Effect of thermal ageing on the complex creep deformation behaviour of carbon steel and its inherent creep strength

Complex creep deformation behaviour which reveals several peaks and local minima in creep strain rate has been investigated on the carbon steel taken from tube for boilers and heat exchangers (JIS STB 410) and discussed from a view point of ''Inherent Creep Strength''. Complex creep deformation phenomena observed on the un-aged steel has been disappeared by ageing prior to creep test. Common creep Strain dependence of 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 concluded that complex creep deformation behaviour is caused by decrease in creep strength due to microstructural change and advent of inherent creep strength.