WO2016172790A1

WO2016172790A1 - Process and apparatus for producing high-manganese steels

Info

Publication number: WO2016172790A1
Application number: PCT/CA2016/050460
Authority: WO
Inventors: Sina MOSTAGHEL; Matthew H. CRAMER; Victor Hugo HERNANDEZ-AVILA
Original assignee: Hatch Ltd.
Priority date: 2015-04-26
Filing date: 2016-04-21
Publication date: 2016-11-03

Abstract

A process for producing high-manganese steel uses a low cost manganese source comprising manganese oxide, such as manganese ore fines. A mixture is provided, comprising the manganese source, an iron source comprising an iron oxide, a carbon source, and a fluxing agent. Micro-pellets comprised of the mixture are prepared, and the micro-pellets are pre-reduced to reduce at least a portion of the manganese oxide and iron oxide. The pre-reduced micro-pellets are then fed into a liquid steel bath in a steelmaking furnace to produce high-manganese steel. An apparatus comprises a pelletizer for pelletizing the mixture; a reducing unit for pre- reducing at least some of the manganese and iron oxides in the pelletized mixture and producing pre-reduced micro-pellets; and an electric steelmaking furnace containing a liquid steel bath, and having an injection port in communication with the liquid steel bath for direct injection of the pre-reduced micro-pellets into the bath.

Description

PROCESS AND APPARATUS FOR PRODUCING HIGH-MANGANESE STEELS CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of United States Provisional Patent Application No. 62/152,953 filed April 26, 2015, the contents of which are incorporated herein by reference.

FIELD

[0002] The present disclosure relates to a process and apparatus for producing high-manganese steels and advanced high strength steels (AHSS), such as Twining Induced Plasticity (TWIP) steels, which can be used for automotive components. In particular, the disclosure provides a process and an apparatus for cost-effective production of such steels, utilizing lower cost materials and/or equipment than those typically used in conventional processes.

BACKGROUND

[0003] The automotive industry is under constant pressure to reduce car weight due to fuel consumption, emissions and safety reasons. It is estimated that a 1% weight reduction in an automobile can save from 0.6 to 1.0% in fuel

consumption and reducing the weight of the vehicle by around 12 kg saves one gram of C0₂ equivalent emissions per kilometer. Most Body-In-White (BIW) and chassis components are presently made of steel, but competition from other metals such as aluminum is growing, especially in luxury cars. [0004] High manganese AHSS such as TWIP are highly desirable for BIW and chassis components due to their high tensile strength (about 1000 MPa), relatively low yield strength (about 400-500 MPa), high elongation (about 50%) and high specific energy absorption (about 0.5 J/mm³). This permits reduction in the gauge of the steel used to form these components, thereby achieving weight reduction, while preserving formability. Steels with these properties are austenitic, have a carbon content of about 0.6%, a manganese content of up to about 25%, and may or not contain aluminum (about 3%) and silicon (3%).

[0005] Traditional steelmaking processes add manganese to steel primarily by additions of ferromanganese (75%Mn) in the ladle treatment after the primary steelmaking process (EAF or BOF). While the electrodes of ladle furnaces may supply enough electrical power to melt manganese additions on the order of about l%Mn in the final steel, they do not have enough capacity to melt manganese additions equivalent to 15-20%Mn in normal tap-to-tap times required for further processing such as casting. Furthermore, such large additions of manganese may not be economical in a standard EAF (electric arc furnace) operation or a BOF (basic oxygen furnace) process due to the high oxygen potential of the steel, which would result in a considerable amount of the manganese being oxidized and reporting to the slag as a loss. The economic loss of manganese is significant as the cost of ferromanganese is on the order of 1,000 USD/tonne of high carbon (7.5%) and about 2,000 USD/tonne of medium carbon (2%). Possible addition in a standard EAF operation may involve longer tap-to-tap times, de-oxidation of the steel prior to manganese alloying, and/or may require the use of other vessels.

[0006] Major problems identified with EAF processes are high vaporization of Mn, and the need to use high-quality (expensive) scrap to avoid other detrimental elements, as discussed in US 2009/0114062 Al . [0007] There remains a need for more cost-effective processes and apparatus for producing high-manganese steels and advanced high strength steels, such as TWIP steels.

SUMMARY

[0008] In one aspect, there is provided a process for producing high- manganese steel. The process comprises: (a) providing a mixture comprising : a manganese source comprising a manganese oxide, an iron source comprising an iron oxide, a carbon source, and a fluxing agent; (b) preparing micro-pellets comprised of said mixture; (c) subjecting the micro-pellets to a pre-reduction step in which at least a portion of the manganese oxide and at least a portion of the iron oxide in the mixture are reduced, thereby producing pre-reduced micro-pellets; and (d) feeding the pre-reduced micro-pellets into a liquid steel bath in a steelmaking furnace to produce said high-manganese steel.

[0009] In an embodiment, the manganese source comprises manganese ore having a manganese content of at least about 50 weight percent. In an

embodiment, the iron source comprises iron ore or other sources of iron oxides. In an embodiment, the carbon source comprises char or coke, such as lignite char. In an embodiment, the fluxing agent comprises one or more of lime and barium oxide.

[0010] In an embodiment, the fluxing agent comprises slag from a basic oxygen furnace, an electric furnace or a ladle metallurgy furnace, wherein the slag has a basicity greater than about 2 and a low sulphur content.

[0011] In an embodiment, the micro-pellets of said mixture have a size from about 3 to about 5 mm. [0012] In an embodiment, the pre-reduction step leaves some unreacted MnO in the pre-reduced micro-pellets. In an embodiment, the pre-reduction step is conducted in a reducing or inert atmosphere having an oxygen potential for reduction of MnO lower than about lxlO^"17. In an embodiment, the pre-reduction step is conducted in a reducing atmosphere comprises a mixture of CO and H₂. In an embodiment, an operating temperature of the pre-reduction step is about 1300°C.

[0013] In an embodiment, the pre-reduced micro-pellets comprise Mn-Fe alloy. In an embodiment, at least a portion of the Mn-Fe alloy in the pre-reduced micro-pellets is in liquid form .

[0014] In an embodiment, the liquid steel bath is covered by a layer of furnace slag, and wherein the step of feeding the pre-reduced micro-pellets into the liquid steel bath comprises direct injection of the pre-reduced micro-pellets under the layer of furnace slag and into the liquid steel bath. In an embodiment, the pre- reduced micro-pellets are injected into the liquid steel bath at a temperature from about 1200°C to about 1300°C. In an embodiment, the pre-reduced micro-pellets are injected into the liquid metal bath in an inert carrying gas, which may comprise argon. In an embodiment, the pre-reduced micro-pellets are injected at an angle into the liquid steel bath so as to maximize residence time of the micro-pellets in the bath. For example, the pre-reduced micro-pellets may be injected by a lance having a tip extending below the layer of furnace slag and into the liquid steel bath.

[0015] In an embodiment, the liquid steel bath is produced by continuously melting solid DRI and scrap in the steelmaking furnace. In an embodiment, the high-manganese steel is tapped from the steelmaking furnace and is then further processed in a ladle metallurgy furnace unit. [0016] In an embodiment, furnace slag is tapped from the steelmaking furnace, and the process further comprises a step of recovering manganese from the furnace slag by dry slag granulation and subsequent magnetic separation of slag granules enriched in manganese-containing spinels.

[0017] In another aspect, there is provided an apparatus for producing high- manganese steel. The apparatus comprises: (a) a pelletizer for pelletizing a mixture comprising : a manganese source comprising a manganese oxide, an iron source comprising an iron oxide, a carbon source, and a fluxing agent; (b) a reducing unit for pre-reducing at least a portion of the manganese oxide and at least a portion of the iron oxide in the pelletized mixture, and producing pre- reduced micro-pellets; and (c) an electric steelmaking furnace containing a liquid steel bath, and having an injection port in communication with the liquid steel bath for direct injection of the pre-reduced micro-pellets into the bath.

[0018] In an embodiment, the reducing unit comprises at least one fluidized bed reactor adapted to operate at a temperature in the range from about 1000°C to about 1350°C. In an embodiment, the reducing unit comprises a plurality of said fluidized bed reactors arranged in series. In an embodiment, the reducing unit comprises a rotary kiln.

[0019] In an embodiment, the apparatus further comprises a reformer unit for producing a reducing fluidizing gas, and a conduit for feeding the reducing fluidizing gas to the fluidizing unit. In an embodiment, the apparatus further comprises one or more conduits for feeding recycled furnace gas, recycled pre-reduction gas and/or natural gas to the reformer unit.

[0020] In an embodiment, the electric steelmaking furnace includes a series of submerged electrodes, a DRI feeder, a scrap feeder, and a flux feeder. In an embodiment, the electric steelmaking furnace includes an off-gas system adapted to capture manganese vapour. In an embodiment, the electric steelmaking furnace is located in close proximity to the reducing unit.

[0021] In an embodiment, the apparatus further comprises a ladle metallurgy furnace (LMF) unit for further processing of the high-manganese steel.

[0022] In an embodiment, the electric steelmaking furnace further comprises a slag taphole for removing furnace slag from the furnace, and wherein the apparatus further comprises a dry slag granulation unit for granulating the furnace slag, and a magnetic separation unit adapted for recovering slag granules enriched in manganese-containing spinels from the granulated slag.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention will now be described, by way of example only, with reference to the attached drawings, in which :

[0024] Figure 1 is a flow diagram illustrating a process and apparatus according to an embodiment described herein; and

[0025] Figure 2 schematically illustrates the injection of pre-reduced pellets into a liquid steel bath in an electric furnace.

DETAILED DESCRIPTION

[0026] The following is a detailed description of a process and apparatus 10 for producing high-manganese steels and advanced high strength steels (AHSS), such as TWIP steels. [0027] The process described herein comprises several steps, including :

peptization, pre-reduction, pellet injection and steelmaking. In addition to these steps, a dry slag granulation and manganese recovery from the slag (using magnetic separation) can also be added to improve the process efficiency. Each of these steps and the apparatus 10 for carrying out the steps are described in detail below.

[0028] One significant aspect of the process described herein is that it uses a manganese source which has a much lower cost than ferromanganese, thereby contributing to a reduction in the cost of producing the steel product. In this regard, a typical manganese source for use in the present process is manganese ore fines, having a manganese content of at least about 50 weight % Mn (for example about 55 weight % Mn) and a much lower cost (less than 120 USD/tonne) than ferromanganese.

[0029] The manganese source is combined with a number of other

components and pre-reduced prior to being added to the steel. The components which may be combined with the manganese source include an iron source, a carbon source, and one or more fluxing agents.

[0030] The iron source may comprise iron ore, containing iron oxides; the carbon source may comprise char or coke; and the fluxing agents may comprise lime and/or barium oxide. Alternatively, it is possible to use materials such as BOF, EAF, and /or LMF (ladle metallurgy furnace) slags as low-cost fluxes, where they have basicities greater than about 2 and low sulphur contents. Ideally, the manganese and iron sources will be low in phosphorus.

[0031] The granulometry of the above raw materials is selected to increase, as much as practically possible, the contact area between reagents, thereby increasing the reaction rate. For example, the raw materials may be combined in finely divided form .

[0032] In an embodiment, the raw materials are combined in a mixer- pelletizing unit 12 to produce self-reducing/self-fluxed micro-pellets which may have a diameter up to about 10 mm, for example from about 1 to about 8 mm, or from about 3 to about 5 mm. To assist in producing pellets, the raw materials may be mixed with water and optionally with a binder such as bentonite.

[0033] The fluxing agents are added to:

[0034] increase the melting temperature of gangue in the raw materials (i.e. to prevent gangue from softening and melting during peptization);

[0035] control the basicity of the slag formed in the downstream smelting furnace 18; and

[0036] facilitate dephosphorization of the liquid metal in the furnace 18 (BaO, in particular, can be added to the pellet for this purpose).

[0037] The size and permeability of the pellets is selected to allow sufficiently fast mass transfer of gases in and out of the pellet, and to provide a sufficiently fast reaction rate of the raw materials during pre-reduction, as discussed below. Also, the size of the pellets is selected to enable them to rapidly melt during injection into the steel bath, as will be further discussed below.

[0038] After the pellets are formed they are dried in a dryer, which is included with pelletizing unit 12 and identified as "PELLETIZER AND DRYER" in Figure 1, However, pellet enduration is not required. [0039] Next, the dried pellets are subjected to a pre-reduction step in a prereduction unit 14, also identified in Figure 1 as "PRE-REDUCER". The aim of the pre-reduction step is to produce a metallic Mn-Fe alloy within the pellet, with a concentration of manganese in the Mn-Fe alloy being greater than about 50 weight % and the carbon content of the Mn-Fe alloy being less than about 4 weight %. It will be appreciated that an amount of unreduced MnO will remain in the pellet after the pre-reduction step. In one aspect, the pre-reduction unit 14 comprises a fluidized bed reactor, or a plurality of fluidized bed reactors arranged in series, wherein the fluidized bed reactor(s) operates at a temperature in the range from about 1000°C to about 1350°C. In another aspect, the pre-reduction unit 14 comprises a rotary kiln.

[0040] During the pre-reduction step, manganese oxides and iron oxides present in the raw materials are reduced to form elemental manganese and iron. Manganese oxide, MnO, is a more stable oxide than iron monoxide, FeO, so the reduction of FeO precedes that of MnO. The mechanisms of reduction are:

[0041] Step 1 : Wustite reduction :

Fe_xO_y(s) + CO→Fe_xO_(y__l)(s) + C0₂ where x= l,2,3 and y= l,3,4. [0042] Step 2 : Manganese oxide reduction : There are two possible mechanisms;

(a) Direct formation of manganese carbide followed by reduction

10C + 10CC →20C< 7MnO + \3CO→Mn₇ ⁷C, ³ + \0CO_? ² , (t. a .kes p ,lace w .h.i.le car .bon . is

^{7 3 2} (takes place when carbon has

Direct reduction followed by manganese carbide formation

7 CD

(limiting reaction, possibly C0₂ mass transfer control)

MnO + CO→Mn + CO lMn + C→Mn₇C₃

[0043] Reduction of FeO and MnO involves CO, which is created by gasification of the carbon source. Accordingly, a carbon source with a high gasification rate will speed the kinetics of reduction. Also, an amount of unreduced MnO is necessary to prevent the formation of the high carbon constituent, manganese carbide (Mn₇C₃). Therefore, the pre-reduction process should leave some unreacted MnO and also minimize the carbon available for the formation of manganese carbides.

[0044] The pre-reduction is carried out in a reducing or inert environment. For example, where the reducing unit 14 comprises one or more fluidized bed reactors, the fluidizing gas may be reducing or inert, with an oxygen potential for reduction of MnO lower than about lxlO^"17. Where a reducing fluidizing gas is used, it may be produced by a reformer unit 20 to which recycled furnace gas, recycled pre-reduction gas and natural gas are fed to produce a mixture of CO and H₂, with the H₂ concentration of the mixture being as high as possible in order to improve the thermodynamics and kinetics conditions. For example, a typical CO/H₂ mixture may contain about 50%CO and about 50%H₂ by volume. At least some of the heat of the pre-reduction step will be supplied by the recycled furnace and/or pre- reduction gases, which will carry with them some heat from the furnace 18 or pre- reducing unit 14. This eliminates or reduces the need for other forms of heating, such as electrical heating, to carry out the pre-reduction, thereby reducing the cost of the process. The flowsheet of Figure 1 shows a conduit 16 carrying recycled off- gas from the furnace off-gas port 22 to the fuel reformer 20. Similarly, Figure 1 shows a conduit 24 carrying reducing gas from the pre-reducer 14 to the reformer 20.

[0045] Reduction of the MnO to Mn, followed by dissolution of Mn into the iron in the pellets, significantly reduces the solidus and liquidus temperatures of the manganese. Therefore, at the operating temperature of the pre-reduction process, which may be about 1300°C, some liquid metallic Mn-Fe alloy will be formed within the pellet, surrounded by a layer of solid gangue that maintains the integrity of the pellet. The gangue includes unreduced components of the manganese ore, and includes an amount of unreduced MnO.

[0046] The inventors have found that the use of lignite char as the carbon source is beneficial because it has a high gasification rate, and because it dissolves less into liquid metals (i.e. the liquid Mn-Fe alloy and liquid steel) than other sources of carbon such as graphite or coke. This helps to prevent recarburization of the steel during the steelmaking step.

[0047] Furthermore, the inventors have found that there may be significant dephosphorization of the liquid alloy in the pellet during the pre-reduction step. In this regard, the relatively low reduction temperature of ~ 1300°C, the high basicity of the gangue, and the presence of MnO all contribute to removing phosphorus.

[0048] After pre-reduction, the pre-reduced pellets are added to a liquid steel bath in electric furnace 18. The addition of the pellets to the furnace 18 is performed while the pellets are hot. For example, the pellets may be at or near the temperature to which they are heated during the pre-reduction step, i.e. around 1300°C, for example above about 1200°C, such that the pellets may contain at least some of the metallic Mn-Fe alloy in liquid form . Thus, for example, the pre- reduced pellets may be transferred from the reducing unit 14 to the electric furnace 18 without substantial heat loss and/or with auxiliary heating to preserve the prereduction heat. Also, it is desirable that the reducing unit and the electric furnace are in close proximity to each other, as shown in Figure 1.

[0049] Furthermore, according to the present embodiment, the pre-reduced pellets are injected directly into the liquid steel bath in the electric furnace, which is at a temperature of about 1600°C to about 1650°C, rather than being fed to the top of the bath in the manner of other feed materials such as scrap and/or DRI (direct reduced iron), which are fed through respective feeders 26, 28 and ports in the roof of furnace 18. In this regard, the pellets are desirably fed directly into the steel bath, below the layer of furnace slag. This injection can be accomplished by using a lance having a tip extending through the slag layer and into the molten steel bath. Figure 1 shows a pellet injection unit 40 in the form of a lance extending through the sidewall of furnace 18 at an angle, having a tip extending into the steel bath. It will be appreciated, however, that the lance may have a more vertical orientation and may extend downwardly through the roof of furnace 18.

[0050] For example, Figure 2 shows an electric furnace 18 having a horizontal bottom wall 54, vertical side walls 56, and a roof 58. Inside the electric furnace 18 is a liquid steel bath 60 covered with a layer of slag 62. A lance 64 extends through the roof 58 of furnace 18, having a tip 66 at its lower end, the tip extending below the slag layer 62 and into the liquid steel bath 60. Pre-reduced micro-pellets 68 in an inert carrier gas are injected into the liquid steel bath 60 from the tip 66 of lance 64. As shown, the tip 66 of lance 64 is oriented to inject the pellets 68 at an angle to the horizontal and vertical directions, causing the pellets 68 to follow a trajectory as they are injected into the steel bath 60, and maximizing their residence time in the steel bath 60, and therefore promoting complete or substantially complete melting of the pellets 68 in the steel bath 60. In order to inject the pellets at an angle, the tip 66 of lance 64, and/or the entire lance 64 itself, may be angled relative to the horizontal and vertical directions which are respectively defined by the bottom wall 54 and side walls 56.

[0051] As shown in Figure 2, the pellets 68 are initially injected in a

downwardly angled direction. As they melt, the pellets 68 travel across the steel bath and unmelted components thereof then move upwardly toward the slag layer 62, and eventually enter the slag layer 62. For example, as shown in Figure 2, the pellets 68 may follow an approximately U-shaped trajectory as they melt and become dispersed through the steel bath 62. Maximizing the residence time of the pellets 68 in the steel bath 60 minimizes the amount of manganese which will be lost to the slag layer 62.

[0052] Although Figure 2 shows the pellets 68 remaining unchanged as they are injected into the steel bath 60, it will be appreciated that the majority of the Mn-Fe alloy contained in pellets 68 will become completely or substantially completely dissolved in the steel layer 60 once they are injected by lance 64, particularly if the Mn-Fe alloy in the pre-reduced micro-pellets is in liquid form.

[0053] Although Figure 2 shows the lance 64 extending through the furnace roof 58, this is not necessarily the case. For example, Figure 2 shows a lance 64' extending through a sidewall 56 of the furnace 18 at an angle.

[0054] As discussed above, direct injection of the pellets helps to ensure maximum contact with the liquid steel, and helps to melt the pre-reduced pellets quickly during addition to the bath. Direct injection also provides higher recovery of manganese, and less manganese volatilization to the gas phase. In addition, direct injection may improve dephosphorization compared to other forms of addition. In this regard, feeding a material such as DRI into the top of the furnace results in dissolution of phosphorus into the steel bath as soon as the DRI melts. In contrast, the high basicity of the directly injected pre-reduced pellets may prevent dissolution of phosphorus into the steel bath, thereby reducing or eliminating the need for further phosphorus removal.

[0055] The injection requires an inert carrying gas that does not dissolve into liquid steel. Argon is one example of such an inert gas. Gases such as nitrogen and/or hydrogen cannot be used, since they will dissolve into the liquid steel and cause problems. The amount and pressure of the carrying gas is selected so that the pellets are immersed deep into the bath. Also, the angle of injection is selected so that the pellets will be injected deep into the bath, for example in a perpendicular (vertical) direction, so as to increase residence time, and thereby promoting maximum contact of the molten pellet with the steel bath.

[0056] Once they are injected into the bath of liquid steel, the hot pre-reduced pellets are rapidly melted and their metallic content (i.e. the Mn-Fe alloy) is dissolved into the steel bath. This rapid melting also allows the manganese- containing gangue to become slag, which facilitates further reduction of the unreacted manganese oxides in the pellets, and contributes to further alloying of the steel. The slag produced by the pellets will float to the top of the steel bath and will be absorbed by the furnace slag. Due to its relatively high basicity, this slag will enhance the dephosphorization in the furnace slag.

[0057] Once the pellets are incorporated into the liquid steel bath, the steelmaking process and the electric furnace unit 18 are the same as, or similar to, those which are described by I. Gordon et al. in US Patent 6,875,251 B2.

[0058] For example, the electric furnace 18 may comprise a vessel designed to contain from about 1.5 to about 13 tap weights. The furnace 18 may also include a series of submerged electrodes 30, a DRI feeder 26, a scrap feeder 28, a flux feeder 32 (shown in Figure 1 as the port which feeds iron oxide, dolomitic lime and/or lime to the furnace), slag taphole(s) 34 (or equivalent techniques to remove slag), metal taphole(s) 36 (or equivalent techniques to remove metal), an off-gas system 22 capable of capturing manganese vapour, and the pre-reduced pellet injection unit 40. A feeding system may also be provided to charge liquid steel to the furnace 18.

[0059] The electric furnace 18 is designed to ensure that a reducing

atmosphere is maintained during operation and that fugitive manganese vapour is contained properly. The steelmaking process may be a continuous process or a batch process. For example, the DRI, scrap and liquid steel (optional) are fed to the furnace 18 as the main iron sources, together with slag building fluxes and the pre- reduced pellets as the main source of manganese, with the DRI and scrap being continuously melted. The DRI, scrap and liquid steel (optional) mixture is designed to minimize the content of carbon and phosphorus in the steel produced. The furnace slag is designed to maximize phosphorus removal, increase manganese recovery and minimize carbon pickup in steel. Tapping of slag and metal are intermittent while maintaining electric power on.

[0060] The furnace slag will contain MnO and to a lesser extent FeO.

However, it is important not to attempt reducing the metal loss through the addition of carbonaceous material, as this will result in carburization of the steel. The steelmaking process will have very limited steel carbon removal capabilities, given the reducing requirements to maintain the manganese in the steel.

[0061] The liquid steel tapped from the furnace 18 may be further processed in a ladle metallurgy furnace (LMF) unit 42. Given the high content of manganese in the steel, the LMF unit 42 may include special equipment to deal with the fugitive manganese emissions. In the LMF 42, a number of different treatments are carried out to obtain the desired composition and properties of the metal. These treatments include:

1. Temperature homogenization or adjustment (typically using inert gas injection and stirring);

2. Chemical adjustments of the melt, including the following :

(a) Removal of carbon (can be done using vacuum ladle degassing, which simultaneously reduces the nitrogen and hydrogen contents as well);

(b) Removal of sulfur (wire and/or powder injection of desulphurization agents such as CaO, Al, CaF₂, CaC0₃, CaC₂);

(c) Removal of phosphorus (powder injection of dephosphorization agents such as CaO, CaF₂, Fe₂0₃, and mill scale soda);

(d) Removal of oxygen (typically using strong deoxidizers such as Al or Si);

(e) Alloying (typically using FeSi, NiO, Mo0₂, FeTi, FeMn); and

3. Inclusion control and modification : for example calcium treatment is the most commonly used method to transform hard and angular alumina inclusions into larger soft calcium aluminates, which more easily are collected in the slag; and/or MnS inclusions are transformed into small globular inclusions which are favourable for the workability of the steel. [0062] In some embodiments, the process may include a step of recovering manganese from the furnace slag by dry slag granulation and subsequent magnetic separation. In this regard, dry slag granulation by slag gas atomization, as described in International Application No. PCT/CA2015/050210, can be performed under conditions which lead to production of magnetic products such as manganese ferrite spinel, Jacobsite, MnFe₂0₄. Also, as described in International Application No. PCT/CA2015/051320, slag granules rich in magnetic manganese-containing spinels 50 can be separated from slag granules having a relatively low

ferrite/manganese content 52 in a slag granulation unit 44 and magnetic separation unit 46. To enhance the efficiency of the separation, the size of the slag granules can be reduced in a grinding unit 48 before they are fed to the magnetic separation unit. The separated manganese ferrite can then be recycled to the process, as a source of manganese to be incorporated into the pellets.

[0063] Although the invention has been described with reference to certain specific embodiments, it is not limited thereto. Rather, the invention includes all embodiments which may fall within the scope of the following claims.

Claims

What is claimed is:

1. A process for producing high-manganese steel, comprising :

(a) providing a mixture comprising : a manganese source comprising a

manganese oxide, an iron source comprising an iron oxide, a carbon source, and a fluxing agent;

(b) preparing micro-pellets comprised of said mixture;

(c) subjecting the micro-pellets to a pre-reduction step in which at least a portion of the manganese oxide and at least a portion of the iron oxide in the mixture are reduced, thereby producing pre-reduced micro-pellets; and

(d) feeding the pre-reduced micro-pellets into a liquid steel bath in a steelmaking furnace to produce said high-manganese steel.

2. The process according to claim 1, wherein the manganese source comprises manganese ore having a manganese content of at least about 50 weight percent.

3. The process according to claim 1 or 2, wherein the iron source comprises iron ore.

4. The process according to any one of claims 1 to 3, wherein the carbon source comprises char or coke.

5. The process according to claim 4, wherein the carbon source comprises lignite char.

6. The process according to any one of claims 1 to 5, wherein the fluxing agent comprises one or more of lime and barium oxide.

7. The process according to any one of claims 1 to 5, wherein the fluxing agent comprises slag from a basic oxygen furnace, an electric furnace or a ladle

metallurgy furnace, wherein the slag has a basicity greater than about 2.

8. The process according to any one of claims 1 to 7, wherein the micro-pellets of said mixture have a size from about 3 mm to about 5 mm .

9. The process according to any one of claims 1 to 8, wherein the pre-reduction step leaves some unreacted MnO in the pre-reduced micro-pellets.

10. The process according to any one of claims 1 to 9, wherein the pre-reduction step is conducted in a reducing or inert atmosphere having an oxygen potential for reduction of MnO lower than about lxlO^"17.

11. The process according to claim 10, wherein the pre-reduction step is conducted in a reducing atmosphere comprising a mixture of CO and H₂.

12. The process according to any one of claims 1 to 11, wherein an operating temperature of the pre-reduction step is about 1300°C.

13. The process according to any one of claims 1 to 12, wherein the pre-reduced micro-pellets comprise Mn-Fe alloy.

14. The process according to claim 13, wherein at least a portion of the Mn-Fe alloy in the pre-reduced micro-pellets is in liquid form .

15. The process according to any one of claims 1 to 14, wherein the liquid steel bath is covered by a layer of furnace slag, and wherein the step of feeding the pre- reduced micro-pellets into the liquid steel bath comprises direct injection of the pre- reduced micro-pellets under the layer of furnace slag and into the liquid steel bath.

16. The process according to claim 15, wherein the pre-reduced micro-pellets are injected into the liquid steel bath at a temperature from about 1200°C to about 1300°C.

17. The process according to claim 15 or 16, wherein the pre-reduced micropellets are injected into the liquid metal bath in an inert carrying gas.

18. The process according to claim 17, wherein the inert carrying gas comprises argon.

19. The process according to any one of claims 17 to 18, wherein the pre-reduced micro-pellets are injected at an angle into the liquid steel bath so as to maximize residence time of the micro-pellets in the bath.

20. The process according to any one of claims 15 to 19, wherein the pre-reduced micro-pellets are injected by a lance having a tip extending below the layer of furnace slag and into the liquid steel bath.

21. The process according to any one of claims 1 to 20, wherein the liquid steel bath is produced by continuously melting solid DRI and scrap in the steelmaking furnace.

22. The process according to any one of claims 1 to 21, wherein the high- manganese steel is tapped from the steelmaking furnace and is then further processed in a ladle metallurgy furnace unit.

23. The process according to any one of claims 1 to 22, wherein furnace slag is tapped from the steelmaking furnace, and the process further comprises a step of recovering manganese from the furnace slag by dry slag granulation and subsequent magnetic separation of slag granules enriched in manganese-containing spinels.

24. An apparatus for producing high-manganese steel, comprising :

(a) a pelletizer for pelletizing a mixture comprising : a manganese source comprising a manganese oxide, an iron source comprising an iron oxide, a carbon source, and a fluxing agent;

(b) a reducing unit for pre-reducing at least a portion of the manganese oxide and at least a portion of the iron oxide in the pelletized mixture, and producing pre- reduced micro-pellets; and

(c) an electric steelmaking furnace containing a liquid steel bath, and having an injection port in communication with the liquid steel bath for direct injection of the pre-reduced micro-pellets into the bath.

25. The apparatus according to claim 24, wherein the reducing unit comprises at least one fluidized bed reactor adapted to operate at a temperature in the range from about 1000°C to about 1350°C.

26. The apparatus according to claim 25, wherein the reducing unit comprises a plurality of said fluidized bed reactors arranged in series.

27. The apparatus according to claim 26, wherein the reducing unit comprises a rotary kiln.

28. The apparatus according to any one of claims 24 to 26, further comprising a reformer unit for producing a reducing fluidizing gas, and a conduit for feeding the reducing fluidizing gas to the fluidizing unit.

29. The apparatus according to claim 28, further comprising one or more conduits for feeding recycled furnace gas, recycled pre-reduction gas and/or natural gas to the reformer unit.

30. The apparatus according to any one of claims 24 to 29, wherein the electric steelmaking furnace includes a series of submerged electrodes, a DRI feeder, a scrap feeder, and a flux feeder.

31. The apparatus according to any one of claims 24 to 30, wherein the electric steelmaking furnace includes an off-gas system adapted to capture manganese vapour.

32. The apparatus according to any one of claims 24 to 31, wherein the electric steelmaking furnace is located in close proximity to the reducing unit.

33. The apparatus according to any one of claims 24 to 32, further comprising a ladle metallurgy furnace (LMF) unit for further processing of the high-manganese steel.

34. The apparatus according to any one of claims 24 to 33, wherein the electric steelmaking furnace further comprises a slag taphole for removing furnace slag from the furnace, and wherein the apparatus further comprises a dry slag

granulation unit for granulating the furnace slag, and a magnetic separation unit adapted for recovering slag granules enriched in manganese-containing spinels from the granulated slag.