Development of Wear-Resistant Cladding Electrodes for Fan Blades

Literature Overview

This 1991 study by Liu Pengshan addresses a critical industrial problem in the fan and blower sector: the rapid abrasive and erosive degradation of fan blades operating in high-velocity gas streams carrying particulate matter. The paper focuses on the formulation and characterization of specialized cladding electrodes designed to deposit hardfacing layers on carbon steel and low-alloy steel fan blades, extending their service life significantly. The work was published in the context of China's rapidly expanding thermal power and cement industries, where fan wear was a dominant maintenance cost driver.

Core Technical Approach

The research adopted a systematic approach to electrode development, beginning with a clear identification of the wear mechanisms involved in fan blade service. Fan blades experience a combination of abrasion from solid particles, erosion from high-velocity gas flow, and sometimes mild corrosion from flue gas constituents. The electrode design targeted a multi-phase hardfacing microstructure containing carbide-forming elements to resist abrasive wear while maintaining sufficient toughness to resist fatigue cracking at the weld interface.

The electrode formulation incorporated key alloying elements including chromium, tungsten, molybdenum, and vanadium. Chromium and tungsten served as primary carbide formers, producing hard Cr7C3, Cr23C6, and W2C-type carbides distributed within a tempered martensite matrix. The carbon content was carefully controlled to balance hardness against brittleness. The flux coating was formulated to ensure stable arc characteristics, adequate slag coverage, and proper deoxidation during manual arc welding.

Microstructure and Wear Mechanism Analysis

The deposited cladding layer exhibited a complex microstructure consisting of a tempered martensite matrix with a high volume fraction of carbide particles. Metallographic examination revealed that the carbides were predominantly Cr7C3 and Cr23C6, with some complex mixed carbides involving tungsten and vanadium. The carbide particle size ranged from 1 to 5 micrometers, and their distribution was relatively uniform across the cladding cross-section when proper welding parameters were maintained.

The wear resistance mechanism was attributed to the combined action of the hard carbide phase and the toughened martensitic matrix. The carbides provided primary resistance to abrasive particle indentation and micro-cutting, while the martensite matrix absorbed energy and resisted crack propagation. This dual-phase architecture was essential because a fully carbide-rich structure would be too brittle, and a purely martensitic structure would lack sufficient hardness for severe abrasion.

The heat-affected zone (HAZ) in the base metal was another critical concern. The high carbon and alloy content of the cladding electrode could induce a hard, brittle zone in the base metal through carbon diffusion and rapid cooling. The study addressed this by recommending multiple thin passes with controlled interpass temperature, typically maintained between 100 and 200 degrees Celsius. This practice limited the peak temperature in the HAZ and allowed for tempering of the prior HAZ microstructure during subsequent passes.

Engineering Practice and Application Experience

From a practical standpoint, the application of these wear-resistant cladding electrodes to fan blades required careful preparation and execution. Fan blade surfaces were typically ground to remove existing oxide scale and rust, exposing clean base metal for optimal metallurgical bonding. The root pass was often applied with a compatible low-carbon electrode to avoid excessive dilution and cracking in the critical bond interface. Subsequent overlay passes used the wear-resistant electrode, building up the cladding layer to a total thickness of 2 to 4 millimeters.

A significant challenge in fan blade cladding was the thin section geometry. Fan blades, particularly in smaller industrial fans, had thicknesses of only 6 to 10 millimeters, which created risks of burn-through, distortion, and incomplete penetration. The study recommended pulse welding techniques or reduced current settings to control heat input. Preheating to 100 to 150 degrees Celsius was generally beneficial to reduce residual stresses and minimize the risk of cold cracking in the HAZ.

Field trials demonstrated that the cladding treatment could extend fan blade service life by a factor of 3 to 5 times compared to unclad blades in cement kiln induced draft fans. The improved durability was most pronounced in the leading edge region, where particle impact velocity was highest. However, the cladding layer did wear over time, and periodic re-cladding was necessary. The economics favored cladding over complete blade replacement because the base metal cost and machining time for new blades was substantially higher than the electrode and labor cost for re-cladding.

Key Technical Insights and Reflections

The 1991 study represents an important early contribution to the Chinese hardfacing electrode industry, particularly for the fan sector. One key insight that remains relevant today is the recognition that electrode selection must be matched not only to the base material but also to the specific wear mechanism. A carbide-rich electrode suitable for sliding abrasion may not perform well under erosive conditions where high-velocity particles impinge at oblique angles.

Another important consideration highlighted by this work is the trade-off between hardness and toughness in the cladding layer. Achieving 60 HRC hardness is relatively straightforward with high-carbon, high-chromium compositions, but maintaining structural integrity under cyclic loading is far more challenging. The tempered martensite matrix with dispersed carbides represents an optimized compromise, and this principle continues to guide modern hardfacing alloy design.

The study also underscores the importance of welding procedure qualification and operator training. Even a well-designed electrode will underperform if deposited with excessive heat input, improper travel speed, or inadequate surface preparation. In modern practice, this translates to the need for documented welding procedure specifications (WPS) and qualified welding procedure qualifications (WPQ) in accordance with standards such as NB/T 47014 and ASME IX.

Summary

The development of wear-resistant cladding electrodes for fan blades, as documented in this 1991 study, represents a foundational contribution to industrial hardfacing technology in China. The work established a practical framework for electrode formulation, microstructure control, and field application that remains broadly applicable today. The key lessons include the necessity of matching cladding composition to the dominant wear mechanism, the critical role of the martensite-carbide dual-phase microstructure in achieving balanced hardness and toughness, and the importance of controlled welding parameters to prevent HAZ cracking and distortion. For modern engineers, this literature provides a useful historical benchmark against which contemporary laser cladding and plasma transferred arc hardfacing technologies can be evaluated, and it reinforces the enduring principle that metallurgical design and welding process control must be integrated for successful hardfacing applications.