Fe-Cr-Ni系不锈钢在热老化和退火过程中铁素体调幅分解的相场法研究

用基于Cahn-Hilliard方程的相场法研究了Fe-Cr-Ni系不锈钢中的铁素体在热老化和后续退火过程中调幅分解的演化过程,结果表明:在热老化过程中调幅分解生成相连的网络状α’相,调幅分解引起的Cr成分波动的波长和振幅都随着热老化时间的延长而增大;在随后的退火过程中α’相逐渐溶解而Cr成分波动的振幅迅速减小,但是波长继续增大。还讨论了热老化时的调幅分解对铁素体纳米压痕硬度的影响以及退火温度对调幅分解回复(α’相溶解)所需时间的影响,结果表明:铁素体的纳米压痕硬度主要与调幅分解的振幅有关,且随着振幅的增大而提高。同时,提高退火温度能显著缩短调幅分解回复所需的时间,退火回复时间与退火温度之间有Arrhenius形式的关系。

A Phase-Field Study on Spinodal Decomposition of Ferrite of Fe-Cr-Ni Stainless Steels during Thermal Ageing and Annealing

In order to investigate the evolution of spinodal decomposition during ageing and annealing, a phase-field model based on Cahn-Hilliard equation has been developed to simulate the microstructure evolution in ferrite of Fe-Cr-Ni stainless steels. The simulation results reveal the formation of inter-connected α' phase during thermal ageing, and the increase of wavelength and amplitude of Cr concentration fluctuation with ageing time. During the subsequent annealing treatment, it is found that α' phase dissolves into the matrix, and the wavelength continues to increase, while the amplitude starts to decrease. The simulation results also indicate that the nano-indentation hardness is positively associated with the amplitude of concentration fluctuation. And the annealing time needed for recovery of spinodal decomposition (dissolving of α' phase) is reduced by increasing annealing temperature remarkably. There is an Arrhenius-type relation between the recovery time and the annealing temperature.