Hydrogen Susceptibility of Nanostructured Bainitic Steels

Abstract

Nanostructured steels with an ultimate tensile strength of 1.6 GPa were produced with austenite content varying from 0 to 35 vol pct. The effect on the mechanical properties was assessed after saturating the steel with hydrogen. Elongation was reduced to 2 to 5 pct and UTS to 65 to 70 pct of prior value. Thermal desorption measurements confirmed the higher solubility of hydrogen in the steel with higher austenite content. The level of hydrogen saturation was found to correlate to the total area of grain boundaries rather than to the volume fraction of retained austenite.

Infusion of hydrogen into nanostructured bainitic steel

“…Peet and Hojo [7] have conducted thermal desorption experiments in nanostructured bainitic steels, including one tempered at 500 °C. In the sample asisothermally transformed with 35.1% retained austenite the amount of hydrogen desorbed was 7.1 ppmw, but in the tempered sample (without retained austenite) the amount of hydrogen desorbed was 3.0 ppmw.…”

“…Previous studies on hydrogen in nanostructured bainite have suggested that the level of hydrogen saturation is correlated to the total area of α/γ interfaces per unit volume rather than to the volume fraction of retained austenite [7,21]. However, this result does not account for the conflicting values of retained austenite after isothermal transformation [21] or assumptions in bainitic ferrite plate width that affect the estimation of surface area per unit volume of the α/γ interfaces [7].…”

“…Nanostructured bainitic steels consist of thin plates of ferrite separated by films of carbon-enriched retained austenite and display an excellent combination of properties including strength and ductility [1][2][3]. The high strength makes them susceptible to hydrogen embrittlement that can lead to delayed fracture and a loss of structure [4][5][6][7].…”

“…The dislocation density increases as the transformation temperature decreases [14][15][16][17][18], and dislocations are known to be trapping sites for hydrogen [9,19,20]. Nanostructured bainite contains a very large surface area of α/γ interfaces per unit volume due to the fine scale of the bainitic ferrite plates [1][2][3] and these α/γ interfaces may also act as hydrogen traps [7,20,21].…”

Electroless Amorphous NiP Coatings Over API X70 Steel: Resistance to Wear and Hydrogen Embrittlement

“…However, NiP-3 coated steel showed a higher increase in the YS than NiP-1 coated steel after H-charging, even though the NiP-3 coating is of a higher thickness (5.5 µm) compared to NiP-1 coating (3.5 µm). A HES study of three different high-strength steels by Peet and Hojo [40] reported that the effect of H-charging on the HES can be well perceived by comparing the %EL values for H-charged and uncharged conditions (Table II in Ref [40]).…”