Microstructure Analysis and Wear Resistance of MIG Melted Injection Tungsten Carbide Reinforced Wear-Resistant Overlay

Literature Overview

The 2011 study by Liu Aiguo from Shenyang Ligong University investigates the microstructure evolution and tribological performance of tungsten carbide (WC) particle-reinforced wear-resistant overlay layers produced through MIG melted injection welding. Published in the Journal of Shenyang Ligong University, this research addresses a critical engineering challenge: extending the service life of components subjected to severe abrasive and adhesive wear conditions through in-situ composite overlay fabrication. The findings have significant implications for pressure vessel components, heat exchanger tubes, and rotating equipment that experience erosive or abrasive service conditions.

Process Description and Microstructure Characteristics

The MIG melted injection welding process combines conventional GMAW with the simultaneous injection of pre-mixed powder into the arc zone. The process parameters and resulting microstructure are characterized as follows:

The microstructure of the overlay layer consists of three distinct zones:

1. Bondline zone (0.2-0.5 mm): Characterized by a thin diffusion layer where WC particles begin to react with the molten pool, forming Fe₃W₃C and Fe₆W₃C intermetallic compounds. This zone provides metallurgical bonding between overlay and base material.
2. Composite zone (bulk of overlay): Contains intact WC particles dispersed in a martensitic or austenitic matrix, depending on the filler composition. The WC particles serve as primary wear-resistant phases, while the matrix provides toughness and crack resistance.
3. Heat affected zone (base metal side): Exhibits grain refinement and potential phase transformation depending on the base material composition. For carbon steel substrates, a tempered martensite structure typically develops.

Wear Resistance Performance Evaluation

The study employs standardized wear testing protocols to quantify the improvement achieved through WC reinforcement:

The exceptional wear resistance improvement is attributed to the combined effect of hard WC particles (HV 2400-2600) acting as primary load-bearing elements and the ductile matrix providing crack initiation resistance. The optimal WC volume fraction of 30-35% provides the best balance between hardness and toughness; beyond this threshold, inter-particle cracking becomes prevalent due to insufficient matrix material to bridge between particles.

Defect Analysis and Quality Control

A critical aspect of this study is the identification and mitigation of common defects in WC-reinforced overlay layers:

The study recommends a systematic quality control approach following the PDCA cycle:

• Plan: Establish acceptable defect density limits based on service requirements
• Do: Implement in-process monitoring of arc voltage, current, and powder feed consistency
• Check: Apply non-destructive examination per JB/T 4730 after each pass
• Act: Adjust parameters based on inspection findings and mechanical test results

Integration with Pressure Vessel Engineering

While this research focuses on general wear-resistant applications, the principles directly apply to pressure vessel components experiencing erosive wear. Specific applications include:

• Hydrogenation reactor internals exposed to high-velocity gas-solid slurries
• Heat exchanger tubesheets where tube insertion causes localized wear
• Pump casings and impellers in slurry service
• Valve seats and guide surfaces in high-pressure service
• Catalyst support structures in fluidized bed reactors

For pressure vessel applications, the overlay layer must satisfy additional requirements beyond wear resistance:

• Hydrogen resistance testing per NACE MR0175/ISO 15156 for sour service
• Intergranular corrosion resistance for stainless steel overlays
• Stress corrosion cracking resistance under operating conditions
• Compliance with NB/T 47002.3 for overlay material specifications
• Acceptable bond strength per ASTM A263/A264/A265 requirements

Study Insights and Practical Recommendations

This research demonstrates that MIG melted injection welding offers a practical and economical route to producing in-situ composite overlay layers with exceptional wear resistance. The key advantage over thermal spray or hardfacing approaches is the metallurgical bonding achieved, which eliminates the risk of overlay spallation under impact loading. For engineers specifying wear-resistant overlays on pressure equipment, I recommend the following practical guidelines based on this study's findings:

1. Maintain WC particle size between 15-30 μm for optimal dispersion and bonding
2. Control total heat input to prevent excessive WC decomposition at the bondline
3. Implement preheating of 150-200°C for carbon steel substrates to reduce residual stresses
4. Use post-weld heat treatment (600-650°C for 2 hours) to relieve stresses without softening WC particles
5. Verify bond strength through shear testing or macrographic examination of cross-sections

The study's comprehensive approach to correlating process parameters with microstructure and performance provides a valuable reference framework for developing and qualifying overlay welding procedures for critical pressure vessel components. Engineers should note that the findings are most applicable to ferritic and austenitic matrix systems; for nickel-based or cobalt-based overlay matrices, additional considerations regarding phase stability and thermal expansion mismatch must be incorporated into the process design.