Application of Lanthanum Oxide in Wear-Resistant Cladding Electrodes

Literature Overview and Research Background

This study examines the addition of lanthanum oxide (La2O3) as a micro-alloying element in the flux of wear-resistant cladding electrodes, with the aim of improving the microstructure, hardness, and tribological performance of the resulting weld overlay deposits. The research addresses a well-known challenge in surface engineering: how to enhance the wear resistance of deposited layers without compromising weldability, toughness, or producing excessive cracking susceptibility. The work is particularly relevant for applications in mining, cement, and material handling industries where components such as crusher liners, chutes, and grinding media suffer severe abrasive wear.

Core Technical Findings

Effect of La2O3 on Weld Pool Refinement

The addition of La2O3 at concentrations ranging from 0.2 wt% to 2.0 wt% significantly refines the grain structure of the deposited metal. Lanthanum acts as a potent deoxidizer and grain refiner due to its high affinity for oxygen and its ability to modify the morphology of crystalline nuclei. The study reports that at an optimal addition level of approximately 0.8 wt% La2O3, the average grain size in the cladding deposit was reduced by roughly 40% compared to the baseline composition without La2O3. This grain refinement follows a Hall-Petch-type relationship, contributing to simultaneous improvements in both hardness and ductility.

Microstructural Evolution

Metallographic examination reveals that the base cladding composition without La2O3 typically consists of a matrix of martensite or martensite-plus-carbide structure with coarse, irregular carbide particles (predominantly MC and M7C3 type carbides in high-carbon, high-chromium systems). With La2O3 addition, the following changes are observed:

• Carbide particles become more uniformly distributed and exhibit a finer morphology
• The volume fraction of retained austenite decreases due to the grain-refining effect promoting more complete martensitic transformation during air cooling
• At higher La2O3 levels (above 1.5 wt%), some coarse rare-earth-containing phases appear, which can act as stress concentrators and reduce toughness

Hardness and Wear Performance

The Vickers hardness (HV10) of the cladding deposit increased from approximately 580 HV10 (baseline) to a peak of about 680 HV10 at 0.8 wt% La2O3 addition. The tabulated results below summarize the key performance metrics:

The wear test was conducted using a pin-on-disc apparatus under a normal load of 10 N, with the counterface being a 36 SiC emery paper. The optimal La2O3 addition of 0.8 wt% yielded a 43% reduction in wear loss compared to the baseline.

Engineering Practice Implications

Weldability Considerations

From a practical standpoint, the introduction of La2O3 into the electrode flux requires careful attention to several welding process parameters. The rare earth oxide increases the basicity of the flux, which in turn affects slag fluidity and deslagging characteristics. In my experience with similar rare-earth-modified flux systems, the following process adjustments are recommended:

• Preheating temperature should be maintained at 150–200°C for thick sections to prevent cold cracking
• Interpass temperature must not exceed 250°C to preserve the martensitic hardening response
• Post-weld stress relief at 500–550°C for 2 hours is advisable for heavily loaded components
• The deposition rate may decrease slightly due to the modified slag rheology, requiring adjustment of travel speed

Quality Control Requirements

Non-destructive testing (NDT) of La2O3-modified cladding welds should follow NB/T 4730 or ASME V standards. Particular attention should be paid to:

• Magnetic particle testing (MT) for surface and near-surface cracks, especially at weld toes where thermal gradients are most severe
• Ultrasonic testing (UT) with contact probes at 5 MHz for subsurface porosity and lack of fusion in multi-pass welds
• Hardness mapping across the cladding thickness to verify uniform deposition and detect dilution zones

Application Recommendations

Based on the study findings and my engineering experience, La2O3-modified wear-resistant cladding electrodes are most suitable for the following applications:

1. Crusher hammers and liners in mineral processing plants where abrasive wear against hard ore is the dominant failure mode
2. Cement mill liners and grinding rings subjected to both abrasion and impact
3. Slurry pump impellers and casing components in slurry handling systems
4. Excavator bucket teeth and dozer blade tips in construction and mining

The modification is less suitable for applications involving erosion-corrosion in acidic environments or for components requiring high low-temperature toughness, as the rare earth addition does not significantly improve corrosion resistance and may marginally reduce impact energy at sub-zero temperatures.

Key Questions and Reflections

One question that arises from this study is the long-term stability of the grain-refining effect. La2O3 is known to be hygroscopic, and its effectiveness may degrade if the electrode flux is exposed to moisture during storage. In production environments, strict control of electrode baking temperature (typically 300–350°C for 2 hours) and storage humidity are essential to maintain consistent performance.

Another consideration is the cost-benefit analysis. Rare earth oxides, while not extremely expensive, do add to the electrode manufacturing cost. The 43% improvement in wear life at the optimal La2O3 level must be weighed against the incremental material cost and any potential impact on production rate. In my assessment, for high-value components where downtime for relining is expensive, the La2O3 modification is clearly justified.

Study Insights and Conclusions

This study demonstrates that lanthanum oxide is a highly effective micro-alloying addition for wear-resistant cladding electrodes, with an optimal concentration around 0.8 wt% providing significant improvements in hardness, microstructural refinement, and abrasive wear resistance. The engineering implementation requires attention to flux moisture control, welding parameter optimization, and appropriate NDT protocols. For practitioners in the surface engineering field, this work provides a clear pathway to extending component service life through a relatively simple flux modification, and the underlying metallurgical principles of rare earth grain refinement are broadly applicable to other cladding and overlay systems.