Effect Of Cold Deformation And Pre-aging On The Distribution Of Carbide In HR3C Steel

HR3C is a steel for superheater and reheater parts with poor working conditions in supercritical units.It has good properties of smoke oxidation resistance and mechanical properties at high temperature.The harsh high-temperature working environment of the unit resulted in the decline of the impact toughness of HR3C steel.The HR3C was brittle during the service which posed a great safety risk to the power station.It is generally believed that the main reason for the brittle fracture of HR3C steel is that a large number of M₂₃C₆ phases are continuously precipitated in the grain boundary and grain boundary embrittlement was caused.Therefore,in this paper,the cold deformation and pre-aging process are used to change the distribution of carbide M₂₃C₆ phase in HR3C steel.It has studied the microstructure of HR3C steel after different cold deformation in pre-aging process,and analyzed their effect on carbide distribution and properties of HR3C during long-term aging process.The research indicates:（1）Through the exploration of process parameters of cold deformation and pre-aging in the early stage.Compared with the small deformation and low-temperature pre-aging,it is found that after 30%cold deformation of HR3C steel at 900°C for 6 h,the distribution of grain boundary carbide M₂₃C₆ phase is less and discontinuous,and the vickers hardness is low,the impact toughness is higher than that of the initial HR3C steel;When the cold deformation of HR3C steel is more than 40%,the dispersion of carbide M₂₃C₆ phase in the grain after pre-aging at 900°C for 6 h;After the cyclic cold deformation pre-aging（10%cold deformation,900°C pre-aging for 6 h+10%cold deformation,900°C pre-aging for 6 h+10%cold deformation,900°C pre-aging for 6 h,the same below）,the M₂₃C₆ phase of the HR3C steel grain boundary shows a typical spherical discontinuous distribution.（2）It was analyzed that the long-term aging microstructure of HR3C steel with 30%cold deformation at 900°C pre-aging for 6 h and cyclic cold deformation pre-aging at 700°C.,then the precipitation ofσphase was observed.The carbide M₂₃C₆ phase was entangled in the grain boundary and the crystal.The distribution of M₂₃C₆ phase in the HR3C steel in service state is continuous in the grain boundary,the impact toughness is also higher than that of the original HR3C steel,and the cyclic cold deformation pre-aging HR3C steel has more obvious impact toughness after long-term aging.The original intergranular fracture becomes a mixed fracture.According to the comprehensive analysis,the suitable cold deformation and pre-aging process can change the distribution of carbides in the long-term aging process of HR3C steel,and also improve its impact toughness to a certain extent,which provides some suggestions to improve the brittleness of HR3C steel in the service mode.