Local Microstructural Stability and Hydrogen Embrittlement of Iron-Base FCC Alloys

In the frame of this work, the influence of microsegregations on local properties of certain austenitic steels is investigated. One intention is to generate “property-maps” dependent on the local chemical composition, more specifically, the local concentration of alloying elements. Previous studies exhibited that the steel AISI 304L is susceptible to hydrogen embrittlement whereas AISI 316L features a high resistance to the embrittlement process by atomic hydrogen. These results are partly connected with the positive influence of the element Ni on the austenite stability. In addition, the value of the stacking fault energy (SFE) affects the deformation mechanism during plastic strain. A low SFE is related with an increase in strength due to the twinning process or an εand α'-martensite transformation, respectively. Austenitic (γ) steels with a low SFE tend to transform in the order γ→ε→α'. On the other hand, austenitic steels with a high SFE show a high resistance to α'-transformation due to the more difficult direct γ→α' transformation. Local concentration differences of alloying elements (microsegregation) lead to an inhomogeneous response during plastic deformation, because of the resulting differences in the local SFE and the local austenite stability. Based on a fundamental knowledge about the local deformation mechanisms, it will be possible to develop new austenitic multicomponent iron-based fcc alloys with a high resistance to hydrogen environment embrittlement. The development of these alloys is focused on the microstructural stability. In this work, measured and calculated results of microsegregations in iron-base fcc alloys are presented. They serve as a basis for calculated local properties which will be discussed in the context of hydrogen embrittlement.

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