Influence of the environmental conditions on the susceptibility against Hydrogen re-embrittlement of high strength steel

摘要

Low alloyed high strength steels are increasingly used in the automotive industry to reduce weight resulting in lower fuels consumptions and reduced emissions. Those alloys show, however, a tendency for hydrogen induced cracking (HAC), where the hydrogen is formed either during processing or in corrosion processes during service. In order to cause hydrogen induced cracking, hydrogen does not only need to be formed, but also needs to penetrate and migrate into the material. A potential parameter for the probability of hydrogen to enter the material is the resulting hydrogen activity on the surface. The hydrogen activity is influenced by various parameters, e.g. temperature, pH-value, oxygen concentration, and duration. In this study, the influence of different environmental conditions were investigated by means of electrochemical permeation measurements to determine the hydrogen activity at the material surface. The electrochemical permeation measurements were performed under different concentrations of the local oxygen content (5% NaCl; pH = 3; flushing with different gases). For the chosen environmental conditions the results show that the local oxygen content has a significant influence on the resulting permeation current. To validate the results of the electrochemical permeation measurements and to examine the susceptibility against hydrogen re-embrittlement, incremental step-loadtests were performed under the same environmental conditions.