Hydrogen Behavior in Ti-Added Reduced Activation Ferritic-Martensitic Steels

Hydrogen behavior and corresponding mechanical degradation were examined in TaTi-RAFM and EUROFER97 steels. Increased Ta content with Ti addition decelerates the hydrogen diffusion but increases the solubility in the lattice. It is mainly led by the higher fraction of Ta-rich MC carbides and dislocation density in TaTi-RAFM steel. Overall activation energy of hydrogen trapping of investigated steels is evaluated to be 25.3 similar to 25.6 kJ/mol in the tempered condition. The activation energy increases to nearly 30 kJ/mol when the steels are re-austenitized and quenched. Higher activation energy with increased dislocation density indicates that the dislocation provides for trap site with higher activation energy than Ta-rich MC carbide. Mechanical degradation by hydrogen with respect to the yield strength, tensile strength and uniform elongation could not be observed in all investigated steels. The presence of hydrogen only has influence on the loss of post-uniform elongation. For a given charging time, the loss of post-uniform elongation is more remarkable in TaTi-RAFM steel due to the larger hydrogen uptake.