抄録
The creep rupture strength of low alloy steels, 1/2Mo, 1Cr-1/2Mo, 21/4Cr-1Mo, 5Cr-1/2 Mo, 9Cr-1Mo was studied in relation to their microstructure.
The results obtained are as follows;
(1) The intersection of the stress-rupture time curves was observed in a steel with different heat treatment. This was observed also in 1Cr-1/2Mo and 21/4Cr-1Mo steels.
(2) High Cr steels (5Cr-1/2Mo, 9Cr-1Mo) show weaker creep strength than low Cr steels (1/2Mo, LCr-1/2Mo, 21/4Cr-1Mo).
(3) The Cr content in the residues does not increase by tempering. As for the amount of Mo in the residues, low Cr steels show remarkable increase in Mo content but high Cr steels show slight increase in Mo content.
(4) Microscopical observation revealed that N. T. treated specimen contained finer precipitates in the ferrite than Ann. treated specimen. Tempered bainite which was observed in N. T. treated 21/4Cr-1Mo steel was apt to form coarse carbides.
In fine the problems with the creep rupture strength of commercial low alloy steels will more clearly be boiled down to alternative between the following two questions:
(1) whether or not the low alloy steels contain in their microstructure either bainite or martensite, or (2) whether or not the ferrite is adulterated with carbide particles.
