CLADDING TECHNOLOGY SHANXI CO., LTDCladding Repair of High-Chromium Cast Iron Grinding Rolls
Literature Overview and Technical Significance
This 1996 publication by Yu Fuxiang, Zhou Haifeng, and Lu Jianqing from Shanghai Electric Power Construction Research Institute and Wuxi Grinding Roll Manufacturing Factory addresses the repair of high-chromium cast iron grinding rolls through weld overlay techniques. Published in Welding Technology journal, this work is particularly relevant to the power generation industry, where coal grinding mills rely on high-chromium cast iron rolls that experience severe wear and periodic damage requiring repair.
Material Characteristics and Repair Challenges
High-chromium cast iron (typically 12-28% Cr) is widely used in coal grinding rolls due to its excellent wear resistance derived from the formation of chromium carbides (primarily M7C3 type). However, this material presents significant challenges for repair welding:
| Challenge | Description | Impact on Repair |
|---|---|---|
| High carbon equivalent | CE > 0.6% | Severe cold cracking tendency |
| High hardenability | Forms martensite in weld zone | High residual stress |
| Graphite formation | In heat-affected zone | Reduced hardness and strength |
| Thermal cracking | Due to high melting range | Cracks in weld metal |
| Dilution control | High Cr content dilutes overlay | Altered overlay properties |
The authors identified that the primary repair approach involved multi-pass overlay welding with carefully selected consumables that could tolerate dilution from the high-chromium base material. The key strategy was to use overlay materials with sufficient chromium and carbon content to maintain desired properties even after dilution.
Process Parameters and Overlay Strategy
The study examined submerged arc welding (SAW) as the primary repair process, supplemented by oxy-fuel preheating for stress relief. The overlay strategy involved a systematic multi-layer approach:
Overlay Layer Design
| Layer | Material | Purpose | Hardness |
|---|---|---|---|
| First layer (transition) | Ni-based alloy (Ni-20Cr) | Prevent cracking, accommodate dilution | 35-45 HRC |
| Second layer | Cr-C hardfacing (Cr18C4) | Build up thickness | 55-62 HRC |
| Third layer | Cr-C hardfacing (Cr18C4) | Achieve final surface hardness | 58-65 HRC |
The welding parameters recommended by the authors included:
- Preheat temperature: 300-400°C (essential for high-chromium cast iron)
- Interpass temperature: Maintain above 200°C throughout welding
- Post-weld heat treatment: 550-600°C for 2-4 hours, followed by furnace cooling
- Welding current: 350-500 A (SAW with HJ431 flux)
- Travel speed: 80-150 mm/min
- Layer thickness per pass: 4-6 mm
Defect Prevention and Quality Assurance
The authors conducted extensive quality control testing including:
- Metallographic examination of the overlay-substrate interface
- Hardness profiling across the overlay thickness
- Wear testing against coal samples
- Impact testing of the overlay layer
| Inspection Method | Purpose | Acceptance Criteria |
|---|---|---|
| MT (Magnetic Particle) | Surface crack detection | No linear indications |
| UT (Ultrasonic) | Internal defect detection | No reflections >6dB above reference |
| Hardness test | Overlay hardness verification | ≥55 HRC in final layer |
| Metallography | Interface quality assessment | No cracks or voids at interface |
| Wear test | Service life prediction | ≥500 hours equivalent operation |
Engineering Practice and Lessons Learned
The authors reported successful field applications where repaired rolls achieved service lives comparable to new rolls, demonstrating the economic viability of overlay repair for high-chromium cast iron grinding equipment. A key finding was that the post-weld heat treatment was absolutely critical — rolls that were air-cooled after welding exhibited cracking within the first few weeks of operation, while properly heat-treated rolls maintained integrity throughout their service life.
The study also highlighted the importance of surface preparation. The authors recommended machining the damaged area to expose sound material before applying the overlay, as welding directly onto damaged or worn surfaces led to poor bonding and premature failure.
Study Insights and Industry Implications
This literature provides a comprehensive approach to repairing high-chromium cast iron components, which remain challenging substrates for weld overlay even in contemporary practice. The systematic use of transition layers to manage the metallurgical incompatibility between high-carbon, high-chromium base materials and overlay consumables represents sound engineering practice. The emphasis on post-weld heat treatment as a non-negotiable step in the repair sequence is particularly valuable, as many operators tend to skip or inadequately perform PWHT to reduce downtime. The economic analysis implicit in this work — comparing repair costs against replacement costs — demonstrates that proper overlay repair can extend equipment life by 3-5 times the original service period, making it a highly cost-effective maintenance strategy.