Transcript Department Seminar Slides

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
2
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.
3
Ladle Metallurgical Furnace
Significant control
challenges:
-Elevated temperatures
-Dusty environment
-Electrical arcing
-Complex multi component
slag/metal systems
4
5
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
6
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 slagmetal interface
Generalized equilibrium
reaction can be stated
as: xM  yO  M x Oy
where:
KM 
{Fe}  [O]  ( FeO)
[ Mn]  [O]  ( MnO)
[ Si]  [O]  ( SiO2 )
[Ti]  [O]  (TiO2 )
[Ca]  [O]  (CaO)
2[ Al ]  3[O]  ( Al2 O3 )
[ Mg ]  [O]  ( MgO)
Slag
(MnO)
Metal
[Mn]
[O]
aM xOy
hM x hO y
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Kinetic Model Formulation
• System represented by series of differential
equations:
•
dX i  kmi A  b
*

X

X

 i
i 
dt  Vm 
Metal:
Slag:
Reaction are coupled using flux
density equations:


M O

kmM CVm X Mb  X M*  ksl x y CVs X M* xOy  X Mb xOy
dX i  ksi A  *
b

 Xi  Xi 
dt  Vsl 

• Newton-Raphson subroutine used
•
to solve overall oxygen balance
Interfacial concentrations were
determined and trajectories updated
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?
20
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
Sample M4
S
SP
SP+L
L
MgO+L
MgO+CaO+L
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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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Future Work
• 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
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Validation with the experimental data
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
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