Calcium ferrite is proposed as an alternative material for limestone and scrap in steelmaking. It contains calcium oxide for rapid slagging, iron oxide as an iron source, and provides a cooling effect through endothermic reactions. The study finds that pre-reducing calcium ferrite can solve issues of insufficient or excessive cooling, and satisfy the heat balance requirements compared to the conventional process without needing additional hot metal. Experimental results show that calcium ferrite systems have faster reduction rates at higher temperatures. Pre-reduction degree can be controlled, and a liquid calcium ferrite phase forms at low temperatures, accelerating reduction rates compared to solid materials.

1. A Study of Calcium Ferrite as an Alternative for Lime and Scrap Charging
in New Steelmaking Process
Kaushik Shubhank , Sung Hoon Jung, Youn-Bae Kang and Hae-Geon Lee
Graduate Institute of Ferrous Technology, Pohang University of Science and Technology
Introduction
Limestone and scrap have been generally used in BOF for
slagging and as source of Iron (and coolant) respectively.
However, the process involves slow dissolution of lime thus
affecting the slagging speed. De-phosphorization suffers a
setback due to these phenomena as well. Furthermore,
consistent supply of scrap remains a concern apart from
the uncontrollable impurities present in it.
Thus, there is a clear scope to improve the efficiency of the
process which has been proposed though Calcium Ferrites
in the present study. Calcium Ferrites (CaO-FeO-Fe2O3)
systems have been studied which has the potential to cater
to the lime, iron and coolant requirements simultaneously.
The alternative process/material should be:
• A source of Fe and heat sink.
• Capable of rapid and efficient slagging.
• Capable of addressing the demerits
of conventional process.
Calcium Ferrite contains:
• Dissolved CaO for rapid slagging.
CF(CaO) + SiO2 CaO.SiO2
• FeO as iron source.
• Coolant properties by reaction
FeOx+ xC Fe + xCO
(Endothermic reduction)
Abstract Objective Feasibility
Liquid
CF
Theoretical Calculations
Problem
10 15 20 25 30
-60000
-40000
-20000
0
20000
Heat balance
Heatbalance(MJ)(MJ/100tonHM)
wt% CaO in Flux
excessive cooling effect
insufficient cooling effect
0
3
6
9
12
15
Additional HM
AdditionalHMrequired(ton)
• Endothermic
reaction by
FeO may
create heat
imbalance.
• High CaO
Insufficient
cooling due
to less FeO,
high Fe
shortage!
• Less CaO
Excessive
cooling due to
high FeO, low
Fe shortage!Pre-reduction of CF can solve both issues!
Pre-reduced CF
CF (13% CaO,
60% pre-
reduced)
satisfies heat
balance
compared to
the conventional
process and
requires no
additional hot
metal.
Case
No.
Initial CF composition
(wt%)
CaO/FeO/Fe2O3/SiO2/Al2O3
CF
Temp.
(°C)
Fe
Reducibility
(%)
Viscosity
(poise)
1 8 / 76 / 11 / 5 / 0 1300 65 0.35
2 10 / 74 / 12 / 0 / 4 1300 88 2.4
4 19 / 63 / 14 / 0 / 4 1300 65 1.6
5 16 / 64 / 15 / 0 / 5 1200 72 3.2
6 19 / 60 / 16 / 0 / 5 1200 58 2.6
7 10 / 74 / 12 / 2 / 2 1300 90 2.4
9 18 / 65 / 13 / 2 / 2 1300 72 1.6
Viscosity
At solid saturation
• Viscosity calculation done by FactSage
• Viscosity increase during pre-reduction is not severe and has virtually no effect on
reduction rate.
Experimental Results
• FeO + CO = Fe + CO2
• CO2 + C = 2CO
• FeO + C = Fe + CO
Reduction rates
Controllable
reduction degree
Higher Fe oxide
content gives higher
reduction rates
No significant effect
by oxide impurities
Experimental Setup Microstructures
Fe(s)+C2F+FeOx Fe(s)+C2F+CaO Fe(s)+CaO Fe(s)+CaO
• Optimum reduction degree <70% to avoid free CaO
• Fe phase increases with C/Ceq
• Ca2(Fe,Al)2O5 forms in presence of Silica and Alumina.
• This phase is easy to melt at high temperatures.
Desired Undesired
Solid Vs Liquid phase reduction rates
• Solid powder
• No pre-melting
• Reductant: C
• Solid powder
• No pre-melting
• Reductant: C
CF systems show
faster rate at higher
temperatures!
Reductant: CO
Proposed mechanism for reduction Summary
Good
GoodGood
Good
• Pre-reduction degree can be controlled by reductants.
• CF can be manufactured with iron ore and limestone
due to negligible effect of viscosity.
• Uniform iron phase nucleation observed with
increasing reductant no need to separate in bulk.
• CaO causes liquid CF phase generation.
• Liquid phase formation at low temperatures
accelerates reduction rates compared to solids.
• Graphite is a superior reducing agent compared to
CO due to easy control on reduction degree.
• Pre-reduced Calcium Ferrite can be a good
alternative in BOF conditions.
Base Level
Conventional system heat balance