JP7246684B2 - Low thermal expansion alloy - Google Patents

Description

The present invention relates to low thermal expansion alloys with high Young's modulus.

Thermally stable Invar alloys are widely used as parts materials for electronics, semiconductor-related equipment, laser processing machines, and ultra-precision processing equipment. However, the conventional Invar alloy has a problem that its Young's modulus is as small as about one-half that of general steel. Therefore, it was necessary to implement a high-rigidity design, such as increasing the thickness of the target parts.

Patent Document 1 describes a mold made of a low thermal expansion Co-based alloy for optical glass lens press molding that is excellent in glass corrosion resistance, and has a high elastic modulus and a linear thermal expansion coefficient of 2 to 8×10 ⁻⁶ /K. It discloses alloys with The alloy desirably has a single crystal structure with the [111] crystal orientation oriented in the pressing axis of the mold.

Patent Document 2 describes a low thermal expansion Co-based alloy that exhibits excellent low thermal expansion characteristics in a cryogenic region below -50°C, which is equivalent to that in the vicinity of room temperature.

JP-A-2003-81648 JP 2009-227180 A

The alloy disclosed in Patent Document 1 has a relatively low thermal expansion coefficient of 2 to 8×10 ⁻⁶ /K, but an even lower thermal expansion coefficient is required for use as a component material for ultra-precision processing equipment. is required. Moreover, since the alloy disclosed in Patent Document 1 is a single crystal, it has the disadvantage of taking a long time to manufacture.

The alloy disclosed in Patent Document 2 exhibits excellent thermal expansion characteristics in a cryogenic region below -50 ° C., but the structure becomes unstable due to the three-phase structure, and martensite at -150 ° C. or lower. Transformation is initiated and thermal expansion properties are lost, limiting the temperature environment that can be used. For example, there are problems such as extremely cold regions, the lunar surface, and the extremely low operating temperature of precision instruments such as radio telescopes in recent years.

The present invention solves the above problems and provides a low thermal expansion alloy that can be produced by ordinary casting, has a high Young's modulus, a low coefficient of thermal expansion, and has a stable structure even at low temperatures, and a method for producing the same. The task is to provide

The present inventors have earnestly investigated a method for obtaining a low thermal expansion alloy that has both a high Young's modulus and a low thermal expansion coefficient and has a stable structure even at low temperatures. As a result, it was found that by optimizing the contents of Ni, Co, and Mn in particular, it is possible to obtain a low thermal expansion alloy that has both a high Young's modulus and a low thermal expansion coefficient, and is stable even at low temperatures.

Even in ordinary low thermal expansion alloys, the Young's modulus and thermal expansion coefficient can be adjusted to some extent by adjusting the composition. However, Young's modulus and coefficient of thermal expansion are almost in a trade-off relationship. That is, the higher the Young's modulus is, the higher the coefficient of thermal expansion is. Conventional Fe--Ni or Fe--Ni--Co alloys have limitations in increasing the Young's modulus.

The inventors of the present invention have found that in low thermal expansion alloys, optimizing the composition of the Fe--Co--Cr alloy improves the Young's modulus even with a small thermal expansion coefficient. Furthermore, since austenite becomes a stable structure even at temperatures as low as −196° C. or lower, martensitic transformation progresses even in extremely cold regions and extremely low temperature environments, and low thermal expansion characteristics are not lost. Found it.

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

(1) In mass%, C: 0.04 to 0.20%, Si: 0.25% or less, Mn: 0.15 to 0.50%, Cr: 8.50 to 10.0%, Ni: 0 to 5.00%, Co: 43.0 to 56.0%, S: 0 to 0.050%, and Se: 0 to 0.050%, the balance being Fe and unavoidable impurities, The contents of Ni, Co, Mn, and C [Ni], [Co], [Mn], and [C] are 55.5 ≤ 2.2 [Ni] + [Co] + [Mn] + 8.2 [C] A low thermal expansion alloy which satisfies ≦57.0 and has an austenite single phase structure.

(2) The method for producing a low thermal expansion alloy according to (1), comprising C: 0.04 to 0.20%, Si: 0.25% or less, Mn: 0.15 to 0.50%, Cr: 8.50-10.0%, Ni: 0-5.00%, Co: 43.0-56.0%, S: 0-0.050%, and Se: 0-0.050% , the balance being Fe and unavoidable impurities, and the contents of Ni, Co, and Mn [Ni], [Co], and [Mn] are 55.5 ≤ 2.2 [Ni] + [Co] + [Mn] + 8 2. A method for producing a low thermal expansion alloy, comprising heating an alloy satisfying [C]≦57.0 to 700 to 1050° C. and then cooling it in a furnace.

According to the present invention, a low thermal expansion alloy having a high Young's modulus, a low thermal expansion coefficient, and a stable structure even at low temperatures can be obtained, so parts that are thermally stable and require high rigidity. etc.

It is an example of the X-ray diffraction of the alloy produced in the example, (a) is the invention example, (b) is the comparative example.

The present invention will be described in detail below. Hereinafter, "%" relating to component composition represents "% by mass" unless otherwise specified. First, the chemical composition of the alloy of the present invention will be explained.

C contributes to the improvement of low-temperature stability of austenite and the improvement of castability. In order to obtain this effect, the content of C is set to 0.40% or more. If the C content increases, the coefficient of thermal expansion increases and the ductility decreases, so the content is made 0.20% or less.

Si is added as a deoxidizer. The alloy after solidification does not need to contain Si, but in reality it is difficult to make the content 0, and the content may be 0.01% or more. Since the thermal expansion coefficient increases as the amount of Si increases, the amount of Si should be 0.25% or less, preferably 0.20% or less. In order to improve the fluidity of the molten metal, the Si content is preferably 0.10% or more.

Mn is added as a deoxidizer. In addition, it contributes to strength improvement by solid-solution strengthening. Furthermore, in the present invention, it contributes to the improvement of the low-temperature stability of austenite, and does not transform to martensite even at -196°C. To obtain this effect, the Mn content is 0.15% or more. Even if the Mn content exceeds 0.50%, the effect is reduced and the cost increases, so the Mn content is made 0.50% or less. It is preferably 0.30% or less.

Cr is an important element for ensuring corrosion resistance, and an optimum combination with Co provides low thermal expansion. The Cr content is set to 8.50% or more to ensure corrosion resistance. If the amount of Cr is too large, the coefficient of thermal expansion becomes large, so the amount of Cr is made 10.0% or less.

Ni, in combination with Co, contributes to lowering the thermal expansion coefficient. In addition, it contributes to the improvement of the low-temperature stability of austenite, and does not transform to martensite even at -196°C. In order to obtain the desired coefficient of thermal expansion, the range of Ni is 0-5.00%, preferably 1.50-5.00%.

Co is an essential element that lowers the coefficient of thermal expansion. If the amount of Co is too large or too small, the coefficient of thermal expansion will not be sufficiently reduced. In the present invention, the Co content is in the range of 43.0-56.0%. A preferred lower limit is 45.0%, and a more preferred lower limit is 48.0%. A preferred upper limit is 54.0%, and a more preferred upper limit is 52.0%.

The low thermal expansion alloy of the present invention is stable in austenite and has an austenite single-phase structure. This structure is obtained by adjusting the balance of Ni, Co, Mn, and C in an appropriate range, and can lower the coefficient of thermal expansion. In order to obtain an austenitic single-phase structure and a low coefficient of thermal expansion, the contents (% by mass) of Ni, Co, Mn, and C [Ni], [Co], [Mn], [C] 5≦2.2[Ni]+[Co]+[Mn]+8.2[C]≦57.0.

Whether or not the structure is an austenite single phase can be examined by X-ray diffraction. In the present invention, the intensity ratio of austenite and ferrite is determined in the X-ray diffraction pattern, and if there is no ferrite peak or if the austenite intensity is 100 times or more the ferrite intensity, it is determined to be an austenite single phase.

In addition, when machinability is required, S or Se may be added in the range of 0.050% or less.

The balance of the component composition is Fe and unavoidable impurities. The unavoidable impurities are those that are inevitably mixed from raw materials, production environment, etc. when industrially producing steel having the chemical composition specified in the present invention. Specific examples include Al, S, P, and Cu. When these elements are unavoidably mixed, the content is about 0.01% or less.

Next, a method for manufacturing the low thermal expansion alloy of the present invention will be described.

The mold used for manufacturing the high-rigidity, low-thermal-expansion alloy of the present invention, and the device and method for pouring molten steel into the mold are not particularly limited, and known devices and methods may be used.

The obtained cast steel or forged steel obtained by forging at 1100° C. is heated to 700 to 1050° C., held for 0.5 to 5 hours, and then cooled in the furnace. The cooling rate is preferably slow, preferably 10° C./min or less, more preferably 5° C./min or less.

The high-rigidity, low-thermal-expansion alloy of the present invention has a high Young's modulus, a low coefficient of thermal expansion, and a stable structure even at low temperatures. Specifically, it has a Young's modulus of 160 GPa or more, preferably 170 GPa or more, a thermal expansion coefficient of ±1.0 × 10 ^-6 /°C or less, preferably ±0.5 × 10 ^-6 /°C or less, and maltene The site transformation point is lower than -196°C.

[Example 1]
Molten metal adjusted to have the composition shown in Table 1 was poured into a mold to produce cast steel. Cast steel is φ100 × 350, and forged steel is forged after heating this ingot to 1150 ° C., forging to make forged steel of φ50, each subjected to heat treatment at 1000 ° C. for 2 hours, cooled in a furnace, and each A test piece was cut into the size of the test piece. A final alloy was obtained by heat-treating the manufactured specimen at 315° C. for 2 hours.

Young's modulus, thermal expansion coefficient, austenite fraction, and -196° C. structural stability were measured for the manufactured test pieces.

Young's modulus was measured at room temperature by the two-point support transverse resonance method. The coefficient of thermal expansion was obtained as an average coefficient of thermal expansion from 0 to 60° C. using a thermal expansion measuring machine. The austenite fraction was determined by the intensity ratio of austenite and ferrite using X-ray diffraction.

FIG. 1 shows an example of X-ray diffraction. (a) is for Example 10 (invention example), and (b) is for Example 9 (comparative example).

The structure stability at -196 ° C. was determined by cooling the test piece to -196 ° C. and holding it for 1 hour, observing the structure, and observing the presence or absence of martensite. When martensite was observed, the structure stability was evaluated as "x".

Table 1 shows the results. As shown in Table 1, the alloys of the examples of the present invention have a low thermal expansion coefficient of 1×10 ⁻⁶ /° C. or less, a high Young’s modulus of 160 GPa or more, an austenitic structure, and −196 The result was that the structure was stable even at °C.

Claims (2)

in % by mass,
C: 0.04 to 0.20%,
Si: 0.25% or less,
Mn: 0.15-0.50%,
Cr: 8.50-10.0%,
Ni: 0 to 5.00%, and
Co: 43.0-56.0 %
containing , the balance being Fe and unavoidable impurities,
Contents of Ni, Co, Mn, and C [Ni], [Co], [Mn], and [C] are 55.5≦2.2 [Ni]+[Co]+[Mn]+8.2 [C] ≦57.0
The filling,
The structure is austenite single phase,
an average coefficient of thermal expansion from 0 to 60°C of −1.0×10 ⁻⁶ /°C or more and +1.0×10 ⁻⁶ /°C or less;
Young's modulus is 160 GPa or more
A low thermal expansion alloy characterized by : A method for producing a low thermal expansion alloy according to claim 1,
in % by mass,
C: 0.04 to 0.20 %,
Si: 0.25% or less,
Mn: 0.15-0.50%,
Cr: 8.50-10.0%,
Ni: 0 to 5.00%, and
Co: 43.0-56.0 %
containing , the balance being Fe and unavoidable impurities,
Contents of Ni, Co, Mn , and C [Ni], [Co], [Mn] , and [C] are 55.5≤2.2 [Ni] + [Co] + [Mn] + 8.2 [C] ≦57.0
an alloy that satisfies
A method for producing a low thermal expansion alloy characterized by heating to 700 to 1050° C. and then cooling in a furnace.

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