Precipitates and hydrogen permeation behavior in ultra-low carbon steel

Abstract

The precipitates and hydrogen permeation behavior were studied in the ultra-low carbon steel for enameling. During the preparation of samples, two annealing processes, heating at 730 °C for 5 h and 870 °C for 6 min, were adopted after cold-rolling. It was found that the samples contained a large number of fine Ti(C,N) and coarse Ti 4C 2S 2 precipitates. The mean phase particle sizes of Ti(C,N) and Ti 4C 2S 2 precipitates in the sample annealed at 730 °C for 5 h were, respectively, larger and smaller than those in the sample annealed at 870 °C for 6 min. The total volume fraction of precipitates in the former was larger than that in the later. The presence of Ti(C,N) and Ti 4C 2S 2 precipitates, acting as irreversible traps for hydrogen atoms, influenced hydrogen diffusivity. The activation energies for hydrogen diffusion in both samples were measured as 44.3 and 42.6 kJ/mol, respectively.