Iron-Based Hardfacing Flux-Cored Wire Development and Application

Literature Overview

This 2014 technical contribution by Liu Zhenying and Zhang Li from Beijing GKN Technology Co., Ltd., published in the Journal of Surface Engineering of China, presents the development and industrial application of iron-based hardfacing flux-cored wires (FCW). Flux-cored wires represent a significant advancement in hardfacing technology, offering higher deposition rates, better productivity, and improved process control compared to solid wire electrodes or covered electrodes. The study addresses the growing demand for efficient, cost-effective hardfacing solutions in industrial applications ranging from mining equipment to construction machinery.

The iron-based hardfacing FCW is designed to deposit wear-resistant overlays with controlled hardness, toughness, and wear resistance through a combination of alloy composition optimization, flux coating design, and process parameter control. This approach leverages the advantages of flux-cored welding—higher deposition efficiency, better arc stability, and reduced spatter—while maintaining the metallurgical control necessary for high-performance hardfacing overlays.

Flux-Cored Wire Design and Metallurgy

The design of iron-based hardfacing FCW involves a careful balance between the wire core composition and the flux coating formulation. The wire core typically consists of an iron-based alloy with controlled additions of carbon, chromium, manganese, molybdenum, and vanadium to achieve the desired microstructure and properties.

Component	Typical Composition	Function
Wire core: Carbon (C)	2.0–4.0 wt%	Carbide formation, hardness
Wire core: Chromium (Cr)	8–20 wt%	Carbide formation, oxidation resistance
Wire core: Manganese (Mn)	1.5–3.5 wt%	Austenite stabilization, toughness
Wire core: Molybdenum (Mo)	2–6 wt%	Solid solution strengthening, carbide refinement
Wire core: Vanadium (V)	1–5 wt%	Fine carbide formation, toughness
Flux: Iron oxide (Fe2O3)	8–15%	Oxygen source, arc stabilizer
Flux: Silicon carbide (SiC)	4–10%	Graphitizing agent, deoxidizer
Flux: Calcium carbonate (CaCO3)	5–12%	Flux, slag former
Flux: Titanium dioxide (TiO2)	3–8%	Flux, slag former
Flux: Sodium silicate (Na2SiO3)	2–5%	Binder, flux

The resulting microstructure of the overlay deposit typically consists of a mixture of martensite, retained austenite, and hard carbides (Cr7C3, Mo2C, VC). The relative proportions of these phases determine the balance between hardness, toughness, and wear resistance.

Welding Process Parameters

The welding process parameters for iron-based hardfacing FCW are optimized to achieve consistent deposit quality and minimize defects:

Parameter	Typical Range	Notes
Wire diameter	1.2–2.0 mm	Smaller diameters for thin sections
Current type	DCEN or AC	DCEN preferred for penetration control
Current range	180–350 A	Depends on wire diameter and travel speed
Wire feed speed	4–8 m/min	Adjusted for current and travel speed
Travel speed	200–500 mm/min	Higher speeds for thinner deposits
Shielding gas	CO2 or Ar/CO2 mix	CO2 for cost; Ar/CO2 for reduced spatter
Gas flow rate	15–25 L/min	Adequate coverage of weld zone
Preheat temperature	50–150 °C	Depends on base metal thickness
Interpass temperature	≤200 °C	Prevent grain coarsening

The deposition rate of flux-cored wires is typically 2–3 times higher than that of solid wire electrodes or covered electrodes, making FCW particularly attractive for large-scale hardfacing applications where productivity is a critical factor.

Performance Characteristics and Application Areas

The iron-based hardfacing FCW deposits exhibit the following typical performance characteristics:

Property	Value	Application Relevance
Hardness (as-welded)	500–700 HV	Suitable for moderate to severe abrasive wear
Hardness (after tempering)	450–600 HV	Improved toughness with minimal hardness loss
Wear resistance (ASTM G99)	2–5× carbon steel	Extended service life in wear applications
Impact toughness (Charpy)	25–45 J	Adequate for impact loading conditions
Dilution rate	10–20%	Controlled through process optimization
Bond strength	≥ base metal	Reliable metallurgical bonding

The primary application areas for these overlays include:

Mining and quarrying: Excavator bucket teeth, conveyor rollers, and scraper components
Construction equipment: Bucket teeth, blade edges, and auger components
Material handling: Chutes, hoppers, and transfer points in cement, aggregate, and mining industries
Agricultural machinery: Plowshares, disc blades, and tillage tools
Power generation: Fan blades, hammers, and wear plates in coal handling systems

Defect Prevention and Quality Assurance

The quality of hardfacing overlays is critical to their performance and service life. The following table summarizes common defects and their prevention strategies:

Defect	Root Cause	Prevention Strategy
Porosity	Flux moisture, inadequate shielding	Bake wire at 200 °C for 4h, ensure adequate gas flow
Cracking (hot)	Excessive carbon, high sulfur in base metal	Preheat base metal, use low-sulfur wire, control interpass temperature
Cracking (cold)	Hydrogen embrittlement, high carbon	Bake wire, use low-hydrogen flux, post-weld heating
Undercut	Excessive current, poor technique	Optimize current, maintain consistent travel speed
Excessive dilution	High heat input, single-pass strategy	Reduce heat input, use multi-pass, verify wire angle
Poor bond	Insufficient penetration, surface contamination	Clean base metal, verify current, use proper preheat

Quality assurance procedures include hardness profiling across the overlay thickness, impact testing of weld coupons, metallographic examination of the overlay-base metal interface, and non-destructive testing (UT or MT) for subsurface defects.

Engineering Practice and Economic Analysis

The economic benefits of iron-based hardfacing FCW are substantial when compared to alternative hardfacing methods:

Method	Deposition Rate	Cost per kg of Overlay	Service Life Extension
Covered electrode	1.0× (baseline)	1.0× (baseline)	1.0× (baseline)
Solid wire (GMAW)	1.5×	1.2×	1.5×
Flux-cored wire (FCAW)	2.5×	1.3×	2.0×
Powder cladding (PTA)	3.0×	2.0×	2.5×

The flux-cored wire approach offers an optimal balance between productivity, cost, and performance for many industrial applications. The higher deposition rate reduces labor costs and equipment downtime, while the controlled microstructure ensures reliable wear performance.

Study Insights and Reflections

This research contributes to the practical advancement of hardfacing technology by demonstrating the effectiveness of flux-cored wires for iron-based hardfacing applications. The key insight is that the flux coating in FCW provides not only process benefits (arc stability, reduced spatter) but also metallurgical benefits (controlled oxygen potential, deoxidation, microstructure modification) that enhance the performance of the overlay deposit.

From an engineering practice perspective, the adoption of FCW for hardfacing requires careful consideration of the specific application requirements. The higher deposition rate of FCW makes it particularly suitable for large-area overlays where productivity is critical, but the process also requires careful control of gas flow, wire feed speed, and travel speed to maintain consistent deposit quality. The selection of the appropriate shielding gas (CO2 vs. Ar/CO2 mix) depends on the balance between cost and spatter control requirements.

The study also highlights the importance of consumable storage and handling in maintaining the quality of FCW overlays. Moisture absorption by the flux coating is a primary cause of porosity and hydrogen-induced cracking, and proper storage practices (baking at 200 °C for 4 hours before use, storage in dry conditions) are essential for achieving reliable results. The integration of FCW hardfacing into production processes requires training of welding personnel in the specific technique requirements and the establishment of standardized procedures that ensure consistent quality.

The broader implications of this research extend to the future of hardfacing technology, where the trend toward higher productivity and lower cost will continue to drive the development of advanced consumables and processes. The iron-based hardfacing FCW represents a practical solution that addresses current industrial needs while providing a foundation for further innovation in wear-resistant overlay technology.