Experimental Measurements for Numerical Simulation of Macrosegregation in a 36-Ton Steel Ingot
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STEEL ingots are necessary for mono-block forgings, such as the pressure vessels for nuclear reactor and the shaft rotors for steam turbine. Macrosegregation, as a compositional heterogeneity, is a common solidification defect in steel ingots. It deteriorates the mechanical properties of products and haunts the manufacturers over decades. Numerous efforts have been devoted to study the macrosegregation in steel ingots. The thermo-solutal convection, shrinkage-induced flow, equiaxed grains movements, and solid skeleton deformation are believed to be the main reasons responsible for macrosegregation formation.[1–3] Nowadays, mathematical modeling acts as an indispensable tool for the research of macrosegregation, and it facilitates the design and the optimization of ingot process. Since the pioneering local solute redistribution equation derived by Flemings et al.[4] in 1960s, various models[5–9] have
ZHENHU DUAN, formerly Ph.D. Student, with the School of Materials Science and Engineering, Tsinghua University, Beijing 100084, P.R. China, is now Assistant Professor, with the School of Engineering and Design, Lishui University, Zhejiang 323000, P.R. China. Contact e-mail: [email protected] WUTAO TU, Ph.D. Student, and HOUFA SHEN and BAICHENG LIU, Professors, are with the School of Materials Science and Engineering, Tsinghua University. BINGZHEN SHEN, formerly Engineer with CITIC Heavy Industries Co., Ltd., Luoyang 471003, P.R. China, is now Engineer, with China North Industries Group Corporation, Beijing 100089, P.R. China. Manuscript submitted July 27, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
been proposed to predict macrosegregation. Among the models, the continuum model[5] and volume averaged model[6] treated the solidification system as a continuum mixture. The two-phase model[7] divided the system into solid and liquid phase focused on the interface transport behavior, and it was further developed into multi-phase models[8,9] considering the different characteristics of sub-phases in solid or liquid. However, the utilizable perspective of mathematical models is still limited due to the contradiction between their accuracies and efficiencies, and the model validation still needs more benchmarks. For the purpose of verification and validation of mathematical models, a call for benchmark contributions has been co-launched by many researchers in 2009.[10] Direct dissection methods have been adopted to investigate macrosegregation in steel ingots. Sulfur prints and local concentration sampling are usually used to acquire the basic knowledge of macrosegregation maps. Sulfur prints give qualitative macrosegregation maps of sulfur solute and exhibit the possible macrosegregation channels.[11] Local sampling helps to construct the quantitative macrosegregation maps, and the map resolution relies on the sampling densities. With the increase of sampling points, more details of macrosegregation can be illustrated on the maps. Figure 1 exhibits the typical carbon macrosegregation maps of steel ingots from literatures
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