To stably maintain the strength of steel at a high temp. by incorporating fine oxide particles of specified particle size essentially consisting of Cr and Mn in specified ranges.
In steel, fine oxide particles of <100 nm particle essentially consisting of Cr and Mn are dispersed. Even in the case the particle size of the oxide particles is ≥10 nm or <100 nm, when the quantity thereof is <100 mass ppm, the effect of maintaining its yield ratio at a high temp. is small. Moreover, in the case of >200 mass ppm, the oxides are coarsened, and the melting of the steel is made difficult. For forming this fine oxides, the steel is added with ≥0.0060% O, ≥0.03% Cr and ≥0.2% Mn. Furthermore, for preventing the check of the formation of the fine oxides, the content of Si in the steel is controlled to <0.01%, Ti and V to <0.005% and Al to <0.005%. Moreover, the content of C is controlled to <0.2% from the points of suppressing the formation of coarse Cr carbides and securing the weldability of the steel.
ISHIGURO YASUHIDE
YAMADA KATSUMI
CHINO ATSUSHI
