Internal and surface damage of multiphase steels and pure iron after electrochemical hydrogen charging

High strength steels appear to be even more prone to hydrogen embrittlement (HE). In this work, pure iron and a ferrite–bainite steel were charged electrochemically using various electrolytes and combinations of current density and charging time to identify the experimental conditions where blister formation occurred. The appearance and propagation of cracks inside the sample were studied also by means of high resolution scanning electron microscopy. The study was repeated for a dual phase (DP) steel; a TRIP steel and a high strength low alloy (HSLA), which allowed to get an indication on the effect of variable microstructural characteristics.

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► Pure iron was found to be more susceptible to hydrogen surface damage than high strength ferrite bainite steel.
► Cracks were formed more easily in pure iron, related with the faster blister formation in these materials.
► Cracks were both inter- and intragranular.
► Mn segregations were observed for the DP600 and TRIP700 and MnS precipitates were identified in the crack for the DP600 steel.
► A correlation between the presence of MnS particles and the initiation of hydrogen induced cracks was found.