11The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Solidification Techniques of Metals under Magnetic Field
En-gang WANG* An-yuan DENG Lin ZHANG Ji-cheng HE
Key Laboratory of EPM (Ministry of Education) Northeastern University, China
2The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Content
Part I : Solidification of Steel Billet in the Initial Stage of Continuous Casting Process with Electromagnetic Field
Part II : Solidification Behavior of Cu-Pb Immiscible Alloys in High Magnetic Field
3The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Principle of Soft-Contact Continuous Casting of Steel with High Frequency Electromagnetic Field
Segment
Slit
Coil
Mold
J
Schematic of Soft-contact Mold
—— new application of Lorentz force in continuous casting process of steel Coil - High Frequency Electromagnetic Field
“Skin Effect” – Mould with Slit
Electromagnetic Pressure
“Soft-contact Effect”
—— eliminate or reduce oscillation marks of strands, to be rolled directly without grinding and reheating.
4The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Joule heating: Molten steel of meniscus is heated
Formation of initial solidifying shell is delayed to inhibit a “hook defect”
Solidification of mold flux is avoid to accelerate heat transfer.
Lorentz Force : Electromagnetic Pressure – “Soft- Contact Effect”
Contact pressure is reduced
Convex free surface is formed to enlarge meniscus curvature so that Inflow of mold flux is easy
Two Function
The concept of electromagnetic casting of steel
5The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Fundamentals of Soft-Contact Continuous Casting of Steel with High Frequency Electromagnetic Field
15mm
Pb-Sn-Bi
-200
-150
-100
-50
0
Bzmax, T
z, m
Parameters: Frequency(10kHz-150kHz), Electric Current (Power), Coil Turn, Coil Location, Molten Steel Level, and so on
-200
-150
-100
-50
0
Bzmax, T
z, m
slit
Effect of coil turns on magnetic flux density
6The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Conditions of Casting Experiment
Billet size: 100mm×100mm Coil Turns: 5 Metal composition: Sn-10%Pb alloy, Coil Location: -5mm
0.6~0.7%C Steel Meniscus level: 100mm Casting speed: 400mm/min Power Supply: 20kHz, ~100kW Oscillation frequency: 30cpm Oscillation stroke: 6mm
Furnace CC Machine HF Power Supply
7The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Casting System in Pilot CC Machine
pumppump
Flow-meter
8The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
With high frequency EM fields, the oscillation marks of Sn-Pb alloy billets were eliminated and smooth surface were obtained,
Surface of Sn-Pb Billet
Surface of Sn-Pb billet
m50µ
m200µ
m200µ
m20µ
Without electromagnetic field
With electromagnetic field
9The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Steel Billets with High Frequency EM Fields
A
AB
Control of meniscus level
2) Structure of Billet:
0.6~0.7C(wt%)
10The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Solidification Structure of Billet
-0.05 0 0.05 0.1
A -- A B -- B
3D flow fieldsthe area of equiaxed gains near surface increases -- Stirring
11The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Outlook 1) Fluctuation of melt surface with high frequency electromagnetic field
Effect: inflow of mold flux, engulfing of inclusion, surface quality, etc
Parameters: frequency, electric current, power, numbers of coil turn, etc
2) Fundamentals of the same technique on round billet, slabs
0 2000 4000 6000 8000 10000 -2
-1
0
1
2
3
-2
0
2
4
Fluctuation of surface with different Ampere- turn (f=29.2Hz)Fluctuation of surface with different frequency (P=107kW)
C oil Sl it
B v
F v
Round billets
12The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Summary
• The strand surface can be remarkably improved by imposing high frequency electromagnetic field near the meniscus. The oscillation marks was remarkably reduced or eliminated.
• Distribution of magnetic flux density in mold is very important to the soft-contact effect of continuous casting of steel
• The molten steel level should be controlled near or little lower the top of coil in order to obtain billets with more smooth surface.
• Increasing electric power, the soft-contact effect is remarkable, but there is an optimal value because of the fluctuation of free surface.
13The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Part II
with High Magnetic Field
14The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Solidification Conditions under High Magnetic Field
Sample dimension φ10mm×20mm
Magnetic field strength: 12T
0 50 100 150 200 250 300 350 400 0
200
400
600
800
1000
12T-100mm Heating history
15The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Macrostructure of Cu-Pb Alloys
Phase diagram of Cu-Pb alloy
• Cu-40wt%Pb: there some large Pb droplets, but no separation of two phase. • Cu-80wt%Pb: there are separation of two phase (two layers) because of the
immiscible gap. • Magnetic field have some influence on microstructure and separation of phase.
16The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Solidification Structure of Cu-40wt%Pb Alloys
The microstructure in the center of sample
The microstructure near the surface of sample 0T 12T
0T 12T For Cu-40wt%Pb, there no
separation of two phase because it is near the monotectic point with little immiscible gap.
With high magnetic fields, the shape of Pb phase is changed to long or rod shape from sphere particles and tend to array in some direction.
Schematic view of acting forces on particle
FM-Pb
y
x
FB
FM-Cu
FD
FA
Viscous forceCu-paramagnetic, Pb-diamagnetic materials
17The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Solidification Structure of Cu-80wt%Pb Alloys
(a) (b) (c) (d) (e)
(a) (b) (c) (d) (e)
12T
0T
There is serious separation of two phase, Cu-rich layer and Pb-rich layer;
With high magnetic fields, the Cu-rich phase is changed to sphere particles from dendrite crystal, and gradually became larger particles from bottom to top owing to their combination.
18The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Microstructure of Cu-80wt%Pb alloys
0T 12T Morphology of Cu-rich phase in Pb matrix (Cu-80Pb) SEM of Cu-rich phase X350
Cu
Pb
Why? Cu-rich phase is changed to sphere particles from dendrite crystal under High magnetic field. The explanation is not enough.
Outlook: mechanism on the formation of solidifying structure, and action of magnetic force under high magnetic fields, etc
19The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Summary
• The morphology of Cu- Pb immiscible alloys have greatly changed under high magnetic field.
• The action mechanism of magnetic field on the solidification immiscible alloys need further detail research
20The 2nd German-Sino Workshop on EPM, Oct. 16-19 2005, Dresden, Germany
Key Laboratory on Electromagnetic Processing of Materials (Ministry of Education) Northeastern University, China
Acknowledge:
National Natural Science Foundation Committee, China
Forschungszentrum Rossendorf, Germany
Part IISolidification Behavior of Cu-Pb Immiscible Alloys with High Magnetic Field
Macrostructure of Cu-Pb Alloys