HOT-ROLLED STEEL SHEET AND METHOD OF ITS PRODUCTION Russian patent published in 2015 - IPC C22C38/14 C21D8/04 C22C38/54 

FIELD: process engineering.

SUBSTANCE: invention relates to metallurgy. Sheet is made of steel containing in wt %: 0,040≤C<0.065, 1.4≤Mn≤1.9, 0.1≤Si≤0.55, 0.095≤Ti≤0.145, 0.025≤Nb≤0.045, 0.005≤A1≤0.1, 0.002≤N≤0.007, S≤0.004, P≤0.020, iron and unavoidable impurities making the rest. Sheet microstructure consists of granular beinite, ferrite, cementite, titanium and niobium carbonitrides. Ratio between drain size d_l measured parallel with rolling direction and gain size d_n perpendicular to rolling direction makes less than or equals 1.4.Method of sheet production includes heating of semi-finished product to 1160-1300°C, hot rolling with rolling end temperature of 880-930°C. Note here that reduction degree of next to last pass is smaller than 0.25, reduction degree of last pass is smaller than 0.15 while the sum of both reduction degree is smaller than 0.37. Initial temperature at next to last is smaller than 960°. Cooling is performed at the rate of 50-150°C/s. Sheet is wound at winding temperature of 470-625°C.

EFFECT: production of sheet with ductility stress over 690 MPa and less or equal to 840 MPa, strength of 780-950 MPa, elongation over 10% and bore expansion factor larger than or equal to 50%.

26 cl, 6 tbl, 1 dwg