Experimental Research On Creep Behaviors Of T92Steel Under Multiaxial State Of Stress

Energy-saving and environmental protection have become the major themes of industrial development. Increasing steam parameters has been applied to improve the thermal efficiency of thermal power units. Ultra supercritical units have been the tendency of developing thermal power units. However, increasing the steam parameters requires high property materials. T92steel has been widely used in ultra supercritical thermal power units for its excellent comprehensive performance. Nowadays, the studies of T92steel creep behavior are generally based on uniaxial creep test, but it does not take multiaxial stress state into consideration. Actually, owing to the complexity of geometry and stress, parts usually bear the multiaxial stress state. In order to ensure the safety of the boiler unit operation, the creep behavior of T92steel under multiaxial stress state must be understand.Creep tests for smooth specimens and notched specimens of T92steel were carried out to study the effect of multiaxial stress state on creep rupture behaviors at600℃～700℃/60～250MPa. Under uniaxial stress state, the effects of stress and temperature on the creep process was investigated, the change laws of the steady state creep rate with time to rupture and stress were analysed, the relations between time to rupture and stress were summarized. The effects of multiaxial stress state on creep rupture life and ductility were study, the failure behavior of multiaxial creep was analyzed, creep rupture life was estimated by’representative’ stress at multiaxial state of stress, the change of hardness was analysed after creep test. The results show that the reason of creep fracture rate increased is caused by the nucleation and propagation of micro-voids and cracks, the micro mechanism of the creep is the movement of dislocation, the notch strengthens rupture life, multiaxial stress state reduces the creep ductility of T92steel, multiaxial rupture behavior is controlled by mixed parameters, the hardness of smooth specimens increases from center to edge at650℃, but the hardness of notched specimens decreases at600℃and650℃, the section average hardness arises with gap sharpness increasing.