HIGH-STRENGTH SHEET STEEL WITH EXCELLENT DEFORMABILITY AND METHOD FOR PRODUCING IT Russian patent published in 2008 - IPC C21D8/02 C22C38/00 C22C38/58 

FIELD: metallurgy, namely processes for making high strength sheet steel with excellent deformability.

SUBSTANCE: steel having high strength, deformability and properties necessary for chemical, conversion treatment and for zinc plating contains, mass %: carbon, 0.03 - 0.20; silicon, 0.005 - 0.3; manganese, 1.0 - 3.1; phosphorus, 0.001 - 0.06; sulfur, 0.001 - 0.01; nitrogen, 0.0005 - 0.01; aluminum, 0.2 - 1.2; molybdenum < 0.5, iron and inevitable impurities, the balance at condition that contents of Si and AL are in mass.% and target strength (TS) of steel is satisfied by next expression: ( 0.0012 x [target strength TS] - 0.26 - [Si])/2.45 < Al < 1.5 - 3 x [Si] where TS - designed strength of sheet steel (MPa) and metal structure contains ferrite, martensite and remaining austenite. Sheet steel is produced by performing steps of hot rolling, etching, cold rolling, recrystallization annealing in mode of continuous process and then it is subjected to skin pass rolling. Temperature of hot rolling process termination is equal to temperature of phase transition Ar₃ or higher temperature. Cooling is realized till temperature 400 - 550°C. Cold rolling is realized at reduction degree 30 - 70% and continuous annealing is realized while heating till temperature Ac₁ - (Ac₃ + 100)°C, soaking for time period from 30 s till 30 min and cooling till temperature 600°C or less at rate no less than X°C/s at next relation: X > ( Ac₃ - 500)/10^a where a = 0.6 [C] + 1.4 [Mn] + 3.7[Mo] - 0.87.

EFFECT: high strength and deformability of steel suitable for chemical treatment and zinc plating.

8 cl, 2 tbl, 3 dwg, 1 ex