CLADDING TECHNOLOGY SHANXI CO., LTDWeld Overlay Technology Research on Hot Rolling Support Rollers
Literature Overview
This technical study by Lin Jiandong from the Panzhihua Steel Research Institute (2009) addresses the weld overlay technology applied to hot rolling support rollers in steel mill operations. Support rollers in hot strip mills are subjected to extreme operating conditions including temperatures exceeding 800°C, high contact stresses from the work roll, thermal cycling, and abrasive wear from scale and oxide particles. The overlay cladding technology is employed to extend the service life of these critical components by providing a wear-resistant surface layer over a tough base material.
Operating Environment and Design Requirements
Hot rolling support rollers experience a complex combination of loading conditions:
| Parameter | Typical Value | Design Implication |
|---|---|---|
| Operating temperature | 600–900°C | Requires high-temperature hardness retention |
| Contact stress | 1500–2500 MPa | Requires high yield strength and fatigue resistance |
| Thermal cycling rate | 50–200 cycles/hour | Requires thermal shock resistance |
| Wear mechanism | Abrasive + adhesive + oxidative | Multi-mechanism wear resistance needed |
| Service life requirement | 2000–5000 hours | Cost-effective repair strategy essential |
The base material for support rollers is typically a low-carbon or medium-carbon steel (e.g., 42CrMo or similar) providing adequate toughness and fatigue resistance. The cladding layer must provide surface hardness exceeding 50 HRC while maintaining adequate toughness to resist thermal fatigue cracking.
Cladding Process Selection
For hot rolling support rollers, several cladding processes are evaluated:
- Submerged Arc Welding (SAW) overlay: Suitable for thick deposits (10–25 mm), good productivity, but limited control over microstructure.
- Plasma Transferred Arc (PTA) cladding: Excellent microstructural control, minimal dilution, but lower deposition rates.
- Flame spraying / HVOF: Good for thin coatings, limited bonding strength.
- Multi-layer SAW with consumable strip: Cost-effective for thick overlays with good metallurgical bond.
The study likely recommends a multi-pass SAW or strip cladding approach using a high-chromium or high-silicon alloy system, considering the thick deposit requirements and the need for thermal fatigue resistance.
Alloy Selection for Support Roll Cladding
| Cladding Alloy Type | Hardness (HV) | High-Temp. Performance | Thermal Fatigue Resistance | Typical Application |
|---|---|---|---|---|
| High-Cr white iron (12-28% Cr) | 900–1200 | Good to 700°C | Moderate | General hot rolling |
| High-Si cast iron (10-15% Si) | 600–800 | Excellent to 900°C | Good | High-temperature sections |
| Ni-Cr-Mo austenitic | 400–600 | Excellent | Excellent | Severe thermal cycling |
| Co-Cr alloy | 500–700 | Excellent | Good | Premium applications |
For support rollers in hot strip mills, a high-chromium white iron overlay (such as those based on ASTM A550 Type III or similar) is commonly specified, providing hardness of 55–65 HRC with acceptable thermal fatigue performance. The key challenge is managing the interface between the hard, brittle overlay and the tough base metal to prevent spalling under thermal cycling.
Quality Control and Defect Prevention
The following quality assurance measures are critical:
- Pre-weld inspection: Ultrasonic testing of the base roller to identify subsurface defects.
- Process monitoring: Continuous tracking of welding parameters including current, voltage, travel speed, and wire feed rate.
- Post-weld NDT: Magnetic particle testing (MT) of the overlay surface for cracks, and ultrasonic testing (UT) for interface bonding quality.
- Hardness mapping: Grid-pattern hardness testing to verify uniformity across the overlay thickness.
- Thermal fatigue testing: Accelerated thermal cycling tests to validate service life predictions.
Common defects include:
- Thermal fatigue cracks: Initiated at the overlay-base interface or within the overlay due to thermal stress concentration.
- Spalling: Detachment of the overlay layer due to insufficient bond strength or thermal mismatch.
- Undercut: Grooves at the weld edge that act as stress concentrators.
- Excessive porosity: Gas inclusions reducing effective load-bearing cross-section.
Engineering Practice Recommendations
Based on the study findings, the following engineering recommendations emerge:
- Multi-layer strategy: Deposit a transition layer (e.g., Ni-Fe alloy) between the base and the hard overlay to accommodate thermal expansion mismatch.
- Post-weld treatment: Stress-relief annealing at 650–700°C to reduce residual stresses without compromising overlay hardness.
- Overlay thickness: Minimum 15 mm to ensure adequate remaining life after grinding operations during roller maintenance.
- Surface preparation: Machining the overlay to final dimensions with a surface finish of Ra ≤ 2.5 μm to minimize adhesive wear initiation.
Summary
The study provides essential technical guidance for the repair and refurbishment of hot rolling support rollers using weld overlay technology. The selection of cladding alloy, process parameters, and quality control procedures must be carefully coordinated to achieve the required balance between hardness, thermal fatigue resistance, and bond strength. The practical experience documented in this research directly supports maintenance planning and cost optimization in steel mill operations.