FIELD OF THE INVENTION:
This invention relates to a process for the decarburization of low-manganese ferroalloys.
This invention further relates to a process for the decarburization of low manganese ferroalloys using high MnO synthetic slag produced using low grade ferriginous ores. This technique can reduce upto 34% carbon present in the melt with maximum 10 tol5% loss in the manganese. This alloy can be used as an alternative of pig iron and other manganese alloys with an additional advantage of lower carbon percentage. This can be suitable for production of high manganese steels such as Hadfield steel, tool steel, cast iron, steel ingots, etc. This process enable production of value added product from low grade manganese ore resources.
B ACKGROUND OF THE INVENTION:
Manganese alloys are used mainly in steel making. There are various kinds of manganese alloys, such as Ferromanganese (HC Fe-Mn with 65 to 80% Mn and 6 to 8% C), SilicoManganese (Si: 14-28%, Mn: 50-74%, C: 2.5%), Spiegeleisen (Mn: 6-30%; C: 4.5-6.5%). Selection of manganese alloy for steel making depends on purpose i.e. whether it is to be used as a deoxidising agent, alloying agent, or for cleansing and also depends on the targeted grade of steel i.e. low carbon, medium carbon, high and ultrahigh carbon steel. During steel making, addition of excessive carbon by manganese alloy is undesired and steel makers select a manganese alloy which provides optimized addition of Mn, C, Si and P to achieve the desired chemistry of steel. There are various decarburisation techniques to remove the excess carbon from the manganese ferroalloys as well as steel melt Most of the known techniques are based on utilization of gaseous oxygen to remove carbon or by the addition of solid oxides. But loss of alloying elements such as Mn, Cr, etc, heat energy requirement and safety are the major limiting factors for decarburisation of ferroalloys as well as for steel.
It is known that low grade manganese ores can be smelted in the blast furnace to produce spiegeleisen and it is also known that similar kinds of product can be produced using ferruginous ores also. Problem with known methods is metal and slag

composition. The metals produced by this process contain relatively higher carbon (4-6.6%) which makes it less suitable as an alternative of high carbon ferromanganese (G 6-8%) or pig iron (C: 3.5-4.5%). The required oxygen to remove the carbon can be provided in gaseous form in the methods such as Argon oxygen decarburization (AOD) or Vacuum Oxygen decarburization (VOD) or addition of oxides ( Iron oxides, mill scale, etc) in the steel melt Decarburisation by using the through the introduction of oxygen (O) by solid state have many advantages over gas purging methods. It provides superior oxygen distribution in the liquid steel, alloying, increased Fe and better process control etc., but it is slow which impact the economic feasibility of process. In case of decarburisation of manganese alloys, loss of manganese during oxygen blowing is also a critical factor and introduction of oxygen in the form of solid oxides is much preferred.
Selection of oxides is based on consideration of the relevant Gibbs free energies of reaction related to the formation of CO through the reaction of oxides with the C present in the alloy melt. Various oxides (Fe2O3, MnO2 NiO, MgO, P2O5, Bi2O3, MnO2, MgCO3 and CaCO3) have been reported in literatures for carbon removal from steel but these are not effective for manganese bearing alloys because addition of these additives impact manganese level in alloy both by dilution as well as by Mn loss in slag in the form of MnO.
OBJECTS OF THE INVENTION:
It is therefore an object of this invention to propose a process for the decarburization of
low-manganese ferroalloys.
It is further object of this invention to propose a process for the decarburization of low-manganese ferroalloys, which can remove carbon from manganese alloys upto an economically attractive level.
A still further object of this invention is to propose a process for the decarburization of low-manganese ferroalloys, which ensures minimum manganese losses.

Another object of this invention is to propose a process for the decarburization of low-manganese ferroalloys, which is simple and safe.
These and other objects of the invention will be apparent from the ensuing description, when read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING.
Fig. 1 Effect of MnO slag composition on carbon removal.
Fig. 2:Carbon removal from different Mn melts using different quality synthetic MnO slags.
SUMMARY OF THE INVENTION-
According to this invention is provided a process for the decarburization of low-manganese ferroalloys. The process has been a manganese alloy (Mn:6-18%, C :2.8-3.3%) using high MnO synthetic slag (MnO :36-55%, FeO :l-20%, SiO2: 12-35%, Al2O3 :7-12% CaO:3-5%, MgO :3-5%) produced using low grade ferruginous ores. This alloy can be' used as an alternative of pig iron and other manganese alloys with an additional advantage of lower carbon percentage. This can be suitable for production high manganese steels such as Hadfield steel, tool steel, cast iron, steel ingots, etc This process enable production of value added product from low grade manganese ore resources.
10 kg low grade ferruginous manganese ores (Mn: 25-35%, Fe: 20-40%, SiO2:5-12% Al2O3 :5-8%) has been melted to a submerged electric arc furnace using electric power (20-30kWh). coke (0.14X17 Kg coke/kg of ore), quartz (0.02-4.1 kg/ kg of ore) and dolomite (0.06-0.2kg/kg of ore). The slag and metal were separated. Different quality slag ((MnO 36-55%, FeO 1-20%, SiO2: 12-35%, A12O3:7-12%, CaO 3-5%, MgO: 3-5%), and metal (Mn: 1-24%, C: 4.4-6.6 %, were produced. The slag generated in this process were classified into three different grades based on chemical composite, (MnO,Mn2O3,Mn3O4,MnO2 MnAl2O4 Mn2SiO4SiO2 FeO) and added in the different composition metal melts (Mn,C) in a 5 kg induction furnace. Presence of different

manganese and iron phases significantly impact the decarburisation process and make it more efficient than the pure manganese or iron oxides. Three different types of slag composition were tested for this purpose and these were added in three different kinds of manganese melts. The major outcomes of these tests are as follow:
Addition of high MnO synthetic slag significantly impact the decarburisation of Mn melts and it can reduce Caron in these alloys up to 34 % for time duration of 20 minutes. The synthetic slag contains various manganese oxides which decompose and release oxygen and various iron and manganese complexes
improve reactivity of the slag to carboa Three different slag compositions have been taken to cover the diversity in oxygen carriers and carbon level in the metal were measured.
It was found that time plays a vital role in this process and maximum decarburisation occurs in initial 15 minutes and after that speed slow down with time. It was found that in all the experiments maximum carbon removal was observed during initial 15 to 20 minutes.
The MnO present in the slag is in various phases and all these phases contribute in Carbon removal. The MnO present in slag reacts with C and produce CO and Mn which compensate the manganese losses due to evaporation and oxidation during the process. These are complex reactions and observe that MnO in the slag on produced during this process reduced by 10-15%. During experiments with different combinations it was observed that Mn reduction varies between 10-15% which increases with pure oxygen purging and with increased time.
The produced high Mn pig iron (Mn : <2%, C: 4-6%) can be converted into desired quality high Mn cast iron (C 3.4, Mn 0.5) by adding desired alloying elements.

DETAILED DESCRIPTION OF THE INVENTION:
Thus according to this invention is provided a process for the decarburization of low-manganese ferroalloys.
In accordance with this invention, the process for the decarburization of low-manganese ferroalloys comprises the steps of smelting reduction of ore blends to produce synthetic slag, separating the metal from the slag, sizing of slag, carbon removal from metal using synthetic high MnO slag followed by casting and sizing of alloy.
In present invention low grade ferruginous manganese ores are melted in carbon deficient atmosphere and low Mn pig iron and Spiegeleisen have been produced along with the high MnO slag. This alloy contains Mn between 1 to 24% and Carbon between 4.5 to 6.6%. The alloy can be used an alternative of silico-manganese and ferromanganese used as an alloying agent for steel and reduced level of carbon in it can make it a preferred choice. So, after the smelting reduction the alloy produced are taken in an induction furnace and different composition of high MnO slag are added to remove the carbon content up to an economically attractive level. The alloy produced contains manganese and iron carbides and graphite flacks. It was found that the MnO, FeO and Si02 present in slag play the critical role in this process and these three reactions impact the carbon level of alloy.

Low grade ferruginous manganese ores (Mn: 25-35%, Fe: 20-40%, Si02:5-12%, AI2O3:5-8%) has been melted in a submerged electric arc furnace using electric power (20-30kWh), coke (0.1-0.17 Kg coke/kg of ore), quartz (0.02-0.1 kg/ kg of ore) and dolomite (0.06-0.2kg/kg of ore). The slag and metal were separated. Different quality slag ((MnO: 36-55%, FeO: 1-20%, Si02: 12-35%, A1203:7-12%, CaO: 3-5%, MgO: 3-5%)) and metal (Mn: 1-24%, C: 4.5-6.6 %) were produced. Decarburisation of the alloy produced using high MnO slag can reduce carbon by 22-34% with minimum manganese loss of 10-15%. There are five major steps in this process:

(a) Slag and Metal production: Low grade ferruginous manganese ores (Mn: 25-35%,
has been melted in a submerged electric arc furnace
using electric power
kg of ore) and dolomite The slag and metal were separated.
Different quality slag
and metal were produced.
(b) Slag- metal separation: The low grade ores are smelted in the furnace and proper
slag viscosity is maintained for proper slag metal separation. Slag is first drained and
casted whereas metal is taken in a separate pan and transferred to induction furnace for
carbon removal. Manganese and carbon level in the alloy is measured for subsequent
processing.
(c) Sizing of Slag: The casted slag cake is comminuted to finer size up to 25mm and
separated for addition in metal for decarburisation.
(d) Decarburisation: The slag of desired chemistry is sized and added (5 to 10% weight
of metal) to alloy melt It is added in a continuous process and as soon as it dissolves the
undissolved slag mainly contains Si02 and FeO which is removed. This process
continues for 15-20 minutes and temperature is maintained between 1550to 1600 Deg C
to minimize the Mn losses. Finally the metal is casted and broken down to suitable sizes
for end users.
This invention will now be explained in greater details with the help of the following non-limiting examples.
Example 1: 5 kg of manganese alloy which contain Mn: 12.8% and C: 5.9% is melted or taken in liquid phase in an induction furnace. The undesired carry over slag particles were removed. 250 grams of high MnO synthetic slag of <25mm size were taken. It contains It was
added in liquid metal at the melt temperature between 1550-1600 Deg. C during 15-20

minutes times. The un dissolved slag particles were removed during this process which enables proper dissolution of fresh material. After the treatment metal and slag samples were taken for chemical analysis. Three different metal and slag composition were selected and trials were conducted. The effect of high MnO slag on carbon and Mn removal was measured and results are given in Table 1. It shows that 22-34% carbon can be removed during 15 minutes time with 10-15% Mn losses.

Example 2: Three lots of 5 kg of manganese alloy which contain Mn: 8.9-12.5% and C: 6.2-4.6 % is melted or taken in liquid phase into an induction furnace. The undesired carry over slag particles were removed. 250 grams of high MnO synthetic slag of <25mm size were taken It contains MnO: 53.10%, FeO: 10.14%, Si02:14.72%, Al2O3:6.09%, MgO: 3.24%. It was added in liquid metal at the melt temperature between 1550-1600 Deg. C for 45 minutes times. The undissolved slag particles were removed during this process

which enables proper dissolution of fresh material. This process repeated for 45 minutes and samples were taken at every 15 minutes. After the treatment metal and slag samples were taken for chemical analysis. Fig 2 shows carbon can be removed by 22-34% during 15 minutes time with 10-15% Mn losses.
It was found that time plays a vital role in this process and maximum decarburisation occurs in initial 15 minutes and after that speed slow down with time. It was found that in all the experiments maximum carbon removal was observed during initial 15 to 20 minutes. Table 2 shows effect of time on decarburisation of different composition melts.

Addition of High MnO synthetic slag in high Mn pig iron and Spiegeleisen alloy melt can reduce Carbon content by 22-34% at temperature range between 1550 to 1600 Deg. C. By this process a medium carbon low manganese ferroalloy (Mn: 6-24%, C: 3.5%) can be produced. This method can minimize the loss of manganese during decarburization to make it economically attractive. This method has minimum manganese losses (10-15%) during moderate decarburization of manganese melts using solid oxides. A medium carbon high Mn pig iron and Spiegeleisen product can be produced by smelting reduction of low grade ferruginous manganese ores which can be used as alternative of high Carbon manganese ferroalloys for steel or cast iron making. The produced high Mn pig iron (Mn : <2%, C: 4-6%) can be converted into desired quality high Mn cast iron (C 3.4, Mn 0.5) by adding desired alloying elements.

WE CLAIM:
1. A process foT the decarburization of low-manganese ferroalloys comprising the steps
of
subjecting a manganese ore to melting in the presence of coke, quartz and dolomite to
obtain slag and metal,
separating said slag and metal and melting said metal casting said slag followed by
comminution of the casted slag and separating finer particles,
adding said slag particles to the melted metal in a continuous process over a period of 15
to 20 minutes at a temperature in the range of 1550 to 1600°C, followed by
casting the metal and forming the same into suitable sizes.
2. The process as claimed in claim 1, wherein said manganese ores are low grade
ferruginous ores comprising

3. The process as claimed in claim 1, wherein said ore is melted in a submerged electric arc furnace at a power of 20-30 kWh.
4. The process as claimed in claim 1, wherein coke is added in 0.1 to 0.17 kg/ kg of ore.
5. The process as claimed in claim 1, wherein quartz is added in 0.02 to 0.1 kg/ kg of ore.
6. The process as claimed in claim 1, wherein dolomite is added in 0.06 to 0.2 kg/kg of ore.

7. The process as claimed in claim 1, wherein said slag has a composition

and metal has the composition

8. The process as claimed in claim 1, wherein said cast slag is comminuted to a size
upto 25 mm.