Effect of Controlled Rolling and Controlled Cooling on Microstructure and Mechanical Properties of Low Carbon Steel Microalloyed With Nb

Continuous cooling transformation diagram of low carbon steel microalloyed with Nb after hot deformation was determined by using Gleeble-1500 hot simulator.Controlled rolling and controlled cooling were carried out by using different schedules.Effect of finish rolling temperature and coiling temperature on the mechanical properties and microstructure were investigated,and strengthening mechanisms of steel were analyzed.Thermal simulation results revealed that bainite structure could be obtained at a cooling rate in range of 0.5-30 ℃/s.and transformation products mainly consist of ferrite and bainite,and the microstructure could be refined and the strength of the steel increased,but yield ratio increased with low finish rolling temperature.The lower coiling temperature is beneficial to strength increment due to the increase of volume fraction of bainite.The effect of bainite on the properties of steel is discussed to provide suitable parameters for production.