Development of Sintered Wear-Resistant and Heat-Resistant Overlay Welding Electrodes

Literature Overview

The paper by Xue Wentao, published in Nonferrous Metals (Smelting Section) in 2007 (Issue 1, pp. 50-52), reports on the development of a sintered-type wear-resistant and heat-resistant overlay welding electrode. Conducted at the Beijing Research Institute of Mining and Metallurgy, this research addresses a critical need in the mineral processing and heavy industry sectors for overlay welding consumables that can simultaneously withstand abrasive wear and high-temperature oxidation environments. The classification code TG422.1 identifies this as a welding electrode development study, with a focus on consumable design rather than welding process optimization.

The cold bonding and extrusion method used to manufacture the electrode is a notable aspect of this work, as it offers advantages in terms of composition control, density uniformity, and manufacturing cost compared to conventional pressed-powder electrode methods.

Core Technical Analysis

Electrode Manufacturing Methodology

The cold bonding and extrusion method involves the following key steps:

1. Powder preparation: Carefully selected metal powders are blended to achieve the target alloy composition. For a wear-resistant and heat-resistant overlay, the powder blend typically includes Fe, Cr, Mo, W, V, C, and possibly other alloying elements.
2. Binder addition: A cold binder is mixed with the powder blend to provide sufficient green strength for extrusion.
3. Extrusion: The powder-binder mixture is extruded through a die to form the electrode core rod. The extrusion process ensures high density and uniform composition throughout the rod.
4. Drying and coating: The extruded core rod is dried to remove residual moisture and then coated with the flux coating.
5. Curing: The coated electrode is cured in an oven to harden the coating and ensure proper adhesion.

The advantages of this manufacturing method include:

• Precise composition control: The powder blending process allows for accurate control of alloy composition, which is critical for achieving the desired microstructure and properties.
• High density: The extrusion process produces a dense, uniform core rod with minimal porosity, which improves arc stability and reduces gas porosity in the weld deposit.
• Cost effectiveness: Compared to sintered powder metallurgy methods, cold bonding and extrusion is less energy-intensive and can be implemented with relatively simple equipment.

Microstructural and Property Characterization

The study characterizes the overlay weld deposit through metallographic examination, hardness testing, wear testing, and high-temperature oxidation testing. The key results are summarized below:

The average hardness of 55.7 HRC indicates the presence of hard carbide phases within a martensitic or austenitic matrix. The relative wear resistance of 1.28 suggests a meaningful improvement over the base material, though this is not exceptional compared to specialized hardfacing alloys that can achieve relative wear resistances of 2.0-5.0 or higher. This suggests that the electrode design prioritizes a balance of wear resistance, heat resistance, and weldability rather than maximizing wear resistance alone.

Application-Oriented Design Considerations

The development of a sintered-type overlay welding electrode for wear and heat resistance applications requires careful consideration of several design factors:

• Alloy composition: The balance between Cr, Mo, W, V, and C content determines the type and amount of hard phases formed. Higher Cr content promotes M7C3 and M23C6 carbides, while Mo and W promote MC carbides. The carbon content must be sufficient to form carbides but not so high as to compromise weldability.
• Weldability: The electrode must produce sound welds with minimal defects (cracks, porosity, spatter). The flux coating composition is critical for arc stability, slag fluidity, and deoxidation.
• Deposition efficiency: The electrode should have a reasonable deposition rate to minimize welding time and cost.
• Dilution tolerance: The overlay alloy should maintain its properties even with some dilution from the base metal, which is inevitable in most overlay welding applications.

Engineering Practice and Quality Control

From a practical standpoint, the development of a new overlay welding electrode requires a comprehensive qualification program that includes:

1. Chemical analysis of the electrode core: Verification of alloy composition against the design specification.
2. Welding procedure qualification: Determination of optimal welding parameters (current, voltage, travel speed, electrode angle) for sound weld formation.
3. Mechanical property testing: Hardness, tensile strength, impact toughness, and fatigue resistance of the overlay deposit.
4. Wear testing: Pin-on-disk or block-on-ring testing under conditions representative of the intended service environment.
5. High-temperature testing: Oxidation testing at service temperatures to evaluate scale formation and spallation resistance.
6. Thermal cycling testing: Assessment of thermal fatigue resistance for applications involving repeated heating and cooling cycles.
7. Non-destructive testing: Visual inspection, magnetic particle testing, and possibly ultrasonic testing to detect surface and subsurface defects.

The study's focus on thermal corrosion and high-temperature oxidation resistance suggests intended applications in environments such as furnace linings, kiln components, and heat exchanger tubes. In these applications, the overlay weld must withstand not only mechanical wear but also chemical attack from molten scale, slag, or corrosive gases.

Study Insights and Implications

The development of sintered-type overlay welding electrodes using cold bonding and extrusion methods represents a practical approach to producing specialized welding consumables with tailored properties. The reported hardness of 55.7 HRC and relative wear resistance of 1.28 indicate a consumable that offers meaningful performance improvement over conventional base materials while maintaining good weldability. For engineers involved in the selection and specification of overlay welding consumables, this study provides a useful reference point for understanding the relationship between electrode manufacturing method, alloy composition, and final deposit properties. The cold bonding and extrusion method is particularly attractive for small to medium production runs where the flexibility to adjust composition and the cost advantages of simpler manufacturing equipment are valued. The key challenge remains in scaling the technology to industrial production while maintaining the quality and consistency achieved in laboratory conditions.