D.J. Abson, TWI,UK
Gains in thermal efficiency over many years have been achieved by the development of steels with improved creep properties. However, creep strength is degraded by welding, with the HAZ being the creepweak region. Compared with parent steel development, less effort has, until comparatively recently, been expended in determining cross-weld creep strength and in understanding the reasons for the lower creep strength of the HAZ. This review considers some of the issues arising in low alloy Cr–Mo steels, particularly the 9−12%Cr steels, in creep service in power plants, including consideration of HAZ behaviour.