Microstructure and Properties of TiC-VC Anti-Abrasive Overlay Welding

Literature Overview

This study published in Journal of Shanghai Jiao Tong University (2004, Vol. 38, No. 7) by researchers from the Shanghai Jiao Tong University Welding Engineering Research Institute and Shandong University investigates the microstructure and properties of a novel anti-abrasive overlay welding electrode containing TiC and VC carbides. The research addresses the challenge of developing overlay consumables that combine high hardness and wear resistance with acceptable weldability and crack resistance.

Electrode Design and Composition

Consumable Configuration

Component	Material	Function
Core wire	H08A	Iron base, structural integrity
Flux coating	Ti-Fe alloy	TiC formation source
Flux coating	V-Fe alloy	VC formation source
Flux coating	Graphite	Carbon source for carbide formation
Flux coating	Synthetic rutile (TiO2)	Flux, slag formation, Ti source

The electrode design leverages high-temperature arc metallurgical reactions to form TiC and VC carbides in situ during the welding process, rather than adding pre-formed carbide particles.

Microstructural Characterization

Carbide Distribution

The carbides formed through arc metallurgical reactions distribute uniformly and dispersely throughout the matrix microstructure. The majority of carbides are located at grain boundaries of the matrix, appearing as irregular block-shaped, angular, or strip-shaped particles.

Matrix Microstructure

The base microstructure is a typical low-carbon martensite morphology. The combination of low-carbon martensite matrix with dispersed carbides provides the microstructural foundation for achieving both good crack resistance and high wear resistance.

Phase Composition

Phase	Symbol	Characteristic
Alpha ferrite	α-Fe	Matrix phase
Gamma ferrite	γ-Fe	Retained austenite
Vanadium carbide	VC	Hard, stable carbide
Titanium carbide	TiC	Hard, stable carbide
Iron carbide	Fe3C	Cementite, less stable

The primary phase composition is α-Fe + γ-Fe + VC + TiC + Fe3C, with TiC and VC being the dominant hard phases responsible for wear resistance.

Performance Results

Hardness and Wear Resistance

Parameter	Value	Comparison
Overlay hardness	HRC 60+	Significantly higher than base material
Relative wear resistance	> D667 electrode	Superior to standard abrasion-resistant electrode
Crack resistance	Acceptable	Maintained despite high hardness
Process performance	Good	Stable arc, smooth bead

Effect of Ti-Fe and V-Fe Addition Rate

Increasing the Ti-Fe and V-Fe addition rates in the flux coating:

Increases overlay hardness due to higher carbide content
Deteriorates process performance due to increased slag viscosity
Reduces crack resistance due to higher carbon activity and brittleness

This trade-off relationship is critical for consumable design optimization.

Engineering Practice Implications

Application Scenarios

This TiC-VC overlay electrode is suitable for:

Coal handling equipment (chutes, hoppers, conveyors)
Mining equipment (shovel teeth, bucket liners)
Cement industry equipment (grinding mill liners, roller surfaces)
Power plant ash handling systems
Aggregate processing equipment

Process Parameters

Welding current: 180-250 A for typical electrode diameters
Arc voltage: 22-28 V
Travel speed: 20-30 cm/min for single pass
Preheating: 100-150°C for thick sections
Interpass temperature: Below 250°C

Quality Control Requirements

Visual inspection for surface defects and bead uniformity
Hardness testing at multiple locations to verify HRC 60+
Bend testing to verify crack resistance
Wear testing for critical applications
Chemical composition verification for Ti and V content

Study Insights and Reflections

This research demonstrates the effectiveness of in-situ carbide formation through arc metallurgy as an alternative to pre-formed carbide particle addition. The advantage of in-situ formation is better carbide-matrix bonding, which improves the overall wear resistance and crack resistance of the overlay. The irregular block-shaped, angular, and strip-shaped morphology of the carbides is beneficial because these shapes provide superior mechanical interlocking with the matrix compared to spherical particles. The retained austenite (γ-Fe) phase in the microstructure is particularly valuable because it provides transformation toughening during impact loading, improving the overall toughness of the overlay. The trade-off between hardness and crack resistance identified in this study is a fundamental challenge in abrasion-resistant overlay design that engineers must navigate based on the specific service conditions. For applications where impact loading is significant, a slightly lower hardness with better crack resistance may be preferable to maximum hardness with poor toughness.