Method of producing steel with low nitrogen content using an eaf

Abstract

Method of producing steel with low nitrogen content using an EAF Method of producing steel using an Electrical Arc Furnace (EAF), the method comprising: (a) melting a metal load (L) in the EAF and generating liquid steel (LS); (c) tapping the liquid steel (LS) from the EAF; and (d) performing secondary metallurgy on the liquid steel (LS) in at least one secondary metallurgy reactor to adjust the chemical composition of the liquid steel (LS), wherein the method comprises adding a first slag compound (SC1) with nitrogen affinity in the liquid steel (LS) during tapping of the liquid steel (LS) from the EAF and creating a ladle slag (S2).

Description

[0001] Method of producing steel with low nitrogen content using an EAF

[0002] The present invention relates to the production of steel with using steel scrap in an Electrical Arc Furnace (EAF).

[0003] Steel can be currently produced through two mains production routes.

[0004] The first main production route, which is currently the most used production route for stringent steel grades, is named “BF-BOF route” and consists in producing hot metal in a Blast Furnace (BF), by use of a reducing agent, mainly coke, to reduce iron oxides and then transform hot metal into steel into a converter process or Basic Oxygen Furnace (BOF). This route releases significant quantities of CO2, both in the production of coke from coal in a coking plant and in the production of the hot metal.

[0005] The second main route involves so-called “direct reduction methods” using Direct Reduced Iron (DRI). Among them are methods according to the brands MIDREX®, FINMET®, ENERGIRON® / HYL, COREX®, FINEX® etc., in which sponge iron is produced in the form of HDRI (hot direct reduced iron), CDRI (cold direct reduced iron), or HBI (hot briquetted iron) from the direct reduction of iron oxide carriers. Sponge iron in the form of HDRI, CDRI, and HBI undergoes further processing in electric arc furnaces to produce steel. Such route is also referred to as “DRI-EAF route”.

[0006] One of the main options chosen by steelmakers to reduce CO2 emissions is to switch from the BF-BOF route towards the DRI-EAF route.

[0007] However, use of DRI products in classical electrical arc furnaces together with ferrous scraps has some limitations. Indeed, scraps contain a lot of impurities and resulting liquid steel will need to be further processed to produce high quality steel grades.

[0008] Moreover, electric arc furnaces were up to now mostly used for production of long products and specialty or stainless grades, which do not have the same constraints in terms of metallurgy as the grades used notably for automotive products.

[0009] For example, liquid steel produced from a basic oxygen furnace contains 20 to 90 parts per million (ppm) in weight of nitrogen, compared to 100 to 140 ppm in weight of nitrogen in liquid steel produced in an electric arc furnace. The nitrogen content of current electric arc furnace steel (or EAF steel) is thus much higher than that of basic oxygen furnace steel (BOF steel) and cannot meet the requirements of high-grade steel. High nitrogen content can result in inconsistent mechanical properties in hot rolled steels, embrittlement of the heat affected zone (HAZ) of welded steels, and poor cold formability.

[0010] One of the aims of the invention is to propose a method of producing steel using an EAF that allows controlling the composition of the steel in a satisfactory manner and notably to reduce nitrogen content of the produced steel. In this view, the invention proposes a method of producing steel using an Electrical Arc Furnace (EAF), the method comprising:

[0011] (a) melting a metal load in the EAF and generating liquid steel;

[0012] (c) tapping the liquid steel from the EAF; and

[0013] (d) performing secondary metallurgy on the liquid steel in at least one secondary metallurgy reactor to adjust the chemical composition of the liquid steel, wherein the method comprises adding a first slag compound with nitrogen affinity in the liquid steel during tapping of the liquid steel from the EAF and creating a ladle slag.

[0014] The use of a slag compound with nitrogen affinity for generating a slag during tapping of the liquid steel allows reducing nitrogen content efficiently, before performing the secondary metallurgy on the liquid steel.

[0015] If needed, the slag generated during tapping can be removed easily before performing the secondary metallurgy, e.g. in a racking station, whereby this slag will not affect the secondary metallurgy.

[0016] This allows producing a steel with low nitrogen content even when using an electric arc furnace for steelmaking.

[0017] In some examples, the method of producing steel comprises one or several of the optional following features, taken individually or according to any technically feasible combination:

[0018] - the ladle slag is separated from the liquid steel before performing the secondary metallurgy;

[0019] - the method comprises killing the liquid steel, preferably after adding the first slag compound to the liquid steel;

[0020] - the first slag compound comprises one or several among barium oxide (BaO) and titanium dioxide (TiC>2);

[0021] - the first slag compound comprises at least 15% by weight of CaO, at least 30% by weight of AI2O3, and from 10% to 35% by weight of BaO , and optionally up to 15% of TiO2;

[0022] - the ladle slag is removed in a raking station;

[0023] - the method comprises adding a second slag compound with sulfur affinity in the liquid steel during tapping of the liquid steel from the EAF;

[0024] - the second slag compound comprises one or several among lime (CaC2), calcium oxide (CaO), magnesium oxide (MgO) and manganese oxide (MnO);

[0025] - the metal load comprises at least 40% by weight of steel scrap ;

[0026] - the metal load comprises at least 40% by weight of direct reduced iron ;

[0027] - the metal load comprises from 40% by weight to 60% by weight of direct reduced iron; - the first slag compound is added such as to lower the nitrogen content of the liquid steel to 50 ppm in weight or less, preferably to 20 ppm in weight or less;

[0028] - the second slag compound is added such as to lower the sulphur content of the liquid steel to 150 ppm in weight or less, preferably to 90 ppm in weight or less;

[0029] - the method comprises casting the liquid steel after performing the secondary metallurgy.

[0030] The invention and its advantages will be better understood upon reading the following description which is given solely by way of non-limiting example, and which is made with reference to the appended drawings, in which:

[0031] - Figures 1 illustrates a method of producing steel with using an Electrical Arc Furnace (EAF) to melt a metal load into liquid steel and performing secondary metallurgy on the liquid steel ; and

[0032] - Figure 2 is a bloc diagram illustrating successive steps of the method of producing steel with using an EAF.

[0033] As illustrated on Figure 1 , an EAF 2 is configured for melting a metal load L by generating electrical arc for heating and melting the metal load L into liquid steel LS.

[0034] The EAF 2 is configured for receiving a metal load L containing metal materials, in particular a metal load L containing steel scrap SC and, optionally, pig iron PI and / or direct reduced iron DRI in addition to the steel scrap SC.

[0035] The EAF 2 comprises for example a shell 4 and a roof 6 delimiting a chamber 8 for receiving the metal load L. The roof 6 is removably attached to the shell 4 such as to open the EAF 2 for loading the steel scrap SC and close the EAF 2 for melting the metal load L.

[0036] The tapping is the operation of transferring the liquid steel LS from the EAF 2 to a ladle 10 that is subsequently used in one or more secondary metallurgy reactors or used for transferring the liquid steel to one or more secondary metallurgy reactors, each secondary metallurgy reactor being configured for performing secondary metallurgy operations (also called “ladle metallurgy operations”) for refining the chemical composition of the liquid steel LS, for example before casting the liquid steel LS.

[0037] The shell 4 comprises for example a liquid steel outlet 12 for tapping the liquid steel LS from the EAF 2. The liquid steel outlet 12 is located such as to discharge the liquid steel LS from the EAF 2 by gravity via the liquid steel outlet 12.

[0038] Melting the metal load L in the EAF 2 results in a bath of liquid steel LS which is topped by a primary slag S1 .

[0039] The shell 4 optionally comprises a primary slag outlet 14 configured for discharging the primary slag S1 from the EAF 2. The primary slag S1 is preferably discharged before tapping the liquid steel from the EAF 2. The primary slag outlet 14 is preferably located higher that the liquid steel outlet 12 such that a primary slag S1 on top of the liquid steel LS can flow via the slag outlet 14 while the liquid steel LS remains in the EAF 2.

[0040] Optionally, the EAF 2 is tiltable for tapping the liquid steel LS by gravity via the liquid steel outlet 12 and / or for tapping the primary slag S1 by gravity via the slag outlet 14.

[0041] The EAF 2 comprises two or more electrodes 16 arranged for generating electrical arc between the electrodes 16 and metal load L received in the chamber 8 when the electrodes 16 are powered with electrical energy. Each electrode 16 is for example made of graphite.

[0042] Each electrode 16 is for example mounted in the shell 4 or on the roof 6. Each electrode 16 mounted on the roof 6 is preferably configured to project downwardly from the roof 6. This allows the electrode 16 to insert into a metal load L formed of a pile of metal materials loaded in the chamber 8 before melting and to extend close to the liquid steel LS after melting.

[0043] The electrical energy is provided by an electrical source 18. Each electrode 16 is for example electrically connected to the electrical source 18.

[0044] The electrical source 18 is configured to provide direct current (DC) or alternative current (AC), in particular two-phase alternative current or three-phase alternative current.

[0045] The EAF 2 is for example configured for connection to an electrical source 18 providing three-phase alternative current (AC). In such case, the EAF 2 comprises three electrodes 16 each connected to one respective phase of the three phases of the electrical source 18. The three electrodes 16 are for example mounted on the roof 6 with projecting downwardly into the chamber 8, in particular towards the bottom 12 of the shell 4.

[0046] In another example (not illustrated), the EAF 2 is configured for connection to an electrical source 18 providing a direct current (DC). In such case, the EAF 2 comprises for example one electrode 16 mounted on the roof 6 with projecting downwardly into the chamber s, in particular towards a bottom of the shell 4, and one electrode mounted on the shell 4, in particular on the bottom of the shell 4.

[0047] The electrical source 18 comprises for example an electrical network and / or an electrical power plant using preferably one or several renewable energy sources.

[0048] The electrical power plant is preferably operated using CO2 neutral electricity which includes notably electricity from renewable sources which is defined as energy that is produced from renewable resources, which are naturally replenished on a human timescale, including sources like sunlight, wind, rain, tides, waves, geothermal heat and biogas. In some embodiments, the use of electricity coming from nuclear sources can be used as it is not emitting CO2 to be produced. The EAF 2 comprises a gas injection system 20 configured for injecting gas in the chamber 8 during operation of the EAF 2, in particular when the EAF 2 is closed, i.e. when the roof 6 is mounted on the shell 4 to close the EAF 2.

[0049] The gas injection system 20 is configured in particular for injecting gas into the EAF 2 during melting of the load L and / or after melting of the load L into liquid steel LS. The gas injection system 20 comprises one or several gas lances 22, each gas lance 22 opening inside the EAF 2 and a gas source 24 fluidly connected to each gas lance 22 for feeding said gas lance 26 with an injection gas.

[0050] The gas source 24 is for example a reservoir, in particular a pressurized reservoir, or a gas distribution network.

[0051] Each gas lance 22 if for example oriented obliquely downwardly to inject a flux of gas towards the surface of the liquid steel LS and / or into the liquid steel LS present in the EAF 2.

[0052] In a preferred embodiment, the gas injection system 20 is configured for injecting a gas containing or consisting of oxygen (O2) into the EAF 2.

[0053] The injection of oxygen into the EAF 2 allows reducing the carbon content of the liquid steel LS because the oxygen injected in the EAF 2 reacts with the carbon present in the liquid steel LS, e.g. for forming carbon monoxide (CO).

[0054] A slag compound feed system 26 is provided. The slag compound feed system 26 is configured for adding one or more slag compounds to the liquid steel LS during tapping of the liquid steel SL from the EAF 2 into the ladle 10. The slag compound feed system 26 comprises at least one slag compound source 28 storing the one or more slag compounds.

[0055] The one or more slag compounds may either be placed in the ladle 10 before tapping, injected in the ladle 10 during tapping and / or run into the tapping stream.

[0056] A slag compound injected in the liquid steel LS can interact selectively with one or several species contained in the liquid steel LS thus reducing the content of said one or several species in the liquid steel LS. This allows adjusting the chemical composition of the liquid steel LS.

[0057] The addition of one or more slag compounds to the liquid steel LS upon tapping the liquid steel LS from the EAF 2 to the ladle 10 allows generating a ladle slag S2 on top of the liquid steel LS in the ladle 10 used for tapping the liquid steel LS form the EAF 2.

[0058] A killing agent feed system 30 is provided. The killing agent feed system 30 is configured for adding one or more killing agents KA in the EAF 2 and / or in the ladle 10 into which the liquid steel LS is tapped from the EAF 2. The killing agent feed system 30 comprises at least one killing agent source 32. The killing agent feed system 30 is configured for adding one or more killing agents KA to the liquid steel LS upon tapping the liquid steel LS from the EAF 2 to the ladle 10, with adding the one or more killing agents KA in the EAF 2 and / or the ladle 10.

[0059] A slag removal station 34 is provided. The slag removal station 34 is configured for removing a slag from the liquid steel LS received in the ladle 10, preferably prior to performing one or more secondary metallurgy operations on the liquid steel LS.

[0060] The slag removal station 34 comprises for example a tilting device allowing tilting the ladle 10 and a rake 36 operable to rake the slag from the top of the liquid steel LS received in the ladle 10.

[0061] The EAF 2 is optionally configured for adding at least one slagging agent to the liquid steel LS in the EAF 2 during the operation of melting the metal load L, for example to generate a primary slag S1 that is subsequently removed before tapping the liquid steel LS.

[0062] It is possible to perform one or several primary slagging operations in the EAF 2 before tapping the liquid steel LS from the EAF.

[0063] For each primary slagging operation performed in the EAF 2, a slag agent is introduced in the EAF 2 and once the primary slag S1 is formed, the primary slag S1 is removed via the slag outlet 14.

[0064] A slag agent injected into the liquid steel LS can either chemically react selectively with one or more species contained in the liquid steel LS and form a primary slag S1 , or modify the composition of the primary slag S1 present on top of the liquid steel to modify the thermodynamic equilibrium and promote chemical reactions of the primary slag S1 with one or more species contained in the liquid steel LS. In both cases, it thus reduces the content of said one or more species in the liquid steel LS. This allows adjusting the chemical composition of the liquid steel LS.

[0065] It is possible to perform one primary slagging operation in the EAF with injecting slag agent for generating a primary slag S1 and removing the primary slag S1 from the EAF 2 via the slag outlet 14 before tapping the liquid steel LS from the EAF 2 or several successive primary slagging operations by repeating steps of injecting slag agents for generating a primary slag S1 and removing the primary slag S1 from the EAF 2 via the slag outlet 14, e.g. with different slag agents.

[0066] As it will be detailed later, at least one slag compound addition is performed when tapping the liquid steel LS from the EAF 2 such that a ladle slag S2 is formed in the ladle 10.

[0067] Each such ladle slag compound addition is performed during tapping by introducing one or several slag compounds in the EAF 2 upon tapping the liquid steel LS or directly in the ladle 10 into which the liquid steel LS is tapped from the EAF 2 or run into the tapping stream. At least one secondary metallurgy reactor 40 is provided, each secondary metallurgy reactor 40 being configured for performing a secondary metallurgy operation on the liquid steel LS.

[0068] The secondary metallurgy reactor 40 illustrated on Figure 1 is a so-called RH reactor. RH stands for Ruhrstahl Heraeus.

[0069] The secondary metallurgy reactor 40 comprises a ladle 42, a vacuum chamber 44, a vacuum system 46 fluidly connected to the vacuum chamber 44 for generating vacuum in the vacuum chamber 44, an up snorkel 48 for sucking liquid steel LS from the ladle 42 to the vacuum chamber 44 and a down snorkel 50 for returning liquid steel LS from the vacuum chamber 44 to the ladle 42.

[0070] The secondary metallurgy reactor 40 is preferably provided with a gas injection system 52 configured for injecting an inert gas in the liquid steel LS, in particular in one of the snorkels of the secondary metallurgy reactor 40 (up snorkel 48 and / or down snorkel 50) and / or in the ladle 42.

[0071] The gas injection system 52 comprises an inert gas source 56. The inert gas, for example, contains or consists of argon (Ar).

[0072] In operation, the lower ends of the up snorkel 48 and the down snorkel 50 are inserted in the liquid steel LS contained in the ladle 42 and the vacuum system 46 is operated to generate a vacuum inside the vacuum chamber 44. The liquid steel LS is sucked from the ladle 42 to the vacuum chamber 44 via the up snorkel 48 and returns from the vacuum chamber 44 to the ladle 42 via the down snorkel 50 thus circulating in a closed loop between the ladle 42 and the vacuum chamber 44.

[0073] When passing via the vacuum chamber 44, the liquid steel LS releases some components or elements in gaseous state whereby the chemical composition of the liquid steel LS can be refined.

[0074] A secondary slag S3 may form on top of the liquid steel LS during secondary metallurgy operation.

[0075] The ladle 10 used for tapping the liquid steel LS from the EAF 2 may be used in the secondary metallurgy reactor 40 or the liquid steel LS may be transferred from the ladle 10 to another ladle 42 dedicated to the secondary metallurgy reactor 40.

[0076] A method of producing steel using the EAF 2 will now be described with reference to Figures 1 illustrating the EAF 2 and the secondary metallurgy reactor 40 and to Figure 2 which is a bloc diagram illustrating steps of the method of producing steel.

[0077] The method of producing steel comprises a step E1 of charging the metal load L in the EAF 2, the metal load L containing steel scrap SC and optionally pig iron and / or direct reduced iron DRI in addition to the steel scrap SC. The loading is performed in one operation or sequentially in a plurality of operations, e.g. with loading steel scrap SC and then loading pig iron PI and / or direct reduced iron DRI. Steel scrap SC is loaded with opening the roof 6 of the EAF 2, loading the steel scrap SC in the shell 4 of the EAF and then closing the EAF 2. If applicable, the loading of pig iron PI and / or direct reduced iron DRI is performed simultaneously or after closing of the roof 6 of the EAF 2, e.g. via a trap.

[0078] In some embodiments, the metal load L comprises at least 40% % by weight of steel scrap SC and, optionally, from 40% by weight to 60% by weight of direct reduced iron DRI.

[0079] Steel scrap SC is for example steel scrap referred to, in the Ell-21 Steel Scrap specification, as old scraps (category E1 or E3), new scraps (category E8), shredded scraps (category E40) or fragmentized scraps (category E46).

[0080] The production method comprises a step E2 of melting the metal load L in the EAF 2 and generating the liquid steel LS. Melting the metal load L is performed with energizing the electrodes 16 of the EAF 2 for generating electrical arcs.

[0081] Optionally, the method of producing steel comprises a step E3 or several successive steps E3 of refining the melt in the EAF 2 by injecting on or more slag agents to generate a primary slag S1 and removing the primary slag S1 from the EAF 2.

[0082] The primary slag S1 is removed via the slag outlet 14. Different slag agents can be used in successive refining steps.

[0083] The method of producing steel comprises a step E4 of tapping the liquid steel LS into a ladle 10. Tapping the liquid steel LS is performed for example by tilting the shell 4 to pour the liquid steel LS via the liquid steel outlet 16.

[0084] The method of producing steel comprises a step E5 of performing one or several secondary metallurgy operations, each secondary metallurgy operation comprising refining the chemical composition of the liquid steel LS in a secondary metallurgy reactor.

[0085] The method of producing steel comprises in particular refining the liquid steel LS in a secondary metallurgy reactor 40 provided as a RH reactor. In such case, the step E5 of refining the liquid steel LS comprises positioning the vacuum chamber 44 relative to the ladle 42 such that the up snorkel 48 and the down snorkel 50 dive into the melt, activating the vacuum system 46 to generate the closed loop circulation of the liquid steel LS between the ladle 42 and the vacuum chamber 44.

[0086] Preferably, inert gas is injected in the ladle and / or in a snorkel (up snorkel 48 and / or down snorkel 50) while generating vacuum in the vacuum chamber 44. The inert gas contains or consists of argon (Ar).

[0087] The method of producing steel comprises adding a first slag compound SC1 with nitrogen affinity upon tapping of the liquid steel LS from the EAF 2 and preferably separating a thus created ladle slag S2 from the liquid steel LS before performing the secondary metallurgy.

[0088] The first slag compound SC1 with nitrogen affinity being added upon tapping of the liquid steel LS from the EAF 2 means that the first slag compound SC1 with nitrogen affinity is added in the liquid steel LS during the operation of transferring the liquid steel LS from the EAF to the ladle 10.

[0089] The first slag compound SC1 may either be placed in the ladle 10 before tapping, injected in the ladle 10 during tapping or run into the tapping stream. This allows using the mixing effect of the tapping stream to promote nitrogen removal from the liquid steel LS.

[0090] By “nitrogen affinity” it is meant that the injected slag contains one or several chemical components which form slag droplets able to capture nitrogen present in the bath before migrating towards the slag layer present on the top of the liquid steel LS. The injected slag preferably has a high nitrogen capacity meaning that nitrogen is soluble within said slag compound.

[0091] The first slag compound SC1 contains or consists of an oxide mixture and preferably of barium oxide and / or titanium oxide. The first slag compound SC1 comprises for example one or several among barium oxide (BaO) and titanium dioxide (TiC>2).

[0092] The first slag compound SC1 consists in or comprises for example at least 15% by weight of CaO, at least 30% by weight of AI2O3, and from 10 to 35% by weight of BaO, preferably from 20 to 30% by weight and optionally up to 15% of TiO2.

[0093] Preferably, the first slag compound SC1 is added such as to lower the nitrogen content of the liquid steel LS to 50 ppm in weight or less, preferably to 20 ppm in weight or less. The person skilled in the art knows how to calculate the amount of first slag compound SC1 to be added, using a mass balance considering the amount of nitrogen in the liquid steel LS, the targeted content of nitrogen in the liquid steel LS and the partition coefficient of the first slag compound SC1.

[0094] Optionally, the method of producing steel comprises killing the liquid steel LS, preferably after adding the first slag compound SC1 to the liquid steel LS.

[0095] By “killing”, it is meant reducing the oxygen content of the liquid steel, e.g. by adding a killing agent KA containing one or several deoxidizing elements, such as aluminum (Al) or silicon (Si).

[0096] Alternatively, or optionally, the method of producing steel comprises adding a second slag compound SC2 having sulphur affinity to the liquid steel LS upon tapping.

[0097] By “sulphur affinity” it is meant that the slag compound will modify the composition of the slag so as to increase the capability of said slag to capture the sulphur, for example by increasing the solubility limit of sulphur in the slag or by modifying a thermodynamic equilibrium within the slag.

[0098] This second slag compound SC2 consist in or comprises for example one or several oxides among lime (CaC2), calcium oxide (CaO), magnesium oxide (MgO) and manganese oxide (MnO).

[0099] The addition of the second slag compound allows performing both nitrogen and sulfur removal form the liquid steel LS.

[0100] Preferably, the second slag compound SC2 is added such as to lower the sulphur content of the liquid steel LS to 150 ppm in weight or less, preferably to 90 ppm in weight or less. The person skilled in the art knows how to calculate the amount of second slag compound SC2 to be added, using a mass balance considering the amount of sulphur in the liquid steel LS, the targeted content of sulphur in the liquid steel LS and the partition coefficient of the second slag compound SC2.

[0101] Preferably, when the method of producing steel comprises killing the liquid steel LS, the killing agent KA is added in the liquid steel LS after adding the first slag compound SC1 , the addition being performed in the ladle 10 into which the liquid steel LS is tapped. If a second slag compound SC2 is added, it is preferably added after the addition of the killing agent KA.

[0102] The method of producing steel optionally comprises a step of removing the ladle slag S2 from the liquid steel LS performed before the secondary metallurgy operation.

[0103] The removal of the ladle slag S2 is performed for example in the slag removal station, e.g. using the rake 36 to rake the ladle slag S2 form the top of the liquid steel LS contained in the ladle 10.

[0104] The implementation of this slag removal step will depend, in particular, on the steel grades to be produced and the subsequent secondary metallurgy steps. Indeed, the ladle slag S2 produced may not have the appropriate composition for the secondary metallurgy steps and may therefore need to be removed beforehand. For example, it may have limited desulphurisation capacity and must be removed for sulfur sensitive grades.

[0105] In other examples, the liquid steel LS is transferred from the ladle 10 used to tap the liquid steel LS from the EAF 2 to a ladle 42 of a secondary metallurgy reactor 40 via a discharge opening provided in the bottom of the ladle 10 used to tap the liquid steel LS from the EAF 2, with stopping the discharge such that the ladle slag S2 is not transferred to the ladle 42 of the secondary metallurgy reactor 40 but remains in the ladle 10 used to tap the liquid steel LS from the EAF 2.

[0106] The ladle slagging operation using a first slag compound SC1 with nitrogen affinity upon tapping the liquid steel LS from the EAF 2 allows controlling the nitrogen content of the liquid steel LS efficiently. Moreover, with the method according to the invention, it is possible to create only a limited amount of slag to target nitrogen removal, which reduces the amount of first slag compound SC1 required, but also the amount of slag produced. This type of slag currently has no valorisation routes, and its quantity must therefore be limited. The method of producing steel is not limited to the embodiments and variants described above. Other embodiments and variants may be contemplated.

[0107] Secondary metallurgy can be carried out in secondary metallurgy reactors different from a RH reactor, such as a ladle furnace (LF), a Vacuum degasser unit (VD), a vacuum oxygen decarburization (VOD) unit, an Argon Oxygen Decarburization (AOD) unit and / or a Vacuum Stream Degassing (VSD) unit.

Claims

CLAIMS1. Method of producing steel using an Electrical Arc Furnace (EAF), the method comprising:(a) melting a metal load (L) in the EAF and generating liquid steel (LS);(c) tapping the liquid steel (LS) from the EAF; and(d) performing secondary metallurgy on the liquid steel (LS) in at least one secondary metallurgy reactor to adjust the chemical composition of the liquid steel (LS), wherein the method comprises adding a first slag compound (SC1) with nitrogen affinity in the liquid steel (LS) during tapping of the liquid steel (LS) from the EAF and creating a ladle slag (S2).

2. Method for producing steel according to claim 1 , wherein the ladle slag (S2) is separated from the liquid steel (LS) before performing the secondary metallurgy.

3. Method of producing steel as in claim 1 or 2, comprising killing the liquid steel (LS), preferably after adding the first slag compound (SC1) to the liquid steel (LS).

4. Method of producing steel as in any one of claims 1 to 3, wherein the first slag compound (SC1) comprises one or several among barium oxide (BaO) and titanium dioxide (TiC>2).

5. Method of producing steel as in any one of claims 1 to 4 wherein the first slag compound (SC1) comprises at least 15% by weight of CaO, at least 30% by weight of AI2O3, and from 10% to 35% by weight of BaO , and optionally up to 15% of TiO2.

6. Method of producing steel as any one of claims 1 to 5, wherein the ladle slag (S2) is removed in a raking station (34).

7. Method of producing steel as any one of claims 1 to 6, comprising adding a second slag compound (SC2) with sulfur affinity in the liquid steel (LS) during tapping of the liquid steel (LS) from the EAF.

8. Method of producing steel according to claim 7, wherein the second slag compound (SC2) comprises one or several among lime (CaC2), calcium oxide (CaO), magnesium oxide (MgO) and manganese oxide (MnO).

9. Method of producing steel as in any one of claims 1 to 8, wherein the metal load (L) comprises at least 40% by weight of steel scrap (SC).

10. Method of producing steel as in any one of claims 1 to 9, wherein the metal load (L) comprises at least 40% by weight of direct reduced iron (DRI).

11. Method of producing steel as in any one of claims 1 to 10, wherein the metal load (L) comprises from 40% by weight to 60% by weight of direct reduced iron (DRI).

12. Method of producing steel as in any one of claims 1 to 11 , wherein the first slag compound (SC1) is added such as to lower the nitrogen content of the liquid steel (LS) to 50 ppm in weight or less, preferably to 20 ppm in weight or less.

13. Method of producing steel as in any one of claims 1 to 12, wherein the second slag compound (SC2) is added such as to lower the sulphur content of the liquid steel (LS) to 150 ppm in weight or less, preferably to 90 ppm in weight or less.

14. Method of producing steel as in any one of claims 1 to 13, comprising casting the liquid steel (LS) after performing the secondary metallurgy.

15. Method of producing steel as in any one of claim 1 to 14, wherein the first slag compound (SC1) is added in the ladle (10) before tapping, injected in the ladle (10) during tapping and / or run into the tapping stream.

Images