CLADDING TECHNOLOGY SHANXI CO., LTDHigh Temperature Aging Performance of Self Made Overlay Welding Electrodes
Literature Overview and Background
This 1999 publication by Zhao Baojun and Wu Yunhua from Jiangsu Lida Building Materials Machinery Group Company addresses a critical but often overlooked aspect of overlay welding consumable development: the long-term high-temperature aging behavior of self-developed overlay welding rods. In industrial applications involving high-temperature service environments such as cement kilns, furnace linings, and thermal processing equipment, the overlay layer must maintain its microstructural integrity, hardness retention, and corrosion resistance over extended exposure periods. The study is particularly significant because many commercially available overlay welding electrodes are designed and qualified based on as-deposited properties, while the actual service conditions involve prolonged exposure to elevated temperatures that can cause grain coarsening, carbide precipitation, phase transformations, and subsequent softening of the overlay layer.
Core Technical Content and Microstructural Analysis
The authors investigated a series of self-developed overlay welding electrodes formulated with specific alloying additions designed to resist high-temperature degradation. The key alloying elements typically employed in such systems include chromium, molybdenum, tungsten, vanadium, and niobium, each serving a distinct metallurgical purpose in the overlay microstructure.
| Parameter | Typical Range | Function |
|---|---|---|
| Chromium (Cr) | 20-30% | Oxidation resistance, solid solution strengthening |
| Molybdenum (Mo) | 2-6% | High-temperature strength, grain refinement |
| Tungsten (W) | 3-8% | Precipitation hardening, creep resistance |
| Vanadium (V) | 1-4% | Carbide formation, wear resistance |
| Niobium (Nb) | 0.5-2% | Grain stabilization, sigma phase suppression |
| Carbon (C) | 0.5-2.0% | Carbide precipitation, hardness |
The aging behavior was evaluated through controlled heat treatment cycles simulating long-term service conditions. The study examined the overlay deposits after aging at temperatures ranging from 600°C to 900°C for various time intervals. Metallographic examination revealed that the as-welded microstructure consisted of a complex mixture of martensite, retained austenite, and dispersed carbides. During aging, the retained austenite gradually transformed to martensite and carbides, while the primary carbides coarsened following a diffusion-controlled mechanism. The rate of grain coarsening was found to be strongly dependent on the cooling rate during welding and the interpass temperature control.
Key Findings on Hardness Retention
The study demonstrated that overlay electrodes with higher tungsten and vanadium content exhibited superior hardness retention after aging at 800°C for 100 hours compared to those with lower alloy content. The hardness drop from the as-deposited condition to the aged condition was approximately 15-20% for the optimized compositions, compared to 35-45% for standard electrode compositions. This difference was attributed to the formation of stable MC-type carbides (WC, VC) that resist coarsening at elevated temperatures, whereas M7C3 and M23C6 carbides in lower-alloy systems coarsen rapidly.
Engineering Practice and Application Considerations
The practical implications of this research extend to the selection and qualification of overlay welding consumables for high-temperature service. The study established a methodology for evaluating overlay electrode performance that should be incorporated into qualification procedures. Key recommendations include:
- Conducting aging tests at the maximum service temperature plus a 50°C safety margin before qualifying any overlay consumable for high-temperature applications.
- Controlling interpass temperature below 150°C during multi-pass overlay welding to minimize grain coarsening in previously deposited layers.
- Performing post-weld stress relief below the maximum service temperature to prevent cracking while avoiding excessive grain growth.
- Verifying hardness profiles across the full thickness of the overlay layer after aging simulation, not just at the surface.
The study also highlighted the importance of bond strength retention after aging. While many qualification procedures focus solely on hardness and microstructure, the bond strength between the overlay layer and the base metal can degrade significantly after prolonged high-temperature exposure due to intermetallic compound formation at the interface. The authors recommended incorporating bond strength testing after aging simulation into the qualification matrix.
Study Insights and Reflections
Reflecting on this research more than two decades after its publication, the methodology remains fundamentally sound and directly applicable to modern overlay welding practice. The emphasis on aging performance rather than as-deposited properties addresses a genuine gap in many current qualification procedures. In contemporary practice, the lessons from this study should be integrated into welding procedure qualification (WPQ) programs, particularly for applications governed by ASME IX or NB/T 47014 where aging resistance is a critical design requirement. The systematic approach to alloy design and aging evaluation provides a valuable framework for developing new overlay consumables for emerging high-temperature applications.