Microstructure and mechanical properties of 18Mn3Si2CrMo steel subjected to austempering at different temperatures below Ms

A low-carbon 18Mn3Si2CrMo steel was subjected to austempering at different temperatures below Ms, and low-temperature bainite was introduced. The multiphase microstructures of martensite, bainite and retained austenite with different volume fractions were obtained, and the relationship among their phase contents and mechanical properties was studied. The 18Mn3Si2CrMo steel with a volume fraction of martensite (VM), bainite (VB) and retained austenite (Vγ) of approximately 80%, 16% and 4%, respectively was obtained by austenitizing at 900 °C followed by austempering at 205 °C for 2 h, and then exhibited the optimal mechanical properties with a yield strength of 944 MPa, a tensile strength of 1512 MPa, a total elongation of 15.4% and an impact toughness of 119 J/cm2. When the austempering temperature was increased from 205 °C to 330 °C, the yield strength, tensile strength and impact toughness of the steel decreased. The poorest comprehensive mechanical properties were observed after 330 °C of austempering. The introduction of low-temperature bainite enhanced the ductility and toughness of the 18Mn3Si2CrMo steel.