Nanoscale cementite and microalloyed carbide strengthened Ti bearing low carbon steel plates in the context of newly developed ultrafast cooling

We describe here the microstructural evolution, mechanical properties and comprehensive strengthening mechanism of Ti-bearing high strength steels with different finish cooling temperatures in the context of newly developed ultrafast cooling system. Pilot-scale studies demonstrated that high yield strength of ~650 MPa can be obtained with ultrafast cooling finish temperature of 580 °C after hot rolling. The underlying reason is that the microalloyed carbides and nanoscale cementites can precipitate simultaneously to improve the precipitation strengthening to a large extent. In order to estimate the precipitation strengthening, the volume fraction of the precipitates in different size ranges was obtained by chemical phase analysis, small-angle X-ray and neutron scattering. The results indicated that Fe₃C, with a higher volume fraction, had a stronger precipitation strengthening effect than nanoscale TiC. The precipitation strengthening contribution of nanoscale precipitates can achieve 350 MPa. Together with solid solution strengthening and grain refinement strengthening, the theoretical calculated values match well with the experimental values.