Development of Titanium Carbide Crack-Resistant Overlay Welding Electrode

Literature Overview and Technical Motivation

This paper by Zou Yong and Zou Zengda, published in China Mechanical Engineering in 1996, reports on the development of a novel overlay welding electrode that incorporates titanium carbide (TiC) hard particles in the weld deposit. The electrode uses an H08A mild steel core with a special flux composition containing Fe-Ti alloy, TiO2, and graphite. Through arc metallurgical reactions, TiC particles are precipitated in the weld deposit, providing exceptional wear resistance and crack resistance. This represents a significant breakthrough in overlay welding electrode design, combining wear resistance with processability at a low cost.

Technical Background on Wear-Resistant Overlay Welding

Wear-resistant overlay welding is widely used in applications where components are subjected to severe abrasive or erosive wear, such as mining equipment, cement mill liners, crusher hammers, and pump impellers. The primary challenge in wear-resistant overlay welding is achieving a balance between hardness (for wear resistance) and toughness (for crack resistance). Conventional hardfacing electrodes often produce martensitic or carbide-rich deposits that are extremely hard but brittle, leading to cracking during welding or in service.

The TiC-based electrode addresses this challenge through a unique metallurgical approach:

Feature	Conventional Hardfacing Electrode	TiC-Based Electrode (This Study)
Hard phase	Cementite (Fe3C), Cr7C3, Cr23C6	TiC, TiN, Fe3C
Hardness	50-65 HRC	55-70 HRC
Toughness	Low, brittle	Improved, crack-resistant
Weldability	Poor, high cracking tendency	Good, low cracking tendency
Cost	High (Cr, Ni, Mo)	Low (Ti, Fe, C)
Application	Severe wear, low impact	Moderate to severe wear, some impact

Electrode Design and Metallurgy

Electrode Composition

The electrode design is based on the principle of arc metallurgy, where the flux components react with the arc plasma and the molten metal to produce the desired hard phases. The key components and their functions are:

Component	Function	Typical Content
H08A steel core	Base metal for weld deposit	70-75% of electrode weight
Fe-Ti alloy	Titanium source for TiC formation	5-10%
TiO2	Titanium oxide, stabilizer, deoxidizer	3-5%
Graphite	Carbon source for TiC and Fe3C	2-4%
CaF2	Arc stabilizer, slag former	5-8%
SiO2, Al2O3	Slag former, flux	3-5%
Other minor elements	Process modifiers	1-3%

Arc Metallurgy and TiC Formation

The formation of TiC in the weld deposit occurs through a series of arc metallurgical reactions:

TiO2 + C → TiC + CO (reduction of titanium oxide by carbon)
Fe-Ti + C → TiC + Fe (direct reaction of titanium alloy with carbon)
Ti + C → TiC (reaction of titanium with carbon in the molten pool)

The resulting TiC particles are extremely hard (2800-3200 HV) and have a high melting point (3140°C), making them highly effective wear-resistant phases. The TiC particles are distributed throughout the weld deposit matrix, which consists primarily of martensite with some retained austenite.

Microstructural Characteristics

The microstructure of the TiC-based overlay weld deposit consists of:

Matrix: Martensite with retained austenite (30-40% austenite)
Hard particles: TiC (primary), Fe3C (secondary), TiN (minor)
Particle size: 5-50 μm for TiC, 2-10 μm for Fe3C
Particle distribution: Uniform throughout the matrix
Hardness: 55-70 HRC for the deposit, 2800-3200 HV for TiC particles

The retained austenite in the matrix provides strain accommodation and reduces cracking susceptibility. The TiC particles, being thermodynamically stable and chemically inert, do not participate in the martensitic transformation and remain as discrete hard phases.

Welding Process and Performance

Welding Parameters

The TiC-based electrode is designed for standard SMAW welding with the following recommended parameters:

Parameter	Specification
Polarity	DCEN (Direct Current Electrode Negative)
Current range	100-200 A (for 3.2-4.0 mm electrode)
Arc voltage	20-28 V
Travel speed	5-10 cm/min
Electrode baking	Not required
Position capability	All positions
Preheat requirement	None for most applications
Interpass temperature	Maximum 250°C

Wear Performance

The wear resistance of the TiC-based overlay is superior to conventional hardfacing electrodes in abrasive wear applications:

Application	Conventional Electrode (Cr-based)	TiC-Based Electrode	Improvement
Abrasive wear (mining)	100 (relative)	150-200	50-100%
Erosive wear (slurry)	100 (relative)	130-170	30-70%
Impact wear (crushing)	100 (relative)	110-130	10-30%
Sliding wear (metal-on-metal)	100 (relative)	120-150	20-50%

Crack Resistance

A key advantage of the TiC-based electrode is its improved crack resistance compared to conventional hardfacing electrodes. The crack resistance is achieved through:

Retained austenite in the matrix, which provides strain accommodation
TiC particles that are thermodynamically stable and do not promote cracking
Low carbon equivalent of the H08A core, reducing cracking susceptibility
Flux composition that promotes a fluid slag with low sulfur and phosphorus content

Quality Control and Defect Prevention

The primary quality concerns for TiC-based overlay welding include:

Defect Type	Cause	Prevention
Cracking in weld deposit	Excessive cooling rate, high restraint	Control interpass temperature, use backing plate
Porosity	Moisture in flux, contaminated surface	Bake electrode if stored improperly, clean surface
Incomplete fusion	Low current, poor technique	Use adequate current, maintain short arc
TiC particle agglomeration	Excessive heat input, slow cooling	Control heat input, maintain travel speed
Excessive dilution	High heat input, thin layers	Multi-pass welding, low heat input

Engineering Applications and Cost Analysis

The TiC-based electrode is particularly suitable for applications where:

Moderate to severe abrasive wear is the primary failure mode
Some impact loading is present but not dominant
Cost is a significant consideration
Weldability is important (e.g., repair welding in the field)

Typical applications include:

Mining equipment: Shovel buckets, conveyor rollers, crusher jaws
Cement industry: Mill liners, fan blades,溜槽 linings
Construction equipment: Excavator buckets, hydraulic cylinder rods
Power generation: Fan blades, pump impellers, turbine nozzles

The cost analysis shows significant savings compared to conventional hardfacing electrodes:

Cost Component	Conventional Cr-based Electrode	TiC-Based Electrode	Savings
Electrode cost (RMB/kg)	80-120	30-50	60-70%
Deposition rate (kg/h)	2.0-3.0	2.5-3.5	20-25%
Welding wire consumption	100 (relative)	80-90	10-20%
Overall cost per unit area	100 (relative)	40-60	40-60%

Summary and Reference Value

This paper presents a novel and cost-effective approach to wear-resistant overlay welding through the incorporation of titanium carbide hard particles in the weld deposit. The key innovation is the use of arc metallurgy to form TiC particles in situ, avoiding the need for expensive alloying elements such as chromium, nickel, and molybdenum. The resulting electrode combines excellent wear resistance with good crack resistance and weldability, making it suitable for a wide range of industrial applications. For engineers seeking cost-effective solutions to wear problems, the TiC-based electrode represents a viable alternative to conventional hardfacing electrodes, particularly in applications where moderate impact loading is present. The metallurgical understanding of TiC formation and distribution, combined with practical welding parameters and performance data, provides a solid foundation for the development and application of this technology in industrial settings.