Abstract
A new ar-chitecture of ultrafine grain (UFG) steel with coarsen bimodal size distribution was realized by high-temperature short time annealing process. Abundant comparisons on ferrite size, precipitates, and dislocation were performed with previous works. In the present study, the synthetical mechanical properties showing a tensile strength of 974.9 ± 27.1 MPa and 18.5 ± 1.66% elongation in UFG steel with grain size of 374 nm was enhanced without much strength sacrifice. High-temperature short time annealing process promoted the intragranular Nb(C, N) particles formation and the recrystallization ferrite coarsening. However, the better work hardening ability confirmed by the increased intragranular Nb(C, N) particles dominated the synthetical mechanical properties in UFG steel. The intragranular Nb(C, N) particles advocated the stimulation and accumulation of geometrically necessary dislocations (GNDs), thus the strength increment by work hardening counteracted the decreased strength resulted from coarsen ferrite grains.
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