ULTRA HIGH STRENGTH AND TOUGHNESS STEEL PLATE HAVING LOW YIELD RATIO AND MANUFACTURING METHOD THEREOF Russian patent published in 2019 - IPC C22C38/54 C21D8/02 

FIELD: metallurgy.

SUBSTANCE: invention relates to a ultra high strength steel plate with a low yield ratio to strength ratio of less than 0.85, used in construction of machinery, building bridges, architectural and engineering structures. Steel is melted having the following chemical composition, by weight: C 0.28–0.34, Si 0.10–0.40, Mn 0.50–1.40, Cr 0.20–0.70, Mo 0.30–0.90, Nb≤0.06, Ni 0.50–2.40, V≤0.06, Ti 0.002-0.04, Al 0.01–0.08, B 0.0006–0.0020, N≤0.0060, O≤0.0040, Ca 0.002–0.0045, and the balance being Fe and unrecoverable impurities. Steel is melted into a slab that has heated temperature of 1,080–1,250 °C and rolling is performed until the sheet is obtained. Rolled sheet is cooled and quenched at a temperature of 860–940 °C and leave to a temperature of 150–350 °C to produce a steel strip containing a microstructure of fine-grained martensite and residual austenite.

EFFECT: high mechanical properties are achieved.

8 cl, 1 dwg, 3 tbl, 6 ex