Correlation of creep fracture lifetime with microstructure evolution and cavity behaviors in G115 martensitic heat-resistant steel

摘要

In order to deepen the understanding towards the creep rupture lifetime of G115 martensitic heat-resistant steel, a series of creep tests using 130-200MPa loading stresses at 923K were carried out to investigate the as-crept microstructural characteristics and cavity behaviors. The significant microstructure deformation and a dramatic increase in the areal density of high-angle grain boundaries occur when the stress loading is over 160MPa. Apart from the strain concentration at elongated grain boundaries and refined grains, the elevated stress also leads to the appearance of a strong α-fiber texture with {001}<110>//RD. The nucleation and growth of cavities can be effectively accelerated by the stress elevation, and ductile fracture is determined as the dominate mechanism within the test stresses. However, a transition towards brittle intergranular fracture is observed due to the rapid coarsening of Laves phase. Furthermore, a good prediction for creep lifetimes of G115 steel has been obtained based on the constrained diffusional cavity growth model.