Interphase precipitation strengthening in ultra-high strength low-carbon Ti-Mo bearing steel

The morphology, size and distribution of interphase precipitation particles formed in Ti- Mo-bearing low-carbon steel after isothermal transformation were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area diffraction analysis. The mechanical properties of the hot-rolled plate were also tested. The results show that as the isothermal temperature decreases, the strength and the ratio of yield strength to tensile strength increase, but the ductility decreases. Two different types of interphase precipitation carbides, planar interphase precipitation and curved interphase precipitation, were observed in the TEM specimens. The average diameter of these carbides is 4.30 nm with an average aspect ratio of 1.375. Interphase precipitation isothermally treated at 650℃ for 1 h can strengthen the ferrite phase by above 400 MPa.