Abstract
A comparative study was conducted to reveal the effect of microstructure on hydrogen permeation in the EA4T and 30CrNiMoV12 railway axle steels. Unlike the EA4T with its sorbite structure, 30CrNiMoV12 steel shows a typical tempered martensitic structure, in which a large number of fine, short, rod-like, and spherical carbides are uniformly dispersed at boundaries and inside laths. More importantly, this structure possesses plentifully strong hydrogen traps, such as nanosized Cr7C3, Mo2C, VC, and V4C3, thus resulting in a high density of trapping sites (N = 1.17 × 1022 cm−3). The hydrogen permeation experiments further demonstrated that, compared to EA4T, the 30CrNiMoV12 steel not only delivered minimally effective hydrogen diffusivity but also had a high hydrogen concentration. The activation energy for hydrogen diffusion of the 30CrNiMoV12 steel was greatly increased from 23.27 ± 1.94 of EA4T to 47.82 ± 2.14 kJ mol−1.
Highlights
Railway axles are among the critical components of high-speed trains, which work under cyclic rotating and bending conditions [1,2]
Metals 2019, 9, 164 limited amount of hydrogen [31,32]. These results strongly indicate that the ability to reasonably control the category, morphology, size, and distribution characteristics of carbides is critical for improving the hydrogen permeation behaviors of the tempered steels
It is clear that the tempered sorbite was achieved in the EA4T steel, consisting of recrystallized ferrite, stripped carbides, and spherical carbides
Summary
Railway axles are among the critical components of high-speed trains, which work under cyclic rotating and bending conditions [1,2]. An axle with high strength, toughness, and fatigue life is always desired for the safe use of high-speed trains [3,4,5]. Hydrogen is a ubiquitous element that can enter steels from different processes, such as smelting, acid pickling, heat working and corrosion [6,7,8,9]. Hydrogen in an axle would cause hydrogen-assisted stress, corrosion cracking and hydrogen embrittlement (HE) [10,11], which gives rise to a huge risk for the safe operation of high-speed railway systems. Achieving H-traps in steel usually decreases hydrogen diffusivity and increases critical hydrogen concentration, which is considered to be an effective method for enhancing resistance to HE [12,13]
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