Instituições de ensino: Pontifícia Universidade Católica, Pontifícia Universidade Católica, Pontifícia Universidade Católica de Minas Gerais, Pontifícia Universidade Católica de Minas Gerais
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This article aims to investigate the microstructure and hardness behavior of SAE 4140 steel after tempering processes at times ranging from 15 minutes to 24 hours and temperatures between 200 and 700ºC. It also intends to investigate changes on the average grain size after austenitizing at different temperatures and times during the quenching process. Microstructural analysis was performed using an optical microscopy and Electron Backscatter Diffraction, X-ray diffraction technique was used to identify the phases fractions on the material. Hot rolled SAE 4140 steel showed a ferritic-pearlitic microstructure containing rod-shaped iron and chromium carbide. After water quenching, an austenitic grain boundary was obtained in a matrix of martensite, as expected. The average grain size remained practically constant after quenching at temperatures between 900 and 1000 ° C in times of austenitizing ranging from 1 to 4 hours. At temperatures above 1050°C there was a significant increase in the average grain size. The mathematical modeling for hardness prediction after the tempering process was based on the Hollomon-Jaffe parameter. The Hollomon-Jaffe constant presented a mean value of 14.36, but at high temperatures it was observed a variation in the C-value due to spheroidization and coalescence of iron-carbide.
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