Microstructural Evolution of Two Automotive Steels Induced by Warm Forging and Subcritical Annealing

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Abstract: During the last decades, environmental and safety regulations have encouraged the production of stronger and lighter steels. For this reason, this paper explores the associative action of grain refinement and carbide precipitation induced by warm forging and subcritical annealing in two automotive steels: C-Mn and HSLA. To do so, several samples were warm forged at 550°C, quenched in water and subcritically annealed between 1 and 10 minutes. Then, the microstructure and hardness of both steels was assessed in each processing stage through optical microscopy, SEM, TEM and Vickers hardness. These tests showed that the thermomechanical treatment significantly refined the grain size in both steels by means of a controlled ferrite recrystallization. Furthermore, the recovery process in the HSLA was slowed by the precipitation of fine carbides in the grain boundaries. Finally, the thermomechanical treatment improved the hardness of both steels.

Authors: W. Hormaza, C.A.S. Oliveira , G.M. Castro Güiza, and L.M. Méndez Moreno

Keywords: Recrystallization, Grain Refinement, Warm Thermomechanical Process; Carbon Steel, Microalloyed Steel

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5 pages

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