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For studying the stress corrosion susceptibility of high manganese austenitic cryogenic steel HM400 in liquid ammonia medium, the slow strain rate test (SSRT) was used to investigate the stress corrosion susceptibility of high manganese austenitic cryogenic steel HM400 in four media: pure liquid ammonia (NH3), air+liquid ammonia (NH3+Air), 0.1 mg/L H2O+pure liquid ammonia (NH3+0.1 mg/L H2O) and air (Air) at room temperature. The fracture micro morphology, crack morphology, change of microstructure and mechanical properties of the samples before and after tests were characterized by scanning electron microscope (SEM), optical microscope (OM), X-ray diffractometer (XRD) and hardness tester. Results showed that strain strengthening occurred in high manganese austenitic cryogenic steel HM400 during tensile deformation. Moreover, HM400 steel possessed poor stress corrosion resistance in liquid ammonia medium, and hence it was not suitable as high parameterization and lightweight materials of liquid ammonia storage and transportation containers.

For studying the critical condition for the transition of the dominant failure mechanism of 304 austenitic stainless steel in OH-+ Cl- medium, the stress corrosion sensitivity of 304 austenitic stainless steel in the mediums of 10% NaOH and 15% NaOH solutions containing different Cl- content at 100 ℃ was investigated by slow strain rate test (SSRT). The surface morphology of the sample fracture and the composition of the corrosion product were characterized by scanning electron microscope (SEM) and energy dispersive analyzer (EDS). Result showed that Cl- could promote the occurrence of alkali stress corrosion of 304 austenitic stainless steel in 10% NaOH + nCl- (n = 100 ～1 000 mg/L) and 15% NaOH + nCl- (n =100～2 000 mg/L). With the increase of Cl- concentration, the interaction mechanism between Cl- and OH- changed from promotion into competition. When the Cl- concentration reached the critical value, the dominant failure mechanism of 304 austenitic stainless steel in OH-+Cl- mixed medium transformed to chloride stress corrosion (CSC). Besides, the critical concentration of Cl- within the scope of experiment for the transition of the dominant failure mechanism of 304 austenitic stainless steel in the mediums of 10% NaOH and 15% NaOH were 500 mg/L and 1 000 mg/L respectively.