COLD LAMINATED STEEL PLATE AND THERMAL TREATED, JOINT WELDED BY RESISTANCE POINTS, METHOD FOR MANUFACTURING A COLD LAMINATED STEEL PLATE AND PROCESS FOR THE PRODUCTION OF A RESISTANCE POINT SOLD JOINT

摘要

cold rolled and heat treated steel sheet, with a composition comprising, by mass: 0.10% = c = 0.40%, 3.5% = mn = 8.0%, 0.5% = si = 2.5%, 0.003% = al = 3.0%, with si + al = 0.8%, 0.001% = mo = 0.5%, s = 0.010%, p = 0.020%, n = 0.008% and, optionally, one or more elements selected from cr, you, nb, veb, such that: 0.01% = cr = 2.0%, 0.010% = ti = 0.080%, 0.010% = nb = 0.080%, 0.010% = v = 0.30%, 0.0005% = b = 0.003%, the remainder of the composition being iron and inevitable impurities resulting from the foundry. The microstructure consists of a surface fraction of between 10% and 50% retained austenite, a maximum of 8% fresh martensite and tempered martensite. the retained austenite comprises: - mn enriched austenite having a mn content of more than 1,3% mn,% of mn designating the mn content of the steel plate, the surface fraction of said mn enriched austenite being for the entire microstructure comprised between 2% and 12% and - austenite poor in mn, with a mn content between 0,5 *% mn and 1,3 *% mn.