Nickel-Based High-Temperature Wear-Resistant Slag-Free Surfacing Electrode and Its Heat Treatment Process

Literature Overview

Published in the Acta Metallurgica Sinica (Welding Journal, Vol. 27, Issue 1, 2006, pp. 109–112), this paper by Wang Zhongwei, Zhang Qinghui, and Xiao Yifeng presents the development and characterization of a novel nickel-based slag-free surfacing electrode designed for high-temperature wear resistance applications. The work was conducted jointly by Zhuzhou Hard Alloy Group Co., Ltd. and the School of Mechanical Engineering at Xiangtan University. The electrode addresses a significant market gap: the absence of suitable manual arc surfacing consumables for nickel-based alloys that combine high-temperature performance with practical field applicability.

Development Rationale and Material Design

The development of this electrode was driven by several practical considerations:

• Market gap: At the time of publication, the market lacked manual arc surfacing materials based on nickel alloys, despite the excellent high-temperature properties of these alloys.
• Environmental concerns: The electrode was designed to produce minimal welding fume with very low levels of harmful gases, addressing occupational health and safety requirements.
• Operational efficiency: The slag-free characteristic eliminates the need for slag removal between passes, significantly improving productivity in multi-pass surfacing operations.
• Cost advantage: Compared to cobalt-based surfacing alloys (such as Stellite), nickel-based alloys offer comparable performance at substantially lower cost.

The electrode's deposited metal contains a higher proportion of alloying elements than conventional surfacing electrodes, resulting in a complex composition that provides excellent performance at approximately 650°C. However, this complexity introduces challenges in terms of residual stress and microstructural stability under rapid cooling conditions.

Welding Metallurgy and Heat Treatment

The paper identifies two critical metallurgical challenges associated with this electrode:

1. High residual stress: The elevated alloy content creates significant thermal and metallurgical shrinkage stresses during solidification and cooling.
2. Unstable as-deposited microstructure: Rapid cooling from the welding thermal cycle produces metastable phases that may transform during subsequent service, leading to dimensional instability and property degradation.

The heat treatment process, though described as a preliminary investigation, is essential for practical application. A typical solution treatment and aging cycle for nickel-based alloys would involve:

• Solution treatment at 900–1050°C for 1–2 hours to dissolve carbides and homogenize the microstructure
• Aging at 600–700°C for 4–8 hours to precipitate fine, coherent carbides that provide wear resistance
• Controlled cooling rate to minimize thermal stresses

Process Advantages and Limitations

The slag-free characteristic of this electrode represents a significant practical advantage. In conventional SMAW surfacing, slag removal between passes introduces several risks:

• Incomplete slag removal can lead to slag inclusion defects
• Mechanical slag removal can damage the previously deposited layer
• Time spent on slag removal reduces overall deposition rate

By eliminating slag formation, this electrode allows for continuous multi-pass deposition without interruption, improving both productivity and deposit quality. The reduced fume generation also improves the working environment and reduces the need for extensive ventilation systems.

However, the slag-free design imposes constraints on the consumable composition. The absence of flux means that alloying elements must be supplied entirely through the electrode core or coating, and the composition must be carefully balanced to ensure:

• Adequate arc stability without flux assistance
• Proper gas protection of the molten pool
• Appropriate solidification behavior without slag modification
• Sufficient dilution resistance to maintain desired deposit composition

Engineering Applications and Practice

This electrode is particularly suited for the following applications:

• Cement industry: Sliders, hammers, and grinding elements in kiln systems operating at elevated temperatures
• Power generation: Boiler tubes, burner components, and fan blades exposed to hot ash and fly ash
• Pulp and paper industry: Hot press rolls and guide rolls operating in high-temperature environments
• Aerospace: Jet engine components requiring high-temperature wear resistance

For field application, the following practices are recommended:

1. Preheat the base material to 200–300°C to reduce thermal gradients and minimize cracking risk
2. Maintain interpass temperature between 150–250°C to control cooling rates
3. Use a slightly lower current than recommended for conventional electrodes, as the higher alloy content increases resistivity
4. Apply a post-weld heat treatment cycle as specified by the manufacturer to stabilize the microstructure
5. Conduct hardness testing and, where applicable, tensile testing of the deposited metal to verify compliance with specifications

Key Reflections

This paper represents an important contribution to the field of surfacing consumables development. The recognition that slag-free operation offers practical advantages in multi-pass surfacing is well-founded, and the development of a nickel-based electrode that achieves this without sacrificing performance is technically significant. The preliminary nature of the heat treatment investigation suggests that further optimization work is needed, particularly regarding:

• The precise relationship between heat treatment parameters and long-term high-temperature wear performance
• The effect of heat treatment on the interface between the deposited layer and the base material
• The influence of welding sequence and thermal history on residual stress distribution

The cost advantage over cobalt-based alternatives (Stellite 6, Stellite 21) is particularly attractive for large-scale industrial applications where the total volume of surfacing material is substantial. For engineers selecting surfacing consumables, this electrode represents a viable alternative to cobalt-based alloys for applications where temperatures do not exceed approximately 650°C.

Summary

This study demonstrates that nickel-based slag-free surfacing electrodes can provide excellent high-temperature wear resistance at a lower cost than traditional cobalt-based alternatives, while offering significant operational advantages in terms of fume reduction and elimination of slag removal between passes. The critical challenge identified—microstructural instability and high residual stress in the as-deposited condition—is addressable through appropriate post-weld heat treatment, though further optimization of the heat treatment cycle is warranted. For practitioners in industrial maintenance and surface engineering, this electrode represents a practical tool for extending component life in high-temperature wear environments, provided that the recommended heat treatment protocol is implemented and the operating temperature does not exceed the validated range of approximately 650°C.