Discussion about continuous cooling transformation behavior of Q345qNH weathering bridge steel
The Q345qNH weathering bridge steel was investigated.The phase transition temperature and time of Q345qNH weathering bridge steel containing Nb and V at different cooling rates were measured using Formastor-F Ⅱ phase transforma-tion tester.The metallographic microstructure,hardness and transformation process were analyzed,and the continuous cool-ing transformation(CCT)curve of Q345qNH steel was created.The results showed that the microstructure of tested steel was mainly composed of pearlite and ferrite when the cooling rate was 0.3-2 ℃/s.As the cooling rate was 2-3 ℃/s,the microstructure was composed of uniform pearlite+ferrite+a small amount of granular bainite.When the cooling rate was 3-20 ℃/s,the microstructure of tested steel was mainly composed of uniform ferrite matrix+uniform granular bainite.When the cooling rate was further increased to 20-50 ℃/s,the lath bainite appeared in the microstructure,but the ferrite and granular bainite were dominant.The relationship between hardness and microstructure could be divided into three sta-ges:the stage of ferrite refined crystalline strengthening,the stage of granular bainite incremental strengthening,and the stage of bainite strip morphology strengthening.
万方数据
维普
