NEW METHOD FOR LIFE ASSESSMENT OF 1%Cr-O.5%Mo LOW ALLOY STEEL ON THE BASE OF GRAIN BOUNDARY CREEP CAVITATION

Life assessment on the base ofgrain boundary creep cavitation of 1%cr - 0.5%mo lowalloy steel has been discussed in this paper. since microstructural degradation is one ofthe mostimportant mechanisms that affects creep life, it is necessary to assess microstructural damage inorder to estimate the life. microstructural damage within the grain boundaries is a continuousphenomena starting from about the beginning of secondary stage of creep process. in thisresearch, the amounts of damage accumulation in the form of grain boundary cavitations forvarious creep times up to the ends ofsecondary creep stage for each creep condition was found byusing quantitative metallography technique, i.e. image analyser. then from the data obtainedforgrain boundary area cavitated and number ofcavities per unit area, which was about linear as afunction of time for each of creep conditions, the amount of damage in the tertiary stage wasestimated for various times. then a creep damage parameter was proposedfor the creep process.finally, having this damage parameter (oj) and using continuum damage mechanics (cdm), anew version ofrabotnov-kachanov equation for tertiary creep rate was established.