| The martensitic transformation and bainite transformation behaviour of austenitedeformed at different tempreatures and the resulting microstructure in a low-carbonSi-rich alloy steel were studied. Compressive deformation and isothermal transformationof the austenite of the steel were performed on a Gleeble-3500thermomechanicalsimulator equipped. The retained austenite fraction was measured by X-ray diffractometry,and the microstructure features were examined by optical microscopy and transmissionelectron microscopy. The Vickers hardness was also measured on a hardometer.Results show that the compressive deformation of austenite can depress the MStemperature and martensitic lath thickness, and increase the hardness. the deformationtemperature decreases with the decreasing of MStemperature and lath thickness, andincreasing the hardness. Austenite deformed at900–355°C can depress the MStemperature from343°C-undeformed to315°C and the lath thickness from134±39nmthat undeformed to58±12nm, and increase the hardness from545±9HV1.0thatundeformed to636±10HV1.0. Samples are composed of α phase with body-centredcubic(BCC) lattice and γ phase with face-centred cubic (FCC) lattice. Strain rate (0.1and1.0s-1) have little effect on MStemperature, hardness and lath thickness.The low-temperature bainite which composed of bainitic ferrite laths and retainedaustenite were obtained by austempering at355and375°C that austenite deformed at900-355°C respectively. Deformed austenite can decrease the lath thickness, and increasethe hardness and volume fraction of retained austenite, and as the deformed temperaturedecrease, the lath thickness decrease, and the hardness and volume fraction of retainedaustenite increase. Austenite deformed at900–355°C can depress the lath thickness from138±32nm that undeformed to71±11nm that deformed, and increase the hardness from436±33HV1.0that undeformed to561±26HV1.0that deformed and the volume fractionof retained austenite from8.6%that undeformed to26.5%.. Samples are composed of αphase with body-centred cubic(BCC) lattice and γ phase with face-centred cubic (FCC)lattice. i.e., bainitic ferrite laths and retained austenite.. Strain rate (0.1and1.0s-1) havelittle effect on hardness、lath thickness and volume fraction of retained austenite. |
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