The H migration behavior in metastable austenitic stainless steels was investigated by using an ultra-high vacuum gaseous permeation method at temperatures of between 100 and 400C. The permeation parameters for the annealed steels were consistent with those for stable austenitic steels. However, after cold deformation, the activation energies for permeation and diffusion decreased exponentially with increasing a' content and the permeation and diffusion values increased. The diffusion and permeation data for annealed AISI321 were described by the expressions:

D (m2/s) = 4.61 x 10-7 exp[-53.79(kJ/mol)/RT]

P (mol/msMPa½) = 2.44 x 10-4 exp[-62.70(kJ/mol)/RT]

and the dependences of the activation energies upon the a' content (tables 67 and 68) were described by the expressions:

D:     Q = Qo exp[-1.112f]

P:     Q = Qo exp[-0.668f]

where the Qo were the pre-exponential values in the absence of the a' phase, and f was the volume fraction of a'.

X.Sun, J.Xu, Y.Li: Acta Metallurgica, 1989, 37[8], 2171-6

Table 67

Diffusion Parameters for AISI 321

Table 68

Permeation Parameters for AISI 321