A MECHANISM FOR STRESS-CORROSION EMBRITTLEMENT. Final Report, June 15, 1958-September 30, 1961

The stress-corrosion cracking behavior of 304 stainless steel in MgCl/ sub 2/ at 140 deg C has been studied. Tensile deformation behavior in the vicinity of the yield point suggested that there is no measurable Rebinder Effect or Roscwo Effect. In static tensile tests, the time to failure was found to decrease with applied strcss in agreement with previous work. No incubation period prior to the onset of cracking was noted, while varying the time in solution prior to the application of stress had no effect on subsequent stress- induced failure. Prestressing at various temperatures in air in the range 110 deg --500 deg C was found to influence subsequent time to failure at 140 deg C in MgCl/sub 2/. Cyclic loading treatments were found to have no influence on time to failure, and there was no evidence of rapid crack propagation characteristic of brittle fracture. Prior deformation carried out at various temperatures reduced the susceptibility of 304 stainless steel. Microstructure was also found to strongly influence cracking behavior; strain-induced martensite resulted in a marked increase in resistance to failure. In the earlier part of the program it was shown through the Stroh-Petch equation relating fracture stress and grain sizemore » that stress-corrosion environments can lead to a lowering of the surface energy associated with the formation of fracture surfaces. A variety of materials and corrosion media were examined. During the final year's work it was demonstrated that the mechanism of stress-corrosion cracking depended on the simultaneous action of both electrochemical and mecham-cal processes. Using a variety of experimental conditions, efforts to separate the electrochemical and mechanical contributions to the phenomenon proved unsuccessful. (auth)« less