The role of (FeCrSi)2(MoNb)-type Laves phase on the formation of Mn-rich protective oxide scale on ferritic stainless steel

Microalloying of stainless steel with reactive elements increases oxidation resistance but makes the alloy prone to microstructural changes. XPS results reveal changes in the initial oxidation mechanism on Ti-Nb stabilized ferritic stainless steel (EN 1.4521) after 120 h heat treatment at 650 degrees C. Age-precipitation of (FeCrSi)(2)(MoNb)-type Laves phase resulted in less pronounced surface segregation and oxidation of microalloying elements. Si oxidizes preferentially at the Laves precipitate locations via outward diffusion forming diffusion barrier for the other scale forming elements. Most significantly the diffusion of Mn and the formation of low volatile (Mn,Cr)(3)O-4 spinel oxide at the surface was strongly suppressed.