The diffusion rates of W in α- and γ-Fe were determined by means of electron probe microanalysis. Alloy concentrations of up to 28.3at%Cr, 5.05at%Mo and 2.9at%W were investigated at 675 to 1485C. For any temperature, in either ferrite or austenite, DMo > DCr > DW. Interdiffusion was found to be independent of concentration over the composition ranges studied. The present data were combined with previous data, and the whole could be described by the Arrhenius expressions:

α-Fe:     D (cm2/s) = 1.60 x 100 exp[-243.5(kJ/mol)/RT]

γ-Fe:     D (cm2/s) = 1.30 x 10-1 exp[-267.4(kJ/mol)/RT]

For diffusion in ferrite, the tracer and interdiffusion coefficients for Cr, Mo and W generally showed close agreement. However, the available data for diffusion in austenite suggested that, for W, interdiffusion was significantly slower than tracer diffusion.

P.J.Alberry, C.W.Haworth: Metal Science, 1974, 8[12], 407-12

Table 81

Effect of Deformation upon H Permeation Parameters

for Fe-Cr-Mo-Ni (AL 29-4-2)

a: 80 to 320C, b: 110 to 260C