Effect of austempering temperature on microstructure and cyclic deformation behaviour of multiphase low-carbon steel

Abstract This paper examined the cyclic deformation behaviour of multiphase low-carbon steel that was subjected to austempering heat treatments at four temperatures (190 °C, 230 275 and 315 °C) below martensite start temperature ( M s = 353 °C). The tests were conducted room temperature, under fully reversed strain-controlled conditions, with strain amplitudes in range 0.5–1.0%. microstructure observed by transmission electron microscopy, fracture surfaces scanning microscopy. had a bainite/martensite microstructure, increasing bainite content for higher temperatures. Irrespective tested it strain-hardened during first two cycles then, strain-softened until failure. did not significantly affect stress-based, strain-based energy-based relationships. However, lower slightly improved fatigue performance.