Skalenübergreifende Charakterisierung kurzer Ermüdungsrisse in artverschiedenen Edelstählen unter dem Einfluss von Wasserstoff

The present work deals with the characterisation of the propagation behaviour of short fatigue cracks in three stainless steels under cyclic loading and under the influence of hydrogen. For this purpose in-situ tests were carried out on a servo-hydraulic testing machine as well as on a miniature testing machine. This characterisation is important because the lifetime of components can be strongly dominated by short crack propagation.
Two meta-stable austenitic stainless steels (X2CrNi19-9 and X2CrNi19-12), which differ in their nickel content, and one completely martensitic steel (X3CrNiMo13-4) were investigated.
For this purpose, with hydrogen precharged samples were compared with corresponding uncharged samples as reference. Both the X2CrNi19-9 and the X2CrNi19-12 tend to deformation-induced martensite formation during fatigue, whereas the X2CrNi19-9 shows, due to its lower nickel content, a higher tendency to deformation-induced martensite formation.
While the crack propagation rate in X2CrNi19-12 samples is hardly influenced by the hydrogen present, X2CrNi19-9 is significantly more susceptible to hydrogen. Therefor, the crack propagation speed in these samples is significantly increased by the present of hydrogen.
A pronounced response to the presence of hydrogen is the change in crack initiation sites and slip band morphology in both austenitic stainless steels. While cracks initiate in reference samples at slip bands and grain boundaries, cracks in precharged samples start at large micro-structural defects such as grain boundary triple points.
The martensitic X3CrNiMo13-4 samples show the greatest possible influence of hydrogen on the fatigue properties. Precharged samples show a significantly higher crack growth rate.