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Characterization of microstructural evolution in austenitic Fe-Mn-Al-C lightweight steels with Cr content
- Characterization of microstructural evolution in austenitic Fe-Mn-Al-C lightweight steels with Cr content
- Kim, Kyeong-Won; Park, Seong-Jun; Moon, Joonoh; Jang, Jae Hoon; Ha, Heon-Young; Lee, Tae-Ho; Hong, Hyun-Uk; Lee, Bong Ho; Han, Heung Nam; Lee, Young-Joo; Lee, Chang-Hoon; Kim, Sung-Dae
- Issue Date
- Materials Characterization, 170, 110717
- Article Type
- Author Keywords
- Lightweight Fe-Mn-Al-C steel; Chromium; Microstructures; Tensile properties; Ferrite; Austenite; kappa-Carbides; DO3; M7C3
- Scanning electron microscopy; Tensile strength; Tensile testing; Textures; Carbide forming elements; Crack initiation sites; Electron back scatter diffraction; Fractured surfaces; Homogenized microstructure; Light-weight steels; Microstructural homogeneity; Microstructural phasis; Chromium steel; Aluminum alloys; Aluminum coated steel; Austenite; Carbides; Chromium compounds; Cracks; Elongation; Ferrite; Grain boundaries; High resolution transmission electron microscopy; Manganese alloys; Manganese steel; Microstructural evolution
- The influence of Cr addition on the microstructures and tensile properties of Fe-20Mn-12Al-1.5C lightweight steels was investigated. Microstructural phases were thoroughly identified through scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), and x-ray diffraction (XRD). Tensile behaviors were characterized using a tensile test and observation around fractured surface. Fe-20Mn-12Al-1.5C lightweight steel without Cr consisted of austenite with fine intragranular κ-carbides, coarse intergranular κ-carbides, and a small amount of ferrite. As Cr content increased to 5 wt%, coarse κ-carbides around grain boundaries disappeared and the fraction of ferrite slightly decreased, while the fraction of austenite slightly increased, leading to a homogenized microstructure consisting of mostly austenite with fine intragranular κ-carbides and a very small amount of ferrite and ordered phase DO3. This results from the addition of Cr, which is a carbide-forming element, which suppresses the formation of κ-carbides and consequently, austenite retains more stability due to an increase in the amount of carbon inside austenite. When Cr content exceeded 5 wt%, the fraction of DO3 increased drastically, the fraction of austenite reduced sharply, and Cr-rich M7C3 carbides precipitated. This is attributed to the role of Cr in steels, which is a carbide former as well as a ferrite stabilizer. As for tensile properties, tensile strength declined, and elongation improved with increasing Cr, up to 5 wt%. The decrease in tensile strength originates from the reduced κ-carbide fraction and growth in grain size, and the improvement in elongation is due to the reduction in coarse κ-carbides which act as crack initiation sites. As Cr content exceeded 5 wt%, the tensile strength increased, but the elongation decreased dramatically, owing to the precipitation of M7C3 carbides which are vulnerable to cracking. The steel containing 5 wt% of Cr showed the best tensile properties due to microstructural homogeneity, namely, a simple microstructure containing austenite with fine κ-carbides inside austenite and the low fraction of ordered phase DO3. © 2020 Elsevier Inc.
- Elsevier Inc.
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