The diffusion of chromium in a duplex alloy steel

Abstract

Diffusion of chromium in a duplex stainless steel containing ∼8% ferrite has been investigated in the temperature range 873–1273 K using the standard serial sectioning technique. The resulting concentration profiles exhibited up to four distinct regions. The two main regions are attributed to volume diffusion in the austenite and ferrite phases, the other zones being due to short-circuiting paths. Volume diffusion in the austenite phase is in good agreement with Cr diffusion in Type 316 steel. The Cr diffusion coefficient in the ferrite phase of approximate composition 25Cr-5 wt.-%Ni is given by:Dα = (6.0⁺¹¹₋₃) X 10⁻⁶ (- 212± 5/RT) m²s⁻¹the activation energy being expressed in kJ mol−1. Little evidence was found for enhanced Cr diffusion along austenite/ferrite interface boundaries.