Advanced high strength steels have been developed in response to the growing requirements of passenger safety and fuel consumption in automotive industry. The main advantage of these steels is a combination of high strength and high formability due to their complex microstructure. However, steels with tensile strength higher than 1000 MPa were found to be susceptible to hydrogen embrittlement. There are a number of techniques for assessment of HE susceptibility and for measurement of hydrogen content and permeability. The electrochemical permeation test is a conventional one.
Two grades of AHSSs were studied in this work: a complex phase high strength steel “CP1000” and a dual phase high strength steel “DP1000”. These steels consists of mainly ferrite, martensite and bainite. Model phases with a predominance of one of the particular phases were prepared by specific heat treatment. Measurements using permeation test were done on CP1000 and DP1000 samples and on model phases. Measurements were performed using permeability build-up and decay transients with different current densities in order to establish the influence of trapping sites on permeation curves. Diffusion coefficients obtained from permeation measurements were compared in view of samples microstructure.