Tungsten Carbide Arc Overlay Welding for Severe Abrasive Wear Components

Literature Overview

This paper by Xu Bingqiang (2009, Welding Journal, Issue 4, pp. 61-63), authored by an engineer at Jiangsu Longtan Heavy Machinery Co., Ltd., addresses the practical application of tungsten carbide (WC) arc overlay welding for heavy-duty wear components. The research focuses on solving the fundamental metallurgical compatibility challenge between WC coating material and structural steel substrates, and presents field validation results from cement roller press applications.

Technical Challenges and Solutions

The Compatibility Problem

Tungsten carbide (WC) is an extremely hard ceramic phase (Vickers hardness ~1500-2000 HV) with a melting point of approximately 2870°C. Direct welding of WC onto carbon or low-alloy steel substrates presents severe challenges:

• Thermal expansion mismatch: WC has a coefficient of thermal expansion (~5.6 × 10⁻⁶/K) significantly lower than steel (~12 × 10⁻⁶/K), generating high residual stresses during cooling.
• Carbide dissolution and embrittlement: WC readily reacts with iron to form Fe₃W₃C and other intermetallic phases that are extremely brittle and prone to cracking.
• Porosity formation: The high melting point of WC relative to the weld pool temperature leads to incomplete melting and pore formation.
• Cracking susceptibility: The thermal stress concentration at the WC/steel interface frequently causes interfacial cracking.

Multi-Layer Overlay Strategy

The author proposes a three-layer approach that elegantly addresses these challenges:

The pearlite underlay layer serves as a thermal buffer, reducing the thermal gradient at the substrate interface. The austenitic transition layer exploits strain-induced martensitic transformation (TRIP effect) to accommodate plastic deformation without cracking. This layered design philosophy is analogous to the metallurgical approach used in tungsten carbide cored wire welding (such as D172-type electrodes) but with greater process flexibility.

Process Parameters and Practical Considerations

For arc overlay welding of WC-containing materials, the following process parameters are critical:

• Current density: Must be kept low (typically 8-12 A/mm² for SMAW) to minimize WC dissolution and maintain carbide integrity.
• Arc length: Short arc operation (arc length < 0.5 × electrode diameter) is essential to maintain stable arc and reduce dilution.
• Travel speed: Slow travel speed (20-40 cm/min for SMAW) ensures adequate heat input for wetting while avoiding excessive melting of WC particles.
• Preheating: Moderate preheat (100-150°C) reduces thermal stress but must not be excessive to avoid softening of the underlying layers.
• Interpass temperature: Should be maintained below 150°C to prevent over-tempering of the hardening layers.

Application in Cement Roller Press

The field validation on cement roller press roller surfaces demonstrates the practical viability of this approach. Roller presses in cement grinding circuits experience extremely severe abrasion from hard cement clinker particles at high contact pressures (50-150 MPa). The WC overlay extends roller surface life significantly compared to conventional hardfacing approaches.

Key performance indicators observed in practice:

• Service life improvement of 3-5 times compared to uncoated roller surfaces
• Acceptable bond strength between overlay and substrate (typically > 200 MPa shear strength)
• No spalling or delamination observed during normal operating conditions
• Reduced downtime for roller replacement

Critical Engineering Insights

This paper, while concise, highlights several important engineering principles:

1. The concept of graded microstructure in overlay welding is more important than maximizing surface hardness alone. A well-designed multi-layer system with controlled hardness gradient can outperform a single-layer high-hardness deposit in terms of durability.
2. Metallurgical compatibility is process-dependent. The same WC material may weld successfully with one electrode type and fail with another, depending on flux composition, wire geometry, and shielding gas selection.
3. The austenitic transition layer is particularly valuable because it can absorb impact energy through strain hardening, which is essential for roller press applications where point loading occurs.
4. Economic considerations: While WC overlay welding consumables are expensive, the extended service life often justifies the cost. A life-cycle cost analysis should always be performed before selecting between overlay welding and alternative wear protection methods (such as surface hardening, ceramic cladding, or solid surface replacement).

The approach described represents a mature engineering solution that balances metallurgical performance with practical weldability, and remains relevant for modern severe-wear applications in mining, cement, and power generation industries.