Over the last decades the automotive industry has experienced increasing requirements regarding polluting emissions and fuel consumption leading to a rapid development of new kinds of steel providing high strength combined with excellent formability to meet those requirements. The occurrence of Hydrogen-induced Delayed Fracture (HDF) needs to be investigated to provide a secure application of constructional parts made from high-strength steels.
In the present work, the hydrogen diffusion behaviour of a high-strength high-manganese TWIP steel as a function of the density of dislocations and mechanical twins has been investigated using Thermal Desorption Analysis (TDA) combined with mass spectrometry. Punched tensile specimens were prestrained in 5 predefined states in order to provide varying densities of mechanical twins and dislocations. The prestrained specimens were electrochemically charged using 3 different current intensities to gain varying concentrations of diffusible and trapped hydrogen. To analyse the diffusion behaviour by TDA, the specimens were heated with 5 different linear heating rates up to 1173 K. The revealed temperature dependent hydrogen effusion peaks were associated with the density of mechanical twins and dislocations showing that these lattice defects work as hydrogen traps. The different linear heating rates allowed the calculation of the activation energies of the traps and the hydrogen diffusion coefficients. By the results, the hydrogen desorption behaviour and characteristic of mechanical twins and dislocations as hydrogen traps was analysed. The results were verified using permeation tests to compare the calculated and measured diffusion coefficients.