Zhuojin Pipe Fitting Co., LtdMicro-Vibration Friction and Wear Properties of Deposited Metal in Different Overlay Layers Within Slip Zone
Literature Overview
This paper, published in the Tribology (Chinese and English) (2007, Vol. 27, Issue 6, pp. 519-523) by researchers from the Institute of Tribology at Southwest Jiaotong University, investigates the micro-vibration friction and wear properties of deposited metal in different overlay layers. The study uses CHR237 low-hydrogen sodium-type chromium-molybdenum-vanadium overlay welding electrode on 45# steel substrate, and systematically analyzes the microstructure, hardness, and micro-vibration friction wear behavior of different overlay layers.
The research was funded by the National Natural Science Foundation of China (Project 50521503), reflecting its significance in the field of tribology and surface engineering. The study addresses a fundamental question in overlay welding: how does the number of overlay layers affect the tribological performance of the deposited metal?
Technical Background
Micro-Vibration Friction and Wear
Micro-vibration friction is a wear mechanism that occurs when two surfaces in contact experience small-amplitude, high-frequency vibrations. This mechanism is particularly relevant in:
- Rail vehicle wheel-rail contacts
- Bearing contacts under dynamic loading
- Machine tool spindle bearings
- Aerospace engine components
- Wind turbine gearboxes
The micro-vibration wear mechanism involves:
- Initial contact: Surface asperities come into contact under normal load
- Vibration-induced micro-sliding: High-frequency, low-amplitude vibrations cause micro-sliding at asperity contacts
- Fretting damage: Repeated micro-sliding causes material removal and surface damage
- Wear scar formation: Accumulation of micro-sliding damage creates visible wear scars
CHR237 Overlay Welding Electrode
CHR237 is a low-hydrogen sodium-type electrode with a chromium-molybdenum-vanadium alloy system. The electrode composition is designed to produce a deposited metal with:
- High hardness and wear resistance
- Good toughness and crack resistance
- Suitable for overlay repair of worn steel components
- Compatibility with common carbon and low-alloy steel substrates
| Electrode Parameter | Specification |
|---|---|
| Type | Low-hydrogen sodium-type |
| Alloy system | Cr-Mo-V |
| Coating type | Basic coating |
| Polarity | DCEN (Direct Current Electrode Negative) |
| Deposition efficiency | ~100% |
| Typical deposit hardness | 35-45 HRC (as-welded) |
45# Steel Substrate
45# steel (equivalent to AISI 1045 or C45) is a medium-carbon steel with the following characteristics:
| Property | Value |
|---|---|
| Carbon content | 0.42-0.50 wt% |
| Tensile strength | 610-700 MPa |
| Yield strength | 355 MPa |
| Hardness | 229 HB (annealed) |
| Typical application | Shafting, gears, structural components |
The 45# steel substrate is representative of many industrial components that require overlay repair for wear protection.
Microstructure Analysis of Different Overlay Layers
First Layer (Closest to Substrate)
The first overlay layer, deposited directly on the 45# steel substrate, exhibits:
- Higher dilution: The base metal dilution is highest in the first layer, typically 20-35%
- Mixed microstructure: A combination of base steel microstructure and deposited metal microstructure
- Lower hardness: Due to higher dilution, the hardness is typically lower than subsequent layers
- Bonding characteristics: The interface between the first layer and substrate is critical for overall joint integrity
Intermediate Layers
The intermediate overlay layers (second, third, etc.) exhibit:
- Reduced dilution: Dilution decreases with increasing layer number, typically 5-15% in intermediate layers
- More uniform microstructure: The microstructure approaches that of the deposited metal with minimal base metal influence
- Higher hardness: Reduced dilution results in higher hardness values
- Thermal cycling effects: Each subsequent layer experiences thermal cycling from the previous layer, which can refine the microstructure
Top Layer (Surface Layer)
The top overlay layer, which forms the surface of the overlay weld, exhibits:
- Lowest dilution: Minimal base metal dilution, typically <5%
- Full deposited metal microstructure: The microstructure is essentially that of the deposited metal
- Highest hardness: Maximum hardness due to minimal dilution
- Wear surface: This layer is the primary wear surface and its properties determine the tribological performance
Hardness Distribution Across Overlay Layers
The hardness distribution across the overlay layers follows a predictable pattern:
| Layer | Hardness (Approximate) | Dilution (%) | Microstructure |
|---|---|---|---|
| Substrate (45# steel) | 229 HB | - | Ferrite + Pearlite |
| First layer | 280-320 HB | 20-35% | Mixed martensite + base structure |
| Second layer | 320-360 HB | 10-20% | Predominantly martensite |
| Third layer | 360-400 HB | 5-10% | Full martensite with carbides |
| Top layer | 400-430 HB | <5% | Martensite + Cr-Mo-V carbides |
The increasing hardness with layer number is primarily due to the decreasing dilution rate. The top layer, with minimal dilution, achieves the highest hardness and is expected to provide the best wear resistance.
Micro-Vibration Friction and Wear Results
Friction Characteristics
The study reveals that the base metal and overlay deposited metal exhibit similar friction characteristics. The coefficient of friction is relatively consistent across different overlay layers, suggesting that the fundamental friction mechanism is similar regardless of the overlay layer number.
| Layer | Coefficient of |
|---|