Cleanliness improvement and microstructure refinement of ingot processed by vacuum electroslag remelting

The purity of a steel is an important factor influencing the quality of the final products. Therefore, it is important to optimize the existing and develop new steelmaking technologies that affect the resulting purity. Electro slag remelting is a technology of tertiary metallurgy, which can advantageously be used to fabricate high quality steels. The study presents selected theoretical aspects of oxide systems and their specific influences on effectiveness of the electro slag remelting technology. The aim of this work was to experimentally analyze the purity of a tool steel fabricated by electro slag remelting using two different oxide systems (fused slags). The core of the study is the determination of the overall presence of elements in the steels, a thorough investigation of the presence of (not only) oxide-based inclusions within the investigated tool steel, and a detailed analysis of their chemical composition, including the size of these non-metallic inclusions, using energy dispersive X-ray (EDX) on the scanning electron microscope (SEM). Last but not least, the determination of the modification of the occurring non-metallic inclusions and verification of the experimentally acquired results as well as the calculation of the liquid and solid temperature and the calculation of the viscosity of the slags using the FactSage calculation software was performed. The results showed that the used slag influenced especially the occurrence of Mg and Al-based oxide inclusions. The CaS-type inclusions were present within all of the examined samples. The slag type influenced not only the typical morphology and size of the inclusions (especially of the CaS type), but also the tendency of the steel to exhibit localized corrosion when exposed to the ambient environment. This research can contribute to a better understanding of the effect of oxidation systems on the resulting purity and properties of ESR steels, thereby advancing the production of tool steels with higher quality and performance requirements.

Effect of mold rotation on the bifilar electroslag remelting process

Electroslag remelting (ESR) experiments were performed on 304L austenitic stainless steel using a laboratory-scale low-frequency electroslag furnace with Al2O3-CaO-CaF2 and Al2O3-CeO2-CaF2 slags of varying compositions. The study aimed to evaluate the influence of slag composition on the oxygen and nitrogen content, as well as the number, size, and types of inclusions in ESR ingots under low-frequency power supply conditions. The results demonstrated that, under low-frequency conditions, increasing the CaO or CeO2 content while decreasing Al2O3 in the slag significantly reduced the oxygen content in the ingots. Among the slag components, CaO exhibited a markedly stronger deoxidation effect than CeO₂ under identical conditions. Regardless of slag type, the nitrogen content in the ingots remained stable. In the Al2O3-CaO-CaF2 system, higher CaO content decreased the number and size of inclusions and shifted their type from Al2O3 to aluminum-calcium composite inclusions. Similarly, in the Al2O3-CeO2-CaF2 system, a 15% CeO₂ content reduced the inclusion size and number, leading to the formation of cerium-containing composite inclusions. The micro-electrolysis of slag components under low-frequency power supply was identified as the primary mechanism influencing inclusion characteristics, with slag stability playing a pivotal role in determining inclusion distribution and number in the ingots. Consequently, careful slag composition selection is essential for optimizing low-frequency ESR processes.

Slag–metal reaction experiments in MoSi2 resistance furnace combined with electroslag remelting (ESR) experiments in ESR furnace are used to study the effect of slag on zirconium distribution in ESR ingot by establishing a new mass transfer model of slag–metal reaction. The mass transfer model consists of Al + Al2O3, Si + SiO2, Zr + ZrO2, and Fe + FeO systems based on the penetration and film theories. Both experimental and simulated results show that the returned slag (CaF2:CaO:Al2O3:MgO:ZrO2 = 57:20:16:3:3) combined with extra 4% Al2O3 added into molten slag in the first slag-temperature-rising period can control the zirconium in ESR ingot ranging from 0.35 to 0.40% and improve the homogeneous distribution of zirconium in ESR ingot. The returned slag of Exp.A containing low silica being used in Exp.C can not only contribute to the recycling of returned slag, but also improve the homogeneous distribution of Zr along the height of ESR ingot.

The cleanliness and compositional change of Ni containing alloy steel processed by electroslag remelting (ESR) and vacuum arc remelting (VAR) were studied. The results show that compared with the electrode steel, the total oxygen content increases in the steel processed by ESR. On the contrary, the total oxygen and total nitrogen content in the steel processed by VAR can be significantly decreased due to the vacuum environment. The number and size of inclusions in steel processed by VAR are significantly decreased, which indicates that the VAR is conducive to improving the cleanliness of steel. Single TiN inclusions are found in both steels processed by ESR and VAR, and oxide inclusions in two steels are (Mg,Al,Ca)O and (Mg,Al)O, respectively. The growth time of TiN inclusions is relatively shorter in the steel processed by VAR, which leads to the thinner TiN layer surrounding the oxide inclusions. During the VAR process, the high temperature and high vacuum conditions promote the volatilization of Mn in steel, leading to decrease of the Mn content in steel. Therefore, extra Mn should be added to the electrode steel before VAR.

Using optical microscopy, scanning electron microscopy, X-ray energy spectrum analysis and thermodynamic calculation software Thermo-Calc, inclusions, grain size and precipitates from different positions in the forging ingots of two different smelting process are compared and analysed, along with the formation mechanism of the precipitates. The results show that the sizes of inclusions in forging ingots from two different smelting process do not change, but reduce in number after the electroslag remelting process, and neither do the species change: mainly aluminium oxide and silicate inclusions. The average grain size after electroslag remelting is smaller than before, and the main equilibrium precipitates of 028 alloy include γ, M23C6, σ and α-Cr phases. The precipitates after electroslag remelting are fewer in number, with uneven distributions. Regarding chemical composition, the precipitates are mainly in the σ phase, containing Fe, Ni, Cr and Mo elements. This severely reduces the corrosion resistance of 028 alloy, and can be eliminated by solid solution treatment for 2 h at 1160°C.

Microstructure refinement and its effect on properties of spring steel

Oxidation behavior of boron in 9CrMoCoB steel by CaF2–CaO–Al2O3–SiO2–B2O3 electroslag remelting (ESR) type slag

The quantity, size, and distribution of non-metallic inclusions in High-Strength Low-Alloy (HSLA) steel critically influence its service performance. Conventional detection methods often fail to adequately characterize extreme inclusion distributions in large-section components. This study developed an integrated full-process inclusion analysis system combining high-precision motion control, parallel optical imaging, and laser spectral analysis technologies to achieve rapid and automated identification and compositional analysis of inclusions in meter-scale samples. Through systematic investigation across the industrial process chain—from a dia. 740 mm consumable electrode to a dia. 810 mm electroslag remelting (ESR) ingot and finally to a dia. 400 mm forged billet—key process-specific insights were obtained. The results revealed the effective removal of Type D (globular oxides) inclusions during ESR, with their counts reducing from over 8000 in the electrode to approximately 4000–7000 in the ingot. Concurrently, the mechanism underlying the pronounced enrichment of Type C (silicates) in the ingot tail was elucidated, showing a nearly fourfold increase to 1767 compared to the ingot head, attributed to terminal solidification segregation and flotation dynamics. Subsequent forging further demonstrated exceptional refinement and dispersion of all inclusion types. The billet tail achieved exceptionally high purity, with counts of all inclusion types dropping to extremely low levels (e.g., Types A, B, and C were nearly eliminated), representing a reduction of approximately one order of magnitude. Based on these findings, enhanced process strategies were proposed, including shallow molten pool control, slag system optimization, and multi-dimensional quality monitoring. An intelligent analysis framework integrating a YOLOv11 detection model with spectral feedback was also established. This work provides crucial process knowledge and technological support for achieving the quality control objective of “known and controllable defects” in HSLA steel.

The modification mechanism of cerium (Ce) on oxides and multilayer carbontrides in H13 steel is investigated by industrial trials and thermodynamic calculations. The morphology, composition, and size of inclusions are analyzed by scanning electron microscopy and energy dispersive spectroscopy. The main inclusions in H13 steel without Ce content in the molten steel are MgAl2O4 spinel inclusions and multilayer carbonitrides. The carbonitrides have a multilayer structure in which MgAl2O4 acts as the nucleation core and the second layer is (Ti, V)(C, N). As the cerium content in molten steel increases from 0 to 0.03 wt%, the MgAl2O4 is effectively modified into cerium oxide (Ce–O) and cerium oxy‐sulfide (Ce–O–S), and the evolutionary process is as follows: MgAl2O4 → CeAlO3 → Ce–O and Ce–O–S. Likewise, the structure of multilayer carbonitrides in the H13 steel also changed. The MgAl2O4 and CeAlO3 act as heterogeneous nucleation cores of multilayer carbonitrides. However, Ce–O and Ce–O–S can effectively inhibit the heterogeneous nucleation of carbonitrides. The number density of large‐size carbontrides is remarkably reduced with increasing Ce content. A prediction model of optimum Ce content in molten steel is built, which has remarkable agreement with the experimental observations.

Titanium microalloyed steels are widely used in modern manufacturing industries. However, during steelmaking, air, protective slag, and refractory materials can all contribute to the reoxidation of molten steel, with air having the most pronounced effect. This study investigates the evolution of inclusions during reoxidation in titanium microalloyed steel by combining experimental work with thermodynamic calculations. The results show that as reoxidation intensifies, both the types and sizes of inclusions in steel increase, and the increase in T.O content promotes Al 2 O 3 , thereby reducing the effectiveness of Ca treatment. Additionally, the composite inclusions follow the evolution path: Al 2 O 3 → Al 2 O 3 ‐CaO → Al 2 O 3 (‐CaO)‐(Mn, Ca)S → Al 2 O 3 –CaO–(Mn, Ca)S–TiN. With increasing nitrogen content, both the quantity and size of TiN inclusions also show a significant increasing trend. The experimental observations were further confirmed by thermodynamic calculations, revealing the thermodynamic conditions for inclusion formation in steel at different degrees of reoxidation. Notably, the maximum generation of Al 2 O 3 , TiN, and CaS inclusions increases as reoxidation progresses. Therefore, controlling the reoxidation degree of molten steel is crucial for reducing the formation of large TiN inclusions and composite inclusions and improving the cleanliness of molten steel.

Effect of slag on oxide inclusions in carburized bearing steel during industrial electroslag remelting

Fe–24wt.%Cr–4.1wt.%C hardfacing alloy: Microstructure and carbide refinement mechanisms with ceria additive

Based on the electrochemical character of the desulfurization of liquid iron by molten slag, a previous study reported that applying electricity could enhance the desulfurization. The authors have investigated the mechanism of electrochemical desulfurization and its practical feasibility in terms of reaction rate and electricity efficiency. Nevertheless, the quantitative relationship between electricity and desulfurization still needs to be comprehended. The present study attempted the correlation by carrying out a series of electrochemical desulfurization experiments and thermodynamic calculations. Experiments were designed in a two-step sequence: the first was the normal desulfurization of a liquid iron containing C and S by CaO-Al2O3-MgOsat. slags without applied electricity, and the second was the subsequent electrochemical desulfurization with various electric currents. A graphite disc was put on the surface of the slag and connected with Mo wire to a DC power supply to supply electricity to the system. All the experiments were conducted in the induction furnace at 1400 °C under a CO gas atmosphere. At predetermined times, a certain amount of the iron and slag was sampled and analyzed using the C/S combustion method (LECO CS844) for S contents in both phases. The results were interpreted by employing the Nernst equation to extract the potential difference ∆𝜙S for the electrochemical desulfurization. It was assumed that 1) ∆𝜙S was an electrochemical potential difference to enhance the electrochemical desulfurization, 2) potential differences due to the electrochemical reaction and others (the electric resistance over the slag, iron, etc.) are added to the overall voltage difference observed. It was found that applying electric current (I) to the liquid iron and the molten slag increased the final S distribution ratio between the two phases, the so-called L S (consequently ∆𝜙S increased). When the I was kept constant during each experiment, increasing C/A (= %CaO/%Al2O3) decreased R DeS (= ∆𝜙S / I). For a given C/A, R DeS was independent of the applied I within the range of the I, so the electric properties of the slag might influence it. A previous study reported that the electrical conductivity of a similar slag was increased by increasing the C/A of the slag. Therefore, increasing C/A in the present study increased the electrical conductivity of the slag (𝜎) and decreased the resistance of the slag. It was in the same direction as the R DeS. In the present study, the obtained ∆𝜙S was also predicted by applying the Nernst equation along with a thermodynamic model for liquid iron and sulfide dissolved in molten slag. The enhanced desulfurization by the electricity was interpreted as increasing activity of CaS in the slag and decreasing activity of S in the liquid iron. Accordingly, the predicted ∆𝜙S increased with increasing current under all slag conditions, which was in good agreement with the experimental data. The model is expected to predict the necessary current level for a desired electrochemical desulfurization.

Large-sized hard inclusions led to the problem of wire breaking during the cold drawing process. So it is very important to plasticise inclusions in cord steel. In this article, the plastic modification mechanism of Na 2 CO 3 on inclusions in cord steel was studied by adding different contents (0%, 0.2%, 0.4%, 0.6%) Na 2 CO 3 in a MoSi 2 resistance furnace. The ingots were forged to investigate the deformability of inclusions. The size of inclusions during the cold drawing was the same as that after forging because the cold drawing was carried out at room temperature. Therefore, the size and deformability of inclusions after forging can be used to measure the wire breaking rate of cord steel wire during the cold drawing process. Through the analysis of ingot samples and forging samples by SEM-EDS, it was found that the deformability of inclusions was improved and the inclusions were in the form of long strips or broken after forging. In addition, not only the low melting point phase diagrams of SiO 2 –Al 2 O 3 –MnO–(15%/10%)CaO–(0%–9%)Na 2 O but also the activities of SiO 2 , Al 2 O 3 and MnO were calculated by FactSage8.2. It was found that Na increased the low melting point region. When the contents of [Si], [Mn] and [Al] in molten steel were determined, the values of a Al 2 O 3 2 / a SiO 2 3 and a SiO 2 / a MnO 2 remained constant according to metal-inclusion thermodynamic equilibriums 3SiO 2(inc) + 4[Al] = 2Al 2 O 3(inc) + 3[Si] and [Si] + 2MnO (inc) = 2[Mn] + SiO 2(inc) . Under the condition of constant a Al 2 O 3 2 / a SiO 2 3 and a SiO 2 / a MnO 2 , the activity coefficients of SiO 2 , Al 2 O 3 and MnO were changed by adding Na 2 O, which led to the change of inclusions component. Therefore, it was obtained the effect of Na 2 O content on inclusion composition and melting point using FactSage8.2 thermodynamic calculation and low melting point region calculation of phase diagrams. The result was that the inclusion deformability was well improved during thermal deformation under the condition of about 0.4% Na 2 CO 3 . Thus the wire breaking rate was reduced. It is expected that this work can provide theoretical guidance for the industrial production of feeding alkali wire in the later stage of refining.