In previous reports (ib. Tetsu-to-Hagané, 45 (1959), 126; 46 (1960), 377) the authors reported the effect of Nb and Ti on properties of 18Cr-12Ni austenitic stainless steels.
This report concerned the effect of Mo and W aging behavior, microstructure, precipitates, tensile properties at various temperatures and creep-rupture strength of the same steel.
The following results were obtained. :
1) The steel was hardened during aging by precipitation of M
6C.
2) The precipitates of M
6C, Cr
23C
6, Fe
2Mo, Fe
2W and σ phase were observed.
The amounts of the precipitates of Fe
2Mo, Fe
2W and σ phase were increased as the aging temperature was elevated and as the C content was decreased and as the Mo, the W content was increased.
3) The precipitation occurred at first on grain boundaries and secondarily within grains, and subsequently, coagulation of precipitates on grain boundaries began.
4) Resistance to oxidation in the air at 1100°C was decreased with the Mo ahd the W contents.
5) Tensile strength was increased linearly with the Mo or the W content at each temperature.
The rate of increase of tensile strength was about 1kg/mmmm
2 with a percent of Mo and from 1·5 to 2·0kg/mmmm
2 with a percent of W.
6) Creep rupture strength was increased with the content. The rate of increase of this strength for the steels with the higher C content was greater than that for the steels with the lower C content because of the precipitation of M
6C.
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