Critical Dynamic Recrystallization Model and Nucleation Mechanisms of an Alumina-Forming Austenitic Stainless Steel duri
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ORIGINAL ARTICLE
Critical Dynamic Recrystallization Model and Nucleation Mechanisms of an Alumina-Forming Austenitic Stainless Steel during Hot Deformation Qi Zheng1 • Leli Chen1 • Rui Luo1 • Yu Qiu2 • Ching-Tun Peng1 • Tian Liu1 Shugang Cui1 • Yun Cao1 • Pei Gao3 • Xiaonong Cheng1
•
Received: 8 May 2020 / Accepted: 25 September 2020 Ó The Indian Institute of Metals - IIM 2020
Abstract The hot deformation behavior of an aluminaforming austenitic (AFA) stainless steel was investigated on a Gleeble-3500 simulator. Moreover, the critical dynamic recrystallization model was established, and the critical stress was determined. Microstructural characterization was analyzed using electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). The microstructure evolution showed that the degree of dynamic recrystallization (DRX) and the content of highangle grain boundaries increased significantly with the increasing temperature and the decreasing strain rate. For recrystallization mechanisms, the bulging mechanism was found dominating, while the sub-grain rotation mechanism played an assisting role. Furthermore, discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) coexisted during the hot deformation. Keywords AFA alloy Deformation Dynamic recrystallization EBSD Misorientation
& Rui Luo [email protected] & Ching-Tun Peng [email protected] 1
School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013, People’s Republic of China
2
AVIC Manufacturing Technology Institute, Beijing 100022, People’s Republic of China
3
Jiangsu Yinhuan Precision Steel Tube Co., Ltd, Yixing 214200, People’s Republic of China
1 Introduction Alumina-forming austenitic (AFA) stainless steels are considered as new promising superalloys, which are of great potential in many energy-conversion applications due to their excellent oxidation resistance and creep resistance [1–3]. Hot deformation is an important step to control the microstructure and enhance the properties of the AFA alloys, and dynamic recrystallization (DRX) is the major softening mechanism [4, 5]. Based on the critical DRX theory [6, 7], the occurrence of critical strain signifies the starting point of DRX, which has been verified in superalloys, magnesium alloys, and aluminum alloys by this theory [8–10]. Up to date, it is well known that DRX nucleation mechanisms primarily consist of discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX). DDRX is characterized by local bulging of preexisting high-angle grain boundaries, which is so-called necklace structure; on the other hand, CDRX is characterized by rearrangement and continuous absorption of dislocations in sub-grain boundaries [11]. Lin et al. [12] recently studied the DRX behavior of nickel-based superalloys and reported that DDRX played a major role in DRX nucleation. However, Zhang et al. [13] investigated low stacking-fault energy materials and found that there were multiple DRX m
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