Avaliação da estrutura e da resistência mecânica de aços IF nitretados a plasma com pré-encruamento

• Ano de defesa: 2014
• Autor(a) principal: Ana Paula de Andrade Manfridini
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Materiais e de Minas; Engenharia Metalúrgica; Engenharia metalúrgica
• Link de acesso: http://hdl.handle.net/1843/BUOS-9KQSBC

In this study the mechanical properties of IF steel surface modified by plasma nitriding process in triode configuration for 4 hours at temperatures of 450°C, 475°C and 500°C were investigated. Physical, morphological characteristics and wear behavior of modified IF steels were also evaluated. The possible influence of a pre-shot peening treatment in the plasma nitriding process was evaluated. It was found that the process of plasma surface modification altered surface morphology of IF steels, introducing precipitates as big and short needles in the ferritic matrix. Systems with pre-shot peening showed no precipitates with needle morphology. Phases obtained after nitriding in all systems evaluated were -Fe2-3N, '-Fe4N, ''Fe16N2 in addition to -Fe matrix of the IF steel. Instrumented microhardness tests exhibit a twofold increase on hardness values at the near surface, compared with the substrate, and a deep hardened region in IF steel. The nanoindentation results showed that the pre-shot peening gave an increase of surface hardness in the IF steel to about 20 m. The hardness obtained for the nitrided steel with mechanical shot peening treatment were very similar to those obtained for the nitrided steel without pre-deformation. The behavior of the friction coefficient of IF steels indicated that they had a tribo-oxidative wear mechanism, with the formation and break-down of the oxide layers, confirmed by EDS analysis of the wear track. The plasma nitriding modified the tribological behavior in IF steels by introducing a steady state with high coefficient of friction at short sliding distances, which was associated with a higher concentration of nitrogen in this region. The shot peening excluded this region, showing only an oxidative wear.