Effect of Pre-Aging on Microstructure and Properties of Cold-Rolled Alumina-Forming Austenitic Steel
ZHANG Shengyu1,2,3, MA Qingshuang1,2, YU Liming4, ZHANG Jingwen4, LI Huijun5, GAO Qiuzhi1,2()
1 School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China 2 School of Resources and Materials, Northeastern University at Qinhuangdao, Qinhuangdao 066004, China 3 CNPC Bohai Equipment Manufacturing Co. Ltd., Tianjin 300457, China 4 School of Materials Science and Engineering, Tianjin University, Tianjin 300354, China 5 Faculty of Engineering and Information Sciences, University of Wollongong, Wollongong, NSW 2522, Australia
Cite this article:
ZHANG Shengyu, MA Qingshuang, YU Liming, ZHANG Jingwen, LI Huijun, GAO Qiuzhi. Effect of Pre-Aging on Microstructure and Properties of Cold-Rolled Alumina-Forming Austenitic Steel. Acta Metall Sin, 2025, 61(1): 177-190.
Alumina-forming austenitic (AFA) steel is expected to be applied to high-temperature components of ultra-supercritical thermal power plants. However, the high-temperature strength and stability of AFA steel need to be improved further. Here, the influence of pre-aging on the precipitation behavior, microstructural evolution, and mechanical properties of cold-rolled AFA steel was investigated. The results showed that pre-aging significantly influences the synergistic strengthening due to dislocations and precipitation in cold-rolled AFA steel during the process of high-temperature aging treatment. The precipitates in a sample that received pre-aging treatment exhibited strong pinning effect on grain boundaries and dislocations, which enhances the effect of precipitation strengthening by boosting the number of nucleation sites and the driving force for the formation of the precipitates. Compared to cold rolling with a 10% thickness reduction but without pre-aging, the formation of the Laves phase and the B2-NiAl phase after pre-aging for 24 h resulted in increased pinning on the dislocations and grain boundaries, which prevented dislocation slip, generated stress concentrations, boosted the number of nucleation sites and the driving force for the formation of the precipitates, and accelerated the phase-transition process; the volume fraction of the precipitates also increased significantly. Hardness and tensile tests at room temperature showed that the strength and hardness resulting from both cold rolling and cold rolling after pre-aging first increased and subsequently decreased.
Fund: National Natural Science Foundation of China(52171107);National Natural Science Foundation of China(52201203);Industry-University-Research Cooperation Project of Hebei Based Universities and Shijiazhuang City(241791237A)
Corresponding Authors:
GAO Qiuzhi, professor, Tel: (0335)8048630, E-mail: gaoqiuzhi@neuq.edu.cn
Fig.2 SEM images of the CR10 sample aged at 700 oC for 0 h (a), 4 h (b), 24 h (c), 100 h (d), 500 h (e), and 1000 h (f) (Insets show the corresponding microstructural details)
Fig.3 SEM images of the PA24-CR10 sample aged at 700 oC for 4 h (a), 24 h (b), 50 h (c), 100 h (d), 500 h (e), and 1000 h (f) (Insets show the corresponding microstructural details)
Fig.4 TEM image of the CR10-A0 sample (a), and EDS results and correponding selected area electron diffraction (SAED) patterns (insets) of δ-ferrite (b) and Laves (c) phases
Fig.5 SEM image and corresponding EDS mapping results of the δ-ferritic region in the PA24-CR10-A24 sample
Fig.6 SEM image and corresponding EDS mapping results of the δ-ferritic region in the PA24-CR10-A500 sample
Fig.7 XRD spectra of CR10 (a, b) and PA24-CR10 (c, d) samples aged at 700 oC for different time (Figs.7b and d are zoom-in views of Figs.7a and c, respectively)
Fig.8 Variations in Vickers hardness of CR10 and PA24-CR10 samples aged at 700 oC for different time
Fig.9 Stress-strain curves of CR10 (a) and PA24-CR10 (b) samples aged at 700 oC for different time
Fig.10 Variations in strength (a) and strain (b) of CR10 and PA24-CR10 samples aged at 700 oC for different time
Fig.11 Tensile fracture morphologies of the CR10 sample aged at 700 oC for 0 h (a), 4 h (b), 24 h (c), 100 h (d), 500 h (e), and 1000 h (f)
Fig.12 Tensile fracture morphologies of the PA24-CR10 sample aged at 700 oC for 0 h (a), 4 h (b), 24 h (c), 100 h (d), 500 h (e), and 1000 h (f)
Fig.13 Statistics on the size of B2-NiAl precipitates (a, b) and Laves precipitates (c, d) in CR10-A100 (a, c) and PA24-CR10-A100 (b, d) samples
Fig.14 Statistics on the volume fractions of precipitates in CR10-A100 and PA24-CR10-A100 samples
Fig.15 TEM images (Insets show the corresponding grain boundary and in-grain details) (a, b), and EDS results and SAED patterns (insets) (b1, b2) of CR10-A0 (a) and PA24-CR10-A0 (b, b1, b2) samples
Fig.16 Schematic of microstructural evolution of 4Al-2Cu-AFA steel
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