CLADDING TECHNOLOGY SHANXI CO., LTDSintered Alloy Flux Cladding of 850mm Steel Rolling Mill Rolls
Literature Overview
This 1993 publication from Anshan Iron and Steel Technical School by Zhang Yazhi, Zhang Wen, and Zhang Bingxiang addresses the specialized challenge of cladding large-diameter (φ850 mm) steel rolling mill rolls using sintered alloy flux technology. The research represents practical engineering innovation in the steel rolling industry, where roll surface integrity directly affects product quality, production efficiency, and maintenance costs. The work bridges the gap between laboratory-scale cladding research and full-scale industrial application on heavy industrial components.
Technical Context and Engineering Challenges
Rolling mill rolls are critical components in steel production, subjected to extreme conditions including:
- Surface temperatures of 500–1100 °C during hot rolling operations
- Contact pressures exceeding 1000 MPa at the roll-billet interface
- Severe abrasive wear from scale, oxide inclusions, and material defects
- Thermal shock from alternating contact with hot and cool steel
- Chemical attack from scale and lubricants
The φ850 mm diameter rolls described in this research are large-diameter finishing rolls used in medium to heavy plate mills, where surface quality requirements are stringent and roll life directly impacts production economics. Traditional roll hardening methods (induction hardening, carburizing, nitriding) provide limited depth of hardening and cannot be easily reapplied to worn rolls without complete removal from service.
The cladding approach offers a significant advantage by enabling surface renewal through additive material deposition, restoring dimensional accuracy and surface properties without requiring complete roll replacement. The use of sintered alloy flux is particularly significant because it combines the advantages of flux-cored arc welding (FCAW) with the controlled composition and consistency of sintered powder metallurgy materials.
Sintered Alloy Flux Technology
Sintered alloy flux for cladding applications consists of powder metallurgically produced mixtures of iron-based alloys, hardening elements (chromium, molybdenum, vanadium, tungsten), and fluxing agents (limestone, dolomite, fluorspar). The sintering process produces a homogeneous, dense powder with controlled particle size distribution and chemical composition, resulting in more consistent weld deposits compared to conventionally produced fluxes.
The typical composition of sintered alloy flux for roll cladding:
| Element | Weight % | Function |
|---|---|---|
| Fe (balance) | 65–75 | Base matrix |
| Cr | 8–12 | Hardenability, wear resistance |
| Mo | 2–4 | High-temperature strength, secondary hardening |
| V | 1–2 | Carbide formation, wear resistance |
| Mn | 1.0–1.5 | Deoxidation, fluidity |
| Si | 0.3–0.8 | Deoxidation, strength |
| C | 0.8–1.2 | Carbide formation, hardness |
| Fluxing agents | 5–10 | Slag formation, protection |
The sintered flux is typically applied as a pre-placed layer on the roll surface or fed through a flux-cored wire or submerged arc welding (SAW) system. The resulting overlay layer contains a dispersion of hard carbides (Cr7C3, Mo2C, VC, WC) in a tempered martensitic or bainitic matrix, providing excellent wear resistance at elevated temperatures.
Process Parameters and Manufacturing Considerations
The cladding of φ850 mm rolls requires careful process planning to accommodate the large diameter, cylindrical geometry, and production schedule constraints. The following process parameters are typical for this application:
| Parameter | Value | Rationale |
|---|---|---|
| Welding method | Submerged arc welding (SAW) | High deposition rate, deep penetration, low spatter |
| Welding current | 600–900 A | Sufficient penetration for multi-pass buildup |
| Arc voltage | 30–38 V | Controls bead width and profile |
| Travel speed | 300–500 mm/min | Optimizes deposition rate and layer thickness |
| Number of passes | 4–6 | Achieves 6–10 mm total overlay thickness |
| Interpass temperature | 200–300 °C | Controls residual stress, prevents cracking |
| Post-weld treatment | Stress relief at 550–600 °C | Reduces residual stress, stabilizes microstructure |
The cylindrical geometry of the roll presents unique challenges for SAW cladding, including:
- Maintaining consistent wire feed and flux coverage as the roll rotates
- Managing heat input distribution around the circumference
- Controlling distortion of the roll barrel during multi-pass cladding
- Achieving uniform layer thickness despite geometric variations
Quality Assessment and Performance Verification
The quality of cladded rolls is verified through comprehensive testing that addresses the specific requirements of rolling mill service:
| Test Method | Acceptance Criteria | Purpose |
|---|---|---|
| Hardness (HV10) | 450–600 HV in overlay | Verify wear resistance |
| Bond strength (transverse tensile) | > 350 MPa | Verify interface integrity |
| Magnetic particle inspection (MT) | No linear indications | Detect surface cracks |
| Ultrasonic testing (UT) | No lack of fusion | Detect subsurface defects |
| Metallographic examination | No microcracks at interface | Verify metallurgical bonding |
| Wear testing (abrasive) | < 5 mm³/1000 m sliding | Verify service performance |
Engineering Practice and Implementation
The successful implementation of sintered alloy flux cladding on large rolling mill rolls requires integration of the cladding operation into the overall roll maintenance cycle. Key practical considerations include:
- Pre-cladding preparation: The roll surface must be thoroughly cleaned of existing scale, oxidation, and previous overlay material. Grinding to a smooth surface ensures proper flux adhesion and uniform heat input distribution.
- Thermal management: The large mass of the φ850 mm roll provides excellent heat dissipation, reducing the risk of overheating and excessive dilution. However, the thermal mass also means that post-weld stress relief requires extended heating times to achieve uniform temperature distribution.
- Dimensional control: After cladding, the roll surface must be ground to precise dimensional tolerances (typically ±0.05 mm for diameter and ±0.01 mm/m for straightness). The cladding layer must be sufficiently thick to allow for multiple regrinding operations during the roll's service life.
- Production scheduling: Cladding operations are typically performed during planned mill shutdowns, requiring rapid execution to minimize production downtime. The process must be optimized for maximum deposition rate while maintaining quality standards.
Study Insights and Reflections
This research demonstrates the successful application of advanced flux technology to a critical industrial component where performance directly impacts production economics. The use of sintered alloy flux provides superior compositional control and microstructural uniformity compared to conventionally produced fluxes, resulting in more consistent overlay properties and longer service life.
The key insight from this work is that the selection of cladding consumable technology is as important as the welding process parameters themselves. The sintered flux approach combines the metallurgical advantages of powder metallurgy with the productivity advantages of submerged arc welding, creating an optimal solution for large-scale industrial cladding applications. For engineers working in rolling mill maintenance, this literature provides a practical framework for implementing cladding technology to extend roll life and reduce maintenance costs.
The research also highlights the importance of process integration in industrial cladding applications. The success of the cladding operation depends not only on the welding process itself but also on surface preparation, thermal management, post-weld treatment, and quality verification — all of which must be carefully coordinated to achieve reliable performance in service.