Microstructural and fractographic investigation of a centrifugally cast 20Cr32Ni + Nb alloy tube in the ‘as cast’ and aged states

Fracture surface and microstructure of tensile samples taken from a centrifugally cast 20Cr32Ni + Nb alloy tube were investigated in the ‘as cast’ state and after being submitted to isochronal aging at temperatures between 670 °C and 820 °C for 200 h. The results show that the main crack path is interdendritic at a macroscopic scale, but that the fracture surface is characterized by dimples at microscale in all samples, suggesting that the fracture micromechanism does not change, in spite of the large ductility loss observed in the aged samples (fracture elongation, ε¯f≈0.16, for samples aged at 770 °C) compared with ‘as-cast’ samples (ε¯f≈0.42).