Chemical Factors Affecting Stress Corrosion Cracking of 18–8 Stainless Steels

Abstract

Transgranular stress corrosion cracking of 18–8 Type 304 specimens in boiling 42% does not depend on rate of stressing (<1 sec to 10 min) nor on small variations in degree of plastic deformation. Cold worked specimens fail in shorter times than annealed, sheared specimens. Addition of to decreases cracking time whereas addition of increases the time. Pre‐exposure of unstressed specimens to slightly decreases cracking times of the same specimens subsequently stressed. Cracks occur along sheared edges of unstressed specimens despite stress relief anneal at 375°C for 2 hr.Cracks propagate along sheared edges of U‐bend specimens at 0.5 to 1 cm/hr through that portion of the specimen cross section in tension, the rate being much slower through the remaining cross section. No induction time for cracks to initiate was observed.Sizeable pits are not necessary for cracking in , but appear to be essential in media like which in absence of pitting is not particularly active in causing cracking. The pitting mechanism produces concentrated low pH metal chlorides within the pit, which like cause immediate cracking. Oxygen is required for pitting of 18–8 by solutions as shown by Uhlig and Morrill, and hence also for stress corrosion cracking as observed by Williams and Eckel, but oxygen is not necessary in or .Cracking can be prevented by cathodic protection at a CD. of 0.03 ma/cm2 or higher. Anodic CD. up to 0.01 ma/cm2 were found to have no effect on cracking tendency, nor did coupling of 18–8 to Pt.