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Theses

Forgeabilité des aciers inoxydables austéno-ferritiques

Abstract : The Duplex Stainless Steels (DSS) are defined as a family of stainless steels consisting of a two-phase microstructure involving ä-ferrite and ã-austenite. Exceptional combinations of strength and toughness together with good corrosion resistance under critical working conditions designate DSS a suitable alternative to conventional austenitic stainless steels. Unfortunately, the relatively poor hot workability of these alloys makes the industrial processing of flat products particularly critical. Cracking of the coils during hot rolling along the edges is frequently reported. As a consequence, additional operations like grinding, discontinuous processing or scraping are often required, leading to a dramatic increase of the manufacturing costs. The different parameters affecting the hot working of duplex stainless steels have been reviewed in order to identify which are the missing pieces of the puzzle. The bibliographical review reveals that two pieces are missing in the hot workability puzzle. On the one hand, it is necessary to develop a new hot ductility test which allows discriminating microstructures in terms of high temperature tearing resistance, and on the other hand, quantitative data about the strain partitioning between ferrite and austenite during the hot working operations are needed. The Essential Work of Fracture concept has been applied at high temperature. It has been demonstrated that this method is a reliable and discriminating tool for quantifying the high temperature tearing resistance and to generate a physically relevant index to guide the optimization of microstructures towards successful forming operations. A modified microgrid technique has been developed to experimentally simulate the local state of deformation of different duplex microstructures at high temperature. This technique provides qualitative results about the deformation features as well as quantitative data about the strain partitioning between ferrite and austenite. The micro-strain distributions measured can be used to validate the models predicting the hot deformation of duplex stainless steels during the roughing-mill operations. The two tools developed in this investigation allow suggesting possible remedies for the edge cracking phenomenon.
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Submitted on : Tuesday, February 21, 2012 - 12:48:24 AM
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Guilhem Martin. Forgeabilité des aciers inoxydables austéno-ferritiques. Matériaux. Institut National Polytechnique de Grenoble - INPG, 2011. Français. ⟨tel-00672279⟩

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