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<p>To develop a low-cost, high-performance medium-Mn steel, a multi-element microalloyed Mn 7 steel (0.34C-7.0Mn-0.5Si-0.5Al-0.2V-0.003B) is designed. Its ingot is then forged at a relatively low final forging temperature. After forging, two heat treatment processes are applied: intercritical annealing (IA) and deep cryogenic treatment (DCT) followed by tempering. The IA at 680&#xa0;°C (680T) results in a tensile strength 1700&#xa0;MPa, an elongation 23.8%, and a low-temperature impact energy 25.5&#xa0;J, while the DCT and 300&#xa0;°C tempering process (DCT-300) achieves a higher tensile strength 1915&#xa0;MPa but reduces ductility (7.3% elongation) and toughness (10.8&#xa0;J impact energy). The newly developed medium-Mn steel exhibits significantly high mechanical properties. Microstructional analysis reveals a stronger redistribution of C elements in the retained austenite (RA), a higher dislocation density of martensite, and a more stable transformation-induced plasticity (TRIP) effect during deformation after DCT and tempering compared with after annealing. Furthermore, the RA with higher stability in the microstructure plays an important role in maintaining the TRIP effect. The elongation is primarily related to the RA transformation ratio during deformation.</p>

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Microstructure and Properties of a Multi-element Microalloyed Medium-Mn Steel after Low-Temperature Forging and Different Heat Treatments

  • 期刊论文

  • 发表日期：

    2026年8月3日

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  • Dejun Li,
  • Pengfei Bai,
  • Jiangzhuo Ren,
  • Wei Shi,
  • Qi Yang,
  • Jinlan Zhao,
  • Feng Cao

摘要

To develop a low-cost, high-performance medium-Mn steel, a multi-element microalloyed Mn 7 steel (0.34C-7.0Mn-0.5Si-0.5Al-0.2V-0.003B) is designed. Its ingot is then forged at a relatively low final forging temperature. After forging, two heat treatment processes are applied: intercritical annealing (IA) and deep cryogenic treatment (DCT) followed by tempering. The IA at 680 °C (680T) results in a tensile strength 1700 MPa, an elongation 23.8%, and a low-temperature impact energy 25.5 J, while the DCT and 300 °C tempering process (DCT-300) achieves a higher tensile strength 1915 MPa but reduces ductility (7.3% elongation) and toughness (10.8 J impact energy). The newly developed medium-Mn steel exhibits significantly high mechanical properties. Microstructional analysis reveals a stronger redistribution of C elements in the retained austenite (RA), a higher dislocation density of martensite, and a more stable transformation-induced plasticity (TRIP) effect during deformation after DCT and tempering compared with after annealing. Furthermore, the RA with higher stability in the microstructure plays an important role in maintaining the TRIP effect. The elongation is primarily related to the RA transformation ratio during deformation.