Formation and Modification of MgO·Al2O3-Based Inclusions in Alloy Steels

The current study performed thermadynamic calculation, laboratory experiments, and industrial trials for the formation and modification of MgO-Al₂O₃ spinel inclusions in alloy steels. The stability Mg-Al-O diagram was obtained using the thermodymanic study. The resulting MgO-Al₂O₃-CaO inclusions from MgO-Al₂O₃ spinel inclusions after the calcium treatment were spherical, and?>?5???m MgO-Al₂O₃-CaO inclusions have a two-layer structure: an outside CaO-Al₂O₃ layer and a MgO-Al₂O₃ core. The modification of?>?5???m MgO·Al₂O₃ spinel inclusions by calcium treatment includes two steps: (1) reducing MgO in the inclusion into the dissolved magnesium by the dissolved calcium in the steel and (2) generating a liquid xCaO·yAl₂O₃ layer at the outside of the spinel inclusion. For <2???m MgO·Al₂O₃ spinel inclusions, they can possibly be modified into a xCaO·yAl₂O₃ inclusion by reducing all MgO component in the spinel inclusions with the added calcium.     

Behavior of MgO· Al2O Based Inclusions in Alloy Steel During Refining Process

The transformation of MgO ? Al₂O₃ based inclusions in alloy steel during refining has been studied by industrial trials. Besides Factsage software is used to study the formation and modification of spinel inclusions in alloy steel using calcium treatment during refining process. The results show that the transformation sequence of inclusions is: MgO ? Al₂O₃→CaO-Al₂O₃-MgO complex inclusions→MgO ? Al₂O₃, and under present experimental condition, in order to avoid forming MgO ? Al₂O₃ inclusions the content of dissolved Ca in the molten steel has to reach 1×10^?6. Also the results show that when more calcium was added to molten steel, the content of Al₂O₃ and MgO will be lower. Besides, increasing the content of CaO in the inclusions will increase even if the content of SiO₂ changes little.     

Control of MgO·Al2O3 Spinel Inclusions during Protective Gas Electroslag Remelting of Die Steel

The effect of calcium treatment and/or aluminum-based deoxidant addition on the oxygen control and modification of MgO·Al₂O₃ spinel inclusions during protective gas electroslag remelting (P-ESR) of H13 die steel with low oxygen content was experimentally studied. It is found that all the inclusions in the consumable electrode are MgO·Al₂O₃ spinels, besides a few MgO·Al₂O₃ spinels surrounded by an outer (Ti,V)N or MnS layer. After P-ESR refining combined with proper calcium treatment, all the original MgO·Al₂O₃ spinels in the electrode (except for the original MgO·Al₂O₃ spinels having been removed in the P-ESR process) were modified to mainly CaO-MgO-Al₂O₃ and some CaO-Al₂O₃ inclusions, both of which have a low melting point and homogeneous compositions. In the case of only Al-based deoxidant addition, all the oxide inclusions remaining in ESR ingots are MgO·Al₂O₃ spinels. The operation of Al-based deoxidant addition and/or calcium treatment during P-ESR of electrode steel containing low oxygen content is invalid to further reduce the oxygen content and oxide inclusions amount compared with remelting only under protective gas atmosphere. All the original sulfide inclusions were removed after the P-ESR process. Most of the inclusions in ESR ingots are about 2 μm in size. The mechanisms of non-metallic inclusions evolution and modification of MgO·Al₂O₃ spinels by calcium treatment during the P-ESR process were proposed.     

Measurements of Solidus and Liquidus Temperatures of CaO?Al2O3?SiO2 and CaO?MgO?Al2O3?SiO2 Slags with MnO Additions

The present work was carried out with a view to re‐examine the phase diagram aspects of CaO? Al₂O₃? SiO₂ and CaO? MgO? Al₂O₃? SiO₂ slags with MnO additions. The aim was to confirm the homogeneous liquid range necessitated for sulfide capacities measurements of the above‐mentioned slags. The liquidus and solidus temperatures of these slags were measured by DSC and X‐ray radiograph techniques. The experimental results were compared with the liquidus and solidus temperatures obtained from literature (Slag Atlas) and commercial softwares ThermoCalc and FactSage. The results indicate that there is good agreement between the experimental values and those retrieved from literature and the commercial software in the case of the ternary system CaO? Al₂O₃? SiO₂. For the CaO? MgO? MnO? Al₂O₃? SiO₂ system, significant deviations were observed between the different sources. The present observations indicate that X‐ray radiography can be a very useful tool in estimating the solidus temperatures of slags while DSC would complement the information with respect to liquidus temperatures.     

Dissolution behaviour of MgO based refractories in CaO–Al2O3–SiO2 slag

Abstract

Magnesium oxide (MgO) based refractories are widely used in secondary refining processes, and their dissolution into refining slag is the primary cause of their shortened lifespan. The dissolution rate was investigated for sintered MgO and commercial MgO–C and MgO–Cr₂O₃ refractories in a synthesised 50CaO–45Al₂O₃–5SiO₂ liquid (mass-%) slag. The change in slag composition was measured after a refractory sample was placed into the molten slag that was stirred by flowing argon gas at 1773?K. The dissolution rate of the sintered MgO was above those of the MgO–C and MgO–Cr₂O₃ refractories under the same gas flowrate, although the dissolution rate of all samples increased as the gas flowrate was increased from 25 to 75?mL·min^??1. The slag containing 5?mass-% FeO considerably promoted the dissolution of the MgO–C refractory because of the oxidation of carbon by FeO. The dissolution of all the refractories was greatly affected by penetration of the liquid slag, with the mass transfer of MgO in the penetrating slag at lower gas flowrates likely being the rate controlling step. At high gas flowrates, Ar bubbles covered the surface and blocked the contact between the liquid slag and the solid phase, reducing the dissolution rate.     

铁矿石中SiO2 CaO MgO及Al2O3的系统分析

以无水碳酸钠、四硼酸钠为熔剂，在装有石墨粉的瓷坩埚内进行快速熔融试样，熔块以盐酸浸取，溶解盐类，对铁矿石、球团矿、烧结矿中二氧化硅、氧化钙、氧化镁、三氧化二铝进行系统分析。与国家标准方法相比，本法具有操作简便，准确性好，速度快，成本低，测定范围宽等特点。     

Surface Tensions of Some CaO–MgO–Al2O3–SiO2 Slags

Abstract

The surface tensions of some high basicity alumino-silicates have been determined by the maximum bubble pressure technique. The results, which lie in the range 440–550 mN m^?1, are lower than estimated from predictive models and the reasons for this discrepancy are discussed. It is suggested that the concept of optical basicity can, under appropriate circumstances, be usefully applied to aid the interpretation of surface tension-composition relationships.

Résumé

Les tensions de surface de certains Alumino-Silicates très alcalins ont été déterminées par la technique de pression maximale de bulles. Les résultats qui fluctuent entre 440 et 550 mN m^?1, sont plus bas que les estimés prévus par modélisation et les raisons de ces écarts sont discutés. Il est suggéré que le concept d'alcalinité optique soit appliqué avantageusement dans certain cas, pour aider à l'interprétation des relations tension de surface-composition.     

Formation Mechanism of MgO·Al2O3 Spinel Inclusions in Stainless Steelmaking Processes

The latest publications regarding the development of technology to control inclusion compositions focusing on MgO?Al2O3 spinel inclusions were summarized in this review article. The problems caused by spinel inclusions, which affect practice as well as products were shown. The formation mechanism of MgO?Al2O3 spinel inclusions is secondly explained thermodynamically from the view points of chemistries of molten steels and slag compositions. Furthermore, crystallization behaviour of spinel was introduced. Countermeasures conducted in practices and laboratories were shown along with some problems still left that should be solved in the future.     

Behavior of MgO·Al_2O_3 Based Inclusions in Alloy Steel During Refining Process

The transformation of MgO·Al2O3 based inclusions in alloy steel during refining has been studied by industrial trials.Besides Factsage software is used to study the formation and modification of spinel inclusions in alloy steel using calcium treatment during refining process.The results show that the transformation sequence of inclusions is:MgO·Al2O3→CaO-Al2O3-MgO complex inclusions→MgO·Al2O3,and under present experimental condition,in order to avoid forming MgO·Al2O3 inclusions the content of dissolved Ca in the molten steel has to reach 1×10-6.Also the results show that when more calcium was added to molten steel,the content of Al2O3 and MgO will be lower.Besides,increasing the content of CaO in the inclusions will increase even if the content of SiO2 changes little.     

Thermodynamic activity of the liquid-phase components in the CaO · SiO2-CaO · Al2O3 · 2SiO2-CaO · TiO2 · SiO2 system with four-phase invariant equilibrium

The CaO · SiO₂-CaO · Al₂O₃ · 2SiO₂-CaO · TiO₂ · SiO₂ system is analyzed. Thermodynamic analysis of monovariant and invariant solidification shows that, for invariant equilibrium and for solidification along the boundary curve between the solidification fields of anorthite and sphene, peritectic processes are observed. The invariant-state parameters of the system are determined: t = 1513 K; a _CaO = 0.0407; $a_{SiO_2 } = 0.5268$ ; $a_{Al_2 O_3 } = 0.00003$ , $a_{TiO_2 } = 0.005$ ). A corrected phase diagram is presented.     

Viscosity of low silica CaO–5MgO–Al2O3–SiO2 slags

Abstract

The viscosity of CaO–5MgO–Al₂O₃–SiO₂ slag with low silica was measured by rotating cylinder method up to 1823 K. Slag compositions were chosen based on five different levels of SiO₂ content between 0 and 11·80%. The MgO content was 5·0%. The mass ratio of CaO/Al₂O₃ was varied from 0·66 to 1·95. It was shown that viscosity decreased with increasing temperature and decreased with increasing the mass ratio of CaO/Al₂O₃, following by an increase with further increasing the mass ratio of CaO/Al₂O₃. The viscosity decreased with the NBO/T ratio increasing, and the trend that flow activation energy changes with the NBO/T ratio of slag was the same as the trend that viscosity changes with the NBO/T ratio. Based on the experimental data as the boundary of the homogenous phase region, the mass triangle model was used to calculate the viscosity of low silica region.     

Viscosity of CaO–MgO–Al2O3–SiO2 melts containing SiC particles

The influence of SiC particle on viscosity of CaO–MgO–Al₂O₃–SiO₂ melts was investigated by the rotating-cylinder method. It was found that temperature dependence of viscosity could be described by the Arrhenius law for systems with or without SiC particle addition. The activation energies of liquid–solid mixtures were mainly determined by liquid phase. Temperature had little influence on the relative viscosity (defined as the viscosity ratio of solid–liquid mixture to pure liquid). Viscosity and relative viscosity increased as decreasing rotation speed and increasing volume fraction of SiC solid particle. For the same volume fraction of SiC particle, relative viscosity was affected by the liquid slag compositions. The relative viscosity was smaller when composition of liquid slag had a larger CaO/SiO₂ ratio or MgO/Al₂O₃ ratio. Meanwhile, it was found that the smaller SiC particle will lead to a larger relative viscosity.     

Effect of Al2O3 and CaO/SiO2 on the Viscosity of Calcium-Silicate–Based Slags Containing 10 Mass Pct MgO

The effect of Al₂O₃ and CaO/SiO₂ on the viscosity of the CaO-SiO₂-10 mass pct MgO-Al₂O₃ slags was studied at fully liquid temperatures of 1773 K (1500 °C) and below. At fixed CaO/SiO₂ between 0.8 and 1.3, higher Al₂O₃ content increased the slag viscosity due to the polymerization of the aluminate structures. At fixed Al₂O₃ of 15 and 20 mass pct, increasing the CaO/SiO₂ from 0.8 to 1.3 resulted in lower viscosity due to the depolymerization of the aluminate structure.     

Experimental measurements and modelling of viscosity in CaO–Al2O3–MgO slag system

Abstract

The viscosity of the CaO–Al₂O₃–MgO slag system has been measured by the rotating cylinder method up to 1823 K. The MgO content was between 0·39 and 11·33 wt-%, and the mass ratio of CaO/Al₂O₃ was between 0·60 and 1·28. The results indicated that both the MgO content and the mass ratio of CaO/Al₂O₃ have an influence on the viscosity of the slag. The effect of the mass ratio of CaO/Al₂O₃ is larger than that of the MgO content. The viscosity decreased with increasing MgO content and then increased. The effect of the mass ratio of CaO/Al₂O₃ on the viscosity was similar. The main mineralogical compositions of the slag were determined by X-ray diffraction, and their effects on viscosity were investigated. The measured results were in good agreement with those given by the Iida model.     

CaO—SiO2—MgO—Al2O3精炼渣的脱硫性能

在实验室用模拟装置研究了ＣａＯ－ＳｉＯ２－ＭｇＯ－Ａｌ２Ｏ３精炼渣脱硫的性能。碱度和助溶剂ＣａＦ２含量对硫分配比Ｌｓ影响较为显著，并分析了ＭｇＯ、Ａｌ２Ｏ３对脱硫反应的作用。