Yanhui Liu

Preparation of stainless steel master alloy by direct smelting reduction of Fe–Ni–Cr Sinter at 1600°C

Feasibility analysis and experimental studies for the production of a stainless steel master alloy by direct smelting reduction have been investigated in this work, showing that the master alloy with proper compositions and satisfactory metal recoveries can be obtained at 1600°C. When the temperature was increased from 1450 to 1600°C, the grades for Fe, Ni and Cr increased from 50.04, 1.1 and 13.36% up to 73.39, 1.77 and 16.42%, respectively. Experiments were then carried out focusing on the influence of various fluxes on the reduction behaviour, showing that CaO resulted in the increase in the recoveries of Fe, Ni and Cr, SiO2 improved the recoveries of Fe and Ni, but did not favour the recovery of Cr because of an increase of CrO and Cr2O3 within the slag. MgO was not effective as a flux because of the formation of spinel. This increased the effective viscosity of the slag because of the presence of suspended solids, and led to a poor separation between the alloy and slag.

Relationship between structure and viscosity of CaO–SiO2–MgO–30.00 wt-%Al2O3 slag by molecular dynamics simulation with FT-IR and Raman spectroscopy

ABSTRACT Structure of CaO–SiO2–MgO–30.00 wt-%Al2O3 slag was investigated using molecular dynamics simulation at 1873 K, and viscosities with different basicities were measured for quantitatively studying the relationship between structure and viscosity. With the increase of basicity, the three-dimensional networks formed by Si and Al are depolymerised, which is consistent with the analysis using FT-IR and Raman spectroscopy. Additionally, FT-IR analysis shows a dampening of [Al–O–Si] trough, indicating a decrease in the linkage between [SiO4] and [AlO4]. Increasing the basicity results in that the BO decreases rapidly, while NBO increases from 32.75% up to 50.23%, which leads to the decrease of viscosity. Variations of CNAl–O and Al–O–Al indicate that Al2O3 prefers to form complicated unit, and Al2O3 within this slag should act as a network former. Calculated activation energies of samples A11–A14 are 212, 186, 168 and 161 kJ mol−1, respectively. Variation of viscosity linearly depends on Q4, and a strong linear relationship could also be found between viscosity and NBO/T. However, the variation of activation energy mainly depends on Q4(Si) comparing with Q4(Al), Q4(Si + Al) or NBO/T.

Reduction Behavior of Chromic Oxide in Ti-Bearing BF Slag

There are almost ten billion tons of vanadium-bearing titanomagnetite in Panzhihua-Xichang area. However, iron ores in Hongge, which has the most abundant reserves in the four mine areas in Panzhihua, have not been utilized sufficiently so far. The reason behind this is the relatively high Cr2O3 in the ores (0.49 %~0.82 %), that due to its high melting temperature will negatively influence the blast furnace reduction and slagging process. Therefore, in the blast furnace process, Cr is hope to be reduced into molten iron, which can reduce slag viscosity problems.

Wettability of Pyrolytic Graphite by Molten Blast Furnace Slag Bearing TiO 2

The wettability of graphite by the molten TiO2-CaO-SiO2-Al2O3-MgO (in mass%) Blast Furnace slag has been investigated using the dispensed drop method at 1673 K under the Argon atmosphere (Pressure≈ 1.10 atm). With the increase of TiO2 content in the slag the contact angle rises from 127° up to 147°, meaning that the TiO2 worses the wettability between the molten slag and the graphite. On the contrary, the CaO/SiO2 mass ratio can promote the wettability. Interfacial tensions between the slag and the graphite were also evaluated by using the Young’s Equation. Thermodynamics calculations were also carried out to study the interfacial reactions, showing that the reaction sequence agree with the following: reduction of MgO, SiO2, TiO2, boudouard reaction and formation of 2CaO Ti2O3.

Influence of Slag Basicity on the Silicon Within the Stainless Steel Master Alloy Prepared by Smelting Reduction of Fe-Ni-Cr Sinters

The purpose of this paper is to study the effect of slag basicity on the Si content in stainless steel master alloys prepared by smelting reduction of Fe-Ni-Cr sinters. Theoretical analysis focusing on the gas, slag and alloy phases of the smelting reduction process at 1600°C was carried out by thermodynamic calculation software----FactSage, showing that the increase of CaO within the slag can result in the decrease of Si within the master alloy. Experiments were also carried out in vacuum melting furnace at 1600 °C, and chemical analysis method was used to detect Si content in the alloys. When the MgO content is 9.00%, the experimental results were consistent with the calculated values. However, when the MgO content rises up to 14%, the content of Si in the alloy reaches the maximum when SiO2 equals to 22.81%.

Experimental Investigation on High Temperature Roasting of Basic Oxygen Furnace Slag

In China, Basic Oxygen Furnace (BOF) slag is traditionally used as an aggregate for civil engineering, for road engineering and fertilizer. In order to make full use of BOF slag, the experiments of BOF slag with high temperature roasting has been carried out and the phase transformation is studied. The BOF slag from Chongqing Iron & Steel is roasted in the electric muffle furnace at three different temperature. The influences of the high temperature roasting on change the phase composition of BOF slag was characterized by XRD. The results revealed that SFCA was produced at the high temperature in air atmosphere and melting temperature of slag was lowered. Therefore, if the BOF slag which treated by roasting was utilized in the sintering process, it is advantageous to improve the sintering strength and the formation of the liquid phase and reduce fuel consumption in the sintering production process.

Prediction for the Surface Tension of FeO-TiO2-Ti2O3-X(SiO2, CaO, MgO) Slag Systems

A thermodynamic model for determining the surface tension of molten slag by considering the surface tension and molar volume of the pure oxide component, and their ionic radii was extended to the slag bearing high TiO2 (varying from 80 to 67%) at 1973 K. The iso-surface tension curves for the FeO-TiO2-Ti2O3 ternary system at 1973 K are almost parallel to the FeO-Ti2O3 line. TiO2 plays a role of surface-active solute, and its surface-active effect is attenuating with increasing the TiO2 content. The iso-surface tension curve shifts away from the TiO2 corner, indicating that the surface tension of the ternary slag decreases along with the addition of SiO2. The reasons include the addition of SiO2 with lower surface tension and the decrease of the total ion moment at the surface. Both CaO and MgO can bring about that the iso-surface tension curve shifts towards the TiO2 corner, indicating that the surface tension of the ternary slag increases along with the addition of CaO or MgO. CaO has a more pronounced effect on increasing the surface tension of the ternary slag than MgO at an equimolar amount addition. The increase of the surface tension results from both the compositional change and the variation of the slag structure.