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Ao meu orientador e, sobretudo amigo Prof. Dr. Hélio Goldenstein pela imensa ajuda, apoio e confiança durante estes vários anos de trabalhos em conjunto sob os mais variados e interessantes temas. Aos colegas do Centro de Pesquisas e da Engenharia de Produto da Villares Metals pelo apoio durante o desenvolvimento das atividades deste projeto. Agradeço em especial ao José Carlos Rillo Rodrigues,

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ResumoEstuda-se efeito do tratamento criogênico em um aço AISI D2 para trabalho a frio com a técnica de difração de raios X utilizando luz síncrotron. Este trabalho tem por objetivo verificar os efeitos: i) do tempo de permanência à temperatura criogênica (3 horas, 10 horas e 30 horas); ii) da temperatura criogênica (-80°C e -196°C); iii) do alívio de tensões (130°C) antes do tratamento criogênico; iv) do duplo revenimento (520°C/2 h cada) após a menor temperatura criogênica (-196°C) e o máximo tempo de permanência a esta temperatura (30 horas), com e sem o alívio de tensões. As difrações de raios X foram realizadas na linha de luz D10B-XPD do Laboratório Nacional de Luz Síncrotron e o tratamento dos padrões experimentais foi realizado por refinamento de Rietveld utilizando o programa TOPAS Academic em conjunto com cartões ICCD-PDF, da base de 2006, com as estruturas da austenita, martensita e carbonetos M 7 C 3 e M 2 C. As amostras após revenimento foram caracterizadas por MEV e MEV-FEG. Determinam-se as frações de austenita retida, as mudanças no reticulado cristalino da martensita e da austenita e as frações volumétricas dos carbonetos. Palavras-chave: Tratamento criogênico; Aço-ferramenta; Difração de raios X; Luz síncrotron. CRYOGENIC AND STRESS RELIEF THERMAL TREATMENTS IN AN AISI D2 STEEL AbstractThe effects of cryogenic treatments on an AISI D2 cold work tool steel using X-ray diffraction from syncronton radiation are studied. The aim of this work is to verify the effects of: i) time at cryogenic temperatures (3, 10 and 30 hours); ii) cryogenic temperatures (-80°C and -196°C); iii) stress relief heat treatment (130°C) before cryogenic treatments; iv) effect of double tempering at 520°C for 2 hours each time, after cryogenic treatment at -196°C for 30 hours, with and without previous stress relief. X-ray diffraction experiments were conducted at the line D10B-XPD of the Laboratório Nacional de Luz Síncrotron and the experimental results were treated using Rietveld refining, with TOPAS Academic in conjunction with cards from the ICCD-PDF 2006 database for austenite, martensite and carbides M 7 C 3 and M 2 C. Tempered samples were characterized using SEM and SEM-FEG. Volume fraction of retained austenite and carbides, as well as changes in the crystal lattices of martensite and austenite are obtained from the X-ray experiments.

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Nickel-based alloys are used in industrial sectors where high mechanical strength and corrosion resistance are required at high temperatures. However, these alloys have low machinability as a consequence of inherent properties. Some of these properties such as high cold work hardening rate and low heat conductivity may cause damages to the machined surface. Among the nickel-based alloys, one that has good properties for oil exploration is alloy 625. As the components made of this alloy are frequently used in very rough environments, this study sought to evaluate the influence of tool geometry, cutting conditions (feed and cutting speed) and tool condition (fresh or worn) on the surface integrity of turned alloy 625 parts in order to discover turning practices for this alloy that result in minimal damage to the workpiece surface. A secondary aim was to evaluate how these input variables affected the life of the coated carbide tools used in the turning experiments with this alloy. The main conclusions are that (a) the surfaces produced with a fresh tool with positive geometry had compressive residual stresses, while those produced with negative tool geometry had tensile residual stresses and (b) when a worn tool was used all the surfaces produced had compressive residual stresses.