Abstract Controlling the recrystallization is an important way to reach grain size refinement and outstanding strength and toughness on alloy metals. This study sets out the application and investigation of mathematical microstructure modeling of a newly designed bainitic steel for hot forging industrial applications. The macro-scale model was used to observe and predict the austenitic grain size behavior during the controlled forging of a gear. Arrhenius grain growth kinetic and recrystallization model for a new class of bainitic steel was established for the given strain rate ranges and temperatures. This model was calibrated through microscopic analysis and used to simulate the unpublished constants of low alloyed bainitic forging steel DIN 18MnCrSiMo6-4 microstructure module using DEFORM® commercial finite element code. The increased temperature due to the adiabatic effect was investigated by numerical analysis, demonstrating its influence on grain coarsening. Local tensile test and Charpy-V notch were compared at different industrial hot forging temperatures and local plastic strain. Changes in yield strength and ductility have demonstrated the grain size influence on the processing parameters. The employed numerical model was an efficient tool to predict and present an alternative path to develop robust industrial forging using semi-empirical models.

As tensões residuais na superfície e subsuperfície de componentes mecânicos, durante sua manufatura e em serviço, podem afetar o desempenho e representar um importante potencial aos seus desvios de forma e dimensão. Estas tensões residuais também representam um dos principais potenciais para distorções (isto é, empenamentos e mudanças dimensionais) em componentes mecânicos durante a manufatura. Por isso são de grande importância a determinação da distribuição e o controle destas tensões residuais em cada etapa do processo de manufatura. Neste trabalho, foram realizadas comparações entre os resultados de medições de tensões residuais pelos métodos de difração de raios X (XRD) e Furo cego (Hole-drilling). Foram realizadas análises da variação das tensões residuais decorrentes do processo de fabricação de barras cilíndricas de aço AISI 1045. As barras foram analisadas com diferentes níveis de tensões residuais. A partir dos valores de deformações obtidos, foram calculadas as tensões residuais na direção longitudinal para cada ponto ensaiado. Com este trabalho, foi obtida uma comparação do desenvolvimento de tensões residuais na região superficial até uma profundidade de 1mm de barras cilíndricas.

The residual stresses in the surface and subsurface of mechanical components during the manufacturing process can affect the behavior and represent a significant potential for deviations in shape and size. These residual stresses also represent one of the main potentials for the distortion (which are bending and dimensional changes) in mechanical components during the manufacture. Therefore, the determination of the distribution and the control of these residual stresses in each stage of the manufacturing process is of great importance. In this work, analysis of the variation of the residual stresses were accomplished in cold-drawed bars of AISI 1045 steel due to the manufacturing process. The bars were analyzed by X-ray diffraction (XRD) and hole-drilling (H.D) to characterize the residual stresses. Starting from the values of strains obtained, the longitudinal residual stresses were calculated for each tested point. With this work, a detailed view of the development of stress in the surface to a depth of 1mm of bars after the process steps was obtained.