Microstructure And Mechanical Properties Of 2.25Cr-1Mo-0.25V Steel

Hydrogenater is the key equipment for modern oil refining industry and it is usually used under the condition of high temperature, high pressure and corrosive medium. The existed Cr-Mo series steels can not be satisfied for the above requirements. Thus it is very important to develop new steels used for hot wall hydrogenater.According to the standard of foreign related steel, 2.25Cr-1Mo-0.25V steel for hot wall hydrogenater were designed and prepared. The phase transformation temperature and CCT curve of experimental steel were measured. The results show that Ac1 and Ac3 temperature are 800℃ and 890℃, respectively. The zone of proeutectoid ferrite and pearlite is departed from that of bainite in CCT figure and the critical cooling velocity of obtaining single bainite microstructure is 0.5℃/s. The temperature effects of annealing, normalizing and quenching on microstructure and mechanical properties were investigated. The results show that after normalized at 930℃, quenched from 930℃ to 940℃ and tempered at 700℃, integrating mechanical properties are satisfactory. In addition, the grain size of austenite at different quenching temperature are measured and the grain growth temperature (TGC) is determined of 1000℃.The properties of the resistance to tempering brittlement of specimens obtained from different positions and different directions of cylinder simulative forging work pieces treated by Min.PWHT and Min.PWHT+S.C. were analysised. The results show that 2.25Cr-1Mo-0.25V steel has higher resistance to temper brittlement and can be used for hot wall hydrogenater.