Study on High-Temperature Mechanical Properties of Fe-Mn-C-Al TWIP/TRIP Steel

In this study, high-temperature tensile tests were carried out on a Gleeble-3500 thermal simulator under a strain rate of epsilon = 1 x 10(-3) s(-1) in the temperature range of 600-1310 degrees C. The hot deformation process of Fe-15.3Mn-0.58C-2.3Al TWIP/TRIP at different temperatures was studied. In the whole tested temperature range, the reduction of area ranged from 47.3 to 89.4% and reached the maximum value of 89.4% at 1275 degrees C. Assuming that 60% reduction of area is relative ductility trough, the high-temperature ductility trough was from 1275 degrees C to the melting point temperature, the medium-temperature ductility trough was 1000-1250 degrees C, and the low-temperature ductility trough was around 600 degrees C. The phase transformation process of the steel was analyzed by Thermo-Calc thermodynamics software. It was found that ferrite transformation occurred at 646 degrees C, and the austenite was softened by a small amount of ferrite, resulting in the reduction of thermoplastic and formation of the low-temperature ductility trough. However, the small difference in thermoplasticity in the low-temperature ductility trough was attributed to the small amount of ferrite and the low transformation temperature of ferrite. The tensile fracture at different temperatures was characterized by means of optical microscopy and scanning electron microscopy. It was found that there were Al2O3, AlN, MnO, and MnS(Se) impurities in the fracture. The abnormal points of thermoplasticity showed that the inclusions had a significant effect on the high-temperature mechanical properties. The results of EBSD local orientation difference analysis showed that the temperature range with good plasticity was around 1275 degrees C. Under large deformation extent, the phase difference in the internal position of the grain was larger than that in the grain boundary. The defect density in the grain was large, and the high dislocation density was the main deformation mechanism in the high-temperature tensile process.

Automated summary

This study investigated the hot deformation process and ductility trough formation mechanism of Fe-15.3Mn-0.58C-2.3Al alloy at different temperatures through high-temperature tensile tests. The phase transformation process was analyzed and it was found that ferrite transformation and presence of impurities affected the mechanical properties. EBSD analysis showed a temperature range with good plasticity around 1275 degrees C, with high dislocation density being the main deformation mechanism at high temperatures.