Refining Slag Research Articles

Improving Cleanliness of 95CrMo Drill Rod Steel by Slag Refining

Industrial experiments were performed to improve the cleanliness of 95CrMo drill rod steel by slag refining. Higher steel cleanliness, lower corrosion, and small inclusions were obtained using the optimal slag composition (pctCaO/pctSiO2 = 3.7 to 4, pctCaO/pctAl2O3 = 6 to 8). Layered composite inclusions formed during vacuum decarburizing refining. CaS first precipitated around the spinel and subsequently formed inclusions in which solid CaS-CaO wrapped around the Al2O3-MgO-SiO2-CaO system as the modification and diffusion progressed. The thermodynamic equilibrium between slag and liquid 95CrMo steel at 1873 K (1600 °C) was also studied to understand the effect of slag composition on the oxygen content and absorption capacity for Al2O3. A mathematical model based on an investigation of slag viscosity and the interfacial tension between slag and inclusions was used to predict the size of critical inclusions for different slags. The evolution of typical inclusions is discussed in terms of the study of reactions between slag and steel.

Laboratory Study on Prevention of CaO-Containing ASTM “D-Type” Inclusions in Al-Deoxidized Low-Oxygen Steel Melts During Basic Slag Refining

Present work was attempted to explore the possibility of preventing CaO-containing inclusions in Al-deoxidized low-oxygen special steel during basic slag refining, which were known as ASTM D-type inclusions. Based on the analysis on formation thermodynamics of CaO-containing inclusions, a series of laboratory experiments were designed and carried out in a vacuum induction furnace. During the experiments, slag/steel reaction equilibrium was intentionally suppressed with the aim to decrease the CaO contents in inclusions, which is different from ordinary concept that slag/steel reaction should be promoted for better control of inclusions. The obtained results showed that high cleanliness of steel was obtained in all the steel melts, with total oxygen contents varied between 0.0003 and 0.0010 pct. Simultaneously, formation of CaO-containing inclusions was successfully prohibited, and all the formed oxide inclusions were MgO-Al2O3 or/and Al2O3 in very small sizes of about 1 to 3 μm. And 90 pct to nearly 98 pct of them were wrapped by relative thicker MnS outer surface layers to produce dual-phased “(MgO-Al2O3) + MnS” or “Al2O3 + MnS” complex inclusions. Because of much better ductility of MnS, certain deformability of these complex inclusions can be expected which is helpful to improve fatigue resistance property of steel. Only very limited number of singular MnS inclusions were with sizes larger than 13 μm, which were formed during solidification because of. In the end, formation of oxide inclusions in steel was qualitatively evaluated and discussed.

Characteristics and Metallurgical Effects of Medium Basicity Refining Slag on Low Melting Temperature Inclusions

Recently, large sized CaO-Al2 O3 inclusions with low melting temperature have been the main reason for lowering mechanical properties of high strength low alloy (HSLA) steel plates. New philosophy, i. e. refining by top slag with relatively low basicity and Al2 O3 content, was proposed to control such kind of inclusions. Firstly, the characteristics of refining slag, such as component activities and sulphide capacity (Cs) of CaO-A12O3-SiO2-MgO slag, were studied through thermodynamic calculation. Then, slag-metal equilibrium experiments were carried out in laboratory to investigate the exact chemical composition of refining slag together with thermodynamic analysis. Finally, industrial trials were done to verify the desulphurization ability and inclusions control in steel refined by the new slag. Thermodynamic calculations indicated that the slags with basicity of 3. 5 and Al2 O3 content of 20% and basicity of 5.0 and A12O3 content of 20% or 25% have high values of CaO activity, sulphide capacity and ratio of MgO activity to Al2 O3 activity. Laboratory equilibrium experiments showed that the slag with basicity of about 4. 5 and Al2 O3 content of about 20% is helpful for increasing the melting temperature of inclusions in steel. After introducing such kind of refining slag in industrial trials, the sulphur content in eight heats of steel is below 20 × 10−6, which meets the requirement of HSLA steel, and most inclusions distribute in relatively high melting zone (±1773 K) of CaO-Al2O3-MgO(-SiO2) quasi-ternary diagram. New philosophy of top refining slag is feasible to control low melting point inclusions of CaO-Al2O3 system in HSLA steel.

Effects of Slag Refining on Boron Removal from Metallurgical-Grade Silicon Using Recycled Slag with Active Component

A new slag refining method to remove boron from metallurgical silicon (MG-Si) by mixed reused slag and active component was proposed. The silicon was refined with CaCl2-CaO-SiO2 slag system in this work. The boron removal efficiency under different temperature and holding time was investigated, particularly for the recycle of the used slag mixed with different amount of CaCl2 in the 2nd and the 3rd run. The multiple slag refining was adopted to test the effect of reused slag; the boron removal ratio was 96% and 94% at 1923 K and 1873 K, respectively. These methods could significantly reduce the slag amount in refining. The total transfer coefficient of boron was also derived by the boron content. The overall boron removal mechanism and effect of slag recycle on boron removal was also discussed.

Stabilization of Metals-contaminated Farmland Soil using Limestone and Steel Refining Slag

The metals contamination of farmland soil nearby abandoned metal mine was serious problem in Korea. Stabilization of contaminated soil was reported using various stabilizers. Application of limestone and steel refining slag was reported as effective stabilizers in the stabilization of metals. The batch studies confirmed that the mixture of limestone and steel refining slag was suitable for stabilization of metals in contaminated soil. The limestone and steel refining slag mixture (2 : 1 and 3 : 2) were used in column studies and it was confirmed that the stabilizers effectively stabilized heavy metals in contaminated soil. The pH of the soil was increased with the addition of stabilizers. Total leached concentration of metals from the column study was reduced 44, 17, and 93% in comparison to the control at arsenic, cadmium and copper, respectively. The sequential extraction studies showed that the exchangeable fraction was changed into carbonate bound fraction (Cd and Cu) and Fe-Mn oxide bound fraction (As). Based on the results we confirmed that 2:1 ratio of limestone and steel refining slag effectively stabilizes the heavy metals. The mixed treatment of lime stone with steel refining slag would be an effective and feasible method for controlling metals leaching in contaminated soil.

Mass Transfer in Slag Refining of Silicon with Mechanical Stirring: Transient Kinetics of Ca and B Transfer

Mechanical stirring was demonstrated to be a potent means to increase the mass transfer rates of B and Ca in slag refining of silicon, and optimal stirring conditions were attained with only a modest kinetic energy input into the melt. Experiments were undertaken to measure mass transfer rates between liquid silicon and CaO-SiO2 slags at 1823 K (1550 °C) with varying stirring speed and slag composition. A remarkable feature of this system is the extreme fluctuation in interfacial area—these changes occur very rapidly and are difficult to capture. As little as 50 rpm stirring speed promotes, significant transient increases in interfacial area. At stirring speeds above 100 rpm, the rates of mass transfer do not increase significantly, so it is evident that above this threshold mass transfer in the bulk phases and interfacial area generation are already maximized. With a sufficiently high content of CaO in the slag, interfacial phenomena induced by the mass flux of calcium facilitate emulsification, and this is explained from a thermodynamic standpoint. It is likely that the calcium transfer enhances boron transfer by increasing the available interfacial area.

Kinetics of Boron Removal from Metallurgical Grade Silicon using a Slag Refining Technique Based on CaO-SiO2 Binary System

The removal of non-metallic impurity boron in metallurgical grade silicon (MG-Si) can be carried out by using a slag refining technique based on CaO-SiO2 system. However, the boron removal in depth in the slag refining process is limited by the kinetic conditions. The refining agents based on the binary and ternary slag systems CaO-SiO2, CaO-SiO2-LiF, CaO-SiO2-Li2O, and CaO-SiO2-K2CO3 were used to remove boron in this paper. The corresponding kinetic equations of boron removal using these slags were established by fitting the relationship between refining time and boron concentration in the refined silicon. It was determined that the rate coefficients of boron removal (kB) are 0.25, 0.24, 0.26, and 0.57, respectively, using CaO-SiO2, CaO-SiO2-LiF, CaO-SiO2-Li2O, and CaO-SiO2-K2CO3 slag refining. It was found that the mass transfer of boron in silicon is the rate controlling step for boron removal using 40%CaO-40%SiO2-20%LiF, 40%CaO-40%SiO2-20%Li2O, and 40%CaO-40%SiO2-20%K2CO3 slag refining. It is opposite to 50%CaO-50%SiO2 slag refining that the mass transfer of boron in slag becomes the controlling step for boron removal.

Treatment Effect of Steel Refining Slag as Admixture of Soil Stabilizing Cement for Heavy Metal Contaminated Stream Sediment and Mine Tailings-Contaminated Soil

Treatment Effect of Steel Refining Slag as Admixture of Soil Stabilizing Cement for Heavy Metal Contaminated Stream Sediment and Mine Tailings-Contaminated Soil

Mass Transfer in Slag Refining of Silicon with Mechanical Stirring: Transient Interfacial Phenomena

Experiments have been carried out to study the rates of mass transfer between liquid silicon and CaO-SiO2 slag with impeller stirring at 1823 K (1550 °C). The occurrence of transient interfacial phenomena related to the mass transfer of calcium has been observed; the evidence suggests that the reduction of calcium oxide at the interface leads to a rapid, temporary drop in the apparent interfacial tension. At low apparent interfacial tension, mechanical agitation facilitates the dispersion of metal into the slag phase, which dramatically increases the interfacial area; here, it has been estimated to increase by at least one order of magnitude. As the reaction rate slows down, the apparent interfacial tension increases and the metal recoalesces. The incidental transfer of calcium very likely promotes the transfer of boron by increasing the interfacial area. Mechanical mixing appears to be an extremely effective means to increase the reaction rate of boron extraction and could feasibly be implemented in the industrial slag refining of silicon to improve reaction rates.

Effect of Basicity on Deoxidation Capability of Refining Slag

Mass action concentration (activity) calculation model was used to analyze the variation rule of mass action concentrations of slag compositions with basicity changing, and the effect of basicity on deoxidation capability and control of spinel and globular inclusions was investigated theoretically. From the calculation and experimental results, it was found that with the increase of basicity, the mass action concentration of A12O3 and SiO2 decreases, while the mass action concentration of FeO and MgO increases at first and then decreases. Slag basicity below 3 to 4 would help to control spinel inclusions formation, and higher basicity improves formation of globular inclusions. Slag with basicity under 2 can effectively control the formation of globular inclusions. Deoxidation capability of slag increases with the increase of basicity, and slag with basicity about 4 could almost reach the maximum deoxidation capability. In order to smelt low oxygen steel with globular inclusions controlled, refining slag basicity should be controlled at about 4.

Industrial Application of Desulfurization Using Low Basicity Refining Slag in Tire Cord Steel

Desulfurization performance with low binary basicity refining slag in 72 grade tire cord steel was calculated using FactSage and it is found that sulfur content in steel decreases with the increase of basicity of slag, MgO content in slag and slag/steel ratio while sulfur partition ratio between slag and steel increases gradually with the increase of basicity of slag as well as MgO content. Experiments were carried out and the results are of great agreements with theoretical calculation. Then industrial application tests were performed in a domestic plant and good results were achieved. Sulfur content in steel decreases gradually during refining process, as a result, sulfur content in the billets is controlled in the range of 0.0071%–0.0081%. Sulfur content in steel refined with slag basicity of 1.21 is lower than that of 1.02, while the plasticity of oxide compound inclusions is a little better controlled in low basicity heats. Using refining slag with basicityof 1.0-1.2 and MgO content of 5%–10% and reducing the slag takeover of LD are favorable for improving the desulfurization performance and the plasticity of inclusions during the industrial production.

The Kinetics of Boron Transfer in Slag Refining of Silicon

Slag refining is one of the few metallurgical methods for efficient removal of boron from silicon. In industrial slag refining for production of silicon for photovoltaic applications, the relationship between the slag composition and the mass transfer rate of boron from metal to slag is of great importance. The kinetics of boron removal from liquid silicon during slag refining has been investigated in the present work by means of several small-scale experimental series at temperatures between 1,600°C and 1,650°C. Slag and metal, in batch weights of 30 g, were heated together in a graphite crucible placed in a resistance-heated tube furnace. The slags were produced from powdered SiO2, CaO, and MgO. The oxides applied were of high purity. Experiments were carried out at slag-to-metal ratios of 1 or 2, where the silicon initially contained approximately 250 ppm boron. Metal–slag mass transfer coefficients were calculated based on chemical analyses of the silicon and ranged from 1.7 μm/s for slag consisting of equal amounts of SiO2 and CaO by weight, to 4.3 μm/s for a 40%–40%–20% SiO2-CaO-MgO slag.

The Estimation of Quality Refining Slag for the Brass Gas-Slag Refining

The Estimation of Quality Refining Slag for the Brass Gas-Slag Refining This article contains information concerning of the analysis the possibility of defining refinery qualities of the slag based thermophysical and thermodynamical data. The paper presents a model of slag refining processes and a method of determining the reduction capability of slag solutions. Slag was analysed with the use of the DTA methods for the brass melting conductions. The study of computer program including the satisfactory number of data there are used in to the design a modern device rotating head used for gas-slag refining. It was achieved that the refining gas and fluxes were distributed ever by the rotating head. High effectiveness of the gas-slag refining processes was proved for the brass.

Effect of Additives on Melting Point and Viscosity of RH Refining Slag

To get suitable ladle slag which can avoid slag sticking onto the RH immersion tube during RH refining process of IF steel, the effect of composition on melting point and viscosity of RH refining ladle slag was studied by different additives which is based on CaO. The results of melting point and viscosity testing experiments indicates that, the melting point and viscosity of RH refining ladle slag would decrease effectively with the add of experimental additives. During RH refining process of IF steel, adjusting the basicity to 4~5, and the content of Al2O3 to 14%~15% by adding additives, it can avoid slag sticking onto the RH immersion tube efficiently, for the reason that the melting point of ladle slag is about 1280 °C, and the viscosity is only 0.65 Pa·s.

Effect of Refining Slag on the Inclusions of Hard Wire Steel during Melting Process

The effect of the refining slag composition on the total oxygen content and inclusions in steel was investigated in 100 t UHP Electric Furnace – LF – Billet CC process. The test steel was 77B hard wire steel and Si-Mn alloy was used as the deoxidizer. Three types slag were used in the industrial tests, which including CaO-CaF2, CaO-CaF2 adding CaC and CaO-Al2O3 refining slag. The results shown that the lowest total oxygen contents of rolled bar can be gained using the CaO-CaF2 refining slag adding CaC, which is 0.0036%, while the total oxygen contents of rolled bar using CaO-Al2O3 refining slag is higher a little than the heats using CaO-CaF2 refining slag. The CaO-SiO2 and CaO-Al2O3-SiO2 compound inclusions with the size of about 5 μm are the main inclusions in the heats refining by the CaO-CaF2 refining slag in the rolled bar, but the pure, indeformable Al2O3 inclusion can also be found with the size of about 10 μm. The CaO-Al2O3-SiO2 and Al2O3-SiO2-MnO compound inclusions are the main inclusions in the heats refining by the CaO-CaF2-CaC refining slag, but most of the inclusion shape is irregular with bigger size of about 10 μm. Similar with the heat using CaO-CaF2 refining slag, the pure Al2O3 inclusion with edge angle can be found in the rolled bar. The inclusions in the rolled bar treated by CaO-Al2O3 refining slag are CaO-Al2O3-SiO2 compound inclusions, most of which are nearly globular shape with the relative small size of about 5 μm. All of the inclusions in rolled bar lie on the low melting zone in the CaO-Al2O3-SiO2 ternary phase diagram in the heats using CaO-Al2O3 refining slag. The similar condition appeared on the most of the inclusions in the heats using CaO-CaF2 and CaO-CaF2 refining slag adding CaC, while part of which are lied on the high melting zone. Therefore, considering of the plastic deformation ability, the CaO-Al2O3 refining slag is the best slag for the melting process of hard wire steel.

Viscosity Determination of High Oxidizability Refining Slag and Its Buildup Solution

The principal purpose of this paper are to determine the viscosity of refining slag with the features of high crystallinity and strongly oxidizability, and to solve the problem that slag sticked onto the RH immersion tube during the RH refining process. Then, the fluid length method was used to determine the viscosity, and the effect of compositions on melting point and viscosity of refining ladle slag was studied. Overall, the relationship between viscosity and fluid length was acquired, and it achieved the slag with lower melting point and good fluidity which can avoid slag building-up on RH immersion tube by adjusting the basicity of refining slag to 4-5, the content of Al2O3 to 14-15% with additives.

Effect of Refining Slag Composition on Inclusions in Molten Steel treated by Barium‐bearing Alloy

AbstractThe effect of the refining slag composition on the inclusions in molten steel was studied in MgO crucible by using MoSi2 furnace. The experimental steel was heavy rail steel and Si‐Ca‐Ba alloy was used as the deoxidizer. The results showed that the total oxygen content of steel, and the total quantities, total areas and average radius of inclusions decreased with the increased basicity of refining slag. The total quantities and total areas of inclusions were the least when Al2O3 content in refining slag was between 13% and 20%, while the proportion of small inclusions increased when Al2O3 content was higher than 20%. The contents of SiO2 and Al2O3 in inclusions were affected directly by the SiO2 and Al2O3 contents in refining slag, and it was very remarkble when the slag composition was CaOAl2O32SiO2. Therefore, it's feasible to control the composition of inclusions by controlling the composition of refining slag.

「角炉」の鉄滓あるいは砂鉄を用いた製銑反応機構

「角炉」の鉄滓あるいは砂鉄を用いた製銑反応機構

Hot Metal Pretreatment and Less Slag Refining in BOF

Hot Metal Pretreatment and Less Slag Refining in BOF

VODにおける溶融18Cr鋼の合成スラグ処理

VODにおける溶融18Cr鋼の合成スラグ処理