STEEL + TECHNOLOGY 01/2020 EXTRACT

STEEL TECHNOLOGY | 39
kg of ladle well filler. To examine the
applied ladle well filler in the well block,
this took place at the end of the refractory
linings lifespan and the well block was
carefully recovered at the start of the relining
process. Figure 3 shows the ladle well
filler covered backup well block.
Result of the ideal application of ladle
well filler is a material cone, peaking 15-18
cm above the ladle bottom. Figure 4 illustrated
the backup well block after the application
of ladle well filler.
After the application of ladle well filler
to the backup system, the steel ladle went
through a routine production cycle lasting
approximately 3-4 hours and tapping via
the main slide gate system. After tapping,
remaining slag was poured out and the
ladle was then transported to the relining
facility to cool. Subsequently the worn
refractory lining was removed and the
backup well block was recovered. During
the removal of the well block from the bottom
lining, flowable ladle well filler was
lost and only solidified structures could be
recovered. The well block containing solidified
material was then bisected vertically
along the casting channel. Figure 5 shows
one of the recovered backup well blocks.
Starting the examination from the bottom
of the casting channel, the first significant
feature is the dome spanned cavity
in the well block. This cavity contained
flowable ladle well filler until the backup
slide gate system was removed and the
well block was excavated from the ladle
bottom lining. The shown ladle well filler
starts to form liquid phases above
1,500°C, thus the flowable mass was
exposed to lower temperatures. The
dome above the cavity consists of a layer
of sintered ladle well filler with a thickness
of 3 – 6 cm. This layer formed during the
cooling of the highly viscous silica melt
phase covered in earlier publications.
Overlying the sintered dome is a layer of
steel pervaded by slag inclusions and
shrinkage cavities. The boundary reactions
between well block, steel and ladle
well filler are subject of ongoing research.
A comparison between the material cone
after addition and the sintered dome
shows a significant reduction in size, i.e.
roughly a third of the added ladle well filler
was eroded through physical mechanisms
or thermochemical processes. The
amount of erosion in the industrial trials
varied over a wide range, determined by
the duration of the secondary metallurgical
treatment and the alloys in the produced
steel quality. This dynamic process
determines the progression of the surface
of the dome into the casting channel. A
more pronounced erosion of the ladle well
filler and a further progression into the
casting channel lead to a smaller diameter
of the dome that can then withstand higher
ferrostatic pressures consequently
reducing the free opening rate. This is a
possible explanation for the correlation of
treatment duration and free opening rate
which is described in numerous publications.
Interaction between steel and ladle
well filler
The effect of the steel grade on the erosion
of ladle well fillers was examined in
laboratory tests conducted by Purmetall
and Forschungsgemeinschaft Feuerfest
with the goal to develop ladle well fillers
especially suited for the conditions during
the production of particular steel grades.
To investigate the reactions between steel
and ladle well filler a new crucible test, distinguished
by the direct exposure of ladle
well filler to liquid steel in an inert atmosphere
at 1,600°C for a duration of two
hours, was developed. Figure 6 shows an
example of the two component crucible
test setup.
To recreate the specific working conditions,
different ladle well fillers and steel
grades were combined in these two com-
Figure 5. Bisected
well block from
the industrial trial
(Picture: Purmetall)
Figure 3. Backup well block with added
ladle well filler shortly before EAF tapping
(Picture: Purmetall)
Figure 4. Illustration of the backup well
block after addition of 50kg of ladle well
filler (Picture: Purmetall)
STEEL + TECHNOLOGY 2 (2020) No. 1