Papers by Author: Cheng Jun Liu

Abstract: A heat transfer and solidification model of slab continuous casting process was developed, and the nail-shooting experiments were carried out to verify and improve the prediction accuracy. The comparison between the simulation and the measurements results showed that, there exists difference between the model predicted liquid core length and the calculated liquid core length according to the measurement results of the solidification shell thickness. In the present study, the value of constant a in the heat transfer coefficient calculation formula was corrected through back-calculation, results showed that, the suitable value of a is 31.650, 33.468 and 35.126 when the casting speed is 0.8m·min^-1, 0.9m·min^-1 and 1.0m·min^-1 respectively, which can meet the liquid core length of the measurement results. The developed model built a foundation for the application of dynamic secondary cooling, and dynamic soft reduction.

Abstract: The pollution of chromium salt industry is increasingly serious in China and becomes a worldwide problem with the rapid development of chromium salt industry. Then a new clean production process with a high recovery rate of chromium and pollution-free was proposed according to the comprehensive summary of existing processes of basic chromium sulphate. Furthermore, a small amount of slag will be discharged in this short process with lower energy consuming. The design concept is also applicable to the preparation of other chromium salts products, which will eliminate the pollution of Cr⁶⁺ during the process of chromium salt production and be helpful to the comprehensive utilization of chromium salt. In addition, the guidance of scholar research and the broad application prospects of this work cannot be neglected.

Abstract: Utilizing Pakistan chromite as raw material, the rapid leaching of chromium and iron could be realized by the sulfuric acid leaching process on the condition of atmospheric pressure and the addition of oxidant A. And the leaching rate of chromium and iron would be 98.5% and 71.9%, respectively. The sulfuric acid leaching processes with different temperature were systematically studied by chemical analysis and phase analysis. The results showed that, with the increase of reaction temperature, the leaching rate of chromium would increase gradually, but the leaching rate of iron increased at first and then decreases and reached its maximum at 140°C. When the temperature > 160°C, the phases of the leaching residue were magnesium iron silicate and a few of silica, no chromohercynite, chrompicotite and magnesioferrite existed in the chromite. The leaching solution of sulfuric acid leaching process could be used for preparing the basic chrome sulfate, and there is no Cr⁶⁺ in the leaching residue and solution. The results would provide theoretical guidance for solving environmental pollution problem of Cr⁶⁺ in traditional chromate production process.

Abstract: Based on the silicate structure theory, the molten slag structure and the existential state of and during micro-carbon Cr-Fe alloy production process were analysised, and then their diffusion coefficients were calculated. The results showed that, during the initial stage, the average diffusion coeffecient of and is close to the , the reaction process is controlled by the diffusion of () and corporately, during the later stage, the diffusion coefficient of is less than average diffusion coefficient of and , the controlling step is the diffusion of . According to the evolution of diffusion coefficient, molten slag composition optimization method was advised to increase the diffusion ability of and for enhancing the reaction efficiency and the recovery rate of chromium.

Abstract: The effect of HCl concentration on the oxide layer removal behaviors were investigated for hot-rolled plate of SUS430 stainless steel which was treated by the pickling technology. The oxide layer of SUS430 stainless steel could be removed by the pickling technology. The oxide layer is with the thickness from 5μm to 15μm, and composed of Fe2O3 and Cr2O3. The outer of oxide layer is iron-rich oxide, and inner that have loose structure is chromium-rich oxide. With the increasing HCl concentration, the weight loss of pickling stainless steel quickly increased, and the weight loss is in linear relationship with pickling time.

Abstract: The effects of the rare earth (RE) element on the microstructure of a hot-rolled low carbon steel (B450NbRE) were investigated under different heat treatment conditions. It was found that the B450NbRE steel with ultrafine grained structure could be successfully prepared with a certain content of RE additive under an appropriate heat treatment temperature between A1 (717°C) and A3 (880°C). The corresponding critical temperature increases with decreasing the RE content. For instance, the critical temperature is 800°C for the RE content of 0.0140 wt.%, but it increases to 850°C as the RE content decreases to 0.0075 wt.%

Abstract: The thermodynamic model which quantificationally described the behavior of cerium in heavy rail steel was proposed. From the model, the effects of cerium on the composition, sequence and transformation condition of inclusions and the content of cerium dissolved in heavy rail steel were studied principally. When the cleanliness of heavy rail steel is low, the sequence of inclusions precipitation in heavy rail steel is Ce₂O₃, Ce₂O₂S, Ce₂S₃ and CeS. With increasing the cleanliness of steel, the sequence of inclusions precipitation is Ce₂O₂S and CeS. At 1783 K, the necessary condition of Ce₂O₃ precipitation in heavy rail steel is a_o/a_s≥0.186, for Ce₂S₃ precipitation is a_o/a_s≤0.394. The content of cerium dissolved in heavy rail steel is mainly affected by Ce₂S₃ inclusion. With the precipitations of all inclusions being stable, the curve between the dissolved cerium content and cerium addition becomes linear.

Abstract: 430 stainless steel is used as raw material and pickling in HCl-based electrolytes is adopted, and the effect of oxidation agent on removal behavior of the oxide layer on stainless steel is systematically studied; study found that the oxide layer of stainless steel after heat treatment in the lab is composed of iron oxide and chromium oxide, and outer oxide layer has dense structure while inner layer has multihole structure; with the increasing oxidation agent addition, corrosion potential of stainless steel after heat treatment increased; under 1.0% oxidation agent addtion condition, only few inner oxide remained and removal tendency of oxide layer is obvious when pickled for 200s; oxide on surface totally got removed, and a smooth surface obtained after pickled for 400s.

Abstract: Clean heavy rail steel was prepared by the process of vacuum induction furnace smelting, forge work and rolling. Effects of Rare earths (RE) on phase transformation and microstructure of heavy rail steel were investigated by thermal simulation machine, metallographic microscope and scanning electronic microscope. Thermal simulate tests indicate that, RE can move the C curve of pearlite transformation to lower right, prolong the incubation period of pearlite and improve the stability of undercooled austenite. The minimum incubation period of pearlite transformation is increased from 24s to 30s by RE. Furthermore, RE can decrease the critical cooling rate of pearlite transformation from 1°C•s^-1 to 0.5°C•s^-1 and the critical cooling rate of quenching from 15°C•s^-1 to 13°C•s^-1. Additionally, RE can fine the annealing and anormalizing pearlite notably. The pearlite laminae distance of heavy rail steel added RE is decreased by 12.9% (annealing) and 13.3% (normalizing), respectively.

Abstract: Accorded with the criteria the X80 pipeline steels with RE additions have been prepared with a vacuum induction furnace. The effect of rare earths (RE) on austenite grain growth behavior in pipeline steel has been discussed in this work. After hot rolled, the effect of RE on austenite grain growth behavior have been studied by the thermal simulator, scanning electron microscopy and metallographic microscope. The results indicate that RE additions inhibit the abnormal growth of austenite grain, trace RE could significantly influence the austenite grain growth behavior, and obtain fine grain size in X80 pipeline steel. For instance, the activation energy of grain growth reduced from 475 kJ/mol to 425 kJ/mol with addition of 0.0220 wt.% RE according with no deliberate RE additions, but the grain growth index increased from 3.5 to 4.5.