オーステナイト耐熱鋼の切欠クリープ破断特性への粒内および粒界強度の影響

抄録

The notch effect on both the rupture strength and the fracture behavior was investigated in 20-11 P austenitic heat resisting steel whose hardness and configuration of grain boundaries were widely changed by heat treatments.
The notch rupture life under constant stress reached the maximum value at some critical hardness value depending on the configuration of grain boundaries. As compared with the result of smooth speimen, the critical hardness for the notched specimen was shifted to the value lower than that of the smooth one. This resulted in the notch strengthening in lower hardness region and the notch weakening in higher hardness region.
The analysis of fracture behavior suggested that stress concentration in notch root would cause the notch weakening in higher hardness region by the accelerated nucleation and propagation of grain boundary cracking, while the constraint of plastic deformation around notch root could cause the notch strengthening in lower hardness region where the ductile fracture occurred and the rupture life would be determined by strain rate. It was also shown that notch weakening of strengthening was strongly dependent on the ductility.