Claims:We Claim:

1. A Process for producing low phos Hadfield Manganese Steel comprising :

step of carrying out stagewise dephosphorisation of High Manganese (12% Min ) High Carbon Hadfield Manganese steel comprising:
de-phosphorise liquid metal without addition of any kind of manganese addition and free of any HCFeMn additions in Electric Arc Furnace(EAF) to produce virgin melt;followed by

involving said virgin melt thus obtained in said Electric Arc Furnace(EAF)for enriching Mn with SiMn and HCFeMn additions, in Ladle furnace avoiding any further dephosphorisation.

2. A process as claimed in claim 1 wherein whatever input “P” is added goes to the metal and Manganese addition is done in reduced bath, such that recovery of Manganese is high, and “P” enrichment is low due to lower volume of Manganese addition; and wherein cost of Manganese addition increases with reduction in “C” and “P” content of ferromanganese.

3. A process as claimed in anyone of claims 1 or 2 wherein relatively cheaper variety of Manganese source as High “C” Ferro manganese is used in the process to achieve desired low P level.

4. A process as claimed in anyone of clams 1 to 3 wherein said two stages comprises at 1st dephosphorisation followed by Manganese addition leading to reduction of average phosphorus from 0.095% to 0.045%.

5. A process as claimed in anyone of clams 1 to 4 which enables achieving smooth rolling index without cracking which has direct relation to “P’ content in Steel and due to reduction in “P’ rolling yield is doubled from 35% to 70%.

6. A process as claimed in anyone of claims 1 to 5, wherein temperature raising and addition is done in LF in atmosphere leading to oxidation of Silicon and Carbon while oxidation of Manganese is very low and recovery of Mn is very high.

7. A process as claimed in anyone of claims 1 to 6, wherein since Manganese addition is being done in reduced bath in LF, so recovery of Manganese is also very high, and phosphorous enrichment is low due to lower volume of Manganese addition.
8. A process as claimed in anyone of claims 1 to 7, wherein since the bath is completely slag free so there is no chance of phosphorous reversion in LF during ladle treatment.

9. A process as claimed in anyone of claims 1 to 8, wherein metal bath is reduced by addition of Silico Manganese in Ladle Furnace.

10. A process as claimed in anyone of claims 1 to 9, wherein heating of metal bath by arcing in the Ladle furnace by approximately 250 º C is required for full manganese addition.

11. A process as claimed in anyone of claims 1 to 10, wherein time taken for arcing is approximately 2 hours for a 12 % alloy containing melt.

12. Low phosphorous containing high carbon high manganese Hadfield Steel produced by the process as claimed in claims 1 to 11 having composition comprising by wt % C: 1.0-1.20%, Mn: 12.50-14.0%, P: 0-0.07%, S: 0-0.20% and Si: 0.30-0.60% .
Dated this the 8th day of May, 2017
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
, Description:FIELD OF THE INVENTION

The present invention relates to a process for producing low phosphorous Hadfield Manganese Steel and more particularly, to a process for Dephosphorisation of High Manganese (12% Min ), High Carbon Hadfield Manganese steel through EAF–LF Route, without using excess of costly Manganese Metal and low phosphorous steel scrap. Advantageously, the process is split up to divide total activities in two stages comprising dephosphorisation at first stage in EAF followed by Manganese addition in LF leading to reduction of average phosphorus from initial 0.095% to 0.045% in final product. As the smooth rolling index without cracking has direct relation to Phosphorous content in Steel, rolling yield is doubled from conventional 35%, to 70% for steel produced by applying the process of the invention, due to reduction in phosphorous content, favouring cost effective production of low phosphorous Hadfield Steel ensuring wide industrial application of such steel for variety of purposes with significant economic advantage.

BACKGROUND OF THE INVENTION
It is well known that the Specification of commercially available Hadfield Manganese Steel is as follows:

Element C Mn P S Si
Min% 1.00 12.5 ------ ---- 0.30
Max% 1.20 14.0 0.07 .020 0.60

Production of Hadfield Manganese Steel with low phosphorus content has been a challenge to the steel makers. De-phosphorisation requires oxidation of “P” in the melt to slag. The Indian scrap and ferro-alloy are traditionally rich in “P” because of the adverse raw material condition and high “P” in majority of Indian coke (this is required to produce high carbon ferro manganese). Composition of Commercial variety of Normal High Carbon Manganese is as follows:

Element C Mn P S Si
Min% 5.00 70.0 ------ ----
Max% 8.00 76.0 0.50 .020 3.0

Before adopting the new process as illustrated herein, Hadfield steel produced earlier used to melt in following methods:

Process 1 :
The steel produced in EAF having Charge mix comprising of Steel Scrap , Pig Iron ,Sponge Iron , High Carbon Ferro Manganese without any Hadfield revert Scrap wherein Charge Calculation and all melt composition is as follows:

"P" burden Calculation in Hadfield with High Carbon Manganese charging in EAF
Wt (Kg) % "P" % "C" %"Si" "P" BURDEN (Kg) "Mn" Burden (Kg "Si" Burden (Kg) "C" Burden
Pig Iron 6000 0.15 4.5 1.4 9 9 84 270
Sponge Iron 20000 0.09 0.15 0.02 18 30 4 30
Other Steel Scrap 24000 0.035 0.2 0.2 8.4 36 48 48
HCFeMn 8900 0.39 7.5 2.5 34.71 6230 222.5 667.5
SiMn 1500 0.1 0.05 20 1.5 825 300 0.75
Total Charge Metallic 60400 71.61 7130 658.5 1016.3
Total Liquid 53756 0.13321 13.2636 1.22498 1.8905
Total Charge to Liquid Yield 89%
Recovery of "Mn" 95%
P% Mn% C% Si%
Theoretical Opening in all melt stage in wt% 0.133 13.264 1.890 1.225
Actual Analysis usually obtained( all melt stage) 0.133 10.611 1.134 0.490

Process 2:

The steel produced by melting in EAF having Charge mix comprising revert Scrap of Hadfield Steel,normal virgin scrap and High Carbon Manganese is used. Charge Mix and process route is as follows:

and wherein Charge Calculation and all melt composition is as follows:

"P" burden Calculation in Hadfield with Hadfield Revert Scrap charging in EAF
Wt (Kg) % "P" % "C" %"Si" "P" BURDEN (Kg) "Mn" Burden (Kg "Si" Burden (Kg) "C" Burden
HADFIELD REVT SCRAP 8000 0.1 1.1 1.4 8 960 112 88
Other Steel Scrap 42000 0.035 0.2 0.2 14.7 63 84 84
HCFeMn 8900 0.39 7.5 2.5 34.71 6230 222.5 667.5
SiMn 1500 0.1 0.05 20 1.5 825 300 0.75
Total Charge Metallic 60400 58.91 8078 718.5 840.25
Total Liquid 53756 0.109588 15.02716 1.336595 1.56308
Total Charge to Liquid Yield 89%
Recovery of "Mn" 95%
P% Mn% C% Si%
Theoretical Opening in all melt stage in % 0.110 15.027 1.563 1.337
Actual Analysis usually obtained 0.110 9.016 0.938 0.535

By the above said processes in EAF, Manganese loss was very high and dephosphorisation was hampered due to high Manganese in slag and “C” content in bath was very high and as a result fully oxidizing slag was not obtained. Due to poor recovery of Manganese and improper de-phosphorisation, always tap metal was having low in Manganese, and high in “C” and “P” . In case of decarburization or dephosphorisation in Electric Arc Furnace further loss of Manganese had been observed. As a result further addition of High Carbon Ferro Manganese is required during secondary ladle treatment till “C” permits. Simultaneously, due to addition of High Carbon Ferro Manganese(HCFeMn), bath “P’ gradually increases. Even after HCFeMn addition, Carbon specification reached but Manganese remain below specification. Thus at this stage Manganese adjustment was done through addition of costly Manganese metal.

Due to high phosphorus in steel more than 0.07% , clicking i.e transverse rupture occurred during rolling which results in very low solid to finishing yield even as low a level as of 25%. As a results productivity decreases, product become costly and profitability decreases.

OBJECTIVES OF THE INVENTION

It is therefore the basic objective of the present invention to provide a process for Dephosphorisation of High Manganese (12% Min ), High Carbon Hadfield Manganese steel through EAF-LF route involving effective de-phosphorisation of steel without use of any costly material like Manganese metal, very low phosphorous iron/steel scrap which is costly and availability is also not abundant.

Another objective of this invention is to provide a process for producing low phosphorous High Manganese (12% Min ), High Carbon Hadfield Manganese steel through EAF-LF route by maximizing the recovery of Manganese which makes the steel cheaper.

A further objective of present invention is directed to a process for Dephosphorisation of High Manganese (12% Min), High Carbon Hadfield Manganese steel through EAF-LF route to finish “P” at minimum level using all normal ferroalloy and scrap which are abundant and cheaper.

Yet another objective of the present invention is directed to a process for Dephosphorisation of High Manganese (12% Min ), High Carbon Hadfield Manganese steel through EAF-LF route to maximize solid to finishing plate yield by reducing material failure on account of crack

A further objective of this invention is directed to a process for Dephosphorisation of High Manganese (12% Min ), High Carbon Hadfield Manganese steel through EAF-LF route favouring reducing soaking time of Ingot prior to rolling, which is conventionally higher on account of higher phosphorus.

A further objective of this invention is directed to a process for Dephosphorisation of High Manganese (12% Min), High Carbon Hadfield Manganese steel through EAF-LF route whereby Hadfield Manganese Steel with low “P” and improved abrasion resistance property will be available in the Market at reasonable price.

A further objective of this invention is directed to a process for Dephosphorisation of steel to ensure that very low “P” bearing Stainless Steel with cheaper rate will be available and due to low “P”,mechanical properties of this steel will be improved.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to a Process for producing low phos Hadfield Manganese Steel comprising :

step of carrying out stagewise dephosphorisation of High Manganese (12% Min ) High Carbon Hadfield Manganese steel comprising:
de-phosphorise liquid metal without addition of any kind of manganese addition and free of any HCFeMn additions in Electric Arc Furnace(EAF) to produce virgin melt;followed by

involving said virgin melt thus obtained in said Electric Arc Furnace(EAF)for enriching Mn with SiMn and HCFeMn additions, in Ladle furnace avoiding any further dephosphorisation.

A further aspect of the present invention is directed to said process wherein whatever input “P” is added goes to the metal and Manganese addition is done in reduced bath, such that recovery of Manganese is high, and “P” enrichment is low due to lower volume of Manganese addition; and wherein cost of Manganese addition increases with reduction in “C” and “P” content of ferromanganese.

A still further aspect of the present invention is directed to said process wherein relatively cheaper variety of Manganese source as High “C” Ferro manganese is used in the process to achieve desired low P level.

A still further aspect of the present invention is directed to said process wherein said two stages comprises at 1st dephosphorisation followed by Manganese addition leading to reduction of average phosphorus from 0.095% to 0.045% .

A still further aspect of the present invention is directed to said process which enables achieving smooth rolling index without cracking which has direct relation to “P’ content in Steel and due to reduction in “P’ rolling yield is doubled from 35% to 70%.

A still further aspect of the present invention is directed to said process wherein temperature raising and addition is done in LF in atmosphere leading to oxidation of Silicon and Carbon while oxidation of Manganese is very low and recovery of Mn is very high.

Another aspect of the present invention is directed to said process wherein since Manganese addition is being done in reduced bath in LF, so recovery of Manganese is also very high, and phosphorous enrichment is low due to lower volume of Manganese addition.

Yet another aspect of the present invention is directed to said process wherein since the bath is completely slag free so there is no chance of phosphorous reversion in LF during ladle treatment.

A further aspect of the present invention is directed to said process wherein metal bath is reduced by addition Silico Manganese in Ladle Furnace.

A still further aspect of the present invention is directed to said process wherein heating of metal bath by arcing in the Ladle furnace by approximately 250ºC is required for full manganese addition.

A still further aspect of the present invention is directed to said process wherein time taken for arcing is approximately 2 hours for a 12 % alloy containing melt.

A still further aspect of the present invention is directed to Low phosphorous containing high carbon high manganese Hadfield Steel produced by the process as described above having composition comprising by wt% C: 1.0-1.20%, Mn: 12.50-14.0%, P: 0-0.07%, S: 0-0.20% and Si: 0.30-0.60%.

The above and other objects and advantages of the present invention are described hereunder with reference to accompanying non limiting illustrative example.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING EXAMPLE

The present invention is directed to provide a process for Dephosphorisation of High Manganese (12% Min ), High Carbon Hadfield Manganese steel through EAF-LF route involving effective de-phosphorisation of steel without use of any costly material like Manganese metal, very low phosphorous iron/steel scrap which is costly and availability is also not abundant.

De-phosphorisation requires oxidation of “P” in the melt to slag .The Indian scrap and ferro-alloy are traditionally rich in “P” because of the adverse raw material condition and high “P” in majority of Indian coke (this is required to produce high C Fe Mn cheaply without use of costly Thermit or Electro-metallurgical process).Unfortunately, along with “P”, the majority of “Mn” are oxidized to slag. If this slag is not removed un stable P205 first reverts back to metal, in an attempt to recover “Mn”.The most apparent method appears to be to throw away oxides of “P” ,”Mn” contain in the slag and then to refresh the steel with stock of “Mn”. The process is technically feasible but economically infeasible because the addition “Cr” and “Mn” can be done only with costly ferro-alloys produced by Thermit/Electro metallurgical process. In some grades these has to be followed to avoid “C” pick up apart from “P” build–up. Such a huge addition is impossible in VOD without “Al” burning for the fear of chilling the bath to partial solidification.

Dephosphorization occurs at low temperature (near steel melting point), high content of oxygen in the metal bath and high slag fluidity, following the reactions (1) & (2) as shown below:
2[Fe P] + 5[FeO] = [P2O5] + 9[Fe] ----------------------(1)
[P2O5 ] (CaO ) = (CaO *P2O5 ) ---------------------------(2)

Metal bath oxidation follows in first phase (intense boiling) a significant decrease in gas content (H and N) and continues the dephosphorization.

So for smooth and effective dephosphoriastion oxidation of metal bath i.e presence of high FeO is compulsory. Reference toEllingham Diagrams goes to show, Mn-MnO line is far below Fe-FeO line i.e at lower temp preferential oxidation of Fe is lower in presence of high Manganese content. At lower temp, to oxidize Fe in presence of high Manganese, Mn will oxidize rather than iron. So to oxidize a steel bath with high Manganese, the slag will enrich with MnO rather than FeO, no dephosphorisation will be obtained, and huge Manganese loss will be observed.

For effective dephosphorisation high oxygen content in the bath is required, the oxygen content in the bath depends on “C” content in the bath.With increase in carbon content, oxygen in the bath reduced, as a result “P” in the metal does not oxidize to P2O5 and reaction shown in equation 1 does not occur.

When following charge in EAF is used for melting for producing molten steel bath of desired composition:
"P" burden Calculation in Hadfield with Hadfield Revert Scrap charging in EAF
Wt (Kg) % "P" % "C" %"Si" "P" BURDEN (Kg) "Mn" Burden (Kg "Si" Burden (Kg) "C" Burden
HADFIELD REVT SCRAP 8000 0.1 1.1 1.4 8 960 112 88
Other Steel Scrap 42000 0.035 0.2 0.2 14.7 63 84 84
HCFeMn 8900 0.39 7.5 2.5 34.71 6230 222.5 667.5
Total Charge Metallic 58900 57.41 7253 418.5 839.5

“C” burden in the charge 839.5Kg, i.e. approx 1.42%, “Mn” burden in the charge 7253Kg i.e approx 12.31%( considering no loss of “C” and “Mn” while melting). With this high “C’ and “Mn” content, oxygen level in the bath is very low and de-phosphorisation has not occurred. For effective dephosphorisation, if oxidation of metal bath is being done by oxygen blowing or by addition of Iron Ore, huge manganese is oxidized as low bath temp Mn-MnO reaction is much more favorable compared to Fe-FeO reaction. As conditions for de-phosphorisation is not achieved “P” in metal remain very high. Melting is occurred in open atmosphere, so “Mn” is also oxidized and as a result “Mn” recovery is very low. To replenish “Mn” further addition is required during further treatment and “P” further increases.

The present invention thus attempts to solve the problem of prior art by involving Ladle furnace as the alternative of effective dephosphorisation of Hadfield Steel without manganese loss comprising:

1. Producing steel in EAF with any kind of virgin charge mix i.e. “Mn” content <0.5%, so that dephosphorisation is very easy and economical. So 44 Mt virgin liquid is tapped from EAF with “P” content <0.01% and bath is completely slag free.

2. As bath is completely slag free so there is no chance of “P” reversion in LF i.e during ladle treatment.

3. Bath is reduced by addition of Silico Manganese in Ladle Furnace.

4. Heating, by arcing in the ladle furnace, by approximately 250 º C required for full “ Mn” addition.For high “Mn” melt, “P” addition through High “C” Ferro Manganese(“P” content <=0.20%) results in final “P” from LF at approximately 0 .04 %.

5. As the full amount of High Carbon Manganese is added in reduced bath so Manganese recovery is very high compared to the earlier process.

The above method of dephosphorisation of Hadfield steel through EAF-LF route is illustrated hereunder with the help of following illustrative example:

Example 1:

(1) The present invention is based on splitting the melting process. In the first stage virgin melt is prepared in EAF wherein HCFeMn is not charged in EAF and in such case charge burden in EAF is as follows:

"P" burden Calculation in Hadfield without Hadfield Revert Scrap & High Carbon Manganese charging in EAF
Wt (Kg) % "P" % "C" %"Si" "P" BURDEN (Kg) "Mn" Burden (Kg) "Si" Burden (Kg) "C" Burden
Pig iron 8000 0.1 4 0.9 8 9.6 72 320
Other Steel Scrap 42000 0.035 0.2 0.2 14.7 63 84 84
Total Charge Metallic 50000 22.7 72.6 156 404
Total Liquid 44500 0.051011 0.163146 0.3505618 0.90787

In these charge Pig Iron is used which is very rich in “P” 0.10% and total “P” burden is 22.7Kg i.e. approx 0.05%. Inspite of having Pig Iron, dephosphorisation is very easy as during melting when oxygen blowing is done, as Manganese content is very low, so enriching FeO in slag is easier, “C” will be reduced to 0.04% gradually and whatever slag will be generated that will be removed and easily “P” level of 0.006% is achieved. From furnace 41Mt of liquid metal is tapped with “P’ level 0.006% with “Mn” 0.10%.

(b) In the second stage, 41Mt Virgin melt is tapped in a ladle, and that ladle is taken to Ladle Furnace for further treatment wherein charge burden in LF is as follows:

Charge Calculation with 41Mt virgin melt from EAF and HCFeMn and SiMn addition in Ladle furnace ( Here normal variety of HCFeMn is used)
Wt (Kg) % "P" % "C" %"Si" "P" BURDEN (Kg) "Mn" Burden (Kg "Si" Burden (Kg) "C" Burden
Liquid Steel 41000 0.006 0.04 0.01 2.46 41 4.1 16.4
MLCSiMn 1800 0.1 0.05 22 1.8 1.8 396 0.9
HCFeMn 8900 0.39 7.5 2.5 34.71 6230 222.5 667.5
Total Charge Metallic 51700 38.97 6272.8 622.6 684.8
Total Liquid 50666 0.076915% 12.38069% 1.228832% 1.3516%

In this method, High carbon manganese of normal variety i.e with “P’ content 0.43% Max and “C” content 7.5% Max is used. High Carbon Manganese along with Silico manganese is added in Ladle furnace. In LF also temperature raising and addition is done in atmosphere, so oxidation of Silicon and Carbon occurred to some extent.Oxidation of Manganese is very low and recovery of Mn is very high compared to addition in EAF. “P” at the level 0.07% is obtained through this process.

(c) In a further trial, to obtain “P’ within 0.05% Max in final steel, High Carbon Manganese with restricted “P” i.e <0.25% is used, with same charge burden recalculated as follows:

Charge Calculation with 41Mt virgin melt from EAF and HCFeMn and SiMn addition in Ladle furnace ( Low phos of HCFeMn is used)
Wt (Kg) % "P" % "C" %"Si" "P" BURDEN (Kg) "Mn" Burden (Kg) "Si" Burden (Kg) "C" Burden
Liquid Steel 41000 0.006 0.04 0.01 2.46 41 4.1 16.4
SiMn 1800 0.1 0.05 22 1.8 1.8 396 0.9
HCFeMn 8900 0.24 5.8 2.5 21.36 6230 222.5 516.2
Total Charge Metallic 51700 25.62 6272.8 622.6 533.5
Total Liquid 50666 0.050566 12.38069 1.228832 1.05297

So the basic methodology of present invention is to de-phosphorise the liquid metal without addition of any kind of manganese addition in Electric Arc Furnace(EAF), asEAF is very good and versatile for dephosphorisation. Now the virgin melt is used for enriching Mn with SiMn and HCFeMn additions, in Ladle furnace there is no scope of further dephosphorisation. Whatever input “P” will be added that will go to the metal. As Manganese addition is being done in reduced bath, so recovery of Manganese also very high, and “P” enrichment is low due to lower volume of Manganese addition. Cost of Manganese addition increases with reduction in “C” and “P” content of ferromanganese. Relatively cheaper variety of Manganese source as High “C” Ferro manganeseis used in the process to achieve desired low P level.

It is thus possible by way of the present invention to provide a method of dephosphorisation of Hadfield steel through EAF-LF route directed to alternative dephosphorisation process for High Chromium and High Manganese melt. The method is based on splitting the melting process wherein in the first stage virgin melt is prepared in EAF without HCFeMn addition with low phosphrous less than 0.01% and in second stage the virgin melt is further treated in LF for enriching Mn with SiMn and HCFeMn additions but no dephosphorisation to obtain “P’ within 0.05% Max in final steel. As the full amount of High Carbon Manganese with restricted phosphorous(<0.25%) is added in reduced bath so Manganese recovery is very high compared to the earlier process. The present method thus advantageously favour wide industrial application by providing very low “P’ bearing Stainless Steel/Hadfield steel with cheaper rate. Due to low “P”content in resulting steel, all mechanical properties will be improved. In case of Hadfield Manganese Steel, abrasion resistance property will be improved with low “P”, and also much desired low “P” variety Hadfield Manganese Steel will be available in the Market.