Abstract
Electrochemical characteristics of polythionic acid stress corrosion cracking have been examined mainly on sensitized Type 304 stainless steel. The test solution was prepared by passing sulfur dioxide gas into deionized water for 4 hours and then bubbling hydrogen sulfide for 3 hours. The rest potential of the steel lies approximately at -100mV (SCE) showing little change during initiation and propagation of cracks. When tested potentiostatically at various potentials, the susceptibility to cracking is greatest at -200 to +100mV, on which potential region the rest potential falls. Above 250mV the susceptibility decreases and beyond 950mV general corrosion accompanied by pitting is the main consequence. At a base potential of -400mV, on the other hand, the susceptibility still persists. Annealed Type 304 does not corrode intergranularly whether stressed or not. The sensitized steel shows intergranular attack which is accelerated by stressing. Evidences indicate that tests in the polythionic acid and in the standard acid copper sulfate solution are electrochemically equivalent.
