CLADDING TECHNOLOGY SHANXI CO., LTDSintered Alloy Flux Cladding of φ850 Steel Rollers Using Sintered Alloy Flux
Literature Overview
This study by Zhang Yazhi, Zhang Wen, and Zhang Bingxiang (1993), conducted at Anshan Steel Technical School, investigates the cladding of φ850 mm steel rollers using sintered alloy flux. Steel rollers are critical components in hot rolling mills, where they operate under extreme conditions of high temperature, high contact pressure, and abrasive wear from hot steel strips. The study focuses on the development of sintered alloy flux formulations and the optimization of submerged arc welding (SAW) parameters to produce durable, wear-resistant overlay layers on large-diameter rollers.
Core Technical Analysis
Application Background and Service Conditions
Hot rolling mill rollers experience:
- Surface temperatures up to 600–800°C from contact with hot steel strips
- Contact pressures of 100–300 MPa
- Abrasive wear from scale and oxide particles
- Thermal fatigue from cyclic heating and cooling
- Chemical attack from scale and mill scale
The base roller material is typically medium-carbon steel (e.g., 45# steel) or low-alloy steel, which provides adequate structural strength but insufficient surface hardness and wear resistance for prolonged service.
| Parameter | Specification |
|---|---|
| Roller diameter | φ850 mm |
| Roller length | 1500–2000 mm |
| Base material | 45# steel or 40Cr |
| Service temperature | 600–800°C |
| Contact pressure | 100–300 MPa |
| Expected roller life (uncladded) | 2000–5000 hours |
| Target roller life (cladded) | 8000–15000 hours |
Sintered Alloy Flux Development
The study develops custom sintered alloy flux formulations to achieve specific overlay properties. Sintered fluxes are produced by blending raw materials, granulating, and sintering at controlled temperatures to achieve desired chemical composition and metallurgical properties.
| Flux Component | Function | Typical Range |
|---|---|---|
| Cr₂O₃ | Chromium source for hardness and corrosion resistance | 15–25% |
| MnO | Manganese source for solid solution strengthening | 10–20% |
| SiO₂ | Silicon source and fluxing agent | 5–15% |
| CaF₂ | Fluxing agent, reduces surface tension | 5–10% |
| Al₂O₃ | Refractory component, stabilizes slag | 3–8% |
| TiO₂ | Titanium source for carbide formation | 2–5% |
| Fe powder | Iron source, controls dilution | 30–50% |
| B₂O₃ | Glass-former, improves slag fluidity | 2–5% |
The sintering process involves:
- Mixing raw materials in precise proportions
- Granulating with water or organic binder
- Drying at 105°C for 4–8 hours
- Sintering at 800–1000°C for 2–4 hours
- Cooling and crushing to desired particle size (0.5–2.0 mm)
SAW Cladding Process Parameters
| Parameter | Value |
|---|---|
| Welding process | Submerged arc welding (SAW) |
| Electrode type | Solid wire (e.g., H08Mn2Si) |
| Arc current | 500–800 A |
| Arc voltage | 28–35 V |
| Travel speed | 200–400 mm/min |
| Flux coverage | 10–20 mm above weld pool |
| Wire stick-out | 25–35 mm |
| Number of passes | 2–4 |
| Interpass temperature | ≤ 250°C |
| Preheat temperature | 150–200°C |
The study emphasizes the importance of flux coverage and wire stick-out in controlling slag composition and dilution. Insufficient flux coverage leads to excessive oxidation and porosity, while excessive stick-out causes arc instability and irregular bead profiles.
Engineering Practice and Quality Control
Defect Analysis and Countermeasures
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Cracking in overlay | High carbon equivalent, excessive cooling rate | Increase preheat, reduce travel speed |
| Inclusion formation | Flux contamination, slag entrainment | Use clean flux, ensure adequate coverage |
| Porosity | Gas evolution from flux, insufficient shielding | Dry flux, maintain stable arc |
| Excessive dilution | High current, low travel speed | Reduce current, increase travel speed |
| Surface irregularity | Flux flow instability | Optimize flux composition and particle size |
| Roller warping | Excessive heat input, asymmetric welding | Use symmetric welding sequence, control heat input |
Quality Verification Protocol
The quality control protocol for φ850 mm roller cladding includes:
- Visual inspection of overlay surface for cracks, porosity, and surface defects.
- Magnetic particle testing (MT) to detect surface and near-surface cracks.
- Ultrasonic testing (UT) to verify bond strength and detect internal defects.
- Hardness testing across the overlay layer (target: 500–600 HV for wear-resistant overlay).
- Metallographic examination to assess microstructure, dilution, and defect presence.
- Wear testing using dry sliding or abrasive wear tests to quantify wear resistance.
- Dimensional inspection using laser scanning or coordinate measuring machine to verify roller geometry.
Wear Performance and Service Life
The study reports significant improvements in roller service life after cladding:
| Condition | Uncladded Roller | Cladded Roller | Improvement |
|---|---|---|---|
| Wear rate (dry sliding) | 8.0 × 10⁻⁴ mm³/N·m | 2.0 × 10⁻⁵ mm³/N·m | 40× |
| Service life (hot rolling) | 3000 hours | 12000 hours | 4× |
| Surface hardness | 250 HV | 550 HV | 2.2× |
| Cost per hour of service | ¥5.0 | ¥3.5 | 30% reduction |
Key Questions and Reflections
A critical challenge in roller cladding is managing residual stresses and preventing warping. Large-diameter rollers (φ850 mm) are susceptible to distortion during welding due to the high heat input required for complete penetration and bond strength. The study proposes using a symmetric welding sequence—alternating welds on opposite sides of the roller circumference—to balance thermal stresses and minimize warping.
Another reflection concerns the long-term stability of the overlay layer under thermal cycling. At service temperatures of 600–800°C, the overlay microstructure may undergo tempering, carbide coarsening, or phase transformation, potentially degrading wear resistance over time. The study suggests incorporating heat-resistant alloying elements (e.g., Cr, Mo, V) into the flux formulation to stabilize the overlay microstructure at elevated temperatures.
Study Insights and Implications
This study provides a comprehensive framework for cladding large-diameter steel rollers using sintered alloy flux and submerged arc welding. The development of custom flux formulations, optimization of SAW parameters, and systematic quality verification demonstrate a practical approach to extending roller service life in hot rolling applications. For engineers working on surface engineering of large industrial components, this study offers valuable insights into flux design, process control, and defect management. The economic analysis—showing a 30% reduction in cost per hour of service—highlights the financial viability of cladding technology for critical industrial components. The emphasis on thermal management and residual stress control is particularly relevant for any large-scale welding operation where dimensional stability is paramount.