Research on Fe-Cr-Mo-B System Wear-Resistant Surfacing Electrode

Literature Overview

The paper by Xu Guojian and Gu Yuxi from Shenyang University of Technology, published in Welding Technology (1996, Vol. 25, No. 1, pp. 10-12), presents a systematic investigation of Fe-Cr-Mo-B system wear-resistant surfacing electrodes. The authors conducted extensive experimental work to develop an electrode with excellent processability and wear resistance, with particular focus on the effects of chromium and boron on the microstructure and properties of the deposited metal. The results showed that the room-temperature wear resistance was 2-3 times that of the conventional D667 electrode, with red hardness reaching HV306.4 at 700°C.

Core Technical Content

The Fe-Cr-Mo-B system represents a classic approach to wear-resistant surfacing alloy design, combining the benefits of multiple alloying elements to achieve a balance between hardness, toughness, and wear resistance. The development of this electrode was driven by the need for high-performance surfacing materials for mining, construction, and heavy industrial equipment subjected to severe abrasive and impact loading.

Alloy Design Philosophy

The Fe-Cr-Mo-B system is designed to produce a microstructure consisting of hard carbide particles (primarily Cr7C3, Mo2C, and boride phases) dispersed in a tough iron matrix. This composite-like microstructure provides excellent resistance to abrasive wear while maintaining adequate toughness to resist impact and fatigue failure.

Performance Characteristics

The wear resistance improvement of 2-3 times over D667 is achieved through the synergistic effect of chromium and boron carbides, which provide higher hardness and better retention of hardness at elevated temperatures compared to the simpler Fe-Cr-C system of D667. The addition of molybdenum further enhances the red hardness by stabilizing the carbide phases and providing solid solution strengthening in the matrix.

Engineering Practice Integration

The Fe-Cr-Mo-B surfacing electrode is suitable for a wide range of applications where severe wear and moderate to high temperatures are encountered:

• Mining equipment: Shovel teeth, bucket liners, conveyor rollers, and crusher components
• Construction machinery: Bulldozer blades, excavator buckets, and dozer shoes
• Cement industry: Kiln liners, mill liners, and rotary parts
• Power generation: Coal handling equipment, ash handling systems, and boiler components
• Pulp and paper: Grinders, crushers, and pulping equipment

Key considerations for practical application include:

1. Welding parameters: Optimal current range of 120-180 A with a travel speed of 200-350 mm/min, depending on the desired layer thickness.
2. Preheating: Preheating to 150-250°C is recommended for thick sections to reduce cracking susceptibility.
3. Interpass temperature: Maintain between 150-250°C to avoid excessive grain growth and stress accumulation.
4. Post-weld treatment: Stress relief at 550-650°C for 1-2 hours per 25 mm of section thickness.
5. Number of passes: Typically 2-3 passes for adequate coverage and wear resistance.

Key Technical Insights and Reflections

The research highlights the importance of alloy design in achieving superior wear resistance. The Fe-Cr-Mo-B system demonstrates that the strategic combination of multiple alloying elements can produce synergistic effects that exceed the sum of their individual contributions. Specifically:

• Chromium provides the primary carbide hardening phase and contributes to oxidation resistance.
• Molybdenum enhances red hardness and stabilizes the microstructure at elevated temperatures.
• Boron refines the grain structure and forms hard boride phases that improve high-temperature hardness.

The red hardness of HV306.4 at 700°C is particularly noteworthy because it indicates that the carbide phases remain stable and effective at temperatures where many conventional surfacing alloys would soften significantly. This makes the electrode suitable for applications where the component operates at elevated temperatures, such as in hot gas ducts or near heat sources.

However, several practical limitations should be considered:

• The high carbon equivalent of the Fe-Cr-Mo-B system may increase cracking susceptibility, particularly in thick sections or when welding to high-carbon base metals.
• The boron content must be carefully controlled to avoid excessive brittleness and to ensure consistent welding performance.
• The electrode requires careful storage and handling to prevent moisture absorption, which can lead to hydrogen-induced cracking.

Study Implications and Outlook

This research contributes significantly to the understanding of Fe-Cr-Mo-B system surfacing alloys and provides a practical electrode formulation for industrial applications. The demonstrated improvement in wear resistance (2-3 times over D667) and red hardness makes this electrode a valuable option for severe wear applications. For engineers, the key takeaway is that alloy design is a critical factor in achieving the desired performance, and the synergistic effects of multiple alloying elements can be leveraged to develop high-performance surfacing materials. Future work could explore the effects of additional alloying elements (such as niobium, vanadium, or tungsten) on the microstructure and properties of Fe-Cr-Mo-B systems, as well as the development of advanced welding processes (such as plasma arc or laser surfacing) to further enhance the performance of these alloys. The research also underscores the importance of systematic experimental investigation and characterization in surfacing alloy development, providing a methodological framework for future alloy design efforts.