Study Note on TiC-VC Based Abrasion Resistant Overlay Welding Electrodes

Overview of the Literature

This paper investigates the development of a composite overlay welding electrode incorporating TiC and VC carbide reinforcements to achieve enhanced resistance against abrasive wear. The research is grounded in the well-established principle that hard ceramic carbides dispersed within a tough metallic matrix can dramatically improve tribological performance. The authors examined the microstructure evolution, hardness distribution, and wear test results of the deposited overlay layers, comparing them against conventional high-carbon steel overlay deposits. The work is particularly relevant for engineers dealing with high-abrasion environments such as mining equipment, cement mill liners, and material handling conveyors.

Core Technical Content

The fundamental approach involves blending TiC and VC powders into the flux coating of a standard overlay welding electrode. The selection of both TiC and VC, rather than a single carbide type, is based on their complementary properties. TiC offers high hardness (approximately 2500 HV) and excellent thermal stability, while VC provides good bonding characteristics with iron-based matrices and contributes to crack resistance. The combined use aims to balance hardness with toughness, avoiding the brittleness often associated with pure TiC systems.

The welding process employed is shielded metal arc welding (SMAW) using the developed composite electrode. The heat input during SMAW is relatively moderate, which allows the carbide particles to survive the melting zone without complete dissolution. The flux coating serves a dual purpose: it provides arc stability and gas shielding, and it acts as a carrier for the carbide particles, ensuring uniform distribution within the deposited metal.

The microstructure of the deposited overlay layer typically exhibits a eutectic cellular structure. The carbide particles, both primary TiC and VC particles and secondary carbides formed during solidification (such as M7C3 and M23C6 type carbides), form a network that impedes dislocation motion and resists material removal during abrasion. The matrix surrounding the carbides is generally an austenite-ferrite dual-phase structure, which provides adequate toughness to prevent catastrophic brittle fracture.

Microstructural Analysis and Hardness Distribution

The authors conducted metallographic examination using optical microscopy and scanning electron microscopy (SEM) to characterize the microstructure. The SEM images reveal that TiC particles are predominantly located at cell boundaries, while VC particles tend to be more randomly distributed within the matrix. This spatial distribution is significant because TiC at cell boundaries creates a more continuous barrier against abrasive particle intrusion.

The hardness profile across the overlay layer depth shows a characteristic gradient. Near the surface, where carbide concentration is highest, hardness reaches 1000-1200 HV. At the bond line region, hardness decreases to approximately 450-550 HV due to dilution with the base metal and reduced carbide concentration. The bond strength, measured by bend test, remains above 350 MPa, indicating adequate metallurgical bonding between the overlay and the substrate.

Engineering Practice Considerations

In practical application, several factors must be considered when deploying TiC-VC composite overlay electrodes. First, the welding sequence should ensure that the first layer (the bond layer) uses a compatible transition material such as a medium-carbon or austenitic stainless steel electrode to minimize dilution and reduce the risk of cracking at the bond line. Subsequent overlay layers can then use the TiC-VC composite electrode to build up the desired thickness and hardness.

The welding parameters are critical. Excessive heat input causes carbide dissolution and coarsening, reducing the number of hard phase particles per unit area. The recommended current density for these composite electrodes is 12-18 A/mm², with a travel speed of 25-45 cm/min. Preheating the base plate to 100-150°C is advisable when welding thick sections to prevent hydrogen-induced cracking, particularly when the base metal has higher carbon equivalent values.

A key insight from this work is that the optimal carbide particle size for abrasion resistance falls in the range of 10-50 μm. Particles smaller than 10 μm tend to dissolve during welding, while particles larger than 50 μm create stress concentration points and reduce the effective load-bearing cross-section of the matrix. The authors achieved good results with a bimodal particle size distribution, combining fine particles (5-15 μm) for matrix strengthening and coarse particles (20-45 μm) for direct abrasive resistance.

Defect Analysis and Countermeasures

The most common defects observed in TiC-VC overlay deposits include carbide cracking, porosity, and incomplete fusion at the bond line. Carbide cracking occurs when the thermal contraction mismatch between the brittle carbide particles and the ductile matrix exceeds the matrix's strain capacity. This can be mitigated by controlling the carbon content in the base metal, using a ductile transition layer, and ensuring adequate interpass temperature control.

Porosity is often caused by insufficient arc shielding or moisture in the flux coating. In field conditions, wind exposure can compromise the shielding gas blanket produced by the flux. Countermeasures include using a wind shield, pre-drying the electrode at 300-350°C for 1-2 hours, and maintaining the electrode in a storage oven between uses. Incomplete fusion at the bond line is typically a result of inadequate base metal cleaning or insufficient penetration current. Thorough surface preparation, including grinding to bare metal within 25 mm of the weld, is essential.

Study Insights and Implications

This research demonstrates that the strategic combination of TiC and VC in a single composite electrode can achieve a superior balance of hardness and toughness compared to single-carbide systems. The engineering implication is significant: rather than developing separate electrodes for different carbide types and applying them in alternating layers (which increases labor and cost), a single composite electrode simplifies the welding procedure and reduces the risk of interlayer incompatibility.

The work also highlights an important principle in overlay welding design: the wear resistance of a composite deposit is not simply proportional to the carbide content. Beyond a critical concentration (approximately 15-18 wt% combined TiC+VC), further addition of carbides leads to increased brittleness and reduced service life due to spalling. This finding underscores the importance of optimizing the carbide-to-matrix ratio through systematic trial welding rather than simply maximizing the hard phase content.

The practical value of this research extends to the development of specialized electrodes for specific service environments. For example, in applications involving both abrasive and adhesive wear (such as slurry pumps), the TiC-VC system provides better resistance than pure VC systems because TiC's higher thermal stability prevents the formation of a ductile debris film that would otherwise accelerate adhesive wear. Engineers should consider these factors when selecting overlay materials for complex tribological environments.

In conclusion, the TiC-VC composite overlay welding electrode represents a practical and economical solution for enhancing abrasion resistance in industrial equipment. The key to successful implementation lies in proper welding procedure control, careful selection of transition layers, and an understanding of the fundamental relationship between carbide distribution and tribological performance. This research provides a solid foundation for further development of multi-carbide composite electrodes tailored to specific service conditions.