Microstructural development during ageing of an 11% chromium steel alloyed with copper

Precipitation reactions occurring during ageing at 600 or 650°C of the 11% chromium steel P122 have been investigated. Atom probe field ion microscopy (APFIM) and energy filtered transmission electron microscopy (EFTEM) were used to measure the volume fraction and size of different types of precipitates present in the structure. It was found that the addition of 0.87 wt.% copper to the steel gives rise to formation of copper precipitates during tempering and ageing. The influence of this copper precipitation on the growth and coarsening of other phases present and possible consequences for the creep strength of the material are discussed.