Wasserstoffinduzierte Korrosion von niedriglegierten Stählen in wäßrigen Medien

Abstract

Die Aufnahme von Wasserstoff aus Medien kann bei Stiihen mit ferritischen Gefiigeanteilen zu Schiidigungen fiihren. Die Wechselwirkung von absorbiertem Wasserstoff und Stahl wird einerseits durch die Wasserstoffaktivitiit, andererseits durch belastungs-und gefiigeabhiingige Grenzwerte bestimmt. Die Arten wasserstotkduzierter Korrosion werden anhand von Versuchen mit niedriglegierten Stahlen dargestellt. Oberfliichenblasen und Innenrisse konnen ohne Einwirkung tiuSerer Belastungen auftreten. Bei wasserstoffinduzierter Spannungsdkorrosion werden Korrosionssysteme, bei denen ruhende Belastung bereits unerwiinschte Wirkungen zeigt, von solchen Systemen unterschieden, bei denen die Spannungsdkorrosion an Dehnraten innerhalb eines kritischen Geschwindigkeitsbereiches gebunden ist.The absorption of hydrogen from media can lead to cracking in steels with a ferritic structure. The interaction of absorbed hydrogen and steel is governed by the hydrogen activity and by stress-and structure-dependent threshold values. Different types of hydrogeninduced corrosion are illustrated by means of tests performed on lowalloy structural steels. Surface blistering and internal cracking can occur on the one hand without external stresses. In the case of hydrogen-induced stress corrosion cracking on the other hand a differentiation is made between corrosion systems in which constant loading displays already cracking and systems in which the cracking is tied to slow strain rates within a critical range.

Control of the diffusible hydrogen content in different steel phases through the targeted use of different welding consumables in underwater wet welding

“…[ 27–31 ] The solubility of hydrogen is significantly greater in the face‐centered cubic austenitic phase than in the body‐centered cubic lattice of the ferritic phase. [ 32 ] At the same time, the diffusion rate of hydrogen in austenitic iron is significantly reduced as compared with ferritic iron [ 32 ] (Figure 1). Hence, after underwater wet welding, the austenitic weld metal can trap more hydrogen.…”

“…Solubility and diffusion coefficient of hydrogen in ferritic and austenitic steel depending on the temperature [ 32 ] …”

“…F I G U R E 1 Solubility and diffusion coefficient of hydrogen in ferritic and austenitic steel depending on the temperature [32] To inhibit this type of corrosion, layers of ferritic weld metal can be used as covering layers above the austenitic root weld metal. This way, the areas of different electrochemical potentials are separated from the electrolyte, and the galvanic corrosion process should be stopped.…”

Analysis of Hydrogen-Induced Changes in the Cyclic Deformation Behavior of AISI 300–Series Austenitic Stainless Steels Using Cyclic Indentation Testing

“…The fact that the steel X2-9 is more susceptible to hydrogen than X2-12 accords well with the literature, which states that the tendency to hydrogen embrittlement increases with the reduced Ni content. The smaller Ni content leads to a lower stacking fault energy, a higher hydrogen diffusion rate as well as a lower austenite stability and thus, an increased content of deformation-induced α'-martensite [43]. However, this alone does not provide information of the relevant hydrogen embrittlement mechanism.…”

“…Note that the transformation from the face centered cubic (FCC) to the BCC crystal structure strongly affects the hydrogen diffusivity of the material by 4 to 5 orders of magnitude [43], and thus, significantly enhances the diffusion rate of hydrogen. Consequently, the hydrogen is transported much faster to the crack tip at X2-9 compared to X2-12.…”