EFFECT OF THERMAL AGING ON THE COMPLEX CR EEP DEFORMATION-BEHAVIOR OFCARBON-STEEL AND ITS INHERENT CREEP STRENGTH

Complex creep deformation behaviour which reveals several peaks and lo cal minima in creep strain rate has been investigated on the carbon st eel taken from tube for boilers and heat exchangers (JIS STB 410) and discussed from a view point of ''Inherent Creep Strength''. Complex cr eep deformation phenomena observed on the un-aged steel has been disap peared by ageing prior to creep test. Common creep Strain dependence o f creep strain rate has been observed for both steels with and without prior ageing, and explained by both an inherent creep strength and an increase in stress during constant load creep testing. It has been co ncluded that complex creep deformation behaviour is caused by decrease in creep strength due to microstructural change and advent of inheren t creep strength.