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SECONDARY STEEL MAKING
&WHEEL CASTING
G. CHOWDHURY Prof. (Met)
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STEEL MELTING PRACTICE
Electric steel making is a SECONDARY
STEEL Making process
High alloy & sophisticated steels are
made in electric arc furnace.
Both S & P can be controlled in this
process
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REFRACTORIES
Basic refractories are used.
Bottom is monolithic made of MagnesiteDry Ramming Mass (DRM).
Slag line is made of Mag-Carb. Brick.
Remaining portion is Magnesite brick.
Roof is high alumina brick.
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CHARGING SEQUENCE & ARCING
Pet coke and 50% of total lime to becharged at the bottom
Then light scrap
Heavy scrap and foundry returns
Light boring & turning
Closing the hood
Lowering of Electrodes
Start Arcing
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DESULPHERISATION
CONDITIONS FOR DESULPHERISATION
Reducing condition of bath.
Low basicity preferably 2.00 High fluidity of slag.
Intimate contact between slag & metal
High temperature of the bath(preferablygreater than 15500C)
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DEPHOSPHORISATION
CONDITIONS FOR DEPHOSPHORISATION
Low temperature
Viscous slag
Oxidizing condition
High Basicity (more than 2.5)
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PROCESS OF OXIDATION
After melting lance oxygen (Carbon boiling) May charge iron ore.
Keep the furnace door open for entry ofadequate air.
This is purification stage of steel.
Phosphorus is eliminated in this stage.
Gases like H2 & N2 are eliminated in thisstage.
Over oxidation is to be avoided.
All siliceous impurities are eliminated as slag.
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PROCESS OF REDUCTION
O2 potential in the bath is brought down
by adding reducing agents
Reducing agents are FeSi, FeMn, Al,SiMn etc.
Based on the steel to be manufactured
reducing agents are to be selected Sulpher is eliminated at this stage
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ALLOYING
Depending on the chemical composition of
steel, it is alloyed.
Alloying always to be made at thereducing state except Ni & V.
Best sequence of alloying is FeSi, FeMn,
FeCr & at the last Al.
Killing by Al to be avoided or else to be
minimised.
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POURING
Final deoxidation should be in the ladle.
Temp of pouring depends on the Carbon &other alloying elements in the steel.
The size and geometry of casting alsodetermines the temp of pouring.
Pouring temp should be optimised in the
lower side. Speed of pouring should be optimised on
the higher side.
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LADLE PREPARATION
Steel shell layered with Alumina brick (IS 8) High Alumina Ramming Mass at the bottom
Layer of High Alumina Brick at the bottom
Gaps are filled up by Ramming Mass Side wall also with High Alumina Brick
Gaps are filled up by High Alumina Mortar
Gap between IS-8 and High Alumina brickfilled with slurry of Burnt Magnesite bricks,Chips of other bricks, Ramming Mass etc.
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LADLE PREPARATION Contd.
The lip and edges are prepared by
Ramming Mass
Allowed to air dry for24 hours Subjected to curing cycle through specific
heating plan to 9000C over72 hours
Brought down to75
00
C Hold Ready Ladle preparation and heating cycle is very
important to get clean metal and long life
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POWER CONSUMPTION
IDEAL CONSUMPTION OF POWER
462 KWH/MT (Ref. MSTS)
Normally it should not exceed more
than 20% of the ideal Power.
Practical power consumption is 650-700
KWH/MT for making medium carbon steel
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POWER CONSUMPTION
TO REDUCE POWER CONSUMPTION
Top surface of the f/c should be loadedwith turning & boring
This will facilitate easy bore-in stage ofelectrodes
Excess heavy scrap should not becharged at the bottom.
This may cause damage to the bottom aswell as will take more time to lift thematerial in melt down stage.
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GOOD MELTING PRACTICE
Power consumption at various stage (PF=0.75)
Bore-in 300 unit
Melt down 396 unit
Refining 066 unit
Total 762 unit
Charge composition
HMS 50% MMS 30%
LMS, Turning & Boring 20%
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GOOD MELTING PRACTICE
Over heating of furnace to be avoided Pre-heat ladle (5000C 7000C) before pouring
Specific pre-heating cycle of ladle is essential
Correct basicity of slag should be maintained
Correct tap positions during melting isessential
Pre-heated Ferro Alloys should be charged
At least 20 point carbon boil is essential
Ferro Alloys should be estimated based on thefurnace condition
Clean steel can be produced in clean andhealthy furnace
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WHEEL CASTING
Major slag is removed from the top of ladle
Ladle placed in JOHN MOHR Pit
Al. star thrust into as final deoxidiser Sample taken for Chemical Analysis & H2 Top cover with Silimenite tube sits on top
Graphite Mould sits on the top of tube
Pit pressurised by air to lift the liq. Metal
Liq. Metal flow to the mould to fill cavity
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WHEEL CASTING Contd
Plunger brought down to seal the gating Mould placed on conveyor, next one in
Stripping after pre-determined time to take
away the Risers along with top Wheels placed on conveyor to tunnel
Moulds go back for cleaning and recycling
Sprue Wash, Stamping & Hub Cutting
Placed to Moving Bed NormalisingFurnace followed by Rim Quenching,Tempering and Hub Quenching
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WHEEL INSPECTION
After Hub quenching, cooled to RT Shot blasting to clean and impart
compressive stress
Visual Inspection in normal light Magnaflux Test for surface & sub-surface
under UV light
Wheels with removable defect sent for defectremoval through grinding & rechecking
Automated Multi probe UT in Sprue area
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WHEEL INSPECTION Contd
Hardness Testing
Final Hub boring
Final shot blasting Warpage checking
Final Dimensional checking
Other Mech. Testing one in each Heat Closure Test & Hardness mapping 1 in 500
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CAST WHEELS AT RWF
Wheels to RDSO Spec. No. R-19 Part-III/1993.
Producing both BOXN & Carriage wheels
Production target this year is 2 lacs Continuous three shift operation
Looking forward for Loco wheel production
Axle forging from bloom a parallel activity Final product: Wheel sets & loose wheels
Total production connected by LAN
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CAST WHEELS AT RWF
Metallurgically forging route better than casting
Special technique of controlled pressure casting
Equivalent to forging route, even better
Cross dendritc structure barrier to dislocation
movement
Mechanical properties as stipulated are well met
High K1C value Resistance against catastrophic failure in service
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CAST Vs FORGED WHEELS
High rate of production
Machining of wheel is eliminated, any plate design
In casting internal defect position is known
So, very easy to ensure soundness Very uniform Quality
No non-uniform quality arising of non-uniform hotworking with wide difference of reduction ratio
Cleanliness is achieved by refining of steel in EAF One thin series of inclusion as per ASTM E-45
Unique deoxidation ensures globulized alumina
This helps in achieving K1C value of the steel
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