Effects of Mn Segregations on Intergranular Fracture in a Medium-Mn Low-Density Steel

Heechan Jung, Gunjick Lee, Minseo Koo, Hyejin Song, Won Seok Ko, Seok Su Sohn

Research output: Contribution to journalArticlepeer-review

Abstract

Al-bearing medium-Mn low-density steels possess great potential in the automotive industry because of their excellent mechanical properties based on transformation-induced plasticity and low specific weight. Reducing the austenite stability against deformation-induced martensitic transformation enables a high strain-hardening capacity to be obtained; however, undesirably low stability often results in considerably reduced tensile ductility and brittle fracture. Herein, the brittle fracture that occurs with increasing annealing temperature for a Fe−0.3C–9Mn−5Al (wt%) steel is investigated in relation to Mn segregation at the phase boundaries between ferrite and austenite. The results demonstrate that annealing at 850 and 900 °C leads to ductile fractures with 72% and 95% tensile elongation, respectively, whereas only 25% elongation is achieved for the specimen annealed at 950 °C, exhibiting predominant intergranular facets. 3D atom probe tomography reveals that annealing at 950 °C promotes considerable Mn segregation at the ferrite/austenite phase boundaries with a peak composition of ≈19 at%, which is sufficient to reduce the boundary cohesion for intergranular fracture. Thermodynamic moving boundary simulation reveals that intercritical annealing is not a prerequisite for segregations; however, low-temperature and prolonged holding should be accompanied, such as the coiling procedures.

Original languageEnglish
JournalSteel Research International
DOIs
Publication statusAccepted/In press - 2022

Keywords

  • atom probe tomography
  • intergranular fractures
  • low-density steels
  • segregations

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Metals and Alloys
  • Materials Chemistry

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