Mechanism of the Interaction Between Hydrogen, Microstructure, and Mechanical Properties in Low-Alloy High-Strength Marine Steel

Herein, the interaction between hydrogen, microstructure, and mechanical properties in low-alloy high-strength marine steel was elucidated via microstructural characterization, internal friction analysis, hydrogen diffusion, and hydrogen-embrittlement sensitivity evaluation. Results indicated that the bainite structure of hot-rolled steel transformed into a coarse ferrite–pearlite structure after normalizing, and the hydrogen trap density decreased with decreasing grain boundary and dislocation densities. Therefore, the effective diffusion coefficient of hydrogen in the normalized steel plates increased with decreasing hydrogen permeation time. Owing to the coarsening of the microstructure, the normalized steel plates exhibited higher sensitivity to hydrogen embrittlement. The diffusion of a large amount of hydrogen into the steel considerably deteriorated its plasticity, resulting in a transition of its fracture mode from microvoid coalescence fracture to cleavage fracture. The internal friction behavior indicated that hydrogen in the microstructure generated a hydrogen-induced Snoek peak, as well as reduced the activation energy of Snoek–Kê–Köster and Kê peaks. Finally, the internal friction spectra revealed that the interaction between hydrogen and point defects, dislocations, grain boundaries, and precipitates was sequentially enhanced due to the increase in activation energy.