1993 年 42 巻 473 号 p. 183-188
Fatigue crack growth and crack closure in 3% NaCl solution have been investigated in spheroidal graphite cast irons with four types of microstructure, i.e. ferrite, pearlite, bull's eye and aus-ferrite. In high ΔK regime, crack growth rates were enhanced by stress corrosion cracking (SCC) due to hydrogen embrittlement. Crack closure level was reduced by SCC, which promoted the acceleration in 3% NaCl solution. In low ΔK regime, crack growth rates were decreased by the corrosion debris induced crack closure, but the crack growth characteristics allowing for crack closure were the same with those in air. Thus, the environmental effect on the essential crack growth resistance was negligible in 3% NaCl solution. These behaviors were seen for all the materials investigated, and thus the dependence of microstructure on environmental effects was obscure. Fracture toughness has also been measured in air and in 3% NaCl solution for these materials. The fracture toughness values in both environments were the same for the ferrite, pearlite and bull's eye microstructures, but the value in 3% NaCl solution was definitely lower than that in air for the aus-ferrite microstructure.