Cold-Rolled Flat Steel Product and Method for the Production Thereof

摘要

A cold-rolled flat steel product where Rm≧1400 MPa and A80≧5% and also a method for producing such product. The product includes, in addition to Fe and unavoidable impurities (in wt. %), 0.10-0.60% C, 0.4-2.5% Si, ≦3.0% Al, 0.4-3.0% Mn, ≦1.0% Ni, ≦2.0% Cu, ≦0.4% Mo, ≦% Cr, ≦1.5% Co, ≦0.2% Ti, ≦0.2% Nb, ≦0.5% V. The microstructure includes (in vol. %) ≧20% bainite, 10-35% residual austenite and martensite as the remainder. A slab, thin slab or a cast strip having said composition, is hot-rolled to form hot strip with a hot-rolling end temperature ≧830° C., coiled at a coiling temperature ≦560° C., cold-rolled at ≧30% reduction and heat-treated by firstly being heated to an annealing temperature ≧800° C., then being cooled at a cooling rate of ≧8° C./s to a holding temperature of 470° C. to greater than the martensite start temperature and then being held at the holding temperature until at least 20 vol. % bainite is present in the microstructure.

主权项

1. A cold-rolled flat steel product, having a tensile strength Rm of at least 1400 MPa and an elongation A80 of at least 5% and comprising, in addition to iron and unavoidable impurities (in % by weight):
C: 0.10-0.60%, Si: 0.4-2.5%, Al: up to 3.0%, Mn: 0.4-3.0%, Ni: up to 1.0%, Cu: up to 2.0%, Mo: up to 0.4%, Cr: up to 2%, Co: up to 1.5%, Ti: up to 0.2%, Nb: up to 0.2%, and V: up to 0.5%, wherein the microstructure of the flat steel product consists of bainite to an extent of at least 20% by volume, of residual austenite to an extent of 10-35% by volume and of martensite as the remainder.