Choosing Refractory Materials for Industrial Furnaces with Frequent Start-Stop Cycles: A Scientific Guide to Thermal Shock Resistance

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2025-11-19

Technical knowledge

Frequent thermal cycling in industrial furnaces poses severe challenges to refractory material integrity. This article provides a scientific analysis of thermal shock resistance mechanisms, comparing the performance of high-alumina brick, fireclay brick, and corundum brick under temperature fluctuations. It reveals that high-alumina insulating bricks—featuring a mullite-corundum plus glass phase composite structure—offer lower thermal expansion coefficients and higher fracture toughness, significantly reducing crack propagation risk. Based on real-world applications in electric arc furnaces and annealing furnaces, recommended specifications include Al₂O₃ content ≥48% and thermal conductivity ≤1.2 W/(m·K). Supported by microstructural images, thermal expansion curves, and fracture toughness test data, this guide empowers engineers and procurement managers to make informed decisions that enhance furnace lifespan and operational efficiency.

Understanding Thermal Shock Resistance in Refractory Materials for Industrial Furnaces

Industrial furnaces operating under frequent start-stop cycles face severe thermal stress—especially when temperature gradients exceed 200°C per minute. This rapid cycling can lead to microcracking, spalling, and premature failure of refractory linings. Choosing the right material isn’t just about composition—it’s about how well it manages internal stresses during thermal excursions.

The Physics Behind Thermal Shock Failure

When a furnace heats or cools rapidly, different layers of refractory material expand or contract at varying rates due to differences in thermal conductivity and coefficient of thermal expansion (CTE). If the material lacks sufficient fracture toughness, these differential movements generate tensile stresses that exceed its strength—leading to crack initiation and propagation. In high-cycle environments like electric arc furnaces (EAFs), where temperatures swing from ambient to over 1600°C, this mechanism becomes dominant.

Material Type	Al₂O₃ Content (%)	CTE (×10⁻⁶/K)	Fracture Toughness (MPa·m¹ᐟ²)
Fireclay Brick	30–40%	6.5–7.5	1.2–1.5
High-Alumina Brick (48% Al₂O₃)	48–65%	4.0–5.0	2.0–2.5
Fused Cast Corundum Brick	≥90%	3.5–4.2	1.8–2.2

As shown above, high-alumina bricks with ≥48% Al₂O₃ offer a balanced combination of low CTE and improved fracture toughness—critical for resisting crack growth under repeated thermal shocks. Their microstructure, composed of mullite and corundum phases embedded in a glassy matrix, provides both stiffness and energy absorption capability.

Why High-Alumina Insulating Bricks Outperform Others

In applications such as annealing furnaces and reheating chambers, where cycle times are short and temperature swings are intense, traditional clay bricks fail within 6–12 months due to cumulative cracking. Our proprietary high-alumina insulating brick, engineered with optimized mullite-corundum architecture, maintains structural integrity after 500+ thermal cycles between 20°C and 1500°C—validated by ASTM C1288 testing protocols.

Key advantages include:

Thermal conductivity ≤1.2 W/(m·K) — reduces heat loss and improves energy efficiency
Low linear expansion (<0.5%) up to 1400°C — minimizes stress buildup
High flexural strength (>15 MPa at 1100°C) — resists mechanical load during operation

Reference: ISO 18893:2017 defines standardized test methods for evaluating thermal shock resistance of refractories through controlled heating/cooling cycles—a benchmark used in our R&D lab to validate performance claims.

For engineers and procurement managers overseeing furnace operations, selecting materials based on real-world performance—not just cost—is essential. A single failure in a steel reheat furnace can cause 2–3 days of downtime, costing $50k–$150k in lost production. Investing in thermally stable refractories pays back quickly through extended lining life and reduced maintenance frequency.