Deformation Behavior of a Double Soaked Medium Manganese Steel with Varied Martensite Strength

Abstract

The effects of athermal martensite on yielding behavior and strain partitioning during deformation is explored using in situ neutron diffraction for a 0.14C–7.14Mn medium manganese steel. Utilizing a novel heat treatment, termed double soaking, samples with similar microstructural composition and varied athermal martensite strength and microstructural characteristics, which composed the bulk of the matrix phase, were characterized. It was found that the addition of either as-quenched or tempered athermal martensite led to an improvement in mechanical properties as compared to a ferrite plus austenite medium manganese steel, although the yielding and work hardening behavior were highly dependent upon the martensite characteristics. Specifically, athermal martensite was found to promote continuous yielding and improve the work hardening rate during deformation. The results of this study are particularly relevant when considering the effect of post-processing thermal heat treatments, such as tempering or elevated temperature service environments, on the mechanical properties of medium manganese steels containing athermal martensite.

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].…”

“…As substantiated in the previous section, the multi-phase microstructure formed during annealing determines the mechanical properties. The contributions by Sevsek et al [15], Glover et al [16], and Allam et al [17] were intended to shed more light on the deformation mechanisms in these alloys. A detailed analysis of the strain-rate-dependent deformation behavior in ultrafine-grained austenitic-ferritic MMnS is presented in [15].…”

“…Varying mechanically induced transformation behavior was found to be responsible for high strain-rate sensitivity. Glover et al [16] studied the effects of athermal martensite on yielding behavior and strain partitioning during deformation using in situ neutron diffraction. It was found that athermal martensite, both as-quenched and tempered, led to an improvement in mechanical properties including promotion of continuous yielding and increased work-hardening rate.…”

Processing Variants in Medium-Mn Steels

“…Tempering effects are being explored in ongoing research, following the double soaking thermal path achieved using molten salt baths with heating rates on the order of 80 • C/s [11,15]. Figure 4 illustrates the tensile property changes, showing engineering stress-strain behavior after the primary soak (intercritical batch anneal-BA), then after double-soaking for 30 s at 800 • C (DS), as well as after subsequent cooling to room temperature and then tempering for 300 s at 450 • C (DS-T) or after subsequent austempering (DS-A) for 300 s at 450 • C [11].…”

Tempering and Austempering of Double Soaked Medium Manganese Steels

“…The substitution of athermal martensite for ferrite, present after the application of a single intercritical annealing heat treatment, is achieved through the application of a second intercritical annealing or austenitizing treatment. This results in the formation of additional austenite, which transforms to athermal martensite upon quenching due to a reduced concentration of carbon and manganese (Glover et al, 2017;Glover et al, 2019). The microstructures of double soaked medium manganese steels demonstrate increased strength while maintaining appreciable ductility, with ultimate tensile strengths above 1700 MPa reported in conjunction with total elongations of 15 pct (Glover et al, 2017;Glover et al, 2019).…”