scope:

An intensive study of the elevated temperature crack growth behavior of the base metal, weld metal, and heat-affected zone regions was performed on 13chromium (Cr)-2molybdenum (Mo) and 23Cr-1Mo steel weldments at 538/C (1000/F). Creep tests were conducted on samples removed from the weld and basemetal regions of the two alloys to determine the creep deformation properties of the two different regions, whereas constant load creep crack growth tests were performed on compact-type specimens taken from all three aforementioned regions of both alloys. By using the information generated in this study, a model was developed to describe the crack growth in these alloys in terms of the accumulated creep damage ahead of the advancing crack front. Creep crack propagation appears to occur by continuous nucleation, growth, and coalescence of grain boundary cavities. Cavity nucleation appears to occur predominately at grain boundary carbides. The area fraction of grain boundaries containing cavities and the area density of cavities display decreasing trends with increasing distance ahead of the crack tip. A model proposed to describe the creep crack growth in these alloys shows good agreement with the experimental results. The model indicates that the crack growth process is heavily dependent on the near tip cavities. The model describes the crack growth in terms of experimental data and measured creep-generated damage ahead of the crack tip. Publication of this document - WRC Bulletin No. 416 was sponsored by the University Research Committee of the Welding Research Council, Inc.