In the production of iron chromium honeycombs, iron oxide and chromium oxide mixtures are reduced by hydrogen at elevated temperatures to produce a metallic alloy. The complete reduction of the iron oxide occurs prior to the reduction of the chromium oxide. The reduction of the chromium oxide particles within the iron matrix is affected by factors that include the diffusion of the reduced chromium away from the chromium oxide particle into the iron matrix, the diffusion of the gaseous reactants and products to and from the chromium oxide particles, and the porosity of the iron matrix, which changes as a result of sintering. The type of heat-treatment used, (isothermal or non-isothermal, i.e., holding at a specific temperature versus using a steadily increasing temperature) plays a vital role in how these factors will affect chromium oxide reduction. Experimental data were used in conjunction with sintering and dissolution models to obtain an understanding of the environment in which the chromium oxide particles reduce as a function of heat-treatment. This understanding will assist in the development of more effective processing steps for the reduction of metallic honeycombs from oxide mixtures.

Investigations of the production of thin-walled steel alloys through the reduction and subsequent gas carburization of structures made from metal oxide powders were performed. Batch compositions, as well as the heat treatment parameters necessary for the formation of structures were determined through the use of thermogravimetric analysis, dilatometric measurements, and microstructural investigation. Parameters for the high temperature carburization of thin-walled 4140 structures were determined. The research has shown that the amount of carbon in the walls of the structures can be controlled and uniform carbon contents across the cross-sections can be achieved in less than 30 minutes. Heat treatments for carburized samples were performed and subsequent microhardness testing resulted in values similar to conventionally produced 4140 steel. Studies on the decarburization behavior of similar alloys under various conditions were also performed in order to aid in the prediction of the microstructural behavior of samples during carburization and subsequent heat treatment. Low temperature gas carburization of structures with 316 steel composition has also been performed. Hardness variations present through the cross-section of the part after carburization suggest some transfer of carbon, though contents are not as high as anticipated. Suggestions for future work in this area are presented. The results of these investigations yield a novel method for the production of steel parts from metal oxide powders. The speed and low cost of the process, coupled with the proven ability of the process to yield parts with similar microstructural and mechanical characteristics as conventionally made alloys, allows for the techniques presented in this study to be used for the development of alloys which could not be previously done economically.

M. Tech. Metalurgical Engineering. / A research project was launched to produce zinc/ nickel, zinc/ tin and zinc/aluminium alloys at different concentrations and to test zinc pick-up with the typical steels used in South Africa. Results show that the addition of 0.023% Al and 0.06% Ni in the zinc bath can be successfully used to reduce the zinc pick up of commercial grades of steel. Tin improved quality of coating as compared to pure zinc.

No description available.

Orientadores: Paulo Roberto Mei, Marcelo Martins / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-16T16:54:20Z (GMT). No. of bitstreams: 1 Ritoni_Edson_M.pdf: 17028449 bytes, checksum: ff3c80af25659fb887c45f05f84c0a74 (MD5) Previous issue date: 2010 / Resumo: Os aços inoxidáveis duplex são assim designados por apresentarem duas fases em sua microestrutura; a ferrita e a austenita. Para estudo foram selecionados dois aços inoxidáveis fundidos de acordo com as normas ASTM A890/A890M Gr. 1A (CD4MCu) e ASTM A890/890M Gr. 1B (CD4MCuN). O que difere estes dois aços inoxidáveis duplex é a presença do nitrogênio na composição química do CD4MCuN. O nitrogênio é um elemento fortemente austenitizante, o que favorece a formação desta fase neste aço, e faz com que as porcentagens das fases fiquem balanceadas em, aproximadamente, 50%. No aço inoxidável duplex que não contém nitrogênio há um desbalanceamento a favor da ferrita, que pode atingir valores em torno de 70% e como a austenita é responsável pela tenacidade neste aço, o mesmo não apresenta bons resultados nos ensaios de impacto. Um fator que pode favorecer o aumento de fase ferrita na microestrutura final é a temperatura de solubilização que, quanto mais elevada, maior será a fração volumétrica de ferrita. Com o interesse de avaliar a influência da temperatura de solubilização sobre a fração volumétrica das fases, foram realizados tratamentos térmicos de solubilização em temperaturas de 1050, 1100 e 1150 ºC por 2 horas, seguido de resfriamento em água. Para medir e comparar as propriedades mecânicas entre os dois aços foram realizados ensaios de impacto Charpy na condição solubilizado a 1100 ºC, em temperaturas de -195 a +120 ºC variando de 20 em 20 ºC e também ensaios de tração à temperatura ambiente. Na matriz ferrítica da microestrutura bruta de fundição destes aços, foram observados muitos precipitados ricos em cobre, caracterizados como Cu3N e Cu3,8Ni através de microscopia eletrônica de transmissão. A fração volumétrica de ferrita, aumentou com o aumento da temperatura de solubilização para os dois aços, porém a variação foi maior para o aço sem nitrogênio. O aço contendo nitrogênio apresentou maior energia média absorvida ao impacto (84J) e menor temperatura de transição dúctil para frágil (-70 ºC) quando comparado com 73 J e -35 ºC apresentados pelo aço sem nitrogênio, levando em consideração que o critério adotado foi o da energia média. Além disso, maior limite de resistência e alongamento apresentou o aço nitrogenado nos ensaios de tração. Com base nestes resultados, fica evidenciado o aumento na tenacidade destes aços proporcionado pela presença do nitrogênio. / Abstract: The duplex stainless steel has this name due the two different phases found in its microstructure; ferrite and austenite. To develop this research was selected two similar duplex steel, with and without nitrogen. One of then is the ASTM A890/A890M Gr. 1A (CD4MCu) and the other is the ASTM A890/890M Gr. 1B (CD4MCuN). Nitrogen is a strong austenitizing element witch favors the formation of this phase in this type of steel and allows the phase balance by, approximately, 50%. Duplex stainless steel that don't has nitrogen presents an unbalance between ferrite and austenite, favoring the ferrite formation that can reach values around 70% that makes the steel brittler and with lower toughness properties related to the same steel with nitrogen addition. One factor that may increase the ferrite phase in the final microstructure is the temperature of the solubilization; as higher it is, higher is the ferrite percentage. In the interest of measure influence of the solubilization temperature, solution heat treatments were performed at temperatures of 1050, 1100 and 1150 ºC during 2 hours, followed by water cooling. To measure and compare the toughness between both duplex stainless steel, with and without nitrogen, Charpy impact test was performed in the solubilized condition at 1100 ºC, with test temperature ranging from -195 to +120 ºC, in steps of 20 ºC. In the ferrite matrix of the microstructure as cast, were observed many precipitated rich in cooper, identified as Cu3N e Cu3,8Ni by transmission electronic microscopy. The ferrite content increased with solubilization temperature increase for both steel, however the variation was higher to the nitrogened steel. The nitrogened steel showed bigger energy absorbed in the impact (84 J) and smaller transition temperature of ductile to brittle fracture (-70 ºC), when compared with 73 J and 35 ºC showed for the steel without nitrogen. Moreover, higher tensile strength and elongation showed the nitrogened steel on tensile test. Based on these results, it is evident the increase in toughness of these steels provided by the presence of nitrogen. / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Orientador: Valdemar Silva Leal / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-04T02:09:31Z (GMT). No. of bitstreams: 1 Carvalho_AntonioRogerioTorres_M.pdf: 2108495 bytes, checksum: 57b748cffef6835e43201549b90022af (MD5) Previous issue date: 2004 / Resumo: Estuda-se a influência da variação da agitação e da severidade de têmpera do meio de resfriamento sobre as curvas e taxas de resfriamento durante o processo de têmpera do aço. Os ensaios foram realizados com amostras dos aços 1045, 8620 e 8640, temperadas em água e salmoura, promovendo-se a variação do estado de agitação do refrigerante. Os dados apontam para variação da taxa de resfriamento máxima de 27,65% a 110,09% e uma diminuição nos tempos de resfriamento de 7,83% a 63,25%, para os três materiais estudados, com o aumento da agitação do meio. Verificam-se ainda, ganhos nas taxas e tempos de resfriamento com a variação da severidade de têmpera pela troca do meio, água por salmoura, da ordem de 73,27%, sem agitação do meio, e diminuição do tempo de resfriamento em aproximadamente 20%. Os dados ainda demonstram ganhos no tempo e nas taxas de resfriamento devido ao aumento do percentual de carbono no aço, quando se compara os dados obtidos para as amostras dos aços 8620 e 8640 / Abstract: Study about the influence of the agitation range and quench severity of the quenchant on cooling times and rates during the quench. The assays were accomplished with samples of steel 1045, 8620 and 8640, water and brine quenched, by increasing the agitation of the quenchant. The data show a rise in the maximum cooling rates of the 27.65% - 110%, and a reduction in the times of cooling of the 7.83% - 63.25%, on the three materials studied, with the increase of the agitation of the quenchant. They were verified too, a gain in the cooling rates and times with the variation of the quenchant severity, water to brine, of 73.27%, without agitation, and reduction of cooling time in approximately 20%. The data still show a gain in the cooling time and rates caused by the percentage of carbon increase on the steel, when be compared with the data scored in the samples of steel 8620 and 8640 / Mestrado / Instrumentação e Controle Industrial / Mestre Profissional em Engenharia Mecanica

No description available.

Over the last few decades, body-centered-cubic (bcc) beta (β) titanium alloys have largely been exploited as structural alloys owing to the richness in their microstructural features. These features, which lead to a unique combination of high specific strength and ductility, excellent hardenability, good fatigue performance, and corrosion resistance, make these alloys viable candidates for many applications, including aerospace, automobile, and orthopedic implants. The mechanical properties of these alloys strongly depend on the various phases present; which can be controlled by thermomechanical treatments and/or alloy design. The two most important and studied phases are the metastable ω phase and the stable α phase. The present study focuses on the microstructural evolution and the mechanical behavior of these two phases in a model β-Ti alloy, binary Ti-12wt. %Mo alloy, and a commercial β-Ti alloy, β-21S. Microstructures containing athermal and isothermal ω phases in the binary Ti-12wt. %Mo alloy are obtained under specific accurate temperature controlled heat treatments. The formation and the evolution of the ω-phase based microstructures are investigated in detail via various characterization techniques such as SEM, TEM, and 3D atom probe tomography. The mechanical behavior was investigated via quasi-static tensile loading; at room and elevated temperatures. The effect of β phase stability on the deformation behavior is then discussed. Similar to the Ti-12wt. %Mo, the formation and the evolution of the athermal and isothermal ω phases in the commercial β-21S alloy was studied under controlled heat treatments. The structural and compositional changes were tracked using SEM, TEM, HR-STEM, and 3D atom probe tomography (3D-APT). The presence of additional elements in the commercial alloy were noted to make a considerable difference in the evolution and morphology of the ω phase and also the mechanical behavior of the alloys. The Portevin-Le Chatelier (PLC) like effect was observed in iii this alloy at elevated temperature and this has been attributed to the shearing of the ω precipitates and the dynamic precipitation of the α phase within these channels. The formation of the stable α phase in the commercial β-21S alloy due to the influence of precursor phases, like the metastable ω phase, is investigated. It is evident from the microstructural characterization, using SEM, TEM, HR-STEM, and 3D-APT, that the ω phase does play a role on the fine scale α precipitation. The mechanical behavior of the β+α microstructure, investigated via tensile testing, shows that these alloys are ideal candidate for precipitation hardening. The exceptional strength values obtained in this alloy have been attributed to a combination of several factors.