CLADDING TECHNOLOGY SHANXI CO., LTDStudy Note on Self-Generated Carbide Particle Metal Overlay Cladding Layer Wear Resistance
Literature Overview
The paper by Ma Zhuang, Wei Lifeng, Shi Haifang, Dong Shizhi, and Li Zhichao from Liaoning Technical University, published in 2011 in the journal "Ordnance Materials and Engineering," investigates the wear resistance characteristics of overlay cladding layers that contain self-generated carbide particles. This research is particularly relevant to engineers working on abrasive wear protection for mining equipment, mining machinery, and industrial components subjected to severe sliding and impact wear conditions.
Core Technical Content
The study focuses on a critical phenomenon in high-carbon overlay welding systems: the in-situ formation of hard carbide phases during the solidification and post-weld heat treatment of the cladding layer. Unlike externally added hard particles, self-generated carbides form during the welding process itself through reactions between carbon and alloying elements such as chromium, molybdenum, and vanadium present in the filler metal composition.
The key findings include:
- Self-generated carbide particles typically exhibit hardness values exceeding 1500 HV when properly formed, providing exceptional resistance to abrasive wear.
- The morphology and distribution of these carbides are strongly influenced by cooling rate, carbon content, and alloying element ratios within the overlay composition.
- Carbide types identified include Cr7C3, Cr3C2, Mo2C, and VC, with their relative proportions depending on the specific filler metal chemistry.
Microstructural Analysis and Phase Evolution
The solidification microstructure of the overlay layer typically shows a dendritic matrix with interdendritic carbide precipitation. The cooling rate in the weld overlay process creates a gradient from the fusion line to the top surface, resulting in varying carbide morphologies:
| Parameter | Near Fusion Line | Mid-Layer | Top Surface |
|---|---|---|---|
| Cooling Rate (°C/s) | High (>500) | Medium (100-500) | Lower (<100) |
| Carbide Morphology | Fine, dispersed | Medium, semi-continuous | Coarse, interconnected |
| Typical Hardness (HV) | 1200-1500 | 1000-1300 | 800-1100 |
| Matrix Structure | Martensite + retained austenite | Martensite + bainite | Bainite + ferrite |
The interplay between the hard carbide phases and the tough matrix is essential for achieving a balance between wear resistance and fracture toughness. Excessive carbide coarseness or network formation can lead to brittle failure under impact loading.
Engineering Practice Implications
From a practical standpoint, this research provides guidance for selecting overlay welding consumables for applications such as:
- Coal mining shovels and bucket teeth subjected to high-impact abrasive wear
- Cement mill grinding rollers exposed to sliding wear
- Mining crusher components experiencing combined abrasion and impact
The critical process parameters for controlling self-generated carbide formation include:
- Preheat temperature: 150-250°C to reduce thermal cracking tendency while maintaining adequate cooling rate
- Interpass temperature: 100-150°C to prevent excessive carbide coarsening in multi-pass overlays
- Heat input range: 15-35 kJ/cm for shielded metal arc welding (SMAW) to optimize carbide morphology
- Post-weld heat treatment: Temper at 500-600°C for 2-4 hours to relieve residual stresses without dissolving primary carbides
Key Defects and Countermeasures
A common defect in carbide-bearing overlay layers is intergranular cracking along the carbide network. This occurs when the continuous carbide network exceeds approximately 30% volume fraction, creating stress concentration sites. Countermeasures include:
- Reducing carbon equivalent in the filler metal to limit total carbide volume fraction
- Adding nickel (2-5%) to improve matrix toughness and reduce carbide network continuity
- Employing multi-pass welding with dilution control to manage carbon distribution
- Applying stress-relief heat treatment immediately after welding
Study Insights and Reflections
This 2011 research remains highly relevant to contemporary overlay welding practice. The fundamental principle that self-generated carbides can provide superior wear resistance compared to externally added particles continues to drive consumable development. However, modern applications increasingly demand multi-functional overlays that combine wear resistance with corrosion resistance and thermal stability, which requires more sophisticated alloy design approaches. The legacy of this work is evident in current high-carbon chrome overlay electrodes and wire consumables used worldwide in mining and aggregate processing industries.