Influence of the microstructure on the hydrogen uptake and embrittlement of 42CrMo4 steel under gaseous hydrogen charging

To determine the microstructural influence on hydrogen uptake and embrittlement behavior, 42CrMo4 was heat-treated to achieve different microstructures with increasing martensite content and tensile strength. Specimens charged at 1000 bar and 25 °C took up between 0.5 and 0.65 wt.-ppm. Charging at 200 °C leads to an increasing hydrogen uptake with increasing material strength and martensite content. Furthermore, CLTs were conducted at the materials yield strength, resulting in a brittle failure of the highest-strength material charged at 1000 bar and 25 °C. To describe the influence of the microstructure on 42CrMo4's embrittlement behavior, in-situ charged SSRTs and the determination of the material's critical hydrogen content were conducted. The critical hydrogen contents are equal to 1.84 wt.-ppm (no martensite), 0.75 wt.-ppm (low martensite content), and 0.23 wt.-ppm (high martensite content), respectively. These results reveal a strongly increasing embrittlement tendency with increasing material strength and martensite content.