CLADDING TECHNOLOGY SHANXI CO., LTDEDC68 High-Hardness Wear-Resistant Overlay Welding Electrode Study Note
Literature Overview
This research, published in 2001 by Yin Ruiming, Yin Shunsheng, Zhong Dingming, and Yin Yuming from the Welding Research Institute of Zhuzhou Institute of Technology, presents the development and characterization of the EDC68 overlay welding electrode. The electrode is designed for high-hardness, high-wear-resistant applications where surface hardness exceeding 60 HRC is required. The study represents a significant contribution to the field of surfacing welding consumables, particularly for components subjected to severe abrasive and impact wear conditions in mining, cement, and material handling industries.
Electrode Composition and Metallurgical Design
The EDC68 electrode belongs to the EDC series developed by the Zhuzhou Institute of Technology, which has a long history of producing specialized surfacing electrodes for the Chinese heavy industry sector. The "68" designation indicates a target hardness of approximately 68 HRC in the as-deposited condition, achieved through a carefully designed alloy system rich in carbon and alloying elements that form hard carbides.
| Designation Element | Specification | Technical Significance |
|---|---|---|
| E | Electrode coating type | Cellulose or rutile coating for DC welding |
| D | Special alloy composition | High carbon, high alloy content |
| C | Carbon content classification | >2.5% C for carbide formation |
| 68 | Target hardness (HRC) | As-deposited overlay hardness |
The base metal composition of the EDC68 electrode wire typically contains 3-4% carbon, 15-20% chromium, and additional elements such as tungsten, vanadium, and molybdenum. These elements form complex carbides (Cr₇C₃, WC, VC, Mo₂C) that provide the wear resistance through a combination of high hardness and good bonding with the matrix. The electrode coating composition is designed to provide a stable arc, good slag coverage, and controlled dilution from the base metal.
Microstructure and Hardness Characteristics
The overlay microstructure of EDC68 consists of a dendritic austenitic or martensitic matrix with a high density of dispersed carbide particles. The as-deposited hardness typically ranges from 65-72 HRC, with the possibility of achieving higher values through proper welding technique. The hardness is primarily attributed to:
- Primary carbides formed during solidification (Cr₇C₃, Fe₃C, WC, VC)
- Secondary carbides precipitated during cooling (fine dispersion strengthening)
- Possible martensitic transformation in the matrix due to high carbon content
- Solid solution strengthening from dissolved alloying elements
The study examined the relationship between welding parameters and overlay hardness. Key findings include:
| Welding Parameter | Low Value | High Value | Effect on Hardness |
|---|---|---|---|
| Current | 80-100 A | 140-180 A | Higher current → more dilution → lower hardness |
| Arc voltage | 20-24 V | 26-30 V | Higher voltage → wider bead → more dilution |
| Travel speed | 200 mm/min | 400 mm/min | Higher speed → less dilution → higher hardness |
| Number of passes | Single | Multi-pass | Multi-pass → tempering effect → lower hardness |
Engineering Application and Performance
The EDC68 electrode is primarily applied to components experiencing severe abrasive wear, such as:
- Excavator bucket teeth and cutting edges
- Cement mill liners and grinding elements
- Crusher jaws and cones
- Conveyor rollers and scraper blades
- Pump impellers and wear plates in slurry service
The study demonstrated that the EDC68 overlay provides 3-5 times the wear life of standard carbon steel in abrasive applications. However, the high hardness comes with trade-offs in toughness and weldability. The overlay layer is susceptible to cracking during welding if proper preheating and interpass temperature control are not maintained. The recommended preheat temperature for carbon steel substrates is 150-250°C, with interpass temperatures maintained below 200°C to prevent excessive softening of previously deposited layers.
Defect Analysis and Countermeasures
Common defects encountered with EDC68 overlay include:
- Cracking in the overlay due to high carbon content and martensitic transformation
- Poor bonding at the overlay-base interface due to excessive dilution
- Porosity from inadequate arc shielding or contaminated base metal
- Excessive spatter and poor bead profile
Countermeasures include:
- Using DCEN (direct current electrode negative) polarity for better penetration control
- Maintaining short arc length for reduced atmospheric contamination
- Applying multiple thin passes with controlled interpass temperature
- Thoroughly cleaning the base metal surface prior to welding
- Using a back purge or backing bar to prevent oxidation at the root
Study Insights and Practical Implications
The EDC68 electrode represents a practical solution for severe wear applications where hardness is the primary performance requirement. The study's systematic approach to correlating composition, microstructure, and wear performance provides a template for developing similar overlay consumables. Engineers should note that while the as-deposited hardness is impressive, the actual service performance depends on the balance between hardness and toughness. In applications involving impact loading, the brittle nature of the high-carbon overlay may lead to spalling or chipping, and a graded approach with a tougher transition layer may be necessary. The research contributes to the broader understanding of carbide-forming systems in surfacing welding and provides a useful reference for selecting appropriate consumables in wear-resistant applications.