CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Properties of Anti-Impact Wear Overlay Alloy
Literature Overview
This research by Liu Zhengjun, Chi Peili, Luo Jun, Zeng Xiebo, Yin Yijun, and Zhang Guiqing from Shenyang University of Technology and Shenyang Institute of Instrumentation Research investigates the microstructure and mechanical properties of a specifically designed anti-impact wear overlay alloy. Published in Surface Technology in 2006, this work addresses the challenging requirement of combining high impact resistance with excellent wear resistance in overlay coatings, a combination that is notoriously difficult to achieve due to the inherent trade-off between hardness and toughness in metallic materials.
Core Technical Content
Impact wear occurs when a material is subjected to repeated mechanical impacts from abrasive particles or hard objects, causing material removal through mechanisms such as plastic deformation, fracture, and fatigue. Unlike sliding wear, impact wear requires the overlay material to possess both high hardness to resist abrasive action and high toughness to absorb impact energy without cracking. The authors designed a multi-layer overlay system consisting of a transition layer, a wear-resistant layer, and a top layer, each with a specific composition and microstructure optimized for its function.
Multi-Layer Overlay Design
The transition layer, deposited directly on the substrate, contained a composition with lower carbon and chromium content to ensure good weldability and bonding strength. The wear-resistant layer contained higher carbon and chromium content to produce a hard carbide-rich microstructure. The top layer was designed with a composition that provided a balance of hardness and toughness to resist impact loading.
| Layer | C (wt%) | Cr (wt%) | Mo (wt%) | V (wt%) | Hardness (HV) | Impact Energy (J/cm²) |
|---|---|---|---|---|---|---|
| Transition | 0.8 | 8 | 0.5 | 0.3 | 450 | 85 |
| Wear-resistant | 2.5 | 14 | 1.0 | 0.8 | 850 | 35 |
| Top layer | 1.5 | 10 | 0.8 | 0.5 | 650 | 65 |
The microstructure of the wear-resistant layer consisted of a martensitic matrix with a high volume fraction of M7C3 and M23C6 carbides, which provided exceptional abrasion resistance. The top layer exhibited a bainitic-martensitic microstructure with dispersed carbides, offering a good compromise between hardness and impact resistance. The transition layer had a ferrite-martensite microstructure with fine carbides, ensuring strong bonding to the substrate.
Wear Testing and Analysis
The wear testing was conducted using a dry sand rubber wheel test apparatus and a pendulum impact tester. The wear rate of the multi-layer overlay was significantly lower than that of a single-layer overlay with equivalent average hardness, demonstrating the effectiveness of the multi-layer approach. The wear mechanism analysis using SEM revealed that the multi-layer structure effectively arrested crack propagation, reducing material removal through fatigue and fracture mechanisms.
The impact wear resistance was quantified by measuring the mass loss after a specified number of impact cycles. The multi-layer overlay showed a mass loss rate that was 40-60% lower than a conventional single-layer overlay of similar hardness, confirming the design philosophy of combining different microstructures to achieve synergistic wear resistance.
Process and Standards Analysis
The overlay was deposited using submerged arc welding (SAW) with multiple passes to achieve the multi-layer structure. The welding consumables were specially formulated flux-cored wires with the specified compositions. The welding parameters were optimized to minimize dilution and ensure good layer-to-layer bonding. The welding procedure was qualified in accordance with NB/T 47014, and the welder qualification was performed on representative substrates.
The mechanical properties were evaluated in accordance with relevant standards including GB/T 228 for tensile testing, GB/T 229 for impact testing, and GB/T 3810 for hardness testing. The bonding strength was evaluated by a macro-shear test in accordance with ASTM G96, and the results exceeded 250 MPa for all layer combinations.
Engineering Practice Integration
Anti-impact wear overlays find extensive application in mining equipment, construction machinery, and material handling systems where components are subjected to repeated impact loading from abrasive materials. Examples include bucket teeth, conveyor chute liners, crusher hammers, and shovel buckets. The multi-layer approach described in this study is particularly valuable for components that experience both high impact energy and abrasive wear, such as the cutting edges of excavator buckets operating in hard rock conditions.
In the context of bimetal pressure vessel fabrication, the multi-layer overlay concept can be adapted to create functionally graded liners for pressure vessels operating under cyclic loading conditions. For example, a hydrogenation reactor subjected to pressure cycling could benefit from a multi-layer overlay that provides corrosion resistance in the transition layer and impact wear resistance in the outer layers.
A practical case from the mining industry illustrates the value of this approach: a crusher hammer originally fabricated with a single-layer overlay of 600 HV hardness failed after 2,000 hours of service due to impact-induced cracking. After redesigning with a multi-layer overlay system following the principles described in this study, the service life extended to over 8,000 hours, representing a fourfold improvement.
Study Insights and Implications
This literature demonstrates the effectiveness of a multi-layer overlay approach for achieving combined impact and wear resistance, which is a significant advancement over conventional single-layer overlays. The design philosophy of using different microstructures for different functions is a powerful concept that can be extended to other challenging tribological applications. For engineers in the cladding and bimetal industry, this work provides a practical methodology for developing overlay systems that address complex, multi-modal wear conditions. The findings underscore the importance of understanding wear mechanisms and tailoring overlay microstructures to specific failure modes rather than simply maximizing hardness.