Page 13 - Steel Tech India eMagazine Volume April 2022

VOL. 16 • NO. 3 • April 2022

in the DRI, quite high and beyond the specification of high volume of slagmainly coming from the gangue
limits for many final products. Just as a flavour, it is not content of the ore/ash content of coal. As theinduction
uncommon to have P in such steel in the range of 0.08 melting crucible is gradually filled with molten metal and
to as high as 0.12% and S in the range of 0.04-0.08%. slag, the later needs to be drained off intermittently in
to a large extent the quality of iron ore and coal used order to free the furnace space inside the crucible for
for making the DRI contributes to this level in the steel further melting of the metal. this drainage is usually
so produced. this if we look at from the final product done either manually using a skimming spoon for small
specification point of view, both these elements ideally and medium capacity furnaces or by tilting the furnace
demand to be reduced to a much lower values for partially towards the tapping side. When the melting
product application fitness. In the primary steel making continues and the crucible is nearly full up to 60-70
process, direct oxygen lancing and putting a basic slag %, bath samples are taken and chemistry checked
in the furnace, oxidises the P and the basic slag absorbs generally through spectrometers and balance charges
the oxidation product mainly P O . however in Induction decided based on mainly carbon content of the sample.
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furnaces this is difficult because effect of oxygen to allow higher cDRI charges as input, the opening
lancing would be minimal as the depth of the steel bath carbon at this stage is aimed higher and around
bath is high in IF and most importantly the basic slag 0.3-0.4%. As the melting continues, progressive
can’t be adopted because most of the IFs have acidic samples for chemical analysis taken till the furnace
lining. this is now being looked into seriously by some melts up to full capacity of the crucible and the carbon
manufacturers who earnestly upgrade the quality and is aimed nearly 0.15 to less than 0.2%.
fortunately ladle Refining is emerging to be a workable After the melting is completed and final sample
solution for the same. It’s a matter of accomplishment chemistry is available, the temperature is raised to
that some IF units have successfully developed the tapping temperature, additions, mainly FeSi, SiMn are
process of secondary ladle refining following induction calculated to achieve the target chemistry on Mn,Si and
melting to achieve sustainable production of finished c contents and requisite cPc (calcined petroleum
steel with acceptable chemistry especially for P and S. coke) is added if needed to finish at target c levels of
this is rather a revolution in induction melting process generally around 0.2% for rebar grade . the ferro alloy
in India and expected to grow exponentially especially additions are made partly in the furnace and balance
for medium to large capacity induction furnaces.
in the ladle before tapping along with cPc and requisite
Process Concept of LF treatment on IF steel: Aluminium quantity.
Generally for making rebar grade steel which is most In general, the finish heat chemistry is aimed at as
pre dominant in India, following input charge mix is under for common rebar grades for major elements
being used:- are:-

• Pig Iron 5-10 % c- 0.15 to .20 %
• Shredded/ HM Scrap- 10-15 % Mn 0.45 to 0.60 %

• CDRI- 70-80 % Si- 0.15-0.25 %
• CPC as per need however, while the chemistry wrt the above elements
can be largely achieved through judicial additions of
the primary process of current induction melting
furnace is to first charge PIG Iron/Scrap and switch cDRI, the ferro alloys and carburiser, the phosphorus
on the power to melt thecharge partially. cDRI is and sulphur contents of the bath can’t be controlled
chargedthereafter semi continuously either manually practically. It is to be noted that throughconventional
or through hoppers/ vibro feeders and the melting induction furnace steel making, other than depletion
continues. The CDRI generally has metallization in of c and to some extent Mn/Si through cDRIadditions,
the range of 78- 84% with total Fe of nearly 86-90 % no reduction is possible in other elements especially.
depending on the quality of ore and DRI process. this As a result, these elements coming from the cDRI and
cDRI is generally produced from either lump ore or other inputs generally are on a higher side and beyond
pellets. the melting of the cDRI results in formation the limits of acceptance in most of the end applications.
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