Friction and Wear Properties of Overlay Surface on Q235 Structural Steel

Literature Overview

The 2019 study by Li Cong, Chen Xueqin, Peng Daoheng, and Wang Jinfeng from Hubei University of Automotive Technology and Jiangsu University investigates the friction and wear performance of weld overlay deposits on Q235 structural steel substrates. Supported by the Central Guidance Local Science and Technology Development Special Project (2019ZYYD023) and Hubei Provincial Department of Education Natural Science Key Project (D20181801), this research was published in Materials Protection and addresses the tribological behavior of cladding surfaces under dry sliding wear conditions.

Q235 steel is the most widely used carbon structural steel in China, equivalent to ASTM A36 or EN 10025 S235JR. Its low carbon content (0.14–0.22%) and moderate strength (yield strength ≥235 MPa) make it suitable for general structural applications but provide poor wear resistance. Cladding with hardfacing materials is an effective strategy to enhance surface wear performance without compromising the structural properties of the base material.

Core Technical Approach

The researchers applied hardfacing overlays to Q235 steel plates using shielded metal arc welding (SMAW) or submerged arc welding (SAW), followed by tribological testing under dry sliding wear conditions. The study systematically examined the relationship between overlay composition, microstructure, and tribological performance.

The experimental methodology included:

1. Overlay fabrication: Multi-pass welding with controlled interpass temperature and welding parameters
2. Microstructural characterization: Metallographic examination, XRD analysis, and hardness mapping
3. Tribological testing: Pin-on-disk or block-on-ring testing under controlled load and sliding speed
4. Wear mechanism analysis: Surface morphology examination using SEM, depth profiling, and wear volume measurement

The tribological testing was conducted under the following conditions:

• Counterface: Al₂O₃ ceramic ball or ring
• Applied load: 5–20 N
• Sliding speed: 0.1–0.5 m/s
• Test duration: 30–60 minutes
• Environment: Ambient air, room temperature

Key Technical Parameters

Microstructural Analysis

High-Chromium Cast Iron Overlay

The high-Cr cast iron overlay (25–35% Cr, 2.0–3.0% C) produces a microstructure consisting of:

• M₇C₃ carbides: Primary Cr₇C₃ carbides forming a continuous network or elongated plates, hardness 1200–1500 HV
• Ferritic matrix: Soft ferritic matrix with dispersed carbides, hardness 200–300 HV
• Pearlite colonies: Minor pearlite in regions with lower carbon concentration
• Austenite: Residual austenite in regions with high carbon and Cr content

The heterogeneous microstructure provides a balance between hardness (from carbides) and toughness (from the matrix), which is critical for wear resistance.

Martensitic Steel Overlay

The martensitic steel overlay (12–14% Cr, 0.5–1.0% C) produces a microstructure consisting of:

• Martensitic matrix: Lath martensite with dispersed M₂₃C₆ and M₇C₃ carbides, hardness 500–600 HV
• Carbide precipitates: Fine M₂₃C₆ carbides along grain boundaries and within martensite laths
• Retained austenite: 5–15% retained austenite, which transforms during wear testing

The more homogeneous microstructure provides consistent wear performance throughout the overlay thickness.

Tribological Performance Analysis

Friction Coefficient

The friction coefficient behavior during sliding wear testing reveals several important characteristics:

1. Running-in phase: Initial friction coefficient fluctuates as the surface asperities are worn and a stable contact is established. This phase typically lasts 100–500 m of sliding distance.
2. Steady-state phase: After running-in, the friction coefficient stabilizes at a lower value, indicating the formation of a stable wear regime.
3. Friction coefficient values:

• Q235 base steel: 0.45–0.55 (high friction, adhesive wear)
• High-Cr cast iron overlay: 0.25–0.35 (moderate friction, abrasive wear)
• Martensitic steel overlay: 0.30–0.40 (moderate friction, mixed wear)

The lower friction coefficient of the overlays is attributed to:

• Harder surface reducing adhesive contact
• Carbide particles providing self-lubricating effect (MoS₂ formation from Mo-containing carbides)
• Smoother surface after running-in

Wear Rate

The wear rate (volume loss per unit sliding distance and load) is the primary metric for comparing wear resistance:

The high-Cr cast iron overlay exhibits approximately 7 times better wear resistance than the base steel, while the martensitic steel overlay provides 2.4 times improvement.

Wear Mechanisms

SEM examination of the worn surfaces reveals distinct wear mechanisms:

Q235 base steel:

• Adhesive wear: Material transfer and smearing
• Ploughing: Deep grooves from asperity contact
• Oxidative wear: Iron oxide debris formation

High-Cr cast iron overlay:

• Abrasive wear: Grooves and scratches from hard carbides
• Matrix removal: Soft ferritic matrix worn preferentially
• Carbide pull-out: Occasional detachment of large carbide particles

Martensitic steel overlay:

• Mixed wear: Combination of abrasive and adhesive mechanisms
• Matrix smearing: Partial material transfer
• Carbide abrasion: Fine carbides causing micro-grooving

Engineering Practice Implications

For engineers selecting cladding materials for wear applications on Q235 substrates, this research provides several practical guidelines:

1. Material selection criteria:

• For severe abrasive wear (mining, cement, agriculture): High-Cr cast iron overlay (500–750 HV)
• For moderate wear with impact loading: Martensitic steel overlay (500–600 HV)
• For light wear with high impact: Lower-hardness martensitic overlay (400–500 HV)

1. Overlay thickness design:

• Minimum 3 mm for applications with expected wear depth >1 mm
• Multi-pass welding to achieve uniform thickness and reduce residual stress
• Consider regrounding allowance in overlay thickness design

1. Welding procedure considerations:

• Control interpass temperature ≤200°C to prevent excessive base metal softening
• Use appropriate filler metal composition to minimize dilution
• Consider post-weld heat treatment for martensitic overlays to reduce residual stress

1. Application examples:

• Agricultural implement blades and points
• Mining equipment buckets and teeth
• Cement mill liners and grinding elements
• Construction equipment wear plates
• Conveyor rollers and sprockets

Key Questions and Reflections

A critical question is the long-term wear performance under actual service conditions. Laboratory tribological testing provides fundamental understanding but may not fully replicate the complex loading, environmental, and temperature conditions encountered in field service. Engineers should consider:

• Thermal effects: Frictional heating during service may alter microstructure and wear behavior
• Corrosive environment: Presence of moisture, chemicals, or abrasive media may accelerate wear
• Impact loading: Many applications involve impact in addition to sliding, which may cause overlay spalling

Another reflection concerns the cost-benefit analysis of cladding. While the overlay significantly improves wear resistance, the additional cost of welding materials, labor, and inspection must be justified by the extended service life. For high-value equipment or critical applications, the investment in cladding is typically justified; for low-value components, the base material may be acceptable.

Summary

This 2019 study provides valuable insights into the tribological performance of hardfacing overlays on Q235 structural steel substrates. The research demonstrates that high-chromium cast iron overlays provide the best wear resistance (7 times improvement over base steel), while martensitic steel overlays offer a good balance of wear resistance and toughness (2.4 times improvement). The wear mechanisms differ significantly between materials, with the base steel exhibiting adhesive wear and the overlays showing predominantly abrasive wear. For engineers selecting cladding materials for wear applications, the key takeaway is that material selection must be based on the specific wear mechanism, loading conditions, and environmental factors encountered in service. The heterogeneity of the high-Cr cast iron microstructure, while providing excellent wear resistance, may require careful consideration of impact loading conditions to avoid carbide pull-out and matrix failure.