This application relates to an 1180MPa grade ultra-
high strength steel and its preparation method, belonging to the field of steel
manufacturing technology. The
chemical composition of the ultra-
high strength steel, by
mass fraction, is: C: 0.04%~0.25%, Si: 0.60%~1.80%, Mn: 1.20%~3.00%, Al: 0.02%~0.10%, P≤0.005%, S≤0.002%, Ti: 0.010%~0.040%, Cr: 0.10%~0.80%, N≤0.004%, B: 0.0010%~0.0030%, with the remainder being Fe and unavoidable impurities. The
microstructure of the ultra-
high strength steel includes ferrite and
martensite. A breakthrough in the performance of ultra-high strength steel is achieved by employing a C-Si-Mn-Cr-B
composition system and a segmented cooling process. After finishing rolling, the slab is air-cooled under a temperature-controlled insulation hood, allowing it to enter the water-cooling stage within the phase transformation temperature range and complete the martensitic phase transformation at an ultra-high
cooling rate. The resulting ultra-high-strength steel possesses both ultra-high strength and good
ductility, while its elongation, cold bending performance, and sheet shape quality are all comprehensively improved. This method effectively overcomes the sheet shape defects, performance fluctuations, and weld
softening problems of traditional methods, and is suitable for the industrial production of ultra-thin ultra-high-strength steel.