The migration of H in annealed and hardened AISI420 and in annealed AISI430 was studied electrochemically (constant-current) at temperatures of between 283 and 343K. The permeation rate, effective diffusivity and solubility were deduced from the data. It was found that annealed AISI420 exhibited higher permeation rates and lower diffusivities than did annealed AISI430. Hardened AISI420 exhibited the highest permeation rate and the lowest effective diffusivity. The diffusion data were described by:

AISI420:     D (m2/s) = 1.80 x 10-5 exp[-33.9(kJ/mol)/RT]

AIS1430:     D (m2/s) = 2.04 x 10-4 exp[-35.8(kJ/mol)/RT]

while the permeation data were described by:

AISI420:     P (mol/ms) = 1.32 x 10-5 exp[-22.8(kJ/mol)/RT]

AIS1430:     P (mol/ms) = 4.99 x 10-6 exp[-20.9(kJ/mol)/RT]

The solubility values which were calculated from the permeation data were in good agreement with those that were obtained by using a new electrochemical H solubility measurement technique.

Electrochemical Methods for Studying Hydrogen Diffusivity, Permeability, and Solubility in AISI 420 and AISI 430 Stainless Steels. C.H.Tseng, W.Y.Wei, J.K.Wu: Materials Science and Technology, 1989, 5[12], 1236-9

Table 52

Diffusivity of D in Various Alloys

Table 53

Effect of Pd upon H Diffusion in AISI 4130