Key Takeaways & Executive Findings
- •• Molecular dynamics simulations reveal that Fe-Mn alloys with 10%–30% Mn all undergo phase transformations and {112}<111>BCC deformation twinning, but follow distinct FCC- and/or HCP-related deformation paths depending on Mn content. • Increasing Mn content raises the stacking fault energy, retards slip system activation and stacking fault formation, and delays the FCC→ε-martensite and ε-martensite→BCC transitions at intersections of ε-martensitic bands. • Mn alloying increases yield strength and reduces elastic modulus of Fe-Mn alloys, while deformation twins enhance work hardening and delay necking and fracture. • These atomic-scale insights provide a theoretical basis for designing and optimizing high-performance steels through tailored Mn content and deformation pathway control.
Abstract
In the present study, molecular dynamic simulation (MD) was used to investigate the plastic deformation process of the Fe-Mn alloys with different Mn contents. The influences of Mn contents ranging from 10% to 30% (at%) on the deformation behavior and the controlling mechanism of the Fe-base alloys were analyzed. The results show that phase transformations and {112} <111>BCC deformation twinning occur in all Fe-Mn alloys but follow different deformation paths. In the Fe-10%Mn alloy the deformation twinning mechanism obeys the FCC-related path, the Fe-20%Mn alloy involves both the FCC- and HCP-related paths, and the deformation of the Fe-30%Mn alloy is dominated by the HCP-related twinning path. The addition of Mn can increase the stacking fault energy and retard the activation of slip systems as well as the formation of stacking faults. Thus, a higher content of Mn can delay the FCC→ε-martensite and the subsequent ε-martensite→BCC phase transition at the intersection of two ε-martensitic bands. Therefore, the addition of Mn alloying element increases the yield strength and reduces the elastic modulus of the Fe-Mn alloys. The formation of deformation twins will contribute to the work-hardening effect and delay the necking and fracture of alloys. It is expected that the results in the present study will provide theoretical reference for the design and optimization of high-performance steels.
1. Introduction
As a new generation of advanced high-strength steel, twinning-induced plasticity (TWIP) steel has the characteristics of high strain hardening rate, high uniform elongation and high ultimate tensile strength [1, 2]. The product of strength and elongation for TWIP steels is 4.5 times that of traditional high-strength low-alloy steels, 2.7 to 3 times that of dual-phase steels and twice that of transformation-induced plasticity (TRIP) steels. This can effectively reduce the weight of automobiles but maintain excellent comprehensive mechanical properties, which guarantees the safety of passengers as well as benefiting energy conservation and emission reduction [3]. The excellent mechanical properties of the TWIP steel are closely related to its high work hardening rate during deformation. For the TWIP steel, the work hardening during deformation is not only related to the dislocation structure and evolution, but also related to the twin-twin interactions, the interactions between dislocations and twins, as well as the interaction between solute atoms and dislocations/twins.
As one of the main alloying elements, manganese plays an important role in determining the microstructural evolution, work hardening and tensile properties of TWIP steels [4]. The addition of manganese will increase the temperature of the ε →γ phase transition and decrease the intrinsic stacking fault energy [5]. Besides, the relationship between intrinsic stacking fault energy and manganese content is nonlinear. Low Mn content in the binary Fe-Mn alloy reduces the intrinsic stacking fault energy. The lowest intrinsic stacking fault energy appears when the mass percentage of Mn ranges between 10% and 16%. With a higher Mn content between 16% and 33%, the intrinsic stacking fault energy of the Fe-Mn alloy can be increased by 18 mJ/m² per 1% of Mn added. The nonlinear relationship between the Mn content and the intrinsic stacking fault energy is due to the influence of Mn on the energy difference of the face-centered cubic (FCC) and hexagonal-close packed (HCP) structure, that is, the increase of Mn content inhibits the formation of HCP structure [6]. Previous investigation [7] also indicates that the deformation mechanism of steels will change from the joint action of TRIP steels and TWIP steels effect at low manganese content to only the TWIP steels effect at high manganese content, which leads to higher elongation of steels with higher manganese content.
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ZHANG Hong-bo, LI Hong-kui, OU Xiao-qin, SHEN Jie, SONG Min (2025). Atomic-scale understanding of martensitic transformation and transition-induced twinning in deformed Fe-Mn alloys. Journal of Central South University. https://doi.org/10.1007/s11771-025-5931-5
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Frequently Asked Questions
What is the main objective of this study?
The study uses molecular dynamics simulation to investigate the plastic deformation of Fe-Mn alloys with different Mn contents (10%–30%) and analyzes how Mn content influences deformation behavior and controlling mechanisms, including phase transformations and twinning.
How does manganese content affect stacking fault energy?
Manganese content has a nonlinear effect on intrinsic stacking fault energy. Low Mn content (10%–16%) reduces it, while higher Mn content (16%–33%) increases it by approximately 18 mJ/m² per 1% Mn added.
What deformation mechanisms are observed in Fe-Mn alloys?
Fe-10%Mn follows an FCC-related twinning path, Fe-20%Mn involves both FCC- and HCP-related paths, and Fe-30%Mn is dominated by the HCP-related twinning path, all accompanied by martensitic transformations.
What are the mechanical effects of adding manganese?
Adding manganese increases yield strength and reduces elastic modulus of Fe-Mn alloys. Deformation twins also contribute to work hardening, delaying necking and fracture.
What is the practical significance of this research?
The findings provide atomic-scale theoretical references for designing and optimizing high-performance steels by controlling Mn content and deformation pathways to achieve superior strength-ductility combinations.
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