Improving strength–ductility synergy in medium Mn steel by combining heterogeneous structure and TRIP effect

Potential Significance of Low Tempering Treatment in Improving the Mechanical Properties of a Cold‐Rolled and Intercritical Annealed Medium Mn Steel

“…Compared with the other samples, the A680‐10 and AT680‐10 exhibit evident heterogeneous microstructure with various morphologies and multiscale (Figure 1,2), as well as the heterogeneous distribution of Mn (Figure 6,7). According to our previous research results, [ 31 ] the heterogeneous deformation‐induced (HDI) stress strengthening and HDI hardening effects during tensile deformation are the reasons for the outstanding strength–ductility synergistic effect of the heterostructured sample. To further elucidate the unusual influence mechanism of tempering on the sample annealed at 680 °C for 10 min, the HDI stress of the AT680‐10 and A680‐10 specimen was studied through loading–unloading–reloading (LUR) experiments ( Figure 8 ).…”

“…In addition, the HDI stress could delay the martensitic transformation of γ to a large strain scope due to the shielding effect of the formed core–shell structure. [ 31 ] Thus, the larger HDI stress results in higher γ stability; Ultimately, the persistent TRIP effect, along with HDI work hardening, is mainly responsible for the higher TE of the AT680‐10 than that of A680‐10. In summary, the present work shows that the strength and ductility of CR and IAed sample could be simultaneously improved significantly by tempering treatment when the IA sample possesses suitable γ content and stability.…”

Study on Prior Austenite Grain Size and Softening Fraction in Governing Microstructure and Mechanical Behavior of Medium Mn Steel after Intercritical Annealing

“…The lower stability of austenite with a larger size in the HD850þIA sample can be clarified based on the strain accommodation of the austenite to martensite transformation. [24] Multi-variant transformation is the main mechanism for the uniform accommodation of the transformation strain due to austenite-to-martensite transformation. If the austenite grain is too small, the multi-variant transformation is difficult to occur because of the reduced size, and single-variant transformation is preferred in smaller austenite grains, thereby increasing the elastic strain energy.…”

Mechanism and Application of Reverse Austenitic Transformation in Medium Mn Steels: A Systematic Review

“…[97] When it has a much lower M s than the room temperature, all reverted austenite grains shall be retained with the Mn concentration gradients, and the RA grains having different sizes and morphologies may form by changing the heat treatment conditions or combining them with the deformation process (see Figure 6b). [98][99][100] They could provide a more sustainable TRIP effect over a wide straining range for enhanced work hardening. Interestingly, it was found that the total faction of reverted austenite could even exceed the equilibrium value when the prior annealing temperature is higher than that of the final IA one.…”

“…Several processing strategies for achieving austenite grains with Mn concentration gradients in MMS. The possible microstructures at room temperature (RT) after the processing routes in a) [91] and b) [98][99][100] are shown in c) while those in d) [92,93] and e) [94][95][96] are shown in f ). A1 and A3 temperature are the austenitic transformation start and finish temperatures, respectively.…”