Abstract
The influence of cold biaxial forging and annealing on the microstructure evolution and mechanical properties of Fe-18Mn-0.6C-0.1N TWIP steel was investigated. The microstructure after thermomechanical treatment was examined by means of scanning electron microscopy (SEM) with electron back-scattered diffraction (EBSD) analyzer and transmission electron microscopy (TEM). The microstructure containing a high density of deformation twins was evolved by cold forging. Then, the deformation microstructure was recovered or partially recrystallized during subsequent annealing for 1 h at 673 or 873 K, respectively. The cold biaxial forging followed by partial recrystallization resulted in a very attractive combination of mechanical properties. The yield strength and the ultimate tensile strength of the steel after cold biaxial forging were 1320 and 1540 MPa, respectively, with elongation of 6 %. On the other hand, the yield and ultimate tensile strength of 770 and 1110 MPa, respectively, and elongation about 40 % were obtained after partial recrystallization. The as-forged and recovery annealed samples showed fatigue limit of 600 and 550 MPa, respectively, and the sample after partial recrystallization showed slightly lower fatigue limit of 500 MPa.

Key words
TWIP-steel, deformation twinning, microstructure, mechanical properties, fatigue

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