Internal friction in hydrogen-charged CrNi and CrNiMn austenitic stainless steels

Relaxation and hysteretic phenomena caused by hydrogen in CrlSNilS, Cr25Ni20, and Cr18Ni16Mn10 steels have been studied by using a low-frequency internal friction (IF) technique. Five IF peaks were observed in the temperature range of 80 to 450 K; three of them are of relaxation nature and two others have a hysteretic character. The enthalpies of activation have been evaluated by means of thermoactivation analysis. Short-range migration of hydrogen atoms has been found to be responsible for the relaxation peaks, while the hysteretic peaks have been attributed to the outgassing processes accompanied by cracking. It follows from the data on orientation dependence of the relaxation strength and values of the activation enthalpies that relaxation has a Snoeklike nature and is caused by reorientation of complexes of hydrogen atoms with substitutional solutes causing noncubic defects, the symmetry of which is not higher than orthorhombic. Study of the composition effects has led to the conclusion that different substitutional solutes contribute to different components of the relaxation spectra in accordance with their influence on hydrogen diffusivity. Effect of electron irradiation on hydrogen-induced relaxation was studied and explained in terms of shortrange atomic order. No indication of hydrogen-induced Snoek-Köster (SK) relaxation was observed in accordance with the data available evidencing absence of SK relaxation in face-centered cubic (fee) metals having low values of stacking fault energy.