HOT-DIP ALUMINUM DEPOSIT AS A PERMEATION BARRIER FOR MANET STEEL

A hot-dip process developed in Forschungzentrum Karlsruhe (FzK), was u sed to produce a hydrogen permeation barrier on MANET II steel. The ho t-dip aluminising method produced an intermetallic layer of AI,Fe by i mmersing the specimens in molten aluminium at 1023 K for either 5 or 2 min. Subsequent heat treatment of the samples at 1023 K for 15 and 30 h, respectively, in air transformed the brittle Al3Fe layer into a so fter phase and additionally produced alumina (Al2O3) on the surface. A ll processes were carried out at temperatures below 1053 K (above Ac-1 b = 1053 K the austenitisation of MANET II begins) in order to avoid t he repetition of the whole MANET II heat treatment (1348 K, 30 min fas t cool; 1023 K, 2 h). The maximum obtained permeation reduction factor (PRF), compared with the uncoated MANET II steel, has been obtained f or the specimens oxidised for 15 h in air: yielding PRF's of 260 at 74 3 K and 1000 at 573 K. (C) 1998 Elsevier Science S.A. All rights reser ved.