MANUFACTURING METHOD OF COLD-ROLLED ROLLED IRON OF HEAVY-DUTY Russian patent published in 2009 - IPC C21D8/04 C21D9/48 C22C38/06 

FIELD: metallurgy.

SUBSTANCE: invention relates to manufacturing process of cold-rolled strip of heavy-duty made of low-alloyed steel, provided for preparation of car parts by die forming method. It is implemented steelmaking, containing, wt %: 0.025-0.10 of carbon; not more than 0.30 of silicon; 0.41-0.70 manganese; 0.04-0.12 of phosphorus; 0.01-0.08 of aluminium; not more than 0.009 of nitrogen; iron and unavoidable admixtures - the rest, slab pouring, slab hot rolling into strips with finishing temperature 825-890°C, cooling by water, winding of strips into coils at temperature 505-630°C, cold rolling, recrystallization annealing in bell-type furnace at temperature 600-700°C with duration 7-20 hours and temper rolling with cobbing 0.8-2.1%. Steel additionally contains 0.0008-0.0030 wt % of boron. Content of carbon and phosphorus relates to required minimal yield point (strength grade) by correlations [C]=(0.0005-K_yp-0.065)±0.02,% and [P]=(0.0005-K_yp-0.05)±0.20,%, where [C], [P]-content of carbon and phosphor in steel, %; 0.0005; 0.065; 0.05 - empirical coefficients, %; K_yp - nondimensional factor, numerically equal to required minimal yield point.

EFFECT: increasing of strength properties with keeping of formability and receiving of required strength grade, corresponding required minimal yield point.

4 cl, 6 tbl