MANUFACTURING METHOD OF HIGH-STRENGTH STEEL PLATES WITH EXCELLENT DUCTILITY AND PLATES MADE BY MEANS OF THIS METHOD Russian patent published in 2010 - IPC C22C38/38 C22C38/14 C21D8/04 

FIELD: metallurgy.

SUBSTANCE: steel which contains the following, wt %, is made: 0.08≤C≤0.23, 1≤Mn≤2, 1≤Si≤2, Al≤0.030, 0.1≤V≤0.25, Ti≤0.010, S≤0.015, P≤0.1, 0.004≤N≤0.012, and one or more elements chosen from the following is optional: Nb≤0.1, Mo≤0.5, Cr≤0.3, the rest is iron and inevitable impurities appearing during melting process. Semi-finished product is cast from this steel, which is then heated to temperature of more than 1200°C. The above semi-finished product is subject to hot rolling so that sheet is obtained, and the obtained sheet is cooled and rolled. Temperature of end of hot rolling T_{rolling end}, cooling rate V_cool and rolling temperature T_roll is chosen so that steel microstructure consisted of ferrite, bainite, residual austenite and martensite as an option. The above sheet is subject to etching and cold rolling is performed so that cold-rolled sheet is obtained. The above sheet is subject to heat treatment with annealing; at that, the above heat treatment includes heating phase with heating rate V_heat, exposure phase at exposure temperature T_exp and exposure time t_exp with further cooling phase with cooling rate V_cool when temperature is below A_r3, and exposure phase at exposure temperature T'_exp and exposure time t_exp. Parametres V_heat, T_exp, t_exp, V_cool, T'_exp and t'_exp are chosen so that steel microstructure consisted of ferrite, bainite, residual austenite and martensite as an option.

EFFECT: steel has increased strength and is not sensitive to deviation of manufacturing parametres.

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