ArcelorMittal S.A.
METHOD FOR PRODUCING A TWIP STEEL SHEET HAVING AN AUSTENITIC MICROSTRUCTURE

Abstract:

A method for manufacturing a recovered steel sheet having an austenitic matrix presenting at least one mechanical property (M) equal or above a target value M.sub.target is provided. The method includes a calibrating process involving heat on at least 2 samples of the steel, corresponding to Pareq values P, submitting said samples to X-ray diffraction so as to obtain spectrums including a main peak whose width at mid height FWHM is being measured, measuring a mechanical property (M) of said samples, measuring a recovery or recrystallization state of each sample, drawing a curve of M as a function of FWMH in a domain where the samples are recovered from 0 to 100%, but not recrystallized. The method further includes calculating a FWHM.sub.target corresponding to a target mechanical property M.sub.target, determining a pareq value P.sub.target of the heat treatment to perform to reach M.sub.target and selecting a time t.sub.target and a temperature T.degree..sub.target corresponding to the P.sub.target value. The method further includes feeding a recrystallized steel sheet having a M.sub.recrystallization, cold-rolling the recrystallized steel sheet in order to obtain a steel sheet having a M.sub.cold-roll and annealing the cold rolled steel sheet at a temperature T.degree..sub.target during a time t.sub.target.