FIELD OF THE INVENTION
The present invention relates to a method to produce lubricating powder with enhanced lubrication properties applicable in a continuous steel casting process.
BACKGROUND OF THE INVENTION
Continuous casting process of steel uses of tundish which acts as a reservoir of liquid steel. The liquid steel is continuously fed from the tundish into an open ended water cooled cupper mould for solidification of steel via a submerged entry nozzle. The open ended cupper mould is continuously oscillated to avoid sticking of the solidifying steel shell with the mould. To provide lubrication and further to control the heat transfer in the mould, a lubricant in the form of a mould powder is added on the top of the mould, which subsequently melts and provides lubrication between mould and solidifying steel strand. Mould powder consists of a complex mixture of oxides of minerals (Silica, Lime, Alumina, Alkali, Fluoride etc.) and carbon from different sources (carbon black, graphite etc.).
The mold powder provides at least five major function of this mould powder during continuous casting of steel, for example, lubrication between mould and solidifying strand, controlling heat transfer between mould and strand, control on reoxidation of liquid steel on the top of the mould, absorption of inclusions from steel, and preventing solidification of steel from the top of the mould.
Mould powder fed from the top of the mould on liquid steel which gradually melts taking the heat from liquid steel. It forms three basic layers on the top of the mould i.e. a Liquid layer close to liquid steel, a Sintered layer above the liquid layer, and a Solid layer on the top (Figure 1). Major function of carbon is to form the sintered layer which helps in the control of melting. Carbon controls the melting rate by creating an inert barrier between slag particles and prevent them

from agglomeration, thereby controls the melting of said mould powder. The sintering temperature and the melting start temperature very well depend on the kind of carbon and the particle size of carbon added in the mould powder.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method to produce lubricating powder with enhanced lubrication properties applicable in a continuous steel casting process.
Another object of the invention is to propose a method to produce lubricating powder with enhanced lubrication properties applicable in a continuous steel casting process, in which the high temperature characteristics of the mould powder is enhanced.
SUMMARY OF THE INVENTION
Accordingly, there is provided a method to produce lubricating powder with enhanced lubrication properties applicable in a continuous steel casting process. According to the disclosed method the high temperature properties of lubricating powder for a continuous steel caster is enhanced by replacing the source of carbon component which controls the sintering and melting properties of lubricating powder and enables better lubrication during continuous casting of steel. Such a technical solution is achieved by use of grapheme oxide as a replacement of different known carbon sources used for preparation of lubricating powder. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Schematic diagram of a continuous casting mould showing

lubricating slag layers.
Figure 2- Shows the role of carbon element to control melting rate of lubricating powder in a continuous casting process.
Figure 3 - Graphically represents the results of a high temperature thermal stability study using TG analysis (showing carbon decomposition at higher temperature).
Figure 4 - Thermogravimetry analysis of Graphene oxide tested in different atmosphere.
Figure 5 - Melting Rate Evaluation of the lubricating powder using boat test Figure 6 - High temperature characteristics observed in heating microscopy
DETAILED DESCRIPTION OF THE INVENTION
The technical solution provided by the present invention is to enhance the high temperature characteristics of lubricating powder. High temperature characteristics include high temperature stability, melting rate, melting range of lubricating powder.
The lubricating powder can be any mould powder used for continuous casting of steel. It comprises of different oxides from minerals such as, CaO, Si02, A1203, MnO, CaF2, Na20, K20 and other oxides along with carbon. The composition range is as mentioned in the Table 1:


The mould powders are prepared by mixing the pulverized or any mechanlcally crushed components of the above materials with different composition. This can be used as a mixture or else can be granulated by making slurry by adding starch at a binder and water. This slurry can be hot air dried by granulation process using an atomizer.
Free carbon is one of the vital components of lubricating powder used for continuous casting of steel. Free carbon (C) present in lubricating powder varies between 1 to 20 percentages. Carbon, in the form of carbon black, graphite or coke dust is added to lubricating powder to control its melting rate and to provide insulation to both the steel and the liquid slag. The different Carbon delays melting by hindering contact, sintering and agglomeration of slag drops. Effect of carbon is correlated both to amount, type and particle size.
Carbon particles are non-wetting to molten slag and thus separate the mineral particles and slow down the agglomeration of molten slag globules as shown in Figure 2. So higher the C content of lubricating powder, it requires more time to agglomerate, thus slower the melting rate. Low free C corresponds to high melting rate and consequently high molten pool depth (keeping constant operative parameters and powder viscosity). Free Carbon content controls how

much liquid slag is produced and viscosity controls how much liquid slag infiltrates. To reduce the viscosity, the free carbon content has to be reduced in order to keep constant liquid slag pool depth.
Type of carbon (crystalline or amorphous) is also another prime factor which controls the melting rate. Metallurgical coke contains the highest amount of amorphous fraction, followed by petroleum coke, amorphous graphite, expandable graphite, vein graphite and synthetic graphite. The composite activation energy of carbon combustion decreases with increasing amorphous carbon content. The combustion temperature of carbon increases with increasing contents of crystalline carbon within the carbonaceous structure. The amount of melting of a lubricating powder decreases with increasing crystallinity of the carbonaceous material. Lubricating powders with metallurgical coke addition shows the greatest amount of melting, while powders with graphite shows relatively less melting because of the higher amount of crystalline material. Melting rate also increases with increasing carbon reactivity means decreasing particle size. Carbon particle size and corresponding combustion temperature depends on carbon source as shown in Table 2.
Table-2: Particle size distribution and Combustion temperature of different types of carbon
Graphene oxide has unique properties. This is crystalline in nature; they are very fine along with having high combustion temperature. This nature of graphene

oxide helps in fulfilling the combined properties of other carbon sources used for preparing lubricating powders. High surface area due to lower particle s.ze of graphene oxide increases the reactivity hence increases melting rate. At the same time crystalline nature and high combustion temperature helps in reducing the melting rate. This unique nature helps in balancing the melting rate of lubricating powder, which is a requirement to maintain liquid slag pool depth during continuous casting of steel.
Lubricating powder which can be used for continuous casting of steel for lubrication, with the carbon component coming from graphene oxide. Three different lubricating powders were prepared with different basicity as shown in Table 3. In all these three powders normal carbon sources were replaced with graphene oxide and both the powders were tested for their high temperature performance.
The tests conducted are: 1) High temperature stability (Thermogratometry-TG), 2) Melting rate evaluation by boat test, 3) Heating microscopy analysis for sintering and melting temperature evaluation.


gravitometry (TG) curve (Figure 3). Combustion temperature range of graphene oxide can be interpreted from TG curve of graphene oxide (shown in Figure 4) tested under different atmosphere. The melting rate of lubricating powder is tested by standard boat test. Where in crystallized alumina boats both powder (one with normal carbon source and other with different percentage of graphene oxide as carbon source) were tested. The results are shown in Figure 5. It can observed that melting rate of both the powder were visibly similar. The sintering temperature and flow temperature of powders are presented in Figure 6 and can been seen that addition of graphene oxide replacing normal carbon source does not change the characteristic temperatures. Similar trend was observed for Lubricating Powder B and C which have different basicity.

WE CLAIM
1. A method to produce lubricating powder with enhanced lubrication
properties applicable in a continuous steel casting process, comprising:
- preparing a mould powder mixture by mixing pulverized or mechanically crushed elements of CaO, Si02, AI203, Na20 + K20, Fe02, MnO, with carbon particles at different proportion;
- optionally the pulverized or mechanically crushed elements at different proportions are mixed with water and a binder to form a slurry, the formed slurry being hot air-dried by granulation process using an atomizer,
Wherein the composition of the powder elements is

and wherein the carbon particles constitutes graphene oxide at a particles size of 0.1-1 un
2. The method as claimed in claim 1, wherein the graphene oxide containing
in the mould powder at a first instance increases reactivity vis-a-vis
melting rate being crystalline in nature, and wherein at a second instance

the graphene oxide having a combustion temperature range of 600-950°C allows reduction melting rate of the mould powder, thereby induces a balancing property in melting of the powder to maintain an optimized liquid slag pool depth during the process of continuous casting of steel.
3. The process as claimed in claim 1, wherein the mould powder exhibits high temperature stability.
4. The process as claimed in claim 1, wherein the sintering temperature of the mould powder is between 900 to 1000°C, and wherein the flow temperature of the powder is between 1000 to 1200°C.