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 α' 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 α' content (tables 66 and 67) 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 α' phase, and f was the volume fraction of α'.

Hydrogen Permeation Behavior in Metastable Austenitic Stainless Steels 321 and 304. X.Sun, J.Xu, Y.Li: Acta Metallurgica, 1989, 37[8], 2171-6

Table 67

Permeation Parameters for AISI 321