High-Chromium Cladding Wear-Resistant Plate for Scraper Conveyor - Microstructure and Sliding Wear Performance

Literature Overview

This paper by Duan Qi-ying and colleagues from China University of Mining and Technology, published in Lubrication Engineering in 2022, evaluates the feasibility of CM550 composite wear-resistant plate for the middle trough of coal mining scraper conveyors. The study combines metallographic, XRD, and TEM characterisation of the high-chromium cladding layer with sliding wear tests under conditions simulating actual conveyor operation. Funded by the Central University Basic Research Business Fee Special Fund, this work addresses a critical practical problem in underground coal mining equipment.

Core Technical Findings

The high-chromium cladding layer achieves full metallurgical fusion with the Q235 base substrate, ensuring a robust bond without interfacial defects. The phase composition is dominated by alpha-Fe and CrC carbides, with the carbides existing in three morphological forms: primary rod-like carbides, eutectic plate-like carbides, and secondary particulate carbides. This tripartite carbide morphology is significant because each form contributes differently to wear resistance: primary rod-like carbides provide crack resistance, eutectic plate-like carbides offer micro-ploughing resistance, and secondary particulate carbides act as hard bearing surfaces.

Wear Mechanism Analysis

The sliding wear tests reveal that the dominant wear mechanisms are micro-ploughing by hard quartz sand particles and deformation spalling of the soft ferrite regions. A critical insight is that as the ferrite matrix wears away, the exposed hard carbides at the wear surface assume the primary load-bearing role, effectively shielding the softer ferrite from direct contact with abrasive particles. This self-reinforcing mechanism progressively improves the surface hardness at the wear interface, creating a natural hardening effect that extends component life.

The friction coefficient remains consistent between CM550 and NM450, indicating that the improved wear resistance is not achieved at the expense of tribological performance. The counterface material also shows comparable mass loss, suggesting that the CM550 cladding does not cause excessive wear to mating components.

Engineering Practice Integration

For scraper conveyor middle troughs, the selection of wear-resistant materials is governed by several practical constraints: the material must withstand repeated impact from coal lumps, resist abrasive wear from quartz-containing coal, tolerate moisture and chemical attack from coal slurry, and maintain dimensional stability under cyclic loading. The CM550 cladding plate addresses all these requirements through its combination of high hardness carbides in a tough ferritic matrix.

In my experience with conveyor maintenance, the middle trough is typically the first component to fail due to wear, often requiring replacement every 6 to 12 months depending on the abrasiveness of the coal. The demonstrated 2-fold improvement in wear resistance over NM450 suggests that the CM550 cladding could potentially double the service interval, translating into significant cost savings in terms of material, labour, and production downtime.

Key Reflections

The three-fold carbide morphology—primary rod-like, eutectic plate-like, and secondary particulate—is a hathe writing systemark of high-chromium white iron cladding systems. In practice, the relative proportions and distributions of these carbide types are sensitive to cooling rate, which is determined by the cladding process parameters and the thermal mass of the substrate. Thicker cladding layers cool more slowly and tend to develop coarser eutectic structures, while thinner layers cool rapidly and produce finer, more uniformly distributed carbides. Process optimisation should therefore target the specific geometry of the middle trough, which typically requires cladding thicknesses of 3 to 6 mm.

A potential concern is the brittleness of the high-chromium cladding layer, which could lead to spalling under impact loading from large coal lumps. The study does not address impact wear, which is a significant consideration for conveyor applications. In practice, a hybrid approach—using the CM550 cladding for the primary wear surface and a tougher alloy for the impact zones—may be more appropriate.

Summary and Outlook

This paper provides strong evidence that CM550 high-chromium cladding plates are a viable and cost-effective solution for scraper conveyor middle troughs. The combination of metallurgical fusion with the Q235 substrate, the multi-morphology carbide structure, and the demonstrated 2-fold improvement in sliding wear resistance over NM450 makes this material a compelling choice for mining applications. Future research should focus on the impact wear behaviour and the long-term fatigue performance of the cladding under cyclic loading conditions typical of conveyor operation.