JP2002088432A - Low thermal expansion corrosion resistant alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a low thermal expansion corrosion resistant alloy combinedly having the characteristics of low thermal expansion and corrosion resistance. SOLUTION: This low thermal expansion corrosion resistant alloy has a composition containing, by mass, <=0.15% C, 7.0 to <9.0% Cr and >54.0 to <56.0% Co, and the balance substantially Fe. Preferably, the low thermal expansion corrosion resistant alloy has a composition containing 0.01 to 0.15% C, 7.0 to <9.0% Cr and 54.5 to 55.5% Co, and the balance substantially Fe, and the average thermal expansion coefficient at 30 to 100 deg.C is 2.0×10-6/ deg.C or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low thermal expansion corrosion resistant alloy having both low thermal expansion and excellent corrosion resistance.

[0002]

2. Description of the Related Art In the field of semiconductor manufacturing and the like, parts of a manufacturing apparatus are required to have corrosion resistance depending on a use environment such as a cleaning process at the time of assembly, and austenitic stainless steel has been conventionally used. In recent years, the precision of parts has advanced,
A low-thermal-expansion member has been required, but austenitic stainless steel has a large coefficient of thermal expansion and does not match with other low-thermal-expansion components, causing distortion or cracks during use due to differences in thermal expansion. was there. Therefore, improvement has been proposed for the purpose of reducing the thermal expansion of stainless steel.

[0003] For example, Japanese Patent Application Laid-Open No. H5-180615 discloses a typical stainless steel invar alloy (Co: 53 to 54%, Cr: 9 to 10%,
Fe: 36-37%) and used as a guide member for a scanning tunneling microscope. Also, in JP-A-7-328509,
A stainless steel invar alloy is used as an organic solvent coating device, and is characterized in that Co: 52.5 to 56.0% and Cr: 9.0 to 10.5% by weight%, the balance being Fe and unavoidable impurities.

[0004]

The austenitic stainless steel described above is advantageous in terms of corrosion resistance, but has a problem in that it has a large coefficient of thermal expansion. The problem of large thermal expansion is a major problem in manufacturing high precision parts in recent years. A stainless invar alloy is also known as a material having low thermal expansion, but there is a problem that sufficient low thermal expansion characteristics cannot be obtained at a practical product level. An object of the present invention is to provide a low thermal expansion corrosion resistant alloy having both low thermal expansion and corrosion resistance characteristics.

[0005]

Means for Solving the Problems The present inventor studied the thermal expansion characteristics of a stainless steel invar alloy, optimized the combination of the amounts of Co and Cr, and further optimized the amount of C to obtain a practical product. It has been found that the thermal expansion characteristics can be greatly improved at the level, and the present invention has been achieved.

[0006] That is, the present invention provides a C: 0.15% or less by mass%.
Below, Cr: 7.0% or more and less than 9.0%, Co: more than 54.0% and less than 56.0%
Full and balance substantially consisting of Fe, low thermal expansion
It is a tension corrosion resistant alloy. Preferably, C: 0.01 to 0.15 by mass%
%, Cr: 7.0% to less than 9.0%, Co: 54.5 to 55.5%, the balance is real
It is made of Fe and has an average thermal expansion coefficient of 30 ° C to 100 ° C.
The number is 2.0 × 10 ^-6/ ° C or lower
It is a corrosion resistant alloy. More preferably, the amount of S in the above alloy is
Low thermal expansion characterized by controlling the amount to 0.005 to 0.5%
It is a tension corrosion resistant alloy.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, an important feature of the present invention is that Co, C, which can provide low thermal expansion characteristics at a practical product level.
The point is that the optimum combination of the r amount and the C amount have been found. In the present invention, the reasons for determining the composition of the alloy as described above are as follows.

C: 0.15% or less C is an essential element in the present invention. C has the effect of stabilizing the austenite phase in a small amount. Generally, all Invar alloys have a face-centered cubic lattice. If the C content is small, a martensite phase is easily formed, and low thermal expansion characteristics cannot be obtained. Preferably, it is necessary to add 0.01% or more. 0.15%
If added in excess of, the precipitation of Cr-based carbides tends to occur and the corrosion resistance deteriorates, so the upper limit was made 0.15%.

Cr: 7.0% or more and less than 9.0% Cr is an important element for ensuring corrosion resistance, and low thermal expansion can be obtained by an optimal combination with Co. Cr content is 9.0%
Above, the thermal expansion coefficient is large, and if it is less than 7.0%, the corrosion resistance is deteriorated.

Co: 54.0-56.0% Co is an important element for obtaining low thermal expansion. When the Co content is outside the above range, the coefficient of thermal expansion increases. Preferably,
By setting the Co content to 54.5 to 55.5%, further low thermal expansion characteristics can be obtained.

Si and Mn: 1% or less Si and Mn are added as a deoxidizing agent, but if added excessively, the amount of inclusions increases and corrosion tends to progress from the inclusions, so that 1% or less. Is preferred. Mn is more preferably 0.5% or less. Mn combines with S to form sulfides and is effective in improving machinability, but when the ratio of Mn in sulfides increases, corrosion resistance deteriorates. Mn
By making the content 0.5% or less, the ratio of Mn in the sulfide is reduced, and instead, the ratio of Cr is increased, and the corrosion resistance of the inclusion is improved.

S: 0.005 to 0.5% S bonds with Mn and Cr and exists as sulfide. By adding S in an amount of 0.005% or more, machinability can be improved without lowering thermal expansion and corrosion resistance. If added in an amount of 0.5% or more, the hot workability becomes extremely poor, and the yield at the time of processing into a final product is lowered, so the upper limit was made 0.5%.

[0013]

EXAMPLE A steel ingot having the components shown in Table 1 was produced by high frequency melting in the air. For the purpose of homogenizing alloy elements
After subjected to soaking treatment at 1200 ° C. for 24 hours, it was heated to 1100 ° C. and forged into a square bar having a side of 30 mm. Thereafter, in order to improve the corrosion resistance by completely dissolving the carbides to form austenite, the square bar was heated at 1000 ° C. for 30 minutes and then water-cooled to obtain a test material. The coefficient of thermal expansion is 30-100
It was measured in the range of ° C. The average linear thermal expansion coefficient is also shown in Table 1. In addition, in order to evaluate the corrosion resistance, a time until rust was generated was measured by a salt spray test. Test conditions are JIS
According to the test conditions of Z 2371, 5% NaCl at 35 ° C. was used.
Table 1 shows the time until the occurrence of rust. Further, a turning test was performed to evaluate the machinability. Co-containing high-speed steel SK
Using H59, the cutting speed was 42 m / min, the feed speed was 0.15 mm / rev, and the cutting time until the wear amount on the flank of the cutting edge of the cutting tool reached 0.2 mm was measured. Table 1 also shows the measurement results.

Nos. 1 to 12 are alloys of the present invention, and have an average coefficient of thermal expansion of 2 × 10 ⁻⁶ / ° C. or less due to an optimal combination of Cr and Co. In particular, the preferred compositions of the present invention are Nos. 1 to 3, 5, 7 to
No. 12 has a smaller coefficient of thermal expansion than Nos. 4 and 6. No.9 ~ 12
The addition of S improves the machinability in addition to low thermal expansion, corrosion resistance, and has a longer cutting time in turning tests than No. 1 to 8, which is effective in reducing cutting tool wear and suppressing burrs. .
Nos. 13 and 14 are representative stainless steel invar alloy compositions, but have large thermal expansion coefficients. Furthermore, No. 13 has a low C content, a martensitic structure, and a large thermal expansion coefficient. No. 15 has a Co content outside the scope of the claims of the present invention, and has a large thermal expansion coefficient. In No. 16, the Cr content was outside the scope of the claims of the present invention, and rust was generated in a short time in a salt spray test, and the corrosion resistance was insufficient compared with the alloy of the present invention.

[0015]

[Table 1]

[0016]

According to the present invention, low thermal expansion and excellent corrosion resistance are provided, which is an indispensable technique for practical use of precision parts in a corrosive environment.

Claims (3)

[Claims] [Claim 1] C: 0.15% or less, Cr: 7.0% or more and 9.0% by mass%
Less than, Co: more than 54.0% and less than 56.0%, the balance is substantially Fe
A low thermal expansion corrosion resistant alloy characterized by comprising: 2. C: 0.01 to 0.15% by mass, Cr: 7.0% or more by mass% 9.
Less than 0%, Co: 54.5-55.5%, the balance consists essentially of Fe,
And the average coefficient of thermal expansion from 30 ℃ to 100 ℃ is 2.0 × 10 ^-6 / ℃
A low thermal expansion corrosion resistant alloy characterized by the following. 3. The corrosion-resistant alloy with low thermal expansion according to claim 1, wherein the alloy comprises, by mass%, S: 0.005% or more and less than 0.5%.