The Effects of Various Hydrogen Bearing Environments on the K_Iscc of AISI Type 4340 and 3.5% NiCrMoV Steels

Rising load K_Iscc tests have been conducted on a high strength Type 4340 and a 3.5% NiCrMoV steel in various hydrogen bearing gases. The test environments included: methane, acetylene, industrial grade natural gas, ammonia, hydrogen chloride, and hydrogen bromide. Tests were also conducted in air to provide a basis for evaluating environment induced cracking susceptibility. The test results are compared with previous data obtained from testing in a H₂S gas environment. Both materials were highly susecptible to cracking in hydrogen bromide and hydrogen chloride environments. They showed only mild susceptibility in ammonia gas and almost no susceptibility in the hydrocarbon environments. An attempt has been made to use the equilibrium dissociation reactions of the non hydrocarbon environments to establish hydrogen cracking susceptibility. This effort was inconclusive in that it appears that strong synergistic effects occur between the components of the gas and the metal resulting in unpredictable behavior. The fractographic features associated with cracking in the various environments were also examined.