Effects of residual stresses on hydrogen trapping in duplex stainless steels

The susceptibility of materials to hydrogen embrittlement is directly related, among others, to the residual stresses state of the metal and hydrogen. In this work, the crystalline development in hydrogen charged duplex stainless steels (DSS) was investigated by X-ray diffraction peak broadening. The Williamson–Hall (W‒H) method was used to study the individual contributions of crystallite size and lattice strain on the peak broadening of DSS with and without hydrogen. At the beginning, for initial data on DSS, we collected information from an as-received, non-charged sample, in order to evaluate the initial micro-stress and domain size by the W‒H method. Next, we built W‒H plots for hydrogen charged samples. Charging was conducted by two techniques: gas-phase charging and electrochemical (cathodic) charging, in order to study hydrogen fugacity's effect on microstrain (low and high, respectively). The results obtained showed significant changes between the domain sizes of hydrogen charged DSS to non-charged DSS; changes were even seen between gas-phase to cathodic hydrogen charged DSS. In addition, hydrogen had a major influence on the magnitude of residual stresses. At high hydrogen fugacity (cathodic), hydrogen significantly decreased the residual stress inside the sample. However, when it was desorbed at room temperature, its effect decreased. At low hydrogen fugacity (gas-phase), however, hydrogen lowered the residual stress even after aging for one month at room temperature, without gaining its initial value. The differences between hydrogen fugacity effect and non-charged DSS on microstrain will be discussed in detail.