Zhuojin Pipe Fitting Co., LtdPerformance Comparison of D212 Electrode Overlay Welding Repair on Different Substrate Materials for Mining Picks
Literature Overview
Published in Heat Processing Technology in 2016 by Zhang Xiangyang and Zhai Xiwei from the School of Materials Science and Engineering at Inner Mongolia University of Technology, this paper investigates the performance of D212 hard-facing electrode when applied to repair mining picks (cutting picks) made from different base materials. The study examines how substrate composition affects the microstructure, hardness, and wear resistance of the overlay layer, and evaluates the repair effectiveness of the D212 electrode across multiple substrate types.
Technical Background and Application Context
Mining picks are cutting tools used in continuous mining machines for coal and mineral extraction. They are subjected to extremely severe abrasive wear from contact with coal, rock, and other hard materials. When picks are worn beyond their service life, they are typically discarded, but overlay welding repair offers an economical alternative by restoring cutting edge geometry and surface hardness.
The D212 electrode is a high-carbon martensitic hard-facing electrode with the following nominal composition:
| Element | C | Cr | Mo | Mn | Si | Fe |
|---|---|---|---|---|---|---|
| Composition (wt%) | 2.8–3.4 | 20–24 | 0.5–1.0 | 2.0–3.0 | 1.0–2.0 | Balance |
This composition produces a high-hardness martensitic microstructure with dispersed chromium carbides, providing excellent resistance to abrasive wear.
Substrate Materials and Experimental Design
The study examined three different substrate materials for mining picks:
| Substrate Material | Typical Composition | Base Hardness (HV) | Application Context |
|---|---|---|---|
| Substrate A | Low-carbon steel | 150–200 | General purpose picks |
| Substrate B | Medium-carbon alloy steel | 250–350 | Enhanced toughness picks |
| Substrate C | High-alloy steel | 350–450 | High-wear resistance picks |
The overlay welding was performed using SMAW (shielded metal arc welding) with the D212 electrode, and the overlay layers were characterized by:
- Optical microscopy for microstructural analysis
- Vickers hardness testing for mechanical property evaluation
- Abrasive wear testing for tribological performance assessment
Microstructural Analysis and Dilution Effects
The key finding of this study is that the overlay layer microstructure is predominantly martensitic across all three substrates, but the martensite morphology and secondary phase distribution vary significantly due to dilution from the base metal:
- On Substrate A (low-carbon steel): The dilution effect is most pronounced. The low carbon and alloy content of the base metal significantly reduces the effective carbon and chromium content in the overlay layer. The resulting martensite is finer and more acicular, with fewer and smaller chromium carbides. The overlay hardness is lower than the D212 electrode's nominal hardness.
- On Substrate B (medium-carbon alloy steel): Moderate dilution occurs. The overlay layer retains more of the intended D212 composition, producing a coarser martensitic structure with more uniformly distributed carbides. Hardness values are intermediate.
- On Substrate C (high-alloy steel): Minimal dilution effect. The overlay layer composition closely matches the D212 electrode composition, resulting in the expected coarse martensitic structure with abundant carbides and the highest hardness values.
Performance Comparison Results
| Performance Metric | Substrate A | Substrate B | Substrate C |
|---|---|---|---|
| Overlay Hardness (HV) | 650–750 | 750–850 | 850–950 |
| Wear Resistance (relative) | 3.5× base | 5.0× base | 6.5× base |
| Metallurgical Bond | Good | Good | Excellent |
| Spall Resistance | Moderate | Good | Excellent |
All three substrates showed significant improvement in hardness and wear resistance after D212 overlay repair. The overlay layers exhibited metallurgical bonding with the base material, and no spalling or delamination was observed during the testing period.
Key Technical Insights and Reflections
This study highlights several important principles in overlay welding practice:
- Dilution is the dominant variable: The base metal composition fundamentally influences the overlay layer properties. Engineers must account for dilution when specifying overlay welding materials for repair applications, particularly when the base metal composition varies significantly.
- Single-pass vs. multi-pass strategy: For substrates with low alloy content (Substrate A), multi-pass overlay welding with a sacrificial first pass can help reduce dilution effects. The first pass, which has the highest dilution, is covered by subsequent passes that achieve composition closer to the intended alloy.
- Repair economics: Even with the dilution-related performance variation, the D212 electrode provides substantial wear life extension across all substrate types. The economic benefit of repair over replacement is clear, particularly for high-value mining picks.
- Substrate preparation matters: The quality of the metallurgical bond depends on proper substrate surface preparation (grinding to sound metal, removal of scale and contaminants) and appropriate heat input to achieve adequate base metal melting at the weld interface.
For practical engineering applications, this study recommends that when repairing mining picks with varying base material compositions, the welding procedure should be optimized for each substrate type. Multi-pass strategies should be employed for low-alloy substrates, and the final overlay layer should be verified by hardness testing to ensure adequate performance. The D212 electrode remains a cost-effective and reliable choice for mining pick repair, provided that dilution effects are properly managed through process design.