Constitutive Modeling and Activation Energy Maps for a Continuously Cast Hyperperitectic Steel
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NTRODUCTION
WITH the development of continuous casting technology, thin-slab casting-direct rolling has become widely accepted as a typical route for the manufacturing of high value flat steel products.[1] To increase product quality and decrease the costs, a better understanding of hot deformation behavior during thin-slab continuous casting is critical. Currently, the Finite Element Method (FEM) is often used as a common and effective tool to optimize the processing parameters. For example, using the elastoplastic and creep FEM model, Okamura et al.[2] studied the relationship between the strain caused by bulging and the internal cracks, and suggested that strains caused by bulging can be reduced by changing the secondary cooling conditions. Sengupta et al.[3] studied the thermal–mechanical behavior during initial solidification in continuous casting for different steel grades using a transient FEM model (CON2D), and their results explained the effect of steel grade on the oscillation mark depth. It was suggested that the shape X. GAO, H.X. LI, and L. HAN are with the State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing, 100083, China. Contact e-mail: [email protected] B. SANTILLANA and D. RUVALCABA are with Research & Development, Tata Steel, 1970 CA IJmuiden, The Netherlands. L.Z. ZHUANG is with the State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing and also with Research & Development, Tata Steel. Contact e-mail: [email protected] Manuscript submitted January 21, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
of the lower side of the oscillation marks can be optimized by reducing the level fluctuations. During the process of FEM model construction, constitutive equations, representing the flow behavior of materials, are used as an input for the FEM simulations.[4] A major obstacle for an accurate mathematical analysis is the need to find and evaluate constitutive equations that adequately describe the complex relationships among stress, strain, and time at elevated temperatures.[5] In practice, the high cost of plant experiments under the harsh operating steel plant conditions makes it difficult to test its constitutive behavior directly. Currently, the popular solution is to establish the constitutive equations of materials at the laboratory scale by measuring hot deformation behaviors of the steels. Due to the high liquidus temperature, lack of ideal testing machine, and other related difficulties related to the increase in the temperature, accurate determination of high-temperature mechanical properties of steels becomes increasingly difficult, especially when the testing temperature exceeds 1473 K (1200 °C). To construct constitutive equations, different states such as liquid, mushy-zone, and solid need to be considered.[6] To date, although some researchers have studied the constitutive equations for liquid crystals/semi-solid state, most efforts are still focused on the deformation behavior of steels i
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