New tundish refractory for cleaner steel

1. Reduced Nonmetallic Inclusions in
Steel Using Next Generation
Disposable Tundish Lining
William. N. Porter
VGH Refractories & Equipment LLC
Mason, Ohio, USA
porter@vgh-ag.com

2. The Tundish as a Metallurgical Vessel
Well Known Practices
• Tundish furniture for increased residence time
and floatation of nonmetallic inclusions.
• Dry vibratable refractory working lining for
reduced hydrogen ppm pickup vs. tundish
sprays that contain > 25% H2O.
• High temperature preheating for less heat lost
from steel during casting for improved steady
state conditions.

3. Tundish Working Lining Refractory
• Both tundish spray and organically bonded tundish dry
vibratable refractory utilize several binders. The initial
binder will burn out at temperatures well below steel
casting temperatures; so a low temperature binder and
a high temperature binder must be utilized.
• Both tundish spray refractory and organically bonded
tundish dry vibratable refractory contain fluxes such as
boron and silicate based additions to bond the
refractory aggregate at steel casting temperatures.

4. Novel Refractory Binder System
Reduces Formation of Nonmetallic Inclusions
• Eliminates need for multiple binders.
• Does not burn out during heat up; stable over entire
casting temperature range.
• Does not require addition of water, organic resins or
sugars, boron based or silicate based fluxes.
• Less reactive with Oxygen or Aluminum in steel for
reduced formation of Alumina and Spinel inclusions.
• Higher hot strength for improved erosion resistance.
• Lower thermal conductivity for less heart lost from
steel to tundish.

5. Tundish as Source of Reoxidation of Steel
• Mantovani, Moraes, da Silva et al (2013) observed three
interactions at the tundish refractory/liquid steel interface:
1. Steel infiltration into the open porosity of the tundish
refractory. This is most apparent with the wet tundish spray
materials.
2. Oxidized layer of solidified steel (FeO formation) at the
steel/refractory interface. This is apparent in both tundish
spray and tundish dry vibratable refractory linings.
3. Nonmetallic oxide formation in the liquid steel phase nearest
to the steel/refractory interface: Al2O3, MgO; SiO2, MnO, and
MgAl2O4 spinel.

6. Tundish as Source of Reoxidation of Steel
• Mantovani, Moraes, da Silva et al postulate that the formation of
the nonmetallic inclusions observed in the tundish are due to solid
phase reactions.
• Given the melting points of MgO are well above steel casting
temperatures and much greater than 1700 oC (3100 oF), we
postulate that liquid formation occurs in the tundish refractory
throughout the steel casting period.
• Our research indicates that the presences of boron based fluxes
such as boric oxide, borosilicate or boric acid in the refractory
lowers the melting point forming a liquid surface on each of the
MgO refractory grains at the hot face of the working lining.

7. Tundish as Source of Reoxidation of Steel
• Gan, Chen, He, et al (2012) have published a
typical formulation for the tundish working lining
refractory material containing:
• Magnesia (MgO) as main aggregate.
• Borax (Na2B4O7·5H2O) as a flux.
• Silica Powder (SiO2) for formation of glassy binder phase.
• Phenolic Resin as a low temperature binder.
• Our research indicates the addition of boron and
silica forms low melting liquid phases for faster
liquid-liquid reactions at the refractory steel
interface.

8. Tundish as Source of Reoxidation of Steel
• Buoro and Romanelli (2012) have shown that the ideal
tundish working lining refractory must be of low oxygen
potential and not be so reactive to alter the steel
composition.
• Buoro and Romanelli (2012) have also shown that the
formation of MgAl2O4 spinel inclusion can also be related to
the thermal conductivity and the depth of sinter of the
refractory.
• With addition of fluxes and silicates there is an increase in
densification at the refractory hot face for higher thermal
conductivity, greater depth of sinter and increased
potential for reactions at the steel/refractory interface.

9. Tundish as Source of Reoxidation of Steel
• Pal, Bharati, Krishna (2012) et al have shown that sintering behavior
of the tundish refractory impacts phase transformation and thermal
conductivity. Greater sintering in the refractory promotes greater
formation of nonmetallic inclusions.
• They state the ideal tundish refractory should exhibit high strength
and low thermal conductivity over the full range of casting
sequences and that attention to following leads to reduced
formation of nonmetallic inclusions:
• Binder Selection
• Grain Sizing
• Pore Formation
• Refractory Quality

10. Formation of Inclusions
MgO(Refractory) + B2O3(Refractory) + FeO(Interface)+ Al(Steel)
TO
Al2O3(Steel) + MgAl2O4(Steel)

12. New Dry and Inorganic Bonded Tundish
Refractory
• No fluxes or silica additions.
• Conventional cement type bond forms when a
hydrous magnesia salt is exposed to heat.
• The magnesia salt serves as a catalyst for
formation of strong bonds that are stable and do
not form liquid phases over the entire casting
sequence.
• Depth of sinter and thermal conductivity of the
refractory are reduced.
• Hot or Cold Installation.

13. New Dry and Inorganic Bonded Tundish
Refractory

14. Hot Tundish Installation
• Residual heat from previous
cast is sufficient heat source
to form the inorganic bond.
• Additional benefits include:
– Time savings for faster
tundish turnaround. No time
lost for cooling the tundish
down or heating it back up.
– Energy savings. No added
energy is required.

15. Hot Tundish Installation
• Open bottom form is set into the
warm tundish.
• Refractory material is placed into
the gap between the form and
the tundish.
• After 45-60 minutes of curing
time the form can be removed.
• Flow control devices (stopper
rods, SENs, tundish furniture) can
be installed during the curing
period.
• After curing, the tundish is ready
to be sent to the caster.

16. Bulk Hopper for Quick Installation

17. Cold Tundish Installation
• Similar to current installation
for dry vibratable refractory.
• Uses same form as DV which
includes a heat source.
• Material is placed into the gap
between form and tundish.
• Unlike dry vibratable
installation, form vibration
may not be required.
• Form can be removed after
45-60 minutes of curing at 230
oC (450 oF).

18. Importance of Thermal Conductivity
• Many studies agree that thermal conductivity of the
tundish refractory may affect the steel quality:
• Temperature lost from steel super heat to heat the
refractory is greater when the refractory has a higher
conductivity.
• Thermal conductivity is generally proportional to
density; higher density imparts higher conductivity.
• Higher conductivity increases the depth of sinter.
• Flux additions increase both the sintered density and
the depth of sintering for higher thermal conductivity.

19. Importance of Thermal Conductivity
Dry and Inorganic Tundish

20. Importance of Thermal Conductivity
Dry and Inorganic Tundish
• Elimination of fluxes and replacement of glassy bond
with refractory cement bond achieves:
• Reduced Δ T. Less heat lost from steel during casting.
• Observed super heat variation from start to end of
casting is less than 1.5 oC (3 oF).
• Lower temperature at tundish working lining refractory
to tundish back up lining refractory (castable).
– Less reaction between working lining and back up lining.
– Cleaner deskulling.
– Longer life of tundish back up lining.

21. The Use of Olivine
• Olivine is a naturally occurring magnesia silicate
material where MgO and SiO2 are locked in tight
forsteritic bonds.
• The use of Olivine as a substitute for magnesia in
conventional tundish spray and dry vibratable has not
met with great success due to increased fluxing of the
olivine by the fluxes used as binders versus Magnesia.
• This increased fluxing not only negatively impacted
density and thermal conductivity, but also reduced
corrosion resistance of the refractory during casting.

22. The Use of Olivine

23. CONCLUSIONS
• Steel cleanliness is improved:
– Formation of nonmetallic inclusions reduced.
– Hydrogen ppm in the mold is reduced.
• Improved steady state casting conditions.
– Less temperature lost from steel during casting.
• Improved castability with less nozzle clogging.
• Addition of olivine is made possible by elimination of fluxes in the
refractory:
– Reduced reaction rates between refractory and steel.
– Less nonmetallic formation than an all MgO lining.
– Lower cost per ton of steel cast.

24. Thank You