On the relative fractions of HCP martensite in Fe-Mn alloys

J. MARTÍNEZ; S. M. COTES; A. F. CABRERA; J. DESIMONI; A. FERNÁNDEZ GUILLERMET

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

Elservier

Lugar: Amsterdam; Año: 2005 vol. 408 p. 26 - 32

0921-5093

Fe?Mn quenched alloys with Mn content between 13 and 27 wt% have been studied using X-ray diffraction, Mössbauer spectroscopy, differential scanning calorimetry and dilatometry. The samples have been structurally characterized using X-ray diffraction and Mössbauer spectroscopy. The composition dependence of the relative fraction of epsilon phase was determined by dilatometry and Mössbauer spectroscopy. Using a differential scanning calorimeter, measurements of the absorbed heat accompanying the epsilon to gamma martensitic transformation were also performed. The relative fractions of epsilon phase determined by dilatometry agree well with those reported in Schumann?s classical work [H. Schumann, Arch. Eisench¨uttenw. 38 (8) (1967) 647?656] for Mn contents up to about 22 wt% Mn, but for higher concentrations, a larger fraction was found. The discrepancy was explained in terms of the differences between the present heat treatments and those applied by Schumann. However, relative fractions of epsilon phase determined by Mössbauer spectroscopy resulted systematically larger than those obtained from dilatometry. On the other hand, independent calculations of the transformation heat were performed for the different compositions. They resulted from multiplying the epsilon fraction by the calculated epsilon to gamma enthalpy change obtained from a recent assessment of the Gibbs functions of the epsilon and gamma phases from literature. Absorbed heat values calculated using the Mössbauer epsilon fractions, reproduced well the experimental differential scanning calorimetry data, except when a high density of stacking faults are expected in the sample.