CLADDING TECHNOLOGY SHANXI CO., LTDFriction and Wear Properties of Weld Overlay on Q235 Structural Steel
Literature Overview
This study examines the tribological performance of weld overlay cladding deposited on Q235 structural steel, a widely used carbon steel grade in construction and general fabrication. The research addresses a practical engineering need: enhancing the wear resistance of Q235 components without replacing the entire component with expensive alloy materials. The overlay system investigated uses a high-alloy filler metal deposited through manual metal arc welding, creating a surface layer with significantly improved hardness and wear characteristics while retaining the structural integrity of the carbon steel substrate.
Microstructural Analysis
The overlay layer exhibits a fully martensitic microstructure with a high volume fraction of cementite and chromium carbides. The rapid cooling rate inherent to manual arc welding on the relatively thin overlay pass promotes martensitic transformation. The microstructure transitions from fine acicular martensite at the surface to coarser martensite with some ferrite at the interface with the Q235 substrate. This gradient reflects the thermal cycle experienced during deposition, with the first pass experiencing the highest cooling rate and subsequent passes experiencing lower cooling rates due to heat input from the previous pass.
| Microstructural Feature | Surface Region | Mid-Region | Interface Region |
|---|---|---|---|
| Matrix phase | Acicular martensite | Plate martensite | Martensite + ferrite |
| Carbide type | M3C + M7C3 | M3C | M3C (coarse) |
| Hardness (HV30) | 620-680 | 520-580 | 320-380 |
| Grain size (μm) | 3-5 | 5-8 | 10-15 |
Friction and Wear Testing Results
The tribological testing is conducted under dry sliding conditions against a hardened steel counterface. The coefficient of friction for the overlay surface ranges from 0.45 to 0.55, compared to 0.62 to 0.70 for the unclad Q235 substrate. This reduction in friction coefficient is attributed to the formation of a protective oxide layer composed primarily of iron and chromium oxides during sliding. The specific wear rate of the overlay is approximately 1.8 times 10^-6 mm³/Nm, compared to 8.5 times 10^-6 mm³/Nm for the bare Q235 steel, representing a fourfold improvement in wear resistance.
Wear Mechanism Analysis
Wear surface examination using scanning electron microscopy reveals that the overlay layer undergoes primarily abrasive wear with secondary adhesive wear. The hard carbide particles embedded in the martensitic matrix act as load-bearing elements, resisting material removal by the counterface. In contrast, the Q235 substrate exhibits severe adhesive wear with extensive material transfer to the counterface. The wear track on the overlay shows shallow grooves aligned with the sliding direction, indicating that the carbide particles are intact and functioning as intended.
Engineering Significance
The practical value of this research lies in the cost-effectiveness of the approach. Q235 steel is among the most economical structural steels available, and applying a thin overlay layer of a few millimeters can extend the service life of wear-critical components by a factor of three to five. This is particularly relevant for components such as guide rails, support brackets, and structural elements in mining and construction equipment where replacement of the entire component is impractical.
From a fabrication standpoint, the manual arc welding process used in this study offers significant flexibility. Unlike automated processes that require specialized equipment, manual welding can be performed in the field, making it suitable for repair applications. The dilution effect from the Q235 substrate is more pronounced in this case due to the large carbon content differential between the substrate and the overlay alloy. Engineers must account for this dilution when specifying the number of passes and the final overlay thickness required to achieve the target properties.
Quality Control Considerations
The transition zone between the overlay and substrate is the most critical area for quality control. Cracking in this region, particularly intergranular cracking in the heat-affected zone of the Q235 substrate, is the most common defect. The study recommends preheating the substrate to 150 to 200 degrees Celsius to reduce the cooling rate and minimize the risk of hydrogen-induced cracking. Post-weld heat treatment at 200 to 250 degrees Celsius for stress relief is also recommended to reduce residual stresses that could lead to delayed cracking.
Study Insights
The research confirms that the combination of martensitic transformation and carbide hardening is the dominant mechanism for wear resistance improvement in medium-alloy overlay systems on carbon steel substrates. The engineering challenge lies in achieving a balance between wear resistance and toughness, as excessive hardness can lead to brittle fracture under impact loading. For pressure vessel applications governed by GB/T 150, the overlay layer must not compromise the structural integrity of the vessel. The overlay thickness should be limited to the minimum required for the intended service life, and the transition zone must be thoroughly inspected using magnetic particle testing or penetrant testing to ensure freedom from cracks.