CLADDING TECHNOLOGY SHANXI CO., LTDResearch on Wear-Resistant Welding Electrodes for Hot Rolling Mill Rolls
Literature Overview
This study focuses on the development and characterization of wear-resistant welding electrodes specifically designed for hot rolling mill roll overlay applications. Unlike general-purpose welding consumables, these electrodes must be engineered to produce overlay layers that withstand the combined effects of high temperature, mechanical loading, and chemical attack encountered in hot rolling operations. The research provides systematic investigation of electrode composition design, welding process optimization, and performance evaluation under simulated and actual service conditions.
Core Technical Findings
Electrode Composition Design
The electrode composition is carefully designed to produce the desired overlay microstructure:
| Component | Range (wt%) | Function |
|---|---|---|
| Carbon | 2.5–4.5 | Carbide formation, hardness |
| Chromium | 20–32 | Oxidation resistance, M₇C₃ carbides |
| Molybdenum | 2–6 | Solid solution strengthening, creep resistance |
| Vanadium | 1–4 | Refractory carbide formation (VC) |
| Nickel | 3–8 | Austenite stabilization, toughness |
| Manganese | 1.0–3.0 | Deoxidation, grain refinement |
| Silicon | 0.5–2.0 | Deoxidation, hardening |
| Iron | Balance | Base matrix |
The study demonstrates that the optimal composition for hot rolling roll applications is a high-carbon, high-chromium martensitic system with minor additions of Mo and V. This composition produces a microstructure consisting of tempered martensite with dispersed M₇C₃ and VC carbides, providing an optimal balance of hardness, toughness, and thermal fatigue resistance.
Welding Process Parameters
The study evaluates multiple welding processes for electrode application:
| Process | Deposition Rate | Dilution | Hardness (HRC) | Thermal Fatigue Life |
|---|---|---|---|---|
| SMAW (Shielded Metal Arc) | 0.5–1.5 kg/h | 15–25% | 58–62 | Moderate |
| SAW (Submerged Arc) | 3–8 kg/h | 12–20% | 56–60 | Good |
| GMAW (Gas Metal Arc) | 2–5 kg/h | 10–18% | 58–63 | Good |
| FCAW (Flux-Cored Arc) | 2–6 kg/h | 12–22% | 57–61 | Moderate |
SAW provides the highest deposition rate and is preferred for industrial-scale roll remanufacturing, while GMAW offers better composition control and is suitable for precision overlay applications.
Performance Evaluation
The study employs multiple testing methods to evaluate electrode performance:
- Hardness testing: Vickers and Rockwell hardness measurements across the overlay depth profile
- Wear testing: Pin-on-disk and block-on-ring tests at room and elevated temperatures
- Thermal fatigue testing: Cyclic thermal loading to simulate roll surface conditions
- Impact testing: Charpy V-notch testing to assess toughness
- Corrosion testing: Acid immersion and salt spray testing for oxidation resistance
The results demonstrate that the developed electrodes produce overlay layers with hardness of 58–63 HRC, wear resistance 3–5 times that of the base steel, and thermal fatigue life exceeding 10,000 cycles at ΔT = 800 °C.
Process and Standards Analysis
Electrode Manufacturing Quality Control
The electrode manufacturing process requires strict quality control:
| Parameter | Specification | Test Method |
|---|---|---|
| Chemical composition | Within ±0.3% of nominal | Spectroscopic analysis |
| Moisture content | < 0.5% | Drying and weighing |
| Coating uniformity | ±5% thickness variation | Visual and measurement |
| Storage conditions | 200–250 °C drying oven | Thermocouple monitoring |
| Electrode straightness | < 1 mm/m deviation | Gauge measurement |
The study emphasizes that electrode moisture control is critical for preventing hydrogen-induced cracking. Electrodes must be stored in drying ovens at 200–250 °C and removed only immediately before use. Any electrodes exposed to atmospheric conditions for more than 2 hours require re-drying.
Welding Procedure Qualification
The study references relevant standards for welding procedure qualification:
- NB/T 47014: Chinese standard for welding procedure qualification
- ASME IX: American standard for welding procedure qualification
- ISO 15614: International standard for welding procedure qualification
The qualification procedure must include:
- Welding procedure specification (WPS) development
- Qualification weld preparation and execution
- Mechanical property testing (tensile, impact, hardness)
- Non-destructive testing (RT, UT, MT)
- Metallographic examination of weld cross-section
Integration with Engineering Practice
In practical application, the developed electrodes have been successfully deployed in:
- Heavy plate mills: Overlay of work rolls for plate thickness reduction
- Strip mills: Overlay of intermediate and finishing mill rolls
- Bar mills: Overlay of rolling mill rolls for bar production
A representative case study involves the remanufacturing of finishing mill work rolls in a strip mill. The conventional overlay process produced rolls with a service life of 400–500 tonnes of steel. The new electrode-based overlay process extended roll life to 800–1000 tonnes, representing a 100% improvement in productivity. The overlay thickness of 4–6 mm was maintained throughout the service life with minimal wear.
Key Questions and Reflections
The study addresses the challenge of maintaining consistent electrode performance across different production batches. Variations in raw material composition, electrode manufacturing process, and storage conditions can lead to significant property variations. The recommended approach is to implement statistical process control (SPC) at every stage of electrode manufacturing, with periodic performance verification through test welds and property testing.
Another important consideration is the welder skill level. The study notes that SMAW and GMAW processes are more sensitive to welder technique than SAW or FCAW processes. Proper training and certification of welders is essential for achieving consistent overlay quality. The study recommends that all welders performing roll overlay work hold valid certifications according to NB/T 47014 or equivalent standards.
Study Insights and Implications
The research demonstrates that specialized electrode development, combined with rigorous process control, can significantly extend the service life of hot rolling mill rolls. The key insight is that electrode composition must be tailored to the specific service conditions—temperature, load, and steel grade—rather than using a generic wear-resistant composition. This application-specific approach, supported by systematic qualification and quality control, represents the path to optimal roll performance and cost reduction in steel production operations. The study provides a comprehensive framework that can be adapted for other heavy-duty wear applications in the metalworking industry.