COLD-ROLLED STEEL SHEET AND METHOD FOR MANUFACTURE THEREOF, AND HOT-FORMED ARTICLE Russian patent published in 2016 - IPC C22C38/06 C21D8/02 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, particularly, to cold-rolled steel plate used in automotive industry. Sheet has chemical composition, containing, wt%: C from 0.1 to 0.3, Si from 0.01 to 2.0, Mn from 1.5 to 2.5, P from 0.001 to 0.06, S from 0.001 to 0.01, N from 0.0005 to 0.01, Al from 0.01 to 0.05, B from 0 to 0.002, Mo from 0 to 0.5, Cr from 0 to 0.5, V from 0 to 0.1, Ti from 0 to 0.1, Nb from 0 to 0.05, Ni from 0 to 1.0, Cu from 0 to 1.0, Ca from 0 to 0.005, REM from 0 to 0.005, Fe and unavoidable impurities - balance. Structure before and after hot forming includes a ferrite with fraction of area from 30% to 90%, martensite with fraction of area of 0 % or more and less than 20 %, pearlite with fraction of area from 0 % to 10 %, residual austenite from 5 % by volume to 20 % by volume, remaining structure - bainite. Hardness of residual austenite, measured with a nano-indentor before and after hot forming, satisfies expression H2/H1 < 1.1 and expression σHM < 20, and ultimate tensile strength and ductility satisfy relationship: TS×El ≥ 20,000 MPa·%, where H1 is hardness of residual austenite present inside surface part on thickness before and after hot forming, wherein surface part on thickness is a zone within 200 mcm in direction of thickness from surface of cold-rolled steel sheet, H2 is a hardness of residual austenite, located inside central part on thickness before and after hot forming, wherein central part on thickness is a zone in range of ±100 mcm along direction of thickness from central plane of cold-rolled steel sheet in direction of thickness, σHM is a change in hardness of residual austenite inside central part on thickness before and after hot forming, TS is tensile strength of cold-rolled steel sheet, MPa, and El is ductility of cold-rolled steel sheet in %.

EFFECT: high ductility and formability.

16 cl, 5 dwg, 8 tbl, 1 ex