Abstract：Through the design of composite microalloyed components of low carbon, low Mo (~0.2%) and Nb, V, Ti, the continuous cooling transition (CCT) curve of the experimental steel was measured by Formastor-Digital automatic phase change tester, using Gleeble-1500 thermal simulation test machine studied the influence of different cooling processes on the microstructure and hardness of the test steel after deformation, and successfully developed Q345 fire-resistant steel, and used SEM, EBSD, TEM and physical phase analysis for hot rolling and The high temperature tensile specimens were microscopically characterized. The results show that the bainite structure begins to appear when the cooling rate of the test steel is above than 1.9oC/S. When the cooling rate is 9.6oC/S, the bainite content and matrix hardness are moderate, which is the best cooling rate after rolling. The content of MC phase and the percentage of particles below 18nm in the experimental steel were increased by 16.4 and 9.8% respectively compared to the hot-rolled samples. These precipitated nano-scale particles played a good role of precipitation strengthening at high temperature, making up for the high temperature. The loss of high-temperature yield strength due to the decrease in shear modulus and the failure of fine-grain strengthening strengthens the experimental steel with excellent high-temperature strength.According to the analysis of the room temperature and high temperature strengthening mechanism of the experimental steel, solid solution and precipitation strengthening are the main strengthening methods of Q345 fire-resistant steel.
2020, Vol. 55 
