Periodicity of Carbon Element Distribution Along Casting Direction in Continuous-Casting Billet by Using Singular Spectr
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ement distribution along the casting direction in a continuous-casting billet indicates the change of carbon mass fraction along the casting direction of billet. This distribution is formed based on the phenomenon of segregation. Segregation is a very important defect for the quality of continuous-casting billets. Over the years, many works have been performed for the segregation in the transverse cross section of the billet (perpendicular to casting direction).[1,2] In fact, element distributions along the casting direction under steadystate condition are always nonuniform. This phenomenon also has a great influence on the quality of a continuous-casting billet and the properties of the final product, especially on the stability of casting-direction ZIBING HOU, Doctor and Lecturer, and GUANGHUA WEN and PING TANG, Professors, are with the Chongqing University, College of Materials Science and Engineering, Chongqing 400044, P.R. China. Contact e-mail: [email protected] GUOGUANG CHENG, Professor, is with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, P.R. China. Manuscript submitted November 13, 2013. Article published online June 13, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
quality.[3–7] However, there are only a few special investigations for the element distribution along the casting direction in a continuous-casting billet.[7–9] The existing research mainly focuses on qualitative analysis.[7,8] In Reference 9, the carbon element distribution along the casting direction in the billet was analyzed quantitatively by the authors using the time-domain time-series analysis technology. Some complex periodicity was found in the element distribution at the centerline position.[9] However, the related periodic characteristics have not been studied quantitatively. There are two main methods as to time-series analysis technology, i.e., the time-domain method and the frequency-domain method. The timedomain method focuses on the correlation between the current value and the past value, but the frequencydomain method focuses on different frequency characteristics (such as frequency or period, the whole harmonic quality). In this article, a frequency-domain time-series analysis technology, singular spectrum analysis (SSA), will be used to quantitatively study the period value and harmonic extent after finding this kind of periodicity. The periodic characteristics at different element distributions of different positions (centerline position, V-shaped segregation band, and columnar to equiaxed transformation [CET] position), at different data layouts (continuous VOLUME 45B, OCTOBER 2014—1817
or discrete) and at different scales (large scale or small scale) will be compared. The SSA technique cannot give some direct thermodynamic information now, but it can give some essential mathematical characteristics of the element distribution. The segregation phenomenon in inner zone of the continuous-casting billet is so complex that it is very difficult to accurately analyz
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