The aim of the work was to prepare an overview about the microstructures present in high-speed steel, focused on the crystallography of the carbides. High-speed steels are currently obtained by casting, powder metallurgy and more recently spray forming. High-speed steels have a high hardness resulting from a microstructure, which consists of a steel matrix (martensite and ferrite), in which embedded carbides of different crystal structure, chemical composition, morphology and size, exist. These carbides are commonly named MxC, where M represents one or more metallic atoms. These carbides can be identified by X-ray diffraction considering M as a unique metallic atom. In this work, it is discussed, in basis of the first principles of physics crystallography, the validation of this identification when it is considered that other atoms in the structure are substitutional. Further, it is discussed some requirements for data acquisition that allows the Rietveld refinement to be applied on carbide crystallography and phase amount determination.

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À minha esposa Marilene O número explica o universo-Lema dos Pitagóricos i AGRADECIMENTOS Agradeço ao PhD. Rubens Nunes de Faria Jr. pela orientação deste trabalho, pela amizade e apoio. Agradeço ao Dr. José Mestnik Filho pela ajuda e tempo dedicado na etapa dos cálculos teóricos utilizados nesta tese, ao apoio e valiosas discussões. Agradeço à Professora Dra. Helena Maria Petrilli pela ajuda na introdução aos cálculos teóricos (ab-initio), pelo tempo dedicado e por permitir o uso de sua área de processamento de dados no CCE-USP.