工程科学学报 (Jun 2024)
Microsegregation models of solute elements during the solidification of high-carbon, medium-magnetic wear-resistant steel
Abstract
The microsegregation behavior of solute elements during the solidification of medium manganese wear-resistant steel has been systematically studied using directional solidification, electron probe microanalysis (EPMA), Factsage, and other experiments. The results showed that the solidification structure of Fe–8.5Mn–2.1Cr–0.95C medium manganese steel was dendrite, and no interconversion occurred between the cell and dendrite. Furthermore, the average secondary dendrite arm spacing of medium manganese steel was 59.77 μm when the pulling speed was 50 μm·s−1 during the directional solidification experiment. The results calculated using Factsage showed that the microstructure transformation of medium manganese steel during solidification was L → L + γ → γ, which belonged to the austenite solidification mode, and no peritectic reaction, δ phase, or other phases appeared. Based on the equilibrium cooling and IF modes, the liquidus and solid temperatures of medium manganese steel calculated using Factsage were 1422.93 ℃ and 1280.98 ℃, respectively. Furthermore, the EPMA experiments indicated that the Mn and Cr contents at the edges of secondary dendrites were considerably higher than those at the center. Specifically, the Mn content decreased from 9.13% to 7.49%, and the Cr content decreased from 2.03% to 1.68% simultaneously. This result indicates that the positive segregation behavior of Mn and Cr occurred during the directional solidification of medium manganese steel. Microsegregation models of Mn and Cr in medium manganese steel were established by solving the characteristic parameters during solidification. The segregation indexes of Mn calculated using the Scheil model were much higher than the experimental EPMA values when the solidification fraction was close to 1. However, the results obtained from the Lever–ruler, Brody–Flemings, Clyne–Kurz, Ohnaka, and Won–Thomas models were closer when the solidification fraction was lower than 0.5. Furthermore, when the solidification fraction was less than 0.7, the segregation indexes of Cr calculated using the Scheil model were lower than those calculated using the EPMA. However, as solidification continued, the Cr results from the Scheil model were much higher than those of the experiments. The segregation indexes of Cr from the Brody–Flemings model showed the opposite trend from the Scheil model. Little difference exists among the Lever–ruler, Clyne–Kurz, Ohnaka, and Won–Thomas models. The Mn segregation indexes correlated well with the Brody–Flemings model, whereas the Cr segregation index correlated well with the Clyne–Kurz model.
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