On the correlation among isothermal transformation, interphase precipitation behaviour and elements partitioning in Ti–Mo microalloyed steel

Abstract

The correlation among isothermal transformation, interphase precipitation behaviour, and elements partitioning during isothermal heat treatment in a Ti–Mo microalloyed steel were investigated. The effect of isothermal holding temperature on the microhardness of different phases was studied. The highest microhardness (184.5 HV0.01) of ferrite was obtained after holding at 650 °C for 600 s, owning to the tiny interphase precipitates and solution strengthening from titanium and molybdenum. As the isothermal temperature decreased, the amount of ferrite increased, whereas the amount of martensite or martensite mixed with bainite decreased. The interphase precipitation sheet spacing and average diameters were refined by decreasing the isothermal holding temperature, which contributes to higher ferrite hardness. Additionally, manifest partitioning of carbon accompanied by ferrite transformation was detected, with an inhomogeneous distribution in martensite. Furthermore, Ti and Mo tend to redistribute at 675 °C and 650 °C, respectively, resulting in slight enrichment in some ferrite but depletion in martensite. The above phenomenon can be explained by the cycle of Ti, Mo segregation at the α/γ interface during ferrite transformation.

Keywords

• Ferrite transformation
• Interphase precipitation
• Elements partitioning
• Ti–Mo microalloyed steel