Mechanical behaviour and microstructure of Fe-20/27Mn–4Al-0.3C low magnetic steel at room and cryogenic temperatures

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2021-03, Vol.809, p.140998, Article 140998
• Main Authors: Li, Changsheng, Li, Kun, Dong, Jingbo, Wang, Jikai, Shao, Zhibao
• Format: Article
• Language: English
• Subjects: Cryogenic temperature; Deformation effects; Deformation mechanisms; Ductile fracture; Elongation; Fracture mechanics; Hardening rate; Low magnetic steel; Low temperature; Magnetic properties; Martensite; Martensitic transformations; Mechanical properties; Microstructure; Plastic deformation; Plastic properties; Steel; Strain hardening; Stress-strain curves; Tensile strength; Tensile tests; TWIP steels; Work hardening; Work hardening behavior
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2021.140998

The stress-strain curves and strain hardening rate curves of Fe–20Mn–4Al-0.3C (20Mn) and Fe–27Mn–4Al-0.3C (27Mn) steels were obtained by tensile tests at room and cryogenic temperatures. The yield strength, tensile strength, and elongation of 20Mn and 27Mn steels at −196 °C were significantly improved, and the product of strength and ductility reached 92.6 GPa·% and 80.1 GPa·%, respectively. There were a large number of deformation twins in 20Mn and 27Mn steels, and the deformation-induced martensite effect also occurred in 20Mn steel. The twinning-induced plasticity (TWIP) and transformation -induced plasticity (TRIP) at −196 °C significantly improved the strength and plasticity of the steels, but TRIP has a stronger effect. The work hardening rate of 20Mn steel was higher than that of 27Mn steel. The fracture mechanism of 20Mn and 27Mn steels at −196 °C was ductile fracture. Plastic deformation of 20Mn steel at low temperature can be divided into the dislocation slipping, twinning, and deformation-induced martensitic transformation stages, whereby a high elongation (77.4%) was obtained, which was also ascribed to the formation of microbands and dislocation cross slipping during the deformation process. The deformation mechanism of 27Mn steel was mainly the TWIP effect, in which the deformation-induced martensite did not form. Therefore, the work hardening rate of 27Mn steel was lower than that of 20Mn steel, and the elongation was relatively low (68.3%). Although 27Mn steel exhibited large plastic deformation during low temperature deformation, there was almost no martensite, which has a more stable austenitic structure and better low magnetic property.