Inclusion Population Evolution in Ti-alloyed Al-killed Steel during Secondary Steelmaking Process

Abstract

This paper presents a new approach towards the evolution of non-metallic inclusion (NMI) populations in Ti-alloyed Al-killed steels, based on an extensive inclusion analysis campaign at Tata Steel Europe, IJmuiden Works. Automated SEM techniques were used to characterize the inclusion populations in 120 steel samples taken from nine heats out of two casting series of this steel grade. As NMI in Ti-alloyed Alkilled steels are overwhelmingly dominated by chemically simple Al2O3, most of the process relevant information lies in the analysis of particle size distribution during the secondary steelmaking process. The population density function (PDF) concept was applied, for the first time, to the characterization of inclusion size distributions sampled from secondary steelmaking practice. Two size distribution forms predominate in the entire dataset: i) Lognormal size distributions associated with active nucleation and growth of alumina (deoxidation and reoxidation), indicating net transfer of matter between NMI and solutes in liquid steel and ii) Power-law size distributions, associated with an inclusion population in chemical equilibrium with the melt and subject to collision/breakup processes controlling the distributions. Based on inclusion PDF observations, it is found that the size distribution of alumina inclusions suspended in steel melt, after equilibration and effective float out of large inclusions, tends to approach a Reference Distribution of powerlaw type function (f(r) = a ⋅ r -3.5 ) that appears to be a fundamental feature of the alumina-steel system. This Reference Distribution can guide efforts to improve and engineer inclusion populations for a better controlled steel product.KEY WORDS: non-metallic inclusion; inclusion population density function; inclusion size distribution; secondary steelmaking.

Modeling of manganese sulfide formation during the solidification of steel

“…As an output, in addition to the 3D size distribution, its Population Density Function [PDF, described in Eq. (23)] can be obtained from the CSD Corrections to minimize the influence of the bin size selection, which has already been applied in the study of the inclusion size distribution [49,50]. Figure 7 compares both the 3D size distribution and PDF of MnS from the measurement and calculation with a collision factor of 200.…”

Evolution of Non-Metallic Inclusions in Secondary Steelmaking: Learning from Inclusion Size Distributions

“…Figure 5(a) shows the evolution of the PDF of Al2O3 inclusions with secondary steelmaking process (after Al deoxidation in RH-OB, after stirring station, and during casting), which is regenerated from the results of heat B1 published in reference. 29) As can be seen, the inclusion PDF just after Al deoxidation shows a lognormal shape, which clearly demonstrates the nucleation of new inclusions, where net mass transfer between solute and inclusion takes place. The PDF changes to a power law distribution with time (linear function in the log-log plots), when chemical equilibrium between solute and inclusions is reached.…”

“…Zinngrebe et al 29) investigated the evolution of nonmetallic inclusions in the series of Ti-alloyed Al-killed steel samples during the entire secondary steelmaking and casting processes using Automated Image Analysis (AIA) implemented with the aid of SEM-EDS technology. The series of samplings were performed in the secondary steelmaking plant of Tata Steel Europe, Ijmuiden work.…”

Transient Behavior of Inclusions during Reoxidation of Si-killed Stainless Steels in Continuous Casting Tundish

“…The stereologically corrected PDF were calculated for all populations of inclusions using this method and plotted against the equivalent diameter of inclusions, a standard plotting procedure on which phenomenologically and genetically distinct distribution functions can most easily be discriminated. 23) For traditional histograms, the size distribution of inclusions depends on the choice of the bins. While, PDF of inclusions with various bins are identical, providing a better way to display the size distribution.…”