Characterization of hydrogen induced cracking in TRIP-assisted steels

The present work evaluates hydrogen induced cracking in a TRIP-assisted steel with a multiphase microstructure, containing ferrite, bainite, retained austenite, and some martensite. When deformed, the retained austenite transforms to martensite, which changes the phase balance in the alloy. Each microstructural constituent demonstrates a different behavior in the presence of hydrogen. The goal of this work is to understand the response of the hydrogen saturated multiphase structure to a mechanical load. Tensile tests on notched samples combined with in-situ electrochemical hydrogen charging were conducted. The test was interrupted at specific points, before the macroscopic failure of the material. Hydrogen induced crack initiation and propagation were examined by studying the microstructure at several intermediate elongations. Characteristic hydrogen induced cracks were only observed after reaching tensile strength and were located at the surface in a specific pattern. Finite element simulations indicated that the observed crack pattern coincides with the increased stress regions induced by the notch presence. This indicates that hydrogen induced crack formation is dominantly stress induced for this steel.