Mechanisms of hydrogen trapping in austenitic, duplex, and super martensitic stainless steels

Hydrogen interaction with structural materials, especially stainless steels, is of great importance due to the acute effect that it can have on them. Stainless steels have become very common in many applications, and in water and high pressure environments in particular, due to their high levels of corrosion resistance and broad range of strength. Steel's durability is very much dependent on its microstructure and interaction with hydrogen. The action of hydrogen can lead to changes in mechanical properties, phase transformation and eventually to environmentally-assisted failure, which is known as hydrogen embrittlement (fracture). The susceptibility of steels to this hydrogen fracture mechanism is directly related to the interaction between traps (defects) and hydrogen. In this research, we study hydrogen fracture mechanisms through hydrogen interaction with trapping sites by thermal desorption spectrometry (TDS), and the calculation of hydrogen trapping energies states. Microstructure effects on hydrogen were investigated by exploring different stainless steels, including: austenitic stainless steel (AUSS), ferritic-austenitic (duplex) stainless steel (DSS), and super martensitic stainless steel (SMSS). The objective of this study is to determine the influences of thermal desorption analysis on the crystal structure of different stainless steels in order to better understand the trapping mechanisms of hydrogen in a variety of structure materials. It was found that the AUSS has the greatest stability of austenitic (γ) phase– ∼22% higher than DSS and ∼45% higher than SMSS. Moreover, the AUSS presented the lowest hydrogen trapping values of ∼31% compared with DSS and ∼25% compared with SMSS. Hydrogen fracture mechanism was found to be highly dependent on the hydrogen trapping states and even more on the γ-phase stability. The hydrogen trapping mechanisms are discussed in detail.