Precipitation-reinforced austenite stainless monocrystal steel and usage thereof

In an austenite steel of the present invention containing less than 0.03wt% of C and up to 0.5wt% of inevitable impurities, a mother phase comprises an austenitic monocrystals containing a ferrite phase in an amount of up to 10% by volume at a room temperature, and contains at least one of Nb, Ta and Ti in an amount of from 0.3 to 3% by weight. Compounds such as intermetallic compounds containing one more of the metals of Nb, Ta and Ti to be added are precipitated finely by a solid-solubilizing treatment and succeeding aging treatments, and dispersed at a room temperature. This steel has more stable tissues than austenite stainless steels which have usually been used, and has excellent corrosion resistance, stress corrosion cracking resistance, strength and irradiation embrittlement resistance. It can extend the working life of structural parts of a reactor core, first walls and structural parts of blankets of a thermonuclear reactor thereby enabling to provide remarkable effects on the improvement of their safety and reliability. (T.M.)