Description:DESCRIPTION:
Field of the invention:
[0001] The present disclosure generally relates to the technical field of a low-melting ladle flux for treating Si-Killed steels, and in specific relates to a method for preparing low-melting ladle flux with recycled stabilized Si/Mn/Al killed ladle furnace slag, reducing melting point and simultaneously increasing the valorisation of ladle furnace (LF) slag.
Background of the invention:
[0002] Steel, the backbone of modern infrastructure and countless essential objects, owes its strength and versatility to more than just iron. In steel raw form, iron comes bundled with an unwelcome guest sulfur. The sulfur element can wreak havoc on steel's properties, making it brittle, prone to corrosion, and difficult to work with. The steel desulfurization that eliminates sulfur and unlocks the true potential of this remarkable metal. Due to the demand for ultra-clean steels, various types of ladle fluxes are developed to aid in the steel desulfurization. The ladle fluxes are ideally introduced during steel tapping into the ladle, which is then treated in secondary metallurgical activities. The ladle fluxes are widely utilised in the treatment of high carbon and Si-Killed steels in order to obtain a more advantageous CaO-Al2O3-SiO2 system than a CaO-MgO-SiO2 system. Depending on the application, many types of ladle fluxes are employed, such as calcium aluminate-based, calcium magnesium aluminate-based, calcium fluoride-based, and alumina-based. The CaO-Al2O3 based ladle fluxes are commonly used due to their low melting point. However, these fluxes are expensive and have low CaO (30-40 wt %), rendering steel desulfurization challenging.

[0003] In existing methodologies, while in the ladle, the molten steel can be subjected to additional refining processes (ladle furnace refining processes). For instance, additional ladle fluxes may be added, particularly in Si-killed steels in order to further remove impurities that remained within the molten steel after being tapped from the furnace. The slags that are formed during the ladle refining process are generally referred to as ladle furnace slags. After the ladle refining process is complete, the refined molten steel is tapped (poured) into a continuous caster after which the ladle slags are poured into a ladle slag pot / emergency container. The Al-killed ladle furnace slag contains a significant amount of CaO and Al2O3, making it a suitable replacement for CaO-Al2O3-based ladle fluxes. However, ladle slag disintegrates into fine powder during cooling due to volume expansion of di-calcium silicate phase. The powdered slag is difficult to recycle, handle and store. Accordingly, most ladle slags are discarded and transported to landfills for disposal. Commercially available CaO-Al2O3 based ladle fluxes contain high alumina and low CaO content. The calcium aluminate phase aids in lowering the melting point of the slag; however, it simultaneously diminishes the available CaO necessary for desulfurization.

[0004] By addressing all the above mentioned problems, there is a need for a method that for preparing low-melting ladle flux with recycled stabilized ladle furnace slag having high CaO content (45-60 weight percent ), thereby reducing melting point of slag and at the same time increasing a (ladle furnace) LF slag valorisation. There is also a need for a method that reduces synthetic slag addition, which result cost saving. There is also a need for a method that improves slag valorisation potential.
Objectives of the invention:
[0005] The primary objective of the invention is to provide a method for preparing low-melting ladle flux from recycled Si/Mn/Al killed ladle furnace slag while also lowering the melting point of slag and increasing LF (ladle furnace) slag valorisation.

[0006] Another objective of the invention is to provide a method for preparing low-melting ladle flux from recycled Si/Mn/Al killed ladle furnace slag that reduces synthetic slag addition, resulting in cost saving.

[0007] Yet another objective of the invention is to provide a method for preparing low-melting ladle flux that significantly improves slag fluidity, thereby reducing the need for synthetic slag.

[0008] Further objective of the invention is to provide a method for minimising disintegration of Si/Mn/Al killed ladle furnace slag using boric acid to increase valorisation potential.

Summary of the invention:
[0009] The present disclosure proposes preparation method of low-melting ladle flux from ladle furnace slag for treating silicon-manganese killed steels. The following presents a simplified summary in order to provide a basic understanding of some aspects of the claimed subject matter. This summary is not an extensive overview. It is not intended to identify key/critical elements or to delineate the scope of the claimed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

[0010] In order to overcome the above deficiencies of the prior art, the present disclosure is to solve the technical problem to provide a method for preparing low-melting ladle flux with recycled stabilized Si/Mn/Al killed ladle furnace slag, reducing melting point and simultaneously increasing the valorisation of ladle furnace (LF) slag.

[0011] According to an aspect, the invention provides a method for preparing low-melting ladle flux for treating Si-killed steels. At one step, a basic oxygen furnace (BOF) process a steel and feeds the steel into a ladle for secondary metallurgical operations. At another step, plurality of Ferro alloys, aluminium and ladle fluxes are added according to the grade of steel. In one embodiment herein, the plurality of Ferro alloys include Fe-Si, Si-Mn, lime, and synthetic slag. At another step, the steel in a ladle furnace is process for desulfurization and inclusion absorption, thereby homogenizing a steel composition and maintains steel temperature required for smooth casting.

[0012] At another step, the steel before casting is deoxidise by adding iron monosilicide (FeSi), silicon manganese (SiMn), and slag modification. At another step, the ladle slag is stabilise by adding boric acid (H3BO3), thereby preventing the disintegration of ladle slag into a fine powder and reducing the melting point of slag.

[0013] At another step, the obtaining ladle slag in the ladle poured into a slag container after completion of casting, and the obtained ladle slag is stabilized. Further, at another step, the low-melting ladle flux is prepared by crushing and sizing the stabilised ladle slag to 30 to 40 mm in size and treating Si-killed steels.

[0014] In one embodiment herein, the low-melting ladle flux is prepared with a mixture of 40 to 60 percentage of Si/Mn/Al killed ladle slag, 20 to 30 percentage of lime, 0 to 30 percent of calcined bauxite, and 0-4 weight percent of boric acid. In one embodiment herein, the ladle slag is obtained in the final stages of the steelmaking process, when the steel is desulfurized in the transport ladle and ladle slag is from Si/Mn/Al-killed steel. In one embodiment herein, the ladle fluxes include lime, Si/Mn/Al killd ladle slag with and without stabilization with H3BO3, calcined bauxite and synthetic slag.

[0015] In one embodiment herein, the obtained ladle slag from the Si/Mn/Al-Killed steel making process include about 45 to 55 percentage of calcium oxide (CaO), 18 to 25 percentage of Al2O3, 6 to 12 percentage of silicon dioxide (SiO2), 8 to 12 percentage of magnesium oxide (MgO), 0 to 0.5 percentage of sulfur, and 0 to 2 percentage of iron manganese oxide (FeO+MnO). In one embodiment herein, the prepared low melting ladle flux improves slag fluidity drastically, thereby reducing synthetic slag addition, results in a reduction in steel production costs.

[0016] Further, objects and advantages of the present invention will be apparent from a study of the following portion of the specification, the claims, and the attached drawings.
Detailed description of drawings:
[0017] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, explain the principles of the invention.

[0018] FIG. 1 illustrates a flow chart of a method for preparing low-melting ladle flux with recycled stabilized ladle furnace slag, in accordance to an exemplary embodiment of the invention.

[0019] FIG. 2 illustrates a pictorial representation of a steel making process, in accordance to an exemplary embodiment of the invention.

[0020] FIG. 3A illustrates a pictorial representation of a disintegrated Si/Mn/Al killed ladle furnace slag, in accordance to an exemplary embodiment of the invention.

[0021] FIG. 3B illustrates a pictorial representation of the Si/Mn/Al killed ladle furnace slag obtained after stabilising with addition of boric acid, in accordance to an exemplary embodiment of the invention.

[0022] FIG. 4 illustrates a flowchart of Si/Mn/Al-killed LF slag recycling at industrial scale, in accordance to an exemplary embodiment of the invention.

[0023] FIG. 5 illustrates a pictorial representation of process for preparing low-melting ladle flux with recycled stabilized ladle furnace slag, in accordance to an exemplary embodiment of the invention.
Detailed invention disclosure:
[0024] Various embodiments of the present invention will be described in reference to the accompanying drawings. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps.

[0025] The present disclosure has been made with a view towards solving the problem with the prior art described above, and it is an object of the present invention to provide a method for preparing low-melting ladle flux with recycled stabilized Si/Mn/Al killed ladle furnace slag, reducing melting point and simultaneously increasing the valorisation of ladle furnace (LF) slag.

[0026] According to an exemplary embodiment of the invention, FIG. 1 refers to a flowchart 100 of a method for preparing low-melting ladle flux for treating Si-killed steels. At step 102, a basic oxygen furnace (BOF) process a steel and feeds the steel into a ladle for secondary metallurgical operations. At step 104, plurality of Ferro alloys aluminium and ladle fluxes are added according to the grade of steel. In one embodiment herein, the plurality of Ferro alloys include Fe-Si, SI-Mn, lime, and synthetic slag. At step 106, the steel in a ladle furnace is process for desulfurization and inclusion absorption, thereby homogenizing a steel composition and maintains steel temperature required for smooth casting.

[0027] At step 108, the steel is deoxidized before casting by adding iron monosilicide (FeSi), silicon manganese (SiMn), and slag modification. At step 110, the ladle slag is stabilized by adding boric acid (H3BO3), thereby preventing the disintegration of ladle slag into a fine powder and reducing the melting point of slag.

[0028] At step 112, obtaining ladle slag in the ladle poured into a slag container after completion of casting, and the obtained ladle slag is stabilized. Further, at step 114, the low-melting ladle flux is prepared by crushing and sizing the stabilised ladle slag to 30 to 40 mm in size for treating Si-killed steels.

[0029] According to another exemplary embodiment of the invention, FIG. 2 refers to a pictorial representation 202 of a steel making process. In one embodiment herein, the steel is further processed at ladle furnace station for de-sulfurization and inclusion absorption. The LF station also helps in homogenizing steel composition and maintaining steel temperature required for smooth casting. The bath stirring is achieved by means of argon purging from the bottom. The Killed steel is steel that has completely deoxidized by the addition of a fluxing agent before casting such that there is practically no evolution of gas during solidification. The steel is fully deoxidised (killed) before casting by the addition usually of silicon, manganese and aluminium, but also sometimes vanadium, titanium etc.

[0030] In one embodiment herein, the method for steel making process. At step 202, the molten iron from a blast furnace is charged into the BOF along with steel scrap and flux. Oxygen is then lanced into the molten metal, which oxidizes impurities such as carbon, silicon, and manganese. The exothermic reaction generates heat, raising the temperature to around 1,700°C (3,092°F). This melts the scrap steel and reduces the carbon content of the molten iron, converting it into steel. At step 204, the plurality of Ferro alloys, flux, and aluminium are added for requirement to grade of steel. At step 206, the steel is tapped from the BOF into the ladle.

[0031] At step 208, the ladle is transported to a station, where it is rinsed with inert gas to remove slag and other impurities. At step 210, the ladle furnace heats the steel and performs additional refining processes, such as adding alloying elements, de-oxidation, and inclusion control. These processes fine-tune the steel's chemical composition and properties to meet the desired specifications. Further, at step 212, the molten steel is then transferred to a continuous casting machine, where it is solidified into slabs, blooms, or billets. These semi-finished products are then rolled into various shapes, such as sheets, plates, bars and wires.

[0032] In one embodiment herein, the Si/Mn/Al killed steel making process, steel is deoxidized with Si, Mn and Al. During taping steel into ladle SiMn, FeSi and Al additions are done in the ladle along with lime. The ladle is further transferred to LF and slag killing is done using Al lumps. Average composition of Al-Killed steel grades is given in Table 1.

[0033] Table 1:
Steel grade Chemical composition (wt %)
C Mn P(max) S(max) Si Cr Al
Al-killed steel 0.10-0.45 0.40-0.90 0.035 0.035 0.3 max 0.05 max 0.02 min

[0034] In the Si/Mn Killed steel making process, steel is deoxidized with Si and Mn. SiMn and FeSi and calcium aluminate based flux additions are carried out during taping steel into ladle. The calcium aluminate based flux consists of Al2O3 and CaO as major constituents almost similar to slag obtained from Si/Mn/Al-killed steel making process. Average composition of high carbon Si-Killed steel grades is given in Table 2.

[0035] Table 2:
Steel grade Chemical composition (wt %)
C Mn P(max) S(max) SI Cr Al
High Carbon
Si-killed steel 0.50-0.85 0.40-0.90 0.035 0.035 0.15-0.35 0.06-0.30 0.02 max

[0036] The Si/Mn/Al killed LF slag has CaO and Al2O3 as major constituents whereas Si/Mn- Killed LF slag has CaO and SiO2 as major constituents. After finish of casting, the left over slag in the ladle which is around 2-3 tons is dumped into slag containers or slag pot. This slag undergoes phase transformation during cooling which is accompanied by 14 percent of volume expansion. This phenomenon leads to disintegration of slag (as shown in Fig 3A). The disintegrated slag is very difficult to handle and store which decreases its valorisation potential. This also leads to environment pollution as the powdered slag gets dispersed in air.

[0037] According to another exemplary embodiment of the invention, FIG. 3A refers to a pictorial representation 302 of the disintegrated aluminium-killed ladle furnace slag. In one embodiment herein, the Disintegration of LF slags can be prevented either by modifying the chemical composition of slag or by suppressing the C2S phase transformation. B2O3 sources stabilize high temperature polymorphs of pure C2S by forming solid solution, which results in stable Ca11B2Si2O4 compound. Boron containing minerals like borax, kernite, colemanite can be used to stabilize LF slag. H3BO3 addition helps in preventing slag disintegration and also decreases slag melting point, which helps in recycling of Si/Mn/Al-Killed LF slag as an effective fluxing material.

[0038] The B2O3 addition helps in lowering the viscosity of slag which helps in eliminating the sticking of slag to ladle cover during refining. Firstly, the low melting temperature of B2O3, which is about 450°C, is favourable for the high melting temperature components such as CaO and Al2O3 fusing into slag, so the melting temperature of system is decreased. At the same time, B2O3 may combine with various oxides of slag to form eutectics such as MgO.B2O3, (melting temperature 988°C, CaO.B2O3 (melting temperature 1100°C) and so on. Because the melting temperatures of these eutectics are low, the forming of eutectics is also favourable for decreasing the melting temperature of slag.

[0039] According to another exemplary embodiment of the invention, FIG. 3B refers to a pictorial representation 104 of the Si/Mn/Al-killed ladle furnace slag obtained after stabilising with addition of boric acid. In one embodiment herein, the B2O3 addition at the industrial scale are assuming 2-3 tons of LF slag per heat. In one example embodiment herein, the method for stabilising Si/Mn/Al-Killed LF slag with H3BO3 industrial scale. After refining is completed at LF, around 20-40 kg of H3BO3 (1-2 weight percent of LF slag) is added in the ladle. The properties of H3BO3 are shown in Table 3. Mild rinsing of steel is required at this step for better mixing of H3BO3 into slag. The ladle is then transferred to caster for casting of steel. The left over slag in ladle which is around 2-3 tons is dumped into slag containers after finish of casting. The cooled slag undergoes crushing and sizing, with crushed slag typically collected at a size range of 30-40 mm. This crushed slag is then recycled to prepare low melting flux.

[0040] Table 3:
B2O3 (wt %) H2O (wt %) Density (g/cm3) Melting point
(°C) Appearance white Packing
56 44 1.435 170.9 crystals 10 kg bags

[0041] In one embodiment herein, the Table 3 depicts properties and composition of H3BO3 (boric acid). In one example embodiment herein, the method for stabilising Si/Mn/Al-Killed LF slag with H3BO3 industrial scale. After refining of steel is finished at LF, the ladle is transferred to continuous caster for casting of steel. The left over LF slag in the ladle after finish of casting is dumped into slag container / slag pot filled with 20-40 kg of H3BO3. The slag is then allowed to air cool and the cooled slag is crushed and sized for further use. After the Si/Mn/Al-Killed LF slag is stabilised, the cooled slag is crushed and sized. Slag of 30-50 mm size is used for treating high carbon Si-Killed steels along with lime and calcined bauxite as additives.

[0042] In one embodiment herein, the industrial trials with low melting flux prepared from Si/Mn/Al-Killed LF slag for treating Si/Mn-killed steel. The proposed recycled Si/Mn/Al killed slag for treating Si/Mn killed steel. Recycled LF slag, lime and CaO-Al2O3 based synthetic slag additions are carried out in various proportions. The composition of CaO-Al2O3 based synthetic slag as depicted in table 4. The composition of lime as shown in table 5.

[0043] Table 4:
Chemical composition (wt %)
CaO MgO SiO2 Al2O3 FeO MnO S
34-38 6-8 5 41-45 <1 <1 <0.5

[0044] In one embodiment herein, the Table 4 depicts composition of CaO- Al2O3 based synthetic slag in weight percent.

[0045] Table 5:
Chemical composition (wt %)
CaO SiO2 LOI
89 1 6

[0046] In one embodiment herein, the Table 5 depicts the composition of lime in weight percent with CaO and SiO2.

[0047] Table 6:
CaO MgO SiO2 Al2O3 FeO MnO S
50-55 10-12 12-15 16-25 <1 <1 <0.5

[0048] In one embodiment herein, the Table 6 depicts the composition of Si/Mn/Al killed LF slag in weight percent. The recycled Si/Mn/Al killed LF slag has Mayenite (Ca12Al14O33), Merwinite (Ca3MgSi2O8), ß-dicalcium silicate (Ca2SiO4) as major mineralogical phases. Average composition of Si/Mn/Al killed LF slag is depicted in Table 6.

[0049] Table 7:
Chemical composition (wt %)
Al2O3 Fe2O3 TiO2
>85 <2 <4

[0050] In one embodiment herein, the Table 7 depicts composition of calcined bauxite in weight percent.

[0051] According to another exemplary embodiment of the invention, FIG. 4 refers to a flowchart 402 of Si/Mn/Al-killed LF slag recycling at industrial scale. In one example embodiment herein, the Si/Mn/Al-killed steel making process, slag which is leftover in the ladle after finish of casting is dumped into slag containers / slag pot. The slag is allowed to cool. This slag disintegrates into fine powder during cooling. The disintegrated slag is collected in 50 kg bags for further recycling. Typical composition of slag collected for the trials consists of 55 percentage of CaO, 11 percentage of MgO, 14 percentage of SiO2, 16 percentage of Al2O3, 0.64 percentage of FeO, 0.56 percentage of TiO2, 0.72 percentage of MnO, 0.23 percentage of P2O5, 0.15 percentage of S. The industrial trials were carried out in high carbon Si-Killed heats using this slag. Around 1.3 to 1.4 tons of flux addition was carried out during tapping steel into the ladle.

[0052] The flux consisted of 60 to 85 percentage of recycled LF slag and 15-38 percentage of CaO-Al2O3 based synthetic slag. The prepared flux used in the present method consists of 45 to 48 percentage of CaO, 8-9 percentage of MgO, 7-9 percentage of SiO2, 25-30 percentage of Al2O3 in weight percentage as major constituents. 100 to 200 kg of Fe-Si and 1500 to 1900 3000 kg of Si-Mn were added during tapping along with 1.3 to 1.4 tons of prepared flux. Addition of extra lime was carried out in LF based on sulphur content of steel at LF entry.

[0053] In another example Si/Mn/Al-killed Ladle furnace slag which is leftover in the ladle after finish of casting is dumped into slag containers. The slag is allowed to cool. This slag disintegrates into fine powder during cooling. The disintegrated slag is collected in 50 kg bags for further recycling. Typical composition of slag collected for the trials consists of 48 percent of CaO, 13 percent of MgO, 12 percent of SiO2, 22 percent of Al2O3, 0.64 percent of FeO, 0.68 percent of TiO2, 0.64 percent of MnO, 0.22 percent of P2O5, and 0.35 percent of S. Industrial trial was carried out in high carbon Si-Killed heat using this slag. Around 1-1.5 tons of flux addition was carried out during tapping steel into ladle.

[0054] The flux consisted of 46 percent of recycled Si/Mn/Al killed LF slag, 26 percent of Lime and 27 percent of calcined bauxite. The prepared flux used in present method consists of 45 percent of CaO, 5 percent of MgO, 6 percent of SiO2 and 34 percent of Al2O3 in weight percent of as major constituents. 100-200 kg of Fe-Si and 1500-1900 kg of Si-Mn were added during tapping along with 1-1.5 tons of prepared flux. Addition of extra lime was carried out in LF based on sulphur content of steel at LF entry.

[0055] In another example embodiment herein, the Si/Mn/Al killed LF slag stabilized with any of the methods. Typical composition of Si/Mn/Al-Killed LF slag used consists of 48 percentage of CaO, 13 percentage of MgO, 12 percentage of SiO2, 22 percentage of Al2O3, 0.64 percentage of FeO, 0.68 percentage of TiO2, 0.64 percentage of MnO, 0.22 percentage of P2O5, and 0.35 percentage of S. Industrial trials were carried out in high carbon Si-Killed heats using slag obtained from Al-killed steel making process. Around 1.25 tons of flux addition was carried out during tapping steel into the ladle.

[0056] The flux consisted of 46 percentage of Recycled Si/Mn/Al-Killed LF slag (stabilized with H3BO3), 38 percentage of lime and 15 percent of calcined bauxite. The flux consisted of 55 percentage of CaO, 5 percentage of MgO, 5 percentage of SiO2 and 24 percentage of Al2O3 in weight percentage of 100-200 kg of Fe-Si and 1500-1900 kg of Si-Mn were added during tapping based on steel composition. Addition of extra lime was carried out in LF based on sulphur content of steel at LF entry.

[0057] The slag and steel samples were collected during ladle treatment corresponding to the two main steps of the secondary refining operation. The first sampling was done after alloying and flux additions i.e., before start of LF treatment. The second sampling was done at the end of the final stirring and heating period in LF slag. The temperature of the molten steel was measured during each sampling. Both the temperature measurements and the steel samples were taken using the automatic sampling equipment at the LF station. Slag samples were collected manually with a slag spoon. The composition of each sample was analysed separately.

[0058] Table 8:
Example No. % of additive in flux mixture Total weight of flux (tons) Chemical composition of flux used (wt %)
Si/Mn/Al-killed LF slag Si/Mn/Al-killed LF slag stabilized with B2O3 Lime Bauxite CaO-Al2O3 based flux CaO MgO SiO2 Al2O3
1 61.5 - - - 38.4 1.3 45.4 8.5 7.7 30.8
2 46.6 - 26 26.6 - 1.45 44.9 4.8 5.9 33.8
3 - 46.6 38 15.3 - 1.25 54.6 4.8 5.4 24.2

[0059] In one embodiment herein, the Table 8 depicts the composition of low-melting flux prepared in various methods.

[0060] Table 9:
Examples Position Chemical composition of slag (wt %)
CaO MgO SiO2 Al2O3 FeO MnO TiO2 S
1 LF entry 43.24 11.85 22.35 12.83 3.76 3.54 1.23 0.16
LF exit 49.23 11.11 26.71 9.43 0.79 0.83 0.82 0.28
2 LF entry 46.75 12.82 16.01 18.26 2.15 1.64 1.19 0.23
LF exit 43.26 12.95 17.81 21.4 1.35 0.99 1.5 0.28
3 LF entry 48.35 13.6 20.42 10.74 1.91 2.66 0.87 0.2
LF exit 49.94 12.71 21.39 11.22 1.11 1.21 0.71 0.5

[0061] In one embodiment herein, the Table. 9 depicts the chemical composition of slags before and after LF treatment in weight percent.

[0062] Table 10:
Parameter Example 1 Example 2 Example 3
CaO/Al2O3 5.2 2.02 4.44
CaO/SiO2 1.93 2.9 2.36
Optical basicity 0.72 0.72 0.74
ERO (FeO+MnO) 1.62 2.34 2.32
LS=(S)/[S] 109 15 20

[0063] In one embodiment herein, the Table. 10 depicts the comparison of various parameters for different methods of LF slag recycling.

[0064] Table 11:
CaO
(%) SiO2
(%) Al2O3
(%) MgO
(%) FeO+ MnO
(%) S (%) H3BO3
(%) Melting Point (°C)
44-54 5-9 25-35 4-10 2 max 0.5 max 0-4 1370-1400

[0065] In one embodiment herein, the Table, 11 depicts the Average composition of Fluxes prepared from Al-Killed LF slag, calcined bauxite and weight percent of H3BO3.

[0066] According to another exemplary embodiment of the invention, FIG. 5 refers to a pictorial representation 502 of process for preparing low-melting ladle flux with recycled stabilized ladle furnace slag. In one embodiment herein, the steel production process involving the BOF and ladle furnace (LF). In one embodiment herein, the basic oxygen furnace is a large, pear-shaped vessel lined with refractory bricks. The oxygen is injected into the molten metal through a lance at the top of the vessel. The chemical reactions that take place in the BOF process floats on top of the molten steel and feed off separately. In one embodiment herein, the ladle is a smaller vessel than the BOF and is also lined with refractory bricks. The ladle furnace can be used for a variety of purposes, such as, alloying, desulphurisation and temperature control.

[0067] In one embodiment herein, the Si/Mn/Al killed ladle slag is a by-product from the steelmaking and consists mainly of oxides of iron, calcium, silicon, and manganese. The Si/Mn/Al killed ladle ladle slag can be modified by adding various materials, such as H3BO3, to improve its properties or to make it more suitable for recycling. The ladle slag is being dumped into a slag pot, where it will solidify and be crushed for further processing or disposal. The Si/Mn/Al killed ladle ladle slag contain high amount of CaO and Al2O3 as major constituents.

[0068] After finishing of casting the leftover slag in the ladle is dumped into slag containers / slag pot. The slag undergoes phase transformation during cooling which is accompanied by 14 percent of volume expansion. This phenomenon leads to disintegration of slag (as shown in Fig. 2). The disintegrated slag is very difficult to handle and store which decreases its valorisation potential. This also leads to environment pollution as the powdered slag gets dispersed in air.

[0069] In one embodiment herein, the disintegration of the Si/Mn/Al killed ladle LF slags can be prevented either by modifying the chemical composition of slag or by suppressing the C2S phase transformation. B2O3 sources stabilize high temperature polymorphs of pure C2S by forming solid solution, which results in stable Ca11B2Si2O4 compound. Boron containing minerals like borax, kernite, colemanite can be used to stabilize LF slag. H3BO3 addition helps in preventing slag disintegration and also decreases slag melting point, which helps in recycling Si/Mn/Al-Killed LF slag as effective fluxing material.

[0070] The addition of boric acid assists in lowering the viscosity of slag which helps in eliminating the sticking of slag to ladle cover during refining. First, the low melting temperature of B2O3, which is about 450°C that is favourable for the high melting temperature components such as CaO and Al2O3 fusing into slag, so the melting temperature of system is decreased. At the same time, B2O3 may combine with various oxides of slag to form eutectics such as MgO.B2O3, (melting temperature 988oC, CaO). B2O3 (melting temperature 1100°C) and so on. Because the melting temperatures of these eutectics are low, the forming of eutectics is also favourable for decreasing the melting temperature of slag.

[0071] In one embodiment herein, the crumbled the Si/Mn/Al killed LF slag is stabilised with the boric acid, thereby reducing the melting point of slag. The stabilised LF slag is crushed and sized for preparing low melting flux. The prepared recycled LF slag is produced from 45 to 55 percentage of calcium oxide (CaO), 18 to 25 percentage of Al2O3, 6 to 12 percentage of silicon dioxide (SiO2), 8 to 12 percentage of magnesium oxide (MgO), 0 to 0.5 percentage of sulfur, and 0 to 2 percentage of iron manganese oxide (FeO+MnO).

[0072] Numerous advantages of the present disclosure may be apparent from the discussion above. In accordance with the present disclosure, a method for preparing low-melting ladle flux with recycled stabilized ladle furnace slag is disclosed. The proposed invention provides the method that reduces synthetic slag addition, resulting in cost saving.

[0073] The proposed invention provides the method that significantly improves slag fluidity, thereby reducing the need for synthetic slag. The proposed invention provides the method that minimises slag disintegration and reduces melting of slag simultaneous increasing the Si/Mn/Al killed ladle slag valorisation.

[0074] It will readily be apparent that numerous modifications and alterations can be made to the processes described in the foregoing examples without departing from the principles underlying the invention, and all such modifications and alterations are intended to be embraced by this application.
, Claims:CLAIMS:
I/We Claim:
1. A method for preparing low-melting ladle flux for treating Si/Mn-killed steels, comprising:
processing steel from a basic oxygen furnace (BOF) route and feeding the steel into a ladle for secondary metallurgical operations;
adding plurality of Ferro alloys, aluminium and ladle fluxes according to the grade of steel;
processing the steel in a ladle furnace for desulfurization and inclusion absorption, thereby homogenizing a steel composition and maintains steel temperature required for smooth casting;
deoxidizing the steel before casting by adding iron monosilicide (FeSi), silicon manganese (SiMn), and slag modification;
stabilising the ladle slag by adding boric acid (H3BO3), thereby preventing the disintegration of ladle slag into a fine powder and reducing the melting point of slag;
obtaining ladle slag in the ladle poured into a slag container after completion of casting, and the obtained ladle slag is stabilized; and
preparing low-melting ladle flux by crushing and sizing the stabilised ladle slag to 30 to 40 mm in size and treating Si-killed steels.
2. The method as claimed in claim 1, wherein the low melting ladle flux is prepared with a mixture of 40 to 60 percentage of Si/Mn/Al killed ladle slag, 20 to 30 percentage of lime, 0 to 30 percentage of calcined bauxite (Al2O3), and 0 to 4 weight percentage of boric acid.
3. The method as claimed in claim 2, wherein the ladle slag is obtained in the final stages of the steelmaking process, when the steel is desulfurized in the transport ladle and ladle slag is Si/Mn/Al-killed steel.
4. The method as claimed in claim 1, wherein the obtained ladle slag from the Si/Mn/Al-Killed steel making process include about 45 to 55 percentage of calcium oxide (CaO), 18 to 25 percentage of Al2O3, 6 to 12 percentage of silicon dioxide (SiO2), 8 to 12 percentage of magnesium oxide (MgO), 0 to 0.5 percentage of sulfur, and 0 to 2 percentage of iron manganese oxide (FeO+MnO).
5. The method as claimed in claim 1, wherein the prepared low melting ladle flux improves slag fluidity drastically, thereby reducing synthetic slag addition, results in a reduction in steel production costs.
6. The method as claimed in claim 1, wherein the plurality of Ferro alloys include Fe-Si, Si-Mn.
7. The method as claimed in claim 1, wherein the ladle fluxes include lime, Si/Mn/Al killed ladle slag with and without stabilization with H3BO3, calcined bauxite and synthetic slag.