Why Does Arc Furnace Cycling Cause Refractory Cracking? A Comparative Study of High-Alumina Brick Thermal Shock Resistance

Sunrise

2025-11-15

Application Tutorial

Frequent start-stop cycles in electric arc furnaces often lead to refractory brick cracking—what’s the root cause? This article explains the physics behind thermal shock resistance, comparing high-alumina, clay, and alumina-silica bricks under repeated temperature changes. It reveals how high-alumina insulating bricks with a mullite-andalusite + glass phase microstructure achieve low thermal expansion and high fracture toughness, making them ideal for intermittent industrial furnaces like arc and annealing furnaces. Real-world case studies demonstrate their superior performance, with recommended material specs: Al₂O₃ content ≥48%, thermal conductivity <1.2 W/(m·K). These properties significantly extend furnace life and reduce energy consumption—an essential consideration for modern steelmaking operations.

Why Does Refractory Brick Crack in Electric Arc Furnaces? A Technical Deep Dive into Thermal Shock Resistance

In industrial furnaces—especially those operating on a frequent start-stop cycle like electric arc furnaces (EAFs)—refractory materials face one of their toughest challenges: thermal shock. Sudden temperature changes can cause internal stresses that exceed the material’s structural limits, leading to cracks, spalling, and premature failure.

Understanding Thermal Shock: It’s Not Just About Temperature

Thermal shock resistance is not merely about withstanding high temperatures—it’s about how well a refractory can handle rapid heating or cooling without fracturing. The key factors include:

Thermal expansion coefficient: Lower values mean less strain during temperature shifts.
Fracture toughness: Higher values resist crack propagation under stress.
Heat conductivity: Too high can lead to uneven temperature gradients inside the brick.

For example, traditional clay bricks may have a linear expansion rate of ~5% over 1000°C, while advanced high-alumina bricks stay below 3%. This difference alone explains why some refractories fail after just 50–100 thermal cycles, while others endure 500+.

Comparing High-Alumina, Clay, and Alumina-Zirconia Bricks

Material Type	Al₂O₃ Content (%)	Thermal Conductivity (W/m·K)	Max Cycles (1000–1650°C)
Clay Brick	35–45%	1.4–1.8	~50
High-Alumina Brick	≥48%	0.9–1.2	300–500+
Fused Cast Alumina-Zirconia	70–80%	1.0–1.3	600+

As shown above, high-alumina bricks offer a compelling balance between cost, performance, and durability—especially when used in intermittent processes such as EAF steelmaking, where furnace cycling is common.

The Microstructure Secret: How High-Alumina Bricks Resist Cracking

What makes modern high-alumina bricks so effective isn’t just their composition—it’s their microstructure. These bricks feature a composite phase system:

Primary phase: Mullite (3Al₂O₃·2SiO₂) provides excellent thermal stability.
Secondary phase: Corundum (Al₂O₃) enhances hardness and wear resistance.
Matrix: Controlled glassy phase reduces porosity and improves fracture toughness.

This combination results in low thermal expansion (~2.5% from room temp to 1650°C), high modulus of rupture (>3 MPa), and minimal crack initiation even after repeated thermal shocks.

A leading European steel producer reported a 40% reduction in refractory replacement frequency after switching to an export-grade high-alumina brick with optimized mullite content—proving that smart material selection pays off in both operational continuity and cost savings.

Real-World Application: Why This Matters for Your Operations

If your plant runs electric arc furnaces, reheating ovens, or batch-type kilns, you’re likely experiencing increased downtime due to refractory degradation. Choosing the right brick isn't just about specs—it's about aligning with your process needs. For instance: