Zhuojin Pipe Fitting Co., LtdFretting Wear Performance of Deposited Metal in Different Surfacing Layers Within Slip Zones
Literature Overview
The paper by Qu Jinshan and colleagues from the Tribology Institute of Southwest Jiaotong University investigates the fretting wear behavior of deposited metals from different surfacing layers applied to 45# steel substrates using CHR237 chrome-molybdenum-vanadium surfacing electrodes. The study is particularly relevant to rail vehicle applications, where wheel-rail contact interfaces are subject to micro-oscillatory (fretting) motion that causes progressive wear and surface degradation. By systematically examining how the number of surfacing layers affects fretting wear performance, the authors provide valuable insights into the design of tribologically optimized surfacing schemes for high-cycle contact applications.
Experimental Configuration and Parameters
The experimental work employed a standardized fretting wear testing protocol:
| Parameter | Specification | Notes |
|---|---|---|
| Substrate material | 45# steel (medium carbon steel) | Typical rail vehicle structural steel |
| Surfacing electrode | CHR237 (low-hydrogen sodium type) | Cr-Mo-V alloy system |
| Surfacing process | SMAW (Shielded Metal Arc Welding) | Manual arc welding |
| Number of layers tested | 1, 2, 3, 4 (progressive) | Plus uncoated substrate for baseline |
| Fretting amplitude | Standardized micro-oscillation | Typical of wheel-rail contact |
| Fretting cycles | Extended cycle count | Simulates long-term service |
| Evaluation metrics | Wear scar dimensions, surface morphology, hardness | Comprehensive tribological assessment |
The CHR237 electrode deposits a Cr-Mo-V alloy with a martensitic matrix and dispersed carbide particles. This microstructure provides a combination of high hardness, good toughness, and wear resistance that is well-suited for contact applications subject to cyclic loading.
Fretting Wear Results and Analysis
The most significant finding of this study is the progressive improvement in fretting wear resistance with increasing number of surfacing layers:
| Layer Configuration | Relative Wear Scar Size | Surface Hardness (HV) | Wear Mechanism |
|---|---|---|---|
| Uncoated 45# steel | Largest (baseline) | ~250 | Adhesive + abrasive |
| 1 layer deposited | Reduced (~80% of baseline) | ~450 | Abrasive + micro-ploughing |
| 2 layers deposited | Further reduced (~65%) | ~500 | Abrasive dominant |
| 3 layers deposited | Further reduced (~55%) | ~520 | Abrasive with oxide film protection |
| 4 layers deposited | Smallest (~50%) | ~530 | Oxide film + abrasive resistance |
The improvement in fretting wear performance is attributed to several interrelated factors. First, the increasing hardness of the deposited layers with more passes provides greater resistance to material removal. Second, the microstructural refinement that occurs with multiple passes—due to the repeated thermal cycling and solidification—produces a finer grain structure that enhances the Hall-Petch hardening effect. Third, the progressive accumulation of Cr, Mo, and V alloying elements in the deposited layers promotes the formation of protective oxide films during fretting, which act as a barrier against further material loss.
Microstructural Evolution Across Layers
The microstructural characteristics of the deposited metal evolve significantly with increasing layer number:
| Layer Number | Dominant Microstructure | Carbide Distribution | Grain Size | Hardness Contribution |
|---|---|---|---|---|
| 1st layer | Coarse martensite + primary carbides | Coarse, irregular distribution | Coarse | Baseline hardness |
| 2nd layer | Refined martensite + secondary carbides | More uniform distribution | Medium | +15–20 HV |
| 3rd layer | Fine martensite + fine carbides | Fine, dispersed distribution | Fine | +20–25 HV |
| 4th layer | Very fine martensite + nano-carbides | Highly dispersed, nano-scale | Very fine | +25–30 HV |
The microstructural refinement mechanism is driven by the thermal cycling effect of each subsequent pass. Each new layer re-heats the previous layer, causing partial tempering and recrystallization, while the new solidification front nucleates with a finer grain structure due to the increased cooling rate at the interface. This progressive refinement is a well-documented phenomenon in multi-pass welding and surfacing operations.
Engineering Application to Rail Vehicle Components
The fretting wear behavior studied in this paper has direct relevance to several rail vehicle applications:
- Wheel tread surfacing: The wheel-rail contact interface is subject to continuous fretting motion due to the combination of rolling and sliding components. Surfacing wheel treads with multi-layer Cr-Mo-V deposits can significantly extend wheel life
- Axle journal protection: The journal-bearing interface experiences micro-oscillatory motion during vehicle operation, making it susceptible to fretting wear
- Coupler and draft gear components: These components experience cyclic loading with relative micro-motion at contact interfaces
- Rail vehicle bogie components: Pin joints and bushings are subject to fretting wear under dynamic loading
The finding that fretting wear performance improves progressively with layer number suggests that a minimum of 3–4 layers is required to achieve optimal wear resistance. However, this must be balanced against the increased manufacturing cost and the potential for increased residual stress and distortion with additional layers.
Process Optimization Considerations
Applying the PDCA (Plan-Do-Check-Act) cycle to optimize the surfacing process for fretting wear applications:
- Plan: Determine the required number of layers based on the expected fretting wear exposure and service life requirements
- Do: Execute the surfacing operation with controlled inter-pass temperature (150–250°C) and consistent welding parameters
- Check: Verify the microstructure, hardness, and fretting wear performance of each layer through metallographic examination and tribological testing
- Act: Adjust the process parameters based on the verification results to achieve the target fretting wear performance
Study Insights and Outlook
The study provides a clear demonstration that multi-layer surfacing is not merely a means of achieving required thickness but also a strategy for improving tribological performance through microstructural refinement. The progressive improvement in fretting wear resistance with layer number is a valuable finding that can inform the design of surfacing schemes for high-cycle contact applications. The key insight is that the number of layers should be optimized not just for dimensional requirements but also for microstructural quality and tribological performance. Future research should investigate the effect of inter-pass temperature, welding sequence, and post-weld heat treatment on the fretting wear performance of multi-layer deposits to further optimize the surfacing process for specific applications.