高Crフェライト系耐熱鋼における長時間クリープ強度に対するReの効果(力学特性)

概要

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There has been a great demand for superior heat resistant steels in order to raise the thermal efficiency of fossil-fuel power plants and to reduce CO_2 emission to the global environment. To this end, by using the d-electrons concept, 9-12% Cr ferritic steels were designed for use of a steam turbine rotor operated in the USC power plants at the steam temperature of 620 to 650℃. The crucial issue for the design is to suppress the deterioration of the long-term creep strength by alloying. First, the Re addition was found to give a beneficial effect on the creep strength of a 10%Cr-4%W steel. Then, the creep tests were performed with the six Re-free and 3.5%W ferritic steels to get an optimum Cr content in the range of 8.5 to 11.5%. As the result, it was found that an excess amount of Cr yielded a detrimental effect on the creep properties, and the 9%Cr steel was the best in view of the very long-term creep strength tested in the condition of 650℃, 98MPa. Subsequently, a series of creep tests was conducted with the steels by fixing at 9%Cr but by varying the W content from 2 to 4% and the Re content from 0 to 0.5%. From the prolonged creep tests for more than 40,000h, it was shown that the 9Cr-4W-0.5Re steel had the longest creep rupture life among all the high Cr ferritic steels so far developed in the world.
社団法人日本鉄鋼協会の論文
2009-02-01