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<p>This study investigates the microstructure evolution and deformation behavior of medium Mn steel (MMS) following caliber rolling, deep cryogenic treatment (DCT), and intercritical annealing (IA). The results indicate that caliber rolling refines austenite grains, while during DCT, martensite formation occurs in Mn-lean layers due to the laminated element segregation in MMS. Subsequently, in IA, a multilayer structure is formed with <i>γ</i><sub>L</sub> + <i>α</i><sub>L</sub> in the Mn-lean layers and <i>γ</i> phase in the Mn-rich layers. This structure establishes a gradient of austenite stability, enabling stepwise martensitic transformations of austenite during plastic deformation. Additionally, tensile testing reveals the presence of Lüders band and Portevin-Le Chatelier (PLC) band in MMS, with the expansion of Lüders band being influenced by the work hardening rate. Enhanced transformation-induced plasticity (TRIP) effect accelerates the expansion of Lüders band and reduces the strain. Consequently, as the IA temperature increases, the stability of austenite first increases and then decreases, peaking at 650&#xa0;°C. This results in MMS annealed at 650&#xa0;°C exhibiting lower TRIP effect plasticity during plastic deformation, extending Lüders bands, and ultimately achieving the highest product of strength-ductility of 34.6&#xa0;GPa%.</p>

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The Influence on Microstructure Evolution and Mechanical Properties of Medium Mn Steel Via Deep Cryogenic Treatment and Intercritical Annealing

  • 期刊论文

  • 发表日期：

    2025年12月20日

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  • Ying Gao,
  • Bao-xi Liu,
  • Hao-chuan Tong,
  • Meng-bang Ding,
  • Fu-xing Yin

摘要

This study investigates the microstructure evolution and deformation behavior of medium Mn steel (MMS) following caliber rolling, deep cryogenic treatment (DCT), and intercritical annealing (IA). The results indicate that caliber rolling refines austenite grains, while during DCT, martensite formation occurs in Mn-lean layers due to the laminated element segregation in MMS. Subsequently, in IA, a multilayer structure is formed with γL + αL in the Mn-lean layers and γ phase in the Mn-rich layers. This structure establishes a gradient of austenite stability, enabling stepwise martensitic transformations of austenite during plastic deformation. Additionally, tensile testing reveals the presence of Lüders band and Portevin-Le Chatelier (PLC) band in MMS, with the expansion of Lüders band being influenced by the work hardening rate. Enhanced transformation-induced plasticity (TRIP) effect accelerates the expansion of Lüders band and reduces the strain. Consequently, as the IA temperature increases, the stability of austenite first increases and then decreases, peaking at 650 °C. This results in MMS annealed at 650 °C exhibiting lower TRIP effect plasticity during plastic deformation, extending Lüders bands, and ultimately achieving the highest product of strength-ductility of 34.6 GPa%.