Microstructure Evolution and Failure Behavior of Stellite 6 Coating on Steel after Long-Time Service
Abstract
:1. Introduction
2. Materials and Methods
3. Results
3.1. Microstructure
3.2. Distribution of Alloying Elementsand Phases
3.3. Failure Analysis
4. Discussion
5. Conclusions
- The microstructure of the Stellite weld overlay near the fusion zone had changed to form a light zone, consisting of Co–Fe substitution solid solutions, σ phases (Fe–Cr metallic compounds) and Cr18.93Fe4.07C6 carbides. The high temperature environment could promote the extent of the light zone. After service, the width of the light zone, combined with fusion zone and diffusion zone, increased significantly to form a large diffusion zone, which could even reach to around 2.5 mm.
- The obvious diffusion of Fe occurred from the steel and fusion zone to the Stellite overlay, resulting in the microstructure evolution and hardness increase in the weld overlay. The content of Fe increased intensively, but the content of Co decreased, which could eventually lead to the formation of hard and brittle Co–Fe phases.
- The micro-hardness in the Stellite weld overlay was higher than that in the steel. After cladding, the micro-hardness in the HAZ increased. After the service process, the micro-hardness values in the Stellite overlay slightly increased to 450–500 HV, while those in the HAZ dropped where the precipitates had coarsened. Moreover, the micro-hardness values in the light zone increased to the maximum (470–680 HV), resulting in changes of micro-hardness between the base material and the Stellite weld overlay.
- The fracture of the Stellite coating samples mainly occurred in the light zone (fusion zone + diffusion zone) after the service process. The formation of these cracks might be caused by formed brittle phases and changes of micro-hardness during service.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Material | Element (wt %) | ||||||
C | Cr | Mo | Ni | W | Nb | V | |
F91 | 0.091 | 9.01 | 0.90 | 0.010 | – | 0.083 | 0.17 |
Stellite 6 | 0.93 | 27.3 | 0.26 | 1.81 | 3.36 | – | – |
Material | Element (wt %) | ||||||
N | Si | Mn | P | S | Co | Fe | |
F91 | 0.040 | 0.33 | 0.42 | 0.014 | 0.0011 | – | Bal. |
Stellite 6 | – | 1.08 | 0.13 | 0.014 | 0.0063 | Bal. | 2.17 |
Position | Element (mol %) | |||
---|---|---|---|---|
Fe | Co | Cr | W | |
A | 46.86 | 28.48 | 20.17 | 4.49 |
B | 89.13 | 1.32 | 9.55 | – |
C | 76.69 | 13.21 | 8.08 | 2.02 |
D | 88.47 | – | 11.53 | – |
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Xiong, J.; Nie, F.; Zhao, H.; Zheng, L.; Luo, J.; Yang, L.; Wen, Z. Microstructure Evolution and Failure Behavior of Stellite 6 Coating on Steel after Long-Time Service. Coatings 2019, 9, 532. https://doi.org/10.3390/coatings9090532
Xiong J, Nie F, Zhao H, Zheng L, Luo J, Yang L, Wen Z. Microstructure Evolution and Failure Behavior of Stellite 6 Coating on Steel after Long-Time Service. Coatings. 2019; 9(9):532. https://doi.org/10.3390/coatings9090532
Chicago/Turabian StyleXiong, Jiankun, Fuheng Nie, Haiyan Zhao, Liangliang Zheng, Jun Luo, Lin Yang, and Zhongbo Wen. 2019. "Microstructure Evolution and Failure Behavior of Stellite 6 Coating on Steel after Long-Time Service" Coatings 9, no. 9: 532. https://doi.org/10.3390/coatings9090532