Influence of Cooling and Strain Rates on the Hot Ductility of High Manganese Steels Within the System Fe-Mn-Al-C

The ductility curves of high manganese steel grades with a stepwise increasing [Al] content of 0, 1, 3, 5, and 8 wt% for two strain rates (0.01 and 0.001 s(-1)) and for a varying cooling rate (-3 and -7 Ks(-1)) have been determined to investigate their influence on the hot ductility behavior. The tests have been conducted at the hot tensile testing unit of the Department of Ferrous Metallurgy of RWTH Aachen University. This equipment is able to perform testing of semisolid samples, e.g., during solidification. After the tensile testing, the specimens are investigated using the scanning electron microscope/energy-dispersive X-ray spectroscopy as well as by light optical microscopy to clarify the role of the cooling and strain rates on the hot ductility of high manganese steels and on the formations of precipitates. Furthermore, thermodynamic modeling using the commercial software ThermoCalc is performed. A shifting of the decay of the ductility maximum to lower temperatures down to approximate to 1273 K for both an increasing strain rate and an increasing cooling rate is determined and this effect is explained through their influences on the microstructure and fracture behavior. Micrograph analyses show that (MnS) precipitates form in contact with early (AlN) precipitates.