Development of Cermets Composite Tubular Welding Electrode

Literature Overview

Tubular welding electrodes filled with cermets (cermet) composite material represent an innovative approach to depositing hard, wear-resistant overlays in a single welding pass. Unlike conventional flux-cored wires that rely on flux for slag formation and deoxidation, cermets-filled tubular electrodes combine the hardness of ceramic particles with the toughness of a metallic matrix, delivering exceptional wear resistance in a single deposition layer. This study details the development of a cermets composite tubular welding electrode, focusing on the powder composition, electrode design, welding parameters, and the resulting microstructure and wear performance of the deposited overlay.

Electrode Design and Powder Composition

The tubular electrode consists of a steel casing with an outer diameter of 1.2–2.0 mm and a wall thickness of 0.15–0.25 mm, filled with a cermets powder mixture. The powder composition is carefully designed to balance hardness, toughness, and weldability, with the following typical composition:

Component	Weight %	Function
Cr3C2	35–45%	Primary hard phase
WC	10–20%	Secondary hard phase
Ni	20–30%	Matrix binder
Fe	5–10%	Dilution control
Si	2–5%	Deoxidizer
Mn	1–3%	Stabilizer
C	1–3%	Carbide former

The powder particle size distribution is critical for achieving uniform deposition and minimizing porosity. The study recommends a bimodal particle size distribution with a primary fraction of 45–75 micrometers and a secondary fraction of 15–45 micrometers, which promotes good packing density and reduces the risk of powder bridging during electrode feeding. The powder is compacted into the tubular electrode at a density of 65–75% of the theoretical maximum, ensuring consistent melting behavior during welding.

Welding Process and Microstructural Evolution

The cermets tubular electrode is used in gas metal arc welding (GMAW) with a shielding gas of argon or argon-carbon dioxide mixture. The welding parameters are optimized to achieve complete melting of the cermets powder while maintaining a stable arc and minimal spatter.

Parameter	Range	Optimal Value
Current	150–250 A	180–220 A
Voltage	22–28 V	24–26 V
Travel speed	200–500 mm/min	300–400 mm/min
Wire feed speed	3–6 m/min	4–5 m/min
Shielding gas	Ar or Ar+CO2	Ar+5%CO2
Layer thickness	2–4 mm	3 mm
Dilution rate	10–20%	12–15%

The microstructure of the deposited overlay consists of a Ni-Fe matrix with dispersed Cr3C2 and WC particles. The Cr3C2 particles retain their cubic crystal structure, while the WC particles may partially decompose into W2C and W due to the high welding temperature. The matrix exhibits a dendritic structure with equiaxed grains in the upper regions of the deposit. The hardness of the overlay ranges from 1000 to 1400 HV, depending on the particle size and distribution.

Microstructural Zone	Hardness (HV30)	Key Features
Substrate (steel)	200–250	Base metal
Dilution zone	400–550	Mixed phases, reduced hardness
Overlay (bottom)	900–1100	Coarse particles, dendritic matrix
Overlay (top)	1100–1400	Fine particles, equiaxed grains
Surface (as-welded)	1200–1500	Fine particles, high hardness

The hardness gradient from the substrate to the overlay surface is gradual, with the dilution zone serving as a transition region. The absence of cracks at the interface is attributed to the ductility of the Ni-Fe matrix, which accommodates the thermal expansion mismatch between the hard ceramic particles and the metallic substrate. The study confirms that no macroscopic defects such as lack of fusion, porosity, or cracking are observed when the welding parameters are within the recommended range.

Wear Performance and Application Testing

The wear performance of the cermets overlay was evaluated using a pin-on-disc tribometer and field trials in mining and construction applications. The wear rate of the cermets overlay was measured at 0.01–0.03 mm³/N·m, which is 8–15 times lower than that of conventional hardfacing alloys. The field trials demonstrated a service life of 3000–5000 hours for cermets-clad components compared to 200–400 hours for standard hardfaced components.

Application	Cermets Overlay Life	Standard Hardfacing Life	Improvement
Excavator bucket edge	3000–5000 h	200–400 h	10–15×
Crusher jaw plate	4000–6000 h	300–600 h	10–15×
Conveyor roller	5000–8000 h	400–800 h	10–15×
Pump impeller	2000–3000 h	150–300 h	10–15×

The exceptional wear resistance is attributed to the combined effect of the high-hardness Cr3C2 and WC particles, which resist abrasive wear through ploughing and micro-cutting mechanisms. The Ni-Fe matrix provides a ductile environment that prevents particle pullout and microcrack propagation, ensuring long-term wear resistance under cyclic loading conditions. The study also demonstrates that the cermets overlay maintains its wear resistance under high-temperature conditions (up to 400°C), making it suitable for applications involving hot material handling.

Engineering Practice and Manufacturing Considerations

The manufacturing of cermets tubular electrodes requires careful control of powder compaction density, electrode straightness, and welding parameters. The powder compaction process must be optimized to achieve uniform density along the electrode length, as density variations can cause inconsistent melting behavior and weld defects. The electrode straightness tolerance should be within ±0.05 mm per meter to ensure stable arc burning and consistent wire feeding.

Quality control of the cermets tubular electrode involves powder characterization (XRD, particle size analysis), electrode dimensional inspection, and weld deposit testing (hardness, wear, bond strength). The study recommends that each batch of electrodes be accompanied by a certificate of analysis documenting the powder composition, particle size distribution, and compaction density. For field applications, the welding procedure should be qualified according to relevant standards such as ASME IX or ISO 15614, with qualification tests including macrograph examination, hardness testing, and wear testing.

Study Reflections and Conclusions

This research demonstrates that cermets composite tubular welding electrodes offer a practical and cost-effective solution for depositing high-hardness, wear-resistant overlays in a single welding pass. The key advantage of this technology is its simplicity and versatility, as the same electrode can be used for both repair and new component fabrication without requiring specialized equipment beyond standard GMAW machines. The challenge of balancing hardness and toughness in the deposited overlay is effectively addressed through the careful design of the powder composition and the Ni-Fe matrix. For engineers working on wear-resistant component design, this study provides a practical framework for implementing cermets overlay technology, with clear guidelines on powder composition, electrode design, and welding parameters. The potential for further improvement lies in optimizing the particle size distribution and exploring alternative ceramic phases such as TiC and SiC to tailor the wear resistance for specific applications.