Effect of cooling rate on the nucleation and growth of large TiC particles in Ti-Mo steel

The mechanism and kinetics of large TiC precipitates in Ti-Mo steel were investigated in situ with a high-temperature confocal laser scanning microscope and analytically evaluated through thermodynamic calculations in Thermo-Calc. The size of the austenite grains and TiC gradually decreased with inc...

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Bibliographic Details
Published in:Journal of alloys and compounds 2020-05, Vol.823, p.153650, Article 153650
Main Authors: Chen, Tianci, Ji, Cheng, Zhu, Miaoyong
Format: Article
Language:English
Subjects:
Avrami equation
Cooling
Cooling effects
Cooling rate
Grain boundaries
High temperature
Kinetics
Molybdenum steels
Nucleation
Precipitates
Solidification
Supercooling
Thermodynamic
Ti-Mo steel
TiC
Titanium carbide
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Summary:The mechanism and kinetics of large TiC precipitates in Ti-Mo steel were investigated in situ with a high-temperature confocal laser scanning microscope and analytically evaluated through thermodynamic calculations in Thermo-Calc. The size of the austenite grains and TiC gradually decreased with increasing undercooling. During the solidification process, strong solute diffusion fields were formed via undercooling, which inhibited the nucleation of TiC; hence, the second phase precipitation temperature was lower than the equilibrium precipitation temperature. Moreover, there was a critical cooling rate between 0.2 and 1.5 K/s that rendered the capacity of γ formation equal to that of TiC formation. The nucleation location of TiC can be changed from grain boundary to grain interior by increasing undercooling. The growth pattern of TiC conformed to the Avrami equation; at higher undercooling, the time exponent was small, and the relationship between the growth length and time was approximately linear. During actual cooling, the driving force exceeded a critical value under a specific degree of undercooling, and the γ/TiC interface became morphologically unstable, leading to a cellular/dendritic pattern. •During the solidification process, strong solute diffusion fields were formed.•The capacity of γ formation equal to that of largeTiC formation in Specific undercooling.•The growth pattern of largeTiC conformed to the Avrami equation.•The γ/TiC interface is a cellular/dendritic pattern.
ISSN:0925-8388
1873-4669
DOI:10.1016/j.jallcom.2020.153650