Abstract
Creep brittle behaviour in tempered martensitic, creep strength enhanced ferritic (CSEF) steels is linked to the formation of micro voids. Details of the number of voids formed, and the tendency for reductions in creep strain to fracture are different for the different CSEF steels. However, it appears that the susceptibility for void nucleation is related to the presence of trace elements and hard non-metallic inclusions in the base steel. A key factor in determining whether the inclusions present will nucleate voids is the particle size. Thus, only inclusions of a sufficient size (the critical inclusion size is directly linked to the creep stress) will act directly as nucleation sites. This paper compares results from traditional uniaxial laboratory creep testing with data obtained under multiaxial conditions. The need to understand and quantify how metallurgical and structural factors interact to influence creep damage and cracking is discussed and the significant benefits available through the use of high quality steel making and fabrication procedures are highlighted. Details of component behaviour are considered as part of well-engineered, Damage Tolerant, design methods.
