CLADDING TECHNOLOGY SHANXI CO., LTDAnalysis of Factors Affecting Wear Resistance of Overlay Deposited Metal
Literature Overview and Research Context
The study by Hu Yawei and Yin Yousheng (2002), published in the Journal of Shenyang University of Technology, provides a comprehensive analysis of the factors that influence the wear resistance of overlay deposited metal. This research is foundational to the field of weld overlay technology, as wear resistance is the primary performance characteristic that determines the service life and economic viability of overlay applications. The authors approach the problem from a materials science perspective, examining the relationship between the microstructure, composition, and mechanical properties of the overlay layer and its wear resistance under various contact conditions.
The significance of this work lies in its systematic treatment of the multiple factors that influence wear resistance, ranging from the intrinsic properties of the overlay material to the extrinsic factors of the operating environment and the welding process parameters. By identifying and quantifying these factors, the study provides a framework for the rational selection and optimization of overlay materials and processes for specific wear applications.
Classification of Wear Mechanisms
The authors begin by classifying the different wear mechanisms that overlay layers are subjected to in service, as the wear resistance of an overlay material is highly dependent on the dominant wear mechanism. The following table summarizes the primary wear mechanisms and the material characteristics that are most effective in resisting each mechanism:
| Wear Mechanism | Dominant Material Characteristic | Typical Overlay Material | Application Example |
|---|---|---|---|
| Abrasive wear | Hardness, carbide morphology | High-carbon martensitic steel, WC-Co composite | Conveyor rollers, crusher jaws |
| Adhesive wear | Hardness, surface finish | Stainless steel, Ni-based alloy | Pump shafts, valve seats |
| Erosive wear | Toughness, hardness | Ni-based alloy, Cr-Mo alloy | Pump impellers, nozzles |
| Corrosive wear | Corrosion resistance, hardness | Duplex stainless steel, Ni-based alloy | Chemical processing equipment |
| Fretting wear | Elastic modulus, hardness | Ni-based alloy, Co-based alloy | Turbine blades, bearings |
| Impact-abrasive wear | Toughness, hardness | High-toughness martensitic steel | Excavator buckets, hammer mills |
Understanding the dominant wear mechanism is the first step in selecting an appropriate overlay material. The authors emphasize that a material that performs well under one wear mechanism may perform poorly under another. For example, a hardfacing alloy with high hardness and excellent abrasive wear resistance may be susceptible to adhesive wear or fretting wear due to its low toughness.
Intrinsic Factors: Microstructure and Composition
The intrinsic factors that influence wear resistance include the microstructure, phase composition, carbide morphology, and mechanical properties of the overlay layer. The authors conduct a detailed analysis of each of these factors and their effects on wear resistance.
Hardness
Hardness is the most directly correlated intrinsic factor with wear resistance, particularly for abrasive wear. The authors present data showing a linear relationship between hardness and wear resistance for abrasive wear, with the wear rate decreasing by approximately 30% for every 5 HRC increase in overlay hardness. However, this relationship breaks down at hardness levels above 60 HRC, where the material becomes susceptible to brittle fracture and the wear resistance begins to decrease.
Carbide Morphology
The morphology of the carbides in the overlay layer is a critical factor in wear resistance. The authors identify three primary carbide morphologies: dispersed fine carbides, network carbides, and coarse blocky carbides. Dispersed fine carbides provide the best combination of hardness and toughness, resulting in the highest wear resistance. Network carbides along grain boundaries reduce toughness and promote crack initiation. Coarse blocky carbides provide high hardness but low toughness, leading to a brittle wear mechanism characterized by carbide pullout and material loss.
Phase Composition
The phase composition of the overlay layer determines the relative proportions of the hard and tough phases that contribute to wear resistance. The authors examine the effect of different phase compositions on wear resistance, including martensite, austenite, ferrite, and carbide phases. A balanced composition of martensite and carbides provides the best combination of hardness and toughness for most wear applications. Excessive austenite reduces hardness and wear resistance, while excessive carbide content reduces toughness and promotes brittle fracture.
Residual Stress
The residual stress state of the overlay layer is another important intrinsic factor. Compressive residual stresses on the surface of the overlay layer improve wear resistance by reducing the effective tensile stress at the crack tip and delaying crack initiation. Tensile residual stresses have the opposite effect, promoting crack initiation and accelerating wear. The authors note that the residual stress state is influenced by the welding process, the number of overlay passes, and the interpass temperature.
Extrinsic Factors: Operating Conditions and Welding Process
In addition to the intrinsic material properties, the authors examine the extrinsic factors that influence the wear resistance of overlay layers in service. These include the contact pressure, sliding speed, temperature, and the properties of the counterface material.
The contact pressure has a significant effect on wear rate. At low contact pressures, the wear rate is relatively low and the dominant wear mechanism is adhesive wear. As the contact pressure increases, the wear rate increases and the dominant mechanism transitions to abrasive wear. At very high contact pressures, the wear rate may decrease due to the formation of a protective oxide film or the development of a plastic deformation wear mechanism.
The sliding speed also influences the wear rate and mechanism. At low sliding speeds, the wear rate is relatively low and the dominant mechanism is adhesive wear. As the sliding speed increases, the wear rate increases due to the generation of heat and the formation of a tribolayer. At very high sliding speeds, the wear rate may decrease due to the formation of a lubricating film or the development of a hydrodynamic lubrication regime.
The operating temperature has a profound effect on wear resistance, particularly for materials that are susceptible to thermal softening. The authors present data showing that the wear rate of a high-carbon martensitic overlay increases by a factor of 3–5 when the operating temperature is raised from room temperature to 400°C. This is attributed to the thermal softening of the martensite phase and the coarsening of the carbides.
Welding Process Effects on Wear Resistance
The authors also examine the effects of welding process parameters on the wear resistance of the overlay layer. The welding process influences the microstructure, hardness, and residual stress state of the overlay, all of which affect wear resistance.
| Welding Parameter | Effect on Microstructure | Effect on Hardness | Effect on Wear Resistance |
|---|---|---|---|
| Heat input (low) | Fine grain, high carbide density | High hardness | High wear resistance |
| Heat input (high) | Coarse grain, coarse carbides | Lower hardness | Reduced wear resistance |
| Interpass temperature (low) | Refined microstructure | Higher hardness | Higher wear resistance |
| Interpass temperature (high) | Coarsened microstructure | Lower hardness | Reduced wear resistance |
| Number of passes (many) | Balanced microstructure | Moderate hardness | Good wear resistance |
| Number of passes (few) | Columnar grain structure | Variable hardness | Variable wear resistance |
The authors recommend the use of low heat input and low interpass temperature to achieve a fine microstructure with high hardness and good wear resistance. They also recommend the use of multiple passes to refine the microstructure and reduce the volume fraction of columnar grains, which can reduce toughness and promote crack initiation.
Key Questions and Reflections
The study provides a comprehensive analysis of the factors affecting wear resistance, but several important questions remain. First, the study does not extensively address the effect of the base material on the wear resistance of the overlay layer. In practice, the base material can influence the dilution rate, the residual stress state, and the microstructure of the overlay layer, all of which affect wear resistance.
Second, the study does not address the effect of the overlay layer thickness on wear resistance. In practice, the thickness of the overlay layer is a critical design parameter that affects both the wear life and the mechanical performance of the component. Too thin an overlay may be worn through before the component reaches the end of its design life, while too thick an overlay may lead to excessive residual stresses and reduced bond strength.
Third, the study does not address the effect of the welding sequence on the wear resistance of the overlay layer. In multi-pass overlay welding, the welding sequence can influence the residual stress state and the microstructure of the overlay layer, both of which affect wear resistance.
Study Insights and Practical Implications
The most valuable contribution of this study is the systematic framework it provides for understanding and optimizing the wear resistance of overlay layers. By identifying and categorizing the intrinsic and extrinsic factors that influence wear resistance, the study provides a roadmap for the rational selection and optimization of overlay materials and processes for specific wear applications.
For engineers involved in the design and application of weld overlay technology, this study provides essential guidance for the selection of overlay materials, the optimization of welding processes, and the prediction of wear life. The emphasis on the importance of microstructure and carbide morphology in determining wear resistance provides a practical basis for the development of overlay materials with improved wear performance.
In conclusion, this research represents a significant contribution to the understanding of the wear resistance of overlay deposited metal, and its systematic approach to the analysis of wear mechanisms and material factors provides a valuable reference for engineers working in the field of weld overlay technology.