Carbon Arc Surfacing of Fe610 Wear-Resistant Alloy on Exhaust Fan Blades

Literature Overview

This 1997 paper by Peng Bo from the Harbin Welding Research Institute introduces Fe610, a newly developed surfacing alloy material applied to exhaust fan blades via carbon arc surfacing (CAO). The study demonstrates that surfacing with Fe610 can extend blade service life by 3 to 5 times compared to the original material. Published in the journal "Welding" (Issue 2, 1997, pp. 17-19), this work represents an early but significant contribution to the field of wear-resistant surfacing for rotating machinery in power generation and industrial applications.

Core Technical Content

The exhaust fan (pulverized fuel fan) operates in a highly abrasive environment where blades are subjected to continuous impact from coal dust particles. The base material typically experiences severe erosive wear, particularly at the leading edges and pressure surfaces. Fe610 is a high-chromium iron-based alloy designed to provide superior abrasion resistance through a combination of hard carbide phases embedded in a tough matrix.

Fe610 Alloy Characteristics

Parameter	Typical Specification
Base composition	High Cr-Fe alloy system
Hardness	58-65 HRC (as-cast)
Carbide type	Cr7C3, Cr23C6
Matrix structure	Martensitic/ferritic
Typical surfacing thickness	2-5 mm
Process	Carbon arc surfacing (CAO)

Carbon Arc Surfacing Process Parameters

Carbon arc surfacing utilizes a consumable carbon electrode to transfer heat to the workpiece while a separate filler rod deposits the alloy. Key parameters include:

Carbon electrode diameter: 6-10 mm depending on base material thickness
Filler rod diameter: 3-5 mm
Arc length: 3-5 mm (maintained manually or semi-automatically)
Travel speed: 50-100 mm/min
Current: DCEN or DCEP depending on base material
Preheating: 200-300°C for low-carbon steel base

Engineering Practice Analysis

The choice of carbon arc surfacing for fan blades is pragmatic. Unlike MIG/MAG or TIG surfacing, carbon arc surfacing does not require shielding gas, making it adaptable to field repair conditions where fans are often serviced in confined spaces. However, the trade-off is higher dilution from the base metal into the surfacing layer, which must be managed to maintain the wear-resistant properties of Fe610.

Dilution Control Strategy

The dilution rate in carbon arc surfacing typically ranges from 20% to 40%, significantly higher than gas-shielded processes. To mitigate this:

Multiple thin passes are preferred over single thick deposits
The first pass should be kept thin (1-2 mm) to minimize base metal dilution
Subsequent passes should be applied to the previous pass rather than directly to the base metal
Preheating and interpass temperature control (maximum 250°C) reduce thermal gradients

Common Defects and Countermeasures

Defect Type	Cause	Countermeasure
Cracking	High dilution, rapid cooling	Preheat base, reduce travel speed
Porosity	Carbon arc contamination	Clean surface, stable arc length
Excessive dilution	Too thin first pass	Build up in multiple layers
Undercut	Poor technique	Maintain consistent angle
Incomplete fusion	Low heat input	Increase current or reduce speed

Study Insights and Reflections

From a metallurgical perspective, the 3-5 times life extension reported in this paper is consistent with what we observe in modern practice. The key mechanism is the formation of a hard carbide network that resists erosive wear. However, I note that the paper does not extensively discuss the residual stress state of the surfacing layer, which is critical for fatigue life in rotating components.

The carbon arc surfacing process, while effective, produces a coarse grain structure compared to modern plasma or laser surfacing techniques. The thermal input is relatively high, leading to a wider heat-affected zone (HAZ) in the base metal. For modern fan designs with thinner blades and advanced materials, alternative processes such as HVOF (High Velocity Oxy-Fuel) or plasma arc surfacing may be more appropriate. Nevertheless, for large-scale industrial fans where repair is performed in the field, carbon arc surfacing remains a practical and cost-effective solution.

The Fe610 alloy system belongs to the broader family of high-chromium irons. Modern equivalents include FeNiCrBSi alloys and high-silicon irons that offer comparable or superior performance. The fundamental principle remains the same: introducing a hard phase through surfacing to resist abrasive wear while maintaining adequate toughness to avoid catastrophic brittle fracture under impact loading.

This 1997 work, though dated, establishes important baseline knowledge that remains relevant for engineers working on rotating machinery maintenance in power plants, cement industries, and coal processing facilities where exhaust fans continue to be a critical wear component.