ELEMENT OF HEAT-TREATED STEEL SHEET AND METHOD OF ITS PRODUCTION Russian patent published in 2019 - IPC C22C38/14 C22C38/38 C22C38/58 C21D1/18 C21D9/46 

FIELD: metallurgy.

SUBSTANCE: invention relates to an element from heat-treated steel sheet and method of its production. Element of heat-treated steel sheet contains, wt. %: C from 0.05 to 0.50, Si from 0.50 to 5.0, Mn from 1.5 to 4.0, P 0.05 or less, S 0.05 or less, N 0.01 or less, Ti from 0.01 to 0.10, B from 0.0005 to 0.010, Cr from 0 to 1.0, Ni from 0 to 2.0, Cu from 0 to 1.0, Mo from 0 to 1.0, V from 0 to 1.0, Ca from 0 to 0.01, Al from 0 to 1.0, Nb from 0 to 1.0, REM from 0 to 0.1, iron and impurities - the rest. Microstructure of steel sheet contains residual austenite from 0.2 to 1.0 vol. % and martensite - balance. Numerical density of residual carbide, which is present in steel element and having diameter of equivalent in area of circle of 0.1 mcm or more, is 4.0 × 10³/mm² or less. Method of producing element from heat-treated steel sheet includes heating of steel sheet to temperature range from point Ac₃ to point  Ac₃ + 200 °C with average rate of temperature increase 5 °C/s or more, hot forming at said temperature, cooling to temperature point Ms with upper critical cooling rate or more and subsequent cooling to 100 °C with average cooling rate of 60 °C/s or higher. Obtained element is characterized by tensile strength of 1.4 GPa or more, ratio of yield strength to ultimate strength of 0.65 or more.

EFFECT: invention can be used in automotive industry, in particular, for manufacture of such shock-proof parts of vehicle as bumper and central post.

9 cl, 4 tbl