CLADDING TECHNOLOGY SHANXI CO., LTDApplication of Surface Weld Overlay Technology on Skid Rolls
Literature Overview and Application Background
Skid rolls (also known as carry rolls, transfer rolls, or skid bars) are essential components in continuous casting, hot rolling, and cold rolling production lines. They support and transport hot steel slabs or strips through various processing stages. The operating environment subjects skid rolls to extreme thermal cycling, mechanical abrasion from steel contact, and occasional impact loading. Surface weld overlay technology provides an effective method for enhancing the service life of skid rolls by depositing wear-resistant alloy layers on the critical bearing surfaces.
Service Conditions and Wear Mechanisms
The wear mechanisms acting on skid roll surfaces are multifactorial:
| Wear Mechanism | Description | Severity Factor |
|---|---|---|
| Abrasive wear | Steel surface particles embed and scrape overlay | High in rough rolling |
| Adhesive wear | Localized cold welding and material transfer | Moderate to high |
| Oxidative wear | High-temperature oxidation of overlay surface | High above 600°C |
| Erosive wear | Impact from falling or misaligned slabs | Intermittent but severe |
| Thermal fatigue | Cyclic thermal stress causing microcracking | Cumulative damage |
The combination of these wear mechanisms requires an overlay material that offers a balanced combination of hardness, toughness, oxidation resistance, and thermal shock tolerance. No single material can optimize all these properties simultaneously, necessitating careful selection based on the specific application conditions.
Overlay Material Selection Matrix
| Operating Temperature | Primary Wear Mechanism | Recommended Material | Expected Life Extension |
|---|---|---|---|
| Below 300°C | Abrasive | High-chrome white cast iron (Cr20) | 3-5x |
| 300-600°C | Abrasive + Oxidative | Martensitic stainless (1Cr13, 2Cr13) | 2-4x |
| 600-900°C | Oxidative + Thermal fatigue | Austenitic stainless (0Cr25Ni20) | 2-3x |
| Above 900°C | Severe oxidation | Inconel 625 or Co-Cr alloy | 1.5-3x |
| Mixed conditions | Multi-mechanism | Multi-layer composite | 3-5x |
For continuous casting skid rolls operating at temperatures between 500-800°C, austenitic stainless steel overlays provide the best balance of properties. The austenitic structure maintains stability at elevated temperatures, resisting phase transformation and associated volume changes.
Process Parameters and Implementation
The weld overlay process for skid rolls typically involves the following parameters:
- Welding method: Submerged arc welding (SAW) for thick deposits; GMAW for thin layers or complex geometries
- Overlay thickness: 3-8 mm depending on severity of service conditions
- Number of passes: 2-5 for multi-layer builds
- Current: 300-400 A for SAW; 200-300 A for GMAW
- Voltage: 28-34 V for SAW; 24-30 V for GMAW
- Travel speed: 250-450 mm/min
- Preheat: 100-200°C for carbon steel skid rolls
- Post-weld treatment: Stress relief at 550-650°C for 2 hours
The geometry of skid rolls, often featuring grooves or channels for strip guidance, adds complexity to the overlay process. Welding must be performed in a sequence that minimizes distortion and ensures uniform coverage of all bearing surfaces.
Defect Analysis and Quality Assurance
| Defect | Detection Method | Acceptance Criteria | Corrective Action |
|---|---|---|---|
| Surface cracks | MT/PT | No cracks > 0.5 mm | Grind out and re-weld |
| Undercut | Visual/UT | Depth < 0.5 mm | Grind and blend |
| Porosity | UT | < 5% area coverage | Grind to sound metal |
| Excessive hardness variation | HV grid test | ±80 HV maximum | Re-overlay affected area |
| Distortion | Dimensional check | Within ±1.0 mm | Straightening or re-machining |
Quality assurance requires a comprehensive inspection protocol including visual examination, magnetic particle testing for surface defects, ultrasonic testing for subsurface discontinuities, and hardness mapping to verify overlay uniformity.
Engineering Practice and Cost-Benefit Analysis
In a hot strip mill application, skid rolls with 4 mm austenitic stainless steel overlay demonstrated a service life of 18 months compared to 6 months for uncladded rolls, representing a threefold life extension. The cost analysis showed that despite the additional overlay material and labor costs, the total cost per ton of steel processed was reduced by 40% due to fewer roll changes and reduced downtime.
The PDCA cycle approach is particularly effective for optimizing skid roll overlay programs:
- Plan: Define overlay specifications based on service conditions and material selection
- Do: Execute overlay process with controlled parameters and documentation
- Check: Monitor service performance through wear measurement and failure analysis
- Act: Adjust material selection or process parameters based on performance data
Summary and Conclusions
Surface weld overlay technology for skid rolls represents a proven and cost-effective solution for extending component life in severe industrial environments. The success of the application depends on proper material selection matched to specific service conditions, disciplined process execution, and systematic quality verification. Engineers should approach skid roll overlay as a systematic engineering program rather than an ad hoc repair activity, incorporating performance monitoring and continuous improvement into the maintenance strategy. The integration of modern welding technologies with rigorous quality control enables significant reductions in maintenance costs and production downtime, delivering substantial economic benefits to steel producers and industrial operators.