Microstructure and Properties of Tungsten Carbide Iron-Based Self-Melting Alloy Weld Overlay

Literature Overview

This 2018 study published in Materials Protection (Cailiao Baohu), authored by Meng Yuanyuan, Ren Ruichen, Qin Haifeng, and Wang Qiang from Liaoning Technical University and Fushun Petrochemical Company, investigates the microstructure evolution and mechanical properties of tungsten carbide (WC) reinforced iron-based self-melting alloy weld overlay deposits. The research was supported by the Liaoning Provincial Department of Education Youth Project (LJ2017QL024) and addresses a critical engineering need for wear-resistant overlays in mining and chemical processing applications.

Core Technical Points

The study focuses on the interaction between WC particles and the iron-based matrix during the welding process, which is fundamental to understanding the wear resistance mechanism of such overlay systems. The self-melting alloy approach means that the alloying elements are pre-blended into the filler material, allowing the molten pool to achieve a homogeneous composition upon solidification without requiring external alloy addition.

Key technical aspects examined include:

The dissolution behavior of WC particles in the molten pool during welding
The formation of carbide phases (W2C, WC, and secondary carbides) in the solidified deposit
The hardness distribution from the fusion line to the surface of the overlay
The microstructural features including grain morphology, phase distribution, and segregation patterns
The relationship between microstructure and abrasive wear resistance

Microstructural Analysis and Phase Evolution

During the welding process, WC particles undergo complex metallurgical transformations. The dissolution rate of WC in the molten iron-based matrix is governed by temperature, cooling rate, and the chemical composition of the matrix. At the high temperatures achieved during welding (typically 1800-2200°C in the arc zone), WC partially dissolves, releasing tungsten and carbon atoms into the melt. Upon solidification, these elements recombine to form various carbide phases.

Parameter	Typical Range	Influence on Microstructure
Welding current	200-350 A	Higher current increases WC dissolution rate
Travel speed	5-15 cm/min	Affects cooling rate and grain size
Shielding gas flow	15-25 L/min	Prevents oxidation of tungsten carbides
Overlay thickness	3-8 mm	Thicker layers show more segregation
Cooling rate	10-50°C/s	Controls grain morphology and phase distribution

The microstructure typically exhibits a gradient from the fusion line to the surface. Near the fusion line, the base metal dilution is significant, resulting in a softer transition zone with reduced carbide concentration. Moving toward the surface, the WC content increases, and the hardness rises accordingly. The surface layer usually achieves hardness values of 700-900 HV, while the transition zone may drop to 300-500 HV.

Wear Mechanism and Engineering Implications

The wear resistance of WC-reinforced iron-based overlays operates through multiple mechanisms:

Abrasion resistance: Hard carbide particles resist abrasive particle penetration and material removal
Fatigue resistance: The ductile iron matrix absorbs energy and prevents crack propagation
Adhesion resistance: The microhardness gradient reduces adhesive transfer during sliding contact

In engineering practice, such overlays are commonly applied to components subjected to severe abrasive wear, including:

Pump impellers and casing components in slurry service
Mining equipment such as drill bits, cutting tools, and conveyor components
Hydraulic cylinder liners and valve components
Chemical processing equipment handling abrasive slurries

Common Defects and Countermeasures

Defect Type	Root Cause	Countermeasure
Tungsten carbide floatation	Low arc voltage, high travel speed	Optimize welding parameters to maintain adequate temperature
Cracking at fusion line	High dilution, residual stress	Reduce dilution rate, apply preheating and post-weld heat treatment
Tungsten carbide dissolution	Excessive heat input	Control welding parameters, use multiple thinner layers
Porosity	Moisture in flux or filler	Dry flux and filler materials, ensure adequate shielding
Delamination	Poor bonding, hydrogen embrittlement	Proper surface preparation, controlled hydrogen content

Study Insights and Engineering Reflections

The study provides valuable insight into the trade-off between WC dissolution and wear resistance. Complete dissolution of WC particles leads to a homogeneous but relatively softer deposit, while excessive retention of undissolved WC particles creates stress concentrators that may initiate cracks. The optimal balance is achieved when approximately 40-60% of the original WC particles remain partially intact, providing hard reinforcement while the dissolved portion contributes to matrix hardening through solid solution and secondary carbide precipitation.

From a practical standpoint, this research reinforces the importance of welding parameter optimization for WC-reinforced overlay systems. The self-melting alloy approach offers advantages in terms of process simplicity and consistent composition, but it also demands careful control of thermal input to prevent excessive WC degradation. For industrial applications, multi-layer welding with progressive parameter adjustments (lower heat input for surface layers) is recommended to achieve the desired hardness profile.

This research contributes significantly to the understanding of WC-iron alloy overlay systems and provides a scientific basis for optimizing welding parameters in industrial applications. The findings are particularly relevant for chemical and mining industries where wear-resistant overlays extend equipment life substantially.