Evaluation of the Aging Effect on the Microstructure of Co-28Cr-6Mo-0.3C Alloy: Experimental Characterization and Computational Thermodynamics
Abstract
:1. Introduction
2. Calculations and Experimental Procedure
2.1. Thermodynamic Calculations
2.2. Experimental Procedure
3. Results and Discussion
3.1. As-Received Alloy
3.2. Thermodynamical Calculations
3.3. Solution Treatment and Quenching
3.4. Aging of the Nearly Fully Solution Treated Sample
3.5. Aging of the Partially Solution Treated Sample
3.6. Microhardness Evolution
4. Conclusions
- (1).
- We used the thermodynamic databases, TCFE8 and TCNI8, for calculations with the ThermoCalc software. Despite observing similarities for the phase transformations at similar temperatures, we also observed some differences, such as the appearance of the sigma phase formation according to the TCNI8 database. The FCC phase also calculated the FCC_L12 and FCC_A1 structures.
- (2).
- Solution treatment at 1230 °C for 3 h resulted in the nearly fully solution of carbides, whilst solution treatment at 1200 °C for 1 h caused most of the primary carbides to remain in the matrix in an undissolved condition. The thermodynamic calculations were also consistent with the experimental results. Based on the calculations, ~1.7–4.3% of the carbides should be present at 1200 °C and 1230 °C.
- (3).
- The undissolved carbides of Cr, Mo, and Co have significant effects on the microstructural and mechanical characteristics of the solution treated and aged sample.
- (4).
- Aging of the nearly fully solution treated sample resulted in the development of HCP1 (straight bands) and HCP2 (lamellar-type constitution) phases, but aging of the partially solution treated sample resulted in formation of the HCP2 phase (lamellar-type constitution) at the grain boundaries.
- (5).
- The presence of undissolved carbides of Cr, Mo, and Co depletes the matrix from the HCP stabilizer elements, and it consequently enhances the FCC peak intensity of the substance after quenching. However, the FCC matrix changes more intensively compared to the HCP during aging. Thermodynamical calculations also indicated a decrease of the Cr and C amount in the FCC phase, with increasing solution temperatures.
- (6).
- The hardness enhancement as a result of aging for the sample solution treated at 1230 °C for 3 h was lower than that for the sample solution treated at 1200 °C for 1 h.
Author Contributions
Funding
Conflicts of Interest
References
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%Cr | %Mo | %C | %Si | %Co |
---|---|---|---|---|
28 | 5 | 0.3 | 1.5 | Balance |
Database | Temperature, °C | ||||
---|---|---|---|---|---|
Liquidus | Solidus | M23C6 | HCP | Sigma | |
TCFE8 | 1399 | 1255 | 1260 | 921 °C | - |
TCNI8 | 1380 | 1248 | 1255 | 942 °C | 950 °C |
Database | HCP | M23C6 | ||||||
---|---|---|---|---|---|---|---|---|
Phase vol.-% | wt.-% in HCP | Phase vol.-% | wt.-% in M23C6 | |||||
Cr | Mo | C | Cr | Mo | C | |||
TCFE8 | 94.36 | 25.84 | 4.28 | 0.037 | 5.64 | 67.85 | 18.32 | 5.237 |
TCNI8 | 93.98 | 25.68 | 4.32 | 0.017 | 6.02 | 67.99 | 16.64 | 5.182 |
Temperature, °C | Database | FCC | M23C6 | ||||||
---|---|---|---|---|---|---|---|---|---|
Phase vol.-% | wt.-% in FCC | Phase vol.-% | wt.-% in M23C6 | ||||||
Cr | Mo | C | Cr | Mo | C | ||||
1200 | TCFE8 | 97.75 | 27.13 | 4.86 | 0.193 | 2.25 | 68.39 | 11.65 | 5.282 |
1200 | TCNI8 | 95.67 | 26.37 | 4.67 | 0.091 | 4.33 | 66.61 | 15.42 | 5.249 |
1230 | TCFE8 | 98.31 | 27.35 | 4.91 | 0.220 | 1.69 | 69.09 | 10.79 | 5.299 |
1230 | TCNI8 | 96.07 | 26.54 | 4.72 | 0.111 | 3.92 | 66.45 | 12.38 | 5.255 |
Solution Treatment | Solutionized and Quenched | Aged at 850 °C for 24 h | Aged at 850 °C for 48 h |
---|---|---|---|
1230 °C for 3 h | 380 ± 10 | 520 ± 15 | 530 ± 25 |
1200 °C for 1 h | 410 ± 15 | 647 ± 23 | 705 ± 30 |
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Zangeneh, S.; Erisir, E.; Abbasi, M.; Ramazani, A. Evaluation of the Aging Effect on the Microstructure of Co-28Cr-6Mo-0.3C Alloy: Experimental Characterization and Computational Thermodynamics. Metals 2019, 9, 581. https://doi.org/10.3390/met9050581
Zangeneh S, Erisir E, Abbasi M, Ramazani A. Evaluation of the Aging Effect on the Microstructure of Co-28Cr-6Mo-0.3C Alloy: Experimental Characterization and Computational Thermodynamics. Metals. 2019; 9(5):581. https://doi.org/10.3390/met9050581
Chicago/Turabian StyleZangeneh, Shahab, Ersoy Erisir, Mahmoud Abbasi, and Ali Ramazani. 2019. "Evaluation of the Aging Effect on the Microstructure of Co-28Cr-6Mo-0.3C Alloy: Experimental Characterization and Computational Thermodynamics" Metals 9, no. 5: 581. https://doi.org/10.3390/met9050581