their combination, the thermal expansion coefficient can be further reduced, so [Ni] + 0.4[Co] is set to 32.0 to 38.0%. The lower limit of [Ni] + 0.4[Co] is preferably 32.5%, more preferably 33.0%. The upper limit of [Ni] + 0.4[Co] is preferably 37.0%, more preferably 36.0%, and even more preferably 35.0%.

[0026] ([Si] + [Mn] ≦ 2.50%) Both Si and Mn are elements that improve machinability, but they also increase the thermal expansion coefficient, so the total content is set to 2.50% or less, preferably 2.30% or less, and more preferably 2.00% or less.

[0027] (Average thermal expansion coefficient between 25 and 100°C is 3.0 × 10-6 / ℃ or less) The low thermal expansion alloy of the present invention has an average thermal expansion coefficient of 3.0 × 10 -6 / °C or less. As mentioned above, this thermal expansion coefficient can be obtained mainly by setting the contents of Ni and Co within appropriate ranges. The average thermal expansion coefficient from 25 to 100°C is 2.80 × 10 -6 / ℃ or less, 2.60×10 -6 / ℃ or less, 2.40×10 -6 / ℃ or less, 2.20×10 -6 / ℃ or less, 2.00×10 -6 / ℃ or less, 1.80×10 -6 / °C or less.

[0028] The thermal expansion coefficient is measured using a thermal expansion measuring device at a temperature rise rate of 3° C. / min in the range of −1 to 130° C. As the thermal expansion measuring device, a TD5030S manufactured by BRUKER can be used.

[0029] Next, an example of a manufacturing method for obtaining the low thermal expansion alloy of the present invention will be described.

[0030] The low thermal expansion alloy of the present invention is (1) A raw material adjusted to have a desired composition is melted and solidified to produce a casting. (2) The resulting casting is subjected to a solution treatment. (3) Stress relief annealing is performed on the castings that have been solution treated. It is manufactured by a manufacturing method including the steps of:

[0031] The casting obtained by the above manufacturing method may be forged to obtain a forged product. Forging is performed after the casting alloy is manufactured and before the solution treatment. That is, the low thermal expansion alloy of the present invention is (1) A raw material adjusted to have a desired composition is melted and solidified to produce a casting. (2) Forging the resulting casting. (3) After forging, the forged product is subjected to solution treatment. (4) Stress relief annealing is performed on the forged product that has undergone solution treatment. The semiconductor device may be manufactured by a manufacturing method including the steps of:

[0032] There are no particular limitations on the mold used to produce the casting, or the device and method for pouring the molten alloy into the mold, and any known device and method may be used.

[0033] The solution treatment involves heating the casting to 750 to 850°C, holding it for 0.5 to 3 hours, and then rapidly cooling it. The cooling rate is preferably 10°C / min or more, and more preferably 100°C / min or more. The solution treatment can reduce the thermal expansion coefficient.

[0034] Stress relief annealing is performed by holding the material at 300 to 350°C for 1 to 5 hours, followed by air cooling.

[0035] The solution treatment and stress relief annealing may be carried out after forging instead of after casting.

[0036] When forging a cast product, the cast product is heated to 1050 to 1250°C in a heating furnace and then hot forged. The forging ratio at this time is preferably 3 or more. Even when hot forging is performed, the low thermal expansion properties of the low thermal expansion alloy of the present invention are almost maintained. It is also possible to process the alloy to a thickness of 0.1 to 10 mm by hot rolling and cold rolling. Even in this case, the low thermal expansion properties are almost maintained.

[0037] As described above, an alloy having the component composition of the present invention can be obtained as a low thermal expansion alloy with excellent machinability without using a special manufacturing method.

[0038] By processing the low thermal expansion alloy of the present invention (including cast products and forged products), alloy parts for use in, for example, electronics and semiconductor-related equipment, laser processing machines, and ultra-precision processing equipment can be obtained. The low thermal expansion alloy of the present invention is thermally stable and has excellent machinability, making it suitable as a material for alloy parts. [Example]

[0039] Using a high-frequency melting furnace, cast products (Y-shaped test materials and 10 kg ingots) were melted to have the chemical compositions shown in Table 1. For the examples listed as "forged products" in Tables 1 and 2, the resulting ingots were heated to 1200°C in a heating furnace and then hot forged to form forged products (40 mm square bars). The forging ratio was set to 5 or more.

[0040] The resulting cast and forged products were each subjected to solution treatment by heating to 800°C and holding for 1.5 hours, and after the solution treatment, stress annealing treatment was performed by holding at 300°C for 3 hours and air cooling.

[0041] Test pieces for measuring the thermal expansion coefficient and test pieces for evaluating machinability were taken from each of the cast and forged products after stress annealing treatment.

[0042] [Table 1]

[0043] The thermal expansion coefficient was measured using a thermal expansion measuring device (TD5030S manufactured by BRUKER) in the range of -1 to 130°C at a temperature increase rate of 3°C / min, and the average thermal expansion coefficient from 25°C to 100°C was determined.

[0044] Machinability and chip crushability were evaluated by drilling the test pieces for machinability evaluation to a depth of 13 mm (non-step drilling) using a drill diameter of φ2.6 mm (cobalt high speed steel, TiN coating) and a water-soluble cutting fluid at a cutting speed of 45 m / min and a feed rate of 0.052 mm / min.

[0045] Machinability was evaluated based on tool wear and chip friability. Referring to Figure 1, tool wear is described. Regarding tool wear, the distance from the visible point of the drill base material (1) to the cutting edge (2) was measured for a drill after drilling 100 holes, as shown in Figure 1. A tool wear of 0.05 mm or less was considered to be good. In Table 2, "Drilling Unavailable" indicates drill breakage or chipping, or abnormal noise during drilling, making it unsuitable for drilling. In addition, for examples marked with "Forging Crack," cracks occurred during forging, so evaluations of the thermal expansion coefficient, tool wear, and chip friability were not performed.

[0046] The chip friability will be explained with reference to Figure 2. The chip friability was evaluated as good and given a "○" if 80% or more of the chips were observed and broken into pieces with a length of 1 cm or less. Figure 2 (a) shows an example of good chip friability, and (b) shows an example of poor chip friability. In Table 2, "× elongation" means that more than 20% of the chips were longer than 1 cm.

[0047] The results are shown in Table 2. Tools that were evaluated as having good tool wear and chip breakability were judged to have good machinability.

[0048] [Table 2]

[0049] Nos. 1 to 14 are examples of the present invention, and have a small thermal expansion coefficient, good tool wear, and good chip crushability. It was confirmed that the low thermal expansion alloy of the present invention has good machinability for both cast and forged products.

[0050] No. 15 had a small amount of Si, resulting in a large amount of tool wear.

[0051] No. 16 had a large Si content, a large [Si]+[Mn] ratio, and a large thermal expansion coefficient.

[0052] No. 17 had a small amount of Mn and a small [Mn] / [S] ratio, which resulted in forging cracks.

[0053] No. 18 had a large Mn content, a large [Si]+[Mn] ratio, and a large thermal expansion coefficient.

[0054] No. 19 had a small amount of S, which resulted in large tool wear and poor chip breakability.

[0055] No. 20 had a large amount of S and a small [Mn] / [S] ratio, which resulted in forging cracks.

[0056] No. 21 had a small amount of Ni and a large thermal expansion coefficient.

[0057] No. 22 had a large Ni content and a large thermal expansion coefficient.

[0058] No. 23 had a large Co content and a large thermal expansion coefficient.

[0059] No. 24 had a small amount of sol. Al and a large amount of O, resulting in a large amount of tool wear.

[0060] No. 25 had a small [Mn] / [S] ratio and forging cracks occurred.

[0061] No. 26 had a small [Ni]+0.4[Co] and a large thermal expansion coefficient.

[0062] No. 27 had a large [Ni]+0.4[Co] and also a large [Si]+[Mn], resulting in a large thermal expansion coefficient.

[0063] No. 28 had a large [Si] + [Mn] and a large thermal expansion coefficient.

[0064] Nos. 29 to 33 had small amounts of Si, Mn, and S, and therefore had large amounts of tool wear and poor chip breakability. [Explanation of symbols]

[0065] 1 Where the drill base material is visible 2 cutting edges

Claims

[Claim 1] In mass%, C: 0.050% or less, Si: 0.30-1.00%, Mn: 0.50-2.00%, S: 0.030-0.150%, Ni: 27.00-38.00%, Co: 0-12.00%, sol. Al: 0.003 to 0.100%, O: 0.010% or less and the balance being Fe and impurities, The contents of Mn, S, Ni, Co, and Si expressed in mass% are [Mn], [S], [Ni], [Co], and [Si], [Mn] / [S]≧10.0, 32.0%≦[Ni]+0.4[Co]≦38.0%, [Si]+[Mn]≦2.50% Fulfilling Average thermal expansion coefficient between 25 and 100°C is 3.0 x 10 -6 / ℃ or less A low thermal expansion alloy.

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