Changes in morphology and composition of carbides during cyclic deformation at room and elevated temperature and their effect on mechanical properties of CrMoV steel

Effect of service-simulated aging on the microstructure and properties of casing casting steel (1CrMoV) vis-à-vis remnant life assessment

“…Many workers [2,3,20,[34][35][36][37][38][39][40][41] discussed the formation of H-type carbide in detail. It was well established that the diffusion of molybdenum takes place in those vanadium carbides that were precipitated at dislocation mesh, and their growth, according to Williams, [35] was due to the dislocation pipe diffusion of molybdenum to vanadium carbide, and up to 85 wt pct of Mo has been reported to go into solution.…”

Crystallography and Morphology of Carbides in a Low-Cycle Fatigued 1Cr-1Mo-0.25V Steel

“…The widespread use of this steel is attributed mainly to a good combination of strength and ductility at elevated temperatures, which results from a careful balance of alloying elements and microstructure. [1][2][3][4][5][6][7][8][9] It is known that many components operating in power-generating plants are subjected to complex cyclic stress-strain conditions at high temperatures, in which low-cycle fatigue (LCF) loadings are expected to result from temperature gradients during the start-up or shut-down of a power plant. [6][7][8] For Cr-Mo-V steel, it consistently has been reported that the cyclic softening is observed under cyclic deformation at room as well as at elevated temperatures.…”

“…This phenomenon should be taken into account in material design because decremental cycle-by-cycle changes in strength or ductility imply gradual losses in load-bearing and fracture-resisting capabilities. [1][2][3][4][5][6][7][8][9] Over the past decades, increasing attention has been paid to the residual life prediction of critical power plant components operating under high temperatures and pressures. [1,9] Residual life analysis usually is based on the determination of observable or measurable damages that occur during service at elevated temperature under sustained steady or multiaxial stress.…”

“…For Cr-Mo-V steel, early works have attempted to relate these property changes to the austenite-ferrite (a) transformation route, but later, many researchers have pointed out that the precipitation behavior of the steel correlates much better with the change in properties. [1][2][3][4][5][6][7][8][9] Longterm service exposure of Cr-Mo-V steel at elevated temperatures (700 K [427°C] to approximately 900 K [627°C]) causes the changes in size, shape, and distribution of the existing carbides as well as the precipitation of new carbides either from solid solution or at the expense of less stable carbides. These precipitation behaviors of various carbides have been regarded as an important factor that may result in damage and fracture of service-exposed steels.…”

“…These precipitation behaviors of various carbides have been regarded as an important factor that may result in damage and fracture of service-exposed steels. [1,[6][7][8][9] Several attempts have been made to correlate the high-temperature cyclic deformation with the microstructural changes in Cr-Mo and Cr-Mo-V steels. [2][3][4][5][7][8][9][10] A consensus exists that the predominant type of carbide formed after normalizing and subsequent tempering is Fe-rich M 3 C-type carbide (hereafter, cementite), and other types of carbides also are identified depending on the chemical composition, thermal history, and testing condition (temperature, stress, or strain condition introduced by cyclic deformation, etc.).…”