Effect of Inclusions and Precipitates on Hydrogen Embrittlement of Mn-Alloyed Austenitic Stainless Steels

The aim of this study was to characterize the inclusions and precipitates of the six austenitic stainless steel test materials by the INCA analysis program as well as to examine the capability of inclusions and precipitates to act as hydrogen traps by utilizing the thermal desorption spectroscopy (TDS). Especially, the hydrogen trapping capability of nano‐sized Nb‐precipitates of the steel 204Cu/Nb was of interest. On the INCA results it was noticed that the average sizes of the inclusions as well as the distribution and the amount of the oxide inclusions were about the same in all test materials. In comparison to the other grades, the distribution of inclusions and precipitates was significantly different in the niobium‐alloyed 204Cu/Nb steel containing a large number of small micro‐ and nano‐sized niobium precipitates. In the TDS study, it was observed that the TDS spectra of 201B, 204Cu, and 204Cu/Nb were similar, although the inclusion and precipitation distribution of these steels differs considerably between the materials. Thus, it was assumed that the nano‐sized Nb‐precipitates or other inclusions were not able to trap sufficiently hydrogen to their interface, which would result in a better resistance against delayed cracking. Inclusions and precipitates in Mn‐alloyed austenitic stainless steels are characterized and their effect on hydrogen trapping examined with thermal desorption spectroscopy. In an experimental Nb‐alloyed stainless steel large number of small precipitates (e.g., NbC, MbN, Nb(C,N)) exist, but they have no beneficial effect on resistance against delayed cracking. Modifications for the manufacturing process are suggested to obtain better hydrogen trapping properties.