Effect of Hydrogen on Crack Propagation Behavior and Microstructures around Cracks in Austenitic Stainless Steels

Abstract

The effect of hydrogen on the crack propagation behavior and the microstructures around cracks in SUS 304H type and SUS 310 type austenitic stainless steels was examined by means of the tensile tests and microscopic observations. The results obtained are summarized as follows:
(1) For austenitic stainless steels, the yield strength and 2% flow stress are hardly dependent on the hydrogen content, whereas the fracture strain and the total energy on plastic deformation decrease remarkably as the hydrogen content increases.
(2) According to the notch tensile tests, the force for crack initiation does not change with the hydrogen content very much but the elongation by crack opening and the amount of work required for the fracture decrease remarkably with increasing the hydrogen content.
(3) An increase of absorbed hydrogen suppresses the strain induced transformation of α′ martensite, while it promotes the formation of ε martensite due to a lowering of the stacking fault energy by hydrogen.
(4) It is concluded that the hydrogen embrittlement of austenitic stainless steels is mainly due to the formation of ε martensite in the vicinity of cracks by the absorption of hydrogen and the easy propagation of cracks along the boundary between austenite and ε martensite.