CLADDING TECHNOLOGY SHANXI CO., LTDEffect of Welding Process on Compatibility between 1Cr16Ni4Mo2Cu2W1VN Steel and Co6B Alloy Cladding Layers
Literature Overview
This 2024 study by Wu Weijian, Liu Chengmiao, and Li Quan, published in Metal Heat Treatment, addresses the compatibility between a high-strength heat-resistant steel (1Cr16Ni4Mo2Cu2W1VN) and a cobalt-based hardfacing alloy (Co6B) in cladding applications. The research is conducted jointly by Shanghai First Machine Tool Works and the Institute of Special Steel Research, Central Iron and Steel Research Institute. This topic is of significant practical importance in machine tool manufacturing, where high-strength structural steels require localized hardfacing for wear resistance while maintaining the structural integrity of the base material.
Core Technical Content
The 1Cr16Ni4Mo2Cu2W1VN steel is a precipitation-hardened martensitic steel with exceptional strength and thermal stability, commonly used in precision machine tool guideways, spindles, and structural components requiring high dimensional stability under load. The Co6B alloy is a cobalt-chromium-tungsten carbide hardfacing alloy known for its excellent wear resistance, hot hardness, and corrosion resistance.
The central challenge addressed by this study is the metallurgical compatibility between these two dissimilar materials during the cladding process. Key issues include:
- Thermal expansion mismatch between the Co6B overlay and the base steel
- Dilution effects on the Co6B overlay properties
- Residual stress and distortion control
- Bond strength at the interface between overlay and base
- Cracking susceptibility in the dilution zone
Welding Process Comparison
| Process Parameter | GTAW (TIG) | SAW | Oxy-Fuel | Plasma Arc (PTA) |
|---|---|---|---|---|
| Heat input | Low (0.5–1.5 kJ/mm) | Medium (2.0–4.0 kJ/mm) | Low-Medium (1.0–2.5 kJ/mm) | Low-Medium (0.8–2.0 kJ/mm) |
| Dilution rate | 10–20% | 25–40% | 15–25% | 15–30% |
| Overlay hardness | 750–900 HV | 600–750 HV | 700–850 HV | 700–880 HV |
| Bond strength | 450–550 MPa | 400–500 MPa | 350–450 MPa | 400–500 MPa |
| Cracking tendency | Low | Medium-High | Medium | Medium |
| Deposition rate | Low | High | Medium | Medium-High |
| Surface quality | Excellent | Good | Moderate | Good |
Process-Property Relationships
The study reveals that welding process selection has a profound impact on the compatibility and performance of the Co6B overlay on 1Cr16Ni4Mo2Cu2W1VN steel. The lower the heat input, the lower the dilution rate, and the better the preservation of Co6B alloy properties. However, excessively low heat input may compromise bond strength due to insufficient melting of the base material surface.
Key Technical Findings
- Dilution control is critical: Dilution rates above 30% significantly degrade the Co6B overlay hardness from the nominal 850–900 HV to below 650 HV, rendering the overlay ineffective for wear applications.
- Multi-pass strategy: A multi-pass approach with the first pass providing a dilution zone (10–15% dilution) and subsequent passes maintaining low dilution (5–10%) achieves the best balance between bond strength and overlay properties.
- Interpass temperature: Maintaining interpass temperature below 150 °C is essential to prevent excessive tempering of the 1Cr16Ni4Mo2Cu2W1VN base material in the heat-affected zone.
- Preheat considerations: A moderate preheat of 150–250 °C reduces cracking susceptibility without excessively increasing dilution or softening the base material.
Engineering Practice Implications
In machine tool manufacturing, the application of Co6B hardfacing to high-strength structural steels is increasingly common for extending the service life of guideways, bed ways, and tool holders. The study provides clear guidance for process selection:
| Application | Recommended Process | Key Consideration |
|---|---|---|
| Precision guideway hardfacing | GTAW or PTA | Low dilution, excellent surface finish |
| Large area bed way overlay | SAW (with multi-pass) | High deposition rate, controlled dilution |
| Repair and restoration | Oxy-fuel or GTAW | Flexibility, moderate dilution |
| High-temperature wear areas | PTA | Consistent properties, good dilution control |
Defect Prevention Measures
- Cracking in dilution zone: Use low carbon, high Ni consumable for the first pass to reduce carbon activity and martensite formation at the interface.
- Porosity in overlay: Ensure thorough deoxidation of the Co6B alloy powder; use dry, uncontaminated filler material.
- Spalling of overlay: Control interpass temperature below 150 °C; avoid excessive multi-pass overlap that causes thermal cycling.
- Insufficient bond strength: Ensure adequate base material melting (0.5–1.0 mm) in the first pass; maintain proper joint preparation.
Study Insights and Reflections
The 2024 publication timing of this study reflects the current industry trend toward high-strength, high-performance base materials in precision manufacturing. The 1Cr16Ni4Mo2Cu2W1VN steel represents the next generation of machine tool structural materials, offering superior strength-to-weight ratios and dimensional stability compared to conventional gray iron or low-alloy steels. The compatibility study with Co6B hardfacing is timely as manufacturers seek to combine the structural advantages of advanced steels with the surface performance of cobalt-based overlays.
A particularly important finding is the non-linear relationship between dilution and overlay properties. While dilution from 5% to 20% causes relatively modest hardness reduction, dilution above 30% leads to precipitous property loss. This suggests that process control must maintain dilution below a critical threshold rather than simply minimizing it.
From a quality assurance perspective, the study emphasizes the need for dilution measurement as a routine inspection parameter. Chemical analysis of the overlay at different depths, combined with hardness profiling, provides a reliable method for verifying process consistency.
Conclusion
This study provides essential guidance for engineers applying Co6B hardfacing to high-strength heat-resistant steels in precision machine tool applications. The key message is that process selection and parameter control must be tailored to the specific base material to achieve optimal dilution, bond strength, and overlay properties. GTAW and PTA processes offer the best compatibility for precision applications, while SAW remains viable for large-area applications with appropriate multi-pass strategies. Future work should explore the long-term wear performance of these overlay systems under actual machine tool operating conditions.