Zhuojin Pipe Fitting Co., LtdEffect of Welding Materials on Wear Resistance of Chromium Carbide Overlay Composite Steel Plates
Literature Overview
This paper by Li Tieying, published in Welding Technology (2014, Vol. 43, No. 7, pp. 48–51), investigates the influence of welding consumable selection on the tribological performance of chromium carbide (Cr3C2) overlay composite steel plates. The study compares two wire types: standard iron-based chromium carbide wire and an iron-based chromium carbide wire with boron addition. The research employs ASTM G65 sliding wear testing and establishes quantitative correlations between microstructural features, surface hardness, and wear resistance. This work is directly relevant to engineers designing wear-resistant linings for mining equipment, cement mill components, and material handling systems where sliding abrasion is the dominant failure mode.
Core Findings
Microstructural Analysis
The overlay layer microstructure is governed by the volume fraction of carbide phases, their morphology, and the matrix composition. The key finding is that boron addition fundamentally alters the carbide formation mechanism:
- Standard Cr3C2 wire: Forms chromium carbide precipitates within an austenitic matrix, with carbide volume fraction determined by the Cr/C ratio and cooling rate.
- Boron-modified Cr3C2 wire: Boron forms boride carbide phases (B4C or CrB) in the austenitic matrix. These fine boride particles act as additional nucleation sites for chromium carbide precipitation, thereby increasing both the number density and volume fraction of Cr3C2 particles in the final microstructure.
Wear Test Results
ASTM G65 pin-on-disk sliding wear tests demonstrated that the boron-modified overlay plate exhibited superior wear resistance compared to the standard chromium carbide overlay plate. The enhanced performance is attributed to the increased carbide volume fraction resulting from the boron-induced nucleation effect.
Quantitative Correlations
| Relationship | Finding |
|---|---|
| Wear resistance vs. Carbide volume fraction | Positive linear correlation |
| Wear resistance vs. Surface hardness | No strong correlation |
| Wear resistance vs. Carbon content | Linear increase with increasing C content |
| Optimal w(Cr)/w(C) ratio for maximum carbide formation | 4.1 |
Technical Interpretation
The finding that wear resistance correlates linearly with carbide volume fraction but not strongly with surface hardness is a critical insight for overlay design. This implies that maximizing hardness alone—through, for example, excessive carbon content or rapid quenching—is not the optimal strategy for wear-resistant overlay design. Instead, the volume fraction of hard carbide phases is the dominant factor.
The optimal Cr/C ratio of 4.1 represents a stoichiometric balance point. Below this ratio, excess carbon may form free cementite (Fe3C), which is less hard than Cr3C2 and may reduce overall wear resistance. Above this ratio, carbon becomes limiting and carbide formation is incomplete, reducing the volume fraction of the effective hard phase.
The Role of Boron
Boron addition serves a dual function:
- Direct hardening: Boride carbides (B4C) are extremely hard (approximately 2500 HV), contributing directly to surface hardness.
- Indirect enhancement: Fine boride particles provide nucleation sites for Cr3C2 precipitation, increasing the total carbide volume fraction beyond what would be achieved by Cr/C ratio optimization alone.
This nucleation effect is analogous to the role of rare earth additions in controlling carbide morphology in high-speed steels, and represents a sophisticated understanding of phase transformation kinetics in overlay welds.
Engineering Application Considerations
For engineers selecting overlay consumables for wear applications, this paper provides actionable guidance:
- Prioritize consumables that maximize carbide volume fraction over those that merely maximize surface hardness.
- Consider boron-modified chromium carbide wires for applications requiring enhanced sliding wear resistance.
- Target a Cr/C mass ratio near 4.1 for optimal carbide formation efficiency.
- Verify performance through ASTM G65 or equivalent sliding wear tests rather than relying solely on hardness measurements.
Study Insights
The distinction between hardness and wear resistance is often blurred in industrial practice, where hardness is used as a surrogate for wear performance. This paper provides rigorous evidence that the two are not always correlated, particularly in carbide-reinforced overlay systems. Engineers should adopt a microstructure-driven approach to overlay design, focusing on carbide volume fraction, morphology, and distribution rather than surface hardness alone. The boron modification strategy is particularly elegant, as it leverages a secondary phase to enhance the primary wear-resistance mechanism, offering a pathway to improved performance without fundamentally changing the base alloy chemistry.