An investigation was made to determine the causes of surface contact fatigue failure of a case hardened driver pinion located in the intermediate shaft of a reducer gearbox used in a sugar and alcohol mill. The examination of the component revealed the presence of a cemented layer substantially thicker than that generally specified for pinions devised for this application. This, associated with the massive presence of brittle threadlike carbon-rich cementite phase (Fe3C) in prior austenite grain boundaries of the pinion teeth, favored surface crack nucleation and propagation during cyclic loading, leading to spallation of the contact surface with the counterpart gear, which impaired the system's operation. Poor carburization practice was discovered as the root cause of the mechanical failure, thus demanding the implementation of a new manufacturing route to avoid problems in similar load-bearing rotating components.

Ensaios de tração a quente e fluência foram realizados na liga Kanthal A1 na faixa de temperatura de 600º a 800ºC. Cada um desses conjuntos de dados foram analisados separadamente de acordo com suas próprias metodologias, mas, neste trabalho, uma tentativa foi realizada para se estabelecer uma correlação entre os mesmos. Um novo critério proposto para converter dados de tração para fluência torna possível a análise conjunta desses dois grupos de resultados de acordo com relações usuais de fluência como: Norton, Monkman-Grant, Larson-Miller e outros. A notável compatibilidade entre os dois conjuntos por esse procedimento sugere que dados de tração a quente podem ser convertidos para dados de fluência para a liga Kanthal A1, como verificado anteriormente para outros materiais metálicos.

Hot tensile and creep tests were carried out on Kanthal A1 alloy in the temperature range from 600 to 800ºC. Each of these sets of data were analyzed separately according to their own methodologies, but an attempt was made to find a correlation between them. A new criterion proposed for converting hot tensile data to creep data, makes possible the analysis of the two kinds of results according to usual creep relations like: Norton, Monkman-Grant, Larson-Miller and others. The remarkable compatibility verified between both sets of data by this procedure strongly suggests that hot tensile data can be converted to creep data and vice-versa for Kanthal A1 alloy, as verified previously for other metallic materials.

This study investigates the influence of quenching/tempering temperatures on the fracture toughness and fatigue life of SAE 5160 steel, considering different phosphorus contents. Quenching and tempering treatments were applied to samples removed from different bars of commercial SAE 5160 steel with different P content. Three different austenitizing temperatures for quenching: 850, 900 and 1000 ºC and a constant holding time of 15 minutes were used. The oil temperature for quenching was kept at 66 ºC and the tempering conditions were 470, 500 and 530 ºC with the necessary time for a final hardness of 45 ± 3 HRC. Therefore, the heat treatments cycles were applied to specimens containing low (0.012 wt. (%)), medium (0.017 wt. (%)) and high (above 0.025 wt. (%)) phosphorus contents, in order to observe the effects of this element on the susceptibility of these steels to enhance quench and tempering embrittlements. The Charpy tests results showed that the phosphorus content analyzed in this work has caused embrittlement, even in the bars with the lowest P content, leading to intergranular fracture. However, if the nucleation life is taken into consideration, this embrittlement has no effect on the nucleation fatigue life of the component.