CLADDING TECHNOLOGY SHANXI CO., LTDEffect of Tungsten Carbide Content on Microstructure and Wear Resistance of Open-Arc Welded Austenitic Overlay
Literature Overview
The paper published in Powder Metallurgy Materials and Science and Engineering (2016) by Wu Huijian, Gong Jianxun, Liu Jiangqing, and Li Yi from the School of Mechanical Engineering, Xiangtan University, investigates how varying tungsten carbide (WC) content influences the microstructure and wear resistance of austenitic alloy overlay layers deposited via open-arc welding (GMAW). Funded by the Hunan Provincial Natural Science Foundation (2015JJ5031) and the National Natural Science Foundation of China (51271158), this work addresses a critical engineering challenge in the design of hardfacing consumables for abrasive wear environments.
Core Technical Points
Influence of WC Content on Microstructural Evolution
The study examines the progressive transformation of the overlay microstructure as WC content increases. At lower WC concentrations, the matrix retains a predominantly austenitic character with dispersed cementite and carbide networks. As WC content rises, the volume fraction of hard phases increases substantially, and the distribution pattern transitions from randomly dispersed particles to interconnected networks. The key microstructural phases identified include:
| Phase Type | Composition | Morphology | Role in Wear Resistance |
|---|---|---|---|
| Austenitic matrix | Fe-Ni-Cr-C | Dendritic/cellular | Provides ductility and toughness |
| Cementite (Fe₃C) | Iron carbide | Network/dendritic | Moderate hardness contribution |
| Tungsten carbide (WC) | Tungsten carbide | Spherical/irregular particles | Primary wear resistance contributor |
| M₆C-type carbides | Mixed transition metal carbides | Dendritic skeleton | Secondary hard phase |
| M₇C₃-type carbides | Chromium/molybdenum carbides | Network | Secondary hard phase |
Wear Resistance Mechanisms
The wear resistance enhancement follows a non-linear trend with increasing WC content. Initially, wear resistance improves significantly due to the introduction of hard carbide particles that resist abrasive penetration. However, beyond an optimal threshold, excessive WC content leads to matrix embrittlement, increased porosity, and potential cracking at the overlay-substrate interface. The study identifies three primary wear mechanisms:
- Abrasive wear: Dominated by hard carbide particles that plough and resist material removal from the counterface
- Adhesive wear: Governed by the austenitic matrix's ability to resist cold welding and material transfer
- Fatigue wear: Related to subsurface crack initiation and propagation under cyclic loading
Process Parameters and Defect Control
Open-arc welding (GMAW) introduces specific challenges when depositing WC-reinforced overlays. The high thermal input and rapid cooling rates can cause partial melting of WC particles, leading to the formation of tungsten-rich phases and loss of the original WC structure. The study highlights the importance of controlling:
- Wire feed rate: Affects dilution rate and WC retention
- Travel speed: Influences cooling rate and grain morphology
- Shielding gas composition: CO₂-rich mixtures increase dilution and carbide degradation
- Preheating temperature: Reduces cracking susceptibility in the heat-affected zone
Integration with Engineering Practice
In practical hardfacing applications, such as wear plates for mining equipment, slurry pumps, and conveyor components, the optimal WC content must balance wear resistance against weldability and service life. Field experience indicates that overlay layers with 30-40% WC content typically deliver the best compromise between hardness (achieving 60-70 HRC), toughness, and resistance to spalling failure. Engineers must also consider the substrate material compatibility; high-dilution situations with carbon steel substrates can significantly reduce the effective hardness of the overlay.
The study's findings are directly applicable to consumable selection for GMAW hardfacing processes, where wire composition design must account for the process-specific dilution behavior. For critical applications, multi-pass welding strategies with alternating hard and ductile layers can mitigate cracking while maintaining surface hardness.
Key Questions and Reflections
A critical question arising from this work is whether the optimal WC content identified under laboratory conditions translates directly to field performance, given the variability in service environments. The study's controlled wear testing provides valuable fundamental data, but real-world wear involves complex tribological conditions including temperature fluctuations, chemical attack, and variable loading. Additionally, the study does not extensively address the long-term stability of the WC phases under thermal cycling, which is crucial for high-temperature applications such as furnace components and hot metal handling equipment.
Study Insights and Implications
The work by Wu et al. provides a systematic understanding of how WC content governs the microstructure-property relationship in austenitic hardfacing overlays deposited by GMAW. The identification of an optimal WC content window, where maximum wear resistance is achieved without compromising mechanical integrity, has direct implications for consumable development and welding procedure qualification. For engineers designing hardfacing specifications, the key takeaway is that simply maximizing hard phase content is counterproductive; instead, a balanced microstructure with adequate matrix ductility is essential for achieving both high hardness and service life in demanding abrasive wear environments.