On the correlation among continuous cooling transformations, interphase precipitation and strengthening mechanism in Ti-microalloyed steel

Abstract

The correlation among continuous cooling transformations, interphase precipitation and their strengthening effect was investigated quantitatively in a Ti- microalloyed steel subjected to a two-stage controlled rolling and cooling process. Interphase precipitates, strain-induced and random precipitates were observed, of which the latter two mainly nucleated on dislocations. Interphase precipitation occurred only at low cooling rates of 0.1–0.5 °C/s and the highest density of nanoscale interphase precipitates with the smallest inter-sheet spacing was obtained at 0.5 °C/s. Subsequently increasing the cooling rate resulted in inhibited precipitation, but the dislocation density gradually increased and the grains were refined. Based on microhardness analysis, the highest peak consisting of 290 HV was located at 0.5 °C/s, where the best strengthening effect was obtained mainly due to interphase precipitation. When the continuous cooling rate exceeded 3 °C/s, dislocation and grain refinement strengthening gradually became more significant, transitioning from interphase precipitation to dislocation and grain refinement strengthening with increasing cooling rate.