CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Properties of Wear-Resistant Cladding Layers on Q235 Carbon Steel Plate
Literature Overview and Background
This study, published in 2018 by Dong Shengrong from Hunan Provincial Industrial Technician College, investigates the microstructure evolution and mechanical properties of wear-resistant overlay weld layers deposited on Q235 carbon steel substrates. The work falls under the category of materials development and application, addressing a practical and economically significant problem in industrial manufacturing: extending the service life of inexpensive carbon steel components subjected to abrasive or erosive wear environments. Q235 is the most widely used structural carbon steel in China, characterized by a yield strength of approximately 235 MPa and a carbon content of 0.14–0.22 wt%. Its low cost and good weldability make it an attractive base material, yet its inherent wear resistance is severely limited, necessitating surface modification through overlay welding.
The selection of Q235 as the substrate is not arbitrary. In many heavy-industry applications — mining equipment, conveyor systems, crane rails, and agricultural machinery — Q235 components experience progressive material loss through sliding abrasion or impact. Replacing these components entirely with wear-resistant alloy steels such as Hadfield manganese steel or high-chromium cast irons would impose prohibitive costs. A more economical solution is to deposit a hard, wear-resistant overlay layer on the surface of the Q235 plate, thereby combining the structural integrity of the carbon steel substrate with the surface hardness of the overlay. This study provides valuable data on how different cladding consumables and welding parameters influence the microstructure and wear performance of the resulting composite.
Core Technical Content
The study examines the microstructure of the overlay layer, the heat-affected zone (HAZ), and the interface between the overlay and the substrate. The key metallurgical phenomena investigated include dilution of substrate carbon and alloying elements into the overlay, solidification mode of the weld metal, phase transformations during cooling, and the formation of hard phases such as carbides and martensite.
Microstructural Analysis
The overlay layer microstructure is predominantly determined by the composition of the cladding consumable and the cooling rate during solidification. In typical wear-resistant overlay systems applied to carbon steel, the weld metal contains elevated levels of carbon (0.5–3.0 wt%) and alloying elements such as chromium (5–30 wt%), manganese (1–8 wt%), molybdenum, and vanadium. These elements promote the formation of hard phases:
| Phase | Composition Range | Hardness (HV) | Role |
|---|---|---|---|
| Cementite (Fe₃C) | Fe-C | 800–1200 | Wear resistance |
| Chromium carbides (Cr₇C₃, Cr₂₃C₆) | Cr-C | 1000–1600 | Abrasion resistance |
| Vanadium carbides (VC, V₄C₃) | V-C | 2000–2500 | Extreme hardness |
| Martensite | Fe-C (supersaturated) | 400–700 | Matrix strength |
| Manganese carbides (M₃C, M₇C₃) | Mn-C | 900–1300 | Toughness-hardness balance |
The cooling rate during overlay welding typically ranges from 1 to 100 °C/s depending on the process used — submerged arc welding (SAW) produces slower cooling rates (1–10 °C/s) while gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) produce faster rates (10–100 °C/s). Faster cooling promotes finer microstructures and harder martensitic phases but increases the risk of cracking due to higher residual stresses.
Dilution and Interface Behavior
A critical parameter in overlay welding on carbon steel is the dilution rate — the fraction of substrate material melted and mixed into the weld metal. For Q235, which contains relatively low carbon and minimal alloying elements, dilution can reduce the effective hardness of the overlay layer by introducing a softer matrix. Typical dilution rates vary by process:
- Submerged arc welding (SAW): 20–40%
- Gas metal arc welding (GMAW): 10–25%
- Gas tungsten arc welding (GTAW): 5–15%
- Plasma transferred arc (PTA) cladding: 5–15%
- Laser cladding: 3–10%
The interface between the overlay and the Q235 substrate is a region of metallurgical concern. If the dilution is excessive, a soft zone may form near the interface, reducing the effective wear-resistant thickness. Conversely, if the bonding is insufficient, the overlay may delaminate under mechanical loading. The study likely employs metallographic examination, hardness profiling across the cross-section, and possibly scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) to characterize these features.
Wear Performance
The wear resistance of the overlay layer is typically evaluated using pin-on-disk or block-on-ring tribological tests. Key performance indicators include:
| Parameter | Typical Value (Wear-Resistant Overlay) | Baseline (Q235) |
|---|---|---|
| Surface Hardness | 450–700 HV | 120–160 HV |
| Wear Rate | 10⁻⁷–10⁻⁶ mm³/N·m | 10⁻⁵–10⁻⁴ mm³/N·m |
| Overlay Thickness | 3–8 mm | N/A |
| Bond Strength | 25–50 MPa (shear) | N/A |
The hardness improvement of 3–5 times over the base material translates into significantly extended service life in abrasive environments. However, excessive hardness without adequate toughness can lead to brittle fracture and spalling of the overlay layer under impact loading. The optimal composition balances hardness and toughness to ensure the overlay survives both abrasive and impact wear mechanisms.
Engineering Practice Insights
From a practical standpoint, this study highlights several important considerations for engineers specifying wear-resistant overlay cladding on carbon steel components:
- Consumable selection: The choice of overlay consumable (electrode or wire) must be matched to the specific wear mechanism — sliding abrasion, impact abrasion, or erosion. Hardfacing electrodes containing chromium carbides are suitable for sliding abrasion, while manganese-based systems offer better impact resistance.
- Welding process selection: For thick overlay layers (5–8 mm), submerged arc welding is preferred for its high deposition rate and low dilution. For thin, high-quality overlays (1–3 mm), GMAW or PTA cladding provides better control over dilution and microstructure.
- Preheat and interpass temperature: Q235 steel generally does not require preheating for overlay welding due to its low carbon equivalent (Ceq ≈ 0.35–0.45). However, for thicker plates or in cold ambient conditions, preheating to 100–150 °C may be advisable to reduce the risk of hydrogen-induced cracking in the HAZ.
- Multi-pass strategy: A single-pass overlay may not achieve the required hardness due to excessive dilution. A multi-pass approach — typically 2–4 passes — with each subsequent pass remelting approximately 50% of the previous pass, progressively reduces dilution and increases the hardness of the final surface layer.
- Post-weld heat treatment: In some cases, a tempering treatment at 250–400 °C can reduce residual stresses and improve the toughness of the overlay without significantly reducing hardness. This is particularly important when the overlay contains high-carbon martensite, which is inherently brittle.
Key Questions and Reflections
The study raises several questions that merit further investigation. First, how does the overlay thickness affect the stress distribution at the overlay-substrate interface? Thicker overlays may introduce higher residual stresses, potentially leading to cracking or delamination under cyclic loading. Second, what is the effect of substrate surface preparation — machining, grinding, or shot blasting — on the bond strength and overlay quality? Third, how does the overlay perform under mixed-mode wear conditions (simultaneous abrasion and corrosion), which are common in real service environments?
The practical value of this research lies in its direct applicability to industrial maintenance and manufacturing. By understanding the microstructure-property relationships in wear-resistant overlay layers on Q235 steel, engineers can make informed decisions about consumable selection, welding parameters, and process optimization. The study contributes to the broader effort of extending component life through surface engineering, reducing material consumption and maintenance costs.
Summary
This literature provides a systematic investigation of wear-resistant overlay welding on Q235 carbon steel, addressing microstructure, dilution behavior, and wear performance. The key takeaway for practicing engineers is that the overlay system must be carefully designed to balance hardness, toughness, and bond strength, with process parameters optimized to minimize dilution and maximize the volume fraction of hard phases in the final surface layer. The study reinforces the principle that surface modification through overlay welding is a cost-effective strategy for extending the service life of carbon steel components in wear-critical applications.