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Blast FurnaceHot Metal Chemical Composition C% - 4 Si% - 0.8 S% - 0.06(max) Mn% - 0.5
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Electric Arc Furnace EAF is prime station of SMS. It is
melting unit of SMS. It’s capacity is 40 ton.
Decarburization & Dephosphorization of steel is carried out by oxidation process.
Basicity of slag is maintained between 1.8 to 2.5 .
Impurity of steel in the form of slag are drained out through slag door.
Estimated oxygen is blow to get desired tap carbon.
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Approximate 80-90% chemistry adjustment is done at EAF during tapping.
EAF is backbone of SMS. Productivity of shop significantly depend upon the performance of EAF.
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Ladle Refining FurnaceLRF is for secondary steel making. Almost
100% chemistry is met here.Steel purification and homogenenization is
accomplished. Refining of steel is done at LRF through
deoxidation and desulphurization. Continuous Argon purging of hot metal is
done. Basicity of slag is maintained 2.5 to 3.0 to
achieve FeO level less than 1%.Calcium treatment is done to change the
morphology of inclusion.
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Normal process time at LRF is 50-60 minutes.
After the required alloy addition heat is transferred for CCM or VD as per requirement.
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Vacuum Degasing A Vacuum Degassing System or Degasser
is used in the secondary refining of steel - subjecting molten metal to a vacuum to remove oxygen, hydrogen and nitrogen to produce ultra-low carbon steel for the automotive, electrical, construction, and rail markets. Vacuum degassing is normally performed in the ladle and the removal of dissolved gases results in cleaner, stronger, higher quality, more pure steel.
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Degasser Principle:
Sieverts law:- Dissolution of diatomic gasses in
steel is directly proportional to partial pressure.
[hH]^2 =Kp H2
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Sources of inclusion of gases:1.Hydrogen : # By absorbed moisture
associated with the raw materials (Lime) used in steelmaking.
# By hot metal (2–5 ppm) and scrap (2–7 ppm).
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2. Nitrogen: # By atmosphere (Mainly)
through air bubbles entrained during tapping.
# By Nitrogen impurities of ferroalloys.
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3. Oxygen: # By Oxygen blowing in furnace. # By atmospheric exposer.
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Effects of inclusion of gases Hydrogen :- Hair Cracks. Nitrogen :- Surface Cracks. Oxygen :- Blow Holes & Pin Holes.
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VACUUM DEGASSING PROCESSES :
Vacuum degassing is practiced in the steel industry for several purposes. They are : -
To remove gases.To improve cleanliness by inclusion
floatation.To produce steel of low carbon content ( <
0.03%)To maintain homogeneity of temperature
and chemistry.To control pouring temperatures, especially
for continuous casting operations.
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Vacuum degassing processes, in the broadest sense, refer to the exposure of molten steel to a low-pressure environment to remove gases (chiefly hydrogen and oxygen) from the steel. The effectiveness of any vacuum degassing operation depends upon the surface area of liquid steel that is exposed to low pressure and slag’s fluidity obtained from LRF.
Hydrogen and Nitrogen removal is a diffusion and partial pressure phenomenon. Oxygen removal is a function of chemical reaction of oxygen with carbon and the partial pressure of carbon monoxide.
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Introduction to VD of JNILMake – METECConsisting of six steam ejectors with
three condensers for vacuum creation.VD also have O ring for sealing of
2. Free Cutting Steel No holding (12L14 & EN-1A) Only 5 min
VD process
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3. Semi Free Cutting No holding
Steel Only 5 min
(EN8M & EN15AM) VD process
4. Alloy steel & all carbon 10 min
steel
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Example For Ball Bearing SteelInclusion at LRF- Oxygen- 20-30 ppm Hydrogen- 1.52 ppm Nitrogen- 80-90 ppm After VD- Oxygen- 10 ppm Hydrogen- 1.1-1.2 ppm Nitrogen- 50-60 ppm
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VD TREATMENT PROCESS VD treatment to be done after achieving
vacuum of 1 torr for specified holding time.After VD treatment send sample for
chemistry confirmation and take temperature.
Feed Al wire as per chemistry required.Then add Ca-Si wire.Now add alloys as per chemistry.Add 120kg Of RADAX to prevent temp loss.Then send final sample and take