Low thermal expansion alloy

Abstract

The object of the present invention is to obtain a low thermal expansion alloy with excellent machinability. The low thermal expansion alloy of the present invention comprises, 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%, O:0.010% or less, and the balance of Fe and impurities, wherein [Mn], [S], [Ni], [Co], and [Si], which represent the content of Mn, S, Ni, Co, and Si, by mass%, respectively, satisfy [Mn] / [S]≥10.0, 32.0%≤[Ni]+0.4[Co]≤38.0%, and [Si]+[Mn]≤2.50%; and the average coefficient of thermal expansion at 25 to 100°C of the low thermal expansion alloy is 3.0×10-6 / °C or less.

Description

FIELD

[0001] The present invention relates to a low thermal expansion alloy, and more particularly, to a low thermal expansion alloy having excellent machinability.BACKGROUND

[0002] Invar alloys having high thermal stability are widely used as component materials for electronics, semiconductor-related equipment, laser working machines, and ultra-precision working equipment. However, conventional Invar alloy has low machinability, and therefore it is limited to a very narrow field of practical use.

[0003] Patent Literature 1 discloses a low thermal expansion alloy having excellent machinability in which S is used as a machinable element. The alloy comprises, by weight%, C:0.05% or less, Si:0.3%, Mn:0.45 to 1.2%, P:0.5% or less, S:0.015 to 0.035%, Ni:33.0 to 34.5%, Co:3.0 to 4.0%, and the balance of substantially Fe, [Mn] / [S] is 15 or more when [Mn] represents the weight% of Mn and [S] represents the weight% of S, and the alloy has an average coefficient of thermal expansion of 1.0×10 -6< / °C or less.

[0004] Patent Literature 2 discloses a low thermal expansion cast iron in which C is used as a machinable element, and a graphite structure is comprised in the austenite base iron. The alloy comprises, by weight%, the solid solution C: 0.09% or more and 0.43% or less, Si: less than 1.0%, Ni: 29% or more and 34% or less, Co: 4% or more and 8% or less, and the balance of Fe, and the coefficient of thermal expansion in the temperature range of 0 to 200°C is 4×10 -6< / °C or less.

[0005] Patent Literature 3 discloses a cast iron comprising C: 0.8 to 3.0%, Si: 1.0 to 3.0%, Mn: 0.4 to 2.0%, Ni: 30.0 to 33.0%, and Co: 4.0 to 6.0%, in which C is used as a machinable element.[CITATIONS LIST][PATENT LITERATURE]

[0006] [PLT 1] JP 2001-262277 A [PLT 2] JP H6-172919 A [PLT 3] JP S 58-210149 A SUMMARY[TECHNICAL PROBLEM]

[0007] An alloy used for a component of a precision equipment is required to have excellent machinability from the viewpoint of ease of working. There is room for further improvement in the machinability of alloys having a low coefficient of thermal expansion. In view of the above circumstances, the object of the present invention is to provide a low thermal expansion alloy excellent in machinability.[SOLUTION TO PROBLEM]

[0008] The inventors have intensively studied a method of obtaining a low thermal expansion alloy with further improved machinability. As a result, it was found that a low thermal expansion alloy having a small coefficient of thermal expansion and excellent machinability can be obtained by appropriately controlling the contents of Si, Mn, S, Ni, and Co.

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

[0010] A low thermal expansion alloy comprising, 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%, O: 0.010% or less, and balance of Fe and impurities, wherein [Mn], [S], [Ni], [Co], and [Si], which represent the content of Mn, S, Ni, Co, and Si, by mass%, respectively, satisfy [Mn] / [S]≥10.0, 32.0%≤[Ni]+0.4[Co]≤38.0%, and [Si]+[Mn]≤2.50%; and the average coefficient of thermal expansion at 25 to 100° of the low thermal expansion alloy is 3.0×10 -6< / °C or less.[ADVANTAGEOUS EFFECTS OF INVENTION]

[0011] According to the present invention, it is possible to obtain a low thermal expansion alloy excellent in machinability. Therefore, for example, it is possible to easily work the component parts of the precision equipment.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] [Fig. 1] Fig. 1 is a diagram for explaining an evaluation of a tool wear amount in examples. [Fig. 2] Fig. 2 is a diagram for explaining an evaluation of crushability of chips in examples. DESCRIPTION OF EMBODIMENTS

[0013] The present invention is described in detail below. Hereinafter, "%" regarding the chemical composition means "mass%" unless otherwise specified. First, the chemical composition of the low thermal expansion alloy of the present invention is described.(C: 0.050% or less)

[0014] C is an element which crystallizes as graphite in castings and improves machinability. However, C is also an element which increases the coefficient of thermal expansion. In the low thermal expansion alloy of the present invention, in order to suppress an increase of the coefficient of thermal expansion, the C content is 0.050% or less. It is preferably 0.040% or less, more preferably 0.030% or less, and still more preferably 0.020% or less.(Si:0.30 to 1.00%)

[0015] Si is an element which improves machinability by combining with S. Since the coefficient of thermal expansion increases as the content of Si increases, Si content is set to 0.30 to 1.00%, considering the balance between machinability and coefficient of thermal expansion. The lower limit of Si content may be 0.40% or 0.50%. The upper limit of Si content may be 0.90% or 0.80%.(Mn: 0.50 to 2.00%)

[0016] Mn is an element which forms a compound with S and improves machinability. Mn is also an element for suppressing cracking during casting and forging. Since the coefficient of thermal expansion increases as the content of Mn increases, Mn content is set to 0.50 to 2.00%, considering the balance between machinability and coefficient of thermal expansion. The lower limit of Mn content may be 0.60%, 0.70%, or 0.80%. The upper limit of Mn content may be 1.90%, 1.80%, or 1.70%.(S: 0.030 to 0.150%)

[0017] S is an element which forms a compound with Mn and improves machinability. When the amount of S is increased, the alloy is embrittled by segregation of S at the grain boundaries, and cracks tend to occur during casting and forging. Therefore, the S content is 0.030 set to 0.150%, considering the balance between machinability and embrittlement of the alloy. 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%.(Ni: 27.00 to 38.00%)

[0018] Ni is an element which decreases the coefficient of thermal expansion. The low thermal expansion alloys of the present invention have an average coefficient of thermal expansion of 3.0×10 -6< / °C or less at the range of 25 to 100°C. The coefficient of thermal expansion can be obtained mainly by setting the content of Ni and Co to an appropriate range. Even if the Ni content is too large or too small, the coefficient of thermal expansion is not sufficiently low. In order to sufficiently decrease the coefficient of thermal expansion, 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%.(Co:0 to 12.00%)

[0019] Co contributes to a decrease in the coefficient of thermal expansion by being combined with Ni. The Co content may be 0. In order to obtain the desired coefficient of thermal expansion, Co is set to 0 to 12.00%. The upper limit of Co content may be 11.00%, 10.00%, or 8.00%.(sol.Al:0.003 to 0.100%)

[0020] Sol.Al is an element which improves machinability. Since sol.Al is also an element which increases the coefficient of thermal expansion, considering the balance between machinability and the coefficient of thermal expansion, sol.Al is set to 0.003 to 0.100%. Sol.Al means an acid-soluble Al which is not a part of an oxide such as Al 2 O 3 and can be soluble in acid. The content of sol.Al is determined as an Al measured by subtracting the undissolved residue on the filter paper generated in the analytical process of Al. The lower limit of sol.Al content may be 0.010%, 0.020%, or 0.030%. The upper limit of sol.Al content may be 0.090%, 0.080%, or 0.070%.(O:0.010% or less)

[0021] O is an element contained as an impurity, and is not an essential element. The lower limit of the O content is 0. O combines with Al to form alumina. Alumina is hard and thus promotes tool wear. In addition, the formation of alumina reduces sol.Al content and lowers the machinability. Therefore, the O content is set to 0.010% or less. The O content is preferably 0.008% or less, more preferably 0.007% or less, and still more preferably 0.006% or less.

[0022] The balance of chemical composition consists of Fe and impurities. Here, the impurities mean elements other than the elements described above which, if contained, do not deteriorate machinability and coefficient of thermal expansion of the low thermal expansion alloys of the present invention, and which are mainly unavoidably contained from raw materials, manufacturing environment, etc., during the industrial manufacture of cast steel with the chemical compositions specified in the present invention. For example, P of 0.050% or less is included.

[0023] Further, in the low thermal expansion alloy of the present invention, [Mn], [S], [Ni], [Co], and [Si], which represent the content of Mn, S, Ni, Co, and Si, by mass%, respectively, satisfy the following formula. Mn / S ≥ 10.0

[0024] [Mn] / [S] is set to 10.0 or more in order for S to sufficiently form a compound with Mn to improve the machinability. [Mn] / [S] is preferably 15.0 or more, more preferably 20.0 or more, and still more preferably 30.0 or more. The small [Mn] / [S] means that the S content is relatively large with respect to Mn content, and since the amount of S segregating at the grain boundaries increases, cracking may occur easily during casting or forging. 32.0 % ≤ Ni + 0.4 Co ≤ 38.0 %

[0025] Both Ni and Co are elements which decrease the coefficient of thermal expansion. By optimizing the combination, the coefficient of thermal expansion can be further decreased, in particular, [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%. Si + Mn ≤ 2.50 %

[0026] Both Si and Mn are elements which improve machinability but increase the coefficient of thermal expansion. Therefore, the sum of the contents is set to 2.50% or less. [Si]+[Mn] is preferably 2.30% or less, more preferably 2.00% or less.(Average coefficient of thermal expansion at 25 to 100°C of 3.0×10 -6< / °C or less)

[0027] The low thermal expansion alloy of the present invention has an average coefficient of thermal expansion at 25 to 100°C of 3.0×10 -6< / °C or less. As described above, this coefficient of thermal expansion is obtained mainly by setting the content of Ni and Co to the appropriate range. The average coefficient of thermal expansion at 25 to 100°C may be 2.80×10 -6< / °C or less, 2.60×10 -6< / °C or less, 2.40×10 -6< / °C or less, 2.20×10 -6< / °C or less, 2.00×10 -6< / °C or less, or 1.80× 10 -6< / °C or less.

[0028] The coefficient of thermal expansion is measured at the range of -1 to 130°C using a thermal expansion measuring device at a heating rate of 3°C / min. As the thermal expansion measuring device, 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 is described.

[0030] The low thermal expansion alloy of the present invention is manufactured by a manufacturing method comprising the steps of: (1) melting and solidifying raw materials prepared so as to have a desired chemical composition to produce a cast product, (2) performing solution treatment to the cast product, and (3) performing stress relief annealing to the cast product which is solution treated.

[0031] The cast product obtained by the above manufacturing method may be forged to form a forged product. The forging is performed after manufacturing the cast alloy and before performing solution treatment. In other words, the low thermal expansion alloy of the present invention comprises the steps of: (1) melting and solidifying raw materials prepared so as to have a desired chemical composition to produce a cast product, (2) forging the cast product, (3) performing solution treatment to the obtained forged product, and (4) performing stress relief annealing to the forged product which is solution treated.

[0032] A mold used for manufacturing the cast product, an injection device used for injecting a molten alloy into the mold, and an injection method are not particularly limited, and known devices and methods can be used.

[0033] In the solution treatment, the cast product is heated to 750 to 850°C, held for 0.5 to 3hr, and then quenched. The cooling rate is preferably 10°C / min or more, and more preferably 100°C / min or more. By the solution treatment, the coefficient of thermal expansion can be decreased.

[0034] In the stress-relief annealing, the cast product is maintained at 300 to 350°C for 1 to 5hr, and then, the cast product is air cooled.

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

[0036] When forging the cast product, the cast product is heated to 1050 to 1250°C in a heating furnace, and then hot forged. In this case, the forging ratio is preferably 3 or more. Even if hot forged, the low thermal expansion characteristic of the low thermal expansion alloy of the present invention is substantially maintained. Further, it is also possible to be worked to a thickness of 0.1 to 10mm by hot rolling or cold rolling. Even in this case, the low thermal expansion characteristic is substantially maintained.

[0037] The alloy has the chemical composition of the present invention has a low thermal expansion alloy excellent in machinability without using a special manufacturing method, as described above.

[0038] By working the low thermal expansion alloy (including cast product and forged product) of the present invention, it is possible to obtain, for example, alloy parts used in electronics, semiconductor-related equipment, laser working machines, and ultra-precision working equipment. The low thermal expansion alloy of the present invention is suitable as a material of an alloy component since it is thermally stable and excellent in machinability.EXAMPLES

[0039] Using a high-frequency melting furnace, a cast product (Y-type test material, and ingot of 10kg) was fused so as to have the chemical composition shown in Table 1. For the examples described as "forged products" in Tables 1 and 2, the obtained ingot was heated to 1200°C in a heating furnace and then hot forged to obtain a forged product (40mm square bar). The forging ratio was 5 or more.

[0040] The obtained cast product and forged product were each subjected to solution annealing treatment by heating to 800°C and holding for 1.5hr, and after the solution treatment, were each subjected to a stress-annealing treatment by holding for 3hr at 300°C and air-cooling.

[0041] A test piece for measuring the coefficient of thermal expansion and a test piece for evaluating machinability were taken from each of the cast product and the forged product after the stress annealing treatment. [Table 1]No.Chemical composition (wt%)CSiMnSNiCosol.AlO[Mn] / [S][Ni]+0.4[Co][Si]+[Mn]1forged product0.0060.350.720.04336.3200.0350.00716.736.31.072forged product0.0080.521.150.10934.890.970.0470.00510.635.31.673forged product0.0160.751.480.11237.150.000.0650.00413.237.22.234cast product0.0050.420.780.04932.813.420.0410.00715.934.21.20forged product"""""""""""5forged product0.0070.711.350.08433.412.860.0400.00516.134.62.066cast product0.0100.591.710.09533.683.220.0690.00418.035.02.30forged product"""""""""""7forged product0.0110.440.910.05231.855.120.0320.00517.533.91.358cast product0.0040.461.460.11131.287.180.0190.00713.234.21.92forged product"""""""""""9forged product0.0070.731.680.08231.535.720.0340.00520.533.82.4110forged product0.0080.611.780.11430.088.520.0390.00515.633.52.3911cast product0.0090.390.670.03928.919.760.0320.00517.232.81.06forged product"""""""""""12forged product0.0070.541.150.05230.3411.230.0450.00522.134.81.6913forged product0.0120.651.240.08529.5810.050.0550.00414.633.61.8914forged product0.0040.821.160.10528.978.420.0230.00611.032.31.9815forged product0.0060.260.850.08232.125.250.0310.00510.434.21.1116forged product0.0101.201.610.07431.884.860.0390.00521.833.82.8117forged product0.0110.650.480.07731.925.080.0270.0066.234.01.1318forged product0.0080.812.140.06932.375.100.0260.00631.034.42.9519forged product0.0030.551.260.02531.635.530.0540.00450.433.81.8120forged product0.0020.880.730.16230.995.040.0390.0054.533.01.6121forged product0.0020.921.240.04926.415.250.0410.00525.328.52.1622forged product0.0020.540.980.08238.505.160.0260.00612.040.61.5223forged product0.0020.351.820.10228.2112.500.0330.00517.833.22.1724forged product0.0060.420.720.06532.055.010.0010.01411.134.11.1425forged product0.0040.590.670.12432.644.690.0470.0055.434.51.2626forged product0.0060.391.250.07128.324.970.0540.00417.630.31.6427forged product0.0050.861.780.05135.277.560.0580.00434.938.32.6428forged product0.0040.921.890.10931.427.160.0210.00617.334.32.8129cast product0.0080.120.240.00835.940.000.0330.00530.035.90.36forged product"""""""""""30forged product0.0110.090.200.00333.573.210.0280.00666.734.90.2931forged product0.0130.100.380.01733.643.100.0240.00622.434.90.4832cast product0.0060.080.160.00432.055.010.0390.00540.034.10.24forged product"""""""""""33cast product0.0100.130.420.01931.954.980.0290.00622.133.90.55forged product"""""""""""* Underline means outside the scope of the invention.

[0042] The coefficient of thermal expansion was measured by using a thermal expansion measuring device (TD5030S manufactured by BRUKER Co., Ltd.) from -1 to 130°C at a temperature increase rate of 3°C / min to obtain the average coefficient of thermal expansion from 25°C to 100°C.

[0043] Machinability and crushability of chips were evaluated by 13mm depth hole drilling the test piece for evaluating machinability (non-step working) with a drill (TiN coated Co-HSS) having a diameter of 2.6 mm and a water-soluble cutting fluid at a cutting speed of 45 m / min and a feed rate of 0.052 mm / min.

[0044] The machinability was evaluated according to tool wear amount and crushability of chips. The tool wear amount is explained with reference to Fig. 1. The tool wear amount was defined as a distance in the drill after drilling 100 holes from from the place where the base metal of the drill is visible (1) to the cutting edge (2), as shown in in Fig. 1, and the tool wear amount of 0.05 mm or less was judged to be good. In Table 2, "not borable" indicates that breakage or defect of the drill was confirmed, or abnormal noise was generated during the drilling, and it was determined that the drill cannot bore the test piece. Further, in the example described as "forging crack", since cracks occurred during forging, coefficient of thermal expansion, tool wear amount, and crushability of chips was not evaluated.

[0045] The crushability of the chips is explained with reference to Fig. 2. Crushability of the chips was evaluated as good as "G", if 80% or more of the chips are divided in the length of 1cm or less when the chips were observed. Fig. 2A is an example in which the crushability of chips is good, and Fig. 2B is an example in which the crushability is poor. Note that "P-elongated" in Table 2 means that the length exceeded 1cm in the chips of more than 20%.

[0046] Table 2 shows the results. It was judged that machinability was good when both tool wear amount and crushability of the chips were evaluated as good. [Table 2]No.Coefficient of thermal expansion (25 to 100°C) [×10 -6< / °C]Tool wear amount [mm]crushability of chips1forged product1.860.043GInv. Ex.2forged product2.130.024GInv. Ex.3forged product2.700.021GInv. Ex.4cast product1.150.035GInv. Ex.forged product1.040.038GInv. Ex.5forged product1.620.015GInv. Ex.6cast product2.960.021GInv. Ex.forged product2.730.016GInv. Ex.7forged product1.650.034GInv. Ex.8cast product1.720.017GInv. Ex.forged product1.410.019GInv. Ex.9forged product2.540.019GInv. Ex.10forged product2.530.016GInv. Ex.11cast product2.070.040GInv. Ex.forged product1.950.045GInv. Ex.12forged product2.610.033GInv. Ex.13forged product2.830.022GInv. Ex.14forged product2.880.013GInv. Ex.15forged product1.200.057GComp. Ex.16forged product3.170.017GComp. Ex.17forged product-forging crackforging crackComp. Ex.18forged product3.050.023GComp. Ex.19forged product1.60not borableP-elongatedComp. Ex.20forged product-forging crackforging crackComp. Ex.21forged product4.780.025GComp. Ex.22forged product3.630.016GComp. Ex.23forged product3.370.018GComp. Ex.24forged product1.100.072GComp. Ex.25forged product-forging crackforging crackComp. Ex.26forged product4.440.025GComp. Ex.27forged product3.560.024GComp. Ex.28forged product3.150.012GComp. Ex.29cast product1.46not borableP-elongatedComp. Ex.forged product1.41not borableP-elongatedComp. Ex.30forged product0.63not borableP-elongatedComp. Ex.31forged product0.78not borableP-elongatedComp. Ex.32cast product0.31not borableP-elongatedComp. Ex.forged product0.26not borableP-elongatedComp. Ex.33cast product0.67not borableP-elongatedComp. Ex.forged product0.52not borableP-elongatedComp. Ex.* Underline means outside the scope of the invention, or the desired properties were not obtained.

[0047] Nos. 1 to 14 are inventive examples, in which the coefficient of thermal expansion is small, the tool wear amount and the crushability of the chips is also good. Therefore, the low thermal expansion alloy of the present invention was confirmed to have good machinability in both cast product and forged product.

[0048] No. 15 had a small amount of Si, and as a result, had large tool wear amount.

[0049] No. 16 had a large amount of Si amount and a large [Si]+[Mn], and as a result, had a large coefficient of thermal expansion.

[0050] No. 17 had a small amount of Mn and a small [Mn] / [S], and as a result, forging cracks occurred.

[0051] No. 18 had a large amount of Mn and a large [Si]+[Mn], and as a result, had a large coefficient of thermal expansion.

[0052] No. 19 had a small amount of S, and as a result, had a large tool wear amount and poor crushability of chips.

[0053] No. 20 had a large amount of S and a small [Mn] / [S] was small, and as a result, forging cracks occurred.

[0054] No. 21 had a small amount of Ni, and as a result, had a large coefficient of thermal expansion.

[0055] No. 22 had a large amount of Ni, and as a result, had a large coefficient of thermal expansion.

[0056] No. 23 had a large amount of Co, and as a result, had a large coefficient of thermal expansion.

[0057] No. 24 had a small amount of sol.Al and a large amount of O, and as a result, had a larger tool wear amount.

[0058] No. 25 had a small [Mn] / [S], and as a result, forging cracks occurred.

[0059] No. 26 had a small [Ni]+0.4[Co], and as a result, had a large coefficient of thermal expansion.

[0060] No. 27 had a large [Ni]+0.4[Co] and a large [Si]+[Mn], and as a result, had a large coefficient of thermal expansion.

[0061] No. 28 had a large [Si]+[Mn], and as a result, had a large coefficient of thermal expansion.

[0062] Nos. 29 to 33 had a small amount of Si, Mn, and S, and as a result, had a large tool wear amount and poor crushability of the chips.REFERENCE SIGNS LIST

[0063] 1Places where base metal of drill is visible 2Cutting edge

Claims

1. A low thermal expansion alloy comprising, 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%, O: 0.010% or less, and balance of Fe and impurities, wherein [Mn], [S], [Ni], [Co], and [Si], which represent the content of Mn, S, Ni, Co, and Si, by mass%, respectively, satisfy Mn / S ≥ 10.0 , 32.0 % ≤ Ni + 0.4 Co ≤ 38.0 % , and Si + Mn ≤ 2.50 % ; and the average coefficient of thermal expansion at 25 to 100° of the low thermal expansion alloy is 3.0 x 10-6 / °C or less.

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