The tundish nozzle is subjected to high-temperature molten steel scouring, chemical erosion and thermal stress during the continuous casting/mold casting process, and its failure directly affects production and the quality of the cast product. The following are the eight typical failure modes and their mechanism analysis:
1. Al₂O₃ Blockage (Most Common)
Failure characteristics:
White/off-white hard deposits on the inner wall of the nozzle
Gradual flow rate decrease until stoppage during the later stages of pouring
Formation mechanism:
mathReproduction
2[Al] + 3[O] → Al₂O₃ (melting point 2050℃)
Free Al in Al-killed steel reacts with O to form high-melting-point inclusions
Deposition rate: up to 1mm/min for high-oxygen steel grades
Solution:
✅ Calcium treatment ([Ca]/[Al] ≥ 0.1) converts Al₂O₃ to 12CaO·7Al₂O₃ (melting point 1450°C)
✅ Gas curtain nozzle (argon flow 3-5L/min)
✅ Anti-blocking coating (CaO-ZrO₂ lining)
2. Slag Line Erosion (Asymmetric Failure)
Failure characteristics:
Circular grooves appear on the outer wall of the nozzle where it contacts the protective slag.
Breakage is likely to occur when the depth of erosion is >10mm
Erosion mechanism:
math
Copy
ZrO₂ + CaF₂ → ZrF₄↑ + CaO
Components such as CaF₂ and FeO in the protective slag react with ZrO₂:
Key data:
Basicity of protective slag (CaO/SiO₂) Erosion rate (mm/furnace)
0.8-1.2 0.3-0.5
1.5-2.0 0.8-1.2
Solution:
✅ Use a composite material with a ZrO₂ content of >85% in the slag line
✅ Optimize the basicity of the protective slag (control CaF₂<5%)
3. Thermal Shock Cracking (Sudden Failure)
Failure characteristics:
The surface of the sprue shows a network of cracks
Most often occurs during preheating or the pouring stage
Conditions for occurrence:
When the temperature rise rate is >15°C/min, the internal stress of the refractory material is >the flexural strength
Critical parameters:
Material Thermal shock resistance (times) Permissible temperature rise rate (°C/min)
Al₂O₃-C 3-5 8-10
ZrO₂-C 8-10 5-8
Solution:
✅ Stepwise preheating (300°C → 800°C → 1200°C)
✅ Use refractory material with a microporous structure (porosity 15-20%)
4. Sliding Mechanism Stuck (Mechanical Failure)
Failure characteristics:
Sliding resistance > hydraulic system set value (usually > 20 MPa)
Steel flow regulation hysteresis or failure
Root cause:
Molten steel seeps into the gap between the slide plates (poor sealing)
Lubricant carbonization failure (> 1400 ℃ continuous exposure)
Solution:
✅ Use self-lubricating slide plates (with BN or MoS₂)
✅ Add graphite-based grease every 2 furnaces
5. Outlet Enlargement (Uncontrolled Flow)
Failure characteristics:
Outlet diameter increases by >5mm (original design φ40mm→φ45mm)
Flow rate increases by 30% at a pulling speed of 1.5m/min
Erosion mechanism:
Turbulent shear of molten steel (flow rate >2m/s)
Chemical erosion of low-melting-point inclusions such as MnS
Solution:
✅ Add SiC reinforcement phase to the outlet area (wear resistance increased by 3 times)
✅ Optimize flow field design (reduce turbulence)
6. Structural Fracture (Catastrophic Failure)
Type of fracture:
Transverse fracture: excessive installation stress
Longitudinal fracture: accumulated thermal stress
Preventive measures:
✅ Optimize wall thickness using finite element analysis (recommended ≥50mm)
✅ Avoid rapid cooling and heating (temperature gradient <100°C/cm)
7. Cold Steel Condensation (Failure During The Initial Pouring)
Formation conditions:
Insufficient nozzle preheating (<800°C)
Molten steel superheat <15°C
Solution:
✅ Two-channel baking (gas + electric heating)
✅ Confirm temperature before pouring (infrared thermometer >1000°C)
8. Abnormal Corrosion (Chemical Failure)
Typical reaction:
SiO2 (refractory material) + [Ca] → CaSiO3 (low melting point)
Countermeasures:
✅ For high-calcium steel grades, use MgO-C materials
