Phase formation and interdiffusion in Al-clad 430 stainless steels

Diffusion annealing treatments were carried out with Al-clad 430 stainless steels for the development of diffusion structures and characterization of interdiffusion of Fe, Cr, and Al. The treatments included isothermal anneals at 600°C for various times with thin foils of 430Y and 430 stainless steels roll-clad with 1100 Al. A two step annealing treatment in which the foils were initially annealed at 600°C followed by a subsequent anneal at 800°C was also investigated for homogenization of the Al-clad steels. The diffusion structures of the various foils were examined by SEM-EDS and X-ray diffraction techniques. The Al-clad 430Y and 430 stainless steel foils annealed at 600°C developed two diffusion layers identified as (Fe, Cr)2Al3 and (Fe, Cr)3Al2 based on composition. Interdiffusion fluxes and integrated interdiffusion coefficients were calculated for these phase layers. The integrated interdiffusion coefficients of Cr, Fe and Al were approximately in the ratios of 1:5:6 and 1:4:5 for the (Fe, Cr)2Al3 and (Fe, Cr)3Al2 phases, respectively. The two-step annealing treatment at 600 and 800°C resulted in the formation of a homogeneous Fe-Cr-Al alloy (bcc) through the foil thickness; the lattice parameter of the alloy was determined to be 2.876 إ. The Al-clad 430Y foils developed less porosity than the Al-clad 430 foils during the homogenization treatment.