CLADDING TECHNOLOGY SHANXI CO., LTDCladding Repair Technology for Hot-Rolled Channel Steel Rolls
Literature Overview
This technical study addresses the cladding repair of worn hot-rolled channel steel (U-channel) rolls in steel rolling mills. Channel steel production imposes severe thermal and mechanical demands on roll surfaces, including repeated contact with red-hot steel at 900–1100 °C, high compressive loads, and abrasive contact with oxide scale. The overlay repair strategy must restore dimensional accuracy while providing wear and thermal fatigue resistance.
Failure Analysis and Repair Requirements
Typical Failure Modes of Channel Rolls
| Failure Mode | Mechanism | Typical Location | Service Life Impact |
|---|---|---|---|
| Surface abrasion | Oxide scale abrasion against roll surface | Working surface, full length | Dimensional tolerance exceeded |
| Thermal cracking | Repeated thermal cycling | Roll surface, near crown | Premature roll failure |
| Bearing (brinelling) | Localized plastic deformation from roll nip | Working surface at roll contact zone | Surface roughness degradation |
| Spalling | Subsurface crack initiation and propagation | Near-surface, 0.5–3 mm depth | Sudden surface loss |
| Roll neck wear | Contact with roll bearing housing | Roll neck journal | Bearing damage |
Repair Specifications
| Parameter | Requirement |
|---|---|
| Overlay hardness | 40–50 HRC (matching or exceeding original roll steel) |
| Dimensional accuracy | ±0.05 mm for roll diameter |
| Surface finish | Ra ≤ 1.6 μm after grinding |
| Bond strength | ≥ 300 MPa (peel test) |
| Thermal fatigue resistance | ≥ 50 cycles at 900 °C without cracking |
| Wear rate | ≤ 0.5 mm per million tons rolled |
Overlay Process Selection and Optimization
Process Comparison for Roll Repair
| Process | Deposition Rate | Dilution | Microstructure | Cost | Suitability |
|---|---|---|---|---|---|
| SAW overlay | High | High (30–50%) | Coarse, equiaxed | Low | Thick repair deposits |
| GMAW overlay | Medium | Medium (20–30%) | Medium grain size | Medium | General repair |
| PTA cladding | Medium | Low (5–15%) | Fine, columnar | High | Precision repair |
| Laser cladding | Low-Medium | Low (5–10%) | Very fine, refined | High | Surface finish restoration |
| ESW overlay | Very High | High (40–60%) | Very coarse | Low | Full resurfacing |
Recommended Overlay Alloy Selection
For hot-rolled channel steel rolls, the overlay alloy must balance wear resistance, thermal stability, and toughness:
| Alloy Type | Composition (wt%) | Hardness (HV) | Application |
|---|---|---|---|
| High-Cr high-C steel | C 0.8–1.2, Cr 12–18, Mo 2–4 | 800–1100 | General hot rolling |
| Ni-Cr-C alloy | C 2.0–3.0, Ni 15–20, Cr 8–12 | 900–1200 | High abrasion conditions |
| Co-Cr alloy | C 3.0–5.0, Co 50–60, Cr 20–25 | 1000–1400 | Extreme wear conditions |
| MCrAl-type | C 1.0–2.0, Cr 25–35, Al 5–10 | 950–1300 | Thermal fatigue resistance |
Process Implementation and Quality Control
Step-by-Step Repair Procedure
- Roll removal and inspection: Measure wear profile, identify defects, document remaining service life.
- Surface preparation: Grind away damaged surface (minimum 3 mm removal), clean with solvent, preheat to 200–300 °C.
- Overlay welding: Apply selected process with controlled heat input, typically 2–4 mm total overlay thickness.
- Post-weld heat treatment: Stress relief at 600–700 °C for 2 hours to reduce residual stresses.
- Machining and grinding: Restore dimensional accuracy and surface finish.
- Quality verification: Hardness testing, magnetic particle inspection, dimensional measurement.
Non-Destructive Testing Requirements
| NDT Method | Purpose | Acceptance Criteria |
|---|---|---|
| Magnetic Particle Testing (MT) | Surface and near-surface cracks | No indications |
| Ultrasonic Testing (UT) | Subsurface defects, bond quality | No Type-2 indications |
| Hardness testing | Overlay hardness verification | Within specified range ±10% |
| Dimensional measurement | Profile and roundness | Within tolerance ±0.05 mm |
Engineering Practice Cases
In a typical hot rolling mill operation, channel rolls undergo replacement or repair every 50,000–200,000 tons of production depending on alloy and process conditions. Overlay repair typically extends roll life by 50%–150% compared to original manufacturing condition, particularly when a higher-performance alloy is selected for the overlay layer. The economic benefit is substantial: roll replacement costs include material, machining, heat treatment, and installation, while overlay repair requires only surface preparation, welding, and final grinding.
The critical engineering challenge is maintaining dimensional accuracy on the cylindrical roll surface. Roll curvature, thermal distortion during welding, and grinding allowance must all be carefully managed. Multi-pass welding with cross-hatch patterns minimizes directional distortion, and in-situ measurement during grinding ensures the final profile meets specification.
Study Insights
The cladding repair of hot-rolled channel rolls exemplifies the practical application of overlay technology in heavy industry. The success of repair depends not only on selecting an appropriate overlay alloy but also on controlling the welding process to minimize thermal distortion, ensuring sound metallurgical bonding, and achieving the required dimensional accuracy through post-weld machining. The economic and environmental benefits of roll repair through cladding are substantial, reducing both material consumption and production downtime. For engineers managing rolling mill maintenance, understanding the relationship between overlay microstructure and service performance is essential for optimizing repair intervals and extending asset life.