Department Seminar Slides

Report
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
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
7
CaO-Al2O3 binary system
P.C. Pistorious, R.J. Fruehan, 2009
8
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
9
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
10
Spinels!!
(shsh….it’s a bad word!)
11
Al2O3.MgO Spinel inclusions
12
Possible sources of dissolved Mg to form
Spinels:
Refractory
Alloying additions
Top slag
13
14
Change in composition slag during
processing of steel
Proces Time
15
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
16
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.
17
Effect of slag(FeO+ MnO) content on
average inclusion content
Kevin Graham, Thesis, 2009
18
Effect of Top Slag on Mg Content of Steel
Kevin Graham, Thesis, 2009
19
Does top slag impact Ca
Content of steel too?
20
Representative study plot for heat processed in LMF2
21
Example of results, sample S1
and M1
22
Example of Results samples M2
23
Sample
M3
24
Sample
M4
Sample M4
S
SP
SP+L
L
MgO+L
MgO+CaO+L
25
Process Conditions and Inclusions Chemistry
26
• 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
27
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
28
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
29
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
30
PEACE
31

similar documents