CLADDING TECHNOLOGY SHANXI CO., LTDCO2 Welding and High Chromium-Molybdenum Alloy Powder Spraying Composite Overlay Layer Wear Resistance on Deep Plough Blades
Literature Overview
This topic, authored by Jiao Renbao, Yang Hai, Wang Guilian, and Shao Dongwei from Jiamusi University's School of Mechanical Engineering (2014), investigates the wear resistance characteristics of composite overlay layers produced by combining CO2 arc welding (GMAW) with high chromium-molybdenum alloy powder spraying on deep plough blade surfaces. The research was funded by the Jiamusi University Science and Technology Fund (L2013-063) and published in the Journal of Inner Mongolia University of Science and Technology. The work addresses a significant practical problem in agricultural machinery: the severe abrasive wear experienced by plough blades operating in high-abrasion soils.
Technical Background and Methodology
Deep plough blades are subjected to intense abrasive and adhesive wear mechanisms when operating in soils containing high concentrations of silica, quartz, and other hard mineral particles. Conventional high-carbon steel blades typically exhibit service lives of only 50 to 150 hours before requiring replacement or repair. The composite overlay approach investigated in this study combines two distinct surface engineering techniques:
- CO2 gas metal arc welding (GMAW): Used to deposit a thick, tough substrate layer that provides a metallurgical bond between the base blade material and the subsequent hardfacing layer.
- High chromium-molybdenum alloy powder spraying: Applied as the top wear-resistant layer, typically through flame spraying or plasma spraying, to achieve high hardness and abrasion resistance.
The composite structure leverages the toughness of the welded underlayer and the hardness of the sprayed top layer to create a synergistic wear-resistant system.
Key Technical Parameters and Microstructural Analysis
| Component | Material/Composition | Typical Hardness | Function |
|---|---|---|---|
| Base blade | Medium-carbon steel (Q235 or 45 steel) | 150 – 200 HV | Structural support |
| GMAW underlayer | H08Mn2SiA or similar | 250 – 320 HV | Metallurgical bonding, stress buffering |
| Sprayed overlay | High Cr-Mo alloy powder (Cr 20-30%, Mo 3-8%) | 700 – 900 HV | Wear resistance |
The microstructural analysis of such composite overlay systems typically reveals a gradient in hardness from the base metal through the underlayer to the sprayed overlay. The high chromium-molybdenum alloy powder, when sprayed, forms a hardfacing microstructure containing chromium carbides (Cr7C3, Cr23C6) and molybdenum carbides (Mo2C, MoC) dispersed in an austenitic or martensitic matrix. These hard carbide phases provide the primary mechanism for abrasion resistance.
Wear Mechanism Analysis
The wear behavior of the composite overlay layer can be understood through the following mechanisms:
- Abrasive wear: The primary wear mechanism in ploughing applications, where hard soil particles (quartz, feldspar) act as micro-abrasives. The hard carbide particles in the sprayed layer resist micro-ploughing and micro-cutting by the abrasive particles.
- Adhesive wear: Occurs at the interface between the plough blade and soil when asperity contacts lead to material transfer. The composite overlay reduces adhesive wear by increasing surface hardness and reducing the real contact area.
- Fatigue wear: Progressive material removal through cyclic loading during repeated ploughing cycles. The tough GMAW underlayer absorbs cyclic stresses and prevents crack propagation from the surface into the substrate.
Process Optimization and Defect Prevention
The interface between the GMAW underlayer and the sprayed top layer is critical to the overall performance of the composite overlay. Poor adhesion at this interface can lead to delamination under service loading. Key process considerations include:
- Surface preparation of the GMAW underlayer before spraying (grinding or shot blasting to create mechanical anchoring)
- Control of spray distance (typically 80 mm to 120 mm for flame spraying)
- Optimization of powder feed rate and carrier gas flow to achieve adequate particle velocity and melting
- Management of residual porosity in the sprayed layer through post-spray compaction or hot isostatic pressing
Common defects observed in such composite overlay systems include:
| Defect | Cause | Countermeasure |
|---|---|---|
| Delamination at interface | Insufficient surface roughness before spraying | Increase surface roughness to Ra 10-20 μm |
| High porosity in spray layer | Inadequate particle melting or velocity | Optimize spray parameters and powder size distribution |
| Cracking in GMAW underlayer | Excessive cooling rate or hydrogen absorption | Apply preheat and use low-hydrogen consumables |
| Uneven overlay thickness | Inconsistent spray gun movement | Implement mechanized spraying with programmed paths |
Study Insights and Engineering Implications
The composite approach of GMAW plus powder spraying represents a pragmatic solution to the wear problem in agricultural implements, particularly in regions where deep ploughing through hard, abrasive soils is common. The key insight from this work is that combining a ductile, metallurgically bonded underlayer with a hard, mechanically bonded top layer can achieve superior wear resistance compared to either technique applied alone. Engineers designing similar composite overlay systems for mining, construction, or agricultural applications should pay particular attention to the interface integrity and the residual stress state of the composite structure. The economic advantage of this approach lies in the use of relatively inexpensive CO2 gas and standard GMAW equipment for the underlayer, with the more expensive high-alloy powder reserved only for the thin top wear layer.