Microstructural Characterization of Hydrogen Induced Cracking in TRIP Steels by EBSD
The present work evaluates hydrogen induced cracking in a high strength TRIP steel with a complex multiphase microstructure, containing ferrite, bainite, retained austenite, and some martensite. Each structural constituent demonstrates a different behavior in the presence of hydrogen and when deformed, the retained austenite transforms to martensite. The goal of this work is to understand the response of the hydrogen saturated multiphase structure to a mechanical load. A tensile test on notched samples combined with in-situ electrochemical hydrogen charging was carried out. The test was interrupted at certain specific points, before the macroscopic failure of the material. Hydrogen induced crack initiation and propagation were examined by studying several intermediate elongations. The microstructure of the samples was characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The EBSD measurements allowed both microstructural and crystallographic characterization of the hydrogen induced crack surroundings. A correlation was found between the occurrence of martensite, which is known to be very susceptible to hydrogen embrittlement, and the initiation of hydrogen induced cracks. These cracks were located at the surface in specific high stressed regions. Finite element simulations indicated that these regions were induced due to the presence of the notch.