CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of High-Hardness Wear-Resistant Overlay Welding Electrodes
Literature Overview
High-hardness wear-resistant overlay welding electrodes are essential for protecting equipment components subjected to severe abrasive and impact wear conditions. This study focuses on the development of a new generation of overlay welding electrodes capable of achieving hardness levels exceeding 60 HRC in the as-deposited condition, with improved weldability and reduced cracking susceptibility compared to existing products. The research addresses the fundamental challenges of achieving high hardness through microstructural engineering while maintaining adequate toughness and weldability.
Core Technical Content
Electrode Design Philosophy
The development follows a systematic approach based on the following design principles:
- Microstructural engineering: Achieve high hardness through a combination of fine grain structure, solid solution strengthening, and controlled carbide precipitation.
- Weldability optimization: Control the carbon equivalent and hydrogen content to minimize hot cracking and cold cracking susceptibility.
- Deposition efficiency: Optimize the slag system for good arc stability, slag fluidity, and spatter control.
- Cost-effectiveness: Use readily available alloying elements while achieving superior performance.
Electrode Composition Design
| Element | Content (%) | Function |
|---|---|---|
| C | 2.8-3.2 | Carbide formation, solid solution strengthening |
| Cr | 12-14 | Carbide formation, oxidation resistance |
| Mo | 2.5-3.5 | Carbide formation, high-temperature strength |
| Mn | 1.2-1.8 | Deoxidation, grain refinement |
| Si | 0.3-0.6 | Deoxidation, slag modifier |
| Ni | 0.5-1.0 | Toughness improvement, grain refinement |
| V | 0.3-0.5 | Fine carbide formation |
| Fe | Balance | Base metal |
The electrode is designed as a low-hydrogen type with a cellulose-based flux coating to ensure low hydrogen content in the weld metal and minimize cold cracking susceptibility.
Microstructure and Hardness Relationship
The as-deposited microstructure consists of a martensitic matrix with dispersed carbides. The hardness is primarily determined by:
- Martensitic matrix: 55-60 HRC (contributes 60-70% of total hardness)
- Primary carbides: 85-90 HRC (Cr₇C₃, Mo₂C, VC)
- Secondary carbides: 70-75 HRC (M₇C₃, M₃C)
- Composite effect: 62-68 HRC (overall overlay hardness)
The study demonstrates that the hardness can be optimized by controlling the cooling rate and interpass temperature:
| Interpass Temperature | Cooling Rate (°C/s) | Hardness (HRC) | Cracking Susceptibility |
|---|---|---|---|
| 50-80°C | 15-20 | 65-68 | Low |
| 100-150°C | 8-12 | 62-65 | Moderate |
| 150-200°C | 5-8 | 58-62 | Moderate |
| 200-250°C | 3-5 | 52-58 | Low |
Weldability and Defect Analysis
Cracking Behavior
The high carbon and alloy content of the overlay deposit makes it susceptible to both hot cracking and cold cracking. The study systematically evaluates the cracking susceptibility using the following tests:
| Test Method | Purpose | Result |
|---|---|---|
| Fillet weld cracking test (ASME IX) | Hot cracking | Pass with controlled interpass temperature |
| Tension test (ASME IX) | Cold cracking | Pass with preheat of 100°C |
| Bend test | Ductility | Pass with 5T bend |
| Hydrogen-induced cracking test | Diffusion hydrogen cracking | Pass with low-hydrogen flux |
The key to achieving good weldability is the use of a low-hydrogen flux coating and controlled welding parameters. The diffusion hydrogen content in the weld metal is maintained below 1.0 mL/100g, which is below the critical threshold for hydrogen-induced cracking.
Common Defects and Countermeasures
| Defect Type | Cause | Countermeasure |
|---|---|---|
| Hot cracking | High carbon equivalent, impurity segregation | Reduce carbon, control sulfur and phosphorus |
| Cold cracking | Diffusion hydrogen, high hardness, low ductility | Low-hydrogen flux, preheat, post-weld heat treatment |
| Excessive spatter | High arc voltage, improper flux composition | Optimize arc voltage, improve flux composition |
| Poor slag removal | High slag viscosity | Optimize slag system, improve slag fluidity |
| Lack of fusion | Low current, improper technique | Increase current, ensure proper joint preparation |
Performance Testing and Comparison
The developed electrode is compared with existing commercial products and the following results are obtained:
| Property | Developed Electrode | Commercial Type A | Commercial Type B | Base Metal |
|---|---|---|---|---|
| Hardness (HRC) | 65-68 | 58-62 | 60-65 | 22-25 |
| Wear resistance (vs. base) | 12-15× | 8-10× | 10-12× | 1× |
| Impact toughness (J) | 15-25 | 8-15 | 10-18 | 80-100 |
| Diffusion hydrogen (mL/100g) | 0.8-1.2 | 1.5-2.5 | 1.0-1.8 | N/A |
| Deposition efficiency (%) | 95-98 | 90-95 | 92-96 | N/A |
The developed electrode achieves the highest hardness while maintaining acceptable toughness and the lowest diffusion hydrogen content, indicating superior weldability.
Engineering Applications
The developed electrode is suitable for the following applications:
- Mining equipment: Crusher jaws, cone liners, and bucket teeth
- Construction equipment: Excavator bucket teeth, dozer blades, and scraper blades
- Cement industry: Mill liners, grinding balls, and kiln wear plates
- Power generation: Boiler tubes, fan blades, and fly ash handling equipment
- Pulp and paper industry: Pulper knives, refiner plates, and screen plates
- Agricultural equipment: Plowshares, disk blades, and seed drill components
Key Insights and Reflections
The most significant insight from this study is that the traditional trade-off between hardness and toughness in wear-resistant overlay deposits can be partially overcome through careful microstructural engineering. The developed electrode achieves 65-68 HRC while maintaining 15-25 J impact toughness, which is a significant improvement over conventional products that typically sacrifice toughness to achieve hardness.
The key to this achievement is the controlled precipitation of fine, uniformly distributed carbides within a refined martensitic matrix. The addition of vanadium promotes the formation of fine VC carbides that do not significantly reduce toughness, while the chromium and molybdenum carbides provide the primary wear resistance.
Another important reflection is regarding the practical welding considerations. The developed electrode requires careful control of welding parameters, particularly the interpass temperature and heat input. The recommended welding parameters are:
- Current: 150-200 A (DCEN)
- Voltage: 22-26 V
- Travel speed: 50-80 mm/min
- Interpass temperature: 50-150°C
- Preheat: 100°C for thick sections (>20 mm)
The study also highlights the importance of proper joint preparation and welding technique. The overlay should be applied in multiple passes, with each pass breaking the previous one at an angle of 45-60 degrees to minimize residual stress and improve bonding.
In conclusion, the development of this high-hardness wear-resistant overlay welding electrode represents a meaningful advancement in surface engineering technology. The electrode achieves superior hardness and wear resistance while maintaining good weldability and toughness, making it suitable for a wide range of severe wear applications. The key to successful application lies in understanding the microstructure-property relationships and in maintaining strict control over welding parameters and technique.