Large-Area Wear-Resistant Alloy Overlay Plate Cladding Technology: Domestic and International Progress

Overview and Industrial Demand

Wear-resistant alloy overlay plates are indispensable in industries subject to severe abrasive, erosive, and impact wear conditions. Applications span mining, cement, power generation, agriculture, and heavy machinery. The demand for large-area overlay plates—typically exceeding 10 m² per plate—has driven significant advancements in both manufacturing technology and material science. This study note examines the current state of large-area wear-resistant overlay plate technology, comparing domestic (primarily Chinese) and international developments, and identifying key technical challenges and solutions.

Core Technical Approaches

Manufacturing Methods for Large-Area Overlay Plates

Method	Typical Overlay Thickness	Max Plate Size	Production Rate	Cost	Key Advantage
SAW (Submerged Arc Welding)	3–25 mm	6000×2500 mm	High	Medium	Best for thick overlays
ESW (Electroslag Welding)	5–50 mm	8000×3000 mm	Medium	Medium	Uniform thick overlay
Strip Cladding (Welded)	1–5 mm	12000×2000 mm	Very High	Low	Continuous production
Explosive Cladding	1–10 mm	6000×2000 mm	Low	High	Superior bonding
Roll-Bonded Cladding	0.5–5 mm	12000×2000 mm	High	Low-Medium	Continuous, thin overlay
Laser Cladding	0.5–3 mm	2000×1000 mm	Low	High	High precision, thin layer

SAW Overlay for Large Plates

Submerged arc welding is the most widely used method for large-area wear-resistant overlay plates. The process involves multi-pass welding with specialized wear-resistant flux-cored wires or solid wires. Key process parameters include:

Wire diameter: 1.6–3.2 mm
Welding current: 400–800 A
Welding voltage: 25–35 V
Travel speed: 150–400 mm/min
Flux type: Specialized wear-resistant flux (e.g., with Cr, Mo, W, B additions)
Number of passes: 3–10 (depending on overlay thickness)

The multi-pass nature of SAW overlay requires careful control of interpass temperature (typically 150–250°C) and pass sequence to minimize residual stress and prevent cracking. The first pass (root pass) is critical for achieving metallurgical bond with the base plate, and often requires a specially designed root flux or wire.

ESW Overlay for Thick Wear Layers

Electroslag welding overlay is preferred for thick wear-resistant layers (10–50 mm) where SAW would require excessive passes. ESW provides:

Excellent weld quality with minimal defects
Uniform overlay composition due to slag pool mixing
High deposition rate (5–15 kg/h)
Reduced dilution (5–10%)

However, ESW requires specialized equipment and is limited to vertical or near-vertical welding positions, which constrains plate geometry.

Material Systems for Wear-Resistant Overlay

Common Overlay Alloys and Their Properties

Overlay Alloy	Hardness (HV)	Typical Application	Wear Mechanism	Key Alloying Elements
Cr-Cr₂C₃ system	800–1200	Mining, cement	Abrasion	Cr (20–30%)
Cr-Mo system	400–700	Impact wear	Impact-abrasion	Cr (5–10%), Mo (2–5%)
High-Cr cast iron	500–800	Slurry wear	Slurry erosion	Cr (10–20%), Si (2–5%)
Hardfacing alloy (Ni-Cr)	600–900	High-temperature wear	Oxidative wear	Ni (base), Cr (5–15%)
WC-Co composite	1200–1600	Severe abrasion	Cutting abrasion	WC (30–70%), Co (10–30%)
Martensitic stainless	400–600	General wear	Sliding wear	C (0.5–1.0%), Cr (12–15%)

Dilution Control

Dilution—the mixing of base metal with overlay metal—is one of the most critical challenges in overlay welding. For wear-resistant applications, dilution directly affects hardness and wear resistance. Typical dilution rates are:

SAW overlay: 10–25%
ESW overlay: 5–15%
Strip cladding: 0–5%
Explosive cladding: 0–2%

Control strategies include:

Using a transition layer (e.g., Ni-Cr or Cr-based) between base and wear alloy
Optimizing welding parameters to minimize base metal melting
Using pre-welded overlay strips as a low-dilution first layer
Applying multiple thin passes instead of fewer thick passes

Domestic vs. International Technology Comparison

International Leaders

European manufacturers (e.g., SSAB, Outokumpu, and specialized German firms) have long led in wear-resistant overlay plate technology. Key characteristics of international technology include:

Advanced flux chemistry with precise alloy control
Automated welding systems with closed-loop parameter control
Extensive qualification databases for specific applications
Integration of overlay plates with structural design (e.g., pre-drilled, pre-cut shapes)

Japanese manufacturers (e.g., JFE, Nippon Steel) have developed specialized overlay alloys for high-temperature and corrosive wear environments, particularly for power generation and chemical processing applications.

Domestic (Chinese) Progress

Chinese manufacturers have made substantial progress in wear-resistant overlay plate technology over the past two decades. Key developments include:

Material innovation: Development of proprietary Cr-Cr₂C₃ and Cr-Mo overlay alloys with enhanced wear resistance and toughness balance.
Process automation: Adoption of robotic SAW and ESW systems with multi-axis coordination for complex plate geometries.
Scale production: Capability to produce overlay plates up to 12,000 mm in length, exceeding many international counterparts.
Cost advantage: Significantly lower production costs due to domestic material supply chains and labor costs.

However, gaps remain in:

Ultra-high-performance overlay alloys (e.g., cermet-based, PTA-applied)
Process consistency and traceability for critical applications
Integration with advanced inspection technologies (e.g., phased array UT)
International standard qualification for export applications

Quality Control and Defect Management

Common Defects in Large-Area Overlay Plates

Defect	Description	Cause	Prevention
Cracking	Transverse or longitudinal cracks in overlay	Hydrogen, residual stress, high CE	Preheat, controlled cooling, low-H consumables
Incomplete fusion	Lack of bond between overlay and base	Insufficient heat input, contamination	Proper flux/wire selection, surface preparation
Excessive dilution	Reduced hardness and wear resistance	High heat input, thin overlay	Low heat input, transition layer, multiple passes
Porosity	Gas porosity in weld metal	Moisture in flux, contamination	Flux drying, clean base metal
Hardness variation	Non-uniform hardness across plate	Parameter variation, composition variation	Process control, online monitoring
Residual stress	High tensile residual stress	Uneven cooling, thick overlay	Post-weld stress relief, peening

Inspection Methods

Visual inspection (VT): Surface quality, cracks, undercuts
Magnetic particle testing (MT): Surface and near-surface cracks
Ultrasonic testing (UT): Volumetric defects, dilution measurement
Hardness testing: Hardness profile across overlay thickness
Chemical analysis: Overlay composition verification
Wear testing: Laboratory wear testing for critical applications

Engineering Practice Insights

Case Study: Cement Mill Liner Plates

In cement mill applications, large-area overlay plates (typically 6000×2500×60 mm) are used as mill liners. The overlay alloy is typically a Cr-Mo system (400–700 HV) with a total overlay thickness of 15–25 mm. Key engineering considerations include:

Plate design: Pre-drilled mounting holes, chamfered edges for installation
Overlay sequence: Strategic welding sequence to minimize distortion
Post-weld treatment: Stress relief at 600–650°C for 2–4 hours
Quality verification: 100% MT for surface defects, hardness mapping

The service life of such plates has been extended from 6–12 months (cast iron liners) to 18–36 months with proper overlay technology, representing a significant economic benefit.

Case Study: Mining Equipment Wear Parts

In mining applications, overlay plates for excavator buckets, conveyor chutes, and crusher hoppers require high abrasion resistance. The overlay alloy selection depends on the wear mechanism:

Abrasive wear (quartz-rich ore): Cr-Cr₂C₃ system (800–1200 HV)
Impact-abrasion (rock breaking): Cr-Mo system (400–700 HV)
Slurry wear: High-Cr cast iron (500–800 HV)

The overlay thickness is typically 10–20 mm, applied by multi-pass SAW with specialized flux-cored wire.

Study Insights and Implications

The study of large-area wear-resistant overlay plate technology reveals several important insights:

Process-material coupling is critical: The selection of welding process must be matched to the overlay alloy and plate geometry. SAW is versatile but requires careful parameter control; ESW is superior for thick overlays but limited in geometry; strip cladding is efficient for thin overlays but requires continuous production.
Dilution management is the key to performance: The wear resistance of the overlay is directly related to dilution. Engineers must adopt a systematic approach to dilution control, including transition layers, process optimization, and post-weld verification.
Quality consistency is the differentiator: The gap between domestic and international technology is less about capability and more about consistency. International manufacturers invest heavily in process control systems, operator training, and quality documentation.
Application-specific design is essential: Generic overlay plates rarely achieve optimal performance. The overlay alloy, thickness, and process must be tailored to the specific wear mechanism, operating environment, and service conditions.
Life-cycle cost analysis drives adoption: The economic justification for overlay plates lies in extended service life and reduced downtime. Engineers must present compelling life-cycle cost analyses to stakeholders, demonstrating the ROI of overlay technology.

The future of large-area overlay plate technology lies in the integration of advanced materials (e.g., functionally graded overlays, cermet composites), intelligent manufacturing (e.g., real-time process monitoring, adaptive control), and digital engineering (e.g., virtual qualification, digital twins). Engineers who master both the metallurgical fundamentals and the manufacturing technology will be best positioned to drive innovation in this field.