CLADDING TECHNOLOGY SHANXI CO., LTDQ235 Structural Steel Weld Overlay Surface Friction Wear Properties A Study Note
Introduction and Technical Context
The wear resistance of weld overlay surfaces on structural steel is a critical consideration in applications involving sliding contact, such as conveyor systems, excavator buckets, mining equipment, and pressure vessel components exposed to erosive media. The literature reviewed here investigates the friction and wear properties of Q235 structural steel surfaces after weld overlay treatment, providing insights into the selection of overlay materials and process parameters for improved wear resistance.
For cladding and pressure vessel engineers, understanding the wear behavior of overlay surfaces is essential for predicting component life and selecting appropriate overlay materials. The literature provides a systematic evaluation of wear mechanisms, tribological parameters, and the influence of overlay microstructure on wear resistance.
Experimental Setup and Wear Testing Methodology
The literature describes a comprehensive wear testing program using a pin-on-disk tribometer in accordance with ASTM G99. The test configuration involves a rotating disk specimen (the overlay surface) in contact with a stationary pin (typically made of Al₂O₃ or GCr15 bearing steel). The key test parameters are:
| Test Parameter | Value | Description |
|---|---|---|
| Normal load | 10, 20, 30, 40 N | Applied vertical force |
| Sliding speed | 0.5 m/s | Disk rotational speed |
| Sliding distance | 1000 m | Total sliding distance |
| Environment | Ambient air | No lubrication |
| Pin material | Al₂O₃ | Cermet pin for minimal pin wear |
| Temperature | 20–25°C | Room temperature |
The wear rate is calculated as the volume loss divided by the sliding distance, expressed in mm³/N·m. The coefficient of friction is measured as the ratio of friction force to normal load.
Wear Mechanisms and Surface Analysis
The literature identifies several wear mechanisms operating on the overlay surface, each dominant under different conditions:
Abrasive Wear: This is the primary wear mechanism at low loads (10–20 N). The hard carbide particles in the overlay material plough through the softer matrix, creating material removal grooves. The literature observes that overlay layers containing Cr₇C₃ or WC carbides exhibit significantly lower abrasive wear rates compared to the base Q235 steel.
Adhesive Wear: This mechanism becomes dominant at higher loads (30–40 N) when the contact pressure exceeds the yield strength of the overlay material. Material transfer occurs from the overlay to the pin and vice versa. The literature notes that adhesive wear is minimized when the overlay contains hard particles that interrupt the adhesive contact area.
Fatigue Wear: At high sliding distances (>500 m), fatigue wear becomes significant. Microcracks initiate at the overlay surface and propagate beneath the surface, leading to material loss in the form of flakes or spalls. The literature identifies that the fatigue life of the overlay is strongly influenced by the hardness gradient and residual stress state.
Oxidative Wear: Under ambient conditions, oxidation plays a secondary role. The literature observes the formation of a thin oxide layer (Fe₂O₃ and Cr₂O₃) on the wear surface, which can either protect or accelerate wear depending on its thickness and adhesion.
Overlay Material Selection and Performance Comparison
The literature evaluates several overlay materials on Q235 substrates, comparing their wear resistance and friction characteristics:
| Overlay Material | Hardness (HV) | Wear Rate (mm³/N·m) | Friction Coefficient | Wear Mechanism |
|---|---|---|---|---|
| Base Q235 | 120 | 8.5 × 10⁻³ | 0.42 | Abrasive + Adhesive |
| Hardfacing (Cr-C) | 850 | 1.2 × 10⁻³ | 0.38 | Abrasive |
| Stellite 6 | 420 | 2.8 × 10⁻³ | 0.45 | Adhesive + Abrasive |
| WC-Co | 1200 | 0.8 × 10⁻³ | 0.35 | Abrasive |
| Cr₃C₂-NiCr | 950 | 1.0 × 10⁻³ | 0.37 | Abrasive |
| High-Cr Cast Iron | 650 | 1.8 × 10⁻³ | 0.40 | Abrasive + Fatigue |
The results clearly demonstrate that the base Q235 steel has a wear rate approximately 7–10 times higher than the optimized overlay materials. The WC-Co overlay exhibits the lowest wear rate due to the extreme hardness of the tungsten carbide particles, but the Cr₃C₂-NiCr overlay offers the best balance of wear resistance, toughness, and cost-effectiveness.
Microstructural Analysis and Wear Mechanism Correlation
The literature provides detailed metallographic analysis of the worn surfaces, revealing the microstructural features that control wear behavior:
- WC-Co overlay: The wear surface shows exposed WC particles embedded in the Co matrix. The Co matrix undergoes plastic deformation and material transfer, while the WC particles remain intact and provide abrasive resistance. The wear mechanism is primarily abrasive, with material removal occurring through ploughing of the soft matrix.
- Cr₃C₂-NiCr overlay: The wear surface shows a mixture of Cr₃C₂ carbide particles and NiCr matrix. The carbide particles are partially dissolved during welding but re-precipitate during cooling. The wear mechanism is a combination of abrasive wear (carbide particles) and adhesive wear (matrix).
- Stellite 6 overlay: The wear surface shows a dendritic microstructure with Cr-rich carbides at the interdendritic regions. The wear mechanism is primarily adhesive, with material transfer occurring at the matrix level. The carbides provide some abrasive resistance but are not as effective as the WC or Cr₃C₂ particles.
The literature emphasizes that the wear resistance is directly related to the hardness and volume fraction of the hard phase in the overlay. However, there is a trade-off between hardness and toughness: overlays with very high hardness (such as WC-Co) are more susceptible to chipping and spalling under impact loading.
Engineering Practice and Application Recommendations
For engineers applying weld overlay technology to improve wear resistance in pressure vessel and structural applications, the literature provides several practical recommendations:
Material Selection: The selection of overlay material should be based on the dominant wear mechanism in the application. For abrasive wear (such as slurry service), WC-Co or Cr₃C₂-NiCr overlays are recommended. For adhesive wear (such as metal-to-metal sliding), Stellite 6 or high-Cr cast iron overlays are more appropriate.
Process Parameters: The overlay process parameters should be optimized to maximize the hardness and volume fraction of the hard phase. For TIG overlay, a lower travel speed and higher current are recommended to promote carbide formation. For plasma arc overlay, a higher powder feed rate and lower arc current produce a harder overlay with higher carbide content.
Surface Preparation: The base metal surface should be machined or ground to remove surface contaminants and provide a clean, flat surface for overlay deposition. The literature recommends a surface roughness of Ra 3.2–6.3 μm for optimal overlay bonding.
Post-Weld Treatment: Heat treatment can be used to modify the overlay microstructure and improve wear resistance. For Cr₃C₂-NiCr overlays, a tempering treatment at 600°C for 1 hour can reduce residual stresses without significantly reducing hardness.
Key Reflections and Study Insights
The study of Q235 structural steel weld overlay surface friction wear properties provides several important insights for cladding and pressure vessel engineers. The systematic evaluation of wear mechanisms and their correlation with microstructure offers a framework for predicting overlay performance in specific service conditions.
A particularly valuable insight is the trade-off between hardness and toughness in overlay materials. The literature demonstrates that while WC-Co overlays offer the highest wear resistance, they are more susceptible to chipping under impact loading. This trade-off must be carefully considered when selecting overlay materials for applications involving both wear and impact, such as pressure vessel components exposed to erosive and cyclic loading.
Another important insight is the role of the overlay-substrate interface in overall wear performance. The literature emphasizes that a sound bond between the overlay and the base metal is essential for long-term wear resistance. Poor bonding can lead to delamination and premature failure, regardless of the overlay material's intrinsic wear resistance.
In summary, the study of Q235 structural steel weld overlay surface friction wear properties provides comprehensive guidance on material selection, process optimization, and performance prediction. The insights gained from this study are directly applicable to cladding and pressure vessel applications where wear resistance is a critical design requirement.