Phase Stability Effects on Hydrogen Embrittlement Resistance in Martensite–Reverted Austenite Steels

Abstract

Earlier studies have shown that interlath austenite in martensitic steels can enhance hydrogen embrittlement (HE) resistance. However, the improvements were limited due to micro-crack nucleation and growth. A novel microstructural design approach is investigated, based on enhancing austenite stability to reduce crack nucleation and growth. Our findings from mechanical tests, X-ray diffraction and scanning electron microscopy reveal that this strategy is successful. However, the improvements are limited due to intrinsic microstructural heterogeneity effects.

Hydrogen Embrittlement of Medium Mn Steels

“…Figure 3c indicates similar H concentrations of the electrochemically H-charged specimens from the H thermal desorption analysis (TDA) results for the two morphologies. The SSRT results of the H-charged specimens, Figure 3d, indicate that the equiaxed microstructure better resisted HE, which is consistent with the interpretation of Cameron et al [35]; it should be noted that, again, the equiaxed condition had a higher strength. Shen et al [37] compared a slightly different combination of microstructures, i.e., a mixture of lamellarized and equiaxed structures having coarse lamellae (10-20 μm in length) and grains (~1.5 μm) versus a mainly fine lamellarized microstructure (lamellae 1-5 μm in length).…”

“…Shen et al [37] compared a slightly different combination of microstructures, i.e., a mixture of lamellarized and equiaxed structures having coarse lamellae (10-20 μm in length) and grains (~1.5 μm) versus a mainly fine lamellarized microstructure (lamellae 1-5 μm in length). The study by Shen et al [37] is also consistent with the studies by Cameron et al [35] and Han et al [36], in that the microstructure containing equiaxed grains exhibited a higher resistance to HE. It should be pointed out, however, that the difference in microstructural feature sizes is also considered a critical factor that affects the HE characteristics in addition to the morphological change in the study by Shen et al [37].…”

“…where TEH-free and TEH-charged are the total elongations obtained from SSRT of tensile specimens in H-free and H-charged conditions, respectively. Interestingly, three separate investigations had similar interpretations with respect to the relative H-resistance of the two morphologies [35][36][37]. Cameron et al [35] applied two different processing routes to a medium-Mn steel (Fe-0.01C-9Mn-3Ni-1.4Al, in wt pct) to generate different microstructures.…”

“…Interestingly, three separate investigations had similar interpretations with respect to the relative H-resistance of the two morphologies [35][36][37]. Cameron et al [35] applied two different processing routes to a medium-Mn steel (Fe-0.01C-9Mn-3Ni-1.4Al, in wt pct) to generate different microstructures. That is, IA of (i) as-quenched and (ii) cold-rolled martensitic microstructures led to lamellarized martensite-austenite and equiaxed ferrite-austenite microstructures, respectively.…”

“…The SSRT results indicated that both microstructures showed similar degrees of elongation loss (91-92 pct) after H charging, despite the observations that the equiaxed morphology absorbed a much higher H concentration for a given H-charging condition (15.6 wppm in equiaxed vs. 1.87 wppm in lamellarized) and had a higher ultimate tensile strength (1100 vs. 900 MPa). In this regard, Cameron et al [35] interpreted that the equiaxed microstructure was more resistant to HE, compared to the lamellarized condition.…”