Surface Cladding Technology for Continuous Casting Guide Rollers

Overview of the Technical Topic

Continuous casting guide rollers are critical components in steelmaking that guide the solidifying steel shell as it moves through the casting mold. These rollers operate under extreme conditions: high temperatures approaching 1000°C, intense thermal cycling, and abrasive contact with the hot steel surface. The literature on surface cladding technology for these rollers addresses the challenge of extending roller life while maintaining dimensional accuracy and surface quality of the cast product.

Core Technical Points

The primary failure modes of guide rollers include surface wear, thermal cracking, oxidation spalling, and dimensional deviation. Cladding technology aims to mitigate these failures by depositing a protective layer with superior thermal stability, oxidation resistance, and wear resistance compared to the base material. The literature discusses various cladding approaches including weld overlay, thermal spray, and plasma transferred arc (PTA) cladding, with emphasis on their respective advantages for this application.

Cladding Material Requirements

Guide roller cladding materials must satisfy several demanding requirements simultaneously. The material must resist thermal fatigue from repeated heating and cooling cycles, maintain dimensional stability at elevated temperatures, resist oxidation and scaling, and exhibit adequate hardness to resist abrasive wear from the steel shell.

Performance Requirement	Target Value	Test Method	Standard Reference
Hardness at operating temperature	≥ 35 HRC at 600°C	High-temperature microhardness	ASTM E92
Thermal expansion coefficient	≤ 13 × 10⁻⁶ /°C	Dilatometry	ASTM E228
Oxidation resistance	Scale thickness < 50 μm after 100 h at 900°C	Thermogravimetric analysis	ASTM G93
Bond strength	≥ 150 MPa	Peel test or tensile bond test	ASTM B571
Thermal conductivity	≥ 20 W/(m·K)	Laser flash analysis	ASTM E1461

Process Selection and Parameters

The literature compares three main cladding processes for guide rollers: submerged arc welding overlay, plasma transferred arc (PTA) cladding, and high-velocity oxygen fuel (HVOF) thermal spray. Each process has distinct characteristics that affect the final performance of the cladding layer.

Process	Typical Deposition Rate	Dilution Rate	Surface Roughness (Ra)	Maximum Operating Temp	Cost Level
SAW overlay	200-500 g/min	10-25%	12.5-25 μm	800-900°C	Low
PTA cladding	50-150 g/min	2-8%	3.2-6.3 μm	900-1000°C	Medium
HVOF thermal spray	100-300 g/min	0% (no dilution)	1.6-3.2 μm	600-800°C	High

PTA cladding is often preferred for guide rollers due to its low dilution rate, excellent surface finish, and ability to deposit thin, uniform layers with precise composition control. The powder feed rate is typically 5-15 g/min, with arc current of 200-400 A and travel speed of 50-150 mm/min. The powder composition is critical, with common formulations including Ni-Cr-Mo alloys, Co-Cr alloys, and Fe-Cr-Ni alloys with oxide additions.

Heat Treatment and Residual Stress Management

A critical aspect discussed in the literature is the management of residual stresses induced during cladding. The thermal gradients between the overlay layer and the base roller material can generate significant tensile residual stresses at the bond interface, leading to delamination under thermal cycling. The recommended approach involves a multi-stage stress relief: a local stress relief pass immediately after each cladding pass using a low-current GTAW pass, followed by a full roller stress relief anneal at 550-650°C for 2-4 hours. This two-stage approach effectively reduces residual stresses below 50 MPa without causing significant distortion.

Engineering Practice Integration

In industrial applications, guide rollers with PTA cladding have demonstrated service life extensions of 4-6 times compared to uncladded rollers. The literature reports a case where a continuous caster using PTA-cladded rollers reduced roller replacement frequency from every 3 weeks to every 16 weeks, resulting in significant cost savings and reduced production interruptions. The dimensional accuracy of cladded rollers is maintained within ±0.05 mm, which is critical for ensuring proper steel shell contact and preventing surface defects in the cast product.

Key Questions and Reflections

The literature raises an important question about the long-term stability of the cladding layer under repeated thermal cycling. While initial performance is excellent, the bond interface is subject to thermal fatigue, and the question of how many thermal cycles the cladding can withstand before delamination becomes a practical concern. The literature suggests that the thermal expansion mismatch between the overlay and base material is the primary driver of thermal fatigue failure, and that minimizing this mismatch through careful alloy design is more effective than simply increasing bond strength.

Study Insights and Implications

The study of surface cladding for continuous casting guide rollers highlights the importance of matching the cladding material's thermal properties to the operating environment. Unlike conventional wear applications where hardness is the primary design criterion, guide roller cladding requires a balanced approach that considers thermal conductivity, thermal expansion, oxidation resistance, and wear resistance simultaneously. The selection of PTA cladding as the preferred process reflects the industry's demand for precision, low dilution, and high-quality bond interfaces. Engineers working in this area should pay particular attention to the thermal expansion matching between overlay and base material, as this single parameter has a profound influence on the long-term durability of the cladding system.