Zhuojin Pipe Fitting Co., LtdDevelopment of Wear-Resistant Composite Lining Plates for Hot Continuous Rolling Mill Frames
Literature Overview
This 2004 paper, published in Special Steel journal, presents the development of wear-resistant composite lining plates for hot continuous rolling mill frames at Baoshan Iron and Steel Co., Ltd. The research was conducted by engineers from Tsinghua University's Department of Mechanical Engineering and Baoshan Steel. The study addresses a significant maintenance challenge in steel pipe hot rolling operations: the rapid wear of mill frame components due to contact with hot steel pipes during the rolling process.
Core Technical Content
The composite lining plates were developed using explosion welding technology to bond a wear-resistant steel overlay to a structural steel substrate. The resulting composite material combines the wear resistance of the overlay with the structural integrity of the substrate, providing a cost-effective solution to mill frame wear problems.
Material Composition
| Layer | Composition (wt%) | Function |
|---|---|---|
| Base plate (16Mn, 10 mm thick) | C: 0.15–0.20, Mn: 0.8–1.5 | Structural support |
| Composite plate (wear-resistant) | C: 0.6–1.0, Si: 0.5–1.0, Mn: 0.8–1.2, Cr: 0.5–1.5, Ni: 0.4–0.6, Mo: 0.4–0.8, B: 0.0005–0.0015, Y: 0.005–0.010, K: 0.008–0.015, Na: 0.008–0.015 | Wear resistance |
The wear-resistant overlay composition is notable for its multi-alloy design, incorporating carbon, silicon, manganese, chromium, nickel, molybdenum, boron, yttrium, potassium, and sodium. Each alloying element serves a specific purpose:
- Carbon (0.6–1.0%): Primary hardening element, forms hard carbides
- Chromium (0.5–1.5%): Forms chromium carbides, improves hardness and wear resistance
- Molybdenum (0.4–0.8%): Enhances hot hardness and oxidation resistance
- Nickel (0.4–0.6%): Improves toughness and thermal stability
- Boron (0.0005–0.0015%): Refines grain structure, improves hardenability
- Yttrium (0.005–0.010%): Rare earth element that refines inclusions and improves hot strength
- Potassium and Sodium (0.008–0.015%): Trace elements that may influence grain boundary properties
Performance Results
| Performance Parameter | Value | Comparison |
|---|---|---|
| Overlay surface hardness | HRC 60 | Significantly exceeds substrate hardness |
| Bond layer shear strength | 340 MPa | Exceeds typical requirements for structural applications |
| Wear after 8 months of service | < 0.2 mm | Lower than conventional surface treatment and rolled composite alternatives |
The HRC 60 hardness of the overlay surface is achieved through a combination of high carbon content, carbide-forming alloying elements, and the fine microstructure developed during the explosion welding process. The shear strength of 340 MPa at the bond interface is well above the minimum requirements for structural applications, ensuring reliable performance under the severe loading conditions of hot rolling mill operations.
Explosion Welding Process Analysis
Process Mechanism
Explosion welding is a solid-state welding process that uses the energy of a controlled explosion to bring two metal surfaces into high-velocity collision, resulting in a metallurgical bond without melting. The process involves:
- Explosive charge detonation: A shaped explosive charge is detonated to accelerate the flyer plate toward the base plate.
- High-velocity collision: The flyer plate impacts the base plate at velocities typically between 200 and 1000 m/s.
- Jet formation: The collision creates a turbulent jet of material along the collision surface, which removes oxide films and contaminants.
- Metallurgical bonding: The clean metal surfaces come into intimate contact under high pressure, forming a metallurgical bond through plastic deformation and mechanical interlocking.
Process Parameters
| Parameter | Typical Value | Effect on Bond Quality |
|---|---|---|
| Collision velocity | 200–1000 m/s | Higher velocity improves bond quality |
| Impact angle | 5–30 degrees | Optimal angle for jet formation |
| Explosive charge thickness | Variable | Determines collision energy |
| Gap between plates | 5–50 mm | Controls collision timing |
| Plate preheating | None or moderate | Can influence bond microstructure |
The explosion welding process produces a distinctive wavy or rippled interface between the two metals, which provides mechanical interlocking in addition to the metallurgical bond. This wavy interface is a key feature that contributes to the high shear strength of the composite.
Engineering Application Analysis
Wear Mechanisms in Hot Rolling Mill Frames
The wear of mill frame components in hot continuous rolling operations is caused by multiple mechanisms acting simultaneously:
- Abrasive wear: Caused by contact with oxide scale on the hot pipe surface and any embedded debris.
- Adhesive wear: Resulting from metal-to-metal contact at asperity level under high pressure and temperature.
- Oxidative wear: Accelerated by the high operating temperatures and the presence of oxygen in the mill atmosphere.
- Erosive wear: Caused by the impact of oxide scale particles and scale fragments ejected during rolling.
- Fatigue wear: Resulting from cyclic loading during the rolling process.
The composite lining plate addresses all these wear mechanisms through the high hardness and multi-phase microstructure of the wear-resistant overlay. The hard carbides in the overlay resist abrasive and adhesive wear, while the alloying elements provide oxidation resistance at elevated temperatures.
Comparison with Alternative Wear Protection Methods
| Method | Hardness | Service Life | Cost | Maintenance |
|---|---|---|---|---|
| Explosion-welded composite | HRC 60 | > 8 months, < 0.2 mm wear | Moderate | Low |
| Rolled composite plate | HRC 50–55 |