高温ボルト用Ｆｅ基耐熱超合金の開発

概要

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In order to develop the γ-strengthened iron-based super alloy for heat resistant fasteners, the influence of Ti/Al ratio in the system of 25Ni-16Cr- Ti-Al-Nb with higher volume fraction of γ than conventional SUH660 on age-hardening behavior, phase stabilities and mechanical properties at elevated temperature were investigated. Increase of Ti/Al ratio accelerates age-hardening and promotes the precipitation of η phases at grain boundaries in over aged condition. Formation of ηphases decreases rupture strength at long term exposure. Ti/Al ratio was optimized by creep rupture strength and age hardening rate. The alloy with Ti/Al=10 was developed for heat resistant fasteners. Fasteners from this alloy had excellent strength at elevated temperatures compared with conventional SUH660 fasteners. Relaxation strength of developed fasteners after 50h at 973K was twice of that of SUH660.