Hydrogen-Induced Phase Transformations in Type 304L Stainless Steels

Abstract

Electrolytic charging of hydrogen into Type 304L stainless steel at room temperature and 100 C (212 F) induced partial transformation) of the austenite to the some martensitic phases [α′ (bcc) and ε (hep)] as are formed by cold-working hydrogen-free austenite at low temperatures (−196 C) (−321 F). No evidence of a hexagonal hydride was found. The formation of the ε phase by cathodic charging suggests that hydrogen lowers the stacking fault energy of austenite. Hydrogen charging expands the austenite lattice, causes the dislocation and stacking fault density to increase with increasing hydrogen concentration, and causes dislocation movement.

The influence of hydrogen on martensitic transformation of austenitic steels

“…High-temperature impregnation of deformed specimens leads to the accumulation of hydrogen at the boundary of the phases and a reduction in plasticity in further tension, which is characteristic of dual phase steels [9]. Therefore, embrittlement of hydrogen-impregnated specimens of 12Khl8N10T steel is markedly strengthened with an increase in the quantity of martensite from 0 to 25% in the range of preliminary deformations of 20-40% (Figs.…”

“…2b). As is known [9], the hydrogen brittleness of dual-phase steels is strengthened only up to a certain content of the second phase, which for 06Khl8N5G9AB steel is reached with low values of plastic deformation. Since the influence of hydrogen on the properties of this steel is caused by intensification of the martensite transformation, with an increase in the degree of preliminary tension, when a significant quantity of aphase is formed before impregnation of the specimen with hydrogen, the sensitivity to hydrogen embrittlement decreases.…”

“…Electron-microscopic and xray analyses show that the energy of stacking faults significantly decreases owing to the hydrogenation of austenite steels [1,5,8]. It is known that the energy of stacking faults determines the stresses and, respectively, strains under which the transverse sliding of dislocations and the formation of a polygonal dislocation substructure occur [1,5,9]. These phenomena promote a uniform distribution of stresses and hydrogen in the metal, and, therefore, remove the danger of premature fracture.…”

“…2). An additional effect can be related to the decrease in the length of the free path of dislocations in cold-worked specimens, which brakes hydrogen transportation by dislocations [8,9,14].…”

Hydrogen Absorption Induced Slow Crack Growth in Austenitic Stainless Steels for Petrochemical Pressure Vessel Industries

“…This subject has become controversial [6][7][8][9][14][15][16][17], due in part to comparison of data obtained from alloys which were not well characterized. For example, it cannot be assumed that a nominally stable steel will always consistently be stable, or, conversely, that a nominally unstable grade will always under go strain-induced martensitic transformation, or that a steel which is stable under one type of deformation will be stable under a different mode.…”