Effect of nano-precipitates and TRIP effect on strain hardening behavior of low-carbon nanostructured steel

A novel microstructure design idea involving co-precipitation strengthening of Cu-rich and NiAl nanoparticles and the transformation-induced plasticity (TRIP) effect has been proposed to greatly improve the strengthductility combination of low-carbon nanostructured steel. The volume fraction of reversed austenite in QPT650 steel reached 16.4 % after quenching-partitioning-tempering treatment, and the ultra-high yield strength of similar to 1237 MPa and excellent uniform elongation of similar to 10.7 % were obtained. The co-precipitated coreshell structure of Cu-rich and NiAl decomposes into separate Cu-rich and NiAl particles during subsequent aging, and the Cu-rich particles are further coarsened into bar-shaped fcc-Cu particles. The secondary precipitation and coarsening of Cu-rich and NiAl nanoparticles significantly enhanced the Orowan strengthening, resulting in an increase of precipitation strengthening from 280.4 MPa to 584.6 MPa. The excellent uniform elongation is attributed to the enhanced work hardening ability in the II stage due to the obvious TRIP effect of reversed austenite (RA). This work provides ideas for the microstructure design of Gpa-grade low-carbon nanostructured steel and achieves excellent strength-ductility.