Zhuojin Pipe Fitting Co., LtdTiC-VC No-Preheat Wear-Resistant Surfacing Welding Electrode Development
Literature Overview
This paper by Wang Xinhong and colleagues from Shandong University, published in Transactions of the China Welding Institution (Volume 23, Issue 4, 2002, pp. 31-34), presents the development of a novel wear-resistant surfacing welding electrode that produces TiC-VC reinforced deposits without requiring preheat treatment. The research was supported by the Shandong Provincial Natural Science Foundation (Z2000F02). The work addresses a critical practical challenge in hardfacing welding: achieving high wear resistance while maintaining good weldability on carbon steel substrates without preheating.
Core Technical Content
Electrode Design Philosophy
The electrode is designed based on the following principles:
- H08A wire core: Low-carbon steel wire providing good weldability and low hydrogen sensitivity
- Flux composition: Ti-Fe alloy, V-Fe alloy, synthetic rutile, and graphite as key alloying and carbide-forming elements
- In-situ carbide formation: TiC and VC are formed during arc melting through reaction between Ti-Fe, V-Fe, and graphite in the molten flux pool
- No-preheat capability: The flux formulation is designed to minimize cracking sensitivity without requiring preheat temperatures
Flux Composition and Its Effects
| Flux Component | Function | Typical Content |
|---|---|---|
| Ti-Fe alloy | TiC formation, deoxidation | 10-18% |
| V-Fe alloy | VC formation, deoxidation | 5-15% |
| Synthetic rutile | Flux stability, slag properties | 30-40% |
| Graphite | Carbon source for carbide formation | 5-12% |
| Other components | Bonding, desulfurization, arc stabilization | Balance |
Microstructure of Cladding Layer
The cladding layer produced by this electrode exhibits:
- Matrix: Low-carbon martensite + retained austenite
- Hard phases: TiC (cubic, space group Fm-3m) and VC (cubic, space group Fm-3m)
- Distribution: TiC and VC particles are uniformly dispersed in the martensitic matrix
- Particle size: Typically 1-10 μm, depending on cooling rate and composition
Performance Characteristics
Hardness and Wear Resistance
| Ti-Fe Content | V-Fe Content | Graphite Content | Hardness (HRC) | Wear Loss (mg) | Electrode Performance |
|---|---|---|---|---|---|
| 10% | 8% | 6% | 58-60 | 120-130 | Good |
| 14% | 10% | 8% | 62-64 | 85-95 | Good |
| 18% | 12% | 10% | 65-67 | 60-70 | Acceptable |
| 18% | 12% | 12% | 67-69 | 50-60 | Marginal |
| 18% | 12% | >12% | 68-70 | 45-55 | Poor |
Critical Composition Limits
The paper identifies important composition limits:
- Ti-Fe content: Above 18%, electrode process performance degrades significantly (arc stability, slag fluidity, spatter increase)
- Graphite content: Above 12%, adverse effects on electrode performance become pronounced (excessive CO gas evolution, slag foaming, poor arc stability)
Crack Resistance
The no-preheat capability is achieved through:
- Low carbon wire core (H08A, 0.08% C) reduces hydrogen-induced cracking risk
- Ti and V act as strong deoxidizers, reducing oxygen content in the weld metal
- Retained austenite in the matrix provides strain accommodation during cooling
- TiC and VC particles are relatively ductile compared to WC, reducing stress concentration
- The martensitic matrix has moderate ductility due to low carbon content
Metallurgical Analysis
Carbide Formation Reactions
During the welding arc process, the following reactions occur in the molten flux pool:
- Ti-Fe → Ti + Fe (dissolution in molten pool)
- V-Fe → V + Fe (dissolution in molten pool)
- C (from graphite) dissolves into molten pool
- Ti + C → TiC (nucleation and growth during solidification)
- V + C → VC (nucleation and growth during solidification)
The reactions occur at arc temperatures of 5000-7000 K in the flux pool, with carbide nucleation beginning during solidification of the weld metal.
Phase Stability
| Phase | Lattice Type | Melting Point (°C) | Hardness (HV) | Thermal Stability |
|---|---|---|---|---|
| TiC | FCC (NaCl type) | 3140 | 2000-2500 | Excellent |
| VC | FCC (NaCl type) | 2830 | 1500-1800 | Excellent |
| WC | HCP | 2870 | 2200-2500 | Excellent |
| M₇C₃ | Orthorhombic | 1350-1500 | 1200-1400 | Moderate |
The high melting points and thermal stability of TiC and VC make them suitable for high-temperature wear applications, potentially offering advantages over M₇C₃-type carbides in terms of thermal stability.
Engineering Practice Considerations
Application Suitability
| Application | Suitability | Notes |
|---|---|---|
| Mining equipment (shovel teeth) | Excellent | Abrasive wear, no preheat needed in field |
| Cement industry (grinding mills) | Very good | High wear, limited preheat capability |
| Agricultural machinery | Good | Field repair conditions, no preheat |
| Steel mill wear parts | Good | Moderate temperature service |
| High-temperature furnace parts | Limited | Matrix softens above 400°C |
| Corrosive environments | Poor | Not designed for corrosion resistance |
Welding Procedure Parameters
| Parameter | Recommended Value | Notes |
|---|---|---|
| Current type | DCEP (DC electrode positive) | Maximum penetration for surfacing |
| Current range | 180-280 A | Depends on electrode diameter (3.2-4.0 mm) |
| Travel speed | 150-250 mm/min | Balance deposition rate and dilution |
| Arc length | 3-5 mm | Short arc for stability |
| Preheat | Not required | Key advantage of this electrode |
| Interpass temperature | < 300°C | To prevent excessive retained austenite |
| Layer thickness | 3-5 mm per pass | Multiple passes for thicker deposits |
Key Questions and Reflections
The development of this no-preheat electrode addresses a significant practical need in field repair and maintenance welding. Several observations and questions arise:
- TiC vs. VC contribution: The paper does not clearly differentiate the relative contributions of TiC and VC to overall wear resistance. Further research with systematic variation of Ti:C and V:C ratios would be valuable.
- Retained austenite stability: The retained austenite content may transform during service (especially at elevated temperatures or under cyclic loading), potentially affecting dimensional stability and hardness.
- Comparison with modern alternatives: Since 2002, significant advances have been made in hardfacing electrode technology. This work represents an early contribution to the field of in-situ carbide formation in SMAW surfacing.
- Microstructural evolution during service: The martensitic matrix may undergo tempering during prolonged service at moderate temperatures, which would reduce matrix hardness but potentially improve toughness.
Study Insights and Implications
This research demonstrates the viability of producing TiC-VC reinforced hardfacing deposits using conventional SMAW electrodes without preheat requirements. The approach is particularly valuable for field applications where preheating is impractical or impossible. The in-situ formation of hard carbide phases during the welding process eliminates the need for expensive composite powders and specialized equipment. For steel pipe and fitting repair applications, electrodes of this type offer a practical solution for protecting wear-critical areas (valve seats, pump impellers, slurry pipe fittings) with minimal pre-weld preparation. The identified composition limits (Ti-Fe ≤ 18%, graphite ≤ 12%) provide clear guidelines for electrode design optimization, balancing wear resistance against processability.