Computation of Phase Fractions in Austenite Transformation with the Dilation Curve for Various Cooling Regimens in Conti
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TRODUCTION
THE properties of materials directly depend on their microstructure states including the microconstituent of the matrix and the existing defects like dislocations and precipitations (or inclusions). The microstructure state is generally connected with the material compositions and the microstructural transformations, and it varies with the subjected thermal and mechanical processes. During the continuous casting process, a complicated thermal condition has been reported.[1] The austenite transformation was found to be important to avoid cracking defects, indicating the necessity for achieving the target thermomechanical properties of specific steel grades. ZHIHUA DONG, Ph.D. Student, is with the College of Materials Science and Engineering, Chongqing University, Chongqing 400044, P.R. China, and also with the Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden. DENGFU CHEN, Professor, MUJUN LONG, Lecturer, and HUABIAO CHEN, Ph.D. Student, are with the College of Materials Science and Engineering, Chongqing University. Contact e-mail: [email protected] WEI LI, Ph.D. Student, is with the Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology. LEVENTE VITOS, Professor, is with the Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, and also with the Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, 75121 Uppsala, Sweden, and also with the Research Institute for Solid State Physics and Optics, Wigner Research Center for Physics, 1525 Budapest, Hungary. Manuscript submitted June 26, 2015. Article published online March 21, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
Typically, the thin film-like ferrite surrounding austenite grains is responsible for the crack occurrence in continuously cast steels due to the stress concentration in the relatively soft paramagnetic ferrite during deformations,[2–4] and 40 pct of ferrite in volume fraction is necessary for achieving a good ductility.[5] The stress configuration of the steel microstructure plays an important role in the crack formation causing the deviations from target properties of as-cast steels.[6] Compared with other residual stresses introduced during cooling the continuously cast steels, the stress generated from solid–solid phase transformation indicates a relatively large influence on the stress configuration of as-cast steels,[7,8] and it sensitively depends on the solid–solid phase transformation including the austenite transformation. Thus, it should be a reasonable way to prevent cracking or even to control the property of continuously cast steels based on the quantitative estimation of microstructure evolution during austenite transformation. The austenite transformation has been widely investigated with both experimental and theoretical methods.[9–11] The most well-known methods are the Kolmogorov-Johnson–Mehl–Avrami (KJMA)
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