HOT-ROLLED SHEET STEEL FOR SMALL-DIAMETER FLEXIBLE TUBING AND ITS MANUFACTURING METHOD Russian patent published in 2021 - IPC C21D8/02 C21D9/46 C22C38/48 C22C38/58 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to hot-rolled sheet steel for flexible tubing. Hot-rolled sheet steel for flexible tubing is characterized by a chemical composition containing, weight percentage: C 0.10-0.16, Si 0.1-0.5, Mn 0.8-1.8, P 0.001-0.020, S 0.0050 or less, Al 0.01-0.08, Cu 0.1-0.5, Ni 0.1-0.5, Cr 0.5-0.8, Mo 0.10-0.5, Nb 0.01-0.05, Ti 0.01-0.03, N 0.001-0.006, optionally one or more components selected from B 0.0005-0.0050, V 0.01-0.10, Ca 0.0005-0.0100, a rare earth metal 0.0005-0.0200, Zr 0.0005-0.0300 and Mg 0.0005-0.0100, Fe and unavoidable impurities being the rest, by a microstructure in a position located at 1/2 the thickness of the sheet steel, including bainite and bainite ferrite at a combined amount of 80% or more, in relation to the surface fraction concentration in which the amount of Nb in the solid state of Nb is 20% or more of the total mass content of Nb. A method for manufacturing hot-rolled sheet steel involves heating the steel slab to the temperature 1100-1250°C, carrying out rough slab rolling, finish rolling at a temperature of 820-920°C, cooling the steel sheet to a temperature 600-450°C with the average cooling rate of 30-100°C /s with respect to the temperature at the central portion in the thickness direction of the sheet steel and scrolling the cooled steel sheet at a temperature of 450-600°C with further cooling of the steel sheet coil at a speed of 15°C /h or more.

EFFECT: resulting sheet steel has a tensile point of 480 MPa or more, a tensile strength of 600 MPa or more, a tensile point of 620 MPa or more.

2 cl, 5 tbl, 2 ex