Environment-enhanced crack propagation of sensitized type 304 stainless steel in simulated B W R environment

A preliminary work on the study of crack propagation of sensitized AISI type 304 stainless steel in simulated boiling water reactor environment is described. Particular stress is placed on the combined effect of cyclic and static stresses, when the material is loaded cyclically with trapezoidal stress wave form of varied holding time at tension. The measurement of propagation was made successful by using the tapered double-cantilever-beam type specimens, which gave a constant stress intensity factor under a fixed load level throughout the test. The effect of chemical environment, therefore, was evaluated by simple comparative examination. The load level and water chemistry were fixed during the test, and th e effect of the time at tension was made a variable. For the two dissolved oxygen levels, ie. low (0.1 ppm) and high (10 to 40 ppm), a strong influence on the mode of cracking was observed. The major findings were; 1) Apparent acceleration of crack propagation in 2000C water comparative to the ambient air environment. 2) Change in fracture mode from transgranular (fatigue) to intergranular (stress corrosion cracking) types either increase of the oxygen content in water or the holding time at tension. The results of measurements were analysed in terms of the combined effect of the time-dependent stress corrosion and the cycle-dependent corrosion fatigue. (auth.)