EFFECTS OF HEAT-TREATMENT ON THE CREEP CRACK-GROWTH OF ALLOY 800H POSSESSING LONG SERVICE HISTORY

Creep crack growth has been studied in Alloy 800H at 650 degrees C usi ng CT-type specimens. The material, taken from a non-stressed inner sl eeve of an expansion bellow in a chemical plant, was investigated for three conditions: (1) the as-received material (used for a long period of 72,000 h at temperatures of around 650 degrees C), (2) material wh ich was prepared by subjecting the as-received material to heat treatm ent by holding for 0.5 h at 900 degrees C, followed by water quenching , and (3) material which had been subjected to a solution heat treatme nt consisting of holding for 0.5 h at 1100 degrees C, followed by wate r quenching. The creep crack growth rate was analyzed by using the par ameter C. There was no significant difference in creep crack growth r ate between the two heat-treated materials. However, the creep crack g rowth rate of the as-received material was higher than that of the hea t-treated materials because of the tendency for cracks to develop inte rgranularly in the as-received alloy.