FIELD: metallurgy.
SUBSTANCE: invention relates to the field of metallurgy. Thermal treatment is carried out in a line comprising a heating section, a curing section and a cooling section with a cooling system and providing mode TPtarget. Thermal treatment includes: A) preparation stage, containing: 1) selection sub-step, on which: a) mtarget and chemical composition is compared to a list of predetermined sheets, microstructure of which includes certain phases and predetermined portions of content of phases, for selection of an article having microstructure mstandard, closest to mtarget, and TPstandard, including at least heating, maintenance and cooling stage to achieve mstandard, b) based on TPstandard, selecting heating mode, holding mode, including holding temperature Tsoaking, cooling capacity of cooling system and cooling temperature Tcooling, and 2) a calculation sub-step, at which, by changing cooling capacity, new cooling modes CPx are calculated based on the product selected at step A.1.a) and TPstandard, the initial steel sheet microstructure mi to achieve mtarget, heating mode and mode holding, including Tsoaking and Tcooling, wherein cooling step TPstandard is recalculated using said CPx to obtain new thermal modes TPx, wherein each TPx corresponds to a defined microstructure mx, wherein TPx includes a time, a heat treatment temperature and at least one mode selected from: cooling, isotherm or heating rate, isotherm values having a constant temperature, wherein cooling mode CPx is calculated based on a given mathematical relationship, a selection step of selecting one TPtarget to achieve mtarget, wherein TPtarget is selected from the calculated thermal modes TPx so that the difference between the phase ratios present in mtarget and mx is ± 3 %, B) the heat treatment step, where TPtarget is performed for the steel sheet.
EFFECT: providing each sheet steel with exceptional properties, such as minimum possible spread of properties.
32 cl, 4 dwg, 1 tbl, 1 ex
