PLATE STEEL CHARACTERISED BY LOW RATIO BETWEEN YIELD POINT AND LIMIT STRENGTH, HIGH STRENGTH AND HIGH IMPACT STRENGTH, AND METHOD FOR ITS MANUFACTURE Russian patent published in 2013 - IPC C22C38/00 C21D8/02 C22C38/14 B21B1/26 

FIELD: metallurgy.

SUBSTANCE: plate steel contains the following, wt %: 0.03% to 0.06% C, 0.01 to 1.0 Si, 1.2 to 3.0 Mn, 0.015 and less P, 0.005 and less S, 0.08 and less Al, 0.005 to 0.07 Nb, 0.005 to 0.025 Ti, 0.010 and less N, 0.005% and less O, and Fe and inevitable impurities are the rest; steel has three-phase microstructure consisting of bainite, martensitic-austenitic component (M-A) and quasi-polygonal ferrite; with that, bainite surface area is equal to 5% to 70%; M-A component surface area is 3% to 20%; and quasi-polygonal ferrite occupies the rest surface area, and equivalent diameter of a circle for M-A component is 3.0 mcm and less. Plate steel is characterised by the ratio between yield point and limit strength, which is equal to 85% and less, and absorbed energy during the Charpy impact test at the temperature of -30°C, which is equal to 200 J and more, before and after treatment in the form of strain ageing at the temperature equal to 250°C and less, during 30 minutes and less.

EFFECT: provision in plate steel of low ratio between yield point and limit strength, high strength, impact strength and stability to strain ageing, which is equivalent to Class API 5L X60 and less.

4 cl, 3 dwg, 3 tbl, 1 ex