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

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

A thermodynamic model for calculating the mass action concentrations of structural units in CaOSiO2MgOFeOMnOAl2O3CaF2 slags, i.e., the IMCT-Ni model, has been developed based on the ion and molecule coexistence theory (IMCT). The calculated comprehensive mass action concentration of iron oxides $N_{{\rm Fe}_{t} {\rm O}} $ has been compared with the reported activity of iron oxide $a_{{\rm Fe}_{t} {\rm O}} $ in 14 FeO-containing slag systems from literatures. The good agreement between the calculated $N_{{\rm Fe}_{t} {\rm O}} $ and reported $a_{{\rm Fe}_{t} {\rm O}} $ indicates that the developed IMCT-Ni model can be successfully applied to predict the activity of iron oxide $a_{{\rm Fe}_{t} {\rm O}} $ as well as the slag oxidation ability of CaOFeO (s1), SiO2FeO (s2), CaOSiO2FeO (s3), CaOFeOAl2O3 (s4), SiO2MgOFeO (s5), SiO2FeOAl2O3 (s6), CaOSiO2FeOAl2O3 (s7), CaOSiO2MgOFeOAl2O3 (s8), SiO2FeOMnO (s9), SiO2FeOMnOAl2O3 (s10), FeOMnO (s11), FeOMnOAl2O3 (s12), CaOFeOCaF2 (s13), and CaOSiO2FeOCaF2 slags (s14) in a temperature range of 14731973K.

A Thermodynamic Model for Prediction of Iron Oxide Activity in Some FeO-Containing Slag Systems

The advantages of the electroslag remelting (ESR) process as to cleanness and homogeneity of the ingot structure are well known. As to homogeneity of composition, the control of titanium in stainless steel with high titanium and low aluminium contents during the ESR process has not been resolved well so far. The current work focuses on designing appropriate slag for controlling titanium content during 1Cr21Ni5Ti remelting based on the interaction of the slag/metal interface. Several kinds of slag containing different CaO contents combined with steel samples of 1Cr21Ni5Ti were employed to investigate the effect of slag on titanium content in an electrical resistance furnace, and metal samples were taken at different times for investigating the change of titanium and aluminium contents in steel. The results show that slag with low CaO content at low temperature has excellent capacity for avoiding loss of titanium content caused by its reaction with the alumina in slag, especially in case of remelting of sta...

Thermodynamic design of electroslag remelting slag for high titanium and low aluminium stainless steel based on IMCT

The phosphate-enrichment behavior has experimentally been investigated in CaO-SiO2-FeO-Fe2O3-P2O5 steelmaking slags. The reaction ability of structural units in the slags has been represented the mass action concentration from the developed ion and molecule coexistence theory (IMCT)- model based on the IMCT. The defined enrichment possibility and enrichment degree of solid solutions containing P2O5 from the developed IMCT- model have been verified from the experimental results. The effects of binary basicity, the mass percentage ratio , and mass percentage of P2O5 in the initial slags on phosphate-enrichment behavior in the slags has also been discussed. The results show that the P2O5 component can easily be bonded by CaO to form tricalcium phosphate 3 CaO center dot P2O5, and the formed 3CaO center dot P2O5 can react with the produced dicalcium silicate 2CaO center dot SiO2 to generate solid-solution 2CaO center dot SiO2-3CaO center dot P2O5 under fixed cooling conditions. The maximum value of the defined enrichment degree of solid-solution 2CaO center dot SiO2-3CaO center dot P2O5 is obtained as 0.844 under conditions of binary basicity as 2.5 and the mass percentage ratio as 0.955 at fixed cooling conditions.

Enrichment Mechanism of Phosphate in CaO-SiO2-FeO-Fe2O3-P2O5 Steelmaking Slags

Experimental and theoretical studies have been carried out to investigate the effects of the slag on desulfurization during the electroslag remelting (ESR) process with a focus of developing a mass transfer model to understand the mechanism of desulfurization. Stainless steel 1Cr21Ni5Ti was used as the electrode and remelted with two different kinds of slags using a 50-kg ESR furnace. The contents of sulfur along the axial direction of product ingots were analyzed. It was found that the sulfur content of 350 ppm in the electrode is reduced to 71 to 95 ppm in the ingot by remelting with the slag containing 5 wt pct of CaO, and lowered more to 47 to 59 ppm with another slag having 20 wt pct CaO. On the basis of the penetration and film theories, the theoretical model developed in this work well elucidates the kinetics of desulfurization revealing the mechanism of sulfur transfer during the ESR process. The calculation results obtained from the model agree well with the experimental results. The model indicates that when sulfur content in electrode is given, there is a corresponding minimum value of sulfur content in the ingot due to the kinetics limit. This lowest sulfur content cannot be further reduced even with increasing L
 S (sulfur distribution coefficient between metal and slag phases) or decreasing sulfur content in the slag. Constant addition of extra amount of CaO to the molten slag with the increase of sulfur content in the slag during the remelting process can improve the macrosegregation of sulfur distributed along the axial direction of ESR ingots. Since the rate-determining steps of the sulfur mass transfer lie in the metal phase, adding calcium as deoxidizer can change mass transfer of sulfur and thus promote desulfurization further during the ESR process.

Mass Transfer Model of Desulfurization in the Electroslag Remelting Process

A thermodynamic model for calculating the phosphorus distribution ratio between top–bottom combined blown converter steelmaking slags and molten steel has been developed by coupling with a developed thermodynamic model for calculating mass action concentrations of structural units in the slags, i.e., CaO-SiO2-MgO-FeO-Fe2O3-MnO-Al2O3-P2O5 slags, based on the ion and molecule coexistence theory (IMCT). Not only the total phosphorus distribution ratio but also the respective phosphorus distribution ratio among four basic oxides as components, i.e., CaO, MgO, FeO, and MnO, in the slags and molten steel can be predicted theoretically by the developed IMCT phosphorus distribution ratio prediction model after knowing the oxygen activity of molten steel at the slag–metal interface or the Fe
 t
 O activity in the slags and the related mass action concentrations of structural units or ion couples in the slags. The calculated mass action concentrations of structural units or ion couples in the slags equilibrated or reacted with molten steel show that the calculated equilibrium mole numbers or mass action concentrations of structural units or ion couples, rather than the mass percentage of components, can present the reaction ability of the components in the slags. The predicted total phosphorus distribution ratio by the developed IMCT model shows a reliable agreement with the measured phosphorus distribution ratio by using the calculated mass action concentrations of iron oxides as presentation of slag oxidation ability. Meanwhile, the developed thermodynamic model for calculating the phosphorus distribution ratio can determine quantitatively the respective dephosphorization contribution ratio of Fe
 t
 O, CaO + Fe
 t
 O, MgO + Fe
 t
 O, and MnO + Fe
 t
 O in the slags. A significant difference of dephosphorization ability among Fe
 t
 O, CaO + Fe
 t
 O, MgO + Fe
 t
 O, and MnO + Fe
 t
 O has been found as approximately 0.0 pct, 99.996 pct, 0.0 pct, and 0.0 pct during a combined blown converter steelmaking process, respectively. There is a great gradient of oxygen activity of molten steel at the slag–metal interface and in a metal bath when carbon content in a metal bath is larger than 0.036 pct. The phosphorus in molten steel beneath the slag–metal interface can be extracted effectively by the comprehensive effect of CaO and Fe
 t
 O in slags to form 3CaO·P2O5 and 4CaO·P2O5 until the carbon content is less than 0.036 pct during a top–bottom combined blown steelmaking process.

A Thermodynamic Model of Phosphorus Distribution Ratio between CaO-SiO2-MgO-FeO-Fe2O3-MnO-Al2O3-P2O5 Slags and Molten Steel during a Top–Bottom Combined Blown Converter Steelmaking Process Based on the Ion and Molecule Coexistence Theory

A method for desulfurizing ultra-low carbon pure steel in a circulating vacuum degassing method comprises the following steps: 1. molten iron pretreatment desulfurization: blast-furnace molten iron isdesulfurized by injecting and blowing granular magnesium, and slag skimming is carried out after desulfurization to skim most desulfurized slag; 2. decarbonization and dephosphorization in a top andbottom combined blown converter: the desulfurized molten iron is added into the top and bottom combined blown converter to carry out converting and decarbonization and dephosphorization, when tapping,alloying is not carried out, and synthetic slag is added in the tapping process; 3. RH deep decarbonization and desulfurization: a. a ladle which is filled with poured molten steel is moved to an RHwork station to carry out vacuum carbon-oxygen reaction deep decarbonization, and carbon reaches 0.001 percent to 0.0025 percent; b. after RH decarbonization is finished, aluminum deoxidation is carried out, and dissolved oxygen is not more than 0.0005 percent; and c. after the deoxidation for 2 to 3min, desulfurater is added, and low-carbon active lime is desulfurized; and 4. continuous casting.The method for desulfurizing ultra-low carbon pure steel in the circulating vacuum degassing method has low cost and high desulfurization rate.

Method for desulfurizing ultra-low carbon pure steel in circulating vacuum degassing method

The utility model belongs to metallurgical casting and pouring molds, and particularly relates to a 5-ton steel ingot mold for pouring, which comprises a mold body and a heat insulation cap arranged on the mold body. The mold body comprises a casing and an inner cavity, and is characterized in that the axial section of the casing is in a 'U' shape, the casing is a conical octagonal frustum, the cross section of the casing of the mold body is octagonal, the section of the inner cavity of the mold body is in an octagonal concave arc shape, the concave arcs are transited through circular arcs, taper alpha of the inner cavity of the mold body ranges from 3.5% to 3.8%, the bottom of the longitudinal section of the inner cavity of the mold body is in a butterfly shape and provided with a bottom hole, a heat insulation cap positioning platform is disposed on the upper end face of the mold body, suspension lugs are disposed on the outer casing, the main structure of the inner cavity of the heat insulation cap is in a circular tubular shape, and the suspension lugs are disposed on a heat insulation cap outer casing. The 5-ton steel ingot mold can be used for directly casting cast products of special specifications, and meets the requirement of developing cast products of special specifications.

Jianchang Wang

Papers

A Thermodynamic Model of Phosphorus Distribution Ratio between CaO-SiO2-MgO-FeO-Fe2O3-MnO-Al2O3-P2O5 Slags and Molten Steel during a Top–Bottom Combined Blown Converter Steelmaking Process Based on the Ion and Molecule Coexistence Theory

Method for desulfurizing ultra-low carbon pure steel in circulating vacuum degassing method

5-ton steel ingot mold for pouring