Microstructure and compression behavior of powder-metallurgy processed fine-grained TWIP steel

• Fine-grained TWIP steels with grain sizes ranging from 2.93 to 11.93 μm were directly fabricated using powder metallurgy. • The dynamically compressed samples demonstrating superior work hardening, higher flow stress, and enhanced positive strain rate sensitivity. • The enhancement was due to the strong interaction of dislocation glide with factors caused by high-speed impact. • Dynamic impact unlocks grain boundaries/precipitation strengthening synergies to compensate suppressed twinning strengthening. To enhance the strength of twinning-induced plasticity (TWIP) steels and promote their engineering application, powder metallurgy (PM) was employed in this study to directly produce fine-grained TWIP steels with average grain sizes of 2.93–11.93 μm, bypassing complex conventional processes involving induction melting, plastic deformation, and heat treatment. The quasi-static and dynamic compression properties of these samples exhibited a typical grain size dependence. Compared to the quasi-statically compressed samples, the dynamically compressed samples demonstrated enhanced work hardening, characterized by a higher flow stress and an increased work-hardening rate, along with a notable positive strain rate sensitivity. High-speed impact activated significant dislocation glide, leading to rapid dislocation multiplication, extensive twin nucleation, and particle deformation that generated high-energy distortion zones. This process also produced a high density of low-angle boundaries (LABs). Grain boundaries (GBs) and precipitation strengthening were the main drivers of work hardening. These mechanisms involved dislocation interactions with single Mn-rich particles, GB-associated particles, and those linked to twins. In contrast, twinning strengthening played a minor role due to the poor twin structure resulting from the suppressed twinning.