Low-Temperature Impact Fracture Behavior of Medium Manganese Steel with Bcc-fcc Duplex Microstructures

Impact fracture behavior at low temperatures was investigated in medium manganese steel with bcc-fcc duplex microstructures. The impact energy was above 150 J (-80 similar to 20 degrees C) and the fractography showed dimples for inter-critical annealing at 630 degrees C (QHA) because of the high retained austenite stability and low martensite dislocation density. The impact energy was from 180 J (20 degrees C) to 60 J (-80 degrees C) and the fractography was intergranular for inter-critical annealing at 610 degrees C (QLA) because of the low stability of RA and carbides precipitated at the prior austenite grain boundaries. The impact energy was below 60 J (-80 similar to 20 degrees C) and the fractography showed cleavage for direct quenching (DQ) because of the high dislocation density of martensite.