Orientador: Paulo Roberto Mei / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-12T11:09:37Z (GMT). No. of bitstreams: 1 Bubani_FrancodeCastro_M.pdf: 7334881 bytes, checksum: 9cc4f96ceff0972bc2552404b4ccee84 (MD5) Previous issue date: 2008 / Resumo: Os efeitos da adição de níquel e da temperatura em ligas ferro-cromo foram estudados. Sete ligas de base ferro, com 18% Cr e teores de níquel variando entre zero e 60%, foram utilizadas no estudo (0, 10, 20, 30, 40, 50 e 60% Ni). Foram realizados ensaios de tração em temperatura ambiente, 350 e 700 ºC; simulação por termodinâmica computacional; microscopia ótica no estado recozido, nas amostras de quick stop, após deformação a frio, a 350 e a 700 ºC; difração de raios X no estado recozido, após deformação a 350 e a 700 ºC; ensaio de dureza a quente a 100, 200, 300 e 400 ºC; ensaio de impacto Charpy em temperatura ambiente e a -196 ºC; e ensaio de quick stop; análise térmica por DTA; ensaios de dureza no estado recozido, nos cavacos obtidos em torneamento, após deformação a 350 e 700 ºC. Os resultados dos ensaios de tração a 350 ºC foram correlacionados com os dados obtidos por Marques (2007), visando relacionar propriedades mecânicas e usinabilidade. A tendência geral de redução da usinabilidade com o aumento do teor de níquel foi relacionada com o aumento da resistência mecânica e da ductilidade a quente, proporcionados pelo níquel. A alta usinabilidade observada na liga 30% Ni foi relacionada com a presença de inclusões com cálcio nesta liga, o que proporcionou ganhos muito expressivos em usinabilidade, mas sem prejudicar as propriedades mecânicas avaliadas. / Abstract: The effects of nickel addition and temperature in iron-chromium alloys have been studied. Seven iron-base alloys with 18% Cr and nickel content varying from zero to 60% were used in the study (0, 10, 20, 30, 40, 50 and 60% Ni). The alloys were submitted to tension tests at room temperature, 350 and 700 ºC; computational thermodynamics simulations; optical metallography observations in annealed state, after deformation at room temperature, 350 and 700 oC, and in quick stop samples; x-ray diffraction, annealed and after deformation at 350 and 700 ºC; hot hardness test at 100, 200, 300 and 400 ºC; Charpy impact tests at room temperature and at -196 ºC; quick stop test; differential thermal analysis tests; Vickers hardness tests: annealed, on chips, after deformation at 350 and 700 ºC. The results of the tension tests at 350 ºC were correlated with the data obtained by Marques (2007), aiming at reaching a relationship between mechanical properties and machinability. The general tendency of reduction in machinability with the increase of nickel content was related to the increase in mechanical strength and hot ductility provided by nickel. The high machinability observed in the 30% Ni alloy was related with the presence of calcium inclusions in this alloy, which allowed for significant gains in machinability, but without loss to the evaluated mechanical properties. / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

A systematic in-depth study has been undertaken to establish the corrosion mechanism of a Model 25Cr-35Ni-Fe alloy and four commercial alloys HP40Nb, AISI314, HP40Al and Alloy 800H in low oxygen, high sulphur and carbon containing environments typically found in coal gasification and fluidised bed combustion processes. A review of present knowledge of corrosion processes in purely oxidizing, sulphidizing and carburizing environments and multiple reactant carburizing/ oxidizing, carburizing/sulphizing and oxidizing/sulphidizing environments is given. The experimental programme was designed to establish the role of sulphur on the corrosion process by studying corrosion mechanisms in a sulphurfree H2-7%C0-1.5%H2o gas, a low sulphur H2-7%C0-1.5%H20-0.2%H 2 S gas (pS2_8= 10 bar), and a high sulphur H 2 -7%C0-1.5%H 2 0-0.6%H 2 S gas (pS = lO bar) at 800'C. All_21j_hree environments had a constant partiaf pressure of oxygen (po2 = 10 bar) and carbon activity (ac = 0.3). In the sulphur-free gas the Model alloy formed a thin uniform cr 2 o 3 layer which grew at a constant parabolic rate throughout the exposure period of 0 - 5000 hours. Surface working increased the growth rate and thickness of the Cr 2 o 3 layer but created a large number of cracks and pores which allowed carbon containing gaseous species to diffuse through the oxide to form carbide precipitates in the alloy substrata. Alloying additions of Si promoted the formation of an inner SiO layer which reduced the corrosion rate by cutting off the outward diffusion of Cr, Mn and Fe. Alloying additions of Mn promoted the formation of an additional outer (Mn, Fe )Cr 2o 4 layer. The 3. 5% Al content of the HP40Al was insufficient to form a complete Al 2 o3 layer. Alloy 800H was susceptible to localised internal oxidation. Adding a low level of sulphur (0.2% H 2 S) to the gas increased the corrosion rate of the Model alloy in the 1nitial stages. This rate gradually slowed down before becoming parabolic after 1000 - 2000 hours. This was due to the nucleation of sulphides in addition to oxides. The oxides and sulphides grew side by side until the oxides overgrew the sulphides to form a complete Cr 2o3 layer which cut off further ingress of sulphur from the gas. The entrapped sulphides promoted localized thickening of the oxide layer. Eventually the sulphur redistributed from the sulphides in the scale to internal sulphide precipitates in the alloy with the corrosion rate returning to that of the sulphur-fre,e gas for the rest of the exposure period (5000 hours total). In the commercial alloys the internal sulphide precipitates prevented the inner Si02 layer becoming complete. Sulphur doped the (Mn, Fe) Cr 2 0 4 outer layer ana the intermediate Cr 2o3 layer formed from the spinal layer, increasing the number of cation . vacancies and the growth rate of the scale. These factors caused a massive Cr depletion of the alloy substrata after several thousand hours. The internal carbides became unstable which led to a massive amount of internal attack and a dramatic increase (breakaway) in the corrosion rate. Due to its thickness and the presence of Si02 inner layer the external scale became susceptible to spallation. If this occurred the oxides and sulphides nucleated on the alloy surface again but sulphides. protective alloy. insufficient Cr was available for the oxides to overgrow the The sulphides therefore grew to form a fast growing nonsulphide scale which soon led to catastrophic failure of the Increasing the level of sulphur in the gas to 0.6% H2S caused oxides and sulphides to nucleate on the surface, but in this case the sulphides overgrew the oxides to form thick fast growing non-protective sulphide scales on all the alloys.

Orientador: Anselmo Eduardo Diniz / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-09T18:35:54Z (GMT). No. of bitstreams: 1 Marques_DanielCirillo_M.pdf: 1133787 bytes, checksum: 7116947050a42005d85657f4c29da1a2 (MD5) Previous issue date: 2007 / Resumo: O objetivo deste trabalho foi estudar a influência do teor de níquel de ligas FeCrNi na vida da ferramenta de metal duro em processo de torneamento em acabamento. Para este estudo foram preparadas ligas com composição básica 18%Cr-0,01%C-0,2%Si-0,4%Mn e com teores de níquel variados (0, 10, 20, 30, 40, 50 e 60%). A medida que o teor de níquel subia, o teor de ferro diminuía na mesma proporção. Os ensaios foram realizados com pastilhas de metal duro classe M15 revestidas com TiC/Al2O3/TiN. Todos os materiais foram usinados nas mesmas condições (vc = 230 m/min, ap = 0,6 mm e f = 0,1 mm/volta), garantindo assim, como única fonte de variação, o teor de níquel. Os resultados mostram que a vida da ferramenta diminui com o aumento do teor de níquel e que o principal mecanismo de desgaste da ferramenta é a adesão e arrancamento de partículas da ferramenta. Uma exceção se deu com o material com 30% de níquel, que apesar de apresentar o mesmo mecanismo de desgaste, mostrouse mais fácil de usinar, gerando maior tempo de vida da ferramenta / Abstract: The aim of this work was to study the influence of nickel content in FeCrNi alloys on the coated cemented carbide tool life during the finish turning process. For this purpose 18%Cr-0,01%C-0,2%Si-0,4%Mn base composition and variable nickel content (0, 10, 20, 30, 40, 50 and 60 weight %) alloys were prepared. As the nickel content increased, the iron content decreased in the same proportion. Tests were carried out with coated cemented carbide inserts, M15 class with TiC/Al2O3/TiN coating. All alloys were machined on the same cutting conditions (vc = 230 m/min, ap = 0,6 mm and f = 0,1 mm/rev), in order to set nickel content as the only input variable. Results indicate that tool life decreases with the growth of nickel content, and the mainly tool wear mechanism is attrition. An exception was the material with 30% of nickel, that presented the same tool wear mechanism but showed out higher machinability, allowing longer tool life / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica