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« Hydrogen-related fracture behavior of martensitic steel »

Séminaire du Docteur Akinobu Shibata, de l'Université de Tokio (Japon)

Le Docteur Akinobu Shibata,

Dept. of Materials Science and Engineering
Kyoto University.

Group of Physical Property of Materials
Laboratory of Structure and Property of Materials

visitera le Centre des Matériaux d'Evry, les 15 et 16 mai 2017.

A cette occasion, il fera un séminaire intitulé

"Hydrogen-related fracture behavior of martensitic steel"

It is well known that the presence of hydrogen leads to catastrophic and premature fracture in metals and alloys. This phenomenon is termed ‘hydrogen embrittlement’, hydrogen-related fracture’, ‘delayed fracture’, etc. Several models have been proposed to account for hydrogen-related fracture. However, the underlying mechanism for hydrogen-related fracture is not fully understood.
From recent economic and environmental viewpoints, demands for high-strength steels are increasing more and more. Because susceptibility to hydrogen embrittlement increases with the increase of the strength of materials, hydrogen embrittlement is now becoming a major concern of steel society.
In this seminar, I introduce our recent research on the microstructural / crystallographic features and propagation process of hydrogen-related fracture in martensitic steels. The martensite structures with relatively low strength exhibited quasi-cleavage fracture. Crystallographic orientation analysis demonstrated that the quasi-cleavage fracture occurred on {011} planes. On the other hand, the macroscopic fracture surface morphologies of the martensite structures with relatively high strength appeared to be intergranular-like. However, nature of the fracture was somewhat different from a typical intergranular fracture, and the fracture surfaces consisted of facets parallel to {011} planes on a microscopic level. The experimental results strongly suggest that the crystallographic feature of {011} plane itself has an important role on the hydrogen-related fracture.
According to the reconstructed fracture propagation process by fracture surface topography analysis (FRASTA), the intergranular fracture at prior austenite grain boundaries initiated and propagated suddenly at the early stages of fracture. The quasi- cleavage fracture along {011} planes then gradually propagated within the prior austenite grains. The results clearly indicate that the fracture propagation path changes with the proceeding fracture from the prior austenite grain boundaries to along {011} planes within the prior austenite grains.

séminaire Dr Akinobu Shibata au CdM Evry - MINES ParisTech
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