Zhuojin Pipe Fitting Co., LtdDevelopment of TiC Crack-Resistant Surfacing Welding Electrode
Literature Overview
This paper by Zou Yong and Zou Zengda from Shandong University of Technology, published in "China Mechanical Engineering" in 1996, describes the development of a novel surfacing welding electrode that produces a deposit containing titanium carbide (TiC) particles. The electrode uses H08A carbon steel wire as the core and a flux formulation containing iron-titanium alloy (Fe-Ti), titanium dioxide (TiO2), and graphite. Through arc metallurgical reactions during welding, TiC and other ultra-hard particles precipitate in the surfacing layer, providing high wear resistance combined with excellent crack resistance. The work was supported by the Shandong Provincial Natural Science Foundation and represents a significant innovation in surfacing electrode design.
Metallurgical Design and Arc Reaction Mechanism
The electrode design is based on a sophisticated understanding of arc metallurgy. The key principle is that the TiC particles are not pre-mixed into the flux as a raw material but are formed in situ through arc reactions. The following reactions occur during welding:
- Titanium reduction: TiO2 in the flux is reduced by carbon (from graphite and the H08A wire) to metallic titanium:
- TiO2 + 2C → Ti + 2CO
- Titanium carbide formation: The metallic titanium reacts with carbon to form TiC:
- Ti + C → TiC
- Fe-Ti alloy contribution: The Fe-Ti alloy in the flux provides additional titanium that participates in carbide formation, while the iron acts as a diluent and helps control the overall composition of the weld metal.
The arc temperature, which can reach 5000-6000 K at the arc root, provides sufficient energy for these reactions to proceed. The rapid cooling of the weld pool then traps the TiC particles in the solidifying microstructure. The size, distribution, and morphology of the TiC particles are determined by the cooling rate and the local composition in the weld pool.
| Electrode Component | Role in Arc Metallurgy | Effect on Weld Metal |
|---|---|---|
| H08A wire | Base metal, carbon source | Provides iron matrix and carbon for TiC formation |
| Fe-Ti alloy | Titanium source | Supplies titanium for carbide precipitation |
| TiO2 | Titanium source, fluxing agent | Reduces to Ti, promotes TiC formation |
| Graphite | Carbon source, deoxidizer | Provides carbon for TiC, reduces weld metal oxygen |
| Flux binder | Electrode integrity | Ensures uniform arc burning |
Performance Characteristics and Comparative Analysis
The resulting surfacing layer exhibits a combination of properties that is difficult to achieve with conventional surfacing electrodes. The following table compares the performance of the TiC electrode with conventional hardfacing electrodes:
| Property | TiC Electrode Deposit | Conventional Hardfacing (Cr-C) | Conventional Hardfacing (Co-based) |
|---|---|---|---|
| Hardness (HV) | 1200-1500 | 800-1100 | 450-600 |
| Wear resistance | Excellent | Good | Moderate |
| Crack resistance | Excellent | Poor | Moderate |
| Ductility | Good | Very poor | Poor |
| Cost | Low | Moderate | Very high |
| Welding consumable type | SMAW | SMAW | SMAW/TIG |
The exceptional crack resistance of the TiC deposit is attributed to several factors. First, the TiC particles act as crack arrestors, deflecting crack propagation and requiring additional energy for crack extension. Second, the matrix surrounding the TiC particles is a tempered martensite or bainitic structure with adequate toughness. Third, the TiC particles are relatively small and uniformly distributed, avoiding the stress concentration effects associated with large, coarse carbide clusters.
The wear resistance is primarily due to the extreme hardness of TiC (HV approximately 2800) and its stability at elevated temperatures. TiC does not undergo significant softening below 1000°C, making it suitable for applications involving frictional heating.
Engineering Application and Practical Considerations
The TiC electrode is particularly suitable for the following applications:
- Mining equipment: Crusher jaws, shovel teeth, and conveyor rollers that experience severe abrasive wear.
- Cement industry: Mill liners, kiln wear plates, and slide plates that are subjected to both abrasive and impact loading.
- Agricultural machinery: Plowshares, seed drills, and harvesting equipment components that operate in abrasive soil conditions.
- Construction equipment: Bucket teeth, blade edges, and track components that experience combined wear and impact.
Practical welding considerations include:
- Preheating: Although the electrode has excellent crack resistance, preheating to 100-150°C is recommended for thick sections to minimize the risk of base metal cracking.
- Welding position: The electrode is suitable for all positions but performs best in flat and horizontal positions where the molten pool can be controlled effectively.
- Layer thickness: Each layer should be deposited to a thickness of 3-5 mm. Thicker layers may result in incomplete TiC precipitation due to insufficient cooling rate.
- Interpass temperature: Maintain interpass temperature below 200°C to ensure adequate cooling rate for TiC particle formation.
- Electrode storage: The electrode should be stored in a dry environment. The flux is somewhat hygroscopic, and moisture absorption can lead to hydrogen-induced cracking.
This work represents a genuine innovation in surfacing electrode design, demonstrating that the in-situ formation of hard particles through arc metallurgy can produce deposits with superior combined properties compared to pre-mixed hardfacing electrodes. The approach is cost-effective, uses readily available raw materials, and produces a consumable that can be manufactured with existing electrode production equipment.