2017 Volume 58 Issue 3 Pages 442-449
The causes of the change in creep rupture ductility with the creep test temperature in Alloy 617 were investigated. The rupture ductility in the creep test was low at 700℃, whereas it was high at 800℃. Although the rupture ductility depended on the creep test temperature, creep fracture occurred due to cavity formation at the grain boundaries under all the creep conditions. In the sample crept at 800℃, subgrains developed with creep deformation. However, the crept sample at 700℃ fractured before the subgrain formation. Although the work hardening due to the creep deformation occurred at 700℃, the work hardening in the sample crept at 800℃ was small. The deformation of the grains was suppressed by the work hardening and by γ' particle dispersion strengthening at 700℃. The difference in the strength in the crystal grains that resulted from the microstructure formed during creep caused the difference in the growth of the cavities.