Research on Iron-Based High-Temperature Wear-Resistant Overlay Welding Electrodes

Literature Overview

The 1995 study by Liu Zhengjun, Ji Jie, and Hao Xuefeng from Shenyang University of Technology and the Shenyang Boiler and Pressure Vessel Inspection Institute investigates the development of iron-based high-temperature wear-resistant overlay welding electrodes. This research addresses a significant industrial need for cost-effective alternatives to cobalt-based and nickel-based hardfacing alloys in high-temperature wear applications. The work represents an important contribution to the domestic development of overlay welding consumables in China during a period of rapid industrial growth.

Core Technical Content

Design Philosophy and Alloy Development

The research was driven by the need to develop iron-based overlay alloys that could achieve high-temperature wear resistance comparable to cobalt-based alloys (such as Stellite) at significantly lower cost. The design approach involved:

• Matrix selection: High-speed steel (HSS) type matrix with elevated Cr, Mo, and V content
• Carbide-forming elements: Strategic addition of Cr, W, Mo, and V to promote formation of hard, thermally stable carbides
• Carbon content optimization: Balancing carbon for carbide volume fraction against carbon for ductility and crack resistance
• Lanthanum addition: Experimental addition of rare earth elements (La) to modify carbide morphology and improve hot workability

Electrode Composition Development

The study developed several electrode compositions, with the optimal composition characterized by:

Microstructural Characteristics

The overlay deposits exhibited a microstructure consisting of:

• Matrix: M martensite with retained austenite (typically 10-25%)
• Primary carbides: M6C, M23C6, and M7C3 phases with sizes of 5-20 μm
• Secondary carbides: Fine M2C and MC carbides (V4C, VC) dispersed in the matrix
• Carbide volume fraction: 25-35% depending on carbon content

Mechanical and Wear Properties

Process Analysis

Welding Process Parameters

The electrodes were designed for use with shielded metal arc welding (SMAW) process, which is the most commonly used process for overlay welding in field repair applications. The recommended parameters included:

• Current type: DCEP (direct current electrode positive) for deeper penetration and better fusion
• Current range: 100-200 A depending on electrode diameter (3.2-5.0 mm)
• Arc voltage: 22-28 V
• Travel speed: 50-80 mm/min
• Preheat: 200-300°C for thick sections (>25 mm)
• Interpass temperature: Maximum 250°C to maintain martensitic microstructure

Heat Treatment Considerations

The iron-based overlay deposits can be further optimized through post-weld heat treatment:

• Tempering at 200-300°C: Reduces residual stresses while maintaining high hardness
• Tempering at 400-500°C: Further reduces stresses but sacrifices some hardness
• Solution treatment at 1000-1100°C: Dissolves carbides for subsequent aging (limited applicability due to substrate constraints)

Engineering Practice and Application

Application Areas

The developed electrodes were targeted for applications in:

• Boiler tube repair in power plants (high-temperature erosion resistance)
• Cement kiln components (abrasion and thermal cycling)
• Mining equipment (high-temperature wear)
• Petrochemical equipment (high-temperature corrosion-wear)

Comparison with Conventional Hardfacing

The iron-based electrodes offer several advantages over conventional hardfacing alloys:

• Cost: 30-50% lower than cobalt-based alloys, 20-30% lower than nickel-based alloys
• Weldability: Generally better than cobalt-based alloys due to lower thermal conductivity differential
• Hardness: Higher than Stellite at room temperature and moderate temperatures
• Availability: Iron-based consumables are more readily available in the domestic market

However, limitations include:

• Lower toughness: Compared to cobalt-based alloys, particularly at elevated temperatures
• Thermal fatigue resistance: Inferior to cobalt-based alloys due to higher thermal expansion coefficient
• Maximum service temperature: Limited to approximately 600°C, compared to 800-900°C for cobalt-based alloys

Key Questions and Reflections

The study raises important questions about the cost-performance optimization of overlay welding consumables. While iron-based electrodes offer excellent wear resistance at lower cost, the trade-offs in toughness and thermal fatigue resistance must be carefully evaluated for each specific application. The choice between iron-based and cobalt-based alloys should be driven by a comprehensive analysis of the service conditions, including temperature range, wear mechanism, loading spectrum, and cost constraints.

Another reflection is the role of rare earth elements in modifying overlay microstructure. The experimental addition of lanthanum showed promise in refining carbide morphology and improving hot workability, but the long-term effects on service performance require further investigation.

Study Insights and Implications

This research represents an important contribution to the domestic development of overlay welding consumables. The developed iron-based electrodes provide a viable alternative to cobalt-based alloys for many high-temperature wear applications, offering a favorable cost-performance ratio. The work demonstrates that systematic alloy design, combined with careful process optimization, can achieve performance comparable to more expensive alloys. For engineers selecting overlay welding consumables, the key takeaway is that the choice should be application-driven, with a thorough understanding of the trade-offs between hardness, toughness, thermal stability, and cost.