Precipitates and hydrogen permeation behavior in ultra-low carbon steel

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 Ti4C2S2 precipitates. The mean phase particle sizes of Ti(C,N) and Ti4C2S2 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 Ti4C2S2 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.