Driving force for γ→ε martensitic transformation and stacking fault energy of γ in Fe-Mn binary system

Abstract

A regular solution model for the difference of the chemical free energy between ␥ and phases during ␥ → martensitic transformation in the Fe-Mn binary system has been reexamined and partly modified based on many articles concerning the M s and A s temperatures of Fe-Mn alloys. Using the regular solution model, the measured M s temperatures, and a thermodynamic model for the stacking fault energy (SFE) of austenite (␥), the driving force for ␥ → martensitic transformation, and the SFE of ␥ have been calculated. The driving force for ␥ → martensitic transformation increases linearly from Ϫ68 to Ϫ120 J/mole with increasing Mn content from 16 to 24 wt pct. The SFE of ␥ decreases to approximately 13 at. pct Mn and then increases with increasing Mn content, which is in better agreement with Schumann's result rather than Volosevich et al.'s result.

Deformation Twinning Behavior of Twinning-induced Plasticity Steels with Different Carbon Concentrations – Part 1: Atomic Force Microscopy and Electron Backscatter Diffraction Measurements

“…The free energy change and molar surface density were extracted from the other references 19,[39][40][41][42][43][44][45] in Nakano's paper. .…”

Twinning effects on strength and plasticity of metallic materials

“…The high concentration of Mn is crucial to preserve the austenitic structure 73 and control the SFE of the Fe-based alloys. 74 TWIP steels typically have low SFE (between 20 and 40 mJ/m 2 ) at room temperature. SFE in the steels can be tuned by adjusting alloy composition.…”

Effect of cooling rate on (ε, α') martensite formation in twinning/transformation-induced plasticity Fe-17Mn-0.06C steel

“…In steels with low SFE, a perfect displacement in the fcc array can easily be divided into two partial dislocations, thus forming a stacking fault. Four or five layers of stacking faults are considered to be a potential nucleus for α' martensite 16 . Thus, the higher the austenitic grain size, the greater the probability of finding nucleation sites for α′ martensite, formed by superimposing stacking faults, leading to a high M s temperature 15,29,30 and consequently, more time for transformation.…”

“…During cooling, the austenitic Fe-Mn steel, within a restricted range of chemical composition, partially transforms into ε hcp and α' bcc martensite, while retaining some the untransformed austenite [12][13][14][15] . Stacking faults and twinning are important for the formation of martensite in Fe-Mn-Si-Al steels because they act as nucleation sites for martensite formation [16][17][18][19] . The fcc-phase transformation γ→ε hcp occurs through the formation of alternate layers of stacking faults in the (111) planes of austenite.…”