METHOD FOR MANUFACTURING HIGH STRENGTH STEEL SHEET HAVING IMPROVED FORMABILITY AND SHEET OBTAINED Russian patent published in 2019 - IPC C21D6/00 C21D8/02 C21D9/46 C21D1/18 C22C38/02 C22C38/04 C22C38/12 

FIELD: metallurgy.

SUBSTANCE: invention relates to a method for manufacturing a steel sheet obtained from steel having a chemical composition containing, in mass percent: 0.1≤C≤0.4, 4.5≤Mn≤5.5, 1≤Si≤3, 0.2≤Mo≤0.5, the rest is Fe and inevitable impurities, and also to a steel sheet. Disclosed method includes the following steps: annealing a rolled sheet obtained from the above-mentioned steel by holding it at an annealing temperature AT greater than the Ac₃ transformation point of the steel, quenching the sheet by cooling it down to a quenching temperature QT in the range between the Ms and Mf transformation points of the steel to obtain a final structure containing at least 50 % of martensite and at least 10 % of residual austenite, while the amount of ferrite and bainite is less than 10 %, heating the sheet up to an overaging temperature PT in the range of 300 °C to 500 °C and maintaining it at said overaging temperature PT for a time Pt greater than 10 s and cooling the sheet down to the ambient temperature.

EFFECT: present invention allows to obtain a high-strength steel sheet, characterized by improved formability.

11 cl, 2 tbl, 11 ex