Hydrogen diffusivity and trapping have been studied in two advanced high strength steel grades and model samples using electrochemical permeation test. Microstructures of CP1000 and DP1000 steels consist of ferrite, martensite and a small fraction of retained austenite. In addition, bainite is present in CP1000. Model phases with predominance of a particular phase have been prepared by specific heat treatment. DP1000 has shown the lowest diffusivity among all materials, while ferritic model sample has shown the highest. Differences in hydrogen diffusion coefficient values are linked to trapping microstructural characteristics and grain size. K E Y W O R D Shydrogen-induced cracking, hydrogen permeability, steel

Over the last 30 years, scanning electrochemical microscopy (SECM) has become a fundamental technique in corrosion research. With its high spatial resolution and its ability to study local electrochemistry, it contributes essentially to the understanding of corrosion processes. By using selective micro- and nano-sensors, concentration profiles of different corrosion relevant species, from protons to metal ions, can be established. This review provides a comprehensive overview about SECM based techniques and discusses various types of microsensors, including materials selection and preparation techniques, and it provides extensive tables on redox-couples for specific corrosion research applications.

Hydrogen absorption into steel during atmospheric corrosion has been of a strong concern during last decades. It is technically important to investigate if hydrogen absorbed under atmospheric exposure conditions can significantly affect mechanical properties of steels. The present work studies changes of mechanical properties of dual phase (DP) advanced high strength steel specimens with sodium chloride deposits during corrosion in humid air using Slow Strain Rate Test (SSRT). Additional annealed specimens were used as reference in order to separate the possible effect of absorbed hydrogen from that of corrosion deterioration. Hydrogen entry was monitored in parallel experiments using hydrogen electric resistance sensor (HERS) and thermal desorption mass spectrometry (TDMS). SSRT results showed a drop in elongation and tensile strength by 42% and 6%, respectively, in 27 days of atmospheric exposure. However, this decrease cannot be attributed to the effect of absorbed hydrogen despite the increase in hydrogen content with time of exposure. Cross-cut analysis revealed considerable pitting, which was suggested to be the main reason for the degradation of mechanical properties.

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