CLADDING TECHNOLOGY SHANXI CO., LTDExperimental Investigation of Tube-Shaped Cast Tungsten Carbide Overlay Welding Process
Literature Overview
This 2025 study by He Kailin, Wang Chen, and Shi Xiaohua from Jiangsu Fengshang Intelligent Technology Co., Ltd. addresses a critical engineering challenge in surface engineering: the application of cast tungsten carbide (WC) overlay welding on tubular geometries. The work falls under the category of hardfacing and wear-resistant surface treatments, specifically targeting the heat treatment stage of the overlay process. The research was published in the context of metal heat treatment technology, reflecting the growing industrial demand for enhanced wear resistance in cylindrical components subjected to severe abrasive environments.
Core Technical Content
The study focuses on the experimental investigation of overlay welding processes for depositing tungsten carbide-based hardfacing layers onto tube-shaped substrates. Unlike flat-plate overlay applications, tubular geometries introduce unique challenges including uneven heat distribution, potential distortion, and the difficulty of maintaining consistent dilution ratios around the circumference. The researchers examined the relationship between welding parameters, heat treatment conditions, and the resulting microstructure and mechanical performance of the overlay layer.
The fundamental objective is to achieve a hardfacing layer with superior wear resistance while maintaining adequate toughness to resist spalling and cracking during service. Tungsten carbide particles dispersed in a binder matrix (typically cobalt or nickel-based) provide exceptional hardness values exceeding 1500 HV, but the challenge lies in controlling the thermal cycle to prevent excessive carbide dissolution or formation of brittle intermetallic phases at the interface.
Key Technical Parameters
| Parameter | Typical Range | Notes |
|---|---|---|
| Substrate material | Carbon steel / Low-alloy steel | Tubular geometry |
| Overlay material | Cast WC-Co or WC-Ni composite | Hardfacing alloy |
| Welding process | SAW / ESW / GTAW | Depends on tube diameter |
| Heat treatment temperature | 800-950°C | Solution treatment |
| Cooling method | Air cool / Furnace cool | Critical for phase stability |
| Target hardness | >1400 HV | Post-heat treatment |
| Dilution ratio | <15% | Substrate into overlay |
Process Analysis and Heat Treatment Considerations
The heat treatment stage is identified as the critical control point in this process. For tungsten carbide overlay layers, the thermal cycle following welding must be carefully managed to achieve the desired balance between hardness and ductility. The researchers likely employed a solution treatment approach where the overlay layer is heated to a temperature sufficient to homogenize the binder matrix without dissolving the WC particles.
The microstructural evolution during heat treatment involves several competing mechanisms:
- Solute diffusion: Carbon atoms diffuse from the WC particles into the binder matrix, potentially forming secondary carbides
- Phase transformation: The binder alloy may undergo phase transformations depending on the cooling rate
- Residual stress relief: Thermal treatment reduces welding-induced residual stresses that could lead to cracking
- Interface bonding: Improved metallurgical bonding at the overlay-substrate interface through controlled diffusion
Defect Analysis and Countermeasures
| Defect Type | Cause | Countermeasure |
|---|---|---|
| Cracking at interface | High residual stress, incompatible thermal expansion | Preheating, post-weld heat treatment (PWHT) |
| WC dissolution | Excessive heat treatment temperature | Strict temperature control, short dwell time |
| Porosity | Gas entrapment during welding | Flux coverage, proper shielding |
| Spalling | Poor interfacial bonding, high dilution | Optimize welding parameters, reduce dilution |
| Distortion | Uneven heating on tubular geometry | Symmetric welding sequence, fixture support |
Engineering Practice Integration
In industrial applications, tubular components with WC overlay layers are commonly used in mining equipment (drill pipes, chutes), cement industry (rotary kiln liners), and power generation (grinding rollers). The tubular geometry requires specific welding access arrangements and often involves multi-pass welding to achieve the required overlay thickness without excessive dilution.
For large-diameter tubes, electroslag welding (ESW) or submerged arc welding (SAW) with wire-fed consumables may be employed for efficiency. For smaller diameters or when precision is critical, gas tungsten arc welding (GTAW) with powder feeding or hot-wire techniques provide better control over the thermal input.
The heat treatment stage must account for the curvature effect: the outer surface of a tube experiences different thermal gradients compared to a flat plate. This can lead to differential cooling rates and potential residual stress patterns that differ from those observed in planar components.
Study Insights and Reflections
This research highlights an important practical consideration that is often overlooked in laboratory studies: the geometry-dependent behavior of overlay welding processes. While flat-plate studies provide fundamental understanding, tubular applications require additional consideration of thermal symmetry, access limitations, and post-weld distortion control.
The emphasis on heat treatment as a critical process step is particularly noteworthy. Many practitioners focus exclusively on welding parameters while neglecting the post-weld thermal cycle. However, for WC-based overlay layers, the heat treatment can significantly influence the final microstructure and performance. An improperly executed heat treatment can either dissolve critical carbide particles or fail to relieve detrimental residual stresses.
From a quality assurance perspective, this study reinforces the need for comprehensive process qualification that includes both welding procedure qualification (per ASME IX or NB/T 47014) and post-weld heat treatment qualification. The acceptance criteria should include hardness profiling across the overlay thickness, dilution measurement at the interface, and non-destructive examination for subsurface defects.
Reference Value and Outlook
The work contributes to the practical knowledge base for surface engineering in the hardfacing domain, particularly for tubular components. Future research should explore advanced monitoring techniques for real-time control of the heat treatment process, as well as the integration of numerical simulation to predict residual stress distributions and microstructural evolution in tubular geometries.
The industrial relevance of this work is substantial, as wear-resistant tubular components represent a significant cost driver in mining, cement, and material handling industries. Optimizing the overlay welding and heat treatment process can extend component service life by factors of 3 to 10 compared to uncoated substrates, providing substantial economic benefit through reduced downtime and replacement frequency.
This study serves as a valuable reference for engineers tasked with specifying and qualifying overlay welding processes for tubular components in severe wear environments, emphasizing the critical role of post-weld thermal treatment in achieving optimal performance.