Yanwu Dong

Mathematical Model for Electroslag Remelting Process

A mathematical model, including electromagnetic field equation, fluid flow equation, and temperature field equation, was established for the simulation of the electroslag remelting process. The distribution of temperature field was obtained by solving this model. The relationship between the local solidification time and the interdendritic spacing during the ingot solidification process was established, which has been regarded as a criterion for the evaluation of the quality of crystallization. For a crucible of 950 mm in diameter, the local solidification time is more than 1 h at the center of the ingot with the longest interdendritic spacing, whereas it is the shortest at the edge of the ingot according to the calculated results. The model can be used to understand the ESR process and to predict the ingot quality.

Effect of Slag on Titanium, Silicon, and Aluminum Contents in Superalloy During Electroslag Remelting

Many factors influence the chemical composition in electroslag remelting (ESR) steel, including atmosphere in crucible, melting rate, slag composition, deoxidation, and so on. Fluoride-based slag, which is exposed to liquid metal directly, influences the chemical composition of ESR ingots to a large extent. The present paper focuses on the effect of slag on the titanium, silicon, and aluminum contents in ingots based on the interaction of the slag and metal. In present work, superalloy of GH8825 and several slags containing different CaO contents have been employed for investigating the effect of slag on titanium, silicon, and aluminum contents in an electrical resistance furnace under argon atmosphere. Results indicate that the higher CaO content in slag has better capacity for avoiding loss of titanium caused by the reaction of titanium with silica in slag, especially in case of remelting superalloy with high titanium and low silicon content. The CaO has a great effect on the activities of TiO2, SiO2, and Al2O3. Thermodynamic analysis is applied to investigate the CaO behavior. Based on the ion and molecule coexistence theory of slag, activity model is established to calculate the activities of components containing titanium, silicon, and aluminum elements in a six-component slag consisting of CaO-CaF2-Al2O3-SiO2-TiO2-MgO. The components containing titanium, silicon, and aluminum in slag are mainly CaO·TiO2, 2CaO·SiO2, CaO·SiO2, CaO·Al2O3, and MgO·Al2O3. With the increase of CaO mass fraction in slag, the activity coefficient of SiO2 decreases significantly, whereas slightly change happens for Al2O3. As a result, the

Hydrogen Pick-Up During Electroslag Remelting Process

\lg ({{\gamma_{{{\text{SiO}}_{2} }} } \mathord{\left/ {\vphantom {{\gamma_{{{\text{SiO}}_{2} }} } {\gamma_{{{\text{TiO}}_{2} }} }}} \right. \kern-0pt} {\gamma_{{{\text{TiO}}_{2} }} }})

Study of Single-Power, Two-Circuit ESR Process with Current-Carrying Mold: Development of the Technique and Its Physical Simulation

lg(γSiO2γTiO2) decreases with increasing CaO content, which is better for preventing loss of titanium caused by the reaction of titanium with silica in slag. The slag with high CaO and appropriate TiO2 content is suitable for electroslag remelting of GH8825.

Comprehensive Mathematical Model for Simulating Electroslag Remelting

Experiment was carried out after the process parameters were calculated by the model previously established. The relationship between interdendritic spacing and local solidification time (LST) mainly determined by process parameters was exposed. Furthermore, the extent of segregation was studied. The results indicate that LST and interdendritic spacing are the largest and the amount of Laves phase as a result of the niobium segregation is the highest in the center of the ingot, whereas the opposite results are obtained at the edge of ingot. The extent of element segregation and the amount of Laves phase can be reduced when appropriate parameters are used. Therefore, the duration of subsequent homogenization treatments for 718 is shortened and the alloy quality is improved.

Research on droplet formation and dripping behavior during the electroslag remelting process

The pick-up of hydrogen during electroslag remelting process for several slags consisting of CaF2-Al2O3−CaO-SiO2−MgO had been investigated. The laboratory-scale remelting experiments had been carried out in open air and water-free argon atmosphere, and then the influencing factors were analyzed. It had been found that the hydrogen content in steel varied with different slag compositions. The compositions and state of slag had significant effect on the hydrogen level in steel. Partial return slag and premelted slag could avoid the hydrogen pick-up especially in the early stages of the process. However, premelted slag was the optimum state to control the hydrogen pick-up in steel. Experimental results indicated that water-free argon atmosphere was very favorable to the control of hydrogen in steel in the normal remelting period.

Effect of Fluoride Containning Slag on Oxide Inclusions in Electroslag Ingot

The hydrides in industrial lime, alumina, magnesia, and calcium fluoride were investigated through differential thermal analysis and X-ray diffraction, and their mass losses during heating up were studied by thermogravimetric analysis method. The results indicate that the industrial alumina, lime, and magnesia, which have more moisture or hydride and mainly include γ-Al2O3, Ca(OH)2, and Mg(OH)2, lose more mass during thermogravimetric analysis process. However, the mass of premelted slag consisting of lime, fluorite, alumina, and magnesia has almost no change, which means no hydride in it. Some relationships for calculating the mass loss were established according to the results of thermogravimetric analysis. These results will be in favor of setting up the rational calcination criterion for slag used in electroslag remelting process.

Mathematical Model of Solidification during Electroslag Casting of Pilger Roll

Physical simulation of a single-power, two-circuit electroslag remelting (ESR) process with current conductive mold (ESR-STCCM) is carried out in this paper. Wood alloy and sodium chloride solution are used to study the current distribution ratio of passing electrode and conductive part of current carrying mold (conductor). A conventional ESR (CESR) process has been studied as a comparison. The total current of ESR-STCCM is larger than the CESR process, which indicates that the resistance in ESR-STCCM is smaller than in CESR. Results show that the ratio of Ielectrode/Iconductor changes with filling ratio, electrode immersion depth, and effective conductor height. Electrode immersion depth plays an important role on the current distribution ratio. Nevertheless, the effective conductor height has a little influence on the current distribution ratio. A larger filling ratio has an obvious effect on the current distribution ratio in ESR-STCCM. Current flowing through the electrode increases with the increasing of electrode immersion depth under a certain filling ratio. The physical model established can provide an important direction to real ESR-STCCM.