The hydrogen concentration in steel is directly related to the hydrogen embrittlement (HE) sensitivity of the steel. This study combined electrochemical hydrogen charging, the slow strain rate test (SSRT), and hydrogen permeation experiments to investigate the variation in the hydrogen concentration in pipeline steel with the electrochemical hydrogen-charging time. The influence of the hydrogen concentration in steel on the mechanical properties of X80 pipeline steel was obtained, and ultimately, a quantitative relationship between the hydrogen concentration in steel and the hydrogen embrittlement sensitivity was established. The results show that the hydrogen concentration in the steel gradually increased with the time of hydrogen charging, and the quantitative relationship formula can be given as C_H = 5.35 − 4.2 exp (−0.26t); the HE index of X80 steel increased with the hydrogen concentration. Additionally, once the hydrogen concentration in steel reaches 5.08 × 10⁻⁶ mol/cm³, even the slightest alteration in the hydrogen content will precipitate a dramatic decrease in plasticity. The quantitative relationship formula between the hydrogen concentration and the HE index (F_H) in X80 steel can be given as $F_{\mathrm{H}}=0.029 \exp (1.5C_{\mathrm{H}}) - 0.029$. When the hydrogen concentration in steel is at a maximum, the F_H of X80 steel reaches 88.6%. This study provides a reference for analyzing the quantitative relationship between the hydrogen concentration and the HE index in steel after electrochemical hydrogen charging.

Exploring the mechanism of the α-ferrite precipitation process on high-temperature properties plays an important guiding role in avoiding slab cracks and effectively regulating quality. In this work, in situ observation of the α-ferrite sustained precipitation behavior for peritectic steel during the austenitic phase transition process has been investigated using high-temperature confocal scanning laser microscopy. Meanwhile, the high-temperature evolution of the phase fractions during the phase transition process was quantitatively analyzed based on the high-temperature expansion experiment using the peak separation method. Furthermore, the high-temperature properties variations of the casting slab during the α-ferrite sustained precipitation process were investigated with the Gleeble thermomechanical simulator. The results show that the film-like ferrite precipitated along the austenite grain boundaries at the initial stage of phase transition, then needle-like ferrite initiates rapid precipitation on film-like ferrite when the average thickness reaches 15~20 μm. Hot ductility reached a minimum at the ferrite phase fraction f_α = 10~15%, while high-temperature properties returned to a higher level after f_α > 40~45%. The appearance of a considerable amount of needle-like ferrite and grain refinement effectively improves the high-temperature properties with the α-ferrite precipitation process advances.