Page 14 - Steel Tech India eMagazine Volume April 2022

VOL. 16 • NO. 3 • April 2022

Some typical ladle/ billet sample analysis of some amount. Since, conventional induction furnace lining is
induction melted steel using 65-75 % cDRI are given in silica based, building a basic slag inside the furnace
table 1 under for reference. which is a necessary condition to reduce phosphorus is
not possible. to overcome this problem and to build up
Table 1: Billet Sample Analysis
an basic slag. efforts were taken to use neutral lining
Heat %C %Mn %S %P %Si %Cr %Al in the furnace instead of silica and thus to allow build
No up of basic slag with higher basicity and using iron ore/
1 0.13 0.47 0.038 0.092 0.16 0.01 0.007 mill scale to increase FeO in the slag and even some
2 0.19 0.50 0.038 0.090 0.14 0.009 0.008 customised de phosphorising compound. But all such
efforts did not fare well and the purpose was not fulfilled
3 0.18 0.46 0.037 0.086 0.17 0.01 0.009 because it increased the tap to tap time of the process

4 0.17 0.53 0.040 0.095 0.19 0.01 0.006 reducing the productivity andsequence castinglength
5 0.18 0.56 0.046 0.090 0.15 0.02 0.009 and hence process efficiency was badly impacted. the
cost of neutral lining was also high.
6 0.24 0.60 0.040 0.092 0.20 0.01 0.008 Finally it was thought of for exploring ladle furnace

From the above examples, it can be seen that the P treatment instead of in situ treatment in the IF itself
levels are generally very high exceeding 0.08 %and for reducing the P content and after initial dilemma,
is not a good fit for the final application worthiness for especially on sustenance of the process and cost of
rebar and structural. treatment, few progressive IF plants ventured into the
use of secondary refining with encouraging results in
Some attempts in the past were made to explore how reduction of P and to some extent S as well.. A snapshot
this P level could be reduced while using high cDRI of the process adopted and the process flow sheet is
IF crucible Aim tap c-.<0.10 tap to lRF lRF ADDN- De Oxydiser/ caster
DRI 75 % chemistry Mn < 0.05 With addition of treatmentwith Ferro Alloys/Slag
Pig-10 % Si- <0.01 lime/Mill Scale/ gas purging - cover to Adjust Final
Scrap 15% Slag Off chemistry /temp
Iron Ore

shown as under:-

Study on the Process Parameters/ Specific
Consumptions:

As we are aware that phosphorus removal during steel
making process happens under oxidising condition with
a highly basic slag which absorbs the phosphorus in
form of phosphorus pent oxide as per the following
reactions
2P + 5O = P O
2 5
P O + 4CaO = 4CaO P O 5
2
5
2
these reactions are, part one is a volume zone and the
part two is a slag metal reaction. Since one molecule
of P O combines with 4 molecules of caO form the
2
5
slag, the lime content and the basicity of slag needs
to be high. Again P O has a rather lower dissociation
5
2
temperature and hence the dephosphorization process
to be controlled at optimum temperature to avoid any
P reversion in the steel. therefore the ladle furnace
operation for this very purpose needs critical controls.
Fig. 3: Typical Induction Furnace

12 Steel tech