Ultra-high-strength steel having excellent plasticity and method for manufacturing same

Abstract

Disclosed is an ultra-high-strength steel having excellent plasticity, comprising in mass percent the chemical elements: C: 0.26-0.30 wt %; Si: 0.8-1.00 wt %; Mn: 2.80-3.30 wt %; Al: 0.04-0.08 wt %; with the balance being Fe and other inevitable impurities. Also disclosed is a manufacturing method for manufacturing the ultra-high-strength steel having excellent plasticity, comprising the following steps: (1) smelting and thin slab continuous casting; (2) heating; (3) hot rolling, wherein an oxide scale on the surface of a hot-rolled steel strip has a thickness of ≤6 μm, and (FeO+FeO)≤40 wt % in the oxide scale on the surface of the hot-rolled strip steel; (4) acid pickling or acid pickling and cold rolling; and (5) continuous annealing: annealing at 800-920° C. and performing slow cooling at 3-10° C./s to 690-760° C.; performing fast cooling to 250-350° C. at 50-100° C.; and then heating to 360-460° C., maintaining the temperature for 100-400 s and cooling to room temperature.