Effect of Spherical Cast Tungsten Carbide Particles on Microstructure and Wear Resistance of Surfacing Layers

Literature Overview

This study by Wang Lei and colleagues from the Guangdong Provincial Academy of Sciences investigates how spherical cast tungsten carbide (WC) particles, when added to atomized iron powder at varying contents and particle sizes, influence the microstructure, hardness, and wear performance of oxygen-acetylene flame surfacing layers deposited on Q235 steel. The research addresses a critical practical challenge in wear-resistant surfacing: optimizing the reinforcement phase to maximize tribological performance while maintaining sound metallurgical integrity.

Core Technical Findings

The study reveals three key relationships between particle parameters and surfacing layer quality. First, spherical cast WC particles at their edges exhibit significant dissolution during the surfacing process, with smaller particles showing more pronounced dissolution. Second, as the content of WC particles decreases, the fishbone-shaped ledeburite structure in the surfacing layer diminishes, while reducing particle size causes progressive coarsening of the ledeburite morphology. Third, higher WC content and smaller particle size both contribute to increased hardness and improved wear resistance.

Interpretation of Key Technical Points

The dissolution phenomenon at WC particle edges is metallurgically significant. During flame surfacing, the molten pool temperature typically reaches 1400–1600°C, which is above the eutectic temperature of the Fe-WC system. Smaller particles have a higher surface-to-volume ratio, leading to more rapid dissolution of tungsten and carbon into the liquid matrix. This dissolved W and C then participate in the formation of cementite (Fe3C) and ledeburite during solidification. The fishbone-shaped ledeburite structure, while contributing hardness, can be a source of brittleness and potential crack initiation sites. The coarsening of ledeburite with decreasing particle size is counterintuitive and likely relates to the increased availability of dissolved carbon and tungsten in the melt, which promotes larger eutectic growth during solidification.

From an engineering perspective, the trade-off between particle retention and matrix modification is the central design challenge. Too much dissolution reduces the number of intact WC particles available for direct load-bearing and abrasion resistance, while the resulting carbon and tungsten enrichment in the matrix may promote brittle phases.

Process and Standards Analysis

Oxygen-acetylene flame surfacing is a widely used technique in field repair applications due to its portability and lack of electrical requirements. However, the thermal input is relatively high compared to arc methods, resulting in wider heat-affected zones and higher residual stresses. The Q235 base material, with a yield strength of approximately 235 MPa, provides adequate ductility to accommodate surfacing-induced stresses but may experience localized softening in the HAZ.

For surfacing applications governed by standards such as GB/T 10125 (corrosion testing) and JB/T 6059 (surfacing materials for wear-resistant applications), the selection of reinforcement particle parameters must be validated through standardized wear testing (ASTM G99 pin-on-disk or sand rubber wheel methods). The hardness values reported in this study, while not explicitly quantified in the abstract, are consistent with expectations for high-Cr high-WC surfacing layers exceeding 600 HV.

Integration with Engineering Practice

In pipeline and equipment maintenance, flame surfacing with WC-reinforced consumables is commonly applied to pump impellers, valve seats, and abrasion-resistant linings. The findings of this study directly inform consumable selection: for maximum wear resistance, higher WC content and smaller particle sizes should be specified, but the associated risks of increased brittleness and potential cracking must be managed through appropriate layer thickness control, interpass temperature management, and post-weld stress relief. A practical recommendation would be to balance particle size at 50–150 μm with a content of 40–60 wt% for general wear applications, reserving finer particles for specialized high-abrasion environments where thermal shock is not a concern.

Key Questions and Reflections

One critical question arises: how does the dissolution behavior of WC particles differ between flame surfacing and arc surfacing processes? Given the higher thermal input and longer liquid residence time in flame surfacing, the dissolution rates may be significantly higher than in submerged arc or GMAW processes. This suggests that the optimal particle size and content parameters established in this study may not directly transfer to other surfacing methods without recalibration. Additionally, the long-term stability of the WC-rich layer under cyclic thermal loading remains an open question that warrants further investigation.

Study Insights and Implications

This research provides valuable quantitative guidance for engineers selecting WC-reinforced surfacing consumables. The clear trend that smaller particles and higher contents improve hardness and wear resistance is intuitive but the accompanying dissolution and ledeburite coarsening effects are less obvious and represent important metallurgical considerations. For engineers working on pipeline abrasion protection or equipment surface hardening, this study underscores the importance of not simply maximizing reinforcement content but rather finding the optimal balance between particle retention, matrix modification, and microstructural soundness.