A METHOD AND A CONTINUOUS CASTING AND ROLLING INSTALLATION FOR PRODUCING HOT-ROLLED STRIP WITH A DUAL-PHASE MICROSTRUCTURE

摘要

The aim of the invention is to be able to produce dual-phase steels under local conditions even in the existing cooling section of a continuous casting and rolling plant by means of controlled cooling of the hot-rolled strip in two cooling stages following the forming process. Said aim is achieved by respecting the chemical composition of the initial steel within precisely defined limits and cooling in two stages from a finished rolled strip temperature Tfinish of ASUB3/SUB -100K Tfinish ASUB3/SUB -50K to a coiling strip temperature Tcoiling of 300 °C ( initial martensite temperature), the cooling speed VSUB1,2/SUB in both cooling stages ranging between 30 and 150 K/s, preferably between 50 and 90 K/s. The first cooling stage is carried out until the cooling curve enters the ferrite range, whereupon the heat released by the transformation of the austenite into ferrite is used for isothermally holding the obtained strip temperature Tconst during a holding time of = 5 s until the beginning of the second cooling stage