Stress Corrosion Cracking of Sensitized Type 304 Stainless Steel in High Temperature Chloride Solutions

The SCC susceptibility of sensitized Type 304 stainless steel was studied using slow strain rate tests in 0.01 M NaCl as a function of applied potential at temperatures ranging from 100 to 250 C. Potential-temperature domains in which purely IGSCC, simultaneous IGSCC and TGSCC, and IGSCC accompanied by pitting corrosion have been determined. A critical potential for IGSCC and its dependence upon temperature was measured. This critical potential is equal to the pitting potential at temperatures lower than 150 C, but at higher temperatures, it lies within the passive range of the alloy. Above 150 C, the potential for breakdown of passivity becomes independent of temperature and corresponds to the potential at which TGSCC occurs on sensitized and on quench-annealed material. Interrupted slow strain rate tests were conducted to determine the time at which intergranular cracks start to propagate. On the basis of these data, average intergranular crack propagation rates were calculated. An apparent activation energy of 29 ± 12 KJ/mol was determined in the temperature range 200 to 275 C. It was also found that propagating intergranular cracks can be arrested by changing the potential to a value which is lower than the critical potential.