Effects of Long-Term Service on Microstructure and Impact Toughness of the Weld Metal and Heat-Affected Zone in CrMoV Steel Joints
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials
2.2. Microstructure
2.3. Toughness Tests
2.4. Auger Electron Spectroscopy Analysis
3. Results and Discussion
3.1. Microstructure
3.2. Impact Energy and FATT50
3.3. Fracture Morphology and Crack Growth Path
3.4. Element Distribution at Grain Boundaries and Its Effects on Toughness
3.4.1. P Segregation at PAG Boundaries
3.4.2. P Segregation in the WMs
3.4.3. High Toughness of the HAZs
4. Conclusions
- (1)
- Compared with the compressor part WM and HAZ, there was no obvious difference in microstructure of the turbine part WM and HAZ, indicating that the microstructure in the turbine part WM and HAZ did not significantly degrade during service at 500–540 °C for 14 years.
- (2)
- The impact toughness of the WMs with intergranular fracture morphology was much lower than that of the HAZs with dimple morphology, suggesting that the WMs were the weak positions of this rotor. Compared to the compressor part WM (38 J), the impact energy of the turbine part WM (15 J) decreased by 61%, and the FATT50 increased from 38 °C to 138 °C.
- (3)
- The low toughness in the WMs was due to the significant segregation of P at the prior austenite grain (PAG) boundaries in the turbine part WM (20.5 at.%) and the compressor part WM (13.2 at.%). The segregation of P decreased the toughness of the WMs, especially the turbine part WM. The segregation of P in the compressor part WM occurred during welding and post-weld heat treatment (PWHT), while the segregation of P in the turbine part WM occurred during welding, PWHT, and service at 500–540 °C. Additionally, the inhomogeneous microstructure in WMs would have aggravated the segregation of P.
- (4)
- The high impact energy in both the compressor part HAZ (177 J) and the turbine part HAZ (156 J) was mainly due to fine grains. In addition, the P element content in the HAZs was low, and the grain boundary area available for P segregation was large. Therefore, the segregation level of P at the PAG boundaries was low, and had little adverse effect on impact toughness.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Element | C | Cr | Mo | Ni | Mn | V | Si | P | S | Cu | Pb | Fe |
---|---|---|---|---|---|---|---|---|---|---|---|---|
BM (HAZ) | 0.20 | 1.32 | 0.92 | 0.66 | 0.42 | 0.28 | 0.19 | 0.004 | 0.001 | 0.11 | 0.04 | balance |
WM | 0.09 | 1.66 | 0.89 | 0.13 | 1.37 | 0.04 | 0.53 | 0.011 | 0.009 | 0.12 | 0.03 | balance |
Parts of the Rotor | Zones of the Joint | Impact Energy at 25 °C (J) | FATT50 (°C) |
---|---|---|---|
The turbine part | WM | 15 | 138 |
HAZ | 156 | \ | |
The compressor part | WM | 38 | 38 |
HAZ | 177 | \ |
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Sun, Q.; Li, X.; Li, K.; Cai, Z.; Han, C.; Li, S.; Gao, D.; Pan, J. Effects of Long-Term Service on Microstructure and Impact Toughness of the Weld Metal and Heat-Affected Zone in CrMoV Steel Joints. Metals 2022, 12, 278. https://doi.org/10.3390/met12020278
Sun Q, Li X, Li K, Cai Z, Han C, Li S, Gao D, Pan J. Effects of Long-Term Service on Microstructure and Impact Toughness of the Weld Metal and Heat-Affected Zone in CrMoV Steel Joints. Metals. 2022; 12(2):278. https://doi.org/10.3390/met12020278
Chicago/Turabian StyleSun, Qixing, Xiaogang Li, Kejian Li, Zhipeng Cai, Chaoyu Han, Shanlin Li, Dangxun Gao, and Jiluan Pan. 2022. "Effects of Long-Term Service on Microstructure and Impact Toughness of the Weld Metal and Heat-Affected Zone in CrMoV Steel Joints" Metals 12, no. 2: 278. https://doi.org/10.3390/met12020278