Electron Back Scattered Diffraction Study of Deformation and Recrystallization Textures of Constituent Phases in a Ferritic-ustenitic Duplex Steel

Bhadak, B V (2014) Electron Back Scattered Diffraction Study of Deformation and Recrystallization Textures of Constituent Phases in a Ferritic-ustenitic Duplex Steel. Masters thesis, Indian Institute of Technology, Hyderabad.

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Abstract

The effect of warm rolling on the evolution of microstructure, microtexture and mechanical properties of a 0.05%C-22%Cr-5%Ni duplex stainless steel (DSS) was investigated. For this purpose, the DSS alloy was homogenized at 1150°C warm rolled at 625°C up to 90% reduction of thickness. Development of ultrafine lamellar morphology with alternate arrangement of the two phases was revealed during warm rolling. The ferrite in DSS developed stronger RD-fiber (RD//<110>) than ND-fiber (ND//<111>) while austenite in DSS showed pure metal or copper type texture. Subsequently, isothermal annealing was carried out at the homogenization temperature. Gradual transformation from lamellar bamboo type morphology to more globular morphology was observed during isothermal annealing. The texture development of the two phases is not significantly affected by the presence of the other phase while the grain growth during recrystallization is strongly affected by the presence of the other phase. Ferrite in annealed DSS showed much stronger RD-fiber which indicated pronounced recovery. Austenite in DSS retained pure metal type texture i.e. recrystallization texture with no preferential orientation selection. The DSS in the as warm-rolled and annealed condition showed remarkable increase in the ultimate tensile strength to ~1.2GPa. Strength and ductility of DSS after annealing were significantly affected by different structural and morphological changes. The present results demonstrated that warm rolling could be used successfully as a novel thermo-mechanical processing route for developing ultrahigh strength DSS.

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