Corrosion Fatigue Investigations of Austenitic Stainless Steels with Different Alloying Concepts and Grades of Cold Working

            For applications under dynamic loads in aqueous, hot chloride containing media, austenitic stainless steels are often used. To reach a full and stable austenitic lattice, two different alloying concepts are common possible. On the one hand, alloying with chromium-nickel and on the second hand, alloying with chromium-manganese-nitrogen reaches to a full austenitic lattice.
            Two steels, one of each group, with different grades of cold working (solution annealed – 14% cold worked – 27% cold worked) are investigated in this paper. Stress versus number of cycles curves and crack propagation rate curves were recorded in inert glycerin as reference medium and in 62% calcium chloride solution as corrosive medium, both at a temperature of 120°C. The ratio between upper and lower stress level (R value) was 0.05 to avoid destruction of the fracture surfaces and the testing frequency was 20 Hertz. The crack growth was recorded with the direct current potential drop method. Crack initiation and fracture mechanisms of the two different steels were investigated and compared.
            In addition, constant load tests, exposure tests, electrochemical tests and atomic force microscopy were done to determine damage mechanisms.
Keywords:     Corrosion fatigue, stainless steels, austenite, fracture mechanism