CLADDING TECHNOLOGY SHANXI CO., LTDPreliminary Exploration of Roll Overlay Welding Process
Literature Overview
This 1999 study published in Special Steel Technology (特钢技术) by Zhang Wen from the Electromechanical Factory of Sichuan Chuantou Changte Group provides an early systematic examination of overlay welding processes for metalworking rolls. The work represents a foundational contribution to the understanding of roll surface restoration and enhancement through weld overlay, a technology that has since become essential in the steel, aluminum, and paper industries.
Core Technical Content
Roll Service Environment
Metalworking rolls are subjected to extremely severe service conditions:
- Hot rolling: Surface temperatures of 800–1200°C with thermal cycling of 50–100°C per pass
- Cold rolling: High contact pressures (1–3 GPa) with abrasive oxide scale
- Thermal fatigue: Rapid heating and cooling cycles causing surface cracking
- Mechanical fatigue: Contact stress cycling leading to spalling and brinelling
- Chemical attack: Oxidation, carburization, and decarburization at elevated temperatures
Roll Base Materials
The substrate material selection depends on the rolling application:
| Roll Type | Typical Base Material | Application |
|---|---|---|
| Hot strip mill work roll | 4Cr5MoSiV or 3Cr2W8V | Hot strip production |
| Cold strip mill work roll | 5CrMnMo or 4CrMoV | Cold strip production |
| Wire rod mill roll | 4Cr5MoSiV | Wire rod finishing |
| Plate mill roll | 4Cr5MoSiV or 5Cr4Mo3Si | Plate rolling |
| Aluminum roll | 5CrMnMo | Aluminum sheet rolling |
Overlay Material Systems for Rolls
The overlay material must provide:
- High hardness at operating temperature (red hardness)
- Thermal fatigue resistance
- Abrasion resistance against oxide scale and workpiece
- Compatibility with the roll base material
- Machinability for crown and diameter restoration
Recommended overlay systems:
| Overlay System | Hardness at RT (HV) | Hardness at 600°C (HV) | Key Feature |
|---|---|---|---|
| Cr-Mo-V (H13 type) | 800–1000 | 600–800 | High toughness, thermal fatigue resistance |
| Co-Cr-W (Stellite) | 1200–1400 | 900–1100 | Excellent hot hardness |
| WC-Co | 1400–1600 | 1000–1200 | Superior abrasion resistance |
| High-speed steel (M2) | 1100–1300 | 700–900 | Good combination of properties |
| Ni-based (Inconel 625) | 400–500 | 350–450 | Thermal fatigue resistance, low thermal expansion |
Process Development and Optimization
The study examines several overlay processes applicable to roll surfaces:
1. Submerged Arc Welding (SAW) with Consumable Insert
- Deposition rate: 2.0–4.0 kg/h
- Layer thickness per pass: 3–6 mm
- Dilution: 20–35%
- Advantage: High productivity, good for large diameter rolls
- Limitation: Higher heat input, potential for distortion
2. Shielded Metal Arc Welding (SMAW)
- Deposition rate: 0.5–1.5 kg/h
- Layer thickness per pass: 2–4 mm
- Dilution: 15–25%
- Advantage: Flexibility, portability, suitable for field repair
- Limitation: Lower productivity, operator dependent
3. Plasma Transferred Arc (PTA) Powder Cladding
- Deposition rate: 1.0–3.0 kg/h
- Layer thickness per pass: 0.5–1.5 mm
- Dilution: 5–15%
- Advantage: Low dilution, excellent microstructure control
- Limitation: Higher equipment cost, requires powder supply
Process Parameters Optimization
The critical process parameters for roll overlay welding include:
| Parameter | Optimal Range | Effect on Quality |
|---|---|---|
| Heat input | 0.5–2.0 kJ/mm | Controls grain size and dilution |
| Travel speed | 80–150 mm/min | Affects bead profile and dilution |
| Arc voltage | 22–30 V | Controls penetration and bead width |
| Wire/feed speed | 4–8 m/min | Controls deposition rate |
| Preheat temperature | 200–400°C | Reduces thermal stress in base metal |
| Interpass temperature | ≤300°C | Prevents excessive grain growth |
Defect Analysis and Countermeasures
Common defects in roll overlay welding and their prevention:
| Defect | Root Cause | Detection Method | Countermeasure |
|---|---|---|---|
| Cracking | High residual stress, hydrogen | MT/UT | Preheat, post-weld stress relief |
| Porosity | Gas entrapment, contaminated base | RT/UT | Clean surface, proper shielding |
| Spalling | High dilution, brittle interface | Visual/MT | Transition layer, low-dilution process |
| Hardness variation | Inconsistent heat input | Hardness test | Process parameter control |
| Distortion | Thermal asymmetry | Dimensional check | Symmetric welding sequence |
| Incomplete fusion | Insufficient heat input | UT/MT | Increase heat input, improve fit-up |
Post-Weld Heat Treatment
The heat treatment sequence for overlay-welded rolls is critical:
- Stress relief: 600–700°C for 2–4 hours to reduce residual stresses
- Solution treatment (for precipitation-hardening overlays): 1050–1150°C, 1–2 hours, water quench
- Aging treatment: 700–850°C for 2–8 hours to precipitate strengthening phases
- Final tempering (for tool steel overlays): 550–650°C for 2–4 hours
The heat treatment must be performed before the roll is ground to final diameter and crowned, as the grinding process introduces its own residual stresses.
Engineering Practice Integration
In industrial practice, roll overlay welding is performed in the following contexts:
1. New Roll Manufacturing: Overlay is applied during roll fabrication to create a wear-resistant surface on a cheaper base material, reducing overall cost while maintaining performance.
2. Roll Restoration: Worn rolls are overlay-welded to restore diameter and apply a fresh wear-resistant surface. This is typically performed during scheduled maintenance intervals.
3. Performance Enhancement: Existing rolls are overlay-welded with superior materials to extend service life in demanding applications.
The economic benefits of roll overlay welding are substantial:
- Cost reduction of 30–50% compared to full replacement rolls
- Extended service life of 2–5 times compared to uncoated rolls
- Reduced downtime due to faster restoration compared to roll replacement
- Ability to apply different overlay materials to different roll zones (e.g., barrel vs. neck)
Study Reflections
This early study from 1999 represents an important contribution to the development of roll overlay technology in China. While the process understanding has advanced significantly since then, the fundamental principles remain valid. The key insight from this work is that roll overlay is not simply a surface treatment—it is a metallurgical engineering challenge that requires careful consideration of the interaction between the overlay, the base material, and the service environment. The selection of overlay material must be based on a thorough understanding of the dominant failure mechanism (thermal fatigue, abrasion, spalling, or a combination), and the process parameters must be optimized to achieve the required microstructure in the deposited layer. Future developments in roll overlay technology should focus on multi-layer designs that combine different functional properties in each layer, and on advanced processes such as laser cladding and cold spray that offer even lower dilution and better microstructural control.