Low thermal expansion alloy
Provided is a low thermal expansion alloy wherein martensitic transformation does not occur even at −120° C. This low thermal expansion alloy contains, in mass %, 1.50-5.00% of Co, while containing Ni in such an amount that if [Ni] (mass %) is the content of Ni and [Co] (mass %) is the content of Co, [Co]≥−4×[Ni]+136 and [Co]≤−4×[Ni]+139 are satisfied, with the balance being made up of Fe and unavoidable impurities. This low thermal expansion alloy has an average thermal expansion coefficient of 0.5×10 −6 /° C. or less for the range of 0-30° C., while having a martensitic transformation temperature of −120° C. or less.
1. A low thermal expansion alloy consisting of, by mass %,
Co: 1.50 to 5.00%,
Ni satisfying
[Co]≥−4×[Ni]+136 and
[Co]≤−4×[Ni]+139
wherein [Ni] (mass %) is a content of Ni and [Co] (mass %) is a content of Co, and
a balance of Fe and unavoidable impurities,
wherein
a mean thermal expansion coefficient at 0 to 30° C. is 0.5×10 −6 /° C. or less and
a martensite transformation temperature is −120° C. or less.
2. A low thermal expansion alloy, consisting of, by mass %,
Co: 1.50 to 5.00%,
Ni satisfying
[Co]≥−4×[Ni]+136 and
[Co]≤−4×[Ni]+139
wherein [Ni] (mass %) is a content of Ni and [Co] (mass %) is a content of Co, and
one or more of:
C: 0 to 0.040%,
Si: 0 to 0.30%,
Al: 0 to 0.20%,
Mg: 0 to 0.100%,
Ca: 0 to 0.100%,
Ce: 0 to 0.100%, and
La: 0 to 0.100%,
and a balance of Fe and unavoidable impurities,
wherein:
a mean thermal expansion coefficient at 0 to 30° C. is 0.5×10 −6 /° C. or less and
a martensite transformation temperature is −120° C. or less.
3. The low thermal expansion alloy according to claim 1 , wherein the mean thermal expansion coefficient at 0 to 30° C. is −0.04×10 −6 /° C. or less.