Microstructure of cast iron resistant to hydrogen embrittlement 2023-36-0063

One of the most promising applications for the use of hydrogen in vehicles is in the combustion engine. According to the legislation proposal being considered by European Union, hydrogen internal combustion engines (H2ICE) are zero emissions solution. Among the existing solutions, H2ICE is becoming the preferred one on long haul trucks and offroad applications. This is due to the high durability of the powertrain, the lower initial investment when compared to other alternatives, and the possibility of using low purity hydrogen. However, despite the high potential use of hydrogen, because of it is the smallest known chemical element, its use can result in the penetration of hydrogen into metallic materials, with the undesirable effect of embrittlement. This effect occurs mainly when the material surface is exposed to high temperatures and pressures, or under corrosion. By diffusing into the crystal lattice, hydrogen is accumulated in the interstices and crystalline defects, reducing the ductility of the metallic material. Unlike high strength steels, cast irons present graphite that can accommodate diffused hydrogen, delaying the embrittlement effect. The morphology and amount of graphite, as well as the alloying elements and phases present, play a key role in this issue. As shown in a previous work, using a pressurized vessel, cast iron specimens where exposed to an atmosphere of 20% H2 and 80% N2 at 150 bar and 300 °C for 7 days, and hydrogen embrittlement was not verified. In the present work, the effects of hydrogen embrittlement on different cast iron microstructure were evaluated by a qualitative fracture analysis technique. To this purpose, a current density of 16 mA/cm2 was applied for 24 h in electrolytic solution. Hydrogen embrittlement was not verified since the fractures presented in all samples showed river marks, characteristic of brittle fracture, and dimples, characteristic of ductile fracture. This indicates that the hydrogen saturation to generate embrittlement was not reached.