Post-Rolling Cooling Phase Transformation and Microstructure of High-Strength Anti-Seismic Rebars with Different Solute Nb and Austenite Microstructure

Three types of 20MnSiNb high-strength anti-seismic steels with different solute niobium and austenite microstructural characteristics were obtained through thermal simulation experiments which involved changing the reheating temperature and finish-rolling temperature; the dynamic CCT curve, microstructure transformation, precipitates and hardness of the steels were also studied. The results show that the ability of solute Nb to refine austenite grains is stronger than that of undissolved Nb. Lowering the reheating temperature and finish-rolling temperature can refine the prior austenite microstructure and keep the deformed austenite after hot rolling, respectively, and make the dynamic CCT curve move to the upper left, which promotes the formation of proeutectoid ferrite and pearlite, and inhibits the formation of bainite at low cooling rates. The increase in solute Nb and the deformed austenite grains effectively promote the precipitation of Nb-containing precipitates during the cooling process after rolling, and improve the precipitation strengthening effect of Nb. This research provides a theoretical basis for the production of Nb microalloyed high-strength anti-seismic rebars.