CREEP-MICROCRACK GROWTH IN ALLOY 800 HT AT ELEVATED-TEMPERATURES

The aim of the presented investigation was to gain information about t he behaviour of the initiation and growth of intercrystalline creep cr acks during creep deformation from the evaluation of metallographic mi crographs. The austenitic steel X10 NiCrAlTi 32 20 HT (Alloy 800 HT) w as investigated by carrying out creep tests at 800 and 900 degrees C w ith different nominal stresses until fracture. Additional tests are ca rried out on certain creep strains in the late tertiary creep stage. T he creep tests are followed by a metallographic investigation of the c rept specimens. The statistical distribution of the microcrack lengths was used to estimate the rate of crack initiation and crack growth, I t is found that the rate of growth of the intercrystalline creep crack s in Alloy 800 HT is dependent on the applied stress and the creep str ain reached. The rate of growth of long cracks was only slightly highe r than that of short cracks and was lower than predictions based on fr acture mechanics concepts.