CLADDING TECHNOLOGY SHANXI CO., LTDMetallurgical Roll Cladding and Bimetal Manufacturing Technology Review and Outlook
Literature Overview
This study note addresses the 2008 publication by Liu Jingfeng, Zhang Di, Bai Bo, and Wang Qingbao from the Welding Research Institute of the China Metallurgical Group Corporation Building Research Institute. The paper was published in the journal "China Surface Engineering" and provides a comprehensive review of metallurgical roll cladding and bimetal manufacturing technologies. Given that this work was published over fifteen years ago, its value lies in establishing foundational knowledge about roll cladding processes that remain relevant to current engineering practice, while also offering a historical perspective on where the technology stood at that time.
Core Technical Content
The paper systematically examines the various cladding methods employed for metallurgical rolls, including explosion cladding, explosion-bonding, electroslag welding overlay, submerged arc welding overlay, and hot-rolling bonding. Metallurgical rolls in steel mills experience extreme conditions—temperatures exceeding 1000°C during hot rolling, severe mechanical impact, and abrasive wear from scale and oxide layers. The overlay material must therefore combine high hardness, excellent wear resistance, and adequate toughness to prevent catastrophic failure.
Cladding Process Comparison
| Process Method | Typical Overlay Thickness | Bond Quality | Cost Level | Application Range |
|---|---|---|---|---|
| Explosion Cladding | 2–10 mm | Excellent (metallic bond) | High | Large diameter rolls |
| Electroslag Welding Overlay | 5–25 mm | Good (controlled dilution) | Medium | Medium to large rolls |
| Submerged Arc Welding Overlay | 3–15 mm | Good | Medium | Medium rolls |
| Hot-Rolling Bonding | 1–5 mm | Moderate | Low | Small diameter rolls |
| Friction Stir Cladding | 2–8 mm | Excellent | Medium-High | Specialized applications |
Key Materials for Roll Overlay
The base substrate is typically medium carbon steel (40Cr, 42CrMo) or low-alloy steel, while the overlay layer consists of high-speed steel grades (W6Mo5Cr4V2, M2), martensitic stainless steels (4Cr13, 9CrSi), or specialized wear-resistant alloys containing chromium carbide formers. The dilution ratio between base metal and overlay is a critical parameter—typically controlled between 5% and 15% to maintain the mechanical properties of the overlay layer while ensuring adequate metallurgical bonding.
Process Parameters and Engineering Considerations
The electroslag welding overlay process, which the paper identifies as the most widely used method for medium-to-large rolls, requires careful control of slag composition, welding current (typically 3000–6000 A), welding speed (30–80 mm/min), and electrode diameter (φ12–φ25 mm). The slag must maintain sufficient fluidity to wet the base metal surface uniformly while preventing excessive dilution. Preheating to 250–350°C is mandatory for medium-carbon steel substrates to prevent cold cracking, and post-weld heat treatment (tempering at 550–650°C) is required to relieve residual stresses and stabilize the microstructure.
Defect Analysis and Quality Control
Common defects in roll cladding include:
- Insufficient bond (lack of fusion): Caused by inadequate preheating, excessive welding speed, or improper slag composition. Detection requires ultrasonic testing (UT) at the bond interface with phased array techniques.
- Cracking: Both transverse and longitudinal cracks can occur in the overlay layer, particularly at the bond interface. These are typically hydrogen-induced and are mitigated by strict moisture control of consumables and appropriate preheating.
- Excessive dilution: Results in softening of the overlay layer and loss of wear resistance. Controlled by limiting slag coverage area and maintaining proper electrode oscillation parameters.
- Porosity: Gas inclusion from contaminated consumables or base metal surface. Detected by radiographic testing (RT) or ultrasonic testing.
Engineering Practice Integration
From practical experience, the success of roll cladding depends heavily on the preparation of the base roll surface. Machining to a surface roughness of Ra 6.3–12.5 μm, followed by thorough cleaning to remove oil, rust, and scale, is essential. The dimensional accuracy of the overlay must be maintained within ±0.5 mm for the final grinding to achieve the required surface finish (Ra 0.8–1.6 μm for finish rolls). After overlay welding, the roll undergoes stress-relieving annealing, followed by hardening and tempering to achieve the target hardness (typically HRC 45–55 for work rolls).
Study Insights and Outlook
The 2008 paper correctly identifies the trend toward higher-performance overlay materials and improved process control. Looking back from current practice, several developments have occurred since publication: laser cladding has become increasingly viable for repair and localized cladding of rolls, plasma transferred arc (PTA) cladding offers superior dilution control for high-value alloy overlays, and advanced flux-cored wire overlay processes have reduced costs while maintaining acceptable quality. The fundamental principles described in this paper—particularly regarding dilution control, bond strength verification, and post-weld heat treatment—remain the cornerstone of successful roll cladding practice. Engineers working in this field today should appreciate that process fundamentals have not changed; what has evolved is the precision of parameter control and the availability of advanced NDE methods for quality assurance.