Zhuojin Pipe Fitting Co., LtdOverlay Welding Remanufacturing of Mining Chain Wheels and Post-Repair Performance Evaluation
Literature Overview
This paper published in "Materials in Mechanical Engineering" in 2025 by Wang Liang from the School of Energy and Power Engineering, Lanzhou Petrochemical Vocational and Technical University, presents a comprehensive study on the overlay welding remanufacturing of worn mining chain wheels made of 40CrNiMoA medium carbon quenched and tempered steel. The research addresses the significant economic and environmental challenges associated with mining equipment maintenance, demonstrating that overlay welding can not only restore but also enhance the performance of worn chain wheels beyond their original condition. This work is supported by the Gansu Provincial Department of Education Science and Technology Innovation Research Project (2022B-319).
Engineering Background and Problem Definition
Mining chain wheels are critical components in underground mining transport systems, subjected to severe abrasive wear from chain links, rock particles, and mineral dust. The 40CrNiMoA steel used for these chain wheels is a medium carbon alloy steel with excellent strength and toughness properties after quenching and tempering, but it lacks inherent resistance to abrasive wear. When chain wheels become worn beyond acceptable limits, traditional replacement requires significant material and financial resources, while discarding worn components contributes to environmental waste.
The remanufacturing approach using overlay welding offers a sustainable alternative by restoring the functional surface while potentially improving wear resistance. The challenge lies in selecting appropriate welding consumables, process parameters, and post-weld heat treatment to achieve a wear-resistant overlay layer with good metallurgical bonding to the substrate, without introducing defects such as cracks, porosity, or excessive residual stress.
Two-Layer Overlay Welding Strategy
The study employs a two-layer overlay welding approach using argon-enriched gas shielded arc welding (GMAW with argon-enriched shielding gas):
Layer 1: Transition Layer
- Welding wire: JM100 structural steel wire
- Thickness: 10 mm
- Post-weld heat treatment: 400°C for 2–3 hours (tempering)
The JM100 structural steel wire was selected for the transition layer because its composition closely matches the 40CrNiMoA substrate, minimizing the risk of cracking at the substrate-overlay interface. The 400°C tempering treatment after depositing the transition layer serves multiple purposes: it relieves welding residual stresses that could lead to cracking during subsequent welding, it stabilizes the microstructure of the transition layer, and it prepares the surface for the deposition of the wear-resistant layer.
Layer 2: Wear-Resistant Overlay Layer
- Welding wire: YD256 wear-resistant flux-cored wire
- Thickness: 10–15 mm
- Post-weld heat treatment: 350°C for 3 hours (tempering)
The YD256 flux-cored wire is specifically designed for depositing high-hardness, wear-resistant overlay layers. The 350°C tempering treatment after the overlay layer deposition optimizes the hardness-toughness balance of the wear-resistant layer while maintaining good metallurgical bonding with the transition layer.
| Parameter | Transition Layer | Wear-Resistant Layer |
|---|---|---|
| Welding wire | JM100 structural steel | YD256 wear-resistant FCAW |
| Thickness | 10 mm | 10–15 mm |
| Post-weld HT | 400°C × 2–3 h | 350°C × 3 h |
| Primary purpose | Metallurgical compatibility | Wear resistance |
| Microstructure | Acicular ferrite + lamellar pearlite | Ferrite + pearlite + tempered martensite + carbides |
Metallurgical Analysis and Microstructural Characterization
Transition Layer Microstructure
The transition layer exhibits a microstructure composed of abundant acicular ferrite and a small amount of lamellar pearlite. The acicular ferrite grains are fine and uniformly distributed, which provides good toughness and resistance to cracking. The formation of acicular ferrite is attributed to the cooling rate achieved during welding and the alloy composition of the JM100 wire, which promotes the nucleation of ferrite at carbon-depleted regions ahead of the advancing austenite grain boundaries.
Wear-Resistant Layer Microstructure
The wear-resistant overlay layer displays a complex microstructure consisting of ferrite, pearlite, tempered martensite, and particulate carbides. This heterogeneous microstructure is the key to achieving the enhanced wear resistance observed in the study. The tempered martensite provides high hardness, while the ferrite and pearlite phases contribute to toughness. The particulate carbides, likely consisting of alloy carbides such as Fe₃C, Cr₇C₃, and possibly Mo₂C, provide additional wear resistance through their high hardness and resistance to abrasive deformation.
Metallurgical Bonding
The interface between the overlay layers and the substrate exhibits good metallurgical bonding with no porosity, cracks, or other defects observed. This is a critical finding because interfacial defects are the primary failure mechanism in overlay welding applications. The absence of defects indicates that the welding parameters, preheating, and inter-pass temperature control were properly managed throughout the welding sequence.
Performance Comparison and Results
The study presents a compelling comparison between the overlay-repaired chain wheel and the unworn new chain wheel:
| Property | Overlay-Repaired | Unworn New | Improvement |
|---|---|---|---|
| Hardness | 57.2 HRC | 52.2 HRC | +9.6% |
| Tensile strength | 842 MPa | 753 MPa | +11.8% |
| Impact energy | 110 J | 87 J | +26.4% |
| Friction wear mass loss | ~32% of new | 100% | -68% |
| Abrasive wear mass loss | ~24% of new | 100% | -76% |
The most remarkable finding is that the overlay-repaired chain wheel outperforms the unworn new chain wheel in all tested properties. The 9.6% increase in hardness, 11.8% increase in tensile strength, and 26.4% increase in impact energy demonstrate that the overlay welding process not only restores but enhances the mechanical properties of the chain wheel. The significant reduction in wear mass loss (68% for friction wear and 76% for abrasive wear) confirms the effectiveness of the wear-resistant overlay layer.
Process Optimization and Practical Considerations
The selection of welding parameters and post-weld heat treatment temperatures is critical to achieving the desired results. The 400°C tempering for the transition layer and 350°C tempering for the wear-resistant layer represent optimized temperatures that balance hardness retention with residual stress relief. Higher tempering temperatures would reduce hardness but provide greater stress relief, while lower temperatures would maintain higher hardness but risk cracking from residual stresses.
The use of argon-enriched shielding gas provides better arc stability and penetration characteristics compared to standard CO₂ shielding, which is particularly important for achieving consistent weld quality across multiple layers. The flux-cored wire used for the wear-resistant layer provides self-shielding properties that complement the external gas shielding, ensuring good weld quality even in field conditions where wind or drafts might affect the shielding gas coverage.
Engineering Practice Implications
From a remanufacturing perspective, this study demonstrates that overlay welding is a viable and economically attractive alternative to replacement for worn mining chain wheels. The key engineering considerations include:
- Surface preparation: Thorough cleaning and machining of the worn surface to remove loose material and provide a good bonding surface for the overlay layer.
- Preheating: Appropriate preheating of the substrate to prevent cracking, particularly important for the high-carbon equivalent 40CrNiMoA steel.
- Layer sequencing: The transition layer followed by the wear-resistant layer ensures metallurgical compatibility and optimal wear performance.
- Post-weld heat treatment: The two-step tempering process (400°C for transition layer, 350°C for overlay layer) optimizes both bonding quality and wear performance.
- Quality control: Visual inspection, magnetic particle testing, and hardness mapping should be performed to ensure defect-free overlay layers.
Key Reflections and Technical Insights
The most significant insight from this study is the demonstration that overlay welding remanufacturing can produce components with superior performance to new components. This challenges the conventional wisdom that remanufactured parts are inherently inferior to new parts. The enhanced performance is attributed to the wear-resistant overlay layer's superior microstructure, which combines high hardness from tempered martensite and carbides with adequate toughness from ferrite and pearlite.
The impact energy improvement of 26.4% is particularly noteworthy because it suggests that the overlay welding process, combined with the post-weld heat treatment, may have produced a more favorable microstructure in the heat-affected zone of the substrate compared to the original quenched and tempered condition. This could be due to the tempering treatment during overlay welding effectively relieving any residual stresses from the original heat treatment and producing a more uniform microstructure.
Reference Value and Outlook
This study provides valuable technical data for the remanufacturing of mining chain wheels and similar abrasive wear components. The two-layer overlay welding approach with optimized post-weld heat treatment offers a practical and effective solution for extending the service life of worn mining equipment. Future research could explore the long-term field performance of overlay-repaired chain wheels, the effect of different welding consumables on overlay layer properties, and the economic analysis comparing overlay welding remanufacturing with component replacement.