Haiyan Tang

Rational argon stirring for a 150-t ladle furnace

Based on the principle of similarity, water modeling experiments were carried out for a 150-t ladle furnace. The rational parameters of argon stirring were determined as the optimized positions of nozzles, top area of the porous brick, and gas flow rate. The following results are obtained: 1) the optimized positions of two nozzles are at 0.333R (R refers to the radius of the ladle at bottom) with an angle of 135°; 2) the top diameter of the porous brick should be 130 mm; 3) the flow rate of gas should be 25.0-30.6 m^3/h. The plant trial shows that the improved process is effective in enhancing the cleanliness of round billets. The total oxygen content, microinclusions, and macroinclusions in round billets are reduced by 12.5%, 8.2%, and 20%, respectively.

Characteristics analysis of inclusion of 60Si2Mn–Cr spring steel via experiments and thermodynamic calculations

A plant trial of the production of 60Si2Mn–Cr spring steel using silicon–manganese combined with aluminium to deoxidise was performed, and the characteristics of inclusions during ladle furnace refining, calcium treatment and in billets were investigated by scanning electron microscope–energy dispersive spectroscopy and thermodynamic calculations. The formation mechanisms of oxide and CaS inclusions are discussed. The experimental observation and thermodynamic analysis showed that calcium treatment cannot entirely modify large-size MgO·Al2O3 spinel inclusions into homogeneous CaO–MgO–Al2O3 inclusions, but formed a liquid xCaO·yAl2O3 layer on its surface. When the Al content was 0.05 mass%, [Mg], [Ca] and [O] in molten steel could be controlled at 2.7∼5 ppm, 2.5∼8 ppm and 4.1∼5.2 ppm, respectively, to achieve inclusions in the low melting point region. A large amount of CaS was generated in the present process due to a higher sulphur concentration in the molten steel and an excessive amount of Ca–Si wire. To avoid/reduce its formation, the sulphur concentration should be controlled to below 70 ppm.

Effect of Acid-Soluble Aluminum on the Evolution of Non-metallic Inclusions in Spring Steel

The content of acidic soluble aluminum in molten steel ([Al]s) is of significance to the control of total oxygen (TO), the formation of non-metallic inclusions, and the improvement of the surface quality of billets. Industrial trials and thermodynamic calculations were performed to study the effects of [Al]s content on the TO and the evolution of non-metallic inclusions in 60Si2Mn-Cr spring steel that was deoxidized by Si-Mn ((low aluminum process (LAP)) and Si-Mn-Al (high aluminum process (HAP)). The results show that the [Al]s contents in billets are within 0.0060 to 0.0069 mass pct in the LAP and 0.016 to 0.055 mass pct in the HAP. The TO content at each station of the LAP is higher than that in the HAP; the inclusions of billets were mainly of the CaO-Al2O3-SiO2 type in the former, and of the CaO-Al2O3-MgO and CaS-Al2O3-MgO types in the latter. A tendency is found that the higher the [Al]s, the easier it is to deviate from the low melting point region of the inclusion distribution and the larger the size of the inclusions. The relationships between [Al]s and the melting point of the oxide inclusions and the Al2O3 content in the oxide inclusions are also discussed in terms of experiment and calculation.

The effect of a dissipative ladle shroud on mixing in Tundish: Mathematical and experimental modelling

Abstract The effect of a dissipative ladle shroud (DLS) on mixing in tundish was investigated, compared with that of a conventional ladle shroud (CLS) using mathematical and physical modelling. The tracer profiles of mathematical results, achieved using large eddy simulation, were validated by physical observations employing high-speed cinephotography. The design of a DLS dramatically changed the flow patterns and contributed the intermixing of fluid elements inside the ladle shroud. The vortex flow encouraged the turbulent mixing and was verified by tracking of physical tracer dispersion inside the DLS. Residence Time Distribution (RTD) curves were obtained in two different sized tundishes to examine the mixing behaviours. The findings indicated that the DLS benefited the tundish mixing in terms of increasing active volume. The effect seemed to be more remarkable in the smaller tundish. The DLS gave rise to a more plug-like flow pattern inside the tundish, showing potential to shorten the transition length during grade change.

Thermo-elasto-visco-plastic finite element analysis on formation and propagation of of-corner subsurface cracks in bloom continuous casting

The formation and propagation of the popular off-corner subsurface cracks in bloom continuous casting were investigated through thermo-mechanical analysis using three coupled thermo-mechanical models. A two-dimensional thermo-elasto-visco-plastic finite element model was developed to predict the mould gap evolution, temperature profiles and deformation behavior of the solidified shell in the mould region. Then, a three-dimensional model was adopted to calculate the shell growth, temperature history and the development of stresses and strains of the shell in the following secondary cooling zones. Finally, another three-dimensional model was used to analyze the stress distributions in the straightening region. The results showed that the off-corner cracks in the shell originated from the mould owing to the tensile strain developed in the crack sensitive regions of the solidification front, and they could be driven deeper by the possible severe surface temperature rebound and the extensive tensile stress in the secondary cooling zone, especially upon the straightening operation of the bloom casting. It is revealed that more homogenous shell temperature and thickness can be obtained through optimization of mould corner radius, casting speed and secondary cooling scheme, which help to decrease stress and strain concentration and therefore prevent the initiation of the cracks.

Inclusion evolution in 50CrVA spring steel by optimization of refining slag

In order to control the CaO-Al2O3-SiO2-MgO system inclusions in 50CrVA spring steel in a lower melting temperature region, high temperature equilibrium experiments between steel and slag were performed in the laboratory, under the conditions of the initial slag basicity within 3–7 and the content of Al2O3 between 18–35 mass%, to investigate the formation and evolution of this type of inclusion. The results indicate that the total oxygen content in the steel decreases with the increase of slag basicity and the decrease of Al2O3 content in slags, and CaO-Al2O3-SiO2-MgO inclusions tend to deviate from the low melting point region with the increase of Al2O3 content in slags. The most favorable composition for the refining slag is composed of 51–56 mass% CaO, 9–13 mass% SiO2, 20–25 mass% Al2O3 and 6 mass% MgO. In this case, the inclusions in 50CrVA spring steel are mostly in the low melting point regions, in which their plasticities are expected to improve during steel rolling. The MgO-based inclusions were observed in the steel matrix and the formation mechanism was theoretically and schematically revealed. It is also found that adding around 11 mass% of MgO into the refining slags is beneficial to reducing the refractory corrosion. Further work should be carried out focusing on the evolution rates of MgO-based inclusions.

Reaction Between MnO-SiO2 Oxides with Low FeO Content and Solid Steel Deoxidized by Si and Mn During Heat Treatment

In order to clarify the reaction between MnO-SiO2 oxides with low FeO content and Fe-Mn-Si alloy, two diffusion couples were produced by the new method using confocal scanning laser microscopy (CSLM). The interface of the alloy and oxide, content of Mn and Si in the alloy near the interface, size distribution and composition of the particles which precipitated in the alloy were observed and analyzed using the electron probe microanalysis (EPMA). Results show that though the FeO content in the oxides decrease to 1% which is lower than the equilibrium with the molten steel at 1873K, the diffusion of oxygen from oxide to alloy still exists during the heat treatment at 1473K and causes shorter Particle Precipitated Zone (PPZ) and Manganese Depleted Zone (MDZ) normally for the reduction of diffusion flux of oxygen.

Research on mineral processing for high silica low grade hematite ore in Xinjiang

Abstract In order to develop and utilise cheap iron ores with low quality for cost reduction, a hematite ore from Xinjiang province was investigated to determine the iron increase and silicon reduction using ore dressing process experiments. Results showed that iron concentrate with 61%Fe and iron recovery of 66% were achieved through the process flowsheet of grinding, high intensity magnetic separation, regrinding of coarse concentrate, clean concentration by high intensity magnetic separation, roughing reverse floatation and cleaning reverse floatation of the high intensity concentrate, with the tailings from this latter stage fed back into the roughing reverse floatation stage.