Microcrack Nucleation and Propagation of TRIP-Assisted Duplex Stainless Steel Fe-19.6Cr-2Ni-2.9Mn-1.6Si
ZHANG Wenbin1, LI Xiaolong1, HAO Shuo1, LIU Shengjie1, CAI Xingzhou1, CHEN Lei1,2, JIN Miao1()
1 College of Mechanical Engineering, Yanshan University, Qinhuangdao 066004, China 2 National Engineering Research Center for Equipment and Technology of Cold Strip Rolling, Yanshan University, Qinhuangdao 066004, China
Cite this article:
ZHANG Wenbin, LI Xiaolong, HAO Shuo, LIU Shengjie, CAI Xingzhou, CHEN Lei, JIN Miao. Microcrack Nucleation and Propagation of TRIP-Assisted Duplex Stainless Steel Fe-19.6Cr-2Ni-2.9Mn-1.6Si. Acta Metall Sin, 2025, 61(4): 608-618.
The transformation-induced plasticity (TRIP) effect considerably enhances the material properties of TRIP-assisted duplex steel due to the martensitic transformation. However, as martensitic transformation progresses, a complex microstructure forms from the intermixing of three phases (i.e., austenite, ferrite, and martensite) in the steel, which results in complex damage behavior, crack nucleation, and propagation characteristics. In this study, under engineering strain up to 55%, TRIP-assisted duplex stainless steel Fe-19.6Cr-2Ni-2.9Mn-1.6Si was characterized to investigate microcrack characteristics. Herein, different types of microcracks were statistically categorized using SEM. Additionally, microcrack nucleation and propagation laws were analyzed in light of microscopic features characterized by EBSD, including phase distribution and grain and phase boundaries. The results show that the majority of microcracks are situated at the phase boundary between original austenite and ferrite, constituting about 70% of all microcracks. The number of microcracks located at the ferrite grain boundary accounts for about 20% of the total, while the number of microcracks located at the original austenite grain boundary accounts for only about 10% of the total. The interface between martensite and ferrite emerged as the primary site for microcrack nucleation. Furthermore, the study identifies three distinct microcrack nucleation sites influenced by various boundary types: at the intersection of martensite, ferrite, and austenite phases; at the junction of martensite/ferrite phase boundary and ferrite grain boundary; and at the cross point of martensite/ferrite phase boundary and the original austenite grain boundary. Therefore, microcracks might propagate along the original austenite/ferrite phase boundary or ferrite grain boundary with a smaller angle (< 30°) to the phase boundary. In addition, microcracks are less apt to propagate along the austenite grain boundary.
Fund: National Natural Science Foundation of China(52275388, 52075474);Natural Science Foundation of Hebei Province(E2022203206);Cultivation Project for Basic Research and Innovation of Yanshan University(2021LGZD009, 2022BZZD002)
Corresponding Authors:
JIN Miao, professor, Tel: (0335)8056775, E-mail: jmiao@ysu.edu.cn
Fig.1 Schematic of sample (a) and observation area for SEM and distribution of microcracks (b) (unit: mm)
Fig.2 Initial microstructure of the as-received Fe-19.6Cr-2Ni-2.9Mn-1.6Si steel (a) SEM image (b) phase distribution (c) inverse pole figure (IPF)
Fig.3 Mechanical properties of Fe-19.6Cr-2Ni-2.9Mn-1.6Si steel during monotonic loading (σE—engineering stress, εE—engineering strain, —true stress, —true strain, θ—work hardening rate, — instability strain) (a) engineering stress-engineering strain curve (b) true stress-true strain and work hardening rate curves
Fig.4 Statistics of microcrack locations of Fe-19.6Cr-2Ni-2.9Mn-1.6Si steel (a-g) microcracks at phase boundary (h) microcracks at original austenite grain boundary (i, j) microcracks at ferrite grain boundary (k) statistical pie chart
Fig.5 Characteristics of microcracks at the original austenite/ferrite phase boundary (a) SEM image (b) phase distribution (c) IPF
Fig.6 Nucleation of a microcrack at the original austenite/ferrite phase boundary and the propagation trend of the microcrack along the ferrite grain boundary (a) SEM image (b) phase distribution (c) IPF
Fig.7 Propagation characteristics of a microcrack on the original austenite/ferrite phase boundary (a) SEM image (b) phase distribution (c) IPF
Fig.8 Characteristics of a microcrack on ferrite grain boundary (a) SEM image (b) phase distribution (c) IPF
Fig.9 Characteristics of microcracks at original austenite grain boundary (a) SEM image (b) phase distribution (c) IPF
Fig.10 Schematics of microcrack nucleation characteristics (a) nucleation at the intersection position of transformed martensite/ferrite/residual austenite (b) nucleation at the intersection position of the ferrite/martensite phase boundary and ferrite grain boundary (c) nucleation at the intersection of ferrite/martensite phase boundary and original austenite grain boundary
Fig.11 Schematics of crack propagation paths (a) crack propagation along the original austenite/ferrite phase boundary (b) crack propagation along ferrite grain boundary with a smaller angle to the phase boundary (c) crack propagation along transformed martensite (original austenite) grain boundary
Fig.12 Schematics of non-nucleated crack at austenite/martensite phase boundary (a) deformation of pre nucleated martensite and austenite (b) formation of new phase boundaries due to martensite growth
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