CLADDING TECHNOLOGY SHANXI CO., LTDApplication of Lincoln Wire in Composite Overlay of Continuous Casting Rolls
Literature Overview
This 1995 study by Zhou Wusheng, published in "Tianjin Metallurgy" and conducted at the Tianjin Metallurgical Spare Parts Repair Center, represents an early and practically significant application of imported Lincoln welding wire in the composite overlay repair of continuous casting (CC) rolls. Continuous casting rolls—both copper-alloyed working rolls and steel backup rolls—are subjected to extreme thermal cycling, molten metal erosion, and mechanical loading. The study explores the use of Lincoln-brand welding consumables for building up wear-resistant, thermally stable overlay layers on these critical components, reflecting the early Chinese metallurgical industry's engagement with international welding technology.
Technical Background of Continuous Casting Roll Repair
Continuous casting rolls endure a uniquely harsh service environment. The working face of a CC roll contacts molten steel at temperatures exceeding 1500 °C, while the interior remains cooled by water channels at approximately 20–30 °C. This creates a thermal gradient of over 1000 °C across the roll thickness, inducing severe thermal stresses that cause surface cracking, spalling, and accelerated wear. The working surface also suffers from erosion by oxidized inclusions and slag entrapped in the solidifying shell.
The base material for steel backup rolls is typically a low-carbon steel (such as Q345 or 16Mn) or a medium-carbon steel, while copper-alloyed working rolls are often made from Cu-Cr or Cu-Sn alloys. The overlay strategy aims to deposit a hard, thermally stable layer that resists thermal fatigue cracking and erosion while maintaining sufficient thermal conductivity to facilitate heat extraction.
Lincoln Wire Selection and Process Parameters
Lincoln Electric, as a leading global welding consumable manufacturer, offered a range of welding wires suitable for overlay applications. For CC roll repair, the relevant consumables would include low-hydrogen flux-cored wires (such as Lincoln Flux-Cored Electrodes) or solid wires designed for high-strength overlay deposits. The study likely evaluated wires with controlled carbon and alloy content to balance hardness, toughness, and thermal stability.
The overlay process parameters are critical. Submerged arc welding (SAW) is often preferred for large-area roll overlay due to its high deposition rate and deep penetration, which promotes good metallurgical bonding. However, for precise surface contouring, gas metal arc welding (GMAW) or flux-cored arc welding (FCAW) may be more suitable.
| Process Parameter | Recommended Range | Rationale |
|---|---|---|
| Welding current (GMAW) | 200–350 A | Controls deposition rate and penetration |
| Arc voltage (GMAW) | 25–32 V | Influences bead width and dilution |
| Travel speed | 150–300 mm/min | Balances deposition rate with heat input |
| Shielding gas | Ar + CO2 (80:20) or CO2 | CO2 provides deeper penetration; Ar reduces spatter |
| Wire diameter | 1.2–1.6 mm | Standard for industrial overlay applications |
| Preheat temperature | 100–200 °C | Reduces thermal stress and cracking risk |
| Interpass temperature | Below 300 °C | Prevents grain coarsening in previous layers |
Microstructure and Performance
The overlay deposit microstructure depends on the wire composition and solidification rate. For low-carbon overlay wires with moderate alloy additions (Mn, Si, Cr), the microstructure typically consists of a ferrite-pearlite matrix with possible martensitic islands in regions of rapid cooling. Higher-alloy wires may produce a fully martensitic or austenitic structure, offering improved thermal stability at the cost of reduced hardness.
A key challenge in CC roll overlay is the development of thermal fatigue cracks in the overlay layer during service. The thermal cycling induces repeated tensile and compressive stresses at the surface. To mitigate this, the overlay material must possess adequate ductility to accommodate thermal strain without cracking. This creates a design tension: increasing hardness through higher carbon or alloy content improves wear resistance but may reduce ductility and increase susceptibility to thermal fatigue cracking.
The study likely reported on hardness profiles, dilution rates, and bond strength between the overlay and base metal. A dilution rate of 15–25% is typical for the first overlay layer, decreasing to below 10% in subsequent layers. Bond strength testing (per ASTM G140 or equivalent) is essential to confirm that the overlay will not delaminate during the thermal and mechanical cycling of CC operation.
Engineering Considerations and Lessons
The 1995 timeframe places this study in a period when Chinese metallurgical enterprises were actively importing and adapting foreign welding technologies. The use of Lincoln wire reflects a pragmatic approach: leveraging proven international consumables to address specific repair challenges. However, this also raises questions about cost, supply chain reliability, and the long-term strategy of developing domestic alternatives.
From a process engineering perspective, the study underscores the importance of multi-layer overlay strategies. A single-layer overlay is insufficient for CC roll repair due to the extreme thermal gradient; a graded overlay structure—starting with a low-alloy bonding layer and transitioning to a high-hardness surface layer—provides the best combination of adhesion, thermal stability, and wear resistance.
Surface preparation is another critical factor. The CC roll surface must be machined to remove any damaged or spalled material, followed by thorough cleaning to ensure metallurgical bonding. Contamination from copper oxide (on copper-alloyed rolls) or carbon buildup (from molten steel oxidation) can severely compromise overlay adhesion.
Key Reflections
This early study demonstrates the practical application of imported welding consumables in a demanding industrial setting. The choice of Lincoln wire was driven by its consistent quality and proven performance in overlay applications worldwide. However, the long-term engineering lesson is that consumable selection must be matched to the specific thermal and mechanical demands of the application, and that process optimization—particularly regarding heat input control, multi-layer strategy, and post-weld treatment—is as important as consumable selection itself. The study also highlights the need for domestic development of specialized overlay wires tailored to the unique requirements of continuous casting roll repair, reducing dependence on imports while enabling better process-material synergy.