A Review of Steel Processing Considerations for Oxide Cleanliness

Abstract

Control of non-metallic inclusions is essential for the production of high-quality steel. This review summarizes processes that change inclusion compositions and concentrations during secondary steelmaking-slower changes are limited by reaction between bulk steel and slag or refractory, and faster changes involve direct additions to the steel bath. An example of the former is conversion of alumina inclusions to spinels during ladle treatment, while reoxidation and calcium treatment are typical exemplars of the fast changes. For the slower changes, inclusions approach equilibrium with the liquid steel and conceptually simple kinetic models correctly describe inclusion evolution during ladle treatment. Disequilibrium from faster changes persists for several minutes under typical ladle conditions, with small-scale inhomogeneity in the steel. Fast scanning electron microscopy with microanalysis has facilitated detailed study of these inclusion evolution processes by providing information on inclusion composition, size, and shape. Machine learning methods are likely to be increasingly important in analysis of the results. Such methods have already shown promise to improve classification of inclusions and recognizing inclusion clusters, from analyses of polished sections. Several unresolved issues that require future study are noted.

Influence of Slag Viscosity and Composition on the Inclusion Content in Steel

“…[1][2][3][4] The inclusion transportation is primarily due to the density difference between the inclusion and steel and promoted by the steel stirring. 5) Many efforts have been made to clarify the mechanism of inclusion separation. [6][7][8][9] Strandh et al 10,11) proposed a mathematical model to study the inclusion behavior at the steel/ slag interface.…”

Evolution of the Inclusion Population During the Processing of Al-killed Steel

“…The Al2O3 inclusions can be modified via inclusion-steel reactions. Consequently, inclusion modification depends on the chemical evolution of the liquid steel during treatment in a ladle furnace (LF), which in turn depends on the addition of alloying elements, reactions of the steel with slag and refractory, and the homogenization of liquid steel [4][5][6][7][8][9]. After Al2O3 inclusions form, they can subsequently transform into Al2O3-MgO inclusions [9,10]; however, inclusions of the type Al2O3-MgO-CaO have been observed during ladle furnace treatment [6,7].…”

“…At the end of LF treatment, the composition of the inclusions is modified by Ca addition to form liquid inclusions of the Al2O3-CaO type [11]. The Ca treatment efficiency seems to depend on the type of inclusions present before the modification treatment, i.e., Al2O3 or Al2O3-MgO inclusions, [5,10,[12][13][14] and the homogenization of dissolved Ca in the liquid bath [15]. In addition, a decrease in temperature occurs progressively in the operations following the LF treatment, i.e., transfer of the ladle to the continuous casting (CC) station and the CC process, and the thermodynamic conditions of the liquid steel-inclusion interactions change and consequently the chemistry of the inclusions can be modified.…”

“…The removal of inclusions during LF treatment depends on numerous factors, such as the chemical compositions and sizes of the inclusions, flow pattern of the liquid steel, and slag properties [5]. Once the LF treatment is finished, the transport of the ladle to the continuous casting station and the CC operation itself provide an additional opportunity for flotation and removal of inclusions [7].…”

Influence of Non-Metallic Inclusions on the Corrosion Resistance of Stainless Steels in Arc Surfacing

“…This article is devoted to a more detailed study of this phenomenon, in particular, the effect of non-metallic inclusions on the corrosion resistance of the deposited metal. The influence of non-metallic inclusions on the corrosion resistance of steels has long attracted the attention of researchers dealing with the problem of increasing the corrosion resistance of various structures, as well as parts and assemblies of machines and mechanisms operating in corrosive environments [Liu 2017, Webler 2020]. The least resistant areas of metal surfaces are, as a rule, areas directly adjacent to the NI.…”