Tungsten Carbide Overlay Welding Process for Feed Grinder Hammer Blades

Literature Overview

This paper by Liu Xuejun and Ma Songbai from Beijing Technology and Business University addresses the practical challenge of extending the service life of feed grinder hammer blades through tungsten carbide (WC) overlay welding. Published in Grain and Feed Industry in 2010, this study compares four hardening treatment processes and analyzes the WC overlay welding technology including material selection, base material considerations, preheating requirements, and robotic welding application.

Application Context and Failure Analysis

Feed grinder hammer blades are subjected to severe abrasive wear during the grinding of grain, feed, and other agricultural materials. The primary wear mechanisms include:

Abrasive wear from hard mineral particles in feed material (silica, quartz fragments)
Impact loading from high-speed rotation (typically 2500–3500 rpm)
Fatigue cracking at stress concentration points

Without surface hardening, hammer blade replacement intervals are typically 2–4 weeks of continuous operation, resulting in significant downtime and material costs.

Process Comparison and Selection

The study evaluates four hardening treatment approaches:

Process	Hardness (HRC)	Service Life Improvement	Cost	Application Suitability
Induction hardening	48–52	1.5–2×	Low	Uniform thickness parts
Flame hardening	45–50	1.3–1.8×	Low	Simple geometries
High-frequency quenching	50–55	2–3×	Moderate	Thick sections
WC overlay welding	60–65	3–5×	Moderate-High	Wear-critical areas

Tungsten Carbide Overlay Welding Process Details

Material Selection

The WC alloy material selection is critical for successful overlay welding:

WC content: Typically 60–80% WC in the alloy matrix provides optimal hardness-wear resistance balance.
Binding matrix: Cobalt-based (Co 15–25%) or nickel-based (Ni 10–20%) matrices are common, with Co offering higher hardness and Ni providing better corrosion resistance.
Carbide particle size: 2–10 μm WC particles provide the best combination of hardness and fracture resistance.

Base Material Considerations

Hammer blades are typically manufactured from:

45 steel or 40Cr steel (medium carbon or low-alloy steel)
Pre-hardened to HRC 35–40 for structural strength

The base material hardness must be compatible with the overlay to prevent cracking at the interface. Excessive hardness differential (>20 HRC) can lead to interfacial cracking during cooling.

Preheating Requirements

Preheating is essential for WC overlay welding on medium-carbon steel hammer blades:

Preheat temperature: 200–300°C
Purpose: Reduce thermal gradient, minimize residual stress, prevent base material quenching and cracking
Method: Induction heating or torch preheating applied uniformly across the welding area

Robotic Welding Application

The study highlights the advantages of robotic welding for WC overlay on hammer blades:

Consistent heat input: Maintains stable molten pool geometry and penetration
Reproducible layer thickness: Critical for uniform wear resistance
Efficiency: High deposition rate with minimal operator fatigue
Quality control: Programmable parameters ensure batch-to-batch consistency

Common Defects and Countermeasures

Defect Type	Cause	Countermeasure
Cracking in overlay	Excessive thermal stress, high carbon in base	Increase preheat, reduce heat input, use low-stress electrode
Porosity	Gas entrapment from flux decomposition	Ensure proper drying of electrode, control welding speed
Poor fusion	Insufficient heat input or contamination	Clean base surface, adjust current/voltage, ensure proper preheat
WC particle dissolution	Excessive heat input	Reduce current, increase travel speed, use lower WC melting point alloy
Delamination	Thermal mismatch, residual stress	Optimize preheat temperature, consider post-weld stress relief

Engineering Practice Integration

For feed processing facilities, the WC overlay welding approach offers significant economic benefits:

Extended service life: 3–5 times the life of unhardened blades, reducing replacement frequency from 2–4 weeks to 8–20 weeks.
Reduced downtime: Fewer blade changes mean less production interruption.
Material savings: Reusing existing blade bodies with overlay repair is more cost-effective than purchasing new blades.

The robotic welding approach is particularly suitable for production environments where multiple hammer blades require consistent overlay treatment. The process can be integrated into scheduled maintenance routines, with blades removed, overlaid, and returned to service within a single shift.

Study Insights and Recommendations

This study demonstrates that WC overlay welding is a technically mature and economically viable solution for extending hammer blade life in feed grinding applications. The key to successful implementation lies in careful attention to preheating, heat input control, and material selection. The robotic welding approach provides the consistency and repeatability needed for industrial-scale application, making it particularly attractive for large feed processing operations with high blade consumption rates.