Grain Size-Dependent Mechanical Properties of a High-Manganese Austenitic Steel

Abstract

The effect of grain size on the mechanical properties of a high-manganese (Mn) austenitic steel was investigated via electron-backscattered diffraction, transmission electron microscope, X-ray diffraction, and tensile and impact tests at 25 °C and − 196 °C. The Hall–Petch strengthening coefficients for the yield strength of the high-Mn austenitic steels were 7.08 MPa mm 0.5 at 25 °C, which increased to 14 MPa mm 0.5 at − 196 °C. The effect that the grain boundary strengthening had on improving the yield strength at − 196 °C was better than that at 25 °C. The impact absorbed energies and the tensile elongations were enhanced with the increased grain size at 25 °C, while they remained nearly unchanged at − 196 °C. The unchanged impact absorbed energies and the tensile elongations were primarily attributed to the emergence of the micro-twin at − 196 °C, which promoted the cleavage fracture in the steels with large-sized grains. Refining the grain size could improve the strength of the high-Mn austenitic steels without impairing their ductility and toughness at low temperature.