Zhuojin Pipe Fitting Co., LtdMicrostructure and Sliding Wear Performance of High-Chromium Surfacing Wear-Resistant Plate for Scraper Conveyor Middle Trough
Literature Overview
This paper, published in Lubrication Engineering (2022, Vol. 47, No. 11, pp. 114–123), investigates the feasibility of CM550 high-chromium surfacing composite wear-resistant plate for the middle trough of coal mine scraper conveyors. The study combines metallographic examination, XRD analysis, and TEM characterization with sliding wear experiments to establish the microstructure-wear mechanism relationship. The research was funded by the Central Universities Basic Scientific Research Business Fee Special Funds Project (2019XKQYMS38).
Core Technical Findings
Microstructure Characterization
The high-chromium surfacing layer forms a metallurgical bond with the Q235 carbon steel substrate, confirming adequate wetting and fusion during the surfacing process. The phase composition of the surfacing layer is dominated by α-Fe (ferrite) matrix with CrC carbides as the primary hardening phase.
The CrC carbides exhibit three distinct morphological forms:
| Carbide Morphology | Formation Mechanism | Wear Role |
|---|---|---|
| Primary rod-like | Solidification from melt | Primary load-bearing phase |
| Eutectic plate-like | Eutectic solidification | Reinforcement of matrix |
| Secondary particulate | Post-solidification precipitation | Fine dispersion strengthening |
This multi-scale carbide distribution provides hierarchical reinforcement of the coating, which is critical for resisting the combined abrasive and impact loading conditions in scraper conveyor service.
Sliding Wear Performance
The relative wear resistance of CM550 wear-resistant plate exceeds that of NM450 wear-resistant steel by more than 2 times under equivalent friction coefficient conditions. The counterface material wear mass loss is at a comparable level, indicating that the high hardness of the surfacing layer does not cause excessive counterface degradation.
Wear Mechanism Analysis
The wear damage mechanism under quartz sand abrasive conditions is characterized by two primary modes:
- Micro-cutting wear: Hard quartz sand particles (Mohs hardness 7) micro-cut the softer ferrite regions of the surfacing layer.
- Deformation and spalling wear: The ferrite matrix undergoes plastic deformation and eventual material removal through spalling.
The critical observation is that once the ferrite matrix is worn away, the exposed hard CrC carbides bear the primary wear load, preventing direct contact between the abrasive particles and the soft ferrite. This creates a self-protecting wear mechanism where the carbide network progressively becomes the primary wear surface.
Engineering Practice Integration
Application to Scraper Conveyor Middle Trough
The middle trough of a scraper conveyor in a coal mine experiences severe sliding abrasion from coal, rock fragments, and conveyor chain links. The CM550 surfacing plate offers significant advantages:
- Service life extension: The 2× improvement over NM450 steel translates directly to reduced replacement frequency and lower maintenance costs.
- Weight reduction potential: The composite plate structure (Q235 base + high-chromium surfacing) may allow thinner overall construction compared to homogeneous high-chromium alloy plates.
- Manufacturability: The metallurgical bond between the surfacing layer and Q235 substrate ensures structural integrity under impact loading from coal chunks.
Comparison with Alternative Wear-Resistant Solutions
| Material | Relative Wear Resistance | Cost Factor | Manufacturability | Application Suitability |
|---|---|---|---|---|
| CM550 high-Cr surfacing | 2× NM450 | Moderate | Good | Conveyor trough, chute lining |
| NM450 wear-resistant steel | Baseline | Moderate | Excellent | General structural wear parts |
| Hardfacing overlay (conventional) | Variable | High | Limited | Specific high-wear zones |
| Rubber lining | Low abrasion resistance | Low | Easy | Low-abrasion conditions |
Key Questions and Reflections
The study raises an important question about the thickness of the surfacing layer required for full service life. If the surfacing layer is too thin, it may be completely worn through before the base plate, exposing the Q235 substrate to rapid degradation. If too thick, the thermal stresses during surfacing may cause cracking or delamination.
Another consideration is the impact of the multi-pass surfacing process on the carbide morphology distribution. The first pass may develop coarse eutectic carbides, while subsequent passes may produce finer particulate carbides due to lower cooling rates. Understanding this gradient effect is essential for optimizing multi-pass surfacing parameters.
The study also does not address the effect of moisture and chemical corrosion on the wear performance. In coal mine environments, the presence of water and acidic compounds may accelerate corrosion-abrasion synergistic degradation, which is not captured in dry sliding wear tests.
Study Insights and Implications
This research provides a clear mechanistic understanding of why high-chromium surfacing coatings outperform homogeneous wear-resistant steels in sliding abrasion conditions. The self-protecting wear mechanism, where hard carbides progressively become the primary load-bearing surface, is an elegant material design principle that warrants broader application.
For coal mine equipment engineers, the CM550 surfacing plate represents a practical solution that balances wear resistance, cost, and manufacturability. The recommendation to use this material for conveyor middle troughs and various mine wear-resistant linings is well-supported by the experimental evidence. Future studies should incorporate field trials with quantitative wear rate measurements under actual mining conditions, including wet abrasion, impact loading, and thermal cycling.