Zhuojin Pipe Fitting Co., LtdExperimental Study on Cladding Welding Process of Tubular Cast Tungsten Carbide
Literature Overview and Research Background
This paper by He Kailin, Wang Chen, and Shi Xiaohua from Jiangsu Fengshang Intelligent Technology Co., Ltd., published in the journal Heat Treatment (2025, Vol. 40, No. 5, pp. 23-28), addresses a practically significant challenge in surface engineering: how to effectively apply cast tungsten carbide (WC) particles onto tubular components through cladding welding and subsequently optimize the cladding layer through post-weld heat treatment. The study is classified under TG455 (welding and cladding processes) and focuses on the metallurgical bonding between the cladding layer and the substrate, as well as the influence of carburizing quenching on the final hardness and wear resistance of the composite surface.
The research motivation is clear from an engineering perspective. Cast tungsten carbide is widely used in applications requiring extreme wear resistance, such as pump shafts, valve stems, and pipe inner linings in slurry transport systems. However, the brittle nature of WC makes it difficult to integrate directly into metallic substrates through conventional welding methods. The dilution of WC by molten weld metal, the formation of complex carbides during solidification, and the potential for poor metallurgical bonding all represent critical technical barriers. This paper systematically investigates these issues through controlled experiments.
Core Technical Findings and Metallurgical Analysis
The authors conducted experiments using two different substrate materials and applied multiple post-weld heat treatment conditions. The investigation employed Vickers hardness testing, metallographic microscopy, and scanning electron microscopy (SEM) to characterize the cladding layer hardness, microstructure, and chemical composition, supplemented by wear performance testing.
Key Results on Cladding Layer Thickness and WC Distribution
The study reveals a critical process window for cladding layer thickness. When the cladding layer is too thin, the molten pool geometry does not provide sufficient volume for uniform WC particle distribution, leading to localized agglomeration. Conversely, when the molten pool is too thick, the excessive volume of liquid metal dilutes the WC concentration and promotes particle settling due to density differences. This finding underscores the importance of precise heat input control and multi-pass strategies in WC cladding applications.
Dilution Effects and Carbide Formation
A particularly important finding is that cast WC particles undergo significant dilution during the cladding process. The WC lattice dissolves into the molten pool, and upon solidification, complex carbides form as secondary phases. The degree of dilution varies with process parameters, and this variation directly correlates with the hardness of the cladding matrix. Higher dilution results in a softer matrix because the reinforcing WC particles are consumed to form thermodynamically less stable carbide phases. This observation has direct implications for process design: the dilution rate must be minimized to preserve the integrity of the WC reinforcement particles.
Metallurgical Bonding and Heat Treatment Response
The paper confirms that metallurgical bonding is achieved between the cladding layer and the substrate, which is a prerequisite for subsequent heat treatment. The authors specifically highlight the effectiveness of medium-frequency induction hardening, particularly carburizing quenching, in enhancing the matrix hardness of the cladding layer. The carburizing treatment introduces additional carbon into the surface layers, forming fine cementite (Fe3C) and other hard carbide phases that complement the existing WC-based reinforcement. This synergistic effect between the original WC particles and the heat-treated matrix significantly improves overall wear resistance.
Process Parameters and Engineering Recommendations
Based on the experimental findings, the following process considerations can be extracted for practical application:
| Parameter | Recommended Range | Rationale |
|---|---|---|
| Cladding layer thickness | Moderate (multi-pass preferred) | Too thin causes uneven WC distribution; too thick increases dilution |
| Heat input | Controlled and moderate | Excessive heat input promotes WC dissolution and coarse carbide formation |
| Post-weld treatment | Carburizing quenching (medium-frequency induction) | Enhances matrix hardness through additional carbon enrichment |
| Substrate material | Compatible with carburizing response | Must withstand quenching without cracking or excessive distortion |
| Number of passes | Multi-pass with interpass inspection | Ensures uniform WC distribution and avoids excessive dilution in a single pass |
Engineering Practice Integration
In the context of pipe and fitting manufacturing, this research has direct relevance to the refurbishment of worn pipe components and the production of new wear-resistant pipe linings. For example, in oil and gas pipelines transporting abrasive slurries, or in mining industry slurry pipelines, the internal surfaces of pipes are subject to severe erosive wear. Applying a WC-reinforced cladding layer followed by carburizing quenching can extend the service life of such components significantly.
From a quality control standpoint, the following inspection protocols should be considered:
- Hardness mapping across the cladding layer cross-section to verify uniformity and confirm that the dilution zone is acceptable.
- Metallographic examination of the fusion line to verify metallurgical bonding without cracks or unmelted particles.
- SEM analysis to assess WC particle integrity and distribution after heat treatment.
- Wear testing under representative operating conditions to validate the cladding performance against design requirements.
Study Insights and Reflections
The most valuable insight from this paper is the recognition that WC cladding is not merely a welding process but a multi-step surface engineering strategy. The welding step alone is insufficient to achieve optimal performance; the post-weld heat treatment is equally critical. This challenges the common engineering practice of treating cladding welding as a standalone operation and emphasizes the need for integrated process design that considers the entire thermal history of the component.
Another important observation is the dilution problem. In practical production environments, operators often focus on deposition rate and productivity, which can lead to excessive heat input and consequently high dilution rates. The findings of this paper serve as a reminder that productivity gains must not come at the expense of coating integrity. Process window optimization should prioritize WC particle preservation, even if it requires slower deposition rates or multi-pass approaches.
The recommendation of carburizing quenching as the preferred heat treatment method is particularly noteworthy. Unlike conventional induction hardening, carburizing introduces additional carbon into the surface, which can form new hard phases and strengthen the matrix. This approach is well-suited for tubular components where medium-frequency induction heating provides efficient and controllable heat treatment without the distortion issues associated with furnace-based methods.
This research provides a solid foundation for developing standardized cladding procedures for WC-reinforced pipe and fitting components. Engineers involved in surface engineering for wear-critical applications should consider these findings when specifying cladding processes and post-treatment requirements. The systematic approach taken in this study—combining process parameter variation, microstructural characterization, and performance testing—sets a good example for rigorous cladding process development.