CLADDING TECHNOLOGY SHANXI CO., LTDApplication of Fe-05 Wear-Resistant Overlay Alloy on Induced Draft Fans
Literature Overview
This 1993 study by Hao Balin from Yichun Xinqing Power Plant examines the application of the Fe-05 wear-resistant overlay alloy on induced draft fan components, published in the journal "Welding" (焊接). Induced draft fans are critical components in power plant boiler systems, responsible for drawing flue gases through the boiler and maintaining the required draft pressure. These fans operate in extremely harsh conditions involving high temperatures, abrasive fly ash, and continuous cyclic loading, making them subject to severe wear and fatigue damage.
Induced Draft Fan Operating Environment
Induced draft fans in power plants operate under conditions that create a unique combination of wear mechanisms. The flue gas temperature typically ranges from 120 to 180 °C at the fan inlet, with localized hot spots potentially reaching higher temperatures. The flue gas contains fly ash particles with varying sizes and hardness, ranging from fine particles below 10 micrometers to coarse particles exceeding 100 micrometers. The angular morphology of fly ash particles contributes to severe abrasive wear on fan blades, inlet cones, and other components in contact with the flue gas stream.
Operating Conditions and Wear Mechanisms
| Parameter | Typical Value | Effect on Wear |
|---|---|---|
| Gas temperature | 120-180 °C | Thermal cycling, oxidation |
| Fly ash concentration | 20-100 g/Nm³ | Abrasive wear intensity |
| Particle size distribution | 1-200 μm | Abrasive mechanism type |
| Particle hardness | 6-8 Mohs (quartz) | Abrasive wear severity |
| Gas velocity | 20-40 m/s | Impact + abrasion |
| Operating hours | 8000-8760 h/year | Cumulative wear |
| Humidity | Variable | Corrosive wear |
| SO2 concentration | 50-500 ppm | Sulfidation corrosion |
The Fe-05 alloy, which is a high-carbon martensitic hardfacing alloy, is specifically designed for applications involving abrasive wear with moderate impact loading. The composition typically includes 5-8% carbon, 5-10% chromium, and 2-4% vanadium, with the balance being iron. The high carbon content promotes the formation of hard carbides, while chromium and vanadium contribute to carbide stability and hardenability.
Fe-05 Alloy Properties and Microstructure
The Fe-05 alloy exhibits a microstructure consisting of tempered martensite with a high volume fraction of hard carbides, primarily vanadium carbides (VC) and chromium carbides (Cr7C3, Cr23C6). The hardness of the as-welded overlay typically ranges from 55 to 62 HRC, depending on the welding parameters and cooling rate. The microstructure is characterized by a fine-grained martensitic matrix with uniformly distributed primary carbides, providing excellent abrasive wear resistance.
The wear resistance of the Fe-05 alloy is primarily attributed to the hard carbide phase, which provides resistance to abrasive particle penetration and material removal. The tempered martensitic matrix provides adequate toughness to resist cracking under impact loading from fly ash particles. The combination of hard carbides and tough matrix creates a synergistic effect that provides superior wear resistance compared to either phase alone.
Fe-05 Alloy Composition and Properties
| Property | Value | Test Method |
|---|---|---|
| Carbon content | 5.0-8.0% | Spectrochemical analysis |
| Chromium content | 5.0-10.0% | Spectrochemical analysis |
| Vanadium content | 2.0-4.0% | Spectrochemical analysis |
| Hardness (as-welded) | 55-62 HRC | Rockwell C scale |
| Hardness (after tempering) | 48-55 HRC | Rockwell C scale |
| Impact energy (25 °C) | 5-15 J | Charpy V-notch |
| Dilution (on steel) | 10-20% | Metallographic |
| Maximum service temperature | 400-500 °C | Thermal stability |
Welding Process and Application
The application of Fe-05 alloy on induced draft fan components typically employs submerged arc welding (SAW) or gas metal arc welding (GMAW) processes. SAW is preferred for large components such as fan blades and inlet cones due to its high deposition rate and excellent weld quality. The welding parameters must be carefully controlled to ensure adequate hardness development while minimizing the risk of cracking.
Preheating is generally required for Fe-05 hardfacing applications, with preheat temperatures of 150-250 °C depending on the substrate material and thickness. The interpass temperature should be maintained below 200 °C to ensure adequate cooling rates and hardness development. Post-weld heat treatment may be required to relieve residual stresses and reduce the risk of cracking, particularly for thick-section components or when welding onto low-alloy steel substrates.
Welding Parameters for Fe-05 Application
| Parameter | SAW | GMAW |
|---|---|---|
| Current (A) | 350-500 | 250-400 |
| Voltage (V) | 28-35 | 25-32 |
| Travel speed (mm/min) | 250-400 | 300-500 |
| Wire diameter (mm) | 2.4-3.2 | 1.2-1.6 |
| Shielding gas | Flux | Ar+CO2 (80:20) |
| Preheat temperature (°C) | 150-250 | 150-250 |
| Interpass temperature (°C) | < 200 | < 200 |
| Post-weld treatment | Stress relief 500-600 °C | Stress relief 500-600 °C |
Performance Evaluation and Service Results
The application of Fe-05 alloy on induced draft fan components has demonstrated significant improvements in service life compared to conventional materials. In typical power plant applications, unhardfaced fan blades made from carbon steel or low-alloy steel typically have a service life of 6-12 months before requiring replacement or major repair. With Fe-05 hardfacing applied to critical wear areas, the service life can be extended to 24-48 months or longer, representing a 2-4 times improvement in service life.
The wear rate of Fe-05 overlays in induced draft fan service is typically in the range of 0.05-0.15 mm per 1000 operating hours, depending on the fly ash characteristics and operating conditions. This wear rate is significantly lower than that of conventional carbon steel or low-alloy steel materials, which typically exhibit wear rates of 0.3-0.8 mm per 1000 hours under similar conditions.
Service Life Comparison
| Component | Material | Service Life (months) | Wear Rate (mm/1000h) |
|---|---|---|---|
| Fan blade (unhardfaced) | Q235 steel | 6-12 | 0.3-0.8 |
| Fan blade (Fe-05 hardfaced) | Q235 + Fe-05 | 24-48 | 0.05-0.15 |
| Inlet cone (unhardfaced) | 20G steel | 8-16 | 0.2-0.5 |
| Inlet cone (Fe-05 hardfaced) | 20G + Fe-05 | 30-60 | 0.03-0.10 |
| Wear ring (unhardfaced) | 45 steel | 3-6 | 0.5-1.0 |
| Wear ring (Fe-05 hardfaced) | 45 + Fe-05 | 18-36 | 0.05-0.15 |
Common Defects and Countermeasures
| Defect | Root Cause | Countermeasure |
|---|---|---|
| Cracking | Excessive cooling rate, high residual stress | Preheat 150-250 °C, stress relief PWHT |
| Insufficient hardness | Excessive heat input, high dilution | Reduce heat input, use transition layer |
| Porosity | Flux contamination, inadequate shielding | Clean flux, ensure proper gas coverage |
| Incomplete fusion | Poor joint preparation, excessive travel speed | Proper bevel preparation, optimize parameters |
| Spalling | Poor bond strength, thermal mismatch | Use transition layer, reduce dilution |
| Excessive wear | Insufficient overlay thickness, wrong alloy | Increase thickness, verify alloy selection |
Study Insights and Engineering Practice
The 1993 study by Hao Balin represents early practical application experience with Fe-05 hardfacing alloys in power plant environments, providing valuable data on the performance of these alloys under actual service conditions. The study demonstrates that Fe-05 alloys are particularly well-suited for induced draft fan applications where the primary wear mechanism is abrasive wear from fly ash particles at moderate temperatures.
A key insight from this study is the importance of proper overlay thickness and geometry design. The overlay must be thick enough to withstand the expected wear during the intended service interval, while also being thin enough to avoid excessive stress concentrations and cracking susceptibility. A typical overlay thickness of 3-6 mm is recommended for fan blade applications, with thicker overlays (6-10 mm) used for high-wear areas such as blade leading edges and inlet cone surfaces.
In conclusion, the application of Fe-05 wear-resistant overlay alloy on induced draft fans demonstrates the effectiveness of hardfacing technology in extending equipment service life in harsh power plant environments. Engineers should apply these findings with careful consideration of the specific operating conditions, fly ash characteristics, and quality requirements to achieve optimal overlay performance and cost-effectiveness in power plant maintenance operations.