Regarding the great importance of fast cooling in steel industry for the production processes, a deep understanding of heat transfer and fluid dynamics must be held. A steel plate is heated up until a maximum temperature of 700 ⁰ C to be the n cooled down seconds later by a configuration of multi ple impinging water jets. Different flow rates are used simultaneously by different adjacent jets to perform quenching over the sample, so different hardness is obtained in the material over a small area . Temperature drop in time i s measured and monitored by embedded thermocouples and LabVIEW program. To achieve greater understanding of the quenching performance with different flow rates , several parameters are selected to be varied in order to achieve the best working conditions. Jet diameter takes values between 4 and 10 mm, initial temperature of quenching varies from 400 to 700 ⁰ C , subcooling temperature is tested for 65 and 75 K, and jet velocity varies between 1.9 and 3.9 m/s. The result of total number of 9 expe riments shown that v ariation of jet diam eter does not influence substantially on the cooling rate if flow rate is kept constant. High initial quenching temperature (600 - 700 ⁰ C ) led to slightly higher cooling rate in the stagnation region of water jets. The peak value of heat transfer rate in the upwash flow zone was more highlighted for initial quenching temperature 600 ⁰ C and below it. High er values of subcooling and jet velocity produce better cooling rates. The result shown higher jet velocity at one column of water jets changes position of upw ash flow slightly toward the adjacent column of jets with lower jet velocity. In general, the result shown that all the studied parameters did not have negative effect on obtaining various cooling rates over the steel plate.

No presente trabalho são relatados os resultados obtidos através de ensaios de caracterização de óleos de têmpera, tais como ponto de fulgor, viscosidade, número de acidez, espectroscopia por infravermelho e curvas de resfriamento, comparando óleos vegetais em estudo, com óleos minerais comerciais já utilizados como meios de resfriamento de têmpera. As curvas de resfriamento foram efetuadas utilizando sonda tipo Wolfson, nas temperaturas de 60, 80, 100 e 120ºC. Os ensaios de viscosidade foram feitos na temperatura de 40ºC. Adicionalmente, também foram efetuados ensaios de envelhecimento e oxidação dos óleos, utilizando um equipamento de envelhecimento acelerado, desenvolvido especialmente para este fim. De maneira geral, os óleos vegetais estudados apresentaram desempenho igual ou superior aos óleos minerais comerciais já utilizados em tratamentos térmico de têmpera. / In the present work are related the results obtained from the quenchant oils characterization test such as flash point, viscosity, acid number, infrared spectroscopy and cooling curves. In all tests the vegetables oils were compared with commercial quenchant mineral oils. Cooling curves were performed using Wolfson\'s probe at 60, 80, 100 and 120ºC. Viscosity tests were made in the temperature of 40ºC. Additional tests were performed for aging and oxidation studies, using an apparatus especially developed for that. In a general way, the vegetable oils have presented equal or best performance than the commercial quenchant mineral oils.

A têmpera, que consiste no resfriamento rápido do aço, após austenitização, é um dos tratamentos térmicos mais utilizados. O objetivo desse tratamento é a obtenção da estrutura martensítica, que oferece ótimas propriedades de dureza e resistência. A água, as soluções de polímeros e os óleos minerais são os meios refrigerantes mais comuns, sendo os óleos responsáveis pelo resfriamento em 80% dos casos. Verificou-se, no Brasil, o desconhecimento, dos mercados produtor e consumidor, quanto ao universo dos óleos de têmpera comercialmente disponíveis e de suas respectivas características de resfriamento. Assim, atentou-se para a necessidade de apresentar aos mercados já descritos, uma classificação dos óleos de têmpera nacionais,relacionando-os como rápidos, intermediários e lentos, destacando ainda, aspectos importantes nos parâmetros de resfriamento. / Quenching of steels, which consist of very fast cooling from austenitizing temperatures, is the most used heat treatment. The aim of this treatment is the obtation of martensitic microstructure. This microstructure confer excellent hardness and strength properties. The most common quenchants are water, polymer solutions and mineral oils, and the oils themselves are responsible by the 80% of the quenchants used during quenching. In Brazil, it was verified consumer lack of knowledge of the oils available as quenchants and their characteristics. Therefore, in this work as attempt was made to present the quenchants available and their classification as fast, intermediary and slow quenchants.

No presente trabalho são relatados os resultados obtidos através de ensaios de caracterização de óleos de têmpera, tais como ponto de fulgor, viscosidade, número de acidez, espectroscopia por infravermelho e curvas de resfriamento, comparando óleos vegetais em estudo, com óleos minerais comerciais já utilizados como meios de resfriamento de têmpera. As curvas de resfriamento foram efetuadas utilizando sonda tipo Wolfson, nas temperaturas de 60, 80, 100 e 120ºC. Os ensaios de viscosidade foram feitos na temperatura de 40ºC. Adicionalmente, também foram efetuados ensaios de envelhecimento e oxidação dos óleos, utilizando um equipamento de envelhecimento acelerado, desenvolvido especialmente para este fim. De maneira geral, os óleos vegetais estudados apresentaram desempenho igual ou superior aos óleos minerais comerciais já utilizados em tratamentos térmico de têmpera. / In the present work are related the results obtained from the quenchant oils characterization test such as flash point, viscosity, acid number, infrared spectroscopy and cooling curves. In all tests the vegetables oils were compared with commercial quenchant mineral oils. Cooling curves were performed using Wolfson\'s probe at 60, 80, 100 and 120ºC. Viscosity tests were made in the temperature of 40ºC. Additional tests were performed for aging and oxidation studies, using an apparatus especially developed for that. In a general way, the vegetable oils have presented equal or best performance than the commercial quenchant mineral oils.

A simulação no tratamento térmico tem-se tornado de vital importância, principalmente na fase de projeto de produto e planejamento e controle produção, reduzindo significativamente o tempo e o custo antes dedicados a estas tarefas. Esta tecnologia quando combinada à medição das curvas de resfriamento, torna-se uma poderosa e confiável ferramenta para a predição das propriedades mecânicas e metalúrgicas em peças tratadas termicamente. A modelagem do processo de têmpera traz como resultados, a exeqüibilidade do processo, a constituição microestrutural final e a distribuição das distorções e tensões residuais da peça. O presente trabalho visa simular a transferência de calor, através do cálculo dos coeficientes de transferência de calor, e das tensões residuais térmicas e distorções em corpos de prova de aço AISI 5160 e de uma sonda de Inconel 600, com a análise posterior dos parâmetros obtidos. / The simulation of heat treating is becoming of vital importance, specially during design of product and production planning and control, reducing significantly costs and time that used to be wasted on these tasks. This technology when combined to measured cooling curves, become a powerful and trustful tool for predicting mechanical and metallurgical properties of heat treated components. Modeling the quenching process shows the feasibility of the process, the final microstructure and the distribution of residual stresses and distortions on workpiece. The present work aims at simulate the heat transfer, the thermal residual stresses and distortions in a workpiece of AISI 5160 steel and of a probe of Inconel 600, with posterior analysis of the obtained parameters.

Este trabalho está inserido em um projeto que procura estudar a viabilidade técnica da aplicação de um relativamente novo conceito de tratamento térmico, chamado de Têmpera e Partição (T&P), como alternativa para o processamento de ferros fundidos nodulares com alta resistência mecânica. O processo T&P tem por objetivo a obtenção de microestruturas multifásicas constituídas de martensita e austenita retida, estabilizada em carbono. A martensita confere elevada resistência mecânica, enquanto a austenita confere ductilidade. No processo T&P, após a austenitização total ou parcial da liga, o material é temperado até uma temperatura de têmpera TT entre as temperaturas Ms e Mf para produzir uma mistura controlada de martensita e austenita. Em seguida, na etapa de partição, o material é mantido isotermicamente em uma temperatura igual ou mais elevada (denominada temperatura de partição TP) para permitir a partição de carbono da martensita para a austenita. O carbono em solução sólida diminui a temperatura Ms da austenita, estabilizando-a à temperatura ambiente. O presente trabalho procurou estudar aspectos de transformações de fases -- com ênfase na evolução microestrutural e cinética das reações -- do tratamento térmico de Têmpera e Partição (T&P) aplicado a uma liga de ferro fundido nodular (Fe-3,47%C-2,47%Si-0,2%Mn). Tratamentos térmicos consistiram de austenitização a 880 oC por 30 min, seguido de têmpera a 140, 170 e 200 oC e partição a 300, 375 e 450 oC por até 2 h. A caracterização microestrutural foi feita por microscopia óptica (MO), eletrônica de varredura (MEV), difração de elétrons retroespalhados (EBSD) e análise de microssonda eletrônica (EPMA). A análise cinética foi feita por meio de ensaios de dilatometria de alta resolução e difração de raios X in situ usando radiação síncrotron. Resultados mostram que a ocorrência de reações competitivas -- reação bainítica e precipitação de carbonetos na martensita -- é inevitável durante a aplicação do tratamento T&P à presente liga de ferro fundido nodular. A cinética da reação bainítica é acelerada pela presença da martensita formada na etapa de têmpera. A reação bainítica acontece, a baixas temperaturas, desacompanhada da precipitação de carbonetos e contribui para o enriquecimento em carbono, e consequente estabilização, da austenita. Devido à precipitação de carbonetos na martensita, a formação de ferrita bainítica é o principal mecanismo de enriquecimento em carbono da austenita. A microssegregação proveniente da etapa de solidificação permanece no material tratado termicamente e afeta a distribuição da martensita formada na etapa de têmpera e a cinética da reação bainítica. Em regiões correspondentes a contornos de célula eutética são observadas menores quantidades de martensita e a reação bainítica é mais lenta. A microestrutura final produzida pelo tratamento T&P aplicado ao ferro fundido consiste de martensita revenida com carbonetos, ferrita banítica e austenita enriquecida estabilizada pelo carbono. Adicionalmente, foi desenvolvido um modelo computacional que calcula a redistribuição local de carbono durante a etapa de partição do tratamento T&P, assumindo os efeitos da precipitação de do crescimento de placas de ferrita bainítica a partir da austenita. O modelo mostrou que a cinética de partição de carbono da martensita para a austenita é mais lenta quando os carbonetos precipitados são mais estáveis e que, quando a energia livre dos carbonetos é suficientemente baixa, o fluxo de carbono acontece da austenita para a martensita. A aplicação do modelo não se limita às condições estudadas neste trabalho e pode ser aplicada para o planejamento de tratamentos T&P para aços. / The present work belongs to a bigger project whose main goal is to study the technical feasibility of the application of a relatively new heat treating concept, called Quenching and Partitioning (Q&P), as an alternative to the processing of high strength ductile cast irons. The aim of the Q&P process is to obtain multiphase microstructures consisting of martensite and carbon enriched retained austenite. Martensite confers high strength, whereas austenite confers ductility. In the Q&P process, after total or partial austenitization of the alloy, the material is quenched in a quenching temperature TQ between the Ms and Mf temperatures to produce a controlled mixture of martensite and austenite. Next, at the partitioning step, the material is isothermally held at a either equal or higher temperature (so called partitioning temperature TP) in order to promote the carbon diffusion (partitioning) from martensite to austenite. The present work focus on the study of phase transformations aspects -- with emphasis on the microstructural evolution and kinetics of the reactions -- of the Q&P process applied to a ductile cast iron alloy (Fe-3,47%C-2,47%Si-0,2%Mn). Heat treatments consisted of austenitization at 880 oC for 30 min, followed by quenching at 140, 170, and 200 oC and partitioning at 300, 375 e 450 oC up to 2 h. The microstructural characterization was carried out by optical microscopy (OM), scanning electron microscopy (SEM), backscattered diffraction (EBSD), and electron probe microanalysis (EPMA). The kinetic analysis was studied by high resolution dilatometry tests and in situ X-ray diffraction using a synchrotron light source. Results showed that competitive reactions -- bainite reaction and carbides precipitation in martensite -- is unavoidable during the Q&P process. The bainite reaction kinetics is accelerated by the presence of martensite formed in the quenching step. The bainite reaction occurs at low temperatures without carbides precipitation and contributes to the carbon enrichment of austenite and its stabilization. Due to carbides precipitation in martensite, growth of bainitic ferrite is the main mechanism of carbon enrichment of austenite. Microsegregation inherited from the casting process is present in the heat treated material and affects the martensite distribution and the kinetics of the bainite reaction. In regions corresponding to eutectic cell boundaries less martensite is observed and the kinetics of bainite reaction is slower. The final microestructure produced by the Q&P process applied to the ductile cast iron consists of tempered martensite with carbides, bainitic ferrite, and carbon enriched austenite. Additionally, a computational model was developed to calculate the local kinetics of carbon redistribution during the partitioning step, considering the effects of carbides precipitation and bainite reaction. The model showed that the kinetics of carbon partitioning from martensite to austenite is slower when the tempering carbides are more stable and that, when the carbides free energy is sufficiently low, the carbon diffuses from austenite to martensite. The model is not limited to the studied conditions and can be applied to the development of Q&P heat treatments to steels.

Aluminum and steel components are usually quenched in forced gas, oil or water flow to improve mechanical properties and improve product life. During the quenching process, heat is transferred rapidly from the hot metal component to the quenchant and the rapid temperature drop introduces phase transformation and deformation in the hot metal component. As a result, quenching problems arise such as distortion, cracking and high tensile residual stresses. To avoid or minimize these problems while improving mechanical properties, process optimization is needed for both part geometry and quenching process design. A series of methods, including four existing methods and two new methods developed in this dissertation, were applied to obtain accurate thermal boundary conditions, i.e., the heat transfer coefficient (HTC) distribution. The commercially available material model DANTE was applied with finite element software ABAQUS to model the phase transformations and constitutive behavior of steel parts during quenching. A user material subroutine was developed for aluminum alloys based on a constitute model and tensile test data. The predicted residual stresses in the quenched parts agreed with those measured using the improved resistance strain gauge hole-drilling method and other methods, which validates the numerical models.

Heat treatment can be defined as a combination of heating and cooling operations applied to a metal or alloy in solid state. It is an important manufacturing process, which controls the mechanical properties of metals, therefore contributes to the product quality. Computerized Heat Treatment Planning System for Quenching and Tempering (CHT-q/t), a windows based stand alone software, is developed to assist the heat treatment process design. The goal of CHT-q/t is to predict the temperature profile of load in batch as well as continuous furnace during heating, quenching and tempering of steel, then to predict the mechanical properties as Quenched & Tempered, and finally to optimize the heat treatment process design. The thesis reviews existing heat treating simulation software and identifies the industrial need of a software tool which integrates part load and furnace model with heat treating process. The thesis discusses cooling curve of specimen and Time Temperature Transformation (TTT) diagram to determine the microstructure evolution and subsequently the mechanical properties of steel after quenching. An extensive database has been developed to support the various function modules. The thesis focuses mainly in the TTT and quenchant database development, property prediction after quenching and tempering and the implementation of software. The properties determined in the thesis are hardness, ultimate tensile strength, yield strength, toughness and percentage elongation. Hardness has been predicted by the use of some well known analytical equations and the TTT database, finally regression analysis has been used to give the value as a function of carbon percentage and volume fraction of martensite. The other mechanical properties are calculated based on a relation of hardness and volume fraction of martensite. Various case studies were performed to show the application of CHT-bf and CHT-cf at Bodycote Thermal Processing, Worcester & Waterbury. The objective behind the case studies was to study the effect of change in load arrangement, production rate and cycle time on the heat treated parts and finally to give recommendations in order to save energy and improve productivity and quality.

"The quench sensitivity of AA7136 has been experimentally investigated using Jominy end quench and test coupons of various heat treatments. It was found that this alloy is not quench sensitive. In addition, the effects of heating rate on both solution and aging treatments on AA7136 and AA7075 were determined using a newly developed reverse Jominy heating test. It was observed that hardness was reduced after rapid heating during aging and hardness increased slightly after rapid heating during solutionizing. These results are discussed in terms of microstructural developments. "

A 6061 aluminum probe was quenched with the CHTE probe-quenching system in distilled water while varying bath temperature and the level of agitation. Time vs. temperature data was collected during the quench by use of an ungrounded K-type thermocouple embedded inside the probe. Cooling rates and heat transfer coefficients, h, were calculated and Quench Factor Analysis (QFA) was also performed to quantitatively classify the quench severity. The data showed an increase in both maximum cooling rate and heat transfer coefficient and a decrease in the Quench Factor, Q, as bath temperature decreased and agitation level increased. Maximum heat transfer coefficient values ranged from 1000 W/m2K to 3900 W/m2K while maximum cooling rates of 50¡ÃƒÂ£C/s to 190¡ÃƒÂ£C/s were achieved. In addition, it was found that at higher levels of agitation, there was also an increase in the variation (i.e. standard deviation) of the cooling rate and therefore h and Q.