Production method and installation for producing thin flat products

An improved method for producing thin, flat steel products from continuously cast slabs in an installation having a single-stand or multi-stand blooming train, a roller table for transporting the rolling stock and optionally for oscillating it, a roller table section having hinged, heat-insulating hoods, an inductive heating device for controlled preheating of the pre-strip to a defined temperature over the length and the width of the pre-strip, a multi-stand finishing train, a delivery roller table with devices for cooling the hot strip, and downstream coiling machines for coiling the finished strip, wherein a fine-grained structure of grain classes 6-10 according to DIN 50,601 is produced by a total reduction of up to about 80% in order to achieve high strength values, the improvement comprising the steps of:

• rolling at least one slab of carbon steel with a medium carbon content of approximately 0.2-0.8% or alloy case-hardened or heat-treatable steel in the single-stand or multi-stand blooming train in a first deformation stage and a second deformation stage with a pause between the stages to allow for intermediate cooling by oscillation on the roller table to obtain one or more pre-strips, the rolling step including setting the rolling temperature of the first stage in the blooming train, which is in the upper austenite region, at a total reduction of 40-70%, to the transformation of the structure of the cast strand to a rolled structure by complete recrystallization;
• heating the pre-strips to a defined temperature over the length and width by a combined action of the heat-insulating hoods and the inductive heating device;
• and
• rolling the heated pre-strips in a multi-stand finishing train in the two-phase region to obtain reduced-thickness finished strips, wherein in the first rolling the transformation starting temperature of the transition to the two-phase region is raised and the transformation time decreased by the fine-grained and partially strengthened structure in order to lower the deformation resistances in the finishing train, the heating step including adjusting the pre-strip uniformly during the first rolling, depending on the thickness and length of the pre-strip, on the thickness of the finished strip, on the entry speed into the finishing train, and on the cooling effect of descaling sprays in front of the finishing train, to a target temperature along its length and across its width by the combined effect of the closed hoods and the inductive heating device so that the rolling in the finishing train occurs in the two-phase region during all passes, the rolling in the finishing train including reversing passes of the strip without a protective atmosphere, the rolling further taking place without a reheating of the edges of the strip.