Trata do estudo experimental da energia específica de corte e sua relação com parâmetros de usinagem, características geométricas e tribológicas das ferramentas, e material da peça usinada. Dentre as variáveis investigadas são destaques a profundidade de usinagem, velocidade de corte, raio de ponta, geometria de quebra-cavaco, tipo de revestimento das ferramentas, dureza, microestrutura e composição química do material da peça. Os seguintes materiais foram empregados nos ensaios: aços SAE 1213, 1020, 1045, ASTM H13 recozido e temperado, e liga de alumínio 2024. As medições de energia específica foram realizadas em uma máquina Charpy instrumentada por meio de um dinamômetro piezelétrico e um encoder ótico rotacional. Vários resultados puderam ser comparados aos obtidos em torno e centro de usinagem CNC devidamente instrumentados. Testes na condição HSM foram implementados nas máquinas-ferramentas. Todas as variáveis pesquisadas mostraram exercer influência sobre a energia específica. O aumento da profundidade de usinagem em 2,3 vezes causou diminuição da energia específica em 21%, na usinagem da liga de alumínio 2024. A elevação da velocidade de corte em torno de 70% conduziu a uma queda da energia específica de 24% para o aço SAE 1020. A geometria da ferramenta influiu mais decisivamente na energia específica sob velocidades de corte convencionais que na condição HSM. Pequenas variações na geometria do quebra-cavaco dos insertos causaram diminuição da energia específica de até 29%, para velocidade de corte convencional, e de 14% para HSM, na usinagem do aço H13 temperado. Diversos resultados de energia específica de corte medidos pelo ensaio Charpy proposto por este trabalho apresentaram boa concordância com os valores equivalentes fornecidos pela literatura científica / This thesis presents an experimental study about the specific cutting energy and its relation with cutting parameters, geometrical and tribological characteristics of tools, and workpiece material. Depth of cut, cutting speed, tool nose radius, chip-breaker geometry, tool coating, hardness, microstructure and chemical composition of the workpiece material are some investigated variables. The following workpiece materials were tested: SAE 1213, 1020, 1045, annealed and tempered ASTM H13 steels, and 2024 aluminum alloy. The specific cutting energy values were measured by using a Charpy machine instrumented through piezoelectric dynamometer and incremental optical encoder. Several results could be compared to ones from instrumented CNC lathe and machining center. Tests under HSM condition were carried out in machine-tools. All researched variables have influence over specific cutting energy. The depth of cut rise in 2.3x caused a decrease of specific cutting energy around 21% when machining 2024 aluminum alloy. The elevation of the cutting speed about 70% leaded to reduction of specific cutting energy around 24% when machining SAE 1020 steel. The tool geometry present more influence on specific cutting energy under conventional cutting speed than at high speed cutting. Small variations of tool chip-breaker geometries caused diminution of the specific cutting energy up to 29% for conventional cutting speed, and 14% on average for HSM condition when machining tempered ASTM H13 steel. Various specific cutting energy results obtained from the Charpy test proposed by this work presented a good concordance with equivalent ones provided by scientific literature

Trata do estudo experimental da energia específica de corte e sua relação com parâmetros de usinagem, características geométricas e tribológicas das ferramentas, e material da peça usinada. Dentre as variáveis investigadas são destaques a profundidade de usinagem, velocidade de corte, raio de ponta, geometria de quebra-cavaco, tipo de revestimento das ferramentas, dureza, microestrutura e composição química do material da peça. Os seguintes materiais foram empregados nos ensaios: aços SAE 1213, 1020, 1045, ASTM H13 recozido e temperado, e liga de alumínio 2024. As medições de energia específica foram realizadas em uma máquina Charpy instrumentada por meio de um dinamômetro piezelétrico e um encoder ótico rotacional. Vários resultados puderam ser comparados aos obtidos em torno e centro de usinagem CNC devidamente instrumentados. Testes na condição HSM foram implementados nas máquinas-ferramentas. Todas as variáveis pesquisadas mostraram exercer influência sobre a energia específica. O aumento da profundidade de usinagem em 2,3 vezes causou diminuição da energia específica em 21%, na usinagem da liga de alumínio 2024. A elevação da velocidade de corte em torno de 70% conduziu a uma queda da energia específica de 24% para o aço SAE 1020. A geometria da ferramenta influiu mais decisivamente na energia específica sob velocidades de corte convencionais que na condição HSM. Pequenas variações na geometria do quebra-cavaco dos insertos causaram diminuição da energia específica de até 29%, para velocidade de corte convencional, e de 14% para HSM, na usinagem do aço H13 temperado. Diversos resultados de energia específica de corte medidos pelo ensaio Charpy proposto por este trabalho apresentaram boa concordância com os valores equivalentes fornecidos pela literatura científica / This thesis presents an experimental study about the specific cutting energy and its relation with cutting parameters, geometrical and tribological characteristics of tools, and workpiece material. Depth of cut, cutting speed, tool nose radius, chip-breaker geometry, tool coating, hardness, microstructure and chemical composition of the workpiece material are some investigated variables. The following workpiece materials were tested: SAE 1213, 1020, 1045, annealed and tempered ASTM H13 steels, and 2024 aluminum alloy. The specific cutting energy values were measured by using a Charpy machine instrumented through piezoelectric dynamometer and incremental optical encoder. Several results could be compared to ones from instrumented CNC lathe and machining center. Tests under HSM condition were carried out in machine-tools. All researched variables have influence over specific cutting energy. The depth of cut rise in 2.3x caused a decrease of specific cutting energy around 21% when machining 2024 aluminum alloy. The elevation of the cutting speed about 70% leaded to reduction of specific cutting energy around 24% when machining SAE 1020 steel. The tool geometry present more influence on specific cutting energy under conventional cutting speed than at high speed cutting. Small variations of tool chip-breaker geometries caused diminution of the specific cutting energy up to 29% for conventional cutting speed, and 14% on average for HSM condition when machining tempered ASTM H13 steel. Various specific cutting energy results obtained from the Charpy test proposed by this work presented a good concordance with equivalent ones provided by scientific literature

Ce travail de thèse concerne l’acier 16MND5 des cuves des Réacteurs à Eau Préssurisée (REP).L’étude vise à caractériser de manière quantitative la microstructure et à comprendre l’effet desparamètres influents (vitesse de refroidissement, température de revenu …) sur sa formation. D’unpoint de vue expérimental, l’étude est menée grâce à l’utilisation des techniques d’observationcomme la métallographie, le MET, MEB et l’EBSD, et la réalisation de traitements thermiquescontrôlés (dilatométrie notamment).Ces observations visent à identifier les différents constituants de l’acier et de déterminer lesgrandeurs quantitatives les caractériser (tailles, fractions volumiques des différentes phases ainsique leurs orientations cristallographiques).Nous avons dans un premier temps caractérisé de manière complète et quantitative, lamicrostructure de l’acier 16MND5 à l’état de réception (trempé et revenu). L’étude a permis demontrer qu’il existe un gradient de microstructure entre la peau interne et le coeur de l’épaisseur dela virole. La microstructure à coeur est constituée de ferrite proeutectoïde, de bainite et d’amas decarbures, tandis qu’en peau interne on est en présence de bainite et d’amas de carbures.Une campagne d’essais de dilatométrie a été réalisée afin de simuler la microstructure brute detrempe de l’acier 16MND5 et d’observer l’effet de la vitesse de refroidissement, des températuresde transformation sur la microstructure des aciers de cuve. Ces essais ont révélé que lamicrostructure de l’acier 16MND5 après refroidissement est constituée de bainite, d’îlots demartensite et d’austénite résiduelle (M-A) enrichie en carbone. Ce sont ces îlots M-A qui donnentnaissance aux amas de carbures lors du revenu final.L’effet de la composition chimique de cet acier a été étudié grâce à l’utilisation d’une tôle ayant unecomposition chimique plus riche en carbone et en éléments d’alliages. Ce travail a montré quel’augmentation des teneurs en carbone et en éléments d’alliages modifiaient la morphologie et lacristallographie de la ferrite.L’étude des comportements mécaniques des constituants présents en peau interne, quart épaisseur etmi épaisseur a été réalisée grâce à des essais de résilience sur des éprouvettes de mini charpy. Cetteétude a permis de montrer qu’à basse température (-120°C) la peau interne présente de meilleurespropriétés de résilience que le quart et la mi épaisseur de la virole. Des examens de la surfacelatérale des éprouvettes de Charpy ont montré que la présence de ferrite proeutectoïde favorise lagermination de micro-fissures de clivage. / Reactor pressure vessel is the second security barrier of the nuclear reactor and it is elaboratedwith a low carbon steel ( C-0.16%). Due to the large size of the ferrule there is temperatureand cooling rate gradient, which lead to microstructure gradient. To develop predictive modelit is necessary to well describe the microstructure which depend to the processing parameters.We focuse our work in investigating the effect of the processing parameters (cooling rate,chemical composition...) on the final microstructure during phase transformation.To get these informations and better describe the microstructure, we have used someexperimental technics like SEM, EBSD, TEM and Optical Microscopy. The steel used is alow carbon steel with a composition of C-0.16%, Mn-1.32%, Ni-0.72%, Mo-0.49%, Si-0.23%, Cr-0.23%, P-0.010%, S-0.004%. The material has been tempered in the range 635°C-660°C after cooling. Three positions have been chosen for examinations, because the coolingrate is not the same between the center and the edge of the material. The results of theobservations made in the different scale, indicate that the microstructure is mainly baniticwith bainitic ferrite and cementite precipitates. Examinations of the precipitates withextractive replicas in TEM reveal that morphology of cementite particles is complex they arecylinder-shaped particles, short bars particles and skeletal particles. OrientationsRelationships (OR) have been determined between ferrite and cementite particles with thinfoils in TEM by using Selected Area Diffraction, in a large number areas the Isaichev andBagaryatskii OR have been observed, a little Pitsch Petch OR have been obtained. The EBSDmap shows that the bainitic ferrite morphologies are both lath like and polygon. Themisorientations inside the laths are very small (0.5° misorientation point to point) andbetween laths we have the range 49-60° misorientation. The profile of misorientationsbetween point to point indicates higher frequency for the range 49-60°. Charpy test have beenperformed to analyze the effect of the microstructure on the fracture energy at lowtemperature. The results show that the fracture energy decreases when the content ofproeutectoid ferrite is high.