Hydrogen effects on phase transformations in austenitic stainless steels

The effects of hydrogen and stress (strain) on the phase transitions of a variety of stainless steels (316, 321, 347) were investigated. Hydrogen was introduced by severe cathodic charging at room temperature. X-ray diffraction was employed to reveal the transformations occurring in thin surface layers. After charging expanded ∈ phase is always present, α′ martensite content increases during ageing and the final content depends on the stability of the austenite. The broadening of diffraction peaks of austenite after cathodic charging is caused by nonuniform distribution of hydrogen. The state of hydrogen distribution in the steel and the relationship between internal stresses, surface cracking and phase transition is discussed.