TECHNICAL FIELD

[0001] The present disclosure relates generally to the technical field of ferrous metallurgy. In particular, the present disclosure pertains to an improved method for production of low oxygen quality rail steels.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Increase in train speeds and loading have made railway transportation more efficient. However, this increase in speed and loading also means more arduous duty conditions for the rails, and further improvements in rail material properties are required to make them more tolerant and resistant to the increased stresses and stress cycles imposed.
[0004] Production of rail steels requires very strict control on input materials, de-oxidation practice, ladle top slag chemistry, and secondary refining. Customers requirement for high quality rail steel is continuously increasing, which meant fewer impurities, more cleanliness (lower inclusion content), more stringent quality steel (less variation of quality from cast to cast) and better surface quality as well as homogeneity. Quality requirement of the rail steel is becoming more and more stringent especially with respect to total oxygen content of about 20 ppm in rail steel.
[0005] A conventional method for production of rail steels includes processing of the raw steel through basic oxygen furnace (BOF) – ladle furnace (LF) - Ruhrstahl Heraeus degassing (RH) – continuous casting (CC) route to meet end quality requirements of high quality rail steels. The typical process for slag de-oxidation in the conventional method is leading to more than 20 ppm total oxygen content in rail steel against requirement of less than or equal to 20 ppm total oxygen content in the rail steel.
[0006] There is, therefore a need in the art to provide a simple, efficient and cost effective method for production of low oxygen steels. Further, there exists a need to method of production of low oxygen rail steels which can overcome the above stated problem.
[0007] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0008] In some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[0009] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0010] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

OBJECTS OF THE INVENTION
[0011] A general object of the present disclosure is to provide an improved method for production of low oxygen steel.
[0012] Another object of the present disclosure is to provide an improved method for production of low oxygen rail steels having total oxygen content less than or equal to 20 ppm.
[0013] Another object of the present disclosure is to provide a method for achieving low oxygen in Si-killed steels.
[0014] Another object of the present disclosure is to provide a simple and cost-effective method for production of low oxygen rail steels.

SUMMARY
[0015] The present disclosure provides a method for production of low oxygen rail steels, in particular it relates to a method for production of low oxygen steel to control total oxygen content in the steel up to a desired level.
[0016] In an aspect, the present disclosure provides a method for production of low oxygen steel comprising steps of: charging input steel material into a furnace for primary refining of the input steel material with respect to carbon, phosphorous and sulfur in a molten steel form; and adding a slag de-oxidiser in the molten steel, wherein the addition of the slag de-oxidiser control total oxygen content in the molten steel up to a desired level.
[0017] In an embodiment, addition of the slag de-oxidiser in the molten steel reduces oxygen content in top slag of the molten steel.
[0018] In an aspect, the slag de-oxidiser is a mixture of predetermined composition of coke and ferro-silicon (FeSi) fines. In an embodiment, addition of the slag de-oxidiser enables controlling of total oxygen content in the molten steel about 20 ppm.
[0019] In an embodiment, the input steel material can be a combination of scrap and hot metal.
[0020] In another aspect, the present disclosure provides a method for production of low oxygen steel, the method comprising steps of: charging input steel material into a furnace for primary refining of input steel material with respect to carbon (C), phosphorous (P) and sulfur (S); blowing oxygen on the molten steel for reducing carbon and phosphorous content in the molten steel; adding a flux into the molten steel material, and tapping the molten steel material in a pre-heated ladle along with de-oxidiser and ferro-alloy; adding a slag de-oxidiser in the molten steel in the ladle; and refining the molten steel using a ladle furnace; and degassing the molten steel using a degasser for removing the dissolved gases from the molten steel, wherein the addition of the slag de-oxidiser control total oxygen content in the molten steel up to a desired level.
[0021] In an embodiment, the de-oxidiser can be any of a ferro-silicon and silicon manganese. In an embodiment, the ferro-alloy can be high carbon ferro-manganese.
[0022] In an aspect, the slag de-oxidiser is a mixture predetermined composition of coke and FeSi fines.
[0023] In an aspect, the method can include a step of Calcium Silicon (CaSi) treatment of the molten steel.
[0024] In an aspect, the method can include a step of argon shrouding of degassed steel during continuous casting of the degassed steel.
[0025] In an embodiment, addition of the slag de-oxidiser in the molten steel reduces oxygen content in top slag of the molten steel. In an embodiment, addition of the slag de-oxidiser effects controlling of total oxygen content in the molten steel about 20 ppm.
[0026] In an embodiment, addition the flux, and the ferro-alloy is performed to achieve chemistry close to the required specification.
[0027] In an embodiment, the flux is selected from any or a combination of calcined bauxite, calcined dolomite and a burnt lime (CaO).
[0028] In an embodiment, blowing of the oxygen is performed for about 16 to 20 minutes. In an embodiment, blowing of the oxygen effect raising temperature of the molten steel material about 1650 0C to 1680 0C.
[0029] In an embodiment, refining the molten steel can include any or a combination of a temperature adjustment, a chemical composition adjustment, a desulphurisation and inclusion flotation.
[0030] In an embodiment, addition of the mixture of the coke and FeSi fines, CaSi treatment of steel, and ladle to tundish argon shrouding during continuous casting improve the internal quality of the steel with respect to total oxygen level.
[0031] In an embodiment, the furnace is a basic oxygen furnace (BOF).
[0032] Those skilled in the art will further appreciate the advantages and superior features of the disclosure together with other important aspects thereof on reading the detailed description that follows in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0034] FIG. 1 illustrates an exemplary representation of the proposed method for production of low oxygen steel, in accordance with an embodiment of the present disclosure.
[0035] FIG. 2 illustrates an exemplary representation of a method flow diagram for production of low oxygen steel, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0036] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such details as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0037] If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[0038] Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. This disclosure may however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the disclosure to those of ordinary skill in the art. Moreover, all statements herein reciting embodiments of the disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure).
[0039] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0040] Embodiments explained herein relate to a method for production of low oxygen rail steels, in particular it relates to a method for production of low oxygen steel to control total oxygen content in the steel up to a desired level.
[0041] In an aspect, the present disclosure provides a method for production of low oxygen steel can include steps of: charging input steel material into a furnace for primary refining of input steel material with respect to carbon (C), phosphorous (P) and sulfur (S) in a molten steel form; and adding a slag de-oxidiser in the molten steel, wherein the addition of the slag de-oxidiser control total oxygen content in the molten steel up to a desired level.
[0042] In an embodiment, addition of the slag de-oxidiser in the molten steel can reduce oxygen content in top slag of the molten steel.
[0043] In an aspect, the slag de-oxidiser is a mixture predetermined composition of coke and FeSi fines. In an embodiment, addition of the slag de-oxidiser can enable controlling of total oxygen content in the molten steel less than or equal to 20 ppm.
[0044] In another aspect, the present disclosure provides a method for production of low oxygen steel, the method can include steps of: charging input steel material into a furnace for primary refining of input steel material with respect to carbon, phosphorous and sulfur in a molten steel form ; blowing oxygen on the molten steel for reducing carbon and phosphorous content in the molten steel; adding a flux into the molten steel, and tapping the molten steel in a pre-heated ladle along with addition of deoxidiser and ferro-alloy in the molten steel; adding a slag de-oxidiser in the molten steel in the ladle; and refining the molten steel using a ladle furnace; and degassing the molten steel using a degasser for removing the dissolved gases from the molten steel, wherein the addition of the slag de-oxidiser control total oxygen content in the molten steel up to a desired level.
[0045] In an embodiment, the de-oxidiser can be any of a ferro-silicon and silicon manganese. In an embodiment, the ferro-alloy can be high carbon ferro-manganese.
[0046] In an aspect, the slag de-oxidiser is a mixture predetermined composition of coke and FeSi fines.
[0047] In an embodiment, the method can include a step of calcium Silicon treatment of the molten steel.
[0048] In an embodiment, the method can include a step of argon shrouding of degassed steel during continuous casting of the degassed steel.
[0049] In an embodiment, addition of the slag de-oxidiser in the molten steel reduces total oxygen content in top slag of the molten steel. In an embodiment, addition of the slag de-oxidiser effects controlling of total oxygen content in the molten steel about 20 ppm.
[0050] In an embodiment, addition a flux, and a ferro-alloy is performed to achieve chemistry close to the required specification.
[0051] In an embodiment, the flux is selected from any or a combination of a calcined bauxite, calcined dolomite and a burnt lime (CaO).
[0052] In an embodiment, blowing of the oxygen is performed for about 16 to 20 minutes. In an embodiment, blowing of the oxygen effect raising temperature of the molten steel material about 1650 0C to 1680 0C.
[0053] In an embodiment, refining the molten steel can include any or a combination of a temperature adjustment, a chemical composition adjustment, a desulphurisation and inclusion flotation.
[0054] In an embodiment, the furnace is a basic oxygen furnace (BOF).
[0055] FIG. 1 illustrates an exemplary representation of the proposed method for production of low oxygen steel. In an embodiment, the proposed method 100 comprising at a step 102, charging input steel material into a furnace for primary refining of input steel material with respect to carbon, phosphorous and sulfur in a molten steel form. In an embodiment, the input steel material can be a combination of scrap and hot metal.
[0056] In an embodiment, the furnace is a basic oxygen furnace.
[0057] In an embodiment, the proposed method 100 can include at a step 104, adding a slag de-oxidiser in the molten steel. In an embodiment, addition of the slag de-oxidiser control total oxygen content in the molten steel up to a desired level. In an embodiment, the slag de-oxidiser is a mixture predetermined composition of coke and ferro-silicon (FeSi) fines.
[0058] In an embodiment, addition of the slag de-oxidiser in the molten steel reduces total oxygen content in the molten steel about 20 ppm.
[0059] FIG. 2 illustrates an exemplary representation of a method flow diagram for production of low oxygen steel, in accordance with an embodiment of the present disclosure. The disclosed method 200 can include at a step 202, charging input steel material into a BOF for primary refining of input steel material with respect to carbon, phosphorous and sulfur in a molten steel form. In an embodiment, the input steel material can be a combination of scrap and hot metal.
[0060] In an embodiment, the disclosed method 200 can include at a step 204, blowing oxygen on the molten steel for reducing carbon and phosphorous content in the molten steel. In an embodiment, blowing of the oxygen is performed for about 16 to 20 minutes. Blowing of the oxygen can effect raising temperature of the molten steel material about 1650 0C to 1680 0C.
[0061] In an embodiment, the disclosed method 200 can include at a step 206, adding a flux into the molten steel material, and tapping the molten steel material in a ladle along with addition of deoxidizer and ferro-alloy in the molten steel. In an embodiment, addition the flux, and the ferro-alloy is performed to achieve chemistry close to the required specification. In an embodiment, the ladle can be a preheated steel ladle.
[0062] In an embodiment, the de-oxidiser can be any of a ferro-silicon and silicon manganese. In an embodiment, the ferro-alloy can be high carbon ferro-manganese.
[0063] In an embodiment, the flux can be selected from any or a combination of a calcined bauxite, calcined dolomite and a burnt lime (CaO).
[0064] In an embodiment, the disclosed method 200 can include at a step 208, adding a slag de-oxidiser in the molten steel in the ladle. In an embodiment, the disclosed method 200 can include at a step 210, refining the molten steel using a ladle furnace.
[0065] In an embodiment, at the step 210, refining of the molten steel can include any or a combination of a temperature adjustment, a chemical composition adjustment, a desulphurisation, inclusion flotation and the like.
[0066] In an embodiment, the disclosed method 200 can include at a step 212, degassing the molten steel using a degasser for removing the dissolved gases from the molten steel. In an embodiment, the degasser can be a R-H degasser.
[0067] In an embodiment, at the step 208, addition of the slag de-oxidiser control total oxygen content in the molten steel up to a desired level. In an embodiment, the slag de-oxidiser is a mixture of predetermined composition of coke and ferro-silicon (FeSi) fines. Addition of the slag de-oxidiser in the molten steel reduces oxygen content in top slag of the molten steel.
[0068] In an embodiment, addition of the slag de-oxidiser can enable controlling of total oxygen content in the molten steel about 20 ppm.
[0069] In an embodiment, the method 200 can include a step of calcium Silicon treatment of the steel.
[0070] In an embodiment, the method 200 can further include a step of argon shrouding of degassed steel during continuous casting of the degassed steel.
[0071] In an embodiment, addition of the mixture of the coke and FeSi fines, CaSi treatment of steel, and ladle to tundish argon shrouding during continuous casting improve the internal quality of the steel with respect to total oxygen level.
[0072] In an embodiment, the proposed method 200 can be used for production of rail steels having total oxygen content of about 20 ppm.
[0073] Comparison of total oxygen level in steel produced by a conventional method and the proposed method.
[0074] Conventional Method,
[0075] Example 1, in an exemplary embodiment, a conventional method for production of steel include processing of the input material through basic oxygen furnace (BOF)- ladle furnace (LF) - Ruhrstahl Heraeus degassing (RH) – continuous casting (CC) route to meet end quality requirements of high quality steel. The conventional process for slag de-oxidation is leading to total oxygen content higher than 20 ppm in the steel. In an exemplary experiment, slag and metal samples were collected at different stages of steel refining and continuous casting i.e. ladle furnace IN (LF IN), ladle furnace out (LF OUT), Ruhrstahl Heraeus degasser out (R-H OUT), and tundish (TND) for mapping of oxygen level of slag and steel material. The oxygen potential of slag and the steel material was analysed to find out the critical process parameters responsible for high total oxygen level in the rail steel.
[0076] The analysis of ladle top slags revealed that slag oxygen potential (FeO+MnO) was on higher side (LF OUT- 7.23% & R-H OUT – 5.55%) even after final refining in R-H degasser which transfers oxygen to steel during casting operation as shown in Table-1.
[0077] The analysis of metal samples for total oxygen at different stages of refining and casting also indicates total oxygen content higher than 20 ppm at R-H out stage and oxygen pickup during continuous casting operation as shown in table Table-2.
[0078] Table-1: Details of ladle top slag analysis at various stages of steel refining.
Table-1

[0079] Table-2: Details of total oxygen at various stages of steel refining and casting.
Table-2

[0080] The analysis of base period data revealed that process parameters or their combination responsible for total oxygen content higher than 20 ppm in the steel may be because of use of aluminium for partial de-oxidation of metal and slag, absence of proper slag de-oxidation practice, improper steel refining, and absence of ladle to tundish argon shrouding system in casters.
[0081] Proposed method,
[0082] Example-2, in an exemplary embodiment, to control total oxygen content in rail steel below 20 ppm, addition of a slag de-oxidiser that is a mixture of coke and FeSi fines in the molten steel before refining in the ladle furnace, CaSi treatment of steel, and argon shrouding during continuous casting for processing of the steel is performed. The analysis of ladle top slag at LF Out and R-H out stage is shown in Table 3. This helped to control oxide inclusions in liquid steel and further pickup of oxygen from slag during casting. The results of the trials showed significant reduction in slag oxygen potential level of ladle top slag and reduction in total oxygen content less than 20 ppm at different stages of steel refining, and casting. The changing of slag de-oxidiser (also referred to as slag de-oxidation particle) and ladle to tundish argon shrouding greatly helped to improve the internal quality of steel with respect to total oxygen level less than 20 ppm as shown in table 4.
[0083] Table-3: Analysis of ladle top slag at LF/VAD out and R-H Out stage.
Table-3

[0084] Table-4: Total oxygen level at different stages of steel processing.
Table-4

[0085] It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C ….and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc. The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.
[0086] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION
[0087] The present disclosure provides an improved method for production of low oxygen steel.
[0088] Another object of the present disclosure is to provide an improved method for production of low oxygen rail steels having total oxygen content less than or equal to 20 ppm.
[0089] The present disclosure provides a method for achieving low oxygen in Si-killed steels.
[0090] The present disclosure provides a simple and cost-effective method for production of low oxygen rail steels.

Claims:

1. A method for production of low oxygen steel, the method comprising steps of:
charging input steel material into a furnace for primary refining of input steel material with respect to carbon, phosphorous and sulfur in a molten steel form ; and
adding a slag de-oxidiser in the molten steel,
wherein the addition of the slag de-oxidiser control total oxygen content in the molten steel up to a desired level, and
wherein the slag de-oxidiser is a mixture of coke and ferro-silicon (FeSi) fines.
2. The method as claimed in claim 1, wherein addition of the slag de-oxidiser in the molten steel reduces oxygen content in top slag of the molten steel material, and wherein addition of the slag de-oxidiser effects controlling of total oxygen content in the molten steel material about 20 ppm.
3. A method for production of low oxygen steel, the method comprising steps of:
charging input steel material into a furnace for primary refining of the input steel material with respect to carbon, phosphorous and sulfur in a molten steel form;
blowing oxygen on the molten steel for reducing carbon and phosphorous content in the molten steel;
adding a flux into the molten steel, and tapping the molten steel in a ladle along with addition of deoxidizer and ferro-alloy in the molten steel;
adding a slag de-oxidiser in the molten steel in the ladle;
refining the molten steel using a ladle furnace; and
degassing the molten steel using a degasser for removing the dissolved gases from the molten steel,
wherein the addition of the slag de-oxidiser control total oxygen content in the molten steel up to a desired level, and wherein the slag de-oxidiser is a mixture of coke and FeSi fines.
4. The method as claimed in claim 3, wherein the method comprising a step of Calcium Silicon (CaSi) treatment of the molten steel.
5. The method as claimed in claim 3, wherein the method comprising a step of argon shrouding of degassed steel during continuous casting of the degassed steel.
6. The method as claimed in claim 3, wherein addition of the slag de-oxidiser in the molten steel reduces oxygen content in ladle top slag of the molten steel, and wherein addition of the slag de-oxidiser effects controlling of total oxygen content in the molten steel about 20 ppm.
7. The method as claimed in claim 3, wherein addition the flux, and the ferro-alloy is performed to achieve chemistry close to the required specification, and wherein the flux is selected from any or a combination of a calcined bauxite, calcined dolomite and a burnt lime (CaO).
8. The method as claimed in claim 3, wherein blowing of the oxygen is performed for about 16 to 20 minutes, wherein blowing of the oxygen effect rising temperature of the molten steel about 1650 0C to 1680 0C.
9. The method as claimed in claim 3, wherein refining of the molten steel comprises any or a combination of a temperature adjustment, a chemical composition adjustment, a desulphurisation and inclusion flotation.
10. The method as claimed in claim 3, wherein the furnace is a basic oxygen furnace (BOF).