Effect of Carbon Content and Microstructure on the Diffusion of Hydrogen in Low Carbon Steels

In this work, the electrochemical permeation technique proposed in the ASTM-G148-97 Ed 2011 standard was used to determine the maximum oxidation current density, i_max; breakthrough time; t_b, effective hydrogen diffusion coefficient, D_eff; and surface hydrogen concentration, C_H^O, for several API 5L steels. The results show that steels with a carbon content of less than or equal to 0.052 %wt and a ferritic-bainitic microstructure have higher D_eff and i_max values than steels with a higher carbon content and a ferritic-pearlitic microstructure, while the C_H^O and tb parameters show a clear tendency to decrease when the microstructure changes from ferritic-pearlitic to ferritic-bainitic. The D_eff values obtained in this work are consistent with published data, both in terms of their magnitude and in relation to the effects of carbon content and microstructure.