Micro-Deformation Behavior of Austenite Containing Chemical Boundary in a Medium Mn Steel: A Crystal Plasticity Modeling
JIA Chunni1, LIU Tengyuan1,2, ZHENG Chengwu1(), WANG Pei1, LI Dianzhong1()
1 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2 School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
Cite this article:
JIA Chunni, LIU Tengyuan, ZHENG Chengwu, WANG Pei, LI Dianzhong. Micro-Deformation Behavior of Austenite Containing Chemical Boundary in a Medium Mn Steel: A Crystal Plasticity Modeling. Acta Metall Sin, 2025, 61(2): 349-360.
Chemical boundaries (CBs) delineate two areas within a continuous lattice that have same structures but exhibit a sharp chemical discontinuity. CBs can be seen as a unique planar defect that is distinct in certain aspects from traditional physical interfaces such as phase boundaries and grain boundaries (GBs). Recently, GBs have been established within the austenite of medium Mn steels; they have been proven to substantially enhance the stability of austenite. This allows austenite to be easily retained at room temperature and offers additional possibilities for managing its mechanical stability. In this study, a crystal plasticity modeling was performed to simulate the deformation behavior of austenite containing a CB. First, an extended dislocation-based crystal plastic model that incorporates the deformation-induced martensitic transformation and stacking fault energy was developed. The inverse Nishiyama-Wassermann (N-W) relation was used to accurately describe the orientation relationship between austenite and newly formed martensite. The Mn content on both sides of the CB is taken as a state variable to calculate the stacking fault energy. This leads to varying responses in the deformation-induced martensitic transformation and dislocation slip within a single austenite grain. Results reveal a strain incompatibility between Mn-rich and Mn-poor austenite that causes a geometrically necessary dislocation to accumulate near the CB. Furthermore, the deformation-induced martensitic transformation on both sides of the CB behaves differently, leading to a “spectral” distribution of mechanical stability within a single austenite grain. This heterogeneity in the mechanical stability of austenite is highly beneficial. It allows a gradual deformation-induced phase transformation throughout the entire deformation process, which is crucial for enhancing the strength and plasticity of transformation induced plasticity (TRIP)-aided steels simultaneously.
Fig.1 Illustration of the intermediate configurations resulting from multiplicative decomposition of the deformation gradient in crystal plasticity model ( Fe——elastic deformation gradient, Fp—plastic deformation gradient)
α
α
1
7
2
8
3
9
4
10
5
11
6
12
Table 1 Slip systems of the fcc crystal
xtr
ytr
ztr
rtr
θtr
1
[100]
[010]
[001]
[010]
+10.26°
2
[100]
[010]
[001]
[010]
-10.26°
3
[100]
[010]
[001]
[001]
+10.26°
4
[100]
[010]
[001]
[001]
-10.26°
5
[010]
[100]
[001]
[100]
+10.26°
6
[010]
[100]
[001]
[100]
-10.26°
7
[010]
[100]
[001]
[001]
+10.26°
8
[010]
[100]
[001]
[001]
-10.26°
9
[001]
[100]
[010]
[100]
+10.26°
10
[001]
[100]
[010]
[100]
-10.26°
11
[001]
[100]
[010]
[010]
+10.26°
12
[001]
[100]
[010]
[010]
-10.26°
Table 2 Martensite transformation systems of the fcc crystal following the inverse Nishiyama-Wassermann (N-W) relation used in the crystal plasticity model
δ
α
1
2
3
4
5
6
7
8
9
10
11
12
1
0
0
0
0
0
0
0
0
0
0
2
0
0
0
0
0
0
0
0
0
0
3
0
0
0
0
0
0
0
0
0
0
4
0
0
0
0
0
0
0
0
0
0
5
0
0
0
0
0
0
0
0
0
0
6
0
0
0
0
0
0
0
0
0
0
7
0
0
0
0
0
0
0
0
0
0
8
0
0
0
0
0
0
0
0
0
0
9
0
0
0
0
0
0
0
0
0
0
10
0
0
0
0
0
0
0
0
0
0
11
0
0
0
0
0
0
0
0
0
0
12
0
0
0
0
0
0
0
0
0
0
Table 3 Projection matrix from the fcc slip systems to the fault-band systems
α
1
7
2
8
3
9
4
10
5
11
6
12
Table 4 Fault band systems of the fcc crystal structure
Fig.2 Self-consistent integration of kinematic quantities within fixed internal material state parameters ( F —deformation gradient, —tangent of plastic deformation gradient, Lp—velocity gradients of plastic deformation gradient, S —second Piola-Kirchhoff stress, —plastic slip rate, —evolution rate of edge dislocation, —martensite fraction)
Fig.3 Geometric model of the Mn chemical boundary in austenite (a) schematic of the chemical boundary (b) representative volume element model (The red part represents the Mn-rich region with Mn content of 13% (mass fraction) and the blue part represents the Mn-poor region with Mn content of 5% (mass fraction). ε—strain)
Fig.4 Simulated microzone strain distributions across the chemical boundary within an austenite grain at strains of 0.025 (a), 0.05 (b), 0.075 (c), and 0.10 (d)
Fig.5 Simulated microzone stress distributions across the chemical boundary within an austenite grain at strains of 0.025 (a), 0.05 (b), 0.075 (c), and 0.1 (d)
ε
εmax - εmin
τmax - τmin / MPa
0.025
0.05 × 10-2
00.8
0.050
0.05 × 10-2
04.4
0.075
1.41 × 10-2
20.4
0.100
2.78 × 10-2
71.1
Table 5 Statistics of the difference value of microzone strain and stress across the chemical boundary
Fig.6 Microzone stress (a, c) and microzone strain (b, d) distributions along the lines L1-L (a, b) and L2-L (c, d) in Figs.4b and 5b at strain of 0.025
Fig.7 Simulated dislocation density distributions across the chemical boundary at strain of 0.1 (a) and profile of the dislocation density along the black line in Fig.7a (b)
Fig.8 Distribution of the martensite volume fraction at strain of 0.05 (a) and kinetics of the martensite transformation within austenite grain on both side of the chemical boundary during deformation (b)
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