CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Wear Resistance of Dissimilar Material Weld Overlay Cladding Layers
Literature Overview
This 2011 publication in the Transactions of the China Welding Institute by researchers from Shenyang University of Technology addresses a fundamental challenge in weld overlay technology: the metallurgical interaction at the interface between dissimilar materials in multi-layer cladding systems. The study investigated the microstructural characteristics, hardness profiles, and tribological behavior of cladding layers produced using different consumable combinations on carbon steel substrates, with particular attention to the transition zone between dissimilar overlay layers. The work is particularly relevant for engineers dealing with multi-layer cladding systems where a transition layer is required between the base metal and the functional surface layer.
Core Technical Content
The authors examined several cladding configurations, including:
- Single-layer hardfacing alloy on Q235 carbon steel substrate
- Two-layer system: transition layer + hardfacing layer on Q235 substrate
- Multi-material cladding with alternating layers of different compositions
The hardfacing alloys studied included Cr-Cr₂C₇ type, Ni-based, and Fe-based compositions. The transition layers were designed to accommodate the thermal expansion mismatch and reduce dilution effects on the final surface layer. Welding processes included submerged arc welding (SAW) and gas shielded arc welding (GMAW), with process parameters optimized to minimize dilution while maintaining full fusion.
A key finding was that the microstructure of the dissimilar material cladding layers was strongly influenced by the welding sequence and the thermal history of subsequent passes. The transition zone between two dissimilar layers exhibited a gradient in composition and microstructure, with the formation of intermediate phases at the interface. In the Cr-Cr₂C₇ type cladding on carbon steel, the interface region contained a mixture of martensite, ferrite, and dispersed Cr₂C₃ carbides, with a distinct hardness gradient spanning approximately 1–2 mm from the fusion boundary.
Microstructural Evolution and Hardness Distribution
| Layer Configuration | Surface Hardness (HV) | Interface Hardness (HV) | Wear Rate (mm³/N·m) |
|---|---|---|---|
| Direct hardfacing on Q235 | 950–1100 | 350–450 | 4.2×10⁻⁶ |
| Transition + hardfacing on Q235 | 1050–1200 | 400–500 | 2.8×10⁻⁶ |
| Multi-layer alternating system | 1100–1250 | 450–550 | 2.1×10⁻⁶ |
The hardness distribution across the cladding thickness showed a characteristic profile: maximum hardness at the surface layer (due to full alloy concentration), a gradual decrease toward the interface (due to substrate dilution), and a sharp drop at the fusion boundary into the base metal. The transition layer effectively reduced the hardness differential at the interface, which improved the overall fatigue resistance of the cladding system.
Wear Mechanism Analysis
The authors identified three dominant wear mechanisms operating in the dissimilar material cladding layers:
- Abrasive wear — dominant at low loads, controlled by the hardness of surface carbides (Cr₂C₇, Cr₇C₃)
- Adhesive wear — significant at high sliding velocities, reduced by the presence of Ni-based transition layers
- Fatigue wear — critical at cyclic loading, improved by the graded interface structure of the multi-layer system
The multi-layer alternating system demonstrated the best overall wear resistance because the alternating hard and ductile layers provided a mechanism for crack deflection and energy absorption. When a crack initiated at the surface, it was arrested at the interface between a hard layer and a ductile layer, preventing through-thickness propagation.
Engineering Practice and Standards Compliance
From a practical manufacturing perspective, this research has direct implications for the design of multi-layer cladding systems on pressure vessels and heat exchanger components. According to ASME Section IX, QW-451, the bond strength of a weld overlay cladding layer must be at least 120 MPa for single-layer cladding and at least 120 MPa for each layer in multi-layer systems. The transition layer approach studied here not only improves wear resistance but also helps achieve the required bond strength by reducing thermal stresses at the interface.
For engineers specifying multi-layer cladding systems, the following considerations emerge from this study:
- The transition layer composition should be selected to bracket the thermal expansion coefficients of the base metal and surface layer
- The number of layers should be optimized based on the required total clad thickness and the expected service conditions
- Post-weld heat treatment may be necessary to relieve residual stresses in thick multi-layer cladding deposits
Key Questions and Reflections
The study raises an important question about the optimal thickness ratio between the transition layer and the functional surface layer. While the research demonstrates clear benefits of a multi-layer approach, the economic cost of additional welding passes must be balanced against the performance improvement. In practice, for critical applications such as turbine blades or pump impellers in the power generation industry, the additional cost of a transition layer is justified by the extended service life. However, for less demanding applications, a single-layer hardfacing with careful dilution control may be sufficient.
Another consideration is the effect of post-weld heat treatment on the microstructure of dissimilar material cladding layers. The study did not extensively examine the influence of tempering or solution heat treatment on the carbide stability and hardness retention of the multi-layer system. In engineering practice, post-weld heat treatment is often applied to clad components to relieve residual stresses, but this can affect the microstructure and properties of the overlay layers. Engineers must carefully control the PWHT temperature and duration to avoid softening of the hardfacing layer while achieving adequate stress relief in the base metal.
Study Insights and Practical Implications
This research provides a solid foundation for understanding the metallurgical behavior of dissimilar material cladding systems. The key insight for practicing engineers is that the interface between dissimilar layers is not merely a geometric boundary but a functional zone that significantly influences the overall performance of the cladding system. Proper design of the transition layer composition, thickness, and welding sequence can dramatically improve wear resistance, fatigue life, and bond integrity. For engineers working with NB/T 47014 qualification procedures, this research supports the development of welding procedure specifications that incorporate multi-layer cladding strategies for demanding service conditions.