微量Ti, Nbを含む18Cr-10Ni鋼および18Cr-10Ni・Mo鋼の高温強度におよぼすN, BおよびPの影響

抄録

It has been previously reported by one of the authors that with the combined addition of small amounts of Ti and Nb the creep rupture strength of 18Cr-8Ni austenitic steel is markedly increased. In this work, the effects of further addition of N, B, and P on the creep rupture properties of 18-10 and 18-10. Mo steels both bearing small amounts of Ti and Nb have been studied.
It has been found that the combined addition of 0.1%N and 0.02%B to these steels is effective for increasing the rupture strength, and the addition of 0.3%P to 18-10·Ti·Nb·Mo steel is more effective, giving a high 700°C-10⁴hr rupture strength of 17kg/mm². The cause of the strengthening effects of these elements have been discussed with relation to changes in distribution of carbide M₂₃C₆ precipitated within austenitic grains, and it has been attributed to a decrease in the misfit between matrix and the carbide M₂₃C₆, resulting in retardation of the carbide coalescence. Especially, electron microstructures of replicas extracted from 18-10 and 18-10·Mo steels bearing 0.3%P look like homogeneous precipitations of the carbide M₂₃C₆, and these fine carbide distributions have been considered to be the main cause of the strengthening action of P.