Metallurgy 163

Argon Injection with Porous Plugs

by B. A. Strathdee and D. M. McFarlane

INTRODUCTION ignored. Any suggestion that a hole, Improving cleanliness could not be
regardless of how small, be made in shown on such a small heat size;
The injection of argon into molten the bottom of a ladle is routinely however, a controlled turbulence,
steel using a porous refractory plug opposed by most steelmakers. These from barely noticeable to the point
has received considerable attention reasons explain why little attempt of ejecting steel from the vessel,
in the past several months. The was made to check the benefits of could be easily obtained. The pre-
technique is not new since it was argon injection with porous plugs. liminary tests showed that the tech-
effectively demonstrated more than At Dofasco, argon was first used nique was safe and simple.
ten years a g o , " 9 u t there has been as a means of shrouding aluminum- There was one other very im-
considerable reluctance by the steel killed steel to reduce secondary oxi- portant factor in t h e acceptance of
industry to take advantage of the dation and thus to reduce the this process. There was a need for a
benefits the process offers. This re- amount of occluded material. Large good technique of mixing, cooling,
port describes the experiences and globular inclusions of A1203 were and possibly cleansing molten steel
success achieved in adapting this found on the surface of shrouded in the ladle. I n particular, heats
process for routine production use aluminum-killed ingots and a very with large exothermic ladle addi-
a t Dofasco. large amount of alumina was found tions, such as aluminum or ferro-
Bubbles of gas rising through in the sprues of the bottom pouring silicon, require reladling or stirring
molten metal, as shown in Fig. 1, setup. This large amount of Al2O3 and cooling with an ingot suspended
can mix, cool, and promote the re- (as in Fig. 2) indicated that sec- from a crane. Both practices are
moval of nonmetallic inclusions and ondary oxidation was not the main undesirable, sloppy, and time-con-
occluded gases. The Gazal process,' culprit. Attention was then focused suming. Argon injection appeared to
invented by Dr. Etienne Spire, on improving the separation of pri- be a welcome solution.
makes use of a porous refractory mary deoxidation products in the The first large porous plug was
plug mounted in the bottom of the ladle. The best shrouding technique
containing vessel. The refractory is could not improve dirty steel, but
permeable to gas flow but not to only prevent it from becoming
molten metal. Very fine bubbles of worse.
gas emitted from the refractory Various lance techniques were
pores create a large surface area tried for injecting aluminum with
and good gas-metal contact even argon as a carrier gas into the ladle
though many of the bubbles quickly of steel to deoxidize. The use of
coalesce. The flow of gas and thus lances proved difficult and cumber-
the turbulence can be readily con- some. Improved lance design was
trolled. needed, but the possibility of intro-
Ten years ago vacuum degassing ducing argon by means of a porous
was in vogue. The Gazal process plug in the bottom of the ladle to
was promoted as a competing de- mix a separate aluminum addition
gassing technique. Unfortunately, it appeared more attractive.
was soon apparent that the large The acceptance of this technique
volumes of argon required for the by the Metallurgical and Production Fig. 1-Schematic of ladle and plug
removal of 02,Ho, and N, produced Depts, required experience and data
excessive turbulence and c ~ o l i n g . ~ generated at Dofasco. Consequently,
Argon injection through porous a small porous plug obtained from
plugs was not an effective degassing Canadian Liquid Air was mounted
technique, and it fell into disfavor. in the bottom of a 100-lb research
The accompanying advantages of induction furnace, and a series of
mixing, cooling, and cleansing were tests was carried out. These tests
showed only a slight resemblance to
the conditions in a 160-ton ladle of
8. A. STRATHDEE and D. M . McFARLANE molten steel. The cooling effect of
are, respectively, manager, applied research, introducing argon could not be
and general foreman, steel production, shown because of the cooling and
Dominion Foundries and Steel, Ltd., Homil- heating effect of the induction coil.
ton, .Canada. The mixing effect of argon was
masked by the inductive stirring. Fig. 2-Bottom pour sprue with A120.:
164 Open Hearth Proceedings, 1969

mounted in the bottom of a 160-ton and the connection made with the
ladle to stir a high-silicon steel. The flexible rubber hose (Fig. 10). The
technique proved successful in the ladle is then moved into position
first attempt, and it was immediately underneath the furnace, and the ar-
adopted as a standard production gon is turned on a t the start of tap-
operation. Since then, it has been ping (Fig. 11). Argon can be used
used effectively in this grade as well throughout the tapping operation as
as an increasing number of other well as after, depending on the
grades of steel. amount of mixing and cooling re-
quired. It is a decided advantage to
DESCRIPTION OF THE have a maximum flow of argon
POROUS PLUG when large ladle additions are being
made. At this time, there is sufficient
The porous plug is a high alumina Fig. 3-Porous plug (side and top view). freeboard to prevent any slopping of
refractory brick, shaped like a trun- steel from the ladle. As thmeladle
cated cone and enclosed in a steel fills, the flow of argon is reduced to
sheath. From the bottom of this give a quiescent, gentle stirring
sheath is welded a threaded hollow without slopping (Fig. 12 shows the
stud, shown in Fig. 3. The refractory surface of the steel during argon
material is 85% All02 and 15% SiOg injection). When the ladle tempera-
in the form of corundum and mul- ture has been taken, the argon flow
lite. It is a far better refractory ma- can be adjusted to give the required
terial than ladle brick. The steel cooling or, if the proper ladle tem-
sheath encasing the plug prevents perature has been obtained, the ar-
any of the gas from escaping out gon can be shut off, the hose dis-
the sides and directs it all out the connected, and the ladle removed
upper surface of the refractory. The for teeming.
plug is approximately 8-in. high and During treatment, argon is main-
6-in. in diameter at the top. tained at 100 psi, and the flow is
Fig. 4-Schematic o f plug in ladle bottom. regulated with a flow-control valve.
LOCATION OF THE PLUG For maximum turbulence, the argon
flow varies from 400 to 600 cubic
At Dofasco, the ladles are elliptical f t per hour. With a full ladle and
in shape, and the plug is mounted minimum freeboard, the maximum
in the bottom on the long axis half- flow is in the order of 200 to 300
way between the center and the end cubic ft per hour. For quiescent
of the ladle furthest from the stopper stirring, the flow is reduced to 50
rod. The ladle bottom consists of two to 75 cubic ft per hour. The length
thicknesses of steel riveted together. of treatment is usually governed by
For convenience, the rivet closest to the temperature of the steel in the
the mounting site is removed, and ladle.
the hole enlarged slightly to accom-
modate the threaded stud as shown
schematically in Fig 4. Only the stud PLUG LIFE
extends through the ladle bottom. Because the porous plug and the
The rest of the plug is entirely within ramming material around it are top
the ladle shell. A square hole is left Fig. 5-Hole in ladle bricks plus plug
quality refractories, they last much
in the brick at the bottom of the ladle longer than the ladle bottom and,
(Fig. 5), and the plug mounted in after a few heats, the plug "stands
place so that the top is flush or proud". When the ladle bottom is
slightly raised above the inner work- removed for rebricking, the plug is
ing bottom of the ladle (Fig. 6). It saved and examined. If there are
is then rammed in place with a high 5 in. of plug intact (and this is an
alumina plastic refractory. As a re- arbitrary figure), the plug is cleaned,
sult, the plug and the rammed re- a longer stud is welded on, and it is
fractory form an integral part of the replaced in the ladle. Fig. 13 shows
ladle bottom (Fig. 7 ) . two plugs that have been removed
from the ladle. The cross section on
ARGON SUPPLY the Ieft indicates some discoloration
and cracking of the refractory due to
Standard piping is used to connect mechanical and possibly thermal
the threaded stud extending through shock, but the usefulness of the plug
the bottom of the ladle to the male Fig. &Plug in hole. has not been impaired. The plug on
half of a quick disconnect couple the right has been removed after
mounted on the side of the ladle two bottom campaigns in the ladle.
(Figs. 8 and 9 ) . Six-ply extra heavy the argon is fed through pressure The plug will live for a minimum
hose on a power reel is used from control regulators, flowmeter, and a of one ladle bottom campaign (12
this quick disconnect couple back flow control valve. These valves are heats) to as many as three ladle
through standard piping to a supply remotely operated from the furnace bottom campaigns. Our average plug
of argon. Fig. 10 shows the argon control room. Since our consumption life is 22 heats, but argon is not
hose connected to the ladle in the of argon is in the order of 1 to 2 necessarily used in all heats. All
transfer car, and Fig. 11 shows the cubic f t per ton of steel, the five ladles are equipped with plugs.
ladle at the start of argon injection cylinders provide a three to five heat
during the tapping of the furnace. supply of argon.
At Dofasco, argon is a by-product
from our oxygen plants, and it is OPERATION At the end of the teeming opera-
supplied to the Melt Shop in stan- tion, there occasionally is a light
dard cylinders. Five of these cylin- A ladle equipped with a porous skull covering the top surface of
ders are manifolded together, and plug is placed on the transfer car the porous plug. This, in effect, seals
 Metallurgy 165

.with having a hole in the bottom

of the ladle. In this case, the hole is
only large enough for the stud and
is covered by a top quality refrac-
tory. There is less chance of steel
breaking out through the porous
plug and the rammed material
around i t than through any other
part of the ladle bottom. This is
borne out by the fact that, at Do-
fasco, porous plugs have been in the
. ladles for over 5,000 heats, and
there has never been a breakout or-
Fig. 7-Overall ladle bottom.
anv indication of one. From this Fig. 1 I-Ladle a t furnace-tapping.
point of view, it is completely safe.
There should be no concern about
breakouts.
WHAT DOES IT DO?
Cools

is used (1 to 2 cubic f t ton),

but it does "open" the slag, exposing
Fig. 8-Piping under ladle.
fresh hot steel to radiate (Fig. 14).
Fig. 12-Bubbling surface of steel in ladle.
Increasing the flow of argon. in-
creases tThe exposure of tlhe 'steel
and increases the cooling rate. Cool-
ine rates in t h e order of 3" to 7 ° F
minute are normal. Without any
stirring, the rate of cooling in a
ladle of steel with a n average slag
cover is less than 1°F per minute.
The practice of stirring with an in-
got cools a t the rate of approxi-
mately 10°F per minute, but the
overall time is greater due to the
necessity of handling the ingot with
a crane. Argon injection is a very
effective way of cooling a heat of
steel. With this technique, it is pos-
Fig. 9-Piping up side of ladle. sible to cool the steel to any-de- Fig. 13-Plugs after use.
sired temperature as closely as can
be measured by a normal tempera-
ture dunker. The uniformity of tem-
perature throughout the ladle is an
advantage. I n the case of high sili-
con steels, it was possible to lower
the teeming temperature by 20°F
and reduce the incidence of "stick-
ers." For continuous casting, it is
essential to reduce "breakouts."
Mixes
With the off-centered plug, argon
produces a circulation of the steel
in the ladle. When the argon is
turned on at the start of tapping, a
Fig. 10-Hose connected to ladle. maximum flow can be accommo- Fig. 14-Bubbling surface of steel in ladle.
dated within t h e ladle and large
ladle additions can be r a ~ i d l vdis-
solved and mixed into thesteel. The
the plug and prevents any further flow can be reduced as the ladle Cleanses
flow of argon. For the first heat, this fills to prevent slopping of steel and Theoretically, bubbles of inert gas
skull was physically removed and, slag from the ladle. But the gentle rising through molten steel absorb
in so doing, a considerable amount circulatory motion continues to dissolved gases in the steel due to
of the plug was also removed. Since homogenize the steel. This effect is the concentration gradient existing
then no attempt has been made to readily determined by analyzing the between the steel and the bubble.
remove this skull. The fresh hot steel during teeming. With silicon There are several papers discussing
steel entering the ladle quickly steels stirred with an ingot, the this." Also, the bubbles may act as
melts this skull and reopens the spread in silicon analysis is as much they do in a flotation cell and lift
plug. as 30 points between ingots. With nunmetallic particles to the surface
NO BREAKOUTS argon stirring the spread is rarely where they can be incorporated in
greater than 5 points (0.30% vs slag. It has also been stated that the
Most steelmakers are concerned 0.05%). circulation brings particles that are
166 Open Hearth Proceedings, 1969

retained near the bottom of the 1. It is extremely flexible. Argon a ladle of steel at the desired tem-
ladle, due to the ferrostatic pressure, can be used during the teeming as perature and of homogeneous com-
up to the top where they can co- well as after, even while the ladle position.
alesce with the slag. A more recent of steel is being moved. As a result, Normally, when steel is tapped
theory by Hamielic at McMastero there is some time saving. from the furnace into the ladle and
states that nonmetallic materials do 2. Greater flows possible. Because all additions have been made, there
not follow Stokes Law when a tem- argon is used a t the start of tapping, iscnothing further that can be done
perature gradient exists. Thus, there to adjust the composition of the
there is a maximum freeboard in
is the possibility that, by stirring the ladle and, consequently, the steel; however, with argon stirring,
and removing temperature gra- maximum turbulence can be used it is possible to make a second ad-
dients; nonmetallics will rise out of without splashing steel from the justment to reach the required
the steel at a faster rate and accord- ladle. analysis. With argon stirring during
ing to Stokes Law. These are all the tap, the ladle of steel is homo-
3. More efficient mixing. The ar- geneous shortly after the ladle is
theories, and no attempt is made to gon flow is at a maximum when the
prove them. filled. At this time, a sample of steel
ladle additions are made. can be obtained and quickly
It is extremely difficult to provide 4. Temperature control. The plug analyzed. On these results, a further
facts on improving steel cleanliness. is more effective and more control- addition of an alloying agent or de-
We have no quality index or inclu- lable as a means of cooling. Up to oxidizer can be made to the ladle
sion rating, only the metallurgist's 20 minutes of treatment time is and mixed in with argon. This is a
statement that it is "felt" that there quite feasible with a porous refrac- decided advantage, and we are only
is an improvement in cleanliness. tory plug. beginning in this area of investiga-
However, a considerable amount of 5. Complete mixing. The plug is tion.
"skelp" (hot rolled steel) is made in the bottom of the ladle and all Argon can be used to mix in a
for the production of pipe. In the the steel is mixed, whereas the desulfurizing agent to hot metal. We
past, considerable difficulty has oc- lance may not reach the bottom of have just carried out preliminary
curred in the customer's welding the ladle and may leave a zone of experiments in this line, and it is
operation when nonmetallic inclu- unmixed steel. too early to report on them here.
sions are found in the weld zone. The porous plug is a means of
Since an improved standard steel- 6 . Simplicity. A simple hose at-
tachment is all that is required. introducing any inert or reducing
making practice, including argon gas into molten steel. There a r e a
stirring, has been developed, the in- considerable number of applications,
cidence of welding difficulties has DISADVANTAGE OF THE many that have not been thought of
aropped considerably. The only POROUS PLUG a t this time. There is a good future
proof that we can offer at this time for argon injection by means of a
for the effect of argon stirring on The lance is used only on heats to porous plug.
steel cleanliness is satisfied custo- be treated. The porous plug is per-
mers. Consequently, our Metallurgi- manently installed in a ladle and is
cal Dept. specifies that all skelp be in contact with the steel whether or
argon-stirred. If it is not, the heat not argon is used. For efficient use ' E. Spire. "Contributions to Discussion."
of the plugs, it is necessary to sched- Proceedings of the Electric Furnace Confer-
is reapplied to a less demanding ence, AIME, Vol. 13, 1955, Pp. 61, 67, 84.
order. ule the ladles with plugs, only on 'E. Spire, U.S. Patent 2,811,346, Oct. 29,
heats that require argon flushing. If 1951.
"R.J. $houlet. R. L . W. Holmes, and L. R.
all heats are to be treated, then this Chrzan. Argon Degassing Practice and Re-
disadvantage disappears. At Dofasco, sults." Proceedings of the Electric Furnace
POROUS PLUG VS LANCE Conference. AIME. Vol. 23. 1965, pp. 80-86.
for ease in ladle scheduling, all our 4 W. G. Davenport. "Desorption of Dis-
IN.IECTION ladles are equipped with porous solved Gases from Liquid Metals into Rising
Bubbles-Rates of Bubble Growth." Canadran
Bubbles of argon injected into the plugs even though all heats are not Metallurgical Quarterly, 1968, Vol. 7. No. 3.
bath of molten steel will cool, stir, treated with argon. SP. Karinthi and J. Galey. "Injection of
Argon into Liquid Steel, Degassing and Agi-
and possibly cleanse regardless of tation of the Bath. The Gazal Process."
C.I.T.. No. 1. 19fi7
whether the bubbles are introduced APPLICATIONS A,' E. ~ a m i e i e c , McMaster Unlversity.
through a porous plug or a lance. Hamilton. Ontario. Canada, Private Commu-
nication. Feb. 1969.
The choice will depend on a number Argon flushing with the porous N. Mevsson and A . Rist. "Theoretical Cal-
of factors. We feel that there are plug can be effective wherever cool- culations i n the ~ e o x i d a t l o nof - ~ i & i d Steel
by Flushing with Methane," Revue de Mdtal-
some decided advantages in favor of ing, mixing, and cleansing are re- lurgie, Vol. 62. No. 2. Feb. 1965. DP. 121-126.
the refractory plug mounted in the quired to molten steel in the ladle. W. Deilmann and E. Klimanek. "Experi-
ence with Flushing Steel in the Castlng Ladle
bottom of the ladle. The advantages Almost any grade of steel can be with Gas." Radex Rundschau, 1968. No. 2.
of the porous plug are: treated where it is important to have pp. 127-136, (Brutcher Trans. No. 7470).