Creep crack growth behavior in weld metal/base metal/fusion zone regions in chromium molybdenum steels

An intensive study of the elevated temperature crack growth behavior of the base metal, weld metal, and heat-affected zone regions was performed on 1{1/4} chromium (Cr)-{1/2} molybdenum (Mo) and 2{1/4} Cr-1 Mo steel weldments at 538 C. Creep tests were conducted on samples removed from the weld and base metal 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. After the mechanical testing of the materials, extensive characterization analyses were performed on samples removed from the test specimens, which included microhardness testing, metallurgical analysis, scanning electron microscopic analysis (SEM), Auger electron spectrography (AES), cleanliness analysis, and quantification of creep-related damage. 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. The creep deformation behavior of these alloys is dominated by secondary and tertiary creep. The creep crack growth behavior of the alloys showed good correlation between the crack growth rate (da/dt) and the crack tip parameter (C{sub t}) inmore » the weld metal and heat-affected zone regions. Creep crack propagation appears to occur by continuous nucleation, growth, and coalescence of grain boundary cavities. The model proposed to describe the creep crack growth in these alloys shows good agreement with the experimental results. 81 refs.« less