Effects of prior austenite grain size on reversion kinetics of different crystallographic austenite in a low carbon steel

• Published in: Materials characterization 2022-08, Vol.190, p.112025, Article 112025
• Main Authors: Zhang, Xianguang, Ren, Yingjie, Zhang, Jian, Yang, Xiaodong, Xie, Xin, Liu, Huan, Yang, Wenchao
• Format: Article
• Language: English
• Subjects: Austenite reversion; Cementite; Growth; Martensite block; Nucleation; Prior austenite grain size
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2022.112025

The effects of prior austenite grain (PAG) size on reversion kinetics of different crystallographic austenite (γ) with acicular and globular morphologies in a low carbon steel with the structure of pre-tempered martensite have been studied. It is unexpected that the coarse PAG (C-PAG) shows a strong inhibition on the reversion kinetics of globular γ, while a weak influence on that of acicular γ. Intragranular globular γ is hardly to be formed in the low carbon steel, and the grain boundary (GB) ones are dominantly formed. C-PAG provides low-density PAGBs for GB globular γ formation, leading to slower reversion kinetics. Theoretical analyses revealed that the low-density and fine cementite particles result in a low nucleation potency for globular γ thus less intragranular ones were formed. On the other hand, C-PAG leads to coarse martensite structure, which was expected to have a strong retardation on the reversion kinetics of acicular γ. However, acicular γ is mainly nucleated at block boundaries for the cases of (Fine) F-PAG, and it is almost equally nucleated at block and sub-block boundaries for C-PAG. This decreased the differences in nucleation density and growth kinetics of the acicular γ between the C-PAG and F-PAG, and the influences of PAG size on the reversion kinetics is weakened. [Display omitted] •Coarse prior austenite grain (C-PAG) shows a strong retardation on the reversion kinetics of globular γ, while a weak influence on acicular γ.•Intragranular globular γ is hardly to be formed in low carbon steel due to the low-density and fine cementite particles providing a low nucleation potency.•Nucleation of acicular γ at sub-block boundaries in the C-PAG weakened the influences of PAG size on the acicular γ reversion kinetics.