CLADDING TECHNOLOGY SHANXI CO., LTDHard Overlay Wear-Resistant Plates and Their Application in Coal Preparation Plant Chutes
Literature Overview
This paper, published in 2010 by Wang Meng, Liu Shuliang, and Tang Linlin from Shandong Borun Industrial Technology Co., Ltd., addresses the critical issue of abrasive wear in coal preparation plant chutes. The authors investigate the characteristics of hard overlay wear-resistant plates and demonstrate their practical application in a coal processing environment. Coal preparation plants face severe wear challenges due to the high-speed impact of coal and slurry particles against structural surfaces, making traditional carbon steel components unsuitable for long-term service without frequent replacement.
Core Technical Content
The study focuses on hard-facing overlay welding techniques applied to produce wear-resistant plates suitable for coal preparation plant chutes. The key technical aspects include the selection of overlay materials with high hardness, good adhesion to the base steel, and resistance to both abrasive and impact wear. The authors discuss the metallurgical characteristics of the overlay layer, including the formation of hard carbide phases and the microstructural features that contribute to enhanced wear resistance.
Key Performance Parameters
| Parameter | Typical Value | Measurement Method |
|---|---|---|
| Overlay hardness | 55-65 HRC | Rockwell C hardness tester |
| Wear life improvement | 3-8 times vs. base steel | Lab abrasion test |
| Overlay thickness | 3-8 mm | Cross-sectional measurement |
| Bond strength | > 100 MPa | Pull-off bond test |
| Base steel grade | Q235 / Q345 | Material certificate |
Microstructural Analysis
The hard overlay layer typically exhibits a matrix structure of martensite or austenite, depending on the alloy composition, embedded with hard carbide particles such as Cr7C3, Mo2C, or WC. The presence of these carbides is the primary mechanism for wear resistance enhancement. The authors note that proper control of the welding heat input is essential to avoid excessive grain coarsening at the fusion boundary, which could compromise the metallurgical bond between the overlay and the substrate.
Engineering Practice Insights
In coal preparation plant applications, the chute geometry presents unique challenges. The material flow creates a combination of sliding abrasion, impact loading, and occasional corrosion from moisture and dissolved minerals. The overlay plates must therefore be designed with adequate thickness to withstand the expected service life while maintaining the structural integrity of the base plate.
Process Considerations
- Pre-heating of the base plate to 150-250°C is recommended to reduce thermal stresses and minimize the risk of cold cracking, particularly when overlaying low-carbon steel substrates.
- Interpass temperature should be maintained between 200-350°C to control the cooling rate and ensure proper phase transformation in the overlay layer.
- Multi-pass welding is necessary to achieve the required overlay thickness, with each pass providing adequate dilution control.
- Post-weld stress relief at 550-650°C for 1-2 hours per 25 mm of thickness is advisable for thick plates to relieve residual stresses.
Common Defects and Countermeasures
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Cracking at fusion line | Excessive cooling rate, high carbon equivalent | Pre-heat and control interpass temperature |
| Porosity | Flux contamination, improper shielding | Clean materials, ensure proper gas flow |
| Incomplete bonding | Low welding current, excessive travel speed | Optimize welding parameters |
| Overlay spalling | Thermal fatigue, excessive dilution | Control dilution ratio, adequate thickness |
Study Reflections
The practical value of this work lies in its direct applicability to industrial conditions. The authors demonstrate that hard overlay technology can significantly extend the service life of chute components in coal preparation plants, reducing maintenance downtime and replacement costs. However, the paper could benefit from more detailed discussion on the long-term field performance data, including actual service life comparisons between overlay plates and conventional carbon steel chutes under identical operating conditions. The selection of overlay consumables should be carefully matched to the specific abrasive medium characteristics, including particle size distribution, hardness, and impact velocity, to achieve optimal wear resistance.