PROCESSO PARA PRODUZIR FERRO FUNDIDO OU UMA LIGA DO MESMO A PARTIR DE FERRO DE REDUÇÃO DIRETA DE BAIXO TEOR DE CARBONO EM UM FORNO ELÉTRICO A ARCO

Abstract

The disclosure relates to a process for producing molten iron or an alloy thereof from low- carbon direct reduced iron (DRI) in an electric arc furnace (EAF). The DRI comprises less than 0.1 wt% carbon. The process comprises a combined charging and melting stage comprising continuously charging DRI to a molten metal bath in the EAF and concurrently operating the EAF to continuously melt the DRI. During this stage, the process is maintained within the following operational window - bath temperature of from about 1580 °C to about 1750 °C; - FeO in slag of from about 25 wt% to about 40 wt%; - slag B2 basicity of from about 1.5 to about 3.5, wherein the B2 basicity is calculated as (wt% CaO) / (wt% SiO2); - MgO in slag of from about 8 wt% to about 13 wt%; and - carbon monoxide (CO) in offgas > 26 Nm3 / h / m2.

Description

1 / 19 PROCESS FOR PRODUCING CAST IRON OR AN ALLOY THEREOF FROM LOW-CARBON DIRECT REDUCING IRON IN AN ELECTRIC ARC FURNACE TECHNICAL FIELD

[001] This disclosure relates to a process for producing cast iron or an alloy thereof from low-carbon direct-reducing iron in an electric arc furnace. More specifically, the disclosure relates to a process for producing cast iron or an alloy thereof from low-carbon direct-reducing iron in an electric arc furnace, as defined in the introductory parts of the independent claims. TECHNICAL BACKGROUND

[002] Steel is the most important engineering and construction material in the world. It is difficult to find any object in the modern world that does not contain steel or that depends on it for its manufacture and / or transport. In this way, steel is intrinsically involved in almost every aspect of our modern lives. Total global crude steel production is approximately 1.9 billion tons annually, far exceeding any other metal, and is expected to reach 2.8 billion tons in 2050, of which 50% is expected to come from virgin iron sources.

[003] Although steelmaking processes have been improved over decades and are approaching theoretical minimum energy consumption, a fundamental issue remains unresolved. The reduction of iron ore using carbonaceous reducing agents results in the production of CO2 as a byproduct. For every ton of steel produced in 2018, an average of 1.83 tons of CO2 was produced. The steel industry is one of the largest emitters of CO2, responsible for approximately Petition 870250083271, dated 09 / 16 / 2025, page 71 / 95 2 / 19 7% of global CO2 emissions. Excessive CO2 generation cannot be avoided in the steel production process as long as carbonaceous reducing agents are used.

[004] The HYBRIT initiative was founded to address this issue. HYBRIT, short for “HYdrogen Breakthrough Ironmaking Technology”, is a joint venture between SSAB, LKAB and Vattenfall, funded in part by the Swedish Energy Agency, and aims to reduce CO2 emissions and decarbonize the steel industry. At the heart of the HYBRIT concept is direct reduction based on a vacuum tube to produce sponge iron from virgin ore. In direct reduction, the ore is reduced in a solid-state reduction process at temperatures below the melting point of iron. Direct reduction processes based on vacuum tubes use pelletized iron ore as feedstock and produce a porous raw iron product known as sponge iron or direct reduction iron (DRI).Instead of using carbonaceous reducing gases, such as natural gas, as in current commercial direct reduction processes, HYBRIT proposes the use of hydrogen gas as a reducing agent, called hydrogen-directed reduction (H-DR). Hydrogen gas can be produced by water electrolysis, using primarily renewable and / or fossil fuel-free primary energy sources. Thus, the critical step of iron ore reduction can be achieved without the need for fossil fuel as an input and with water as a byproduct instead of CO2.

[005] Sponge iron produced by direct reduction is normally further processed in an electric arc furnace to melt and refine the base iron before any further secondary metallurgical processing. However, DRI produced by direct reduction with hydrogen (H2-DRI) has different properties when compared to traditional DRI, mainly due to the lack of incorporated carbon. This means that the established means Petition 870250083271, dated 09 / 16 / 2025, page 72 / 95 3 / 19 of traditional DRI processing methods are not necessarily applicable to H2-DRI processing. Thus, there remains a need to develop downstream steelmaking processes beyond the direct reduction stage that are suitable for processing essentially carbon-free DRI, such as that obtained by direct reduction with hydrogen. SUMMARY OF THE INVENTION

[006] The HYBRIT initiative has been operating a direct reduction pilot cell since 2020, in which it is possible to produce DRI using hydrogen-based methods on a semi-industrial and commercially relevant scale. Based on experience with subsequent processing of H2-DRI in an electric arc furnace, the inventors of the present invention have identified the following considerations regarding conventional means of processing DRI.

[007] Sponge iron produced using traditional carbonaceous reducing agents of fossil origin typically comprises significant amounts of dispersed carbon (typically up to 5% by weight) due to the incorporation of carbon from the carbonaceous reducing gas during the reduction of the iron ore. The dispersed carbon is predominantly in the form of cementite (Fe3C), with a smaller proportion consisting of graphite dispersed throughout the sponge iron. The eutectic (melting) temperature of the ferrocementite system is 1147 °C (lower than the melting point of pure iron, 1536 °C), and the cementite dissociates exothermically in the molten bath. This aids in the melting of the sponge iron and leads to the production of a beneficial foaming slag due to the boiling of carbon, where carbon from the DRI (and often additional carbon) reacts with oxygen to produce carbon monoxide (CO).The foaming slag serves to isolate the molten metal bath, resulting in greater energy efficiency, lower consumption of the EAF electrodes, and a reduced risk of unwanted nitrogen incorporation into the molten mass. Petition 870250083271, dated 09 / 16 / 2025, pp. 73 / 95 4 / 19 However, due to the excess carbon present, such conventional processes typically require a refining stage in the EAF after melting and before flow, in which oxygen is supplied to the bath until the carbon reaches acceptable levels.

[008] Sponge iron produced by direct hydrogen reduction (H2DRI) does not contain carbon and is therefore more difficult to melt in the EAF. In cases where the localized rate of DRI loading exceeds the furnace's melting capacity, it can result in the accumulation of ferrobergs (unmelted mounds) of DRI, and such ferrobergs may require prolonged time and electricity consumption to be melted and dispersed. This reduces the efficiency of the process. Furthermore, the lack of carbon also means that no carbon boiling and therefore no frothy slag will be obtained without the provision of exogenous carbon.

[009] In addition to being used for DRI melting, when available, electric arc furnaces are also used in the processing of scrap metal. Scrap metal can also have a low carbon content, which can lead to problems related to carbon melting and boiling. However, when melting scrap, the EAF is normally operated with a large excess of carbon in the bath. This mitigates the problem of insufficient carbon boiling, but at the cost of requiring extensive post-melting and pre-draining refining to remove the excess carbon. Furthermore, scrap metal is normally loaded as a single batch into the furnace before the EAF roof is closed and the melting of the entire batch begins.

[010] It would be advantageous to obtain a method that overcomes, or at least alleviates, at least some of the limitations mentioned above. In particular, it would be desirable to make viable an EAF-based method for processing low-carbon DRI that is efficient and alleviates the disadvantages of the formation of Petition 870250083271, dated 09 / 16 / 2025, pp. 74 / 95 5 / 19 ferrobergs and the formation of poor foaming slag, normally associated with the processing of low-carbon DRI. In order to more effectively address one or more of these issues, a process with the attributes defined in the independent claim is provided.

[011] The process is for producing cast iron or an alloy thereof from low-carbon direct reducing iron (DRI) in an electric arc furnace (EAF). The DRI comprises less than 0.1% carbon by weight.

[012] The process comprises a combined charging and melting stage, comprising the continuous charging of DRI into a molten metal bath in the EAF and the simultaneous operation of the EAF to continuously melt the DRI. During the charging and melting stage, DRI, electrical power, carbon, oxygen and, optionally, one or more slag formers are supplied as inputs to the EAF; and the bath temperature, slag composition and residual gas composition are determined. During the charging and melting stage, a DRI feed rate, an applied power, a carbon feed rate, an oxygen feed rate and a slag former feed rate are adapted to maintain the process within the following operating window: - Bath temperature of approximately 1580 °C to approximately 1750 °C; - FeO content in the slag of approximately 25% by weight to approximately 40% by weight; - basicity B2 of the slag from about 1.5 to about 3.5, where basicity B2 is calculated as (% by weight of CaO) / (% by weight of SiO2); - MgO content in the slag of approximately 8% by weight to approximately 13% by weight; and - carbon monoxide (CO) in residual gas > 26 Nm3 / h / m2.

[013] Keeping the process within the specified operating window, Petition 870250083271, dated 09 / 16 / 2025, pp. 75 / 95 6 / 19 achieves an efficient low-carbon / carbon-free DRI melt. That is, keeping the process within the specified operating window provides a melting process that avoids ferroberg formation, provides adequate frothing slag, and avoids the unnecessary addition of large quantities of other inputs such as carbon, slag formers, and oxygen. This ultimately provides a highly efficient process in terms of time, material, and energy.

[014] The objectives, advantages and additional innovative attributes of the present invention will become apparent to a person skilled in the art from the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[015] For a more complete understanding of the present invention and its additional objectives and advantages, the detailed description presented below should be read in conjunction with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which: Figure 1 is a graph representing a variety of heating processes in EAF in terms of raw material (C-free DRI or with 1.5% C), FeO in the slag (%), and DRI feed rate (tons / h). For each heating process, it is indicated whether a ferroberg was formed or not; Figure 2 is a graph representing a variety of heating processes in EAF in terms of raw material (C-free or with 1.5% C), FeO in the slag (%), and CO in the residual gas (Nm3 / h). For each heating process, it is indicated whether or not a suitable foaming slag was obtained.

[016] The invention will now be described in more detail with reference to certain exemplary embodiments and figures. However, the invention is not limited to the exemplary embodiments discussed in the present invention. Petition 870250083271, dated 09 / 16 / 2025, pp. 76 / 95 7 / 19 and / or shown in the figures, and may be altered within the scope of the appended claims. Furthermore, the figures should not be considered to be drawn to scale, as some attributes may be exaggerated to illustrate certain attributes more clearly. DETAILED DESCRIPTION

[017] This disclosure relates to a process for producing cast iron or an alloy thereof from low-carbon direct reducing iron (DRI) in an electric arc furnace (EAF). By cast iron alloy is meant, for example, cast steel. The process is applicable to any electric arc furnace, including AC and DC electric arc furnaces, but may be particularly suitable for a three-electrode AC electric arc furnace. DRI

[018] The main raw material for the process is low-carbon DRI, i.e., DRI comprising less than 0.1% carbon by weight. DRI may preferably comprise less than 0.05% carbon by weight and, even more preferably, be essentially carbon-free. Such carbon-free DRI may, for example, be obtained as a product from the direct reduction of hydrogen-based iron ore. DRI may be in the form of pellets, cold-briquetted iron (CBI) or hot-briquetted iron (HBI). Under the International Maritime Solids in Bulk Cargo Code (IMSBC Code), DRI pellets and cold-briquetted DRI are designated Type B DRI, while hot-briquetted DRI is designated Type A DRI.

[019] The DRI may preferably have an average metallization greater than or equal to 95%. Metallization is conventionally defined in the art as (Femetallic / Fetotal) x 100. Metallization was determined in the present invention using X-ray diffractometry (XRD), but it can also be determined Petition 870250083271, dated 09 / 16 / 2025, pp. 77 / 95 8 / 19 using other methods. Such other methods include: ISO 2597-1:2006 (Iron ores — Determination of total iron content — Part 1: Titrimetric method after reduction with tin(II) chloride)) in combination with ISO 5416:2006 (Directly reducing iron — Determination of metallic iron — Bromo-methanol titrimetric method); and ISO 10276-1:2000 (Chemical analysis of ferrous materials — Determination of oxygen in steel and iron — Part 1: Sampling and preparation of steel samples for oxygen determination) in combination with ISO 10276-2:2003 (Chemical analysis of ferrous materials — Determination of oxygen content in steel and iron — Part 2: Infrared method after melting under inert gas).

[020] The process may use additional metallic feedstocks in limited quantities. For example, conventional carbon-containing DRI or scrap metal may be used as up to 20% by weight of the total amount of metallic feedstock, with the remainder consisting of low-carbon (or essentially carbon-free) DRI. If such additional feedstocks are used, they may be continuously fed to the EAF in the same manner as low-carbon DRI. Operating Window

[021] The process disclosed in the present invention utilizes a combined loading and melting stage. This contrasts with conventional EAF processes, which typically have separate loading and melting stages, in which the raw metal is first loaded in a batch into the EAF, before the EAF roof is closed and melting begins by applying power. A combined loading and melting stage implies that the DRI is continuously loaded into the EAF, and the loading and melting of the DRI are performed simultaneously. Initially, after furnace rotation, the EAF may normally contain a hot remnant from the previous melting, and this Petition 870250083271, dated 09 / 16 / 2025, pp. 78 / 95 9 / 19 remaining heat can assist in the fusion of the initially charged DRI. [ 022] After the start of the charging and melting stage, DRI, electrical energy, carbon, oxygen and, optionally, one or more slag formers are supplied as inputs to the EAF. The objective is to keep the process within the following operational window: - Bath temperature of approximately 1580 °C to approximately 1750 °C; - FeO content in the slag of approximately 25% by weight to approximately 40% by weight; - basicity B2 of the slag from about 1.5 to about 3.5, where basicity B2 is calculated as (% by weight of CaO) / (% by weight of SiO2); - MgO content in the slag of approximately 8% by weight to approximately 13% by weight; and - carbon monoxide (CO) in residual gas > 26 Nm3 / h / m2.

[023] This is done by determining the bath temperature, slag composition and waste gas composition at regular intervals; and by adjusting the various inputs, including the DRI feed rate, the applied power, the carbon feed rate, the oxygen feed rate and the slag former feed rate, in order to keep the process within the operating window.

[024] It was found that by keeping the process within the specified operating window, efficient melting of low-carbon / carbon-free DRI is achieved. Ferroberg formation is avoided, which could otherwise represent a significant challenge in melting carbon-free DRI. The process avoids the unnecessary addition of large quantities of material inputs, such as carbon, oxygen, and slag formers, while controlling impurities such as nitrogen, phosphorus, and sulfur to acceptable levels. A suitable foaming slag is obtained, which Petition 870250083271, dated 09 / 16 / 2025, pp. 79 / 95 10 / 19 provides greater energy efficiency and prevents wear on refractories and electrodes. Ultimately, the process provided is highly efficient in terms of time, materials, and energy.

[025] The bath temperature, slag composition and residual gas composition can be easily measured or otherwise determined using conventional means and methods in the art.

[026] A limit of approximately > 26 Nm3 / h / m2 of carbon monoxide in the waste gas of the EAF has been shown to be sufficient to provide adequate slag foaming, provided other parameters are maintained within the specified window. The reference unit is normal cubic meters of carbon monoxide per hour, per square meter of EAF bath surface area. Electric arc furnaces typically have vertical or nearly vertical walls, and therefore the bath surface area is more or less constant during heating. The bath surface area can be easily calculated from the diameter or other relevant dimensions of the EAF.

[027] The carbon monoxide (CO) limit of > 26 Nm3 / h / m2 in the waste gas is based on a theoretical carbon yield of 100%, i.e., all the carbon carried in the process is dissolved in the bath and contributes to increasing the carbon content of the bath or to CO formation by reducing FeO. In practice, a proportion of the carbon carried in the EAF will burn without dissolving in the bath and will not contribute, for example, to the formation of frothy slag. A typical carbon yield for an efficient industrial EAF process is around 75%, and therefore the CO in the waste gas can be maintained at > 35 Nm3 / h / m2(26 / 0.75) to compensate for “unused” carbon. In the case of a process with a slightly lower carbon yield, such as around 60%, the CO in the waste gas can be maintained at > 43 Nm3 / h / m2(26 / 0.6) to compensate for “unused” carbon. Petition 870250083271, dated 09 / 16 / 2025, pages 80 / 95 11 / 19

[028] The CO in the waste gas can be kept below 150 Nm3 / h / m2, such as below 120 Nm3 / h / m2, such as below 90 Nm3 / h / m2, such as below 60 Nm3 / h / m2. This can help avoid wasting material inputs and can prevent excessive foam formation in the slag.

[029] The carbon content of the molten metal bath can be maintained at less than 0.7% by weight, such as less than 0.5% by weight, such as less than 0.3% by weight, such as less than or equal to 0.2%. In addition to providing material savings, maintaining a low carbon content in the bath means that there is a decrease or no need for a separate refining stage to remove excess carbon. Consequently, shorter tapping times and additional higher productivity can be achieved. The carbon content of the molten metal can be determined by direct measurement or determination of the bath composition, or it can be determined by a differential determination with reference to the charged carbon and CO in the residual gas.

[030] The bath temperature can be maintained at a temperature of less than 1700 °C, as well as at a temperature of less than 1650 °C. Lower bath temperatures can provide greater energy efficiency and result in lower levels of phosphorus impurities in the cast iron.

[031] FeO in slag can be kept between about 30% by weight and about 40% by weight. Within this range, there may be a lower tendency for ferroberg formation and the resulting steel may have lower phosphorus impurities.

[032] The B2 basicity of the slag can be maintained between about 1.5 and about 2.5. Within this range, the resulting steel can have fewer phosphorus impurities, resulting in a suitable foaming slag.

[033] MgO in slag can be maintained between about 8% by weight and about 13% by weight. Operating within this range helps to limit wear. Petition 870250083271, dated 09 / 16 / 2025, pp. 81 / 95 12 / 19 refractory, while providing adequate slag viscosity and therefore proper foaming slag formation.

[034] The loading and melting stage can be completed as soon as the desired level of the molten bath is reached in the EAF. Inputs for the EAF

[035] The various inputs (energy input in the form of electrical energy and material inputs in the form of DRI, carbon, oxygen and, optionally, slag formers) can interact with each other and affect more than one of the parameters in the operating window. For example, from nominal levels of all inputs, the following effects may occur. Increasing the DRI feed rate may tend to decrease the bath temperature, and decreasing the DRI feed rate may tend to increase the bath temperature. Increasing the applied power may tend to increase the bath temperature, and decreasing the applied power may tend to decrease the bath temperature. Increasing the carbon feed rate may tend to increase CO in the waste gas and decrease FeO in the slag. Decreasing the carbon feed rate may tend to decrease CO in the waste gas and increase FeO in the slag.Increasing the oxygen feed rate may tend to increase FeO in the slag and increase CO in the waste gas. Decreasing the oxygen feed rate may tend to decrease FeO in the slag and CO in the waste gas. Varying the feed rate of the slag formers may increase or decrease the B2 basicity of the slag and may increase or decrease MgO in the slag, depending on whether the slag formers comprise CaO, SiO2 and / or MgO (or analogs thereof).

[036] Each of the inputs can initially be supplied at nominal levels and subsequently adjusted based on the determination of various operational parameters. Theoretical nominal feed rates for the Petition 870250083271, dated 09 / 16 / 2025, pp. 82 / 95 13 / 19 various inputs can be calculated as follows.

[037] Preferably, to provide a fast process, the nominal power applied Pnom should be equal to or close to the maximum appropriate for the system, such as greater than 90% of the maximum nominal power, or greater than 95% of the maximum nominal power.

[038] The DRI feed rate must be adjusted subsequently. A suitable nominal DRI feed rate mDRLnom can be determined empirically or can be calculated using the following equation: (pnom - pperda\ ™DRI_nom _ f / pDRI _spec where mDRLnomé is the nominal DRI feed rate in mass units per unit time (e.g., tonne / h), Pnomé is the nominal applied power in units of energy per unit of time (e.g., kW / h). Power losses are the estimated power losses of the system in units of energy per unit of time (e.g., kW / h, and can be determined empirically for any system and rated power). EDRI_spec is the specific energy required to melt a unit mass of DRI (e.g., the specific heat required to bring the DRI from room temperature to the melting temperature, plus the specific heat of fusion), expressed in units of energy per unit mass (e.g., kWh / ton).

[039] A suitable nominal carbon feed rate may be a carbon feed rate sufficient to provide CO in the waste gas of > 35 Nm3 / h / m2 for an industrial EAF process with good carbon yield. This corresponds to approximately 44 kg / h / m2CO, which corresponds to approximately 19 kg / h / m2 of carbon. For an industrial process with Petition 870250083271, dated 09 / 16 / 2025, pages 83 / 95 14 / 19 a lower carbon yield, such as around 60%, which means a CO requirement in the waste gas of > 43 Nm3 / h / m2, this corresponds to approximately 54 kg / h / m2CO, which corresponds to approximately 23 kg / h / m2 of carbon.

[040] An adequate nominal oxygen feed rate may be an oxygen feed rate sufficient to provide CO in the waste gas of > 35 Nm3 / h / m2 for a typical industrial EAF. This corresponds to approximately 18 Nm3 / h / m2.

[041] The appropriate nominal feed rates for slag formers will depend on the intrinsic composition of the slag formers in the DRI, as well as the nominal feed rate of the DRI.

[042] The actual nominal feed rates used may be within a suitable range of these calculated theoretical nominal rates, for example, within + / - 20% of the theoretical nominal rate, such as within + / - 10% of the theoretical nominal rate, such as within + / - 5% of the theoretical nominal rate.

[043] The DRI can be continuously loaded into the furnace using means known in the art. For example, the DRI can be continuously loaded into the furnace through the roof of the EAF (e.g., fifth hole) or by side loading.

[044] Carbon can be loaded into the furnace by top feeding (e.g., through the top of the furnace) or by direct injection into the melt, as known in the art. The carbon can be conventional metallurgical-grade carbon (e.g., anthracite) or it can be biocarbon. The use of biocarbon can provide a steel with lower sulfur levels.

[045] Oxygen can be supplied to the furnace using means known in the art, such as the use of oxygen lances.

[046] Slag formers can be loaded into the furnace by Petition 870250083271, dated 09 / 16 / 2025, pages 84 / 95 15 / 19 top feeding or injection feeding, as known in the art. Suitable slag formers may include, but are not limited to, CaO, SiO2, calcined dolomite and combinations thereof. Alternatively, autogenous slag formed by melting DRI may have sufficient properties so that no additional slag formers are required. Flow stage

[047] Once the loading and melting stage is complete, a flow stage can be initiated directly. This contrasts with typical EAF processes, which may typically require one or more refining stages to burn off oxidizable impurities and remove excess carbon. In the flow stage, all material inputs are stopped. Flow may be conditioned on achieving a suitable flow temperature by the bath, such as greater than or equal to 1600 °C, such as greater than or equal to 1630 °C, such as greater than or equal to 1650 °C. If the bath does not reach the flow temperature, the application of electrical power may continue until the appropriate temperature is reached. Then, the power is stopped and the EAF is drained, releasing the molten iron or alloy from it. Experimental

[048] The delineation of an optimal process window had already been established from previous pilot campaigns, using a variety of H2-DRI and NG-DRI materials. The previous pilot campaigns consisted of a total of approximately 200 heatings to investigate the melting of: hydrogen-reduced DRI pellets (type B), both with and without carbon; hydrogen-reduced HBI (type A), both with and without carbon; DRI pellets produced using conventional natural gas-based reducing gas; and HBI produced using conventional natural gas-based reducing gas. This optimal window was established to provide good foaming, good Petition 870250083271, dated 09 / 16 / 2025, pages 85 / 95 16 / 19 productivity (i.e., no ferrobergs) and a stable process (i.e., stable temperature and slag characteristics).

[049] In the most recent campaign, a total of 44 additional heatings were carried out. The feedstock for each heating was carbon-free H2-DRI or, for comparison purposes, H2-DRI that was subsequently carburized using a natural gas-based carburizing gas until it reached a carbon content of approximately 1.5%. All DRI feedstock used was supplied by Hybrit's pilot DRI plant. The degree of metallization per batch of incoming DRI for each heating was typically between 90% and 100%. The pilot-scale 3-electrode AC electric arc furnace used has a circular diameter of approximately 2.1 m, providing a bath surface area during operation of approximately 3.46 m2.

[050] From this outlined process window, the heatings were carried out and the following data were collected / measured and evaluated: Analysis and quantities of input materials Samples of steel and slag Temperature Tons of steel and slag drained Analysis and temperature of residual gas Dust in waste gas; quantity and analysis Formation of foaming slag (Classified as 1-poor, 2-fair, or 3-good) Ferroberg records (Yes / No) CO generation from waste gas analysis Carbon yield from waste gas, steel and slag, record of material additions. Oxygen yield from waste gas, steel and slag, record of Petition 870250083271, dated 09 / 16 / 2025, pages 86 / 95 17 / 19 material additions Energy balance of steel and slag, temperature measurements, material quantities. Electrical data

[051] Some of the results obtained are summarized below.

[052] It was found that, despite the significant variation in the degree of metallization of the input DRI, it was possible to maintain reasonable levels of FeO in the slag by means of carbon balancing during the heatings. Most heatings were maintained at FeO levels in the slag of about 25% by weight to about 40% by weight.

[053] Some heatings were carried out using biocarbon and other heatings were carried out using anthracite. Carbon was either top-fed or injected, and the carbon used was appropriately adapted with respect to, for example, particle size for the specific loading method. In general, biocarbon and anthracite showed similar carbon yields, and the yields obtained by top-feeding and injection were also similar. It was found that heatings in which biocarbon was used typically had lower final sulfur content in the steel, although sulfur levels were generally acceptable for all heatings.

[054] The effect of various process parameters on key results, such as ferroberg formation, frothing slag formation and impurity content in steel (nitrogen, phosphorus, sulfur) was investigated.

[055] Some examples of the results obtained are shown in Figures 1 and 2.

[056] Figure 1 is a graph representing the various heatings in terms of raw material (C-free DRI or with 1.5% C), FeO in the slag (%) Petition 870250083271, dated 09 / 16 / 2025, pp. 87 / 95 18 / 19 and DRI feed rate (ton / h). For each heating, it is indicated whether or not a ferroberg was formed. It can be noted that ferrobergs were formed only with the use of carbon-free DRI feedstock; there were no cases of ferroberg formation during the melting of carbon-containing DRI. Observing the heatings using carbon-free DRI, it can be noted that FeO in the slag is a critical parameter. No ferroberg formation was observed in heatings with approximately 30% to approximately 40% FeO in the slag, while for lower and higher proportions of FeO in the slag, ferroberg formation was observed in some heatings. In this figure, it can also be noted that, within the identified %FeO in the slag window, ferroberg formation is relatively insensitive to the DRI feed rate, and heatings were carried out with relatively high feed rates without ferroberg formation being observed.

[057] Figure 2 is a graph representing the various heating processes in terms of raw material (C-free DRI or with 1.5% C), FeO in the slag (%), and CO in the residual gas (Nm3 / h). For each heating process, it is indicated whether good foaming was obtained or not. It can be noted that poor foaming tends to be correlated with low CO in the residual gas (< approx. 100 Nm3 / h) and high FeO in the slag (> approx. 37%). It is worth noting that the CO levels indicated in Figure 2 are not corrected for carbon yield.

[058] It was found that the phosphorus content of the steel decreased with increasing FeO content in the slag and with temperatures below 1650 °C in the bath. The nitrogen content was generally considered acceptable. The sulfur content was generally acceptable and varied depending mainly on whether biocarbon or anthracite was used.

[059] Based on the accumulated data from these and previous heatings, the optimal process window, as defined in the present invention, Petition 870250083271, dated 09 / 16 / 2025, pp. 88 / 95 19 / 19 can be derived. Petition 870250083271, dated 09 / 16 / 2025, pp. 89 / 95

Claims

1 / 3 CLAIMS 1. Process for producing cast iron or an alloy thereof from low-carbon direct reducing iron (DRI) in an electric arc furnace (EAF), characterized in that: the DRI comprises less than 0.1% by weight of carbon; and in which the process comprises a combined charging and melting stage, comprising continuously charging the DRI into a molten metal bath in the EAF and simultaneously operating the EAF to continuously melt the DRI; in which, during the charging and melting stage, DRI, electrical energy, carbon, oxygen and, optionally, one or more slag formers are supplied as inputs to the EAF; the bath temperature, slag composition and residual gas composition are determined;and a DRI feed rate, applied power, carbon feed rate, oxygen feed rate, and slag former feed rate are adapted to maintain the process within the following operating window: - bath temperature from about 1580 °C to about 1750 °C; - FeO content in the slag from about 25% by weight to about 40% by weight; - B2 basicity of the slag from about 1.5 to about 3.5, where B2 basicity is calculated as (% by weight of CaO) / (% by weight of SiO2); - MgO content in the slag from about 8% by weight to about 13% by weight; and - carbon monoxide (CO) in the waste gas > 26 Nm3 / h / m2.

2. Process, according to claim 1, characterized by the fact that the carbon content of the molten metal bath is maintained at less than 0.7% by weight during the loading and melting stage.

3. Process, according to claim 1 or 2, characterized in that the power applied during the loading and melting stage is greater than 90% of the maximum nominal power, and in that the DRI feed rate is reduced if the determined bath temperature falls below 1580 °C.

4. Process, according to any one of claims 1 to 3, characterized in that the DRI has an average metallization greater than or equal to 95%.

5. Process, according to any one of claims 1 to 4, characterized in that the DRI is DRI or HBI pellets.

6. A process according to any one of claims 1 to 5, characterized in that the carbon supplied to the process is biocarbon.

7. A process according to any one of claims 1 to 6, characterized in that the carbon is supplied by charging the carbon in the EAF above a level of the molten metal bath.

8. A process according to any one of claims 1 to 7, characterized in that the carbon is supplied by injecting powdered carbon into the molten metal bath.

9. A process according to any one of claims 1 to 8, characterized in that, during the loading and melting stage, the carbon monoxide in the residual gas is maintained at more than 35 Nm3 / h / m2, such as more than 43 Nm3 / h / m2.

10. Process, according to any one of claims 1 to 9, characterized in that, during the loading and melting stage, the carbon monoxide in the residual gas is maintained at less than 120 Nm3 / h / m2, such as less than 90 Nm3 / h / m2. Petition 870250083271, dated 16 / 09 / 2025, p. 91 / 95 3 / 3 11. A process, according to any one of claims 1 to 10, characterized in that one or more slag formers are supplied to the EAF during the loading and melting stage.

12. Process according to claim 11, characterized in that one or more slag formers are selected from CaO, SiO2, calcined dolomite and combinations thereof.

13. Process, according to any one of claims 1 to 12, characterized in that the molten metal bath is maintained at a temperature of less than 1650 °C during the loading and melting stage.

14. A process according to any one of claims 1 to 13, characterized in that the process does not comprise a refining stage.

15. A process, according to any one of claims 1 to 14, characterized in that immediately after the completion of the loading and melting stage, a flow stage is initiated, wherein the flow stage comprises: interrupting all material inputs to the molten iron bath; if the bath temperature is less than 1600 °C, increasing the bath temperature to a value greater than or equal to 1600 °C by applying power; when the bath temperature is greater than or equal to 1600 °C, interrupting the application of power; and flowing the molten iron or alloy thereof. Petition 870250083271, dated 16 / 09 / 2025, p. 92 / 95

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