Claims:WE CLAIM:
1. A method for an electrolytic extraction of non-metallic inclusions (NMIs) from a steel substrate, comprising:
a. providing the steel substrate as an anode, providing a cathode comprising a metal and placing the anode and the cathode in an electrolyte comprising 10% (v/v) acetylacetone, 4% (v/v) tetramethylammonium chloride and 86% (v/v) methanol;
b. providing a current between the cathode and the anode, and throughout the duration of the current, stirring the electrolyte at about 250-350 rpm and maintaining the temperature of the electrolyte at about room temperature to obtain an electrolyte containing NMIs extracted from the steel substrate.
2. The method as claimed in claim 1, wherein the cathode comprises stainless steel or platinum.
3. The method as claimed in claim 1 or 2, wherein the current is between 1.5-2.5 A and is provided at a constant voltage of 9-13V.
4. The method as claimed in any one of claims 1-3, wherein the room temperature ranges from about 15-30?.
5. The method as claimed in any one of claims 1-4, wherein the method provides a current density of about 280-320 mA/mm2.
6. The method as claimed in any one of claims 1-5, wherein the electrolytic extraction of NMIs is completed in about 30 minutes.
7. The method as claimed in any one of claims 1-5, wherein the electrolyte containing extracted NMIs is filtered to collect the extracted NMIs on a filter paper followed by a three-dimensional analysis of the extracted NMIs by a scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).
8. The method as claimed in claim 7, wherein the filter paper comprises a cellulose membrane or a polycarbonate and has a pore size of about 0.5µm, 0.8 µm or 1 µm.
9. The method as claimed in claim 7 or 8, wherein filtration is carried out by applying vacuum.
10. The method as claimed in any one of claims 7-9, wherein the filter paper containing the extracted NMIs is sputtered for about 45-60 seconds prior to the three-dimensional analysis.
11. A system for an electrolytic extraction of non-metallic inclusions (NMIs) from a steel substrate, comprising:
a. an inert vessel comprising:
i. a cathode and the steel substrate as an anode in contact with an electrolyte, wherein the electrolyte comprises 10% (v/v) acetylacetone, 4% (v/v) tetramethylammonium chloride and 86% (v/v) methanol, and
ii. a stirrer and a temperature probe inserted in the electrolyte;
b. a power source connected to the cathode and the anode to provide current;
c. a cooling chamber or a cooling jacket surrounding the inert vessel; and
d. a cooling unit connected to the cooling chamber or cooling jacket to maintain the temperature of the electrolyte.
12. The system as claimed in claim 11, wherein the cathode comprises stainless steel or platinum.
, Description:TECHNICAL FIELD
The present disclosure relates to the field of steel manufacture. Particularly, the present disclosure relates to a method for an electrolytic extraction of non-metallic inclusions (NMIs) from a steel substrate. The disclosure also relates to a system for an electrolytic extraction of non-metallic inclusions (NMIs) from a steel substrate.

BACKGROUND OF THE DISCLOSURE
One of the biggest challenges faced by steel makers across the globe is the production of high-quality steel with minimal impurities. Non-metallic inclusions (NMIs) are a major part of impurities formed during steel production and therefore controlling the same is crucial. The mechanical property of steel is adversely affected by the size, morphology, composition and the number of inclusions present in it.
Some NMIs are formed during steel refining process (e.g., Ladle Furnace (LF)/Ruhrstahl Heraeus (RH) process/CAS-OB (Composition Adjustment by Sealed Argon Bubbling – Oxygen Blowing)) while some exogenously get into the system (e.g., Refectory Erosion). Based on chemical composition, oxides, nitrides and sulphides are major types of inclusions in steel. Physical properties, chemistry and morphology of an inclusion depends a lot on the way steel is produced. Each station in steel making process i.e., BOF (Basic Oxygen Furnace), LF/RH, Caster and Rolling have a significant impact on inclusion generation and modification. Therefore, it is necessary to categorise different NMIs to understand their generation and accordingly take steps to reduce them in the final product.
There are different methods currently available to detect inclusions in a steel matrix of which the 2-D method or surface analysis method are mostly widely used. While these methods may help determine the composition and number of inclusions in steel, they are unable to detect the morphology and correct size of inclusions. In view of the same, they do not provide complete information on the inclusions. For determining the correct size and morphology of inclusions, 3-D method or volume analysis method is required. One way to get that information is the electrolytic extraction of inclusions from steel matrix. However, one of the major drawbacks of this method is the total time taken for completion. The presently available methods for electrolytic extraction of inclusions from steel matrix take around 4-5 hours. Thus, there is a need in the art to provide a method where electrolysis time is reduced substantially. The present disclosure attempts to address said need.
STATEMENT OF THE DISCLOSURE
The present disclosure relates to a method for an electrolytic extraction of non-metallic inclusions (NMIs) from a steel substrate, comprising: a) providing the steel substrate as an anode, providing a cathode comprising a metal and placing the anode and the cathode in an electrolyte comprising 10% (v/v) acetylacetone, 4% (v/v) tetramethylammonium chloride and 86% (v/v) methanol; and b) providing a current between the cathode and the anode, and throughout the duration of the current, stirring the electrolyte at about 250-350 rpm and maintaining the temperature of the electrolyte at about room temperature to obtain an electrolyte containing NMIs extracted from the steel substrate.

The present disclosure also relates to a system for an electrolytic extraction of non-metallic inclusions (NMIs) from a steel substrate, comprising: a) an inert vessel comprising: i) a cathode and the steel substrate as an anode in contact with an electrolyte, wherein the electrolyte comprises 10% (v/v) acetylacetone, 4% (v/v) tetramethylammonium chloride and 86% (v/v) methanol, and ii) a stirrer and a temperature probe inserted in the electrolyte; b) a power source connected to the cathode and the anode to provide current; c) a cooling chamber or a cooling jacket surrounding the inert vessel; and d) a cooling unit connected to the cooling chamber or cooling jacket to maintain the temperature of the electrolyte.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1 shows a schematic diagram (left panel) and an exemplary embodiment (right panel) of the stainless-steel sheet used as a cathode in the present disclosure.
Figure 2 shows a schematic diagram (left panel) and an exemplary embodiment (right panel) of a steel sample used as an anode from which Non-metallic Inclusions were extracted.
Figure 3 shows a schematic of the system for the electrolytic extraction according to one embodiment of the present disclosure.
Figure 4 shows an exemplary embodiment of the inert vessel containing the electrode assembly according to one embodiment of the present disclosure.
Figure 5 shows an exemplary embodiment of the system for the electrolytic extraction according to one embodiment of the present disclosure.
Figure 6 shows a schematic of filtration Assembly used to filter the electrolyte solution after electrolysis.
Figure 7 shows an exemplary embodiment of the filtration assembly used to filter the electrolyte solution after electrolysis.
Figure 8 shows the size, morphology and composition of non-metallic inclusions captured using SEM-EDS.
Figure 9 shows the size, morphology and composition of non-metallic inclusions captured using SEM-EDS.
Figure 10 shows the size, morphology and composition of non-metallic inclusions captured using SEM-EDS.
Figure 11 shows the size, morphology and composition of non-metallic inclusions captured using SEM-EDS.
Figure 12 shows the size, morphology and composition of non-metallic inclusions captured using SEM-EDS.
Figure 13 shows the size, morphology and composition of non-metallic inclusions captured using SEM-EDS.
Figure 14 shows the unextracted steel substrate analysed under the SEM (panel a), the steel substrate after extraction of NMIs using the present method (panel b), and the filter paper containing the extracted NMIs (panel c).

DETAILED DESCRIPTION OF THE DISCLOSURE
With respect to the use of any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results. Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising” or “containing” or “has” or “having” wherever used, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Reference throughout this specification to “some embodiments”, “one embodiment”, “an embodiment” or “a preferred embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases “in some embodiments”, “in one embodiment”, “in an embodiment” or “a preferred embodiment” in various places throughout this specification may not necessarily all refer to the same embodiment. It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The term “about” as used herein encompasses variations of +/-10% and more preferably +/-5%, as such variations are appropriate for practicing the present invention.

The terms “method” and “process” are used interchangeably throughout the present disclosure.

Method for Extraction of Non-Metallic inclusions (NMIs) from a Steel Substrate
The present disclosure provides a method for extraction of non-metallic inclusions (NMIs) from a steel substrate. The method of extraction of the present disclosure is broadly based on electrolysis.

In some embodiments, a method for an electrolytic extraction of non-metallic inclusions (NMIs) from a steel substrate, comprises: a) providing the steel substrate as an anode, providing a cathode comprising a metal and placing the anode and the cathode in an electrolyte comprising 10% (v/v) acetylacetone, 4% (v/v) tetramethylammonium chloride and 86% (v/v) methanol; and b) providing a current between the cathode and the anode, and throughout the duration of the current, stirring the electrolyte at about 250-350 rpm and maintaining the temperature of the electrolyte at about room temperature to obtain an electrolyte containing NMIs extracted from the steel substrate.

In some embodiments, the cathode may be any material which is inert and does not take part in any reaction occurring in the electrolytic solution. In some embodiments, the cathode is a metal selected from platinum or stainless steel. In an exemplary embodiment, the cathode is stainless steel.

In some embodiments of the present disclosure, current is applied for the electrolysis to start. In some embodiments, a constant voltage of about 9-13 V is applied between cathode and anode that provides a current of about 1.5-2.5A.

As charge flows into the circuit, Fe2+ ions from the anode (Steel sample) leave the steel matrix and get dissolved in the electrolyte. As this process continues, more Fe2+ ions get dissolved in the solution.
Fe =?Fe?^(2+)+ 2e^-
2CH_3 OH+2 e^-=2CH3O^-+ H_(2(g))?
As the process continues, inclusions which are present in the steel matrix also get detached and get dissolved in the solution.

The inventors unexpectedly and surprisingly found that if the electrolyte is stirred continuously and if the temperature of the electrolyte is kept low, the flow of ions between the anode and the cathode increases which enhances dissolution of steel in the electrolyte thereby reducing the electrolysis time and providing a quicker analysis of NMIs. With regard to the temperature of the electrolyte, when ions flow between the cathode and the anode, the temperature of the electrolyte increases which in turn hurdles the flow. Therefore, maintaining the electrolyte solution at a low temperature enhances dissolution of the steel sample in the electrolyte. Further, the specific electrolyte composition of the present disclosure increases the current through the circuit, which further reduces the total time taken to extract NMIs.

In some embodiments of the present disclosure, the electrolyte is kept in motion by stirring to constantly rotate the complete mixture. In some embodiments, the stirring is magnetic stirring. In some embodiments, the magnetic stirring is carried out at a speed of about 250-350 rpm such as about 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, or 350 rpm. In an exemplary embodiment, the magnetic stirring is carried out at a speed of about 300 rpm.

In some embodiments of the present disclosure, the electrolyte solution is maintained at a room temperature throughout the electrolysis process. In some embodiments, the room temperature ranges from about 15°C to 30°C, such as about 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30?. In some embodiments the temperature of the electrolyte is maintained using a cooling unit or chiller unit.

Once the desired amount of the steel sample is dissolved in the electrolyte solution, the process is stopped. The electrolyte solution at the end of the electrolysis contains NMIs extracted from the steel sample.

In some embodiments of the present disclosure, current is continuously monitored during the method and the current density calculated by measuring the dissolved area.

In some embodiments, the present method provides a high current density of about 280-320 mA/mm2, which in turn enables the method to be completed within about 30 minutes.

In some embodiments, the NMIs dissolved in the electrolyte solution are separated from the electrolytic solution. Separation is carried out using techniques selected from a group comprising filtration, magnetic particle separation, and centrifuge particle separation. In an exemplary embodiment of the present disclosure, separation of the NMIs is carried out by filtration.

In some embodiments, a filter paper of desired diameter and pore size is used for the filtration of NMIs. In some embodiments, the filter paper comprises a cellulose membrane or a polycarbonate and has a pore size of about 0.5µm, 0.8 µm or 1 µm.

In some embodiments of the present disclosure, the filtration is carried out by applying vacuum.

In some embodiments of the present disclosure, after collection of extracted inclusions on a filter paper, the filter paper containing the extracted NMIs is sputtered for about 45-60 seconds. In an exemplary embodiment, the filter paper containing the extracted NMIs is subjected to gold sputtering for 45-60 seconds to prepare the filter paper for SEM-EDS.

After sputtering, a three-dimensional analysis of the NMIs is carried out. For this purpose, a part of the paper is cut and observed under Scanning Electron Microscope (SEM) and with Energy Dispersive Spectroscopy (EDS). This generates a complete data of the NMIs including size, composition, morphology and number of inclusions.

The present disclosure also provides a system for an electrolytic extraction of non-metallic inclusions (NMIs) from a steel substrate.

In some embodiments, the system comprises: a) an inert vessel comprising: i) a cathode and the steel substrate as an anode in contact with an electrolyte, wherein the electrolyte comprises 10% (v/v) acetylacetone, 4% (v/v) tetramethylammonium chloride and 86% (v/v) methanol, and ii) a stirrer and a temperature probe inserted in the electrolyte; b) a power source connected to the cathode and the anode to provide current; c) a cooling chamber or a cooling jacket surrounding the inert vessel; and d) a cooling unit connected to the cooling chamber or cooling jacket to maintain the temperature of the electrolyte.

In some embodiments, the cathode is a metal selected from platinum or stainless steel. In an exemplary embodiment, the cathode is stainless steel.

In some embodiments, the cooling chamber comprises a water bath (e.g., drawing numeral (7) in Figure 3) and the insert vessel comprising the electrode assembly is placed in the water bath. In some embodiments, the inert vessel is surrounded by a water jacket (e.g., a water-filled casing surrounding the inert vessel).

Figure 1 shows an exemplary embodiment of the cathode used in the present disclosure. In this embodiment, the cathode used is a very thin rectangular sheet of stainless steel, which is bent in a tube-like structure to form the cathode.

Figure 2 shows an exemplary embodiment of the steel sample used as an anode in the present disclosure.

Figure 3 shows a schematic of an exemplary embodiment of the system for the electrolytic extraction of non-metallic inclusions (NMIs) from a steel substrate. The purpose of the system is to dissolve the desired steel sample (6) in the Electrolyte (7). Anode and Cathode are required to complete the circuit, wherein the anode is the steel sample/substrate and the cathode is a stainless steel sheet (5). A rectifier (3) is used to deliver charge into the system and current and voltage settings are adjusted from this device. Copper wires (4) are used for connections. As the charge is induced in the system, the overall temperature of system rises due to the reaction between the anode and the electrolyte solution. To continuously observe the temperature, a temperature probe (9) is used. The whole setup is kept inside an inert vessel such as a glass beaker (10), due to its inert behaviour. During the electrolysis process, as the anode gets dissolved, it is mixed well in the solution so that the flow of ions is favoured. This is done using a magnetic stirrer (8), which continuously rotates throughout the process. Additionally, to keep the temperature below a desirable range (room temperature), a chiller unit/cooling unit (13) is used. The glass beaker is kept in a cooling chamber/water bath (11), which is maintained at a low temperature by circulating chilled water with the help of connecting pipes (12) and the cooling unit. Figure 4 shows the actual set-up of the electrode assembly employed in one of the experiments. Figure 5 shows the actual set-up of the electrolytic extraction system comprising the electrode assembly, the rectifier (power source), and the cooling chamber.

Figure 6 is an exemplary embodiment of a filtration assembly of the present disclosure. The filtration assembly enables filtering of non-metallic inclusions from the electrolyte solution. After the completion of the electrolysis process, the electrolyte is poured onto a filter paper (15) mounted in a glass funnel (19). The solution flows through the filter paper (15), wherein the total time for filtration depends on the material type and pore size of the filter paper. The filter paper sits on a fritted glass filter base (16). After passing through the filter paper, the solution falls into a conical glass flask (17). To accelerate this filtration process, vacuum is used to force the solution from the glass funnel into the glass flask. This is done with the help of a vacuum pump (20). The filtration assembly and the pump are connected with a connecting rubber pipe (18).

The method of the present disclosure provides several advantages. The method enables achieving a high current density up to 280-320 mA/mm2. Additionally, the stirring, maintaining the electrolyte at the room temperature, and the specific electrolyte composition employed in the method of the present disclosure increases the current through the circuit, thus reducing the total time taken to dissolve the steel sample. The method of the present disclosure is completed in a short time of about 30 minutes, which is 80% less compared to the time taken for conventional electrolytic extraction methods. Further, 3D Images of NMIs extracted from steel sample by the method of the present disclosure can be captured successfully with the help of SEM. Furthermore, actual size, morphology and composition of the extracted NMIs are captured successfully using SEM-EDS.

It is to be understood that the foregoing descriptive matter is illustrative of the disclosure and not a limitation. While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Similarly, additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein.

Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above-described embodiments, and in order to illustrate the embodiments of the present disclosure certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the following examples should not be construed as limiting the scope of the embodiments herein.

EXAMPLES

Example 1: Method for an electrolytic extraction of non-metallic inclusions (NMIs) from a steel substrate according to the present invention:
A cylindrical steel sample of about 8 cm length and about 1cm diameter was taken as the anode. Its surface was polished and etched and also cleaned with the help of a bath sonicator before starting the experiment. A rectangular SS-316 or SS-410 grade stainless-steel sheet was used as the cathode. The rectangular sheet was bent and fitted into a laboratory scale glass beaker. An electrolytic solution having the composition: 10% Acetylacetone, 4% Tetramethylammonium chloride and 86% Methanol by volume was prepared. The rectifier was set at a constant voltage of about 10 Volts and maximum current obtained at this voltage varied from about 1.5A to 2.5A and this current was provided to start the electrolysis process. The complete setup was kept inside a glass beaker and the glass beaker was kept inside the water bath which was connected to a cooling unit to maintain the electrolyte solution at room temperature. Water was used for transferring heat from the electrolyte solution to the cooling unit. Throughout the complete process, the electrolyte solution was continuously stirred using a magnetic stirrer of about 4 cm at about 300 rpm. The process was stopped after 30 minutes. About 1.5-2 g of anode was dissolved in the solution after 30 minutes of extraction. Additionally, during the process, the current was continuously monitored and at the end, the current density was calculated by measuring the dissolved area and found to be about 300 mA/mm2.

Example 2: Analysis of the Extracted NMIs
The steel sample at the end of the electrolytic method of Example 1 was cleaned and weighed, and the solution was kept aside for filtration. The filtration of the electrolyte solution was done using different types of filter paper such as cellulose membrane and polycarbonate, having different pore sizes such as about 0.5µm, about 0.8 µm and about 1 µm. After the filtration process, one piece (1/6) of filter paper containing the extracted NMIs was cut and mounted over a conductive carbon tape. The mounted sample then was sent for gold sputtering for about 45-60 seconds and then analysed using SEM-EDS.

3D Images of the NMIs extracted from steel sample were successfully captured with the help of SEM. A complete 4 hour run on SEM-EDS machine was done with an inbuilt program of inclusion analysis where certain amount of area was looked at for size, composition and number of inclusions. Also, the inclusions were clustered according to their chemical composition. The actual size, morphology and composition of Non-Metallic inclusions was captured successfully using SEM-EDS (Figures 8-13). Inclusion mass percentage was captured to account for cleanliness of Steel Grade. Number of inclusions per unit volume for the specific steel sample was also captured, which is only possible by using Electrolytic Inclusion extraction technique.
A comparison was made between a 2-D method and the 3-D method. In the 2-D method, the steel substrate was observed under SEM without electrolytic extraction (Figure 14, panel (a)). In the 3-D method, the NMIs in the steel substrate were first extracted electrolytically by the method described herein, the extracted NMIs were collected on a filter paper and the filter paper was observed under SEM (Figure 14, panels (b) and (c)). The inclusion mass percentage data is shown in Table 1 below.
Table 1
2-D Method 3-D Method
Percentage of Non-classified Inclusion - 33%
(MnCa)S
Al2O3-SiO2
Alumina
CaO-Al2O3-SiO2
High Fe
MnS
Spinel
Oxysulfide (>50%O)
Oxysulfide (>50%S) Percentage of Non-classified Inclusion - 7%
(MnCa)S
Al2O3-SiO2
Al2O3-TiO2
Alumina
CaO-Al2O3-MgO
CaO-Al2O3-SiO2
High Fe
MnS
SiO2
Spinel
Oxysulfide (>50%O)
Oxysulfide (>50%S)

A total number of inclusions per unit volume were calculated as follows:

Ni = The number of inclusions from SEM pictures in each size category.
Wdis = The weight decrease after the electrolytic extraction.
Afil = The area of the film filter used which is 1200 mm2.
Aobs = The area of the film filter which has been observed under the SEM
? = The density of the metal which is taken as 0.0078g/mm3.

Thus, the total number of inclusions per unit volume (mm-3) were 78,779.