Hardfacing Welding Wires Produced by Vacuum Suction Casting and Continuous Process

Literature Overview and Technical Significance

The article published in Chinese Surface Engineering (1993, Vol. 10, No. 3, p. 12) by Liao Qianchu provides a concise but technically rich overview of hardfacing welding wires manufactured through vacuum suction casting combined with continuous processing techniques. The wire sizes range from Φ1.5 mm to Φ8 mm and are available in cobalt-based (Co-based), nickel-based (Ni-based), and iron-based (Fe-based) alloy systems. The article highlights the versatility of these wires, which can be applied using conventional welding processes including oxyacetylene welding and tungsten inert gas (TIG/GTAW) welding, for the repair and surfacing of heat-resistant, wear-resistant, and corrosion-resistant components.

This work is particularly notable for its mention of Ni-Al intermetallic compound welding electrodes, which exhibit excellent cavitation resistance—a property of significant importance in marine engineering, hydraulic machinery, and pump impeller repair applications.

Core Technical Analysis of Wire Manufacturing

The vacuum suction casting process represents a significant advancement over traditional ingot casting and subsequent drawing methods for hardfacing wire production. The key advantages of this manufacturing route include:

• Homogeneous microstructure: Vacuum casting minimizes gas porosity and inclusion content, resulting in a cleaner, more uniform base wire that translates to improved weld deposit quality.
• Controlled alloy composition: The vacuum environment prevents oxidation of reactive alloying elements such as chromium, molybdenum, tungsten, and aluminum, ensuring accurate final chemistry in the wire.
• Continuous processing: Integration with continuous drawing and annealing operations enables consistent dimensional accuracy and mechanical property uniformity along the wire length.

The Ni-Al intermetallic compound (specifically the Ni₃Al phase) is of particular interest because it combines high-temperature strength with exceptional resistance to cavitation erosion. In pump and propeller applications, cavitation damage occurs when vapor bubbles form and collapse on metal surfaces, creating localized pressures exceeding 1000 MPa. The ordered B2 crystal structure of Ni₃Al provides resistance to this mechanism through its high cohesive energy density and the ability to accommodate cyclic plastic deformation without microcrack initiation.

Welding Process Considerations and Application Guidelines

The article specifies that these wires are suitable for both oxyacetylene welding and TIG welding, which are the two most common processes for hardfacing applications involving consumable wire. The selection between these processes depends on several factors:

Oxyacetylene welding offers:

• Lower equipment cost and greater portability for field repair work
• Deeper penetration, which can improve bond strength but increases dilution
• Suitability for thicker overlay layers and multi-pass applications
• Lower productivity compared to TIG for thin deposits

TIG (GTAW) welding offers:

• Superior control over heat input and deposition geometry
• Lower dilution rates, preserving the alloy composition of the overlay
• Cleaner welds with fewer defects such as porosity and spatter
• Better suitability for thin-walled components and precision surfacing

For the Ni-Al intermetallic compound electrodes, special process considerations apply. The high reactivity of aluminum with oxygen necessitates excellent shielding, making TIG welding with high-purity argon (≥ 99.99%) the preferred process. The preheating temperature should typically be maintained between 150–250 °C to reduce thermal cracking susceptibility, and the interpass temperature should not exceed 300 °C to prevent excessive grain growth in the overlay.

Engineering Practice Integration and Key Reflections

The practical significance of this literature extends beyond the wire manufacturing process itself. For engineers involved in equipment maintenance and repair, the availability of hardfacing wires in multiple alloy systems and sizes provides the flexibility to address diverse service conditions. The key decision framework involves matching the wire alloy system to the dominant failure mode:

1. Abrasive wear: Select high-carbon, high-chromium Fe-based wires (e.g., Fe-25Cr-4Mo) or Co-based Stellite-type wires, depending on whether the wear is dry or lubricated.
2. Corrosive wear: Select Ni-based wires with chromium and molybdenum additions, or Co-based wires for more aggressive environments.
3. Cavitation erosion: Select Ni-Al intermetallic compound wires, which provide the best cavitation resistance among commercially available hardfacing alloys.
4. High-temperature oxidation and wear: Select Co-based wires, which maintain hardness and oxidation resistance at temperatures up to 1100 °C.

From a quality control perspective, the vacuum suction casting method provides a consistent starting material, but the final overlay quality depends critically on the welding procedure. Engineers should establish qualification procedures that include metallographic examination of the overlay cross-section, hardness profiling across the overlay thickness, and, where applicable, corrosion or cavitation erosion testing. The dilution rate should be monitored through optical emission spectroscopy (OES) or laboratory chemical analysis of the overlay layer.

This 1993 publication, while concise, captures an important technological development in hardfacing consumable manufacturing. The vacuum suction casting approach has since become standard practice for high-quality hardfacing wire production, and the alloy systems described remain commercially available today. For engineers engaged in surface engineering and equipment repair, understanding the relationship between wire manufacturing quality, welding process selection, and final overlay performance is essential for achieving reliable, long-lasting results.