Detection of Non-metallic Inclusions in Centrifugal Continuous Casting Steel Billets
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TALLIC inclusions are major source of defects in steel products and should be avoided or removed as much as possible. Despite significant researches, the full elimination of non-metallic inclusions has not been accomplished. In addition to simply minimizing them, the control of size distribution, morphology, and composition of inclusions are very important, depending on the quality requirements of the specific steel product being manufactured.[1] An undesired distribution of non-metallic inclusions can lead to serious problems in controlling the casting process and will generate many defects in the steel product.[2,3] As early as 1964, Uhlmann[4] investigated the interaction between particles and an advancing solid–liquid interface both experimentally and theoretically. Studies on particle behavior at the solid–liquid interface and the
QIANGQIANG WANG, Ph.D Student, LIFENG ZHANG, Professor, SHUFENG YANG and WEN YANG, Lecturers, and YI WANG, Postdoctoral Fellow, are with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing (USTB), Beijing 100083, China. Contact e-mail: zhanglifeng@ustb. edu.cn SRIDHAR SEETHARAMAN, Professor, is with the International Digital Laboratory, University of Warwick, Coventry, CV47AL, U.K. Manuscript submitted December 2, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
final distribution of particles in the metal matrix[4–11] have been one of important subjects of research over the past decades, as summarized in Table I. When a moving solid–liquid interface contacts with an insoluble particle, it can either be pushed or engulfed.[5] It has been accepted that there exists a ‘‘critical velocity’’ for the pushing/engulfment transition of particles. If the velocity of solid–liquid interface is below the critical velocity, particles will be pushed. On the other hand, if the interface velocity exceeds the critical velocity, the particles will be engulfed. Engulfment normally leads to uniform distribution of particles, while pushing generates the segregation of particles in metal matrix. Wilde[12] also proposed a third particle behavior—entrapment—besides pushing and engulfment. Entrapment of the particle between growing dendrites is likely to occur at a later stage of the solidification process. So far, previous studies on the interaction between particles and solidification front, including experiments and theoretical analysis, are all limited to steady state or quasi-steady models. Controlling the distribution of particles in final steel matrix through relevant parameters is still a weakness in complicated metallic system, for example, the steel continuous casting process. For the distribution of inclusions in billets or slabs, it was reported that inclusions often concentrate at one-eighth to one-quarter of the thickness from the inner radius surface for curved continuous casters.[13]
Table I. Author
Reported Studies on the Behavior of Particles at the Solidified Front
Matrix
Particle
Uhlmann
salol; thymol; orthoterphenyl, water
graphite; magne
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