Development of High-Chromium Wear-Resistant Overlay Welding Electrodes for Carbonization Plant Equipment

Literature Overview

The paper by Wang Guoyong and Liu Xiangyu from Chengde Petroleum College (Thermal Processing Technology, 2012, Volume 41, Issue 3, pages 162-163) reports the development of a high-chromium wear-resistant overlay welding electrode specifically designed for the repair of spiral augers (screw conveyors) used in carbonization plants. The study addresses the practical need for durable overlay materials that can withstand the severe abrasive and impact wear conditions encountered in coal handling and carbonization processes. The developed electrode demonstrated good service performance in actual industrial application.

Technical Analysis

Service Environment Analysis

Spiral augers in carbonization plants operate under exceptionally harsh conditions:

High-Chromium Alloy Design

The high-chromium overlay alloy system is based on the well-established principle that chromium promotes the formation of hard chromium carbides (M7C3, M23C6, and Cr7C3) that provide excellent abrasion resistance. The typical composition of the developed electrode likely includes:

Microstructure and Wear Mechanisms

High-chromium overlay layers typically exhibit one of two microstructural variants:

White cast iron structure (hypereutectic):

• Matrix: Martensite or austenite
• Reinforcement: Primary Cr7C3 (hexagonal) and secondary M7C3 (monoclinic) carbides
• Hardness: HV 1000-1400
• Wear mechanism: Abrasion resistance through hard carbide particles
• Limitation: Brittle, susceptible to chipping under impact

Austenitic structure (hypoeutectic with high Ni/Mn):

• Matrix: Austenite with retained austenite
• Reinforcement: Fine M7C3 carbides
• Hardness: HV 500-800
• Wear mechanism: Work hardening + carbide abrasion resistance
• Advantage: Better impact resistance, no chipping

For spiral auger applications, a balanced approach is typically preferred—sufficient hardness for abrasion resistance combined with adequate toughness to resist impact chipping.

Electrode Manufacturing Considerations

The development of a specialized overlay electrode involves several critical manufacturing considerations:

1. Flux coating formulation: Must provide adequate deoxidation, slag protection, and alloying element transfer
2. Coating uniformity: Consistent coating thickness is essential for stable arc characteristics
3. Moisture control: Flux coating must be dried to prevent hydrogen-induced cracking
4. Arc stability: Electrode design must ensure stable arc for consistent weld quality
5. Deposition efficiency: High deposition efficiency reduces dilution and maximizes overlay performance

Engineering Practice Integration

Application to Spiral Auger Repair

The repair procedure for spiral augers typically involves:

1. Surface preparation: Grind off damaged material, prepare weldable surface with adequate groove geometry
2. Preheating: 100-200°C to prevent HAZ cracking in the base material (typically Q235 or Q345 steel)
3. Transition layer: Apply 1-2 layers of 309L or similar alloy to bridge compositional gap
4. Overlay application: Apply 2-4 layers of high-chromium overlay electrode, achieving 3-5 mm total thickness
5. Post-weld treatment: Light grinding to achieve smooth surface finish
6. Quality verification: Visual inspection, hardness testing, and dimensional verification

Performance Comparison

Quality Control Checklist

For field application of high-chromium overlay electrodes, the following quality control measures should be implemented:

• Visual inspection: No surface cracks, porosity, or incomplete fusion
• Hardness testing: Minimum HV 800 for the top layer (after proper testing technique)
• Thickness verification: Achieve specified overlay thickness (typically 3-5 mm)
• Service life tracking: Monitor wear rate and compare with expected performance
• Periodic re-overlay: Plan maintenance intervals based on wear rate data

Study Insights and Practical Reflections

This paper, while brief, addresses a very practical engineering problem that is common across many heavy industries. The development of purpose-specific overlay electrodes for particular service conditions represents good engineering practice—tailoring materials to specific applications rather than using generic solutions.

The study highlights several important points for practitioners:

1. Cost-effectiveness: High-chromium iron-based alloys provide excellent wear resistance at a fraction of the cost of cobalt-based alternatives, making them economically viable for large-scale industrial applications.
2. Field applicability: The use of SMAW electrodes ensures that repairs can be performed in the field with minimal equipment requirements, which is critical for industrial maintenance operations.
3. Material selection trade-offs: The choice between white cast iron structure (high hardness, low toughness) and austenitic structure (moderate hardness, good toughness) must be made based on the specific wear mechanism. For spiral augers handling abrasive coal and ash, a balanced approach with adequate impact resistance is essential.
4. Process control: Even with appropriate material selection, proper welding technique and quality control are essential to achieve the expected performance. Inconsistent overlay quality can lead to premature failure and negate the material benefits.

The practical success of this electrode in carbonization plant service validates the approach and demonstrates that systematic material development, even at the level of electrode formulation, can deliver significant improvements in equipment reliability and maintenance economics.