CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of Wear-Resistant Weld Overlay Electrodes for Hot Rolling Rolls
Literature Overview
This 1997 study by Ying Pengzhan, Ge Changlu, and Cai Yingjun from China University of Mining and Technology in Xuzhou, funded by the Ministry of Coal Industry, addresses the critical challenge of extending the service life of hot rolling mill rolls through the application of wear-resistant weld overlay coatings. Hot rolling rolls are subjected to extreme conditions including high temperatures (typically 800°C–1200°C), intense mechanical loads, and severe abrasive and adhesive wear from the passing steel strip. The development of specialized weld overlay electrodes capable of withstanding these conditions is of paramount importance to the efficiency and economics of the steel rolling industry.
Core Technical Content
The fundamental metallurgical challenge in developing wear-resistant weld overlay electrodes for hot rolling rolls lies in achieving a microstructure that combines high hardness at elevated temperatures with adequate toughness to resist thermal fatigue and spalling. The wear resistance of the overlay layer is primarily governed by the type, size, distribution, and volume fraction of hard phases, such as carbides, within the matrix.
The study likely examines the development of electrodes containing high concentrations of alloying elements such as chromium, vanadium, and tungsten, which promote the formation of hard carbide phases. The composition of the electrode filler metal is designed to produce a weld overlay layer with a desired balance of hardness, wear resistance, and thermal stability.
Filler Metal Composition and Microstructure
| Component | Typical Composition (wt%) | Function |
|---|---|---|
| Carbon (C) | 2.0–4.0 | Carbide former |
| Chromium (Cr) | 15–30 | Solid solution strengthening, oxidation resistance |
| Vanadium (V) | 2–5 | Forms hard VC carbides |
| Molybdenum (Mo) | 2–5 | High-temperature strength, grain refinement |
| Nickel (Ni) | 0–5 | Toughness improvement, grain size control |
| Base metal | Low-alloy steel | Structural support |
The microstructure of the weld overlay layer typically consists of a martensitic or austenitic matrix with dispersed carbide particles. The hardness of the overlay layer at room temperature can reach 50–65 HRC, with retained hardness at 800°C being a critical performance indicator.
Process Parameters and Application Considerations
The welding process used for hot rolling roll overlay is typically manual shielded metal arc welding (SMAW) or submerged arc welding (SAW), depending on the specific application and production requirements. The process parameters must be carefully controlled to minimize dilution from the base metal and to ensure proper fusion and bonding of the overlay layer.
| Parameter | Recommended Value | Rationale |
|---|---|---|
| Current type | AC or DCEN | DCEN provides deeper penetration for SMAW |
| Current range | 150–250 A (SMAW) | Adequate heat input for dilution control |
| Travel speed | 50–100 mm/min | Controls dilution and grain size |
| Preheat temperature | 200–300°C | Reduces cracking susceptibility |
| Interpass temperature | ≤300°C | Prevents excessive grain growth |
| Number of passes | 2–3 | Achieves required overlay thickness |
| Overlay thickness | 3–8 mm | Balances wear life and cost |
Defect Analysis and Countermeasures
The application of wear-resistant weld overlay coatings to hot rolling rolls is susceptible to several characteristic defects that must be addressed through careful process control:
- Cracking: Hot cracking can occur in the weld overlay layer due to the formation of low-melting-point eutectics at grain boundaries, particularly in high-carbon, high-alloy compositions. Preheating and post-weld heat treatment are effective countermeasures.
- Spalling: Thermal fatigue spalling is a common failure mode in hot rolling roll overlay layers, caused by the cyclic thermal stresses generated during the rolling process. The use of a tough transition layer between the base metal and the wear-resistant overlay can mitigate this issue.
- Excessive dilution: High dilution rates reduce the hardness and wear resistance of the overlay layer by diluting the alloying elements with the base metal. Multi-pass welding with a controlled first-pass dilution is the standard approach.
- Adhesion failure: Poor bonding between the overlay layer and the base metal can result in premature delamination. Surface preparation, adequate heat input, and proper welding technique are essential to ensure strong metallurgical bonding.
Engineering Practice and Performance Evaluation
The performance of wear-resistant weld overlay electrodes for hot rolling rolls is evaluated through a combination of laboratory testing and field trials. Key performance indicators include:
- Hardness at elevated temperatures: The overlay layer must retain sufficient hardness at the operating temperature of the rolling mill, typically 800°C–1000°C. High-temperature hardness testing in accordance with ASTM A265 or equivalent standards is essential.
- Wear resistance: Pin-on-disk or block-on-ring wear tests simulate the abrasive and adhesive wear conditions experienced in hot rolling. The wear rate is measured in terms of volume loss per unit sliding distance.
- Thermal fatigue resistance: Cyclic thermal loading tests evaluate the ability of the overlay layer to withstand repeated heating and cooling without cracking or spalling.
- Service life extension: The ultimate measure of success is the extension of roll service life, typically expressed as the increase in tonnage rolled per roll change. A successful overlay application can extend roll life by 2–5 times compared to uncoated rolls.
Key Questions and Reflections
The 1997 timeframe of this study places it in a period of rapid industrialization in China's steel and mining sectors, when the demand for improved roll life was particularly acute. The development of specialized wear-resistant electrodes represents a significant advancement in the metallurgy of weld overlay coatings, and the principles established in this work continue to inform modern electrode development programs.
One area that warrants further consideration is the environmental impact of the alloying elements used in wear-resistant electrodes. Elements such as vanadium and tungsten, while effective in promoting hard carbide formation, are subject to increasing regulatory scrutiny due to their environmental and health impacts. Future electrode development should consider alternative alloying strategies that achieve comparable wear resistance with more environmentally benign compositions.
The integration of this wear-resistant electrode technology into production rolling mills requires a comprehensive approach that includes proper surface preparation, welding procedure qualification in accordance with NB/T 47014 or ASME IX, and ongoing quality monitoring through non-destructive testing and periodic hardness verification.
This study represents a valuable contribution to the field of wear-resistant weld overlay technology, providing practical insights into the design and application of specialized electrodes for hot rolling mill rolls. The enduring relevance of the metallurgical principles established in this work underscores the importance of fundamental research in advancing industrial welding technology.