HIGH STRENGTH STEEL EXHIBITING GOOD DUCTILITY, AND METHOD OF PRODUCTION VIA IN-LINE HEAT TREATMENT DOWNSTREAM OF MOLTEN ZINC BATH Russian patent published in 2018 - IPC C21D9/46 C22C38/02 C22C38/06 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, in particular to the processing of steel sheets. Sheets are made of steel containing the following elements, wt%: 0.15–0.4 carbon; 1.5–4 manganese; 2 or less silicon, aluminum, or some combination thereof; 0.5 or less molybdenum; 0.05 or less niobium and the balance is iron and unavoidable impurities. Sheets are heated to first temperature (T1), which is at least above the temperature at which the steel sheet undergoes conversion to austenite and ferrite. Steel sheets are cooled to second temperature (T2) by cooling with a cooling rate, where T2 is below the temperature (M_s) of the onset of martensitic transformation, and this cooling rate is high enough to convert austenite to martensite. When the sheets are cooled to T2, hot-dip galvanising or hot-dip galvanising with annealing is performed. Steel sheets are reheated to a distribution temperature that is sufficient to allow carbon diffusion in the structure of said steel sheet. Austenite is stabilised by holding the steel sheets at distribution temperature for a holding time sufficient to allow carbon diffusion from martensite to austenite. Steel sheets are cooled to room temperature.

EFFECT: resulting sheets have high strength and good formability.

4 cl, 12 dwg, 7 tbl, 9 ex