Atom-probe study of phosphorus segregation to the carbide / matrix interface in an aged 9% chromium steel

By means of atom-probe field-ion microscopy (APFIM) a B-doped 9%Cr-steel was investigated. This kind of steels finds its application at elevated temperatures leading to detrimental segregation of non-metallic elements. The material was aged at 480°C and 650°C for up to 10 000 h. Specimens with M23C6 carbides close to the tip apex were prepared by controlled backpolishing to study the P segregation to the carbide/matrix interface. P was found to be enriched at the interface layer and was not incorporated into the carbides. On the contrary B was clearly enriched within the carbides, but a segregation of B to the interfaces was not detected.