Ultrafine microstructures developed during torsional testing of Hadfield manganese steels

Three Hadfield manganese steels were investigated containing 1·15, 1·40, and 1·70 wt-%C, all with about 13 wt-%Mn. The as processed steels consisted of austenite grains, 10–12 μm in size, with a dispersion of carbides. The steels were deformed at temperatures in the range 500–950°C in three different phase regions, namely, three phase (austenite + carbide + ferrite), two phase (austenite + carbide), and single phase (austenite). Ultrafine microstructures were developed during large strain torsional deformation. The large torsional deformation in the two phase region resulted in grain refinement through dynamic recrystallisation with the austenite grains pinned by carbide particles, minimising grain growth. Strain assisted transformation followed by spheroidisation of carbides was obtained on testing in the three phase region. The concurrent deformation and transformation resulted in ultrafine microstructures of submicrometre size constituents. Torsional properties were evaluated and related to the observed microstructural changes. Stress exponents of about 7 were obtained. The activation energy for the deformation process was found to be close to that for lattice self diffusion of iron in austenite.Peer reviewe

Ultrafine microstructures developed during torsional testing of Hadfield manganese steels

Three Hadfield manganese steels were investigated containing 1·15, 1·40, and 1·70 wt-%C, all with about 13 wt-%Mn. The as processed steels consisted of austenite grains, 10–12 μm in size, with a dispersion of carbides. The steels were deformed at temperatures in the range 500–950°C in three different phase regions, namely, three phase (austenite + carbide + ferrite), two phase (austenite + carbide), and single phase (austenite). Ultrafine microstructures were developed during large strain torsional deformation. The large torsional deformation in the two phase region resulted in grain refinement through dynamic recrystallisation with the austenite grains pinned by carbide particles, minimising grain growth. Strain assisted transformation followed by spheroidisation of carbides was obtained on testing in the three phase region. The concurrent deformation and transformation resulted in ultrafine microstructures of submicrometre size constituents. Torsional properties were evaluated and related to the observed microstructural changes. Stress exponents of about 7 were obtained. The activation energy for the deformation process was found to be close to that for lattice self diffusion of iron in austenite.Peer reviewe