By using a radioactive tracer method, the bulk and grain-boundary diffusion of 59Fe was determined in commercial Alloy 800, and in melts with additional P and S, at temperatures ranging from 900 to 1000C. In the case of Alloy 800H, the activation energy for grain-boundary diffusion was 209kJ/mol. Dissolved elements, especially P, increased the activation energy for grain boundary Fe diffusion by segregating to the boundaries. In the case of Alloy 800 with 0.088wt%P, an enrichment of about 14at%P was observed at the grain boundaries. The overall relationships for the triple-product were:

Alloy 800H:      sδD (cm3/s) = 3.1 x 10-5 exp[-209(kJ/mol)/RT]

Alloy 800HT:      sδD (cm3/s) = 8.9 x 10-5 exp[-221(kJ/mol)/RT]

Alloy 800LC:      sδD (cm3/s) = 1.3 x 10-5 exp[-194(kJ/mol)/RT]

Alloy 800+S:      sδD (cm3/s) = 9.9 x 10-4 exp[-242(kJ/mol)/RT]

Alloy 800+P:      sδD (cm3/s) = 9.8 x 10-2 exp[-288(kJ/mol)/RT]

J.Lindemann, K.Hennesen, C.Derder, R.Mast, H.Viefhaus, H.J.Grabke: Materials Science Forum, 1999, 294-296, 557-60

Table 167

Parameters for H Diffusion in 34KhN3M Steel with or without 0.5wt%Pd