Zhuojin Pipe Fitting Co., LtdCurrent Status of Nitrogen Alloying in Wear-Resistant Surfacing Materials
Literature Overview
This 2012 review paper by Liu Yue and colleagues from Henan University of Science and Technology provides a comprehensive overview of nitrogen alloying in wear-resistant surfacing materials. The work examines nitrogen content evolution during welding, carbide and nitride precipitation behavior, strengthening mechanisms, and the influence of nitrogen on hardness, high-temperature wear resistance, corrosion resistance, and tensile strength of surfacing layers.
Core Technical Content
Nitrogen Behavior During Welding
Nitrogen is a reactive gas that readily dissolves in molten steel and nickel-based alloys. During surfacing welding, nitrogen content in the deposited layer is influenced by:
- Base metal nitrogen content
- Filler metal composition and nitrogen retention
- Shielding gas composition (nitrogen-containing shields increase content; pure inert gases allow some pickup from atmosphere)
- Welding process type (submerged arc welding has lower nitrogen pickup than GMAW)
- Solidification rate and cooling conditions
| Welding Process | Typical N Content in Surfacing Layer | Shielding Condition |
|---|---|---|
| SMAW (basic flux) | 0.01–0.03% | Flux protection |
| GMAW (Ar) | 0.02–0.05% | Pure argon |
| GMAW (Ar + 5% N₂) | 0.05–0.15% | Nitrogen-containing |
| SAW (flux-cored) | 0.02–0.08% | Flux protection |
| Flux-cored wire with N addition | 0.10–0.30% | Intentional alloying |
Precipitation Behavior of Carbonitrides
The formation of carbonitrides (Cr₇C₃, Cr₄C, Cr₂N, Cr₇C₃₋ₓNₓ) in nitrogen-alloyed surfacing layers follows specific precipitation sequences depending on composition and cooling rate:
- High-temperature phase: Cr₇C₃-type complex cubic carbide precipitates first during solidification
- Medium-temperature phase: Cr₄C and Cr₂₃C₆ may form during cooling
- Low-temperature phase: CrN and Cr₂N precipitate during final cooling or subsequent tempering
The morphology of these precipitates—spherical, plate-like, or network-type—directly affects wear resistance and toughness.
Strengthening Mechanisms
Nitrogen alloying contributes to wear resistance through multiple mechanisms:
- Solid solution strengthening: Nitrogen atoms in interstitial sites distort the crystal lattice, increasing dislocation resistance
- Precipitation strengthening: Fine, dispersed carbonitride particles impede dislocation motion
- Grain refinement: Nitrogen can act as a grain refiner during solidification
- Transformation strengthening: Nitrogen stabilizes certain metastable phases that transform during cooling
Performance Characteristics
Hardness and Wear Resistance
| Nitrogen Content | Hardness (HV) | Dry Wear Rate (mg/1000m) | Application |
|---|---|---|---|
| 0.02% (baseline) | 400–450 | 80–120 | General wear |
| 0.05% | 500–550 | 50–80 | Moderate wear |
| 0.10% | 550–650 | 30–60 | High wear |
| 0.20% | 650–750 | 15–40 | Severe wear |
| 0.30% | 700–800 | 10–30 | Extreme wear |
High-Temperature Performance
Nitrogen-alloyed surfacing layers maintain hardness at elevated temperatures better than conventional carbide-only overlays due to the higher melting point of nitride phases. At 600 °C, nitrogen-alloyed layers typically retain 80–85% of room-temperature hardness, compared to 60–70% for conventional high-carbon overlays.
Corrosion Resistance Considerations
Excessive nitrogen content can degrade corrosion resistance by promoting pitting in chloride environments. The optimal nitrogen content for combined wear and corrosion resistance is typically 0.05–0.15%, depending on the base alloy composition.
Engineering Applications and Selection Criteria
Nitrogen-alloyed surfacing materials are particularly suitable for:
- Mining equipment components (shovel buckets, conveyor rollers)
- Cement mill liners and grinding media
- Coal handling equipment
- Agricultural machinery (plowshares, seed drills)
- High-temperature wear applications (kiln liners, furnace components)
Selection Guidelines
- For applications requiring hardness above 700 HV with moderate toughness, select nitrogen content of 0.15–0.25%
- For combined wear and corrosion resistance, limit nitrogen to 0.05–0.10%
- For high-temperature applications above 500 °C, nitrogen content of 0.10–0.20% provides optimal performance
- For applications requiring good weldability and low cracking susceptibility, keep nitrogen below 0.10%
Study Insights and Development Outlook
The review clearly establishes nitrogen alloying as a promising direction for developing next-generation wear-resistant surfacing materials. The key advantage is the ability to achieve high hardness without the brittleness associated with high-carbon systems. However, several challenges remain:
- Controlling nitrogen content uniformly throughout multi-layer deposits
- Preventing nitrogen loss during high-temperature service
- Developing welding consumables with stable nitrogen retention
- Establishing standardized testing protocols for nitrogen-alloyed overlays
The field is moving toward composite approaches that combine nitrogen alloying with other strengthening elements (Ti, Al, Si) to achieve synergistic effects. Future developments should focus on optimizing the carbon-to-nitrogen ratio for specific service conditions and developing process windows that ensure consistent nitrogen distribution in production welding.