成果報告書詳細
管理番号20110000000761
タイトル*平成22年度中間年報 省エネルギー革新技術開発事業 挑戦研究 耐用温度800℃級蒸気タービン用新鍛造材料の開発(2)
公開日2011/6/7
報告書年度2010 - 2010
委託先名国立大学法人東北大学
プロジェクト番号P09015
部署名エネルギー対策推進部
和文要約和文要約等以下本編抜粋:1. 研究開発の内容及び成果等 石炭は貯蔵量が豊富であり、世界的に分散されていることからエネルギー資源の中では今後も比較的安定した価格で入手できることが期待される。しかし、従来の石炭火力ではCO2排出量が多いため、環境問題の面からより一層の高効率化技術が望まれており、現在、700℃超級超々臨界圧発電(Advanced Ultra Super Critical;以下A-USCと記載)の技術開発が欧米や日本で行われている。蒸気温度を上昇させることで効率の向上が可能となることから、従来、ボイラおよびタービンの高温部材に使用されていた鉄鋼材料を、A-USCでは高温強度に優れたNi基超合金を用いることで、蒸気温度を大幅に向上させ、効率を大幅に向上させている。
英文要約It is recognized that the CO2 emission is large in the conventional coal fired power generation although coal can be supplied by stable price since the reserve is bountiful and is not localized. Therefore, the high efficiency technology is required and currently US, Europe and Japan are developing Ni-based superalloys for 700°C-class advanced ultra super critical (A-USC) plants. For further improvement of energy efficiency, it is necessary to develop materials to be applied at 800°C, however, it is not easy to satisfy both the high-temperature strength and manufacturability in one material. This project is aimed at 800°C-class wrought superalloy newly designed based on phase diagram.
Development of 800°C-Calss Middle Scale Wrought Alloy (Alloy B)
a) Alloy Design
We have determined the phase equilibria between the liquidus and solidus temperatures in each binary and ternary system of Co-Ni-Al-W-Cr using DSC. Because it was found that Ta is one of the important element for the Co-based alloy, we have also determined the phase equilibria in Co-Ta binary system. The phase equilibria are revised by this work and new data are effective for constructing the database.
b) Preparation of Laboratory Scale Samples and Microstructural Observations
1 kg ingots of Co-Ni-Al-W-Cr-C-B alloys were prepared by induction melting. These ingots were heat-treated and the microstructure was observed using optical microscope, SEM and EPMA. Grain boundary precipitation for grain boundary strengthening has been obtained by choosing suitable alloy composition and heat treatment.
Co-based alloys with alloying element including Ta, Ti, Nb and Mo were also prepared. It was found that the addition of alloying elements change the volume fraction of carbide, and we have designed the alloy composition to obtain the suitable microstructure with γ/γ’ and grain boundary precipitates.
c) Manufacturability
30 kg ingots were prepared by induction melting, and bars with 16 mm in diameter were successfully obtained. The microstructure was observed and the γ’, carbide and μ phases were confirmed in the γ matrix.
It was found that the strength at 1050 °C is lower than that in IN617, indicating that the designed alloys have high manufacturability.
Evaluation of New Material
a) Microstructural Stability
The microstructure of the samples after the creep tests was observed. The phase constituent was the same as that before the test and no ~ and ~ phases were observed, and the coarsening of the γ’ phase was also confirmed.
b) High-Temperature Strength
The tensile and creep tests of were carried out at 800°C. The high-temperature strength and elongation are in the same level with those in conventional high-strength Ni-based alloy. The creep properties are excellent and the extrapolation of them to lower stress levels indicates the higher creep strength required for service at 800°C for 105 hours.
c) Segregation
The partition coefficient was determined in Co-Al-W-Ni-Cr-X alloys. Using these experimental data and Scheil equation, we have designed the alloy composition with low segregation index.
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