The effects of non-metallic inclusions in nucleating acicular ferrite in steels during cooling from a weld or cooling from an austenitic temperature are reviewed. The influence of the acicular ferrite (AF) structure on mechanical properties of steels such as strength and toughness is briefly mentioned. The different factors affecting the formation of acicular ferrite, such as the soluble content of alloying elements in steel, cooling rate from austenitizing temperature, austenite grain size and inclusion characteristics in steel, are discussed. The mechanisms of acicular ferrite formation on non-metallic inclusions, such as reduction of interfacial energy, mismatch strain between the inclusion and ferrite/austenite, thermal strains at the inclusions and changes in matrix composition near the inclusions are also discussed. Finally, the effects of inclusion characteristics, such as size, number and composition are described and their effectiveness in nucleating acicular ferrite is discussed.KEY WORDS: non-metallic inclusions, intragranular acicular ferrite formation, strength and toughness, steel. 1063

Considerable research has been conducted over recent decades on the role of non-metallic inclusions and their link to the machinability of different steels. The present work reviews the mechanisms of steel fractures during different mechanical machining operations and the behavior of various non-metallic inclusions in a cutting zone. More specifically, the effects of composition, size, number and morphology of inclusions on machinability factors (such as cutting tool wear, power consumption, etc.) are discussed and summarized. Finally, some methods for modification of non-metallic inclusions in the liquid steel are considered to obtain a desired balance between mechanical properties and machinability of various steel grades.

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The internal surfaces of modern submerged entry nozzles (SENs) were coated with a glass/silicon powder layer to prevent SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. The results indicated that penetration of the formed alkaline rich glaze into the alumina/graphite base refractory occurs during preheating. More specifically, the glaze reacts with graphite to form carbon monoxide gas. Thereafter, dissociation of CO at the SEN/molten metal interface takes place. This leads to reoxidation of dissolved rare earth metals, which form 'in situ' rare earth metal oxides at the interface between the SEN and the molten steel. In addition, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high viscous alumina rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. The 'in situ' formation of the rare earth metal oxides together with the uneven internal surface of the SEN may facilitate the accumulation of the primary inclusions on the refractory walls.

A mathematical model describing heat and fluid flow in an electric arc has been developed and used to predict heat transfer from the arc to the steel bath in a DC Electric Arc Furnace. The arc model takes the separate contributions to the heat transfer from each involved mechanism into account, i.e. radiation, convection, condensation and energy transported by electrons. The model predicts heat transfer for different currents and arc lengths. Model predictions show that arc efficiency is higher for lower power input. The model also predicts shear stresses and current density distribution at the steel surface. This information can be used as boundary condition input to simulate the effect of heating with electrodes in a DC EAF on the heat and fluid flow in the steel bath.KEY WORDS: modeling; arc; heat transfer.model. More specifically these authors used three different methods to determine the Lorentz forces responsible for the fluid flow. These methods are i) The Laplace equation for electric potential ii) the magnetic diffusion equation, and iii) the complete magnetic transport equation. The first two methods, however, do not include the induced electric field term, vϫB, in the solution. Assuming that the magnetic Reynolds number is much less than unity, these methods give a good approximation of the Lorentz forces. However, this is not always the case for high-current arcs, as in the case of EAFs. The third method does include this term, but a disadvantage with this method is that the system of equations becomes more difficult to solve. In the present work, the Poisson equation for electric potential is used to overcome these problems since the induced electric field is included and the current in the system can be correctly described. Mathematical Model of a DC Electric ArcIn the model presented in this report the arc is treated as a fluid [1][2][3][4][5][6][7][8][9][10][11][12] with temperature-dependent thermodynamic properties. 15,16) The coupled conservation equations of energy, mass and momentum, which define plasma temperature, pressure and velocity, are solved together with Maxwell's equations. First the problem is stated and a description of the fluid-flow model is provided. Then source terms, boundary conditions and heat transfer mechanisms are discussed. Statement of the ProblemIn Fig. 1 a schematic representation of the region of integration of the DC arc model is given. The system consists of the cathode (graphite electrode), the arc column, and the anode (steel bath). The calculation domain is defined so as to allow for entrainment and general interaction with the surrounding gases. Mathematical Formulation of the FlowThe following assumptions are made in the statement of the mathematical model of a DC arc:• The arc is axis symmetric.• The operation of the arc is independent of time, i.e. steady state.• The arc is in local thermal equilibrium (LTE), 17) i.e. the electron and heavy-particle temperatures are very similar. This assumption has been shown to be valid throughout most of a gas tungsten ...