Pérdida de ductilidad debido a la descarburación y pérdida de Mn de un acero TWIP de tamaño de grano grosero

A clear transition in the tensile ductility behavior has been observed for grain sizes D in the range of 15 μm - 20 μm (1.50 μm ≤ D < 50 μm) in a 22% Mn, 0.6% C (in mass %) TWIP steel. This behavior is a combination of the intrinsic effect of grain size D on strength and work hardening rate of the material, with an extrinsic effect, superficial decarburization and Mn depletion processes occurred during annealing treatments at T ≥ 1000 ºC. In the present work, this extrinsic effect happened in TWIP steel has been studied in depth. GDOES (Glow Discharge Optical Emission Spectrometry) analyses have been carried out in order to study quantitatively the C and Mn concentration profiles. The depth of surface decarburization has been modeled by using Birks-Jackson theory. Two micro-constituents have been observed via Ferritoscope into decarburized volume: α’-martensite and α-austenite. The ductility of coarse-grained TWIP steel, subjected for high annealing temperatures and long annealing times, declines as a consequence of the formation of α’-martensite and less stable α-austenite with lower stacking fault energy, SFE, due to the Mn depletion in the decarburized volume