The diffusion rates of Mo 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 Arrhenius expressions:

α-Fe:     D (cm2/s) = 7.85 x 10-1 exp[-225.5(kJ/mol)/RT]

γ-Fe:     D (cm2/s) = 3.60 x 10-2 exp[-239.8(kJ/mol)/RT]

For diffusion in ferrite, the tracer and interdiffusion coefficients for Cr, Mo and W generally showed close agreement.

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

 

Table 79

Diffusivity of H in 2¼Cr-1%Mo Steel

 

Temperature (F)

PH2 (psig)

D (cm2/s)

700

1000

1.01 x 10-4

850

250

0.88 x 10-4

850

500

1.50 x 10-4

850

1000

1.17 x 10-4

1000

125

1.22 x 10-4

1000

500

1.34 x 10-4

1000

1000

1.43 x 10-4

Table 80

Effect of Deformation upon H Diffusion Parameters

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

 

Deformation (%)

Do (cm2/s)

E (kJ/mol)

0

6.40 x 10-5

7.0a

0

8.45 x 10-2

33.7b

25

1.71 x 10-2

36.7

50

2.34 x 10-2

37.2

75

9.03 x 10-2

45.5

a: temperatures greater than 170C

b: temperatures less than 170C