Abstract
A study has been made on the effect of microalloying with phosphorus(P) and carbon(C) on creep and high-temperature tensile properties of a modified type 316 austenitic stainless steel which has a similar composition to a candidate alloy for the first wall application in the fusion reactor.
The P addition up to 0.1 mass% increases markedly the creep life and decreases the steady state creep rate. P is more effective than C, and the combined addition of P and C is most helpful in increasing the creep strength. Void formation at grain-boundaries during creep is considerably suppressed by P and C additions. Finely dispersed Laves phases by the P addition and M23C6 type carbides by C and P-C additions are precipitated on the crept specimen, resulting in improvement of the creep strength. The P addition contributes to enhance the fine dispersion and stabilization of the precipitates. Cold working and aging are also effective for increasing the high-temperature tensile strength. The following relationship between effective stress, (σ−σi) and creep rate, \dotε, is confirmed by measuring the internal stress σi:
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\
oindentwhere, σ is the applid stress and B a constant.
The relation suggests the Orowan type precipitation strengthening mechanism.
