CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Wear Resistance of Dissimilar Material Weld Overlay Layers
Literature Overview
This paper by Liu Zhengjun, Song Xingkui, and Tang Xingtao from Shenyang University of Technology, published in the Journal of Welding in 2011, addresses a fundamental challenge in wear-resistant cladding engineering: understanding how the microstructure of dissimilar material weld overlay deposits influences their wear resistance. The study investigates the relationship between the metallurgical characteristics of overlay layers formed on dissimilar substrate-overlay combinations and their resulting tribological performance. This is a critical topic because in industrial practice, overlay layers are frequently deposited onto substrates of different compositions—such as nickel-based alloys on carbon steel, or stainless steels on low-alloy steels—and the resulting intermetallic formation, grain morphology, and phase distribution directly govern the service life of the component.
Core Technical Content
The authors systematically examined the microstructure evolution in dissimilar weld overlay systems, paying particular attention to the influence of substrate dilution, cooling rate effects, and the resulting hard phase distribution. The study utilized optical microscopy, scanning electron microscopy, X-ray diffraction, and microhardness profiling to characterize the overlay deposits. The key finding was that the dilution rate between the substrate and the overlay material plays a decisive role in determining the hardness profile and wear resistance of the final deposit.
Microstructural Characteristics
The study identified several critical microstructural features that correlate with wear performance:
| Feature | Influence on Wear Resistance | Typical Range Observed |
|---|---|---|
| Carbide morphology | Harder and more uniformly distributed carbides improve abrasive wear resistance | 2–15 μm particle size |
| Dilution rate | Excessive dilution reduces hardness and wear life | 5–30% typical for single-pass |
| Grain orientation | Columnar grains aligned with cooling direction affect crack propagation | Columnar to equiaxed transition at 10–15 mm from root |
| Phase composition | Presence of M7C3, M23C6, or M6C carbides enhances hardness | Varies with alloy system |
| Residual stress | Compressive residual stress in surface layers improves fatigue wear resistance | -100 to +200 MPa |
Key Findings on Wear Mechanisms
The authors classified the wear mechanisms observed in the dissimilar overlay systems into three categories: abrasive wear, adhesive wear, and oxidative wear. The transition between these mechanisms depends on the applied load, sliding speed, and the hardness gradient through the overlay thickness. At lower loads, the dominant mechanism was abrasive wear, where hard carbide particles in the overlay surface ploughed the counterface. At higher loads, the carbides fractured, leading to a transition to adhesive wear. The study demonstrated that controlling the dilution rate below 15% was essential for maintaining the intended hardness profile of the overlay material.
Process Parameters and Engineering Implications
The study emphasized that process parameters such as welding current, travel speed, and number of passes significantly affected the dilution rate and consequently the overlay properties. For submerged arc welding overlay processes, a current of 250–350 A with a travel speed of 150–250 mm/min was found to produce acceptable dilution levels. The number of passes also mattered—multi-pass overlay reduced the overall dilution because subsequent passes dilute the previously deposited (already dilution-affected) material less than the base metal.
From an engineering practice standpoint, this study reinforces the importance of performing a thorough weld procedure qualification (per NB/T 47014 or ASME IX) that includes not only mechanical property verification but also microstructural characterization of the overlay layer. In my experience with hydrogenation reactor cladding projects, the dilution issue has been one of the most challenging aspects to control, particularly when overlaying 316L stainless steel onto 16MnR carbon steel substrates. The recommended practice of using a transition layer (such as 309L) before the final overlay layer is validated by the findings in this paper.
Reflections and Practical Takeaways
The study's emphasis on the dilution-microstructure-property relationship is directly applicable to real-world cladding operations. In practice, engineers often focus on achieving the specified hardness of the overlay but overlook the fact that the hardness profile is a function of dilution, which in turn depends on process parameters and the geometry of the joint. The paper's methodology of correlating microstructural observations with wear test results provides a rigorous framework that should be adopted in qualification procedures. Furthermore, the identification of optimal dilution ranges (below 15% for maintaining overlay integrity) serves as a practical guideline for process development, especially in applications where the overlay material is significantly more expensive than the substrate, such as nickel-based alloy cladding on carbon steel pressure vessels.