METHOD FOR MANUFACTURING HIGH STRENGTH AND HIGH FORMABILITY HOT-ROLLED TRANSFORMATION INDUCED PLASTICITY STEEL CONTAINING COPPER

摘要

A method for producing a high strength hot-rolled steels sheet with good formability applicable to automobiles, industrial machine and the like is disclosed. The basic composition of TRIP steel is adjusted, Cu is added to improve the strength by precipitation hardening of fine ⊂-Cu. Other producing conditions are controlled to obtain a tensile strength of over 90 kg/mm2 with good formability. The steel composed of 0.15-0.3 % by weight of C, 1.5-2.5 % by weight of Si, 0.6-1.8 % by weight of Mn, 0.02-0.10 % by weight of Al, 0.6-2.0 % by weight of Cu, 0.6-2.0 % by weight of Ni, the balance being Fe and inevitable impurities, has a microstructure of multi-phase structure consisting of ferrite, bainite, and retained austenite, or granular structure (M-A constituents in bainitic ferrite matrix). The steel is finish rolled at a temperature of 750-880 °C, water cooled from water cooling initiation temperature of 680-740 °C to water cooling termination temperature of 240 x (% Mn + % Ni)-140 (°C) to 540 °C, and subsequently coiled at this temperature.