HIGH STRENGTH AND PLASTICITY STEEL SHEETS AND METHOD OF MANUFACTURING THE SAME Russian patent published in 2012 - IPC C22C38/14 C22C38/04 C21D8/02 C21D9/46 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, more particularly, to manufacturing hot-rolled sheets and details from polyphase steel used in motor industry. Steel contains the following, wt %: 0.050 ≤ C ≤ 0.090, 1 ≤ Mn ≤ 2, 0.015 ≤ Al ≤ 0.050, 0.1 ≤ Si ≤ 0.3, 0.10 ≤ Mo ≤ 0.40, S ≤ 0.010, P ≤ 0.025, 0.003 ≤ N ≤ 0.009, 0.12 ≤ V ≤ 0.22, Ti ≤ 0.005, Nb ≤ 0.020, and, if required, Cr ≤ 0.45, iron and unavoidable impurities make the rest. Semi-finished material is cast from steel, the semi-finished material is heated to temperature of more than 1150°C, subjected to hot-rolling up to temperature T_FL within 870-930°C temperature range when microstructure of steel is fully austenitic, produced sheet is cooled with cooling speed V_R from 75 to 200°C/sec. Sheet then is wound in a roll at temperature T_bob from 500 to 600°C. To produce details, a sheet is cut into parent sheet which is partially or fully heated up to a temperature range from 400 to 690°C, soaked during less then 15 min and blanking is conducted to produce a detail which is then cooled to the ambient temperature at speed from 25 to 100°C/sec. Microstructure of produced sheets and details contains in the superficial part at least 80% of upper bainite, and possible complement consists of lower bainite, martensite and residual austenite, wherein total content of martensite and austenite in less than 5%.

EFFECT: steel is of high-strength exceeding 800 MPa and has ultimate elongation factor exceeding 10%.

20 cl, 3 dwg, 4 tbl, 2 ex