Evaluation of stress corrosion cracking susceptibility of austenitic stainless steels in CaCl2 solution by the constant load method

Stress corrosion cracking susceptibility of austenitic stainless steels in CaCl2 solutions was studied using a constant load method. Initiation and propagation of stress corrosion cracks were examined with fractography. The number and distribution of cracks were classified. A model for mechanical response of the specimen under constant load testing and a physical model for cracking was introduced, and some creep deformation measurements were performed and analysed. The steady state strain rate obtained from the corrosion elongation curve (elongation vs. time curve) showed a linear function of time to failure. This implies that the steady state strain rate can be applied as a parameter for prediction of time to failure. The steady state strain rate below which no failure occurs within a laboratory time scale was estimated. On the basis of the results obtained, the critical values of stress below which no SCC occurs are evaluated. Based on creep measurements in a non-corrosive environment the influence of the environment on the steady state strain rate is more than five-fold. Cracking characteristics were divided into three categories according to the crack initiation distribution. Fractography showed that the cracking mode changed from transgranular to intergranular cracks and then to ductile dimpled fracture. Transgranular cracking predominates at relatively low stresses and steady state strain rates.