Influence des séquences de traitements thermiques sur les transformations structurales de l'alliage beta-cez : easpects cinétiques et morphologiques

Texte intégral accessible uniquement aux membres de l'Université de LorrainePhase transformation sequances of the beta-Cez and Ti-6246 titanium alloys were studied during several thermal treatments. Several technics were used to show the structural changes : transmission electron microscopy, X-ray diffraction patterns, electrical resistance and analytical electron microscopy. The different transformation sequences occurring during heating and (alpha+beta) annealing treatments were studied for three initial structures for the beat-Cez alloy, which present different degree of metastability obtained by different cooling rates from the stable beta temperature range. We showed that an initial structure (beta metastalbe + omega anisothermal) transforms in different ways depending on the heating rate. For a slow heating rate, the omega phase precipites in the beta transient matrix followed by alpha clusters ; which coarsen to form the alpha lamellae at higher temperatures; For a rapid heating rate (Vc=5 degrés C/s), the omega phase is not observed. However, a supposed orthorhombixal phase is observed nearby 450 C. Whatever the reating rate, a maximum of alpha phase content is observed up to 700 C. For temperatures higher than 700 C, the matrix homogenization and the dissolution and coarsening of alpha phase are observed, up to 830 C and continue during the annealing treatments. For an initial structures (beta metastable + alpha + alpha clusters) stemed from the beta range during a slow cooling (1,5 C/s), only a weak growth in the alpha phase is observed during heating up to 560 C. After this temperature, alpha clusters dissolve themselves up to 700 C. For temperature higher than 700 C, the same structural changes as for the previous initial microstructure are observedLes séquences de transformations de phases des alliages de titane beta-cez et ti-6246 ont été étudiées au cours de différentes séquences thermiques. Plusieurs techniques ont été utilisées pour mettre en évidence les changements structuraux. Les différentes transformations se produisant au cours du chauffage et de la mise en solution dans le domaine (alpha+beta) ont été étudiées pour les trois structures initiales différentes. Nous avons montré qu'un mélange (beta métastable + oméga trempé) se décompose différemment suivant la vitesse de chauffage. Pour les vitesses les plus lentes la phase beta transitoire se décompose d'abord en phase oméga et puis en phase alpha amas qui coalescent pour former des lamelles à plus hautes températures. Au voisinage de 700c, un maximum de taux de phase alpha est observé quelle que soit la vitesse du chauffage. Au-delà de cette température, seule l'homogénéisation de la matrice, la dissolution partielle et la coalescence de la phase alpha sont observées, mécanismes qui se poursuivent au cours du maintien. Pour une structure (beta transitoire + alpha + alpha amas) issue d'un refroidissement lent, seule une faible croissance de la phase alpha se dissout complètement. Au-delà de 700c et au cours du maintien les changements structuraux sont identiques à ceux observés pour la structure précédente. Pour ces deux structures initiales, la morphologie d'alpha, après mise en solution en alpha + beta est très différent

Influence des séquences de traitements thermiques sur les transformations structurales de l'alliage beta-cez : easpects cinétiques et morphologiques

Texte intégral accessible uniquement aux membres de l'Université de LorrainePhase transformation sequances of the beta-Cez and Ti-6246 titanium alloys were studied during several thermal treatments. Several technics were used to show the structural changes : transmission electron microscopy, X-ray diffraction patterns, electrical resistance and analytical electron microscopy. The different transformation sequences occurring during heating and (alpha+beta) annealing treatments were studied for three initial structures for the beat-Cez alloy, which present different degree of metastability obtained by different cooling rates from the stable beta temperature range. We showed that an initial structure (beta metastalbe + omega anisothermal) transforms in different ways depending on the heating rate. For a slow heating rate, the omega phase precipites in the beta transient matrix followed by alpha clusters ; which coarsen to form the alpha lamellae at higher temperatures; For a rapid heating rate (Vc=5 degrés C/s), the omega phase is not observed. However, a supposed orthorhombixal phase is observed nearby 450 C. Whatever the reating rate, a maximum of alpha phase content is observed up to 700 C. For temperatures higher than 700 C, the matrix homogenization and the dissolution and coarsening of alpha phase are observed, up to 830 C and continue during the annealing treatments. For an initial structures (beta metastable + alpha + alpha clusters) stemed from the beta range during a slow cooling (1,5 C/s), only a weak growth in the alpha phase is observed during heating up to 560 C. After this temperature, alpha clusters dissolve themselves up to 700 C. For temperature higher than 700 C, the same structural changes as for the previous initial microstructure are observedLes séquences de transformations de phases des alliages de titane beta-cez et ti-6246 ont été étudiées au cours de différentes séquences thermiques. Plusieurs techniques ont été utilisées pour mettre en évidence les changements structuraux. Les différentes transformations se produisant au cours du chauffage et de la mise en solution dans le domaine (alpha+beta) ont été étudiées pour les trois structures initiales différentes. Nous avons montré qu'un mélange (beta métastable + oméga trempé) se décompose différemment suivant la vitesse de chauffage. Pour les vitesses les plus lentes la phase beta transitoire se décompose d'abord en phase oméga et puis en phase alpha amas qui coalescent pour former des lamelles à plus hautes températures. Au voisinage de 700c, un maximum de taux de phase alpha est observé quelle que soit la vitesse du chauffage. Au-delà de cette température, seule l'homogénéisation de la matrice, la dissolution partielle et la coalescence de la phase alpha sont observées, mécanismes qui se poursuivent au cours du maintien. Pour une structure (beta transitoire + alpha + alpha amas) issue d'un refroidissement lent, seule une faible croissance de la phase alpha se dissout complètement. Au-delà de 700c et au cours du maintien les changements structuraux sont identiques à ceux observés pour la structure précédente. Pour ces deux structures initiales, la morphologie d'alpha, après mise en solution en alpha + beta est très différent

Efeito da Velocidade de Soldagem e Anisotropia no Cálculo de Tensões Residuais em Chapas Soldadas pelo Processo GMAW

Esse trabalho busca estudar os efeitos da mudança da velocidade de soldagem e o efeito da anisotropia no cálculo de tensões residuais calculadas pelo método de deslocamento de pontos coordenados (DPC) de chapas laminadas soldadas pelo processo de soldagem GMAW. O material utilizado foi um aço estrutural naval ASTM A131 Grau AH-36, soldado no sentido da laminação e transversalmente a ela com duas velocidades de soldagem, 3,5 e 5,4mm/s. Para analisar o efeito da velocidade de soldagem e a mudança do sentido da laminação em relação ao cordão de solda na tensão residual, e se existe interação entre essas duas condições na resposta da tensão residual foram realizados os testes de hipóteses e do ANOVA, onde encontramos uma forte interação da mudança de velocidade de soldagem na tensão residual e uma influência da combinação da velocidade de soldagem com o sentido de laminação na resposta da tensão residual

Previsão das Dimensões da Zona Termicamente Afetada de Juntas Soldadas com Variação de Parâmetros de Soldagem

A escolha de parâmetros de soldagem é uma etapa importante do processo de soldagem, influenciando diretamente no aporte térmico fornecido às juntas soldadas. Esse valor de aporte térmico juntamente com a distribuição de temperatura nas juntas soldadas fornece ao projetista condições de prever o tamanho da zona termicamente afetada, o tipo de microestrutura formada e consequentemente prevenir os efeitos das tensões residuais. Neste estudo foram variados três parâmetros que nos forneceram condições de soldagens diferentes. Cada condição foi analisada pelo software SmartWeld 2011 e por macrografias para encontrar e comparar o tamanho da zona termicamente afetada (ZTA). Ainda, foram calculadas as tensões residuais através do método de Deslocamento por Pontos Coordenados (DPC). É possível escolher os melhores parâmetros para a junta de topo soldada pelo processo GMAW considerando os parâmetros em questão

Study for Performance Increase of a Extractor Device by Steel Replacement of AISI 304 Steel for AISI 420 Steel

The performance of an extractor device used in the food industry was studied from the development of structural analysis through computational modeling based on finite elements. These analyses considered the mechanical properties of AISI 304 and 420 stainless steels, in addition to the tribological aspects of the device in operation. Initially, uniaxial tensile tests were carried out according to the ABNT NBR 6892 standard and hardness tests were carried out according to ASTM E384, E92, and E18 standards. From the mechanical tests, structural analyses were carried out numerically on each of the components of the extractor device. After analyzing all the components, the device was assembled to be tested in operation. The wear and service life of devices made from these two materials were evaluated. From this study, it could be concluded that the extractor device made with AISI 420 stainless steel, in addition to having a lower manufacturing cost, suffered less wear and had an increase in service life of up to 650% compared to the extractor device made with steel stainless steel AISI 304

Study of phase transformations In API 5L X80 Steel in order to increase its fracture toughness

Phase transformations in API 5L X80 steel were studied in different thermomechanical sequences with a view to increasing the fracture toughness of this steel. Dilatometry tests performed on the quenched steel detected a phase transformation occurred, during heating, in the temperature range 593-618 K. This phase transformation was identified as the dissolution of M-A islands. Based on preliminary dilatometric tests, ten thermal and thermomechanical treatments were performed on X80 steel samples. Initially, the material was hot rolled and quenched and only quenched. On the material without deformation, aging was also performed at temperatures of 603, 673, 723, 773, 823 and 873 K. These treatments resulted in the formation of the acicular ferrite constituent, among others. Tensile tests showed that the aging treatments produced reductions in yield strength and increases in the elongation and toughness of X80 steel. All the treatments resulted in an increase in the tensile strength of steel