Creep rupture test were conducted at 538°C (1000°F), 565°C (1050°F) and 593°C (1100°F) on the 1Cr-11/4 Mo-1/4V steel which is used as the high- and medium-pressure turbine rotor shaft up to 1100mm diameter.
Specimens were taken out of inner and outer part of an actual rotor, having radial, tengential and longitudinal direction, respectively.
Test results are summarized as follows:
(1) The longitudinal specimen has about 10% higher creep rupture strength than radial specimen which has higher strength than tangential specimen also by about 10% in terms of 1000 to 10000 hour creep rupture stress at each temperature.
(2) Specimens from outer part of rotor show lower rupture strength than specimens from inner part. Though both inner and outer part have the bainite microscopic structure, the inner part has the upper bainite structure and the outer part has the lower bainite structure, since the cooling rate at quenching is slower in the inner part.
The present result which shows that the upper bainite has better creep rupture strength than the lower bainite is in conformity with the previous results on small specimens.
(3) The creep rupture stress of the notched specimen is higher than that of the smooth specimen in a short time range of testing and lower in a long time range.
This intersecting of the rupture stress vs. time-curve for the notched and the curve for the smooth occurs at a shorter time of testing and when the testing temperature is made higher.
(4) Comparing with the results of the tests by Werner et al.2), Conrad et al.4) and Rankin et al.5) on the 1 Cr-11/4 Mo-1/4V steel turbine rotor shaft, the present result shows nearly similar creep rupture strength to their results, and speaking at some length, the present data show a little lower strength in short time range and a little higher strength in long time range than theirs.
(5) Elongation at creep rupture in the present test is similar to or a little higher than Rankin's.
The specimen from inner part of a rotor gives longer rupture time but shorter elongation at rupture than the specimen from outer part.
