Wear Resistance of Overlay Welding Electrodes A Technical Study Note

Literature Overview and Context

The paper by Zhang Qinghui of Xiangtan University, published in the Journal of Welding in 1994, addresses a fundamental question that remains central to overlay welding engineering: how to design and select welding electrodes that produce overlay deposits with superior wear resistance. In 1994, China's industrial base was rapidly expanding, and the demand for cost-effective surface hardening solutions was growing significantly. The study reflects a mature understanding of the relationship between electrode composition, microstructural evolution during welding, and the resulting tribological performance of the overlay layer.

This work is particularly noteworthy because it bridges the gap between electrode metallurgy and service performance. The author examines multiple electrode types and correlates their chemical composition with hardness, microstructural features, and abrasion resistance test results. For engineers working in today's overlay welding practice, this paper provides a foundational framework that still holds relevance when selecting consumables for wear-critical applications such as mining equipment, cement mill liners, and pump impellers.

Core Technical Content and Key Findings

The study investigates the wear resistance of various overlay welding electrodes through a systematic approach combining chemical analysis, metallographic examination, hardness measurement, and pin-on-disk abrasion testing. The key findings can be summarized as follows:

The study demonstrates that the primary mechanism governing wear resistance in iron-based overlay deposits is the volume fraction and distribution of hard carbide phases within a tough matrix. Electrodes with higher carbon content (3-5 wt%) combined with chromium (12-20 wt%) produce the highest hardness and wear resistance due to the formation of chromium carbides (Cr7C3 and Cr23C6) dispersed within a tempered martensitic matrix.

Microstructural Analysis

The metallographic examination reveals that the microstructure of overlay deposits is strongly influenced by the cooling rate during welding, which is itself determined by the welding parameters, plate thickness, and preheating temperature. The author identifies three distinct microstructural regimes:

1. Rapid cooling regime (thin deposits, low heat input): Produces fine martensite with uniformly dispersed carbides, yielding high hardness but potentially elevated residual stresses and reduced toughness.
2. Moderate cooling regime (medium deposits, normal heat input): Produces tempered martensite with coarser carbide particles, offering the best balance between hardness and toughness.
3. Slow cooling regime (thick deposits, high heat input): Produces bainite and pearlite with coarse carbides, resulting in lower hardness but improved ductility.

Welding Process Considerations

The study emphasizes that achieving the target microstructure requires careful control of welding parameters. For multi-pass overlay welding, the interpass temperature should be maintained between 150-250°C to prevent excessive grain growth while ensuring adequate stress relief. The author recommends using a weaving pattern to ensure uniform heat distribution and minimize dilution from the base metal.

Engineering Practice Implications

From a practical standpoint, this 1994 study provides several actionable guidelines for modern overlay welding operations:

• Electrode selection: For severe sliding wear conditions, high-Cr-Hi-C electrodes (such as those conforming to GB/T 10045 or equivalent) are recommended. For abrasion wear with moderate impact, Cr-Mo alloy electrodes offer a better toughness-to-hardness ratio.
• Welding procedure qualification: The study implicitly supports the need for welding procedure qualification per NB/T 47014 or ASME IX, particularly regarding heat input ranges and preheating requirements.
• Post-weld treatment: For applications requiring high toughness, stress-relief annealing at 500-550°C for 2 hours per 25 mm of thickness is recommended to reduce residual stresses without significantly softening the overlay.

Defect Prevention

The author notes that common defects in overlay welds include cracking, porosity, and insufficient bond strength. Cracking is primarily associated with high carbon equivalent (CE > 0.55) and inadequate preheating. Porosity results from contaminated electrode coatings or excessive arc length. Bond strength failures typically occur at the interface when dilution exceeds 30% or when the base metal surface is contaminated.

Study Insights and Reflections

Reviewing this paper after more than three decades of engineering practice, I find it remarkable how the fundamental principles described here remain valid. The understanding that wear resistance is governed by the hard phase volume fraction and matrix toughness is still the cornerstone of overlay material design. What has changed since 1994 is the availability of advanced analytical techniques (such as SEM-EDS, XRD, and nanoindentation) that allow more precise characterization of these microstructural features.

One area where modern practice has advanced significantly is in the development of flux-cored wire and self-shielded electrode systems that offer better arc stability, lower dilution, and more consistent composition control compared to the solid rod electrodes studied here. Nevertheless, the systematic approach of correlating composition with microstructure and then with wear performance remains the gold standard for overlay material development.

The lasting value of this work lies in its pedagogical clarity. Engineers entering the field of overlay welding can benefit from understanding these foundational relationships before moving on to more advanced techniques such as plasma transferred arc (PTA) cladding, laser cladding, or high-velocity oxy-fuel (HVOF) thermal spray. The principles of carbide formation, dilution control, and heat input management are universal across all cladding processes.

In conclusion, Zhang Qinghui's study serves as an essential reference for any engineer involved in overlay welding material selection and process optimization. Its systematic methodology and clear correlation between electrode composition, weld metal microstructure, and wear performance provide a framework that continues to guide engineering decisions in the design and fabrication of wear-resistant components.