Effect of Cr on κ-carbide precipitation behavior in Fe-28Mn-12Al-1.6C steel
ZHAO Kang1,2, WU Zhifang1, SUN Ting2
1. Key Laboratory of Iron and Steel Metallurgy and Resource Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China; 2. Research Institute of Special Steels, Central Iron and Steel Research Institute Company Limited, Beijing 100081, China
Abstract：With the requirements of sustainable development strategy, Fe-Mn-Al-C lightweight steel has gradually become one of the main development goals of the automotive industry. The effect of chromium on the precipitation behavior of κ-carbide in Fe-28Mn-12Al-1.6C austenitic low density steel was investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), thermodynamic calculation and first principles. The results show that after solution treatment at different temperatures, the hardness of 0Cr steel increases gradually with time at room temperature and the increment reaches 10HRC. The κ-carbide precipitated at room temperature is confirmed by TEM analysis. The Gibbs free energy of precipitated at room temperature is -19.580 6 kJ/mol. It has been verified that 0Cr steel can precipitate κ-carbide at room temperature. With the increase of Cr content, the mass fraction of κ-carbide in the rapidly solidified sample after rolling decreases gradually, and the hardness increment decreases at room temperature aging. The increase of Cr content also significantly slows down the growth rate for κ-carbide, whose particle size is refined from 60-200 nm to 20-40 nm and 5-27 nm. At the same time, the first-principles calculation results show that the formation energy of κ-carbide is increased by doping Cr atom in the κ-carbide structure, which makes the formation of κ-carbide difficult. In addition, with the increase of Cr content, the lattice mismatch between γ-austenite and κ-carbide increases, and the elastic strain energy between the two phases increases, which leads to the slowing down of the growth rate for κ-carbide. The result provides theoretical basis for the composition design and performance control of Fe-Mn-Al-C steel with higher Al content in the future.
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2023, Vol. 33 
