LOW THERMAL EXPANSION ALLOY EXCELLENT IN LOW TEMPERATURE STABILITY AND ITS MANUFACTURING METHOD

To provide a low thermal expansion alloy having an average thermal expansion coefficient in a range of 0 to 1.0 ppm/°C in a wide temperature range from an ultralow temperature near a liquid nitrogen temperature to 200°C, and capable of obtaining low temperature stability of a Ms point of -196°C or lower and its manufacturing method.SOLUTION: A low thermal expansion alloy comprising, by mass %, C: 0.01% or less, Si: 0.05% or less, Mn: 0.05% or less, Ni: 35.5 to 36.0%, Co: less than 1.0%, and Ni + 0.8 Co: 35.7 to 36.3%, the balance consisting of Fe and unavoidable impurities, having a solidified structure with a dendrite secondary arm spacing of 5 μm or less, an average thermal expansion coefficient of -190 to 200°C. in the range of 0 to 1.0 ppm/°C, and a Ms point of -196°C or less is provided.SELECTED DRAWING: None 【課題】液体窒素温度付近の極低温から２００℃までの広い温度範囲で平均熱膨張係数が０～１．０ｐｐｍ／℃の範囲であり、Ｍｓ点が－１９６℃以下の低温安定性が得られる低熱膨張合金およびその製造方法を提供する。【解決手段】質量％で、Ｃ：０．０１％以下、Ｓｉ：０．０５％以下、Ｍｎ：０．０５％以下、Ｎｉ：３５．５～３６．０％、Ｃｏ：１．０％未満を含有し、かつＮｉ＋０．８Ｃｏ：３５．７～３６．３％であり、残部がＦｅおよび不可避的不純物からなり、デンドライト２次アーム間隔が５μｍ以下である凝固組織を有し、－１９０～２００℃の平均熱膨張係数が０～１．０ｐｐｍ／℃の範囲で、かつＭｓ点が－１９６℃以下である低熱膨張合金が提供される。【選択図】 なし