Microstructural evaluation and non-destructive examination of 2.25 Cr--1 Mo steel

Specimens of 2.25 Cr-1 Mo steel were damaged to various levels by creep and combined creep-fatigue cycling at 8860K (11000F) with hold periods. Ultrasonic shear wave velocity measurements were performed and showed small changes with large amounts of creep or fatigue damage; these changes were deemed too small for practical application. Measurements of magnetic properties were unsuccessful in following damage. Optical and transmission electron microscopy (TEM) were performed on the samples. TEM observations showed that microstructural changes which occurred at 8860K (11000F) did not occur homogeneously throughout the matrix; during creep, carbide spheroidization and coarsening began in widely separated regions, with an increasing fraction of the material undergoing the process with time. A precipitate was observed to form during fatigue which did not occur during simple aging or creep