Guoguang Cheng

Periodicity of Carbon Element Distribution Along Casting Direction in Continuous-Casting Billet by Using Singular Spectrum Analysis

The periodicity of carbon element distributions along the casting direction in a continuous-casting billet was investigated quantitatively in this article after finding it in the preceding research. By using singular spectrum analysis (SSA), this study focuses on the changes of periodicity at different positions (centerline position, V-shaped segregation band, and columnar-to-equiaxed transformation position), at different data layouts (continuous or discrete) and at different scales (large scale or small scale). SSA is a frequency-domain mathematical method. Based on SSA, two values, the extracting average period value (Pea) and the extracting comprehensive harmonic extent (Eech), have been defined for investigating the periodic characteristics of time series, which reflects the influence of the segregation on the casting-direction quality stability (fluctuation frequency and disorder extent) of the billet. First, it is found that there are different periodic characteristics (period value and harmonic extent) at different positions as to the carbon element distribution along the casting direction in a continuous-casting billet, and the corresponding variation trend with position may be different at different data layouts or at different scales. Moreover, as to the studied element distributions, the variation trends of the period value with position in the same data layout results are the same, but it is different in the same scale results of different data layout; the variation trends of the harmonic extent with position in the same scale results are the same, but it is different in the same data layout results of a different scale. This point may reveal a universal phenomenon in the object of different data layouts and different scales. Hence, when the solidified element distribution, the related solidification process and the properties of steel product (especially about the fluctuation of quality) are investigated, special attentions should be paid to the data layout and the scale of the raw data.

Time-Series Analysis Technologies Applied to the Study of Carbon Element Distribution Along Casting Direction in Continuous-Casting Billet

The carbon element distributions along casting direction at centerline position, V-shaped segregation band, and columnar to equiaxed transformation (CET) position in continuous-casting billet have been first obtained by the original position statistic distribution analysis (OPA). Different location points at a certain position were formed along the opposite direction of casting direction with the lapse of the time, so the carbon mass fractions of different location points at a certain position can be considered as a time series. Based on the actual result, some typical time-series analysis technologies, such as the autoregressive integrated moving average (ARIMA) model, were used to analyze the characteristics of the three time series. It is found that there is some periodicity in the carbon element distribution at centerline position, and the correlation relationship between centerline position and CET position is closer than that between the centerline position and V-shaped segregation band at the same location point along the casting direction. Moreover, the element distribution along the casting direction is one of the solidifying results with the lapse of the time, so it is possible to investigate the characteristics of the system about the solidification process of continuous-casting billet by using these time series. Then it shows that there is a chaos feature in the system about the solidification process of studied continuous-casting billet on the basis of Hurst exponents and saturated correlative dimensions. Meanwhile, the formation process of carbon element distribution along casting direction can be described as fractional Brownian motion, and the upper and lower limits of the number of internal independent variables were determined in order to describe the formation process of carbon element distributions at different positions of the studied billet. Finally, the stochastic extent at V-shaped segregation band is found to be the largest, and it needs more independent variables to describe its formation process than the other two positions.

Evolution Mechanism of Oxide Inclusions in Titanium-Stabilized AISI 443 Stainless Steel

The evolution mechanism of oxide inclusions in Ti-bearing AISI 443 stainless steel was investigated by industrial experiment and thermodynamic calculation. The chemical compositions of steel and the characteristics of inclusions in steel were analyzed. After the addition of Al, the main type of inclusions in molten steel was irregular MgO·Al2O3 spinel. The MgO·Al2O3 inclusions were modified to be spherical CaO-Al2O3-MgO inclusions after calcium treatment. Thermodynamic calculation results indicated that several ppm Ca could significantly expand the liquid oxide phase field and decrease the stability of spinel. After titanium addition, two types of inclusions were formed: spherical Al2O3-TiOx inclusions and complex CaO-TiOx-Al2O3-MgO inclusions. The compositions of steel after Ti addition were mostly located in Al2O3-TiOx stability phase field. Based on the characteristics of inclusions in steel and thermodynamic calculation, inclusions consisting of liquid and CaTiO3 were formed in molten steel with more than 10 ppm Ca during the Ti addition process. The evolution mechanism of oxide inclusions was discussed with the consideration of the initial calcium content before Ti addition.

Erratum to: A Mathematical Modeling Study of Tracer Mixing in a Continuous Casting Tundish

Specifically, in the transport equations for the mass fraction of water, tracer, and the scalar (Eqs. [7], [8], and [13], respectively). The density properties were the density of the mixture in Eq. [10] instead of the density of the water or the tracer itself. Second, the update of one of the result in the article. Regarding the result (1) KCl density only (OD) in Table II and the text in p. 179: ‘‘Apart from the KCl molecule diffusion, the mesh difference could also, to some extent, influence the differences in the results.’’ The result (1) KCl density only (OD) was based on a mesh of 168 9 71 9 70 grids, while the other results (2) through (5) were based on a mesh of 193 9 79 9 117 grids. A new simulation for the (1) KCl density only (OD) were recently made based on a mesh of 193 9 79 9 117 grids to maintain the consistency. It was difficult to distinguish the difference between the RTD curves of the case that implemented with density only (OD) and the case implemented with both density and KCl molecule diffusion (KMD). To conclude, all the properties of tracer (except for the density) that implemented in the CFD model could not affect the calculated RTD curves.