Microstructural Characteristics and Sliding Wear Properties of High-Chromium Overlay Wear-Resistant Plates for Scraper Conveyor Middle Troughs

Literature Overview

This 2022 publication by Duan Qiyin, Yue Honglin, Song Hanke, and Wang Qingliang from China University of Mining and Technology and Tianjin Zhongkuang New Materials Technology Co., Ltd. investigates the microstructural characteristics and sliding wear properties of high-chromium alloy overlay wear-resistant plates designed for scraper conveyor middle troughs in underground coal mining applications. The research was supported by the Central Universities Basic Research Business Fee Special Fund Project (2019XKQYMS38).

Scraper conveyors are critical material handling equipment in underground coal mines, transporting mined coal from the longwall face to the main haulage system. The middle trough sections are subjected to severe abrasive wear from coal, rock fragments, and water-saturated slurry, often leading to premature failure and frequent replacement. The development of high-chromium overlay wear-resistant plates represents a significant advancement in extending the service life of these critical mining components.

Core Technical Points

Material System and Microstructural Analysis

The high-chromium overlay material system typically contains 12-30 wt% Cr, 2-5 wt% C, with additional alloying elements such as Mo, V, Ni, and B to optimize wear resistance and toughness. The microstructure of high-chromium cast irons and weld overlay deposits is characterized by:

The key to achieving excellent wear resistance in high-chromium overlay materials is the formation of a fine, uniformly distributed network of hard chromium carbides within a tough martensitic matrix. The carbide morphology (stringer-like, rod-like, or granular) and size distribution significantly influence wear performance.

Sliding Wear Mechanisms

Sliding wear in scraper conveyor applications involves complex interactions between the overlay surface and the transported material. The wear mechanisms include:

1. Abrasive wear: Hard particles in coal and rock fragments plow and cut the overlay surface, removing material through microplowing and microcutting mechanisms
2. Adhesive wear: Localized welding and tearing at asperity contacts leads to material transfer between surfaces
3. Fatigue wear: Repeated cyclic loading from passing scraper chains causes subsurface crack initiation and spalling
4. Tribochemical wear: Chemical reactions between the overlay surface and the transported material (particularly in wet conditions) contribute to material degradation

The dominant wear mechanism depends on operating conditions including sliding speed, normal load, particle size distribution, and environmental conditions (temperature, humidity, chemical composition of transported material).

Performance Characteristics

The dramatic improvement in wear resistance achieved by high-chromium overlay plates translates directly into significant economic benefits for mining operations. The extended service life reduces replacement frequency, minimizes unplanned downtime, and lowers overall maintenance costs.

Engineering Practice Integration

Application in Underground Coal Mining

The practical application of high-chromium overlay wear-resistant plates in scraper conveyor middle troughs involves several important considerations:

Manufacturing process:

• Substrate preparation: Carbon steel trough sections (typically Q345 or Q460) are prepared by machining or grinding the wear surface to Ra ≤ 6.3 μm
• Cladding process: Submerged arc welding (SAW) or flux-cored arc welding (FCAW) with specialized high-chromium filler metal
• Multi-pass deposition: 3-5 passes of 2-3 mm each to achieve total overlay thickness of 8-15 mm
• Post-weld heat treatment: Tempering at 550-600 °C for 2-4 hours to relieve residual stresses and optimize microstructure
• Final machining: Surface grinding to achieve required profile and surface finish

Quality control requirements:

• Hardness testing: Minimum 500 HB in the overlay layer, with uniform distribution across the surface
• Bond strength testing: Minimum 250 MPa shear strength at the overlay-substrate interface
• Non-destructive testing: UT or MT inspection to detect subsurface defects and cracks
• Wear testing: Laboratory sliding wear tests against representative coal and rock samples
• Impact testing: Charpy V-notch impact testing to verify adequate toughness (minimum 27 J at -20 °C for cold environments)

Process Optimization and Defect Prevention

Key Questions and Reflections

The research addresses a critical need in the mining industry for improved wear-resistant materials for conveyor components. However, several challenges remain for practical implementation. First, the high-carbon high-chromium overlay materials are difficult to machine after deposition, requiring specialized grinding tools and techniques. Second, the brittleness of high-chromium materials may be problematic in applications involving impact loading, such as when large rock fragments strike the trough surface.

The balance between wear resistance and toughness is the central metallurgical challenge in this application. While increasing carbon and chromium content improves wear resistance through increased carbide volume fraction and hardness, it simultaneously reduces toughness and increases susceptibility to cracking. The optimal composition must be tailored to the specific service conditions, considering the relative importance of abrasive wear versus impact damage in the particular mining environment.

The economic benefits of high-chromium overlay wear-resistant plates are substantial. For a typical longwall mining operation with multiple scraper conveyors, the extended service life can result in annual savings of USD 50,000-200,000 per conveyor system, depending on production volume and replacement costs. This economic advantage, combined with reduced downtime and improved safety, makes the technology highly attractive for modern mining operations.