Low thermal expansion alloy

Abstract

The present invention provides a low thermal expansion alloy that exhibits minimal tool wear and a low coefficient of thermal expansion over a wide temperature range. [Solution] The low thermal expansion alloy of the present invention contains, by mass%, C: 0.050% or less, Si: 0.50~1.00%, Mn: 0.30~2.00%, P: 0.050% or less, S: 0.120% or less, Ni: 29.0~31.0%, Co: 14.0~17.0%, and the remainder: Fe and impurities, and the mass%, expressed as [Si], [Mn], and [S], satisfies 1.4 × [Si] + [Mn] ≤ 3.200 and [Mn] / [S] ≥ 15.0, and the average thermal expansion coefficient at 25~350℃ is 7.00 × 10⁻⁶. -6 It is below / ℃.

Description

[Technical Field]

[0001] This invention relates to low thermal expansion alloys, and more particularly to low thermal expansion alloys that result in less tool wear. [Background technology]

[0002] Thermally stable Invar alloys are widely used as component materials for electronics and semiconductor-related equipment, laser processing machines, and ultra-precision machining equipment. However, conventionally, Invar alloys have suffered from high tool wear, which has limited their practical application to a fairly narrow range of fields.

[0003] Patent Document 1 describes a means to solve this problem, using sulfur (S) as a free-cutting element, with a composition by weight percent of C: 0.05% or less, Si: 0.3% or less, Mn: 0.45-1.2%, P: 0.5% or less, S: 0.015-0.035%, Ni: 33.0-34.5%, Co: 3.0-4.0%, with the remainder being substantially iron, and characterized in that when [Mn] is weight percent of Mn and [S] is weight percent of S, the [Mn] / [S] ratio is 15 or more, resulting in an average thermal expansion coefficient at room temperature of 1.0 × 10⁻⁶. -6 This invention discloses a low thermal expansion alloy with excellent machinability, having a thermal expansion coefficient of less than / °C.

[0004] Patent Document 2 describes a cast iron having a graphite structure in an austenite iron matrix, using carbon as a free-cutting element, comprising, by weight %, 0.09% to 0.43% solid solution carbon, less than 1.0% silicon, 29% to 34% nickel, 4% to 8% cobalt, with the remainder being iron, and having a thermal expansion coefficient of 4 × 10 in the temperature range of 0 to 200°C. -6 The document discloses low thermal expansion cast iron with a temperature of less than / ℃.

[0005] Patent Document 3 discloses an Fe-Ni alloy in which the hot workability is improved by selecting the Mg% / S% ratio within a specific range. This alloy contains C: 0.020% or less, Si: 0.50% or less, Mn: 1.5% or less, Ni: 32.0~55.0%, Cr: 10.0% or less, and Al: 0.10% or less, with the remainder being Fe and impurities. Specifically, the Fe-Ni alloy contains Mg: 0.030% or less, S: 0.020% or less, and Mg% / S%: 0.30~4.0. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2001-262277 [Patent Document 2] Japanese Patent Application Publication No. 6-172919 [Patent Document 3] Japanese Patent Application Publication No. 57-155353 [Overview of the project] [Problems that the invention aims to solve]

[0007] Alloys used in components of precision equipment require low tool wear (tool wear amount) for ease of processing. There is still room for improvement in reducing tool wear of alloys with a low coefficient of thermal expansion over a wide temperature range. In view of the above circumstances, the present invention aims to provide a low thermal expansion alloy with a low coefficient of thermal expansion over a wide temperature range and low tool wear. [Means for solving the problem]

[0008] The inventors diligently investigated methods for obtaining low thermal expansion alloys that further reduce tool wear. As a result, they found that by appropriately controlling the content of Si, Mn, and S, a low thermal expansion alloy with a small coefficient of thermal expansion and low tool wear can be obtained.

[0009] The present invention has been made based on the above findings and includes the following aspects.

[0010] (1) By mass%, C: 0.050% or less, Si: 0.50 - 1.00%, Mn: 0.30 - 2.00%, P: 0.050% or less, S: 0.120% or less, Ni: 29.0 - 31.0%, Co: 14.0 - 17.0%, and the balance: Fe and impurities containing, where [Si], [Mn], and [S] representing the contents of Mn and S in mass% satisfy 1.4×[Si] + [Mn] ≤ 3.200 [Mn] / [S] ≥ 15.0 and the average coefficient of thermal expansion at 25 - 350°C is 7.00×10 -6 / °C or less is a low - thermal - expansion alloy.

[0011] (2) The low - thermal - expansion alloy according to (1) above, wherein the content of Mn is 0.30 - 0.80 mass% and the content of S is 0.005 - 0.030 mass% or less, and the average coefficient of thermal expansion at 25 - 350°C is 6.00×10 -6 / °C or less.

[0012] (3) The low - thermal - expansion alloy according to (1) above, wherein the content of Mn is 0.80 - 2.00 mass% and the content of S is 0.030 - 0.120%.

Advantages of the Invention

[0013] According to the present invention, a low - thermal - expansion alloy with a small tool wear amount and a small coefficient of thermal expansion in a wide temperature range can be obtained. For example, processing of components of precision instruments used at high temperatures can be easily performed.

Brief Description of the Drawings

[0014] [Figure 1]Figure 1 illustrates the evaluation of tool wear in the embodiment. [Figure 2] Figure 2 illustrates the evaluation of the chip crushing ability in the example. [Modes for carrying out the invention]

[0015] The present invention will be described in detail below. Hereafter, "%" in relation to chemical composition will represent "mass%" unless otherwise specified. First, the elements contained in the chemical composition of the low thermal expansion alloy of the present invention will be described.

[0016] (C: 0.050% or less) Carbon (C) is an element that crystallizes as graphite in castings, improving machinability, but it is also an element that increases the coefficient of thermal expansion. In the low thermal expansion alloy of the present invention, the C content is 0.050% or less in order to suppress the increase in the coefficient of thermal expansion. Carbon is not an essential element, and the C content may be 0%. The C content may be 0.045% or less, 0.040% or less, 0.035% or less, 0.030% or less, or 0.025% or less. The C content may be 0.001% or more, 0.002% or more, 0.003% or more, 0.005% or more, 0.007% or more, or 0.010% or more.

[0017] (Si: 0.50~1.00%) Si is an element that reduces tool wear, either on its own or in combination with S. As the Si content increases, the coefficient of thermal expansion increases. Therefore, considering the balance between tool wear and the coefficient of thermal expansion, the Si content should be between 0.50 and 1.00%. The Si content may be 0.52% or more, 0.55% or more, 0.58% or more, 0.60% or more, or 0.65% or more. The Si content may be 0.95% or less, 0.90% or less, 0.88% or less, 0.85% or less, 0.82% or less, or 0.80% or less.

[0018] (Mn: 0.30~2.00%) Mn is an element that forms compounds with S, improving machinability. It is also an element that suppresses cracking during casting and forging. As the Mn content increases, the coefficient of thermal expansion increases, so considering the balance between machinability and the coefficient of thermal expansion, the Mn content should be set at 0.30 to 2.00%.

[0019] To further reduce the coefficient of thermal expansion, the Mn content may be 0.30 to 0.80%. In this case, the Mn content may be 0.32% or more, 0.35% or more, 0.38% or more, 0.40% or more, or 0.45% or more. Alternatively, the Mn content may be 0.78% or less, 0.75% or less, 0.72% or less, 0.70% or less, or 0.65% or less.

[0020] When machinability is to be further enhanced and chip fracture properties are prioritized, the Mn content may be 0.80 to 2.00%. In this case, the Mn content may be 0.85% or more, 0.90% or more, 0.95% or more, 1.00% or more, 1.20% or more, or 1.40% or more. Alternatively, the Mn content may be 1.95% or less, 1.90% or less, 1.85% or less, 1.70% or less, 1.65% or less, or 1.60% or less.

[0021] (P:0.050% or less) P is an element that is contained as an impurity and does not need to be contained in the low thermal expansion alloy of the present invention; the P content may be 0%. Since a large amount of P can easily cause casting cracks, the P content should be 0.050% or less. The P content may be 0.040% or less, 0.035% or less, 0.030% or less, 0.025% or less, or 0.020% or less. Since excessively reducing the P content increases manufacturing costs, the P content may be 0.001% or more, 0.002% or more, 0.003% or more, or 0.005% or more.

[0022] (S:0.120% or less) S is an element that improves machinability by combining with Si and forming compounds with Mn. If the S content is too high, S segregates at grain boundaries, making the alloy brittle and prone to cracking during casting and forging. Therefore, considering the balance between machinability and alloy brittleness, the S content should be kept below 0.120%.

[0023] To further reduce the coefficient of thermal expansion, the S content may be 0.030% or less. In this case, the S content may be 0.025% or less, 0.020% or less, 0.015% or less, 0.012% or less, or 0.010% or less. The effect of reducing tool wear can be obtained with Si alone, so the inclusion of S is not essential, but to enhance the effect of reducing tool wear, it is preferable to have an S content of 0.001% or more. The S content may be 0.002% or more, 0.003% to 0.004% or more, 0.005% or more, 0.006% or more, or 0.008% or more.

[0024] When prioritizing improved machinability and chip fracture properties, the sulfur content may be 0.030-0.120%. In this case, the sulfur content may be 0.115% or less, 0.100% or less, 0.095% or less, 0.090% or less, or 0.080% or less. Alternatively, the sulfur content may be 0.035% or more, 0.040% or more, 0.045% or more, 0.050% or more, 0.060% or more, or 0.070% or more.

[0025] (Ni: 29.0-31.0%) Ni is an element that reduces the coefficient of thermal expansion. The low thermal expansion alloy of the present invention has an average coefficient of thermal expansion of 7.00 × 10⁻¹⁰ at 25 to 350°C. -6 / ℃ or lower, preferably 6.00 × 10 -6The thermal expansion coefficient is less than or equal to / °C. This coefficient of thermal expansion is mainly obtained by setting the Ni and Co content within an appropriate range. If the Ni content is too high or too low, the coefficient of thermal expansion will not be sufficiently low. Also, if the Ni content is too high, the machinability will decrease. To make the coefficient of thermal expansion sufficiently low, the Ni content should be 29.00 to 31.0%. The Ni content may be 29.2% or higher, 29.3% or higher, 29.4% or higher, or 29.5% or higher. The Ni content may be 30.9% or lower, 30.8% or lower, 30.7% or lower, 30.6% or lower, or 30.5% or lower.

[0026] (Co: 14.0~17.0%) Co, when combined with Ni, contributes to a decrease in the coefficient of thermal expansion. To obtain the desired coefficient of thermal expansion, the Co content should be in the range of 14.0 to 17.0%. The Co content may be 14.2% or more, 14.4% or more, 14.6% or more, 14.8% or more, or 15.0% or more. The Co content may be 16.8% or less, 16.6% or less, 16.4% or less, 16.2% or less, or 16.0% or less.

[0027] The remainder of the chemical composition consists of Fe and impurities. These impurities are primarily those that inevitably become mixed in from raw materials and the manufacturing environment during the industrial production of castings having the chemical composition defined in this invention. These impurities, other than those mentioned above, do not impair the machinability or thermal expansion coefficient of the low thermal expansion alloy of this invention. For example, 0.050% or less of O is included.

[0028] The low thermal expansion alloy of the present invention further satisfies the following formula when the content of Si, Mn, and S, expressed in mass%, is [Si], [Mn], and [S].

[0029] 1.4 × [Si] + [Mn] ≤ 3.200

[0030] Both Si and Mn are elements that improve machinability, but on the other hand, they are also elements that increase the coefficient of thermal expansion. In order to obtain the desired coefficient of thermal expansion, 1.4×[Si]+[Mn] is set to 3.200 or less. 1.4×[Si]+[Mn] may be 3.100 or less, 3.000 or less, 2.900 or less, 2.800 or less, 2.700 or less, or 2.500 or less. Since the minimum content of Si is 0.50% and the minimum content of Mn is 0.30%, 1.4×[Si]+[Mn] is 1.000 or more. 1.4×[Si]+[Mn] may be 1.050 or more, 1.100 or more, 1.150 or more, 1.200 or more, 1.300 or more, or 1.500 or more.

[0031] ([Mn] / [S]≧15.0) [Mn] / [S] is set to 15.0 or more so that S forms a compound sufficiently with Mn and reduces tool wear. [Mn] / [S] may be 16.0 or more, 17.0 or more, 18.0 or more, 19.0 or more, or 20.0 or more. A small [Mn] / [S] means that the content of S is relatively large with respect to the content of Mn, and the amount of S segregating at grain boundaries increases, so there is a possibility that cracks are likely to occur during casting and forging. Even if [Mn] / [S] is large, there is no problem and there is no upper limit, but [Mn] / [S] may be, for example, 100.0 or less, 90.0 or less, 80.0 or less, or 70.0 or less.

[0032] (The average coefficient of thermal expansion from 25 to 350 °C is 7.00×10 -6 / °C or less) The low thermal expansion alloy of the present invention has an average coefficient of thermal expansion from 25 to 300 °C of 7.00×10 -6 / °C or less, preferably 6.00×10 -6 / °C or less. As described above, this coefficient of thermal expansion is mainly obtained by setting the contents of Ni and Co within an appropriate range. When the content of Mn is 0.80 to 2.00% and the content of S is 0.030 to 0.120%, the average coefficient of thermal expansion from 25 to 350 °C is 6.​​​​​​-6 / ℃ or below, or 6.00 × 10 -6 It may be less than / ℃. The average coefficient of thermal expansion between 25 and 350℃ is 5.8 × 10 when the Mn content is 0.30 to 0.80% and the S content is 0.030% or less. -6 / ℃ or below, 5.5 × 10 -6 / ℃ or below, 5.2 × 10 -6 / ℃ or below, 5.0 × 10 -6 / ℃ or below, 4.8 × 10 -6 / ℃ or below, 4.5 × 10 -6 / ℃ or below, 4.2 × 10 -6 / or 4.0 × 10 -6 It may be below / ℃.

[0033] The coefficient of thermal expansion is measured using a thermal expansion measuring device in the range of 0 to 400°C at a heating rate of 3°C / min. The NETZSCH DIL402C can be used as the thermal expansion measuring device.

[0034] Next, an example of a manufacturing method for obtaining the low thermal expansion alloy of the present invention will be described.

[0035] The low thermal expansion alloy of the present invention is (1) A raw material adjusted to have the desired chemical composition is melted and solidified to produce a casting. (2) The obtained casting is subjected to solution treatment, (3) The casting that has undergone solution treatment is subjected to stress relief annealing. It is manufactured using a manufacturing method that includes a specific process.

[0036] The casting obtained by the above manufacturing method may be forged to produce a forged product. Forging is performed after the production of the cast alloy but before the solution treatment. That is, the low thermal expansion alloy of the present invention is (1) A raw material adjusted to have the desired chemical composition is melted and solidified to produce a casting. (2) The obtained casting is subjected to forging, (3) After forging, the forged product is subjected to solution treatment. (4) The forged product that has undergone solution treatment is subjected to stress relief annealing. It may be manufactured by a manufacturing method that includes a process.

[0037] The molds used in the manufacture of castings, the apparatus for injecting molten alloy into the molds, and the injection methods are not particularly limited; known apparatuses and methods may be used.

[0038] Solution treatment involves heating the casting to 750-850°C, holding it at that temperature for 0.5-3 hours, and then air-cooling it. Solution treatment can reduce the coefficient of thermal expansion.

[0039] Stress relief annealing involves holding the material at 300-600°C for 1-5 hours, followed by air cooling.

[0040] Solution treatment and stress relief annealing may be performed after forging instead of after casting.

[0041] When forging a casting, the casting is heated to 1050-1250°C in a heating furnace, and then hot forging is performed. A forging ratio of 3 or higher is preferable. Even after hot forging, the low thermal expansion properties of the low thermal expansion alloy of the present invention are largely maintained. Furthermore, it is possible to process the alloy to a thickness of 0.1-10 mm by hot rolling and cold rolling. In these cases as well, the low thermal expansion properties are largely maintained.

[0042] As described above, if an alloy having the chemical composition of the present invention is used, it is possible to obtain a low thermal expansion alloy with reduced tool wear without using a special manufacturing method.

[0043] By processing the low thermal expansion alloy of the present invention (including castings and forgings), alloy parts for use in electronics and semiconductor-related equipment, laser processing machines, and ultra-precision machining equipment can be obtained. The low thermal expansion alloy of the present invention is thermally stable and exhibits low tool wear, making it suitable as a material for alloy parts. [Examples]

[0044] Castings (Y-type test material and 10 kg ingot) were melted using a high-frequency induction melting furnace to achieve the chemical composition shown in Table 1. In Table 1, 1.4 × [Si] + [Mn] and [Mn] / [S] represent the mass %) of Si, Mn, and S, expressed in terms of [Si], [Mn], and [S], respectively. For the examples labeled "Forged Products" in Tables 1 and 2, the obtained ingots were heated to 1200°C in a heating furnace and then hot forged to produce forged products (40 mm square rods). The forging ratio was set to 5 or higher.

[0045] Each of the obtained castings and forgings was subjected to a solution treatment by heating to 800°C and holding for 1.5 hours, followed by a stress annealing treatment by holding at 300°C for 3 hours and then air-cooling.

[0046] Test specimens for measuring the coefficient of thermal expansion and for evaluating machinability (tool wear and chip fracture properties) were taken from both the castings and forgings after stress annealing.

[0047] [Table 1]

[0048] The coefficient of thermal expansion was measured using a thermal expansion measuring device (NETZSCH DIL402C) in the range of 0 to 400°C at a heating rate of 3°C / min, and the average coefficient of thermal expansion from 25°C to 350°C was determined.

[0049] Tool wear was evaluated by drilling a 2.6mm diameter drill (cobalt high-speed steel, TiN coated) with a water-soluble cutting fluid at a cutting speed of 45m / min, a feed rate of 0.013mm / rev, and a machining depth of 13mm (non-step machining).

[0050] Refer to Figure 1 to explain tool wear. For a drill after machining 200 holes, tool wear is defined as the distance from the visible part of the drill's base material (1) to the cutting edge (2), as shown in Figure 1. A tool wear of 0.05 mm or less was considered good. Note that "Drilling Impossible" in Table 2 indicates that drill breakage or damage was observed, or that abnormal noise occurred during drilling, resulting in a determination that drilling was impossible.

[0051] The chip-breaking properties were evaluated by drilling a test piece for machinability evaluation using a φ2.6 mm drill (cobalt high-speed steel, TiN coated) with a water-soluble cutting fluid at a cutting speed of 45 m / min and a feed rate of 0.052 mm / rev, to a machining depth of 13 mm (non-step machining).

[0052] Refer to Figure 2 to explain the chip fragmentation properties. Chip fragmentation properties were evaluated as good if 80% or more of the chips were broken into pieces less than 1 cm in length, and marked with a "○". Figure 2(a) shows an example of good chip fragmentation properties, and (b) shows an example of poor fragmentation properties. Note that "stretches" in Table 2 means that more than 20% of the chips were longer than 1 cm.

[0053] In the examples described as "forging cracks," the coefficient of thermal expansion, tool wear, and chip fracture properties were not evaluated because cracks occurred during forging.

[0054] The results are shown in Table 2. In this example, the average coefficient of thermal expansion at 25-350°C was 7.00 × 10⁻⁶. -6 If the temperature is below / ℃ and the tool wear is 0.05 mm or less, it is determined that the problem of the present invention has been solved.

[0055] [Table 2]

[0056] Comparative Example 1 had a low Si content, resulting in high tool wear and poor chip fracture properties.

[0057] Comparative Example 2 had a higher Si content, resulting in a larger coefficient of thermal expansion.

[0058] Comparative Example 3 had a low Mn content and a small [Mn] / [S] ratio, resulting in forging cracks.

[0059] Comparative Example 4 had a high Mn content, resulting in a larger coefficient of thermal expansion.

[0060] Comparative Example 5 had a higher proportion of 1.4 × [Si] + [Mn], resulting in a larger coefficient of thermal expansion.

[0061] Comparative Example 6 had a high sulfur content and a low [Mn] / [S] ratio, resulting in forging cracks.

[0062] Comparative Example 7 had a small [Mn] / [S] ratio, resulting in forging cracks.

[0063] Comparative Example 8 had a lower Ni content and a higher coefficient of thermal expansion.

[0064] Comparative Example 9 had a high Ni content, resulting in a larger coefficient of thermal expansion.

[0065] Comparative Example 10 had a low Co content and a high coefficient of thermal expansion.

[0066] Comparative Example 11 had a high Co content, resulting in a larger coefficient of thermal expansion.

[0067] Comparative Example 12 had low Si, Mn, and S content, resulting in increased tool wear.

[0068] On the other hand, in the present invention examples 1 to 22, the average thermal expansion coefficient at 25 to 350°C is 7.00 × 10⁻⁶. -6It was confirmed that the problem of the present invention was solved, with a temperature of 0.05 mm or less and tool wear of 0.05 mm or less. In particular, Invention Examples 1, 2, 4, 6, 7, 9, 10, 13, 14, 15, 16, 17, 18, 20, and 22 had a relatively high sulfur content, resulting in low tool wear and good chip crushing properties. Furthermore, Invention Examples 3, 5, 8, 11, 12, 19, and 21 had a relatively low sulfur content, resulting in inferior chip crushing properties, but the average thermal expansion coefficient at 25-350°C was 6.00 × 10⁻⁶. -6 We were able to reduce it even further, to below / ℃. [Explanation of Symbols]

[0069] 1. Where the drill bit is visible. 2 cutting edges

Claims

1. In mass percent, C: 0.050% or less, Si: 0.50-1.00%, Mn: 0.30-2.00%, P: 0.050% or less, S: 0.120% or less, Ni: 29.0 to 31.0%, Co: 14.0-17.0%, and Remainder: Fe and impurities It contains, The Mn and S content expressed in mass percent is [Si], [Mn], [S]. 1.4×[Si]+[Mn]≦3.200, [Mn] / [S]≧15.0 Satisfying the conditions, The average coefficient of thermal expansion at 25-350°C is 7.00 × 10⁻⁶. -6 / ℃ or below It is a low thermal expansion alloy.

2. The Mn content is 0.30 to 0.80 mass%, the S content is 0.030 mass% or less, and the average thermal expansion coefficient at 25 to 350°C is 6.00 × 10⁻⁶. -6 The low thermal expansion alloy according to claim 1, wherein the temperature is less than or equal to / °C.

3. The low thermal expansion alloy according to claim 1, wherein the Mn content is 0.80 to 2.00 mass%, and the S content is 0.030 to 0.120%.

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