The present work provides an overview of the work on the interaction between hydrogen (H) and the steel’s microstructure. Different techniques are used to evaluate the H-induced damage phenomena. The impact of H charging on multiphase high-strength steels, i.e., high-strength low-alloy (HSLA), transformation-induced plasticity (TRIP) and dual phase (DP) is first studied. The highest hydrogen embrittlement resistance is obtained for HSLA steel due to the presence of Ti- and Nb-based precipitates. Generic Fe-C lab-cast alloys consisting of a single phase, i.e., ferrite, bainite, pearlite or martensite, and with carbon contents of approximately 0, 0.2 and 0.4 wt %, are further considered to simplify the microstructure. Finally, the addition of carbides is investigated in lab-cast Fe-C-X alloys by adding a ternary carbide forming element to the Fe-C alloys. To understand the H/material interaction, a comparison of the available H trapping sites, the H pick-up level and the H diffusivity with the H-induced mechanical degradation or H-induced cracking is correlated with a thorough microstructural analysis.

Thermal desorption spectroscopy (TDS) is a very important tool in hydrogen embrittlement (HE) related research and has been applied on many different materials over the last decades in order to improve knowledge on the HE phenomenon. TDS provides the opportunity to distinguish between different types of hydrogen traps based on the analysis of a spectrum with different peak temperatures each corresponding to hydrogen desorption from a specific trap. These peak temperatures, and consequently the different traps in a material, arise from the various microstructural characteristics of the material. However, TDS results are also influenced by many other parameters, such as the sample surface preparation, the electrolytes used for hydrogen charging, sample geometry, charging time, current density, charging temperature. Even though the use of thermal desorption to evaluate hydrogen-metal interactions has increased over the past years, a careful evaluation of the effect of these other parameters was not yet performed. In this work, the impact of some of the above mentioned parameters was studied. It was demonstrated that the sample geometry, the surface roughness, and the initial total pressure of the TDS chamber influenced significantly the obtained TDS spectrum.

High Mn steels, alloyed with Si and Al, present large plasticity when deformed due to the TRIP/TWIP effect. The present work studies the microstructural evolution and its influence on the mechanical behavior of a steel containing 17%Mn and 0.06%C after cold rolling to 45 and 90% reduction and subsequent annealing at 700 °C for different times. The microstructural analysis is performed by X‐ray diffraction (XRD), scanning electron microscopy (SEM)‐electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). It is observed that cold reduction induces the formation of ϵ‐ and α′‐martensite. The material exhibits yield and tensile strength around 700 and 950 MPa, respectively, with a total elongation around 43% and a work hardening exponent of around 0.30 after 45% cold rolling and subsequent annealing and a yield and tensile strength of 750 and 950 MPa, respectively, with a total elongation of almost 50% when 90% cold rolling and subsequent annealing. The austenite texture contains brass, copper, and Goss components, while the α′‐ and ϵ‐martensite textures mainly consist of rotated cube and prismatic and pyramidal fibers, respectively.

Resumo A dissolução de precipitados ricos em Nb durante o reaquecimento de placas é uma das etapas mais importantes no processamento dos aços microligados. O conhecimento do teor de nióbio em solução ao fim dessa etapa é essencial no projeto termomecânico do aço. Neste estudo, aplicou-se a termodinâmica computacional para avaliar os efeitos do ciclo de reaquecimento de placas sobre o teor de nióbio dissolvido na austenita. Os resultados mostraram que, para determinado ciclo, há um limite máximo de tamanho de precipitado que pode ser dissolvido e que a homogeneidade da distribuição do nióbio em solução na austenita é dependente do ciclo empregado. Os resultados indicam que é possível aplicar ferramentas de termodinâmica computacional para otimizar os ciclos de processamento dos aços microligados. Palavras-chave: Nióbio; Aço microligado; Dissolução de precipitados; DICTRA.

No abstract