A method of producing a steel sheet, a process for producing one component, a steel sheet, a welded structure comprising at least ten strength welds of at least two components, using a steel sheet and using a weld resistance points

摘要

It is a method of producing a steel sheet, the method comprising the following successive steps - providing a cold rolled steel sheet, the chemical composition of the steel containing by weight%: 0.15% = c = 0 , 23%, 2.0% = mn = 2.8%, 1.0% = si = 2.1%, 0.02% = al = 1.0%, with 1.7% = si + al = 2.1%, 0 = nb = 0,035%, 0 = mo = 0,3%, 0 = cr = 0,4%, the remainder being fe and unavoidable impurities, - annealing the steel sheet at an annealing temperature ta in order to obtain a structure comprising at least 65% austenite and up to 35% intercritical ferrite, - abruptly cool the sheet to a cooling rate of at least 20 ° c / s from a temperature of at least 600 ° c to a rough cooling temperature qt comprising from ms-170 ° c and ms-80 ° c, - heating the sheet to a partitioning temperature pt between 350 ° c and 450 ° c and maintaining the sheet at this temperature for a partition time pt comprising between 80s and 440s, - immediately cool the sheet to room temperature, and the steel sheet contains a final microstructure composed of 40% to 70% of tempered martensite in the surface fraction - 7% to 15% retained austenite - 15% and 35% ferrite, - maximum 5% fresh martensite, - maximum 15% bainite