Abstract
Stress corrosion tests were conducted on the notched plates of SNCM 8 steel tempered at low temperatures in 3.5% NaCl solution environment. The effects of notch radius and plate thickness on nucleation and growth of cracks were analysed from a viewpoint of fracture mechanics.
The results obtained are summarized as follows:
(1)The time to crack nucleation at the notch root tn was correlated to the notch radius ρ and the stress intensity factor K0 by the following equation:
tn=5.8×1027(K0/√ρ)-12.5
(2) The relation between crack growth rate and stress intensity factor was divided into three regions I, II and III. In regions II and III, the growth rate was found to be higher in thicker specimens than in thinner ones, while there was no thickness effect on growth rate in region I including KISCC.
(3) Scanning electron microscopic observations of fracture surfaces indicated that intergranular fracture along prior austenite grain boundaries was predominant in the region of low stress intensity factors and that the fraction of grain boundary fracture area in the total fracture surface decreased with increasing stress intensity factor.
