Thermodynamic Stacking Fault Energy, Chemical Composition, and Microstructure Relationship in High-Manganese Steels
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HADFIELD steels have elevated Mn levels. These steels have high wear resistance due to their austenite to martensite (c ! a¢) transformation when submitted to stress/strain.[1,2] Currently, steels with manganese content higher than 20 wt pct have been produced with an excellent combination of high strength and ductility.[3–5] They have been classified in terms of their
GIOVANI GONC¸ALVES RIBAMAR is with the Universidade de Sa˜o Paulo, Escola Polite´cnica, Departamento de Engenharia Metalu´rgica e de, Materiais, Av. Professor Mello Moraes, 2463, Sa´o Paulo, CEP: 05508-030, Brazil. Contact e-mail: [email protected] TATHIANE CAMINHA ANDRADE, HE´LIO CORDEIRO DE MIRANDA, and HAMILTON FERREIRA GOMES DE ABREU are with the Universidade Federal do Ceara´, Departamento de Engenharia Metalu´rgica e de Materiais, Campus do Pici, Bloco 729, Ceara´, CEP 60.440-554, Brazil. Manuscript submitted October 13, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
plasticity-enhancing mechanisms,[6] where twinning-induced plasticity (TWIP)[7–9] and transformation-induced plasticity (TRIP)[10–12] have been designated to those steels that present twin and martensite formation, respectively, when submitted to a stress/strain. In addition, the relationship between mechanical behavior and stacking fault energy (SFE) that austenite presents at some temperatures and compositions has been published.[7,13,14] A stacking fault (SF) in the face-centered cubic (FCC) structure is a bi-dimensional fault formed between partial dislocations when normal stacking sequence of the (111) plane is disturbed.[7] This change in stacking sequence produces an interface separating two regions in the matrix and is related to interface energy. Otte[15] and Smallman and Westmacott[16] studied the influence of manganese and chromium content in the presence of SFs and the influence of elevated temperature deformation on the probability of faulting. These authors reached the conclusion that these alloying elements increase the susceptibility of FCC austenite to faulting,
as well as decrease the deformation temperature. The SFE can be determined by transmission electron microscopy (TEM)[17] and X-ray diffraction.[18] In addition, SFE has been calculated by Ab-initio[19,20] and thermodynamic models,[7,14] among others. The latter was used to determine the SFE for all welding samples in this study. These methods of determining the SFE through calculations and thus the ability to predict the microstructure and mechanical behavior from the SFE value make the SFE an excellent tool to design materials with specific properties. In general, high-manganese steel with SFE close to 0 mJ/m2 has been reported to present -martensite after a rapid cooling from a c phase field. However, an increase in SFE until approximately 15 mJ/m2 presents -martensite and twins when the material is submitted to a deformation, which is characteristic of a TRIP steel.[6,7,13] Above approximately 15 mJ/m2, twins are formed in austenite when the material is submitted to a stress/strain, whi
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