Thermodynamics on the formation of spinel nonmetallic inclusion in liquid steel

Abstract

The nonmetallic spinel inclusion, MgO⅐Al 2 O 3 , has a high melting point and produces an undeformed C-type inclusion in steel products. Therefore, it is very harmful in the production of high grade wire, spring, and bearing steels. Thus, it is necessary to develop a methodology by which we can predict the occurrence of such defects.The thermodynamics of the formation of spinel nonmetallic inclusions during co-deoxidation with aluminum and magnesium is discussed in the present work. Previous literature thermodynamic values for strong deoxidizers such as aluminum, magnesium, and calcium are not in good agreement with the observed results and measurements. This discrepancy between predicted and measured results is due to an incomplete expression of the activities of dissolved oxygen and deoxidizers in current literature. Namely, only first-order interaction parameters are available despite the very strong interactions among the dissolved elements.In the present work, the deoxidation equilibrium with magnesium in liquid iron was studied in order to evaluate the activities of oxygen and dissolved magnesium and, include in the thermodynamic description, the first-and second-order interaction parameters, including the cross-product terms. A dolomite crucible was used to enhance the magnesium content in liquid iron in the present experiment on thermodynamics of spinel formation with reference to the study on desulfurization with a dolomite crucible undertaken by Ototani et al. [1] The assessment of aluminum-oxygen equilibrium in liquid iron reported by other investigators was also reviewed to develop values for the second-order interaction parameters. Finally, thermodynamic data on calcium deoxidation equilibrium were obtained.The iron sample was melted by a high frequency induction furnace. Iron of about 90 grams was charged into a crucible. The added weight of a deoxidizer such as magnesium and calcium was 1 mass pct of the weight of iron. The experimental procedure is briefly shown as follows.After the iron melted under a gas flow of a mixture of Ar-50 vol pct H 2 , hydrogen was impinged onto the melt surface to reduce dissolved oxygen content until it was less

Formation and Evolution of Non-metallic Inclusions in Medium Mn Steel during Secondary Refining Process

“…The formation of MgO·Al 2 O 3 spinel in Al-killed steel has been studied by many researchers. 7,9,10,21) Most of them believed that if there is a trace of dissolved Mg in steel, alumina inclusions tend to transform into spinel inclusions. In the present study, as shown in Table 3, before LF refining and at the middle of LF, several ppm dissolved Mg has been generated.…”

“…Some of them [7][8][9][10]12,21,29) thought that the formation of MgO·Al 2 O 3 spinel inclusions depends on the concentration of dissolved Mg, Al and O in liquid steel. Meanwhile, some researchers 18,19,21) found that MgO·Al 2 O 3 spinel could still precipitate from CaO-SiO 2 -Al 2 O 3 -MgO system inclusions during the cooling of liquid steel, although the composition of Mg, Al and O in steel was not in the stable region of MgO·Al 2 O 3 .…”

Nucleation, Growth, Transport, and Entrapment of Inclusions During Steel Casting

“…72,[75][76][77][78][79] Particle growth occurs at microscales depending on the microscale phenomena of bubble attachment, turbulent collisions, 27,72,75,76 interface reactions, reoxidation, and local thermodynamics. 20,[80][81][82][83] Finally, inclusion transport and removal at the slag or by bubble flotation 24,26,84,85 and particle entrapment in solidifying dendritic interfaces [3][4][5]73 depend on flow transport and on the nature of the flow pattern and shape of the metallurgical vessel. Different nano-and microscale models have been used to predict important specific phenomena.…”

The Evolution and Thermodynamic Analysis of Inclusions in Gear Steel after Magnesium Treatment

“…Table 3 shows the Gibbs free energy of chemical reactions involved in the present work. Table 3 Free energy data of reactions considered in the present work [4,5,6,7] Reaction…”