Abstract
Creep fracture behaviour of 1.3Mn-0.5Mo-0.5Ni steel has been investigated metallographically using creep tested specimens with rupture times up to about 80000h in order to clarify creep fracture mechanisms and construct a creep fracture mechanism map. The results obtained are as follows:
(1) The transition from transgranular to intergranular creep fracture was found to occur with increasing time to rupture. This transition in creep fracture modes leads to a decrease in rupture ductility and stress index of rupture life.
(2) The intergranular creep fracture is caused by the formation and growth of grain boundary creep cavities, most of which are associated with grain boundary carbides.
(3) The creep fracture mechanism map, which was constructed experimentally in stress-temperature space, indicates that the operating conditions of temperature and stress for the steel at steam power plants should be kept within the field of intergranular creep fracture due to cavitation.
(4) The observed stress index and apparent activation energy of rupture life in the field of intergranular creep fracture are in reasonable agreement with the calculated values from the cavitation fracture model, which assumes that the number of cavities increases with creep strain and the growth of the cavities is controlled by grain boundary diffusion.
