Influence of Cold Deformation on Stress Corrosion Cracking Resistance of Highly Alloyed Austenitic Stainless Steels in Chloride Media

摘要

Constant load tests (CLT) and slow strain rate tests (SSRT) were done with three CrMnN stainless steels and one CrNiMoN stainless steel in saturated boiling magnesium chloride solution (45 %) at 155℃. Materials were tested in solution annealed and electropolished condition and four different degrees of cold working between 14 and 50 %. Additionally amount of surface attack and crack densities were evaluated qualitatively. Additional electrochemical tests were done in the test solution. Threshold stress for initiation of stress corrosion cracking (SCC) is almost independent from degree of cold working and from type of steel. Threshold stress is between 200 and 400 Mpa for all investigated materials. CrMnN steels show a lower crack density and time to failure in both CLT and SSRT saying for a faster crack propagation rate when compared to CrNiMoN stainless steel. Crack propagation is claimed to happen by film induced cleavage. Crack propagation of CrNiMoN steel is slower than applied strain rate of 2.78x10 2.78x10-6 -s-1 -yielding to a significant reduction of area for this material.