SOJKA Jaroslav VSB - TU, FMME

Spoluautoři ŠTĚPÁN Petr, VÁŇOVÁ Petra

The presented contribution is devoted to evaluation of hydrogen diffusion characteristics in the TRIP 800 steel, based ot C-Mn-Si-P composition, i.e. in steel with increased phosphorus content. Steel was studied after standard heat treatment, including intercritical annealing and annealing in the range of bainitic transformation. Hydrogen diffusion characteristics in the TRIP 800 steel were obtained by means of electrochemical permeation method introduced by Devanathan and Stachurski. Specimens were used in the form of thin discs with thickness of 0.5 mm approximately. On the output side specimens were palladium coated to prevent hydrogen recombination when leaving specimen. Diffusion characteristics of hydrogen were obtained by recording output current density as a function of time. Experimental procedure included initial hydrogen charging followed by polarisation reversion to activate specimen surface. After that two hydrogen chargings were performed with increasing current density. Hydrogen diffusion coefficient in the TRIP 800 steel was calculated from all growing transients and also from decay transient at the end of experiment. The lowest hydrogen diffusion coefficient (10-8 cm2.s-1 approximately) was observed at the first hydrogen charging, which reflected hydrogen trapping during this period of experiment. The highest measured hydrogen diffusion coefficient was recorded during last hydrogen charging. Its value was 10-7 cm2.s-1 approximately, which is much lower in comparison with common steels having bcc crystal lattice. This fact can be attributed to the presence of about 10 % of retained austenite in the structure of the steel. Subsequently, hydrogen surface concentration at the input surface was calculated.

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