Microstructure and Properties of Wear-Resistant Weld Overlay on Q235 Steel Plate

Literature Overview

This study investigates the microstructural evolution and mechanical properties of wear-resistant weld overlay layers deposited on Q235 carbon steel plates, focusing on the dilution behavior between the base metal and the overlay material, the formation of hard phases, and the resulting tribological performance. The work is significant for engineers dealing with cost-effective surface hardening solutions for structural steel components subjected to abrasive wear environments.

Core Technical Points

The study examines the interface between Q235 base metal and the overlay layer, analyzing how carbon dilution from the base metal affects the hardness distribution across the overlay thickness. Key findings include the formation of martensitic and carbide-rich microstructures in the first few millimeters of the overlay, with hardness values ranging from 450 to 620 HV in the hardened zone, gradually decreasing toward the base metal side. The dilution rate was found to be a critical parameter, with first-pass dilution typically reaching 35% to 50% depending on the welding process and parameters employed.

Microstructural Analysis

Metallographic examination reveals a gradient structure in the overlay layer. The region adjacent to the fusion line exhibits a coarse martensitic structure with carbide networks, while the outer layers show finer tempered martensite with uniformly distributed alloy carbides. The presence of M7C3 and M23C6 type carbides was confirmed through X-ray diffraction analysis, contributing significantly to the wear resistance of the overlay.

Process Parameters and Their Influence

The study compared submerged arc welding (SAW) and gas metal arc welding (GMAW) for depositing the overlay layers. SAW produced deeper penetration with higher dilution rates, resulting in a broader hardened zone at the interface but requiring more passes to achieve adequate hardness in the outer layers. GMAW offered better control over dilution with shallower penetration, producing a more uniform hardness profile but at a lower deposition rate.

Engineering Practice Insights

From an engineering perspective, the key takeaway is that multi-pass welding is essential for achieving the required surface hardness. A single-pass overlay on Q235 steel cannot achieve the target hardness due to excessive dilution. The recommended approach involves depositing a transition layer with moderate carbon content followed by the final wear-resistant layers. Preheating at 150-200°C is advisable to prevent cracking at the fusion line, and interpass temperature should be maintained below 250°C to preserve the hardness of previously deposited layers.

Common defects observed include porosity from inadequate flux coverage in SAW, and lack of fusion at the edges of deposited beads. Countermeasures include proper flux moisture control (below 0.5% moisture content for low-hydrogen fluxes) and adequate edge preparation to ensure complete fusion.

Study Reflections and Implications

This literature provides valuable guidance for selecting appropriate welding processes and parameters when applying wear-resistant overlays to low-carbon steel substrates. The dilution behavior is the central challenge, and understanding the relationship between process parameters, dilution rate, and final hardness allows engineers to design overlay schemes that meet specific service requirements. For applications requiring extreme wear resistance, alternative approaches such as plasma transferred arc (PTA) cladding or laser cladding should be considered, as these processes offer significantly lower dilution rates (below 10%) and can produce overlay layers with hardness exceeding 700 HV on Q235 substrates.