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High-throughput screening based on CALPHAD (CALculation of Phase Diagram) was employed to investigate potential chemical compositions within the Fe-C-Mn alloy system for the hydrogen resistance application. The primary objective was to identify a range of compositions that would exhibit a stable FCC phase while simultaneously expanding the austenitization temperature window. Processing the high-throughput CALPHAD screening led to the composition Fe-1.1C-18.72Mn-6Al-5.01Cr-1.05Si-0.03Cu. Stacking fault energy (SFE) was calculated for this alloy using a thermodynamic model, and the result indicated a relatively high SFE of 66 mJ·m−2, which suggests high stability of the austenite matrix. The designed alloy displays a yield strength (YS) of 426 ± 4 MPa, an ultimate tensile strength (UTS) of 830 ± 10 MPa, and an elongation of 85 ± 2 %. After subjecting the material to hydrogen gas charging, a small elongation loss (around 7.69 ± 1.9 %) was observed, attributable to the hydrogen embrittlement effect. Notably, the dominant mechanism of hydrogen embrittlement was suggested as a plasticity driven mechanism such as Hydrogen-Enhanced Localized Plasticity (HELP) or Hydrogen-Enhanced Strain-Induced Vacancy (HESIV). the high density of void formation near the fracture point of the charged sample and the observation of dimples in the fracture surface provided compelling evidence for this possible embrittlement mechanisms, however more investigations are needed to confirm the dominant mechanism.

A novel, low-alloy steel has been designed for use in the oil and gas industry. Its high strength and hydrogen trapping potential are derived from a martensitic microstructure containing a dispersion of fine vanadium-molybdenum alloy carbides that evolve during tempering. In this second paper, the effect of quench rate from austenitisation and tempering conditions are investigated with respect to the microstructure. The alloy loses its tempering resistance following slow-cooling from austenitisation as a result of MC precipitation, leading to vanadium depletion and significant M2C coarsening. This is predicted using computer simulation and confirmed by high energy X-ray diffraction, combined with electron microscopy., QC 20190412

A new thermally stable, nanocrystalline bainitic steel has been developed, rich in nickel and aluminium. During tempering, it is expected that a significant quantity of intermetallic precipitates will form. This was confirmed by X-ray diffractometry, scanning transmission electron microscopy, Fourier transform analysis of atomic column images, energy dispersive X-ray spectroscopy and selected area electron diffraction. These are the first intermetallics to be produced in a nanocrystalline bainitic steel., QC 20190110

The idea of carbide-free bainitic (CFB) microstructure, a mixture of bainitic ferrite and retained austenite (RA), in high-silicon steels has been recently thoroughly investigated by numerous researchers. In this research, two medium-carbon steel grades were tested in a wear tumbling machine to investigate microstructural changes under wet sliding abrasive wear conditions and to benchmark their performance against conventional tempered martensitic steels. The nature and type of defects responsible for material removal were analysed using scanning electron microscopy. To observe microstructural evolution of heavily deformed top layers of test specimens, special layer-by-layer X-ray diffraction methodology was applied. This technique allows accurate quantification of the volume fraction of RA transformed into untempered martensite at different depths from the worn surface. The results suggest that better performance is achieved in specimens heat treated to carbide-free bainitic microstructure containing higher volume fraction of RA, however with blocks of RA thermally stable at room temperature. The improved wear resistance is due to the increased surface hardness caused by stress-induced transformation of RA into untempered martensite during wear, while maintaining good toughness in the subsurface zones, which prevent brittle cracking., QC 20170703