Overlay Welding for Composite Wear-Resistant Materials on Carbon Steel Substrates

Literature Overview

The paper by Zhang Wanhong, Gong Weimin, and Liang Shankun, published in the journal Mining Machinery (2012, Vol. 40, No. 11, pp. 97–101), investigates the preparation of composite wear-resistant surfaces through overlay welding on two common carbon steel substrates, Q235 and 45 steel. The study employs ER50-6 electrodes via the shielded metal arc welding (SMAW) process and systematically examines how welding parameters and substrate selection influence the microstructure and mechanical properties of the overlay layer. This work is particularly relevant to engineers dealing with mining equipment, hydraulic cylinders, and structural components that require enhanced surface durability without the cost of full material replacement.

Core Technical Content and Process Parameters

The experimental design centers on the SMAW process using ER50-6 consumables, a rutile-type low-hydrogen electrode widely used in structural steel welding. The key process variables examined include welding speed, base material type, and the resulting dilution between the overlay and the substrate. The following table summarizes the principal experimental conditions and outcomes:

The authors report that the overlay layer exhibits significant grain refinement compared to the base material, which is a direct consequence of the rapid solidification rates inherent to arc welding. The cooling rate in the weld zone, typically ranging from 10 to 100 °C/s depending on heat input, promotes the formation of fine acicular ferrite and martensite structures in the overlay. This microstructural refinement is the primary mechanism responsible for the hardness enhancement observed in the overlay zone.

Microstructure and Property Analysis

Metallographic examination reveals that the overlay layer consists of a mixture of martensite, bainite, and retained austenite, with the relative proportions varying according to the cooling rate and substrate thermal conductivity. On Q235 steel, the lower carbon and alloy content of the base material results in a more dilute overlay with slightly lower hardness but better toughness. On 45 steel, the higher carbon content leads to increased dilution, producing a harder but more brittle overlay layer. The hardness profile typically shows a gradient from the fusion line outward, with the highest values occurring in the region immediately adjacent to the fusion boundary where the dilution ratio is highest.

The grain refinement effect is particularly pronounced in the heat-affected zone (HAZ) of the overlay, where grain sizes can be reduced by 30–50% compared to the base material. This refinement contributes to both increased hardness and improved wear resistance. The authors note that welding speed has a significant influence: higher speeds result in lower heat input, faster cooling, and consequently finer microstructures with higher hardness values. However, excessively high speeds can lead to incomplete fusion and porosity defects, representing a critical process window that must be carefully controlled.

Engineering Practice Implications

From an engineering perspective, this study provides valuable guidance for selecting overlay welding parameters for wear-resistant applications. The following considerations should be incorporated into practical implementation:

• Substrate preheating should be maintained at 100–150 °C for Q235 and 150–250 °C for 45 steel to prevent cold cracking, particularly in thicker sections.
• Interpass temperature should not exceed 250 °C to avoid excessive grain growth and softening of previously deposited layers.
• Multiple passes should be applied with each subsequent pass providing partial tempering of the previous layer, which helps relieve residual stresses.
• Post-weld heat treatment at 550–650 °C for 1–2 hours is recommended to reduce residual stresses and improve toughness without significantly compromising hardness.

A common defect encountered in overlay welding is cracking at the fusion line, which can be mitigated by ensuring adequate preheat, using low-hydrogen electrodes with proper storage, and avoiding excessive拘束 (constraint) on the base material. The use of ER50-6, while effective for structural applications, may not provide optimal wear resistance for severe abrasion conditions. For such applications, specialized wear-resistant electrodes such as those containing chromium carbide or tungsten carbide particles should be considered.

Study Insights and Reflections

The principal insight from this study is that overlay welding with standard structural electrodes can produce meaningful wear resistance improvements on common carbon steels, but the effectiveness is highly dependent on process parameters and substrate selection. The grain refinement mechanism is well-established in welding metallurgy, yet the specific quantification of how welding speed affects overlay hardness provides actionable data for process optimization. One limitation of the study is the absence of quantitative wear testing; hardness alone does not fully characterize wear resistance, as factors such as fracture toughness, oxidation resistance, and fatigue behavior also play significant roles in real-world service conditions.

For engineers tasked with extending the service life of mining equipment or structural components, this research confirms that overlay welding is a viable and cost-effective strategy. However, the selection of electrode type must be matched to the specific wear mechanism encountered in service. Abrasive wear, adhesive wear, and erosive wear each demand different overlay compositions and microstructures. The study serves as a useful baseline for further investigation into more advanced overlay systems.