Castability From Alumina Spinels

Prévia do material em texto

Castability -
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tolerance to clogging. The same steelmaking practices that
are successful on one caster will not always work on
another caster. In general, the larger cross section casters
ave a greater tolerance to the types and amounts of
inclusions present in the steel. These larger cross section
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From Alumina to Spinels
Larry A. Frank
Inland Steel Bar Company
troduction
The interest in castability problems and especially
solutions to castability problems has increased
amatically as the per cent of continuously cast products
s increased. If you are reading this paper looking for
mple and easy solutions to these castability problems –
TOP NOW! You will not find easy answers.
This paper grew out of two inter-related issues.
he first was my own interest and struggles with castability.
he second issue was how best to educate the younger
etallurgists about castability. Even the metallurgists are
oking for a quick understanding of castability and related
sues.Many would p~fer to be handed an answer that only
kes a few minutes to hear, understand and implement.
nfortunately, it requires a thorough understanding of
eelmaking slags, inclusions, and the steehnaking process.
he purpose of this paper is not to provide that quick
swer but rather to provide an historical perspective of
w the technical knowledge of castability has evolved to
s current level. The reader carL however, use both the
rspective and the refererws as educational tools that will,
ith considerable study, lead to a more thorough
nderstanding of the subject of caatability. The main fmus
f this paper will be toward bar product grades. This
enerally implies signillcantly more alloy content than flat
roduct grades usually including higher carbon, higher
licon, and higher manganese. The one exception to this is
at most of the bar products grades have aluminum levels
f 0.020 to 0.040 ‘%0 and some of the flat products grades
ay have higher aluminum levels.
verview of castability
The nature of casters has changed overtime with
e development of new technology. There are a
emendous variety of casters each with its own
ombination of ladle, tundisk and steel flow control
stems. Each of these systems also displays a different
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1998 ELECTRIC
sters have larger tundish nozzle systems that do not clog
sily. In contrast a small cross section caster, with either
mall metering nozzle or slidegate system is way sensitive
any buildup. These small cross section casters clog very
sily and require close attention to steehnaking, ladle
tallurgy, and casting practices.
eezimz.Inelusions, and Refiactones
There are a number of types of castability
oblems. including iieezing, refractory problems and
clusions. Freezing or temperature control is a common
e especially with higher carbon grades. In these grades,
wer casting temperatures are desirable for internal
ucture but the lower temperatures also can result in
ezing. Tundish refractory or tundish gate failure can also
use clogging type problems. A piece of reffactmy can
dge in the nozzle well or gate mechanism and restrict the
w. The third general type of clogging problem is related
the build up of inclusions in the nozzle well and gate
eas. It is often very diilIcult to be able to tell the
fference between these three potential source causes,
ually, an examination of the solidified steel in the nozzle
ll area or gate is required to properly determine the
use.
In the course of this paper, only castability
oblems caused by inclusion buildup will be discussed.
wever, refractory and temperature control issues should
t be ignored by any one as they can and do cause
stabilityproblems. The vast majority of this paper will be
voted to three types of inclusions –
Alumina – Al*03
Calcium Sulf3de - CaS
Spinel - MgO- A1203
These are the enemy! All of these inclusions are
lid at steelrnaking temperatures and will buildup on the
fractories and cause clogging of the nozzle area or tundish
tes. The goal of good castab@ practices is to reduce
ese inclusions far enough to have good casting with no
ge inclusions breaking off into the steel, It should be
ted that it might not be necessary to mod@ all of the
clusions to a liquid form. Good castability can be
hieved even with a portion of the inclusions being either
lid or semi-solid.
FURNACE CONFERENCE PROCEEDINGS – 543
Castabilitv the Earlv Davs
One of the first mentions of clogging attributable
to inclusion buildup was in an article in the Journal of the
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published in the Iron and Steelmaker in 1975. These
articles clearly stated that alumina inclusions could be
modified to a liquid form by the addition of calcium to form
544
merican Ceramic Society in 1949 written by Snow and
heal. In this article, they described a ladle clogging
tuation using stopper rod nozzles while teeming an
uninum deoxidized steel. However, it wasn’tuntil years
ter with the advent of continuous casting that the literature
owed an increase in the interest in the subject of clogging.
The work of Farrell and Hilty in the late 60’s and
rly 70’s represent an incredible additionto the knowledge
inclusionsin general and to the field of castability. Much
this work involved the irdluence of calcium on the flow
steel through nozzles. The 1971 article “Steel Flow
rough Nozzles: Influence of Deoxidizers “2 revealed a
markable (ahnost prophetic) overview and grasp of
stability problems and solutions even at that time. It
ade the following important points.
) The difference between casters was recognized
specifically as related to the cast section size and
nozzle diameter, Smaller cast sections, especially
those using metering nozzles, are very vulnerable
while larger cast sections (with larger bores) are more
tolerant of inclusion build up.
The following quote from this article states one of the
most basic and important tenets of castability
improvement work. “The observations made indicate
that any deoxidation treatment producing an oxide
phase that is solid at steel casting temperatures can be
expected to impede the flow of steel through a nozzle,
and ultimatelycause the nozzle to plug by precipitatizm
and accumulation of the oxide in the nozzle bore.”
) This article also recognized that such things such as
oversize nozzles, bubbling nozzles, and others are
mechanical in nature. While these things may alleviate
the symptomsof cloggingby also can adverselyeffect
the steel quality by causing large agglomerations of
inclusions to break loose and end up in the steel.
The most prophetic comment from this article was the
tlnal one “The simplest and most desirable solution
would be a chemical one in which the melting
temperatures of the oxides produced by strong
deoxidizers would be lowered belowzthat of steel, as
occurs with manganese and silicon.”
Followingthe 1971 article by these authors,P~41 and
of “Modification of Inclusions by Calcium” ‘ was
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lcium aluminates. The article also described the potential
forming solid calcium sulfides that can also cause
ogging.
These articles included many photographs of
clusions and also schematic ternary soli~lcation
agrams. With these photographs and diagrams, it is
latively easy to understand the formation of the various
pes of inclusions.Part II of this article also discusses the issues of
oxidation. While it does not directly address reoxidation
d its effect on castability, it did describe the types of
clusions formed. Based upon experience at Inland Steel,
oxidation is perhaps the fastest way to encounter severe
stability problems. Air infiltration in the ladle gate area
the ladle to tundish area will result in the onset of
ogging. A similar response has been observed if steel is
ured unshrouded between the ladle and tundish.
eoxidation may also occur in the tundish to mold area if
ere is any air aspiration into the steel. Poor assembly of
idegate plates, not sealing plates to the upper nozzle in the
ndish area or cracks in the slidegates could cause
oxidation clogging.
Another type of reoxidation would be the madt of
eel reaction with either ladle or tundish slags containing
gh levels of Educible oxides. The slags will absorb some
the alumina produced by such reoxidation but some of it
ill also be swept into the steel where it can cause clogging
oblems.
There are no special cures for these types of
oxidation problems. Proper attention must be paid to
fractory assembly and fit to assure no air can penetrate.
n additiomnitrogen or argon flow around vulnerable areas
n assure no oxygen can get into the steel. In terms of
ags or tundish fluxes, high levels of easily reducible
ides must be avoided.
rocess Check
By the middle of the 1970’s, the problem
ncerningclo@.ng due to alumina was clearly reoognizd
ven the direction for the solution was recognized - turn
e solid inclusions into liquid ones. With al- this
uld be done with calcium forming liquid calciurn-
uminates. Now, it was time to turn the technical
owledge into more practical application.
In 1980, Farrell and Hilty in conjunction with
loria Fauhing published a pa er “Steel Flow through?.ozzles: Intluence of Calcium” . Tlus was an important
GS
article through its attempt to quant@ the required amount
of calcium as a function of aluminum present in the steel.
couple of papers concerning castability of aluminum killed
steels by utilizing calcium treatment. One of these describe
e experiments performed at Inland Steel’s #1 Electric
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The following graph (Figure 1) presents the data developed
in this article and shows the relationship of the ratio of
aan ml al 1
0/’Ca 1’10 Al
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Figure 1. Steel Flow as a function of the Ca/Al Ratio
Ca/Al on the amount of steel which flowed through a
tundishnozzle into an ingot before clogging occurred This
article clearly demonstrated the potential of calcium
treatment to decrease clogging as well as the importance of
the proper amount of calcium.
Their data showed that the type of inclusion
changes as the calcium to aluminum ratio increases. As
would be expected, the inclusion composition changes as
this ratio increases.
A1203~ CaO-6Alz03. ~ CaO-2A1203~
l CaO-A120@ CaS
The best steel flow was obtained with CaO-
2A1203and CaO-AlzOs. This is a very often-cited paper
and demonstrated the cm.xpts initiated in the 1970’s and
showed that a emversion of solid aluminates to liquid
calcium aluminates is possible and will prevent buildup of
inclusion matter.
Solutions to Alumina and Calcium SuMde Clotig
The 1970’s were characterized by the recognition
of the castability problem of aluminum and alumina. For
continuous casting of billets, the casting of aluminum fie
grained steels was avoided as much as possible in favor of
utilizing columbium or vanadium as a grain refiner. The
next period of time from 1981 through 1989 was a period
of gaining a theoretical understanding of the
thermodynamics and a translation into shop practices.
In 1982-1984, Pielet and Bhattacharya wrote a
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1998ELECTRIC
nace and Billet Caster to cast these steels through
tering nozzlesc. This paper included both high and low
bon steels and discussed some of the practices used for
ducing them. The inclusions produced by these
ctices wem microprobe and the inclusicmanalysiswere
pared to the castability of the heat.
In 1984, they also published “Thermodynamicsof
zzle Blockage ~ Continuous Casting of Calcium –
ntaining Steels” in Metallurgical Transactions B, ThiS
s a detailed look into the thermodynamics of calcium
dificationof inclusions and formation of calcium suliide.
ntains appropriate equilibrium constants, b energy
ormations, activities, and interaction coefficients. While
type of paper and analysis is often difiicuh for many
p metallurgists, it provi&s &tails in table form to show
various calculations were performed. This is an
ellent article to study to gain a better understanding of
tability.
In 1984 and 1986, two very interesting papers
re published by British Steel in England which described
cium treatment for castability. The fist one8 in 1984,
n Stocksbridge Works, described the production
ilities and parameters utilized to mod@ aluminates and
id calcium sulildes. The second oneg in 1986 horn
therham Works provided a facilityoverview and some of
process parameters. It also described work comparing
moditlcation of aluminates with CalSil cored wire and
ce injection of CalSil. This paper is especially worth a
iew because of the descriptions of the types of
lusions found at several stages of steelmaking
duction.
By the middle of the 1980’s, considerable
erience had been gained in understanding and applying
thermodynamics of calcium modification of aluminates
avoiding the formation of calcium sultides. In 1988,
re was a one-day “Calcium Symposium” in Glasgow in
junction with the International Slag Conference. There
re several papers presented which demonstrated a
rough understanding of the subject. Two exeellent ones
luded “Gui&lines for Cal#un Treatment of Steel and
te of Calcium Retained” by Pellicani, Durand and
eussier andl ~“ResuRuized Steels for Improved
chinability” by Boussard, Szezesny, Pellicani, and
eussier. Both of these used an interesting diagram first
eloped by IRSID to illustrate the relationships involved
odification of aluminates by calcium and the avoidance
alcium sulfides. A copy of this diagram is included in
FURNACECONFERENCEPROCEEDINGS– 545
Appendix 1 at the end of this paper. Working through these
two papers and deriving the diagram from the chemical
reactions will lead to an increased understanding of the
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be to avoid or suppress the formation of spinels.
At this point, it is worthwhile to look back at some
the other earlier papers for prior evidence or information
ncerning the spinels and the link to castability problems.
546-
ermodynamics and the necessary requirements to
ccessfullycast aluminum killed products.
Beware, this is not an easy process, but the
ginning of this paper warned you ahead of time. There
ems to be no real short cut to gain an understanding of
e inter-relations~p~l between the chemical reactions.
hese two articles ‘ and equations provide an excellent
undation for understanding and resolving castability
oblems due to alumina and calcium modification of the
uminates.
he Dirtv Word - SPINELS
As clearly as the 1988 symposiumpointed out the
ay to handle the modification of aluminates and to avoid
lcium sulfldes, it also contained a dire warning. There
as another enemy out there and it was to prove to be even
ore formidable than the first one. This enemy, spinel
clusions, was describedin Kor’s aper titled “Calcium
reatment of Steel for Castsbili~ ?1 in which he described
periences with 0.20/0 .40°Acarbon AK grades produced
a bloom caster. The fit part of this article was a review
the basics of calcium treatment of aluminates to improve
stability. The results of taking steel samples from the
eel before and after CalSil additions were discussed. One
the observations made based upon SEM analysisof these
mples was that “majority of altil~te inclusions
ntained vaxyingamounts of magnesium” The amount
magnesium in inclusions varied up to a ratio of magnesia
alumina of 0.25. Kor fkt.her analyzed the potential of
odifying the magnesium aluminates with calcium
wrding to the following chemical reaction.
a (v)+ (1 + 1/3) [AlzOs+ y MgO] l
~ CaO-x Alz03-y(x+l/3)Mg0 1+ 2/3&
e concluded that the moditlcation of the magnesium
uminates by calcium would be less effective than the
odification of pure aluminates. He also speculated that
e magnesium may have originated from the aluminum
sed for deoxidation.
This paper is important as it was one of the first to
rmally recognize the issue of the magnesia aluminate
inels as a major problem with castabilityand to recognize
e difhcuhy of mod@ing them with calcium to a liquid
pe inclusion.
This implies that the solution proposed by Farrell
d Hilty 2 of turning solid inclusions into liquid ones may
t be possible. Given this, the alternative solution would
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1998 ELECTRIC FURNACE CONFERENCE PROCEEDING
In the 1980 article5by Faulrin~ Farrell, and Hilty,
one of the experiments showed clogging due to
the buildup MgO-A1203 spinels in the nozzle.
The authors speculated that the source of the
magnesium was ffom the refracto~ used in the
crucible in which the steel had been held and
treated.
In tie 1986 articleg by Faires, Gibbons and
GAam, MgO-A1203,was listed as a “emnrnon”
inclusion observed in the ladle, hmdish, and
tundish nozzle. These spinels were especially
prevalent on medium carbon grades.
In the 1986 article13 by Pellicani, Villette and
Dubois, spinels were observed in heats produced
via an Eccentric Bottom Tapping Furnace with a
mean total oxygen of 16.2 ppm, The observed
spinel was small at around 4 microns.
It is clear, from these earlier papers, spinels are
t a new phenomena. However, perhaps as more and
ore steel was being wntinuously cast and cleanliness
vels improv~ they gained more importance as a limiting
ctor of casting.
In 1989, ScanInject V was held in Sweden and
cluded a paper titled “Reoxidation of Al-Killed Steels by
gO Containing Basic Refiactories”14by L.oscher,Fix and
eiffer. They described what occurred in a ladle that was
tensively stirred for desulfurization that improved
oxidation, desulfmizatio~ and degassing. Under these
nditionswith a very basic slag vexylow oxygen activities
re achieved. Also, they reported that MgO tiom the
fiactcxywas being continuously reduced and according to
is paper, the dissolved magnesium in the steel can reach
vels of 7,5 x 10-3’%0to 7.5 x 10-b?. Figure 2, obtained
m this paper, shows magnesium in solution as a function
both aluminum levels and alumina activity.
As the aluminum concentration increases, the
agnesium in solution also increases. Perhaps, more
curately, as the oxygen activity goes down, the rate of
duction of MgO increases and the magnesium in solution
es up.
S
Interestingly,the article does not discuss anyof the
above in the context of castability issues but rather in terms
of desulfurizatim the effect on ladle refractories and the
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magnesium in solution in the steel decrease as the basicity
(lime to silica ratio) decreases (Figure 3). The greatest
decrease in these two elements occurs between a basicity of
.4 to 1.1 and, at the same time, the oxygen activity in the
xidation of the steel.
0.1
0.001
J AIUminllI
--A- 0.01
+ 0.001 I
0.001 0.01 0.1 1
Soluble Al, V.
gure 2. Al versus Mg in solution as a function of
umina Activity
By 1990, the problem of the magnesium
minates had been observed but only rather sporadically
orted. What followed was a period of relative silence
ncerning spinels. Clearly, people were becoming aware
the problem and most likely working on it but were not
king or publishing very much about it. The same can be
id of work that was being done at Inland Steel Bar
mpany. Thankfully,several years later, starting in about
94, more technical information was published.
In 1994 there was one article which discussed
ntrolling inclusion composition in wire cord type grades
t had applicability to the issue of spinel formation. This
icle written by Gaye et al was presented at the 1994
ectric Furnace-Co~erence and titled “Secondary Sl~&
eatment for Inclusion Control in Semi-Killed Steels”
hile this article did not mention castability concerns and
s mm fmused on tire cord type grades, there was a clew
plicability to the spinel castability issues. The article
cussed ladle slag treatments for these grades. “The
rpose of the slag treatment is to decrease the contents in
and ~ to such low levels as to avoid the form~tion of
mina, spinels or olivine phases in inclusions.”
The conditions required to avoid these alumina
d spinel inclusions in either alumina or magnesia lined
les was described. In either case the amount of
gnesium and aluminum in solution in the liquid steel or
refore the levels of spinels in the steel are greatly
ected by the slag basicity. Both the aluminum and
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1998 ELECTRIC
eel increases. The article clearly demonstrated how to
void spinel formation in tire cord grades but also explains
at such slags have very little desulfurization potential.
6
5
0
0.7 0.9 1.1 1.3 1.5
0/’CaO/%Si02
igure 3. Effeet of slag Basicity on Ma and Al in
olution
InApril of 19%, the 1mInternational Congress on
cience and Tedmology of Steelmaking was held in Chiba,
pan. This congress was onother indication that the
rought of articles concerning castability and especially
inels had come to an end. This congress contained two
ery good papers on the modification of aluminates, The
rst was titled “Calcium Treatment T~.hnologies for
pecial Steel Bars and Wire Rods.” This paper
oncerned the production of various grades at Nippon Steel
Muroran on a 162-mIn square billet caster. Three steel
rades were in included in the discussions: 0.45% carbon
luminum - silicon kill~ 0.25% carbon aluminum - silicon
illed and 0.08% carbon aluminum killed (low silicon).
One very interesting point was the differences
etween the clogging tendencies of the 0,45% and 0.25V0
arbon grades with respect to the calcium modification of
luminates. The diflkrence is described as being due to the
ct that the calcium sulfide forms easier in the higher
arbon grades due to the interaction dects of carbon and
xygen and the difference in the temperature at which
alcium is injected, Another very interesting observation
as that the low carbon aluminum killed (low silicon)
rades, clogging tends to decrease with increased calcium
dditions. The opposite trend seems to be true for the
igher carbon Si-Al killed grades where castability
proves slightlywith increased calcium addition to a point
nd then gets worse with increased calcium additions.
The second paper on the modification of
FURNACE CONFERENCE PROCEEDINGS – 547
aluminates was Wlwrmodynamics and Kinetics of the
Modification of Altos h)GhBiOnS”17by two Swedish
authors Jonsscmand Lund. The basics of this paper were an
The paper described experimentation in whichahuninum killed steel was held in an MgO-C crucible.
Atler holding at 16000 C for 60 minutes, the steel was
owed to solidifyin the refiacto~ crucible. The steel was
54
examination of the following equation for alumina
modification and formation of CaS.
3CaO+3S+2M = 3CaS+ Alz03
According to the authors, the results of this
equation and the application of it depend strongly on the
thermodynamicdata especiallyfor the activities of CaO and
A1203in calcium aluminates. The authors presented data
fiam several diflkrent sources and point out the differences.
For this article, they used data as calculatedby the program
ThermoCalc to obtain the relevant activities. This data
could be used to calculate and then gmph a diagram similar
to that presented in the 1988 Calcium Symposium with
perhaps some better thermodynamic data.
In addition, the kinetics and progression of the
modification of the aluminates were described. This
information helps to understand the speed of the
modification and the various steps.
While the above-described articles provide more
insight into the moditlcation of aluminatesby calciurmmost
of this information has been available for some time.
However, there were several papers on the topic of spinels.
The most applicable paper tiom this conference was
probably the one written by V. Brabie from the Royal
Institute of Technology in Sweden and titled “Mechanism
of Reaction between Refiacto Materials and Aluminum
Deoxidized Molten Steel.” z In this paper, Brabie
described the steps involved in the reaction of the magnesia
from refractory to form spinel inclusions in the steel.
1) Reduction of magnesia in the refractory with the
carbon in the refiactmy to produce magnesium
gas and carbon monoxide gas.
2) DitTusionof the magnesium aud carbon monoxide
gases through the refractory to the steel.
3) Reaction at the steel refractory interface of carbon
monoxide gas going to carbon and oxygen in
solution and the magnesium also going into
solution.
4) DiiThsionof the magnesium, carbon and oxygen
into the liquid steel.
5) Precipitation of spinel inclusions as a thin layer or
particles in the steel.
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8 – 1998 ELECTRICFURNACECONFERENCEPROCEED
oss sectioned aud examined. Inclusions found in the steel
cluded MgO, MgO-A1203 ~d M@A1203 clusters.
ven that heats of aluminum killed steels are frequently
ld in ladles even longer than 60 minutes, the formation of
inel type inclusionsin liquid steel under acti production
nditions is easily imaginable.
Another interesting aspect of the 1996 Congress
Japan was the paper published by Higuichi et al tlom
mitomo ~$ed “Inclusion Modification by Calcium
eatment.” The paper, as published in the ISIJ, had an
jective of developing a mathematical model of the
netics. Of interest with respeet to the relative silence in
e industry on spinels was that the abstract contained
talizing refmences to spinel formation. The abstract
iefly suggested the magnesia flom the flux or a crucible
uld be reduced. It also indicated observing the presence
ppm of magnesium in solution in the liquid steel. None
the information on spinels appeared in the final version
the paper.
In 1997, Itoh, Hino, and Ban-ya published
hermodynamics on the Formation of Non-Metallic
clusions of Spinel (MgO-A1203) in Liquid Steel”20as a
mmunication in Metallurgical Transactions B. This
per covers the formation of spinels from the
ermodynamicpoint of view by presenting the equilibrium
nstants, oxide activities and interaction coefficients.
tilizing this data, the authors constructed two stability
agrams for the following components.
MgO - MgO-A1203 - A1203
MgO - M@A1203- CaO - 2A1203
In additiorL data developed for tl-is work and tim
her investigators were super-imposed on the diagrams to
monstrate agreement between the theoretical and actual
ta. In general, observations on the formation of spinels
der production conditions at Inland Steel’s #1 Electric
rnace and Billet Caster agree well with these diagrams.
is is an example of a diflicult technical article. However,
provides a significant amount of the thermodynamic data
cessary to understand the conditions under which spinels
ll form.
In 1997, Ahlborg of LTV published a paper at
e International Steelmaking Conference held in Hungary
led “The Relationship Between Ladle Furnace Slag
INGS
OxygenPotential an~lContaminationof Alumina Inclusions
by CaO and M@” This paper concentrated on clogging
pr
El
th
th
M
th
fin
le
in
Fi
C
m
in
th
th
be
pr
al
re
be
a1
Su
is
fo
et
th
sp
th
flom the refiacto~. Then in 1995 to 1997 a number of
important papers broke the silent period on spinels. These
uded the paper by ~8abie on the reduction of MgO by
on in the refhctory , the paper by Hino et a120on the
oblems encountered in producing LCAK slabs.
During this work, the slag probe, as developed by
ectronite, proved to be a usefhl tool to quickly measure
e FeO + MnO in the ladle slag. Data from LTV showed
at the incidence of clogging increased as the slag FeO +
nO decreased. This paper includes a plot (Figure 4) of
e A1-Mginclusion content in the tundish as a Ilmction of
al ladle slag FeO+MnO. Most of these inclusions were
ss than 10 microns. Ahlborg also found that, the A1-Ca
clusions also increased as FeO+MnO decreased.
#
=!
50 l
40- l 4 l
30- :.
**
20-
c? 7:s
4 4b
10- l 9 l
l l ‘4 +4.**: :**. s
o A
o 5 10 15
FtmlLadle~FeO+MnO
gure 4. Slag FeO+MnO Versus Inclusion Mg
ontent
Ahlborg discussed two possible sources for the
agnesium in the inclusions. The first was the magnesium
the aluminumused for&oxidation. Trials were in which
e magnesium decreased hm 0.25?40to 0.09V0resulted in
e number of inclusions containing more than 5% MgO
ing reduced by 55’%0.Kcr12 had pointed out the potential
oblems associated with the higher levels of magnesium in
uminum in detail in 1988.
The other potential source mentioned was the
duction of MgO horn the slag or rethictory. This had
en pointed out as a potential source by both Loscher et
14in 1989 and Brabiel* in 1996.
mmarv of Literature on the Formation of SDinels
Even with the silent years in the early 1990’s, there
now significant literature on the subject of spinel
rmation. It starts with the early observations of Fading
a15on the surprising appeorauce of spinels. Following
is were two papers*2’14 in 1988 and 1989 which
eculated on the sources of the magnesium as being from
e deoxidation aluminum and the reduction of magnesium
incl
carb
ther
Ahl
incl
cont
form
stee
stee
tech
emp
Cas
spin
disc
app
prod
dete
form
utili
sim
sam
proc
furn
temp
time
fluxe
sam
obse
oxyg
inclu
imm
micr
bein
the
befo
simi
bille
prov
inclu
are
resu
need
popu
wou
1998 ELECTR
mod amics of spinel formation and the paper by1?borg who described the amount of magnesium in the
usions to be a iimction of the slag FeO and MnO.
With respect to the spinel issue, the literature now
ains a significant amount of information eonceraing the
ation of these inclusions. For each particular
lmaking shop, the conditions at each stage of
lmaking needs to be studied and understood. Then the
niques discussed in the technical articles can be
loyed to reduce the formation of this inclusion,
tabilitv Develo~ment Techniques
The techniques for avoiding the fmation of
els and other unwanted types of inclusions are
ussed in the technical literature. However, the
lication of this technical information to actual
uction practices is not easy. The first step is to
rmine what is actually happening in terms of inclusion
ation. At #1 Electric Furnace and Billet Caster, we
ze a straightforwardmegtiodologyfor doing this. It is
ilar to what Faires et al described in their paper with
pling inclusions at various stages in the process, The
ess starts by sampling a heat just before tap getting a
ace slag sample, chemical sample, active oxygen, and
erature, The tapping processes are observed and all
s are recorded with respect to the addition of alloys and
s. As soon as the heat arrives at tie ladle furnace,
pling is started again and includes similar testing and
rvations as done at the fiumace but also includes total
en and inclusion sampling. These total o~gen and
sion samples are obtained utilizing a quartz tube
ersion sample, The steel samples are examined
oscopically for inclusions with appropriate inclusions
g selected for microprobe analysis,
This process is repeated periodically throughout
LMF process including critical points such as just
re calcium treatment and just before exit. In addition,
lar samples are obtained horn the tundish and the cast
t. We call this process the “biography of a heat,” It
ides an overview of the process and the evolution of the
sions size and composition. Typical results of a trial
illustrated in Table 1,
The data in the table provides an example of
lts and indicates where and what changes might be
ed. For example, if in the tundish significant
lations of unmodiikl aluminates were observed, it
ld be necessary to look for sources of reoxidation such
ICFURNACECONFERENCEPROCEEDINGS-549
a gate or shroud which is allowing air into the steel.
Sumrnalv of Castability
1) Since about 1988, the necesstuy technical data on
the modification of aluminates by calcium has
been well established in the literature.
2) The problem of spinels and their impact on
castability was probably first noticed in the late
1970s and early 1980’s. Only sporadic mention
appears in the literature wi~ the main one being
in the late 1980’sby Kor.
3)
4)
al
to
su
ah
re
in
su
a
ex
th
st
pr
lit
sp
1
2
3
R. B. Snow and J. A. She% “Mechanism of Erosion
of Nozzles in Open Hearth Ladles,” J. Am. Ceramic
Society, Vol. 32, No. 6,1949, pp. 187-194.
550
There appears to be a silent period with respect to
spinels and castabilityfrom 1990 through 1995 in
which many people were struggling and perhaps
solving it but not revealing their work.
Several papers were published in 1996 and 1997
that finally addressed the technical issues of
spinels and provided some guidance for
addressing those problems.
The production of clean high carbon silicon -
uminumkilled steel via continuous casting is difficult due
the issues of castability. While the literature contains
tlicient information on the calcium modification of
uninates while avoiding calcium sulfide, it is only
cently that sticient information on spinels has appeared
the literature, Even with the technical data, the
ccessful application is far tim easy. As a starting point,
consistent steehnaking operation is required. After that,
haustive studies of the steehnaking conditions from tap
rough casting are needed. This includes analyzing slag,
eel and inclusions. By thoroughlyunderstandingyour own
ocess, it is possible to take advantage of the technical
erature and achieve victory both over the aluminates and
inels.
4
5
6
7
8
9
– 1998 ELECTRIC FURNACE CONFERENCE PROCEEDIN
J. W. Farrell and D. C. Hilty, “Steel Flow Through
Nozzles: Influence of Deoxidizers,” Electric Furnace
Conference Proceedings, ISS-AIME, Vol. 29, 1971,
pp. 31-46.
J. W. Farrell and D. C. Hilty, “Moditlcation of
Inclusions by Calcium - Part I,” Iron and
Steelmaker, May 1975, pp. 17-22.
J. W. Farrell and D. C. Hilty, “Modificationof
Inclusions by Calcium - Part II,” Iron and
Steehnaker, June 1975, pp. 20-27.
G. M. Fauhing, J. W. Farrell and D. C. I-I@, “Steel
Flow Through Nozzles: Intluence of Calcium,”
Electric Furnace Conference Proceedings, ISS-
AIME, 1979, Voi. 37, pp. 219-229.
D. Bhattach~a, H. M. Pielet, and J. Wagner, “Effkct
of Calcium Injection on Nozzle Blockage and on the
Quality of Strand Cast Aluminum Fine Grain-Steel,”
Electric Conference Proceedings, ISS-AIME, 1982,
Vol. 40, pp. 145-152.
D. Bhattachmya and H. M. Pielet, “Thermodynamics
of Nozzle Blockage in Continuous Casting of
Calcium-Containing Steels,” Metallurgical
Transactions B, Vol. 15B, September 1984, pp.
547-562.
1.G. Davies and P. C. Morgan, “Seccmduy
Steehnaking Developments on Engineering Steels at
Stocksbridge Works,” Secondary Steelmaking for
Product Improvement Conference, The Institute of
Metals, 1985, pp. 153-164.
F. Fairies, P. C. Gibbins, and C. Graham,
“Comparison of Different Calcium Injection Methods
for Production of Aluminum-treated Steels for Billet
Casting,” Ironmaking and Steehnaking, 1986, VO1.
13, pp. 26-31.
GS
10 F. Pellicani, B. Durand, and A. Gueussier,
“Guidelinesfor Calcium Treatment of Steel and State
11
12
13
14
15
16
17
18
19
20 H. Itoh, M. Hino, and S. Ban-ya, “Thermodynamics
on the Formation of Spinel Nonmetallic Inclusion in
Liquid Steel,” Metallurgical Transactions B, Vol.
28B, 1997, pp. 953-956.
21 K. Ahlborg, “Relationship between Ladle Furnace
Slag OWgen Potential and Contamination of
Alumina Inclusions by MgO and CaO,” International
Conference on Clean Steel, 1997, pp. 151-156.
of Calcium Retained,” First International Calcium
Treatment Symposium, The Institute of Metals,
1988, pp. 15-22.
P. Boussard, R, Szezeny, F. Pellicani, and A.
Gueussier, “Resutlurized Steels for Improved
Machinability With Calcium Treatment,” First
International Calcium Treatment Symposim The
Institute of Metals, 1988, pp. 103-108.
G. J. W. Kor, “Calcium Treatment of Steels for
Castability,” First International Calcium Treatment
Symposium, The Institute of Metals, 1988, pp. 39-
44.
F. Pellicani, F. Villette, J. Dubois, “The Production
of Clean, Isotropic Steels by means of Calcium
Treatment with Ailival Cored Wire,” ScanInject IV,
Part 2, 1986, p. 16.
W. Loscher, W. Fix and A. Pfeii%r, “Reoxidation of
Al-Killed Steels by MgO-Containing Basic
Refractories,” ScanInject V, Part II, 1989, pp. 395-
408.
F. Stouvenot, H. Gaye, C. Gatellier, and J. LehmamL
“Seconday Steehnaking Slag Treatment for
Inclusions Control in Semi-Killed Steels,” Electric
Furnace Conference Proceedings, ISS-AIME,
1994,V01.52, pp. 423-428.
Y. Kusano et al, “Calcium Treatment Technologies
for Special Steel Bars and Wire Rods,” ISIJ
International, Vol. 36 Supplement, pp. S77-S80.
G. Ye, P. Jonsson and T. LunL “Thermodynamics
and Kinetics of the Modification of A1203
Inclusions,” ISIJ International, Vol. 36 Supplement,
pp. S105-S1O8.
V. Brabie, “Mechanism of Reaction between
Refiactog Materials and Aluminum Deoxidised
Molten Steel,” ISIJ International, Vol. 36
supplement, pp. S109-S1 12.
Y. Higuichi et al, “InclusionModification by
Calcium Treatment,” ,“ ISIJ International, Vol. 36
supplement, pp. S151-S154.
1998 ELECTRI
C FURNACE CONFERENCE PROCEEDINGS – 551
Table 1. Results of Biography of a Heat
Total
Oxygen Inclusion Types
Slag Oxygen
FeO Activity
Before
3050 30 ‘YO 500 ppm --- ---
,
552
Ca
Activity,
ppm
10
1 I
Ca
Activity
ppm
.0
-
40% CaO
/
Solid t
1
.100 .010 .001
s, ‘?40
.010 .100
Al, %
-t-
Tap
Arrive
LMF 2850
I I
25 ppm Al*03CaO-6AlzOs4?40 I 20 ppm
Before
CalSil 2905 15 ppm
18 ppm
Al*03
CaO-6A12031.5’% 3 ppm
l,lVO 2 ppm
2% 2 ppm
CaO-Alz03
CaSExit LMF I 2885
CaO-A1203
CaS
CaO-2A1203
Tundish I 2835 15 ppm
CaO-A1203
CaS
CaO-2A1203
2ast Billet --- 12 ppm--- I ---
Appendix L Fe-A1-O-Ca-S Diagram at 16000 C
100
t
1100I #I I,
1
– 1998 ELECTRIC FURNACE CONFERENCE PROCEEDINGS
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