Study of cleavage fracture in ferritic stainless steels. Part I: Development and characterization of model microstructures
Résumé
A major drawback in ferritic steels production and usage is their mechanical brittleness at temperatures close to ambient temperature. Precipitation and grain size appear as two major parameters in such cleavage brittle behavior. This is why six model microstructures have been elaborated from the same base of chemical composition, but with different elements additions and thermal treatments. The base composition is 18% chromium and 2% molybdenum to ensure an entirely ferritic matrix at any temperature even with 0.015% of both carbon and nitrogen. The addition of titanium or niobium changed the nature, size and location of the carbides and nitrides, while carefully chosen heat treatments varied the size of the grains. Microstructure characterizations down to very fine scales (TEM, SANS) combined with thermodynamics and diffusion modeling allowed analyzing precipitates formation as well as remaining interstitial elements (carbon and nitrogen) in solution in the ferritic matrix. This multi-scale analysis of the microstructures is important to understand the mechanical behavior of the alloys, which will be presented in a companion paper.
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MSEA-D-22-06050-revised manuscript-clean version.pdf (2.32 Mo)
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