Abstract
The effect of addition of nitrogen up to 0.66%, of carbon up to 0.20%, and of nitrogen plus carbon on the creep rupture strength of 25Cr-20Ni heat-resisting steel was studied, and some strengthening mechanisms in this kind of steel due to the addition of nitrogen and carbon were discussed. The stress rupture strength of the steels at 700°C was improved remarkably with increasing amount of nitrogen up to 0.36%, above which the strength decreased due probably to a discontinuous precipitation of Cr2N. Further improvementof the strength was obtained by combinated addition of carbon and nitrogen, while the improvement withaddition of carbon only was very small relative to that of nitrogen. It was deduced from the results that strengthening with addition of nitrogen may be attributed mainly to an action similar to the I-S effect (chemical interaction between interstitial atoms and substitutional atoms), which had been proposed for low alloy heat-resisting steels, and to the SUZUKI's effect, and in the case of addition of nitrogen pluscarbon, dispersion hardening with carbide M23C6, in addition to above two mechanisms, may become also to effective, since coagulation of the carbide retard by the coexisting nitrogen.
