JP7776181B2 - Low thermal expansion alloy - Google Patents

Description

The present invention relates to a low thermal expansion alloy, and in particular to a low thermal expansion alloy with excellent machinability.

Thermal stable Invar alloys are widely used as a component material for electronics and semiconductor-related equipment, laser processing machines, and ultra-precision machining equipment. However, conventional Invar alloys have poor machinability, which has limited their practical use to a fairly narrow range of fields.

As a means for solving this problem, Patent Document 1 discloses an alloy with excellent machinability and a low thermal expansion coefficient at room temperature of 1.0 x 10-6/°C or less, which uses S as a free-cutting element and is characterized by the following weight percentages: C: 0.05% or less, Si: 0.3% or less, 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 being essentially iron, and having an average thermal expansion coefficient at room temperature of 1.0 x ^10-6 /°C or less, where [Mn] is the weight percentage of Mn and [S] is the weight percentage of S.

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

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

Japanese Patent Application Laid-Open No. 2001-262277 Japanese Patent Application Publication No. 6-172919 Japanese Unexamined Patent Publication No. 58-210149

Alloys used in components of precision equipment require excellent machinability in order to be easily processed. However, there is room for further improvement in the machinability of alloys with low thermal expansion coefficients. In light of the above, the objective of the present invention is to provide a low thermal expansion alloy with excellent machinability.

The inventors have conducted extensive research into methods for obtaining low-thermal expansion alloys with improved machinability. As a result, they have discovered that by appropriately controlling the content 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.

The present invention was made based on the above findings, and its gist is as follows:

In 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. A low thermal expansion alloy characterized by containing Al: 0.003 to 0.100%, O: 0.010% or less, the balance being Fe and impurities, and the contents of Mn, S, Ni, Co, and Si expressed in mass % as [Mn], [S], [Ni], [Co], and [Si] satisfying the following conditions: [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 to 100°C is 3.0× ^10-6 /°C or less.

The present invention provides a low thermal expansion alloy with excellent machinability, making it easy to process into components for precision equipment, for example.

FIG. 1 is a diagram for explaining the evaluation of tool wear in the examples. FIG. 2 is a diagram illustrating the evaluation of chip crushability in the examples.

The present invention will be described in detail below. Hereinafter, "%" in relation to the component composition will represent "mass %" unless otherwise specified. First, the component composition of the low thermal expansion alloy of the present invention will be described.

(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 suppress the increase in the thermal expansion coefficient. Preferably, it is 0.040% or less, more preferably 0.030% or less, and even more preferably 0.020% or less.

(Si: 0.30-1.00%)
Si is an element that improves machinability by combining with S. Since the thermal expansion coefficient increases as the Si content increases, 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%. The upper limit of the Si content may be 0.90% or 0.80%.

(Mn: 0.50-2.00%)
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% in consideration of 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%.

(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%.

(Ni: 27.00-38.00%)
Ni is an element that lowers the thermal expansion coefficient. The low thermal expansion alloy of the present invention has an average thermal expansion coefficient of 3.0 × 10 ^-6 /°C or less at 25 to 100°C. 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 low. 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%.

(Co: 0-12.00%)
Co contributes to a decrease in the thermal expansion coefficient in combination with Ni. The Co content may be 0. To obtain a desired thermal expansion coefficient, the Co content ranges from 0 to 12.00%. The upper limit of the Co content may be 11.00%, 10.00%, or 8.00%.

(sol. Al: 0.003 to 0.100%)
Sol. Al is an element that improves machinability. Since it also increases the thermal expansion coefficient, the sol. Al content is set to 0.003 to 0.100% in consideration of the balance between 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%.

(O: 0.010% or less)
O is an element contained as an impurity, not an essential element, and the lower limit is 0. O forms alumina when combined with Al. 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.

The remainder of the composition is Fe and impurities. The term "impurities" refers primarily 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 this invention. These elements 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 this invention. For example, 0.050% or less of P is an example.

The low thermal expansion alloy of the present invention further has the following formula: [Mn], [S], [Ni], [Co], [Si], where [Mn], [S], [Ni], [Co], and [Si] are the contents of Mn, S, Ni, Co, and Si expressed in mass %.

([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.

(32.0%≦[Ni]+0.4[Co]≦38.0%)
Both Ni and Co are elements that reduce the thermal expansion coefficient, and optimizing their combination can further reduce the thermal expansion coefficient, 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%.

([Si]+[Mn]≦2.50%)
Both Si and Mn are elements that improve machinability, but 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.

(Average thermal expansion coefficient between 25 and 100°C is 3.0 x ^10-6 /°C 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 from 25 to 100°C. As described above, this thermal expansion coefficient is obtained mainly by setting the Ni and Co contents within appropriate ranges. The average thermal expansion coefficient from 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.

The thermal expansion coefficient is measured using a thermal expansion measuring device in the range of -1 to 130°C at a heating rate of 3°C/min. A BRUKER TD5030S thermal expansion measuring device can be used.

Next, we will explain one example of a manufacturing method for obtaining the low thermal expansion alloy of the present invention.

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) It is manufactured by a manufacturing method including a step of subjecting a casting that has been subjected to solution treatment to stress relief annealing.

The casting obtained by the above manufacturing method may be forged to produce 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 can be produced by: (1) melting and solidifying raw materials adjusted to have a desired composition, and producing a casting;
(2) Forging the obtained casting;
(3) The forged product is subjected to a solution treatment,
(4) The steel sheet may be manufactured by a manufacturing method including a step of subjecting a forged product that has been subjected to a solution treatment to stress relief annealing.

There are no particular restrictions on the mold used to produce the casting, the equipment used to inject the molten alloy into the mold, or the method of injecting the alloy, and any known equipment or method may be used.

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

Stress relief annealing involves holding the material at 300-350°C for 1-5 hours, followed by air cooling.

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

When forging a casting, the casting is heated to 1050-1250°C in a heating furnace and then hot forged. A forging ratio of 3 or more is preferable. Even when hot forging is performed, the low thermal expansion properties of the low thermal expansion alloy of the present invention are largely maintained. It is also possible to process the alloy to a thickness of 0.1-10 mm by hot rolling and cold rolling. Even in this case, the low thermal expansion properties are largely maintained.

As mentioned above, an alloy having the component composition of the present invention can be used to obtain a low thermal expansion alloy with excellent machinability without using any special manufacturing methods.

By processing the low thermal expansion alloy of the present invention (including cast 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.

Using a high-frequency melting furnace, cast products (Y-type test material and 10 kg ingots) were melted to have the chemical composition shown in Table 1. For the examples labeled "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.

The resulting cast and forged products were each subjected to solution treatment by heating to 800°C and holding for 1.5 hours.After solution treatment, they were subjected to stress annealing by holding at 300°C for 3 hours and then air-cooling.

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

The thermal expansion coefficient was measured using a thermal expansion measuring device (BRUKER TD5030S) in the range of -1 to 130°C at a heating rate of 3°C/min, and the average thermal expansion coefficient from 25°C to 100°C was calculated.

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 2.6 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.

Machinability was evaluated based on tool wear and chip friability. Referring to Figure 1, tool wear is explained. 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. Tool wear of 0.05 mm or less was considered to be good. Note that "Drilling Unavailable" in Table 2 indicates drilling unavailability due to confirmed breakage or chipping of the drill or the generation of abnormal noise during drilling. Furthermore, in examples marked with "Forging Crack," cracks occurred during forging, so evaluation of the thermal expansion coefficient, tool wear, and chip friability were not performed.

Referring to Figure 2, chip friability will be explained. Chip friability was evaluated as good if 80% or more of the chips were observed and broken into pieces with a length of 1 cm or less, and given a "○" rating. Figure 2 (a) shows an example of good chip friability, while (b) shows an example of poor chip friability. Note that "x elongation" in Table 2 means that more than 20% of the chips exceeded 1 cm in length.

The results are shown in Table 2. Tools with good evaluations of both tool wear and chip friability were judged to have good machinability.

Nos. 1 to 14 are examples of the invention, and have a low thermal expansion coefficient, good tool wear, and good chip friability. It was confirmed that the low thermal expansion alloys of the present invention have good machinability for both cast and forged products.

No. 15 had a low Si content, resulting in increased tool wear.

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

No. 17 had a low Mn content and a low [Mn]/[S] ratio, resulting in forging cracks.

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

No. 19 had a low S content, resulting in high tool wear and poor chip crushability.

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

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

No. 22 had a high Ni content and a high thermal expansion coefficient.

No. 23 had a high Co content and a high thermal expansion coefficient.

No. 24 had a low amount of sol. Al and a high amount of O, resulting in increased tool wear.

No. 25 had a small [Mn]/[S] ratio, resulting in forging cracks.

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

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

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

Nos. 29 to 33 had low amounts of Si, Mn, and S, resulting in high tool wear and poor chip crushability.

1. The drill base material is visible. 2. Cutting edge

Claims (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, 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
A low thermal expansion alloy characterized in that the average thermal expansion coefficient at 25 to 100°C is 3.0 x 10 ^-6 /°C or less.