オーステナイト耐熱鋼平滑材のクリープ破断特性への粒内および粒界強度の影響

抄録

This study was carried out to clarify the contribution of the grain-and the grain boundary-strengths to the creep rupture properties in a 20-11 P austenitic heat resisting steel (0.3C-0.2P-20Cr-11Ni-2Mo) having a wide variation in hardness and the configuration of grain boundaries.
The rupture life under a stress increased with the increase in hardness until it reached the maximum value at some critical hardness, but further increases in hardness led to the drop of the rupture life in spite of decrease in minimum creep rate. From the analysis of fracture behavior, it was clarified that the transition of fracture mode from ductile to brittle with increasing hardness is responsible for this variation on the rupture life. When the grain boundaries were strengthened by serration, the critical hardness shifted to higher values and the remarkable increase in the rupture life was obtained as a result of preventing the formation and the growth of cracks and cavities along grain boundaries.
This result suggests that in order to improve the rupture strength, the hardness, i. e. the strength of grains, must be increased in keeping a balance with the strength of grain boundaries depending on their configuration.