| 摘要 |
PROBLEM TO BE SOLVED: To provide low alloy heat resistant steel as a CrMoV based heat resistant steel used for a large-sized member such as a turbine rotor which has uniform material between the surface part and the central part in the member, has excellent high temperature strength, and does not undergo creep embrittlement in particular, a heat treatment method therefor, and a turbine rotor using the steel. SOLUTION: In the CrMoV based heat resistant steel, trace impurities such as phosphorous, sulfur, copper, aluminum, arsenic, tin and antimony are reduced to specified levels or lower, the heat treatment conditions therefor are controlled, and the JIS grain size number of the crystals is controlled to 3 to 6. The grain size can be controlled by precipitating a suitable amount of pro-eutectoid ferritic phase. As the heat treatment method, the one in which the steel is rapidly cooled from a high temperature region, is next let to cool in the air for a fixed time, and is again rapidly cooled, or the one in which the steel is slowly cooled in a high temperature region, and is thereafter cooled at a low temperature region, or at an accelerated cooling rate can be adopted.
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