The diffusion of Cr in a duplex 25Cr-5Ni stainless steel containing some 8% ferrite was investigated at 873 to 1273K by using standard serial sectioning techniques. The resultant concentration profiles exhibited up to 4 distinct regions. The 2 main regions were attributed to volume diffusion in the austenite and ferrite phases; the other zones being due to short-circuit paths. The bulk diffusion in the austenite phase was in good agreement with Cr diffusion in AISI316 steel. The Cr diffusion coefficient in ferrite with an approximate composition of 25Cr-5wt%Ni was given by:

D (m2/s) = 6.0 x 10-6 exp[-212(kJ/mol)/RT]

Little evidence was found for enhanced Cr diffusion along austenite/ferrite interface boundaries.

A.F.Smith, R.Hales: Metal Science, 1976, 10[12], 418-23

 

Table 85

Grain Boundary Diffusion of Cr in Fe-18Cr-12wt%Ni

 

Temperature (K)

G (m3/s)

1223

1.78 x 10-20

1173

5.72 x 10-21

1123

1.18 x 10-21

1073

1.07 x 10-21

1023

1.91 x 10-22

973

4.42 x 10-23