Influence of Microstructural Morphology on Hydrogen Embrittlement in a Medium-Mn Steel Fe-12Mn-3Al-0.05C

Abstract

The ultrafine-grained (UFG) duplex microstructure of medium-Mn steel consists of a considerable amount of austenite and ferrite/martensite, achieving an extraordinary balance of mechanical properties and alloying cost. In the present work, two heat treatment routes were performed on a cold-rolled medium-Mn steel Fe-12Mn-3Al-0.05C (wt.%) to achieve comparable mechanical properties with different microstructural morphologies. One heat treatment was merely austenite-reverted-transformation (ART) annealing and the other one was a successive combination of austenitization (AUS) and ART annealing. The distinct responses to hydrogen ingression were characterized and discussed. The UFG martensite colonies produced by the AUS + ART process were found to be detrimental to ductility regardless of the amount of hydrogen, which is likely attributed to the reduced lattice bonding strength according to the H-enhanced decohesion (HEDE) mechanism. With an increase in the hydrogen amount, the mixed microstructure (granular + lamellar) in the ART specimen revealed a clear embrittlement transition with the possible contribution of HEDE and H-enhanced localized plasticity (HELP) mechanisms.

Physical Metallurgy of High Manganese Steels

“…This Special Issue gathers manuscripts from internationally recognized researchers with stimulating new ideas and original results. It consists of fifteen original research papers, seven contributions focus on steels with manganese content above 12% mass [4][5][6][7][8][9][10], whereas eight deal with alloys having less manganese [11][12][13][14][15][16][17][18].…”

“…Finally, the scientifically very challenging and industrially relevant topic of hydrogen embrittlement is the focus of the contribution by Shen et al [18]. Distinctly different microstructures were formed in the same alloy as a consequence of varied annealing treatment after cold rolling, i.e., only ART and austenitization followed by ART.…”

Hydrogen Embrittlement of Medium Mn Steels

“…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.…”

“…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). 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.…”

Hot Compression Behavior of New Al-6Mg and Al-8Mg Alloy with Improved Hot Workability Fabricated by Direct Chill Casting Method

“…GOS is a value obtained by averaging the orientation difference between adjacent EBSD data points in one identical grain, so that it can provide local strain information like the case of KAM data in Figure 5. In other words, the GOS value represents the degree of average dispersion of the misorientation within one grain [20,21]. Therefore, some low GOS values can be obtained if some restoration, such as recrystallization and recovery, occurred in the chosen grain.…”