1998 Volume 47 Issue 4 Pages 267-274
The effect of strain rate on stress corrosion cracking (SCC) for Type 304L stainless steel was investigated in a 20mass% NaCl aqueous solution containing 10-2kmol m-3 Na2S2O3 under air open condition by using a slow strain rate testing (SSRT) apparatus with a dynamic observation system. This technique can in-situ observe the growth of multiple cracks on a smooth tensile specimen, and can provide the information on the initiation and propagation of an individual crack separately. A decrease in strain rate led to a decrease in the strain where the maximum stress appears in a stress-strain curve, which is one of convenient SCC susceptibility indexes for SSRT. It is clear from the dynamic observation that the cumulative number of pits and cracks at the same strain is similar above the strain rate of 10-6 s-1 and decreases below that rate. In addition, stress intensity factor for SCC (KISCC) was found to show the Weibull probability distribution, and its mode was about 2MN. m-3/2, independent of strain rate. While, crack growth rate showed log-normal probability distribution, and its mode was in a narrow range from 0.8×10-8 to 1.5×10-8m/s, almost independent of strain rate. In comparison with Type 316 L stainless steel, Type 304 L stainless steel had higher SCC susceptibility of the lower KISCC, but had similar susceptibility of almost same crack growth rate. It is concluded that the effect of strain rate on the strain where the maximum stress appears is controlled by crack initiation process, not by crack propagation process.
