Hot deformation characterization of duplex low-density steel through 3D processing map development

The high temperature deformation behavior of duplex low-density Fe-18Mn-8Al-0.8C steel was investigated at temperatures in the range of 600-1000 degrees C. The primary constitutive analysis indicated that the Zener-Hollomon parameter, which represents the coupled effects of temperature and strain rate, significantly varies with the amount of deformation. Accordingly, the 3D processing maps were developed considering the effect of strain and were used to determine the safe and unsafe deformation conditions in association with the microstructural evolution. The deformation at efficiency domain 1(900-1100 degrees C\10(-2)-10(-3) s(-1)) was found to be safe at different strains due to the occurrence of dynamic recrystallization in austenite. The safe efficiency domain II (700-900 degrees C\1-10(-1) s(-1)), which appeared at logarithmic strain of 0.4, was characterized by deformation induced ferrite formation. Scanning electron microscopy revealed that the microband formation and crack initiation at ferrite \ austenite interphases were the main causes of deformation instability at 600-800 C degrees\10(-2)-10(-3) s(-1). The degree of instability was found to decrease by increasing the strain due to the uniformity of microbanded structure obtained at higher strains. The shear band formation at 900-1100 degrees C\1-10(-1)s(-1) was verified by electron backscattered diffraction. The local dynamic recrystallization of austenite and the deformation induced ferrite formation were observed within shear-banded regions as the results of flow localization. (C) 2015 Elsevier Inc. All rights reserved.