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Study of kinetics of Inclusions Transformations in Ladle Metallurgical Furnace for the Production of LCAK Steels Departmental Seminar Presentation Mahshid Fathi- May 27/2011 1

Study of kinetics of Inclusions Transformations in Ladle Metallurgical Furnace for the Production of LCAK Steels Departmental Seminar Presentation Mahshid

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Study of kinetics of Inclusions Transformations in Ladle

Metallurgical Furnace for the Production of LCAK Steels

Departmental Seminar Presentation

Mahshid Fathi- May 27/2011

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Outline• Objectives• Introduction

– Ladle Metallurgical Furnace– Non Metallic Inclusions and Inclusion Engineering

• Literature Review:– Role of slag on formation of spinels

• Experimental results• Summary• Future work• Acknowledgement

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Objectives

• Investigation of the impact of processing parameters on the kinetics of transformations of inclusions formed after deoxidation of the LCAK steels and during the Ca treatment in full scale Industrial Ladle.

• Development of a mathematical model for the kinetics of inclusions transformations– With focus on Spinels and calcium aluminates

• Validation of the model by experimental results.

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Significant control challenges:-Elevated temperatures-Dusty environment-Electrical arcing-Complex multi component slag/metal systems

Ladle Metallurgical Furnace

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Non Metallic Inclusions during refining

• Oxides and sulfides• Mostly oxides, deoxidation products• By adding Al in LCAK steels• Initially Al2O3 oxide Particles

– High melting point, solid (above 2000C)

• Remain in the steel• Degrade mechanical properties• Cause problem in casting

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Inclusion Modification• Calcium Treatment

• Adding calcium– Lowered melting point– Enhanced castability

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CaO-Al2O3 binary system

P.C. Pistorious, R.J. Fruehan, 2009

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Mass Transfer steps in steelmaking bath• Assumption of equilibrium at the interface

• 1-Transfer of reactants from the metal phase to the slag/metal interface

• 2-Chemical reaction at the slag-metal interface (very fast in steelmaking T)

• 3-Transfer of products away from the slag metal interface

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Mass Transfer Metal- Inclusion

• Initial alumina inclusion content and size• levels of Sulfur• levels of Oxygen• Calcium feed rates • Presence of multiple pumping source of dissolving

element as in MgO.Al2O3 spinels

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Spinels!!

(shsh….it’s a bad word!)

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Al2O3.MgO Spinel inclusions

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Possible sources of dissolved Mg to form Spinels:

Refractory Alloying additions Top slag

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Change in composition slag during processing of steel

Proces Time

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Multi-Component Reaction Model• Work based on the model of Robertson et al. (1984)

• Local equilibrium assumed at the slag-metal interface

• Generalized equilibrium reaction can be stated as:

where:

Metal

Slag

[Mn] [O]

(MnO)

2

2

2 3

{ } [ ] ( )[ ] [ ] ( )

[ ] [ ] ( )[ ] [ ] ( )

[ ] [ ] ( )2[ ] 3[ ] ( )

[ ] [ ] ( )

Fe O FeOSi O SiO

Mn O MnOTi O TiO

Ca O CaOAl O Al O

Mg O MgO

x yxM yO M O

x yM O

M x yM O

aK

h h

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• System represented by series of differential equations:

• Reaction are coupled using flux density equations:

• Newton-Raphson subroutine used to solve overall oxygen balance

• Interfacial concentrations were determined and trajectories updated

Kinetic Model Formulation

* *x y

x y x y

M OM b bm Vm M M Vs M O M Oslk C X X k C X X

*i

bi mi i

m

dX k AX X

dt V

*

ibi s

i isl

dX k AX X

dt V

Metal: Slag:

Robertson, D.G.C., Deo, B., and Ohguchi, S., 1984, Ironmaking and Steemaking, Vol. 11, No. 1, pp. 41-55.

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Effect of slag(FeO+ MnO) content on average inclusion content

Kevin Graham, Thesis, 2009

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Effect of Top Slag on Mg Content of Steel

Kevin Graham, Thesis, 2009

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Does top slag impact Ca Content of steel too?

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Representative study plot for heat processed in LMF2

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Example of results, sample S1 and M1

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Example of Results samples M2

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Sample M3

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Sample M4

MgO+CaO+L

SP

L

MgO+L

SP+L

S

Sample M4

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Process Conditions and Inclusions Chemistry

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• there seems to be a close relationship between the Max MgO as seen in M3 of heats with the amount Sulfur decreased from its initial value to the value it reached in M3

Heat # dS up to M3 Max % MgO inc

100548 0.0194 5

100541 0.0198 8

100545 0.0201 11

100543 0.0204 16

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Summary• Kinetics of inclusions transformations are

controlled by mass transfer in metal• Composition of both metal and slag changes

during the processing which can be described by the multi-component kinetic model

• There is a strong relation between the chemical composition of slag and the injection of Mg in the metal and forming spinel inclusions

• There can be a link between the conditioning of slag specially for desulfurization and increase of MgO level in steel

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• Continuing the study on impact of industrial process parameters– Slag carryover from EAF– Slag conditioning– Additions

• Composition• Time of addition

• Impact of initial size and distribution of inclusions• Kinetics of oxygen removal, measurements of total

oxygen• Investigation of the impact of refractory and other

possible sources of Mg to form spinel inclusions• Calcium is injected as wire into the steel, and the

rates of dissolution need to be determined.• Completion of the model• Validation with the experimental data

Future Work

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Acknowledgements• My Supervisor Dr. Gordon Irons• Dr. Ken Coley and Dr. Chris Swartz• Steel Research Centre, John

Thompson• Arcelor Mittal Dofasco Team, Don

Holdridge, Steve Waterfalls, Dongsheng Liao

• My sister, Shideh Fathi• All of you, my friends in MSE

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PEACE