Effect of Thermomechanical Heat Treatment in the Magnetic Field on the Creep Properties and Microstructures of the High Cr Ferritic Heat Resistant Steel

摘要

Effect of thermomechanical and magnetic treatment on creep characteristics of advanced heat resistant ferritic steels for USC power plants has been investigated to explore fundamental guiding principles for improving creep rupture strength at elevated temperatures over 600 deg C . A model steel with a composition of Fe-0.08C-9Cr-3.3W-3Co-Q.2V-0.05Nb-0.05N-0.005B0.3Si-0.5Mn (in mass percent) has been prepared by vacuum induction furnace. Creep tests at 650 deg C and microstructural observations were performed on the thermomechanical and magnetic treated specimens after tempering. New thermomechanical treated samples without magnetic field showed some improvement in creep strength comparing with ordinarily normalized and tempered specimens. Further improvement was observed in the specimen that had been exposed to a magnetic field during transformation into the martensite. From the result of microstructural observation, it was found that the finely distributed precipitates such as MX and M23Cg caused this improvement. And it was suggested that the magnetic treatment at martensitic transformation increase the precipitation sites during tempering, resulting in increasing the amount and preventing the growth of the precipitates.