Microstructure and Properties of TiC-VC Abrasion-Resistant Overlay Welding

Literature Overview

The paper by Yang Shanglei, Lü Xueqin, Lou Songnian, Wu Yixiong, and Zou Zengda, published in Journal of Shanghai Jiao Tong University (2004, Volume 38, Issue 7, pages 1105–1108), presents the development and characterization of a novel abrasion-resistant overlay welding electrode based on TiC-VC carbide reinforcement. The electrode is manufactured using H08A steel core wire with a flux coating containing graphite, ferro-titanium, ferro-vanadium, and synthetic rutile. The research focuses on the microstructure, hardness, and relative wear resistance of the overlay deposit. This work is of enduring relevance to engineers selecting hardfacing consumables for severe abrasion applications such as mining equipment, material handling, and cement grinding components.

Electrode Design and Metallurgical Reaction

The electrode design philosophy is based on arc metallurgy reactions that generate TiC and VC carbides in-situ during welding. The ferro-titanium and ferro-vanadium in the flux coating react with carbon from the graphite and H08A steel core wire to form thermodynamically stable carbides. The synthetic rutile (TiO2) serves as both a flux and a source of additional titanium. The H08A steel core wire provides the iron matrix and additional carbon for carbide formation.

Electrode Composition and Performance

The resulting overlay deposit exhibits a complex microstructure consisting of α-Fe + γ-Fe + VC + TiC + Fe3C phases. The matrix is a typical low-carbon martensite morphology, while the carbides form dense aggregates of TiC and VC. The carbides are distributed relatively uniformly within the matrix, with a majority located at grain boundaries. Their morphology is irregular, appearing as blocky, angular, or strip-like particles.

Microstructural Analysis

The microstructural characterization reveals several important features:

Carbide Morphology and Distribution

The TiC and VC carbides form as dense aggregates rather than isolated particles. This aggregation behavior is typical of multi-component carbide systems where the equilibrium phase diagram predicts carbide clustering. The irregular blocky and angular morphology suggests rapid solidification from the weld pool, where nucleation and growth kinetics favor non-equilibrium shapes. The concentration of carbides at grain boundaries is attributed to the lower energy of grain boundary sites, which serve as preferential nucleation locations during solidification.

Matrix Microstructure

The low-carbon martensite matrix provides a balance between hardness and toughness. Unlike high-carbon martensite, which is inherently brittle, the low-carbon variant retains sufficient ductility to accommodate plastic deformation during abrasive contact. This combination of a tough matrix with hard carbide reinforcements is the fundamental microstructural basis for achieving both good crack resistance and high wear resistance simultaneously.

Performance Characteristics

The overlay deposit achieves a hardness exceeding HRC 60, with relative wear resistance significantly exceeding that of the commercial D667 welding electrode. The D667 electrode is a widely used high-carbon martensitic hardfacing electrode known for its excellent abrasion resistance. The fact that the TiC-VC based overlay outperforms D667 demonstrates the effectiveness of the in-situ carbide formation approach.

Performance Comparison

Process-Structure-Property Relationships

The study establishes clear relationships between electrode composition, microstructure, and performance:

1. Increasing ferro-titanium and ferro-vanadium content in the flux coating increases the volume fraction of TiC and VC carbides, leading to higher overlay hardness. However, excessive addition deteriorates process performance and crack resistance, as higher carbide content increases the brittleness of the weld metal and promotes hot cracking during solidification.
2. Increasing graphite content provides more carbon for carbide formation but also increases the carbon content of the matrix, potentially transforming the low-carbon martensite into higher-carbon martensite with reduced toughness.
3. The balance between carbide volume fraction and matrix toughness is the critical design parameter. Too much carbide leads to poor crack resistance; too little carbide leads to insufficient wear resistance.

Optimization Windows

Engineering Practice Applications

The TiC-VC overlay system is particularly suited for applications involving sliding abrasion where hard particles are embedded in a softer matrix and slide across the overlay surface. Typical applications include:

• Mining equipment: bucket teeth, conveyor rollers, and crusher liners
• Cement industry: grinding balls, mill liners, and kiln wear plates
• Material handling: chutes, hoppers, and transfer points
• Agricultural equipment: plowshares and tillage implements

For pipe and fitting applications, this overlay technology can be applied to protect pipe sections in slurry pipelines, where abrasive particles in the fluid cause rapid wear. The overlay can be deposited on the internal surface of pipes or on the external surface of fittings at high-wear locations.

Study Insights and Outlook

This research demonstrates the effectiveness of in-situ carbide formation as a strategy for developing high-performance abrasion-resistant overlay welding consumables. The key insight is that the combination of a tough low-carbon martensite matrix with hard TiC and VC carbide reinforcements provides a superior balance of wear resistance and crack resistance compared to conventional high-carbon martensitic hardfacing systems. The work highlights the importance of microstructural engineering in overlay welding, where the performance is not determined by hardness alone but by the synergistic interaction between the matrix and reinforcement phases. The findings provide a solid foundation for further development of multi-carbide overlay systems tailored to specific abrasion conditions and service environments.